first observations of the cold water coral lophelia pertusa in mid atlantic canyons of the usa abstract the structure forming cold water coral lophelia pertusa is widely distributed throughout the north atlantic ocean and also occurs in the south atlantic north pacific and indian oceans this species has formed extensive reefs chiefly in deep water along the continental margins of europe and the united states particularly off the southeastern u s coastline and in the gulf of mexico there were however no records of l pertusa between the continental slope off cape lookout north carolina nc 34 n 76 w and the rocky lydonia and oceanographer canyons off cape cod massachusetts ma 40 n 68 w during a research cruise in september 2012 l pertusa colonies were observed on steep walls in both baltimore and norfolk canyons these colonies were all approximately 2 m or less in diameter usually hemispherical in shape and consisted entirely of live polyps the colonies were found between 381 m and 434 m with environmental observations of temperature 6 4 8 6 c salinity 35 0 35 6 and dissolved oxygen 2 06 4 41 ml l 1 all of which fall within the range of known l pertusa distributions all colonies were observed on vertical walls or underneath overhangs in areas of high current which differs from observations further south where l pertusa colonizes rocky ledges and outcroppings often forming large bioherms we discuss observations from baltimore and norfolk canyons in the context of the known distribution of this species in the north atlantic

regional metamorphism of non calcareous manganiferous sediments from india and the related petrogenetic grid for a part of the system mn fe si o

reefs of the deep the biology and geology of cold water coral ecosystems coral reefs are generally associated with shallow tropical seas however recent deep ocean exploration using advanced acoustics and submersibles has revealed unexpectedly widespread and diverse coral ecosystems in deep waters on continental shelves slopes seamounts and ridge systems around the world advances reviewed here include the use of corals as paleoclimatic archives and their biogeological functioning biodiversity and biogeography threats to these fragile long lived and rich ecosystems are mounting the impacts of deep water trawling are already widespread and effects of ocean acidification are potentially devastating

early messinian manganese deposition in ne cyprus related to cyclical redox changes in a silled hemipelagic basin prior to the mediterranean salinity crisis abstract unusual bedded manganese deposits occur within hemipelagic carbonates dated as early messinian 5 97 ma based on calcareous nannofossils these sediments accumulated during a time of increased isolation of the mediterranean sea from the atlantic ocean but prior to major sea level fall and evaporite precipitation during the messinian salinity crisis the manganese deposits form six main laterally continuous beds up to 70 cm thick compositionally they are dominated by poorly crystalline manganese oxide birnessite with associated mild enrichment in some trace elements e g ba ni cu mo as u background minerals include magnesian carbonate kaolinite chlorite mixed layer clays and talc serpentinite derived a tectonically controlled deep water basin existed to the south of a topographic ridge future kyrenia range in which seawater alternated between oxidising and oxygen depleted at depth orbital precession influenced the weathering of continental source areas that included basic igneous rocks and some pre existing hydrothermal deposits after entering the basin via land runoff manganese was retained in solution below the chemocline during stagnant low oxygen periods manganese oxide and associated trace elements e g mo u precipitated in response to cyclical seawater oxidation to form manganese rich layers up to layers with up to with up to c 30 mno to reach these very high concentrations soluble manganese may have fluxed upwards from an anoxic environment represented by early messinian sapropels manganese precipitation events diminished with time giving way to well oxygenated hemipelagic marl accumulation with a shelly infauna gypsum appears abruptly upwards above the marls in adjacent sections the mn deposition mainly represents an interplay between tectonically controlled basin formation chemically favourable source climatic conditions possible sea level change effects and likely diagenetic manganese enrichment the regional tectonic setting relates to early stage collision of the african and tauride eurasian plates

archean banded iron formations yilgarn block western australia banded iron formation is a widely distributed although relatively minor lithology in the archean yilgarn block western australia occurring in supracrustal sequences composed mainly of metamorphosed volcanogenic rocks in the northern and eastern parts of the yilgarn block and also in highly deformed and metamorphosed predominantly metasedimentary sequences in the gneissic terrain in the southwest in the central part of the yilgarn block structural mapping and stratigraphic reconstruction indicates that individual banded iron formation units extend over an area of at least 40 x 60 km and could extend over a much larger area most banded iron formation units appear to be 5 to 50 m thick and units of 100 to 150 m are uncommon three scales of layering occur in iron formation units a interlayering of banded iron formation and fe shale fe shales range in thickness from several millimeters to 5 to 6 m b mesobanding is the most prominent structure in the banded iron formations c millimeter scale laminations including microbanding occur in both banded iron formation and fe shales other structures in the banded iron formation include pods macules and small spheroidal nodules despite modification by metamorphic and deformation processes which among other effects have caused thinning of mesobands all the structures can readily be equated with those in the hamersley basin iron formations there is a wide range in metamorphic grade at the lowest grades banded iron formation contains quartz magnetite greenalite stilpnomelane minnesotaite siderite and ankerite fe shales contain chamosite stilpnomelane siderite and pyrite the highest grades are characterized by quartz magnetite clinopyroxene orthopyroxene in iron formation and hornblende almandine or biotite assemblages in fe shale mineral assemblages are essentially identical to those in many metamorphosed proterozoic iron formations the bulk chemical compositions of the yilgarn block iron formations are very similar to other precambrian iron formations from very different stratigraphic settings fe shales have highly variable compositions characterized by a marked positive al 2 o 3 tio 2 correlation and high cr contents the similarity in the bulk chemical composition of iron formations in the yilgarn block and other precambrian sequences implies that deposition of these iron formations occurred in very similar chemical environments it is suggested that although fe shales may be related in some way to volcanic activity the main constituents of the banded iron formations are not directly derived from volcanic sources banded iron formations appear to have been precipitated from ocean waters which relative to younger oceans contained higher concentrations of fe and si in solution

