morphology and environment of cold water coral carbonate mounds on the nw european margin cold water coral carbonate mounds owing their presence mainly to the framework building coral lophelia pertusa and the activity of associated organisms are common along the european margin with their spatial distribution allowing them to be divided into a number of mound provinces variation in mound attributes are explored via a series of case studies on mound provinces that have been the most intensely investigated belgica hovland pelagia logachev and norwegian mounds morphological variation between mound provinces is discussed under the premise that mound morphology is an expression of the environmental conditions under which mounds are initiated and grow cold water coral carbonate mounds can be divided into those exhibiting inherited morphologies where mound morphology reflects the morphology of the colonised features and developed morphology where the mounds assume their own gross morphology mainly reflecting dominant hydrodynamic controls finer scale surface morphological features mainly reflecting biological growth forms are also discussed

cold water coral habitats of rockall and porcupine bank ne atlantic ocean sedimentary facies and benthic foraminiferal assemblages the extent of the cold water coral mounds in the modern ocean basins has been recently revealed by new state of the art equipment however not much is known about their geological extent or development through time in the facies model presented here seven different types of seabed substrate are distinguished which may be used for reconstruction of fossil coral habitats the studied substrates include off mound settings foram sands hardgrounds dead coral debris and substrates characterized by a variable density of living coral framework whereas sediment characteristics only provide a basis for distinguishing on and off mound habitats and the loci of most prolific coral growth benthic foraminiferal assemblages are the key to identifying different mound substrates in more detail specific foraminiferal assemblages are distinguished that are characteristic of these specific environments assemblages from off mound settings are dominated by attached epifaunal species such as cibicides refulgens and cibicides variabilis the attached epibenthic species discanomalina coronata is also common in off mound sediments but it is most abundant where hardgrounds have formed in contrast the settings with coral debris or living corals attract shallow infaunal species that are associated with more fine grained soft sediments the typical living coral assemblage is composed of cassidulina obtusa bulimina marginata and cassidulina laevigata the abundance of these species shows an almost linear increase with the density of the living coral cover the benthic foraminifera encountered from off mound to top mound settings appear to represent a gradient of decreasing current intensity and availability of suspended food particles and increasing availability of organic matter associated with fine grained sediment trapped in between coral framework

210pb derived sediment accumulation and mixing rates for the washington continental slope abstract total sediment accumulation rates g yr in four canyons indenting the washington continental shelf are about twice those on the nearby open slope even though canyons comprise less than 40 of the depositional area of the entire slope this is because 210 pb derived sediment accumulation rates g cm 2 yr for astoria and quinault canyons are 3 4 times greater than those for willapa and grays canyons and intermediate open slope areas supporting the hypothesis that columbia river derived solids are preferentially transported to these two canyons quinault canyon currently appears to be accumulating solids at rates much greater than its low long term accumulation rate which is attributed to turbidity currents transporting solids down this canyon roughly every 500 years the following four different approaches all show that mixing may cause 210 pb derived sediment accumulation rates for slope and canyon sediments to be 2 3 times higher than true accumulation rates 1 comparison between accumulation rates calculated from 210 pb profiles with and without surface zones in which mixing has obviously affected 210 pb distributions 2 comparison between 210 pb derived and independently determined long term accumulation rates 3 comparison between 210 pb derived accumulation and modern columbia river discharge rates 4 comparison between two and three layer steady state one dimensional diffusion advection decay models mixing coefficients for surface sediments calculated using a one dimensional two layer vertical eddy diffusion model show large differences within the region with most in the 3 30 cm 2 yr range mixing rates are several times larger in canyon sediments from 0 2 1 1 km water depth probably due to physical reworking processes erroneously neglected mixing at depth of no more than 5 of that calculated for the surface mixed layer can cause the 2 3 fold calculated overestimation of true sediment accumulation rates and 2 4 fold calculated underestimation of true mixing coefficients

