lower miocene to present stratigraphy of the equatorial pacific sediment bulge and carbonate dissolution anomalies 1 the bulge is a 600 m thick regional deposit of pelagic sediment accumulated around the equator its stratigraphy reflects a number of factors how accumulation rates have varied over time how accumulation has been spatially focused around the equator how much carbonate dissolution and reworking or nondeposition by bottom currents have occurred and how much the deposits have been translated northward by motion of the pacific tectonic plate on which they have accumulated in order to fully explore the effects of these processes a spatially continuous stratigraphic database is desirable as existing cores provide information at only discrete points and they tend to be sited in locally thicker accumulations we illustrate the utility of seismic data tied to drill cores by comparing the carbonate dissolution effect in two north south lines crossing the sediment bulge bathymetry over our easterly seismic line deepens relatively little going north whereas our westerly line deepens by 750 m from 4 n to 7 n at a common latitude the primary pelagic input to both these lines will have been similar so the difference of their sediment mass should reflect mostly their relative carbonate loss due to dissolution we use this fact to calculate the slope of the carbonate dissolution curve and find a remarkably small slope little relative carbonate dissolution compared to that expected from previous studies the techniques here may suggest a possible way forward for studying the equatorial carbonate stratigraphy more generally

temporal variability in currents and the benthic boundary layer at an abyssal station off central california abstract current meter records from seven sequential moorings were collected during 1993 1996 at an abyssal station off central california sta m 4100 m depth the entire 2 1 4 yr time series of the flow at 600 50 and 2 5 m above bottom above near the top of and within the benthic boundary layer were analyzed for mean flow statistics and subtidal and tidal variability the mean current vectors at each altitude were southward at profiles of light transmission and potential temperature collected intermittently during the 2 1 4 yr period showed that the benthic mixed layer at sta m extended on average 40 m above bottom range 15 80 mab evidence for local resuspension of recently deposited detritus came from time lapse photographs of the sea floor that showed a period of near bottom turbidity that corresponded to a period of high near bottom flow however rough estimates of friction velocity indicated that the bed stress usually was too low at sta m to cause local resuspension of sediments we hypothesize that the observed benthic mixed layers contained suspended particles advected from more energetic areas to the north of sta m

erosional troughs in deep sea carbonates and their relationship to basement structure abstract a detailed survey of a small area in the eastern equatorial pacific with the marine physical laboratory s deep tow instrument package reveals erosionally excavated troughs in an area of relatively rapid accumulation of carbonate the troughs lie on top of a basement high implying a relationship between the troughs and the basement feature differential accumulation and compaction may explain the origin of the troughs sediment deposited around the basement high preferentially accumulates on gentle slopes and in troughs this results in a thick sequence of sediment on the flanks of the basement high and a thin sequence above on top of the hill unstable sediment masses and differential compaction generate a tensile stress field above the peak of the basement high which causes slumping and faulting the steep slopes generated by faulting and slumping may then serve to intensify tidal currents or act as spillways and locally generate increased turbulence this increased turbulence results in local erosion by dissolution a trough will form above a basement high however only when a combination of 1 basement steepness 2 high sedimentation rate 3 sediment thickness and 4 sediment erodibility are present

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

resuspension measured with sediment traps in a high energy environment the near bottom sedimentation rates were measured by placing cylindrical sediment traps 10 m above the sea floor on each of six moorings deployed between 4100 and 5100 m along a transect across an energetic deep sea current in the hebble area centered at 40 n 63 w on the nova scotian rise sedimentation rates above the sea floor were monitored with additional traps at 23 54 100 200 and 500 m above the bottom mab on the mooring at 4950 m the total flux at 500 mab for the two week period consisting mostly of primary particles from surface water was 166 mg m2 day and increased exponentially towards the bottom the total flux at 10 mab increased down slope from 1160 mg m2 day at 4158 m where the mean current speed was 8 cm s to a maximum of 77 300 mg m2 day at 5022 m where the mean current speed was 32 cm s then decreased to 59 400 mg m2 day at the mooring at 5076 m the size frequency distributions of large discrete particles such as foraminifera diatoms radiolarians and fecal pellets were quantified in all trap samples to examine whether the large variation in fluxes was due to artifacts such as current velocity or trap tilt based on the source persistence and distribution of these particles we conclude that the large variations in fluxes across the rise and with distance from the sea floor are due primarily to resuspension and resettling of bottom sediments with tilt and current effects on trapping having only a secondary effect the vertical gradients of large particle fluxes suggest effective vertical eddy diffusivities of 102 104 cm2 s using a two dimensional model horizontal advection and secondary circulation probably play a large role in moving large rapidly falling up to 1 cm s particles to a height of 50 100 m above the sea floor

deep sea fluid and sediment dynamics influence of hill to seamount scale seafloor topography abstract deep sea sediments play a central role in a wide range of subject areas a number of important controls on the formation of sedimentary deposits have been studied however to date the impact of submarine landscape geometry as a possible control has received comparatively little attention this seems to be particularly true for intermediate scale topographic features such as abyssal hills knolls and seamounts that can be found in many regions of the global seafloor recent estimates suggest that in the deep open oceans away from continental margins there might be as many as 25 106 abyssal hills knolls and seamounts despite this large number very little is known about how they influence environmental complexity and patchiness biogeochemical fluxes and the formation of sedimentary records this paper reviews the currently known types of fluid flow interactions with abyssal hills knolls and seamounts that could potentially influence the way sediments are formed the main types of relevant flow components are quasi steady to eddying background flow internal lee and near inertial waves barotropic and baroclinic tides and seamount trapped waves previous studies looking into systematic links between fluid dynamics and sediments at hills knolls and seamounts are reviewed finally a case study is presented which aims to combine our current knowledge and investigate whether a given combination of recent fluid flow components leaves a detectable imprint in the recent sediments on and around a short seamount the main conclusions and implications are as follows 1 topographically generated flow field geometries that are composed of a number of different prevailing fluid flow components can be reflected and detected in properties of the underlying sediments 2 tidal and other higher frequency lee wave near inertial components of deep ocean currents can be essential for locally driving total current velocities across threshold values for non deposition erosion resuspension of freshly deposited deep sea sediments moreover there is evidence suggesting that not only maximum current speeds but also intensities of higher frequency tidal and or near inertial current direction variability might control sediment dynamics and sediment formation this relativises the view that current speed is the main or even only controlling factor for sediment dynamics and sediment formation 3 when it comes to the reconstruction of paleo flows these findings imply that certain sedimentary records may well reveal more about variability in the higher frequency flow components than about variability in the basin scale net flow component that often is the focus of paleoceanographic studies 4 single core paleo records from hill seamount or similarly controlled sediment deposits may be biased due to the asymmetry of flow fields around these topographic features to arrive at unbiased paleo records for non fluid dynamic parameters the influence of the flow field geometry would have to be removed from the record first 5 it seems the mechanistic understanding of hill and seamount related flow topography interactions and their links to sediment dynamics is approaching a level that may a facilitate improved interpretation of topographically controlled sedimentary paleo records b help fill in the knowledge gap that exists for functional deep sea biodiversity at intermediate space scales and c improve predictive capabilities for exploration of economically relevant iron manganese fe mn crusts on seamounts

crystal chemistry of trioctahedral micas in alkaline and subalkaline volcanic rocks a case study from mt sassetto tolfa district latium central italy this work provides a crystal chemical description of trioctahedral micas from volcanic rocks lavas tuffs ignimbrites and xenoliths outcropping at mt sassetto tolfa district tuscan province central italy mica crystals vary in composition from ferroan phlogopite to magnesian annite heterovalent octahedral substitutions are mainly related to al 3 ti 4 and only in a few samples to fe 3 the two main mechanisms regulating ti inlet into the mica structure are the ti oxy vi ti 4 vi mg fe 2 1 oh 2o2 2 and ti vacancy vi ti 4 vi vi mg fe 2 2 substitutions in these micas ti content is the predominant crystal chemical parameter and signi cantly affects octahedral and interlayer topology as well micas with the highest ti contents deviate from the expected fractional crystallization trend in the ti vs mg mg fetot diagram possibly as a consequence of a variation in intensive parameters t p fh2 fo2 fh2o during crystallization in the magmatic chamber in micas with signi cant fe 3

