segmented lateral dyke growth in a rifting event at barðarbunga volcanic system iceland crust at many divergent plate boundaries forms primarily by the injection of vertical sheet like dykes some tens of kilometres long1 previous models of rifting events indicate either lateral dyke growth away from a feeding source with propagation rates decreasing as the dyke lengthens2 3 4 or magma flowing vertically into dykes from an underlying source5 6 with the role of topography on the evolution of lateral dykes not clear here we show how a recent segmented dyke intrusion in the bar arbunga volcanic system grew laterally for more than 45 kilometres at a variable rate with topography influencing the direction of propagation barriers at the ends of each segment were overcome by the build up of pressure in the dyke end then a new segment formed and dyke lengthening temporarily peaked the dyke evolution which occurred primarily over 14 days was revealed by propagating seismicity ground deformation mapped by global positioning system gps interferometric analysis of satellite radar images insar and graben formation the strike of the dyke segments varies from an initially radial direction away from the bar arbunga caldera towards alignment with that expected from regional stress at the distal end a model minimizing the combined strain and gravitational potential energy explains the propagation path dyke opening and seismicity focused at the most distal segment at any given time and were simultaneous with magma source deflation and slow collapse at the bar arbunga caldera accompanied by a series of magnitude m 5 earthquakes dyke growth was slowed down by an effusive fissure eruption near the end of the dyke lateral dyke growth with segment barrier breaking by pressure build up in the dyke distal end explains how focused upwelling of magma under central volcanoes is effectively redistributed over long distances to create new upper crust at divergent plate boundaries

the magmatic plumbing system of the askja central volcano iceland as imaged by seismic tomography the magmatic plumbing system beneath askja a volcano in the central icelandic highlands is imaged using local earthquake tomography we use a catalog of more than 1300 earthquakes widely distributed in location and depth to invert for the p wave velocity vp and the vp vs ratio extensive synthetic tests show that the minimum size of any velocity anomaly recovered by the model is 4 km in the upper crust depth 8 km below sea level bsl increasing to 10 km in the lower crust at a depth of 20 km bsl the plumbing system of askja is revealed as a series of high vp vs ratio bodies situated at discrete depths throughout the crust to depths of over 20 km we interpret these to be regions of the crust which currently store melt with melt fractions of 10 the lower crustal bodies are all seismically active suggesting that melt is being actively transported in these regions the main melt storage regions lie beneath askja volcano concentrated at depths of 5 km bsl with a smaller region at 9 km bsl their total volume is 100 km3 using the recorded waveforms we show that there is also likely to be a small highly attenuating magmatic body at a shallower depth of about 2 km bsl

controlling factors on earthquake swarms associated with magmatic intrusions constraints from iceland abstract the currently two most important surveying tools in volcano monitoring are observations of seismicity and surface deformation magma migration within the earth s crust is frequently associated with seismic activity often occurring as distinct earthquake swarms understanding the exact nature and significance of these swarms is important when evaluating volcanic crisis situations there seems however to be no general correlation between the amount of seismic energy release and the rate and volume of magma on the move which may complicate an immediate risk evaluation it has previously been shown that stressing rate appears as the controlling factor on the occurrence of seismicity during intrusion however in this paper we emphasize that this is only true under specific circumstances other factors influence the evolution and resulting seismic energy release and each intrusion scenario needs to be evaluated separately three icelandic cases where seismic swarms have been confirmed through deformation measurements to be related to magmatic movements were selected we show how the relationship between volume change and resulting seismicity varies greatly between cases and suggest that in a general approach the most important factor governing the level of seismic energy release is the background stress state tectonic setting regional stresses and tectonic history are therefore all of great importance when evaluating a magmatically induced seismic crisis the stressing rate only plays the dominant role when either a stress in the intruded area is close to the yield strength before intrusion or possibly b when the intrusion is extraordinarily voluminous and rapid

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

explosive expansion of a slowly decompressed magma analogue evidence for delayed bubble nucleation 1 while ascending in the plumbing system of volcanoes magma undergoes decompression at rates spanning several orders of magnitude and set by a number of factors internal and external to the volcano slow decompression generally results in an effusive or mildly explosive expansion of the magma but counterexamples of sudden switches from effusive to explosive eruptive behavior have been documented at various volcanoes worldwide the mechanisms involved in this behavior are currently debated in particular for basaltic magmas here we explore the interplay between decompression rate and vesiculation vigor by decompressing a magma analogue obtained by dissolving pine resin into acetone in varying proportions analogue experiments allow direct observations of the processes of bubble nucleation and growth flow dynamics and fragmentation that is not currently possible with magmatic systems our mixtures contain solid particles and upon decompression nucleation of acetone bubbles is observed we find that mixtures with a high acetone content containing smaller and fewer solid particles experience strong supersaturation and fragment under very slow decompressions despite having low viscosity while mixtures with lower acetone content with more and larger solid particles degas efficiently without fragmentation we interpret our results in terms of delayed bubble nucleation due to a lack of efficient nucleation sites we discuss how a similar mechanism might induce violent explosive expansion in volatile rich and poorly crystalline low silica magmas by analogy with the behavior of rhyolitic magmas

a reinterpretation of seismicity associated with the january 1983 dike intrusion at kilauea volcano hawaii in january 1983 a dike intrusion fissure eruption generated a swarm of 375 magnitude 1 to 3 earthquakes along a 16 km segment of kilauea s middle east rift zone we searched the hawaiian volcano observatory catalog for multiplets of similar events from this region from 1980 through 1985 and obtained precise relative locations by waveform cross correlation over 150 of the intrusion earthquakes could be grouped into 14 multiplets of five or more events with sufficient similarity for accurate relocation some multiplets were active for only a few minutes during the downrift migration phase of the seismic swarm consistent with generation near the propagating dike tip while others were active for several days the two multiplets nearest the origin of the seismic swarm include events from the preceding days and months most multiplets span only 50 to 100 m following relocation are located at about 3 to 4 km depth and appear to deepen downrift the catalog depths of those earthquakes in multiplets and those not in multiplets are similar suggesting that most of the recorded seismicity may have come from a very limited depth interval despite the fact that the dike breached the surface by analogy with a mechanical model used to explain a similar clustering of background seismicity in the upper east rift in 1991 we infer that the earthquakes are generated in regions of high stress concentration immediately above kilauea s deforming deep rift body this conclusion is consistent with the depth of the top of the deep rift body inferred from geodetic data and with numerical calculations suggesting that a significant ambient differential stress is required for dikes to produce earthquakes larger than magnitude 1

the behavior of trace elements during schwertmannite precipitation and subsequent transformation into goethite and jarosite schwertmannite is a ubiquitous mineral formed from acid rock drainage ard and plays a major role in controlling the water chemistry of many acid streams the formation of schwertmannite was investigated in the acid discharge of the monte romero abandoned mine iberian pyrite belt sw spain schwertmannite precipitated from supersaturated solutions mainly owing to the oxidation of fe ii to fe iii and transformed with time into goethite and jarosite in a few hours schwertmannite precipitation removed more than half of the arsenic load from solution whereas the concentration of divalent trace metals zn cu pb cd ni and co remained almost unchanged in the laboratory natural schwertmannite was kept in contact with its coexisting acid water in a flask with a solid liquid mass ratio of 1 5 for 353 days during this time the ph of the solution dropped from 3 07 to 1 74 and the concentrations of sulfate and fe increased during the first 164 days schwertmannite transformed into goethite plus h3o jarosite but subsequently goethite was the only mineral to form some of the trace elements such as al cu pb and as were depleted in solution during the first stage as schwertmannite transformed into goethite plus h3o jarosite on the contrary the transformation of schwertmannite to goethite with no jarosite during the second stage released al cu and as to the solution despite the variation in their concentrations in solution approximately 80 of the total al and cu inventories and more than 99 as and pb remained in the solid phase throughout the entire aging process