giant carbonate mud mounds in the southern rockall trough seismic profiles sidescan sonar data bottom photography and sampling proved for the first time that there are giant carbonate mounds bioherms in the rockall trough the pelagia mounds on the northern porcupine bank are relatively isolated whereas most of the logachev mounds on the southeast rockall bank form a field of closely spaced contiguous mounds they are all found on the upper slope at depths between about 500 and 1200 m and as a result of this study about 500 have been mapped they have a variety of shapes and the larger ones are very steep sided up to 350 m high and 2 km wide at the base sediment samples show that the mounds consist of pale coloured muds mainly aragonite usually with live and or dead cold water corals at the seafloor and with buried dead corals coral thickets appear to be detected as a brush like signature on high resolution profiles and as a speckled pattern on high resolution sidescan sonar records shelly sands are found on the seabed between the mounds currents in the mound areas are strong enough to transport sands along slope as medium sized sand waves and to prevent pelagic deposition thus providing surfaces for initial coral settlement by the winnowing of fines to leave glacial dropstones and exposed rocks these observations show that the poleward directed upper slope current of the eastern north atlantic extends further south than hitherto known and that there is a southwesterly directed current on rockall bank there are waves on the logachev mounds with a wavelength of about 20 30 m that are thought to be moulded in carbonate muds by across slope directed internal tidal currents and or cascading currents mounds develop above erosional surfaces seen on seismic data the huge amount of carbonate mud seems to be produced by the rapid growth and breakdown of cold water corals living in a very favourable environment intermediate nepheloid layers formed upstream by the strong currents may provide the food source for the deep water suspension feeders conditions for giant mound growth require an ideal balance between current speed and sedimentation rate among other factors no evidence for the suggested link to methane seepage has been found so far

hydrochemical and isotopic δ18o δ2h 87sr 86sr δ37cl and δ81br evidence for the origin of saline formation water in a gas reservoir abstract the permo triassic kangan gasfield in southern iran is composed of an aquifer the kangan aquifer ka and an overlying gas reservoir it is located in the kangan and dalan formations and consists predominantly of limestone and dolomite the kangan gasfield is exploited from 36 wells at depths from 2300 to 2860 m the quality of the produced formation waters pfw varies from fresh to saline with salinities of up to 60 000 mg l the present study aims to identify the origin of the salinity of the pfws the concentration of major ions li sr and br as well as 18o d 87sr 86sr 37cl and 81br isotope compositions of the ka water and pfw samples a fresh and a brine spring and the persian gulf water were all measured the suite of isotopic 37cl and 81br and hydrochemical data li cl and br concentrations and cf index in this study indicates that the salinity origin of the pfws is evaporated seawater which could be either the ka water or the intergranular saturated brine in the kangan gas reservoir kgr both derived from permo triassic evaporated seawater 18o and 87sr 86sr data exclude the ka water as the source of the saline pfw leaving the intergranular brine of the kgr as the most likely source although further isotopic and geochemical tests are needed to verify this this work also proposes for the first time the use of a li cl versus br cl diagram to distinguish between evaporate formation water water modified by halite dissolution and fresh water it is recommended to apply these comprehensive methods to deep brine aquifers especially related to gasfields

size sorting in marine muds processes pitfalls and prospects for paleoflow speed proxies the basis for and use of fine grain size parameters for inference of paleoflow speeds is reviewed here the basis resides in data on deposited sediment taken in conjunction with flow speed measurements in the field experimental data on suspended sediment transport and deposition and theoretical treatments of the generation of size distributions of deposits from suspension controlled by particle settling velocity and flow speed in the deep sea sorting events occur under resuspension deposition events in benthic storms at flow speeds below 10 15 cm s 1 size in the noncohesive sortable silt 10 63 m range is controlled by selective deposition whereas above that range removal of finer material by winnowing also plays a role the best particle size instruments to measure a flow speed related grain size employ the settling velocity method while laser diffraction sizers can yield misleading results because of particle shape effects potential problems including source effects downslope supply on continental margins spatial variability of flow over bedforms and influence of ice rafted detritus are examined a number of studies using the sortable silt flow speed proxy are reviewed and inverse modeling of grain size distributions is examined outstanding problems are that corroboration is sparse because almost no studies have yet used the full range of proxies for flow rate and water mass identification and that the sortable silt mean size is not yet properly calibrated in terms of flow speed