the dangeard and explorer canyons south western approaches uk geology sedimentology and newly discovered cold water coral mini mounds the celtic margin is a complex area in terms of sedimentary dynamics and evolution with a number of submarine canyons dissecting the continental slope and outer continental shelf the complex terrain and diverse range of sea bed sediments play a part in submarine canyons being described as areas of high habitat heterogeneity this study has concentrated on the heads of two canyons dangeard also known as dangaard and explorer first named here located in uk territorial waters in water depths between 138 and 1165 m multibeam echosounder 2d reflection seismic and photographic ground truthing data have been combined to map the sea bed geomorphology sedimentary features and canyon megafauna of these canyons in addition two previously unknown provinces of cold water coral cwc mini mounds were discovered on the interfluves of the dangeard and explorer canyons the study area comprises a dendritic network of gullies feeding into the canyon thalwegs amphitheatre rims where slope angles are commonly in excess of 20 occur along the margins and heads of both canyons and are interpreted as drainage basins indicative of retrogressive mass wasting in a shelfward direction the cwc mini mounds occur in water depths between 250 m and 410 m with more than 400 mounds identified they are up to 3 m in height and 50 150 m in diameter with no sub surface expression suggesting these mounds are in geological terms relatively young and possibly holocene in age biological analyses revealed that the mounds form a habitat for ophiuroids and munida associated with lophelia pertusa coral rubble suggesting these mini mounds are not present day living features

acoustic facies and depositional processes in the upper submarine canyon swatch of no ground bay of bengal abstract the swatch of no ground song is a canyon that incises the bengal shelf deeply over more than 100 km length landward of the shelf edge and 100 km west of the ganges brahmaputra meghna river mouth it acts as conduit for the fluvially discharged sediment that bypasses the shelf and reaches the deep sea fan what transport deposition and mass wasting processes contribute to the sediment export and what sediment structures and main pathways are associated with these processes is studied by closely spaced bathymetric hydrosweep swath sounder and parasound sediment echosounder profiles over the upper song an analogue side scan sonar profile completes the acoustic data set from the parasound sediment echosounder data three main acoustic facies types related to undisturbed normal deposition mass wasting and erosive transport are defined and mapped with respect to the hydrosweep bathymetry of the song generally nearly all facies types show an unusually high sediment echosounder signal penetration of 80 100 m indicating that unconsolidated high porosity sediments occur on the canyon floor flanks and banks additionally the acoustic facies distribution map yields that about half of the canyon floor is covered by undisturbed well stratified fine grained muddy and coarse grained graded beds they are deposited from a suspension plume transported to the canyon either during fine weather conditions by westward oriented tidal currents or by storm events that mobilize sediments on the inner shelf curved or inclined faults or growth faults are found at all steep flanks indicating that active mass wasting processes occur along all channels and gullies on both canyon flanks such mass wasting processes are probably initiated by severe storms earthquakes high sediment load or excess pore pressure and lead to slides slumps or mudflows they stop in regions with low inclination angle and form acoustically transparent deposits of various extents on the channel and gully floors and on the southwestern canyon thalweg current marks identified on the canyon floor by high backscatter amplitudes in the side scan sonar images indicate that low density turbidity currents episodically flow down the canyon they are generated in an area of very high sedimentation rates close to the canyon head by high energy conditions like severe storms or earthquakes additionally a small gravity driven flow along the main channel s obviously continuously erode the steeper northeastern branches and inhibit sediment deposition in the more gentle southwestern channel below 450 500 m water depth together with larger scale mudflows and low density turbidity currents this gravity driven flow contributes to an active growth of the channel levee system in the deep sea fan

late proterozoic outer shelf manganese and iron deposits at otjosondu namibia related to the damaran oceanic opening the otjosondu manganese mining area is located at the eastern exposed extent of the inland branch of the late proterozoic damara orogen in spite of intense deformation and a high grade metamorphic overprint the sedimentological interpretation of the manganeserich rocks and their associated lithologies has led to a paleoenvironmental model which gives insight into ore genesis at least two manganese silicate ore horizons manganese formations are associated with banded iron formations this sequence is sandwiched between supermature metaquartzarenites interpreted as a shoreface deposit derived from a cratonic basement and deposited under high energy conditions manganese ore varieties and their country rocks have been classified using their texture mineralogy and geochemistry and have thus been interpreted in sedimentological and facies terms the evaluation of the vertical facies sequences their lateral distribution and their contact relationships renders a spatial reconstruction of the environmental setting for the manganese ores possible the development of facies from a near shore clastic regime to manganese bearing hemipelagic sediments and ultimately to pelagic manganostones and ironstones reflects a zonation on a marine shelf the facies evolution indicates transgressive conditions on a large scale onto a tectonically stable but subsiding shelf starting with the transgressive quartzarenites overlying an unconformity to the pre damara basement followed by chemical sediments of the ore bearing horizon and overlying carbonates and ending up with pelitic schists on a smaller scale both transgressive and regressive conditions prevailed during manganese precipitation small scale sedimentary cycles are interpreted as due to glaciogene influenced fluctuations of the sea level the source of manganese and iron is proposed to have been situated in the deeper oceanic parts of the associated basin initial spreading in the khomas sea and the formation of oceanic crust is documented by tholeiitic volcanics and associated base metal orebodies representing more proximal manifestations of the exhalative activity these base metal sulfide deposits are associated with pyrite bearing graphitic pelagics and this was the first site to partition iron and other base metals from manganese upwelling along the shelf edge was involved and additional separation of mn and fe was due to a change in eh conditions associated with a redox interface intersecting with the outer shelf environment the evolution of the khomas sea provided the ore forming solutions and also initiated the subsidence of the passive shelf margin fluctuations in sea level were due to the basin development on one hand and glacial interglacial cycles on the other the latter fluctuations controlled the amount of terrigenous input into an otherwise pelagic regime

the europium anomalies in banded iron formations and the thermal history of the oceanic crust abstract the ree rare earth element patterns in banded iron formations bif s from various sites in north america two sites in finland and three drillcores of the hamersley basin in western australia have been investigated using icp ms inductively coupled plasma mass spectrometry and inaa instrumental neutron activation analysis the results of this study as well as existing data show trends in the eu anomalies bif s older than 2 5 ga exhibit positive eu anomalies while younger ones exhibit none in chemical sediments between 2 5 and 2 3 ga both trends can be found because of the worldwide distribution of bif s this feature can be considered as a global change in the conditions controlling ree mobilization consideration of the redox conditions of bif formation in comparison with the calculated and measured eu redox equilibria suggests that a eu anomaly points to a dominantly hydrothermal source of ree s with solution temperatures above 175 c we suggest that the disappearance of the eu anomaly towards the proterozoic marks a change from mainly high temperature hydrothermal to dominantly low temperature alteration