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

eustatic sea level controls on the flushing of a shelf incising submarine canyon turbidity currents are the principal processes responsible for carving submarine canyons and maintaining them over geological time scales the turbidity currents that maintain or flush submarine canyons are some of the most voluminous sediment transport events on earth long term controls on the frequency and triggers of canyon flushing events are poorly understood in most canyon systems due to a paucity of long sedimentary records here we analyzed a 160 m long ocean drilling program odp core to determine the recurrence intervals of canyon flushing events in the nazare canyon over the last 1 8 m y we then investigated the role of global eustatic sea level in controlling the frequency and magnitude of these canyon flushing events canyon flushing turbidity currents that reach the iberian abyssal plain had an average recurrence interval of 2770 yr over the last 1 8 m y previous research has documented no effect of global eustatic sea level on the recurrence rate of canyon flushing however we find that sharp changes in global eustatic sea level during the mid pleistocene transition 1 2 0 9 ma were associated with more frequent canyon flushing events the change into high amplitude long periodicity sea level variability during the mid pleistocene transition may have remobilized large volumes of shelf sediment via subaerial weathering and temporarily increased the frequency and magnitude of canyon flushing turbidity currents turbidite recurrence intervals in the iberian abyssal plain have a lognormal distribution which is fundamentally different from the exponential distribution of recurrence intervals observed in other basin turbidite records the lognormal distribution of turbidite recurrence intervals seen in the iberian abyssal plain is demonstrated to result from the variable runout distance of turbidity currents such that distal records are less complete with possible influence from diverse sources or triggering mechanisms the changing form of turbidite recurrence intervals at different locations down the depositional system is important because it ultimately determines the probability of turbidity current related geohazards

deep fault plane geometry inferred from multiplet relative relocation beneath the south flank of kilauea dense microearthquake swarms occur in the upper south flank of kilauea providing multiplets composed of hundreds of events the similarity of their waveforms and the quality of the data have been sufficient to provide accurate relative relocations of their hypocenters a simple and efficient method has been developed which allowed the relative relocation of more than 250 events with an average precision of about 50 m horizontally and 75 m vertically relocation of these events greatly improves the definition of the seismic image of the fault that generates them indeed relative relocations define a plane dipping about 6 northward although corresponding absolute locations are widely dispersed in the swarm a composite focal mechanism built from events providing a correct spatial sampling of the multiplet also gives a well constrained northward dip of about 5 to the near horizontal plane this technique thus collapses the clouds of hypocenters of single event locations to a plane coinciding with the slip plane revealed by previous focal mechanism studies we cannot conclude that all south flank earthquakes collapse to a single plane there may locally be several planes perhaps with different dips and depths throughout the south flank volume the 6 northward dipping plane we found is too steep to represent the overall flexure of the oceanic crust under the load of the island of hawaii this plane is probably an important feature that characterizes the basal slip layer below the upper south flank of kilauea volcano differences in seismicity rate and surface deformations between the upper and lower south flank could be related to the geometry of this deep fault plane the present work illustrates how high precision relative relocations of similar events in dense swarms combined with the analysis of geodetic measurements can help to describe deep fault plane geometry systematic selection and extensive relative relocation of similar earthquakes could be attempted in other well instrumented highly seismic areas to provide reliable basic information especially useful for understanding of earthquake generation processes

time dependent dike propagation from joint inversion of seismicity and deformation data dike intrusions both deform earth s surface and induce propagating earthquake swarms we develop methods to utilize both deformation and seismicity from brittle volcano tectonic earthquakes to image time dependent dike propagation dieterich s 1994 seismicity rate theory is used to relate dike induced stress changes to seismicity rate and is combined with elastic green s functions relating dike opening to deformation different space time patterns of seismicity develop if earthquakes occur at the same depth as the dike compared to above below the dike in the former seismicity initiates near the dike s leading edges but shuts off as the dike tips pass and seismogenic volumes fall into stress shadows in the latter seismicity continues at a decaying rate after the tips pass we focus on lateral propagation and develop a nonlinear inversion method that estimates dike length and pressure as a function of time the method is applied to the 2007 father s day intrusion in kilauea volcano seismicity is concentrated at 3 km depth comparable to geodetic estimates of dike depth and decays rapidly in time with lateral propagation only and a vertical dike tip line it is difficult to fit both gps data and the rapid down rift jump in seismicity suggesting significant vertical propagation for the events to have occurred below the dike requires a very short aftershock decay time hence unreasonably high background stressing rate the rapid decay is better explained if the dike extends somewhat below the seismicity we suggest that joint inversion is useful for studying the diking process and may allow for improved short term eruption forecasts

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

seismic amplitude ratio analysis of the 2014 2015 bar arbunga holuhraun dike propagation and eruption magma is transported in brittle rock through dikes and sills this movement may be accompanied by the release of seismic energy that can be tracked from the earth s surface locating dikes and deciphering their dynamics is therefore of prime importance in understanding and potentially forecasting volcanic eruptions the seismic amplitude ratio analysis sara method aims to track melt propagation using the amplitudes recorded across a seismic network without picking the arrival times of individual earthquake phases this study validates this methodology by comparing sara locations filtered between 2 and 16hz with the earthquake locations same frequency band recorded during the 2014 2015 bar arbunga holuhraun dike intrusion and eruption in iceland integrating both approaches also provides the opportunity to investigate the spatiotemporal characteristics of magma migration during the dike intrusion and ensuing eruption during the intrusion sara locations correspond remarkably well to the locations of earthquakes several exceptions are however observed 1 a low frequency signal was possibly associated with a subglacial eruption on 23 august 2 a systematic retreat of the seismicity was also observed to the back of each active segment during stalled phases and was associated with a larger spatial extent of the seismic energy source this behavior may be controlled by the dike s shape and or by dike inflation 3 during the eruption sara locations consistently focused at the eruptive site 4 tremor rich signal close to ice cauldrons occurred on 3 september this study demonstrates the power of the sara methodology provided robust site amplification quality factors and seismic velocities are available plain language summary locating earthquakes usually implies picking phase arrivals p and s waves another technique called seismic amplitude ratio analysis sara was recently introduced to locate them only by using the amplitude recorded at different pairs of seismic stations however this technique was never proven to be true this study shows that the earthquake locations derived by sara compares remarkably well with the locations of 30 000 seismic events triggered when magma migrated in the icelandic crust prior to the 2014 2015 holuhraun eruption but the results also provide new insight into the magma dynamics that led to the largest eruption of the last two centuries in europe we show that ground vibration was continuously triggered during the 2week period preceding the eruption when magma forced its way toward the eruption site but also during the eruption itself several intriguing features were observed including low frequency vibrations possibly associated with eruption below the ice or large patches of seismic activity when the magma stopped propagating toward the eruption site this methodology performs very well provided some parameters are available and allows to gain insights into the complex dynamics associated with magma movements

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

arsenic and metal mobility from au mine tailings in rodalquilar almeria se spain in the old mining area of rodalquilar mine wastes soil and sediments were characterized and the results revealed high concentration of au ag as bi cu fe mn pb se sb and zn in tailings and sediments the contaminant of greatest environmental concern is as the mean concentration in the tailings was 679 9 and 345 mg kg in the sediments of playazo creek the groundwater samples from the alluvial aquifer showed high concentration of al as cd fe hg mn ni pb se sb and zn and very high concentration of chloride and sulfate which were above the concentration defined in the european standards for drinking water the presence of as in groundwater may be caused by the oxidation of arsenian pyrite the possible as desorption from goethite and ferrihydrite and the jarosite dissolution groundwater concentrations of cd fe mn and possibly cu were associated with low values of eh indicating the possible dissolution of oxy hydroxides of fe and mn the mobility of metals in the column experiments show the release of al fe mn cr cu ni v and zn in significant concentrations but below the detected values in groundwater however as cd sb se pb and au are generally mobilized in concentrations above the detected values in groundwater the possible mass transfer processes that could explain the presence of the contaminants in the aquifer and the leachates was simulated with the phreeqc numerical code and revealed the possible dissolution of the following mineral phases jarosite natrojarosite arsenian pyrite alunite chlorite kaolinite and calcite