millennial scale glacial variability versus holocene stability changes in planktic and benthic foraminifera faunas and ocean circulation in the north atlantic during the last 60 000 years two piston cores ds97 2p from the reykjanes ridge in the central north atlantic ocean 1685 m water depth and enam33 from southwest of the faeroe islands in the ne atlantic 1217 m water depth have been investigated for their planktic and benthic foraminiferal content ds97 2p is situated near the subarctic front and productivity measured by accumulation rates of benthic and planktic foraminifera has been generally high during the holocene the productivity shows a clear decrease from an early holocene maximum to a late holocene minimum coeval changes in the benthic faunas indicate that the food supply changed from large irregular pulses during the early holocene to a more sustained flux during the late holocene presumably in concert with decreasing bottom current activity oxygen conditions in the bottom water became poorer another feature of the late holocene is an increasing instability of the north atlantic thermohaline circulation regime nevertheless the changes in faunal composition and productivity during the holocene were gradual as compared to the discontinuous distribution patterns and abrupt productivity shifts during the glacial the glacial shifts were on a millennial time scale and correlate with the interstadial stadial phases of the dansgaard oeschger cycles in the greenland ice cores the faunas of the warm interstadial phases resembled the holocene faunas and both surface and bottom productivity was high the faunas suggest that the interstadial circulation pattern was very similar to the modern system with convection in the nordic seas and generation of north atlantic deep water the planktic faunas during the cold stadials and heinrich events were completely dominated by the polar species neogloboquadrina pachyderma s and surface conditions were cold and the productivity low the benthic faunas were dominated by species that presently thrive in areas with a low amount of food and reduced oxygen content the water column was probably stratified with low saline cold surface water overlying poorly aerated intermediate water masses

foraminiferal stratigraphy and environment of late weichselian deposits on the continental shelf off troms northern norway abstract based on the analysis of 8 selected gravity cores from the upper sediment layers of andfjorden and malangsdjupet off northern norway six late weichselian foraminiferal assemblage zones are defined the two oldest assemblage zones 8 and 7 are found in basal tills and contain mixed faunas reworked and deposited by glaciers which reached the shelf edge during the early late weichselian during the earliest phase of the deglaciation of the continental shelf a sparse fauna characterized by buccella frigida zone 6 was deposited zone 5 is dominated by cassidulina laevigata and a fairly high content of planktic foraminifera indicating periods of ice free normal marine surface waters during a glacial advance between 14 000 and 13 000 b p the fauna zone 4 was dominated by elphidium excavatum this fauna reflects near glacial conditions characterized by unstable bottom water conditions the last c 500 years of this period suffered from oxygen depleted bottom waters zone 3 formed between 13 000 and 10 000 b p comprises several species e g cassidulina reniforme nonion barleeanum n labradoricum and cibicides lobatulus during the first 2000 years of this period the fauna reflects a climatic amelioration e g an increase in temperature salinity and current activity probably due to intrusion of atlantic water during the younger dryas zone 3 reflects a climatic deterioration

north atlantic nordic seas exchanges abstract the northeastern part of the north atlantic is unique in the sense that it is much warmer in the surface than other ocean areas at similar latitudes the main reason for this is the large northward transport of heat that extends to high latitudes and crosses the greenland scotland ridge to enter the nordic seas and the arctic there the warm atlantic water is converted to colder water masses that return southwards over the ridge partly as surface outflows and partly as overflows through the deep passages across the ridge in this paper the state of knowledge on the exchanges especially across the eastern part of the greenland scotland ridge is reviewed based on results from the ices nansen north atlantic norwegian sea exchanges project from the nordic woce project and from other sources the accumulated evidence allows us to describe the exchanges in fair detail the origins of the waters the patterns of their flow towards and over the ridge and their ultimate fate there is also increasing information on temporal variations of the exchanges although dynamical changes are still not well understood quantitative estimates for the volume transport of most of the overflow branches seem reasonably well established and transport measurements of the atlantic inflows to the nordic seas are approaching acceptable levels of confidence which allows preliminary budgets to be presented the deep overflows are driven by pressure gradients set up by the formation of deep and intermediate water the dominance of deep overflows over surface outflows in the water budget argues that this thermohaline forcing also dominates over direct wind stress and estuarine forcing in driving the atlantic water inflow across the greenland scotland ridge while wind stress seems to influence the characteristics and distribution of the atlantic water north of the ridge

sedimentary labile organic carbon and pore water redox control on species distribution of benthic foraminifera a case study from lisbon setubal canyon southern portugal abstract rose bengal stained benthic foraminifera were studied from 11 cores collected along two depth transects off southern portugal one in the lisbon setubal canyon and the other along the canyon edge the total standing stocks and distribution of foraminifera were investigated in relation to sediment and pore water geochemistry nitrate was used as a redox indicator sedimentary chlorophyll a and cpe chloroplastic pigment equivalents contents as a measure of labile organic matter and total organic carbon as a measure of bulk organic matter availability the canyon sediments were enriched in organic carbon and phytopigments at all water depths in comparison with the canyon edge water depth seemed to control sedimentary phytopigment content but not total organic carbon no significant correlation was seen between pigment and total organic carbon content the abundance of calcareous foraminifera correlated with the phytodetritus content whereas a weaker correlation was observed for the agglutinated taxa therefore calcareous foraminifera appear to require a fresher food input than agglutinated taxa the foraminiferal species composition also varied with pigment content and nitrate penetration depth in the sediment in line with the trox concept phytopigment rich surficial cpe content 20 g cm3 sediments with a shallow nitrate penetration depth 1 cm depth were inhabited by generally infaunal species such as chilostomella oolina melonis barleeanus and globobulimina spp as the nitrate penetration increased to 2 cm depth in sediment and the pigment content remained relatively high 15 g cm3 uvigerina mediterranea and uvigerina elongatastriata became dominant species with declining cpe content and increasing nitrate penetration depth the foraminiferal assemblages changed from the mesotrophic cibicides kullenbergi uvigerina peregrina assemblage to the oligotrophic abyssal assemblage mainly consisting of agglutinated taxa

