three dimensional attenuation structure beneath north island new zealand abstract three dimensional attenuation structure beneath north island new zealand is determined by inversion of seismic intensity data the method developed by hashida and shimazaki is used the seismic intensity is converted to the maximum acceleration of the s wave to obtain the acceleration at a point source and the attenuation structure because seismic intensity data have been accumulated on a uniform scale in new zealand since the 1950 s we were able to use more than 2000 seismic intensity data from 26 earthquakes the results show a remarkable contrast in the attenuation structure in the top crustal layer a low q area corresponding to the central volcanic region is found this low q area becomes wider to the northeast of north island suggesting that the central volcanic region continues to the havre trough a young back arc basin the southeastern part of the upper mantle beneath north island shows high q while the northwestern part shows low q the cross section shows that the high q region is dipping to the northwest with a large amount of dip in the northeast and a smaller dip in the southwestern part of north island a comparison of the attenuation structure with microearthquake distribution indicates that this high q zone is the obliquely subducting pacific plate a zone of abnormally low q which has cut the high q slab is found at a depth range of 130 to 230 km beneath the active volcanoes in the taupo volcanic zone a tear in the pacific plate is suggested by this discontinuity in the attenuation structure

shear velocity structure in the aegean area obtained by inversion of rayleigh waves summary the purpose of this work is to derive a 3 d tomographic image of the shear wave velocity structure of the crust uppermost mantle in the aegean area using the group velocities of rayleigh wave fundamental mode the database consists of 185 regional earthquakes recorded at broad band stations that were installed for a period of 6 month in the aegean area within the framework of a large scale experiment in a previous work karagianni et al 2002 an averaged group velocity has been determined using the method of frequency time analysis ftan for each epicentre station ray path and the data were used in order to determine the local group velocities for different periods over the area covered by the seismic ray paths taking into account additional resolution results obtained for the local group velocities a grid of 0 5 was adopted for the aegean area and a local dispersion curve was defined for each gridpoint more than 80 local dispersion curves were finally inverted using a non linear inversion approach deriving the corresponding 1 d shear velocity models the interpolation of these models resulted in a 3 d s wave tomographic image of the crust and uppermost mantle in the broader aegean area as expected as a result of the complex tectonic setting of the aegean area strong lateral variations of the s wave velocities of the crust and uppermost mantle of the studied area are found in the southern aegean sea as well as in a large part of the central aegean sea a thin crust of approximately 20 22 km is observed whereas the remaining aegean sea area exhibits a crustal thickness less than 28 30 km on the contrary a crustal thickness of 40 46 km is observed in western greece along the hellenides mountain range whereas in the eastern continental greece the crust has a typical thickness of approximately 30 34 km for shallow depths 10 km low s wave velocities are observed under the sedimentary basins of the north aegean sea the gulf of thermaikos axios basin and western greece at depths ranging from 10 to 20 km low s wave velocities are mainly found in western greece under peloponnesus as well as in rhodes this low velocity zone seems to extend along the hellenic arc and can be correlated to the hellenides mountain range and the alpine orogenesis in agreement with previous p wave tomographic results in the southern aegean sea very low s wave velocities 3 6 4 0 km s 1 are observed at depths of approximately 30 40 km just below the moho discontinuity while in the rest of the inner aegean sea and continental greece the uppermost mantle is characterized by velocities around 4 3 4 4 km s 1 this low velocity zone in the southern aegean sea can be associated with the high temperatures and the presence of significant percentage partial melt in the mantle wedge of the southern aegean subduction zone in agreement with previous studies

seismic investigation of the transition from continental to oceanic subduction along the western hellenic subduction zone 1 the western hellenic subduction zone whsz exhibits well documented along strike variations in lithosphere density i e oceanic versus continental subduction rates and overriding plate extension differences in slab density are believed to drive deformation rates along the whsz however this hypothesis has been difficult to test given the limited seismic constraints on the structure of the whsz particularly beneath northern greece here we present high resolution seismic images across northern and southern greece to constrain the slab composition and mantle wedge geometry along the whsz data from two temporary arrays deployed across greece in a northern line nl and southern line sl are processed using a 2d teleseismic migration algorithm based on the generalized radon transform images of p and s wave velocity perturbations reveal n60e dipping low velocity layers beneath both nl and sl the 8 km thick layer beneath sl is interpreted as subducted oceanic crust while the 20 km thick layer beneath nl is interpreted as subducted continental crust the thickness of subducted continental crust inferred within the upper mantle suggests that 10 km of continental crust has accreted to the overriding plate the relative position of the two subducted crusts implies 70 85 km of additional slab retreat in the south relative to the north overall our seismic images are consistent with the hypothesis that faster sinking of the denser oceanic portion of the slab relative to the continental portion can explain the different rates of slab retreat and deformation in the overriding plate along the whsz

classification of sea ice types in envisat synthetic aperture radar images in this paper sea ice in the central arctic has been classified in synthetic aperture radar sar images from envisat using a neural network nn based algorithm and a bayesian algorithm since different sea ice types can have similar backscattering coefficients at c band hh polarization it is necessary to use textural features in addition to the backscattering coefficients the analysis revealed that the most informative texture features for the classification of multiyear ice myi deformed first year ice fyi dfyi and level fyi lfyi and open water nilas are correlation inertia cluster prominence energy homogeneity and entropy as well as third and fourth central statistical moments of image brightness the optimal topology of the nn trained for envisat wide swath sar sea ice classification consists of nine neurons in input layer six neurons in hidden layer and three neurons in output layer the classification results for a series of 20 sar images acquired in the central part of the arctic ocean during winter months were compared to expert analysis of the images and ice charts the results of the nn classification show that the average correspondences with the expert analysis amount to 85 83 and 80 for lfyi dfyi and myi respectively the bayesian pixel based method can provide a higher resolution in the classified image and therefore better capability to identify leads compared to the nn method both methods may be effectively used in the central arctic where myi is predominant

organic matter characterization and distribution in sediments of the terminal lobes of the congo deep sea fan evidence for the direct influence of the congo river the terminal lobe complex of the congo river submarine fan sits on the abyssal atlantic plain at 5000 m water depth 760 km offshore from the river mouth estuarine area while most rivers deliver particulate material to the continental shelf particulate matter from the congo river largely bypasses the shelf and is transported by turbidity currents through the congo submarine canyon system we determined the quantity and quality of the organic matter reaching the terminal lobe complex at five sites with marked morphological differences that may influence the distribution of organic matter a suite of bulk geochemical oc 13corg 15n c n 137cs and palynofacies analyses were done on cores collected from the terminal lobe area these results were also compared to the composition of sediments collected upstream at the malebo pool congo river distal lobe complex sediments contain high amounts of terrestrial organic carbon 3 5 wt that is homogeneously distributed in surficial 22 cm and deeper sediments 580 cm silty clay facies strongly altered soil derived organic matter with well preserved land plant detritus from the congo river predominates a terrestrial soil origin for the particulate load was confirmed by the elevated 137cs activity in lobe sediments the vertical distribution of the 137cs signal suggests that there has been a massive arrival of terrestrial sediments since 1963 consistent with a turbiditic origin from the locations surveyed we estimate a maximum accumulation of terrestrial organic carbon of ca 1 kg oc m 2 y 1 for the distal lobe however transport modifies the organic matter both in terms of quantity and quality observed differences were attributed to preferential degradation of nitrogenous matter during diagenesis and to the addition of highly remineralized marine organic matter results from our temporal reference site e suggest that organic matter may be preserved in turbidite facies for thousands of years the good preservation state of the accumulated organic matter shows that turbiditic lobe complexes should be considered as a sink for terrestrial organic carbon in the deep ocean

aliphatic hydrocarbons and triterpenes of the congo deep sea fan abstract hydrocarbons were analyzed in sediments from the congo river deep sea fan from the congo river and in sinking particles collected by sediment traps 40 m above the sediment studied sites encompassed three lobes of decreasing age of formation along the canyon sites a f and c and a another lobe system disconnected from the active channel since 4 ka site e terrestrial long chain odd n alkanes were dominant in all sediments of the lobe system unsaturated terpenoids sourced by higher plants such as gammacerene lupene ursene and oleanene were also detected at site c characterized by high accumulation rates 10 20 cm yr 1 the organic matter spends less time in the oxic layer than at other sites and high phytadiene concentrations 10 17 g g oc 1 evidenced recent terrestrial and phytoplanktonic remains reworked in anaerobic conditions in these sediments organic carbon normalized concentrations of terrestrial alkanes and terpenoids were several fold higher than in the lobe sediments with lower accumulation rates sites a and f arguing for a more rapid degradation of terrestrial hydrocarbons than bulk organic carbon in the first steps of pre diagenesis ample variations in the contributions of biomarkers from higher plants ferns bacteria and angiosperms indicate an heterogeneous contribution of the soil and vegetation detritus delivered to the congo lobe sediments lower concentrations in terrestrial hydrocarbons at site e 45 km away from the active canyon indicated that river particles are still admixed to the dominant marine organic matter diploptene and hop 7 21 ene have a dual origin from terrestrial and marine microorganisms scatter in their relationship to gammacerene argues for a contribution of marine microorganisms in addition to soils sourced microorganisms the close distribution patterns of diploptene hop 21 ene hop 7 21 ene and neohop 13 18 ene is in line with the hypothesis of sequential clay catalyzed isomerisation of bacterial hopenes terrestrial biomarker accumulation fluxes at site c are one order of magnitude higher than vertical pelagic flux demonstrating the magnitude of the inputs delivered through turbiditic transport in the submarine canyon crude oil contamination was evidenced at the disconnected site e ucm c 21 to c 26 tricyclic diterpanes cpi and in smaller amounts in some sediments from sites a and c it may be related to marine crude oil extraction and transport a short chain mode of alkanes with an even predominance is evidenced in sediments of the lobe complex and likely sources crude oil microorganisms and ferns are discussed

