factors influencing recent benthic foraminifera distribution on the guadiana shelf southwestern iberia abstract benthic foraminiferal assemblages in 24 sediment surface samples collected at water depths ranging from 9 to 103 m on the continental shelf off guadiana river were analysed leading to the identification of a total of 270 species cluster analyses performed on species with a relative abundance higher than 5 led to the identification of four assemblages the shallowest assemblage down to 12 m water depth is represented by ammonia beccarii asterigerinata mamila eggerelloides scaber mississipina concentrica planorbulina mediterranensis elphidium crispum and quinqueloculina laevigata a second assemblage between 12 and 40 m water depth is characterised by bulimina elongata cribrononion gerthi and nonion fabum the assemblage between 40 and 95 m water depth is characterised by bolivina dilatata epistominella vitrea bulimina aculeata bolivina ordinaria spiroloxostoma croarae and nonionella iridea finally below a depth of 95 m on the upper outer shelf an assemblage exists characterised by brizalina spathulata bulimina marginata cassidulina minuta brizalina subaenariensis cassidulina laevigata and uvigerina peregrina the spatial distribution of assemblages is closely associated with sea bottom sedimentary environments and bathymetry the number of benthic foraminiferal tests and the distribution of several nearshore species within the two shallowest assemblages are clearly influenced by the outflow of the guadiana estuary and by local hydrodynamic conditions the deeper water assemblages on the other hand were found to be more related to low levels of tidal energy low oxygen environments associated to fine grained sediments and cold water filaments related to seasonal upwelling

hyperpycnal plume formation from riverine outflows with small sediment concentrations a series of laboratory experiments has been conducted in order to elucidate the sediment induced mixing processes accompanying riverine outflows specifically the discharge of a warm fresh particle laden fluid over a relatively dense cool brine in a parameter regime analogous to recently acquired field measurements hypopycnal surface plumes were subject to a convective instability driven by some combination of heat diffusing out of the warm fresh sediment laden plume and particle settling within it convection was robust in the presence or absence of intense turbulence at sediment concentrations as low as 1 kg m 3 and took the form of millimetre scale sediment laden fingers descending from the base of the surface plume a consequence of the convective instability of the original hypopycnal plume is the generation of a hyperpycnal bottom riding flow the experiments presented here indicate that natural river outflows may thus generate hyperpycnal plumes when sediment concentrations are 40 times less than those required to render the outflow heavy relative to the oceanic ambient the resulting hyperpycnal plumes may play an important role in transporting substantial quantities of sediment to the continental slope and beyond

storm wave reactivation of a submarine landslide submarine landslides move large amounts of sediment and are often hazardous to offshore installations marine surveying techniques effectively define landslide locations and geometries for example refs 1 4 in various underwater geological settings including deltas fjords and earthquake prone areas1 5 movement rates and mechanics are generally inferred from indirect evidence such as cable breaks and damage to sea floor structures for example refs 6 8 but actual measurements of landslide behaviour are sparse using bottom deployed pressure sensors tiltmeters and accelerometers we have collected data on sea floor landslide reactivation involving sediment collapse and remoulding on the submarine slopes of the huanghe delta china the sensors were emplaced into sea floor clayey silts on 4 october 1987 and recovered on 16 october after the passage of three severe storms

