observed cross shelf flow induced by mesoscale eddies in the northern south china sea abstractcross shelf flow induced by mesoscale eddies has been investigated in the northern south china sea nscs using velocity observations from long ranger adcp moorings mesoscale eddies influe

weakening of the kuroshio intrusion into the south china sea over the past two decades inferred from the satellite and in situ hydrographic data from the 1990s and 2000s the kuroshio intrusion into the south china sea scs had a weakening trend over the past two decades associated with the weakened kuroshio intrusion the kuroshio loop and eddy activity southwest of taiwan became weaker whereas the water above the salinity minimum became less saline in the northern scs the sea surface height southwest of taiwan increased at a slower rate compared to other regions of the scs because of the weakened kuroshio intrusion simulations using the regional ocean modeling system roms pacific model show that the strength of the kuroshio intrusion into the scs decreased from 1993 to 2010 with a negative trend 0 24 sverdrups sv yr 1 1 sv 10 6 m 3 s 1 in the total luzon strait transport lst although wind induced ekman transport through the luzon strait became weaker the magnitude at 0 001 sv yr 1 was too small to compensate for the negative trend of the lst on the other hand the piling up of the water induced by monsoon winds was an important mechanism for changing the pressure gradient across the luzon strait and eventually affecting the lst the sea level gradient between the western pacific and the scs had a negative trend 0 10 cm yr 1 corresponding to a negative trend in the geostrophic transport at 0 20 sv yr 1 the kuroshio transport east of luzon island also had a negative trend which might also be linked to the weakening kuroshio intrusion

do critical stresses for incipient motion and erosion really exist the concept of critical stress for the initial motion of noncohesive sediment beds under turbulent flow conditions is reviewed observational definitions of incipient motion are many and not entirely compatible some laboratory flume observations of sediment movement suggest that no true threshold exists current understanding of turbulent fluid motion at a sediment bed suggests that some particle movement must occur at all nonzero time mean velocities a combined model for flume flow and sediment transport having no threshold is seen to explain features of data that have been previously used to support the threshold concept

anti cyclonic eddies northwest of luzon in summer fall observed by satellite altimeters anti cyclonic eddies northwest of luzon of the philippines in summer fall are identified in the merged data products of satellite altimeters of topex poseidon jason 1 and european research satellites the generation and propagation of the anti cyclonic eddies which are confirmed by satellite ocean color data are found to be a seasonal phenomenon that is phase locked to the onset of the southwesterly monsoon and the relaxation of the cyclonic wind curl in the northeastern south china sea the eddies originate from northwest of luzon in summer move across the northeastern south china sea to reach the china continental slope in fall and propagate southwestward along the continental slope in fall winter inducing shelfbreak current variations in the western south china sea in fall winter the anti cyclonic eddy discovered by li et al 1998 in the northern south china sea is found to originate from northwest of luzon and carry primarily the south china sea waters it does not appear to be an eddy shed from the kuroshio in the luzon strait area as alluded by li et al 1998 and others

vims sea carousel a field instrument for studying sediment transport preliminary results from field experiments using a newly developed annular sea bed flume vims sea carousel are presented to illustrate a method of in situ determination of critical threshold shear stress necessary for sediment entrainment this flume has been deployed in the lower chesapeake bay and on the inner shelf of the middle atlantic bight we applied a series of controlled bed shear stresses by changing the stress sequentially to examine the responses of nearly undisturbed natural sediment beds an optical backscatter sensor mounted on the flume indicated the occurrences of resuspension of bed material we identified clear threshold values of bed shear stress for resuspension generally the sandy inner shelf sediment had a higher critical bed shear stress 0 22 pa for resuspension than that for silty sediments 0 1 0 19 pa data from partially cohesive sediments in the lower chesapeake bay indicate significant seasonal differences in critical bed shear stress 0 19 pa at the beginning of summer and 0 11 pa at the end of summer these differences may be attributed to bioturbation the seasonal difference in the microflora living on the grains or spatial heterogeneity of bed

the influence of oceanic swell on flows over an estuarine intertidal mudflat in san francisco bay in this study we examine the role that remotely forced ocean waves play in the hydrodynamics of an intertidal estuarine mudflat the observations indicate that long period 10 20 s ocean waves are a potentially important source of near bed energy and shear stress in this environment over a two week period in february 2001 we deployed an autonomous sontek hydra system on a mudflat in central san francisco bay and measured velocity and sediment concentration approximately 10 cm from the bed using an acoustic doppler velocimeter adv and an optical backscatter sensor obs the experiment continued through wet high tide and dry low tide periods over an entire spring neap cycle and thus included the variation of near bed velocity over a range of timescales results show that during large ebb tides tidally forced flows dominate the near bed dynamics during calm conditions wind waves dominate whenever the wind direction exposes the mudflat to wind coming off the bay from the south and southwest as occurs during winter storms during periods when tidal forcing is limited and wind waves are small remotely forced ocean swells become an important energy source these motions appear in the burst samples at frequencies between 0 1 and 0 04 hz and their energy correlates well q 0 8 with ocean swell measured from a buoy offshore of san francisco spectral analysis of data shows that the average energy of ocean waves per tide varied between 2 and 15 of total energy load moreover extreme values in the distribution of ocean waves bring episodic bursts of greater energy onto the estuarine mudflat which may influence local suspension of sediments 2003 elsevier ltd all rights reserved

