on the origin of the warm inflow to the nordic seas abstract warm and saline waters enter the nordic seas from the south as part of the warm to cold water transformation of the thermohaline circulation of the northern north atlantic one explanation for the origin of the nordic seas inflow is a shallow source hypothesis under which the inflow waters are a modification of upper ocean subtropical waters warm waters from the subtropical gyre are carried to the eastern north atlantic by the north atlantic current and branch northwards joined by poleward upper thermocline flow along the upper continental slope to provide the nordic seas inflow along this pathway the upper water column is progressively cooled and freshened by winter convection the subpolar mode water transformation process and this sets the inflow characteristics a deep source hypothesis provides an alternative explanation for the characteristics of the nordic seas inflow and the pathway delivering the waters to the inflow under this hypothesis inflow waters originate from the core of the mediterranean overflow waters in the gulf of cadiz carried northward at mid depth by the eastern boundary undercurrent in the subtropics continuing into the subpolar gyre along the eastern boundary and rising from depths near 1200m in the rockall trough to less than 600m to cross the wyville thomson ridge into the faroe shetland channel and thence to the nordic seas the deep source hypothesis focus is on lower thermocline source waters beneath the sill depth for the nordic seas inflow in contrast to the shallow source hypothesis focus of transformation of upper thermocline waters above the sill depth on the basis of regional water mass distributions geostrophic shear and direct current measurements we reject the deep source hypothesis in favor of the shallow source hypothesis rather than a flow of deep mediterranean overflow water along the eastern boundary rising from depth to feed the nordic seas the inflow is supplied directly by transformed north atlantic current waters from the same depth range as the inflow mediterranean overflow water is a constituent of the inflow but only through its contribution to defining the temperature salinity relationship of the interior of the subtropical gyre from which the north atlantic current draws its water rather than by direct northward advection of mediterranean outflow water via the eastern boundary undercurrent crossing from the subtropics into the subpolar domain instead the eastern boundary undercurrent wholly expels its transport of mediterranean overflow water into the eastern edge of the subtropical gyre creating the mid depth westward extending subtropical salinity plume for the lower thermocline isopycnal range of the core of the mediterranean overflow water measurements show that at the wyville thomson ridge the flow is southward and descending rather than northward and rising representing cold spillover from the faroese channels entraining warm upper ocean waters as the spillover plume descends and warms into the northern rockall trough no evidence is found in rockall trough northward of 54 n porcupine bank for direct advection of mediterranean overflow waters via an eastern boundary undercurrent extension and the very dilute mediterranean overflow waters in the trough reflect the interaction of the wyville thomson ridge plume descending into the trough from the north and lower thermocline waters delivered to the trough from the south

first nd isotope record of mediterranean atlantic water exchange through the moroccan rifian corridor during the messinian salinity crisis we present the first neodymium isotope reconstruction of mediterranean atlantic water exchange through the moroccan rifian corridor 8 5 ma this covers the late miocene messinian salinity crisis msc a period when progressive tectonic restriction of the mediterranean atlantic seaways resulted in extreme basin wide mediterranean salinity fluctuations the rifian corridor was one of these seaways and until now relatively poor age constraints existed for the timing of corridor closure due to the impact of uplift and erosion on the sedimentary record the bottom water nd isotope record from the continuous bou regreg valley succession in northwest morocco allows us to explore corridor connectivity with the atlantic data from the interior and mediterranean edge of the rifian corridor respectively the taza guercif and melilla basins northern morocco provide new information on corridor shallowing and the provenance of water flowing through the seaway as a result we can constrain the age of rifian corridor closure to 6 64 6 44 ma we also find no evidence of the siphoning of atlantic waters through the seaway 7 20 6 58 ma our results cannot exclude the possibility that at times during the messinian salinity crisis mediterranean outflow water reached the atlantic

on the variability of the mediterranean outflow water in the north atlantic from 1948 to 2006 1 recent work has shown that variability in the properties and or transport of mediterranean seawaters spilling across the strait of gibraltar into the north atlantic have had little impact on the variability of mediterranean outflow water mow in the that basin over the past fifty years here we investigate whether circulation changes are the dominant source of mow variability in the north atlantic between 1948 and 2006 using a 1 3 north atlantic configuration of the hybrid coordinate ocean model combined with the marginal sea boundary condition model two simulations forced by either climatological or interannual atmospheric fields are performed the interannual simulation reproduces the observed mow variability without mediterranean seawater changes thus we conclude that mow variability in the last 60 years is a consequence of circulation changes in the north atlantic a series of simulations that separate the mechanical effect of the wind from the impact of buoyancy forcing show that mow variability can be attributed to shifts between its dominant northward and westward pathways the pathway shifts from predominantly northward between 1950 and 1975 to predominantly westward between 1975 and 1995 and finally back to northward after 1995 though these pathway shifts appear to be wind induced the property changes are caused by the combined impact of wind and buoyancy forcing on the circulation of the north atlantic

seismic geomorphological reconstructions of plio pleistocene bottom current variability at goban spur abstract high resolution single channel sparker reflection seismic data revealed the presence of large scale sediment waves nearby dsdp site 548 located on goban spur they developed in a gentle terraced environment which contrasts with the canyon incised celtic margin and the relatively smooth porcupine seabight to the north based upon the morphological characteristics of the observed seabed and buried sediment waves energetic alongslope bottom currents are thought to be the driving mechanism for the sediment wave development these currents are driven on their turn by an enhanced internal tide regime that could be attributed to the introduction of the mediterranean outflow water the dsdp site 548 downhole geophysical data and the seismic stratigraphic analysis allowed the differentiation of three sequences that relate to evolutionary stages since the lower pliocene the sequences are bounded by local erosional events associated with mass wasting events which seem to occur roughly synchronously to major northern hemisphere glaciations respectively during the lower pleistocene 2 5 to 2 15 ma and the middle pleistocene 0 45 ma the lower sequence from 4 5 to 2 15 ma shows no morphological evidence of bottom current driven sedimentation it is however settled over a smooth erosional surface which could indicate the introduction of the mediterranean outflow water the intermediate sequence is characterised by large scale sediment waves that have gradually developed in close association with palaeo seafloor irregularities it is inferred that the sedimentation resumed with a relative bottom current energy increase the youngest sequence recorded active sediment wave formation similar to the previous sequence although the goban spur sediment waves cannot be regarded as contourite drifts as such their stratigraphic evolution corresponds to other well documented contourite depositional systems influenced by the mediterranean outflow water

