annual biogenic particle fluxes to the interior of the north atlantic ocean studied at 34 n 21 w and 48 n 21 w abstract in order to clarify the annual quality quantity and export processes of biogenic particles from the euphotic zone to the deep ocean interior an array of automated time series sediment traps were deployed for 1 year from 4 april 1989 to 17 april 1990 at 34 n 21 w and 48 n 21 w as part of the joint global ocean flux program jgofs north atlantic bloom experiment nabe three sediment traps with 13 time series sediment collectors were placed at both stations approximately 1 and 2 km below the surface and 0 7 km above the bottom they collected settling particles during 26 14 day intervals for 376 days with an 20 day hiatus in september october 1989 for changeover of the trap moorings the collection periods of the six traps were synchronized forming a spatio temporal matrix of 156 samples the annual mass flux at about 2 km deep during this experiment was 22 and 27 g m 2 y 1 at the 34 and 48 n stations consisting of biogenic particles with traceable quantities of lithogenic particle flux the spring particle bloom characterized by the sedimentation of particles relatively enriched by norg began in january at the 34 n station and in march at the 48 n station the bloom continued for 4 5 and 3 months and provided 62 and 50 of the annual biogenic particle mass flux at 2 km at the 34 and 48 n stations the surface bloom penetrated to the ocean interior within a few weeks with apparently accelerated settling speed at deeper layers the order of susceptibility of biogenic elements to mineralization while settling in the 0 7 1 km a b water column was from least to most resistant p norg corg si and ca the c n p ratio at 0 7 km a b was 154 18 1 at the 34 n station and 148 18 1 at the 48 n station

a damage model for volcanic edifices implications for edifice strength magma pressure and eruptive processes monitoring of large basaltic volcanoes such as piton de la fournaise la reunion island france has revealed preeruptive accelerations in surface displacements and seismicity rate over a period of between 1 h and several weeks before magma reaches the surface such eruptions are attributed to ruptures of pressurized magma reservoirs elastic models used to describe surface deformation would assume that accelerations in surface deformation are due to increases in reservoir pressure this assumption requires changes in magma or pressure conditions at the base of the magma feeding system that are unrealistic over the observed timescale another possible cause for these accelerations is magma pressure in the reservoir weakening the volcanic edifice in the present study we modeled such weakening by progressive damage to an initially elastic edifice we used an incremental damage model with seismicity as a damage variable with daily increments elastic moduli decrease linearly with each damage increment applied to an initially elastic edifice with constant pressure at the base of the system this damage model reproduces surface displacement accelerations quite well when damage is sufficient process dynamics is controlled by the damage parameter taken as the ratio between the incremental rupture surface and the surface to be ruptured in this case edifice strength and magma reservoir pressure decrease with decreasing elastic moduli whereas surface displacement accelerates we discuss the consequences of pressure decreases in magma reservoirs

environmental versus biomineralization controls on the intratest variation in the trace element composition of the planktonic foraminifera g inflata and g scitula the intratest variation in the chemical composition of globorotalia scitula and g inflata recovered from a sediment trap sample collected at 3000 m in the north atlantic in early spring has been investigated using laser ablation inductively coupled plasma mass spectrometry and electron microprobe mg ca li ca b ca mn ca and ba ca vary by up to a factor of 10 through the test walls water column properties including temperature and salinity are well documented at the trap site and the observed variations are too large to be explained by vertical migration of the foraminifera however changes in calcite precipitation rate crystal structure or the chemical composition of the internal calcification reservoir also cannot by themselves fully account for the pattern of intratest variability nevertheless the average mg ca for each chamber generally produces a mg ca temperature that matches that measured in the water column the exception is small morphologically distinct g inflata tests that have anomalously high mg ca

the cleft revealed geologic magnetic and morphologic evidence for construction of upper oceanic crust along the southern juan de fuca ridge 1 the geology and structure of the cleft segment of the southern juan de fuca ridge jdfr have been examined using high resolution mapping systems observations by remotely operated vehicle rov rov mounted magnetometer and the geochemical analysis of recovered lavas bathymetric mapping using multibeam em300 coupled with in situ observations that focused on near axis and flank regions provides a detailed picture of 0 to 400 ka upper crust created at the southern terminus of the jdfr a total of 53 rock cores and 276 precisely located rock or glass samples were collected during three cruises that included sixteen rov dives our observations of the seafloor during these dives suggest that many of the unfaulted and extensive lava flows that comprise and or cap the prominent ridges that flank the axial valley emanate from ridge parallel faults and fissures that formed in the highly tectonized zone that forms the walls of the axial valley the geochemically evolved and heterogeneous nature of these near axis and flank eruptions is consistent with an origin within the cooler distal edges of a crustal magma chamber or mush zone in contrast the most recent axial eruptions are more primitive higher mgo chemically homogeneous lobate sheet and massive flows that generate a distinct magnetic high over the axial valley we suggest that the syntectonic capping volcanics observed off axis were erupted from near axis and flank fissures and created a thickened extrusive layer as suggested by the magnetic and seismic data this model suggests that many of the lavas that comprise the elevated ridges that bound the axial valley of the cleft segment were erupted during the collapse of a magmatic cycle not during the robust phase that established a new magmatic cycle

variable crustal structure along the juan de fuca ridge influence of on axis hot spots and absolute plate motions multichannel seismic and bathymetric data from the juan de fuca ridge jdfr provide constraints on axial and ridge flank structure for the past 4 8 ma within three spreading corridors crossing cleft northern symmetric and endeavour segments along axis data reveal south to north gradients in seafloor relief and presence and depth of the crustal magma lens which indicate a warmer axial regime to the south both on a regional scale and within individual segments for young crust cross axis lines reveal differences between segments in moho two way traveltimes of 200 300 ms which indicate 0 5 1 km thicker crust at endeavour and cleft compared to northern symmetric moho traveltime anomalies extend beyond the 5 15 km wide axial high and coincide with distinct plateaus 32 and 40 km wide and 200 400 m high found at both segments on older crust moho traveltimes are similar for all three segments 2100 100 ms indicating little difference in average crustal production prior to 0 6 and 0 7 ma the presence of broad axis centered bathymetric plateau with thickened crust at cleft and endeavour segments is attributed to recent initiation of ridge axis centered melt anomalies associated with the cobb hot spot and the heckle melt anomaly increased melt supply at cleft segment upon initiation of axial volcano and southward propagation of endeavour segment during the brunhes point to rapid southward directed along axis channeling of melt anomalies linked to these hot spots preferential southward flow of the cobb and heckle melt anomalies and the regional scale south to north gradients in ridge structure along the jdfr may reflect influence of the northwesterly absolute motion of the ridge axis on subaxial melt distribution

near bottom particle concentration and flux temporal variations observed with sediment traps and nepholometer on the meriadzek terrace bay of biscay abstract the meriadzek terrace a 2100m deep plateau on the north east atlantic continental slope was chosen as the experimental site for a multidisciplinary programme to observe the parameters needed for a better understanding of biological processes in the benthic environment two approaches were used to study the input of particulate matter to the bathyal seabed sediment traps and indirect particle concentration measurements with nephelometry these two technologies do not measure particles of the same size range but as we are interested in the fluctuations of the particle supply their results are complementary vertical profiles of nephelometry show that over the meriadzek terrace there is 125m thick nepheloid layer immediately above the bottom the dynamics in the deep layer has been determined by measurements made with a module autonome pluridisciplinaire map an in situ monitoring device developed at ifremer which measures currents nephelometry temperature vertical profile near the bottom throughout six months of measurements in 1984 the currents at 0 5m and 120m above the bottom were subject to semi diurnal tidal oscillations the intensity of light scattering recorded with the nephelometer on the map was highly correlated with current velocities especially with semidiurnal tidal oscillations which seem to induce local resuspension there are also longer term fluctuations notably a very strong event which lasted several days during august this event lagged behind a period of high intensity of internal waves correlated with a reversal in current direction the sediment trap pieges a particules pap observations showed that the particle fluxes on the meriadzek terrace have a cycle of variation similar to primary production which is characterized by a maximum in may during the phytoplankton bloom and a minimum during january there was also interannual fluctuation these two kinds of results point out the different time scales from some hours to several months of the large temporal fluctuations which affect the near bottom particle behaviour

constraining spatiotemporal characteristics of magma migration at piton de la fournaise volcano from pre eruptive seismicity volcano tectonic seismicity has been recorded for decades on various volcanoes and is linked with the magma transport and reservoir pressurization yet earthquakes often appear broadly distributed such that magma movement is difficult to infer from its analysis we explore the seismicity that occurred before eruptions at piton de la fournaise in the last 5 years using template matching and relocation techniques we produce a refined image of the summit seismicity demonstrating that most earthquakes are located on a ring structure however only a portion of this structure is activated before each eruption which provides an indication as to the direction of the future eruptive site furthermore we show that the delay between the pre eruptive swarm and the eruption onset is proportional to the distance of the eruptive fissures relative to the summit cone this reveals that the beginning of the intrusion already bears information regarding the future eruption location

can the aluminum and titanium contents of ocean sediments be used to determine the paleoproductivity of the oceans in the central equatorial pacific settling particles collected with sediment traps have al ti values greater than those of a typical crustal source the al ti values of the sediment trap material are not well correlated with either the flux of organic carbon or with total particle mass suggesting that this ratio cannot be used as a simple index of paleoproductivity however the al ti values of some trap samples are more than 3 times the ratio for typical crustal materials indicating a noncrustal source of excess al numerical analysis using linear programming indicates that the excess al is associated with opal and that this biological component carries as much as 1200 ppm of al because of the low particulate fluxes of lithogenic material in the equatorial pacific and the relatively high opal content of equatorial sediment trap material opal appears to be the predominant conveyor of al to the equatorial sediments our sediment trap al ti values are similar to ratios previously measured in equatorial sediments suggesting that measurements of this element pair in ocean sediments may be an indicator of opal rain to the seafloor the particle reactive nature of al and ti means their ratios in sediments may be relatively insensitive to opal preservation or other diagenetic processes however the al ti values of raining particles are highly sensitive to the relative proportion of opal and lithogenic material where opal lithogenic ratios are less than 20 the al ti values are indistinguishable from a crustal source ratio in addition the amount of excess al associated with opal in settling particles may be a function of the concentration of al in the water column and of the processes that fractionate dissolved al and ti these issues must be evaluated before the al ti values of ocean sediments can be used as a reliable proxy of opal flux to the seafloor