mesoarchaean palaeoproterozoic stratigraphic record of the singhbhum crustal province eastern india a synthesis the mesoarchaean palaeoproterozoic stratigraphic record of the singhbhum crustal province eastern india implies sedimentation and volcanism in a changing tectonic scenario and thus assumes immense geological significance although efforts have been made by many researchers in the past several decades to summarize various geological aspects of the singhbhum crustal province a critical synthesis of various stratigraphic issues was long overdue the present contribution is an updated critical synthesis of the mesoarchaean palaeoproterozoic stratigraphic record of the singhbhum crustal province we have pointed out the problematic stratigraphic issues of the singhbhum crustal province that deserve careful scrutiny in order to gain better insights into the mode of stratigraphic sequence building

rare earth elements in river waters we measured rare earth element ree concentrations in river waters to characterize the suspended and dissolved river flux of the ree to the oceans the ree pattern of river suspended materials is sensitive to drainage basin geology a positive correlation is observed between la yb ratios and nd model ages for the rivers studied major rivers have light ree enriched patterns relative to the north american shale composite nasc with la yb n 1 6 2 7 river water dissolved material 0 2 m is heavy ree enriched relative to suspended material and the most pronounced negative ce anomalies occur in rivers of high ph light ree concentrations vary by approximately 3 orders of magnitude and are inversely related to ph and major cation concentrations from these data we estimate that typical major river runoff has heavy ree depleted suspended material with la yb n 1 9 we conclude that the terrigenous input to the oceans from major rivers is heavy ree depleted relative to shales from the available data average river water dissolved material appears to be heavy ree enriched with la yb n 0 4 estuarine removal processes lower the dissolved ree river flux by approximately 60 and result in a flux that is more heavy ree enriched with la yb n 0 2 calculated oceanic residence times with respect to river input range from 2300 to 21 000 years are shortest for ce and greatest for the heavy ree and la such long residence times may suggest the presence of additional sources of ree in seawater

initial characterization of cold seep faunal communities on the new zealand hikurangi margin abstract cold seep communities have been known from the north atlantic and north pacific for more than 20 years but are only now being explored in the southern hemisphere while fisheries bycatch had suggested the presence of cold seeps on the new zealand margin the biodiversity and distribution of these communities remained unknown explorations using towed cameras and direct sampling gear revealed that cold seep sites are abundant along the new zealand hikurangi margin initial characterization of the faunal communities at 8 of these sites indicates a fauna that is associated with particular sub habitats but which varies in abundance between sites community composition is typical at higher taxonomic levels of cold seep communities in other regions the dominant symbiont bearing taxa include siboglinid tube worms vesicomyid clams and bathymodiolin mussels at the species level much of the seep associated fauna identified so far appears either to be new to science or endemic to new zealand seeps suggesting the region may represent a new biogeographic province for cold seep fauna some overlap at the species and genus level is also indicated between the sampled seep communities and the fauna of hydrothermal vents on the kermadec arc in the region further taxonomic and genetic identifications of fauna from this study will allow us to fully test the levels of species overlap with other new zealand chemosynthetic ecosystems as well as with other cold seep sites worldwide these apparently novel communities exhibit evidence of disturbance from a deep bottom trawl fishery and appear to be threatened along the entire new zealand margin as bottom fisheries mining and fossil fuel exploitation move into deeper waters seep communities may be endangered worldwide necessitating the initiation of conservation efforts even as new seep ecosystems are discovered and explored our findings highlight the unique nature of anthropogenic impacts in the deep sea in which reservoirs of biodiversity can be impacted long before they are even known

defining biological assemblages biotopes of conservation interest in the submarine canyons of the south west approaches offshore united kingdom for use in marine habitat mapping in 2007 the upper part of a submarine canyon system located in water depths between 138 and 1165 m in the south west sw approaches north east atlantic ocean was surveyed over a 2 week period high resolution multibeam echosounder data covering 1106 km2 and 44 ground truthing video and image transects were acquired to characterise the biological assemblages of the canyons the sw approaches is an area of complex terrain and intensive ground truthing revealed the canyons to be dominated by soft sediment assemblages a combination of multivariate analysis of seabed photographs 184 1059 m and visual assessment of video ground truthing identified 12 megabenthic assemblages biotopes at an appropriate scale to act as mapping units of these biotopes 5 adhered to current definitions of habitats of conservation concern 4 of which were classed as vulnerable marine ecosystems some of the biotopes correspond to descriptions of communities from other megahabitat features for example the continental shelf and seamounts although it appears that the canyons host modified versions possibly due to the inferred high rates of sedimentation in the canyons other biotopes described appear to be unique to canyon features particularly the sea pen biotope consisting of kophobelemnon stelliferum and cerianthids

the whittard canyon a case study of submarine canyon processes submarine canyons are large geomorphological features that incise continental shelves and slopes around the world they are often suggested to be biodiversity and biomass hotspots although there is no consensus about this in the literature nevertheless many canyons do host diverse faunal communities but owing to our lack of understanding of the processes shaping and driving this diversity appropriate management strategies have yet to be developed here we integrate all the current knowledge of one single system the whittard canyon celtic margin ne atlantic including the latest research on its geology sedimentology geomorphology oceanography ecology and biodiversity in order to address this issue the whittard canyon is an active system in terms of sediment transport the net suspended sediment transport is mainly up canyon causing sedimentary overflow in some upper canyon areas occasionally sediment gravity flow events do occur some possibly the result of anthropogenic activity however the role of these intermittent gravity flows in transferring labile organic matter to the deeper regions of the canyon appears to be limited more likely any labile organic matter flushed downslope in this way becomes strongly diluted with bulk material and is therefore of little food value for benthic fauna instead the fresh organic matter found in the whittard channel mainly arrives through vertical deposition and lateral transport of phytoplankton blooms that occur in the area during spring and summer the response of the whittard canyon fauna to these processes is different in different groups foraminiferal abundances are higher in the upper parts of the canyon and on the slope than in the lower canyon meiofaunal abundances in the upper and middle part of the canyon are higher than on adjacent slopes but lower in the deepest part mega and macrofauna abundances are higher in the canyon compared with the adjacent slope and are higher in the eastern than the western branch these faunal patterns reflect the fact that the whittard canyon encompasses considerable environmental heterogeneity related to a combination of organic matter trapping current regimes due to focused internal tides and different substrates we conclude that coordinated observations of processes driving faunal patterns are needed at a fine scale in order to understand the functioning of communities in this and other submarine canyons