deep marine tidal bottom currents and their reworked sands in modern and ancient submarine canyons abstract submarine canyons provide a unique setting for tidal processes to operate from shallow marine to deep marine environments in modern canyons current meter measurements at varying water depths 46 4200 m show a close correlation between the timing of up and down canyon currents and the timing of semi diurnal tides these tidal bottom currents in submarine canyons commonly attain maximum velocities of 25 50 cm s based on core and outcrop studies of modern and ancient deep marine deposits it is proposed here that sand mud rhythmites double mud layers climbing ripples mud draped ripples alternation of parallel and cross laminae sigmoidal cross bedding with mud drapes internal erosional surfaces lenticular bedding and flaser bedding can be used to interpret deposits of deep marine tidal currents this approach is an alternative to the conventional approach in which most deep water traction structures e g climbing ripples and cross bedding would be attributed to deposition from turbidity currents underwater photographs show active mass flows i e slides slumps grain flows and debris flows in modern canyons box cores taken from modern submarine canyons e g la jolla california and conventional cores and outcrops of ancient canyon fill facies oua iboe pliocene nigeria and the annot sandstone eocene oligocene se france contain deposits of both tidal processes and mass flows this facies association in the rock record can be used as a criterion for recognizing submarine canyon settings in a channel mouth environment deep marine tidal deposits are likely to develop elongate bars that are aligned parallel to the channel axis within the channel whereas turbidites are more likely to develop depositional lobes that are aligned perpendicular to channel axis turbidite depositional lobes are much larger than the channel width whereas tidal sand bars are much smaller than the channel width therefore the wrong use of a turbidite lobe model with sheet geometry in lieu of a tidal bar model with bar geometry will result in an unrealistic overestimation of sandstone reservoirs in deep water exploration

deep sea benthic foraminiferal recolonization of the 1991 mt pinatubo ash layer in the south china sea a census count of rose bengal stained benthic foraminifera from the surface area on top of a 2 to 6 cm thick ashfall layer at three deep water stations along the western margin of the philippines exhibits a unique assemblage composition of benthic foraminifera the total number of benthic foraminifera is low and the ratio of living individuals to empty tests is high specific diversity is low with a significant dominance of infaunal morphotypes including species of the genus reophax r scorpiurus r bilocularis and r dentaliniformis which are regarded as successful recolonizers assemblages below the ash layers are diverse and contain many epifaunal suspension feeding agglutinated and calcareous foraminifera the 1991 mt pinatubo eruption caused mass mortality of benthic foraminifera in a vast area of the eastern south china sea followed by step wise recolonization of the ash substrate three years after the eruption the benthic foraminiferal community structure is still far from recovery to background levels

slope transport of suspended particulate matter on the aquitanian margin of the bay of biscay abstract spatial and temporal characteristics of the water masses and the dispersion of the suspended particulate matter were investigated using current meter hydrographic and nephelometric observations gathered during the ecofer experiment 1989 1991 in the cap ferret canyon on the aquitanian margin of the bay of biscay while characteristics of the deep water masses were stable from one year to another large hydrographic change in the upper 500 m related to winter renewal induced by poleward advection of warm and saline water along the continental slope the slope circulation and seasonal eddy activity appear as important dynamical mechanisms that control the entrainment and the dispersion of the suspended particulate matter from the neritic domain to the deep ocean a predominantly northward along slope current with occasional reversal characterizes this circulation the nephelometric structures also showed seasonal changes in the overall suspended particulate matter content but recurrent features such as the presence of intermediate nepheloid layers at the shelf break depth and various depths along the slope 500 1000 and 2000 m were observed these nepheloid layers extended off the slope to about 10 30 km but especially laterally along the slope their presence indicated that suspended particulate matter exchanges between the shelf and the slope occurred mainly in the head of the canyon and along the southern open slope the intermediate nepheloid layers around 500 m depth detached from the slope particularly in regions where the bottom slope is close to critical for the m2 internal tide