fluctuations of beam attenuation coefficient in the lowest 2 m on the continental rise off nova scotia abstract two sets of time series observations of the light beam attenuation coefficient at 0 5 1 0 and 2 0 m above the bottom were made from a tripod on the nova scotia rise the three transmissometers sampled once every 16 s and operated for approximately three days beginning september 27 and five days beginning october 2 1980 temporal variations consisted of slowly varying components superimposed with occasional bursts of highly turbid waters semidiurnal periodicity prevailed in the september mooring the rapidly varying components showed larger vertical gradients than the slowly varying components suggesting that the rapid fluctuations are local resuspension events the magnitude of high frequency fluctuations and vertical gradients also contained semidiurnal periodicity spectral analysis of fluctuations of beam attenuation coefficients indicate that higher energy densities tend to be associated with the lower level 0 5 m than the higher levels 1 0 and 2 0 m semidiurnal periodicity was not apparent in the october mooring vertical gradients between 0 5 and 1 0 m above the bottom during the october mooring contained semidiurnal periodicity but not in the layer between 1 0 and 2 0 m above the bottom power spectra of the vertical gradients indicate that fluctuations are more uniform in the vertical over the frequencies lower than the semidiurnal frequency and less uniform more variable over the frequencies higher than the semidiurnal frequency

ultrahigh pressure minerals and metamorphic terranes the view from china abstract ultrahigh pressure uhp metamorphism refers to mineralogical modifications of continental and oceanic crustal protoliths associated mafic ultramafic rocks initially formed or emplaced in shallow levels of the lithosphere but which subsequently have experienced p t conditions within or above the coesite stability field 2 7 gpa 700 c typical products include eclogite garnet peridotite and uhp varieties of metapelite quartzite marble paragneiss and orthogneiss uhp metamorphic assemblages require relatively cold lithospheric subduction to mantle depths some recrystallization even occurs under forbidden p t conditions characterized by a geotherm of the current explosion of research on continental uhp terranes reflects their significance for mantle dynamics and the tectonics of continental subduction collision exhumation mantle slab interactions and geochemical recycling a further characterization of uhp phases and positive identification of uhp minerals requires new experimental studies coupled with state of the art analyses for example the very rare occurrence of microdiamond inclusions in zircons from dabie sulu uhp rocks may reflect high f o 2 attending recrystallization inasmuch as epidote is rather common rutile needles within garnets from sulu uhp eclogitic rocks may not be the result of exsolution so in such cases the apparent uhp pressure may have been over estimated hadean igneous microdiamond inclusions in jack hills detrital zircons could have originated from mantle xenoliths whereas abundant detrital phanerozoic diamonds containing inclusions of coesite and other eclogitic minerals from new south wales might have been derived from unexposed uhp metamorphic terranes micro mineral intergrowth and nano size minerals may hold important key to deciphering the actual p t paths of subduction and mantle return flow although most exhumed terranes have returned surfaceward relatively rapidly after short time of uhp condition the long duration of storage at great depth and slow exhumation for the largest uhp terranes remain as major problems

turbidity of waters over the northwest iberian continental margin in omex ii ii 9 cruises gathered optical data principally by transmissometer the distribution of optical turbidity caused by concentration of particulate matter pmc in the water column over the northern iberianmargin shows several features related to hydrography it is concluded that a signal of pmc seen in mediterranean water mw found north of 42 n is not carried from its source at the gibraltar sill and gulf of cadiz because it is shown using intermediate stations that this turbid plume decays mainly by fall out but also partly by mixing to very low levels around southern portugal pmc maxima sometimes seen in mw on the northern iberianmargin are thus most likely to result from intermittent local resuspension by mw interacting with slope sediments the highest turbidity is found over the upper slope and is the result of i shelf edge resuspension and off shelf flow of turbid plumes mainly between 100 and 300 m depth and ii resuspension under the slope current aided by internal waves in the depth range 500 800 m where the density gradient between enacw and mw is maximal below the mw flows are generally slow and turbidity is low the bottom nepheloid layer in deep water is also weak with pmc values 100 mg m 3 the focus of resuspension activity on the upper slope means that the region is an efficient exporter to the ocean of sediment that either escapes from the shelf or sinks to the bed from surface production this accounts for upper slope sediments recorded in other studies as sandy or in places as rocky bottom

an analysis of the optical features of the near bottom and bottom nepheloid layers in the area of the scotian rise profiles of light transmission versus depth have been studied in the region of the scotian rise of the north atlantic at bottom depths between 4900 and 5000 m a component model has been developed and consists of three components of transmission which can be combined to duplicate accurately any given transmission profile two of the components are shown to be representative of several basic phenomena the particle concentration within a uniform flow and the separation of a benthic nepheloid layer in the case of a uniform flow it is the relative magnitudes of settling and eddy diffusion which determine the shape of the transmission profile separation of the benthic nepheloid layer was inferred to be caused by an occasional cross slope velocity component the physical interpretation of the third component was ambiguous eulerian and lagrangian transformations of the data show that benthic storms that were detected at one location and time appeared nearly identical at a later time downstream and that benthic storms can be detected over a large distance distance and time scales obtained from these transformations show the area of the scotian rise to be one characterized by bottom storms which keep their general form over periods of at least 2 weeks and for distances traveled of at least 400 km

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

particle fluxes induced by benthic storms during the 2012 dense shelf water cascading and open sea convection period in the northwestern mediterranean basin abstract the effects of deep dense shelf water cascading and open sea convection on the sediment dynamics of the northwestern mediterranean basin were studied by near bottom moored instruments recording trapped particle fluxes suspended particle fluxes water properties and hydrodynamics from november 2011 to july 2012 during this period near bottom currents induced by winter dense water formation generated benthic storms that caused resuspension at 2450 m water depth increasing by more than one order of magnitude the ambient suspended sediment concentrations the trapped particle fluxes and the suspended sediment fluxes during the preconditioning phase of the open sea convection from december 2011 to mid february 2012 currents 1 10 cm s 1 suspended sediment concentrations

deep sea epibenthic echinoderms and a temporally varying food supply results from a one year time series in the n e pacific abundance and distribution of epibenthic echinoderms and detrital material at an abyssal site 4100 m in the n e pacific were examined between june 1994 and june 1995 camera sled surveys time lapse photographs and observations from the submersible alvin revealed a sequence of detrital deposition events detrital aggregates were present in summer and fall of 1994 but rare in winter and spring 1995 a layer of white flocculent material covered the sea floor from july through november 1994 constituting the first direct observations of a detrital carpet in this area large radiolarian patches also were observed from august 1994 through february 1995 distribution and abundance of echinoderm species were estimated from camera sled surveys and showed few consistent temporal patterns abundance varied spatially and distributions generally could not be distinguished from random in contrast to the clumped pattern observed for detrital aggregates statistically the spatial distributions of several echinoderm species correlated significantly with the distributions of detrital aggregates but these correlations were not consistent across transects or taxa the lack of consistent correlation between echinoderm distribution and abundance and the presence of aggregate material is not surprising when the long duration of extensive detrital coverage of the sea floor is considered

coupling of near bottom pelagic and benthic processes at abyssal depths in the eastern north pacific ocean a time series site was established in the eastern north pacific ocean to study the coupling between near bottom pelagic and benthic processes at abyssal depths in an area with well documented seasonality in surface water productivity particulate total mass ptm particulate organic c poc particulate total n ptn and particulate calcium carbonate p caco fluxes were measured from sediment trap collections at 600 and 50 m above bottom from february 1990 to october 199 1 606 d the sea floor at 4 100 m was concurrently monitored with a time lapse camera over a 386 d period from july 1990 to july 199 1 during this study in situ measurements of sediment community oxygen consumption scoc were made and surface sediment samples collected seasonally with a free vehicle grab respirometer ptm poc ptn and p cac0 fluxes exhibited a strong seasonal signal with episodic peaks from spring through fall and lows in winter scoc increased sharply between winter and summer coinciding with spring peaks in particulate fluxes detrital aggregates appeared on the sea floor in pulses over a 6 month period from july to december 1990 coinciding with periods when particulate fluxes were elevated but delayed 1 5 months after the initial peaks in particulate flux mobile epibenthic megafauna monitored with time lapse photography consisted primarily of holothuroids and echinoids and were twice as active when detrital aggregates were observed on the sea floor as during the rest of the year our results show a temporal relationship between the flux of particulate matter entering the benthic boundary layer the arrival and residence of detritus on the sea floor and the activity of the sediment community and mobile epibenthic megafauna

element accumulation rates in and growth histories of manganese nodules from the southwestern pacific basin abstract accretion rates and element accumulation rates of seven manganese nodules collected from the southwestern pacific basin during r v sonne cruise so 14 on a tahiti east pacific rise new zealand transect have been determined the accretion rates of the nodules lie in the range 3 5 6 0 mm 10 6 yr the highest rates correspond to areas with higher biogenic silica contents in the sediment suggesting a higher diagenetic contribution to the nodules in one nodule 143gb dated with 10 be nodule growth began at about 14 5 ma there is a change in structure of the nodule at 6 ma and concentric layers filled with detritus occur at 3 2 ma and 1 3 ma there is also a major change in the flux rates of the elements at the 6 ma time marker with the authigenic elements mn cu and ni showing greater accumulation rates in the outer zone and the detrital fraction al showing a greater accumulation rate in the inner zone the variations in the element accumulation rates probably reflect a change of abyssal circulation pattern at 6 2 ma however the precise nature of this change remains a matter for speculation