recent benthic foraminiferal assemblages in deep high energy environments from the gulf of cadiz spain the benthic environment in the gulf of cadiz north eastern atlantic is strongly affected by the mediterranean outflow water undercurrent mow which flows northwards along the western iberian margin at 500 1500 m water depth foraminiferal census counts of living and dead assemblages from 27 surface samples ranging from 103 to 1917 m water depth and the examination of hard substrates reveal a close correlation of the fauna with the local hydrography and sediment facies four different faunal groups are separated by factor analysis of the living fauna assemblage 1 contains typical lower slope species and dominates samples from the lower mow core layer and in the north atlantic deep water below shelf edge foraminifera are common in assemblage 2a which shows the highest proportions in samples from 103 to 272 m assemblage 2b is dominated by upper slope species and suspension feeders that are frequent in the upper mow core layer and in distal settings between 396 and 901 m species from assemblage 3 prefer epibenthic habitats and are recorded with high proportions exclusively in the immediate flow paths of the upper mow between 496 and 881 m colonisation structures and species composition of epibenthic assemblages from the proximal facies largely differ from those in distal settings in general epibenthic foraminifers only use elevated substrates under the influence of near bottom flow under high current velocities epibenthic foraminifers prefer large and heavy objects they colonise high attachment levels where a maximum yield of advected food particles can be achieved in distal settings at lower flow velocities the elevation height does not exceed 20 mm above the surrounding sediment surface this level is related to a hydrologic transition layer with high concentrations of suspended particles the comparison of microhabitat preferences and faunal structure under high and low current velocities reveal that substrate stability may be a confining environmental variable for endobenthic and shallow epibenthic foraminifers the observations also indicate that the preferential settling height of epibenthic foraminifera is related to the highest lateral flux rates of food particles within reach from the sea floor a dynamic selection of elevated microhabitats is only used by 7 8 of all species recognised in the gulf of cadiz area

carbonate mound development at the sw rockall trough margin based on high resolution tobi and seismic recording abstract in 2002 high resolution sidescan sonar images of a mound area at the sw rockall trough margin were recorded with the tobi deep towed sidescan sonar processed tobi images with a pixel resolution of 6 m provide a unique overview of the carbonate mound distribution and related sedimentary features around the mounds three morphologically distinct areas can be recognised on the tobi mosaic in area i between 500 and 600 m water depth upslope of the mounds giant sediment waves are found with wavelengths up to 500 m with wave crests of more than 10 km long and with an amplitude of up to 30 m reflected with a high backscatter on the tobi image area ii between 600 and 1000 m water depth along the upper margin flank is characterised by clustered and isolated carbonate mounds forming elongated ridges with an orientation perpendicular to the slope sedimentary structures such as flow ridges sediment waves local scouring at the foot of some mounds and draping of sediment around mounds indicate the influence of strong near bed currents oriented in two main current directions parallel to the margin as well as in a similar direction as the mound clusters the mound clusters are several kilometres long can be over 380 m high and are dissected by downslope directed channels on the tobi image the mounds appear as regions of high backscatter caused by the presence of cold water coral colonies on the sediment and by distinct shadows all mounds have their tops at a specific depth level 500 600 m water depth area iii between 900 and 1200 m water depth below the mounds is characterised by disturbed sediments with distinct slump scars and flow ridges 2d high resolution seismic profiling perpendicular and parallel to the slope across the mounds does in general not reveal strong internal reflectors within the mounds in contrast three strong reflectors can be observed in the sedimentary sequence underneath the mounds the upper reflector c10 of early pliocene age is an erosional unconformity above which most of the mounds and sediment waves seem to have developed the second erosional unconformity c20 of middle miocene age is formed by an apparent irregular surface that locally is dissected by some small faults reflectors c10 and c20 have been found in two different mound clusters in the mound area indicating that mound development possibly started after formation of reflector c20 the third reflector forms the acoustic basement which is locally dissected by some small faults that are located below the mounds at least two stages of mound formation are recognised on the seismic profiles