a benthic annular flume forin situmeasurement of suspension feeding biodeposition rates and erosion potential of intertidal cohesive sediments abstract a portable benthic annular flume for thein situmeasurement of suspension feeding biodeposition rates and erosion potential of undisturbed intertidal cohesive sediments with benthic biota is described the experimental procedures used during deployment are also outlined results showing the changes in biodeposition rates sediment resuspension erosion rates and critical erosion velocities associated with large scale km and small scale m spatial differences are presented comparison between laboratory andin situmeasurements demonstrated marked differences in sediment erodability if the physical and biological properties of the sediment are not maintained

low frequency circulation at the edge of the scotian shelf abstract records of current temperature and salinity from a two year mooring program at the shelf break off nova scotia are examined to determine the low frequency oceanic responses to the driving surface wind field and fluctuating offshore currents associated with the gulf stream the seasonal mean and subtidal variance at periods of 2 10 days of the cross shelf currents reflect the strong annual cycle in the wind field measured at sable island the mean vertical shear suggests a simple ekman response to winter increases in the longshore wind component but this model fails quantitatively because 1 the inferred surface layer 20 m transport is much too large and 2 the deep 150 m return flow shows no annual signal the excessive offshore near surface transport in winter must be reconciled with the relatively stationary position of the shelf slope water boundary ssb by invoking intense cross frontal mixing and or a seasonal mean alongshore pressure gradient the seasonal mean longshore currents

intraseasonal variability of cross slope flow in the northern south china sea abstractcross slope flow plays an important role in the exchange of material heat and momentum between the continental shelf and the open sea in the northern south china sea scs long period ob

a model study on the large scale effect of macrofauna on the suspended sediment concentration in a shallow shelf sea abstract the activity of macrofauna on the sea floor is since long known to mediate deposition and erosion of sediment but so far most studies addressed this effect at a local scale in the present paper the contribution of the observed macrofauna distribution exemplified by a bivalve the bean like tellin fabulina fabula formerly known as tellina fabula on large scale sediment transport in the southern north sea is investigated by means of a model study macrofauna effects are considered with respect to the critical bed shear stress and erodibility which are two important factors that control the resuspension rate simulation results for a typical winter month revealed for the first time that the suspended sediment concentration ssc is increased not only locally but beyond the inhabited zones this alteration is not confined to near bed zones but can be observed throughout the entire water column especially during storm events these effects are most prominent in the fine silt fraction coarser and finer fractions are less affected for a selected storm event in february 2010 we explain the counter intuitive decrease in near bed ssc in some areas with a high macrofauna abundance compared to a simulation excluding such macrofauna a high macrofauna induced entrainment rate leads to rapid exhaustion of available sediments at the bed in the model and consequently limits the near bed ssc

reappraisal of anoxia and organic richness with emphasis on cretaceous of north atlantic accumulation of anoxic sediments in the north atlantic during barremian through turonian time early to middle cretaceous was controlled mainly by local conditions although global climatic and oceanographic factors played a supporting role evidence does not support the popular hypothesis developed over the past few years of global or oceanwide anoxia data which contradict this hypothesis are based on 1 a reevaluation of criteria for identifying sediments that accumulated in anoxic water 2 a critical reappraisal of reported worldwide occurrences of anoxic sediments of these ages and 3 an examination of the spatial and temporal distribution of anoxic sediments in the north atlantic and elsewhere a model is proposed in which the earliest anoxic sediments of cretaceous age in the north atlantic were deposited in deep restricted basins by middle cenomanian time about 97 m y ago sluggish circulation had led to a gradual expansion of the oxygen minimum layer permitting deposition of anoxic sediment in nonbasinal settings as well expansion of the oxygen minimum layer caused the calcite compensation depth to rise promoting oxidation of organic carbon and causing contraction of the oxygen minimum layer development of anoxia was thus self damping anoxia effectively disappeared by early senonian time 88 m y ago when improved circulation created oceans more like those of the present some evidence indicates that enhanced biologic productivity and upwelling may have been local factors in fostering anoxia but the early and middle cretaceous were generally not highly productive times

relationships between wave induced currents and sediment grain size on a sandy tidal flat studies of sedimentation on sandy tidal flats have long acknowledged that tidal flows and waves are the most influential hydrodynamic forcing factors operating on surficial sediments tidal flows influence the long term evolution of tidal flats because of the asymmetry of tidal regimes flood and ebb tidal current activity is mainly confined to channels outside the channels mainly on the upper tidal flats tidal current velocities decrease and sediment entrainment is frequently ascribed to wave action the role of wave induced processes on intertidal flat sediments is frequently stated but has seldom been investigated apparently because of methodological constraints in this paper we report on investigations into the role of wave processes in determining surficial sediment distribution patterns on a sandy tidal flat at newtownards at the northern end of strangford lough northern ireland spring tidal range 3 5 m the main aim of this paper is to investigate the potential relationship between wave induced processes and surficial sediments without attempting to achieve a comprehensive analysis of other sedimentation the methodological approach involves numerically modeling wave propagation and comparing this with sediment distribution on a controlled field site the method enables the role of waves on tidal flats to be more fully assessed waves were modeled at a variety of tidal levels and wave data were extracted from the model grid at positions co incident with sediment sampling locations multiple correlation of sediment mean grain size with simulated wave induced orbital velocity showed a distinctive variation in correlation coefficients according to water level the best and statistically significant correlations occur when water levels occupy a vertical range between 0 15 and 1 0 m local ordnance level od in the absence of strong tidal currents sediment distribution appears to be best explained by waves acting at these water levels it is inferred that at lower than optimum water levels wave energy is less influential on sediment texture since 1 part of the tidal flat is still exposed and 2 the fetch over which the waves are generated is reduced at higher than optimum water levels wave energy may be sufficient to transport sediment but the wave penetration in the column of water is not sufficient to permit wave energy dissipation at the sediment surface tidal currents are dominant at low tidal elevations so outside channels wave induced currents exert most influence on the tidal flats