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

characterization of deep sea storms abstract to describe and quantify the physical forcing of sediment transport events at the hebble site velocity stress and sediment concentration data were obtained during a year long deployment through the year a variety of intense sediment transporting events were recorded careful analysis of these events reveals that only a small proportion of the peaks in suspended sediment concentration correspond to local erosion most sediment events were clouds of fine suspended material advected into the region analysis of progressive vector diagrams reveal that these advected clouds were bounded by regions with concentration gradients as high as 200 g 1 1 km 1 the high gradients suggest streams of sediment bearing water with sharp fronts of sediment concentration along their sidewalls were veering across the region the largest concentrations of suspended sediment were observed during local suspension events the growth and decay of the sediment clouds during the local events did not exactly track the boundary shear stress rapid erosion occurred as the stress exceeded a critical shear stress maximum suspended concentrations occurred shortly after erosion began indicating a source limited erosion process the depositional period lasted for several weeks whereas the erosion occurred in only a few days photographs of the bottom reveal depositional features crag and tail dunes which are aligned with the post storm flow not the erosional flow direction

hydrothermal pits in the biogenic sediments of the equatorial pacific ocean 1 a recent expedition to the equatorial pacific surveyed over 60 000 km2 of seafloor using swath map imaging and high resolution seismic profiling this survey revealed the common occurrence of large pits in the biogenic sediments that are usually associated with basement highs the pits range in size up to a few kilometers across and are on the order of 50 m 100 m deep they were found on seafloor ranging in age from 15 ma to 55 ma with overlying sediment cover up to 500 m thick we link their origin with hydrothermal discharge through conduits created by differential compaction and fracturing over basement highs and by basement faulting that penetrates the overlying sediments although carbonate dissolution is likely to be associated with the formation of the pits their occurrence shows no consistent relationship with the present calcite compensation depth ccd

phase relations of peridotites under h2o saturated conditions and ability of subducting plates for transportation of h2o phase relations of peridotites under h2o saturated conditions up to 28 gpa and 2600 c have been clarified based on the high pressure experimental results in the mgo feo sio2 h2o mgo sio2 al2o3 h2o cao mgo al2o3 sio2 h2o and natural systems based on the phase assemblages deduced and the chemical compositions of the phases the maximum h2o contents for two bulk rock compositions lherzolite and harzburgite have been calculated using mass balance then the potential ability of subducting plates for transportation of h2o is discussed by simple models combining the phase relations and the thermal structures of subduction zones as a function of the age of subducting plate a 15 130 ma the subduction velocity u0 2 25 18 cm year and angle 30 and 60 and the mantle potential temperature tp 1300 and 1350 c the results confirm the importance of choke point a cusp around 6 2 gpa and 550 c at which the stability field of major hydrous phases is minimized in terms of temperature although the choke point is exceeded by the mg sursassite bearing assemblage that has the maximum h2o content of 0 4 0 7 wt around 5 7 gpa and 550 700 c if the geotherm of the coldest part across the subducting plate passes below the choke point maximum 4 6 wt h2o can subduct whereas h2o less than 0 4 0 7 wt can subduct above the choke point the critical conditions are clarified as follows if 30 and tp 1300 c a 15 ma with u0 9 cm year or a 30 ma with u0 2 25 cm year is the critical condition if 60 and tp 1300 c or 30 and tp 1350 c the critical conditions slightly shift to an older age or a greater velocity e g a 30 ma with u0 3 5 cm year the slab thermal parameter au0sin is useful to predict roughly the critical condition however within the younger plate the spatial extent of a cold region with major hydrous phases is thinner hence less h2o is subducted even with the same slab thermal parameter this indicates that the age of the plate and the subduction velocity act differently on the h2o transportation ability of subducting plates

western north atlantic evidence for millennial scale changes in ocean circulation and climate two late quaternary series of high resolution percent carbonate data from western north atlantic sediment drifts bermuda rise and bahama outer ridge show millennial scale oscillations superimposed on the familiar longer period oscillations of orbital origin the dominant high frequency oscillation in these records has a quasi period of about 4000 years these percent caco3 changes most likely result from the influence of climate change on the flux of terrigenous material from eastern canada the resuspension of continental margin sediment by deep eddy kinetic energy and carbonate dissolution sediment is transported to the bermuda rise by deep recirculating gyres and to the bahama outer ridge by the deep western boundary current system stable isotope results on foraminifera across several of these oscillations from interstadial climate conditions and from a glacial inception display variability similar to that of percent caco3 oxygen isotope ratios of planktonic foraminifera suggest large variations in near surface temperature and or salinity and carbon isotope ratios of benthic foraminifera indicate that there were significant oscillations in the flux of north atlantic deep water nadw these data support models which couple surface ocean conditions in the north atlantic production of nadw north atlantic heat flux and evidence for temperature oscillations in ice cores

stability of phase a in antigorite serpentine composition determined by in situ x ray pressure observations abstract here we precisely determined the low pressure stability limit of phase a in the mg end member antigorite bulk composition defined as the reaction forsterite water phase a enstatite water line or water storage line in a multi anvil apparatus pressures were determined by in situ synchrotron x ray diffraction measurements using nacl as an internal pressure standard results demonstrate that the water line is located at 800 c and 8 5 gpa and at 550 c and 5 1 gpa with a clapeyron slope of 13 6 mpa c we also examined the conditions for the formation of phase a by the decomposition of antigorite on the basis of the phase relations in the systems mgo sio 2 h 2 o msh and mgo al 2 o 3 sio 2 h 2 o mash a descending slab peridotite retains water in phase a beyond the stability of antigorite only when temperature in the slab is lower than 550 or 660 c at 5 1 gpa corresponding to 160 km depth in the system msh or mash respectively the double seismic planes observed within the slabs may be caused by the dehydration reaction of antigorite or chlorite their merging depths which could represent the high pressure stability limit of antigorite or chlorite are 160 km or deeper beneath northeast japan aleutian kamchatka and kuril water included in hydrous slab peridotite is transported into the transition zone and deeper mantle in these areas but recycled to the surface in other subduction zones

the high pressure stability of mg sursassite in a model hydrous peridotite a possible mechanism for the deep subduction of significant volumes of h2o the stability of the high pressure phase mg sursassite previously mgmgal pumpellyite in ultramafic compositions has been determined in experiments in the system mgo al2o3 sio2 h2o mash the breakdown of mg sursassite forsterite enstatite to pyrope vapour with increasing temperature was bracketed at 6 0 and 7 0 gpa below 6 0 gpa mg sursassite forsterite vapour reacts to chlorite enstatite this reaction provides a mechanism for transfer of water from chlorite to mg sursassite bearing assemblages at pressures of 7 0 gpa and above the assemblage mg sursassite phase a enstatite was found phase relations involving mg sursassite and phase a are considered for bulk compositions with a low water content the vapour absent reaction mg sursassite forsterite pyrope phase a enstatite determines the upper pressure stability of mg sursassite and provides a mechanism for the complete transfer of water from mg sursassite to phase a bearing assemblages mg sursassite plays an important role in peridotite compositions in the subducting slab because at temperatures below 700 c it can transfer water from hydrous phases such as antigorite and chlorite to high pressure stable phases such as phase a

faulting in madeira abyssal plain sediments abstract interpretation of high resolution seismic data revealed the occurrence of faults in the sediments of two north atlantic abyssal plain environments the madeira abyssal plain map and the nares abyssal plain nap most of the data are from the map where faulting appears to be confined to particular locations from our data individual faults cannot be traced from one seismic section to another a positive correlation exists between the concentration of faults and the maximum sediment thickness although the mechanism that caused the faulting is still not understood the faults apparently are related to processes which have been active for a long period of time

fluorine partitioning between humite group minerals and aqueous fluids implications for volatile storage in the upper mantle phase equilibrium experiments were performed in the mgo sio2 h2o system along with fluorine msh f at conditions between 800 1000 c and 2 0 2 5 gpa to constrain the solubility of fluorine in humite group minerals and to determine fluorine partitioning between humite group minerals and aqueous fluid fluorine solubility in humite group minerals ranges between 1 and 11 wt f and is dependent on the salinity of the fluid 0 2 3 5 wt f indicating that humite group minerals have exceedingly high saturation limits for f and that a full solid solution between f and oh is possible within the crystal structure raman spectroscopy reveals the preferential ordering of f promoting the formation of a stable oh f bond mineral fluid partition coefficients are always greater than unity with average coefficients of d f clinohumite fluid 3 d f humite fluid 2 d f chondrodite fluid 4 and d f norbergite fluid 4 partition coefficients are independent of pressure or temperature but decrease with increasing fluid salinity fluorine is therefore highly soluble and compatible within this group of ultramafic mantle minerals high solubility and mineral fluid partition coefficients together with wide stability fields in pressure and temperature space demonstrate that humite group minerals are potential storage sites for f and by extension h2o during subduction upon the breakdown of less stable hydrous and or fluorine rich phases during lower grades of subduction zone metamorphism fluorine may redistribute into phases such as humite group minerals and be transported beyond the volcanic arc and to the upper mantle

