methane fluxes and carbonate deposits at a cold seep area of the central nile deep sea fan eastern mediterranean sea abstract high acoustic seafloor backscatter signals characterize hundreds of patches of methane derived authigenic carbonates and chemosynthetic communities associated with hydrocarbon seepage on the nile deep sea fan ndsf in the eastern mediterranean sea during a high resolution ship based multibeam survey covering a 225 km2 large seafloor area in the central province of the ndsf we identified 163 high backscatter patches at water depths between 1500 and 1800 m and investigated the source composition turnover flux and fate of emitted hydrocarbons systematic parasound single beam echosounder surveys of the water column showed hydroacoustic anomalies flares indicative of gas bubble streams above 8 of the high backscatter patches in echosounder records flares disappeared in the water column close to the upper limit of the gas hydrate stability zone located at about 1350 m water depth due to decomposition of gas hydrate skins and subsequent gas dissolution visual inspection of three high backscatter patches demonstrated that sediment cementation has led to the formation of continuous flat pavements of authigenic carbonates typically 100 to 300 m in diameter volume estimates considering results from high resolution autonomous underwater vehicle auv based multibeam mapping were used to calculate the amount of carbonate bound carbon stored in these slabs additionally the flux of methane bubbles emitted at one high backscatter patch was estimated 0 23 to 2 3 106 mol a 1 by combined auv flare mapping with visual observations by remotely operated vehicle rov another high backscatter patch characterized by single carbonate pieces which were widely distributed and interspaced with sediments inhabited by thiotrophic chemosynthetic organisms was investigated using in situ measurements with a benthic chamber and ex situ sediment core incubation and allowed for estimates of the methane consumption 0 1 to 1 106 mol a 1 and dissolved methane flux 2 to 48 106 mol a 1 our comparison of dissolved and gaseous methane fluxes as well as methane derived carbonate reservoirs demonstrates the need for quantitative assessment of these different methane escape routes and their interaction with the geo bio and hydrosphere at cold seeps

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

antarctic cryogenic sediments biotic and inorganic facies of ice shelf and marine based ice sheet environments abstract cryogenic sediments defined as marine deposits that form in association with ice icebergs sea ice ice shelves or marine based ice sheets are widespread in high latitude regions existing models for cryogenic depositional processes are of limited utility because of 1 lack of direct observational data 2 reliance on older land exposed sections from which inferential conclusions have been drawn 3 employment of inadequate glaciologic and oceanographic concepts and 4 failure to incorporate adequately information on the biotic content of these deposits as a first step toward developing a synthetic model for cryogenic deposition we relate glaciologic sedimentologic and biotic processes of the modern ice shelf and marine based ice sheet environments using data from antarctic continental shelves the principal deposit beneath grounded marine based ice sheets is lodgement till which often contains reworked and fragmented fossil material this till is identical in all important sedimentologic respects with terrestrial lodgement deposits marine lodgement tills commonly form geographically extensive sheets which are restricted to continental shelf sites and which may be differentiated from other cryogenic deposits by their high degree of compaction and reworked fossils waterlain till may form beneath grounded ice in areas where debris melting out of the glacier sole falls through a thin water layer up to a few m between the ice and its bed waterlain till usually lacks fossil material unless the source material for the subglacial debris is fossiliferous and is less compact than lodgement till deposition beneath large polar ice shelves e g ross filchner ronne is largely restricted to a zone probably km in width near the grounding line in this zone a complex of primary and secondary cryogenic deposits including waterlain till ice shelf rafted detritus isrd flow till slumps etc is likely to interfinger processes controlling this deposition include local basal conditions of the ice sheet and ice shelf freezing or melting presence or absence of subglacial outflow marine currents and tidal action sediment supply long and short term grounding line movement sea floor topography and water depth deposition of isrd is limited elsewhere beneath these large ice shelves because high surface accumulation rates cause downward particle paths for ice and debris thus most debris is released soon after passing the grounding line biotic activity beneath ice shelves declines rapidly in diversity and abundance between the calving margin and grounding line deposition rates seaward of the calving margin are much higher than beneath the large ice shelves here icebergs derived from outlet glaciers and ice streams that terminate directly in the sea may carry significant loads of subglacial englacial or superglacial debris which is released by a variety of mechanisms as the icebergs melt this ice rafted detritus mixes with biotic material from planktonic organisms as it falls through the water column to form compound ibrd if currents are present in the water column or at the seafloor sorting may occur to form residual ibrd on shallow banks grounded icebergs carrying subglacial debris may melt in situ forming iceberg till and iceberg ploughing of sediment may form iceberg turbate both these deposits may be difficult to distinguish from lodgement till but both are restricted to areas with modern water depths less than 450 m

run out distance and erosion of debris flows in the nile deep sea fan system evidence from lithofacies and micropalaeontological analyses abstract debrites with different volumes depositional periods and setting are observed in the nile deep sea fan system here we present debrites from four late quaternary environments i within the rosetta submarine channel at 1700 m ii within small basins created by salt tectonics in the eastern province at 1300 m iii on the open slope outside of channels at 2600 m and iv in the distal part of the fan fringe beyond channel terminations at 3050 m water depth the debrites comprise mud clasts in a generally ungraded muddy sand matrix they are relatively thin 20 150 cm in fan fringe in channel and salt tectonic basin settings and somewhat thicker 8 m in the open slope setting benthic foraminiferal assemblages and variation in the planktonic benthic foraminiferal ratios are considered as a useful tool for tentatively evaluating the origin of sediment in these debris flows and estimation of their run out distance similar microfaunal contents of clast matrix combinations document that the debrites in the rosetta channel and salt tectonic basin were locally sourced the debrite from the open slope travelled farther up to 150 km three separate debrites in a fan fringe core were deposited by debris flows that originated over 200 km away in water depths shallower than 1000 m these far travelled debris flows appear to have eroded remarkably little sediment as they travelled for 200 km across low 0 8 1 2 gradient seafloor this lack of erosion is attributed to hydroplaning or increasing pore fluid pressure at the base of debris flows this study confirms that remarkably mobile debris flows can travel long distances to produce thin debrites in the distal fringes of submarine fans

global positioning system measurements of present day crustal movements in the arabia africa eurasia plate collision zone we present and interpret global positioning system gps measurements of crustal motions for the period 1988 1994 at 54 sites extending east west from the caucasus mountains of southern russia georgia and armenia to the aegean coast of turkey and north south from the southern edge of the eurasian plate pontus block to the northern edge of the arabian platform viewed from a eurasia fixed reference frame sites on the northern arabian platform move n38 13 w at 20 3 mm yr roughly consistent with the velocity implied by nuvel 1a circuit closure n23 7 w at 24 2 mm yr the motion of arabia appears to be transferred directly to the region of turkey north of the suture however eastern turkey is characterized by distributed deformation while central western turkey is characterized by coherent plate motion involving westward displacement and counterclockwise rotation of the anatolian plate internal deformation within the central part of the anatolian plate is less than 2 mm yr the anatolian plate is decoupled from eurasia along the right lateral strike slip north anatolian fault naf this different response in eastern and western turkey to the collision of arabia may result from the different boundary conditions the hellenic arc forming a free boundary to the west and the asian continent and oceanic lithosphere of the black and caspian seas forming a resistant boundary to the north and east we derive a best fitting euler vector for anatolia eurasia motion of 29 2 0 8 n 32 9 0 4 1 3 0 1 m y the mapped surface trace of the naf corresponds well to a small circle about this pole the new euler vector implies an upper bound for naf slip rate of 30 2 mm yr i e assuming all relative motion is accommodated along the naf using the nuvel 1a euler vector for arabia eurasia and the gps euler vector for anatolia eurasia we determine an arabia anatolia euler vector of 31 2 n 45 2 e 0 9 0 1 m y and an upper bound on the east anatolian fault slip rate of 15 3 mm yr the aegean trough region of western turkey deviates significantly from coherent plate rotation in addition to rotating with anatolia this region shows roughly n s extension at a rate of 14 5 mm yr taken together with satellite laser ranging results along the hellenic arc the contemporary pattern of deformation indicates increasing motions toward the arc suggesting that the westward displacement and counterclockwise rotation of anatolia is driven both by pushing from the arabian plate and by pulling or basal drag associated with the foundering african plate along the hellenic subduction zone

the influence of changing orbital parameters and surface boundary conditions on climate simulations for the past 18 000 years abstract general circulation model experiments at 3000 year intervals for the past 18 000 years were made to estimate the magnitude timing and pattern of the climatic response to prescribed changes of orbital parameters date of perihelion axial tilt eccentricity and glacial age lower boundary conditions ice sheets land albedo sea ice and sea surface temperature the experiments used the community climate model ccm of the national center for atmospheric research ncar the response of monsoon circulations and tropical precipitation to the orbitally produced solar radiation changes was much larger than the response to changes of glacial age boundary conditions the continental interior of eurasia was 2 4 k warmer in summer and summer monsoon precipitation of north africa south asia was increased by 10 20 between 12 000 and 6000 yr bp before present when perihelion occurred during northern summer rather than in winter as now and the earth s axial tilt was larger than now southern hemisphe

uniqueness and stability analysis of hydrogeophysical inversion for time lapse ground penetrating radar estimates of shallow soil hydraulic properties precise measurement of soil hydraulic properties at field scales is one of the prerequisites to simulate subsurface flow and transport processes which is crucial in many research and engineering areas in our study we numerically analyze uniqueness and stability for integrated hydrogeophysical inversion of time lapse off ground ground penetrating radar gpr data in estimating the unsaturated soil hydraulic properties in the inversion hydrodynamic modeling based on the one dimensional 1 d richards equation is used to physically constrain a full waveform radar electromagnetic model synthetic gpr data in terms of 3 d multilayered media green s functions were generated for three different textured soils coarse medium and fine and assuming different infiltration events inversion was performed iteratively to estimate three key soil hydraulic parameters n and ks of the mualem van genuchten model using the global multilevel coordinate search optimization algorithm for the coarse and medium textured soils inversions converged to the actual solution for all scenarios for the fine soil estimation errors occurred mainly because of the higher attenuation of the electromagnetic waves in such a soil high electric conductivity the procedure appeared to be generally stable with respect to possible errors in the hydrodynamic and petrophysical model parameterization however we found that particular attention should be given to an accurate estimation of the saturated water content and infiltration flux for real field applications the results from our numerical experiments suggest that in theory the proposed method is promising for the noninvasive identification of the shallow soil hydraulic properties at the field scale with a high spatial resolution

