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

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

the late devensian 22 000 bp irish sea basin the sedimentary record of a collapsed ice sheet margin the late devensian 20 ka bp glacial geology of the irish sea basin 4000 km2 is an event stratigraphy recording the entry of marine waters into a glacio isostatically depressed basin and the rapid retreat of the irish sea glacier as a tidewater ice margin marine limits occur up to 140 m o d across much of the central basin the ice margin was uncoupled from its bed exposing a subglacially scoured topography to glaciomarine processes the irish sea glacier was a major drainage conduit of the last british ice sheet calving of the marine ice margin resulted in fast flow surging of ice streams recorded by drumlin fields around the northern basin margin and tunnel valleys rapid evacuation of the basin may have stranded large areas of dead ice in peripheral zones e g cheshire shropshire lowlands and initiated the collapse of the ice sheet thick wedges of ice contact glaciomarine sediments were deposited during ice retreat as morainal bank complexes by successive tidewater ice margins stabilized at pinning points around the irish sea coast where morainal banks occur on the seaward side of drumlin swarms there is a clear sequential relationship between rapid ice loss from calving ice margins the development of fast flowing ice streams drumlinization and the pumping of subglacial sediment to tidewater raised delta complexes are locally associated with marine limits along the high relief coastal margins of wales east central ireland and the lake district associated valley infill complexes record downslope resedimentation of heterogenous sediments into the marine environment during ice retreat co eval offshore deposits are represented by well stratified glaciomarine complexes that infill a subglacially scoured topography that shows networks of tunnel valleys glaciomarine mud drapes occur well to the south of the maximum limit of grounded ice in the basin e g north devon scilly islands southern ireland the age of these distal sediments previously mapped as pre devensian tills is constrained by amino acid ratios basin rebound following deglaciation was rapid with over 100 m recovery in 3 ka and was followed by a low marine still stand peat accumulating in offshore areas now as much as 55 m below sea level has been drowned by the postglacial eustatic rise in sea level the glacio sedimentary model identified in this paper involving rapid ice retreat and related sedimentation triggered by rising relative sea level suggests that isotatic downwarping is an important mechanism for deglaciating continental shelves

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

mound forming cold water corals and bryozoans in the early palaeocene of denmark the faxe quarry in south east denmark offers excellent exposures of early palaeocene danian deep water intercalated coral and bryozoan mounds that form complexes at least 40 m thick and a few kilometres wide along and over submarine highs the co existing coral and bryozoan mounds represent two different biogenic carbonate factories with a highly dynamic interplay during growth the sedimentary facies mound geometries and the density diversity and palaeoecology of the associated benthic invertebrates and nannofossils allow recognition of six successive growth units unit 1 represents an outer shelf bryozoan mound belt characterized by an oligotrophic cool water nannofossil assemblage unit 2 comprises a mixed faunal assemblage of bryozoans and octocorals with an initial sparse colonization of hexacorals the nannofossil assemblage records a decrease in diversity and an increase in warm water forms unit 3 marks the onset of dense colonization of the scleractinian coral dendrophyllia candelabrum with associated low diversity macrofauna and nannofossil assemblages unit 4 represents the main coral build up phase with frame building hexacorals of dendrophyllia and faxephyllia associated with a high diversity invertebrate fauna and relatively low diversity nannofossil assemblages unit 5 represents the late coral mound phase showing extensive lateral distribution and finally death and erosion of the coral mounds this event was contemporaneous with a warming trend in the pelagic environment the succeeding unit 6 marks the burial and overgrowth of the coral mound complex by bryozoan rich sediments the coral mound complex in the faxe quarry initiated and terminated in global nannofossil zone np3 and regional nannofossil zones nntp2g 3 suggesting a mound growth duration of approximately 300 kyr and a mean vertical accretion of the coral mound of 13 cm kyr the mound complex probably serves as the best exposed analogue to modern deep and cold water coral mounds in the north atlantic this article is protected by copyright all rights reserved

deepwater source variations during the last climatic cycle and their impact on the global deepwater circulation the degree of similarity of the 13c records of the planktonic foraminiferal species n pachyderma and of the benthic foraminiferal genus cibicides in the high latitude basins of the world ocean is used as an indicator of the presence of deepwater sources during the last climatic cycle whereas continuous formation of deep water is recognized in the southern ocean the norwegian sea stopped acting as a sink for surface water during isotope stage 4 and the remainder of the last glaciation however deep water formed in the north atlantic south of the norwegian sea during the last climatic cycle as early as isotope substage 5d and this area was also the only active northern source during stages 4 2 a detailed reconstruction of the geographic distribution of 13c in benthic foraminifera in the atlantic ocean during the last glacial maximum shows that the most important deepwater mass originated from the southern ocean whereas the glacial north atlantic deep water cannot be traced south of 40 n at shallower depth an oxygenated 13c rich intermediate water mass extended from 45 n to 15 s in the pacific ocean a ventilation higher than the modern one was also found in open ocean in the depth range 700 2600 m and is best explained by stronger formation of intermediate water in high northern latitudes

growth and erosion of a cold water coral covered carbonate mound in the northeast atlantic during the late pleistocene and holocene the first detailed stratigraphic record from a deep water carbonate mound in the northeast atlantic based on absolute datings u th and ams 14c and stable oxygen isotope records reveals that its top sediment sequences are condensed by numerous hiatuses according to stable isotope data mainly sediments with an intermediate signal are preserved on the mound while almost all fully glacial and interglacial sediments have either not been deposited or have been eroded later the resulting hiatuses reduce the late pleistocene sediment accumulation at propeller mound to amounts smaller than the background sedimentation the hiatuses most likely result due to the sweeping of the mound in turn with the re establishment of vigour interglacial circulation patterns after sluggish current regimes during glacials thus within the discussion if internal fluid driven or external environmentally driven processes control the evolution of such carbonate mounds our findings for propeller mound clearly point to environmental forcing as the dominant mechanism shaping deep water carbonate mounds in the ne atlantic during the late pleistocene and holocene

iceberg discharges into the north atlantic on millennial time scales during the last glaciation high resolution studies of north atlantic deep sea cores demonstrate that prominent increases in iceberg calving recurred at intervals of 2000 to 3000 years much more frequently than the 7000 to 10 000 year pacing of massive ice discharges associated with heinrich events the calving cycles correlate with warm cold oscillations called dansgaard oeschger events in greenland ice cores each cycle records synchronous discharges of ice from different sources and the cycles are decoupled from sea surface temperatures these findings point to a mechanism operating within the atmosphere that caused rapid oscillations in air temperatures above greenland and in calving from more than one ice sheet