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

ice volcano interaction of the 1996 gjalp subglacial eruption vatnajokull iceland volcanic eruptions under glaciers can cause dangerous floods and lahars1 2 3 and create hyaloclastite fragmented glassy rock mountains4 5 6 7 8 but processes such as the rate of heat transfer between ice and magma edifice formation and the response of the surrounding glacier are poorly understood because of the lack of data here we present observations from the fissure eruption at vatnajokull ice cap iceland in october 1996 in the 13 days of the eruption 3 km3 of ice were melted and the erupted magma fragmented into glass forming a hyaloclastite ridge 6 7 km long and 200 300 m high under 500 750 m of ice meltwater of temperatures of 15 20 c flowed along a narrow channel at the glacier bed into the grimsvotn subglacial lake for five weeks before draining in a sudden flood or jokulhlaup subsidence and crevassing of the ice cap occurred over the eruptive fissure and the meltwater path whereas elsewhere the glacier surface remained intact suggesting that subglacial eruptions do not trigger widespread basal sliding in warm based glaciers

effect of solidification on a propagating dike 1 magma migration through the brittle crust from depth occurs by the propagation of hydraulic fractures or dikes volcanic eruptions occur at the last stage if and when a propagating dike reaches the surface dike propagation involves complex physics because of several processes that are simultaneously occurring such as viscous flow of magma rock fracture elastic deformation of the host rock and potentially large changes of the physical properties of the magma crystallization degassing solidification etc currently the most practical way in the field or in terms of field measurements to follow the migration of magma before it reaches the surface is the analysis of the seismicity generated nevertheless a physical model that quantitatively relates the flux of magma in the dike to the seismicity is lacking we present here laboratory experiments involving propagation of a fluid filled crack such that the fluid solidifies upon contact with the cold elastic host we show that this can lead to a way of estimating the flux of the injection as a function of the surface creation rate the latter is shown to be a more reliable gauge of magma flux than the upward propagating velocity in the geologic application of a propagating dike the rate of creation of surface area may be related to the rate of release of seismic energy although this latter relation needs further work to be quantitatively reliable our new model nevertheless indicates how a new general framework can be constructed

burial of terrestrial organic matter in marine sediments a re assessment 1 calculations based on recent observations indicate that approximately one third of the organic matter presently being buried in marine sediments may be of terrestrial origin with the majority of this terrestrial organic matter tom burial occurring in muddy deltaic sediments these calculations further suggest that the remineralization of terrestrial organic matter in the oceans is also much less efficient than that of marine organic matter these two underappreciated observations have important implications in terms of our understanding of the controls on the global carbon cycle from a paleoceanographic perspective the results presented here also suggest that changes in tom burial on glacial interglacial timescales have the potential to impact the global carbon cycle i e atmospheric co2 levels

multiple coincident eruptive seismic tremor sources during the 2014 2015 eruption at holuhraun iceland we analyze eruptive tremor during one of the largest effusive eruptions in historical times in iceland 2014 15 holuhraun eruption seismic array recordings are compared with effusion rates deduced from moderate resolution imaging spectroradiometer modis recordings and ground video monitoring data and lead to the identification of three coexisting eruptive tremor sources this contrasts other tremor studies that generally link eruptive tremor to only one source usually associated with the vent the three sources are i a source that is stable in back azimuth and shows bursts with ramp like decrease in amplitude at the beginning of the eruption we link it to a process below the open vents where the bursts correlate with the opening of new vents and temporary increases in the lava fountaining height ii a source moving by a few degrees per month while the tremor amplitude suddenly increases and decreases back azimuth and slowness correlate with the growing margins of the lava flow field whilst contact with a river led to fast increases of the tremor amplitude iii a source moving by up to 25 southwards in 4 days that cannot be related to any observed surface activity and might be linked to intrusions we therefore suggest that eruptive tremor amplitudes energies are used with caution when estimating eruptive volumes effusion rates or the eruption explosivity as multiple sources can coexist during the eruption phase our results suggest that arrays can monitor both the growth of a lava flow field and the activity in the vents

fracture movements and graben subsidence during the 2014 barðarbunga dike intrusion in iceland abstract a dike propagated 48 km from the bar arbunga central volcano into one of its fissure swarms in august and early september 2014 the dike intrusion was accompanied by caldera subsidence in the ice covered bar arbunga central volcano as well as a propagating earthquake swarm graben subsidence and fissure eruptions in the fissure swarm most of the dike was emplaced in the glacier covered part of the fissure swarm but a 10 km long section at the distal northern end of the dike is ice free new ground fractures were observed in the ice free part during the dike propagation and prior to the outbreak of a major lava producing eruption the fractures delineate two graben structures in direct continuation of each other here we show the extent and depth of the grabens and maps of fractures and eruptive fissures that were formed or reactivated north of the vatnajokull glacier during the dike intrusion the active graben subsidence was identified 3 days after seismicity reached the ice free area then fractures delineated a 700 1000 m wide and 5 km long graben visible from the northern edge of the vatnajokull glacier farther north a narrower 250 450 m wide graben was seen a short lived minor eruption occurred between these grabens on the 29th of august 2014 2 days after the grabens were identified the northern graben was extended southwards during or before the eruption and included the eruptive fissure on the 31st of august 2014 a much larger eruption began on the same eruptive fissure the fissure quickly obtained its maximum length of 2 km this eruption lasted 6 months a minor eruption lasting 2 days or less occurred on the southern graben on the 5th of september 2014 the first two eruptions took place on the same eruptive fissure that formed the pre existing holuhraun lava presumably in the 18th century measurements in january 2015 show that the southern graben was 3 5 5 5 m deep but the northern graben had been covered by lava from the depth and the opening of the graben we estimate that the dip of the boundary faults of the graben is 75 the narrow grabens observed before the eruptions indicated that magma was at shallow depth likely much less than 300 m 2 days before it opened to the surface such observations can serve as a tool to estimate likelihood of eruptions during dike intrusions

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

multiple melt injection along a spreading segment at askja iceland lower crustal earthquakes 12 25 km depth have been detected since august 2005 in the askja volcanic system along the north iceland rift in the normally ductile part of the crust the earthquakes occur in three clusters which have stable dimensions and locations through time and are interpreted as positions of repeated melt supply from the mantle to the lower crust seismic velocity vp vs ratios are consistent with the presence of partial melt in the lower crust at askja the spatial separation of the clusters shows that there are multiple positions of melt injection within this one magmatic segment and all three positions are currently active this pattern of melt supply is more like that observed on fast spreading ridges than slow spreading ridges and is probably a consequence of the increased melt production beneath iceland compared to the rest of the mid atlantic ridge however the relative number of earthquakes in each cluster shows that two thirds of the melt is supplied to the central volcano askja i e segment center during the last major rifting episode shallow lateral melt migration occurred from the magma chamber beneath the volcano therefore on long time scales melt supply is probably greater at the segment center with melt redistribution in the upper crust even though there are multiple points of lower crustal injection along the segment

evolution of a lateral dike intrusion revealed by relatively relocated dike induced earthquakes the 2014 15 barðarbunga holuhraun rifting event iceland abstract understanding dikes is vital as they serve both as bodies that build the crust and as conduits that feed eruptions and must be monitored to evaluate volcanic hazard during the 2014 15 bar arbunga rifting event iceland intense seismicity accompanied the intrusion of a 50 km lateral dike which culminated in a 6 month long eruption we here present relocations of earthquakes induced by the lateral dike intrusion using cross correlated sub sample relative travel times the 100 m spatial resolution achieved reveals the complexity of the dike propagation pathway and dynamics jerky segmented and allows us to address the precise relationship between the dike and seismicity with direct implications for hazard monitoring the spatio temporal characteristics of the induced seismicity can be directly linked in the first instance to propagation of the tip and opening of the dike and following this after dike opening indicate a relationship with magma pressure changes i e dike inflation deflation followed by a general post opening decay seismicity occurs only at the base of the dike where dike imposed stresses combined with the background tectonic stress from regional extension over 200 yr since last rifting are sufficient to induce failure of pre existing weaknesses in the crust while the greatest opening is at shallower depths emplacement oblique to the spreading ridge resulted in left lateral shear motion along the distal dike section studied here and a prevalence of left lateral shear failure fault plane strikes are predominately independent of the orientation of lineations delineated by the hypocenters indicating that they are controlled by the underlying host rock fabric this high resolution study provides unprecedented opportunity for comparison with both geodetic and field frozen dike observations and development and consolidation of analytical and analogue models with implications for rifting processes and real time monitoring of magma intrusion

mobility of arsenic in groundwater in the obuasi gold mining area of ghana some implications for human health arsenic in drinking water from streams shallow wells and boreholes in the obuasi gold mining area of ghana range between 0 5 probably as a result of methylation and reduction reactions mediated by bacteria and algae concentrations of as in groundwaters reach up to 64 gl 1 being highest in deeper 40 70 m and more reducing 220 250 mv waters the as is thought to build up as a result of the longer residence times undergone by groundwaters in the deeper parts of the aquifer the proportion of as present as as iii is also higher in the deeper groundwaters deep mine exploration boreholes 70 100 m have relatively low as contents of 5 17 gl 1 possibly due to as sorption onto precipitating ferric oxyhydroxides or to localized low as concentrations of sulphide minerals median concentrations of inorganic urinary as from sample populations in two villages one a rural streamwater drinking community and the other a suburb of obuasi using groundwater for potable supply were 42 gl 1 and 18 gl 1 respectively the value for the community drinking groundwater is typical of background concentrations of urinary as the slightly higher value for the streamwater drinking community probably reflects different provenance of foodstuffs and higher as concentrations of water sources local to the village the low value obtained for the inhabitants of the obuasi suburb living close to and abstracting groundwater from the area of major mining activity suggests that groundwater can form a useful potable supply of good inorganic quality provided that deep long residence time sources are avoided