ocean surface wind speed retrieval from c band sar images without wind direction input two new models for wind speed retrieval from c band synthetic aperture radar sar data have been developed based on a large body of statistics on buoy observations collocated and coinciding with radarsat 1 and 2 scansar images the first model s independent variables are co polarization hh normalized radar cross section nrcs and antenna beam incidence angle the second model s predictors are hh nrcs cross polarization hv nrcs instrument noise floor and incidence angle the latter model has better accuracy than the first because of using an additional hv variable furthermore we found that the proposed models without wind direction input demonstrated a better accuracy than cmod ifr2 and cmod5 n models in combination with the sad hh co polarization ratio vv hh which require wind direction input these results were confirmed on a large independent subset of collected data the developed wind speed retrieval models in conjunction with our previously developed ice motion tracking algorithm can be a useful tool for studying sea ice dynamics processes in the marginal ice zone the developed models have been integrated into a quasi operational system at the meteorological service of canada

mean mixed depth of sediments the wherefore and the why the activities and consequently the bioturbational effects of deposit feeding organisms are largely restricted to a narrow surficial zone of marine sediments with a worldwide environmentally invariant mean of 9 8 cm with a standard deviation of 4 5 cm currently available theories of infaunal behavior cannot predict quantitatively this observation a new simple model that accounts for the feedback between resource food abundance its reactivity and the intensity of bioturbation leads to a quantitative estimate of 9 7 cm this model constitutes a fundamental advance in our understanding bioturbation

spatial and temporal patterns of benthic macrofaunal communities on the deep continental margin in the gulf of guinea abstract density taxonomic composition at higher taxon level and vertical distribution of benthic macrofaunal communities and sediment characteristics pore water nitrogen organic carbon sulfur c n ratio n alcohol biomarkers were examined at three deep sites on the congo gabon continental margin this study was part of the multidisciplinary biozaire project that aimed at studying the deep benthic ecosystems in the gulf of guinea sampling of macrofaunal communities and of sediment was conducted during three cruises january 2001 december 2001 and december 2003 at two downslope sites 4000 m depth one located near the congo submarine channel 15 km in the south and the other one far from the channel 150 km in the south the third area located 8 km north of the congo channel in the surroundings of a giant pockmark at 3160 m depth was sampled during one cruise in december 2003 at these three locations the macrofaunal communities presented relatively high densities 327 987 ind 0 25 m 2 compared with macrofaunal communities at similar depths that is due to high levels of food input related to the congo river and submarine system activities that affect the whole study area the communities were different from each other in terms of taxonomic composition at higher taxon level phylum class order for all the groups except for the polychaetes classified into families the polychaetes dominated the communities and were responsible for the increase in densities observed at both deep sites 4000 m between january 2001 and december 2003 whereas the tanaidaceans the isopods and the bivalves were the other most abundant taxa responsible for the spatial differences between these sites the community at 3150 m differed from the two deep communities by higher abundances in bivalves nemerteans and holothuroids the composition of the polychaete community also differed among sites in the vicinity of the congo channel the expected positive effect of the additional organic matter transported through the turbiditic currents on to the surrounding benthic communities was not observed as the increase in densities during the study period was higher at the site located away from the congo channel than near the channel 80 vs 30 that may be due to the low food value of the organic matter of terrestrial origin carried through the turbidites and or to the disturbance caused by these turbidites conversely far from the channel the macrofaunal communities benefit from organic matter of higher energetic value originating mainly from marine sources but also from continental sources carried by the congo plume or by near bed currents across or along the continental slope spatial and temporal variability in trophic and physical characteristics of the sediment habitat at both deep sites also affected the vertical distribution of the macrofaunal communities the activities of the very active congo system structure the deep macrofaunal communities on a large area in terms of densities composition and vertical distribution the food input is enhanced at regional scale as well as the heterogeneity of the sediment characteristics mainly in terms of organic matter quality marine vs terrigenous in turn the densities are enhanced as well as the regional diversity of the macrofaunal communities in terms of taxonomic composition and distribution

terrestrial organic carbon accumulation on the amazon deep sea fan during the last glacial sea level low stand abstract sediment cores from the amazon deep sea fan recovered during r v meteor cruise 16 2 show in detail the modern areal distribution of sedimentary organic carbon stable organic carbon isotopes of the organic matter om as well as variations in the depositional processes in addition we studied up to 300 m long drilled sediment records recovered during odp leg 155 which allow evaluation of temporal variations on the amazon fan our results reveal new evidence for a very rapid change of fan depositional processes and organic carbon source at times of sea level change over the middle and lower amazon fan to estimate the amount of terrestrial organic carbon stored in sediments from the last glacial in the amazon fan we used stable organic carbon isotopes of the om 13 c org organic carbon content corg and age models based on oxygen isotopes faunal data and magnetic excursions following our results the organic carbon accumulation on the amazon deep sea fan is controlled by glacio eustatic sea level oscillations interglacial sea level high stand sediments are dominated by marine om whereas during glacial sea level low stands terrestrial organic carbon is transported beyond the continental shelf through the amazon canyon and deposited directly onto the amazon deep sea fan glacial sediments of the amazon fan stored approximately 73 1015 g terrestrial corg in 20 000 years or 3 7 1012 g terrestrial corg yr 1 equivalent to 7 12 of the riverine organic carbon discharge assuming constant paleo discharge which is about the same amount of terrestrial organic carbon as deposited on the amazon shelf today 3 1 1012 g terrestrial corg yr 1 or 6 10 of the modern riverine organic carbon discharge

anisotropic radiation modelling of macroseismic intensities for estimation of the attenuation structure of the upper crust in greece a method is suggested for the analysis of macroseismic intensity data in order to accurately determine an average attenuation structure of the upper part of the crust in an area the method is based on a model which assumes that the observed intensities depend on source properties radiation pattern size focal depth geometrical spreading and anelastic attenuation the method is applied to 13 008 intensity values observed in corresponding sites of greece and grouped in 4228 groups according to their spatial clustering in order to diminish observational errors and site effects an average intensity attenuation coefficient c 0 0039 0 0016 corresponding to a quality factor q 350 140 is determined for the upper 20 km of the crust in this area this value is relatively low in good agreement with the relatively high heat flow and high seismic activity of this area a byproduct of the present study is the determination for each earthquake of a macroseismic focal depth and of a macroseismic size which is strongly correlatted with both the earthquake s magnitude and its seismic moment determined by independent methods

transport of terrestrial organic carbon to the oceans by rivers re estimating flux and burial rates this study re estimates one important component in the global carbon cycle the modern global fluviatile organic carbon discharge and burial rates according to these results approximately 430 1012 g of terrestrial organic carbon are transported to the ocean in modern times this amount is higher than the latest estimates but takes into account new data from oceania not previously considered in global flux studies however only the minor amount of 10 or approximately 43 1012 gc year 1 is most likely buried in marine sediments this amount is similar to the burial of marine organic carbon in the coastal ocean 55 1012 gc year 1 adding both estimates gives approximately 100 1012 gc year 1 which is the value calculated by berner 1982 for terrestrial deltaic shelf sediments however the results in this study suggest that on a global scale the organic carbon content in coastal ocean sediments is not solely of terrestrial origin but a mixture of nearly equal amounts of marine and terrestrial organic carbon the major part of the terrestrial organic carbon that enters the ocean by rivers approximately 400 1012 gc year 1 seems to be either a remineralised in the ocean whereas the mechanism by which the terrestrial organic carbon is oxidised in the ocean are unknown or b is dispersed throughout the oceans and accumulates in pelagic sediments

a benthic si mass balance on the congo margin origin of the 4000 m dsi anomaly and implications for the transfer of si from land to ocean to elucidate the origin of the silicic acid dsi anomaly observed along the 4000 isobath on the congo margin we have established a benthic si mass balance and performed direct measurements of biogenic silica bsio2 dissolution in the deep waters and in the sediments results strongly suggest that the anomaly originates from the sediments the intensity of dsi recycling is consistent with the degradation of organic matter as observed from si o2 ratios in the benthic fluxes compared to that ratio observed in the anomalies strong imbalances observed in both the si and c mass balances suggest that the biogenic matter that degrades and dissolves in these sediments near 4000 m does not come from pelagic sedimentation it is probably not coming also from the deep channel because observations were similar in the deep channel vicinity site d and further south far from its influence site c the composition of the sediments with an si c ratio close to that observed on continental shelves suggests that this matter is coming from downslope transport a first estimate of the magnitude of this flux at global scale close to 12 t mol si yr 1 suggests that it may be an important path for transferring si from land to ocean