the moira mounds small cold water coral mounds in the porcupine seabight ne atlantic part b evaluating the impact of sediment dynamics through high resolution rov borne bathymetric mapping large cold water coral carbonate mounds are well known from several locations along the north east atlantic continental margin with these mound structures which can measure up to 350 m in height often smaller mounds are found in the same hydrodynamic settings this paper illustrates the importance of local sediment dynamics on the morphology and development of small sized mounds the moira mounds in the belgica mound province porcupine seabight sw of ireland through rov borne microbathymetry and video data the data set illustrates the sedimentary setting of small mounds in the porcupine seabight gives new insights in the sedimentary processes acting around the small mounds and sheds more light on the interaction between hydrodynamics sedimentation and erosion cold water coral mound initiation and mound growth the high resolution bathymetry over the moira mounds reveals the presence of several well delineated zones each characterized by typical sedimentary structures bearing witness of active sediment transport the most important ones are 1 regular e w directed sediment waves 2 irregular overgrown sediment waves and 3 furrows and ridges associated with straight crested sediment waves the moira mounds appear as small mounded features subcircular in shape measuring 30 50 m across and up to 5 m tall the evolution of the moira mounds can be explained by the interaction between cold water coral growth and sediment baffling through a positive feedback mechanism however it is suggested that the small mound build ups represent nowadays rather a way of mound formation under stressed conditions due to high sediment fluxes than an initial phase of extensive mound growth

coupled primary production benthic foraminiferal assemblage and sulfur diagenesis in organic rich sediments of the benguela upwelling system abstract episodically deposited dark organic rich pleistocene and late pliocene sediments from the lower continental slope off southwest africa reveal complex interactions between changes in primary production benthic foraminiferal assemblage and anaerobic microbial processes the organic rich layers contain diatom assemblages characteristic of intense seasonal coastal upwelling whereas stratigraphically adjacent sediments reflect pelagic primary production coastal upwelling dominated depositional intervals coincide with periods of enhanced carbon flux to the seafloor enhanced organic carbon export during dark layer deposition was accompanied by decreases in the diversity of benthic foraminifera to few opportunistic species adapted to high phytodetritus accumulation rates and low o 2 conditions in all sediments the sulfur isotopic composition of pyrite indicates redox cycling of sulfide close to the sediment water interface the sulfur isotopic evidence and the permanent presence of abundant low o 2 adapted benthic foraminifera throughout the organic rich layers suggest an oxygenated benthic environment efficient oxidation of sulfide and removal of sulfide by sulfidization of organic matter inhibited buildup of toxic hydrogen sulfide from bacterial sulfate reduction at the sediment water interface these data imply that in continental slope sediments underneath productive surface waters benthic dysoxic conditions are maintained by the lateral advection of dissolved oxygen to support a small but well adapted benthic community

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

gas hydrate crystals may help build reefs during a recent cruise in the porcupine basin off southwest ireland we discovered two extensive and hitherto largely unsuspected deep water reef provinces including a giant cluster of hundreds of buried mounds the ring shapes of many reefs suggest that they are caused by an axial fluid expulsion at the sea bed a transient flow well confined in space and time we are exploring various hypotheses but a stimulating avenue for research is opened by a glacially controlled growth pulse and subsequent decay of a shallow layer of gas hydrates as a methane buffer and probably indirectly as a ground for overlying biological communities

generalized sorting profile of alluvial fans alluvial rivers often exhibit self similar gravel size distributions and abrupt gravel sand transitions experiments suggest that these sorting patterns are established rapidly but how and how fast this convergence occurs in the field is unknown we examine the establishment of downstream sorting patterns in a kilometer scale alluvial fan the sharp transition from canyon to unconfined channelized fan provides a well defined boundary condition the channel changes from deep and entrenched at the fan apex to shallow and depositional over a short distance exhibiting nonequilibrium behavior the resulting gravel fining profile is not self similar the particle size distribution narrows until approximate equal mobility is achieved downfan the gravel sand transition appears to exhibit a self similar form field and laboratory data collapse when downstream distance is normalized by the location of the transition results suggest a generalized sorting profile for alluvial fans as a consequence of the threshold of motion and nonequilibrium channels

late glacial and holocene palaeocurrents around rockall bank ne atlantic ocean core samples and hydrographic data from 50 to 60 n and 15 to 25 w in the northeast atlantic ocean are used to study changes in current activity from the last glacial to present we establish a new method to distinguish between the effects of changing bottom current speed and varying size input by drawing upon sediment flux data and detailed grain size analysis changes in current speed are recorded by the mean size of the sortable coarse noncarbonate silt component which increases with current vigor by winnowing away of fines our method involves the definition of an ideal sortable silt input function recorded at a site accumulating unmodified pelagic flux only the ideal profile is then compared with records from other sites to determine the history of current speed at a range of water depths the upper surface of southern source water ssw probably shoaled during the glacial as indicated by the covariation of sortable silt records from sites presently covered by ssw and lower north atlantic deep water lnadw the data suggest that production of lnadw was suppressed during the glacial increased following the last glacial maximum and declined at the start of termination 1a a second pulse of production occurred immediately before the younger dryas event intermediate waters were generally faster flowing during the glacial and may have expanded their depth domain such that a single glacial intermediate water mass covered depths from 1100 to more than 2000 m

water mass exchange between the north atlantic and the norwegian sea during the past 28 000 years the greenland iceland and norwegian gin seas are important regulators of heat transport in the northern hemisphere and of ocean atmosphere co2exchange1 5 rapid changes in the circulation of surface and deep waters in this region may induce nonlinear climatic effects and climate instabilities2 3 here we present carbon and oxygen isotope data that provide a record of circulation changes in the gin seas during and at the termination of the last glacial maximum lgm inflow of nutrient depleted waters from the gin seas to form intermediate waters of the north atlantic resulted in nutrient enrichment of north atlantic deep water and consequent enhanced drawdown of atmospheric co2 contributing to the lower atmospheric during the lgm the onset of deglaciation occurred at a time of low salinity in the gin seas and thus of reduced thermohaline circulation although strong thermohaline circulation was later reinitiated in the north atlantic as deglaciation proceeded it cannot therefore have caused the onset of warming similarly we find that rapid changes in thermohaline circulation cannot account for the transient return to a cooler climate during the younger dryas episode

