modern sedimentary processes in the wilmington canyon area u s east coast abstract sedimentary processes active in the wilmington canyon area during the past century are documented from geochronologic sedimentologic and radiographic analysis of sediment cores collected using primarily d s r v alvin site selection for the alvin dives and for collection of box and kasten cores was achieved using sea marc and seabeam data allowing accurate sampling of numerous subenvironments from this extensively dissected area of the continental margin 210 pb sediment accumulation rates from intercanyon areas are highest on the upper slope 1 7 mm yr 140 mg cm 2 yr and decrease with water depth to about 0 4 mm yr 36 mg cm 2 yr on the upper rise within submarine canyons accumulation rates vary dramatically from a maximum of 6 mm yr 500 mg cm 2 yr to less than 0 3 mm yr 22 mg cm 2 yr higher accumulation rates in canyons occur as a result of additional supply of older sediment probably from bioerosion of the canyon walls this is supported by observations from d s r v alvin reduced 210 pb activities and indurated mud clasts observed in several canyon cores extremely low accumulation rates in wilmington and south wilmington canyons are probably the result of strong episodic boundary currents non steady state 210 pb profiles and sedimentologic data indicate small scale mass wasting in south heyes canyon and on the lower slope and rise just north of wilmington canyon

errors in bathymetric retrievals using linear dispersion in 3 d fft analysis of marine radar ocean wave imagery the phenomenon of ocean wave shoaling and the associated reduction of ocean wave phase speed with decreased water depth provides useful information for inferring water depth d bathymetry in coastal environments one strategy for relating d to phase speed c and wave vector k of long wavelength ocean waves involves using the one dimensional 1 d linear gravity wave dispersion relationship c sup 2 g tanh kd k in principle this approach has limitations because the approach is based on a wkb approximation so it cannot be applied when d varies appreciably over the wavelength of a shoaling wave also the approach is restricted to waves that have small wave height the author uses a set of marine radar image sequences and applies this linear approximation using a 3 d fft analysis of 88 sets of image sequences spaced half an hour apart the author inverts the dispersion relation to solve for d depths between 3 6 and 5 8 m were tested for root mean square rms wave heights offshore between 8 and 3 m the author shows that for low to moderate wave heights the approach does generally retrieve the correct depth in water depths of 5 m and greater for moderate wave rms heights however an increase in the rms wave height from 1 m to 3 5 m produced a much poorer depth estimate proving the need for an application of a nonlinear wave model to the problem the errors also increase with shallower depths as expected as the error dependence on depth and wave height is determined

morphology and filling of incised submarine valleys on the continental shelf near the mouth of the fly river gulf of papua 1 much historical perspective about terrestrial and marine processes can be obtained from examination of fluvial valleys formed during lower sea level on surfaces that are now continental shelves the continental shelf near the mouth of the fly river gulf of papua has three incised valleys which were not extensively modified or filled during the holocene transgression multibeam mapping of the valleys documents their morphology seismic profiling reveals stratigraphy of sediment fill and coring within and near the valleys suggests mechanisms of filling kiwai valley is deep 20 50 m relief narrow 1 km wide steep sided and meandering due to river flows that caused its excavation through competent sedimentary deposits purutu valley is shallow 10 20 m relief and broad 2 km wide umuda valley is widest 14 km and has multiple channels with variable incision depths suggesting more extensive fluvial activity than the other two valleys valley filling has occurred in several ways reflecting valley morphology and location relative to the present river mouth kiwai and umuda valleys reveal three stages of infill 1 hemipelagic sedimentation at distal sites 2 gravity driven flows spreading down the valley and 3 subsequent clinoform progradation that completely fills the valley purutu valley fill is dominated by clinoform progradation clinoform progradation in umuda valley is driven by intense sediment reworking on the surrounding topset regions and its large width allows progradation from the sides as well as down its axis most shelf valleys around the world were filled long ago and available techniques have severe limitations for documenting the details of morphology and the mechanisms of filling the shelf valleys described in this paper provide a unique perspective to terrestrial and marine processes before during and after the holocene transgression

benthic fluxes and porewater concentration profiles of dissolved organic carbon in sediments from the north carolina continental slope abstract numerous studies of marine environments show that dissolved organic carbon doc concentrations in sediments are typically tenfold higher than in the overlying water large concentration gradients near the sediment water interface suggest that there may be a significant flux of organic carbon from sediments to the water column furthermore accumulation of doc in the porewater may influence the burial and preservation of organic matter by promoting geopolymerization and or adsorption reactions we measured doc concentration profiles for porewater collected by centrifugation and sipping and benthic fluxes with in situ and shipboard chambers at two sites on the north carolina continental slope to better understand the controls on porewater doc concentrations and quantify sediment water exchange rates we also measured a suite of sediment properties e g sediment accumulation and bioturbation rates organic carbon content and mineral surface area that allow us to examine the relationship between porewater doc concentrations and organic carbon preservation sediment depth distributions of doc from a downslope transect 300 1000 m water depth follow a trend consistent with other porewater constituents co2 and so42 and a tracer of modern fine grained sediment fallout pu suggesting that doc levels are regulated by organic matter remineralization however remineralization rates appear to be relatively uniform across the sediment transect a simple diagenetic model illustrates that variations in doc profiles at this site may be due to differences in the depth of the active remineralization zone which in turn is largely controlled by the intensity of bioturbation comparison of porewater doc concentrations organic carbon burial efficiency and organic matter sorption suggest that doc levels are not a major factor in promoting organic matter preservation or loading on grain surfaces the doc benthic fluxes are difficult to detect but suggest that only 2 of the dissolved organic carbon escapes remineralization in the sediments by transport across the sediment water interface

relative paleointensity rpi in the latest pleistocene 10 45 ka and implications for deglacial atmospheric radiocarbon abstract we report magnetic properties and relative paleointensity rpi proxies from a suite of 10 conventional piston cores and kasten cores from the sw iberian margin collected during cruise jc089 of the rss james cook in august 2013 mean sedimentation rates are in the 10 20 cm kyr range age models were acquired by correlation of ca ti and zr sr xrf core scanning data to l reflectance from the cariaco basin that is in turn tied to the greenland ice core chronology the natural remanent magnetization nrm is represented by a single magnetization component carried by a low coercivity mineral magnetite although reflectance and bulk magnetic properties indicate the presence of a high coercivity hematitic magnetic phase possibly from eolian dust the presence of fine grained hematite means that the sediments are not ideal for rpi studies however the detrital hematite does not appear to contribute to the nrm or anhysteretic remanent magnetization arm in order to test the usefulness of the rpi data we construct a stack of 12 rpi records from the sw iberian margin for the 0 45 ka interval and compare it with a stack of 12 globally distributed marine and lake records chosen on the basis of mean sedimentation rates 15 cm kyr and superior age models the two stacks are similar but different from published rpi stacks particularly for the 10 30 ka interval and imply a virtual axial dipole moment vadm high at 15 18 ka followed by a drop in field strength from 15 to 13 ka a revised vadm estimate calculated from greenland 10be ice core flux using a contemporary age model is remarkably consistent with the new overall rpi stack based on iberian margin and global rpi records the elevated atmospheric 14c levels of the last ice age cannot however be fully explained by this rpi stack although relative changes such as the long term drop in atmospheric 14c from 30 to 15 ka are reproduced supporting the hypothesis of a combined influence of production rate and ocean ventilation on 14c during the last ice age

implementation of s band marine radar for surface wave measurement under precipitation abstract civil marine radar which operates at a low grazing incidence angle and with horizontal polarization in transmitting and receiving can be modified and used as a primary tool for surface wave monitoring the high spatial resolutions of sea clutter image sequences from x band radar offer a means of deriving individual waves and wave field at low cost however the performance of x band radar is impaired under rainy conditions which are usually accompanied by the severe weather at sea in the present study we examine the effectiveness of s band radar for wave measurements under precipitation the results of comprehensive comparative studies with sea truth data show that s band radar is capable of carrying out wave measurements in rainy conditions although the longer wavelength of the s band leads to a coarser resolution of radar imagery the s band radar features at least the equivalent performance of the x band system in non rainy conditions in terms of wave height measurement the results suggest that the s band and x band could be complementary systems in rainy conditions the s band is more efficient but in the non rainy periods the x band gives more confident results the relationship of significant wave height with radar signal to noise ratio snr and the modulation transfer function mtf between radar spectrum and wave spectrum for the used x band and s band radars are established and discussed in this paper

glacial interglacial variation in organic carbon burial on the slope of the n w european continental margin 48 50 n the sources and fate of organic carbon corg were examined at two sites on the goban spur and a single site within the porcupine sea bight on the n w european slope between 48 n and 50 n here we present data on the sedimentary corg concentration its 13c 12c composition 13corg and corg n of 224 total and 119 fine fraction 63 m samples as a time series running from the instantaneous marker horizon heinrich layer 2 25 5 ka bp through the last glacial isotope stage 2 and interglacial isotope stage 1 to the present the significance of the n w european slope as a depositional sink for corg has declined in the past twenty thousand years with flux values decreasing two to three fold from the late glacial 60 70 mg c cm 2 ka 1 to low late holocene values significant shifts are seen in the 13corg signature of both the total and fine fractions between the present interglacial and last glacial the open slope of the goban spur is characterised by relatively low values over the last glacial with minimum values for the total sediment of around 24 5 occurring at ca 18 ka bp and generally increasing values during the holocene with the most recent samples having values of ca 19 2 to 20 2 in the porcupine sea bight a different relationship is evident with samples from the last glacial maximum being generally higher while values from the holocene are lower with a minimum of 23 3 occurring just below the mixed layer similar trends are observed in the fine fraction albeit with a different dynamic range paired analysis of 13corg and corg n are consistent with the organic matter being a climatically forced mixture from c3 photosynthetic terrigenous and marine organic matter sources an increased influence of terrestrial corg is suggested on the glacial goban spur and holocene porcupine sea bight and vice versa we suggest that this may be explained by modern wind driven flushing of terrigenous carbon across the armorican and celtic shelves to the n w and thence into porcupine sea bight during the last glacial increased strength of westerly winds created a residual current regime driving material to the s w where it was transported in vigorous tidal off shelf flushing to the upper slope followed by slope current transfer to the goban spur much of this material was presumably delivered by the great channel river to the outer shelf thus leading to enhanced flux of terrestrial corg on the goban spur the influence of a freshwater plume from meltwater discharge of the european ice sheet in this region is supported by foramininiferal 18o data from which a palaeo salinity reconstruction shows a greatest negative anomaly of 2 55 that is s 35 at the time of maximum terrestrial corg content in the sedimentary material in addition to showing that surface waters over goban spur were relatively fresh throughout the glacial our results also reveal variability in surface salinity on shorter timescales