ocean circulation its effects on seasonal sea ice simulations a diagnostic ice ocean model of the arctic greenland and norwegian seas is constructed and used to examine the role of ocean circulation in seasonal sea ice simulations the model includes lateral ice motion and three dimensional ocean circulation the ocean portion of the model is weakly forced by observed temperature and salinity data simulation results show that including modeled ocean circulation in seasonal sea ice simulations substantially improves the predicted ice drift and ice margin location simulations that do not include lateral ocean movment predict a much less realistic ice edge

marine geologic evidence for a levantine sinai plate a new piece of the mediterranean puzzle marine geophysical data recorded offshore egypt illustrate the presence of an active fault belt trending n145 e that obliquely transects the eastern nile deep sea fan this belt more than 150 km long consists of a series of linear transtensive faults with an apparent right lateral horizontal component these fault zones bound thick sediment filled grabens where linear salt ridges and diapirs represent likely messinian salt reactive response to regional transcurrent geodynamics we infer that this tectonic belt might correspond to an offshore extension of the gulf of suez rift system if our hypothesis is correct this fault belt might represent the western boundary of a levantine sinai microplate locked between the major arabia and africa plates and the anatolian aegean microplate

inferred gas hydrates and clay diapirs near the storegga slide on the southern edge of the voring plateau offshore norway this paper presents a new data set including single channel airgun seismic lines okean long range side scan sonar data and gravity cores acquired on the edge of the voring plateau and in the region of the storrega slide the data acquisition was part of the 8th training through research ttr 8 expedition with r v professor logachev the acoustic profiles clearly show two laterally separated zones characterised by the presence of bottom simulating reflectors bsrs at about 350 ms twt subbottom depth the lower bsr zone is located on the slope of the voring plateau in the immediate vicinity of the northern headwall of the storegga slide and in some places below the slide deposits this zone runs parallel to the general trend of the continental slope the spatial distribution of the upper bsr zone located upslope in an area where diapir like structures are found does not demonstrate any topographic control interpretation of high backscatter patches on the okean sonographs associates the observed structures with fluid escape features on the seabed most of them are pockmarks but in a few places diapirs are cropping out and form dome like elevations after analysing the behaviour of the bsr sometimes crosscutting and its acoustic characteristics reversed polarity and after applying seismic inversion processing to estimate the acoustic velocity change across the bsr this reflector is interpreted to represent the base of the local gas hydrate stability field ghsf this information was used to derive the regional geothermal gradient spatial variations of the inferred geothermal field appeared to be negligible the observation of two separated bsr zones suggests different environmental controls for the growth of the hydrates enhanced reflectors observed in the intermediate zone can be explained by the presence of strata bound free gas accumulations and migration combined with overlying permeability barriers therefore a model for gas hydrate formation in relation to directional fluid migration processes fluid escape features and the presence of diapiric structures is proposed in this paper our model is supported by sedimentological analyses of seafloor samples which demonstrate the presence of stiff clays with evidence of gas migration and by paleontological studies of the cores retrieved from the pockmarks the presence of a bsr in the sedimentary section within the slide scar area implies the repositioning of hydrates to newly established equilibrium conditions after the slide event this observation allows us to simply estimate an upper limit of the fluid migration velocity in the order of several cm year finally the effect of hydrate dissociation on slope instability is considered assuming that the in situ decomposition of hydrates due to instantaneous depressurisation is slow enough to permit the excess volume of released gas and water to be re distributed through the whole sedimentary section above the paleo bsr with consuming heat and increasing pore pressure dissociation tends to shift the pt conditions back to equilibrium values it appears that the dissociation of hydrates due to sliding would cause only 0 2 increase of the pore pressure which would hardly contribute to further slope instability

menes caldera a highly active site of brine seepage in the eastern mediterranean sea in situ observations from the nautinil expedition 2003 abstract this paper reports the first in situ seafloor observations of fluid escape structures in a fault controlled caldera type depression of about 8 km diameter named the menes caldera in the eastern mediterranean sea off egypt western province of the nile deep sea fan a detailed analysis of seven nautile dives performed during the nautinil cruise in 2003 focused on determining the nature origin importance mechanisms and environmental impacts of the fluid escape processes from the geological observations seafloor maps constructed from direct visual observations and video records made from the submersible and sampling results for three mud volcanoes of the caldera cheops chephren and mykerinos show differences in activity but many common characteristics the three volcanoes show a crater like depression the study reveals a strong contrast between mykerinos where no seepage activity was found and the craters of cheops and chephren where an intense activity of brine seepage was discovered on cheops a dome of dark grey mud raises slightly above the brine surface in the central part of the brine lake and shows numerous circular vents of 1 2 m diameter that become gradually colonized by microbial mats chephren hosts a deep 200 m and warm 45 c brine lake alternations of areas void of or covered with microbial mats at the surface of the chephren brine lake indicate large surface disturbances that may result from the occurrence of several active vents at the bottom of the lake a special feature at chephren is a brine overflow at the western edge of the crater also indicative of the very high activity of brine seepage the nautinil observations indicate that the menes caldera in the eastern mediterranean is a highly active site of brine seepage growth faults rooted in pre messinian sediment layers provide pathways for warm fluids to escape pressurized source levels below the messinian salt

origins of hydrocarbon gas seeping out from offshore mud volcanoes in the nile delta abstract this paper discusses the origin of gas seepages free gas or dissolved gas in ground water or brine sampled with the nautile submarine during the nautinil cruise at the seafloor of the deep water area of the nile turbiditic system on different mud volcanoes and brine pools generally the gas is wet and includes c1 c2 c3 ic4 nc4 co 2 these gas samples show no evidence of biodegradation which is not the case of the gas present in the deep hydrocarbon accumulations at depth it indicates that the gas expelled by the mud volcanoes is not issued from direct leakages from deep gas fields the collected gas samples mainly have a thermogenic origin and show different maturities some samples show very high maturities indicating that these seepages are sourced from great depths below the messinian salt moreover the different chemical compositions of the gas samples reflect not only differences in maturity but also the fact that the gas finds its origin in different deep source rocks carbon dioxide has an organic signature and cannot result from carbonate decomposition or mantle fluids the crustal derived radiogenic isotopes show that the analyzed gas samples have suffered a fractionation processes after the production of the radiogenic isotopes due either to oil occurrence at depth interacting with the flux of gas and or fractionation during the fluid migration

paleoglaciology s grand unsolved problem the paleoglaciological concept that during the pleistocene glacial hemi cycles a super large structurally complex ice sheet developed in the arctic and behaved as a single dynamic system as the antarctic ice sheet does today has not yet been subjected to concerted studies designed to test the predictions of this concept yet it may hold the keys to solutions of major problems of paleoglaciology to understanding climate and sea level changes the russian arctic is the least known region exposed to paleoglaciation by a hypothetical arctic ice sheet but now it is more open to testing the concept implementation of these tests is a chaillenging task as the region is extensive and the available data are controversial well planned and coordinated field projects are needed today as well as broad discussion of the known evidence existing interpretations and new field results here we present the known evidence for paleoglaciation of the russian arctic continental shelf and reconstruct possible marine ice sheets that could have produced that evidence

seismo stratigraphic evidences for deep base level control on middle to late pleistocene drift evolution and mass wasting along southern levant continental slope eastern mediterranean abstract since early pliocene a counterclockwise surface gyre transported nile derived silt and clay northeastwards along the levant coast where a basinward prograding plastered drift emerged based on high resolution seismic reflection data we develop a middle to late pleistocene sequence stratigraphic scheme for this plastered drift for creating stacked sections of the seismic data we used the common reflection surface crs stack technology which enhanced lateral reflection continuity and visibility of deep reflections the shelf comprises stratigraphic sequences which show classical systems tract like stacking patterns of sea level controlled sequences such as offlapping forced regression deposits or diachronous ravinement surfaces which formed during base level rise on the slope base level was periodically located well below the wave base and thus rather controlled by hydrodynamics presumably by high velocity contour currents hence the term deep base level is introduced the deep base level controlled especially down and backstepping slope deposits this example shows that care has to be taken when interpreting subsurface data containing typical systems tract like seismic sequences since such geometries do not necessarily imply shallow water deposition of the sediments a chronostratigraphic analysis based on the seismic stratigraphy indicates that base level fluctuations were related to eccentricity driven glacio eustatic fluctuations periodic mass wasting facilitated by foreset over steepening and possibly triggered by salt tectonics or erosion by the contour current occurred during late base level fall or early base level rise

the great cenozoic ice sheet abstract ocean floor sediments contain a record of quaternary continental glaciations in which global cooling prevails over a 100 000 year cycle and the intensity of the last glacial maximum is as strong as any of the earlier glaciations yet the areal extent of quaternary glacial drift in north america and eurasia during the last glaciation is much less extensive than during several earlier glaciations in an attempt to explore this problem two versions of a great cenozoic ice sheet were reconstructed the minimum version transformed a frozen bed beneath high interior ice domes and along southern margins during the last glaciation into a thawed bed during more extensive earlier glaciations this allowed thinner ice to cover a larger area with little change in ice volume thereby satisfying both the continental and oceanic records of quaternary glaciation the maximum version extended frozen basal conditions beneath high interior ice domes and along southern margins so that a greater areal extent could only be accommodated by thicker ice a greater ice volume is required in this case and would seem to put the great cenozoic ice sheet in the late tertiary where some evidence for global cooling on a 400 000 year cycle exists and might provide the longer timespan needed to produce a larger ice sheet