detection classification and location of seismovolcanic signals with multi component seismic data example from the piton de la fournaise volcano la reunion france we apply three different methods based on the analysis of the multi component seismic data to detect seismovolcanic tremors and other seismovolcanic signals to propose an approach to classify them and to locate their sources we use continuous seismograms recorded during one year by 21 stations at the piton de la fournaise volcano la r eunion france the first method allows to detect seismovolcanic signals based on stability in time of the inter components cross correlations function two other methods based on the simultaneous analysis of the whole network can be used to detect seismovolcanic signals and to locate their sources in the first network based method the seismic wave field is analyzed by calculating the width of the network covariance matrix eigenvalue distribution the second network based method consists in performing the 3d back projection of the inter stations cross correlations in order to calculate the network response function simultaneous analysis of the parameters measured by the three different methodscan be used to classify different types of seismovolcanic tremors our results demonstrate that all three methods efficiently detect seismovolcanic tremors accompanying the 2010 eruptions and the preceding pre eruptive seismic swarms furthermore methods 2 and 3 based on simultaneous analysis of the whole network detect a large number of volcanic earthquakes our location results show that each seismovolcanic tremor is located in a distinct region of the volcano close to the eruptive site at a shallow depth and the pre ceding seismic crisis is located deeper at about the sea level under the summit crater

tremor rich shallow dyke formation followed by silent magma flow at barðarbunga in iceland magma movement is thought to trigger volcanic tremor however analysis of seismic data suggests that tremor prior to the bar arbunga eruption in iceland instead marked the crust cracking open whereas subsequent magma flow was seismically silent

volcanic episodicity and a non steady state rift valley along northeast pacific spreading centers evidence from sea marc i sea marc i side looking sonar images and sea beam bathymetry along a 400 km stretch of the juan de fuca ridge crest provide evidence that excessive extrusive volcanism periodically builds a crestal ridge along the axis of seafloor spreading an elongate summit depression esd or rift valley is commonly observed in the spine of this crestal ridge the crestal ridge volcanic landform has a distinctive shape that is recognized in bathymetric contours both along the spreading axis and at least up to 30 km away from the axis the landform has a plan form shape that resembles a side view of an archer s bow with the long dimension of the bow form parallel to the strike of the ridge in cross section the bow form is flat on top and has steep flanks these bow form shapes can be explained by magma that rises into the crust at a discrete center and flows laterally into belts of ridge parallel dikes similar to icelandic fissure eruptions both the variable dimensions of the esd along axis of the juan de fuca ridge and the relationship among volcanic flow morphologies within and beyond the esd suggest the four different segments of the juan de fuca ridge presented in detail here display different stages in a cycle of oceanic crust accretion this cycle includes episodes in which there is 1 extrusive volcanic construction which widen the crestal ridge prior to the collapse of the summit depression 2 collapse within the summit region of the crestal ridge to form an esd during a phase of volcanic inactivity and 3 renewed magmatism in the esd as its floor widens by extension and brittle fracture of the upper crust this episodic model implies that the width of the young seafloor affected by volcanic extrusion or dominated by tectonic stretching varies through time

can neap spring tidal cycles modulate biogeochemical fluxes in the abyssal near seafloor water column before particulate matter that settles as primary flux from the interior ocean is deposited into deep sea sediments it has to traverse the benthic boundary layer bbl that is likely to cover almost all parts of the seafloor in the deep seas fluid dynamics in the bbl differ vastly from fluid dynamics in the overlying water column and consequently have the potential to lead to quantitative and compositional changes between primary and depositional fluxes despite this potential and the likely global relevance very little is known about mechanistic and quantitative aspects of the controlling processes here results are presented for a sediment trap time series study that was conducted on the porcupine abyssal plain in the abyssal northeast atlantic with traps deployed at 2 40 and 569 m above bottom mab the two bottommost traps were situated within the bbl affected part of the water column the time series captured 3 neap and 4 spring tides and the arrival of fresh settling material originating from a surface ocean bloom in the trap collected material total particulate matter tpm particulate inorganic carbon pic biogenic silica bsi particulate organic carbon poc particulate nitrogen pn total hydrolysable amino acids aa hexosamines ha and lithogenic material lm were determined the biogeochemical results are presented within the context of time series of measured currents at 15 mab and turbidity at 1 mab the main outcome is evidence for an effect of neap spring tidal oscillations on particulate matter dynamics in bbl affected waters in the deep sea based on the frequency decomposed current measurements and numerical modelling of bbl fluid dynamics it is concluded that the neap spring tidal oscillations of particulate matter dynamics are less likely due to temporally varying total free stream current speeds and more likely due to temporally and vertically varying turbulence intensities that result from the temporally varying interplay of different rotational flow components residual tidal near inertial within the bbl using information from previously published empirical and theoretical relations between fluid and biogeochemical dynamics at the scale of individual particle aggregates a conceptual and semi quantitative picture of a mechanism was derived that explains how the neap spring fluid dynamic oscillations may translate through particle dynamics into neap spring oscillations of biogeochemical aggregate decomposition microbially driven organic matter breakdown biomineral dissolution it is predicted that during transitions from neap into spring tides increased aggregation in near seafloor waters and or reduced deposition of aggregates at the seafloor coincides with reduced biogeochemical particulate matter decomposition in near seafloor waters by contrast during transitions from spring into neap tides enhanced biogeochemical particulate matter decomposition in near seafloor waters is predicted to coincide with increased deposition of particulate matter at the seafloor this study suggests that in addition to current speed the specifics and subtleties of the interplay of different rotational flow components can be an important control on how the primary flux from the interior ocean is translated into the depositional flux with potential implications for sedimentary carbon deposition benthic food supply and possibly even the sedimentary records of environmental change

persistent shallow background microseismicity on hekla volcano iceland a potential monitoring tool abstract hekla is one of iceland s most active volcanoes since 1970 it has erupted four times with a period of quiescence of 14 years since the last eruption we detected persistent levels of background microseismicity with a temporary seismic network in autumn 2012 an amplitude based as well as an arrival time based location method was applied to two populations of events and located them at shallow depths on the northern flank close to the summit this seismicity has not been identified previously by the permanent seismic network in iceland as it is below its detection threshold the detected events were either short higher frequency events with distinct arrivals located beneath the summit on the northern flank of hekla or longer emergent lower frequency events about 4 km northeast of the summit at 200 400 m depth below the surface estimated moment magnitudes were m w 1 1 to 0 1 and m w 0 9 to 0 0 and local magnitudes m l 0 5 to 0 3 and m l 0 3 to 0 3 respectively this seismicity does not show any correlation with gas output but is located at the steepest slopes of the edifice hence we suggest that the current shallow microseismicity at hekla is structurally controlled this offers a possible opportunity of using near summit microseismicity as a tool for monitoring emerging unrest at hekla microseismicity rates will be very sensitive to small stress perturbations due to magma migration at depth currently in the absence of microseismicity monitoring hekla switches from apparently quiescent to fully eruptive on the order of only 1 h

biological and physical controls on the flux and characteristics of sinking particles on the northwest atlantic margin biogenic matter characteristics and radiocarbon contents of organic carbon oc were examined on sinking particle samples intercepted at three nominal depths of 1000 m 2000 m and 3000 m 50 m above the seafloor during a 3 year sediment trap program on the new england slope in the northwest atlantic we have sought to characterize the sources of sinking particles in the context of vertical export of biogenic particles from the overlying water column and lateral supply of resuspended sediment particles from adjacent margin sediments high aluminum al abundances and low oc radiocarbon contents indicated contributions from resuspended sediment which was greatest at 3000 m but also significant at shallower depths the benthic source i e laterally supplied resuspended sediment of opal appears negligible based on the absence of a correlation with al fluxes in comparison caco3 fluxes at 3000 m showed a positive correlation with al fluxes benthic sources accounted for 42 63 of the sinking particle flux based on radiocarbon mass balance and the relationship between al flux and caco3 flux episodic pulses of al at 3000 m were significantly correlated with the near bottom current at a nearby hydrographic mooring site implying the importance of current variability in lateral particle transport however al fluxes at 1000 m and 2000 m were coherent but differed from those at 3000 m implying more than one mode of lateral supply of particles in the water column

a 65 k y time series from sediment hosted glasses reveals rapid transitions in ocean ridge magmas studies of ocean ridge magmatism have been hampered by the difficulty in constructing time series data over more than a few thousand years sediment rapidly covers newly formed ocean crust and older rocks even when recovered from fault scarps cannot be dated accurately ridge eruptions however disperse pyroclastic glass over distances as far as 5 km and these glasses have been shown to persist for thousands of years in on ridge sediment push cores here we present data on such glasses from a piston core that impacted basement in much older 600 ka sediment the age of deposition was determined using established stratigraphic methods to date the host sediment yielding an average sample resolution of a few thousand years and a continuous 65 k y time series the new time series data show systematic temporal variations in magma compositions related to a change to the dynamics of crustal storage which led to greater extents of pre eruptive differentiation shortly thereafter was a small but discernable shift toward more enriched primary melt compositions these events coincide with the onset of enhanced crustal production previously identified using seismic data and interpreted to reflect the capture of a hotspot by the ridge these results show the long term preservation of pyroclastic glasses and suggest that the construction of high resolution volcanic stratigraphy over a million years or more may be possible at ocean ridges using multiple piston cores that impact basement sediment hosted glasses have the potential to transform ocean ridges from the volcanic setting with the worst time series data to that with the best