non stoichiometry deformation and high pressure properties of the humite group of minerals in the marbles of the kerala khondalite belt india

optics particles stratification and storms on the new england continental shelf in situ beam attenuation and chlorophyll fluorescence were correlated with concentration and bulk composition of particles in shelf waters during summer and spring under different physical forcing conditions to determine if optical parameters could be used as an additional tracer in examining the process of mixing in shelf waters time series measurements were made for two 18 day periods during high stratification late summer 1996 t 3 0 kg m 3 surface to bottom and low but rapidly developing stratification spring 1997 t 0 05 to 0 5 kg m 3 in 70 m of water in a midshelf environment south of martha s vineyard massachusetts when defined by hydrography and optical profiles four layers were identified during the summer the surface mixed layer the particle chlorophyll maximum the midwater particle minimum and the bottom nepheloid layer fast moving solitons perturbed the water column briefly but no storms perturbed the system until large surface swells from hurricane edouard intensified and thickened the nepheloid layer bulk composition and optics of particles in and above the nepheloid layer were distinctly different after the passage of hurricane edouard the hurricane passage demonstrated that intense atmospheric forcing greatly influences both hydrographic and optical properties in the entire water column even when highly stratified t 3 0 kg m 3 decreasing to 0 8 kg m 3 post hurricane and causes massive resuspension due initially to wave shear stress that was later dominated by current shear restratification progressed rapidly after the hurricane passed during spring the water column started as a weakly stratified two layer system hydrographically and optically but evolved into three layers as stratification developed strong spring storms affected both surface and bottom layers but with decreasing impact as the water column stratified

formation of hydrothermal pits and the role of seamounts in the guatemala basin equatorial east pacific from heat flow seismic and core studies we acquired seismic and heat flow data and collected sediment cores in three areas in the guatemala basin cocos plate eastern pacific to investigate the process by which depressions pits in the sedimentary cover on young oceanic crust were formed median heat flow of 55 mw m2 for the three areas is about half of the expected conductive cooling value the heat deficit is caused by massive recharge of cold seawater into the upper crust through seamounts which is inferred from depressed heat flow in the vicinity of seamounts heat flow inside of pits is always elevated in some cases up to three times max 300 mw m2 relative to background none of the geochemical pore water profiles from cores inside and outside of the pits show any evidence of active fluid flow inside the pits all three areas originated within the high productivity equatorial zone and moved northwest over the past 15 to 18 ma pits found in the working areas are likely dissolution structures formed by diffuse hydrothermal venting in a zone of high biogenic carbonate production which were sealed when they moved north it is likely that these pits were discharge sites of hydrothermal siphons where recharging seamounts could feed cold seawater via the upper crust to several discharging pits probably pit density on the whole cocos plate is similar to the three working areas and which may explain the huge heat deficit of the cocos plate this article is protected by copyright all rights reserved

influence of sedimentation local and regional hydrothermal circulation and thermal rebound on measurements of seafloor heat flux 1 we quantify the influence of environmental processes on measurements of seafloor heat flux with a new one dimensional thermal model that includes time varying sedimentation and boundary conditions represents several scales of hydrothermal and transient conductive processes within basement and allows fluid seepage through accumulating sediments variations in basement thermal conductivity the extent of hydrothermal mixing in upper basement and fluid seepage through sediments each influence seafloor heat flux by 2 8 conductive thermal rebound following the cessation of advective heat loss from the crust may lower seafloor heat flux values by 5 10 even after several to several tens of million years the new models indicate that thermal rebound takes much longer than suggested by earlier analytical calculations mainly because earlier models did not account for the heat capacitance of the conductive lithosphere application of the new model to 3 5 3 6 ma seafloor on the eastern flank of the juan de fuca ridge suggests that anomalously low heat flux in this area is best explained by incomplete conductive thermal rebound in the last 100 200 ka following the burial of numerous basement outcrops application of the new model to the eastern flank of the east pacific rise and extrapolation out to the age of some of the oldest remaining seafloor indicate that sedimentation corrections may be important even where accumulation rates are typical of global values model results also suggest that conductive thermal rebound through thick sediments may bias measurements made on moderate to old seafloor even where there is little evidence at present for ridge flank hydrothermal circulation

biotite oxidation processes in ash flow tuffs mendoza argentina a mossbauer spectroscopy and chemical study abstract biotites and their alteration products muscovites and chlorites from six different cooling units of a dacitic to rhyodacitic ash flow tuff of early permian age yacimiento los reyunos formation mendoza argentina have been examined by means of mossbauer spectroscopy xrd and electron microprobe techniques four different types of layer silicate minerals were identified normal biotites oxybiotites muscovites and biotite chlorite oxybiotites were distinguished by means of mossbauer spectroscopy based on the presence of a fe3 doublet called des which is characteristic of biotites that were dehydroxilated under heat treatment in laboratory experiments and also on the very low fe 2 fe 3 ratios obtained fe3 is present only at the octahedral sites mossbauer spectroscopy data suggested that some of the muscovites originated from oxybiotites whereas biotite chlorite seem to have been altered from normal biotites the chemistry of layer silicate minerals showed that both the octahedral sites and the interlayer occupancy are deficient with respect to normal biotites oxybiotites are enriched in mg and k muscovites in si al and k and biotite chlorite in mg and al the fe fe mg ratio decreases in oxybiotites the rocks from which biotites and muscovites were extracted show oxidation ratios that correlate with those of the layer silicate minerals this trend was not observed for the biotite chlorite samples the presence of muscovites and biotite chlorite intergrowths are readily explained as due to hydrothermal alteration processes the fact that oxybiotites plot well above the haematite magnetite buffer curve in the fe2 fe3 mg diagram indicates a high fo2 value suggesting that they were formed during postmagmatic processes related to eruptive conditions rather than in the magma chamber the possible mechanisms for oxidizing biotites are discussed considering three different stages the presence of normal biotites only at the lowermost unit would indicate different eruptive conditions for this unit

sediment mixing in the tropical pacific and radiolarian stratigraphy 1 the reworking of older radiolarian microfossils into near surface sediments of the tropical pacific has long been the source of confusion for the development of radiolarian stratigraphy and of puzzlement over the mechanism s that could effect such pervasive reworking widespread dissolution pits in the sediments of the tropical pacific are believed to be associated with hydrothermal circulation cells in the older oceanic crust and are here linked to processes which expose older sections and inject older non carbonate material into near bottom waters discharging waters of these circulation cells tend to dissolve carbonate in near surface sediments thus only the non carbonate material including radiolarians is preserved and reworked into younger sediments results from the study of two sites in the tropical pacific indicate that reworked older stratigraphically important radiolarians are less than 2 of the total radiolarian assemblage this constitutes a minimum estimate of the amount of reworked non carbonate material in the younger sediments the oldest reworked radiolarians are no more than 10 m y younger than the underlying basement and radiolarians from the entire older section above that level can be found in the reworked material a time series of the flux of reworked material at one site is not constant but instead has varied by a factor of 3 to 4 over the past 2 5 m y during times when the flux of reworked material is particularly low the proportion of older more robust radiolarians is larger

abyssal currents and advection of resuspended sediment along the northeastern bermuda rise abstract an integrated study using current meters time series nephelometers and water samplers for measurements of particulate matter concentration revealed an intense nepheloid layer centered on the slopes of the eastward scarp the northeastern boundary of the bermuda rise these slopes also contained extensive furrows truncated seismic reflectors and wisconsin age and older surface sediments the abyssal circulation in this region appears to be accelerated when it encounters the steep topography of the eastward scarp eroding sediments creating the erosional furrows and moving eroded sediment upslope instruments on top of the bermuda rise recorded episodic events benthic storms where particle concentrations at 25 m above the bottom increased from a background level of 60 g 1 1 to maximum of 251 g 1 1 and current velocities were nearly 20 cm s 1 net transport of both water and entrained sediment was to the west northwest during the largest benthic storm water temperature decreased by 0 1 c consistent with a 300 600 m upslope transport of water and resuspended sediments from the upper slopes of the eastward scarp when currents carry resuspended sediment over the rim of the eastward scarp to the plateau region the current slows depositing its sediment load thus the plateau is growing upwards slowly at the expense of the surrounding scarps