sediment lithofacies processes and sedimentary models in the central bransfield basin antarctic peninsula since the last glacial maximum abstract this work provides a regional perspective on the links between glacial glacimarine and marine sedimentary processes occurring since the last glacial maximum along the central bransfield basin antarctic peninsula from shallow to deep areas by combining information provided by gravity cores from shelf to deep basin settings swath bathymetry and high resolution reflection seismic and sub bottom topas profiles seven lithofacies have been identified their textural compositional and x radiographic characteristics as well as their spatial distribution allow the differentiation of two stages of deposition involving distinct sedimentary processes the last glacial maximum was characterised by subglacial deformation by the antarctic peninsula ice sheet as it reached its most extended position on the distal mid slope platforms of the central bransfield basin proglacial debris flows occurred on the external edges of the mid slope platforms and lower slope since the last deglaciation glacimarine proglacial debris flows glacimarine proglacial processes and turbid glacial meltwater and open marine sedimentary processes turbidity currents sliding and contour current activity have predominated in the central bransfield basin glacial cyclicity is the main factor controlling the sedimentary processes in the basin but several secondary factors including physiography sediment entry points and oceanography have been identified as local controls on the sediment distribution the unusual physiography of the central bransfield basin where slope platforms form wide flat surfaces seaward from glacial troughs is a key factor in the widespread occurrence of glacial and glacimarine processes on the entire continental margin

the nile deep sea fan an example of interacting sedimentation salt tectonics and inherited subsalt paleotopographic features abstract structural analysis of the nile deep sea fan ndsf indicates that post miocene deformation is largely controlled by down slope movement above a messinian salt layer in contrast to other similar systems the ndsf shows significant lateral asymmetry and three distinct provinces can be recognized regional variations in salt thickness and base salt geometry within the system have led to the presence of structures typical of both gravity gliding and gravity spreading trends of structures within the western and central parts of the ndsf are consistent with forming due to gravity gliding processes this pattern contrasts with that in the eastern ndsf that seem to be much more consistent with deformation due to gravity spreading observed differences in structural style across the ndsf can be related directly to the paleomorphological evolution of the nile cone during messinian time which is perhaps partly related to features that have been inherited from early mesozoic evolution of the north egypt passive margin in the east part of the ndsf the structural evolution has been significantly influenced by the proximity of eratosthenes seamount this large topographic buttress has served to both limit and deflect northeastward allochthonous advance of the messinian evaporites and has thus severely complicated deformation of the overlying plio quaternary sedimentary cover within the broad corridor that runs nnw sse and cuts obliquely across the modern bathymetry of the nile cone

natural gas formation in the western nile delta eastern mediterranean thermogenic versus microbial abstract the offshore part of the nile delta is an emerging gas and condensate province and one of the most promising areas for future petroleum exploration and supply in northern africa while the nile delta s hydrocarbon potential and its geological and stratigraphic pattern has been the focus of numerous studies the origin of its gas has been poorly studied in order to characterize the natural gas and to determine whether microbial or thermogenic processes are the dominant generation pathways of methane a regional geochemical study was performed on 38 test gases collected from 9 neogene western nile delta discoveries main constituents of the gases are methane 89 4 99 4 up to pentane with traces of carbon dioxide and nitrogen methane carbon isotopic composition ranges from 66 0 to 39 6 displaying a mixed microbial and thermogenic character for most of the gases microbial gas contributions range from 15 to 95 the mixed and the more thermogenic gases are frequently accompanied by light oils and condensates 41 59 api calculated maturities of the thermogenic gas proportions suggest source rock maturities between 0 8 and 1 4 ro which are actually present in the pre miocene section evidence for microbial alteration of petroleum accumulations in the nile delta is largely manifested in anomalously heavy isotopic compositions of both wet gas components propane and n butane and preferential removal of higher n alkanes from condensates the hydrocarbon accumulations affected by biodegradation are trapped within shallow pliocene reservoirs

transgressions rethinking beringian glaciation abstract the purpose of this investigation is to encourage a fresh look at pleistocene beringia heretofore flooding of bering strait has been cited as the only barrier to migration with marine sea transgressions being a sea gate that closed off migration during glacial interstadials and interglaciations however the possibility exists that glacial advances were also barriers with marine ice transgressions being an ice gate that closed off migration during glacial stadials and glacial maxima this possibility proceeds from the marine ice transgression hypothesis mith which states that marine ice sheets form on the broad arctic continental shelf of northern hemisphere continents when sea ice thickens grounds and domes in shallow water and then transgresses landward as continental ice sheets and seaward as floating ice shelves hughes 1987 landward transgression is onto coastal lowlands during pleistocene glaciations a marine ice sheeet extending from spitsbergen to greenland may have transgressed the circumpolar continental landmass at its lowest and narrowest gap central beringia and calved into the pacific ocean four models of beringian glaciation are presented based on the distinction between marine glaciation and highland glaciation central beringia was glaciated only in highlands in the traditional model hopkins et al 1982 was also glaciated by a self sustaining ice shelf floating over the deep ocean basins of the bering sea in the model by grosswald and vozovik 1984 was glaciated by a marine ice sheet that covered highlands the continental shelf and supplied the ice shelf in a model for maximum pleistocene glaciation and was glaciated by a marine ice sheet in the chukchi sea that merged with highland glaciers transgressed the continental shelf of the western bering sea and calved into the southern bering sea along the edge of the continental shelf in a model for the last glaciation field tests are suggested to assess the viability of these four models the first model is already established for highland glaciation in alaska but less established in siberia the last model should be the easiest to evaluate for marine glaciation the last model limits human migration across the beringian land bridge to brief intervals between stadials and interstadials of the last glaciation cycle when both the ice gate and the sea gate were opened to human migration this model can influence the sea change now underway among quaternary scientists studying peopling of the americas based on the archaeological linguistic and ethnic diversity among native american populations

submarine fans and related depositional systems ii variability in reservoir architecture and wireline log character abstract the architecture and heterogeneity of deep marine clastic reservoir systems can be assessed at three scales at the macroscale lateral and vertical variations in the stacking patterns of submarine fans or fan complexes fundamentally affects the shape and scale of a reservoir and its trapping geometry at the mesoscale the distribution and type of architectural elements e g channel levees lobes sheet sands within the fan system have a major impact upon reservoir compartmentalisation and the distribution continuity and connectivity of sand shale bodies finally at the microscale the vertical and horizontal arrangement of reservoir and non reservoir facies and lithotypes defines flow units which fundamentally control fluid flow and production performance each type of submarine fan and related deep marine clastic reservoir system sand rich fans mixed sand mud ramps etc exhibits a predictable arrangement of architectural elements which form the basic building blocks of the system these features control reservoir architecture seismic expression and the geometry of sandbodies and non reservoir section a suite of reservoir architectural models is proposed for different deep marine clastic systems using unpublished and cited data from outcrop and subsurface studies these conceptual models are idealised simplifications which provide a preliminary framework for understanding broad scale reservoir archsitecture and wireline log character within contrasting types of fan and related systems the models are of value in the exploration for turbidite reservoirs by highlighting the risk on reservoir presence and distribution from an appreciation of the architectural style within appraisal and production they provide a basic framework from which an objective reservoir description can be made use of such conceptual analogue models for reservoir description will not adequately reflect the reality and individuality of a specific reservoir their use in understanding detailed reservoir complexity should therefore be approached with caution

new insights on the post rift seismic stratigraphic architecture and sedimentary evolution of the antarctic peninsula margin central bransfield basin abstract a seismic stratigraphic study of the antarctic peninsula margin of the central bransfield basin was conducted using seismic and bathymetric data the study focused on seismic sequences and units deposited after the basin opened and yield a record of the evolution of the northern most antarctic peninsula ice sheet two seismic sequences compose the post rift stratigraphic succession on the central bransfield basin slope platforms both sequences are composed of seismic units that record glacial interglacial cycles and show evidence of the antarctic peninsula ice sheet having grounded on the continental shelf and slope platform on several occasions in the past this evidence includes glacial and glaciomarine related sedimentary and erosional features within the seismic units glacial unconformities glacial troughs till wedges prograded wedges trough mouth fans glaciomarine sheet deposits and moraines which are bounded by glacial unconformities the antarctic peninsula lower slope also registered in its eastern sector the deposition of gravity flow deposits during ice sheet retreat and interglacial stages the deposition of seismic units on the middle slope produced the present day step like profile of the margin composed of wide flat slope platforms and narrow and steep upper and lower slopes seismic units show changes in thickness and distribution that record the effect of the physiography and climatic changes on margin sedimentation these variations produced an overall change from more line sourced deposition to more point sourced deposition as ice streams evolved the stacking of units shows a change in the stratigraphic architecture through time from dominantly progradational s2 to progradational aggradational s1 this change is correlated with a change in the frequency of ice sheet grounding events which was probably driven by a higher rate of eustatic rise and fall in relation with the mid pleistocene global climatic change

tertiary oxygen isotope synthesis sea level history and continental margin erosion tertiary benthic and planktonic foraminiferal oxygen isotope records are correlated to a standard geomagnetic polarity time scale making use of improved chronostratigraphic control and additional oligocene isotope data synchronous changes in both benthic and planktonic 18o values which occurred in the oligocene to miocene 36 5 2 ma are interpreted in part to represent ice growth and decay the inferred ice growth events correlate with erosion on passive continental margins as interpreted from seismic and chronostratigraphic records this association is consistent with a link between oligocene to miocene erosional events and rapid 15 m m y glacioeustatic lowerings of about 50 m high benthic foraminiferal 18o values suggest the presence of continental ice sheets during much of the oligocene to recent 36 0 ma substantially ice free conditions probably existed throughout the paleocene and eocene 66 36 ma the mechanisms and rates of sea level change apparently were different between the early and late tertiary with glacioeustatic changes restricted to the past 36 m y pre oligocene erosion on passive continental margins was caused by eustatic lowerings resulting from global spreading rate changes we apply a model which suggests that large areas of the continental shelves were subaerially exposed during such tectonoeustatic lowstands stimulating slope failure and submarine erosion the different mechanisms and rates of eustatic change may have caused contrasting erosional patterns between the early and late tertiary on passive continental margins this speculation needs to be confirmed by examination of data from several passive margins