early diagenesis in the sediments of the congo deep sea fan dominated by massive terrigenous deposits part ii iron sulfur coupling abstract deep sea fans are well known depot centers for organic carbon that should promote sulfate reduction at the same time the high rates of deposition of unconsolidated metal oxides from terrigenous origin may also promote metal reducing microbial activity to investigate the eventual coupling between the iron and sulfur cycles in these environments shallow sediment cores

the three dimensional attenuation structures beneath the philippine archipelago based on seismic intensity data inversion abstract attenuation structures were determined for the philippine archipelago by inversion of earthquake intensity data set from 1957 to 1992 the intensity data based on the adapted rossi forel intensity scale were translated into acceleration values using a modified acceleration intensity equation a damped least squares method was used in our inversion we correlated the inversion results with other data such as observed anomalous intensity distribution present seismicity and the location of trenches and volcanic centers our results strongly indicate the association of low attenuation values with subducted slabs along the known location of trenches in the philippines for example the configuration of the philippine trench is suggested by the concentration of low attenuation values along the east side of central and southern philippines while on the western side of luzon island a low attenuation structure is consistent with the location of the manila trench the extent and depth of low attenuation values are also apparent along the eastern side of luzon in southern luzon through negros island in the central philippines the site where anomalous intensity distribution was observed coincided with the location of a noticeable low attenuation structure determined in this study moreover possible locations of an upwelling magmatic body along the numerous areas in the philippines are also indicated by the concentration of high attenuation values furthermore a possible aseismic slab which probably represents a structure that connects the manila trench with the negros trench was also inferred in eastern mindoro however it is also possible that these low attenuating values are due to the presence of continental material in this area on the basis of these initial results we suggest some modifications of the configuration of tectonic structures in several portions of the archipelago

geochemical and biological recovery of the disturbed seafloor in polymetallic nodule fields of the clipperton clarion fracture zone ccfz at 5 000 m depth environmental data were obtained on the nodule fields of the clipperton clarion fracture zone at 5 000 m depth in june 2004 during the nodinaut cruise the long term effects of physical disturbance made by a dredge 26 yr ago on the sediment were investigated we focused our study on its track which is still visible on the bottom the first major consequence of the passage of this equipment was to remove 4 cm 6 0 5 cm of superficial sediment the physical and chemical properties of this disturbed sediment sampled in the track did not change significantly over time and has not shown any recovery since the disturbance however an exception was observed for depth variations of manganese concentration in the sediment which were similar in the track to those in the surrounding undisturbed sediment and can be explained by the diffusion over time of oxygen from the sea water on the other hand the biological activity measured in the track with the respirometer rap2 carried by the submersible nautile did not differ from the unperturbed site which suggests that the benthic fauna has completely recovered as have nutrient fluxes at the water sediment interface

attenuation of s waves in the lithosphere of the sea of crete according to obs observations five obs were installed in the sea of crete in 1987 during a period of nine days 430 local earthquakes were recorded hypocentres were determined for 85 microearthquakes a correlation between magnitude ml and duration of seismic events on the records of the ocean bottom seismographs obs was found from data of 14 shocks recorded simultaneously by obs and some land based greek stations a magnitude frequency relationship for earthquakes recorded by obs was obtained in the magnitude range ml 2 4 amplitude curves describing the attenuation of body waves in the lithosphere of the sea of crete were compiled assessment of quality factor qs was made by comparison of empirical and theoretical amplitude curves the values of qs for the lithosphere of the sea of crete were calculated and found equal to 200 300 low values of qs and consequently strong attenuation of s waves in the lithosphere of the sea of crete could be explained by extension of the lithosphere accompanied by its partial contamination with melted magma

three dimensional seismic attenuation structure beneath the taiwan region and its tectonic implication abstract three dimensional 3 d attenuation structures were determined for taiwan region by inversion of earthquake intensity data set the seismic intensity which is assumed to be a measure of the maximum acceleration of the s wave at the seismic station is used to estimate the attenuation structure the intensity data set consists of about 5500 intensity readings for 1410 earthquakes reported by the central weather bureau of taiwan from 1987 to 2010 the 3 d attenuation maps consisting of five layers were constructed to a depth of 74 km the obtained model reveals the following features first a high absorption zone exists in the westernmost okinawa trough these high attenuation anomalies seem to extend from upper crust to mantle beneath the yilan plain and kueishantao island we interpret the high absorption zone as the presence of the relatively hot lower crust and uppermost mantle in response to the local opening of the okinawa trough second strong lateral variation of seismic attenuation is observed from the source region of the chi chi earthquake in the central taiwan most aftershocks were occurred beneath the western foothills which is characterized by a transition from high attenuation to low attenuation between the chelungpu fault and chuchih fault however the region east to the chuchih fault is relatively quiescent this study suggests that the high vp vs and lateral variation of attenuation features existing beneath the western foothills could be associated with porous materials containing fluid which might affect the generation of the chi chi earthquake

cold seep like macrofaunal communities in organic and sulfide rich sediments of the congo deep sea fan methane rich fluids arising from organic matter diagenesis in deep sediment layers sustain chemosynthesis based ecosystems along continental margins this type of cold seep develops on pockmarks along the congo margin where fluids migrate from deep buried paleo channels of the congo river acting as reservoirs similar ecosystems based on shallow methane production occur in the terminal lobes of the present day congo deep sea fan which is supplied by huge quantities of primarily terrestrial material carried by turbiditic currents along the 800 km channel and deposited at depths of up to nearly 5000 m in this paper we explore the effect of this carbon enrichment of deep sea sediments on benthic macrofauna along the prograding lobes fed by the current active channel and on older lobes receiving less turbiditic inputs macrofaunal communities were sampled using either usnel cores on the channel levees or rov blade cores in the chemosynthesis based habitats patchily distributed in the active lobe complex the exceptionally high organic content of the surface sediment in the active lobe complex was correlated with unusual densitiesof macrofauna for this depth enhanced by a factor 7 to 8 compared with those of the older abandoned lobe whose sediment carbon content is still higher than in angola basin at same depth macrofaunal communities dominated by cossurid polychaetes and tanaids were also more closely related to those colonizing low flow cold seeps than those of typical deep sea sediment in reduced sediments microbial mats and vesicomyid bivalve beds displayed macrofaunal community patterns that were similar to their cold seep counterparts with high densities low diversity and dominance of sulfide tolerant polychaetes and gastropods in the most sulfidic habitats in addition diversity was higher in vesicomyid bivalve beds which appeared to bio irrigate the upper sediment layers high beta diversity is underscored by the variability of geochemical gradients in vesicomyid assemblages and by the vesicomyid population characteristics that vary in density size and composition by modifying the sediment geochemistry differently according to their morphology and physiology the different vesicomyid species play an important role structuring macrofauna composition and vertical distribution dynamics of turbiditic deposits at a longer temporal scale thousands of years and their spatial distribution in the lobe area also resulted in high heterogeneity of the cold seep like communities dynamics of chemosynthetic habitats and associated macrofauna in the active lobe area 2 please note that this is an author produced pdf of an article accepted for publication following peer review the definitive publisher authenticated version is available on the publisher web site resembled those previously observed at the regab pockmark along the congo margin and rapid succession is expected to cope with high physical disturbance by frequent turbiditic events and huge sedimentation rates finally we propose a model of the temporal evolution of these peculiar habitats and communities on longer timescales in response to changes in distributary channels within the lobe complex

three dimensional seismic attenuation structure beneath the aegean region and its tectonic implication abstract the three dimensional attenuation structure beneath the aegean sea and the surrounding regions is determined by inversion of seismic intensity data a large number of seismic intensity data have been accumulated in a uniform scale in the aegean region where the seismic activity is much higher than that of the other mediterranean regions nearly 7000 seismic intensity data from 50 earthquakes that have occurred in these regions are used to determine seismic attenuation structure and source acceleration of the earthquakes the resultant structure reveals a remarkable contrast of attenuation in the top layer depth 0 40 km low q is dominant in the aegean sea while high q is dominant in the surrounding land areas except for the southwestern turkey the low q regions correspond to areas of neogene quaternary grabens where the high seismicity of shallow earthquakes appears in the upper mantle high q zones corresponding to the subducting african plate dominate along the hellenic arc the irregular shape of high q zones might reflect the split or disintegration of the african slab some low q spots corresponding to the distribution of volcanoes exist along the volcanic arc the low q spots might correspond to diapirs causing the subduction volcanism

reexposure and advection of 14c depleted organic carbon from old deposits at the upper continental slope represents an additional source of 14 c depleted organic carbon supplied to the ocean in parallel with the weathering of fossil organic carbon delivered by rivers from land to understand the dynamics and implications of this reexposure at the shelf edge a biogeochemical study was carried out in the gulf of lions mediterranean sea where erosive processes driven by shelf dense water cascading are currently shaping the seafloor at the canyon heads mooring lines equipped with sediment traps and current meters were deployed during the cascading season in the southwestern canyon heads whereas sediment cores were collected along the sediment dispersal system from the prodelta regions down to the canyon heads evidence from grain size x radiographs and 210 pb activity indicate the presence in the upper slope of a shelly coarse surface stratum overlying a consolidated deposit this erosive discontinuity was interpreted as being a result of dense water cascading that is able to generate sufficient shear stress at the canyon heads to mobilize the coarse surface layer eroding the basal strata as a result a pool of aged organic carbon d 14 c 944 5 24 7 mean age 23 650 3 321 ybp outcrops at the modern seafloor and is reexposed to the contemporary carbon cycle this basal deposit was found to have relatively high terrigenous organic carbon lignin 1 48 0 14 mg 100 mg oc suggesting that this material was deposited during the last low sea level stand a few sediment trap samples showed anomalously depleted radiocarbon concentrations d 14 c 704 4 62 5 relative to inner shelf d 14 c 293 4 134 0 mid shelf d 14 c 366 6 51 1 and outer shelf d 14 c 384 47 8 surface sediments therefore although the major source of particulate material during the cascading season is resuspended shelf deposits there is evidence that this aged pool of organic carbon can be eroded and laterally advected downslope