fluxes and budget of on the continental margin of the bay of biscay northeastern atlantic abstract as part of the ecofer experiment ecomarge program jgofs france concentrations of the natural radionuclide 210 pb were measured in particulate matter collected by sediment traps deployed for a 14 month period june 1990 august 1991 on two mooring lines within the cap ferret canyon on the french continental slope of the bay of biscay northeastern atlantic 210 pb concentrations range 63 218 dpm g 1 and fluxes range 0 1 11 2 dpm cm 2 yr 1 displayed typical gradients increasing with depth at both mooring sites also at equivalent trap depths 210 pb activities were systematically higher on the deep slope mooring 3000 m compared to the shallow one 2300 m fluxes of 210 pb generally decreased seaward and exhibited temporal variations but with no marked seasonal trend essentially matching variations in total mass flux various correlations between 210 pb activities and major constituents of trapped particles were examined 210 pb activities were independent of the particle composition indicating that in this area scavenging of this nuclide from the water column was not directly tied to the quality of settling particles the 210 pb budget as determined by the balance of local supply flux and fluxes to sediment traps and sediments implies important lateral inputs to both mooring sites 65 89 of the flux measured by traps a feature typical of continental margin environments on the basis of annual mean 210 pb activity in traps of the two mooring sites two particle sources are hypothesized the first source located in shallow waters of the shelf and upper slope supplies the entire slope region the second source probably composed of resuspended particles from upper slope sediments feeds essentially the upper and intermediate slope region maximum sedimentation rates determined on seven box cores decreased with bottom depth from 0 3 to 0 4 cm yr 1 at the canyon heads down to 0 06 cm yr 1 at 3000 m a good agreement was observed at both mooring sites between 210 pb fluxes registered by the near bottom traps and excess 210 pb inventories within the underlying sediments suggesting that nuclide fluxes measured by traps during this experiment are representative of fluxes on a longer time scale 10 100 yr nevertheless total mass fluxes measured by traps were 3 4 times lower than 210 pb determined sediment accumulation rates a discrepancy that may be more apparent than real given the possible errors in the latter due to bioturbation

silicon isotope compositions of dissolved silicon and suspended matter in the yangtze river china abstract silicon isotope compositions of main channel samples of the yangtze river were systematically investigated along with their chemical compositions the concentration of suspended matter in the yangtze river tends to decrease from the upper reaches to the lower reaches corresponding to settling of the sediments in the lakes and reservoirs due to reduction of the velocity of water flow the silica contents of suspended matter vary from 52 1 to 56 9 and their 30si values vary from 0 to 0 7 both similar to those of shales from the upper to lower reaches the silica contents of suspended matter tend to increase whilst their 30si values tend to decrease both trends reflect the increase of clay minerals and decrease of carbonates in suspended matter the concentrations of dissolved silicon vary from 97 to 121 mol l and their 30si values vary over a wide range from 0 7 to 3 4 from the upper to lower reaches dissolved silica concentrations tend to decrease and their 30si values tend to increase these trends mainly reflect the change of chemical and isotopic characteristics of the tributaries from the upper to lower reaches the major factors responsible for these changes may be the high meteoric precipitation and significant silicon absorption by grass in wetlands and rice in paddy fields in drainage areas of the middle and lower reaches there is no correlation between 30si of dissolved silicon and that of suspended matter the 30sidiss spm values vary over a wide range of 1 0 3 7 indicating that 1 they are out of isotopic equilibrium 2 dissolved silicon and the associated suspended matter do not belong to one physico chemical system and 3 isotopic exchange rate between them is very slow the 30si value of dissolved silicon output from the yangtze river to the east sea is estimated to be 3 0 much higher than the values reported for the amazon and congo rivers this increases the 30si range of dissolved silicon in the world s rivers from 0 4 1 2 to 0 4 3 4

manganese cerium and iron in the sulu celebes and philippine seas this study was undertaken to investigate trace metals in southeast asian seas that have different hydrographic settings the philippine the celebes and the sulu seas results reveal characteristics of dissolved and leachable manganese dissolved cerium and leachable iron in the water column remarkable increases of mn ce and fe exist at the bottom layer of the water column in the celebes sea the ce mn molar ratios in the bottom waters of the celebes sea are identical to those in the porewaters of the underlying sediment both ce and mn show similar geochemical cycles in these deep waters of the celebes sea in the sulu sea s deep waters the leachable particulate fractions are dominant for fe and mn the residence time of fe in the sulu sea is estimated as 12 years this residence time estimate is very similar to the particle residence time in the water column implying that resuspension of sediment derived particles affects leachable fe distributions in the sulu sea