a possible marine mechanism for internally generated long period climate cycles abstract by reinterpreting the sea ice extent discussed in a recently proposed model of auto oscillatory climatic change saltzman et al 1981 to represent high inertia grounded and shelf sea ice forms instead of thinner marine ice forms it is possible for the model to yield a much longer period of auto oscillation perhaps as much as 100 000 years the dominant period of ice volume variations revealed by deep sea ocean cores the physical basis of the model can in principle be tested by future evidence regarding the long term variations of bulk ocean temperature and atmospheric co2 concentration

newly recognized eastern extension of the nile deep sea fan a previously unreported easternmost segment of the nile river deep sea fan complex has been identified in the deep levant basin offshore israel based mainly on a recently released high quality three dimensional seismic data set this segment is characterized by densely spaced seabed and subseabed turbidite channel complexes generally fed from the region of the historically active northeastern damietta and pelusian branches of the nile this pattern suggests a previously unnoticeable symmetry in the modern channel distribution between the eastern and western branches of the deep sea fan the base of the nile9s eastern deep sea fan is determined by a nw trending system of pre nile turbidite slope channels at the top of the messinian evaporites the overlying pliocene holocene fan complex is further divided into two distinct stratigraphic units a lower stratified sand rich unit deposited in a basin floor setting and an upper heterogeneous mud rich unit consisting of downslope mass transport and hemipelagic sediments with encased slope channel complexes richer in sand due to gravity gliding and spreading above the underlying thick mobile messinian salt both stratigraphic units as well as the upper part of the messinian salt layer are faulted and folded

nature and origin of sedimentary clasts associated with mud volcanoes in the nile deep sea fan relationships with fluid venting abstract during the last 10 years several marine geological geophysical surveys conducted on the nile deep sea fan have provided much new information about the large fluid seepage phenomenon which characterizes this passive margin segment among the data more than 60 sediment cores have been recovered in this area rock clasts were collected from eight of them as well as during deep sea dives notably in the area of isis osiris and amon mud volcanoes in few areas especially in the western and the north eastern provinces of the nile fan some clasts consist of crust fragments resulting from cementation of muddy sediment by precipitation of high mg calcite these clasts correspond to a simple cementation of the mud by precipitation of high mg calcite as a consequence no obvious textural or faunal difference with the ambient matrix mud can be observed these clasts are made of autochthonous crusts derived from microbial anaerobic oxidation of methane and release of bicarbonate and sulphide in the surrounding pore water these clasts also lack aragonite in most of the other cases menes caldera isis osiris and amon mud volcanoes allochthonous clasts characterized by low mg calcite cement siderite or dolomite mixed with expelled mud outcrop on the seafloor nannofossils have allowed us to date some of these clasts most of the ages range from pliocene to pleistocene one clast is lower cretaceous in age the lithological facies often indicate coastal or deltaic environments some clasts are closely linked to an evaporite rich environment halite gypsum and analcime they all provide useful information on the nature of buried sedimentary series covering the margin their presence on the seafloor is due to the expulsion of a pressurized mixture of sediment water and gas this process is believed to have used pre existing tectonic conduits

environmental constraints on west antarctic ice sheet formation on etudie la formation et le developpement de l indlandsis marine par un modele numerique qui simule l evolution de la couverture de glace de l antarctique ouest en relation avec le niveau de la mer la vitesse d accumulation et l affluence de glace de l antarctique est

evidence for fluid migration following pockmark formation examples from the nile deep sea fan a large number of pockmarks have been identified in the rosetta region of the western nile deep sea fan co located high resolution 2d and chirp datasets have been used to identify seabed and buried pockmarks which are interpreted to span the holocene to pleistocene period the pockmarks range in size and stratigraphic position from large buried pockmarks to small unit seabed pockmarks clusters of small unit pockmarks are stratigraphically positioned above the centre of large buried pleistocene pockmarks and are used to infer 1 rejuvenation of the larger pockmark conduit once burial has occurred and 2 a change in the frequency and magnitude of pockmark formation events

a coupled marine ice stream ice shelf model theorie des variations climatiques du pleistocene a aujourd hui liees a la dynamique des couvertures marines de glace couplee aux glaces libres flottantes on neglige les effets thermodynamiques et on etudie les processus de flottaison en relation avec les rapports de densite entre la place et l eau de mer

bathymetry of the levant basin interaction of salt tectonics and surficial mass movements abstract a new high resolution bathymetric map of the levant basin between israel and the eratosthenes seamount reveals previously undetected folds faults and channels the map facilitates a regional map view analysis of structures that were previously examined only in cross section the systematic mapping of morpho structural elements in the entire basin is followed by a kinematic interpretation that distinguished between two main processes sculpting the seabed from bottom and top salt tectonics and sediment transport we show that the contractional domain related to salt tectonics is far more complex than previously thought ridges previously interpreted as contractional folds are in fact surficial undulations of the seabed reminiscent of sediment waves moreover other folds previously interpreted as downdip contraction of the westward gliding plio quaternary section are in some parts of the basin caused by updip climbing of this section eastwards as a result of the regional pattern of salt flow away from the nile cone in the context of sediment transport we show that the northern sinai continental slope is covered by a dense net of turbidite channels whereas the levant slope has no channels at all particularly interesting is the levant turbidite channel described and named here for the first time this feature begins at the southeastern corner of the mediterranean at water depths of 1100 m continues along the valley between the sinai and levant slopes and reaches the deepest part of the basin in water depths of 2500 m northeast of the eratosthenes seamount however this prominent feature cannot be explained by the current drainage consisting of two minor rivers that enter the basin at that point and thus most likely reflects periods of wetter climate and or lower sea level when these rivers were more active and possibly connected to the submarine channel system

the eurasian ice sheet formation and collapse resulting from natural atmospheric co2 concentration variations finite element model simulations of ice sheet dynamics are conducted to investigate the role of natural atmospheric co2 variations obtained from ice core bubbles in creating climatic conditions necessary to glaciate the eurasian arctic effects of co2 variations are sufficient to support extensive marine ice sheet and ice shelf development at the last glacial maximum and to deglaciate the region during the holocene from approximately 14 ka to 9 ka the ice sheet coverage simulated for the last glacial maximum agrees with evidence for extensive ice sheet grounding over the shallow continental shelves of the barents kara laptev and east siberian seas an ice shelf also forms over the arctic ocean and greenland and norwegian seas

detailed morphology sedimentary structure and evolution of the continental margin of the western provencal basin south of france since the late miocene abstract seabeam bathymetry and high resolution seismic profiles allow the study of different sedimentary units existing off western provence and to establish their continuity throughout the continental margin from the shelf to the rise the morphology of the slope is greatly controlled by gravity processes leading to phenomena such as canyon piracy or channel avulsion this morphology quite accurately expresses the configuration of the old underlying sedimentary and tectonic structures the sedimentary structure of this domain is the result of the complex arrangement of lobes and ridges that originated from different continental sources and were deposited during different epochs of the plio quaternary knowledge of the old hydrographic networks draining provence during the different quaternary climatic stages allows palaeogeographic reconstructions to be proposed linking these sedimentary units to their continental sources

physical limitations on detecting tunnels using underground focusing spotlight synthetic aperture radar this paper examines the feasibility of underground focusing spotlight synthetic aperture radar uf sl sar systems for tunnel detection applications a general formulation is reviewed for generating uf sl sar imaging by using multiple frequencies across a wide band and by focusing in space to subsurface points using well known ray refraction at the nominal ground surface a full wave finite difference frequency domain model is used to consider wave propagation in realistic soil with loss and frequency dependent dielectric constant and a randomly rough ground surface both of which serve to obscure and distort the returned tunnel target signal imaging results are presented for two representative soil scenarios dry sand and moist clay loam considering the ground surface ray refraction for focusing greatly improves the sar image relative to conventional sar focusing at the ground surface using uf sl sar a small shallow tunnel is reasonably imaged for the sand case despite the roughness of the ground interface however for higher conductivity moist clay loam the clutter from the rough surface overwhelms the significantly attenuated target signal which must propagate through the lossy intervening soil it is demonstrated that despite ideal focusing the tunnel is successfully imaged only for the sand case

the tributary valley systems of the almeria canyon alboran sea sw mediterranean sedimentary architecture three tributary valley systems of the almeria canyon dalias andarax and gata located on the almeria margin alboran sea sw mediterranean were studied using high resolution techniques including swath bathymetry and topas seismic reflection profiles a detailed morphological and seismic stratigraphy study shows that the tributary valley systems tvs are formed by two types of valleys gullies and leveed channels dalias tvs is the best developed system covering an area of more than 300 km 2 from the shelf edge off cabo de dalias to the almeria canyon 100 1500 m depth andarax tvs covers about 65 km 2 from the shelf off the andarax river mouth to the westernmost branch of the almeria canyon 40 300 m depth gata tvs covers more than 100 km 2 from the shelf edge off cabo de gata to the almeria canyon 200 650 m depth tributary valley systems can be divided into two models based on the detailed morpho seismic study the sea level controlled model and the sediment supply controlled model the sea level controlled model includes the dalias and gata tvs this model is mainly governed by sea level fluctuations and the valleys grow as a result of the activity of turbidity currents and hemipelagic sedimentation displaying a retrogressive upslope pattern the valleys development would have been favoured by glacio eustatic oscillations during the late quaternary a tentative chronostratigraphic correlation has been made relating the evolution of dalias and gata tvs with the marine isotopic stages and sea level curves tectonics and margin physiography play a secondary role in the development of this type of valley the sediment supply controlled model is applicable to the andarax tvs the growth of the valleys is controlled by the ephemeral sediment discharges from the andarax river the valleys are small scale gullies located on the shelf and slope which would grow as a result of the turbidity currents which channel the fluvial sediment supplied in form of hyperpycnal currents this model would have been developed during the last highstand of sea level once the coast line reached its present situation d 2005 elsevier b v all rights reserved