salinity driven thermocline transients in a wind and thermohaline forced isopycnic coordinate model of the north atlantic abstract an isopycnic coordinate oceanic circulation model formulated with the aim of simulating thermodynamically and mechanically driven flow in realistic basins is presented special emphasis is placed on the handling of diabatic surface processes and on thermocline ventilation the model performance is illustrated by a 30 year spinup run with coarse horizontal resolution 2 mesh in a domain with north atlantic topography extending from 10 to 60 n latitude the vertical structure encompasses 10 isopycnic layers in steps of 0 2 units capped by a thermodynamically active mixed layer from an initially isohaline state with isopycnals prescribed by zonally averaged climatology the model is forced by seasonally varying wind stress radiative and freshwater fluxes and by a thermal relaxation process at the surface after a mechanical spinup time of about 15 years a quasi stationary pattern of mean circulation and annual variability ensues characterized by pronounced subtropical mode water formation

wood recruitment and retention the fate of eroded trees on a braided river explored using a combination of field and remotely sensed data sources abstract this paper investigates wood recruitment and deposition dynamics in a large gravel bed braided river tagliamento river italy we used a combination of field measurements automatically repeated ground images and remotely sensed surveys to quantify wood input through bank erosion and associated downstream deposition two sites were investigated where floods caused the erosion of vegetated island edges a lidar survey preceding the erosion events provided data on the morphology and vegetation structure of the eroded areas allowing estimation of the number of trees that were uprooted sequences of ground based images acquired automatically and supported by field measurements showed the time number and location of deposited trees results show that the complex morphology of braided rivers induces specific deposition patterns we observed wide dispersal of wood on gravel bars with jams characterised by a small number of logs on average 2 3 and in many cases only a single log a large proportion of the eroded trees up to 40 were deposited on the nearest downstream bar this illustrates significant wood retention close to the recruitment site with the remaining wood dispersed widely downstream differences in the observed level of local wood retention were associated with the proximity of the erosion site to the main channel and differences were also observed in retention between the peak and the falling limb of flood events confirming that water depth and probably flow velocity are the crucial parameters controlling wood deposition

circulation characteristics in three eddy permitting models of the north atlantic a systematic intercomparison of three realistic eddy permitting models of the north atlantic circulation has been performed the models use different concepts for the discretization of the vertical coordinate namely geopotential levels isopycnal layers terrain following sigma coordinates respectively although these models were integrated under nearly identical conditions the resulting large scale model circulations show substantial differences the results demonstrate that the large scale thermohaline circulation is very sensitive to the model representation of certain localised processes in particular to the amount and water mass properties of the overflow across the greenland scotland region to the amount of mixing within a few hundred kilometers south of the sills and to several other processes at small or sub grid scales the different behaviour of the three models can to a large extent be explained as a consequence of the different model representation of these processes

applications of diffusion data to high temperature earth systems diffusion in general is such a widespread phenomenon in nature that a basic knowledge can serve very effectively to address well known applications not only to thermochronology and petrology but also to environmental geology e g paleoclimate sedimentology and applied geosciences e g assessing contamination of gas stations indeed the list of potential applications of diffusion phenomena is so long that an exhaustive treatment would quickly exceed the scope of this review the reader is therefore referred to reviews covering various aspects of diffusion in the earth sciences including diffusion in melts watson 1994 chakraborty 1995 diffusion processes during diagenesis berner 1980 krom and berner 1980 boudreau 2000 and diffusion phenomena in general e g lasaga 1998 ganguly 2002 watson and baxter 2007 zhang 2008 all of these treatments are based on the same general concepts of diffusion which do not need restating here in great detail applications of diffusion profiles in igneous systems have been thoroughly reviewed a recent reviews in mineralogy and geochemistry volume rimg 69 putirka and tepley 2008 and there is also an excellent volume on low temperature thermochronology rimg 58 reiners and ehlers 2005 describing the impact and application of diffusion theory for age and thermal history determination with these precedents in mind we focus the present review on the application of diffusion in high temperature regimes i e systems at t 500 c both igneous and metamorphic systems are addressed but because of the recent precedents noted above we emphasize recent developments and challenges in metamorphic studies in a broad sense diffusion describes the statistical non directional movement of molecules or heat through a medium of interest as independent theories of diffusion were developed in the early 19th century and compared with the principles of statistical variance it was

on the temporally varying northward penetration of mediterranean overflow water and eastward penetration of labrador sea water abstract historical hydrographic data in the eastern north atlantic are used to suggest a connection between the northward penetration of mediterranean overflow water mow and the location of the subpolar front the latter of which is shown to vary with the north atlantic oscillation nao during persistent high nao periods when the subpolar front moves eastward waters in the subpolar gyre essentially block the northward flowing mow preventing its entry into the subpolar gyre conversely during low nao periods the subpolar front moves westward allowing mow to penetrate past porcupine bank into the subpolar gyre the impacts of an intermittent penetration of mow into the subpolar gyre including the possible effect on water mass transformations remain to be investigated