effects of biological activity on the entrainment of marine sediments nowell a r m jumars p a and eckman j e 1981 effects of biological activity on the entrainment of marine sediments mar geol 42 133 153 the effects of animal tracks and fecal pellet production on the critical entrainment velocity of marine sediments were examined experimentally laboratory measurements in a free surface seawater flume were made using three sediment sizes effects of three species of polychaetes and two species of bivalves were tested boundary shear velocity was calculated from the mean velocity profile in the logarithmic region of the boundary layer measurements were made with a hot film anemometer tracking doubled the boundary roughness and decreased the critical entrainment velocity by 20 ambient or free sediments were more easily entrained than fecal mounds which were restrained from movement by mucous adhesion between the fecal coils isolated pellets such as those egested by amphicteis scaphobranchiata transported readily as bedload over a cohesive sediment surface

cretaceous black shale deposition within an oxidized red clay turbidite environment southern angola basin south atlantic ocean abstract beds of black shale intercalated with red and green claystone of albian to coniacian age were recovered at dsdp site 530 in the southern angola basin the 260 beds of black shale have an average thickness of 4 3 cm range of 1 to 62 cm and an average organic carbon content of 5 7 range of 1 4 to 16 the green claystone beds resulted from reduction of iron in red claystone beds around black shale beds a green black green reduced sequence may occur alone within predominant oxidized red claystone or several closely spaced reduced sequences may merge to form interbedding of black and green lithologies the predominant red claystone beds were deposited as distal turbidites many of the black shale beds contain graded silt laminae very low amplitude ripple cross lami ation and fine indistinct discontinuous laminae suggesting that the material in the black shale beds also may have been transported by turbidity currents all lithologies are commonly bioturbated the sequence including the black shales at site 530 suggests that deposition of the distal turbidites low in organic matter in an oxidized bottom water environment was interrupted periodically by the deposition of organic carbon rich clay we conclude that the cyclic interbeds of more and less reduced strata with frequencies and durations measured in thousands or even hundreds of years resulted from variable supply of organic matter most of which is of marine origin and not from bottom water stagnation we favor periodic regional increases in organic productivity that resulted in i creases in production of organic matter and an expanded and intensified mid water oxygen minimum that impinged on the continental margin as a cause of periodic increases in accumulation of organic matter these conditions would produce variations in the amount of organic matter in both time and space and result in interbedding of organic carbon rich reduced sediments and organic carbon poor oxidized sediments a characteristic of all so called anoxic sequences in the atlantic ocean end of article last page 917

in situ flume measurements of resuspension in the north sea abstract the in situ annular flume voyager ii was deployed at three sites in the north sea in order to investigate resuspension events to determine the physical characteristics of the seabed to determine the threshold of resuspension of the bed and to quantify erosion rates and erosion depths these are the first controlled in situ flume experiments to study resuspension in the north sea and were combined with long term measurements of waves and currents resuspension experiments were undertaken at two muddy and one sandy site north of the dogger bank dg water depths 80 m very fine poorly sorted very fine skewed sediment experiencing seasonal thermal stratification of the water column along with oxygen depletion the oyster grounds og 40 m similar bed properties year round water column thermal stratification atlantic forcing and in the sean gas field sgf 20 m moderately sorted very coarse skewed sand and well mixed water column the erosion thresholds of the bed were found to be 0 66 1 04 pa dg and 0 91 1 27 pa og with corresponding erosion depths of 0 1 0 15 mm and 0 02 0 06 mm throughout the experiments evaluation of a year of current velocities from 2007 indicated that at og resuspension of the consolidated bed was limited to on average 8 of the time as a result of tidal forcing alone for short resuspension of bed material and erosion rates were closely related to applied bed shear stresses and eroded depths were significantly correlated with the physical properties of the bed therefore while complex variations in biogeophysical factors affected the critical threshold of erosion once exceeded erosion rates were related to the nature of the sediment

deep south china sea circulation 1 the analysis of an updated monthly climatology of observed temperature and salinity from the u s navy generalized digital environment model reveals a basin scale cyclonic circulation over the deep south china sea scs the cyclonic circulation lies from about 2400 m to the bottom the boundary current transport of the cyclonic circulation is around 3 0 sv our results suggest that the cyclonic circulation is mainly forced by the luzon overflow with bottom topography playing an important role the structures of potential temperature salinity and potential density in the deep scs are consistent with the existence of the cyclonic circulation specifically low salinity water is found in the interior region west of luzon island and surrounded by saline pacific water in boundary current regions to the north west and southwest our results show the potential density distribution and the corresponding cyclonic circulation in deep scs are primarily controlled by salinity variations in the deep basin