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

earthquake activity related to the 1991 eruption of the hekla volcano iceland the 1991 eruption of the hekla volcano started unexpectedly on 17 january no long term precursory seismicity was observed the first related activity was a swarm of small earthquakes that began approximately half an hour before the eruption intensive seismicity both earthquakes and volcanic tremor accompanied the violent onset of the eruption almost 400 events up to ml magnitude 2 5 were recorded during the first few hours during the later phases of the eruption the earthquake activity was modest and the main volcano related seismic signal was the persistent volcanic tremor the tremor died away together with the eruption on 11 march and hekla was seismically quiet until the beginning of june 1991 when a sudden swarm of numerous small shallow earthquakes occurred this activity is atypical for hekla and is interpreted to be a failed attempt to resume the eruption

a comparison of atmospheric inputs and deep ocean particle fluxes for the sargasso sea trace metal distributions in ocean waters are dominated by internal recycling processes however fluxes out of the water column must balance inputs if steady state is to be maintained we use deep sea particle fluxes at 3200 m in the sargasso sea as measured by sediment traps to define the flux to the sediments beneath the sargasso sea and compare this flux to the atmospheric input for a group of trace metals despite the uncertainties associated with the comparison several important features are revealed for elements predominantly associated with crustal particles al mn fe and v lateral advection provides a significant part of the deep sea particle flux for cd cu ni pb and zn this lateral component is minor and atmospheric inputs to the sargasso sea exceed deep sea particle fluxes these excesses appear to be consistent with calculations of the export of these metals from the sargasso sea arising from ocean boundary scavenging pb and release from decomposing organic matter in the southward flowing north atlantic deep water cd cu ni and zn in the atmospheric deposition itself wet deposition exceeds dry deposition for cd cu mn ni pb and zn while wet and dry deposition are of similar magnitudes for v fe and al

calibration and comparison of the ldgo nephelometer and the osu transmissometer on the nova scotian rise gardner w d biscaye p e zaneveld j r v and richardson m j 1985 calibration and comparison of the ldgo nephelometer and the osu transmissometer on the nova scotian rise in a r m nowell and c d hollister editors deep ocean sediment transport preliminary results of the high energy benthic boundary layer experiment mar geol 66 323 344 during the survey of the hebble high energy benthic boundary layer experiments area two optical instruments were used to determine the spatial and temporal structure of the benthic nepheloid layer both instruments showed a linear response to suspended particle mass and volume over the typical range of concentrations found in the ocean 10 250 ug l at higher concentrations the transmissometer response remains linear but as previously noted and as shown here by theory the nephelometer has a predictable second order response due to multiply scattered light at the low concentrations found in mid water both instruments seem near their limit of sensitivity small differences between instruments at low concentrations may result from variations in response to particle types found in mid water or may be minor second order effects of temperature or pressure on the instruments the comparison made here shows that either instrument can be effectively used to study the nepheloid layer and that data from different study areas using these instruments can consistently be compared the hebble region was ideal for testing the range of these instruments because it yielded the highest concentrations of particles ever recorded in the deep sea

the formation of deep sea limu o pele deep sea sheet hyaloclastite consists mostly of sand sized blocky and splinter shaped shards but also contains subordinate mm to cm sized thin curved and wrinkled plates and sheets of sideromelane this latter type of shard termed limu o pele has been observed forming subaerially on kilauea by entrapment of water in flowing lava followed by expansion of steam to form large bubbles which burst into thin fragments deep marine limu has been inferred from comparative morphological studies and assessment of physical bubble forming conditions to form in a similar way but with the increased ambient pressure and the higher viscosity of water reducing bubble expansion differing mechanisms of heat transfer and rates of magma chilling also modify the limu forming process in the deep sea this paper evaluates a variety of deep sea limu forming processes and develops a new and quantitatively supported model based on observed limu forming processes and criteria derived from dive samples and observations at seamount six cocos plate it is inferred that water and or water saturated sediment was trapped in extremely thin fluid and rapidly advancing lava flows by various processes bubble formation might also occur during small scale magma fountaining driven by magmatic volatile exsolution and extreme vent constriction or during collapse of pillows and rapid drainage of the magma but we found no deposits clearly resulting from these processes

the nepheloid bottom layer and water masses at the shelf break of the western ross sea in the austral summers of 2000 2001 and 2002 2003 the italian clima project carried out two oceanographic cruises along the northwestern margin of the ross sea where the antarctic bottom water forms here there is an interaction between the water masses on the sea floor of the outer shelf and slope with a consequent evolution of benthic nepheloid layers and an increase in total particulate matter we observed three different situations a the presence of triads bottom structures characterized by a concomitant jump in turbidity temperature and salinity data and high re suspension phenomena related to the presence of the circumpolar deep water and its mixing with cold salty shelf waters associated with gravity currents b the absence of triads with high re suspension implying that when the gravity currents are no longer active the benthic nepheloid layer may persist until the suspended particles settle to the sea floor suggesting that the turbidity data can be used to study recent gravity current events and c the absence of turbidity and sediment re suspension phenomena supports the theory that a steady situation had been re established and the current interaction no longer occurred or had finished sometime before

sedimentation resuspension and chemistry of particles in the northwest atlantic abstract sediment traps were deployed to sample vertical fluxes of particulate matter both immediately above and within the nepheloid layer on the continental slope and rise of the western north atlantic the data from the traps are used to estimate the settling flux of particles and to attempt to distinguish between the primary flux settling material from the upper water column and the resuspended flux settling material that has been resuspended from some region of the sea floor from these data and from measurements of the net nepheloid standing crop of particles estimates of the mean residence time for particles resuspended in the nepheloid layer are on the order of weeks to months from 15 to 500 m above bottom horizontal advection and diffusion are more important than vertical mixing in maintaining the upper portion of the nepheloid layer the estimated flux of al to the north atlantic as atmospheric dust is one to two orders of magnitude less than the primary flux of al measured just above the nepheloid layer yet the range of accumulation rates of al measured on the sea floor with radioisotopes is close to the values we define as the primary flux horizontal transport of al rich particles mostly aluminosilicates must therefore be significant even above the nepheloid layer the size of 80 90 of the particles collected in the traps both above and within the nepheloid layer was less than 63 m the mean size of particles trapped in the nepheloid layer was about 22 m and above the nepheloid layer 11 m the particles were probably in large aggregates when they encountered the traps but identifiable fecal pellets are only a small fraction of the material collected in the traps between 6 and 15 of the primary production of particulate organic carbon in the euphotic zone was collected in floating sediment traps at the 100 m depth indicating that most particulate organic carbon is recycled in the surface water only 2 3 of primary production of organic carbon was collected as primary flux 500 m above the sea floor from an intercomparison of the composition of particles falling rapidly collected in traps falling slowly or not at all collected in water bottles and resting on the sea floor from core tops it was found that elements associated with biogenic matter such as ca sr cu and i were carried preferentially by the rapidly falling particles once these particles reached the sea floor the concentration of those elements was decreased through decomposition respiration or dissolution dissolution appears to be rapid near or on the sea floor because radiolarians diatoms and juvenile foraminifera were rare in core samples even though abundant in all traps the dynamic nature of the nepheloid layer makes it possible for particles to be resuspended many times before they are finally buried enabling sediment to be carried long distances from its origin the recycling of particles near the sea floor may also increase dissolution of siliceous and carbonate matter

the global ocean flux of particulate organic carbon areal distribution and magnitude the magnitude and distribution of the particulate organic carbon poc rain rate to the seafloor in the atlantic pacific and indian ocean basins between 61 n and 61 s has been estimated from benthic oxygen flux estimates for water depths 1000 m only the calculation utilizes the extensive data sets of sedimentary organic carbon caco3 and accumulation rate to extrapolate between individual benthic flux measurement sites using an empirically derived correlation between the seafloor oxygen flux and these parameters the poc flux through the 1000 m depth horizon was then estimated from published correlations between sediment trap determined fluxes and water depth total oxygen utilization in the deep ocean is estimated to be 1 2 1014 mol o2 yr 1 a value that agrees well with previous estimates which were based on surface water primary productivity sediment trap and depth relationships and with deep water respiration rates estimated from apparant oxygen utilization aou 14c relationships on the basis of the derived global ocean flux distribution it is concluded that 1 dissolved organic carbon doc inputs are not required to account for estimated deep water respiration rates 2 the majority of the poc input to the deep ocean occurs within 30 of the equator 3 the proportion of primary production that reaches the deep sea does not vary greatly with latitude 4 gyre and continental margin regions contribute roughly equally to the deep poc flux with a relatively minor contribution from the equatorial divergence region 5 of the estimated 7 2 1013 mol c yr 1 of poc that sinks below the 1000 m depth horizon 45 3 3 1013 mol c yr 1 reaches the seafloor where it is oxidized 6 when normalized to basin area average deep flux rates in the atlantic and pacific are similar while highest rates are observed in the indian ocean and 7 the results can be fully reconciled only if the benthic flux of doc is significantly less than the benthic o2 flux

biogenic flux of al to sediment in the central equatorial pacific ocean evidence for increased productivity during glacial periods we examined the flux of al to sediment accumulating beneath the zone of elevated productivity in the central equatorial pacific ocean along a surface sediment transect at 135 w as well as downcore for a 650 kyr record at 1 3 n 133 6 w across the surface transect a pronounced broadly equatorially symmetric increase in al accumulation is observed relative to ti with al ti ratios reaching values 3 4 times that of potential detrital sources the profile parallels biogenic accumulation and the modeled flux of particulate 234th suggesting rapid and preferential adsorptive removal of al from seawater by settling biogenic particles normative calculations confirm that most al is unsupported by the terrigenous fraction the observed distributions are consistent with previous observations of the relative and absolute behavior of al and ti in seawater and we can construct a reasonable mass balance between the amount of seawater sourced al retained in the sediment and the amount of seawater al available in the overlying column the close tie between al ti and biogenic accumulation as opposed to concentration emphasizes that biogenic sedimentary al ti responds to removal transport phenomena and not bulk sediment composition thus in these sediments dominated by the biogenic component the bulk al ti ratio reflects biogenic particle flux and by extension productivity of the overlying seawater the downcore profile of al ti at 1 3 n displays marked increases during glacial episodes similar to that observed across the surface transect from a background value near al ti of average upper crust the excursions in al ti are stratigraphically coincident with maxima in both bulk and caco3 accumulation and the excess al appears to not be preferentially affiliated with opaline or organic phases consistent with the similar behavioral removal of al and 234th the latter of which responds to the total particle flux the al flux reflects carbonate accumulation only because carbonate comprises the dominant flux in these particular deposits these results collectively indicate that 1 al in biogenic sediment and settling biogenic particles is strongly affected by a component adsorbed from seawater therefore the common tenet that al is dominantly associated with terrestrial particulate matter and the subsequent use of al distributions to calculate the abundance and flux of terrestrial material in settling particles and sediment needs to be reevaluated 2 the al ti ratio in biogenic sediment can be used to trace the productivity of the overlying water providing a powerful new paleochemical tool to investigate oceanic response to climatic variation 3 the close correlation between the al ti productivity signal and carbonate maxima downcore at 1 3 n suggests that the sedimentary carbonate maxima in the central equatorial pacific ocean record increased productivity during glacial episodes