laboratory studies of radar sea spikes at low grazing angles we report on measurements of low grazing angle radar sea spikes in a laboratory wave tank using an x band radar with 10 cm range resolution and multiple range bin capability the sea spikes were observed to have a horizontal vertical polarization ratio much larger than unity this is similar to observations in earlier field experiments but is in contrast to a ratio of unity recently observed for moderate grazing angles jessup et al 1990 our experiment was designed to validate the low grazing field results and to establish design criteria for spatial temporal measurement instrumentation single point measurements currently used as surface truth cannot provide water surface profiles needed for modeling of radar scatter from deterministic surface features surface scattering features were generated using a paddle generated wave combined with wind waves for a series of wind speeds the surface feature responsible for the sea spike echo was visually identified as a short wave crest occurring on the windward side of the paddle wave driven to extreme steepness by the passage of the faster paddle wave crest long decorrelation times observed in the field are also seen in these studies of the order of 500 ms for horizontal polarization and less than 5 ms for vertical we suggest that rather than bragg scatter the occurrence of similar ubiquitous features on the ocean are responsible for horizontally polarized low grazing angle sea scatter at the x band for low to moderate winds and perhaps at other frequencies as well

geochemical mass balance for lithium boron and strontium in the gulf of papua papua new guinea project tropics a mass balance has been calculated for the elements li b and sr in the gulf of papua from sampling undertaken during 1993 to 1999 parameters measured included fly kikori and purari river inputs of dissolved and particulate phases removal flux to sediment traps at the base of the continental shelf slope and century scale accumulation rates in shelf and slope sediments derived from excess 210pb profiles in sediment cores about 91 of river input li was in particulate form and there was conservative behavior of dissolved li in the salinity gradient of the estuaries li accumulation rate in inner shelf sediments was slightly less than river inputs suggesting that more than 90 of li river inputs were trapped in rapid aluminosilicate mud accumulation zones of the inner shelf 50 m depth li removal rate to sediment traps at the base of the slope at 1000 m water depth was an order of magnitude smaller than the inner shelf sedimentation export of li to deep water coral sea was estimated to be 1 2 108 mol yr 1 and this amount is equivalent to the riverine dissolved li annual supply rate about 66 of river input of b was in the particulate phase and low dissolved b concentrations in freshwater were conservatively mixed with higher concentrations of b in seawater across the salinity gradient removal of b to inner shelf sediments was about 83 of the total river input indicating a small export of b 1 2 108 mol yr 1 to the coral sea about half of the dissolved b input from rivers is sorbed to particles and trapped in inner shelf sediments only 24 of river input of sr was in particulate form and low freshwater concentrations of dissolved sr were conservatively mixed with higher concentrations of sr in seawater across the salinity gradient only 20 of total river inputs of sr were buried in shelf sediments and there was a large export 7 3 108 mol yr 1 of sr off the shelf to the coral sea a sediment core from a rapidly accumulating mud deposition zone of the inner shelf shows twofold sympathetic variations in li b and sr ca supply rates over 200 to 1000 yr time intervals

late pleistocene holocene marine conditions in the ross sea antarctica evidence from the diatom record statistical analyses of diatom assemblages from radiocarbon dated sediment cores were used to reconstruct changing palaeoceanographic conditions in the western and west central ross sea antarctica from c 12 14c kyr bp to the present data from three kasten cores support a north to south time transgressive glacial interglacial transition assemblages at the base of each core suggest that glacial processes affecting frustule preservation were significant during the late pleistocene increasing biogenic silic and decreasing per centages of reworked species suggest that upper water column productivity instead of preservational processes increasingly dominates diatom assemblages during grounding line recession c 12to c 6 14c kyr bp a warm ing during the middle to late holocene c 6to c 3 14c kyr bp may have resulted in a spring sea ice melting prior to the annual inception of the ross sea polynya in the west central ross sea and b increased plateletice delivery due to increased melting beneath t

chronology for climate change developing age models for the biogeochemical ocean flux study cores we construct age models for a suite of cores from the northeast atlantic ocean by means of accelerator mass spectrometer dating of a key core bofs 5k and correlation with the rest of the suite the effects of bioturbation and foraminiferal species abundance gradients upon the age record are modeled using a simple equation the degree of bioturbation is estimated by comparing modeled profiles with dispersal of the vedde ash layer in core 5k and we find a mixing depth of roughly 8 cm for sand sized material using this value we estimate that age offsets between unbioturbated sediment and some foraminifera species after mixing may be up to 2500 years with lesser effect on fine carbonate 10 mu m ages the bioturbation model illustrates problems associated with the dating of instantaneous events such as ash layers and the heinrich peaks of ice rafted detritus correlations between core 5k and the other cores from the bofs suite are made on the basis of similarities in the downcore profiles of oxygen and carbon isotopes magnetic susceptibility water and carbonate content and via marker horizons in x radiographs and ash beds

marine cold seeps and their manifestations geological control biogeochemical criteria and environmental conditions characteristics of cold seeps at different geologic settings are the subject of this review primarily based on results of the research consortium sfb 574 criteria are drawn from examples on the erosive convergent margin off costa rica the accretionary margin off chile supplemented by examples from the transform margin of the golf of cadiz and the convergent hikurangi margin off new zealand others are from well studied passive margins of the black sea the golf of mexico the eastern mediterranean sea and the south china sea seeps at all settings transport water and dissolved compounds to the ocean through the seafloor by different forcing mechanism and from different depths of the submerged geosphere 10s of meters to 10s of km the compounds sustain oasis type ecosystems by providing bioactive reductants sulfide methane and hydrogen hereby the interaction between fluid composition flux rates and biota results in a diagnostic hydrocarbon metazoan microbe carbonate association currently well over 100 active sites are known the single most important reaction is microbially mediated anaerobic oxidation of methane with secondary reactions involving s biogeochemistry and carbonate mineral precipitation seep fluids and their seafloor manifestations provide clues as to source depth fluid sediment rock interaction during ascent lifetime and cyclicity of seepage events but less so on the magnitude of return flow at erosive margins cl depleted and b enriched fluids from clay dehydration provide criteria for source depth and temperature the upward material flow generates mud volcanoes at the seafloor above the projected location of dehydration at depth at accretionary margins fluids are derived from more shallow depths by compaction of sediments as they ride on the incoming oceanic plate they are emitted through thrust faults at highly sedimented margins organic rich and evaporite containing strata when present determine the final fluid composition by emitting characteristically gas hydrate derived methane brine associated non methane hydrocarbons or leached elements and their isotopes li 7li b ba from host sediments smectite illite transformation and associated cl depletion from release of interlayer water is a pervasive process at these margins rare earth element pattern in conjunction with redox sensitive metals retained in seep carbonates indicate whether or not they precipitated in contact with oxic bottom water or suboxic fluids clear environmental characterization though currently remains inconclusive more deeply sourced fluids as in transform margins may be characterized by their 87sr 86sr ratios from interaction with oceanic crustal rocks below quantification of flow and reliable estimates of total volatile output from fore arcs remain a challenge to seep research as does understanding the role of geologically derived methane in the global methane cycle

cross polarization geophysical model function for c band radar backscattering from the ocean surface and wind speed retrieval the wind speed sensitivity of cross polarization cross pol radar backscattering cross section vh from the ocean surface increases toward high winds the signal saturation problem of vh if it exists occurs at a much higher wind speed compared to the copolarization copol vv or hh sea returns these properties make vh a better choice over vv or hh for monitoring severe weather combined with high spatial resolution of the synthetic aperture radar sar the development of hurricane wind retrieval using vh is advancing rapidly this paper describes a cross pol c band radar backscattering geophysical model function gmf with incidence angle dependence for the full wind speed range in the available data sets up to 56 m s the gmf is derived from radarsat 2 r2 dual polarization dual pol scansar modes with 300 and 500 km swaths the proposed gmf is compared to other published algorithms the result shows that the simulated vh cross section and the retrieved wind speed with the proposed gmf is in better agreement with measurements with careful treatment of noise the vh retrieved wind speeds may extend to mild or moderate conditions the higher fraction of non bragg contribution in vh can be exploited for analysis of surface wave breaking

measurements of sea clutter at low grazing angle in mediterranean coastal environment results of a coastal measurement campaign called mediterranean rfc and clutter environmental experiment marlene are presented and studied the campaign was held in spring 2014 on a dga site in the mediterranean sea region of toulon france three coastal measurement radar systems millimeter wave experimental multifrequency polarimetric high resolution interferometric system fraunhofer fhr marsig wtd 71 and medycis onera were deployed to simultaneously acquire sea clutter measurements during the campaign the in situ oceanic and meteorological conditions were characterized from the rv planet meteorological ship deployed by wtd 71 and by modeling from wavewatch iii and swan wave models radar measurements were performed at the c x ku ka and w bands the measurement results are presented in terms of reflectivity and mean doppler spectrum according to low grazing angle and azimuth variations reflectivity variations are compared with the empirical git model and close results are obtained at the c and ka bands at the same frequency bands mean doppler spectrum velocity is presented and analyzed according to grazing and azimuth angles physical interpretations of electromagnetic interaction with sea surface are discussed

ocean surface determination from x band radar image sequences 1 an empirical inversion method is presented for determination of time series of ocean surface elevation maps from nautical radar image sequences the method is based on the determination of the surface tilt angle in antenna look direction at each pixel of the radar images thereby in situ sensors are not required an external calibration is not necessary a conventional nautical x band radar operating at grazing incidence and horizontal polarization in transmit and receive is used as a sensor radar image sequences with their high spatial resolution and large coverage offer a unique opportunity to derive and study individual waves and wave fields in space and time and therefore allow the measurement of individual wave parameters and wave groups for validation of the inversion scheme the significant wave heights derived from the inverted radar data sets and from colocated wave records are compared it is shown that the accuracy of the radar retrieved significant wave height is within the accuracy of the in situ sensors furthermore a wave elevation time series is directly compared to a buoy record to show the capabilities of the proposed method