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

mobility and microbially mediated mobilization of gold and arsenic in soils from two gold mines in semi arid and tropical australia the mobility and microbially mediated solubilization of au and as in regolith materials from two au mines in australia i e the peak hill gold mine in semi arid new south wales and the hit or miss gold mine in tropical northern queensland was studied using a combination of geochemical and microbiological techniques gold is highly mobile in both environments the mobility of au increases with increasing degree of weathering of host materials and the resident microbiota are capable of mediating its solubilization the results of the microcosm experiments demonstrate that the activity of microorganisms needs to be taken into account when studying the mobility and solubilization of au in the australian regolith in primary unweathered mineralization material from the hit or miss mine 99 wt of au was extracted only in the strongest final step of the sequential extractions in concentrated aqua regia in alteration zone material from the peak hill gold mine 80 wt of au was associated with the operationally defined mn and fe oxides in contrast in auriferous soils overlying mineralization at both sites 90 95 wt of au was associated with the operationally defined exchangeable claybound and organic fractions microcosm experiments were incubated biologically active and inactive sterilized in 1 4 w v aqueous slurries at 25 c in the dark for up to 95 days in biologically active microcosms with soils from the peak hill and the hit or miss gold mines approximately 55 wt 907 ng g 1 d w soil and 20 wt 233 ng g 1 d w soil of the total au respectively was solubilized during the incubation in contrast no or significantly lower au concentrations were observed in biologically inactive microcosms the mobility and microbially mediated release of as was limited at both sites and appears to be mostly controlled by abiotic adsorption and desorption on mn and fe oxides arsenic has a low solubility in the more mobile fractions and is mostly associated with mn and fe oxides and the residual fraction the release of as was not elevated in biologically active compared to inactive microcosms from the peak hill gold mine in contrast in biologically active microcosms with samples from the hit or miss mine elevated concentrations of as were detected in solution compared to the biologically inactive experiments crown copyright 2006 published by elsevier inc all rights reserved

increasing arsenic mobility in the fine fraction of the dry stream sediments of the semi arid san antonio gold mining district baja california peninsula mexico the geochemical mobility of arsenic and some metals in the fine fraction of 20 alluvial sediment samples collected along the thalweg of the san antonio arroyo was assessed in the abandoned gold mining district of the semi arid southeastern baja california peninsula acid digested element concentrations were determined by treating the fine fraction of the sediments with concentrated hno3 via microwave heating a separate leaching of the diluted acid soluble as and some metals from the samples was carried out using 1 m hcl the most reactive as phase was extracted from the subsamples using an ascorbic solution of na citrate buffered at ph 8 the high abundance of sulphosalts tennantite cu12as4s13 and proustite ag3ass3 in the sediments from the head of the arroyo changes downstream to the predominance of arsenic trioxide arsenolite as2o3 and arsenate scorodite feaso4 2h2o acid digested as concentrations were always found to be high 230 270 mg kg 1 from the san antonio village until the end of the arroyo the concentration of reactive as and its relative contribution increased from low values of 2 3 mg kg 1 and 1 respectively at the upstream of the arroyo to 191 220 mg kg 1 and 75 89 in the middle and lower parts and is probably a result of as release from the mineral sulfide fraction of the tailings metallic contaminants exhibited different behavior with a peak of acid digested and diluted acid leached concentrations observed in the central part of the arroyo and an almost permanent geochemical mobility

the behaviour of arsenic in muddy sediments of the bay of biscay france abstract we have studied particulate and dissolved arsenic species in sediment and porewaters at sites in the bay of biscay france ranging in depths from 150 to 2 800 m at all stations major redox species oxygen nitrate ammonia total and reactive iron and manganese sulphate and sulphur reflect early diagenetic depth sequences of redox reactions comparable to other marine environments vertical distributions of dissolved and particulate as species and major redox species are related to changes in redox conditions and their major carrier phases such as fe and mn oxides arsenic diagenesis appears strongly dependent on fe cycling a subsurface maximum of dissolved as and surface enrichment of particulate as correspond to dissolution and precipitation of fe iii phases except for the shallowest and most bioturbated site flux calculations show three different vertical diffusive as fluxes two upwards and one downwards phase changes of recycled as result in local accumulations of reactive as at different redox fronts mass balance calculations indicate that the upward as flux toward the oxidized layer can explain the enrichment of hcl extractable particulate as in this layer a portion of the upward diffusing as can escape the sediment and may be fixed onto settling fe oxides by adsorption or co precipitation and contribute to reactive particulate as input i e as is recycled across the water sediment interface

a review of the source behaviour and distribution of arsenic in natural waters the range of as concentrations found in natural waters is large ranging from less than 0 5 g l 1 to more than 5000 g l 1 typical concentrations in freshwater are less than 10 g l 1 and frequently less than 1 g l 1 rarely much higher concentrations are found particularly in groundwater in such areas more than 10 of wells may be affected defined as those exceeding 50 g l 1 and in the worst cases this figure may exceed 90 well known high as groundwater areas have been found in argentina chile mexico china and hungary and more recently in west bengal india bangladesh and vietnam the scale of the problem in terms of population exposed to high as concentrations is greatest in the bengal basin with more than 40 million people drinking water containing excessive as these large scale natural as groundwater problem areas tend to be found in two types of environment firstly inland or closed basins in arid or semi arid areas and secondly strongly reducing aquifers often derived from alluvium both environments tend to contain geologically young sediments and to be in flat low lying areas where groundwater flow is sluggish historically these are poorly flushed aquifers and any as released from the sediments following burial has been able to accumulate in the groundwater arsenic rich groundwaters are also found in geothermal areas and on a more localised scale in areas of mining activity and where oxidation of sulphide minerals has occurred the as content of the aquifer materials in major problem aquifers does not appear to be exceptionally high being normally in the range 1 20 mg kg 1 there appear to be two distinct triggers that can lead to the release of as on a large scale the first is the development of high ph 8 5 conditions in semi arid or arid environments usually as a result of the combined effects of mineral weathering and high evaporation rates this ph change leads either to the desorption of adsorbed as especially as v species and a range of other anion forming elements v b f mo se and u from mineral oxides especially fe oxides or it prevents them from being adsorbed the second trigger is the development of strongly reducing conditions at near neutral ph values leading to the desorption of as from mineral oxides and to the reductive dissolution of fe and mn oxides also leading to as release iron ii and as iii are relatively abundant in these groundwaters and so4 concentrations are small typically 1 mg l 1 or less large concentrations of phosphate bicarbonate silicate and possibly organic matter can enhance the desorption of as because of competition for adsorption sites a characteristic feature of high groundwater as areas is the large degree of spatial variability in as concentrations in the groundwaters this means that it may be difficult or impossible to predict reliably the likely concentration of as in a particular well from the results of neighbouring wells and means that there is little alternative but to analyse each well arsenic affected aquifers are restricted to certain environments and appear to be the exception rather than the rule in most aquifers the majority of wells are likely to be unaffected even when for example they contain high concentrations of dissolved fe