deep magma storage at hekla volcano iceland revealed by insar time series analysis 1 hekla volcano is one of the most active volcanoes in iceland the most recent eruption occurred from 26 february to 8 march 2000 when about 0 19 km3 of magma was erupted we present deformation data from multitemporal analyses of synthetic aperture radar sar images acquired between 1993 and 2008 focusing on pixels with low phase variance using persistent scatterer and small baseline approaches prior to and after the 2000 eruption we find a broad area of inflation around the volcano radius about 20 km with satellite line of sight los shortening of up to 5 mm yr we interpret this signal as the result of pressure increase in a deep seated magma chamber which we model as a spherical source at 14 20 km depth increasing in volume by 0 003 0 02 km3 yr within a 6 km radius of the summit of the volcano a los lengthening is superimposed on the broad inflation signal which correlates partly with recent lava flows we interpret this signal as the result of thermally contracting lava flows combined with viscoelastic yielding due to the load of the volcano and its lavas coeruptive deflation during the 2000 eruption was similar to the cumulative inflation from 1993 to 2000 and is consistent with a spherical magma chamber at 14 18 km depth that decreases in volume by 0 04 0 08 km3 interferograms spanning the 2000 eruption show a local coeruptive deformation signal near the eruptive fissure this is consistent with a dike opening from the surface to depths up to 5 8 km with a volume of 0 005 0 006 km3

variability of particulate flux over the mid atlantic ridge abstract the magnitude and composition of the sinking particle flux were studied over the northern mid atlantic ridge mar from june 2007 to july 2010 four moorings equipped with dual sediment traps 100 m and 1000 m above the sea floor sampled regions north and south of the charlie gibbs fracture zone between 49 n and 54 n and east and west of the mar biogenic data were coupled with satellite estimates of primary production and modelled particle source to assess the variability in export flux large variations were found in the seasonality chemical composition magnitude and source of sinking particulate material between mooring sites the northern moorings recorded both greater mean primary production and greater particle mass flux than the southern moorings although the large inter annual variability within the sites exceeded inter site differences while estimates of primary production and organic carbon fluxes are comparable to other investigations of this type they are notably lower than previous estimates for the abyssal plain of the north atlantic the deeper traps consistently recorded a higher mass flux compared to the shallower traps however we suggest that the overall flux recorded by the shallower traps was reduced by trapping inefficiency which in the light of the low current velocities may largely be due to the physical nature of the sinking material although deep trap flux estimates may be more susceptible to errors due to re suspended and advected material from nearby topography mass flux and current velocity are not linked in addition the relatively low aluminium concentration of the deep trap material indicates that this contribution is relatively small the organic carbon flux to the ne nw se and sw station was 0 8 1 2 1 1 and 1 1 g m 2 y 1 respectively corresponding to an export flux of 0 6 over this region of the mar

seismic tracking of lahars using tremor signals debris flows or lahars frequently occur in volcanic regions and cause serious disasters to nearby communities lahars are commonly observed as long lasting high frequency tremor in seismic records we propose a seismic technique to locate the source of tremor originating from lahars by using waveform data from a seismic network in this method we fit the surface wave amplitudes from point sources positioned over the surface of a volcano to the observed tremor amplitudes and estimate the spatial distributions of the normalized residuals in successive time windows the observed tremor amplitudes at individual stations are corrected by site amplification factors independently estimated from coda waves of tectonic earthquakes the positions of time windows applied to the observed tremor signals are corrected for the travel times of individual source and receiver pairs we track the source of tremor or lahars as temporal changes of the best fit locations in the residual distributions this method is an extension of the existing methods used to locate seismic events and tremor associated with volcanic eruptions we applied this technique to tremor signals of lahars observed by a seismic network at cotopaxi volcano ecuador our analysis showed regions with small residuals on the ne flank of the volcano this suggests that lahars descended on this flank which is consistent with the result of a field survey that found fresh lahar deposits on the ne flank our method which can be easily automated may be useful for the rapid detection and monitoring of lahars

steady and non steady state magma chambers below the east pacific rise volcanic rocks collected on flowline traverses on the flanks of the east pacific rise epr document changes in axial magma chemistry with time providing a record of the thermal history of axial magma chambers amc we present data for a sample set of closely spaced 1 2 km samples along epr flowlines at three localities out to 800 ka showing both steady constant average temperature and non steady state behavior of magma chambers on time scales of 200 500 ka though based on only three symmetrical traverses so far it appears that magmatically robust ridge locations 11 20 n and 9 30 n have steady state chambers whereas a magmatically starved axis 10 30 n shows large temperature changes with time these observations provide a new petrologic perspective to the ongoing debate regarding the significance and causes of morphologic variations along the axis of the east pacific rise

eruptive fracture location forecasts from high frequency events on piton de la fournaise volcano piton de la fournaise la reunion island is a very active basaltic volcano with five eruptions between nov 2009 and dec 2010 pre eruptive seismic crises usually last for a few hours and mainly consist of a volcano tectonic swarm during the quiescent period between the volcano tectonic swarm and the eruptive tremor we identify another swarm of events with a very high frequency content these events are shallow and are located close to the future eruption site they seem associated with the opening of the path for the magma propagating laterally at shallow depth as these events start to occur while the magma is still in a vertical propagation phase this seismicity seems to be related with the generic response of the volcano to the stress perturbation and not directly induced by the magma pressure this new observation brings new insights to short term forecasting of the eruption location

seismic monitoring and modeling of an active volcano for prediction we describe seismic monitoring and modeling of an active volcano for the purpose of predicting the magma transport process in real time we selected the piton de la fournaise which has been monitored by an observatory since the early 1980s and is active with 28 eruptions from 1980 until august 1992 it erupted on march 9 1998 after an unusually long quiet period the eruption lasted until september 21 1998 before the march eruption we completed the initial construction of a model of a magma system based primarily on long period lp events and coda localization we found that lp events are associated with the lateral movement of magma to the rift zone and not with the vertical movement to the summit we also found that the source of 2 hz lp events is located below that of 1 hz lp events the coda localization is a newly discovered phenomenon that helped to locate a magma body this model was used for interpreting the incoming information from the precursory seismic crisis and the eruption tremor during the 6 months of the eruption the simultaneous monitoring and modeling of an active volcano led us to a quantitative simulation of the eruption process computing excess pressure and flow rate in a system of reservoirs connected by channels

new insights into volcanic activity from strain and other deformation data for the hekla 2000 eruption abstract hekla is one of iceland s most active volcanoes its eruptions characterized by surface fissuring and repeated lava flows during its post glacial activity have built up an 800 m high elongated mountain since 1970 it has erupted every 10 years the previous repose interval averaged 60 years for the last eruption in 2000 we constrain the magma geometry by using a wide variety of deformation data campaign gps an insar interferogram dry tilt data and borehole strain data the dike that causes surface fissuring extends no more than 0 5 km in depth and the reservoir depth is 10 km these are connected by a conduit of small lateral extent data for previous eruptions are consistent with this model we propose that the marked change in eruption interval is because this conduit remains liquid during the short interval between recent eruptions only a small pressure increase is required to rupture the thin crustal seal such a state is consistent with precursory seismicity being confined to very shallow depths and may be applicable to other volcanoes that undergo abrupt changes in eruption interval

glacial cycles drive variations in the production of oceanic crust glacial cycles redistribute water between oceans and continents causing pressure changes in the upper mantle with consequences for the melting of earth s interior using plio pleistocene sea level variations as a forcing function theoretical models of mid ocean ridge dynamics that include melt transport predict temporal variations in crustal thickness of hundreds of meters new bathymetry from the australian antarctic ridge shows statistically significant spectral energy near the milankovitch periods of 23 41 and 100 thousand years which is consistent with model predictions these results suggest that abyssal hills one of the most common bathymetric features on earth record the magmatic response to changes in sea level the models and data support a link between glacial cycles at the surface and mantle melting at depth recorded in the bathymetric fabric of the sea floor

seismic activity related to the 2000 eruption of the hekla volcano iceland the 2000 hekla eruption took place from february 26 to march 8 its seismic expressions were a swarm of numerous small earthquakes related to its onset and low frequency volcanic tremor that continued throughout the eruption a swarm of small earthquakes was observed some 80 min before the onset of the eruption and the size of the events increased with time low frequency volcanic tremor with a characteristic frequency band of 0 5 1 5 hz and dominant spectral peak s at 0 7 0 9 hz became visible at 18 19 gmt on february 26 marking the onset of the eruption the tremor amplitude rose quickly and was very high in the beginning of the eruption however it soon began to decrease after about an hour in general the seismic activity related to the 2000 hekla eruption was very similar to what was observed in the previous eruption in 1991 based on knowledge gained from seismicity and strain observations from 1991 this was the first time that a hekla eruption was predicted

helicopter vs volcanic tremor characteristic features of seismic harmonic tremor on volcanoes abstract we recorded high frequency 10 hz harmonic tremor with spectral gliding at hekla volcano in iceland particle motion plots indicated a shallow tremor source we observed up to two overtones beneath our nyquist frequency of 50 hz and could resolve a source of closely spaced pulses of very short duration 0 03 0 1 s on zoomed seismograms volcanic tremor with fundamental frequencies above 5 hz frequency gliding and or repetitive sources similar to our observations were observed on different volcanoes around the world however this frequency content duration and occurrence of volcano related tremor was not observed in the last 35 years of seismic observations at hekla detailed analysis reveals that this tremor was related to helicopters passing the volcano this study relates the gps track of a helicopter with seismic recordings of the helicopter at various distances we show the effect the distance number of rotor blades and velocity of the helicopter has on the observed up and down glidings at up to 40 km distance we highlight similarities and differences between volcano related and helicopter tremor in order to help avoid misinterpretations

variations in earthquake size distribution across different stress regimes the earthquake size distribution follows in most instances a power law1 2 with the slope of this power law the b value commonly used to describe the relative occurrence of large and small events a high b value indicates a larger proportion of small earthquakes and vice versa statistically significant variations of b values have been measured in laboratory experiments mines and various tectonic regimes such as subducting slabs near magma chambers along fault zones and in aftershock zones3 however it has remained uncertain whether these differences are due to differing stress regimes as it was questionable that samples in small volumes such as in laboratory specimens mines and the shallow earth s crust are representative of earthquakes in general given the lack of physical understanding of these differences the observation that b values approach the constant 1 if large volumes are sampled4 was interpreted to indicate that b 1 is a universal constant for earthquakes in general5 here we show that the b value varies systematically for different styles of faulting we find that normal faulting events have the highest b values thrust events the lowest and strike slip events intermediate values given that thrust faults tend to be under higher stress than normal faults we infer that the b value acts as a stress meter that depends inversely on differential stress