regime of the filchner ronne ice shelves antarctica seismic radio echo twerle balloon and oceanographic data of the filchner ronne ice shelves are analysed a large thin area in the central ronne ice shelf is found to differ from the morphology of the ross and filchner ice shelves this area is partly filled by basal saline ice which can be attributed to regional regelation caused by oceanic circulation

near bottom sedimentation processes revealed by echo character mapping studies northwestern mediterranean basin subbottom echoes recorded on 3 5 khz echo sounders in the northwestern mediterranean basin from 1978 to 1991 can be classified into five main categories of echo character 1 continental shelf cs echo character characterizes the continental platform and areas of shallow relief and commonly is related to consolidated sediments 2 hyperbolic h echo character is recorded from areas with rough bottom morphology echo type h1 corresponds to steep slopes echo type h2 reflects very coarse grained sediments deposited by energetic turbidity currents 3 bedded b echo character is widely observed throughout the study area and corresponds to terrigenous deposits distributed by turbidity currents echo type b1 is related to thin turbidites deposited on overbank portions of channel levees by lateral overflow of turbiditic currents moving down the channels echo type b2 corresponds to coarser turbiditic materials 4 rugged r echo character is observed in the axes of submarine canyons and channels and characterizes hard sea floor with coarse heterogeneous turbiditic deposits subjected to energetic gravity flow processes 5 transparent t echo character is ubiquitous in the study area and is attributed to mass movement deposits the widespread occurrence of those deposits testifies to the general instability of the study area types and distribution of echo character throughout the study area show the importance of gravity dominated depositional processes turbidity currents and mass wasting in this region this remobilization of siliciclastic sediments induced by high sediment rates steep slopes and halotectonics theoretically could create potential hydrocarbon reservoirs within the deep water portions of the continental margin

combination of advanced inversion techniques for an accurate target localization via gpr for demining applications we used advanced ground penetrating radar gpr inversion techniques for detecting landmines in laboratory conditions the radar data were acquired with a calibrated vector network analyzer combined with an off ground monostatic horn antenna thereby setting up a stepped frequency continuous wave radar major antenna effects and interactions with the soil and targets were filtered out using frequency dependent complex antenna transfer functions the proposed strategy first exploits inversion approaches that are able to give an accurate characterization of the antenna soil interaction and a reliable estimate of the soil permittivity the outcomes of this first phase are at the basis of the application of a microwave tomographic approach based on the born approximation to achieve the imaging of the subsurface the algorithms were applied for imaging three landmines of different sizes and buried at different depths in sand although the radar system was off the ground the results showed that it was possible to reconstruct all mines including a shallow plastic mine as small as 5 6 cm in diameter this last mine was invisible in the raw radar data and the use of common gpr imaging techniques did not lead to satisfactory results the proposed integrated method shows great promise for shallow subsurface imaging in a demining context particularly because it automatically provides accurate information on the shallow soil dielectric permittivity

deposition processes from echo character mapping along the western algerian margin oran tenes western mediterranean abstract the westernmost algerian margin south algero provencal basin depicts a few offshore active faults moderate to rare seismicity and generally very steep slopes 16 we classified and mapped 12 echo types according to their sub bottom acoustic facies observed on this margin on 2 5 2 khz chirp echo sounder data maradja 2003 cruise the echo character maps are interpreted in terms of sedimentary processes the b1 echo type parallel to subparallel high to low amplitude sub bottom reflections mainly in the deep basin corresponds to hemipelagic sedimentation r1 prolonged single echo with no sub bottoms and r2 small irregular overlapping hyperbolae echo types generally near or in canyon systems are associated with turbidity currents or more rarely to contour currents or mass transport deposits such as slumps slides and debris flows the transparent echo types t1 t5 and r3 chaotic lens of low amplitude reflections on top of higher amplitude often located at the foot of the slope or canyons walls typically indicate mass transport deposits like slides or turbidites large zones that display a large variety of echo types are evidenced in the study area and are generally associated with turbidity currents but could also be associated with bottom currents it appears that active tectonics plays a significant role in this part of the margin which presents a few active faults offshore but also a strong and relatively frequent seismicity onland the general pattern of the distribution of mass transport deposits is particular i e many but small slides all along the margin and suggests a probable triggering by recurrent earthquake shakings however active tectonics is not the only factor influencing the deposition pattern as some zones seem characterized by predominant strong turbidity currents transporting sediments far away from the foot of the margin whereas others depict retrogressive erosion features on the slope i e small slides scarps in gullies rather than transport by turbidity currents in particular the rivers sediment discharge fluxes and the geomorphologic characteristics of the margin seem to be very important factors too

acoustic facies of holocene megaturbidites in the eastern mediterranean abstract the acoustic facies of holocene megaturbidites in the central western abyssal plains of the eastern mediterranean sea is analysed combining core lithology and synthetic seismograms produced on the basis of p wave velocity profiles derived by multi sensor core logging from a core in the western herodotous trough the acoustic facies of the megaturbidite is divided in two layers 1 an upper transparent low velocity layer corresponding to structureless mud 2 a lower highly reflective high velocity layer corresponding to the graded sandy base correlation with sub bottom profiler data allowed us to estimate in about 21 23 m the maximum total thickness of the two layer megaturbidite in the ionian abyssal plain these results demonstrate that thicknesses traditionally computed on the basis of the acoustically transparent layer alone may produce a relevant underestimation of the total volume of the deposit the total volume of the megaturbidite extending over the ionian and sirte abyssal plains including the western herodotous trough is therefore estimated in about 162 10 km 3

gpr phase based techniques for profiling rough surfaces and detecting small low contrast landmines under flat ground we present a new technique whereby phase variation signatures are used to profile two dimensional 2 d rough surfaces and to discern shallowly buried small low contrast landmines under a flat ground the method has been tested using data measured over a composite surface containing two rough dielectric surface patches and over a flat ground under which small low contrast antipersonnel landmines are shallowly buried the results show that the phase based technique is capable of profiling rough surfaces and of detecting small low contrast landmines with different internal structures buried underneath a flat ground

morphostructure growth patterns and tectonic control of the rhone and nile deep sea fans a comparison the rhone and the nile rivers shape the sediment distribution of the ligurian and the levantine basins in the mediterranean sea respectively both rivers cut huge canyons in their bed rock during the messinian desiccation of the mediterranean and the subsequent early pliocene marine transgression reached far inland both in france and in egypt the sediment supply of both rivers was affected by climatic variations during the pleistocene but whereas glacial periods were associated with reduced water flow in the rhone they can be correlated with enhanced flow of the nile the sediment distribution and accumulation patterns of both rivers built large deltas on their continental shelves during high sea level stands during lowstands both rivers flowed as far as the shelf e ge and transported their sedimentary load through the continental slopes directly to their deep sea fans the patterns of sediment distribution and accumulation in the marine basins of the ligurian and the levantine seas were affected also by pliocene quaternary tectonic activity and halokinetic offsets that led to sediment instability the present hydrographic and sedimentological regimes of both rivers do not represent their natural potential due to artificial interference the principal economic significance of the deep sea fan accumulation process is the transportation of medium and coarse grained sediments into the deep marine basin considering the effect of these sediments on stratal permeabilities and hydrocarbon potential the presented comparative overview emphasizes recent and subrecent sedimentological aspects that are critical to petroleum exploration in active and extinct deep sea depositional environments

new perspectives on paleoglaciology abstract paleoglaciology deals with glaciation cycles of the quaternary ice age it combines the dynamics of present day ice sheets deduced from glaciology with the history of former ice sheets deduced from glacial geology cosmogenic dating now makes a detailed chronology of a cycle possible radiocarbon dating has provided a detailed chronology for termination of the last cycle but cannot date how the cycle began here we identify the central challenge in applying paleoglaciology to quaternary glaciation cycles in general and initiation of these cycles in particular the challenge is the role of thickening sea ice in the arctic ocean possibly becoming thick ice shelves floating over deep arctic basins and high marine ice sheets grounded on shallow arctic continental shelves in that case an arctic ice sheet existed that was larger and less stable than the antarctic ice sheet is now or in the past two approaches to this problem are presented as part 1 and part 2 in part 1 the height of these former ice sheets is linked primarily to the strength of ice bed coupling which is deduced from glacial geology it provides snapshots of ice sheets that give ice elevations independent of the past history and largely independent of ice surface conditions temperatures and the mass balance in particular in part 2 heights of former ice sheets depend on both their past history particularly initial conditions and changing surface conditions during the glaciation cycle this provides a motion picture of ice sheets during the full cycle the challenge is to establish a mind meld of these two approaches they allow new perspectives on paleoglaciology

the relative importance of gravity induced versus current controlled sedimentation during the quaternary along the mideast u s outer continental margin revealed by 3 5 khz echo character abstract a detailed echo character map based on more than 50 000 km of 3 5 khz echograms reveals the relative importance of contour currents turbidity currents and mass wasting processes for the upper 50 100 m of sea floor sediments along the u s continental margin between southern georges bank and cape hatteras nineteen individual echo types are mapped and interpreted as deposits produced either by current controlled or gravity induced processes based on echo type distribution analysis of selected sediment core samples and the published results of other workers turbidity currents and mass wasting have apparently been the primary depositional agents throughout 60 of the region in contrast contour currents alone appear to have influenced only 10 of the region however combined processes i e non separable interaction between downslope and parallel to contour processes have influenced an estimated 25 of the margin the remaining 5 of the study area constitutes the outermost continental shelf echo types here reflect the influence of fluvial deltaic and shallow marine sedimentary processes changes in the relative distributions of various echo types with sea floor depth indicate that the dominant sedimentary processes change downslope and are significantly different within each physiographic province deposits formed by mass wasting dominate the continental slope where 50 of the sea floor is eroded and gullied by slides slumps and the heads of debris flows deposits developed under the influence of combined processes are most wide spread on the upper continental rise and cover 40 of the sea floor primarily in the form of deep sea channel levees modified by contour currents on the lower continental rise turbidites form more than 50 of the sea floor deposits the downslope deposits turbidity currents slumps debris flows etc were emplaced primarily during the pleistocene glacioeustatic sea level lowering moved beaches and rivers across the exposed continental shelf to the shelf edge where massive fluxes of terrigenous sediment could be delivered to the continental slope and rise by turbidity currents significant amounts of this sediment were transported through submarine canyons and leveed deep sea channels to the lower continental rise and formed the lower continental rise terrace a flat turbidite basin ponded behind the hatteras outer ridge southwest of the wilmington channel this glacially derived influx was diminished however depositional patterns indicate that downslope processes continued to be dominant at least as far south as cape hatteras where rapid deposition on the continental slope and uppermost continental rise created instabilities slope failure produced slumps slides and debris flows and provided an additional volumetrically important redistribution of sediment downslope the influence of contour currents is clearly observed only in those areas topographically shielded from the masking effects of downslope processes in particular along the seaward side of the buried chesapeake drift and the hatteras outer ridge