ferromanganese deposits from the gulf of alaska seamount province mineralogy chemistry and origin ferromanganese oxide deposits dredged from four seamounts welker miller murray and patton in the gulf of alaska seamount province include poorly crystallized microlaminated crusts on basalt substrate well crystallized mn oxide veins in epiclastic sedimentary rocks and crystalline mn oxide layers and micronodules in phosphorite the principal rock types dredged are alkali basalt pillow fragments and tuffaceous conglomerate and sandstone the glassy rims of pillow fragments the glassy goundmass of large volcanic clasts and the tuffaceous component of the sediment are altered to palagonite other low temperature alteration products include phillipsite smectite and carbonate apatite thick 10 50 mm fe mn crusts consist mainly of 6 mn0 straight and cuspate growth laminae indicate variable growth rates and periods of nondeposition a larger number of detrital particles toward the top of thick crusts record the increasing influence of active volcanoes of the aleutian arc during northwestward movement of the pacific plate thick crusts on basalt substrate have higher mnife ratios and lower co content than fe mn crusts from low latitude seamounts of the central pacific region thin 10 rnm crusts on volcaniclastic substrate contain todorokite and bimessite and have higher mnife ratios ni and cu and lower fe and co than thick gulf of alaska crusts veins of todorokite and cryptomelane with complex internal structure occur in altered tuffaceous sandstone and conglomerate from miller seamount fibrous todorokite has a composition similar to those of other marine examples but may contain up to 7 mn2 in m2 sites microprobe analysis of the marine cryptomelane indicates a composition that is approximately k ba 2 mn4 co 8016 x h20 a third type of fe mn deposit in phosphorite is an intimate mixture of todorokite and minor 6 mn02 bearing layers and micronodules carbonate apatite and phillipsite that encloses grains of altered volcanic glass and lithic fragments the microlaminated structure mineralogy predominantly 6 mn02 and composition mnife ratio and transition metal rare earth element u and th contents of the thick crusts are characteristic of hydrogenetic fe mn crusts elsewhere in the pacific conversely the crystallinity and chemical composition of the mn oxide veins and thin crusts indicate formation during diagenesis of the volcanogenic sediment substrate mn and other transition metals are mobilized during lowtemperature oxidative alteration palagonitization of basaltic volcanic glass the oxidation of fez to fe3 during palagonitization and the dissolution of the dilute biogenic fraction of the sediment combine to lower the eh of ambient pore fluid and enhance the mobility of mn2 diagenesis in the phosphatic sandstone from patton seamount involves organic rich sediment and pore waters elevated in phosphorus owing to upwelling above a large volcanic edifice les cchantillons de dcp6ts de ferromangankse draguks sur quatre monts sous marins welker miller murray et patton dans la province des monts sous marins du golfe de i alaska sont formts de crodtes microlaminces et pauvrement cristallisces sur un substratum de basalte de veines d oxyde de mn bien cristallisc encaisstes dans des roches stdimentaires cpiclastiques et de couches et micronodules d oxyde de mn cristallin dans une phosphorite les principaux types de roches dragutes sont des fragments de coussins de basalte alcalin et de conglomcrat et de grks tufaccs les franges vitrifices des fragments des coussins la matrice vitrifice des gros fragments volcaniques et la composante tufacke du scdiment sont altcr6es en palagonite les autres mincraux d altkration sont phillipsite smectite et carbonate apatite

deep sea bio physical variables as surrogates for biological assemblages an example from the lord howe rise abstract little is known about diversity patterns of biological assemblages in deep sea environments primarily because sampling deep sea biota over vast areas is time consuming difficult and costly in contrast physical mapping capabilities are increasing rapidly and are becoming more cost effective consequently the growing need to manage and conserve marine resources particularly deep sea areas that are sensitive to anthropogenic disturbance and change is leading the promotion of physical data as surrogates to predict biological assemblages however few studies have directly examined the predictive ability of these surrogates the physical environment and biological assemblages were surveyed for two adjacent areas the western flank of lord howe rise lhr and the gifford guyot spanning combined water depths of 250 2200 m depth on the northern part of the lhr in the coral sea multibeam acoustic surveys were used to generate large scale geomorphic classification maps that were superimposed over the study area forty towed video stations were deployed across the area capturing 32 h of seabed video 6229 still photographs that generated 3413 seabed characterisations of physical and biological variables in addition sediment and biological samples were collected from 36 stations across the area the northern lord howe rise was characterised by diverse but sparsely distributed faunas for both the vast soft sediment environments as well as the discrete rock outcrops substratum type and depth were the main variables correlated with benthic assemblage composition soft sediments were characterised by low to moderate levels of bioturbation while rocky outcrops supported diverse but sparse assemblages of suspension feeding invertebrates such as cold water corals and sponges which in turn supported epifauna dominated by ophiuroids and crinoids while deep environments of the lhr flank and lower slopes of the gifford guyot were characterised by bioturbation with high occurrences of trails burrows and mounds evidence for bioturbation was significantly less on the upper sections of gifford guyot with mostly trails on the more sediment starved environments the seamount summit also supported a variety of taxa such as benthic ctenophores and rock associated fishes that were not recorded in the deeper basin habitats physical characteristics of the seabed particularly geomorphology were good predictors of biological assemblage composition and percent cover of key taxa of the nine geomorphic classes assessed in this study six predicted different physical habitats that supported distinct biological assemblages however other classes that were defined by spatial features e g valleys seamount dunes where surficial physical variables were not unique provided little predictive power of biological assemblages but rather had characteristics that were shared with adjacent surrounding geomorphic classes given the growing need to use surrogates in the management and conservation of marine environments these results are promising however our findings suggest that there is a pressing need for careful testing and validation of surrogates such as geomorphic classes before classification schemes can be deemed effective and employed as a management tool to predict seabed habitats and their biological assemblages