linking benthic hydrodynamics and cold water coral occurrences a high resolution model study at three cold water coral provinces in the ne atlantic observations from numerous cold water coral locations in the ne atlantic show energetic near bottom flow dynamics along the european continental margin at individual coral mounds and mound clusters dynamics are largely controlled by tide topography interaction generating and enhancing periodic motions such as trapped waves freely propagating internal tides and internal hydraulic jumps in this study linkages between key abiotic parameters and cold water coral occurrences are explored across entire cold water coral mound provinces using an integrated modelling and observational approach the 3 d ocean circulation model roms agrif was applied to simulate near bottom hydrodynamic conditions at three provinces in the ne atlantic logachev mounds arc mounds and belgica mounds adopting a nested model setup with a central grid resolution of 250 m simulations were carried out with a focus on accurate high resolution topography and tidal forcing the central model bathymetry was taken from high resolution inss irish national seabed survey seafloor mapping data the model was integrated over a full one year reference period starting from the 1st january 2010 interannual variability was not considered tidal forcing was obtained from a global solution of the oregon state university osu inverse tidal model modelled fields of benthic currents were validated against available independent in situ observations coral assemblage patterns presence and absence locations were obtained from benthic surveys of the eu fp7 coralfish programme and supplemented by data from additional field surveys modelled near bottom currents temperature and salinity were analysed for a 1 month subset 15th april to 15th may 2010 corresponding to the main coralfish survey period the model results show intensified near bottom currents in areas where living corals are observed by contrast with coral absence and random background locations instantaneous and time mean current speeds at mound clusters in the logachev province exceeded typical values in non coral areas by up to a factor of three currents at cold water coral locations in the arc and belgica mound provinces were less energetic but still elevated compared to non coral locations an analysis of dynamical processes associated with oscillatory flow interacting with topography suggests that these motions are locally important food supply mechanisms to cold water corals by promoting large amplitude local vertical mixing and organic matter fluxes it is shown that their presence varies considerably between provinces based on the interplay of topographic slope flow magnitude and ambient stratification

ten years of marine current measurements in espartel sill strait of gibraltar more than 10 year of acoustic doppler current profiler observations collected at the westernmost sill espartel sill of the strait of gibraltar by a monitoring station have been carefully processed to provide the most updated estimation of the mediterranean outflow a comprehensive quality control of the factors affecting the uncertainty of the measurements has been carried out and great care has been paid to infer the current at the bottom layer where direct observations are lacking the mean outflow in the southern channel of the sill section has been estimated as 0 82 sv 1 sv 1 106 m3 s 1 with an average contribution of the eddy fluxes of 0 04 sv this figure is an overestimation as the mooring measurements assumed valid for the whole section ignore the lateral friction on the other hand it only gives the flow through the southern channel and disregards the fraction flowing through shallower northern part both drawbacks have been addressed by investigating the cross strait structure of the outflow from hindcasts produced by the mitgcm numerical model run in a high resolution domain covering the gulf of cadiz and alboran sea basins an overall rectifying factor of 1 039 was found satisfactory to correct the first estimate so that the final mean outflow computed from this data set is 0 85 sv complemented with an uncertainty of 0 03 sv based on the interannual variability of the series the temporal analysis of the series shows an outflow seasonality of around the 8 of the mean value with maximum outflow in early spring

x ray imagery and physical core logging as a proxy of the content of sediment cores in cold water coral mound provinces a case study from porcupine seabight sw of ireland three provinces characterized by the presence of carbonate mounds interpreted as cold water coral banks have been reported in porcupine seabight sw of ireland and were recently subjected to many detailed studies this contribution discusses the use of x ray imagery and physical properties in deciphering palaeoceanographic sedimentological and biological processes physical property core logging and x ray imagery are used to identify and describe sedimentation regimes and so their respective palaeoceanographic and palaeoclimatological settings in two mound provinces respectively the belgica mound province and the magellan mound province both provinces show at present time clear differences in the hydrodynamic environment this study confirms that also during the past the oceanographic and sedimentological environment of both provinces differ clearly impacts of glacial interglacial variations and locally derived ice rafting events ire comparable with the north atlantic heinrich events he have been recognized in both provinces moreover the combination of x ray imagery magnetic susceptibility gamma density and p wave velocity makes it possible to estimate the coral content and coral distribution in unopened cores localized on top of carbonate mounds a comparison between on mound and off mound cores in both provinces allowed revealing some mechanisms of mound evolution and coral growth versus time

the climatology of the north atlantic abstract data from approximately 144 000 hydrographic stations in the north atlantic have been retrieved from the national oceanic data centre and analysed to produce maps of mean pressure temperature salinity and oxygen on selected potential density surfaces for the domain bounded by 0 85 w and 0 65 n the data span the period from 1904 to 1990 with the majority of the data from the last four decades the data set for this region is 60 larger than that used in the production of levitus climatological world atlas this increase in stations coupled with smoothing scales specific to the north atlantic rather than the global ocean considerably improves the resolution of the basin s features the mean property fields and their associated standard deviations are resolved on a one degree grid with little smoothing contrasting with the levitus atlas where properties although presented on a one degree grid have been smoothed on the order of 1000km another important feature of this database is the process by which irregularly spaced data are averaged onto a regular grid in a significant departure from the levitus analysis which averaged on depth surfaces these data were averaged on potential density surfaces thus eliminating an artificial mixing of water mass properties the database is used to describe the baroclinicity of well known features such as the gulf stream the north atlantic current and the deep western boundary current and to elucidate the recirculations associated with these currents it additionally resolves several new features in the intermediate and deep north atlantic these features include the signature of a large scale deep recirculation that extends southwestward from the eastward extension of the north atlantic current to the separation point of the gulf stream near cape hatteras this recirculation which spans approximately 2000m of the water column encompasses more local recirculations and potentially mixes subpolar and subtropical waters furthermore in the upper thermocline this database reveals a coherent azores current that stretches from the gulf stream system south of the tail of the grand banks to madeira this flow is marked by divergences to the south and convergences from the north such that its downstream transport is not much changed