delay time tomography of the upper mantle below europe the mediterranean and asia minor summary the method of linearized delay time tomography is applied to retrieve the p velocity heterogeneity of the upper mantle in central europe the mediterranean and asia minor the upper mantle is parametrized in slowness cell functions with lateral dimensions of 1 the model parametrization includes event mislocation vectors and station delay time corrections in all 20 000 parameters describe the model delay time data selected from the isc data base 1964 1982 from regional events and from stations up to 90 of epicentral distance are used about 18 000 events and 937 stations contributed nearly 500 000 delay times we discuss the tomographic method the data processing the cell model employed the computation of the ray geometry the use of composite rays in tomography and the cell hit count the inversions are performed with two different iterative row action methods lsqr and sirt results obtained with the lsqr method will be shown only the spatial resolution is investigated with sensitivity analyses using two different synthetic velocity models a spike model and a model with harmonically varying velocity anomalies the spatial resolution is estimated to be high on the order of the cell size in the mantle below central and southeastern europe the mapped velocity heterogeneity exhibits primarily low velocities around a depth of 200 km and just above the transition from upper to lower mantle this indicates a systematic deviation of the reference model jeffreys bullen from the radially averaged earth structure which may violate the basic assumptions underlying the linearized approach a posteriori investigation of the data also indicates the presence of a low velocity zone and the existence of strong velocity depth gradients

particle mixing rates in sediments of the eastern equatorial pacific evidence from 210pb 239 240pu and 137cs distributions at manop sites abstract particle mixing rates db calculated from excess 210pb gradients in sediments of the east equatorial pacific range from 0 04 to 0 5 cm2 y with variation of a factor of 3 4 at a single site diffusion of the 236ra daughter 222rn may affect 210pb distributions under conditions of slow mixing and low 210pb flux to the seafloor as shown by a siliceous ooze clay core which contained the fallout radionuclides 239 240pu and 137cs but no excess 210pb relative to 226ra there is no clear relationship between 210pbderived mixing rates and sediment type accumulation rate or organic carbon flux to the sediments comparison of 210pb mixing rates with those calculated from 239 240pu and 137cs distributions reveals better agreement for a pulse input of the fallout radionuclides db 0 03 0 4 cm2 y than for continuous input at a constant rate db 0 1 1 6 cm2 y although the pu and 137cs data are better fit by the latter model the agreement may be fortuitous because 239 240pu and 137cs appear significantly deeper than 210pb in at least one core tracer separation could be caused by particle size selective mixing by the benthic fauna or by chemical mobilization if the fallout radionuclides are scavenged from surface waters by large organic rich particles such as fecal pellets their release and migration may result from decomposition of the carrier in surface sediments either a relatively unreactive form of pu e g oxidized pu has been released by this process or a one dimensional model is inadequate to explain its observed penetration into the sediments activity ratios of 239 240 pu 137 cs in the sediments decrease with increasing north latitude and the trend reflects higher fluxes of 239 240pu near the weapons test site at christmas island 2 n the 239 240 pu 137 cs ratios and fluxes to the sediment assuming constant input at the siliceous ooze red clay site are consistent with published sediment trap data from a nearby site thus if fallout radionuclide fluxes to the sea floor were higher in the past both 239 240pu and 137cs have been released from sinking particles

back arcs basins and p wave crustal velocity in the ionian and aegean regions tomographic images of the lower crust and uppermost mantle beneath the central mediterranean have been obtained from arrival times of regional earthquakes we find a low velocity belt at about 25 km beneath the hellenic arc a low velocity anomaly at a depth of 40 km extends under the aegean back arc basin high velocities are present at moho depth beneath the ionian sea close to the calabrian and aegean arcs and under the aegean sea the results suggest a close relation between p wave crustal velocity and the subduction systems of the studied area

accelerated contribution of the paleo congo river to global seawater 87 sr 86 sr change following eocene oligocene collapse of the african surface

carbon and silica megasink in deep sea sediments of the congo terminal lobes carbon and silicon cycles at the earth surface are linked to long term variations of atmospheric co2 and oceanic primary production in these cycles the river sea interface is considered a biogeochemical hotspot and deltas presently receive and preserve a major fraction of riverine particles in shallow water sediments in contrast periods of glacial maximum lowstand were characterized by massive exports of sediments to the deep sea via submarine canyons and accumulation in deep sea fans here we calculate present day mass balances for organic carbon oc and amorphous silica asi in the terminal lobe complex of the congo river deep sea fan as an analogue for glacial periods we show that this lobe complex constitutes a megasink with the current accumulation of 18 and 35 of the oc and asi river input respectively this increases the estimates of organic carbon burial by 19 in the south atlantic ocean in a zone representing less than 0 01 of the basin these megasinks might have played a role in carbon trapping in oceanic sediments during glacial times

tomography of the crust and upper mantle in southeast europe compressional velocity structure of the crust and the upper mantle in southeastern europe broader aegean area is studied by inverting residuals of the first p arrivals from earthquakes in this region 16 e 31 e 34 n 43 n the data used are from regional events recorded by the permanent network of stations during the period 1971 1987 enriched with data from experiments with portable seismographs in four regions of this broad area this study confirms the strong variations of crustal thickness in this area as well as the subduction of the eastern mediterranean lithosphere under the southern aegean and gives further detailed information on the crustal and upper mantle structure of the area important new information is the existence of a low velocity crustal layer in western greece and albania and that the velocity anomaly in the mantle under the southern aegean extends much farther and deeper to the northeast than the benioff zone of the intermediate depth earthquakes indicates furthermore evidence is presented about the possible existence of older subduction in the northern aegean and about the influence of the tectonic regime on the velocity field

attenuation of coda waves in northern greece the single scattering model has been applied for the estimation of codaq values for local earthquakes that occurred in northern greece during the period 1983 1989 and recorded by the telemetered network of the geophysical laboratory of the university of thessaloniki codaq estimations were made for four frequency bands centered at 1 5 hz 3 0 hz 6 0 hz and 12 0 hz and for the lapse time windows 10 20 sec 15 30 sec 20 45 sec 30 60 sec and 50 100 sec the codaq values obtained show a clear frequency dependence of the formq c q 0 f n whileq 0 andn depend on the lapse time window q 0 was found equal to 33 andn equal to 1 01 for the time window of 10 to 20 sec while for the other windowsq 0 increased from 60 to 129 withn being stable close to 0 75 this lapse time dependence is interpreted as due to a depth dependent attenuation the high attenuation and the strong frequency dependence found are characteristic of an area with high seismicity in agreement with studies in other seismic regions

fauna and habitat types driven by turbidity currents in the lobe complex of the congo deep sea fan abstract this study characterizes the habitats and megafaunal community of the congo distal lobe complex driven by turbidity currents through the use of remotely operated vehicle rov still imagery transects covering distances in the order of kilometers in this sedimentary abyssal area about 5000 m deep and 750 km offshore from western africa large quantities of deposited organic material supplied by the congo river canyon and channel support aggregations of large sized foraminifers bathysiphon sp and vesicomyid clams christineconcha regab abyssogena southwardae often associated with methane cold seeps as well as opportunistic deep sea scavengers additionally bacterial mats assumed to be formed by large sulfur oxidizing filamentous bacteria beggiatoa type and black patches of presumably reduced sediment were seen which are together with sulfur oxidizing symbiont bearing vesicomyids indicators of sulfide rich sediments habitat and faunal distribution were analyzed in relation to the microtopography obtained with the rov multibeam echosounder at three sites from the entrance of the lobe complex where the channel is still deep to the main flatter area of turbidite deposition specific characteristics of the system influence animal distributions both the forams and the vesicomyid clams tended to avoid the channels characterized by high speed currents and are therefore preferentially located along channel flanks affected by sliding and on levees formed by channel overspill foram fields are found in flat areas and form large fields whereas the vesicomyids have a patchy distribution and appear to show a preference for regions of local topographical relief such as slide scars or collapsed blocks of sediments which likely facilitate sulfide exhumation the colonization of sulfide rich sediments by vesicomyids is limited but nonetheless was seen to occur in the main deposition area where they have to cope with very high sedimentation rates up to 20 cm yr and frequent turbidity currents other biological adaptations to the local conditions likely determine the presence and survival of animals in the system large agglutinated forams are known to be adept at quickly colonizing disturbed sediment and capitalizing on abundant but irregular food sources and vesicomyid clams have a mobile lifestyle that enables them to maintain their population in the ever changing landscape of sulfide rich sediment outcrops turbiditic systems appear to be intermediate between other energy rich habitats sustaining chemosynthesis in the deep sea being locally less stable in terms of energy supply than cold seeps limiting the number of cold seep specialists able to colonize but constituting a longer lived habitat than food falls turbidite fans therefore represent distinct deep sea habitats that contribute to sustaining populations of both chemosynthesis based and opportunistic taxa in the deep sea