geochemistry of hydrothermal mn oxide deposits from the s w pacific island arc abstract hydrothermal mn oxide crusts have been removed from the tonga kermadec ridge the first such hydrothermal deposits to be reported in the s w pacific island arc in several respects the deposits are similar to hydrothermal mn crusts from oceanic spreading centre settings they are limited in areal extent comprise well crystalline birnessite and generally display extreme fractionation of mn from fe they are strongly depleted in many elements compared to hydrogenous mn deposits but are comparatively enriched in li zn mo and cd the group ia and group iia metals show strong intercorrelations and the behaviour of mg in the purest samples may indicate the extent to which normal seawater has influenced the composition of the deposits certain aspects of the deposits are not typical of hydrothermal mn deposits in particular at least some of the crusts have developed on a sediment or unconsolidated talus substrate some crusts or specific layers within some crusts display a chemical composition which suggests a significant input from normal seawater

ree in the great whale river estuary northwest quebec we report rare earth element ree concentrations of a longitudinal profile within the estuary of the great whale river in northwest quebec and in hudson bay all of the measured ree have concentrations less than those predicted by conservative mixing of seawater and river water demonstrating removal of the ree from solution ree removal is rapid occurring primarily at salinities less than 2 removal of the ree is greatest for the light ree and ranges from about 7 for the light ree to no more than 40 for the heavy ree fe removal is essentially complete at low salinity the shape of the fe and ree vs salinity profiles is not consistent with a simple model of destabilization and coagulation of iron and ree bearing colloidal material a linear relationship between the activity of free ion ree3 and ph is consistent with a simple ion exchange model for ree removal surface and subsurface samples of hudson bay seawater are characterized by high ree concentrations and high la yb relative to average seawater the subsurface sample has a nd concentration of 100 pmol kg and an end of 29 3 0 3 these characteristics are consistent with the high ree concentration high la yb and low end of river inputs into hudson bay these results indicate that rivers draining the canadian shield are a major source of non radiogenic nd and ree to the atlantic ocean we estimate that outflow of water from hudson bay to the labrador sea could supply 30 of the non radiogenic nd in north atlantic deep water

geochemistry and origins of lacustrine ferromanganese nodules from the malawi rift central africa abstract ferromanganese nodules recovered from 100 130 m depth near likoma island eastern lake malawi have been analysed for some thirty four elements by dc arc optical emission spectrometry the concretions routinely hold in excess of 50 fe mn although actual fe mn ratios appear to vary inversely with nodule size subcrustal values are recorded for mg al si k ca and ti the abundance of these major elements is considered to primarily reflect the amount and mineralogy of detrital impurities within the nodule structures of the twenty six analysed trace elements zn co pb ba y la v zr ag be and nb are present at levels exceeding their average crustal abundances while subcrustal or subdetection limit values are recorded for sr ni cu cr sc rb ga li b mo cd bi sn ce and nd the high enrichment factor noted for ba 21 95 the limited enrichment of co 5 53 and zn 2 06 and depletion of ni 0 62 and cu 0 09 are characteristic of most lacustrine ferromanganese deposits and adequately distinguish the lake malawi nodules from their deep ocean counterparts while the ferromanganese deposits of the malawi rift are predominantly of diagenetic origin hydrothermal exhalations may significantly control the supply of elements such as fe v and be this implies a need to extend existing classification systems to include nodules formed through the simultaneous precipitation of metals from two or more sources the nodule sequences in the vicinity of likoma island are physically suited to economic exploitation but fail to meet prescribed chemical criteria for mn or ni co cu ores

banded iron formations through much of precambrian time similarities between proterozoic 1 8 2 5 gyr and archean 2 5 gyr banded iron formations are probably more significant than their differences the contrasts largely reflect differences in the tectonic settings of proterozoic and archean terrains archean banded iron formations are not as thick nor laterally as extensive as the major proterozoic iron formations nevertheless some archean iron formations have strike lengths of over 150 200 km and may have been quite extensive prior to the deformation that has affected most archean terrains stratigraphic sequences in which iron formations occur are highly variable and indicate that iron formations formed in many depositional environments sedimentary textures in the iron formations are dominated either by granules and oolites or laminations including microbanding reflecting differences in their physical conditions of deposition granular and oolitic textures are abundant in only three proterozoic depositional basins and most precambrian iron forma

compositional variations in manganese micronodules a possible indicator of sedimentary environments manganese micronodules from various environments were analyzed with the electron microprobe chemical characteristics of marine manganese nodules were examined in relation with their depositional environments and compared with those of manganese macronodules the compositional variation has a connection with accumulation rates and chemical features of the associated sediments mg and ti tend to be enriched in micronodules relative to the host sediments these elements may produce authigenic mineral phases in micronodules these observations show that manganese micronodules are chemically formed under approximately the same condition as that for macronodules but coexisting pairs of micronodules and macronodules collected from the same sediments suggest that oxic diagenesis plays a more important role in the formation of micronodules than that of macronodules the chemical features of manganese micronodules collected from several marine environments such as a marginal sea hemipelagic regions and the cent

large deep water coral banks in the porcupine basin southwest of ireland the porcupine basin southwest of ireland was one of the earliest sites from where the deep water corals lophelia sp and madrepora sp were recovered these deep water corals have since been found all along the atlantic margins of europe in water depths ranging from 50 to more than 2000 m recent geophysical studies have demonstrated the mound building potential of deep water corals available data indicate that three major provinces of coral bank occurrences can be identified in the porcupine basin 1 high relief surface mounds which have a dimension of 1 by 5 km and a height up to 200 m hovland mounds flanked to the north by 2 a swarm of buried mounds somewhat smaller up to 90 m and with more irregular shapes than those recognised in area 1 magellan mounds and 3 outcropping or buried conical mounds single or in elongated clusters up to 150 m high occurring on the southeastern slope of the basin belgica mounds as far as can be inferred from shallow cores the surface lithology predominantly consists of an upper layer rich in foraminiferal sand and terrigenous silty clay with intercalations of biogenic rubble the banks host a remarkable number of colonies of living and dead lophelia pertusa and madrepora oculata the living and dead assemblages are underlain by a significant layer of coral debris in a muddy matrix deep water coral debris together with a living association of the same species covers the surface of the belgica and hovland mounds which may suggest that these corals have played a significant role in the development of the mound structures the capacity for mound formation by scleractinian corals in the aphotic zone has been known for some time examples are found at different locations along the shelves and the continental margins of the north atlantic the role of the corals in these deep water build ups is still a point of debate though the genesis and initial control of mound settings in this basin might be related to hydrocarbon seeps it appears that the major development of the porcupine coral banks in recent geological times has most likely been controlled by oceanic circulation and dynamics in water masses and nutrient supply