the impact of the 1991 mt pinatubo eruption on deep sea foraminiferal communities a model for the cretaceous tertiary k t boundary the ash layer from the 1991 mt pinatubo eruption provided a natural laboratory to assess mass mortality and the rates of recovery of deep marine ecosystems after a catastrophic event and to draw a parallel with the environmental impact of the k t boundary event on deep sea foraminiferal communities the first recolonization assemblages of benthic foraminifers after the mt pinatubo ash fall exhibit surprising similarities with benthic foraminiferal communities established following the k t boundary event i e comparatively low abundance and diversity absence of suspension feeders dominance of mobile infaunal taxa and a high proportion of agglutinated foraminifers the first foraminifers to recolonize the deep sea after both catastrophic events were opportunistic forms with high capability for rapid dispersal however major differences are evident in the timing and duration of the faunal transitions post eruption assemblages with high proportions of epibenthic suspension feeders became established after a short initial recolonization phase of approx 6 7 years on the mt pinatubo ash layer in the k t sections comparatively stable new benthic foraminiferal assemblages including suspension feeders only became established several thousand years after the event delayed recovery of the pelagic ecosystem and poor deep water ventilation probably slowed down the recovery of the benthic community structure after the k t boundary c 2005 elsevier b v all rights reserved

quantifying tidal signatures of the benthic nepheloid layer in gaoping submarine canyon in southern taiwan abstract the benthic nepheloid layer bnl has been observed in the head region of the gaoping kaoping submarine canyon kpsc throughout a year the top of the bnl could be as high as 100 m above the canyon floor in which the suspended sediment concentration ssc could be as high as 30 mg l in the bnl sand sized particles comprise the largest size class in the suspended sediment population based on three one month time series observations near the canyon floor of along canyon velocity water temperature and the volume concentration vc of clay very fine to medium silt coarse silt and sand size classes in 2000 2002 and 2004 the bnl is strongly modulated by the tides at semidiurnal diurnal quarter and sixth diurnal and spring neap frequencies in the course of a semidiurnal tidal cycle the flood up canyon current brings colder water from the seaward part of the canyon causing the ssc and the thickness of the bnl to increase the ssc immediately near the canyon floor also increases in response to the maximum flood and ebb currents of the m 2 tide the tidal to total energy ratio er of the along canyon flow is between 70 80 and between 50 80 among the suspended sediment of clay very fine to medium silt coarse silt and sand size classes the m 2 is the most important tidal constituent in the temporal variations of along canyon flow water temperature and the vc of the four size classes the local phase differences between the forcing velocity and the responses temperature and vc at the m 2 frequency show distinct phase lock that suggests patterns of standing and progressive internal tides suspended sediments in the bnl also respond to the m 2 forcing in a coherent fashion suspended sediment movements are strongly affected by nonlinear processes as indicated by the elevated values of the amplitude ratio of m 4 m 2 of the suspended sediment size classes comparing to that of the flow the cross canyon geometry and the slope of the submarine canyon floor affect the propagation of the barotropic and internal tides which in turn affect the nonlinearity generation in the bnl

post mortem onshore transportation of epiphytic foraminifera recent example from the tunisian coastline abstract the barrier island system that connects jerba island to the tunisian coastline is composed mainly of carbonate bioclastic sands well preserved tests of dead epiphytic foraminifera are abundant on the foreshore and backshore but they are scattered and poorly preserved on the shoreface where very fine sand size eolian quartz peloids and broken bioclasts are the main components the reason for this paradoxical pattern is that most epiphytic foraminifera are very easily removed as suspended load by storm generated currents and concentrated on beaches washover fans and small eolian dunes kilometers away from their original life environment similar bioaccumulations are common in the fossil record and have often been interpreted incorrectly as prolific biocoenoses