three dimensional seismic attenuation structure beneath the japanese islands and its tectonic and thermal implications a three dimensional 3 d seismic attenuation structure beneath the japanese islands is determined by inversion of seismic intensity data the result clearly reveals a remarkable contrast in the attenuation structure and reflects the lateral variation of thermal structure beneath the japanese islands for the inversion the method developed by hashida and shimazaki is used the intensity which is assumed to be a measure of the maximum acceleration of the s wave at the observation point is inverted to estimate the attenuation structure and the acceleration at the seismic source the data consist of about 15 000 intensity readings for about 800 earthquakes reported by the japan meteorological agency between 1951 and 1983 by combining 3 d structures of eight districts in japan 3 d attenuation maps consisting of three layers are constructed to a depth of 90 km the obtained structure reveals the following features first a distinct difference exists in the crustal structure between ne and sw japan in ne japan low q high attenuation areas on the continental side of the arc are dominant whereas some high q low attenuation areas exist on the pacific side of the arc in sw japan except for the kyushu district high q areas are dominant and small low q areas exist mainly on the pacific coast these crustal features generally continue down to the uppermost mantle second the obtained crustal structure shows that attenuation is age dependent low qareas correspond to the distribution of quaternary volcanic materials and high q areas correspond to the geological provinces where pre cenozoic rocks are distributed since the thermal structure strongly depends on the crustal age this feature suggests that the attenuation structure reflects the thermal structure third in the upper mantle low q loci are found which correspond to the distribution of active and other quaternary volcanoes forming the arc volcanic chain it should be noted that even on the continental side of the volcanic front these loci do not exist beneath areas where no volcano exists this suggests that the upper mantle attenuation is controlled by the existence of upwelling diapirs which are considered to lie beneath a volcano or a group of volcanoes fourth high q zones in the upper mantle exist on the pacific side of the volcanic front along the kurile northeast honshu arc and along ryukyu arc the high q mantle lying above the sinking slab seems to reflect a cooling effect of the subducting cold oceanic plates the thickness of the lithosphere may reach 60 km or more in such outer arcs although the thickness has been considered to be about 30 km or so in sw japan where the high q uppermost mantle also lies a thick lithosphere of about 60 km may exist possible thermal cross sections are proposed for ne and sw japan based on the obtained 3 d attenuation structure and other geophysical considerations in the uppermost mantle of ne japan a higher temperature is expected than in sw japan the thermal structures reflect the difference of tectonic settings in the two regions such as the subducting plate overriding lithosphere and volcanic activity

rayleigh wave group velocity tomography in the aegean area data from a large scale experiment which took place in greece during the period january july 1997 have been used to investigate the structure of the aegean area using surface waves during this experiment 30 seismic broadband instruments were deployed throughout the whole greek area additional data during the period 1996 2000 from other temporary networks have been included in the dataset one hundred eighty five events with magnitudes 4 0vmwv5 5 recorded by these stations have been collected and processed the individual dispersion curves of the group velocity of rayleigh waves for each source station path have been calculated producing more than 700 paths covering the studied region these curves have been used to determine rayleigh group velocity maps using a 2d tomography method on the basis of a regionalization of the dispersion measurements local averaged dispersion curves have been obtained and non linearly inverted to obtain models of shear wave velocity versus depth since the dispersion curves in the period range 5 svtv30 s are mostly affected by the crustal structure the model velocities are estimated down to a depth of approximately 35 45 km the results from the non linear hedhehog inversion as applied to a few local dispersion curves show a crustal thickness of approximately 32 km for the northern aegean sea and a relatively thin crust of approximately 22 24 km for the southern aegean sea d 2002 elsevier science b v all rights reserved

shear wave attenuation tomography of the lithosphere asthenosphere system beneath the mediterranean region abstract 3 d tomographic images of the shear wave attenuation structure of the lithosphere asthenosphere system beneath the mediterranean region are derived from the inversion of anelastic attenuation coefficients obtained for the fundamental mode of nearly 3100 rayleigh wavetrains recorded at very broad stations placed in the mediterranean region the two station method is used to compute 124 interstation path averaged attenuation coefficients within the 15 120 s period range an adaptation to attenuation coefficients of the yanovskaya ditmar formulation specifically devoted to path averaged surface wave dispersion data and body waves permits to obtain the local attenuation coefficients and their uncertainties for all the period range at every node of a grid covering the studied region maps of stretching azimuths and mean radii of the resolution ellipses are also obtained for every period all of these parameters are strongly related to the spatial path coverage data quality and data coherency a local attenuation dispersion curve is defined then in each grid node and the stochastic inversion of these curves yields 1 d models of inverse shear wave intrinsic quality factor q 1 the shear wave velocity models obtained for every grid node in an elastic tomography developed in a previous work for the same domain are taken as reference models for the inversion process the kriging contouring algorithm is used to represent the resulting 3 d q 1 structure by means of horizontal and vertical cross sections down to 160 km depth the main patterns of this anelastic structure are mostly in agreement with the structural and tectonic features obtained in the reference shear velocity tomography the local attenuation maps manifest notable lateral changes for periods of 20 and 40 s whereas more moderate spatial variation is observed for longer periods the 3 d anelastic models show that at shallow levels the attenuation in the western mediterranean is usually slightly higher than in the central eastern part the area from corsica sardinia islands to italy presents high q 1 values of 40 0 70 0 10 3 down to 75 km depth whereas q 1 does not exceed 20 0 10 3 in the rest of the mediterranean basin except for the south eastern part where slightly higher values are obtained 20 0 30 0 10 3 those high q 1 values suggest the presence of asthenospheric material at shallow levels which would be related to distensive tectonic processes responsible for the recent opening of extensional basins as the tyrrhenian sea and the ligurian provencal basin in the eastern mediterranean the vertical cross sections at different latitudes and longitudes reveal at deep levels some structural patterns consistent with signs of subduction which are linked to the convergence between the african and eurasian plates

3 d structure of the lithosphere in the aegean region summary p wave traveltime residuals from about 300 local and 400 teleseismic earthquakes recorded by the athens seismological network were used to study the structure of the lithosphere in the aegean region teleseismic data included readings from local stations which do not routinely report to the isc the large values of the residuals up to f3 s and their variation with azimuth and epicentral distance indicate significant velocity heterogeneity in the upper mantle p wave traveltime residuals were inverted simultaneously for both local and teleseismic earthquakes tomographic results which are best resolved at lithospheric depths reveal a heterogeneous lithosphere down to a depth of 100km or so a high velocity anomaly is found dipping at an average of 45 to the ne away from the hellenic trench and supports the hypothesis of subduction due to a cooler descending slab of oceanic composition an area of low velocities is observed at depths less than 80 km in the aegean back arc corresponding well with observed high heat flow values in the area in contrast an area of relatively higher velocity anomalies is resolved in the lithosphere underlying the sea of crete the tectonic structure of the crust and upper mantle in the eastern mediterranean area results from the complex interaction of several different geodynamic processes not all of which can be described by simple plate tectonic models at present the eurasian and african plates are converging at a rate of about lcmyr in an approximately n s direction minster jordan 1978 with the latter descending

evidence and age estimation of mass wasting at the distal lobe of the congo deep sea fan on continental margins sulfate reduction occurs within the sedimentary column it is coupled with the degradation of organic matter and the anaerobic oxidation of methane these processes may be significantly disturbed by sedimentary events leading to transient state profiles for the involved chemical species yet little is known about the impact of turbidity currents and mass wasting on the migration of chemical species and the redox reactions in which they are involved due to its connection to the river the congo deep sea fan continuously receives huge amount of organic matter rich sediments primarily transported by turbidity currents which impact on the development of the associated ecosystems rabouille et al 2016 thus it is well suited to better understand causal relationships between sedimentary events and fluid flow path with consequences on the zonation of early diagenesis sequences here we combined sedimentological observations with geochemical analyses of pore water and sediment samples to explore how sedimentary instabilities affected the migration of methane and the distribution of organic matter within the sedimentary column the results unveiled mass wasting processes affecting recent turbiditic and pelagic deposits and are interpreted as being slides slumps and debrites two slides were responsible for the exhumation of an organic matter rich sedimentary block of more than 5 m thick and the movement of a methane rich sedimentary block while turbidity currents enable the intercalation of sandy intervals within a pelagic clay layer the youngest slide promoted the development of two sulfate methane transition zones smtz and may have possibly triggered a lateral migration of methane numerical simulation of the sulfate profile indicates that the youngest sedimentary event has occurred around a century ago our study emphasizes that turbidity currents and sedimentary instabilities can significantly affect the transport paths and the distribution of both methane and organic matter in the terminal lobe complex with consequences on geochemical zonation of the sequential early diagenetic processes within the sedimentary column