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

triggered earthquakes suppressed by an evolving stress shadow from a propagating dyke the role of static versus dynamic stresses in earthquake clusters is unclear analysis of earthquakes triggered by a dyke intrusion at an icelandic volcano unambiguously demonstrates that static stresses are important for earthquake clustering large earthquakes can generate small changes in static stress increases that trigger aftershock swarms or reductions that create a region of reduced seismicity a stress shadow1 2 however seismic waves from large earthquakes also cause transient dynamic stresses that may trigger seismicity3 4 this makes it difficult to separate the relative influence of static and dynamic stress changes on aftershocks dyke intrusions do not generate dynamic stresses so provide an unambiguous test of the stress shadow hypothesis here we use gps and seismic data to reconstruct the intrusion of an igneous dyke that is 46 km long and 5 m wide beneath bar arbunga volcano central iceland in august 2014 we find that during dyke emplacement bursts of seismicity at a distance of 5 to 15 km were first triggered and then abruptly switched off as the dyke tip propagated away from the volcano we calculate the evolving static stress changes during dyke propagation and show that the stressing rate controls both the triggering and then suppression of earthquake rates in three separate areas adjacent to the dyke our results imply that static stress changes help control earthquake clustering similar small static stress changes may be important for triggering seismicity near geothermal areas regions being hydrofractured and deflating oil and gas fields

stress changes focal mechanisms and earthquake scaling laws for the 2000 dike at miyakejima japan faulting processes in volcanic areas result from a complex interaction of pressurized fluid filled cracks and conduits with the host rock and local and regional tectonic setting often volcanic seismicity is difficult to decipher in terms of the physical processes involved and there is a need for models relating the mechanics of volcanic sources to observations here we use focal mechanism data of the energetic swarm induced by the 2000 dike intrusion at miyakejima izu archipelago japan to study the relation between the 3 d dike induced stresses and the characteristics of the seismicity we perform a clustering analysis on the focal mechanism fm solutions and relate them to the dike stress field and to the scaling relationships of the earthquakes we find that the strike and rake angles of the fms are strongly correlated and cluster on bands in a strike rake plot we suggest that this is consistent with optimally oriented faults according to the expected pattern of coulomb stress changes we calculate the frequency size distribution of the clustered sets finding that focal mechanisms with a large strike slip component are consistent with the gutenberg richter relation with a b value of about 1 conversely events with large normal faulting components deviate from the gutenberg richter distribution with a marked roll off on its right hand tail suggesting a lack of large magnitude events mw 5 5 this may result from the interplay of the limited thickness and lower rock strength of the layer of rock above the dike where normal faulting is expected and lower stress levels linked to the faulting style and low confining pressure

an image of a magma intrusion process inferred from precise hypocentral migrations of the earthquake swarm east of the izu peninsula summary earthquake swarms in the area east of the izu peninsula central japan have been active and have been repeated intermittently since 1978 after 40 years of quiescence the activities were always accompanied by crustal deformations which were well modelled by dyke intrusions to study the process of a dyke intrusion precise hypocentres of the latest activity occurring in 1998 are obtained in this paper using waveform similarity by which new images of volcanic processes have been successfully acquired at several volcanoes the relocated hypocentres are mainly aligned on a thin vertical plane with a circular shape at a depth of 3 7 km and there is an aseismic area at the centre the normal direction to the plane coincides well with the direction of tectonic extensional stress around the hypocentral area and matches theoretical models well at the beginning of the activity a small fraction of the events occurred at greater depth where hypocentres align on a vertical line and migrate upward at a rate of 1 km h 1 the migration rate in this stage agrees well with a theoretical model of buoyancy driven dyke propagation after 1 day from the beginning earthquakes began to occur around the aseismic area and hypocentres spread on the thin circular plane described above during this activity the hypocentres seemed to migrate downwards and upwards from the centre the earthquakes are caused by shear fracture at the tip of the dyke and the migration of hypocentres reflects that the dyke expands downward and upward from the neutrally buoyant layer that is located at the centre of the swarm in this paper we also propose a process of magma intrusion based on the precise migration of hypocentres and show that the 1998 activity is composed of a few simple volcanic processes magma rising by buoyancy it staying at a neutral buoyancy point and spreading outward from the neutral point with elastic fracture by an inside excess magma pressure

evidence from the ad 2000 izu islands earthquake swarm that stressing rate governs seismicity magma intrusions and eruptions commonly produce abrupt changes in seismicity far from magma conduits that cannot be associated with the diffusion of pore fluids or heat such swarm seismicity also migrates with time and often exhibits a dog bone shaped distribution the largest earthquakes in swarms produce aftershocks that obey an omori type exponential temporal decay but the duration of the aftershock sequences is drastically reduced relative to normal earthquake activity here we use one of the most energetic swarms ever recorded to study the dependence of these properties on the stress imparted by a magma intrusion a 1 000 fold increase in seismicity rate and a 1 000 fold decrease in aftershock duration occurred during the two month long dyke intrusion we find that the seismicity rate is proportional to the calculated stressing rate and that the duration of aftershock sequences is inversely proportional to the stressing rate this behaviour is in accord with a laboratory based rate state constitutive law suggesting an explanation for the occurrence of earthquake swarms any sustained increase in stressing rate whether due to an intrusion extrusion or creep event should produce such seismological behaviour

comparison of dike intrusions in an incipient seafloor spreading segment in afar ethiopia seismicity perspectives 1 oceanic crust is accreted through the emplacement of dikes at spreading ridges but the role of dike intrusion in plate boundary deformation during continental rupture remains poorly understood between 2005 and 2009 the 70 km long dabbahu manda hararo rift segment in ethiopia has experienced 14 large volume dike intrusions 9 of which were recorded on temporary seismic arrays a detailed comparison of the seismic characteristics of the seismically monitored dikes is presented with implications for dike intrusion processes and magmatic plumbing systems all of the migrating swarms of earthquakes started from a 80 of energy is released during the propagation phase with minimal seismic energy release after the dike propagation ceases we interpret that faulting and graben formation above the dikes occurs hours after the passage of the dike tip coincident with the onset of low frequency earthquakes dike lengths show no systematic reduction in length with time suggesting that topographic loading and stress barriers influence dike length as well as changes in tectonic stress the propagation velocities of all the dikes follow a decaying exponential northward propagating dikes had faster average velocities than those that propagated southward suggesting preconditioning by the 2005 megadike or ongoing heating from a subcrustal magma source north of the midsegment

vertical accumulation of potential toxic elements in a semiarid system that is influenced by an abandoned gold mine abstract the mining zone at el triunfo baja california sur mexico was exploited for gold extraction for 200 years this area includes more than 100 abandoned mining sites these sites contain mine tailings that are highly contaminated with potential toxic elements pte such as as cd pb sb zn and other associated elements over time these wastes have contaminated the sediments in the adjacent fluvial systems our aim was to assess the vertical pte variations in the abandoned mining zone and in the discharge of the main arroyo into a small lagoon at the pacific ocean sediments were collected from the two following locations in the mining zone near the arroyo basin tailings 1 an old alluvial terrace overbank and a test pit tp and 2 two sediment cores locations at the arroyo discharge into a hypersaline small lagoon samples were analyzed by icp ms icp oes and inaa and the methods were validated the overbank was the most contaminated and had as cd pb sb and zn concentrations of 8690 226 84 700 17 400 and 42 600 mg kg 1 respectively which decreased with depth in addition the tp contained elevated as cd pb sb and zn concentrations of 694 18 8 5001 39 2 and 4170 mg kg 1 respectively the sediment cores were less contaminated however the as cd pb sb and zn concentrations were greater than the concentrations that are generally found in the earth s crust the normalized enrichment factors nefs which were calculated from the background concentrations of these elements in the system showed that extremely severe as cd pb sb and zn nef 50 enrichment occurred at the overbank the tp was severe to very severely enriched with as cd pb sb and zn nef 10 50 the sediment cores had a severe enrichment of as pb and zn nef 10 25 their vertical profiles showed that anthropogenic influences occurred in the historic sediment deposition at the overbank and tp and in the sediment cores in addition the as pb and zn concentrations in the sediment cores were related to the deposition of fine sediments and organic carbon