global comparison of benthic nepheloid layers based on 52 years of nephelometer and transmissometer measurements abstract global maps of maximum bottom particle concentration benthic nepheloid layer thickness and integrated particle mass in benthic nepheloid layers bnl based on 2412 global profiles collected using the lamont thorndike nephelometer from 1964 to 1984 are compared with maps of those same properties compiled from 6392 global profiles measured by transmissometers from 1979 to 2016 outputs from both instruments were converted to particulate matter concentration pm the purposes of this paper are to compare global differences and similarities in the location and intensity of bnls measured with these two independent instruments over slightly overlapping decadal time periods to combine the data sets in order to expand the time scale of global in situ measurements of bnls and to gain insight about the factors creating sustaining bnls the similarity between general locations of high and low particle concentration bnls during the two time periods indicates that the driving forces of erosion and resuspension of bottom sediments are spatially persistent during recent decadal time spans though in areas of strong bnls intensity is highly episodic topography and well developed current systems play a role these maps will help to understand deep ocean sediment dynamics linkage with upper ocean dynamics the potential for scavenging of adsorption prone elements near the seafloor and provide a comprehensive comparison of these data sets on a global scale during both time periods bnls are weak or absent in most of the pacific indian and atlantic basins away from continental margins high surface eddy kinetic energy is associated with the kuroshio current east of japan both data sets show weak bnls south of the kuroshio but no transmissometer data have been collected beneath the kuroshio itself sparse nephelometer data show moderate bnls just north of the kuroshio extension but with much lower concentrations than beneath the gulf stream strong bnls are found in areas where eddy kinetic energy in overlying waters mean kinetic energy near bottom and energy dissipation within the bottom boundary layer are high areas of strongest bnls include the western north atlantic argentine basin south atlantic areas around south africa tied to the agulhas current region and somewhat random locations in the antarctic circumpolar current of the southern ocean

phytodetritus at the abyssal seafloor across 10 of latitude in the central equatorial pacific fresh phytoplankton detritus or phytodetritus has been reported from numerous deep seafloor sites in the temperate north atlantic and pacific oceans following seasonal phytoplankton blooms here we report the first strong evidence for abyssal accumulations of phytodetritus in the tropics in the central equatorial pacific in november december 1992 we obtained photographs and or sediment core samples from 61 abyssal stations water depths of 4280 5012 m between 12 s and 9 n along 140 w greenish flocculent material was recovered from the top of multiple core samples from 5 s to 5 n this material was most abundant from 2 s to 2 n in some areas forming continuous layers at least 5 mm thick and individual aggregates 1 cm in diameter the greenish material was clearly visible in bottom photographs as a green veneer that covered 95 of the seafloor near the equator and as individual cm scale aggregates covering 1 of the seafloor occasionally thick accumulations of cm scale aggregates occurred in biogenic pits cleared trails and feeding traces suggest that surface deposit feeding holothurians and echiurans grazed the greenish material microscopic examination of greenish material recovered from core tops and a burrow lumen revealed relatively intact diatoms including rhizosolenia sp and other microalgae with chloroplasts containing chlorophyll the greenish material was 1 12 5 organic carbon by weight i e 5 39 times richer than associated seafloor sediments it also contained high excess activities of 234th suggesting arrival from the water column in the previous 100 days samples of the greenish flocculent material from 0 and 5 n incubated at simulated environmental pressure and temperature with 14c labeled glutamate exhibited 5 fold higher rates of microbial activity than underlying sediments or brown floc from 9 n surface sediment samples which included the greenish flocculent material from 5 s to 5 n also contained significant concentrations of chlorophyll a and other chloropigments the chloropigment concentrations were roughly comparable to deep sea phytodetritus collected in the north atlantic we conclude that fresh organic rich phytodetritus was present on the seafloor from 5 s to 5 n along 140 w in november december 1992 with highest concentrations within 2 3 of the equator this material is likely to be a concentrated high quality food resource for deep sea microbes and metazoans we estimate an upper limit for the standing stock of this phytodetritus to be 2 6 mmol corg m2 this corresponds to 3 of the annual flux of organic carbon to the seafloor at these latitudes in 1992 because the degradation rate of this material appears to be very high its presence at the seafloor for several months per year could yield significant phytodetrital contributions to the annual seafloor organic carbon budget we also suggest that the phytodetrital aggregates are formed at intense convergence zones resulting from seasonal passage of tropical instability waves within 5 of the equator if so phytodetrital accumulations are likely to recur seasonally over broad areas of the abyssal equatorial pacific

an assessment of bottom current controlled sedimentation in pacific ocean abyssal environments the effect of the circulation of polar sourced dense waters on the deep seafloor is still largely unknown this paper presents multibeam bathymetric evidence for the existence of present day contourite drifts on the central pacific ocean at depths ranging between 4000 and 5000 m based on the identification of their diagnostic erosive moats linear moats furrows and abyssal sinuous channels and depositional plastered elongated separated and abyssal contourite fan drifts contourite morphological features these contourite drifts display a patchy distribution sculpted by the secondary flows of the lower circumpolar water lcpw and the north pacific deep waters npdw as well as local dynamics of the flow in the form of internal waves and bottom currents modulated by tides which are capable of accelerating the typically sluggish bottom currents and contribute to the erosion transport and deposition of sediments the formation of contourites is also predominantly controlled by the presence of large scale tectonic and volcanic features ridges seamounts and deep elongated valleys which affect the morphology and distribution of the basins and induce the acceleration of bottom currents overall this study allows to re assess the effects distribution and significance of bottom current controlled sedimentation in abyssal environments where examples of contourite features are still rather scarce in part because of the technical challenges and their remote location but also because the effect of bottom currents is not well known in the central oceanic basins and only capable of marginally affecting their sedimentological record

global assessment of benthic nepheloid layers and linkage with upper ocean dynamics abstract global maps of the maximum bottom concentration thickness and integrated particle mass in benthic nepheloid layers are published here to support collaborations to understand deep ocean sediment dynamics linkage with upper ocean dynamics and assessing the potential for scavenging of adsorption prone elements near the deep ocean seafloor mapping the intensity of benthic particle concentrations from natural oceanic processes also provides a baseline that will aid in quantifying the industrial impact of current and future deep sea mining benthic nepheloid layers have been mapped using 6 392 full depth profiles made during 64 cruises using our transmissometers mounted on ctds in multiple national international programs including woce save jgofs clivar repeat hydrography and go ship during the last four decades intense benthic nepheloid layers are found in areas where eddy kinetic energy in overlying waters mean kinetic energy 50 m above bottom mab and energy dissipation in the bottom boundary layer are near the highest values in the ocean areas of intense benthic nepheloid layers include the western north atlantic argentine basin in the south atlantic parts of the southern ocean and areas around south africa benthic nepheloid layers are weak or absent in most of the pacific indian and atlantic basins away from continental margins high surface eddy kinetic energy is associated with the kuroshio current east of japan data south of the kuroshio show weak nepheloid layers but no transmissometer data exist beneath the kuroshio a deficiency that should be remedied to increase understanding of eddy dynamics in un sampled and under sampled oceanic areas

particulate size spectra behavior and origin of nepheloid layers over the nova scotian continental rise 1 26 32 m measured by coulter counter on 10 cm 3 samples correlate linearly with light beam attenuation coefficient correlation between particle volume and weight concentration indicates lower apparent particle density for low concentration suspensions a feature that is attributed to aggregation during aging of the suspension particle size distributions show unimodal form with a peak at 4 m in high concentrations near the bed changing to a bimodal form with an additional mode at 16 m in low concentrations high above the bed 500 and 1000 m a b meters above bottom the presence of the coarse mode at 1000 m a b coupled with its increase in the lower 250 m of the water column suggests that it both settles from the surface and is resuspended from the bed ultrasonic disaggregation experiments show that much of the fine mode is of aggregates but the coarse mode is single solid particles distributions with a low volume concentration increase in volume when disaggregated and are interpreted as having a relatively large part of their total distribution in unmeasured sizes 32 m distributions with a high concentration decrease in counted volume on disaggregation inversions in the light attenuation profiles are taken to indicate the presence of former bottom mixed layers and their occurrence suggests thickening of the nepheloid layer by detachment and lateral injection of these turbid mixed layers they occur at levels sufficiently high as to provide a nepheloid layer over 1500 m thick over the adjacent sohm abyssal plain the coarse mode probably comprises solid particles with a calculated settling velocity of 12 m day its absolute concentration increases toward the bed but as a proportion of the distribution it increases upward it is thus thought to be particles of surface origin both settling to the bottom and in the lower 250 m of the water column resuspended from the bed the fine mode at 4 m has a spatially constant form thought to be controlled by physical coagulation mechanisms rates of coagulation estimated from shear mechanisms suggest that the postulated change of peaked into flat size distribution by particle aggregation and settling has a time scale of a few years rather than months which is probably long when compared with the lateral injection process lower in the nepheloid layer for that reason distribution with a fine mode peak are found well above the bottom mixed layer