magma transport and storage at piton de la fournaise la reunion between 1972 and 2007 a review of geophysical and geochemical data abstract since the middle of the 20th century improvement in volcano monitoring techniques has provided large data sets that can be used to evaluate the evolution of magma plumbing systems at piton de la fournaise volcano abundant eruptive activity and a dense monitoring network are especially conducive to such research analysis of the extensive set of geophysical and geochemical data associated with the last 35 years of activity provides new insights into magma transport and storage at piton de la fournaise two periods of frequent eruptions separated by 6 years of inactivity can be distinguished 1972 1992 and 1998 2007 considering these two periods we show evidence of major changes in the shallow plumbing system in 2000 during 1972 1992 and 1998 2000 lava compositions and weak long term eruptive precursors lasting few days to three weeks characterized by no significant summit inflation and about ten volcano tectonic earthquakes per day suggest that eruptions were fed by the progressive drainage of an occasionally recharged shallow magma reservoir geophysical evidence of shallow magma reservoir recharge was only recorded in 1986 and 1998 in contrast from 2000 to 2007 geophysical data highlight the appearance of long term precursors 1 to 5 months of summit inflation and strong seismicity up to one hundred events per day preceding cycles of successive eruptions each cycle of eruptions was characterized by a sequence 3 to 10 months in duration of summit and near summit proximal eruptions and ended with a distal low altitude oceanite olivine abundances 20 vol eruption on the eastern flank of the volcano within each of these eruptive cycles lavas became progressively more magnesian over time the preferential motion of the eastern flank caused by continuous recharging of the shallow reservoir since 2000 would favour the occurrence of distal eruptions towards this flank at the end of a cycle

the hekla eruption 1980 1981 the sixteenth eruption of hekla since 1104 began on august 17th 1980 after the shortest repose period on record only ten years the eruption started with a plinian phase and simultaneously lava issued at high rate from a fissure that runs along the hekla volcanic ridge the production rate declined rapidly after the first day and the eruption stopped on august 20th a total of 120 million m3 of lava and about 60 million m3 of airborne tephra were produced during this phase of the activity in the following seven months steam emissions were observed on the volcano activity was renewed on april 9th 1981 and during the following week additional 30 million m3 of lava flowed from a summit crater and crater rows on the north slope

imbalance in the carbonate budget of surficial sediments in the north atlantic ocean variations over the last millenium abstract fluxes contributing to the particulate carbonate system in deep sea sediments were investigated at the bengal site in the porcupine abyssal plain northeast atlantic deposition fluxes were estimated using sediment traps at a nominal depth of 3000 m and amounted to 0 37 0 1 mmol c m 2 d 1 dissolution of carbonate was determined using flux of total alkalinity from in situ benthic chambers is 0 4 0 1 mmol c m 2 d 1 burial of carbonate was calculated from data on the carbonate content of the sediment and sedimentation rates from a model age based on 14c dating on foraminifera 0 66 0 1 mmol c m 2 d 1 burial plus dissolution was three times larger than particle deposition flux which indicates that steady state is not achieved in these sediments mass balances for other components bsi 210pb and calculations of the focusing factor using 230th show that lateral inputs play only a minor role in this imbalance decadal variations of annual particle fluxes are also within the uncertainty of our average long term change in dissolution may contribute to the imbalance but can not be the main reason because burial alone is greater than the input flux the observed imbalance is thus the consequence of a large change of carbonate input flux which has occured in the recent past a box model is used to check the response time of the solid carbonate system in these sediments and the time to reach a new steady state is in the order of 3 kyr thus it is likely that the system has been perturbed recently and that large dissolution and burial rates reflect the previously larger particulate carbonate deposition rates we estimate that particulate carbonate fluxes have certainly decreased by a factor of at least 3 and that this change has occurred during the last few centuries

lava bubble wall fragments formed by submarine hydrovolcanic explosions on lō ihi seamount and kīlauea volcano glassy bubble wall fragments morphologically similar to littoral limu o pele have been found in volcanic sands erupted on l ihi seamount and along the submarine east rift zone of k lauea volcano the limu o pele fragments are undegassed with respect to h2o and s and formed by mild steam explosions angular glass sand fragments apparently form at similar and greater depths by cooling contraction granulation the limu o pele fragments from l ihi seamount are dominantly tholeiitic basalt containing 6 25 7 25 mgo none of the limu o pele samples from l ihi seamount contains less than 5 57 mgo suggesting that higher viscosity magmas do not form lava bubbles the dissolved co2 and h2o contents of 7 of the limu o pele fragments indicate eruption at 1200 300 m depth 120 30 bar these pressures exceed that generally thought to limit steam explosions we conclude that hydrovolcanic eruptions are possible with appropriate pre mixing conditions at pressures as great as 120 bar

petrological variability of recent magmatism at axial seamount summit juan de fuca ridge 1 a combined study of mapping observational age constraint and geochemical data at the summit of axial seamount juan de fuca ridge has revealed its recent petrological history multiple basalt types erupted at the summit in a time sequence at least three different magma batches have been present beneath the axial summit caldera during the last millennium each with a range in differentiation the first prior to 1100 ce was compositionally diverse dominantly aphyric t morb the second from 1220 to 1300 ce was dominantly plagioclase phyric more mafic n morb erupted mostly in the central portion of the caldera since 1400 ce lavas have been more differentiated and nearly aphyric t morb mostly erupted in the caldera s rift zones parental magmas vary subtly due to small coupled differences in the degree of melting and sources but all share a uniform differentiation trend indicating pooling at similar depths thus melts percolate through melt rich lenses that remain partially isolated in space and or time centennial magmatic timescales at axial seamount are similar to those for fast spreading ridge segments the fluctuation between aphyric and plagioclase phyric lava likely reflects different pathways or velocities of melt migration

sedimentation stratigraphy and physical properties of sediment on the juan de fuca ridge abstract sedimentation near mid ocean ridges may differ from pelagic sedimentation due to the influence of the ridges rough topography on sediment deposition and transport this study explores whether the near ridge environment responds to glacial interglacial changes in climate and oceanography new benthic 18o radiocarbon multi sensor track and physical property sedimentation rates density magnetic susceptibility data for seven cores on the juan de fuca ridge provide multiple records covering the past 700 000 years of oceanographic history of the northeast pacific ocean systematic variations in sediment density and coarse fraction correspond to glacial interglacial cycles identified in benthic 18o and these observations may provide a framework for mapping the 18o chronostratigraphy via sediment density to other locations on the juan de fuca ridge and beyond sedimentation rates generally range from 0 5 to 3 cm kyr with background pelagic sedimentation rates close to 1 cm kyr variability in sedimentation rates close to the ridge likely reflects remobilization of sediment caused by the high relief of the ridge bathymetry sedimentation patterns primarily reflect divergence of sedimentation rates with distance from the ridge axis and glacial interglacial variation in sedimentation that may reflect carbonate preservation cycles as well as preferential remobilization of fine material

locating pyroclastic flows on soufriere hills volcano montserrat west indies using amplitude signals from high dynamic range instruments pyroclastic flows are located using amplitude signals from a seven station high dynamic range seismograph array located 1 9 6 1 km from soufriere hills volcano in montserrat west indies locations are determined by measuring the seismograph signal amplitude for an event recorded at several stations in a moving time window analysis for a given window the measured amplitudes are corrected to a trial source location by removing the effect of the surface wave geometric spreading instrument gain and the attenuation at calculated travel times the trial source location is then compared to other trial locations via an iterative localised grid search where the root mean squared amplitude residual a is minimised the process is repeated for subsequent time steps resulting in a best fit event location and size through time the method has been tested on four small events occurring on april 8 1999 august 12 1999 february 25 2001 and july 4 2001 when visual observations of pyroclastic flows coincided with good seismograph station coverage number of stations 5 azimuthal gap 160 based on the location results the four events propagated 0 5 1 4 1 3 and 1 0 km from the dome and had maximum attenuation corrected reduced displacements drq of 9 0 2 8 6 9 and 2 3 cm2 and maximum pyroclastic flow velocities of 7 30 20 and 8 ms 1 respectively a time lapse video of the event of august 12 1999 shows that amplitude based location through time closely matches the observed run out distance and velocity in contrast amplitude based locations for the events of april 8 1999 and july 4 2001 underestimated the actual flow run out by 1 5 km underestimation of the true run out distance is probably due to both the increased distribution of sources as coherent dome material disaggregates into many blocks and signal contamination from other sources results indicate that pyroclastic flows and rockfalls can be located using amplitude signals from high dynamic range seismograph stations yielding estimates of size and trajectory regardless of visibility conditions on the volcano this new method is being tested as a hazard mitigation and research tool on montserrat

holocene sediment fluxes in the northeast atlantic from 230thexcess and radiocarbon measurements radiocarbon and 230thexcess data from six ne atlantic box cores are considered the cores form a transect from the porcupine abyssal plain over the east thulean rise to the southern end of feni drift the chronology for the cores is established from bulk sediment carbonate radiocarbon data and reveals that sections exhibiting constant accumulation rates can be identified in all the cores with rates of 3 0 3 5 cm kyr 1 on the plain through the holocene and late holocene rates of 4 3 6 6 cm kyr 1 elsewhere five out of the six cores show accumulations of more 230thexcess than is produced in the overlying water column with the greatest inventories up to 225 of production in the cores from the rise and drift a size fraction comparison between two cores from the plain and rise reveals that the higher overall accumulation rates and 230thexcess inventories in the off plain cores are due to an increased fine 5 m component fraction whereas the flux of coarser material is similar to that received on the plain this suggests that the higher fluxes of materials observed are physically rather than biogeochemically driven and also that drift formation has been continuously active in the late holocene sections of all the cores where regular accumulation is defined by the radiocarbon data are modeled first by a linear radiocarbon age depth model and second by a constant rain 230thexcess 0 model prorated for the observed core inventories these modeling approaches yield historical mass accumulation rate estimates which are generally in reasonable agreement 30 but the differences observed appear to be well organized in time rather than random

dispersal of volcaniclasts during deep sea eruptions settling velocities and entrainment in buoyant seawater plumes abstract we use tank experiments to measure settling rates of deep sea volcaniclastic material recovered from the arctic 85 e gakkel ridge and pacific juan de fuca ridge loihi seamount oceans we find that clast size and shape exert a strong influence on settling velocity with velocities of 30 cm s for large 8 mm blocky clasts compared to velocities of 2 5 cm s for small

imaging the dynamics of magma propagation using radiated seismic intensity 1 at shallow depth beneath the earth s surface magma propagates through strongly heterogeneous volcanic material inversion of buoyancy and or solidification have strong impacts on the dynamics of propagation without any change of magma supply in this paper we study the spatial and time evolution of magma intrusions using induced seismicity we propose a new method based on ratio analysis of estimates of radiated seismic intensities recorded at different stations during seismic swarms by applying this method to the january 2010 piton de la fournaise volcano eruption we image complex dike propagation dynamics which strongly differ from a model of constant velocity dike propagation we provide a new method to image in real time the dynamics of dike propagation and to infer the position of eruptive fissures