latest pliocene through holocene paleoceanography of the eastern indian ocean benthic foraminiferal evidence multivariate analyses of latest pliocene through holocene benthic foraminifera from 61 samples from deep sea drilling project dsdp site 214 eastern indian ocean were carried out the 46 highest ranked species were used in r mode factor analysis which has enabled to the identification of three environmentally significant assemblages at site 214 assemblage 1 is characterized by uvigerina hispido costata osangularia culter gavelinopsis lobatulus cibicides wuellerstorfi and karreriella baccata as principal species this assemblage is inferred to reflect high energy well oxygenated and probably low organic carbon deep sea environment at site 214 assemblage 2 is defined principally by globocassidulina pacifica and u proboscidea and is considered to indicate an organic carbon rich environment which resulted from high surface productivity irrespective of dissolved oxygen content assemblage 3 is marked by oridorsalis umbonatus textularia lythostrota hoeglundina elegans pyrgo murrhina and pullenia quinqueloba as principal species this assemblage is inferred to indicate a low organic carbon environment with high pore water oxygen concentration leading to better preservation of deep sea sediments

structure and development of giant carbonate mounds at the sw and se rockall trough margins ne atlantic ocean abstract high resolution seismic reflection profiling carried out in 1997 1999 showed that giant carbonate mounds occur between 500 and 1200 m water depth along both the se and sw margins of rockall trough the mounds rise 5 300 m above the surrounding seafloor and have diameters at their bases of up to 5 km buried mounds at relatively shallow depths below the seafloor are also found both individual and complex clusters of mounds can be recognized smaller and individual sometimes buried mounds are found at the upper slope on the sw rockall trough margin higher steeper and individual mounds are found deeper downslope 900 1100 m at the middle slope the mounds merge into a complex structure and form complex clusters with a very irregular upper surface and an apparent lack of internal reflectors 600 1000 m depth initial results of high resolution 3d seismic profiling at 30 m line spacing in august 2000 in two boxes of 750 m 14 5 km covering a small central part of the sw rockall trough mound area indicate two stages of mound development here the latest probably of pliocene holocene age this age based on the presence of a regionally recognizable unconformity below the mounds is also assumed for the mounds of the se rockall trough porcupine bank margin

growth and demise of cold water coral ecosystems on mud volcanoes in the west alboran sea the messages from the planktonic and benthic foraminifera the dhaka and maya mud volcanoes mvs located in the mud diapir province in the western alboran basin along the moroccan coasts were cored during the ttr 17 leg 1 cruise cores were taken on the top of the volcanoes at a water depth of 370 m on the dhaka mv core ttr17 ms411g and at 410 m water depth on the maya mv core ttr17 ms419g respectively on both mud volcanoes the extruded mud breccia provides the nucleation point for the colonization and development of cold water corals and associated ecosystems two phases of cold water coral growth are observed 1 between slightly older than 4175 62 years bp and around 2230 59 years bp at dhaka and 2 between slightly older than 15583 185 years bp and around 7613 38 years bp at maya mv on the top of the maya mv only a small patch reef and or isolated corals proliferated whereas a more extended patch reef colonized the top of the dhaka mv at both sites the cold water coral developmentwas triggered by the availability of a suitable substrate for initial coral settling provided either as a firm ground or as single clasts subsequently coral growth was supported by enhanced nutrient flux possibly related to upwelling and or strong currents during the intervals of coral growth planktonic foraminiferal assemblages were dominated by neogloboquadrina incompta the decline of coral ecosystems on the mud volcanoes is accompanied at surface by a shift fromthe n incompta dominated assemblage to a globorotalia inflata dominated assemblage possibly reflecting more oligotrophic conditions this shift is coeval to the passage from wet to arid conditions at the end of the african humid period at mayamv it is interpreted as an effect of an early human impact on a fragile environment which was already stressed by desiccation at the time of the development of complex human society along the mediterranean coasts at dhaka mv