multibeam backscatter as a tool for sea floor characterization and identification of oil spills in the galicia bank this study is focused on the potential of using the multibeam acoustic backscatter both for sea floor characterization of the galicia bank and for identification of sea bottom oil spills an extended multibeam data set was acquired during the rg 1 and rg 2 surveys aboard rv hesperides in 2003 for the geological and geophysical characterization of the galicia bank where the oil tanker prestige wreck is located 3 d images have been made by integrating bathymetry and backscatter data multibeam data have been additionally supported by gravity core information in order to correlate sea floor acoustic backscatter with the surficial sediments and their physical properties the major factors that seem to control the zonation of the backscatter intensity images are i the type of the sedimentary processes gravitational turbiditic hemipelagic which control at the same time the grain size distribution and ii the sea bottom morphologies such as basement outcrops however there are some backscatter halos that cannot be explained by these processes in the backscatter maps the bow and stern of the prestige wreck are clearly marked by a high backscatter intensity anomaly whose existence is discussed

a novel signal processing technique for clutter reduction in gpr measurements of small shallow land mines a signal processing technique is developed to reduce clutter due to ground bounce in ground penetrating radar gpr measurements this technique is especially useful when a gpr is used to detect subsurface antipersonnel mines the gpr clutter is modeled using a simple parametric model buried mine and clutter contributions are separated through a pair of coupled iterative procedures the algorithm outperforms existing clutter reduction approaches and also yields target features that are useful for detection and identification of these mines the proposed technique effectively reduces clutter resulting in a significant decrease in false alarm rates

turbidites and megaturbidites from the herodotus abyssal plain eastern mediterranean unrelated to seismic events abstract a transect of 9 piston and gravity cores was taken across the southeast flank of the mediterranean ridge the transect extends from the abyssal plain to a location 290 m shallower than the abyssal plain and 50 km north of the edge of the ridge each core contains two or more turbiditic layers which belong to two discrete types here called a and b type a essentially consists of black plastic clays rich in smectite with silt fraction of terrigenous nature source area is the nile cone and age is middle or late pleistocene type b turbidites are pale brown to whitish in color coarse grained carbonate rich and bioclastic in composition with shallow water fossils dominant they are poor in smectite and the silt fraction is very rich in carbonates calcite and aragonite the source area is the north african shelf south of the abyssal plain a megabed belonging to type b turbidites is correlatable from core to core with a thickness in excess of 10 m in the abyssal plain and an estimated volume of 10 km 3 its stratigraphic position in the latest pleistocene suggests that its origin is related to a sudden collapse of bioclastic sediments accumulated in a canyon head during a low sea level stand the source areas of the two discrete turbidite types belong to the essentially aseismic north african continental margin although they are presently recorded on the tectonically active mediterranean ridge no seismic events are required to account for the presence of either type of turbidite

the spatial pattern and drainage cell characteristics of a pockmark field nile deep sea fan over 25 300 seabed pockmarks were mapped from the rosetta channel region of the western niledeepseafan ndsf using concurrent high resolution 2d chirp profiler and multibeam bathymetry data which spans the holocene pleistocene period within the region apockmarkfield containing 13 800 pockmarks was analysed using spatial statistics to determine the distribution of pockmarks within the field pockmarks within the field are small 16 m diameter shallow 0 5 m deep circular depressions which formed within the last 6500 years the fluid source for the field is identified as an accumulation generation of gas beneath a hemipelagic seal c 20 40 ms beneath the seabed the position of the pockmarks is shown to be unrelated to the depth to the fluid source and an irregular high amplitude acoustic anomaly which is tentatively interpreted as a possible carbonate precipitate of biogenic microbial activity statistical spatial analysis of the field confirms the distribution of pockmarks is not random an exclusion zone surrounding each individual pockmark is identified the exclusion zone is a unique minimum radius around each pockmark which is not penetrated by any other pockmark the exclusion zone works in unison with self organised criticality soc in determining the spatial distribution of pockmarks within the field the exclusion zone is interpreted as apockmark drainagecell a conceptual model for apockmarkdrainagecell is proposed whereby pockmark formation dissipates a radius area of fluid and overpressure thereby preventing the formation of another pockmark within that cell consequently pockmarks are observed to separate or produce anti clustering tendencies within the field

multi disciplinary investigation of fluid seepage on an unstable margin the case of the central nile deep sea fan we report on a multidisciplinary study of cold seeps explored in the central nile deep sea fan of the egyptian margin our approach combines in situ seafloor observation geophysics sedimentological data measurement of bottom water methane anomalies pore water and sediment geochemistry and 230 th u dating of authigenic carbonates two areas were investigated which correspond to different sedimentary provinces the lower slope at 2100 m water depth indicates deformation of sediments by gravitational processes exhibiting slope parallel elongated ridges and seafloor depressions in contrast the middle slope at not vert 1650 m water depth exhibits a series of debris flow deposits not remobilized by post depositional gravity processes significant differences exist between fluid escape structures from the two studied areas at the lower slope methane anomalies were detected in bottom waters above the depressions whereas the adjacent ridges show a frequent coverage of fractured carbonate pavements associated with chemosynthetic vent communities carbonate u th age dates 8 kyr bp pore water sulphate and solid phase sediment data suggest that seepage activity at those carbonate ridges has decreased over the recent past in contrast large 1 km2 carbonate paved areas were discovered in the middle slope with u th isotope evidence for ongoing carbonate precipitation during the late holocene since 5 kyr bp at least our results suggest that fluid venting is closely related to sediment deformation in the central nile margin it is proposed that slope instability leads to focused fluid flow in the lower slope and exposure of fossil carbonate ridges whereas pervasive diffuse flow prevails at the unfailed middle slope

slow physics of large continental ice sheets and underlying bedrock and its relation to the pleistocene ice ages very simple two component models of the earth s cryosphere lithosphere system are analyzed the models consist of a continental ice sheet coupled to a responding earth model because of relatively long response times of the bedrock at least over shorter wavelengths long period of the order of 50 000 years internal or free oscillations in the system occur over a wide range of parameters and parameterizations the oscillatory mechanism operates primarily in the ablation zone and in particular at the firn line these free oscillations could play a dynamic role in the response of the climate system to eccentricity forcing a simple analysis presented strongly suggests that for the simplest rheological models of the earth response to pleistocence ice sheets elastic response is confined to a layer considerably less than the thermal thickness of the lithosphere furthermore because of the striking lack of geological evidence for large depressions of bedrock at the leading edge of growing continental ice sheets predicted by viscoelastic models of the earth more sophisticated rheological models of the earth s uppermost layer appear necessary

submarine fan systems i characterization and stratigraphic prediction submarine fan and related deep marine clastic systems such as submarine ramps and slope aprons are important hydrocarbon reservoirs in many parts of the world the origin and character of these systems reflect a complex interplay between a range of autocyclic and allocyclic controls including sea level fluctuations basinal tectonics and the rate type and nature of sediment supply these controls are commonly interdependent this paper reviews the characteristics which distinguish different submarine fans and their subsurface prediction then proposes a classification framework for fans which discriminates between different systems on the basis of their fundamental controls the proposed classification is discussed in terms of its value as a predictive tool in hydrocarbon exploration development and production a modus operandi is developed which uses the classification for reservoir description and prediction and involves three stages of investigation basin screening fan delineation and fan characterization each stage demands the integration of a range of tools and techniques including sequence stratigraphy seismic facies analysis seismic redisplay and geophysical modeling these stages of analysis are linked in turn with core and wireline log data to constrain the range of possible fan types within a basin fill and assess the implications for reservoir seal and trap development this structured approach to stratigraphic analysis is also valuable in constraining the range of reservoir architectural options in appraisal development and production

the mode and mechanism of the last deglaciation oceanic evidence changes in ocean temperature carbonate productivity and ice rafted detritus in the north atlantic suggest that half of the northern hemisphere ice volume at the last glacial maximum had disappeared by 13 000 yr b p despite the still extensive limits of the ice sheets this early thinning of the ice sheets occurred during a time when summer insolation values were slowly rising but when pollen evidence south of the ice margins indicates cold dry air masses we infer that this rapid early ice disintegration 16 000 13 000 yr b p was caused by oceanic mechanisms 1 rising sea level causing increased calving along ice margins 2 the chilling of the sea surface by icebergs and meltwater reducing moisture extraction by the atmosphere and transport to the ice sheets and 3 winter freezing of the low salinity meltwater layer suppressing local moisture extraction and the regional influx of moisture bearing storms from lower latitudes in winter and hence starving the ice sheets these oceanic feedback mechanisms were strongest from 16 000 to 13 000 yr b p and weaker but still active from that date until the end of deglaciation at 6000 yr b p