non steady state 210pb flux and the use of 228ra 226ra as a geochronometer on the amazon continental shelf the recovery of quasi cyclic 210pb profiles from the foreset region of the amazon subaqueous delta has raised questions concerning the non steady state flux of 210pb to this region of the shelf radioisotopic profiles 210pb 234th 228ra 226ra 137cs from seven kasten cores along with the analysis of grain size organic carbon and clay sized mineralogy are used to investigate the time scale and the controlling mechanisms of the 210pb cyclicity a common assumption used in 210pb geochronology is that the initial specific activity is constant with time an assumption that is invalid in this region variations of particle affinity for 210pb have been shown to affect the initial specific activity reaching the seabed in various other studies however investigations of grain size organic carbon and mineralogy have revealed no relationship with the fluctuating 210pb activity in this area a new geochronometer 228ra 226ra is used to determine sediment accumulation rates over a 30 year time scale which range from 10 to 60 cm yr in the study area spectral analysis of the 210pb cyclicity has revealed that the major component of 210pb cyclicity has a frequency of approximately 2 3 years in addition components of the 210pb cyclicity occur on annual and semi annual frequencies the controlling mechanism for the 210pb cyclicity on these time scales appears to be the seaward transport and accumulation of low activity fluid muds from the topset region

seafloor facies related to upward methane flux within a giant pockmark of the lower congo basin the origin of the cold fluid venting from a giant pockmark within the lower congo basin has been elucidated based upon results of precise mapping submersible dives gravity coring and isotopic analyses realized under a total ifremer cooperative project zaiango and biozaire projects during four dives of the ifremer rov victor 6000 the bottom was filmed hard and soft samples were lifted from the sediment and water samples were collected with a ctd rosette system the detailed dip map shows that the 800 m wide giant pockmark is a composite feature due to the coalescence of multiple 100 m wide depressions that displays a broad range of biological mineralogical and chemical features on the seafloor leading to a seafloor anomaly recorded on the multibeam imagery methane rich fluids migrating through the sedimentary column from a buried palaeochannel clearly react with the sulphate rich circulating sea water to produce hydrogen sulphide and bicarbonate ions this situation leads to a concentrical arrangement of the sedimentary facies with methane related features in the centre and sulphide related features at the periphery this organization is correlated with high levels of methane up to 20 mol l measured in the centre of the giant pockmark responsible for the crystallization of gas hydrates at the bottom in this model the concentrical organization of mineralogical and biological features reflects a geochemical partitioning related to the peripheral progressive mixing of the methane flux

carbon burial rates in sediments and a carbon mass balance for the herbert river region of the great barrier reef continental shelf north queensland australia the largest century scale carbon reservoir in the herbert river sector of the great barrier reef continental shelf is carbonate carbon this carbonate carbon is produced by corals coralline algae and other benthic organisms and is stored on less than 13 of the area of the shelf maximum organic carbon burial rates 1 28 mol m 2 yr 1 occur within a wind protected 20 m water depth embayment 1 area of the shelf where the highest bulk sedimentation rates 1 12 kg m 2 yr 1 were determined from 210pb and137 cs profiles in 1 4 m cores sediment organic carbon oc and carbonate carbon cc accumulation rates are very low in the great barrier reef lagoon shelf and slope where most annual productivity 8 15 mol oc m 2 yr 1 is decomposed by algal and microbial respiration a carbon mass balance indicated that approximately 1 of combined river and marine organic carbon production was preserved in across shelf sedimentation but 3 of river and mangrove organic carbon input was preserved in this small wind protected embayment an across shelf carbon mass balance model predicted average shelf organic matter respiration correctly and the ratio of organic carbon fixation to respiration corrected for burial losses was 1 06

measurements of sea spikes in microwave backscatter at moderate incidence previous authors have associated large events or sea spikes in the radar cross section of the sea surface with steep or breaking waves here we present a method based on an intensity threshold and the mean doppler frequency to identify and quantify sea spikes likely to be associated with large scale wave breaking this method is applied to microwave measurements of ku band made with a dual polarized doppler scatterometer at a moderate incidence angle 45 from a fixed platform in the north sea for vv and hh polarization the mean normalized radar cross section 0 the frequency of sea spike occurrence n and the sea spike contribution to the mean normalized radar cross section ss0 are correlated with direct measurements of the friction velocity u in the range 13 u 49 cm s 1 the friction velocity exponents for both n and ss0 indicate an approximately cubic dependence while the residual radar cross section res0 0 ss is approximately proportional to friction velocity for u greater than approximately 20 cm s 1 at high friction velocities u 40 50 cm s 1 these data show that the contribution of large sea spikes to the mean radar cross section for measurements between 25 and 45 relative to the wind is in the range of 5 10 for vv polarization and 10 20 for hh polarization

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

natural flux of greenhouse methane from the timor sea to the atmosphere 1 methane gas bubbles from the cornea seep were sampled at the sea surface in the timor sea continental shelf area in june 2005 total bubble gas flux was 0 076 to 0 76 l m 2 h 1 during the 6 h d 1 periods of low neap tides in june 2005 this bubble gas contained an average of 26 mmol ch4 l 1 and about 0 16 and 0 006 mmol l 1 of ethane and propane we estimate the daily flux from the sea surface to the atmosphere to be 0 012 to 0 12 mol ch4 m 2 d 1 or 0 13 to 1 3 t ch4 d 1 from an area of about 0 7 km2 this methane flux came from a 500 1400 m carbonate pavement dome on the seafloor at 84 m water depth the seep hard ground was swath mapped and 3 5 khz subbottom profile data indicate that the seep dome was strongly reflective with poor penetration into the subsurface consistent with the presence of a carbonate hard ground carbon and deuterium isotope ratios 13c 41 to 42 d 157 to 158 of the seep bubble gas indicate that this methane had a thermogenic origin and was in the same isotopic range as gas within the late cretaceous cornea oil and gas field we could not detect inputs of fluids containing nutrients or short lived radium isotopes at this site commonly associated with other cold seeps tens to a hundred of kilometers seaward from the cornea seep site water column dissolved methane concentrations in this sector of the timor sea shelf and slope were 100 500 times supersaturated with respect to the atmosphere and thus the water column is expected to be degassing additional methane to the atmosphere perhaps there are thousands of other methane seeps of similar magnitude to the cornea seep on this shelf and slope to account for all the excess dissolved methane 86 000 t measured in the water column these measured and calculated fluxes provide evidence for the hypothesis that shallow sea seeps may be a significant source of atmospheric methane in contrast to deep sea vents where most of the methane is dissolved and oxidized in seawater and does not reach the atmosphere

biological indicators of sedimentary dynamics in the central gulf of papua seasonal and decadal perspectives 1 benthic and pelagic communities in the central gulf of papua a major deltaic clinoform located on the south coast of papua new guinea reflect the spatial and seasonal patterns in physical sedimentation conditions and the availability of food resources across this system the distribution of terrigenous and marine organic substrates the transport of riverine derived sediment and seafloor dynamics are largely controlled by two seasons and wind patterns the relatively quiescent nw monsoon and more energetic se trades the physically disturbed inner topset deposits 20 m are dominated at all times by bacterial biomass and have depressed numbers of macrofauna with evidence of periodic recolonization recorded in sedimentary structures the inner topset region also shows strong seasonality in the production and availability of labile organic matter and in bacterial activity as measured by the concentrations of photopigments and microbial biomass in the upper 2 cm of surface sediments and in the water column the comparatively quiescent nw monsoon period is associated with net delivery of reactive substrates as labile organic matter to the bottom and net growth of the benthic microbial community whereas the transition period between the nw monsoonal winds nw monsoon and se trade winds se trades and the se trades are periods of reactive substrate depletion in bottom deposits and decreased benthic bacterial and macroinfaunal biomass in contrast to the inner topset the less physically disturbed outer topset and foreset show relatively enhanced but still low abundances of large macrobenthos and possible evidence of variation related to food supply the greatest observed seasonal variation in macrofauna occurs in the umuda valley off the fly river an apparent mobile sediment conduit

sediment dispersal and accumulation off the ayeyarwady delta tectonic and oceanographic controls abstract recent sediment dispersal and accumulation on the northern andaman sea continental shelf off the ayeyarwady irrawaddy and thanlwin salween rivers are investigated using seabed water column and high resolution seismic data collected in december 2017 210pb and 137cs derived sediment accumulation rates are highest up to 10 cm y 1 in the mid shelf region of the martaban depression a basin that has formed on the eastern side of the n s trending sagaing fault where rapid progradation of a muddy subaqueous delta is occurring landward of the zone of highest accumulation in the shallow gulf of martaban is a highly turbid zone where the seabed is frequently mixed to depths of 1 m below the sediment water interface frequent resuspension in this area may contribute to the formation of extensive fluid muds in the water column and consequent re oxidation of the shallow seabed likely reduces the carbon burial efficiency for an area where the rivers are supplying large amounts of terrestrial carbon to the ocean sediment cores from the gulf of martban have a distinctive reddish brown coloration while x radiographs show sedimentary structures of fine silt laminations in mud deposits which indicates strong tidal influences the seaward part of the martaban depression off the modern subaqueous delta is covered by relict sediment with no apparent connection between the modern sediment deposit and the offshore martaban canyon on the western side of the sagaing fault the mouths of the ayeyarwady represent a large promontory where the subaerial delta has prograded seaward some 200 km along the eastern flank of the indo burman range since the holocene maximum transgression the shelf area off the mouths of the ayeyarwady presently exhibits low sediment accumulation rates 1 cm y 1 and a relative coarse sandy texture the reduced accumulation and coarse texture in the western shelf region at the present time is attributed to frequent wave resuspension and subsequent transport of finer river derived sediment eastward into the martaban depression during the sw monsoon a mud drape accumulation rates

facet based investigation on microwave backscattering from sea surface with breaking waves sea spikes and sar imaging a complete facet model for the backscattering from rough sea surface with breaking waves is proposed in this paper in consideration of the spatial distribution of breaking waves on sea surface the model is able to give a good interpretation to the super events under high sea states such as sea spikes and high polarization ratios based on the proposed model normalized radar cross section plots of sea surface under backscattering configuration are calculated and compared with measured data the comparisons show that the proposed model is tractable to estimate the scattering from electrically large ocean surface under high sea states with accuracy and efficiency in addition the non gaussian statistics and spatial correlation properties of sea clutter are analyzed under different range resolutions and incident angles the results show that high kurtosis value which means a sea spike phenomenon mostly happens in lower grazing angle and higher range resolution cases the comparisons of simulated sar images of sea surface with and without breaking waves also reveal that sea spikes and high polarization ratios are caused by breaking waves all the simulation results prove that our model not only is able to explain the physical mechanism of the scattering but also can be applied to the analyses of statistical properties of sea clutter under high sea states