forecasting the path of a laterally propagating dike an important aspect of eruption forecasting is predicting the path of propagating dikes we show how lateral dike propagation can be forecast using the minimum potential energy principle we compare theory to observed propagation paths of dikes originating at the bar arbunga volcano iceland in 2014 and 1996 by developing a probability distribution for the most likely propagation path the observed propagation paths agree well with the model prediction we nd that topography is very important for the model and our preferred forecasting model considers its in uence on the potential energy change of the crust and magma we tested the in uence of topography by running the model assuming no topography and found that the path of the 2014 dike could not be hindcasted the results suggest that lateral dike propagation is governed not only by deviatoric stresses but also by pressure gradients and gravitational potential energy furthermore the model predicts the formation of curved dikes around cone shaped structures without the assumption of a local deviatoric stress eld we suggest that a likely eruption site for a laterally propagating dike is in topographic lows the method presented here is simple and computationally feasible our results indicate that this kind of a model can be applied to mitigate volcanic hazards in regions where the tectonic setting promotes formation of laterally propagating vertical intrusive sheets

early diagenetic processes in the muddy sediments of the bay of biscay abstract in order to understand the early diagenesis processes occurring in continental margin environment modern sediments collected in six different sites from the bay of biscay have been studied these sites can be separated into two groups in the shallowest stations where sediments are highly bioturbated organic carbon levels are higher than 2 in the deepest stations sediments are much less bioturbated and organic carbon levels are lower in all sites the vertical distribution of redox sensitive species can be explained by the well established depth sequence of redox reactions based on the bacterially mediated oxidation of organic matter we have considered some alternative reaction pathways to explain the profiles of fe mn and n species these reactions deal with the ammonia oxidation by manganese oxide the aerobic denitrification and the oxidation of dissolved iron ii by nitrate or mn oxides vertical flux calculations with a simple diffusion model indicate that these reactions could account for the reduction of all the mn oxides and the oxidation of all the upward diffusing fe ii they may also be responsible for a significant part of the total dinitrogen production the relative importance of these pathways on early diagenetic processes and benthic fluxes has not been determined and must be examined with additional experimental works our study suggests however that the coupling between the benthic cycles of iron manganese and nitrogen could strongly influence the carbon cycling at the ocean floor

cosmogenic 32si reveals biogenic silica burial in deltas rivals the southern ocean siliceous ooze measurements of natural cosmogenic 32si t1 2 140 y in tropical deltaic sediments demonstrate for the first time that most 32si is present in rapidly formed authigenic clays and not biogenic opaline silica bsi the burial of bsi in deltaic and continental margin sediments has likely been greatly underestimated because of diagenetic alteration of bsi to clay little of which dissolves in the classically used operational bsi leach rapid reverse weathering reactions during early diagenesis must be considered as a significant pathway of reactive si storage in deltaic deposits based on 32si actual storage may be 2 3 the best recent estimates extrapolated from diagenetic models or attempts to modify operational bsi methods to include authigenic clay 900 mol g vs 250 mol g measurements of natural 32si inventories in sediments and initial specific activities in biogenic silica provide a means to independently constrain the marine si cycle

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

metal fractionation in oxic sediments of an estuary affected by acid mine drainage south western spain abstract fractionation of fe cu zn as cd and pb was studied in 17 surface sediment samples of the ria of huelva in all the cases total concentration of these elements was high especially for fe 11 2 zn 1519 ppm followed by cu 1413 ppm pb 716 ppm as 442 ppm and cd 3 26 ppm the enrichment factors of these metals follow this order cd cu zn pb as fe with respect to the regional background the highest concentrations associated with exchangeable or labile fractions are shown by zn 85 of total concentration followed by cd 76 12 fe 58 41 cu 40 80 pb 37 44 and as 33 88 the main sources of metal input are the tinto and odiel rivers which discharge acidic water ph

evolution of the danube deep sea fan since the last glacial maximum new insights into black sea water level fluctuations abstract the danube deep sea fan nw black sea is one of the most developed deep sea sediment depositional systems in europe although the morphology and the architecture have been widely described in the past years little is known about the stratigraphy of this depositional system for the late quaternary this results from the lack of significant stratigraphic markers the scarcity of radiocarbon ages and the difficulty in constraining reservoir ages recent robust quantification of reservoir ages has allowed the construction of a new stratigraphic framework for the black sea from the end of the last glacial period to the holocene thus giving the opportunity to correlate sedimentological and geochemical features previously described on the nw black sea margin with climatic events identified in the northern hemisphere based on this approach we propose an improved chrono lithostratigraphic framework for the danube deep sea fan channel levees since the last glacial maximum we show that the danube deep sea fan was active during the last glacial maximum until the younger dryas early holocene transition ca 11 700 cal a bp when the turbidite activity abruptly terminated in the whole system throughout this period the danube river was the main source of the deep depositional system except between ca 17 200 cal a bp and 15 700 300 cal a bp at that time the deposition of red turbidites in the deep basin concomitant with the deposition of the so called red layers onto the continental shelf and the upper slope emphasises the direct impact of the increased meltwater runoff of the dnieper river as far as the danube deep sea fan some significant changes in the location of the depocentre of the danube deep sea fan occurred through time the main change in depocentre location occurred at ca 28 000 cal a bp with the northward avulsion leading to the formation of the middle channel although the middle and northern channel became the preferential turbidite depocentres after this event the deposition of turbidites has persisted in the southern channel levee until 14 700 cal a bp indicating that the southern channel was definitely not abandoned after the upstream northward avulsion unsurprisingly water level fluctuations and river sediment flux acted as the main forcings on the evolution of the danube deep sea fan based on these results and on the morphology of the danube canyon we propose that i lowstand conditions 110 m prevailed during the last glacial maximum and possibly between 15 700 300 cal a bp and 14 700 cal a bp ii water level ranged from 110 and 70 m between 14 700 and 11 700 cal a bp and iii water level ranged from 70 and 30 m from 11 700 cal a bp and until the reconnection of the black sea lake with the global ocean at ca 9000 cal a bp

new constraints on dike injection and fault slip during the 1975 1984 krafla rift crisis ne iceland correlation of kh9 spy and spot5 satellite images airphotos digital elevation model differencing electronic distance measurement and leveling survey data is used to constrain the deformation resulting from the 1975 1984 krafla rifting crisis we find that diking typically extends to depths of 5 km while the dike tops range from 0 km in the caldera region to 3 km at the northern end of the rift extension is accommodated by diking at depth and normal faulting in the shallowest crust in the southern section of the krafla rift surface opening is 80 of the dike opening at depth over the 70 80 km length of the rift the average dike opening was 4 3 5 4 m from these estimates we calculate the total geodetic moment released over the krafla rift crisis 4 4 9 0 10 19 nm which is an order of magnitude higher than the seismic moment released over the same time period 5 8 10 18 nm the total volume of magma added to the upper crust was 1 1 2 1 10 9m 3 this study highlights how optical image correlation using inexpensive declassified spy satellite and airphotos combined with simple models of crustal deformation can provide important constraints on the deformation resulting from past earthquake and volcanic events

eustatic control of turbidites and winnowed turbidites global changes in sea level primarily the results of tectonism and glaciation control deep sea sedimentation during periods of low sea level the frequency of turbidity currents is greatly increased episodes of low sea level also cause vigorous contour currents which winnow away the fines of turbidites in the rock record the occurrence of most turbidites and winnowed turbidites closely corresponds to global lowstands of paleo sea level this observation may be useful in predicting the occurrence of deep sea reservoir facies in the geologic record

arsenic from gold mining in marine and stream sediments in baja california sur mexico the environmental impacts associated with arsenic as from historical mining areas may persist for many years we evaluated the influence of as in smelter and tailing wastes from a historic gold mine near san antonio in the south east of the baja california mexico on fluvial and marine sediments in the san juan de los planes basin and la ventana bay respectively arsenic levels in the smelter and in the surrounding tailing wastes ranged from 82 000 to 208 000 mg kg 1 and from 4220 to 92 000 mg kg 1 respectively the as concentrations in fluvial sediments were much lower as these derived from wastes that had been scattered and had been subject to weathering for some time as concentrations in surface sediments in the san antonio stream close to the smelter and further downstream ranged from 477 to 1100 mg kg 1 and from 64 to 613 mg kg 1 respectively as concentrations were between 0 05 and 9 mg kg 1 in surface shelf sediments from the coast adjacent to la ventana bay the concentration was highest in sediment collected close to the outlet of the main stream la bocana of the los planes basin the as concentrations in all the solid waste samples from near san antonio exceeded the effect range medium erm of the sediment quality guidelines 70 mg kg 1 overall 71 and 43 of the stream samples exceeded the effect range low erl 8 2 mg kg 1 and the erm respectively indicating potential risks for biota and humans