a constant influx model for dike propagation implications for magma reservoir dynamics 1 most observations of seismicity rate during dike propagation on basaltic volcanoes show 1 rate stationarity despite possible variations of the dike tip velocity 2 frequent lack of clear and monotonic hypocenter migration following dike propagation and 3 event occurrences located backward with respect to the dike tip position on these bases the origin of the seismicity contemporary to dike intrusion within basaltic volcanoes cannot be solely related to the crack tip propagation seismicity rather appears to be the response of the edifice itself to the volumetric deformation induced by the magma intruding the solid matrix the volume change induced into the volcano edifice over time by the intruding magma is equal to the magma flux injected into the dike from the reservoir the consequence of this is that the stationary seismicity rate observed during the intrusion is a proxy for the magma flux withdrawn from the reservoir we consider a two phase dike propagation model including a first vertical propagation followed by a lateral migration along a lithological discontinuity we explore 1 under which geophysical conditions the vertical dike is fed at constant flow rate of magma and 2 dike propagation patterns implications entailed by constant volumetric flux on the piton de la fournaise volcano case study suggest a minimum size for the magma reservoir of about 1 km3 and a maximum value for the initial magma reservoir overpressure of about 2 2 mpa considering similar magma inflow rates during vertical and lateral dike propagation phases we reproduce independent estimates of propagation velocities rise times and injected volumes when applying the model to the august 2003 piton de la fournaise eruption

broadband seismic monitoring of active volcanoes using deterministic and stochastic approaches 1 we systematically used two approaches to analyze broadband seismic signals for monitoring active volcanoes one is waveform inversion of very long period vlp signals assuming possible source mechanisms the other is a source location method of long period lp events and tremor using their amplitudes the deterministic approach of the waveform inversion is useful to constrain the source mechanism and location but is basically only applicable to vlp signals with periods longer than a few seconds the source location method assumes isotropic radiation of s waves and uses seismic amplitudes corrected for site amplifications this simple approach provides reasonable source locations for various seismic signals such as a vlp event accompanying lp signals an explosion event and tremor associated with lahars and pyroclastic flows observed at five or fewer stations our results indicate that a frequency band of about 5 12 hz and a q factor of about 60 are appropriate for the determination of the source locations in this frequency band the assumption of isotropic radiation may become valid because of the path effect caused by the scattering of seismic waves the source location method may be categorized as a stochastic approach based on the nature of scattering waves systematic use of these two approaches provides a way to better utilize broadband seismic signals observed at a limited number of stations for improved monitoring of active volcanoes

the millennium eruption of hekla in february 2000 the 18th historic eruption of hekla started on 26 february 2000 it was a short lived but intense event emitting basaltic andesitic 55 5 wt sio2 pyroclastic fragments and lava during the course of the eruption monitoring was done by both instruments and direct observations together providing unique insight into the current activity of hekla during the 12 day eruption a total of 0 189 km3 dre of magma was emitted the eruptive fissure split into five segments the segments at the highest altitude were active during the first hours while the segments at lower altitude continued throughout the eruption the eruption started in a highly explosive manner giving rise to a subplinian eruptive column and consequent basaltic pyroclastic flows fed by column collapses after the explosive phase reached its maximum the eruption went through three more phases namely fire fountaining strombolian bursts and lava effusion in this paper we describe the course of events of the eruption of hekla and the origin of its magma and then show that the discharge rate can be linked to different style of eruptive activity which are controlled by fissure geometry we also show that the eruption phases observed at hekla can be linked with inferred magma chamber overpressure prior to the eruption

the 1991 eruption of hekla iceland the eruption that started in the hekla volcano in south iceland on 17 january 1991 and came to an end on 11 march produced mainly andesitic lava this lava covers 23 km2 and has an estimated volume of 0 15 km3 this is the third eruption in only 20 years whereas the average repose period since 1104 is 55 years earthquakes as well as a strain pulse recorded by borehole strainmeters occurred less than half an hour before the start of the eruption the initial plinian phase was very short lived producing a total of only 0 02 km3 of tephra the eruption cloud attained 11 5 km in height in only 10 min but it became detached from the volcano a few hours later several fissures were active during the first day of the eruption including a part of the summit fissure by the second day however the activity was already essentially limited to that segment of the principal fissure where the main crater subsequently formed the average effusion rate during the first two days of the eruption was about 800 m3 s 1 after this peak the effusion rate declined rapidly to 10 20 m3 s 1 then more slowly to 1 m3 s 1 and remained at 1 12 m3 s 1 until the end of the eruption site observations near the main crater suggest that the intensity of the volcanic tremor varied directly with the force of the eruption a notable rise in the fluorine concentration of riverwater in the vicinity of the eruptive fissures occurred on the 5th day of the eruption but it levelled off on the 6th day and then remained essentially constant the volume and initial silica content of the lava and tephra the explosivity and effusion rate during the earliest stage of the eruption as well as the magnitude attained by the associated earthquakes support earlier suggestions that these parameters are positively related to the length of the preceeding repose period the chemical difference between the eruptive material of hekla itself and the lavas erupted in its vicinity can be explained in terms of a density stratified magma reservoir located at the bottom of the crust we propose that the shape of this reservoir its location at the west margin of a propagating rift and its association with a crustal weakness all contribute to the high eruption frequency of hekla

seasonal and interannual changes in the north atlantic subpolar gyre from geosat and topex poseidon altimetry sea surface slopes from the altimetric satellites geosat and topex poseidon are used to calculate eddy kinetic energy of the north atlantic subpolar gyre 40 65 n 60 5 w using two years of data from each satellite december 1986 to december 1988 and october 1992 to september 1994 respectively interannual differences in the north atlantic current nac are revealed in regions of strong currents the eddies are driven by baroclinic instability of the mean flow are not seasonally varying and may therefore be used as a surrogate for the mean flow itself wind stress curl fields for the same periods show that the northward and southward shifts in the current branches across the mid atlantic ridge are related to interannual differences in the winter wind stress curl pattern when the zero in wind stress curl is well defined and wind stress is at a maximum outside the nac the eddies are driven primarily by wind stress indicated by a significant seasonality time series of eddy kinetic energy and wind stress are generated for the 4 years and the magnitude phase and significance of annual and semiannual signals are determined interannual changes in the timing of the maximum eddy kinetic energy are associated with that of the maximum wind stress with each being shifted by a month or two later or earlier throughout much of the northern north atlantic a significant annual signal in eddy kinetic energy is observed lagging the wind stress by on average 6 weeks a negligible lag is found in the region of the east greenland current and irminger sea whereas the greatest lag about 2 months is found in the labrador sea

temporal variations of non volcanic tremor nvt locations in the mexican subduction zone finding the nvt sweet spot epicentral locations of non volcanic tremors nvt in the mexican subduction zone are determined from the peak of the energy spatial distribution and examined over time nvt is found to occur persistently at a distance of 215 km from the trench which we term the sweet spot because this region probably has the proper conditions i e temperature pressure and fluid content for the nvt to occur with minimum shear slip high energy nvt episodes are also observed every few months extending 190 km to 220 km from the trench with durations of a few weeks during the 2006 slow slip event sse the duration and the recurrence rate of the nvt episodes increased low energy episodes were also observed independent from the high energy episodes 150 km to 190 km from the trench during the 2006 sse both the high and low energy episodes were made up of many individual nvt s that had a range of energy release rates however the highest energy release rates of the high energy episodes were consistently double those of the low energy episodes and the persistent activity at the sweet spot we suggest that all of the high energy episodes are evidence of small short repeat interval sse given this model the increased recurrence rate of the high energy nvt episodes during the 2006 long term sse implies that short term sse s also increase during the sse and are therefore triggered by the sse

the benthic silica cycle in the northeast atlantic annual mass balance seasonality and importance of non steady state processes for the early diagenesis of biogenic opal in deep sea sediments within the framework of the eu funded bengal programme the effects of seasonality on biogenic silica early diagenesis have been studied at the porcupine abyssal plain pap an abyssal locality located in the northeast atlantic ocean nine cruises were carried out between august 1996 and august 1998 silicic acid dsi increased downward from 46 2 to 213 m mean of 27 profiles biogenic silica bsi decreased from ca 2 near the sediment water interface to 1 at depth benthic silicic acid fluxes as measured from benthic chambers were close to those estimated from non linear dsi porewater gradients some 90 of the dissolution occurred within the top 5 5 cm of the sediment column rather than at the sediment water interface and the annual dsi efflux was close to 0 057 mol si m 2 yr 1 biogenic silica accumulation was close to 0 008 mol si m 2 yr 1 and the annual opal delivery reconstructed from sedimentary fluxes assuming steady state was 0 065 mol si m 2 yr 1 this is in good agreement with the mean annual opal flux determined from sediment trap samples averaged over the last decade 0 062 mol si m 2 yr 1 thus ca 12 of the opal flux delivered to the seafloor get preserved in the sediments a simple comparison between the sedimentation rate and the dissolution rate in the uppermost 5 5 cm of the sediment column suggests that there should be no accumulation of opal in pap sediments however by combining the bengal high sampling frequency with our experimental results on bsi dissolution we conclude that non steady state processes associated with the seasonal deposition of fresh biogenic particles may well play a fundamental role in the preservation of bsi in these sediments this comes about though the way seasonal variability affects the quality of the biogenic matter reaching the seafloor hence it influences the intrinsic dissolution properties of the opal at the seafloor and also the part played by non local mixing events by ensuring the rapid transport of bsi particles deep into the sediment to where saturation is reached