oceanic eddy formation and propagation southwest of taiwan 1 oceanic eddies are active and energetic southwest of taiwan the formation and propagation of eddies in this area were investigated using 17 year satellite altimeter data cyclonic eddies ces and anticyclonic eddies aces often coexisted but there were more ces than aces generated during the period from october 1992 to october 2009 aces were stronger and in general lived longer than ces aces occurred more often in winter than in other seasons while ces were more frequent in summer compared with the direct local wind forcing the kuroshio path variability appears to be a dominant factor for eddy formation in this area a conceptual model of an eddy kuroshio interaction is proposed in summer there exists an outflow northwest of luzon island and the kuroshio likely leaps across the luzon strait to the north of the outflow and left of the kuroshio axis ces are often formed which in turn induce aces to the west of ces in winter under the influence of northeasterly monsoon the kuroshio current loop kcl appears southwest of taiwan more frequently than in other seasons and aces are frequently shed from the kcl most of the aces propagate westward and as a result ces are often spun up to the east of the aces the surface south china sea outflow in summer and the kcl in winter are however likely related to the monsoons therefore the indirect effects of monsoon winds are also evident in the seasonal variations of eddy occurrence

abrasion of detrital grain coating clays during sediment transport implications for diagenetic clay coats abstract detrital grain coating clay minerals have been identified as precursors of diagenetic grain coating clay minerals that inhibit quartz cementation and preserve good reservoir quality properties in deeply buried sandstone reservoirs between initial and final deposition detrital grain coats are likely to be affected by sediment transport processes to date it has not been demonstrated that detrital grain coating clays are able to survive sediment transport flume experiments simulating open channel flow conditions were performed using sediments from the ravenglass estuary cumbria uk where the distribution and characteristics of modern detrital grain coating clays is well established scanning electron microscopy and automated mineralogy techniques were employed to study the sediment before and after transport to determine the stability of the detrital grain coating clays the experimental results show that detrital grain coating clays are still present after sediment transport in turbulent flows with velocities up to 0 5 m s 1 the stability of the detrital grain coating clays was enhanced by 1 high initial clay coat coverage 2 turbulence characteristics of the flow and 3 entrapment of the detrital grain coating clays in bedforms this work documents the first quantifiable evidence that estuary derived detrital clay coats are routinely preserved after sediment transport clay coat rich estuarine sediments can therefore act as the source of clay coated grains found in cleaner estuarine sandstones and may even survive transport out into open marine settings

stochastic wave radiation by the gulf stream abstract a linear small amplitude model of rossby waves forced by idealized meanders is presented in order to ascertain whether or not the observed low frequency motions near the gulf stream are capable of being so generated two crucial ingredients are shown to be necessary the meandering activity must vary in the downstream direction and the meanders must have a transient behavior cast as a stochastic average over a large number of meanders the predicted amplitudes of the kinetic energy and reynolds stresses are similar to those observed implications for the forcing of a mean flow are discussed

the effect of bedforms crest and trough systems on sediment erodibility on a back barrier tidal flat of the east frisian wadden sea germany abstract the erosion potential over bedforms in a tidal flat of the east frisian wadden sea was studied by conducting erosion and physical and biological sediment property measurements on the crests and troughs of bedforms five stations along a cross shore transect of 1 5 km length from immediately below the salt marsh to the mid tide level of the tidal flat were visited during two field campaigns in june and september 2002 measurements of sediment erodibility were made on both crests and troughs using an eromes erosion device and quantified in terms of critical erosion shear stress and erosion rate surface sediment scrape samples upper 1 mm layer were taken from crests and troughs to determine various physical and biological properties of the sediment the results show that crests are generally more stable i e higher critical erosion shear stresses and lower erosion rates than troughs in general crests contained more chlorophyll a colloidal carbohydrate and eps extracellular polymeric substance than troughs median grain size water content and wet bulk density of the crests showed no statistically significant difference from those of the troughs with the exception at the most landward station immediately below the salt marsh margin where crests had significantly lower water content and higher wet bulk density than troughs two different processes were identified for the difference in erodibility between crests and troughs 1 at stations with emersion times less than 6 h the higher benthic diatom biomass measured as chlorophyll a concentration on the crests increases the amount of eps which is likely to stabilize the sediment surface of these features 2 in a saltmarsh transition area most landward station physical processes such as surface drying and compaction seem to enhance in a synergistic way the sediment stability on the crests

simulation of mesoscale variability in the gulf of mexico sensitivity studies comparison with observations and trapped wave propagation abstract a primitive equation gulf of mexico model was used to examine variability of the loop current lc and loop current eddies lce realistic results were obtained for a certain range of values of the horizontal mixing coefficient eddy paths were west and southwestward eddy propagation speeds from 3 to 5 km day 1 the ratio of minor to major eddy axes about 0 8 eddy shedding periods from 200 to 500 days eddy lifetimes from 100 to 200 days eddy sizes from 200 to 400 km and eddy swirl transports as fractions of the specified inflow of 30 sv were from 0 55 to 0 85 on the other hand the maximum vertical deepening of the 20 c isotherm was 15 to 50 less than that observed resulting in weaker near surface currents of about 0 65 m s 1 in comparison to observed values of 0 88 to 1 7 m s 1 a strong correlation between eddy shedding and decreasing or reversing lower layer below 750 m transport in the yucatan channel is found in the western gulf current variability is produced by eddy arriva