ocean wind fields retrieved from radar image sequences 1 the dependency of radar backscatter on the surface wind field is investigated using a nautical x band radar operating at grazing incidence and horizontal polarization in transmit and receive this resulted in development of an algorithm for wind retrieval from nautical radar image sequences the algorithm consists of two parts in the first part wind directions are extracted from wind induced streaks that are in line with the mean surface wind direction these streaks are visible in the temporal integrated radar images at scales between 100 and 500 m the orientation of the streaks is determined from the local gradients which are derived from the radar images smoothed and reduced to the appropriate scales in the second part wind speeds are derived from the backscatter of the temporal integrated radar image sequence and the radar retrieved wind direction the dependency of the radar backscatter on the local surface wind and geometry of the radar is parameterized by training a neural network the algorithm is applied to radar image sequences acquired by a nautical x band radar mounted aboard an offshore platform in the north sea the radar derived winds are validated by comparison to in situ wind data measured at the platform the comparison of wind directions resulted in a correlation of 0 99 with a standard deviation of 14 2 for wind speeds the correlation is 0 97 with a standard deviation of 0 85 m s 1 in contrast to traditional offshore wind sensors the retrieval of the wind field from the backscatter of the ocean surface makes the system independent of the sensors motion and installation height and reduces the effects due to platform induced blockage and turbulence effects

glacial interglacial changes in water mass structure and flow in the sw pacific ocean eight to ten point depth profiles from 1200 to 4800 m water depth of oxygen and carbon isotopic values derived from benthic foraminifera averaged over selected times in the past 160 ka are presented the data are from 10 sediment cores off eastern new zealand mainly north chatham rise this lies under the deep western boundary current in the southwest pacific and is the main point of entry for several water masses into the pacific ocean the benthic isotopic profiles are related to the structure of water masses at present and inferred for the past these have retained a constant structure of lower circumpolar deep water upper circumpolar deep water north pacific deep water antarctic intermediate water with no apparent changes in the depths of water mass boundaries between glacial and interglacial states sortable silt particle size data for four cores are also examined to show that the vigour of the inflow to the pacific while variable appears to have remained fairly constant on average among the lowest last glacial maximum values of benthic 13c in the world ocean 1 03 based on cibicidoides wullerstorfi occurs here at 2200 m comparable values occur in the atlantic sector of the southern ocean while those from the rest of the pacific are distinctly higher confirming that the southern ocean was the source for the unventilated nutrient enriched water seen here oxygen and carbon isotopic data are compatible with a glacial cold deep water mass of high salinity but lower nutrient content or better ventilated below 3500 m depth this contrasts with the south atlantic where unventilated nutrient enriched water extends all the way to the sea bed comparison with previous studies also suggests that the deeper reaches of the antarctic circumpolar current below 3500 m are not homogeneous all around the southern ocean with the kerguelen plateau and or the macquarie balleny ridges posing barriers to the eastward spread of the deepest low 13c water out of the south atlantic in glacials these barriers combined with inferred high density of bottom waters restricted inter basin exchange and allow three glacial domains dominated by bottom waters from weddell sea adelie coast and ross sea to be defined we suggest that the ross sea was the main source of the deep water entering the pacific below 3500 m

a long square barrel gravity corer for sedimentological and geochemical investigation of fine grained sediments abstract large volume undisturbed sediment cores 3 m long are obtained using a modified gravity corer the corer is square in cross section 12 7 12 7 cm and is designed to facilitate acquisition and subsampling of fine grained sediments sedimentological and geochemical data demonstrate that the modified gravity corer obtains undisturbed cores and preserves the sediment water interface

new gastropods from deep sea hydrocarbon seeps off west africa thirteen new species of gastropods are described from the zairov 1 2 and biozaire 1 3 cruises to the methane seeps off the congo river patellogastropoda paralepetopsis sasakii sp nov neolepetopsidae cocculiniformia pyropelta oluae sp nov and p sibuetae sp nov pyropeltidae tentaoculus granulatus sp nov pseudococculinidae neomphalina leptogyra costellata sp nov family uncertain vetigastropoda puncturella similis sp nov fissurellidae lepetodrilus shannonae sp nov lepetodrilidae caenogastropoda provanna reticulata sp nov and p chevalieri sp nov cordesia provannoides gen et sp nov provannidae phymorhynchus coseli sp nov and p cingulata sp nov conidae heterobranchia hyalogyrina rissoella sp nov hyalogyrinidae all species except t granulatus from a settlement trap belong to groups known from cold seeps and the entire seep fauna here is new to science biogeographical affinity of this gastropod fauna is to the west atlantic seeps not to the mediterranean seeps or mid atlantic vents fragments of the autecology of the species are presented the evolution of the seep gastropod fauna is briefly discussed and a continuous immigration of taxa is supported the oldest verified occurrences of modern taxa in the seeps date back to cenomanian cretaceous time while some taxa seem not to appear until very late tertiary

analysis of radar sea return for breaking wave investigation 1 low grazing angle backscattering data collected by a coherent dual polarized radar installed on a fixed tower in the ocean are analyzed to investigate the properties of sea spikes attributable to wave breaking the distribution of breaking wave speed is narrow banded with an average speed between 2 0 and 2 6 m s in mixed seas with wind speeds between 7 and 14 5 m s the corresponding breaking wavelength is between 2 5 and 4 3 m the length or velocity scale of wave breaking is not proportional to the length or velocity scale of the dominant wave this observation reflects the localized nature of the breaking process and may have significant implications on quantifying various breaking properties such as the energy dissipation or area of turnover by breaking waves the fraction of sea spike coverage generally increases with wind speed but the trend of increase is modified by the intensity and relative direction of background swell parameterizations of sea spike coverage needs to take into consideration both wind and wave factors similarities and differences between sea spikes and whitecaps are discussed in particular while both quantities show a similar power law dependence on wind speed the fraction of sea spike coverage is considerably higher than that of whitecap coverage this result reflects the prevalence of steep features that produce quasi specular facets and short scale waves bounded to intermediate waves during breaking these quasi specular facets and bound waves contribute significantly to enhancing the radar sea return but may not entrain air to produce whitecap signature

on the instability and evolutionary age of deep sea chemosynthetic communities abstract though not directly dependent on photosynthesis deep sea chemosynthetic communities have not been sheltered from catastrophic changes affecting earth s photic zone instead the constituent animals may be particularly vulnerable to large climatic changes that have historically affected ocean temperatures and circulation patterns chemosynthetic animals occupy narrow redox zones mostly at hydrothermal vents hydrocarbon seeps or sites of organic deposition where subsurface fluids laden with reduced gases e g sulfides methane hydrogen meet oxygenated seawater dependence on chemolithoautotrophic bacteria as primary producers may render these deep sea communities particularly susceptible to climatic changes that alter the breadth of the oxic anoxic interface the fossil record clearly reveals major transitions of chemosynthetic faunas during the middle to late mesozoic failing to support prior hypotheses that these environments harbor an extraordinary number of ancient relics and living fossils the molecular phylogenetic analyses summarized herein support cenozoic

early diagenetic remineralization of sedimentary organic c in the gulf of papua deltaic complex papua new guinea net loss of terrestrial c and diagenetic fractionation of c isotopes oceania supplies 40 of the global riverine flux of organic carbon approximately half of which is injected onto broad continental shelves and processed in shallow deltaic systems the gulf of papua on the south coast of the large island of new guinea is one such deltaic clinoform complex it receives 4 mt yr 1 particulate terrestrial organic carbon with initial particle corg loading 0 7 mg m 2 corg loading is reduced to 0 3 mg m 2 in the topset upper foreset zones of the delta despite additional inputs of mangrove and planktonic detritus and high net sediment accumulation rates of 1 4 cm yr 1 carbon isotopic analyses 13c 14c of co2 and corg demonstrate rapid 100 yr remineralization of both terrestrial 13c 28 6 and marine corg 13c 20 5 ranging in average age from modern bomb 14c 60 to 1000 yr 14c 140 efficient and rapid remineralization in the topset upper foreset zone is promoted by frequent physical reworking bioturbation exposure and reoxidation of deposits the seafloor in these regions particularly 20 m apparently functions as a periodically mixed suboxic batch reactor dominated by microbial biomass although terrestrial sources can be the primary metabolic substrates at inshore sites relatively young marine corg often preferentially dominates pore water co2 relative to bulk corg in the upper foreset thus a small quantity of young rapidly recycled marine organic material is often superimposed on a generally older less reactive terrestrial background whereas the pore water co2 reflects both rapidly cycled marine and terrestrial sources terrestrial material dominates the slower overall net loss of corg from particles in the topset upper foreset zone i e recycled marine corg leaves little residue preferential utilization of corg subpools and diagenetic fractionation of c isotopes supports the reactive continuum model as a conceptual basis for net decomposition kinetics early diagenetic fractionation of c isotopes relative to the bulk sedimentary corg composition can produce changes in 14c activity independent of radioactive decay in the gulf of papua topset upper foreset 14c of pore water co2 averaged 300 greater than corg sediment between 1 3 m depth in deposits diagenetic fractionation and decomposition aging of sedimentary corg compromises simple application of 14c for determination of sediment accumulation rates in diagenetically reactive deposits

a sediment record of cyclic bottom current variability from the northwest weddell sea cores and 3 5 khz sub bottom profiles collected from the continental slope and rise near 64 s 52 w off the tip of the antarctic peninsula reveal transport and depositional processes in a high energy environment a large channel runs downslope from the shelf break the remaining slope area is smooth and shows no acoustic penetration except locally in the lee of topography sediments on the slope and rise were mainly deposited by suspension from a 150 to 300 m thick nepheloid layer periodic resuspension and winnowing by bottom currents has produced coarse lags of ice rafted debris throughout these deposits and has also produced an elongated field of mudwaves running parallel to the base of the slope these low amplitude asymmetric features were formed by currents flowing from west to east parallel to the local slope short gravity cores show a compositional and textural cyclicity developed between two distinct lithologies intervals of poorly sorted sediment barren of fauna and with mud dominated size distributions are interpreted to result from a cold climate and low bottom current strength production of weddell sea bottom water probably lessened during these times and there was a greater duration of sea ice cover these sediments are interbedded with winnowed and better sorted deposits comprising fine sands and silts that contain abundant planktonic foraminifera interpreted as implying warmer climatic conditions and stronger current activity a varied calcareous benthic foraminiferal assemblage also indicates that these intervals lay above the ccd during deposition renewed and invigorated production of bottom water is implied contemporaneous with a shorter duration of sea ice cover petrographic evidence indicates an antarctic peninsula source throughout the cycles are considered to be the result of climatic fluctuations occurring over the timespan of glacial interstadials although confirmation of this timescale awaits acquisition of an absolute chronology