petrology and geochemistry of basalts from the southern juan de fuca ridge controls on the spatial and temporal evolution of mid ocean ridge basalt three morphologically distinct regions within the neovolcanic zone of the cleft segment of the southern juan de fuca ridge were investigated and sampled in detail using the dsrv alvin additional along strike and off axis samples were recovered by dredge the southernmost region the southern cleft site is characterized by a 3 km wide axial valley floored by ponded sheet flows and bisected by a 30 to 50 m wide cleft farther north at the young sheet flow site the ridge axis is characterized by a distinct 500 m wide inner graben that is largely covered by distinctly younger looking sheet flows the northernmost of the three regions is defined by a linear series of discontinuous constructional pillow mounds that extend the trend of the cleft segment well into the zone of overlap with the neighboring vance segment the pillowed lavas at the young pillow mound site represent the most recent episode of volcanism along the cleft segment strong correlations exist between degrees of fractionation relative ages of lavas and latitude lavas are progressively younger looking and more mafic to the north the compositional range of mid ocean ridge basalts from the neovolcanic zone can generally be accounted for by 35 40 low pressure fractional crystallization of relatively primitive but not primary depleted n type melts scatter of the geochemical data about calculated liquid lines of descent is probably the result of mixing of magmas with slightly different parental compositions generated from small scale mantle heterogeneities furthermore the chemical variability may be the result of mixing of very depleted and more enriched sources or melts that are present beneath the southern juan de fuca ridge the more primitive nature of the young pillow mound basalts and their slightly different chemical characteristics indicates they cannot be simply related to the older southernmost lavas by along axis flow in a continuous axial magma chamber or conduit rather the data suggest lavas were derived from discrete magma chambers or lenses each in a different stage of evolution the youngest events may be associated with a new influx of magma into the northern part of the segment and subsequent northward diking and propagation to form the new pillow mounds the oldest stage 40 additional crystallization of the most mafic composition is associated with focused hydrothermal activity and tectonic extension whereas the youngest events are characterized by ridge inflation diking and dispersed hydrothermal activity geochemical and tectonomagmatic features observed along the cleft segment are similar to those recently documented along the east pacific rise from 9 30 n 10 n suggesting the scales processes and stages of magmagenesis are similar along medium to fast spreading ridge segments

observations of wind forced deep ocean currents in the north pacific this study examines the atmospheric response of the deep ocean using 200 instrument years of moored current measurements from across the breadth of the mid latitude north pacific we have found evidence of a seasonal modulation in the ocean eddy kinetic energy beneath the thermocline at several locations north of 35 n this modulation is often in phase with the local atmospheric forcing function at frequencies between 0 1 and 0 01 cpd correlations between the local wind stress curl and the deep currents have been found for a few locations the local forced response is parallel to the potential vorticity gradient f h and consistent in amplitude with a local topographic sverdrup balance nonlocal forcing in the form of flow along isolines of potential vorticity has been estimated and it is comparable to the observed flow at some locations but the modeled flow is not correlated with the observations throughout the mid latitude north pacific the bottom slope tends to enhance the effect this suggests that topography narrows the available bandwidth for forced barotropic rossby waves facilitating a quasi steady topographic sverdrup response over most of the basin however the enhanced effect reduces the magnitude of the ocean s response to wind forcing nonlocally forced sverdrup currents flow along isolines of f h are the dominant component but are only of the order of 1 cm s 1 locally forced sverdrup currents flow across isolines of f h are typically of the order of 0 1 cm s 1 rms and are not commonly measured hence these wind forced variations are a background level signal in the mid latitude eddy kinetic energy in a few isolated areas the bottom slope reduces the effect in these regions the local sverdrup response is amplified and has been observed

rift topography linked to magmatism at the intermediate spreading juan de fuca ridge new seismic observations of crustal structure along the juan de fuca ridge indicate that the axial rift topography reflects magma induced deformation rather than alternating phases of magmatism and tectonic extension as previously proposed contrary to predictions of the episodic models crustal magma bodies are imaged beneath portions of all ridge segments surveyed at average depths of 2 1 2 6 km the shallow rift valley or axial graben associated with each juan de fuca segment is 50 200 m deep and 1 8 km wide and is well correlated with a magma body in the subsurface analysis of graben dimensions height and width shows that the axial graben narrows and graben height diminishes where the magma body disappears rather than deepening and broadening as expected for rift topography due to tectonic extension we propose an evolutionary model of axial topography that emphasizes the contribution of dike intrusion to subsidence and fault slip at the seafloor in this model an evolving axial topography results from feedbacks between the rheology of the crust above a magma sill and dike intrusion rather than episodic magma delivery from the mantle

investigating the source characteristics of long period lp seismic events recorded on piton de la fournaise volcano la reunion abstract magmatic and hydrothermal processes play a significant role in generating seismicity at active volcanoes these signals can be recorded at the surface and can be used to obtain an insight into the volcano s internal dynamics long period lp events are of particular interest as they often accompany or precede volcanic eruptions but they are still not well understood piton de la fournaise volcano la reunion island is one of the most active volcanoes in the world however lp events are rarely recorded there a seismic network of 20 broadband seismometers has been operational on piton de la fournaise volcano since november 2009 between november 2009 and january 2011 the volcano erupted five times but only 15 lp events were recorded three of these eruptions were preceded by lp events and several lp events were recorded during an intrusive phase a family of three repeating lp events exists within the dataset in order to characterize these events we locate and perform moment tensor inversion on the lp family the lp events are located within the summit crater at shallow depths

geologic history of the summit of axial seamount juan de fuca ridge 1 multibeam 1 m resolution and side scan data collected from an autonomous underwater vehicle and lava samples radiocarbon dated sediment cores and observations of flow contacts collected by remotely operated vehicle were combined to reconstruct the geologic history and flow emplacement processes on axial seamount s summit and upper rift zones the maps show 52 post 410 ce lava flows and 20 precaldera lava flows as old as 31 2 kyr the inferred age of the caldera clastic deposits 1 2 m thick accumulated on the rims postcaldera between 31 ka and 410 ce there are no known lava flows near the summit the oldest postcaldera lava 410 ce is a pillow cone se of the caldera two flows erupted on the w rim between 800 and 1000 ce from 1220 to 1300 ce generally small eruptions of plagioclase phyric depleted mafic lava occurred in the central caldera and on the east rim larger post 1400 ce eruptions produced inflated lobate flows of aphyric less depleted and less mafic lava on the upper rift zones and in the n and s caldera all caldera floor lava flows and most uppermost rift zone flows postdate 1220 ce activity shifted from the central caldera to the upper s rift outside the caldera to the n rift and caldera floor and then to the s caldera and uppermost s rift where two historical eruptions occurred in 1998 and 2011 the average recurrence interval deduced from the flows erupted over the last 800 years is statistically identical to the 13 year interval between historical eruptions

burst resuspension of seabed material at the foot of the continental slope in the rockall channel to better understand the relationship between near bottom hydrodynamics and sediment resuspension in the transition zone between the continental slope and the abyssal plain an array of three moorings equipped with near bottom sediment traps and current meters was deployed in a triangular configuration of at the foot of the south east slope of the rockall channel north atlantic in addition a fast sampling adcp was moored in the centre of the triangle microscopic observations combined with grain size analysis revealed that the material intercepted by the traps was mainly composed of loose phytodetritus and aggregates organic carbon and 13corg analyses further indicate that this material is relatively fresh and hence probably only transported over short distances the total mass flux measured by the traps suggests input from either laterally advected or resuspended material during the deployment period the measured flux was variable in time and space with a strong increase at the deepest site at the very foot of the slope the measured flux did not correlate significantly with daily averaged current speed suggesting that processes other than those related to elevated bed shear stress are involved in the resuspension mechanism rapid changes in the hydrodynamics probably related to internal motions are evidenced by abrupt bursts in the current velocity and in the near bottom turbidity their occurrence at slack tidal waters appears to be at the origin of the resuspension observed at the foot of the slope of the rockall channel high resolution current velocity measurements suggest that resuspension is dominated by energetic highly localised and short term resuspension events despite the abyssal depths part of these events resemble in many ways the solibores which have been previously observed to enhance sediment transport at much shallower depths over the continental slope while others rather appear to be associated to gravity waves

seismicity around the hekla and torfajokull volcanoes iceland during a volcanically quiet period 1991 1995 the volcano hekla in south iceland had its latest eruption in january march 1991 the eruption was accompanied and followed by considerable seismic activity this study examines the seismicity in the hekla region 63 42 64 18 n 18 30 20 12 w during a period when the high activity related to the eruption had ceased from july 1991 to october 1995 the aim is to define the level of the normal background seismicity of the area that can be compared to the eruption related activity the hekla volcano proper was generally aseismic during the study period the most prominent earthquake cluster is in the neighbouring torfajokull volcano the epicentres are concentrated in the western part of the caldera and west of it the hypocentres are located at all depths from the surface down to 14 km with highest activity at 5 12 km inside this cluster in the northwest part of the caldera is a spherical volume void of earthquakes approximately 4 km in diameter and centred at 8 km depth this is interpreted as a cooling magma body small low frequency events of volcanic origin were occasionally recorded at torfajokull this activity has mainly occurred in swarms and was most abundant during the first year of the study period presumably reflecting some kind of connection to the 1991 hekla eruption our study area also includes the easternmost section of the south iceland seismic zone a transform zone characterized by bookshelf faulting on transverse faults two lineaments of epicentres were identified roughly corresponding to mapped faults of the south iceland seismic zone the hypocentres are relatively deep mainly at 6 12 km matching the general trend of hypocentral depth increasing toward the east the seismicity is highest in the area of the mapped faults however the epicentres extend beyond them and indicate greater width of the south iceland seismic zone or 20 30 km rather than approximately 10 km as indicated by the length of the surface faults the seismicity in the volcanic systems of hekla and vatnafjoll shows some characteristics of the south iceland seismic zone epicentres are concentrated into two n s lineaments one of which coincides with the location of the 1987 vatnafjoll earthquake mw 5 9 a strike slip event on a n to s trending fault the hypocentres of the hekla vatnafjoll events are mainly at 8 13 km depth which indicates a continuation of the depth trend of the earthquakes of the south iceland seismic zone the events located at hekla proper and immediately north of it are all of low frequency character which can be held as an indication of volcanic origin on the other hand they show clear s arrivals at observing stations like normal high frequency tectonic earthquakes

volcano deformation at active plate boundaries deep magma accumulation at hekla volcano and plate boundary deformation in south iceland volcano deformation at active plate boundaries deep magma accumulation at hekla volcano and plate boundary deformation in south iceland

a seasonal signal in ocean currents to abyssal depths long term 9 32 month current meter records from the eastern north atlantic 41 n 59 n suggest that remote from the influence of the western boundary current eddy kinetic energy ke at all depths is principally a function of wind stress and stratification generated during the winter and early spring propagating to abyssal depths and decaying to a minimum in late summer although this seasonal variation in ke has not previously been described from the midlatitude ocean some theoretical basis for it is presented