diversion and morphology of submarine channels in response to regional slopes and localized salt tectonics levant basin abstract in the levant basin submarine channels are abundant around the nile deep sea fan ndsf an area which is also affected by salt tectonics related to the messinian salt giant here we focus on the relationship between submarine channels and obstacles formed by salt tectonics initially we use methods developed for terrestrial morphological analysis and quantify channel sinuosity width and slope in search for consistent relationships between morphometric parameters and channel response to obstacles however this traditional analysis did not yield robust conclusions then we apply two new morphometric parameters suggested here to express the distortion of channels by obstacles incident angle defined as the acute angle between the regionally influenced channel direction and the strike of the tectonic obstacle and diversion angle defined as the angle between the direction of the regional bathymetric slope and the average direction of the channel these parameters illustrate the influence of the regional scale basin geometry and the superimposed tectonic influenced seabed patterns on channel development we found hyperbolic relationships between incident angle and diversion angle in which channels flowing approximately parallel 0 to tectonic folds are obviously not diverted channels nearly orthogonal 90 to obstacles crosscut them right through and again not diverted much in contrast channels with a general direction diagonal to the obstacles 40 are diverted by ten degrees 10 this diversion accumulates along large distances and significantly influences the regional development of channels around the ndsf noteworthy this phenomenon of channel diversion indirectly deteriorate normal slope sinuosity relationships known from terrestrial studies in light of these findings we suggest that these new parameters can be applied to other basins where submarine channels interact with seabed obstacles

the effects of basal melting on the present flow of the ross ice shelf antarctica on utilise un modele mixte aux elements finis et differences finies de l ecoulement et du transfert de chaleur avec deux hypotheses fusion nulle partout et fusion equilibrant tout epaississement a grande echelle

marine ice sheet decoupling as a mechanism for rapid episodic sea level change the record of such events and their influence on sedimentation abstract unlike terrestrial ice sheets marine ice sheets display more sensitivity to sea level than to climate and they are capable of rapid mass wasting this mass wasting involves ice shelf decoupling from the sea floor and rapid collapse followed by drawdown of the ice sheet glaciologists argue that the marine ice sheet decoupling mechanism could cause sea level rises of a few meters within several hundred years information regarding late wisconsinan holocene glacial history suggests that ice sheet deterioration did not occur at a steady rate studies of the antarctic continental shelf indicate ice sheets grounded over large portions of the shelf during the late wisconsinan glacial maximum and that their retreat from the continental shelf was rapid a study of the trinity sabine incised valley of the texas continental shelf yields a continuous record of holocene sedimentation and sea level change paired upper bay and tidal inlet estuarine systems reflect periods when relative sea level was either at a still stand or slowly rising the flooding surfaces of back stepping parasequences reflect periods of rapid sea level rise large sand bodies on the adjacent shelf used to derive previous sea level curves for the region may represent former shoreline deposits but they also show extensive reworking therefore the curves generated from studies of these sand bodies are inaccurate marine ice sheets have existed in antarctica since at least the late eocene so this mechanism for rapid sea level rise has been active throughout much of cenozoic time as well as during older glacial episodes

salt tectonics driven by sediment progradation part ii radial spreading of sedimentary lobes prograding above salt experimental models indicate that sedimentary lobes deposited above mobile evaporites deform gravitationally by spreading outward radially radial spreading forms both concentric and radial families of thin skinned grabens that are then pierced diapirically by salt ridges the overburden blocks located between the ridges become subsiding depocenters later continued spreading after depletion of the salt layer forces salt ridges and diapirs to fall forming rapidly subsiding bathymetric lows that channel or trap younger sediments spreading causes large horizontal overburden movements whose distribution and orientation change when the locus of regional deposition shifts

early deglaciation of the greenland sea during the last glacial to interglacial transition abstract isotopic and sedimentological analysis of a core from the southern greenland sea northwest of the present polar front exhibits a high input of ice rafted acidic continental material between 9000 and 18 000 yrs b p replacing basic icelandic products which are commonly found before and after that period this indicates that summer melting of sea ice in the norwegian greenland basin began as early as 18 000 b p permitting the southward drift of icebergs produced by rapid ablation of northern ice sheets

on the structure and origin of major glaciation cycles 2 the 100 000 year cycle climate over the past million years has been dominated by glaciation cycles with periods near 23 000 41 000 and 100 000 years in a linear version of the milankovitch theory the two shorter cycles can be explained as responses to insolation cycles driven by precession and obliquity but the 100 000 year radiation cycle arising from eccentricity variation is much too small in amplitude and too late in phase to produce the corresponding climate cycle by direct forcing we present phase observations showing that the geographic progression of local responses over the 100 000 year cycle is similar to the progression in the other two cycles implying that a similar set of internal climatic mechanisms operates in all three but the phase sequence in the 100 000 year cycle requires a source of climatic inertia having a time constant similar to 15 000 years much larger than the other cycles similar to 5 000 years our conceptual model identifies massive northern hemisphere ice sheets as this larger inertial source when these ice sheets forced by precession and obliquity exceed a critical size they cease responding as linear milankovitch slaves and drive atmospheric and oceanic responses that mimic the externally forced responses in our model the coupled system acts as a nonlinear amplifier that is particularly sensitive to eccentricity driven modulations in the 23 000 year sea level cycle during an interval when sea level is forced upward from a major low stand by a milankovitch response acting either alone or in combination with an internally driven higher frequency process ice sheets grounded on continental shelves become unstable mass wasting accelerates and the resulting deglaciation sets the phase of one wave in the train of 100 000 year oscillations whether a glacier or ice sheet influences the climate depends very much on the scale the interesting aspect is that an effect on the local climate can still make an ice mass grow larger and larger thereby gradually increasing its radius of influence

recent depositional patterns of the nile deep sea fan from echo character mapping the nile deep sea fan was surveyed in 1998 using swath multibeam bathymetry backscatter imagery and 3 5 khz and seismic profiling on the basis of this new data set the fan has been divided into three main provinces western central and eastern recent sedimentary patterns as deduced from echo character mapping show that gravity induced sedimentary deposits are predominant and are expressed through either slides debris flows or turbidites turbidity processes are particularly active in the westernmost province through a well developed network of deep sea channels this network controls turbiditic flows that subsequently overflow levees mass wasting processes are extremely efficient all over the nile deep sea fan in the upper central province a broad allochthonous tongue of mass flow deposits generated by slope destabilizations may have led to channel avulsions and migrations in the eastern province a northwest southeast deformed belt resulting from combined deep seated and salt related tectonics contains large proportions of destabilized sediments i e originating from destabilization processes such as mass movements probably settled by recent tectonic activity this article highlights 1 the influence of both thin skinned and thick skinned tectonics on sedimentary distribution and 2 the predominance of gravity induced sediments turbidites slides and mass flows in such submarine fans the distribution of debris flows and sedimentary deposits settled by turbidity currents appears fundamental in predicting reservoir geometry and economic potential

three dimensional imaging of multicomponent ground penetrating radar data scalar imaging algorithms originally developed for the processing of remote sensing measurements e g the synthetic aperture radar method or seismic reflection data e g the gazdag phase shift method are commonly used for the processing of ground penetrating radar gpr data unfortunately these algorithms do not account for the radiation characteristics of gpr source and receiver antennas or the vectorial nature of radar waves we present a new multicomponent imaging algorithm designed specifically for vector electromagnetic wave propagation it accounts for all propagation effects including the vectorial characteristics of the source and receiver antennas and the polarization of the electromagnetic wavefield a constant offset source receiver antenna pair is assumed to overlie a dielectric medium to assess the performance of the scalar and multicomponent imaging algorithms we compute their spatial resolution function which is defined as the image of a point scatterer at a fixed depth using a

ground penetrating radar for high resolution mapping of soil and rock stratigraphy ground penetrating radar is a technique which offers a new way of viewing shallow soil and rock conditions the need to better understanding overburden conditions for activities such as geochemical sampling geotechnical investigations and placer exploration as well as the factors controlling groundwater flow has generated an increasing demand for techniques which can image the subsurface with higher resolution than previously possible the areas of application for ground penetrating radar are diverse the method has been used successfully to map ice thickness water depth in lakes bedrock depth soil stratigraphy and water table depth it is also used to delineate rock fabric detect voids and identify karst features the effective application of the radar for the high resolution definition of soil stratigraphy and fractures in bedrock is highlighted the basic principles and practices involved in acquiring high quality radar data in the field are illustrated by selected case histories one example demonstrates how radar has been used to map the bedrock and delineate soil horizons to a depth of more than 20 m two case histories show how radar has been used to map fractures and changes of rock type to 40 m range from inside a mine another case history demonstrates how radar has also been used to detect and map the extent of groundwater contamination the corroboration of the radar results by borehole investigations demonstrates the power and utility of the high resolution radar method as an aid for interpolation and extrapolation of the information obtained with conventional coring programmes with the advent of new instrumentation and field procedures the routine application of the radar method is becoming economically viable and the method will see expanded use in the future

the rotation of arabia and the levant fault system abstract we establish the kinematics of the rotation of arabia with respect to africa and show that the rotation rate of africa increased by a factor of about four in late serravallian time about 12 13 ma ago we discuss evidence that oceanic accretion started simultaneously in the gulf of aden and in the red sea at this time it is also at this time that the levant and anatolian fault systems were initiated our initial reconstruction of the red sea rift in late oligocene early miocene time approximately superposes the present shore lines which coincide with the mid point of the zones of rapid crustal thinning the future continental slopes the amount of extension during the early phase of continental rifting is obtained by assuming that the total volume of continental crust is conserved during extension and by checking these estimates through closure around the sinai triple junction in the late miocene the southern evant fault zone was a zone of distributed shear deformation through counterclockwise block rotation extending soul h ward within the northernmost red sea since the early pliocene the shear motion has been localized within the gulf of aqaba changing the tectonic pattern in the northern red sea