distribution and sources of particulate organic matter in the water column and sediments of the fly river delta gulf of papua papua new guinea suspended particles from surface and bottom waters and surficial sediments from the seabed were collected throughout the fly river subaqueous delta region during the monsoon season in january 2003 because of the unusually low river discharge associated with a strong el nino water column salinities were relatively high 10 to 32 throughout most of the delta with brackish salinities 4 wt relatively high organic carbon nitrogen molar ratios oc n 20 mol mol and quite depleted stable isotopic compositions of organic carbon 13coc 27 in contrast surface sediments in the seabed displayed spatially uniform compositions that were characterized by markedly lower oc contents 1 1 0 8 wt lower oc n ratios 17 9 mol mol and relatively enriched 13coc compositions 25 5 1 1 the radioisotopic compositions of oc from a selected set of seabed samples 14coc of 408 82 indicate om in surface sediments is old 14c ages of 2800 to over 6000 years before present the ratios of organic carbon to mineral surface area exhibited by these sediments are within the typical mono layer equivalent ranges characteristic of shelf sediments and do not reflect the preferential removal of terrigenous om overall these compositions indicate that while water column pom appears to be derived mainly from terrigenous vascular plant debris and riverine estuarine phytoplankton the source of most of the sedimentary pom is aged soil oc ultimately derived from c3 vegetation we speculate that the concentrations and sources of suspended pom in the water column of the fly river delta region reflect the conditions of low river discharge low wave energy and neap tides encountered at the time of sampling in contrast pom compositions in surface sediments are consistent with the transport and deposition of old mineral bound oc most likely eroded from the upland regions of the fly river watershed which is characterized by steep slopes high precipitation and c3 tropical forests and grasslands

sea bed mixing and particle residence times in biologically and physically dominated estuarine systems a comparison of lower chesapeake bay and the york river subestuary biologically dominated lower chesapeake bay and the physically dominated york river subestuary are contrasted in terms of the dynamics of sediment mixing strata formation and sea bed particle residence times two lower bay sites were examined both are located within the bay stem plains and are characterized by muddy sand and an abundance of large deep dwelling organisms x radiographs indicate extensive biological reworking of sediments with no long term preservation of physical stratification 210pb profiles reveal low sediment accumulation rates at both lower bay sites 80vs6 30 cm2year 1 in contrast the york river site located within a partially filled palaeochannel is predominantly mud with a depauperate benthic community dominated by small short lived shallow dwelling organisms although210pb accumulation rates at the york river site 0 2 cm year 1 are similar to those measured in the lower bay there is little bioturbation in addition transient bed forms at the york river site form laterally persistent linear ridges and furrows sub parallel to the channel spaced 10 20 m apart these observations coupled with evidence of episodic erosion and deposition from radioisotope and porosity profiles and x radiographs suggest that the upper 60 120 cm of the sea bed are dominated by physical mixing deep mixing and low accumulation rates result in long residence times of particles in the mixed upper portion of the sea bed 102year at both locations despite different mixing controls i e biological diffusive vsphysical advective

defining and quantifying microscale wave breaking with infrared imagery breaking without air entrainment of very short wind forced waves or microscale wave breaking is undoubtedly widespread over the oceans and may prove to be a significant mechanism for enhancing the transfer of heat and gas across the air sea interface however quantifying the effects of microscale wave breaking has been difficult because the phenomenon lacks the visible manifestation of whitecapping in this brief report we present limited but promising laboratory measurements which show that microscale wave breaking associated with evolving wind waves disturbs the thermal boundary layer at the air water interface producing signatures that can be detected with infrared imagery simultaneous video and infrared observations show that the infrared signature itself may serve as a practical means of defining and characterizing the microscale breaking process the infrared imagery is used to quantify microscale breaking waves in terms of the frequency of occurrence and the areal coverage which is substantial under the moderate wind speed conditions investigated the results imply that bursting phenomena observed beneath laboratory wind waves are likely produced by microscale breaking waves but that not all microscale breaking waves produce bursts oceanic measurements show the ability to quantify microscale wave breaking in the field our results demonstrate that infrared techniques can provide the information necessary to quantify the breaking process for inclusion in models of air sea heat and gas fluxes as well as unprecedented details on the origin and evolution of microscale wave breaking

methane seepage effects on biodiversity and biological traits of macrofauna inhabiting authigenic carbonates abstract authigenic carbonate rocks at methane seeps are recognized as hosting diverse and abundant invertebrate assemblages with potential forcing from fluid seepage and hydrography mensurative studies of carbonate macrofauna 0 3 mm at hydrate ridge or revealed little effect of water depth and overlying oxygenation at 600 m and 800 m but a large influence of seepage activity on density taxonomic composition diversity and biological traits feeding lifestyle motility size and calcification rocks exposed to active seepage had 3 4 higher total macrofaunal densities than under inactive conditions assemblages exhibited higher species richness and reduced evenness greater dominance under active seepage than inactive conditions but no difference in h or rarefaction diversity actively seeping sites were characterized by errant motile bacterial grazing small and medium sized heavily calcified species whereas inactive sites exhibited a greater diversity of feeding modes and more burrowers sessile large and lightly calcified species active rocks supported more exogonid syllidae ampharetid and cirratulid polychaetes provannid snails pyropeltid limpets nemerteans and sponges whereas inactive rocks supported higher densities of ophiuroids isopods gammarid amphipods hydroids typosyllis syllidae and tanaids transplant experiments in which rocks were transferred between active and inactive sites at hydrate ridge north 600 m revealed that assemblages respond within 13 months to increase or cessation of seepage taking on the feeding size and calcification characteristics of the background fauna at the new site lifestyles and motility patterns shifted more slowly as the sessile attached species did not track seepage as quickly provannid snails and pyropeltid limpets rapidly colonized rocks transplanted to active sites and disappeared when transplanted to inactive sites given the known variability of fluid fluxes and rapid community response a mosaic of communities changing in space and time is hypothesized to generate the relatively high species diversity at methane seeps

vertical fluxes of hydrocarbons on the northwest shelf of australia as estimated by a sediment trap study abstract sediment traps were deployed on the northwest shelf nws of australia in november 1996 to determine fluxes of organic matter and inorganic elements from the photic zone to deeper waters transecting the exmouth shelf to exmouth plateau dry weight fluxes from the traps ranged from 124 to 616 mg m 2 day 1 and poc fluxes ranged from 22 8 to 43 9 the biogenic hydrocarbons consisted of biomarkers indicative of marine zooplankton phytoplankton and bacteria gc analyses also revealed a significant component of petroleum derived hydrocarbons through the presence of an unresolved complex mixture ucm that was approximately 4 times the biogenic hydrocarbon flux at shallow stations and up to 7 times at the most offshore station the molecular characteristics of these hydrocarbons were investigated using gc ms and gc ms ms and compared with local and regional petroleum accumulations gc ms analysis showed the hydrocarbons included n alkanes alkylated aromatics plus hopane and sterane biomarkers indicating a mature and moderately degraded crude oil the sterane and triterpane signatures also indicated that the source rock of this oil was marine sediment with a calcareous lithology and of probable mesozoic age commercially exploited oils of similar composition are mostly not known on the nws however there are indications that there is an active petroleum system with some similar characteristics in the southern carnarvon basin as shown by oils of anomalous composition to the chervil north herald and south pepper fields these results indicate that exploration strategies in the region should not be confined to oil reserves based on the upper jurassic dingo claystone source

glacial interglacial paleoenvironments of the eastern atlantic ocean the biogeochemical ocean flux study bofs paleoceanography program the papers in this special section discuss many aspects of paleoenvironmental analysis performed using various proxies on cores collected in the northeastern and tropical eastern atlantic during two cruises in the framework of the nerc biogeochemical ocean flux study program bofs coring of the northern bofs leg was carried out on leg 3 of the 1989 bofs program rrs discovery cruise 184 mccave 1989 forty one cores were taken on a north south transect at about 20 w from the flanks of the mid atlantic ridge 47 n to gardar drift 59 n at water depths between 1150 and 4050 m of these 15 cores were taken using a 3 m long large diameter kastenlot corer designed by zangger and mc cave 199o cruise and core data are given by manighetti et al this issue the southern leg coring was carried out on leg c of the 1990 bofs program rrs charles darwin cruise 53 shimmield 199o forty six cores including 14 using the kastenlot corer were taken along a transect at about 2o w between 18 and 42 n at depths between 3000 and 4900 m and focusing on an area off northwest africa

an empirical mode decomposition method for sea surface wind measurements from x band nautical radar data in this paper sea surface wind direction and speed are obtained from x band nautical radar images a data control strategy is proposed to distinguish rain free and rain contaminated radar data the radar data are decomposed by an ensemble empirical mode decomposition method into several intrinsic mode functions imfs and a residual a normalization scheme is applied to the first imf to obtain the amplitude modulation am component wind direction is determined from the residual for the rain free and high wind speed rain contaminated data and from the am portion of the first imf for the low wind speed rain contaminated data based on curve fitting a harmonic function wind speed is determined from a combination of the residual and the am part of the first imf for both rain free and rain contaminated data using a logarithmic relationship results employing ship borne radar and anemometer data collected in a sea trial off the east coast of canada are presented the root mean square differences for wind direction and speed measurements are 11 5 and 1 31 m s respectively compared with reference values from anemometers

wind retrieval from shipborne nautical x band radar data in this paper we study the retrieval of wind information from nautical x band radar data in contrast to previous studies where data from stationary research platforms were used this study focuses on data from a moving platform encountering a larger variety of conditions than a platform at a fixed location compared to traditional in situ sensors wind data derived from nautical radar images are much less susceptible to air flow distortion by the platform since the images cover a large area around the ship images collected with a standard nautical hh polarized x band radar operating at grazing incidence exhibit a single intensity peak in upwind direction the wind retrieval method developed here uses a harmonic function that is least squares fitted to the radar backscatter intensity as a function of antenna look direction the upwind direction is given by the direction that corresponds to the peak of the fitted function an empirical model function is derived to retrieve the wind speed from the average radar backscatter intensity contrary to wind retrieval methods that have been proposed before this approach is well suited for data acquired from a moving platform as it functions well even if the radar field of view is partially shadowed and does not require ship motion correction here we focus on data that were collected during two storms using the first storm to derive and the second to test the empirical model functions the method is validated using measurements from two ship based anemometers