transition from partly standing to progressive internal tides in monterey submarine canyon monterey submarine canyon is a large sinuous canyon off the coast of california the upper reaches of which were the subject of an internal tide observational program using moored profilers and upward looking moored adcps the mooring observations measured a near surface stratification change in the upper canyon likely caused by a seasonal shift in the prevailing wind that favoured coastal upwelling this change in near surface stratification caused a transition in the behaviour of the internal tide in the upper canyon from a partly standing wave during pre upwelling conditions to a progressive wave during upwelling conditions using a numerical model we present evidence that either a partly standing or a progressive internal tide can be simulated in the canyon simply by changing the initial stratification conditions in accordance with the observations the mechanism driving the transition is a dependence of down canyon supercritical internal tide reflection from the canyon floor and walls on the depth of maximum stratification during pre upwelling conditions the main pycnocline extends down to 200 m below the canyon rim resulting in increased supercritical reflection of the up canyon propagating internal tide back down the canyon the large up canyon and smaller down canyon progressive waves are the two components of the partly standing wave during upwelling conditions the pycnocline shallows to the upper 50 m of the watercolumn above the canyon rim resulting in decreased supercritical reflection and allowing the up canyon progressive wave to dominate

radionuclide dates and foraminiferal accumulation rates examples from submarine canyons abstract caesium 137 an anthropogenic radionuclide has been present in the global environment for the past 40 years and may be detected in sediment using non destructive gamma spectrometry 137cs peaks can be used to date layers within core material the effect of bioturbation upon the dating results has been considered using x radiography of the core material recent sedimentary material from submarine canyons cutting the portuguese continental margin has been dated using 137cs and this information used in conjunction with foraminiferal assemblage data has allowed benthic and planktic foraminiferal test accumulation rates to be calculated benthic foraminiferal accumulation rates range from 55 to 687 tests yr 10 cm2 and planktic rates range from 51 to 1338 tests yr 10 cm2 at water depths of 385 to 3400 accumulation rates have been calculated for selected genera and brizalina has the highest overall value

benthic foraminifera from capbreton canyon revisited faunal evolution after repetitive sediment disturbance abstract at a 650 m deep site in the axis of capbreton canyon an 18 cm thick turbidite was deposited in december 1999 during subsequent campaigns an almost monospecific fauna of the benthic foraminifer technitella melo considered as a pioneer species was found in may 2000 in 2001 this fauna had disappeared and was replaced by an exceptionally rich fauna strongly dominated by the opportunistic species bolivina subaenariensis we present sedimentological radionuclide and foraminiferal data of new cores sampled in 2005 and 2011 taken with the aim to study the further evolution of the benthic ecosystem cores sampled in 2005 show that in the canyon axis a new ca 5 cm thick turbidite has been deposited the live benthic foraminiferal faunas were much poorer than in 2001 but still had a high dominance and low diversity although less extreme than in 2001 we conclude that in the canyon axis benthic foraminiferal faunas remain in an early stage of ecosystem colonization it appears that the very thick 1999 turbidite marks an exceptional event the uncommonly rich faunas observed in 2001 could be a response to the concentration of organic rich material in the fine grained top of this deposit in 2011 cores were sampled at a slightly different site on the lower canyon flank the sedimentary sequence here is marked by the absence of coarse turbidite layers although some levels show slightly increased grain size and lower 210 pb xs activities indicative of an admixture with advected older sediments live foraminiferal faunas are much more equilibrated as shown by their higher diversity lower dominance and deeper penetration into the sediment all these characteristics are indicative of a much more stable ecosystem dead faunas are present throughout the core indicating that the levels with slightly elevated grain size are not typical turbidites resulting from hyperpycnal currents which are characterized by levels barren of foraminifera but denote other more long term sedimentary processes leading to the advection of older material such as bottom nepheloid layers or repetitive fine grained turbidite deposits due to small scale slumping the comparison of live and dead fauna shows that at both sites the foraminiferal turnover rates are fairly low at the lower canyon flank site sampled in 2011 the foraminiferal faunas are renewed every 1 5 2 years such a fairly long foraminiferal lifespan corresponds to earlier estimates but is surprisingly high for the opportunistic taxa that dominate the faunal assemblages in these unstable and food enriched submarine canyon settings