contrasting mineralogical geochemical signatures of manganese oxides guides to metallogenesis manganese oxides have a strong sorption capacity for cationic species in the depositional fluid this sorption capacity is reflected in the chemistry of the oxides which is different from that for the oxides precipitated from fresh water seawater and hydrothermal fluids characteristic mineralogical geochemical enrichment and geochemical association defined statistically signatures in conjunction with several diagnostic plots can be employed to distinguish between the following different genetic types of manganese deposits supergene hydrothermal supergene marine terrestrial supergene dubhite and supergene marine hydrothermal sedimentary exhalative sedex dubhites are manganese oxides derived from the weathering of a mineralized sequence i e base and precious ore minerals and gangue hydrothermal deposits characteristically show geochemical enrichments in the assemblage as ba cu li mo pb sb sr v zn and an mn as geochemical association supergene marine deposits show na k ca mg sr and co cu ni geochemical enrichments whereas supergene terrestrial deposits tend to have very high ba contents and an mn ba association dubhites contain high levels of pb and zn show an mn pb base metal association and are composed of significant quantities of base metal bearing manganese oxides bixbyite braunite hausmannite huebnerite jacobsite and pyrochroite occur predominantly only in hydrothermal deposits whereas chalcophanite coronadite crednerite delta mno 2 groutite hollandite lithiophorite manganite nsutite quenselite ramsdellite romanechite todorokite and woodruffite are generally of supergene origin in addition to established plots presently used to identify marine sedimentary exhalative deposits the following diagnostic graphs were devised na vs mg distinguishes deposits of marine and fresh water origin co ni vs as cu mo pb v zn discriminates between hydrothermal and supergene oxides and pb vs zn can be used to recognize dubhites and therefore prospective sequences

hydrothermal mn deposits of the franciscan assemblage ii isotope and trace element geochemistry and implications for hydrothermal convection at spreading centers abstract major element trace element and sr nd pb and o isotopic data for a franciscan mn deposit suggest an origin by seafloor hydrothermal circulation based on q mode factor analysis the cherts and mn lenses of the blue jay mine formed from a combination of 4 components representing 1 biogenic 1 hydrothermal and 2 detrital sources rb sr u th pb and o isotopic systematics in the mn lenses were affected by input from the hydrothermal circulation of material leached from the underlying basalts nd isotopic compositions in both cherts and mn lenses are identical and within the range measured for pacific ocean water suggesting the ree were not mobilized by hydrothermal activity correlation of 18 o with sio 2 and mno 2 in the mn lenses implies the lenses formed by simple mixing of hydrothermally derived mn oxides with seawater and biogenic silica 18 o of the cherts is both uniform and depleted relative to dsdp jurassic cherts but similar to microquartz bearing cherts of the monterey formation this suggests that diagenetic activity exerted more control on oxygen isotope compositions then hydrothermal alteration or metamorphism finally a well defined rb sr isochron of 158 5myr was obtained for these cherts and opens the possibility of determining absolute radiometric ages for similar cherts throughout the geologic record

origin of rhythmical bedding in middle miocene siliceous rocks of the onnagawa formation northern japan abstract centimeter to decimeter scale rhythmical alternation of dark and light layers is common in siliceous rocks of the middle miocene onnagawa formation of northern japan the siliceous rocks may also show micrometer scale laminae considered to be varves dark layer frequency shows meter scale cyclic variation with dominant spectral peaks of approximately 10 5 4 3 4 2 3 and 1 6 m for these a varve tuned average sedimentation rate of 139 m yr yields periods of 72 39 24 17 and 12 kyr respectively a sedimentation rate of 100 m yr which is within the range of biostratigraphically calculated rates yields 100 54 34 23 and 16 kyr respectively considering the uncertainty in the estimation of the average sedimentation rate these values are in relatively good agre ment with orbital eccentricity obliquity and precessional cycles respectively bottom water oxygenation levels deduced from the lamina preservation index are in phase with the frequency variation of dark layers suggesting that it is also controlled by orbital cycles mineral and chemical analyses suggest that the siliceous rocks are mainly composed of biogenic diagenetic silica terrigenous detritus dolomite and organic matter with minor amounts of carbonate fluorapatite the dark colors are due to detritus and organic matter thus alternation of dark and light layers and variation in the frequency of dark layers reflect compositional variation mass accumulation rates mars of biogenic silica and terrigenous detritus are calculated from the average thickness of a lamina couplet dry bulk density and chemical composition of individual samples at the level of centimeter to decimeter layers mar of detritus is nearly constant whereas mar of biogenic silica varies by a factor of 2 on the other hand mar of detritus shows meter scale variation with amplitudes as high as a factor of 10 which is in phase with frequency cycles of dark layers whereas mar of biogenic silica does not show significant meter scale variation compositional variation represented by dark and light alternation and frequency cycles of the dark layers are a result of the interplay of centimeter to decimeter scale 102 3 years variation in mar of biogenic silica and meter scale 104 years variation in mar of detritus the latter could be related to global sea level oscillation caused by orbital cycles