were the north atlantic heinrich events triggered by the behavior of the european ice sheets theories explaining the origin and distribution of heinrich layers abrupt massive discharges of ice rafted detritus generally attribute these layers to the laurentide ice sheet however doubt has been cast by the discovery that sediments also originated from european ice sheets here we present isotopic sr nd fingerprints of heinrich layers obtained in cores from the european margin they reveal that for most of the heinrich layers the icebergs were calved first from the european ice sheets predating the laurentide surges accelerator mass spectrometry 14c ages reveal that the oceanic heinrich events were synchronous with their dust equivalents in the greenland ice cores implying a direct ocean atmosphere link the typical laurentide surge seems to have occurred over a short time span after about 1 5 k y of iceberg release from the european ice sheets this suggests that the laurentide ice sheet responded to a stimulus created by events in the european sector

the memin research unit scaling impact cratering experiments in porous sandstones the memin research unit multidisciplinary experimental and modeling impact research network is focused on analyzing experimental impact craters and experimental cratering processes in geological materials memin is interested in understanding how porosity and pore space saturation influence the cratering process here we present results of a series of impact experiments into porous wet and dry sandstone targets steel iron meteorite and aluminum projectiles ranging in size from 2 5 to 12 mm were accelerated to velocities of 2 5 7 8 km s 1 yielding craters with diameters between 3 9 and 40 cm results show that the target s porosity reduces crater volumes and cratering efficiency relative to nonporous rocks saturation of pore space with water to 50 and 90 increasingly counteracts the effects of porosity leading to larger but flatter craters spallation becomes more dominant in larger scale experiments and leads to an increase in cratering efficiency with increasing projectile size for constant impact velocities the volume of spalled material is estimated using parabolic fits to the crater morphology yielding approximations of the transient crater volume for impacts at the same velocity these transient craters show a constant cratering efficiency that is not affected by projectile size

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

recent calcium carbonate dissolution in the barents sea paleoceanographic applications abstract studies of benthic foraminifera in surface sediments of the arctic epicontinental barents sea show several indications of calcium carbonate dissolution low values of calcium carbonate correspond to low ratios of calcareous agglutinating foraminifera planktic benthic foraminifera high ratios of living dead foraminifera corroded calcareous foraminifera and high numbers of exposed organic linings of foraminifera dissolution increases eastwards and northwards in the study area we suggest that the dissolution is caused by the presence of dense cold saline and co 2 rich bottom water which is linked to sea ice production and the position of the oceanic polar front we also think calcium carbonate dissolution in this area indicates a sink for atmospheric co 2

benthic foraminifera as indicators of changing mediterranean atlantic water exchange in the late miocene abstract benthic foraminifera and stable isotopes from homogeneous sediments in an upper miocene tortonian lower messinian cyclic succession of homogeneous marls and sapropels from the island of gavdos greece show significant changes in bottom water oxygenation presumably related to changes in the mediterranean atlantic water exchange the benthic foraminifera prove to be excellent indicators of variations in the oxygen contents of the bottom waters even more so than the stable isotopes our data indicate a step wise restriction of the mediterranean atlantic water exchange resulting in increasing sluggishness of deep water circulation the first indication of restricted circulation is seen at 8 5 ma which may correspond to a severe restriction of the external zone of the betic strait a second event which had a very serious influence on the fauna in the deeper mediterranean occurred at 7 16 ma this event was presumably linked to the partial closure of the rifian corridor the restricted mediterranean atlantic connection also seems to have led to a gradual salinity increase and possibly to the formation of a brine in the deepest basins thus marking the first development towards the messinian salinity crisis

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

impact of bottom water currents on benthic foraminiferal assemblages in a cold water coral environment the moira mounds ne atlantic abstract strong bottom currents play a key role in cold water coral environments by shaping their morphology and providing the necessary food for the corals to thrive this study investigates the differences between living and dead benthic foraminiferal assemblages in such environments more precisely on the moira mounds ne atlantic a specific focus is to understand the role of currents and their influence on the taphonomy of benthic foraminiferal assemblages here we analyze high resolution sediment grain size distributions coupled with benthic foraminiferal assemblage composition to assess how much deep sea bottom currents affect benthic foraminiferal assemblages we suggest that the dead benthic foraminiferal assemblage consists of a reworked glacial fauna associated with contemporary species reworked glacial species elphidium excavatum sigmoilopsis schlumbergeri are the most abundant dominant species that are present almost exclusively in the living assemblage alabaminella weddellensis nonionella iridea trifarina spp are associated with high phytodetritus input possibly as a response to the later phase of the north east atlantic spring bloom dead assemblages are further characterized by the scarcity of organic walled agglutinated foraminifera in comparison to living assemblages sediment grain size distributions show that the downslope moira mounds consist of well sorted fine sand typical of contourite deposits in the area grain size distributions and the average shannon diversity of living and dead foraminiferal assemblages indicate that the coral cover offers a sheltered environment baffling eroded sediment and preventing post mortem transport of dead foraminifera we conclude that cold water coral environments provide a valuable paleoenvironmental archive by trapping sediment in an otherwise non depositional system

hydrodynamics and cold water coral facies distribution related to recent sedimentary processes at galway mound west of ireland abstract cold water coral carbonate mound development is the result of complex and interactive hydrographical biological and geological processes that can result in morphostructures several hundred meters high the case study presented here investigates one of these large mounds galway mound in the eastern porcupine seabight to build an understanding of mound forming processes and the driving factors for the first time bottom current data have been recorded at six locations over a mound thus allowing an interpretation of the local flow field to be made in addition to the overall flow pattern in the porcupine seabight the recorded data display distinct diurnal tides comparison of the local flow field coral facies distributions current induced seabed features and grain size distributions over the galway mound highlights a correlation between the abundance of living corals with areas of enhanced bottom currents however the interplay of contour currents tidal currents and the local topography further influences the coral facies and results in a distinct asymmetry in the coral facies distribution at galway mound by baffling sediment the corals also affect sedimentation on the mound