high rates of benthic carbon remineralisation in the abyssal arabian sea during the large scale deep sea programme bigset in situ measurements of sediment community oxygen consumption scoc were carried out during three cruises between 1995 1998 at five abyssal sites 3190 4450 m water depth in the deep arabian sea in order to elucidate the regional and temporal variation of benthic carbon remineralisation scoc ranged from 0 9 6 3 mmol o2 m 2 d 1 with highest values in the western and northern arabian sea and lowest values in the southern arabian sea for the central arabian sea intermediate oxygen uptake rates were detected this regional pattern mirrors the overall regional pattern of primary productivity in surface waters and vertical particulate organic carbon poc flux at 1000 mab primary productivity in arabian sea surface waters and particulate flux into the deep sea are controlled by the monsoon system and the flux maxima during the sw and ne monsoon are among the highest particle fluxes recorded in the deep open ocean highest flux rates were recorded in the western and northern arabian sea and decreased towards the central and southern arabian sea scoc at our western northern and eastern arabian sea stations wast nast and east were considerably higher than so far detected in other abyssal areas of the global oceans and vertical poc flux can account for only 20 50 of benthic carbon remineralisation bcr possible explanations for the high rates of bcr at these stations that are situated close to the continental margins are discussed the accelerated deposition of very labile organic matter due to eolian dust particles enhanced rain efficiencies and lateral advection a significant temporal variability in scoc only could be detected at the eastern and western arabian sea stations wast and east

in situ particle size spectra and density of particle aggregates in a dredging plume abstract an in situ laser particle sizer the lisst 100 was used to describe the spatial variation of beam attenuation coefficient in situ particle size spectra and aggregate densities in a dredging plume in the sound oresund between denmark and sweden the results proved that the above mentioned parameters varied significantly within the investigated length of the plume approximately 2 km it is shown how the small single primary particles aggregate and change the in situ particle size spectra into a slightly better sorted and coarser size distribution and at the same time how the mean density of particles aggregates decreases significantly this shift in the state in which the particles exist in the water effectively changes the optical response of the mass of particles suspended in the water it is shown that adequate correlations between mass concentrations and beam attenuation coefficients can only be obtained if parameters describing the in situ quality and state of the mass of particles e g standard deviation of the size spectra and volume concentration is included in the regression from the spatial variation in mean density and in situ particle size it was possible to calculate the spatial difference in settling velocity it was found that the difference in settling velocity was only about a factor of 1 7 because increasing in situ particle size was counter balanced by decreasing mean density furthermore the time scale of flocculation within the plume was found to be in the order of 50 min

a honeycomb seafloor morphology in carbonate sediment of the carnegie ridge offshore ecuador formation and potential geodynamic significance based on swath bathymetry two dimensional high resolution seismic reflection profiles and ocean drilling program deep sea drilling project odp dsdp data we describe a seafloor honeycomb pattern and propose a model for its formation in pliocene miocene carbonate deposited on the uneven oceanic basement of the carnegie ridge offshore ecuador hydrothermal fluids derived from the basement aquifer fractured and dissolved carbonate sediment creating seafloor pits above basements highs fluids expelled along polygonal faults may have assisted the nucleation of seafloor depressions at the pliocene pleistocene boundary strong bottom currents scoured previously damaged sediments enlarging the initial depressions and producing the seafloor honeycomb pattern this regional erosive episode was contemporaneous with the final closing of the isthmus of panama and the clogging of the ecuador trench by the subduction of the carnegie ridge so that the honeycomb pattern may be viewed as a regional marker of these two geodynamic events

long term photographic current and nephelometer observations of manganese nodule environments in the pacific long term measurements on and near the seafloor were made at five locations in the pacific as part of the manganese nodule project manop bottom ocean monitor bom tripods deployed at each site contained a time lapse camera nephelometer and current meter from nearly three years of photographs of the seafloor there was no evidence that benthic organisms turned over rotated or moved nodules there were indications however that benthic organims cleaned sediment from the tops of nodules and in some cases deposited sediment underneath nodules currents never exceeded the expected threshold for sediment resuspension of nodule movement particle concentrations in the water remained uniformly low throughout the deployments degredation of fecal pellets and organic matter proceeded more rapidly than expected all changes of the seafloor morphology were attributable to the activity of organisms as opposed to currents the occurrence in one photo sequence of dark fluffy globs may be related to phytoplankton blooms in the region of equatorial upwelling

fluorine partitioning between hydrous minerals and aqueous fluid at 1 gpa and 770 947 c a new constraint on slab flux abstract mechanisms of volatile element transfer from subducting slab to the melting region beneath arc volcanoes are probably the least understood process in arc magma genesis fluorine which suffers minimal degassing in arc primitive melt inclusions is highly enriched in arc lavas and retains information about the role of volatiles during magma genesis at depth experimentally determined solubility of f in aqueous fluids and partition coefficients of f between fluid and minerals provide first order geochemical constraints about the character of the volatile transporting agent we present experimentally determined f solubility in fluid in equilibrium with hornblende and a humite group mineral at 1 gpa from 770 to 947 c and partition coefficients between these phases the composition of the fluid is determined by mass balance calculations and consistency is verified by high pressure liquid chromatography measurements of the quenched fluids the partition coefficient d f flu hb can be represented by a single value of 0 13 0 03 the average f concentration in the fluid is 2700 ppm for f rich experiments constraining the maximum amount of f carried by fluid in the presence of amphibole where the initial natural f concentrations in the slab are much lower than in our experiments the increase of f concentration in the sub arc mantle by a fluid in equilibrium with hornblende is expected to be no more than a few ppm thus significant arc lava f enrichments cannot result from aqueous fluids deriving from an amphibole bearing subducting slab

excepftonally strong near bottom flows on the continental rise of nova scotia recent current velocity measurements across the lower continental rise of nova scotia show a deep equatorwardflow with speeds maximum 73 centimeters per second among the highest recorded for the deep sea silicate measurements indicate that this flow usually consists of southern source antarctic bottom water these measurements confirm the existence of a second and deeper western boundary flow that was earlier inferredfrom geological observations

equilibrium experiments in the system mgo sio2 h2o msh stability fields of clinohumite oh mg9si4o16 oh 2 chondrodite oh mg5si2o8 oh 2 and phase a mg7si2o8 oh 6 the water pressure and temperature stability fields of clinohumite oh chondrodite oh and phase a were determined in reversed equilibrium experiments up to 100 kbar within the system mgo sio2 h2o their pt fields differ from results from former synthesis experiments bracketing experiments on the reaction phase a low p clinoenstatite forsterite water resulted in a slightly steeper dp dt slope compared to earlier experiments for this equilibrium clinohumite oh and chondrodite oh both have large stability fields which extend over pressure ranges of more than 80 kbar however they are hardly relevant as hydrous minerals within the subducted oceanic lithosphere both are too mg rich for a typical mantle bulk composition in addition the dehydration of subducted oceanic lithosphere due to forsterite water forming reactions will occur before the two humite group phases even become stable restricted to the cool region of cold subducting slabs phase a however might be formed via the reactions phase a low p high p clinoenstatite forsterite water or antigorite brucite phase a water before dehydration of the oceanic lithosphere occurs

local variability of manganese nodule facies on small abyssal hills of the central pacific basin abstract local variability of manganese nodule facies and associated sediments were studied around abyssal hills 60 60 km 2 located in the equatorial zone of the central pacific basin small scale variations in nodule occurrence mineralogy chemistry and internal structure are discussed in relation to seismic records and sediment lithology the slow sedimentation rate from the late tertiary to the quaternary appear to have promoted formation of nodules around the abyssal hills although the plio pleistocene hiatus at depths below sediment surface suggests no clear evidence of increased growth of nodules during the period in the area of rapid and continuous sedimentation away from the hill areas nodules are rare probably because of insufficient lifting force for nodules mineralogical and chemical studies reveal that the two principal nodule morphologies smooth and rough surfaces result from preferential deposition of hydrogenous or diagenetic manganese minerals in relation to early diagenesis of surface siliceous sediments regional variability of nodule surface morphology and composition suggests a very local change in sedimentary conditions in space and internal mineral variation suggests changes in sedimentary conditions with time the geological factors controlling the small scale variability of nodule facies seem to be similar to those controlling regional scale variations