field observations of radar backscatter from the ocean surface under low wind speed conditions unique simultaneous field observations of wind speed and images of vertically polarized radar backscatter from the ocean surface at low grazing angles during low wind and weakly stable stratification show interesting similarities and an important difference depending on whether the average wind is falling or rising when the wind speed begins to fall there is a delay before the area averaged radar backscatter begins to fall when the wind speed begins to rise the backscatter rises immediately this observation points to hysteresis in the relationship between radar backscatter and wind speed such that more wind is necessary to generate radar backscatter of a given intensity than is necessary to maintain it this likely arises from differences between the generation of wind driven gravity capillary waves and the maintenance of gravity capillary waves and or microbores also saturation was observed in the radar backscatter at wind speeds between 2 1 and 2 8 m s 1 for both rising and falling winds this saturation may be related to the energetics of the centimeter scale gravity capillary waves and or microbores that cause the backscatter during rising winds the backscatter may saturate because fine scale features of the ocean surface reach a maximum amplitude well before wind derived energy is transferred upscale to larger waves whose tilting effect would ultimately produce the familiar increase in radar backscatter with increasing wind during falling winds the backscatter may saturate because of residual momentum in the surface wave field finally for both rising and falling winds radar backscatter and wind speed are in general correlated above a wind speed of 1 7 m s 1 while below this value they are not this observation of the critical wind speed necessary to generate or maintain wind related backscatter is consistent with results from a recent field observation and with existing laboratory based observations

breaking wave contribution to low grazing angle radar backscatter from the ocean surface 1 the anomaly of radar sea spikes defined here as the non bragg scattering events with backscattering cross section of horizontal polarization exceeding that of the vertical polarization has been associated with steep wave features possibly going through wave breaking process with or without whitecap manifestation this property is exploited for using a dual polarized radar as a remote sensing breaking wave detector field data collected in the ocean covering wind speeds from 7 to 15 m s grazing angles from 1 4 to 5 5 and with different levels of background swell influence are analyzed to quantify the radar cross section and doppler velocity from sea surfaces with and without wave breaking key results of the breaking effects are increasing significantly the doppler velocity of both polarizations about 50 faster enhancing the horizontally polarized backscattering cross section drastically with 10 15 db increase and producing relatively small change in the vertically polarized cross section about 1 2 db increase the presence of swell in the same direction of wind waves reduces both the radar backscatter and the impact of breaking waves on radar return by inference the swell presence decreases the ocean surface roughness and breaking activity these results are consistent with earlier in situ surface wave measurements and our expectation of swell modification of breaking process due to interaction of short waves and the orbital velocity of long swell

seabed dynamics of the inner amazon continental shelf temporal and spatial variability of surficial strata the continental shelf southeast and northwest of the amazon river mouth is overlain by a sediment layer of about a meter in thickness characterized by 210pb profiles consisting of one or more segments with nearly uniform excess activity uniform 210pb activity profiles in shelf environments commonly are a result of intense biological reworking of sediments however biological activity is minimal in this area hence this surficial layer sl is a result either of physical reworking of the sediments or of rapid possibly episodic deposition of sediment factors controlling the formation of the sl were examined during the amasseds project between august 1989 and october 1991 primarily using 210pb t1 2 22 3 yr activity profiles and x radiography the thickness and character of the sl were assessed at four locations reoccupied during four seasonal periods corresponding to various riverine and oceanographic conditions e g discharge stage wind stress one of these stations was reoccupied during semidiurnal and fortnightly periods additionally replicate sediment cores were obtained at stations in order to assess small scale spatial variability of geochemical and sedimentological characteristics in the seabed the sl thicknesses in replicate sediment cores obtained at each site were found to vary within 5 cm normalized thickness of the sl decreased by an average of 17 cm between august 1989 and february 1990 a period of increasing wind stress during falling to rising river discharge the sl thickness subsequently increased slightly 8 cm from february to may 1990 and increased again 27 cm between may 1990 and october 1991 the maximum sl thicknesses were observed in october a period of low wind stress and minimal river input suggesting that the observed seasonal changes are dictated by oceanographic conditions as well as by sediment discharge variations in sl thickness are reflected by changes in suspended sediment mostly as fluid muds as the highest suspended sediment inventories and most extensive fluid muds are observed during the period when sl thickness is at a minimum although a significant sl was present during all of the sampling periods changes in the character of 210pb profiles at two of the stations suggest that substantial perhaps complete removal and redeposition of the sl occurred some time between february and may preserved strata i e below the sl is characterized by greater evidence of bioturbation and increased sand content but otherwise is similar to that of the sl long term preservation of strata is thought to occur through episodic suspension and redeposition of the sl with net accumulation of decimeter thick hiatus bounded layers

studies of dual polarized low grazing angle radar sea scatter in nearshore regions reports on experiments featuring horizontally hh and vertically vv polarized x band marine radar sea scatter imagery in the coastal environments of bermuda and la jolla under light to moderate winds and the absence of long gravity waves these conditions allowed the study of fundamental scattering mechanisms from small scale roughness and short waves of a few meters wavelength or less shorter than the radar pulse while a large fraction of radar data collected revealed the presence of slick bands the authors analyze the radar echo of ambient background outside of the slicks sea scatter data were digitally recorded for 360 spl deg azimuthal coverage for grazing angles between 1 3 5 spl deg and were converted to normalized radar cross section nrcs or spl sigma spl deg images the hh and vv polarizations show quite different spatial texture with hh exhibiting a discrete character and vv being more nearly spatially homogeneous grazing angle dependencies are different for hh and vv upwind downwind differences of mean nrcs show ratios of just 4 6 db for vv but are equal or greater than the 16 db noise imposed limit for hh for the low wind conditions hh nrcs grazing angle characteristics are shown to correlate with biological activity indicators of the coastal waters with a fourth power dependence in relatively unproductive waters to a nearly quadratic in productive waters arguments are presented that suggest different scattering mechanisms for the two polarizations evenly distributed bragg scatter patches for vv and scatter from small asymmetric bore features for hh a multipath illumination model for small bore features is outlined and scale sizes for the small scale breakers inferred from the experimental results presented are between 2 and 4 cm in height with crest widths between 24 and 48 cm

probability of wave breaking and whitecap coverage in a fetch limited sea the analytical model of snyder and kennedy 1983 for the whitecap coverage w and that of srokosz 1985 for the probability of wave breaking b are developed into practically applicable forms by closely combining theoretical analysis and data fitting the database consists of two parts the data collected from published literature and those recently measured in the bohai bay a time averaging technique is used to estimate the fourth spectral moment of the mean joint north sea wave project spectrum the resulting expressions are simple in which w and b depend only on the nondimensional fetch for a fetch limited sea

a redesigned kasten core barrel and sampling technique abstract a modified kasten core barrel was developed to obtain cores with nearly 100 sediment retrieval while minimizing disturbance of the sediment water interface one side of the 15 15 cm square barrel is doubled by a second movable plate which can be moved upwards by a series of hand screws thus enabling complete sideways extrusion of the core this produces a set of subcores or slabs of equal quality with preserved stratigraphy which can be x rayed subsampled stored or frozen for geochemical studies the new kasten core barrel is effective in rough weather inexpensive to build easy to handle and enables fast core processing on board

deep flow in the madagascar mascarene basin over the last 150 000 years the sw indian ocean contains at least four layers of water masses with different sources deep antarctic lower circumpolar deep water flow to the north midwater north indian deep water flow to the south and upper circumpolar deep water to the north meridional convergence of intermediate waters at 500 1500 m and the shallow south equatorial current flowing west sedimentation rates in the area are rather low being less than 1 cm ka 1 on madagascar ridge but up to 4 cm ka 1 at amirante passage bottom flow through the madagascar mascarene basin into amirante passage varies slightly on glacial interglacial time scales with faster flow in the warm periods of the last interglacial and minima in cold periods far more important are the particularly high flow rates inferred from silt grain size which occur at warm to cold transitions rather than extrema this suggests the cause is changing density gradient driving a transiently fast flow corroboration is found in the glacial interglacial range of benthic d18o which is ca 2 suggesting water close to freezing and at least 1 2 more saline and thus more dense glacial bottom waters than present significant density steps are inferred in isotope stage 6 the 5e 5d and 5a 4 transitions oxygen isotope data suggest little change by mixing in glacial bottom water on their northward path benthic carbon isotope ratios at amirante passage differ from glacial southern ocean values due possibly to absence of a local productivity effect present in the southern ocean

uranium geochemistry on the amazon shelf evidence for uranium release from bottom sediments in amazon shelf waters as salinity increases to 36 5 10 3 dissolved uranium activities increase to a maximum of 4 60 dpm 1 1 this value is much higher than the open ocean value 2 50 dpm 1 1 indicating a source of dissolved uranium to shelf waters in addition to that supplied from open ocean and riverine waters uranium activities are much lower for surface sediments in the amazon shelf seabed mean 0 69 09 dpm g 1 than for suspended sediments in the amazon river 1 82 dpm g 1 data suggest that the loss of particulate uranium from riverine sediments and the consequent input of dissolved uranium to shelf waters is probably the result of uranium desorption from the ferric oxyhydroxide coatings on sediment particles and or uranium release by mobilization of the ferric oxyhydroxides the total flux i e riverine flux plus desorbed remobilized particulate flux of dissolved 238u from the amazon shelf about 1 2 1015 dpm yr 1 constitutes about 15 of uranium input to the world ocean commensurate to the amazon river s contribution to world river water discharge approximately 18 measurement of only the riverine flux of dissolved 238u underestimates by a factor of about 5 the flux of dissolved238u from the amazon shelf to the open ocean