northeastern atlantic benthic foraminifera during the last 45 000 years changes in productivity seen from the bottom up we studied benthic foraminifera from the last 45 kyr in the 63 mu m size fraction in biogeochemical ocean flux studies bofs cores 5k 50 degrees 41 3 n 21 degrees 51 9 w depth 3547 m and 14k 58 degrees 37 2 n 19 degrees 26 2 w depth 1756 m at a time resolution of several hundreds to a thousand years the deepest site showed the largest fluctuations in faunal composition species richness and benthic foraminiferal accumulation rates the fluctuations resulted from changes in abundance of epistominella exigua and alabaminella weddellensis in the present oceans these species bloom opportunistically when a spring plankton bloom results in seasonal deposition of phytodetritus on the seafloor the phytodetritus species had very low relative abundances and accumulation rates during the last glacial maximum a strong increase in absolute and relative abundance of e exigua and a weddellensis during deglaciation paralleled the decrease in abundance of the polar planktonic foraminifer neogloboquadrina pachyderma s and the increase in abundance of warmer water planktonic species such as globigerina bulloides this strong increase in relative abundance of the phytodetritus species and the coeval increase in benthic foraminiferal accumulation rate were thus probably caused by an increase in the deposition of phytodetritus to the seafloor and thus probably of surface productivity when the polar front retreated to higher latitudes the abundance of phytodetritus species decreased during the younger dryas but not to the low levels of fully glacial conditions during heinrich events periods of excessive melt water formation and ice rafting benthic accumulation rates were very low as were the absolute and relative abundances of the phytodetritus species supporting suggestions that surface productivity was very low during these events in both cores pullenia and cassidulina species were common during isotope stages 2 3 and 4 as were bolivinid buliminid and uvigerinid species high relative abundances of these species have been interpreted as indicative either of sluggish deep water circulation or of high organic carbon fluxes to the seafloor in our cores relative abundances of these species are negatively correlated with benthic foraminiferal accumulation rates and we can thus not interpret them as indicative of increased productivity during glacials the percentage of these low oxygen species calculated on a phytodetritus species free basis decreased slightly at deglaciation at 5k but not at 14k this suggests that decreased production of north atlantic deep water during the last glacial might have slightly affected benthic foraminiferal faunas in the eastern north atlantic at 3547 m depth but not at 1756 m in conclusion major changes in deep sea benthic foraminiferal faunas over the last 45 000 years in our cores from the northeastern atlantic were the result of changes in surface water productivity not of changes in deep water circulation productivity was lower during the glacial probably because of extensive ice cover

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

millennial scale depositional cycles related to british ice sheet variability and north atlantic paleocirculation since 45 kyr b p barra fan u k margin lithology lithic petrology planktonic foraminiferal abundances and clastic grain sizes have been determined in a 30 m long core recovered from the barra fan off northwest scotland the record extends back to around 45 kyr b p with sedimentation rates ranging between 50 and 200 cm kyr the abundance of ice rafted debris indicates 16 glacimarine events including temporal equivalents to heinrich events 1 4 enhanced concentrations of basaltic material derived from the british tertiary province suggest that the glacimarine sediments record variations in a glacial source on the hebrides shelf margin glacimarine zones are separated by silty intervals with high planktonic foraminifera concentrations that reflect an interstadial circulation regime in the rockall trough the results suggest that the last british ice sheet fluctuated with a periodicity of 2000 3000 years in common with the dansgaard oeschger climate cycle

carbonate budget of a cold water coral carbonate mound propeller mound porcupine seabight high resolution studies from the propeller mound a cold water coral carbonate mound in the ne atlantic show that this mound consists of 50 carbonate justifying the name carbonate mound through the last 300 000 years approximately one third of the carbonate has been contributed by cold water corals namely lophelia pertusa and madrepora oculata this coral bound contribution to the carbonate budget of propeller mound is probably accompanied by an unknown portion of sediments buffered from suspension by the corals however extended hiatuses in propeller mound sequences only allow the calculation of a net carbonate accumulation thus net carbonate accumulation for the last 175 kyr accounts for only 0 3 g cm2 kyr which is even less than for the off mound sediments these data imply that propeller mound faces burial by hemipelagic sediments as has happened to numerous buried carbonate mounds found slightly to the north of the investigated area

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

deglacial upslope shift of ne atlantic intermediate waters controlled slope erosion and cold water coral mound formation porcupine seabight irish margin abstract turbulent bottom currents significantly influence the formation of cold water coral mounds and sedimentation processes on continental slopes combining records from coral mounds and adjacent slope sediments therefore provide an unprecedented palaeo archive to understand past variations of intermediate water mass dynamics here we present coral ages from coral mounds of the belgica province porcupine seabight ne atlantic which indicate a non synchronous holocene re activation in mound formation suggested by a temporal offset of 2 7 kyr between the deep start 11 3 ka bp at 950 m depth and shallow start 8 6 ka bp at 700 m depth mounds a similar depth dependent pattern is revealed in the slope sediments close to these mounds that become progressively younger from 22 1 ka bp at 990 m to 12 2 ka bp at 740 m depth based on core top ages we suggest that the observed changes are the consequence of enhanced bottom water hydrodynamics caused by internal waves associated to the re invigoration of the mediterranean outflow water mow and the development of a transition zone tz between the mow and the overlying eastern north atlantic water enaw which established during the last deglacial these highly energetic conditions induced erosion adjacent to the belgica mounds and supported the re initiation of mound formation by increasing food and sediment fluxes the striking depth dependent patterns are likely linked to a shift of the enaw mow tz moving the level of maximum energy 250 m upslope since the onset of the last deglaciation

glacial cold water coral growth in the gulf of cadiz implications of increased palaeo productivity a set of 40 uranium series datings obtained on the reef forming scleractinian cold water corals lophelia pertusa and madrepora oculata revealed that during the past 400 kyr their occurrence in the gulf of cadiz goc was almost exclusively restricted to glacial periods this result strengthens the outcomes of former studies that coral growth in the temperate ne atlantic encompassing the french iberian and moroccan margins dominated during glacial periods whereas in the higher latitudes irish and norwegian margins extended coral growth prevailed during interglacial periods thus it appears that the biogeographical limits for sustained cold water coral growth along the ne atlantic margin are strongly related to climate change by focussing on the last glacial interglacial cycle this study shows that palaeo productivity was increased during the last glacial this was likely driven by the fertilisation effect of an increased input of aeolian dust and locally intensified upwelling after the younger dryas cold event the input of aeolian dust and productivity significantly decreased concurrent with an increase in water temperatures in the goc this primarily resulted in reduced food availability and caused a widespread demise of the formerly thriving coral ecosystems moreover these climate induced changes most likely caused a latitudinal shift of areas with optimum coral growth conditions towards the northern ne atlantic where more suitable environmental conditions established with the onset of the holocene

sediment accumulation on a cold water carbonate mound at the southwest rockall trough margin abstract cold water corals build isolated and clustered carbonate mound ridges several kilometres long and wide and up to 380 m high at the southwest rockall trough margin photo and video observations as well as coring have shown that mainly the upper mound flanks and summits are covered with a thriving living coral cover and associated fauna box cores prove the presence of living coral colonies on top of a thick layer of coral debris which is to a large extent abraded and bio eroded before being buried the coral framework is filled with sediment from settling pelagic material and parts of the fauna living at the mounds resulting in a 120 cm thick layer of sediments since 10 800 yr component analysis of a piston core from the top of a carbonate mound shows a complete record of cold water coral mound facies comprising many different species living at the mounds an alternation of skeletal and cement dominated intervals was distinguished in the piston core stable isotope analysis of planktonic and benthic foraminifera indicates a continuous sedimentation pattern since the younger dryas the deeper and older part of the core showing mainly intermediate isotope values is dominated by the presence of large hiatuses spanning a total of up to 200 000 yr hiatuses in the core may reflect periods of non deposition or erosion which may be linked to glacial interglacial variability environmental conditions probably change at glacial interglacial timescales influencing the local hydrodynamic regime food supply and sedimentation rate around the carbonate mounds affecting coral growth and therefore carbonate mound development