organic enrichment of submarine canyon and continental shelf benthic communities by macroalgal drift imported from nearshore kelp forests remotely operated vehicle rov surveys were conducted over a 3 year period to evaluate the importance of macroalgal drift exported from nearshore forests of giant kelp macrocystis pyrifera to adjacent submarine canyon and continental shelf benthic habitats abundant macroalgal drift was found in the carmel submarine canyon 153454 m depth but was rare at pt joe a continental shelf habitat 9 km away 87 357 m depth most of the drift parcels consisted of brown algae but 10 other categories were found including green and red algae and the surfgrass phyllospadix spp m pyrifera drift accounted for as much as 20 of the density of drift parcels in the carmel submarine canyon and up to 50 of the drift parcels at pt joe from previously determined turnover rates of drift m pyrifera and the standing stock estimates from the present study we estimated that the rate of carbon flux associated with drift m pyrifera to the benthos of the cannel submarine canyon was 45 2 mg c m z d i based on published estimates of carbon flux from vertically sinking particulate organic carbon at 400 m depth in the nearby monterey submarine canyon and our estimates of kelp derived carbon flux drift m pyrifera can account for 20 83 of the total particulate organic carbon reaching the sea floor in the carmel submarine canyon we conclude that drift macrophytes provide significant enrichment of organic carbon to the benthos above that provided by vertically sinking particulate organic material the extent to which this alters the structure of benthic communities compared to areas without organic enrichment by drift macrophytes remains unknown and awaits further study deep sea benthic communities are entirely dependent on imported primary production for metabolic energy except hydrothermal vent and cold seep communities whose energy is provided by chemolithoautotrophy organic carbon arrives at the sea floor as small detrital particles episodic deliveries of large organic parcels such as large animal carcasses actively swimming zooplankton turbidity currents and macrophyte detritus rowe 1981 the relative importance of these organic carbon pathways no doubt varies with habitat and distance from shore although quantification of these pathways is still in its infancy gage and tyler 1991 pilskaln et al 1996 rowe 1981 the macrophyte detritus pathway may be particularly important in deep sea environments adjacent to productive neat shore habitats such as seagrass meadows or kelp forests where macrophyte detritus removed from these habitats may be transported offshore to deep sea benthic communities via bottom currents josselyn et al 1983 menzies et al 1967 suchanek et al 1985 vetter and dayton in press forests of giant kelp

fluorine geochemistry of quaternary volcanic rocks from southwestern british columbia some petrogenetic implications fluorine contents in 38 quaternary volcanic rocks representing calc alkaline andesite eruptive groups from the garibaldi lake area were determined by a selective ion electrode method a close relationship is evident between f abundance and the type of ferromagnesian phenocrysts present in the andesitic rocks hypersthene andesites have the lowest f contents 142 212 ppm whereas hornblende biotite andesites exhibit the highest f values 279 368 ppm hornblende andesites have intermediate f contents 238 292 ppm the hornblende free desolation valley basaltic andesite has a lower f content than the hornblende bearing sphinx moraine basaltic andesite 122 ppm versus 317 333 ppm

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

chemical environments of deposition of ancient iron and manganese rich sediments and cherts despite detailed classification criteria to distinguish between marine and freshwater environments of deposition in fine grained non clastic sedimentary rocks are scanty data on recent lacustrine and marine chemical precipitates reveal that these two environments can be distinguished in terms of their composition in the cao mgo na2o k2o system provided carbonates and detrital components associated with them are trivial lacustrine ferromanganese precipitates display low na2o and k2o but a high cao cao mgo ratio 0 70 similar to the world average river water in contrast diagenetically mature marine ferromanganese precipitates and nodules show a lower 0 60 cao cao mgo ratio in general and variable na2o and k2o recent pelagic cherts reveal an average cao cao mgo ratio comparable to that of ocean water whereas those affiliated to ocean floor hydrothermal activity span a wide range of composition in cao mgo na2o k2o space and mostly avoid the lacustrine field extension of the observed relations to the ancient archean bifs and cherts from 1 isua supracrustals greenland 2 yilgarn block australia 3 montana usa and proterozoic bifs from 4 hamersley basin australia 5 labrador trough canada 6 biwabik iron formations usa and the late proterozoic 7 upper tindhir group iron formation alaska and many others reveal a marine signature corroborating the inferences based on ree and isotope studies however chemical data on a number of deposits including the late proterozoic bifs mn deposits and cherts from the damara orogen africa bifs from rapitan formation northwest territories canada and several proterozoic mn deposits and cherts from india suggest a freshwater chemical environment of deposition the concurrence in the results obtained from studies on iron and or manganese deposits and coexisting cherts from several archean proterozoic and phanerozoic basins suggests that the chemistry of the more abundant siliceous sedimentary rocks can provide an additional tool for palaeogeographic reconstruction

the archaean nucleus of singhbhum the present state of knowledge abstract the supracrustal rocks of the older metamorphic group omg consisting of metasediments and ortho amphibolite constitute the oldest unit in the archaean nucleus of singhbhum however there are indications that still older 3 4 3 8 ga crust of both sialic and mafic composition existed in this region the omg ortho amphibolites were formed by partial melting of mantle with near chondritic composition ca 3 3 ga ago probably as a result of plume activity shortly afterwards partial melting of the underplated mafic material produced a tonalitic melt older metamorphic tonalitic gneiss omtg which intruded the omg supracrustals and the entire suite was deformed and metamorphosed to upper amphibolite facies subsequent to this melting of the omg ortho amphibolites and the lower crustal material of probable andesitic composition produced melts varying in composition from tonalite to granite and these intruded in different phases to produce plutons of singhbhum granite bonai granite and kaptipada granite which together form volumetrically the major part of the archaean nucleus the older omg and omtg occur as enclaves within these younger granitoids the time difference between the emplacements of the omtg and the early phases of younger granitic intrusion was of the order of 100 200 ma thus serial additions of juvenile material led to the formation of a stable microcontinent by 3 2 ga thermally triggered stretching in this microcontinent produced basins peripheral to the present day singhbhum granite pluton and in these basins the younger supracrustal rocks of the iron ore group iog consisting of bif associated argillaceous and subordinate arenaceous rocks and mafic lavas were laid down there is inadequate field or geochronological evidence to resolve the issue of whether the different iron ore basins were coeval or not meagre geochronological data suggest that some of the bifs are older than ca 3 1 ga post iog activity is confined to the intrusion of mafic dyke swarms and formation of intracratonic basins the ages of both being uncertain