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

coalescence microseismic mapping earthquakes are commonly located by linearized inversion of discrete arrival time picks made from signals recorded at a network of seismic stations if mis picks are made these will contribute to the location therefore causing potential bias for data recorded by a dense seismic array direct imaging methods can be applied instead we describe the coalescence microseismic mapping method which is a bridge between the two approaches and will operate with seismic data recorded continuously on a sparse array by continuously mapping scalar signals derived from the envelope of seismic arrivals we derive robust estimates of the spatio temporal coordinates of the origins of seismic events noisy data are migrated away from the correct origin so do not contribute to errors in location the method is rooted in a bayesian formulation of event location traveltime inversion allows imaging of source locations and has the capacity to handle errors in modelled traveltimes it has the advantage of working with any 3 d velocity model which therefore may include anisotropy it also automatically incorporates both p and s wave data a multiresolution grid search leads to an efficient implementation with a search over a larger domain including joint inversion for location and velocity structure possible where warranted by the data quality we discuss the theory and implementation of this method and illustrate it with real data from microseismic events in iceland caused by melt intrusion in the crust

propagation and arrest of dikes under topography models applied to the 2014 bardarbunga iceland rifting event dikes along rift zones propagate laterally downslope for tens of kilometers often becoming arrested before topographic reliefs we use analogue and numerical models to test the conditions controlling the lateral propagation and arrest of dikes exploring the presence of a slope in connection with buoyancy and rigidity layering a gentle downslope assists lateral propagation when combined with an effective barrier to magma ascent e g gelatin stiffness contrasts while antibuoyancy alone may be insufficient to prevent upward propagation we also observe that experimental dikes become arrested when reaching a plain before opposite reliefs our numerical models show that below the plain the stress field induced by topography hinders further dike propagation we suggest that lateral dike propagation requires an efficient barrier rigidity to upward propagation assisting antibuoyancy and a lateral pressure gradient perpendicular to the least compressive stress axis while dike arrest may be induced by external reliefs

arsenic content and groundwater geochemistry of the san antonio el triunfo carrizal and los planes aquifers in southernmost baja california mexico the san antonio el triunfo mining district located at a mountainous region 45 km south east of la paz baja california has been worked since the late 1700s mine waste material produced during 200 years of mineral extraction area poses a risk of local groundwater pollution and eventually regional pollution to the carrizal west basin and the los planes east basin aquifers there are different types of deposits in the mining area these are dominated by epithermal veins in which arsenopyrite is an important component carrillo and drever 1998a concluded that even though the amount of mine waste is relatively small in comparison to the large scale area significant as in groundwater derived from the mine waste piles is found locally in the groundwater this paper shows the results of geochemical analyses of groundwater samples from the san antonio el triunfo area and the carrizal and los planes aquifers during several years of monitoring 1993 1997 the highest values of total dissolved solids tds and as are in the mineralized area where the mining operations occurred 1500 ppm tds and 0 41 ppm as the lowest concentrations of tds and as are in general away from the mineralized area 500 ppm tds and 0 01 ppm as sulfate and bicarbonate alkalinity are in general high near the mineralized area and low away from it the arsenic concentrations vary seasonally especially after the heavy summer thunderstorms geochemical modeling minteqa2 and netpath and analysis of the regional geochemical evolution of the groundwater from the mining area towards the aquifer of los planes shows that the most likely hydrochemical processes include dilution precipitation of calcite and adsorption of as onto surfaces of iron oxyhydroxides ferrihydrite these processes act as natural controls to the extent and amount of as pollution in the carrizal and los planes aquifers

long period seismicity reveals magma pathways above a laterally propagating dyke during the 2014 15 barðarbunga rifting event iceland abstract the 2014 15 bar arbunga holuhraun rifting event comprised the best monitored dyke intrusion to date and the largest eruption in iceland in 230 years a huge variety of seismicity was produced including over 30 000 volcano tectonic earthquakes vts associated with the dyke propagation at 6 km depth below sea level and large magnitude earthquakes accompanying the collapse of bar arbunga caldera we here study the long period seismicity associated with the rifting event we systematically detect and locate both long period events lps and tremor during the dyke propagation phase and the first week of the eruption we identify clusters of highly similar repetitive lps which have a peak frequency of 1 hz and clear p and s phases followed by a long duration coda the source mechanisms are remarkably consistent between clusters and also fundamentally different to those of the vts we accurately locate lp clusters near each of three ice cauldrons depressions formed by basal melting that were observed on the surface of dyngjujokull glacier above the path of the dyke most events are in the vicinity of the northernmost cauldron at shallower depth than the vts associated with lateral dyke propagation at the two northerly cauldrons periods of shallow seismic tremor following the clusters of lps are also observed given that the lps occur at 4 km depth and in swarms during times of dyke stalling we infer that they result from excitation of magmatic fluid filled cavities and indicate magma ascent we suggest that the tremor is the climax of the vertical melt movement arising from either rapid repeated excitation of the same lp cavities or sub glacial eruption processes this long period seismicity therefore represents magma pathways between the depth of the dyke vt earthquakes and the surface notably we do not detect tremor associated with each cauldron despite melt reaching the base of the overlying ice cap a concern for hazard monitoring

strike slip faulting during the 2014 barðarbunga holuhraun dike intrusion central iceland over a 13 day period magma propagated laterally from the subglacial bar arbunga volcano in the northern rift zone iceland it created 30 000 earthquakes at 5 7 km depth along a 48 km path before erupting on 29 august 2014 the seismicity which tracked the dike propagation advanced in short bursts at 0 3 4 7 km h separated by pauses of up to 81 h during each surge forward seismicity behind the dike tip dropped moment tensor solutions from the leading edge show exclusively left lateral strike slip faulting subparallel to the advancing dike tip releasing accumulated strain deficit in the brittle layer of the rift zone behind the leading edge both left and right lateral strike slip earthquakes are observed the lack of non double couple earthquakes implies that the dike opening was aseismic

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

solid phases controlling the mobility of potentially toxic elements and the generation of acid drainage in abandoned mine gold wastes from san antonio el triunfo mining district baja california sur mexico in many countries of latin america mexico included as and other toxic elements in water and soils may have a natural geogenic origin however the anthropogenic activities specially in mining areas trigger the metal loid s mobilization mainly by acid mine drainage aggravating the environmental pollution problem in san antonio el triunfo mining district sa et md baja california sur state mexico 200 years of intermittent mining activities have left around 800 000 tons of mine waste scattered across 400 km2 of the sa et area some environmental studies in the area assume mining wastes as the main source of contamination of groundwater not considering the geothermal source moreover recent studies have shown that the pollution in the region has occurred as consequence of seasonal erosion caused by winds and irregular episodes of heavy rainfall nevertheless the actual potential to release as and other potentially toxic elements as well as the hazardousness derived from this mine waste and the geochemical mineralogical mechanism that influence such mobilization has not been assessed yet through the detailed physicochemical and mineralogical characterization x ray diffraction and scanning electron microscopy this novel study shows that jarosite and arsenolite are the key mineral phases controlling the potential release and arsenic mobilization and therefore the hazardousness of the mining wastes what is more from ph and acid base accounting results it has been found that 35 of the analyzed samples maintain basic to near neutral conditions due to the neutralizing potential of aluminosilicates feldspar muscovite etc while in the remaining 65 of analyzed samples the mineral composition is not enough to neutralize the generated acidity hence those samples present the potential of generating acid mine drainage and consequently they are considered hazardous

quantifying the opal belt in the atlantic and southeast pacific sector of the southern ocean by means of 230th normalization 1 a set of 114 samples from the sediment surface of the atlantic eastern pacific and western indian sectors of the southern ocean has been analyzed for 230th and biogenic silica maps of opal content th normalized mass flux and th normalized biogenic opal flux into the sediment have been derived significant differences in sedimentation patterns between the regions can be detected the mean bulk vertical fluxes integrated into the sediment in the open southern ocean are found in a narrow range from 2 9 g m 2 yr 1 eastern weddell gyre to 15 8 g m 2 yr 1 indian sector setting upper and lower limits to the vertically received fraction of open ocean sediments the silica flux to sediments of the atlantic sector of the southern ocean is found to be 4 2 1 4 1011 mol yr 1 just one half of the last estimate this adjustment represents 6 of the output term in the global marine silica budget