critical shear stress of cohesive bottom sediments the main purpose of this study is to obtain a simple critical shear stress function for cohesive soft bottom sediments a series of experiments concerning threshold levels of mud transport and two series of tests of their rheological and setting properties were conducted to find some correlation among these indices we defined two threshold levels for mud transport and divided muds into two groups by their characteristics settling type flow curve resuspension behavior etc in discussing the factors determining the characteristics of the two groups we found that natural muds usually belong to the first group in which the two critical shear stresses are given as a function of yield value y1 defined in paper independent of material following a new definition of threshold for sediment detachment from the bed finally the correlation between this yield value and the final settling volume ratio is also discussed

deep currents in the gulf of mexico abstract direct current measurements using moored arrays have been made below 1000 m in the eastern central and western gulf of mexico basin the major low frequency velocity fluctuations in the lower 1000 to 2000 m of the water column in the three regions have the characteristics of topographic rossby waves trws spectral peaks are observed at periods of about 25 days and 40 to 100 days motions are highly coherent with depth variances increase toward the bottom despite the very weak stratification of the deep waters of the gulf wave lengths are about 150 250 km and phase propagation is offshore with energy propagation westward a group velocity of about 9 km day 1 could be directly estimated from significantly coherent signals between eastern and western arrays this value is consistent with estimates derived from the dispersion relation and is higher than the westward translation speed of 3 to 6 km day 1 of the large anticyclonic eddies shed from the loop current it appears that a major source of

deep eddy energy and topographic rossby waves in the gulf of mexico abstract observations suggest the hypothesis that deep eddy kinetic energy eke in the gulf of mexico can be accounted for by topographic rossby waves trws it is presumed that the trws are forced by loop current lc pulsation loop current eddy lce shedding and perhaps also by lce itself although the hypothesis is supported by model results such as those presented in oey the existence of trws in the model and how they can be forced by larger scale lc and lces with longer period vacillations have not been clarified in this paper results from a 10 yr simulation of lc and lces with double the resolution of that used by oey are analyzed to isolate the trws it is shown that along an east to west band across the gulf approximately over the 3000 m isobath significant eke that accounts for over one half of the total spectrum is contained in the 20 100 day periods bottom energy intensification exists in this east west band with vertical decay scales of about 600 300 m decreasing westward the de

accumulation of organic matter in cretaceous oxygen deficient depositional environments in the central pacific ocean abstract complete records of organic carbon rich cretaceous strata were continuouslycored on the flanks of the mid pacific mountains and southern hess rise in the central north pacific ocean during dsdp leg 62 organic carbon rich laminated silicified limestones were deposited in the western mid pacific mountains during the early aptian a time when that region was south of the equator and considerably shallower than at present organic carbon rich laminated limestone on southern hess rise overlies volcanic basement and includes 136 m of stratigraphic section of late albian to early cenomanian age this limestone unit was deposited rapidly as hess rise was passing under the equatorial high productivity zone and was subsiding from shallow to intermediate depths the association of volcanogenic components with organic carbon rich strata on hess rise in the mid pacific mountains is striking and suggests that there was a coincidence of mid plate volcanic activity and the production and accumulation of organic matter at intermediate water depths in the tropical pacific ocean during the middle cretaceous pyrolysis assays and analyses of extractable hydrocarbons indicate that the organic matter in the limestone on hess rise is composed mainly of lipid rich kerogen derived from aquatic marine organisms and bacteria limestones from the mid pacific mountains generally contain low ratios of pyrolytic hydrocarbons to organic carbon and low hydrogen indices suggesting that the organic matter may contain a significant proportion of land derived material possibly derived from numerous volcanic islands that must have existed before the area subsided the organic carbon in all samples analyzed is isotopically light 13 c 24 to 29 per mil relative to most modern rine organic carbon and the lightest carbon is also the most lipid rich there is a positive linear correlation between sulfur and organic carbon in samples from hess rise and from the mid pacific mountains the slopes and intercepts of c s regression lines however are different for each site and all are different from regression lines for samples from modern anoxic marine sediments and from black sea cores the organic carbon rich limestones on hess rise the mid pacific mountains and other plateaus and seamounts in the pacific ocean are not synchronous but do occur within the same general middle cretaceous time period as organic carbon rich lithofacies elsewhere in the world ocean particularly in the atlantic ocean strata of equivalent age in the deep basins of the pacific ocean are not rich in organic carbon and were deposited in oxygenated environments this observation together with the evidence that the plateau sites were considerably shallower and closse to the equator during the middle creataceous suggests that local tectonic and hydrographic conditions may have resulted in high surface water productivity and the preservation of organic matter in an oxygen deficient environment where an expanded mid water oxygen minimum developed and impinged on elevated platforms and seamounts