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

a coupled climate model simulation of the last glacial maximum part 2 approach to equilibrium the climate of the last glacial maximum lgm is simulated with a coupled climate model the simulated climate undergoes a rapid adjustment during the first several decades after imposition of lgm boundary conditions as described in part 1 and then evolves toward equilibrium over 900 model years the climate simulated by the coupled model at this period is compared with observationally based lgm reconstructions and with lgm results obtained with an atmosphere mixed layer slab ocean version of the model in order to investigate the role of ocean dynamics in the lgm climate global mean surface air temperature and sea surface temperature sst decrease by about 10 c and 5 6 c in the coupled model which includes ocean dynamics compared to decreases of 6 3 and 3 8 c in slab ocean case the coupled model simulates a cooling of about 6 5 c over the tropics which is larger than that of the climap reconstruction 1 7 c and larger than that of the slab ocean simulation 3 3 c but which is in reasonable agreement with some recent proxy estimates the ocean dynamics of the coupled model captures features found in the climap reconstructions such as a relative maximum of ocean cooling over the tropical pacific associated with a mean la nina like response and lead to a more realistic sst pattern than in the slab model case the reduction in global mean precipitation simulated in the coupled model is larger 15 than that simulated with the slab ocean model 10 in conjunction with the enhanced cooling some regions such as the usa and the mediterranean region experience increased precipitation in accord with proxy paleoclimate evidence the overall much drier climate over the ocean leads to higher sea surface salinity sss in most ocean basins except for the north atlantic where sss is considerably lower due to an increase in the supply of fresh water from the mississippi and amazon rivers and presumably a decrease in salt transport by the weakened north atlantic overturning circulation the north atlantic overturning stream function weakens to less than half of the control run value the overturning is limited to a shallower depth less than 1000 m and its outflow is confined to the northern hemisphere in the southern ocean convection is much stronger than in the control run leading to a stronger overturning stream function associated with enhanced antarctic bottom water formation as a result southern ocean water masses fill the entire deep ocean the antarctic circumpolar current acc transport through the drake passage increases by about 25 the acc transport despite weaker zonal winds is enhanced due to changes in bottom pressure torque the weakening of the overturning circulation in the north atlantic and the accompanying 30 decrease in the poleward ocean heat transport contrasts with the strengthening of the overturning circulation in the southern ocean and a 40 increase in heat transport as a result sea ice coverage and thickness are affected in opposite senses in the two hemispheres the lgm climate simulated by the coupled model is in reasonable agreement with paleoclimate proxy evidence the dynamical response of the ocean in the coupled model plays an important role in determining the simulated and undoubtedly the actual lgm climate

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

influence of benthic sediment transport on cold water coral bank morphology and growth the example of the darwin mounds north east atlantic the darwin mounds are small up to 70 m in diameter discrete cold water coral banks found at c 950 m water depth in the northern rockall trough north east atlantic formerly described in terms of their genesis the darwin mounds are re evaluated here in terms of mound growth processes based on 100 and 410 khz side scan sonar data the side scan sonar coverage is divided into a series of acoustic facies representing increasing current speed and sediment transport erosion from south to north pockmark facies mounds within depressions facies darwin mound facies stippled seabed facies and sand wave facies mound morphometric changes are quantified and show a south to north divergence from an inherited morphology reflecting the outline of coral colonized fluid escape structures to developed downstream elongated elevated mound forms it is postulated that increasing current speeds and bedload sand transport favour mound growth and development by a process of enhanced sand sedimentation within mounds due to current deceleration by frictional drag around coral colonies comparisons are made with similar growth processes attributed to comparably sized cold water coral mounds in the porcupine seabight offshore ireland

paleoseawater density reconstruction and its implication for cold water coral carbonate mounds in the northeast atlantic through time carbonate buildups and mounds are impressive biogenic structures throughout earth history in the recent ne atlantic cold water coral cwc reefs form giant carbonate mounds of up to 300 m of elevation the expansion of these coral carbonate mounds is paced by climatic changes during the past 2 7 myr environmental control on their development is directly linked to controls on its main constructors the reef building cwcs seawater density has been identified as one of the main controlling parameter of cwc growth in the ne atlantic one possibility is the formation of a pycnocline above the carbonate mounds which is increasing the hydrodynamic regime supporting elevated food supply and possibly facilitating the distribution of coral larvae the potential to reconstruct past seawater densities from stable oxygen isotopes of benthic foraminifera has been further developed a regional equation gives reliable results for three different settings peak interglacials e g holocene peak glacials e g last glacial maximum and intermediate setting between the two extremes seawater densities are reconstructed for two different ne atlantic cwc carbonate mounds in the porcupine seabight indicating that the development of carbonate mounds is predominantly found at a seawater density range between 27 3 and 27 7 kg m 3 notation comparable to recent conditions we interpret the reconstructed density range as a pycnocline serving as boundary layer on which currents develop carrying nutrition and possibly coral larvae the close correlation of cwc reef growth with reconstructed seawater densities through the pleistocene highlights the importance of pycnoclines and intermediate water mass dynamics

thousands of cold water coral mounds along the moroccan atlantic continental margin distribution and morphometry abstract coral mounds formed by framework forming cold water corals pierce the seabed along most continental margins of the atlantic ocean and new sites are continuously being discovered here we describe an extremely high accumulation of coral mounds at the nw moroccan atlantic margin between 35 n and 35 5 n within an area of only 1440 km2 3400 mounds were found exposed at the seabed the coral mounds are nowadays characterized by an almost complete lack of living cold water corals in addition numerous buried mounds were identified in hydroacoustic sub bottom profiles and are estimated to be 3 7 times more frequent than the exposed mounds consequently a total of 16 000 buried and exposed mounds is estimated for the entire study area the exposed mounds are rather small with a mean height of 18 m and show a conspicuous arrangement in two slope parallel belts that centre in water depths between 720 and 870 m and 890 980 m respectively putting them among the deepest mound occurrences discovered so far in the atlantic the mostly elongated mounds largely stretch downslope pointing to a significant influence of internal waves in the mound formation process moreover based on their average dimensions the entire coral mound volume can be estimated as 1 3 km3 which means the mounds store a considerable amount of coral carbonate highlighting their potentially important role as regional carbonate factories in combination with further occurrences of coral mounds along the moroccan margin both in the mediterranean and in the atlantic ocean these new findings underline morocco s role as a hotspot for the occurrence of cold water coral mounds