the influence of congo river discharges in the surface and deep layers of the gulf of guinea the main feature of the congo angola margin in the gulf of guinea is the congo ex zaire deep sea fan composed of a submarine canyon directly connected to the congo river a channel and a sediment lobe area during the multi disciplinary programme called biozaire conducted by ifremer from 2000 to 2005 two ctd o2 sections with discrete water column samples were performed biozaire3 cruise 2003 2004 to study the influence of the congo river discharges both in the surface layer and in the deep and near bottom layers the surface layer water is greatly diluted with river water that has a heavy particle load the deep layer is affected by episodic turbidity currents that flow in the deep congo channel and reach deep areas far from the coast previous studies revealed deep anomalies in oxygen deficit and nutrient excess concentrations at not vert similar4000 m depth and assumed that they resulted from mineralisation of the particulate organic matter from the congo river the biozaire3 sections were designed to explore these phenomena in more detail near the congo channel oxygen and nutrients were measured as well as additional parameters including stable isotopes of oxygen and carbon dissolved inorganic carbon and ph for the surface layer the effect of the congo river was studied with reference to salinity deviations from the theoretical dilution of various inorganic solutes suggested the occurrence of mineralisation and consumption processes for the deep layer the network of ctd o2 stations gave a more detailed description of the deep anomalies than in previous studies from the east west section anomalies appeared on the bottom at 4000 m depth and became slightly shallower when they spread to the west they were also present north and south on the bottom along the 4000 m isobath in these deep waters the decrease in the 13c values of dissolved inorganic carbon confirmed that the mineralisation of organic matter plays a role in generating these anomalies the location of the origin of this deep anomaly is debated here arguments are given in favour of mineralisation of the particulate organic matter input that overflows from the congo channel at not vert similar4000 m depth during turbidity current events other authors suggest that this input comes from downslope particle transport anomalies of the same origin but weaker also occurred deeper on the congo lobe where the congo channel ends but with a significant ph decrease on the bottom which was not seen at 4000 m depth

attenuation of shear waves in the back arc region of the hellenic arc for frequencies from 0 6 to 16 hz abstract q for shear waves is determined for the inner part of the hellenic arc the back arc area as a function of frequency in the range 0 6 16 hz we used 314 digital records from 32 earthquakes with magnitudes m w ranging from 3 9 to 5 1 epicentral distances ranged from 65 to 515 km the data were obtained in 1997 during a 6 month operation of a digital portable network in greece the q estimates were made for five frequency bands centred at 0 8 1 5 3 0 6 0 and 12 0 hz and the q values obtained were 47 79 143 271 and 553 respectively the results show that q for s waves increases with frequency taking the form q 55 f 0 91 or q 1 0 018 f 0 91 the high attenuation and the strong frequency dependence found which is close to the frequency dependence of coda q for greece are characteristic of an area with high seismicity rapid extension and in agreement with other similar studies in greece

organic matter budget in the southeast atlantic continental margin close to the congo canyon in situ measurements of sediment oxygen consumption abstract a study of organic carbon mineralization from the congo continental shelf to the abyssal plain through the congo submarine channel and angola margin was undertaken using in situ measurements of sediment oxygen demand as a tracer of benthic carbon recycling two measurement techniques were coupled on a single autonomous platform in situ benthic chambers and microelectrodes which provided total and diffusive oxygen uptake as well as oxygen microdistributions in porewaters in addition sediment trap fluxes sediment composition org c tot n caco3 porosity and radionuclide profiles provided measurements of respectively input fluxes and burial rate of organic and inorganic compounds the in situ results show that the oxygen consumption on this margin close to the congo river is high with values of total oxygen uptake tou of 4 0 6 3 6 0 5 mmol m 2 d 1 at 1300 and 3100 m depth respectively and between 1 9 0 3 and 2 4 0 2 mmol m 2 d 1 at 4000 m depth diffusive oxygen uptakes dou were 2 8 1 1 2 3 0 8 0 8 0 3 and 1 2 0 1 mmol m 2 d 1 respectively at the same depths the magnitude of the oxygen demands on the slope is correlated with water depth but is not correlated with the proximity of the submarine channel levee system which indicates that cross slope transport processes are active over the entire margin comparison of the vertical flux of organic carbon with its mineralization and burial reveal that this lateral input is very important since the sum of recycling and burial in the sediments is 5 8 times larger than the vertical flux recorded in traps transfer of material from the congo river occurs through turbidity currents channelled in the congo valley which are subsequently deposited in the lobe zone in the congo fan below 4800 m ship board measurements of oxygen profiles indicate large mineralization rates of organic carbon in this zone which agrees with the high organic carbon content 3 and the large sedimentation rate 19 mm y 1 found on this site the lobe region could receive as high as 19 mol c m 2 y 1 1 3 being mineralized and 2 3 being buried and could constitute the largest depocenter of organic carbon in the south atlantic

three dimensional structure and constraints on the nature of the coupled subduction spreading process in the aegean area abstract p wave travel time residuals from stations of the athens observatory network are inverted by a tomographic technique to investigate the velocity structure of the lithosphere in the aegean region both local and teleseismic data are used the velocity anomalies are best resolved in the mantle lithosphere and indicate a markedly heterogeneous velocity structure these results described elsewhere in more detail are correlated in this paper with other geophysical fields in the area the velocity heterogeneity observed in the upper mantle is very well correlated with thermal data and other geophysical fields in the aegean in particular the present day active extension in the aegean takes place behind the volcanic arc where in the mantle lithosphere velocity anomalies lower than normal are observed consisted with a stretched lithosphere in the back arc the area associated with the strongest bouguer and free air anomalies occurs in the southern aegean sea of crete above a zone of relatively higher velocity anomalies

the congolobe project a multidisciplinary study of congo deep sea fan lobe complex overview of methods strategies observations and sampling the presently active region of the congo deep sea fan around 330 000 km2 called the terminal lobes or lobe complex covers an area of 2500 km2 at 4700 5100 m water depth and 750 800 km offshore it is a unique sedimentary area in the world ocean fed by a submarine canyon and a channel levee system which presently deliver large amounts of organic carbon originating from the congo river by turbidity currents this particularity is due to the deep incision of the shelf by the congo canyon up to 30 km into the estuary which funnels the congo river sediments into the deep sea the connection between the river and the canyon is unique for major world rivers

terrestrial and marine n alcohol inputs and degradation processes relating to a sudden turbidity current in the zaire canyon abstract n alcohol biomarkers from sediment trap samples collected during a turbiditic event and surficial sediments on a levee of the zaire canyon equatorial west african margin one of the world s largest and still very active deep sea fans were examined the initial goal was to study the benthic ecosystem in relation to organic matter inputs as the quantity and quality might influence its development two criteria were used the relative abundance of short 20 and long chain c 22 n alcohols derived from marine organisms and higher plants respectively and the ratio of odd to even carbon numbered 20 n alcohols to assess the extent of alteration the material collected in the trap 30 m above the bottom when the turbiditic current occurred exhibited a high abundance of terrigenous n alcohols this trap did collect the turbidity material in contrast to the one located at 400 m the influence of the turbidity current was also revealed in the surficial sediment sampled nine months after the event the initial turbiditic material from the 30 m trap settled on to the sediment and extensive degradation was apparent upon this settling assuming a first order degradation rate the degradation rate constants were 3 4 and 0 9 y 1 for 19 and c 22 n alcohols respectively

seismic wave attenuation in the upper mantle beneath the aegean region a detailed study of p and s waves from earthquakes located along the hellenic arc and recorded by the greek seismological network shows an abnormal distribution of the seismic waves in the central aegean sea the data indicate a zone of anomalously high seismic wave attenuation in the upper mantle beneath the cyclades plateau and the inner part of the volcanic arc several independent observations suggest the presence of magma beneath the cyclades massif

early diagenesis in the sediments of the congo deep sea fan dominated by massive terrigenous deposits part iii sulfate and methane based microbial processes abstract geochemical profiles so 4 2 h 2 s ch 4 13 ch 4 and phylogenetic diversity of archaea and bacteria from two oceanographic cruises dedicated to the lobes sediments of the congo deep sea fan are presented in this paper in this area organic rich turbidites reach 5000 m and allow the establishment of patchy cold seep like habitats including microbial mats reduced sediments and vesicomyid bivalves assemblages these bivalves live in endosymbiosis with sulfur oxidizing bacteria and use sulfides to perform chemosynthesis in these habitats unlike classical abyssal sediments anoxic processes are dominant total oxygen uptake fluxes and methane fluxes measured with benthic chambers are in the same range as those of active cold seep environments and oxygen is mainly used for reoxidation of reduced compounds especially in bacterial mats and reduced sediments high concentrations of methane and sulfate co exist in the upper 20 cm of sediments and evidence indicates that sulfate reducing microorganisms and methanogens co occur in the shallow layers of these sediments simultaneously anaerobic oxidation of methane aom with sulfate as the electron acceptor is evidenced by the presence of anmes anaerobic methanotroph dissolved sulfide produced through the reduction of sulfate is reoxidized through several pathways depending on the habitat these pathways include vesicomyid bivalves uptake adults or juveniles in the bacterial mats habitats reoxidation by oxygen or iron phases within the reduced sediment or reoxidation by microbial mats sulfide uptake rates by vesicomyids measured in sulfide rich sea water 90 18 mmol s m 2 d 1 were similar to sulfide production rates obtained by modelling the sulfate profile with different bioirrigation constants highlighting the major control of vesicomyids on sulfur cycle in their habitats