transport of terrestrial organic matter in the ogooue deep sea turbidite system gabon abstract in order to define the nature and distribution of the organic matter om preserved in the modern ogooue deep sea turbidite system gabon bulk geochemical techniques rock eval pyrolysis elemental and isotopic analyses and palynofacies were applied to three piston cores collected in the cape lopez canyon and lobe and on the continental slope north of the canyon the hemipelagic sedimentation in the study area is characterized by high accumulations of well preserved om 2 3 wt toc bulk geochemical and palynofacies analysis indicate both a marine and terrestrial origin of the om contribution of the marine source is higher on the slope than in the canyon and lobe om accumulation in turbidites is strongly controlled by the combined influence of the cape lopez canyon and littoral drift in the canyon and lobe turbidites show generally low toc content 0 5 wt and om is oxidized the origin of the om is interpreted as both marine and terrestrial with a higher contribution of continental source versus marine source the low toc contents are due to the large siliciclastic fraction transported by the littoral drift and diverted in the cape lopez canyon during high energy processes e g storms which tend to dilute the om in the turbidites transport by long shore currents and or turbiditic flows leads to oxidation of the om on the continental slope located north of the cape lopez canyon large amounts of om are deposited in turbidites up to 14 wt the om is predominantly derived from terrestrial land plants and has not been subjected to intense oxidation these deposits are characterized by high hydrocarbon potential up to 27 kg hc t rock indicating a good potential as gas prone source rock because cape lopez canyon captures a significant part of the sediment transported by the littoral drift the siliciclastic sedimentary flux is reduced north of the canyon om is thus concentrated in the turbidites variation in toc content within turbidite laminae can be explained by the burst and sweep deposition process affecting the boundary layer of the turbulent flow this study confirms that gravity flows play a preponderant role in the accumulation and preservation of om in deep water and that deep sea turbidite systems could be regarded as an environment where organic sedimentation occurs

laboratory apparatus for calibrating optical suspended solids sensors abstract an apparatus for testing and calibrating miniature to medium sized optical suspended solids sensors is described stable suspensions of sedimentary particles ranging in size from 10 6 to 4 10 3 m can be produced in water with concentrations exceeding 100 g 1 1 flow velocities in the test volume can be varied continuously from 0 1 to 1 5 m s 1 and samples of suspensions can be withdrawn directly with a peristaltic pump for gravimetric and particle size analyses the apparatus has been used to evaluate the effects of particle size flow speed and air bubbles on the performance of optical backscatterance sensors and transmissometers

anoxic events in the mediterranean sea in relation to the evolution of late neogene climates stable isotopic and micropaleontological studies were made of selected sapropels organic rich sediments deposited in the mediterranean sea during the last 5 0 m y to determine the processes responsible for their formation distinct isotopic and faunal changes occur across sapropels of late pleistocene early pleistocene and latest pliocene age while smaller isotopic changes and more stable faunal assemblages are associated with the early and mid late pliocene sapropels the large 18o depletions and euryhaline fauna associated with latest pliocene pleistocene sapropels supports a density stratification model with a low salinity surface layer in contrast early pliocene and mid late pliocene sapropels appear to have been formed as the result of sluggish circulation and low oxygen contents in bottom waters of the eastern mediterranean due to the stable warm climatic conditions of that time period

an analysis of the current deflection around dongsha islands in the northern south china sea based on the in situ data and adcp observation in fall it is found that a northeastward current at inter middle level flows on the northern south china sea nscs continental shelf this current flows almost along the isobaths and it deflects from the isobaths veering toward deep water when flowing over the dongsha islands geographic currents derived from the climatologic hydrography data woa01 and absolute dynamic topography adt data confirm the deflection of the northeastward current on nscs continent a fine resolution regional ocean model which can well reproduce the large scale circulation in the nscs is used to analyze the dynamic about the deflection the vorticity term balances shows that jebar joint effect of baroclinicity and relief drives the water column to depart from the isobaths to the east of the dongsha islands the isopycnal is almost orthogonal to the isobaths the joint effect of the topographic and the baroclinic effect supplies negative vorticity and drives the water column to deflect from the isobaths and veer to deeper water momentum analysis along the stream line shows that when the sea water flows around the dongsha islands the pressure gradient along the isobath pushes the sea water to accelerate and then the coriolis force orthogonal to the isobath increases and overcomes the corresponding pressure gradient which drives the water deflected from the isobath toward the deep sea citation wang d q wang w zhou s cai l li and b hong 2013 an analysis of the current deflection around dongsha islands in the northern south china sea j geophys res oceans 118 490 501 doi 10 1029 2012jc008429

deep current variability near the sigsbee escarpment in the gulf of mexico abstract observations of deep currents from a closely spaced array deployed at the base of the sigsbee escarpment south of the mississippi delta are dominated by energetic short period 10 days topographic rossby waves over a 2 yr interval distinct trains of waves occurred with differing characteristic periods wavelengths and horizontal energy distribution usually initiated with a burst of large amplitude current fluctuations that slowly decay over the next 2 3 months two of the wave trains were associated with the shedding and westward passage of major loop current anticyclones however one event occurred when upper layer currents were quiescent this latter wave train showed that bottom trapped topographic wave motions can be traced to within 300 m of the surface in a 2000 m water column ray tracing showed that a likely source region of the short period waves was the west side of an extended loop current the data and ray paths suggest that through refraction and reflection the steep es