pleistocene geochemical stratigraphy of the borehole 1317e iodp expedition 307 in porcupine seabight sw of ireland applications to palaeoceanography and palaeoclimate of the coral mound development stable isotopes and element compositions of the fine grained matrix were measured for iodp expedition 307 hole u1317e drilled from the summit of challenger mound in porcupine seabight northeast atlantic to explore the palaeoceanographic and palaeoclimatic background to development of the deep water coral mound the 155 m long mound section was divided into two units by an unconformity at 23 6 mbsf unit m1 2 6 1 7 ma and unit m2 1 0 0 5 ma results from 519 specimens show a difference in 13c value between unit m1 0 6 to 5 0 and unit m2 1 0 to 1 0 but such a distinct difference was not seen in 18o values 1 0 2 5 caco3 content 40 60 wt sr ca ratio 2 0 8 0 mmol mol 1 and mg ca ratio 10 0 20 0 mmol mol 1 through the mound positive 18o and negative 13c shifts at the mound base are consistent with the oceanographic changes in the northeast atlantic at the beginning of the quaternary the positive 13c regression in unit m2 suggests a linkage to the mid pleistocene intensified glaciation in the northern hemisphere warm mediterranean upper core water of mediterranean outflow water eastern north atlantic water and cold labrador sea water of north atlantic deep water are key oceanographic features that cause spikes and shifts in stable isotope and element composition however the stable isotope values of the sediment matrix could not primarily record the glacial interglacial eustatic temperature change but indirectly indicate current regimes of the intermediate oceanic layer where the coral mound grew similarly elemental ratios and caco3 content may not represent the productivity and temperature of surface sea water respectively but superpose the fractions from both surface and bottom water it is concluded that palaeoceanographic change coupled to the pleistocene glacial interglacial cycles is a key control on the geochemical stratigraphy of the matrix sediments of the carbonate mound developed in porcupine seabight copyright 2011 john wiley sons ltd

late pliocene variations of the mediterranean outflow late pliocene changes in the advection of mediterranean outflow water mow derivates were reconstructed at northeast atlantic dsdp odp sites 548 and 982 and compared to records of wmdw at west mediterranean site 978 neodymium isotope end values more positive than 10 5 11 reflect diluted mow derivates that spread almost continuously into the northeast atlantic from 3 7 to 2 55 ma reaching rockall plateau site 982 from 3 63 to 2 75 ma from 3 4 to 3 3 ma average mow temperature and salinity increased by 2 4 c and 1 psu both at proximal site 548 and distal site 982 the rise implies a rise in flow strength coeval with a long term rise in both west mediterranean sea surface salinity by almost 2 psu and average bottom water salinity bws by 1 psu despite inherent uncertainties in bws estimates the changes were linked with major mediterranean aridification and a drop in african monsoon humidity in contrast to model expectations the rise in mow salt discharge after 3 4 ma did not translate into improved ventilation of north atlantic deep water since it possibly was too small to significantly influence atlantic meridional overturning circulation right after 2 95 ma with the onset of major northern hemisphere glaciation long term average bottom water temperature bwt and bws at site 548 dropped abruptly by 5 c and 1 2 psu in contrast to more distal site 982 where bwt and bws continued to oscillate at estimates of 2 c and 1 5 2 5 psu higher than today until 2 6 ma we relate the small scale changes both to a reduced mow flow and to enhanced dilution by warmwaters of a strengthenednorth atlantic current temporarily replacingmowderivates at rockall plateau

the 2 6 ma depositional sequence from the challenger cold water coral carbonate mound iodp exp 307 sediment contributors and hydrodynamic palaeo environments during iodp expedition 307 the first complete sequence through a cold water coral carbonate mound a bio geological seafloor feature created through successive stages of cold water coral mediated sediment accumulation was successfully acquired the full recovery of the challenger mound one of the large ca 155 m high coral carbonate mounds along the ne atlantic continental margin belgica mound province eastern porcupine seabight facilitates for the first time the study of the entire development of a coral carbonate mound and hence allows the identification of the environmental conditions driving and maintaining the entire build up of these remarkable seafloor habitats in this study the different sediment contributors to the challenger mound are identified and assessed throughout its entire 2 6 ma long development high resolution siliciclastic particle size end member modelling and its ground truthing xrd quartz sand surface microtextures indicate the influence of an all dominant contour current system operating in variable energetic modes for most of the sediment accumulation history of the challenger mound only local short distance current controlled sediment re dispersal is evidenced while iceberg rafting is identified as an important depositional mechanism throughout the whole mound development period furthermore evidence for icebergs repeatedly reaching the eastern porcupine seabight continental margin even in the early stages of northern hemisphere glacial expansion is preserved in the mound sequence supporting the existing coral stratigraphy the challenger mound depositional sequence reveals a two phase development separated by a significant hiatus the lower mound phase m1 2 6 1 7 ma indicates a semi continuous steadily changing fast accumulating current controlled depositional environment the condensed upper mound phase m2 998 1 5 ka bears witness of a distinct shift to a more glacially influenced low accumulation environment most likely resulting from a reduced capacity to deposit and or preserve sediments cold water coral density at the site of deposition is assumed to play an essential role in sediment deposition and preservation on challenger mound it enabled the preservation of a unique higher resolution record in the lower m1 sequence in the otherwise erosive non depositional early pleistocene environment along the nw european continental margin the potential of coral carbonate mounds as intermediate water depth continental margin plio pleistocene palaeo archives is thereby showcased

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

the enya mounds a lost mound drift competition the genesis and evolution of cold water coral banks along the northeastern atlantic margin is known to be influenced by several factors among which the palaeotopography and nature of the coral settling surface the presence of bottom currents and sediment supply in this paper a case study is presented of the enya mound cluster located in the southernmost tip of the belgica mound province west of ireland below this mound cluster seismic stratigraphy revealed a yet unmapped local unconformity rd1b being part of a composite erosion event rd1 as such from the late miocene to late pliocene at least two erosional events have incised the margin ending with the final rd1a moundbase unconformity acting as a base for the enya mounds during the quaternary the mounds became outgrown and were covered by a mounded contourite drift in addition they are closely associated with a cluster of seabed pockmarks the bottom current regime which became active since the middle pleistocene has certainly influenced the fate of this mound cluster the occurrence of the pockmarks seems to be related to relatively recent fluid migration processes however leaving an open question if any previous seepage phases were involved in the growth or initiation of the coral banks

a model analysis of the behavior of the mediterranean water in the north atlantic abstract the behavior of the mediterranean water in the north atlantic ocean sector of a global ocean general circulation model is explored starting from its entry point at the strait of gibraltar the analysis focuses primarily on one experiment in which explicit watermass exchange between the mediterranean sea and the atlantic at the strait of gibraltar is permitted the model produces an exchange rate of approximately 1 sv sv 106 m3 s 1 this is comparable to estimates derived from field measurements the density of the mediterranean outflow however is lower than observed mainly because of its high temperature more than 2 c higher than in reality the lower density of the outflow and the model s inadequate representation of the entrainment mixing in the outflow region cause the mediterranean water to settle in a depth range 800 1000 m in the north atlantic about 200 m shallower than observed here an interesting current system forms in response to the intrusion of the mediterranean water i