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

depositional fluxes palaeoproductivity and ice rafting in the ne atlantic over the past 30 ka over the last 30 ka sediment flux to the northeast atlantic ocean has been strongly influenced by the growth and decay of northern hemisphere ice sheets input of ice rafted detritus the migration of the polar front and associated changes in patterns of biological productivity we examined cores from 47 n to 60 n along 20 w to determine the flux of components including carbonate organic carbon and terrigenous material and divided into size fractions during the glacial period fine carbonate flux was low and ice rafted input high burial flux during the holocene became dominated by coccolith and foraminiferal carbonate with minor organic matter and biogenic silica estimates of palaeoproductivity are ambiguous a method which corrects for water depth and sedimentation rate suggests no clear glacial to holocene change whereas a method based on percentage of organic carbon suggests increased productivity from glacial to holocene of around 60 sites of sediment focusing saw a change from enhanced fine terrrigenous flux in the glacial to enhanced fine carbonate in the holocene after compensating for sediment focusing glacial ice rafted flux distribution shows a decrease from south to north across the area reflecting cyclonic surface water circulation deposition of ice rafted detritus during heinrich events h1 and h2 led to enhanced preservation of organic matter immediately beneath the layers indicating a rapid accumulation rate

structures and evolution of the plumbing system of piton de la fournaise volcano inferred from clustering of 2007 eruptive cycle seismicity analysis of seismic activity associated with the eruptions of 2007 which led to the collapse of the dolomieu crater on april 5th reveals the link between the seismicity and the magma transfers at piton de la fournaise three eruptive phases occurred on february 18th march 30th and april 2nd 2007 at the summit 2 000 m and 600 m high on the south east flank respectively illustrating the three types of eruptions defined for the current piton de la fournaise activity we use cross correlation of seismic waveforms and clustering to improve the earthquake locations and determine the best constrained focal mechanisms with an average of 78 p phase polarities the pre eruptive seismicity of the february and march eruptions is composed of time extended clusters that also preceded other distal eruptions from 2000 to 2007 our analysis shows that the seismic swarm prior to the february eruption initiated the intrusion that led to the april 2007 eruption the seismicity preceding the dolomieu crater collapse consists of numerous but time limited clusters and specific seismic activity that accompanied the dolomieu crater collapse from april 1st to april 5th earthquakes with clvd mechanisms combined with normal faulting sources occurred between 0 8 and 0 km asl until the complete rupture of the shallow magma storage roof this collapse induced the propagation of a de pressurization front and triggered a migration of seismicity from 0 to 8 km along a very narrow path

imbricated aseismic slip and fluid diffusion drive a seismic swarm in the corinth gulf greece the primary processes driving seismic swarms are still under debate here we study the temporal evolution of a seismic swarm that occurred over a 10 day period in october 2015 in the extensional rift of the corinth gulf greece using high resolution earthquakes relocations the seismicity radially migrates on a normal fault at a fluid diffusion velocity 125 m day however this migration occurs intermittently with periods of fast expansion 2 to 10 km day during short seismic bursts alternating with quiescent periods moreover the growing phases of the swarm illuminates a high number of repeaters the swarm migration is likely the results of a combination of multiple driving processes fluid up flow in the fault may induce aseismic slip episodes separated by phases of fluid pressure build up the stress perturbation due to aseismic slip may activate small asperities that produce bursts of seismicity during the most intense phase of the swarm

sedimentation of particulate organic carbon on the amundsen shelf antarctica abstract we examined the recent history of sedimentary organic carbon soc accumulation on the western amundsen shelf to help characterize the biological carbon pump in the amundsen sea antarctica vertical sedimentary profiles in the upper 21 cm of soc content radio and stable carbon isotopes were obtained at four locations in the western amundsen sea near the shelf break inside the polynya near the dotson ice shelf and at both the periphery and the center of the amundsen sea polynya profiles were representative not only of various distances from the coast but also of various summertime sea ice conditions and bottom depths the soc content up to 1 1 and the radiocarbon content were distinctly higher at the periphery and at the center of the polynya than at the other sites the soc and 14c contents were generally consistent with the spatial distribution of primary productivity in the surface water a linear soc accumulation rate of about 1 0 g c m 2 yr 1 was determined from the conventional 14c ages of bulk soc below the surface mixed layer at the periphery and at the center of the polynya for the time period of 3 1 4 7 kyr before present bp this linear soc accumulation rate was about 20 times greater than the rates determined at the two other sites for the period of 4 6 15 7 kyr bp note that all values are for uncorrected 14c ages at the center of the polynya a sudden change in soc accumulation rate was observed at about 16 cm depth corresponding to 4 7 kyr bp implying that changes during this time period in physical environments greatly affected primary production soc burial and or supply of allochthonous particles to this site the vertical distribution of 14c content in the sediments implies that aged organic matter likely associated with resuspended sediments was also being deposited inside the polynya in addition to autochthonous biogenic particles if our estimation of soc accumulation is extrapolated to the western amundsen shelf between 110 w and 120 w approximately 3 1010 g c yr 1 is buried on the shelf with 90 of soc accumulation occurring in the amundsen sea polynya

near bottom particle flux in the abyssal northeast atlantic during a 17 month study at a site on the porcupine abyssal plain of the northeast atlantic approx 48 n 20 w the downward flux of particulate material within and above the benthic nepheloid layer bnl was measured using sediment traps 1455 m above bottom mab 3100 m depth and 90 mab 4465 m depth flux at 90 mab is usually higher than the primary flux at 3100 m depth and this enhancement is especially pronounced during the winter the additional material found in the near bottom trap comprises recently deposited resuspended material rebound flux but with an admixture of refractory sediment it is unlikely that scavenging of either bnl particles or dissolved material contributes greatly to the near bottom flux fluxes of metal tracers 232th and al and cyanobacteria into traps were used to examine the process of resuspension the ratio of tracer flux at 90 mab to that at 3100 m depth was taken as a measure of the strength of the resuspension process the resuspension factor rf and reflects clearly the enhanced resuspension in winter this seasonal variation appears to be related to both the magnitude of near bottom currents and to the wave height at the surface 40 days before it is also possible that recently deposited material forms a partly cohesive blanket on the sediment surface that restricts resuspension to the benthic boundary layer

no depth limit to hydrovolcanic limu o pele analysis of limu from lō ihi seamount hawai i deep sea limu o pele are shards of basaltic glass commonly described as bubble walls when first identified they were inferred to form in submarine fire fountains but were then reinterpreted as the products of hydrovolcanic volcanism formed when submarine lava flows entrapped and vaporised seawater limu discovered below the c 3 km critical depth of seawater where superheated water exists as a supercritical fluid instead of a vapour led to the hydrovolcanic model of limu o pele formation being discarded in favour of a magmatic co2 driven strombolian like model this revised magmatic mechanism has been widely accepted by the scientific community we describe a newly discovered limu o pele rich deposit at 1 052 mbsl on the northeast summit plateau region of l ihi seamount hawai i the limu at this site is concentrated in a chemically monomict ash lens interbedded with thin lava sheets that are separated from overlying volcaniclastic material by a discontinuity the geometry and geochemistry of the deposit provide compelling evidence for a hydrovolcanic sheet flow related origin the exceptional abundance and preservation of limu at this site allows 4 morphologic subtypes of limu thin film plateau border convex film and pele s hair to be identified and linked to portions of the isolated rupturing bubbles from which they are derived we extend our discussion to beyond this new l ihi deposit by including a review of limu o pele occurrences and thermodynamic considerations that demonstrate the hydrovolcanic model of limu formation to be more tenable than the magmatic model at all depths including below the critical depth of seawater

hydrothermal deposition on the juan de fuca ridge over multiple glacial interglacial cycles abstract hydrothermal systems play an important role in modern marine chemistry but little is known about how they may have varied on 100 000 year timescales here we present high resolution records of non lithogenic metal fluxes within sediment cores covering the last 500 000 years of hydrothermal deposition on the flanks of the juan de fuca ridge six adjacent gridded cores were analyzed by x ray fluorescence for fe mn and cu concentrations corrected for lithogenic inputs with ti and normalized to excess initial 230 th to generate non lithogenic metal flux records that provide the longest orbitally resolved reconstructions of hydrothermal activity currently available fe fluxes vary with global sea level over the last two glacial cycles suggesting higher hydrothermal deposition during interglacial periods the observed negative relationship between fe and mn indicates variable sediment redox conditions and diagenetic remobilization of sedimentary mn over time thus mn fluxes may not be a reliable indicator for hydrothermal activity in the juan de fuca ridge sediment cores cu fluxes show substantial high frequency variability that may be linked to changes in vent temperature related to increased magmatic production during glacial periods deglacial hydrothermal peaks on the juan de fuca ridge are consistent with previously published records from the mid atlantic ridge and the east pacific rise moreover on the juan de fuca ridge the deglacial peaks in hydrothermal activity are followed by relatively high hydrothermal fluxes throughout the ensuing interglacial periods relative to the previous glacial period

accumulation rates of volcaniclastic deposits on loihi seamount hawaii ams radiocarbon age dating of planktonic foraminifera in volcaniclastic deposits on loihi seamount yields ages ranging from 590 years before present y bp at 10 cm depth to 5 880 y bp at 1 007 cm depth in an 11 m thick section exposed along inward facing caldera bounding faults on the eastern side of loihi s summit the accumulation rate of the deposit was about 0 37 cm y from 5 880 to 3 300 y bp and it consisted of subequal amounts of alkalic and tholeiitic fragments the rate slowed dramatically at about 3 300 y bp to an average 0 04 cm y and the particles that have accumulated since consist mostly of alkalic glass fragments the decrease in accumulation rate could indicate a decrease in volcanic activity at loihi beginning about 3 300 y bp this lower level of activity appears to be continuing today

anomalous pacific antarctic ridge volcanism precedes glacial termination 2 we present results from a well dated sediment core on the pacific antarctic ridge par that document a 15 cm thick layer of basaltic ash shards that precedes the penultimate deglaciation termination 2 the glasses have morb composition consistent with an axial source and their morphologies are typical of pyroclastic deposits created by submarine volcanism the ash layer was deposited 7 km from the par axis a distance that implies buoyant plumes lofted debris high into the water column with subsequent fallout to the core location we infer plume rise height using grain settling velocities the water depth at the core site and deep ocean current speeds from argo floats rise heights of 1 5 km or less require unrealistically large current speeds to transport grains to the core site instead the data are consistent with a plume rise height of at least 2 km implying that t2 was an interval of anomalous volcanism along this segment of the par the timing and duration of the ash deposit is consistent with glacial interglacial modulation of ridge magmatism volcaniclastic records from additional locations will be necessary to assess whether the par record is a rare find or it is representative of mid ocean ridge volcanism during glacial terminations