rare earth major and trace elements in chert from the franciscan complex and monterey group california assessing ree sources to fine grained marine sediments abstract rare earth element ree major and trace element analyses of 77 samples from the mesozoic franciscan complex and miocene monterey group of california usa indicate that magnitudes of the ce anomaly ce ce and total ree abundances sree in these rocks are controlled dominantly by a the amount of included metalliferous material b the amount of direct terrigenous input and c the overall burial rate the relative importance of these individual processes varies across an ocean basin in such a way that ree relative fractionations and sree correspond with its depositional environment our conclusions are supported by an extensive review of published ree data from various river coastal open ocean and ridge influenced waters as well as terrigenous pelagic and metalliferous sediment the chert sequences record deposition in spreading ridge open ocean basin and continental margin environments the relative importance of metalliferous and terrigenous influences and the role of scavenging from seawater may be estimated from a sample s inferred depositional distance km from the spreading ridge the major element chemistry and the stratigraphie context the ce ce values are low 0 29 in the vicinity of spreading ridges and trend to successively higher 1 values with decreasing metalliferous and increasing terrigenous influences other ree indicators ree lu n la n eu eu also respond to metalliferous and terrigenous influences near the spreading ridge chert ree appears determined by burial rate while shale ree responds to metalliferous abundance in open ocean and continental margin environments ree is controlled by sediment exposure time and therefore is related inversely to burial rate ree data are consistent with the major elements fe2o3 mno and al2o3 in reflecting the respective metalliferous and terrigenous sources p2o5 and cao do not vary with ce ce in any environment but cao shows a weak negative correlation with ree trace element trends e g v cr cu ge si rb sr y th u in general can similarly be accounted for in the context of depositional position relative to metalliferous and terrigenous inputs rees in chert appear less affected by post depositional processes than either major or trace elements indicating that rees are better tools for paleoceanographic or tectonic reconstructions that are based on chert chemistry this work complements recent efforts to elucidate the factors determining large scale ree distributions in marine sediments and has direct bearing on previous attempts to use the ce anomaly in older rocks and sediments as a recorder of secular variations and anoxic events in the overlying water column

limited depth zonation among bathyal epibenthic megafauna of the gully submarine canyon northwest atlantic abstract the gully is a large submarine canyon incised into the scotian shelf in the northwest atlantic a submersible mounted camera was used to collect 17 km of high resolution video imagery of the soft sediment flanks and floor of the canyon between 1000 and 2500 m depth a depth stratified random survey design with two transects per stratum was followed depth strata were drawn at 1000 1500 m 1500 2000 m and 2000 2500 m reflecting global and regional faunal boundaries the 47 614 individuals or colonies observed on the transects were identified into 49 unique taxa drawn from 7 phyla while 21 additional taxa were observed between the transect lines cnidaria was the most diverse phylum 22 taxa on the transects followed by the echinodermata 15 taxa most fauna were sessile or sedentary suspension feeders a species of xenophyophorida likely syringammina sp was the most abundant taxon cluster analysis of transects based on a bray curtis bc matrix of species abundance identified one cluster of five transects and one independent transect the deepest transect 2406 m average depth a similarity profile test indicated that this structure is not random there was a significant change in the megafaunal assemblage with depth over scales of 10s of kilometers accounting for 65 of the variation in the bc matrix both total organic carbon and labile carbon were higher in cores from the 1000 1500 m stratum than at greater depth consistent with transport of food and sediments into the canyon from shallower waters the first principal component calculated from species abundances separated the two transects from the 1000 1500 m depth stratum from the others indicating that sediment food supply influences community structure and composition over small spatial scales 10 m eight groups of species associations were identified however the associations between the species within each group were not strong with the highest correlation between the xenophyophorida and the pennatulacea 0 66 at this spatial scale substrate type was an important factor with hard and soft bottom species associations being identified

environments and processes of manganese deposition concentration of manganese in solution and its deposition takes place by redox controlled processes in a variety of modern and ancient geologic and geochemical environments modern mn deposition occurs predominantly in deep sea areas rather than shallow water domains although deep sea sedimentary deposits dominate hydrothermal contribution of mn to the ocean system may be substantial mn deposition from hydrothermal solutions at or near sea floor spreading centers and less commonly in island arc areas is known in addition near and far field dispersion of mn from vent sites is also substantial such distributions are controlled by the flow rate and egress temperature of the solution and the residence time of mn in seawater thus even in sedimentary deposit domains at least partial derivation of mn from a hydrothermal source is possible sedimentary fe mn crusts on older volcanic substrates on seamounts form by hydrogenous deposition of metal concentrated from terrigenous sources in the mid water column oxygen minimum zones thus the presence or absence of volcanic rocks is not a clear indication of whether sedimentary mn deposits particularly in the ancient geologic record are the result of a totally terrigenous or a totally volcanogenic source abyssal fe mn nodules are considered to form from a basin water hydrogenous and or pore water early diagenetic supply of metals but in most cases the extent of supply from either of the sources is unknown the metal incorporation mechanisms of free moving nodules is little understood and it is possible that in most cases both sources contribute to the nodule composition therefore no nodule should be considered as totally hydrogenous or totally early diagenetic based only on its bulk composition the determined growth rate giving only an average value cannot by itself reveal the growth history of the nodules biological participation directly or indirectly controls mn deposition the stratified black sea demonstrates the concentration of mn in solution in an anoxic zone its advection toward the redox interface and its precipitation in an oxygenated condition similar stratified basins are contemplated for ancient mn deposition in shallow water basin margin areas geologic and geochemical signatures indicate that during sea level highstands stratified basins formed in which mn was concentrated in solution in the anoxic part corresponding transgression led to the impingement of the redox interface on the continental shelf and precipitation of mn oxides could take place across the interface during transgression regression cycles offshore in anoxic or dysaerobic conditions mn carbonate could form by early diagenetic reaction of mn super 2 with co 2 or hco 3 super produced by organic carbon oxidation critical mn deposits occurring in transgressive glaciogenic and black shale bearing ancient sequences support this paleoenvironmental model for mn deposition

acoustical detection of high density krill demersal layers in the submarine canyons off georges bank high density demersal layers of krill have been detected in the submarine canyons off georges bank by means of a high frequency dual beam bioacoustical technique krill densities in these demersal layers were observed to be two to three orders of magnitude greater than the highest densities observed in water column scattering layers such abundances may help explain the unusually high squid and demersal fish production estimates attributed to the georges bank ecosystem

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