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

structure transports and transformations of the water masses in the atlantic subpolar gyre we discuss the distributions and transports of the main water masses in the north atlantic subpolar gyre naspg for the mean of the period 2002 2010 ovide sections 2002 2010 every other year as well as the inter annual variability of the water mass structure from 1997 4x and meteor sections to 2010 the water mass structure of the naspg quantitatively assessed by means of an optimum multiparameter analysis with 14 water masses was combined with the velocity fields resulting from previous studies using inverse models to obtain the water mass volume transports we also evaluate the relative contribution to the atlantic meridional overturning circulation amoc of the main water masses characterizing the naspg identifying the water masses that contribute to the amoc variability the reduction of the magnitude of the upper limb of the amoc between 1997 and the 2000s is associated with the reduction in the northward transport of the central waters this reduction of the northward flow of the amoc is partially compensated by the reduction of the southward flow of the lower limb of the amoc associated with the decrease in the transports of polar intermediate water and subpolar mode water spmw in the irminger basin we also decompose the flow over the reykjanes ridge from the east north atlantic basin to the irminger basin 9 4 4 7 sv into the contributions of the central waters 2 1 1 8 sv labrador sea water lsw 2 4 2 0 sv subarctic intermediate water saiw 4 0 0 5 sv and iceland scotland overflow water isow 0 9 0 9 sv once lsw and isow cross over the reykjanes ridge favoured by the strong mixing around it they leave the irminger basin through the deep to bottom levels the results also give insights into the water mass transformations within the naspg such as the contribution of the central waters and saiw to the formation of the different varieties of spmw due to air sea interaction

representing topographic stress for large scale ocean models abstract interaction of eddies with seafloor topography can exert enormous systematic forces on the ocean circulation this interaction has been considered previously under idealized circumstances theoretical results are here simplified and extended toward practical application in large scale ocean circulation models among the suggestions is that coarse resolution models can correct a depth independent part of the velocity field toward a velocity given by z flh where z is the vertical unit vector f is coriolis form l is a length scale o 10 km and h is the total depth absence of this tendency may be implicated in a number of systematic defects that appear in present ocean models

benthic dynamics at the carbonate mound regions of the porcupine sea bight continental margin a brief review is given of some dynamical processes that influence the benthic dynamics within the carbonate mound provinces located at the porcupine bank sea bight margin ne atlantic the depth range of the mounds in this region 600 1 000 m marks the upper boundary of the mediterranean outflow water above which eastern north atlantic water dominates both water masses are carried northwards by the eastern boundary slope current in the benthic boundary layer both the action of internal waves and other tidal period baroclinic waves may enhance the bottom currents and add to both the residual and maximum flow strength both residual and maximum bottom currents vary at different mound locations with stronger currents found at belgica se porcupine sea bight mound and pelagia nw porcupine bank mound regions whilst weakest currents are found at the hovland and magellan mounds at the northern sea bight margin the differences may be attributed to the presence of internal waves pelagia or bottom intensified diurnal waves belgica these different dynamical regimes are likely to have implications for the distribution patterns of live coral at the different locations

vivaldi 1991 a study of the formation circulation and ventilation of eastern north atlantic central water abstract a synoptic hydrographic data set comprising 32 full depth ctd casts and 2500 ctd seasoar profiles to 500 m is used to describe the s properties and circulation of central water east of the mid atlantic ridge and between 39 n and 54 n eastward transport of 20 10 6 m 3 s 1 in the north atlantic current turns entirely northwards to the west of 54 n 20 w this transport consists in the upper layers of western north atlantic water freshened at temperatures below 10 c by mixing with subarctic intermediate water northern and southern branches of the north atlantic current are well defined and both turn northwards west of 20 w a further 10 10 6 m 3 s 1 of eastern north atlantic water forms and recirculates anticyclonically to the west of spain south of the north atlantic current and north of 40 n eastern north atlantic water is most weakly stratified east of 20 w and there is clear correlation between weakly stratified pycnostads and positive salinity anomalies relative to western north atlantic water thus eastern north atlantic water is a winter mode water in which strong winter cooling has increased the density and hence also the salinity anomaly at a given temperature near the southern entrance to the rockall trough there is evidence that salinities are also increased by mediterranean water influence circulation south of the north atlantic current is complex there is no evidence for direct ventilation southwards across 40 n where water properties s potential vorticity and cfc 113 and historical data all indicate westward ventilation east of 24 w with weak southward ventilation occurring further west in the vicinity of the azores the circulation pattern suggested is remarkably similar to that proposed by helland hansen and nansen in 1926 the eastern north atlantic geophysiske publicajoner 4 1 76 with anticyclonic circulation of colder eastern north atlantic water north of 40 n meeting warmer water from south of 40 n circulating cyclonically north of the azores current the distribution of pycnostads and s properties between 20 w and 35 w north of the azores indicates alternate bands of western and eastern north atlantic water moving eastward and westward respectively including evidence for westward motion immediately south of the southern branch of the north atlantic current possibly by westward propagation of anticyclonic eddies containing deep pycnostads