polycyclic aromatic hydrocarbon distribution within lower hudson river estuarine sediments physical mixing vs sediment geochemistry abstract sediments and porewaters from two cores one from the east river new york and one from newark bay new jersey were sampled for polycyclic aromatic hydrocarbons pahs and other geochemical markers including 210 pb specific activities despite what appears to be similar sources of pahs to sediments within each core as inferred by ratios of alkylated to non alkylated pahs and pah isomer ratios sediments and associated pahs have undergone distinctly different depositional processes at each site sediments from the core in the east river appear to have been subject to intense physically driven resuspension resulting in selective depletion of low molecular weight pahs within the core presumably due to processes such as enhanced desorption and scouring of particle surfaces although sediment pah concentrations were higher in the east river core compared to the newark bay core porewaters were depleted of the majority of pahs analysed in the east river core relative to the newark bay core precluding quantifying sediment porewater pah distribution coefficients in this core sedimentary variables such as c n ratio particle surface area and sedimentary soot carbon were not related to organic carbon normalized pah distribution coefficients k oc obs rather in the core from the newark bay site k oc obs were influenced by sediment mixing and porewater dissolved organic carbon doc results indicate that in urban coastal areas the physical factors influencing time scales of sediment resuspension and deposition may be of primary importance over particle geochemistry in determining whether pahs will likely equilibrate between sediments and pore waters

sedimentary structures on the bengal shelf a multi scale approach to sedimentary fabric interpretation abstract sedimentary structures on the bengal shelf are examined using x radiographic thin section and scanning electron microscopic sem techniques which reveal contrasting depositional processes for the inner and middle shelf as well as for either side of a major submarine canyon indenting the western shelf margin the inner shelf is characterized by tidally produced interlaminated silts and muds that reveal a neap spring cyclicity the cyclicity is more pronounced for the winter season when high discharge monsoon conditions do not obscure the tidal signature on the middle shelf alternating beds of silts and muds probably represent high discharge and low discharge conditions respectively silty beds on the western margin of the submarine canyon are thinner than those found on the eastern margin the western margin receives predominantly fine grained ganges sediments in contrast to the eastern area which receives both ganges and coarser brahmaputra sediments these observations indicate that the submarine canyon presently intercepts westward along shelf sediment transport muddy beds and laminae that appear internally homogeneous in the x radiographs and exhibit faint bedding in thin sections often are composed of resistant protruding and less resistant recessed microlaminae as observed with the sem on the inner shelf resistant microlaminae are composed of fine grained polymineralic equant particles the less resistant microlaminae are composed of large platy illite grains rimmed by smaller platy or lath like illite particles resistant and less resistant microlaminae within middle shelf muddy sediments have the same textural characteristics observed on the inner shelf however both types essentially are monomineralic on the middle shelf the smallest particles within the less resistant microlaminae exhibit an open flocculated structure that may result from higher salinity and or decreased bottom shear stress associated with tidal currents biological structures predominantly occur on the western inner and middle shelf particularly in intervals of high smectite concentrations this relationship may exist because of a preferential organic affinity for expandable minerals providing a favorable substrate for benthic organisms

analysis and modelling of gravity and piston coring based on soil mechanics the effects of gravity and piston corers on the dimensional accuracy of marine sediment cores is analysed using principles of soil mechanics a model for the coring process is built around the feedback that arises and develops between the core barrel and the sampled sediment this model for sediment response is applied to different hypothetical coring scenarios which are then compared to real examples providing insights into the specific effects of each sampling method and the development of these effects down core four cores from a single location on the iberian margin are found to contain stratigraphically intact successions that differ in length by a factor of up to 2 7 due solely to the different effects of each coring method these dimensional discrepancies are attributed to the combined effects of over sampling in the upper portions of the piston cores due to cable rebound causing upward piston acceleration and under sampling dominant in the basal portions of the open barrel gravity type cores it is suggested that heavier piston corers deployed on longer lighter cables are prone to greater over sampling ratios over longer stratigraphic intervals due to the increased likelihood and extent of cable rebound cable rebound may also give rise to double penetration of gravity corers resulting in repeated stratigraphic intervals knowledge of the dimensional accuracy of marine sediment cores is essential to an evaluation of past sedimentation rates and hence interpretations of past depositional processes it is therefore essential that we recognise the sampling effects of each coring method and their variability down core lest coring artefacts be interpreted as sedimentary signals different core types may be more suited to different palaeoceanographic investigations hence failing the development of a practical cable deployed recoilless piston corer a combination of a variety of core types will permit the best acquisition of the in situ stratigraphic truth our results suggest that a large diameter dc 20 30 cm square barrel gravity corer for the top 10 12 m combined with a cylindrical piston corer below 10 m may provide the least deformed material

long hydroplastic plastic barrel sediment cores suitable for geotechnical testing abstract long large diameter 8 cm sediment cores are obtained by outfitting the pvc core barrels with a sliding weight placed near its bottom no metal barrel is needed laboratory tests prove that the cores thus obtained are undisturbed and suitable for geotechnical testing

early diagenetic cycling incineration and burial of sedimentary organic carbon in the central gulf of papua papua new guinea 1 the clinoform complex of the gulf of papua represents a major deltaic system in oceania two seasons largely control seafloor dynamics and sedimentary c cycling the relatively quiescent nw monsoon and the se trades characterized by remobilization and reoxidation of topset deposits surface sediments 20 cm are reactive with co2 production fluxes 35 42 mmol m 2 d 1 at mangrove channel and topset sites during the monsoon and 10 20 mmol m 2 d 1 on the foreset bottomset 40 m fluxes decrease by a factor of 0 3 on the topset during the transition period and trades the 13 14c isotopic compositions of pore water co2 reveal diagenetic fractionation with dominant utilization of young 14c 1 4 31 1 terrestrial c substrates inshore channels topset 13c 29 to 25 and a progressive increase of young marine c sources seaward outer topset foreset bottomset 13c 22 2 to 19 5 remineralization patterns of terrestrial and marine corg demonstrate cross shelf exchange multiple tracers show that a suboxic mobile mud layer 10 60 cm thick usually 10 30 cm characterizes the central gulf topset and umuda valley off the fly river and unconformably overlies methanic deposits releasing old co2 14c 159 to 229 residual terrestrial corg delivered to the bioturbated foreset continues to be remineralized slowly generating co2 having net 14c 270 within sediments deposited 100 200 years ago the reactivity of corg below 0 5 m in the foreset is 10 20 times lower than expected based on accumulation rates reflecting loss of 50 of sedimentary corg on the topset which functions as a suboxic incinerator

comparison of composite bragg theory and quad polarization radar backscatter from radarsat 2 with applications to wave breaking and high wind retrieval 1 depolarized de pol radar backscatter is now produced by many spaceborne satellites analysis of radarsat 2 r2 quad polarization quad pol data with collocated in situ ocean wind measurements reveals that the de pol radar backscatter does not saturate in high winds this is a significant development for radar wind sensing because wind retrieval with copolarized co pol backscatter suffers from problems of incidence and azimuth angle dependent signal saturation and dampening in high winds we present a study comparing satellite quad pol measurements with the composite surface bragg cb theory of radar backscattering from the ocean surface the co pol data are in good agreement with the cb theory de pol data are more sensitive to wind speed compared to theoretical prediction thus retrieval of high winds is more accurate using the de pol return the cubic wind speed dependence of de pol returns in high winds reflects the significant breaking wave contributions the relationship can be used to obtain wave breaking properties from space

observation and intercomparison of wave motion and wave measurement using shore based coherent microwave radar and hf radar shore based coherent microwave radar and high frequency hf surface wave radar are two components of a rapidly emerging set of technologies suitable for ocean wave remote sensing to investigate their differences this paper describes and analyzes the relationship between the water particle velocity and the wave height spectrum based on linear wave theory which underpins the algorithms developed for the analysis of data collected by coherent microwave radar the backscatter mechanism which addresses the interaction of the hf radio waves with the ocean surface waves as well as the empirical method adopted in our hf radar is also presented the wave characteristics observed by the shore based coherent s band radar microwave ocean remote sensor morse are analyzed a multifrequency hf mhf radar based on a circular receiving array which is capable of sensing waves up to 100 km offshore is also introduced an intercomparison of the wave height measurements obtained from the morse mhf radar and wave buoy is made the comparison indicates that the wave heights measured by the morse and the mhf radar are consistent with the buoy derived wave heights with the root mean square differences rmsds of 0 27 and 0 37 m respectively

a numerical study of the retrieval of sea surface height profiles from low grazing angle radar data a numerical study of the retrieval of sea surface height profiles from low grazing angle radar observations is described the study is based on a numerical method for electromagnetic scattering from 1 d rough sea profiles combined with the ldquoimproved linear representationrdquo of creamer for simulating weakly nonlinear sea surface hydrodynamics numerical computations are performed for frequencies from 2975 to 3025 mhz so that simulated radar pulse returns are achieved the geometry utilized models a radar with an antenna height of 14 m observing the sea surface at ranges from 520 to 1720 m the low grazing angles of this configuration produce significant shadowing of the sea surface and standard analytical theories of sea scattering are not directly applicable three approaches for retrieving sea height profile information are compared the first method uses a statistical relationship between the surface height and the computed radar cross sections versus range an incoherent measurement a second method uses the phase difference between scattering measurements in two vertically separated antennas ldquovertical interferometry in the retrieval the final technique retrieves height profiles from variations in the apparent doppler frequency coherent measurements versus range and requires that time stepped simulations be performed the relative advantages and disadvantages of each of the three approaches are examined and discussed

influence of seep emission on the non symbiont bearing fauna and vagrant species at an active giant pockmark in the gulf of guinea congo angola margin detailed surveying with an rov found that a dense and diverse cold seep community colonises a giant pockmark located at 3200 m depth 8 km north from the deep congo channel several types of assemblages either dominated by mytilidae and vesicomyidae bivalves or siboglinidae polychaetes are distributed on the 800 m diameter active area the site is characterised by a most active central zone in a depression with abundant carbonate concretions and high methane fluxes where high density clusters of mussels and siboglinids dominate in contrast the peripheral zones display large fields of dead and live vesicomyids on soft sediment with a lower mean density and lower methane concentration in seawater the associated megafauna includes alvinocarididae shrimps echinoids holothurians of the family synaptidae several species of gastropods two species of galatheids and zoarcidae and ophidiidae fishes multivariate analyses of video transect data show that the distribution of these major megafauna species at the pockmark scale is influenced by the habitat heterogeneity due to fluid or gas emission occurrence of hydrates substratum variability and by the presence of large symbiont bearing species several assemblages dominated either by mytilids vesicomyids or siboglinids have been sampled for megafauna densities and biomass estimations and stable isotope measurements 13c and 15n of dominant species and food sources the highest estimates of megafauna densities have been obtained in mytilid beds according to their stable isotopes values non symbiont bearing species mainly rely on chemosynthesis originated carbon either as primary consumers of chemoautotrophic microorganisms or at higher trophic level recycling organic matter or relying on bivalve and tubeworm production most of them likely feed on different sources like shrimps but differences according to habitat have been evidenced carbon and nitrogen isotope ratios of galatheids and benthic or benthopelagic fishes captured by trawls at increasing distances from the pockmark provide evidence of the high variability in the proportion of chemosynthesis originated carbon in their diet from 15 to 38 according to the species captured as far as 4 km to the site