changes in fossil assemblage in sediment cores from mingulay reef complex ne atlantic implications for coral reef build up ct scanning and descriptions of sedimentary sequences have been conducted to describe the internal structure and define the evolutionary sequence of events leading to the build up of cold water coral reef constructed by the azooxanthellate scleractinian lophelia pertusa two vibrocores containing coral clasts and associated fauna embedded in a matrix of marine sediment were taken at the mingulay reef complex an inshore 120 190 m water depth l pertusa reef off western scotland the cores were scanned using computed x ray tomography ct scan with the aim of 1 reconstructing and quantifying the relative abundance and preservation of coral fragments in the cores 2 identifying distinct reef facies and hence 3 providing data that could lead to a conceptual model of reef growth u series dates were obtained on l pertusa clasts from the two sediment cores to provide a temporal framework of the reef build up after exploring a range of methods for processing ct scans three simple parameters were used to classify different strata within the cores the overall density of the cores the number of fossil clasts and the sum of the area of clasts detected by the ct scan these parameters were validated by comparing with density measurements from a multi sensor core logger mscl and physical dissection and analysis of fossils in the cores from the ct scan analyses three distinct reef facies were evident coral rich sediment rich and shelly coral hash layers the succession and rapid cycle of reef framework forming l pertusa development disturbance and recovery allow us to provide a model of cold water coral reef build up including shifts in biodiversity physical chemical biological processes and the sedimentary regime

the oxygen isotopic composition of seawater during the last glacial maximum high resolution oxygen and hydrogen isotope measurements were made on pore fluids from deep sea sediments from sites in the north and south atlantic the data provide direct measurements of changes in the isotopic composition of bottom waters during the last glacial maximum lgm results from ocean drilling program odp site 981 in the north atlantic currently bathed in north atlantic deep water nadw reproduces previous results from the ceara and bermuda rises constraining the glacial interglacial change in 18 o of the deep atlantic to be 0 7 0 8 results from site 984 which is located north of site 981 and at a shallower water depth yield a similar value 0 8 providing insight into the properties of glacial north atlantic intermediate water gnaiw sites from odp leg 177 in the south atlantic span the modern boundary between northern and southern sources of deep water data from the northern site 1088 yield a similar result to sites in the tropical and north atlantic 0 7 at the southern site 1093 located south of the polar front the change is substantially larger 1 1 representing the change in 18 o of southern source waters since the lgm these results confirm previous estimates that the global average change in 18 o of seawater is 1 0 0 1 hydrogen isotopes measured on pore fluids from three sites are consistent with the oxygen isotopes from these locations giving further support to these results at all sites studied the temperature of the deep ocean during the lgm calculated by combining the pore fluid results with oxygen isotope data from benthic foraminifera was within 1 c of the freezing point of seawater

the faroe shetland gateway late quaternary water mass exchange between the nordic seas and the northeastern atlantic abstract thirteen piston and gravity cores from the faroe shetland area were investigated for their planktic and benthic foraminiferal and oxygen isotopic distributions eight time slices between 18 ka bp and the present were reconstructed to study variations in surface and deep water exchange between the se norwegian sea and the northeast atlantic ocean today a relatively strong northward flow of warm north atlantic surface water is counterbalanced by a southward outflow of newly convected cold bottom water the norwegian sea overflow water during the last glacial maximum at 18 ka bp both the surface and bottom flows were slow and the climate conditions were arctic the convection north of the faroe area was weak and unstable the first indication of the deglaciation is a decrease in the planktic oxygen isotope values discernible southwest of the faroe islands at 15 5 ka bp the deglaciation proceeded northeast and eastward synchronous with a gradual intensification of northward flowing warmer atlantic intermediate water along the sea bottom meltwater fluxes increased between 14 and 13 ka bp producing cold surface waters and the climatic cooling was extreme there was no southward overflow of cold bottom water during this time period and the exchange of water masses between the nordic seas and the north atlantic ocean was essentially reversed i e estuarine during the bolling interstadial at 12 5 ka bp northward flowing warm surface water was present to the east of the faroe shetland channel wedged below a tongue of polar water spreading from the northwest and reaching into the faroe shetland channel convection in the nordic seas and overflow of cold deep water started during the bolling interstadial the polar water spread more eastward and southward during the following cold spell the younger dryas around 10 3 ka bp the polar water was overlying the warmer but more saline atlantic water which flowed northward below the cold surface water the overflow of cold bottom water was supposedly only slightly weaker than during the bolling interstadial strong inflow of warm surface water took place during the early holocene at 9 5 ka bp and relatively dense cold water flowed southward along the bottom the rate of water mass exchange reached a maximum at 6 5 ka bp when both the inflow of warm atlantic surface water and the outflow of cold dense bottom water appear to have been stronger than today

the moira mounds small cold water coral banks in the porcupine seabight ne atlantic part a an early stage growth phase for future coral carbonate mounds this paper presents a comprehensive overview of the moira mounds in the porcupine seabight combining a review of currently published material with new data and interpretations the moira mounds are circular to ovoid shaped individual or clustered coral banks referred to as scleractinian spaced cluster macroreefs located in the belgica carbonate mound province porcupine seabight west of ireland they are up to 10 m high and 20 to 35 m in diameter for the first time a map showing the complete extent and location of the moira mounds is published revealing 256 examples grouped into four areas mainly between 800 and 1100 m water depth rov groundtruthing revealed the importance of bedload sand transport in moira mound formation and development processes through sediment entrapment by coral frameworks lophelia pertusa and madrepora oculata new estimated growth rates for the moira mounds are comparable to those measured for much larger irish coral carbonate mounds but an order of magnitude lower than rates from comparably sized reefs offshore norway as well as the framework corals 26 macrobenthic invertebrate species were identified from a single box core that were similar to those communities found in adjacent off mound habitats it is proposed that the moira mounds are an example of the early stage growth phase of nearby giant coral carbonate mounds and represent a westward extension of the zone of active cold water coral mound growth and therefore a deepening of the zone of cold water coral growth over recent climate cycles