mediterranean outflow water dynamics across the middle pleistocene transition based on a 1 3 million year benthic foraminiferal record off the portuguese margin abstract reconstruction of the mediterranean outflow water mow dynamics in the geologic past contributes to exploring its influence on the north atlantic ocean circulation and global climate the middle pleistocene transition mpt is one of the most important characteristics of quaternary climate change but until now research on the mow variability during this time interval has been limited to decipher the mow variability over the last 1 3 myr this work presents the first continuous and high resolution 2 kyr foraminiferal stable oxygen and carbon isotopes and benthic foraminiferal records from integrated ocean drilling program iodp site u1391 which was drilled off the portuguese margin in the northeast atlantic ocean and is currently bathed by the lower mow core based on spectral analysis results of the foraminiferal 18o record the mpt peaked from 0 9 to 0 7 ma the epibenthos group was previously found attached to elevated substrates only within the mow current and more abundant at higher current velocities so the relative abundance of the elevated epibenthos group was adopted as an indicator of mow strength in this study the mow indicator suggests that the mow strengthened during mis 1 mis 5 mis 7 mis 9 mis 11 mis 13 mis 15 mis 17 early mis 18 to late mis 19 mis 21 miss 23 25 miss 28 30 early mis 34 to mis 35 early mis 36 to late mis 37 and mis 40 with a 100 kyr cycle superimposed on the long term variability of the mow current the 41 kyr and 20 kyr cyclic fluctuations are also evident whereby the 41 kyr cycle is more significant the results of cross spectral analyses indicate that the 20 kyr cyclic variation in the mow intensity was drived by the precession forcing the 41 kyr cyclic variation in the pre mpt mow dynamics and the 100 kyr cyclic variation in the post mpt mow dynamics were strongly controlled by the earth s obliquity the variation in the abundance of the elevated epibenthos group was dominated by the 41 kyr cycle prior to the mpt and by the 100 kyr cycle after the mpt which suggested there was a mpt related shift in the mow dynamics benthic 13c record of the last 0 56 myr shows precessional 23 kyr and glacial interglacial 100 kyr cycles indicating cyclic variations in bottom water ventilation enhanced ventilation coincides with precession maxima and reduced ventilation with precession minima bottom water was well ventilated by mow during the interglacial periods and by gnaiw during the glacial periods and pooly ventilated during the glaical terminations

on the origin and pathway of the saline inflow to the nordic seas insights from models the behaviours of three high resolution ocean circulation models of the north atlantic differing chiefly in their description of the vertical coordinate are investigated in order to elucidate the routes and mechanisms by which saline water masses of southern origin provide inflows to the nordic seas an existing hypothesis is that mediterranean overflow water mow is carried polewards in an eastern boundary undercurrent and provides a deep source for these inflows this study however provides an alternative view that the inflows are derived from shallow sources and are comprised of water masses of western origin carried by branches of the north atlantic current nac and also more saline eastern north atlantic water enaw transported northwards from the bay of biscay region via a shelf edge current sec flowing around the continental margins in two of the models the mow flows northwards but reaches only as far as the porcupine bank 53 n in third model the mow also invades the rockall trough extending to 60 n however none of the models allows the mow to flow northwards into the nordic seas instead they all support the hyporthesis of there being shallow pathways and that the saline inflows to the nordic seas result from nac derived and enaw water masses which meet and partially mix in the rockall trough volume and salinity transports into the southern rockall trough via the sec are in the various models between 25 and 100 of those imported by the nac and are also a similarly significant proportion 20 75 of the transports into the nordic seas moreover the highest salinities are carried northwards by the sec these being between 0 13 and 0 19 psu more saline at the southern entrance to the trough than those in the nac derived waters this reveals for the first time the importance of the sec in carrying saline water masses through the rockall trough and into the nordic seas furthermore the high salinities found on density surfaces appropriate to the mow in the nordic seas are shown to result from the wintertime mixing of the saline near surface waters advected northwards by the sec nac system throughout we have attempted to demonstrate the extent to which the models agree or disagree with interpretations derived from observations so that the study also contributes to an ongoing community effort to assess the realism of our current generation of ocean models

seismic evidence of current controlled sedimentation in the belgica mound province upper porcupine slope southwest of ireland the porcupine seabight is an embayment that takes a particular position in the ne atlantic slope sonographs a few current measurements and hydrodynamic modelling suggest the presence of a strong northward flowing bottom current locally enhanced by internal tides affecting the eastern slope of the seabight at this location a province of coral banks is described expressed as mounds lined up in along slope trending ridges in this paper very high resolution single channel seismic profiles are used to evaluate to what extent the bottom currents influenced the deposition of the sediments surrounding the mounds throughout the late cenozoic three seismostratigraphic units p1 p2 and p3 can be identified in the belgica mound area separated by two margin wide discontinuities rd2 and rd1 within unit p1 probably early to middle miocene upslope migrating sediment waves are observed suggesting strong bottom currents were already active in the miocene after an early middle miocene erosion event represented by reflector rd2 an acoustically transparent layer unit p2 of as yet unknown lithology was deposited in the studied area a second margin wide erosional event marked by the late pliocene rd1 reflector removed a large part of unit p2 and has cut deeply into unit p1 subsequently the belgica mounds were constructed spectacularly fast on topographic irregularities on the rd1 paleobathymetry the onlap within the quaternary unit p3 which surrounds these mounds suggests that the mounds were already present before the deposition of p3 and were big enough to affect the intensity of the currents around them furthermore the channels and the mounds are together with the complex oceanographic regime the key morphological elements responsible for the shaping of a contourite system in the belgica mound area during the quaternary one drift body is formed by an inferred south north directed current with a drift levee and associated channel located on its western side between this channel and the mounds large scale sediment waves suggest an intensified bottom current running along the foot of the steep flanks of the mounds the belgica mounds are embedded in another drift body here an interaction of bottom and turbidity currents is suggested creating short turbidite channels at the southern and northern flanks of the mounds locally small confined drifts can be observed where unit p3 is deposited in a narrow passage made by the paleobathymetry of rd1 and the mounds