recent sediment transport and deposition in the nazare canyon portuguese continental margin processes pathways and fluxes of sediment transport and deposition in the nazare submarine canyon portuguese continental margin were investigated by water column profiling of suspended particulate matter recording of near bottom currents and suspended particulate matter fluxes with benthic landers and by analysis of surface sediment cores the results show that fine grained suspended sediment from the adjacent shelf is captured in the upper canyon and actively transported through the canyon to the abyssal plain under influence of tidal currents and intermittent sediment gravity flows tidal currents are actively resuspending and transporting sediment in the upper to middle canyon as reflected by high concentration of suspended particles in bottom waters high horizontal and vertical sediment fluxes in the bottom water layer and high sediment accumulation rate on the seabed diminishing strength of tidal currents leads to focussed sediment deposition in the middle canyon further transport of sediments toward the lower canyon takes place predominantly by sediment gravity flows occurring on yearly or longer timescale turbidity currents strong enough to transport sand sized material to the lower canyon occur only on centennial or longer timescales

environmental changes and growth history of a cold water carbonate mound propeller mound porcupine seabight on and off mound sediment cores from propeller mound hovland mound province porcupine seabight were analysed to understand better the evolution of a carbonate mound the evaluation of benthic foraminiferal assemblages from the off mound position helps to determine the changes of the environmental controls on propeller mound in glacial and interglacial times two different assemblages describe the holocene and marine isotope stage mis 2 and late mis 3 31 kyr bp the different assemblages are related to changes in oceanographic conditions surface productivity and the waxing and waning of the british irish ice sheet biis during the last glacial stages the interglacial assemblage is related to a higher supply of organic material and stronger current intensities in water depth of recent coral growth during the last glaciation the benthic faunas showed high abundances of cassidulinid species implying cold bottom waters and a reduced availability of organic matter high sedimentation rates and the domination of elphidium excavatum point to shelf erosion related to sea level lowering 50 m and the progradation of the biis onto the shelf a different assemblage described for the on mound core is dominated by discanomalina coronata gavelinopsis translucens planulina ariminensis cibicides lobatulus and to a lower degree by hyrrokkin sarcophaga these species are only found or show significantly higher relative abundances in on mound samples and their maximum contribution in the lower part of the record indicates a higher coral growth density on propeller mound in an earlier period they are less abundant during the holocene however this dataset portrays the boundary conditions of the habitable range for the cold water coral lophelia pertusa which dominates the deep water reefal ecosystem on the upper flanks of propeller mound the growth of this ecosystem occurs during interglacial and interstadial periods whereas a retreat of corals is documented in the absence of glacial sediments on mound glacial conditions with cold intermediate waters a weak current regime and high sedimentation rates provide an unfavourable environmental setting for lophelia corals to grow a late pleistocene decrease is observed in the mound growth for propeller mound which might face its complete burial in the future as it already happened to the buried mounds of the magellan mound province further north

deep marine seabed erosion and gravel lags in the northwestern rockall trough north atlantic ocean a zone of active seabed erosion has been identified in the northwestern rockall trough using seismic reflection profiles and cores the region from george bligh bank to rockall bank has been subject to vigorous bottom current activity for at least the last 35 ma bottom currents originate from southward flowing north atlantic deep water in water depths of 500 2000 m acoustic character mapping reveals a zone of erosion extending over 8500 km 2 along the northwestern margins of the trough the erosion surface is characterized by an acoustically reflective seabed with occasional parallel to transparent reflectors these are the result of strong bottom currents exposing the underlying volcanic basement drift sequences and fan sediments the erosion surface is covered by a

validation of accumulation rates in teluk banten indonesia from commonly applied 210pb models using the 1883 krakatau tephra as time marker abstract teluk banten is a tropical shallow marine embayment on the north coast of java close to the krakatau volcanic complex the tsunami generated by the 1883 krakatau eruption resulted in the deposition of a tsunamite tephra layer on the bottom of teluk banten the krakatau event layer has been used as a time marker to validate 210 pb geochronological dating models this validation was performed to answer the question why should we believe excess 210 pb derived mass accumulation rates the commonly used models have therefore been applied to 210 pb activity profiles from 25 gravity cores models that have been validated are the constant flux and constant sedimentation cf cs with and without a surface mixed layer the constant initial concentration cic the constant rate of supply crs and the flux balance model after comparison of the mass accumulation rates mars of the different models with the mars obtained from the krakatau layer the following could be concluded firstly activity profiles without a surface mixed layer gave cf cs mars which were on average a factor 1 4 0 3 n 8 too high including a mixing rate of 0 5 0 4 cm 2 yr 1 into the model could explain this overestimation secondly for 210 pb activity profiles with a surface mixed layer the mars were in good comparison 1 0 0 3 n 12 with the mars derived from the krakatau event layer thirdly increased accumulation instead of reworking had to be the main cause of the comparatively thick upper layer of five cores with very high inventories fourthly assuming a variable accumulation rate and applying the cic model and crs model for these five cores the weighted average cic mars were in general more accurate than the crs mar finally the flux balance model which is not often used gave mars that were a factor 1 3 0 2 n 25 too high the advantage of this model is that it is independent of the profile shape the disadvantage is that a reliable and accurate initial activity over longer time scales has to be obtained