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

growth history of a cold water coral covered carbonate mound galway mound porcupine seabight ne atlantic abstract during the past decade knowledge about the ecology and the environment of giant carbonate mounds has been growing continuously however still little is known about their growth dynamics three gravity cores from galway mound belgica mound province in the porcupine seabight off ireland were investigated for their sedimentological geophysical and geochemical properties to get insight into the long term development of this cold water coral covered carbonate mound these data were supplemented by radiometric age determinations on planktonic foraminifera and coral skeletons the records from three different settings on galway mound reveal a coherent growth history that in general is similar to what is known from other carbonate mounds at the irish margin however whereas other cores are often disturbed by numerous and not correlateable hiatuses galway mound in contrast appears to be characterised by only one major hiatus representing a time gap of 250 kyr several mechanisms are discussed in this study as possible causes for the observed stratigraphic record at galway mound the most likely explanation is that the hiatus has its origin in a major mass wasting event on an instable possibly glacial unit that could have acted as a slip plane the overall late quaternary growth history of galway mound fits well into existing cyclical mound development models pointing to galway mound being an actively growing mound coral bank stage at present

new data for the last glacial maximum in great britain and ireland abstract understanding the history of the british and irish ice sheet biis at the last glacial maximum lgm has been advanced by new approaches in particular by cosmogenic nuclide surface exposure dating aminostratigraphy of shelly glacial deposits ams radiocarbon dating and the evidence from continental margin marine cores all of which supersede the previously weak geochronologic control it was formerly believed that great britain and ireland was largely ice free between the last interglacial oxygen isotope sub stage 5e and the late devensian when the lgm occurred as such the biis was effectively out of phase with laurentide and scandinavian ice sheets as well as inferences of ice volume from oxygen isotope stratigraphy the biis during the late devensian maximum was also perceived as having been relatively stationary new evidence shows that the lgm was an important event during the evolution of an earlier biis when the extent of ice was greater repeated iceberg rafting events over the past 50 ka are shown by marine cores while the derivative inference of numerous corresponding glacial advances is supported by several clusters of 36 cl ages on glaciated surfaces and glacial boulders that are indicative of deglacial events between 40 and 12 ka these appear to be associated with heinrich events the earliest being inferred as heinrich 4 at about 40 ka during this advance the biis and scandinavian ice sheet sis were in contact and all of ireland was glaciated the ice sheet appears to have fluctuated several times between 40 and 25 ka although evidence for this is poorly preserved but the 36 cl and 14 c evidence is clear that the biis reached its lgm maximum size about 22 ka soon after heinrich event 2 when the biis and sis were not in contact one cluster of 36 cl and 14 c ages at 21 4 1 3 ka records an initial pulse of deglaciation that was followed by extensive deglaciation about 17 4 0 4 ka just before heinrich event 1 when the ice sheet readvanced contrary to previous views the biis probably existed throughout much of devensian time as a mobile and sensitive ice sheet during which the lgm advance was but one important event in places glacial deposits of the earlier devensian glaciation have previously been incorrectly identified as products of the later lgm glaciation

the le danois contourite depositional system interactions between the mediterranean outflow water and the upper cantabrian slope north iberian margin abstract the le danois contourite depositional system cds located in an intraslope basin along the cantabrian margin is unique with respect to the known sedimentary systems along the upper slope of the biscay margin whereas the steep biscay slopes are dominated by downslope processes the le danois cds has been generated by alongslope processes and has a strong potential to contain a record of the neogene palaeoceanography this paper will focus on the onset development and present day functioning of this system with respect to its unique morphological control and the responsible local oceanographic processes new bathymetric and seismic reflection data show that the past and present le danois cds is shaped by the mediterranean outflow water conditioned by seafloor irregularities and two topographic highs the large le danois bank and the smaller vizco high the seismic stratigraphic analysis carried out on the contourite deposits has allowed to identify 3 seismic sequences separated by 3 major regional discontinuities changes in depositional styles the vertical stacking of seismic units and the nature of the discontinuities suggest a correlation with the development of the cadiz cds and well known palaeoceanographic events along the ne atlantic margin the first clues for bottom current deposits are identified in the lower sequence which is developed after tentatively the lower pliocene the drift deposits of both the lower and middle sequences were confined into two palaeobasins within the intraslope basin however from the middle pleistocene revolution 0 9 ma onwards the contouritic deposition is intensified due to the switch to a full glacial mode with 100 ka cyclicity this has allowed the development of the present day depositional and erosive features such as respectively elongated mounded and separated drifts plastered drifts moats and slide scars

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

terrigenous fluxes at the celtic margin during the last glacial cycle the sedimentary sections of three cores from the celtic margin provide high resolution records of the terrigenous fluxes during the last glacial cycle a total of 21 14 c ams dates allow us to define age models with a resolution better than 100 yr during critical periods such as heinrich events 1 and 2 maximum sedimentary fluxes occurred at the meriadzek terrace site during the last glacial maximum lgm detailed x ray imagery of core md95 2002 from the meriadzek terrace shows no sedimentary structures suggestive of either deposition from high density turbidity currents or significant erosion two paroxysmal terrigenous flux episodes have been identified the first occurred after the deposition of heinrich event 2 canadian ice rafted debris ird and includes ird from european sources we suggest that the second represents an episode of deposition from turbid plumes which precedes ird deposition associated with heinrich event 1 at the end of marine isotopic stage 2 mis 2 and the beginning of mis 1 the highest fluxes are recorded on the whittard ridge where they correspond to deposition from turbidity current overflows canadian icebergs have rafted debris at the celtic margin during heinrich events 1 2 4 and 5 the highresolution records of heinrich events 1 and 2 show that in both cases the arrival of the canadian icebergs was preceded by a european ice rafting precursor event which took place about 1 1 5 kyr before two rafting episodes of european ird also occurred immediately after heinrich event 2 and just before heinrich event 1 the terrigenous fluxes recorded in core md95 2002 during the lgm are the highest reported at hemipelagic sites from the northwestern european margin the magnitude of the canadian ird fluxes at meriadzek terrace is similar to those from oceanic sites 2002 elsevier science b v all rights reserved

deep sea benthic foraminiferal assemblage response to a surface ocean productivity gradient a test a transect of samples from the eastern equatorial pacific where surface ocean productivity is the only changing environmental variable was used to test the response of benthic foraminiferal assemblages to an open ocean productivity gradient the transect runs along the east pacific rise from the highly productive waters near the equator to the oligotrophic south pacific subtropical gyre surface sediment benthic assemblages show progressive change along the transect with strong compositional shifts corresponding to the rapid productivity gradient near the equator and to the position of the southern convergence near 18 19 s the relationship of the assemblages to surface ocean productivity was tested by statistical regression of quantitative estimates of productivity on the assemblage principal component scores calculated for each sampling location the regression yielded an r squared of 0 87 demonstrating a clear relationship between surface ocean productivity and deep sea benthic foraminiferal assemblage composition the species most important to this relationship display a consistent response to oceanic productivity for long stretches of geologic time this conservative behavior and the results of the regression analysis indicate that benthic foraminiferal assemblages can be used to estimate surface ocean productivity for the geologic past