how topographic smoothing contributes to differences between the eddy flows simulated by sigma and geopotential coordinate models abstract the characteristics of the mesoscale turbulence simulated at a resolution of by a sigma coordinate model spem and a geopotential coordinate model opa of the south atlantic differ significantly these two types of models differ with respect to not only their numerical formulation but also their topography smoothed in spem as in every sigma coordinate application in this paper the authors examine how these topographic differences result in eddy flows that are different in the two models when the topography of the agulhas region is smoothed locally in opa as is done routinely in spem the production mechanism of the agulhas rings their characteristics and their subsequent drift in the subtropical gyre are found to converge toward those in spem furthermore the vertical distribution of eddy kinetic energy eke everywhere in the basin interior becomes similar in spem and opa and according to some current meter data becomes more realistic when mesoscale topographic roughness is re

the magellan mound province in the porcupine basin the magellan mound province is one of the three known provinces of carbonate mounds or cold water coral banks in the porcupine seabight west of ireland it has been studied in detail using a large and varied data set 2d and 3d seismic data sidescan sonar imagery and video data collected during rov deployment have been used to describe the mounds in terms of origin growth processes and burial the aim of this paper is to present the magellan mounds and their setting in an integrated holistic way

burst resuspension of seabed material at the foot of the continental slope in the rockall channel to better understand the relationship between near bottom hydrodynamics and sediment resuspension in the transition zone between the continental slope and the abyssal plain an array of three moorings equipped with near bottom sediment traps and current meters was deployed in a triangular configuration of at the foot of the south east slope of the rockall channel north atlantic in addition a fast sampling adcp was moored in the centre of the triangle microscopic observations combined with grain size analysis revealed that the material intercepted by the traps was mainly composed of loose phytodetritus and aggregates organic carbon and 13corg analyses further indicate that this material is relatively fresh and hence probably only transported over short distances the total mass flux measured by the traps suggests input from either laterally advected or resuspended material during the deployment period the measured flux was variable in time and space with a strong increase at the deepest site at the very foot of the slope the measured flux did not correlate significantly with daily averaged current speed suggesting that processes other than those related to elevated bed shear stress are involved in the resuspension mechanism rapid changes in the hydrodynamics probably related to internal motions are evidenced by abrupt bursts in the current velocity and in the near bottom turbidity their occurrence at slack tidal waters appears to be at the origin of the resuspension observed at the foot of the slope of the rockall channel high resolution current velocity measurements suggest that resuspension is dominated by energetic highly localised and short term resuspension events despite the abyssal depths part of these events resemble in many ways the solibores which have been previously observed to enhance sediment transport at much shallower depths over the continental slope while others rather appear to be associated to gravity waves

fingerprinting northeast atlantic water masses using neodymium isotopes dissolved neodymium nd isotopic composition expressed as end has been analysed for 82 seawater samples collected from 13 stations stretching from the alboran sea to the iceland basin the distribution of the end values of water masses was thus investigated for the first time along the western european margin in order to explore whether the water masses flowing in the eastern subpolar and subtropical atlantic reveal distinct isotopic patterns the modified atlantic water maw in the alboran sea displays end values between 9 2 0 2 and 8 9 0 2 that are significantly more radiogenic than those reported in previous studies 10 8 0 2 to 9 7 0 2 suggesting temporal variations in the nd isotopic composition of the water that enters the mediterranean sea from the strait of gibraltar the end value of the underlying modified winter intermediate water wiw has been established for the first time 9 8 0 3 and is compatible with a nd signature acquired from the sinking of maw in the northwestern mediterranean sea within the gulf of cadiz southern mediterranean sea water msw 10 6 0 2 differs slightly from the northern msw 9 9 0 4 owing to a significant contribution of modified east antarctic intermediate water eaaiw 10 9 0 2 in the northeast atlantic the north atlantic current surface water located in the inter gyre region north of 46 n displays end values of between 14 0 0 3 and 15 1 0 3 reflecting the subpolar gyre signature along the western european margin end values of surface water decrease toward the north from 10 4 1 6 to 13 7 1 0 in agreement with the gradual mixing between subtropical and subpolar water at intermediate depth end values decrease from 9 9 0 4 within the gulf of cadiz to 12 1 0 3 within the porcupine seabight indicating a strong dilution of the msw with subpolar water within the rockall trough and the iceland basin the more negative end values at mid depth 13 5 0 3 indicate that the msw has no influence even during periods of low nao index water masses deeper than 1200 m in the northeast atlantic are clearly influenced by the less radiogenic labrador sea water lsw 13 2 0 3 and 14 5 0 3 that mixes locally end between 10 3 0 2 and 11 3 0 3 in the iceland basin with the iceland scotland overflow water isow

paleoceanography of the atlantic mediterranean exchange overview and first quantitative assessment of climatic forcing 1 the mediterranean sea provides a major route for heat and freshwater loss from the north atlantic and thus is an important cause of the high density of atlantic waters in addition to the traditional view that loss of fresh water via the mediterranean enhances the general salinity of the north atlantic and the interior of the eastern north atlantic in particular it should be noted that mediterranean water outflowing at gibraltar is in fact cooler than compensating inflowing water the consequence is that the mediterranean is also a region of heat loss from the atlantic and contributes to its large scale cooling uniquely this system can be understood physically via the constraints placed on it by a single hydraulic structure the gibraltar exchange here we review the existing knowledge about the physical structure of the gibraltar exchange today and the evidential basis for arguments that it has been different in the past using a series of quantitative experiments we then test prevailing concepts regarding the potential causes of these past changes we find that 1 changes in the vertical position of the plume of mediterranean water in the atlantic are controlled by the vertical density structure of the atlantic 2 a prominent early holocene contourite gap within the gulf of cadiz is a response to reduced buoyancy loss in the eastern mediterranean during the time of sapropel 1 deposition 3 changes in buoyancy loss from the mediterranean during mis3 caused changes in the bottom velocity field in the gulf of cadiz but we note that the likely cause is reduced freshwater loss and not enhanced heat loss and 4 strong exchange at gibraltar during atlantic freshening phases implies that the gibraltar exchange provides a strong negative feedback to reduced atlantic meridional overturning given the very counterintuitive way in which the strait of gibraltar system behaves we recommend that without quantitative supporting work qualitative interpretations of how the system has responded to past external forcing are unlikely to be robust