deep sea habitat heterogeneity influence on meiofaunal communities in the gulf of guinea to estimate the degree of spatial heterogeneity of benthic deep sea communities we carried out a multiple scale from m s to 200 km investigation in the congo angola margins equatorial west african margin 3150 4800 m in which we examined the metazoan meiofauna at a variety of habitats along the congo channel system and in the associated cold seep we investigate the structure density vertical distribution patterns in the sediment and biomass of meiofaunal communities in the gulf of guinea and how they are controlled by hydrologic and biogeochemical processes the meiofaunal communities in the gulf of guinea were shaped by heterogeneous conditions on the margin and reflect the multiple scale spatial variability that corresponds with the different identified habitats the two control sites located at 100 km away from the canyon were inhabited by very dense and the most diverse meiobenthic communities similar meiobenthic communities inhabited the transition zone between the canyon and the cold seep sites located along the congo channel were obviously affected by the local high velocity bottom currents and unstable sedimentary conditions in this active submarine system extremely low meiobenthic densities and very low proportions in the most surficial sediment layers provided evidence for recently highly disturbed sediments at these sites the remote operated vehicle rov victor 6000 provided images of the cold seep showing a patchy distribution of several types of patchy distributed megafaunal communities dominated by three key symbiotic taxa mytilidae vesicomyidae and siboglinidae these cold seep sediments were colonised by a unique meiobenthic community characterised by a high small scale m s patchiness low species richness and the prominent dominance of two large sized nematode species sabatieria mortenseni which is a cosmopolitan nematode known from littoral habitats and an undescribed desmodora species the high individual body weight of s mortenseni and its dominance at the cold seep site resulted in a significantly higher nematode biomass at the seep compared to the surrounding sites in addition the vertical nematode profiles with maximum proportions in subsurficial layers points to a chemosynthesis based meiobenthic community in this cold seep in contrast to the phytodetritus based communities at the control sites and at the transition zone

seismic source parameters from a new dial up seismological network in greece a regional dial up pt telemetric network of eight digital short period seismic stations has been in full operation since the beginning of 1995 in greece during the first year of full operation three destructive earthquake sequences struck different regions of central and northern greece the dial up network managed to successfully record more than 85 of these seismic events including foreshocks main shocks and aftershocks and 45 of these events were selected in order to determine their seismic source parameters by spectral analysis the results show that seismic moment correlates very well with earthquake magnitude fault radius and fault displacement the determined scaling relations are in general agreement with those obtained by other studies for greek earthquakes that used different methodologies since digital seismic instrumentation is now expanding in greece these first results from spectral analysis of digital short period data can be considered useful for future seismic hazard studies

turbidity events observed in situ along the congo submarine channel abstract as part of the multidisciplinary programme biozaire devoted to studying deep sea benthic ecosystems in the gulf of guinea particulate input and its relationship with near bottom hydrodynamics were monitored using long term moorings from 2000 to early 2005 particular attention was given to material input through the congo ex zaire submarine channel that extends 760 km from the congo river mouth to the abyssal plain 5100 m near 6 s due to its direct connection to the congo river the congo canyon and channel system are characterised by particularly active recent sediment transport during this first in situ long term monitoring along the channel an energetic turbidity event was observed in january 2004 at three locations along the channel from 3420 to 4790 m in depth this event tilted and displaced the moorings installed at 3420 m site zr and 4070 m site zd and resulted in high sediment deposition at all three mooring sites the event moved at an average velocity of 3 5 m s 1 along the numerous channel meanders between 3420 and 4070 m then at 0 7 m s 1 between 4070 m and the end of the channel at 4790 m the particle cloud rose above the top of the valley at 4070 m site zd but not at 3420 m site zr where the channel was too deep lastly the mooring line broke at site zd in october 2004 probably due to a strong event like that of 2001 previously described by khripounoff et al khripounoff a vangriesheim a babonneau n crassous p denniellou b savoye b 2003 direct observation of intense turbidity activity in the zaire submarine valley at 4000 m water depth marine geology 194 151 158 between these strong events several peaks of high turbidity and particle flux occurred but without noticeable current increases these events were probably due to local sliding of sediment accumulated on the walls or terraces on the side of the channel the area near 4000 m depth and the lobe appear to be the main depocentres of particulate input rich in organic matter derived from the congo river

shear velocity structure in the aegean region obtained by joint inversion of rayleigh and love waves we present a shear velocity model of the crust and uppermost mantle under the aegean region by simultaneous inversion of rayleigh and love waves the database consists of regional earthquakes recorded by portable broadband three component digital stations that were installed for a period of 6 months in the broader aegean region for each epicentre station ray path group velocity dispersion curves are measured using appropriate frequency time analysis ftan the dispersion measurements for more than 600 love wave paths have been used we have also incorporated previous results for c 700 rayleigh wave paths for the study area the single path dispersion curves of both waves were inverted to regional group velocity maps for different values of period 6 32 s via a tomographic method the local dispersion curves of discrete grid points for both surface waves were inverted nonlinearly to construct 1d models of shear wave velocity v depth in most cases the joint inversion of rayleigh and love waves resulted in a single model from the multiple models compatible with the data that could interpret both rayleigh and love wave data around 60 local dispersion curves for both rayleigh and love waves were finally jointly inverted as expected because of the complex tectonic environment of the aegean region the results show strong lateral variations of the s wave velocities for the crust and uppermost mantle our results confirm the presence of a thin crust typically less than 28 30 km in the whole aegean sea which in some parts of the southern and central aegean sea becomes significantly thinner 20 22 km in contrast a large crustal thickness of about 40 45 km exists in western greece and the remaining part of continental greece is characterized by a mean crustal thickness of about 35 km a significant sub moho upper mantle low velocity zone lvlmantle with velocities as low as 3 7 km s is clearly identified in the southern and central aegean sea correlated with the high heat flow in the mantle wedge above the subducted slab and the related active volcanism in the region the results obtained results are compared with independent body wave tomographic information on the velocity structure of the study area and exhibit a generally good agreement although significant small scale differences are

estimation of attenuation structure and local earthquake magnitude based on acceleration records in greece hatzidimitriou p papazachos c kiratzi a and theodulidis n 1993 estimation of attenuation structure and local earthquake magnitude based on acceleration records in greece in s j duda and t b yanoskaya editors estimation of earthquake size tectonophysics 217 spec sect 243 253 strong motion accelerograms are used for the estimation of attenuation coefficient in the upper crust in greece on the assumption that direct s waves are responsible for the strong near source motion this coefficient was then used to derive a calibration formula for the estimation of local earthquake magnitude for epicentral distances a 130 km and 4 0 i m i 6 1 q values are calculated by the spectral decay of the log spectrum of the accelerograms the resulting values exhibit the high attenuation of seismic waves in greece and indicate the existence of a highly attenuative surface sedimentary layer which strongly controls the total wave attenuation

high frequency shear wave propagation across the hellenic subduction zone abstract this study investigates shear wave propagation across the hellenic subduction zone using high quality waveforms of 71 intermediate depth events 40 160 km depth the data have been recorded by a permanent seismic network consisting of 22 broadband three component stations that cover most parts of greece shear waves can be efficiently transmitted with low attenuation q s 1100 through the descending slab which extends laterally over much of the forearc area with a northwest southeast strike the slab also appears to be continuous downdip in the depth range 60 160 km even though it was found that a gap smaller than 10 km would not affect shear wave efficiency significantly two highly attenuating areas have been detected one in the central southeast aegean corresponding to the mantle wedge and the other in the northern aegean probably caused by elevated upper mantle temperatures owing to the ongoing extension in that area these results provide additional constraints for the geometry of the hellenic subduction zone and the geodynamic setting of the aegean region

spatial and temporal variability of downward particle fluxes on a continental slope lessons from an 8 yr experiment in the gulf of lions nw mediterranean abstract a long term experiment of downward particle fluxes and currents has been initiated in 1993 on the continental slope of the gulf of lions nw mediterranean and pursued within the frame of several french and european projects pnec euromarge nb mtp ii mater eurostrataform sediment traps and current meters were deployed at several locations on this slope deeply incised by numerous canyons with an extensive spatial coverage for the first 2 years canyons at the entrance middle and exit of the gulf with respect to the general along slope circulation head and mid canyon depths adjacent open slope from late 1995 onwards this design was reduced to the two mid canyon moorings at the entrance and exit of the gulf monthly fluxes and hourly temperatures and currents were recorded at 500 m 30 m above bottom mab in the canyon heads at 500 and 1000 m respectively 530 and 30 mab nominal depths at the mid canyon sites and at 750 m 30 mab open slope this study aims at describing the spatial seasonal and interannual variability of flux intensity and composition of settling particles and at analyzing the role of diverse forcings in the control of particle exchange across the margin results from the first 8 years 1993 2001 show that total mass fluxes in the 101 104 mg m 2 d 1 range increase along slope particularly for the near bottom traps between the ne planier canyon and the sw lacaze duthiers canyon limits of the gulf of lions indicating an increased shelf export of particulate matter in the western part of the system bulk chemical composition organic matter carbonate opal and lithogenic fraction remained rather stable during the course of the experiment tending towards values typical of superficial shelf sediments at higher mass fluxes first order calculations using a simple two component mixing model suggest a decreasing contribution of primary particles settling out of the overlying waters to the total flux from the entrance towards the exit of the system particulate material transferred to the deeper slope in the southwestern part of the gulf of lions appears therefore to predominantly originate in resuspended shelf and or upper slope sediment downward particle fluxes and potential forcing parameters exhibit a high seasonal variability with higher values from late autumn to early spring furthermore unprecedented winter flux peaks observed in 1999 dominated the interannual differences which otherwise were quite limited correlations between sources of particulate material on the shelf i e river and atmospheric inputs phytoplankton biomass and sediment resuspension cross slope exchange mechanisms derived from in situ temperature and current records and flux data indicate a predominant effect of dense cold water cascading on the exchange of particulate matter between the shelf and the slope