dating the death of mediterranean deep sea scleractinian corals abstract several c 14 datings of deep sea scleractinians indicate that the major decline of this coral population in the mediterranean sea took place around 30 000 15 000 yrs b p it is probable that the most important factor causing such an event was the rise of temperature that either directly affected the physiology of the corals or more likely triggered unfavorable hydrological conditions

carbonate mound development in contrasting settings on the irish margin cold water coral carbonate mounds formed by framework building cold water corals are found in several mound provinces on the irish margin differences in cold water coral mound development rates and sediment composition between mounds at the southwest rockall trough margin and the galway mound in the porcupine seabight are investigated variations in sediment composition in the two mound provinces are related to the local environmental conditions and sediment sources mound accumulation rates are possibly higher at the galway mound probably due to a higher influx of hemipelagic fine grained non carbonate sediments in both cold water coral mound areas mound growth has been continuous for the last ca 11 000 years before this period several hiatuses and unconformities exist in the mound record the most recent unconformity can be correlated across multiple mounds and mound provinces at the irish margin on the basis of apparent age on the southwest rockall trough margin these hiatuses unconformities are associated with post depositional aragonite dissolution in and lithification of certain intervals while at galway mound no lithification occurs this study revealed that the influx and types of material transported to cold water coral mounds may have a direct impact on the carbonate mound accumulation rate and on post depositional processes significantly the logachev mounds on the sw rockall trough margin accumulate slower but because they contain lithified layers are less susceptible to erosion this net effect may account for their larger size compared to the belgica mounds

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

carbonate mounds in shallow and deep time over a decade of research on recent cold water coral mounds in various oceans has set the stage for comparative studies between recent and ancient carbonate mound systems with the aim to unravel generic processes and reveal the red thread in a fundamental strategy of life building geology a strategy nearly as ancient as life itself natural laboratories have been identified in the present ocean which provide new insights in oceanographic controls on species migration and settlement in the interaction of currents and carbonate build up in the earliest diagenesis which overprints environmental signals and shapes the template of compartmentalization of carbonate build ups and in so many other processes and factors ultimately shaping carbonate bodies comparable in size and properties to the large scale carbonate hydrocarbon reservoirs in the geological record ocean drilling and coring is an essential component of this research ideally this process is a two way avenue between shallow and deep time where fundamental and industrial knowledge about fossil carbonate mounds can drive further investigations and even experimentation in the present seas while the discoveries and process studies on live systems can yield new insights in the architecture and evolution of ancient reservoir systems this bridging exercise is the quintessence of cocarde cold water carbonate reservoir systems in deep environments an international network under the auspices of ioc unesco http www cocarde eu cocarde has organised two workshops in 2009 with a significant support of european programmes e g esf magellan workshop series and partner projects e g esf eurodiversity project microsystems this special issue groups 12 papers all addressing observations which by their nature have the potential to provide keys to generic processes of relevance for past carbonate systems as cocarde proceeds it is the objective to reciprocate in near future with an equivalent grouping of contributions from the study of fossil studies to guide further research in the present ocean it is the purpose of cocarde to strengthen such a reflux from the studies of fossil systems by stimulating relevant continental drilling exercises with comparable sampling protocols resolution and analytical procedures where relevant to allow direct comparisons with records from ocean drilling the papers in this special issue have been structured in four themes i keys to palaeoenvironmental control ii mound initiation growth and demise iii of microbes and mounds and iv tracking organominerals recent and ancient

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

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

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

on the role of the azores current in the ventilation of the north atlantic ocean three high resolution ocean circulation models of the north atlantic differing chiefly in their description of the vertical coordinate are used to examine the ventilation of the north atlantic subtropical gyre all the models produce mode waters of realistic densities in the sargasso sea and the european basin but have azores currents of differing strengths which are categorised as strong of realistic transport intermediate and weak these differences have a critical impact upon the ventilation of the gyre most importantly the strong azores current forms an effective barrier to the southward ventilation of eastern north atlantic water from the northern european basin initially driving it southwestwards into the central gyre before turning it back eastwards again in a general cyclonic circulation north of the current the intermediate and weak azores currents instead allow the southward ventilation of this water mass near the european and african coasts the situation in nature appears to be intermediate between these two cases with the azores current acting as a partial block the study also raises the possibility of the azores current forming an advective connection between the sargasso sea mode waters in the western basin and modes of similar densities found in the eastern basin on the southern side of the current although there are high levels of variability in the extent of these lighter modes in the eastern basin in nature this postulate is supported by a number of observational studies in addition the present study also provides some support for the local production of madeira mode water in the eastern basin associated with retroflecting current branches on the southern side of the azores current overall the azores current is therefore likely to have a critical impact upon the ventilation of the subtropical gyre over a large area rather than just locally affecting the potential vorticity and density structure of the upper ocean between subtropical latitudes and the northern european basin the study also contributes to an ongoing community effort to assess the realism of our current generation of ocean models

role of panama uplift on oceanic freshwater balance comparison between planktic foraminiferal oxygen isotope records from the caribbean sea ocean drilling program odp site 999 and the equatorial east pacific odp site 851 suggests an increase in caribbean surface water salinity between 4 7 and 4 2 ma the modern atlantic pacific salinity contrast of about 1 became fully established at 4 2 ma as reflected by a 0 5 planktic foraminifera 18o enrichment in the caribbean sea this is interpreted as the result of restricted surface water exchange between the tropical atlantic and pacific in response to the shoaling of the central american seaway as a consequence the atlantic and pacific surface ocean circulation regime changed as did the freshwater balance between the major ocean basins simultaneous shifts in benthic carbon isotope records in the caribbean sea suggest an intensification in north atlantic thermohaline circulation these results indicate that the panamanian isthmus formation caused several new ocean atmosphere feedback mechanisms that have affected climate since the early pliocene

links between climate and sea levels for the past three million years the oscillations between glacial and interglacial climate conditions over the past three million years have been characterized by a transfer of immense amounts of water between two of its largest reservoirs on earth the ice sheets and the oceans since the latest of these oscillations the last glacial maximum between about 30 000 and 19 000 years ago approximately 50 million cubic kilometres of ice has melted from the land based ice sheets raising global sea level by approximately 130 metres such rapid changes in sea level are part of a complex pattern of interactions between the atmosphere oceans ice sheets and solid earth all of which have different response timescales the trigger for the sea level fluctuations most probably lies with changes in insolation caused by astronomical forcing but internal feedback cycles complicate the simple model of causes and effects