a record of fluctuating bottom currents on the slopes west of the porcupine bank offshore ireland implications for late quaternary climate forcing abstract both local and regional controls on slope sedimentation west of porcupine bank are assessed using an array of 25 gravity cores integrated with shallow seismic tobi side scan and high resolution bathymetry data the cores were retrieved from an area of smooth distally steepened slope between 52 and 53 n in water depths of 950 to 2750 m the slope here is unmodified by gravity failures and is swept by bottom currents that flow from s to n along the margin the cores reveal a coherent shallow stratigraphy that can be traced along and between transects at upper mid and lower slope levels ams 14 c dating oxygen isotopes and carbonate profiles suggest the cored record could extend as far back as 500 ka in the longest cores with most cores providing details of the slope response to the last interglacial last glacial and holocene forcing the facies indicate deposition was dominated by a combination of bottom currents ice rafting and hemipelagic settling with carbonate prone deposits during interglacials and siliciclastic deposits during glacials inferred contourites imply that strong currents operated during interglacials with weaker current reworking during glacial conditions a pair of erosion surfaces record significant mid and upper slope scouring during marine isotope stage mis 3 and in the early holocene the lateral facies distribution implies stronger currents at shallower levels on the slope although there is evidence that the core of the current migrated up and down the slope and that sand might locally have spilt down slope the bathymetry influenced both the wider geometry of the condensed contourite sheet and the local thickness and facies variation across the slope a significant result of the study is the identification of a pair of thin sand mud contourite couplets that record enhanced bottom current reworking corresponding to periods of interstadial warming during mis 3 the couplets can be correlated to the terrestrial records onshore ireland and imply that the ne atlantic margin oceanographic and onshore climate records are strongly coupled at interstadial level

textural analyses of sidescan sonar imagery from two mound provinces in the porcupine seabight large mound structures have been discovered in the porcupine seabight northeast atlantic at a depth of 500 1200 m associated with the growth of cold water deep sea coral species such as lophelia pertusa l or madrepora oculata l during the training through research cruise in 1997 high resolution oretech sidescan sonar data were acquired over two provinces of these structures this article focuses on the presentation and quantitative interpretation of representative sections of these sidescan data from areas around the belgica and hovland mounds several image analysis tools were used but texture analysis based on grey level co occurrence matrices gave the best results entropy and homogeneity indices were calculated and the resulting images made it possible to discriminate between different seabed features on a quantitative basis mounds moats and background sediments could be delineated accurately and the image textures could be linked to the actual seafloor appearance through core descriptions and deep towed video data a major difference was found in the acoustic returns from the two provinces studied the belgica province shows much rougher textures this is due to an actual difference in seabed roughness caused by a difference in bottom currents and sediment dynamics in the two areas the combined effect of the northward directed north atlantic slope current and superimposed internal waves and tides appears to be much stronger in the belgica province the reported difference in current strength might well influence the growth of the deep water coral species in both areas

cold water coral carbonate mounds as unique palaeo archives the plio pleistocene challenger mound record ne atlantic through the interplay of a stabilising cold water coral framework and a dynamic sedimentary environment cold water coral carbonate mounds create distinctive centres of bio geological accumulation in often complex continental margin settings the iodp expedition 307 drilling of the challenger mound eastern porcupine seabight ne atlantic not only retrieved the first complete developmental history of a coral carbonate mound it also exposed a unique early pleistocene sedimentary sequence of exceptional resolution along the mid latitudinal ne atlantic margin in this study a comprehensive assessment of the challenger mound as an archive of quaternary palaeo environmental change and long term coral carbonate mound development is presented new and existing environmental proxy records including clay mineralogy planktonic foraminifer and calcareous nannofossil biostratigraphy and assemblage counts planktonic foraminifer oxygen isotopes and siliciclastic particle size are thereby discussed within a refined chronostratigraphic and climatic context overall the development of the challenger mound shows a strong affinity to the plio pleistocene evolution of the northern hemisphere climate system albeit not being completely in phase with it the two major oceanographic and climatic transitions of the plio pleistocene the late pliocene early pleistocene intensification of continental ice sheet development and the mid pleistocene transition to the more extremely variable and more extensively glaciated late quaternary mark two major thresholds in challenger mound development its late pliocene 2 74 ma origin and its middle late pleistocene to recent decline distinct surface water perturbations i e water mass polar front migrations productivity changes melt water pulses are identified throughout the sequence which can be linked to the intensity and extent of ice development on the nearby british irish isles since the earliest pleistocene glaciation induced shifts in surface water primary productivity are thereby proposed to fundamentally control cold water coral growth which in turn influences on mound sediment accumulation and hence coral carbonate mound development throughout the pleistocene as local factors such as proximal ice sheet dynamics and on mound changes in cold water coral density significantly affected the development of the challenger mound they can potentially explain the nature of its palaeo record and its offsets with the periodicities of global climate variability on the other hand owing to this unique setting a regionally exceptional high resolution palaeo record of early pleistocene ca 2 6 to 2 1 ma environmental change including early british irish ice sheet development broadly in phase with the 41 ka paced global climate system is preserved in the lower challenger mound all in all the challenger mound record highlights the wider relevance of coral carbonate mound archives and their potential to capture unique records from dynamic continental margin environments

the production of north atlantic deep water sources rates and pathways updating an earlier account by dickson et al 1990 this paper reviews the initial development phase of north atlantic deep water nadw production from the points where the dense inflows from nordic seas cross the greenland scotland ridge to the point off south greenland where the buildup of new production appears almost complete in particular three long term current meter arrays totaling 91 instruments and set at 160 km intervals south from the denmark strait sill are used to validate earlier short term arrays by others and in combination with these earlier arrays to describe the downstream evolution of mean speed depth and entrainment the variability of the overflow current in space and time and the likely contribution of the other three main constituents of nadw production at densities greater than 27 8 from the points of overflow 5 6 sv the transport within this range increases by entrainment and confluence with other contributory streams to around 13 3 sv at cape farewell while recirculating elements prevent us from determining the net southgoing transport a nadw transport of this order appears consistent with recent estimates of net abyssal flow passing south through the north and south atlantic