3 d velocity structure beneath the crust and upper mantle of aegean sea region the region of the aegean sea and the surrounding areas in the eastern mediterranean lies on the boundary zone between the eurasian and the african plates it is a zone of widespread extensive deformation and therefore reveals a high level of seismicity

detection of first year and multi year sea ice from dual polarization sar images under cold conditions this paper presents a new technique for automated detection of multi year my and first year fy sea ice from radarsat 2 dual polarization hh hv scansar wide images under cold environmental conditions the approach is applied to 2 05 km times2 05 km 41 times 41 pixels spatial window in the situation where the area is labeled as ice by our recently introduced ice and open water detection approach the probability of the presence of my ice is modeled as a function of the two selected predictor parameters computed over each spatial window the hv hh polarization ratio and the standard deviation of the hv signal the proposed my ice probability model was built based on thousands of synthetic aperture radar sar images and corresponding canadian ice service cis image analysis products covering the 2010 2016 time period not including 2013 our verification results for the independent testing subset for the year 2013 against the cis image analysis products suggest that approximately 50 of pure my and fy ice samples were classified with an accuracy of 98 2 the incidence angle correction of hh and hv backscatter does not improve my and fy ice detection results in the space of the selected predictor parameters the proposed technique will be used as part of the environment and climate change canada regional ice ocean prediction system in support of assimilation of ice thickness retrievals from cryosat 2 and soil moisture and ocean salinity mission data

origin and distribution of the organic matter in the distal lobe of the congo deep sea fan a rock eval survey the congo river the second largest river in the world is a major source of organic matter for the deep atlantic ocean because of the connection of its estuary to the deep offshore area by a submarine canyon which feeds a vast deep sea fan the lobe zone of this deep sea fan is the final receptacle of the sedimentary inputs presently channelled by the canyon and covers an area of 2500 km the quantity and the source of organic matter preserved in recent turbiditic sediments from the distal lobe of the congo deep sea fan were assessed using rock eval pyrolysis analyses six sites located at approximately 5000 m water depth were investigated the mud rich sediments of the distal lobe contain high amounts of organic matter 3 5 to 4 corg the origin of which is a mixture of terrestrial higher plant debris soil organic matter and deeply oxidized phytoplanktonic material although the respective contribution of terrestrial and marine sources of organic matter cannot be precisely quantified using rock eval analyses the terrestrial fraction is dominant according to similar hydrogen and oxygen indices of both suspended and bedload sediments from the congo river and that deposited in the lobe complex the rock eval signature supports the 70 to 80 of the terrestrial fraction previously estimated using c n and 13corg data in the background sediment the organic matter distribution is homogeneous at different scales from a single turbiditic event to the entire lobe and changes in accumulation rates only have a limited effect on the quantity and quality of the preserved organic matter peculiar areas with chemosynthetic bivalves and or bacterial mats explored using rov victor 6000 show a rock eval signature more or less similar to background sediment this high organic carbon content associated to high sedimentation rates 2 to 20 mm yr 1 in the congo distal lobe complex implies a high burial rate for organic carbon consequently the congo deep sea fan represents an enormous sink of terrestrial organic matter when compared to other turbiditic systems over the world

organic carbon accumulation in modern sediments of the angola basin influenced by the congo deep sea fan geochemical data total organic carbon toc content 13corg c n rock eval analyses were obtained on 150 core tops from the angola basin with a special focus on the congo deep sea fan combined with the previously published data the resulting dataset 322 stations shows a good spatial and bathymetric representativeness toc content and 13corg maps of the angola basin were generated using this enhanced dataset the main difference in our map with previously published ones is the high terrestrial organic matter content observed downslope along the active turbidite channel of the congo deep sea fan till the distal lobe complex near 5000 m of water depth interpretation of downslope trends in toc content and organic matter composition indicates that lateral particle transport by turbidity currents is the primary mechanism controlling supply and burial of organic matter in the bathypelagic depths

coseismic crustal deformation on a fault zone defined by microseismicity in the pavliani area central greece summary pavliani is an area of high microseismicity in northern central greece there is no evidence in the historical record of large damaging earthquakes in this area since at least 600 bc we examine contemporary crustal deformation in this area using microearthquake data recorded during 1983 84 by the volos seismic network principally and to a lesser extent by the patras seismic network the microseismicity 1 4 6 ml defines an approximately vertical fault zone trending wsw ene of 55 km length and 25 km depth the fault plane solution for the 4 6 m earthquake shows a strike consistent with the trend of the microseismicity zone and an extension direction consistent with many large earthquakes in central greece associated with the extensional greater aegean spectra of the microearthquakes are estimated using p waves obtained by selective windowing designed to exclude other p phases from the coda seismic moments in the range 1 95 x 10 n m are obtained accompanied by estimates of seismotectonic source parameters including source radii average stress drop and average coseismic slip of prime utility is an excellent correlation found between seismic moment and magnitude and with coseismic slip this allows heterogeneity in the distribution of individual microearthquake source parameters to be mapped onto the vertical fault zone plane and the history of coseismic deformation for the whole seismicity observed during 1983 84 to be examined using cumulative slip and moment release rate peaks of high moment release rate occur in the east and centre of the fault zone that in the east is dominated by a few large moment release events that in the centre by a large number of small events both moment release rate peaks despite their different component seismicity are associated with high cumulative coseismic slip only the eastern peak is also associated with high stress drop it is also shallower and therefore any surficial interaction is less likely to be attenuated the surface projection of this peak is within 3 km of a mapped normal fault coincident with an alpine thrust front delineated by a major scarp of mesozoic limestone surface evidence of recent movement on this normal fault is only slight friable fault gouge is seen at a few localities displacement could not be determined because the limestone surfaces are deeply weathered and lack kinematic indicators however considering the whole fault zone as a cohesive entity and using a brune estimate of slip at the current moment release rate throughout the present extensional tectonic regime suggests a total vertical displacement of order 175 m similar to the elevation of the scarp

assessing three waveform retrackers on sea ice freeboard retrieval from cryosat 2 using operation icebridge airborne altimetry datasets abstract in this study three previously proposed echo waveform retracking techniques are assessed for their performances in measuring lead and sea ice elevations from cryosat 2 cs 2 sar l1b data these derived cs 2 sea ice elevations and freeboards are compared with those from seven operation icebridge oib flights dedicated as the cs 2 underflights during the late winter early spring of 2011 2012 and 2013 results show that sea ice elevation measured by cs 2 is mostly ranged between 1 0 m after the mean sea surface mss is subtracted the mean absolute biases between the cs 2 and atm elevations in different underflights are mostly ranged between 0 02 0 71 m for multi year ice empirical lead and threshold floe retracker eltf is the best choice for ice elevation measurement and the waveform fitting retracker wff is the best choice for ice freeboard retrieval for first year ice the wff is the best choice for ice elevation measurement and the threshold first maximum retracker tfmra is the best choice for ice freeboard retrieval this study also suggests when the tfmra retracker is used to retrieve lead elevation a 70 threshold of the first local maxima power is better than the 50 threshold previously used

shear wave velocity models from rayleigh wave dispersion in the broader aegean area an analysis of rayleigh waves generated by earthquakes in the broader aegean is undertaken to estimate variations in the shear wave velocity structure in the crust and upper mantle down to about 70 km depth the study centres literally on the vertical component long period standard seismograph at athens ath and is only possible because this station has provided good quality data over many years of continuous operation rayleigh waves from 81 earthquakes during 1963 87 with surface wave magnitudes in the range 4 2 to 5 4 and epicentral distances of 300 500 km from athens are analysed these earthquake epicentres are selected in clusters defining 12 propagation paths across the broader aegean and radial to athens the highest concentration of azimuthal sampling traverses the hellenic volcanic arc the ensuing group velocity curves over these radial paths are inverted to shear wave velocity depth models using linear and then monte carlo hedgehog inversion schemes the resulting velocity depth solutions from both schemes presented as individual path velocity depth profiles 3 d azimuthal perspectives and contoured velocity depth panoramas over the whole broader aegean are corroborative the western arc of azimuths extending from chalkidiki north of athens to sw crete south of athens have velocity depth profiles which consistently reach sub moho velocities at about 45 km depth the most striking feature revealed by the contoured shear wave velocity depth panoramas is an extensive zone of relatively low velocity about 3 8 km s 1 centred around 30 km depth which may extend from 20 to 40 km depth this low velocity zone is contained in the wedge of paths from carpathos rhodes and sw turkey which traverse the hellenic volcanic arc and subtend an angle of about 33 at athens there is also slight evidence for anomalously low velocities at greater depths around 4 1 4 2 km s 1 at about 50 60 km depth but these are at the limits of useful resolution of the available data nevertheless these indications are at their strongest in the same wedge below the hellenic volcanic arc