sediment sorting and focusing in the eastern equatorial pacific abstract the interpretation of sedimentary records in terms of glacial interglacial changes in particle flux in the eastern equatorial pacific eep has been controversial here we analyze disaggregated inorganic grain size digs distributions of three marine sediment cores from this region focusing on the last 21 ka to investigate evidence of sediment redistribution on the sea floor grain size sorting coefficients show that sediments in the eep are moderately to well sorted indicating sediment reworking in this region due to bottom currents furthermore a systematic correlation between focusing factors and sorting coefficients at two sites shows that more focused sediments are also better sorted we conclude that grain size based sedimentary records are consistent with the 230 th based evidence of lateral sediment redistribution on the sea floor in the eep

thorium distributions in high and low dust regions and the significance for iron supply thorium and uranium isotopes 232th 230th 238u and 234u were investigated to refine their use for estimating mineral dust deposition and fe delivery to the ocean u concentrations and isotope ratios were consistent with conservative behavior and can safely be described using published u salinity relationships and global average seawater isotopic composition near barbados waters affected by the amazon outflow contained elevated 232th this signals one region where the thorium dust method is inaccurate because of a confounding continental input dissolved 232th fluxes in this region suggest that amazonian fe supply to the adjacent open ocean is much larger than local atmospheric deposition the colloidal content of dissolved th south of bermuda was found to be quite small 2 6 similar to that found north of hawaii despite the order of magnitude higher dust deposition in the atlantic this finding supports the assumption that dissolved 232th and 230th are scavenged at the same rate despite their different sources and also sheds light on the increase of dissolved 232th fluxes with integrated depth outside the region influenced by amazon river waters dissolved 232th fluxes are compared with bermudan aerosol fe deposition to estimate that fractional th solubility is around 20 in this region finally new dissolved and soluble fe mn and cr data from the subtropical north pacific support the idea that fe concentrations in the remote ocean are highly buffered whereas 232th has a larger dynamic range between high and low dust regions

patchy deposits of cenozoic pelagic sediments in the central pacific export of pelagic carbonate tests from surface waters and their deposition at the seafloor plays a significant role in the co 2 cycle and ability of the oceans to absorb atmospheric co 2 sediment 2 3 0 th and 3 he measurements have been interpreted as evidence that significant lateral advection of pelagic material occurs in the water column leading to marked spatial variations in deposition rates and in particular to significant focusing of deposits on the pacific equator we report spatially continuous stratigraphy from two 1000 km seismic lines that show evidence of depositional anomalies near the equator accumulation rates were apparently enhanced locally by a factor of two similar to the proposed modern sediment focusing factors but the anomalies are surprisingly patchy over the 20 m y period analyzed they are not confined to an equatorial region and they are not necessarily found on adjacent seismic profiles these intermediate scale anomalies are 100 km across and represent areas of seafloor that received more deposits for one period less in following periods and vice versa variogram analysis was used to determine how the spatial scales of deposition changed over the neogene the period when the spatial scale of depositional variability was largest correlates with hiatuses in drill cores a correlation that we interpret as caused by enhanced and spatially heterogeneous carbonate dissolution at that time the study suggests that seismic stratigraphy has the potential to reveal spatial patterns related to unsteady bottom water flow and chemistry

suspended particulate matter transport through the vema channel richardson m j biscaye p e gardner w d and hogg n g 1987 suspended particulate matter transport through the vema channel mar geol 77 171 184 sixteen month time series measurements of water velocity and light scattering were coupled with hydrographic and suspended particulate matter sections to determine the flux and the variability in flux of suspended particulate matter through the vema channel the northward flux of spm through the vema channel ranged from 3 to 10 5 104 g s 1 with a mean of 6 5 104 g s 1 the largest fluxes were measured in the deepest and eastern portions of the channel with maximum fluxes of suspended particulate matter at specific sites being roughly two to four times the mean flux some of the suspended particulate matter in the channel may be eroded from the channel itself by the swift currents or eddy like features however the known manganese encrustation and hard floor of the channel suggest that the deep channel floor is not a likely source of sediment a primary source of the suspended particulate matter in the channel may be the sediment drifts in the argentine basin with their associated high standing crops of resuspended particulate matter this resuspended material would then be transported by the antarctic bottom water into and through the vema channel into the brazil basin the northward flux of suspended particulate matter through the vema channel is presently a significant but not dominant influence on sedimentation in the brazil basin

biotite chloritization process in hydrothermally altered granites abstract chloritization of biotite in a hydrothermal environment was studied in two granitic rocks of the massif central france four types of transformation were observed 1 mg chlorite growth upon 001 biotite planes in contact with quartz 2 biotite pseudomorphosed by a corrensite residual biotite assemblage 3 corrensite residual biotite pseudomorphosed by a ferromagnesian chlorite and 4 biotite pseudomorphosed by chlorite these transformations induce an expansion of the site of the ferromagnesian minerals which can be observed by the corrosion of neighbouring minerals and fracturation of the rock around the new chlorites open fractures or chloritic veinlets if al is considered as a strictly inert component the reaction biotite chlorite produces a decrease of the ferromagnesian mineral volume of 13 ferry 1979 this is not in agreement with petrographic observations of the rocks studied here therefore writing of a chloritization reaction must take into account a volume increase in this case al does not behave as an inert component but as a mobile one at the scale of the microsystem biotite neighbouring crystals albitization of plagioclase which occurs simultaneously with the chloritization process is the al furnisher in addition fe and mg must be brought into the microsystem during the transformation of biotite into chlorite this explains why the mg mg fe ratio is not the same between biotite chlorite growths and chlorite pseudomorphs because the bulk rock composition is enriched in these components the hydrothermal fluids must contain fe and mg before they flow into the rock chloritization in propylitized granites is not an isochemical process

a model dependent method for inverting vertical profiles of scattering to obtain particle size spectra in boundary layers abstract a method for obtaining particle size spectra from vertical profiles of scattering strength in planetary boundary layers is presented it is assumed that the boundary layer is horizontally homogeneous and that the vertical turbulent diffusion of particles can be modeled from a knowledge of the surface friction velocity equilibrium boundary layer profiles for each class of suspended particles are assumed to be established resulting from the balance between vertical turbulent diffusion and gravitational settling the forward problem thus models the depth dependent scattering as the sum across size classes weighted by number density and scattering cross section in accordance with established scattering theory constrained inverses produce the size spectra results of inversions from synthetic ocean data are presented for optical transmissometry and acoustic backscattering inversions of acoustic field data from the hebble experiment are also presented finally the applications of the work presented for the design of ocean boundary layer experiments its application in other fields and the directions for future research are discussed

temporal variations of beam attenuation coefficient on the continental rise off nova scotia two separate time series observations of light transmission in the bottom water on the continental rise off nova scotia show fluctuations of light transmission in a wide range 0 50 transmission at 660 nm the range corresponds approximately to spm concentrations of 12 mg l to 150 g l the former is the maximum value determined by filtration biscaye 1980 and the latter is determined by an empirical relation between beam attenuation coefficient and particle volume determined by a particle counter nepheloid layers of significant turbidity called benthic storms were observed in 30 and 10 of the time respectively for the two observations and each storm lasted 2 5 days high frequency fluctuations represented by pulse lengths less than 10 min were observed superimposed on the low frequency fluctuations during 16 and 4 of the time both the major storms and the high frequency pulses are interpreted to be a result of resuspension of bottom sediments at varying distances from the instrument the high frequency pulses are thought to be a result of erosion at a relatively short distance while the low frequency fluctuations result from erosion at greater distance

gas induced erosion features in the north sea pockmarks are prominent features on the seafloor at two main regions of the north sea the south fladen area and the norwegian trench the pockmarks vary in size from 5 m across to about 150 m and in depth from 1 m to about 20 m some of the features consist of several very small unit pockmarks these are probably gas induced erosion features and found only in soft finegrained marine and glaciomarine sediments they are probably caused by shallow or deep seated gas or fluid release through the seabed whereby the finest particles are thrown into suspension and redistributed by nearbottom currents on the north sea plateau a small pockmarked area has recently been found a close relationship exists here between mobile gas in the upper sediments faulting in the soft sediments and the morphology of the seabed other morphological features in the north sea such as coast parallel depressions and elongated depressions or terraces are also interpreted here as gas induced erosion products this applies yet again to the mottled seabed features which appear as patches of high reflectivity on side scan sonar records from the north sea plateau they correspond to shallow seabed depressions on the deep towed boomer records judging from reported observations from several shallow seas world wide volatile transport through the seabed is probably quite common and several morphological features are undoubtably induced by this process several erosion features of similar origin are probably common also in deep ocean basins