late tertiary structure and stratigraphy of north sinai continental margin new seismic data provide information on the structural development and late tertiary stratigraphy of the continental slope and rise off northern sinai the upper continental slope is characterized by a marginal plateau composed of a series of platforms or steps the lower continental slope is smooth except for a low ridge paralleling the western part numerous diapiric structures along the continental margin north of the sinai peninsula emerge from an evaporitic layer of late tertiary age the diapirs usually are aligned along west northwest trending faults a salt ridge 90 km long produces a submarine ridge in the lower continental rise two main fault trends have been mapped in the western part of the continental margin they trend west northwest and in the eastern part northeast these trends parallel the continental slopes of northern sinai and southern israel respectively the structural grain of the sinai margin appears to be controlled by two main tectonic elements 1 rejuvenated basement faults of the continent ocean transition zone and 2 salt diapirism due to loading of messinian evaporites with nile derived upper tertiary clastics

sedimentation on the ross sea continental shelf antarctica abstract glacial marine sedimentation has prevailed throughout most of the early glacial history of the ross sea region however since late miocene to early pliocene time the west antarctic ice sheet has advanced onto the continental shelf perhaps several times glacial troughs of the western ross sea may also have formed at this time these glacial troughs border outlet glaciers of the east antarctic ice sheet a widespread lodgement till facies was deposited during this glacial advance holocene retreat of this expanded ice sheet left no conspicuous meltwater record so decoupling of the ice sheet from the seafloor rather than rapid melting is implied modern glacial sediment is far less prevalent than biogenic sediment and reworked glacial sediment except in coastal areas adjacent to small ice shelves and ice tongues little or no debris is being transported beyond the calving line of the ross ice shelf siliceous mud and ooze occurs in the western ross sea where surface circulation is most vigorous and warm deep waters up well this siliceous sediment along with terrigenous silt and clay blankets the seafloor below approximately 300 m water depth most of the ross sea continental shelf is deeper than this surface sediments on shallow banks and coastal platforms have clearly been reworked by marine currents the most vigorous bottom current activity occurs in those areas where geostrophic currents impinge onto the shelf debris flows and turbidity currents are also important in eroding and redistributing glacial sediments on the shelf terrigenous silt and clay are more abundant in surface sediment than basal till the source of this silt and clay is problematic the most plausible sources being onshore transport of suspended sediment by impinging currents and subglacial meltwater input

the influence of continental ice sheets on the climate of an ice age the climate influence of the land ice that existed 18 000 years before present 18k b p is investigated by use of a general circulation model of the atmosphere coupled with a static mixed layer ocean simulated climates are obtained from two versions of the model one with the land ice distribution of the present and the other with that of 18k b p in the northern hemisphere the tropospheric flow field is strongly influenced by the laurentide ice sheet and features a split flow straddling the ice sheet with a strong jet stream forming the southern branch the northern branch of the flow brings very cold air over the north atlantic ocean where thick sea ice is maintained the distribution of sea surface temperature sst difference between the two experiments in the northern hemisphere resembles the difference between the sst at 18k b p and at present as estimated by the climap project 1981 the 18k b p ice sheets have very little influence upon atmospheric temperature and sst in the southern hemisphere this is because the interhemispheric heat transport hardly changes as the loss of heat energy due to the reflection of solar radiation by continental ice sheets in the northern hemisphere is almost completely counterbalanced by the in situ reduction of upward terrestrial radiation hydrologic changes in the model climate are also found with statistically significant decreases in soil moisture occurring in a zone located to the south of the ice sheets in north america and eurasia these findings are consistent with some geological evidence of regionally drier climates from the last glacial maximum

global positioning system constraints on plate kinematics and dynamics in the eastern mediterranean and caucasus we present and interpret global positioning system gps measurements of crustal motions for the period 1988 1997 at 189 sites extending east west from the caucasus mountains to the adriatic sea and north south from the southern edge of the eurasian plate to the northern edge of the african plate sites on the northern arabian platform move 18 2 mm yr at n25 5 w relative to eurasia less than the nuvel 1a circuit closure rate 25 1 mm yr at n21 7 w preliminary motion estimates 1994 1997 for stations located in egypt on the northeastern part of africa show northward motion at 5 6 2 mm yr also slower than nuvel ia estimates 10 1 mm yr at n2 4 e eastern turkey is characterized by distributed deformation while central turkey is characterized by coherent plate motion internal deformation of 2 mm yr involving westward displacement and counterclockwise rotation of the anatolian plate the anatolian plate is de coupled from eurasia along the right lateral strike slip north anatolian fault naf we derive a best fitting euler vector for anatolia eurasia motion of 30 7 0 8 n 32 6 0 4 e 1 2 0 1 myr the euler vector gives an upper bound for naf slip rate of 24 1 mm yr we determine a preliminary gps arabia anatolia euler vector of 32 9 1 2 n 40 3 1 1 e 0 8 0 2 myr and an upper bound on left lateral slip on the east anatolian fault eaf of 9 1 mm yr the central and southern aegean is characterized by coherent motion internal deformation of 2 mm yr toward the sw at 30 1 mm yr relative to eurasia stations in the se aegean deviate significantly from the overall motion of the southern aegean showing increasing velocities toward the trench and reaching 10 1 mm yr relative to the southern aegean as a whole

formulation of ice shelf dynamic boundary conditions in terms of a coulomb rheology coastal boundaries where fast flowing ice shelves shear past stagnant grounded ice are typically riven with surface crevasses seawater filled basal crevasses and tidal strand cracks here we formulate a boundary condition describing stress transmission through these fractured boundaries in terms of the coulomb law as a result of this formulation agreement between finite element simulations of the ross ice shelf flow and field observations is improved over agreement obtained with formulations which do not account for ice failure our results additionally suggest that shear stress transmitted through ice shelf boundaries is lower than previously thought

paleoclimatic constraints on the maintenance of possible ice shelf cover in the norwegian and greenland seas we examine the controversial issue of whether or not an integrated ice shelf existed in the norwegian and greenland seas during glacial events of the pleistocene our method consists of testing for equilibrium ice shelf configurations with the use of a finite element model that predicts ice shelf evolution under a variety of atmospheric and oceanic forcing conditions ice flow at the margins of the simulated hypothetical ice shelf is determined from one of denton and hughes 1981 reconstructions of continental glaciation applicable to the last glacial maximum our results suggest that the existence of the ice shelf and possibly surrounding marine based ice sheets depends most sensitively on oceanic heat flux a heat flux of approximately 4 80 j m 2 s 1 corresponding to an area average basal melting rate of 0 50 m a 1 ice equivalent is near the upper limit allowing ice shelf equilibrium greater heat flux is found to cause an initial 450 m thick ice shelf to rapidly collapse the equilibrium ice shelf configurations examined provide effective buttressing support for the marine ice sheet grounded in the barents sea 18 kyr b p tests confirming the existence of ice shelf cover in the norwegian and greenland seas are possible through a comparison of the sedimentary record of ice rafted debris with ice shelf flow patterns deduced from our simulations

widespread active seepage activity on the nile deep sea fan offshore egypt revealed by high definition geophysical imagery fluid escape structures on the nile deep sea fan were investigated during the mediflux mimes expedition in 2004 mud volcanoes pockmarks and authigenic carbonate structures were surveyed for the first time with a high resolution deep towed 75 khz sidescan sonar and a 2 8 khz chirp sediment echosounder in combination with existing multibeam bathymetry and detailed seafloor in situ geological observations these new data allowed detailed seep analyses about 60 gas flares were detected acoustically in the water column from the sidescan sonar raw data atwater depths from 770 to 1700 m these gas flares coincide at the seabed with 1 the centres of the mud volcanoes where mud is also extruded 2 the borders of the mud volcanoes where the emitted gases contribute to the precipitation of authigenic carbonates and 3 to the edges of broad sheets of authigenic carbonates subsurface sediments are commonly disturbed by ascending fluids throughout the delta with an abundance of seep related carbonate structures on the seafloor the feeder channels below mud volcanoes similar to the gas conduits below the widespread carbonate crust structures and pockmarks are relatively narrow and for the vast majority of them do not exceed a few metres in diameter the seeps on the nile deep sea fan clearly follow lineations on the seafloor that ee can relate to faults

filtering soil surface and antenna effects from gpr data to enhance landmine detection the detection of antipersonnel landmines using ground penetrating radar gpr is particularly hindered by the predominant soil surface and antenna reflections in this paper we propose a novel approach to filter out these effects from 2 d off ground monostatic gpr data by adapting and combining the radar antenna subsurface model of lambot with phase shift migration first the antenna multiple reflections originating from the antenna itself and from the interaction between the antenna and the ground are removed using linear transfer functions second a simulated green s function accounting for the surface reflection is subtracted the green s function is derived from the estimated soil surface dielectric permittivity using full wave inversion of the radar signal for a measurement taken in a local landmine free area third off ground phase shift migration is performed on the 2 d data to filter the effect of the antenna radiation pattern we validate the approach in laboratory conditions for four differently detectable landmines embedded in a sandy soil compared to traditional background subtraction this new filtering method permits a better differentiation of the landmine and estimation of its depth and geometrical properties this is particularly beneficial for the detection of landmines in low contrast conditions

geodetic determination of the kinematics of central greece with respect to europe implications for eastern mediterranean tectonics we use a new satellite laser ranging global positioning system slr gps solution at seven sites in anatolia and aegea to obtain a better definition of the extrusion motion of the anatolian aegean block with respect to europe we show that this motion can be described in a first approximation by a counterclockwise rotation which transfers most of the motion of arabia to anatolia we combine 78 displacement vectors obtained at common points of two triangulation nets measured in central greece in 1895 and 1975 with the slr gps measurements to compute the velocity field over greece with respect to europe these measurements indicate that central greece is a zone of extension between the anatolian aegean counterclockwise rotation to the south and the northern greece clockwise rotation to the north this extension is principally localized within the gulf of corinth to the east but is distributed to the west we then extrapolate this velocity field to the whole aegea and western anatolia using recently published gps results as well as the slr results the narrow dextral north anatolian fault which limits the velocity field to the north progressively gives way to a much wider boundary zone where extension becomes dominant we show that the collision between the mediterranean ridge and africa began 3 6 ma and we describe the modifications that this collision has produced on the kinematic pattern both in aegea and on the mediterranean ridge