accumulation rates of recent sediments in puget sound washington abstract sixteen profiles of unsupported 210pb activity from long cores along the axis of the main basin of puget sound show that bottom sediments are accumulating at rates of 0 26 0 03 to 1 20 0 16 g cm 2 yr 1 these rates and seven others published earlier suggest that highest accumulation occurs nearly midway along the length of this tidal current dominated basin bioturbated surface layers of cores are as deep as 40 cm but biologic mixing rates are poorly determined individual 210pb accumulation rates along the axis of the main basin range from approximately one to five times greater than the predicted areal average accumulation rate based on estimates of recent sediment input from adjoining rivers and shorelines

neodymium isotopic composition of intermediate and deep waters in the glacial southwest pacific abstract neodymium nd isotopes tracers of deep water mass source and mixing were measured on sedimentary planktic foraminifera with authigenic coatings from a depth transect of cores 1400 4800 m from chatham rise in the southwest pacific over the past 30 ka we observe deglacial variations in the nd isotopic composition which showed an average glacial composition of e nd 5 0 1 0 3 n 4 for cores sites below 3200 mbsl no significant deglacial variation was observed in the nd isotopic composition of intermediate depth waters 1400 mbsl in contrast with benthic foraminifera c 13 data the deglacial e nd shift of cdw in the southwest pacific is consistent with changes observed in the deep south atlantic and equatorial indian ocean but e nd values are offset by 1 e nd unit to more radiogenic values throughout the deglacial records likely due to admixture of a nd isotope signal which was modified in the southern ocean or pacific perhaps by boundary exchange however this modification did not overprint the deglacial nd isotope change the consistent deglacial evolution of e nd in the south atlantic equatorial indian and southwest pacific cdw is evidence for the connection of cdw during the glacial and propagation of diminished north atlantic deep water export to the glacial southern ocean in contrast spatial heterogeneities in the benthic foraminifera c 13 of cdw have been observed in the atlantic indian and pacific basins of the deep glacial southern ocean the nd isotope data implies a well connected deep southern ocean which transported waters from the atlantic to the indian and pacific oceans during the glacial this suggests that basin scale variability in the glacial c 13 composition of cdw was unrelated to circulation changes

radar scattering behavior of estuarine outflow plumes we present results of dual polarized radar scattering measurements of the chesapeake bay outflow plume near unity polarization ratios ratios of horizontally polarized radar echoes over vertically polarized ones are observed in large incidence angle 60 spl deg to 80 spl deg radar echoes from the outflow plume and its frontal boundary normally referred to as a front under strong surface current convergence 0 008 0 02 s sup 1 suggesting the existence of steepened and breaking waves in the regions cumulative distribution functions of the horizontally polarized radar returns from the front show approximately 90 of the radar echoes are from steepened and breaking waves vertically polarized echoes do not show this effect these experimental results substantiate early modeling investigators speculation of featured scattering contributing to horizontally polarized radar signatures of oceanic fronts our results also suggest that horizontal radar polarization can be used to remotely sense additional hydrodynamic processes such as wave trapping blocking and breaking near oceanic fronts better than what is possible with only vertical polarization

the behavior of particle reactive tracers in a high turbidity environment 234th and 210pb on the amazon continental shelf excess 234th and 210pb seabed inventories were measured in cores collected from the amazon continental shelf to examine particle scavenging and seabed dynamics typical excess 210pb inventories range from 100 to 300 dpm cm 2 and the total excess 210pb inventory for the amazon shelf was determined to be 2 7 1017 dpm the 210pb measurements indicate that particle reactive species are scavenged not only from the amazon river but also from the lateral advection of offshore water in order to sustain the 210pb inventories the volume of water supplied by the lateral advection from offshore must be approximately five to ten times the water discharge of the amazon river this lateral advection supplies about 67 of the total excess 210pb to the amazon continental shelf with relatively small contributions from riverine input 31 atmospheric fallout 2 3 and in situ production 0 1 the 234th inventories were measured on four cruises which occurred during periods of differing river discharge wind stress and flow rates of the north brazil current the 234th excess seabed inventories show large spatial and seasonal variability with a range from 0 to 22 dpm cm 2 ratios of predicted 234th inventories over observed 234th inventories indicate that a large portion of the inventories on the inner and mid shelf occur in the fluid mud layer or the suspended sediments the 234th excess seabed inventories are controlled by resuspension cycling the inventories between the water column and the seabed 210pb and 234th excess seabed inventories are compared directly using corrections for the different time scales and offshore concentrations this approach indicates that for most of the shelf the inventories of the shorter term tracer 234th are less than predicted by the inventories of the longer term tracer 210pb there are two explanations for this trend the first is that a larger portion of the 234th inventory occurs in the fluid muds or the water column relative to 210pb the second is that the supply of offshore water scavenging efficiency and or deposition have been lower over the two year study period relative to the last one hundred years

sea surface temperature variability in the subpolar atlantic over the last two millennia 1 a decadal resolution time series of sea surface temperature sst spanning the last two millennia is reconstructed by combining a proxy record from a new sediment sequence with previously published data from core md99 2275 north of iceland the alkenone based sst reconstruction is validated with historic observational data and compared to a new similar temporal resolution reconstruction obtained from sediment core rapid21 3k in the subpolar north atlantic the two sst paleorecords show consistent multidecadal scale coolings throughout the interval and similar expressions during the contrasted climatic periods colloquially known as the medieval climatic anomaly mca and little ice age lia in order to further understand the temporal and spatial sst variations and investigate the influence of natural forcings on the observed sst changes during the last millennium we compare our time series to simulations using the institut pierre simon laplace ipslcm4 v2 climate model this comparison highlights the potential importance of volcanism as a natural forcing driving coherent abrupt cooling events captured in the subpolar north atlantic records

mapping surface currents and waves with interferometric synthetic aperture radar in coastal waters observations of wave breaking in swell dominant conditions airborne and spaceborne interferometric synthetic aperture radars insars produce surface velocity measurements at very high spatial resolutions over a large area the data allow construction of the velocity strain field for highlighting ocean surface processes such as wave breaking and rip currents also coherence between signals from two interferometric channels is a descriptor of the correlation condition of the surface roughness that scatters back the radar signals and it is an indication of the ocean surface turbulence wave breaking is a major turbulence source causing surface roughness decorrelation thus the coherence parameter serves as an independent means for detecting wave breaking the results of breaking detection using roughness decorrelation and critical local acceleration are comparable in this paper the breaking fraction in swell dominant mixed seas along a cross shore transect is compared with several steepness parameters characterizing different length scales of surface waves the highest correlation coefficient from 0 90 to 0 99 is between the breaking fraction and windsea mean square slope contributed primarily by short waves this result reinforces the previous field observations showing that the length scales of breaking waves are much shorter than the energetic components near the spectral peak although dominant waves and the associated wave group modulation are important in triggering the breaking process the large spatial coverage of airborne or spaceborne operation further offers the opportunity to investigate evolution of the surface wave spectrum in high spatial subkilometer resolution this capability is very useful for monitoring the coastal wave and current environment

an examination of froude supercritical flows and cyclic steps on a subaqueous lacustrine delta lake chelan washington u s a density driven submarine flows including turbidity currents play an important role in the transfer of sediment into deep water these bottom hugging flows often produce flow transverse bedforms along their path a sedimentological and geophysical survey of the stehekin river delta in lake chelan washington reveals a downslope elongate field of bedforms on the delta foreset associated with hyperpycnal discharges of the stehekin river an analysis of the bedform morphologies delta geometry and density contrast between lake and river water suggests that these hyperpycnal flows are froude supercritical the bedforms are likely cyclic steps flow transverse bedforms that are bounded by stable hydraulic jumps between alternating subcritical and supercritical flow regimes the ability to examine the three dimensional bed configuration produced by natural density driven flows adds valuable information to the body of experimental work focused on the behavior of cyclic steps in flumes

high resolution dinoflagellate cyst record of environmental change in effingham inlet british columbia canada over the last millennium abstract we present a high resolution sedimentary record of dinoflagellate cysts spanning the last 900 years recovered from effingham inlet a glacial fjord on the west coast of vancouver island canada the combination of seasonal coastal upwelling supporting high levels of marine primary productivity in surface waters together with restricted bottom water circulation in the silled fjord fosters the preservation of laminated sediments in the inner basin of effingham inlet geochemical data are used to assess the sedimentary facies of the core which is composed primarily of laminated units 50 2 occasionally interrupted by seismites 39 5 and homogenous units 10 2 the chronology of the 2 m long core is based on varve counting and fifteen 14c dates and is anchored by a seismite previously dated at ad 1946 the dinoflagellate cyst assemblages are diverse total of 47 taxa abundant average concentrations of 102 900 cyst g 1 of dry sediment and characterized by a proportionally equal contribution of autotrophic and heterotrophic cyst taxa in most samples overall cyst assemblages are characterized by operculodinium centrocarpum 36 2 accompanied by brigantedinium spp 18 0 and dubridinium spp 6 6 multivariate analyses are used to extract the dominant patterns of variability in autotrophic and heterotrophic dinoflagellate cyst assemblages separately and help in identifying the temperature and primary productivity gradients encoded in the cyst sedimentary record in this particular estuary specific intervals identified in the dinoflagellate cyst record are interpreted to represent the local expression of the medieval climate anomaly from the base of the record ad 1090 to 1230 the little ice age ad 1230 to late 19th century and warming in the second half of the 20th century the timing of these intervals are consistent with the regional paleoclimate and help constrain past climatic and oceanographic variability on the west coast of vancouver island the origin of homogenous units in the sedimentary record of effingham inlet and paleoseismicity in the region are also discussed

authigenic ferrimagnetic iron sulfide preservation due to nonsteady state diagenesis a perspective from perseverance drift northwestern weddell sea we document magnetic mineral diagenesis with high resolution magnetic susceptibility hysteresis isothermal remanent magnetization and other rock magnetic measurements through a shallow sulfate m