macrofaunal communities within and adjacent to a detritus rich submarine canyon system abstract macrofaunal abundance biomass diversity and species assemblages within scripps and la jolla submarine canyons are compared with those on the nearby continental shelf and slope our primary objective was to examine the effect of detrital aggregates on infaunal communities within canyons two submarines a remotely operated vehicle rov and a soutar box corer were used to collect samples within the canyons organic enrichment by macrophyte detritus was evident from canyon heads down to 550 m and evidence of strong currents coarse sediment was found down to 700 m infaunal density and biomass were higher in the canyons than outside at all depths where comparative data were available 100 500 m infaunal assemblages in canyons were distinct from those at reference stations both the canyon and non canyons samples showed community differentiation with depth species diversity was generally high but decreased with depth outside of canyons and increased with depth within the canyons low diversity at shallow depths within the canyon is attributed to a combination of organic enrichment and physical disturbance submarine canyons are commonly found to contain distinct species assemblages or higher faunal densities and or biomass than nearby non canyon regions at similar depths canyons are regular features along most ocean margins and appear to be important as sites of enhanced secondary production provide diverse habitats and act as conduits of coastal detritus to the deep sea

benthic foraminiferal thanatocoenoses from the cap ferret canyon area ne atlantic a complex interplay between hydro sedimentary and biological processes abstract benthic foraminiferal thanatocoenoses from the cap ferret canyon area were studied in the 150 m fraction of 4 5 cm deep sediment levels at 13 stations the shallowest station 151 m depth is located at the shelf break close to the canyon head all other stations are located along two bathymetric transects seven stations along the canyon axis between 300 and 3000 m depth and five stations from 300 m to 2000 m depth along the southern flank of the canyon the comparison between the live rose bengal stained and dead assemblages shows that biological i e population dynamic and taphonomic processes i e test destruction transport generate important discrepancies between live and dead assemblages an important question is to what degree post mortem transport and redeposition of foraminiferal tests contribute to the difference between living and dead assemblages the composition of the thanatocoenoses 150 m from the inner continental shelf to the cap ferret canyon axis however transport of tests from outer shelf or upper canyon axis towards deeper sites occurs as indicated by an increase of diversity indices of the dead fauna along the canyon axis moreover some species e g cassidulina carinata are observed in the living fauna restricted to the shallow sites but occur in important amounts in the dead fauna at deeper stations suggesting that these taxa have been transported from upper canyon stations toward deeper sites since cap ferret canyon is inactive in terms of massive sediment transport i e gravity events downslope transport of foraminiferal tests probably takes place in nepheloid layers downslope transports of foraminiferal tests may create important biases for the utilisation of paleoceanographic proxies using the assemblage characteristics and or the geochemical composition of selected species however the study of dead assemblages along a canyon axis can give important clues about the sedimentary dynamics especially an idea of the quantity of reworked foraminifera transported through the canyon axis along the adjacent flank such evidence of downslope transport was not observed despite taphonomic test destruction and biological processes population dynamics the live fauna closely resembles the distribution and the composition of the dead assemblage therefore ecological information obtained from the fossil flank samples can be more reliably used to reconstruct paleoenvironmental conditions