an in situ erosion rate for a fine grained marine sediment near bottom current and particulate concentration data and a theoretical model of sediment resuspension together have led to inferences about the erosional response of a fine grained sediment to bottom stress tidal boundary layer observations made 5 m from the bottom in the main basin of puget sound washington show that currents with speeds exceeding 40 cm s cause an increase in concentration as much as sixfold from a background level of 1 mg 1 when the erosion rate e is given a power law dependence on bottom stress in accord with laboratory fine sediment entrainment measurements the field data and theoretical model together suggest that 4 0 and 1 7 10 6 g cm2 s uncertainty in these values stemming from a variety of factors is discussed the analysis also points to sediment resuspension of material with relatively large settling velocity ws 0 1 cm s taking place against a background of much finer particles and a depth of sediment reworking of approximately 0 3 mm under typical strong flow conditions comparison of this in situ erosion rate with previous laboratory rate estimates shows it to be comparable to rates measured for some freshwater sediments

day night variation of intertidal flat sediment properties in relation to sediment stability the majority of investigations that have measured sediment properties related to intertidal sediment stability have been undertaken during daylight subaerial exposure periods as a consequence models based upon such data represent only partially the intertidal flat surface conditions within any 24 h period in this contribution a comparison is made between surface sediment properties related to sediment stability measured during six consecutive day night semi diurnal subaerial exposure periods at three stations on an intertidal sand flat in late march 1999 the study site was selected on the basis of its suitability for sampling and data collection at night with special regard to safety and logistics seawater temperatures ranged from 4 1 to 9 6 c and salinities from 33 9 to 34 8 eleven parameters related to intertidal flat sediment stability were measured or derived these variables included the critical erosion shear stress c chlorophyll a phaeopigment and colloidal carbohydrate content mean grain size and settling velocity of the surface 0 1 mm sediment fraction bed elevation was described using an acretion erosion parameter aep west and west 1991 whilst additional physical terms included ambient seawater salinity and temperature as well as tidal range and wind speed during the preceding immersion periods one way anova was used to detect significant differences between day and night time emersion periods similarly principal components analysis pca was applied to detect continuous variation between properties the results show a high degree of temporal and spatial variability between day and night time intertidal flat variables the pca differentiating clearly between day and night conditions surface sediments across the intertidal flat exhibited varying degrees of biostabilisation the maximum biostabilisation coefficient 18 was recorded at night in high microalgal biomass areas the minimum 5 occurred during both day and night in areas with lower microalgal biomass all surface sediment parameters varied rhythmically between day and night time significant differences were found between day and night time biostabilisation coefficients however differences between day and night time c values were not detected it is suggested that sediment stability at night is enhanced in high microalgal biomass areas as a result of degradation products from bound extra cellular polysaccharides eps not easily detected using standard extraction procedures

biological mediation of the settling velocity of bed material eroded from an intertidal mudflat the danish wadden sea abstract the equivalent settling diameter of the eroded material from erosion experiments in situ has been examined for almost two years on a temperate intertidal mudflat the erosion experiments were carried by use of a portable eromes erosion equipment after each erosion experiment the eroded material was allowed to settle for some minutes and the settling velocity distribution and hereby equivalent settling diameters were calculated using stoke s law the settling velocities were strongly dependent on the fecal pellet content of the material showing larger settling diameters with increasing contents of fecal pellets whereas velocities were not dependent on applied bed shear stress primary grain size dry bulk density organic content or chlorophyll a content of the bed material the pellets at the investigated mudflat were produced by the snail hydrobia ulvae which lives in densities up to about 300 000 indiv m 2 at the site the average settling diameter for eroded material without fecal pellets was about 20 m whereas it was about 80 m for highly pelletized material the pellets are eroded quite easily but will probably not escape from the tidal basin due to the increase in settling velocities and associated increase in settling lag and scour lag therefore it is argued that although h ulvae will tend to destabilize the surface of the mudflat the net effect with respect to the fine grained sediment budget is probably positive due to the increase in settling velocity caused by the pelletisation by the snail the temperature dependent ingestion by h ulvae causes a clear seasonality in the pellet content and hereby settling velocity of the material eroded at the mudflat this may partly explain earlier observations of seasonal variations in erosion and deposition on the mudflat

working with natural cohesive sediments summary of stabilizing and destabilizing biotic in uenceson natural cohesive sediment stabilizing destabilizingeps secretion extracellularpolymeric substances bybacteria and microphytobenthosenhances cohesion promotes occulation and hence deposition blistering trapping ofoxygen bubbles in bio lmsincreases buoyancy of thebio lm to such an extentthat it pulls away fromthe sediment sediment compaction burrowingmacrofauna increasesediment densityand hence stability pelletization theformationof faeces and psuedo faeces can enhanceerodibility increased drainage burrowand channel formationpromotes dewatering grazing organismsfeedingon intertidal ats causesphysical disturbance andresuspensionof the sediment andreduces the stabilizingin uence ofmicrophytobenthos network effects filamentous biotaramify through the sediment matrixbinding sediment particles together burrow cleaning somebenthic fauna cleantubes they inhabit inthe sediment giving riseto a localizedbenthic ux flow effects