sediment concentration profiling in hebble using a 1 mhz acoustic backscatter system abstract as part of the high energy benthic boundary layer experiment hebble a 1 mhz acoustic backscatter system abss was deployed in 4800 m of water on the nova scotian continental rise the purpose of the instrument was to measure non intrusively a time series of the vertical concentration profile over the course of one year from september 1985 to september 1986 in this paper we discuss the details of the abss instrument the results of the time series data analysis and the implications of the results on sediment transport modeling in hebble the systematic variation in the abss and light transmissometry calibration with changes of particle size distribution caused by environmental variability is discussed a comparison of the abss estimates of particle concentration with those obtained from light transmissometers seems to indicate that the suspended particle size distribution changed surprisingly little throughout the experiment

faultlike features in abyssal plain sediments possible dewatering structures seismic reflection profiles from the southern nares abyssal plain and the madeira abyssal plain show faultlike displacements of subbottom reflections in areas of thickest sediment accumulation a remarkable aspect of these faults on the crests of basement highs is that their displacement is reverse rather than normal we propose that these faults are primarily the result of dewatering processes and that the apparent reverse faults around basement highs reflect more extensive dewatering hence greater compaction of the sediments overlying the basement high estimates of cumulative compaction with depth demonstrate that these abyssal plain sediments may have been reduced in thickness by as much as 120 m over the present 300 m this could have been accompanied by an average rate of water explusion of 0 02 m3 m 2 yr 1 this evidence of instability of abyssal plain sediments has important implications in terms of evaluating the concept of using these sediments as a disposal medium for high level radioactive waste

erosion and reworking of pacific sediments near the eocene oligocene boundary 1 the eocene oligocene e o boundary interval marks one of the largest and most rapid changes in climate during the last 50 myr because of a very shallow calcium carbonate compensation depth in the eocene as well as the reworking of sediments and hiatuses in the boundary zone it has also been one of the most difficult stratigraphic boundaries to study in deep water marine sections especially in the pacific ocean recently three drill sites have recovered complete sections of the e o boundary interval in the tropical pacific a detailed study of these sections shows a series of pulses of reworked older radiolarians in the upper eocene and lowermost oligocene the two largest pulses are coincident with the two sharp steps in carbon and oxygen isotope values that bracket the e o boundary several smaller peaks in reworked material precede these two maxima it is proposed that immixing of the older radiolarian species results from erosion and redeposition possibly linked to pulses of new bottom water formation and the formation of a deep pycnocline

nepheloid layer distribution in the whittard canyon ne atlantic margin article i nfo article history the dynamics and distribution of nepheloid layers in multiple branches of the whittard canyon were observed during three hydrographic surveys carried out between 2011 and 2013 the sources of permanent and temporal variation of the layers were investigated seasonal variations in primary production at the surface were reflected in the nepheloid layers extending down in the water column particularly in the upper reaches of the canyon benthic nepheloid layers were observed along the canyon axes to depths greater than 2500 m a distance of 30 km intermediate nepheloid layers were detected as lateral extensions of the benthic nepheloid layer centredat 550m 850m 1150 mand1600m and stretching 20 25kmoff slope criticalandsupercriticalcon ditions for semidiurnal tide reflection were identified coinciding with the occurrence of intermediate nepheloid layers with other hotspots found at the boundaries of the permanent thermocline and mediterranean outflow water weak seasonal stratification during the survey in 2012 appeared to permit storm induced mixing at deeper water depths than expected altering the distribution of material in the nepheloid layers the dynamic conditions of the canyon encourage nepheloid layer formation with implications ensued for deposition rates and food supply to the unique communities that are found in the whittard canyon and likely other similar can yon systems

periodic resuspension in baltimore canyon by focusing of internal waves high concentrations of particulate matter are frequently reported in submarine canyons this study demonstrates that in baltimore submarine canyon elevated concentrations result from periodic resuspension events the sloping bottom and v shaped topography of submarine canyons could accelerate tidal flows in the canyon axis sufficiently to cause resuspension which occurs predominantly at tidal frequencies however current meter and transmissometer data show that resuspension events are often associated with a borelike intrusion of cold water moving upslope near the canyon head an event that is consistent with the focusing of internal wave energy toward the canyon head at tidal frequencies hydrographic conditions for the focusing of energy are most favorable in late winter and early spring when stratification in the canyon is diminished direct observations reveal that the most pronounced resuspension events occur during those seasons bottom stresses generated in the canyon are sufficient to resuspend sediment along the axis at least between 200 and 800 m with little resuspension occurring deeper along the axis on the canyon walls adjacent slope or shelf during a resuspension event the sediment laden water is forced upcanyon then sloshes back down the canyon until it reaches a layer of higher density water detaches from the canyon floor and moves seaward along a density surface this is a means of transferring sediment and associated pollutants intercepted at the canyon head to deeper water across the shelf slope front over geologic time frequent resuspension and seaward transport may aid in the headward erosion of submarine canyons or at least inhibit their infilling during interglacial times

an optical settling tube for the determination of particle size distributions abstract the particle size distribution the settling velocity distribution and the concentration weighted settling velocity are important parameters in the study of sediment dynamics these parameters can be determined by means of an optical settling tube in which the concentration of particles is determined by means of a beam attenuation meter and the particle size is determined by stokes settling results obtained by this method compare very well with coulter counter and gravimetric settling tube data various correction factors are discussed the instrument is designed for eventual use in situ

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

dissolution and collapse features on the eastern mediterranean ridge abstract morphologic features similar to subaerial karstic dolines and zanjones have been observed on the eastern mediterranean ridge using a near bottom towed geophysical instrument package these features are found only on the floors of certain large depressions which lie above the crests of subcropping evaporite diapirs the coincidence of dissolution controlled morphology with the subcropping soluble evaporite confirms earlier suggestions that the large depressions result from dissolution of the evaporites and collapse of the overlying strata

sediment focusing in the central equatorial pacific ocean at four sites in the central equatorial pacific ocean the flux of extraterrestrial he determined using the excess 230th profiling method is 8 10 13 cm stp cm 2 ka 1 this supply rate is constant to within 30 at these same sites however the burial rate of he determined using chronostratigraphic accumulation rates varies by more than a factor of 3 the lowest burial rates which occur north of the equator at 1 n 139 w are lower than the global average rate of supply of extraterrestrial he by 20 and indicate that sediment winnowing may have occurred the highest burial rates which are recorded at the equator and at 2 s are higher than the rate of supply of extraterrestrial he by 100 and these provide evidence for sediment focusing by analyzing several proxies measured in core pc72 sediments spanning the past 450 kyr we demonstrate that periods of maximum burial rates of 230th he 10be ti and barite with a maximum peak to trough amplitude of a factor of 6 take place systematically during glacial time however the ratio of any one proxy to another is constant to within 30 over the entire length of the records given that each proxy represents a different source 234u decay in seawater interplanetary dust upper atmosphere continental dust or upper ocean our preferred interpretation for the covariation is that the climate related changes in burial rates are driven by changes in sediment focusing

a study of the optical characteristics of the suspended particles in the benthic nepheloid layer of the scotian rise light transmission profiles have been used to study the optical properties of the suspended particles which are characteristic of the area of the scotian rise in the north atlantic ocean this area is typified by very strong bottom currents and a highly variable bedform morphology a good correlation r 0 96 has been found between the suspended volume and the light beam attenuation coefficient this correlation is consistent with the fact that the cumulative slope of the hyperbolic particle size distribution is nearly constant throughout the region slope 3 1 0 3 numerical analysis of the optical data in conjunction with particle size analysis yields values of the index of refraction of the suspended particles of 1 20 0 07 relative to water the conclusion drawn from these results is that the scotian rise benthic zone is characterized by suspended particles of high relative index of refraction and size distributions which do not vary much with altitude above bottom or over periods of time of more than a year in spite of the extensive fluctuations in activity of the region

direct evidence for the origin of low 18o silicic magmas quenched samples of a magma chamber s partially fused granitoid walls crater lake oregon abstract partially fused granitoid blocks were ejected in the climactic eruption of mount mazama which was accompanied by collapse of crater lake caldera quartz plagioclase and glass in the granitoids have much lower 18 o values 3 4 to 4 9 than any fresh lavas of mount mazama and the surrounding region 5 8 to 7 0 oxygen isotope fractionation between phases in granitoids is consistent with equilibrium at t 900 c following subsolidus exchange with hydrothermal fluids of meteoric origin assimilation of 10 20 of material similar to these granitoids can account for the o and sr isotopic compositions of lavas and juvenile pyroclasts derived from the climactic magma chamber many of which have 18 o values 0 5 or more lower than comparable lavas of mount mazama the o isotope data provide the only clear evidence for such assimilation because the mineralogy and chemical and radiogenic isotopic compositions of the granitoids dominantly granodiorite are similar to those of erupted juvenile magmas the granitoid blocks from crater lake serve as direct evidence for the origin of 18 o depletion in large shallow silicic magma bodies