diagenetic processes in carbonate mound sediments at the south west rockall trough margin cold water coral covered carbonate mounds at the south west margin of the rockall trough form ridges several kilometres long and up to 380 m high piston cores obtained at three mound crests reveal the complex internal structure of the mound build up with alternating unlithified coral dominated intervals and lithified intervals the most recent lithified interval is covered by corals embedded in a fine grained matrix comprising ca 11 000 years of continuous mound evolution before this time 230th u dating shows the presence of several hiatuses in mound build up aragonitic coral material is absent or only present as mouldic porosity in the lithified intervals and coccoliths display widespread overgrowth downcore x ray fluorescence scanning computer tomography scan images and petrographic observations indicate different degrees of diagenetic alteration the upper boundary of the most recent lithified interval shows some erosional features but petrographic observations indicate that initial lithification of the sediments is not related to this erosive event or to long term non sedimentation but to earlier sub surface diagenesis organic matter oxidation and the subsequent lowering of the saturation state of the carbonate system drives dissolution of the unstable aragonitic coral skeletons depending on the openness of the system this can lead to precipitation of a more stable low magnesium carbonate a model is presented describing the sedimentary and diagenetic processes leading to the formation of lithified intervals

shear wave velocities in the upper mantle of the western alps new constraints using array analysis of seismic surface waves it remains challenging to obtain absolute shear wave velocities of heterogeneities of small lateral extension in the uppermost mantle this study presents a cross section of vs across the strongly heterogeneous 3 d structure of the western european alps based on array analysis of data from 92 broad band seismic stations from the cifalps experiment and from permanent networks in france and italy half of the stations were located along a dense sublinear array using a combination of these stations and off profile stations fundamental mode rayleigh wave dispersion curves were calculated using a combined frequency time beamforming approach we calculated dispersion curves for seven arrays of approximately 100 km aperture and 14 arrays of approximately 50 km aperture the latter with the aim of obtaining a 2 d vertical cross section of vs beneath the western alps the dispersion curves were inverted for vs z with crustal interfaces imposed from a previous receiver function study the array approach proved feasible as vs z from independent arrays vary smoothly across the profile length results from the seven large arrays show that the shear velocity of the upper mantle beneath the european plate is overall low compared to ak135 with the lowest velocities in the internal part of the western alps and higher velocities east of the alps beneath the po plain the 2 d vs model is coherent with i a 100 km thick eastward dipping european lithosphere west of the alps ii very high velocities beneath the po plain coherent with the presence of the alpine european slab and iii a narrow low velocity anomaly beneath the core of the western alps from the brianconnais to the dora maira massif and approximately colocated with a similar anomaly observed in a recent teleseismic p wave tomography this intriguing anomaly is also supported by traveltime variations of subvertically propagating body waves from two teleseismic events that are approximately located on the profile great circle

late glacial to holocene history of the mediterranean outflow evidence from benthic foraminiferal assemblages and stable isotopes at the portuguese margin records of benthic foraminiferal assemblage variations and benthic 13c along 12 sediment cores from the western iberian margin between 36 and 42 n at water depths from 820 to 3580 m are used to monitor fluctuations of the mediterranean outflow water mow during the past 30 ka the chronostratigraphy of the cores is based on planktonic 18o records 14c ams dating and the recognition of heinrich events h1 through h4 increased abundances of suspension feeding benthic foraminifers denoted as epibenthos group closely match areas where the recent mow core layers impinge on the continental slope at 800 and 1300 m water depth and near bottom current velocities are enhanced elevated epibenthos group abundances increased benthic 13c and sedimentological evidence for winnowing and erosion are found in glacial sections up to the earliest termination i in cores at water depths between 1600 and 2200 m off southern portugal the combined evidence reveals enhanced current activity at these depths due to a deep glacial mow the mow advection at the portuguese margin during the last glacial was about 700 m deeper than today conceivably forced by increased mow density due to higher salinity and colder temperatures of mediterranean waters the deep mow current gradually decreased in strength and shoaled to 1300 m water depth during the termination and early holocene a shallow mow core layer became active with the onset of termination i at depths between 600 and 1000 m both the shallow and deep mow current culminated during the younger dryas period the present flow pattern with two mow core layers centred at 800 and 1300 m water depth was established between 7 5 and 5 5 ka