bathyal suprabenthic assemblages from the southern margin of the capbreton canyon kostarrenkala area se bay of biscay abstract the bathyal suprabenthic fauna of the kostarrenkala area capbreton canyon se bay of biscay was sampled during daytime at eight stations located on a bathymetric transect between 175 and 1000 m depth using a multinet suprabenthic sled two hundred and five suprabenthic taxa were recorded in this area mainly amphipods cumaceans isopods and mysids total abundances ranged from 752 to 2640 ind 100 m 2 showing a decreasing trend with depth diversity values h ranged between 3 83 and 5 72 increasing significantly with depth multivariate analysis of abundance data discriminated three assemblages according to depth shelf break 72 sp 1924 ind 100 m 2 upper slope 93 sp 1485 ind 100 m 2 and mid slope 135 sp 857 ind 100 m 2 assemblages each assemblage was characterised by a distinct dominant species the shelf amphipod westwoodilla caecula at the shelf break the isopod munnopsurus atlanticus on muddy sand bottoms of the upper bathyal and the amphipod rhachotropis gracilis on mid slope muddy bottoms below the mud line such a structure of bathyal assemblages seems to be generalised for the whole margin of the bay of biscay

canyon conditions impact carbon flows in food webs of three sections of the nazare canyon submarine canyons transport large amounts of sediment and organic matter om from the continental shelf to the abyssal plain three carbon based food web models were constructed for the upper 300 750 m water depth middle 2700 3500 m and lower section 4000 5000 m of the nazare canyon eastern atlantic ocean using linear inverse modeling to examine how the food web is influenced by the characteristics of the respective canyon section the models were based on an empirical dataset consisting of biomass and carbon processing data and general physiological data constraints from the literature environmental conditions most notably organic matter om input and hydrodynamic activity differed between the canyon sections and strongly affected the benthic food web structure despite the large difference in depth the om inputs into the food webs of the upper and middle sections were of similar magnitude 7 98 0 84 and 9 30 0 71 mmol c m 2 d 1 respectively om input to the lower section was however almost 6 7 times lower 1 26 0 03 mmol c m 2 d 1 carbon processing in the upper section was dominated by prokaryotes 70 of total respiration though there was a significant meiofaunal 21 and smaller macrofaunal 9 contribution the high total faunal contribution to carbon processing resembles that found in shallower continental shelves and upper slopes although the meiofaunal contribution is surprisingly high and suggest that high current speeds and sediment resuspension in the upper canyon favor the role of the meiofauna the high om input and conditions in the accreting sediments of the middle canyon section were more beneficial for megafauna holothurians than for the other food web compartments the high megafaunal biomass 516 mmol c m 2 their large contribution to respiration 56 of total respiration and secondary production 0 08 mmol c m 2 d 1 shows that these accreting sediments in canyons are megafaunal hotspots in the deep sea conversely carbon cycling in the lower canyon section was strongly dominated by prokaryotes 86 of respiration and the food web structure therefore resembled that of lower slope and abyssal plain sediments this study shows that elevated om input in canyons may favor the faunal contribution to carbon processing and create hotspots of faunal biomass and carbon processing along the continental shelf

recent sediment transport and deposition in the lisbon setubal and cascais submarine canyons portuguese continental margin abstract recent sediment transport and deposition in the lisbon setubal and cascais submarine canyons portuguese continental margin were investigated on the basis of water column profiles of suspended particulate matter records of near bottom currents and settling fluxes of particulate matter obtained with benthic landers and analysis of surface sediments the results show that fine grained predominantly lithogenic sediment derived from adjacent shelf areas accumulates in the upper reaches of the canyons sediment deposited further down in the middle and lower reaches of the canyons is essentially similar to the hemipelagic sediment found on the adjacent continental slope indicating that down canyon transport of sediment from the upper to the lower canyon is limited tidal currents measured at various depths in the lisbon setubal canyon appear sufficiently strong to resuspend and transport sediment but net up canyon flow of the bottom water may retain shelf derived lithogenic sediment in the upper canyon sediment gravity flows which in the nearby nazare canyon are an effective mechanism for down canyon sediment transport appear rare in the lisbon setubal canyon and probably also in the cascais canyon turbidity current events recorded in the sedimentary record of the canyons may correspond to seismic events of 1969 and 1755 ad