sea carousel a benthic annular flume a benthic annular flume sea carousel has been developed and tested to measure in situ the erodibility of cohesive sediments the flume is equipped with three optical backscatter sensors a lid rotation switch and an electromagnetic em flow meter capable of detecting azimuthal and vertical components of flow data are logged at rates up to 10 66 hz erodibility is inferred from the rate of change in suspended sediment concentration detected in the annulus the energy density wave number spectrum of azimuthal flow showed peaks in the energy spectrum at paddle rotation wave numbers k of 14 and 7 m 1 macroturbulent time scales but were not significant friction velocity u measured 1 at 1 hz using a flush mounted hot film sensor and 2 derived from measured velocity profiles in the inner part of the logarithmic layer gave comparable results for 1 at higher values of u method 2 underpredicted by up to 20 method 1 showed radial increases in in the annulus for y 0 32 m s 1 radial velocity gradients were proportional to y 0 32 m s 1 maximum radial differences in u were 10 for y 0 5 ms 1 suspended sediment mass concentration s in the annulus resulted in a significant decrease 10 5 in derived by method 1 over the range 0 s 1 these decreases were not evident in method 2 method 1 may therefore be subject to changes in stress sensor calibration with changes in s subaerial deployments of sea carousel caused severe substrate disturbance water losses and aeration of the annulus submarine deployments produced stable results though dispersion of turbid flume water took place results clearly demonstrated the existence of type i and type ii erosion documented from laboratory studies

energetic topographic rossby waves in the northern south china sea abstracttopographic rossby waves trws are reported to make a significant contribution to the deep ocean current variability on the northern south china sea nscs continental slope trws with pe

kuroshio intrusion into the south china sea a review the kuroshio carrying the northwestern pacific water intrudes into the south china sea scs through the luzon strait significantly affecting the temperature salinity circulation and eddy generation in the scs thus the kuroshio intrusion makes important contributions to the momentum heat and salt budgets in the scs in the past decades much work has been done on the kuroshio intrusion this paper reviews past efforts and summarizes our current understanding of the kuroshio intruding processes from observational evidence laboratory results theoretical analyses and a range of numerical model simulations in addition discrepancies between results simulated by models as well as those between simulations and observations are presented specifically this paper addresses the following topics 1 different types of the kuroshio intrusion into the scs and their identification 2 vertical structure of the kuroshio in the luzon strait 3 an overview of the luzon strait transport resulting from observations and numerical model simulations 4 seasonal and interannual variations of the kuroshio intrusion as well as eddy generation due to the kuroshio path variation and 5 dynamical mechanisms e g wind forcing interbasin pressure gradient beta effect and hysteresis potential vorticity eddy activity controlling the kuroshio intrusion into the scs finally several future research topics for gaining a better understanding of the kuroshio intruding processes are suggested c 2014 the authors published by elsevier ltd

factors controlling critical shears for deposition and erosion of individual grains abstract we have quantified critical deposition and erosion shear stresses for individual fine 24 141 m natural quartz particles in a flow chamber with radial parallel flow in seawater 30 10 15 c critical erosion shear stresses as expected are slightly larger than estimates from previous studies which strove for cohesionless conditions while critical deposition shear stresses are three orders of magnitude larger than predicted by hjulstrom 1935 and equal to the stress on a particle settling at stokes terminal fall velocity manipulative experiments indicate that critical deposition shear stress of medium to coarse silt is little affected by physical chemical adhesion bed roughness or microbial adhesion while critical erosion shear stress is at least doubled by microbial adhesion or bed roughness critical stresses for individual grains of comparable size are normally distributed supporting the concept of well behaved thresholds for both erosion and deposition because the thresholds do not differ greatly in magnitude for particles of a given size organism produced and maintained features e g pits and tubes can be important in shifting local conditions from erosive to depositional and vice versa

research on erosive properties of cohesive sediments to describe the transport of cohesive sediments it is necessary to specify the erosion flux at the bed experiments on the erosion of soft mud layers in a steady flow were performed in the delft tidal flume and in an annular flume the results were analyzed using the erosion rate function as derived by parchure and mehta it is concluded that a reasonable description is possible however the floc erosion rate appeared to be a function of the bed shear stress in one case the erosion rate function needed to be adjusted slightly in order to obtain agreement between measured and calculated suspension concentrations

gulf stream generated topographic rossby waves abstract an inverse ray tracing model is applied to observations of 40 day topographic rossby waves on the continental slope off of cape hatteras north carolina to determine their origin the rays are traced seaward and extend into the deep gulf stream where the bottom slope remains strong enough that topographic dominates planetary this enable coupling to occur between eastward propagating gulf stream meanders and topographic waves with eastward phase speed and matching zonal wavelength previous satellite observations indicate that the most frequently occurring gulf stream meanders have a period of 40 days and the model reveals that as these meanders pass a topographic bend near 71 72 w they are able to couple to the observed topographic waves traced back from cape hatteras the 40 day gulf stream meanders occur in bursts which leads to associated bursts of the topographic waves

use of in situ flume to quantify particle flux biodeposition rates and sediment erosion for an intertidal mudflat in relation to changes in current velocity and benthic macrofauna