the effect of sediment mixing on pb 210 accumulation rates for the washington continental shelf abstract nine cores from the washington continental shelf were examined by radiochemical techniques in order to evaluate the effect of mixing on the calculation of sediment accumulation rates from pb 210 profiles th 234 profiles indicate mixing coefficients of 140 cm 2 yr 1 for the seabed offshore from the columbia river and 47 cm 2 yr 1 for the seabed of the mid shelf silt deposit 75 km north of the columbia river these large mixing coefficients demonstrate that particles can penetrate to the base of the intensely mixed surface layer 10 cm within one year after emplacement at the seabed surface observed depths of cs 137 penetration within the seabed are compared with depths predicted from the surface mixed layer thickness and the pb 210 accumulation rate the observed and predicted depths agree well at all but one station at this station a combination of th 234 co 60 pb 210 and cs 137 profiles suggests that active mixing occurs below the intensely mixed surface layer the agreement of pb 210 and cs 137 data at the other stations however indicates a general absence of deep mixing on the washington shelf thus the apparent accumulation rates calculated from pb 210 profiles below the intensely mixed surface layer on the washington shelf generally reflect the true rates of sediment accumulation

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

benthic foraminiferal assemblages from the eastern south atlantic polar front region between 35 and 57 s distribution ecology and fossilization potential abstract surface sediment samples taken with a multiple corer from the polar front region along two profiles in the eastern south atlantic sector between 35 and 57 s have been investigated for their benthic foraminiferal content live fauna was differentiated from the death assemblage based on the dead assemblages potential fossil assemblages dead fauna reduced by non resistant agglutinants were calculated for comparison with upper neogene core material the distribution of the potential fossil assemblages defined byq mode principal component analysis mirrors the recent hydrographic as well as the trophic situation in the eastern south atlantic ocean circulation and productivity two southern component bottom water faunas reflect the northward flow of antarctic bottom water aabw and lower circum polar deep water lcdw an assemblage dominated by the arenaceousmultifidella nodulosa below the calcite compensation depth ccd and anuttallides umbonifer dominated assemblage above the ccd in the region of highest bio silicious primary productivity south of the polar front and north of the winter sea ice limit these faunas are overprinted by a southern high productivity fauna dominated by infaunal species such aspullenia bulloides melonis pompilioides andm zaandamae north atlantic deep water nadw meets the circum polar deep water cdw at intermediate depth as reflected in the distribution of the northern component deep water fauna dominated byepistominella exigua the high productivity assemblage overprinting this fauna the northern high productivity fauna is dominated by the shallow endobenthicbulimina aculeata a strong bottom current fauna dominated byangulogerina angulosa characterizes areas between 400 and 900 m water depth with sandy sediment independent from water mass characteristics and food supply

hydrography and through flow in the north eastern north atlantic ocean the nansen project abstract the circulation and hydrography of the north eastern north atlantic has been studied with an emphasis on the upper layers and the deep water types which take part in the thermohaline overturning of the oceanic conveyor belt over 900 hydrographic stations were used for this study mainly from the 1987 1991 period the hydrographic properties of subpolar mode water in the upper layer which is transported towards the norwegian sea showed large regional variation the deep water mass was dominated by the cold inflow of deep water from the norwegian sea and by a cyclonic recirculation of lower deep water with a high antarctic bottom water content at intermediate levels the dominating water type was labrador sea water with only minor influence of mediterranean sea water in the permanent pycnocline traces of antarctic intermediate water were found geostrophic transports have been estimated and these agreed in order of magnitude with the local heat budget with current measurements with data from surface drifters and with the observed water mass modification a total of 23 sv of surface water entered the region of which 20 sv originated from the north atlantic current while 3 sv entered via an eastern boundary current of this total 13 sv of surface water left the area across the reykjanes ridge and 7 sv entered the norwegian sea while 3 sv was entrained by the cold overflow across the iceland scotland ridge approximately 1 4 sv of norwegian sea deep water was involved in the overflow into the iceland basin which with about 1 1 sv of entrained water and 1 1 sv recirculating lower deep water formed a deep northern boundary current in the iceland basin at intermediate depths where labrador sea water formed the dominant water type about 2 sv of entrained surface water contributed to a saline water mass which was transported westwards along the south icelandic slope