temporal monitoring of subglacial volcanoes with tandem x application to the 2014 2015 eruption within the barðarbunga volcanic system iceland on august 29 2014 a lava eruption commenced in the holuhraun plain north east of the bar arbunga caldera in iceland the eruption ended on february 27 2015 thus lasting for a period of about 6 months during these months the magma chamber below the caldera gradually deflated feeding the eruption and causing the rare event of a slow caldera collapse in this scenario tandem x remote sensing data are of particular interest by producing medium high resolution and accurate elevation models of the caldera it is possible to evaluate volume losses and topographical changes to increase the knowledge about the ongoing activity in particular five tandem x bistatic acquisitions have been commanded between august 01 2014 and november 08 2014 two of them before the volcanic eruption and three of them during the event additionally to fully cover the volcanic activity the lava field 48 km north east of the caldera has also been monitored in the first part of the paper the expected elevation accuracy is studied on two levels absolute and relative height accuracies are analyzed by inspecting the x band signal propagation into snow and by investigating the impact of the main geometrical system parameters and the local geomorphology in the second part of the paper the analysis is applied to the bar arbunga volcanic system including a validation performed using complementary altimeter data the main geophysical outcome is the accurate temporal height tracking of the entire caldera and the glacial volcanic system the measured volume loss at the caldera location is about 1 billion cubic meters in two months with an average rate of subsidence of nearly 50 cm day these numbers confirm other independent sources and can be compared to lava volume measurements finally the last segment of the dyke that propagated from the bar arbunga caldera to the holuhraun lava field is mapped and a graben structure with a width of up to 1 km and a sinking of a few meters is reported

a quantitative approach to the dike intrusion process inferred from a joint analysis of geodetic and seismological data for the 1998 earthquake swarm off the east coast of izu peninsula central japan 1 a series of earthquake swarms off the east coast of izu peninsula central japan is typically associated with dike intrusion around active volcanoes numerous studies in this region have documented the seismic activity and ground deformations without fully resolving the process of dike intrusion this study involves a joint analysis of geodetic and seismic data from the most recent major activity in this region occurring in 1998 to reveal the process of dike intrusion quantitatively we combine data from a dense gps array including 10 temporary stations with seismic analysis published previously we estimate the location of the dikes from seismic data and the volume of intruded magma from geodetic data combined analysis of both data sets enables us to reveal the kinematic process of dike intrusion associated with the 1998 earthquake swarm the process of dike intrusion is quantitatively modeled using the time evolution of recorded dike volume and the use of seismic hypocenters as an indicator of the site of instantaneous dike intrusion on the basis of these observations we propose the following process of the dike intrusion the magma rose upward through a pathway aligned vertically and created a dike when it lost buoyancy we also evaluate the dike intrusion process quantitatively using a model of a circular dike that grows under a continuous magma supply from a deep magma reservoir from the observational data we infer the time evolution in the dike shape pressure distribution and magma viscosity in the dike the acquired viscosity increases over time and it may be reasonable because magma cools gradually however its value is too large compared to typical basaltic magma expected in this region it may represent magma within the dike that is nearly solidified otherwise the magma is supplied intermittently and the dike growth is mainly controlled by the magma supply rate from a deep reservoir the quantitative description of the dike intrusion process in nature described in this study is very rare and our results provide constraints on several parameters that have not been solved in many previous theoretical studies on the dike intrusion process

benthic remineralization at the land ocean interface a case study of the rhone river nw mediterranean sea abstract biogeochemical processes in sediments under the influence of the rhone river plume were studied using both in situ microelectrodes and ex situ sediment core incubations organic carbon oc and total nitrogen tn content as well as stable carbon isotopic composition of oc 13 c oc were analysed in 19 surface sediments to determine the distribution and sources of organic matter in the rhone delta system large spatial variations were observed in both the total o 2 uptake 5 2 to 29 3 mmol m 2 d 1 and nh 4 release 0 1 to 3 5 mmol m 2 d 1 rates at the sediment water interface the highest fluxes were measured near the rhone river mouth where sedimentary oc and tn contents reached 1 81 and 0 23 respectively values of 13 c oc ranged from 26 83 to 23 88 with a significant seawards enrichment tracing the dispersal of terrestrial organic matter on the continental shelf the amount of terrestrial derived oc reaches 85 in sediments close to the rhone mouth decreasing down to 25 in continental shelf sediments on the prodelta high terrestrial oc accumulation rates support high oxygen uptake rates and thus indicating that a significant fraction of terrestrial oc is remineralized a particulate organic carbon poc mass balance indicates that only 3 of the deposited poc is remineralized in prodelta sediments while 96 is recycled on the continental shelf it was calculated that a large proportion of the rhone poc input is either buried 52 or remineralized 8 mostly on the prodelta area the remaining fraction 40 is either mineralized in the water or exported outside the rhone delta system in dissolved or particulate forms

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

seismic anisotropy in the crust at the mid atlantic plate boundary in south west iceland summary seismograms of microearthquakes recorded on stations of the sil network in south western iceland exhibit strong shear wave splitting and are consistent with being caused by aligned parallel cracks in the uppermost crust splitting times of 0 1 0 3 s are observed with the larger values 0 2 0 3 s occurring beneath stations in the highly heated western volcanic zone and the smaller values 0 1 s in the younger less fractured south iceland seismic zone five of the stations have a fast shear wave polarization azimuth of n30 e n40 e7 parallel to the axis of the western volcanic zone i e the mid atlantic ridge in iceland and in the direction of maximum horizontal compression defined by fault dyke and fissure strikes and microearthquake focal mechanisms station gyg in the north western part of the network has the significantly different azimuth of n70 e this is parallel to one of the local strike slip fault trends and is probably due to a heated rock fabric caused by those faults

sea level control on turbidite activity in the rhone canyon and the upper fan during the last glacial maximum and early deglacial abstract the timing routing and processes of sediment transfer from the continents to the oceans at millennial time scale are still largely unknown the potential of turbidite systems dominantly deposited during sea level lowstands to record global or regional environmental fluctuations is usually under exploited because of the difficulty to obtain robust chronostratigraphic constraints in turbiditic deposits and therefore to tie changes in sedimentary processes to environmental fluctuations we were able to obtain a millennial scale chronostratigraphy based on oxygen isotopes of the scarce foraminifera preserved in turbiditic deposits of the rhone turbidite system within the western mediterranean our results show that 1 objective criteria can be defined for the selection of foraminifera preserved within the pelagic intervals between the turbiditic sequences in order to obtain a reliable isotope stratigraphy 2 turbidites triggered by hyperpycnal currents are described for the first time within the rhone turbidite system they are related to the periods of direct fluvial connection with the canyon head during the sea level lowstand and early rise and to a period of high sediment flux in relation to the massive recession of the rhone glaciers in the alps 3 the lithofacies change passing from hyperpycnal to bouma type is dated at ca 19 cal ka bp which might correspond to an acceleration of sea level rise 19 ka meltwater pulse

the accumulation and cycling of biogenic silica in the southern ocean revisiting the marine silica budget abstract in many of the recent marine silica budgets e g science 268 1995 375 a majority of the world s biogenic silica accumulation is attributed to the siliceous ooze deposits in the antarctic deep sea based on 230 th normalized sediment accumulation rates as well as comparative studies of silica preservation seabed accumulation compared to surface biogenic production the rate of biogenic silica accumulation in antarctic siliceous ooze deposits has been over estimated by as much as 35 the current estimate for silica accumulation in these high latitude deposits is 3 1 10 12 mol yr 1 as compared to previous values of 4 1 4 8 10 12 mol yr 1 to maintain balance between silicate supply and biogenic silica removal in the oceans an additional repository is needed evidence from continental shelf and upper slope sediments suggests that biogenic silica accumulation in continental margin deposits may account for a much larger fraction of the marine silica burial than previously thought compensating for the diminished accumulation in the antarctic deep sea if biogenic silica accumulation in continental margin sediments replaces nearly a third of the silica accumulation in the antarctic deep sea the marine cycles of organic matter and biogenic silica are coupled to a greater extent than reported in previous budgets