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

the impact of the mediterranean outflow water mow on benthic foraminiferal assemblages and surface sediments at the southern portuguese continental margin benthic foraminifera and surface sediments were analyzed from 23 box core and core top samples from 250 to 3600 m depth at the southern portuguese continental margin between 37 and 38 n this area is affected by the mow which flows northwards along the slope between 600 and 1500 m waterdepth sediment structures grain size distribution and clay mineral assemblages of surface sediments indicate active winnowing in the upper part of the mow and deposition of the fine fraction near its lower boundary r mode cluster analyses of foraminiferal census data from the 250 m fraction revealed four associations the shelf edge association occurs on glauconitic shelf and upper slope sands down to 268 m the upper slope association is recognized between 498 and 1300 m where sand silt clays to clayey silts are encountered the lower slope association is found between 1405 and 2985 m and differs markedly from assemblages below 3000 m deep water association where the near surface sediments are soft hemipelagic clays the boundary layer association shows no significant depth limits but abundance maxima both in the density interface above the mow and in the interval of decreasing turbulence below it the boundaries of the shelf edge and upper slope association correspond to these hydrographic boundary layers whereas the boundary between lower slope and deep water assemblage is related to threshold values of nutrient flux to the benthic community examination of hard substrates reveals 27 different species of epibenthic foraminifera six of these the epibenthos group were found attached to elevated substrates only within the mow above the mow elevated substrates were inhabited by different species whilst below the mow they were not used by any epibenthic foraminifers evidently the hydrodynamic environment of the mow current provides an ecological niche which is efficiently used by opportunistic suspension feeders the epibenthos group is more abundant in the middle part of the study area between 37 20 and 37 40 n where the sand content of surface sediments is also higher both indicate an enhanced sediment water interaction in this area which results from an obstruction of the mow flow by the principes d avis basement spur

210pb sediment radiochronology an integrated formulation and classification of dating models abstract environmental archives such as sediments banded corals and tree rings are widely used to reconstruct past environmental conditions of ecosystems in particular 210 pb has been used during more than 4 decades through dating of undisturbed sediment cores to study ecosystem changes during the last 100 yr since its inception diverse dating models have been proposed developed used and validated in numerous environments but their nomenclature and formulation is not homogenous in this work we emphasize that conceptual models used to date undisturbed sediment cores can be deduced from a single fundamental equation which relates excess 210 pb concentration in sediment its flux to the sediment surface and mass accumulation rate from this equation models were consistently named based on the main hypothesis used and using a unified and logical nomenclature dating equations were derived in detail we applied in detail most of the described models to a sediment core from mexico and uncertainty expressions were also included finally some recommendations to use the models are proposed we believe that this work can facilitate the use of 210 pb as a tool to date sediment cores in a more homogeneous way

present deep submarine canyons activity in the bay of biscay ne atlantic present sedimentation in three canyons of the bay of biscay audierne blackmud and capbreton is studied by the combined analysis of cores and current meter data collected over a 7 month period at the current meter mooring locations interface cores were collected to characterize the recent sedimentation processes in the two canyons located in the northern part of the bay of biscay audierne and blackmud there is no evidence of recent sedimentary deposits canyons are by passing or erosive areas in the southern part of the bay of biscay capbreton recent turbidite are deposited in the three canyons current meters recorded energetic currents with velocities showing alternating upslope and downslope motions and a period corresponding to the semi diurnal component m2 these currents are supposed to be related to deep internal tides the high speed of the current 1 m s in audierne and blackmud is consistent with the lack of preservation of recent sediments on the canyon floors in capbreton canyon the magnitude of currents is less and recent turbidites are preserved in addition to periodical current motion small magnitude gravity event corresponding to a low concentration turbulent surge or a high concentration nepheloid layer initiated during a storm was recorded during the mooring period these results suggest that deep sea canyons in the bay of biscay have behaviour at present varying between by passing or erosion areas and sediment trapping these examples suggest that sediments are moved up and down by low energy tide initiated hydrodynamic events during most of the time during higher magnitude short duration gravity events the sediments are transferred down canyon towards the deep sea