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

quartz sand grain shape and other criteria used to distinguish glacial and non glacial events in a marine core from frobisher bay baffin island n w t canada analyses of quartz sand grain shape sediment influx rates and foraminifera define glacial and non glacial episodes in a 9 69 m core from frobisher bay arctic canada five radiocarbon dates on organic matter provide a preliminary core chronology with a basal date of 11 910 yr bp quartz sand grain morphology is measured for samples at seven core levels using 1 fourier shape analysis 2 percentage of grain surface conchoidally fractured samples at 2 0 and 7 5 m are most fractured and have fourier roughness coefficients similar to particles sampled directly from glacier ice these two samples probably represent glacial events in the core major intervals of non carbonate sand influx occur at 9 0 4 5 m and 3 5 1 5 m separated by several thousand years of slower sedimentation detrital carbonate influx rates are relatively high prior to 4 3 m then decline rapidly indicating a shift in sediment provenance from limestones flooring frobisher bay to rafting from far travelled icebergs bio and lithostratigraphic analysis allows definition of five core units 1 an environment similar to today below 8 5 m 2 glacial conditions from 8 5 6 8 m associated with ice proximal to the core site 3 ameliorating conditions from 6 8 to 3 2 m 4 cooler conditions from 3 2 to 0 5 m probably related to increased iceberg flux rather than neoglacial advances of nearby ice caps 5 an environment similar to today from 0 5 m sand grains sampled at 7 5 and 2 0 m whose shapes indicate they are derived from glacier ice lie within the cooler or glacial units defined from foraminiferal analysis this indicates that quantitative measurement of particle surface morphology can provide useful environmental information in studies of marine cores

cenozoic ice rafting history of the central arctic ocean terrigenous sands on the lomonosov ridge the cenozoic ice rafted debris ird history of the central arctic is reconstructed utilizing the terrigenous coarse sand fraction in iodp 302 cores from 0 to 273 meters composite depth this holocene middle eocene quantitative record of terrigenous sand accumulation on the lomonosov ridge along with qualitative information on grain texture and composition confirms the interpretation that ice initiation sea ice and glacial ice occurred 46 ma in the arctic and provides a long term pattern of arctic ice expansion and decay since the middle eocene ird mass accumulation rates range from 0 to 0 13 g cm2 ka in the middle eocene and from 0 to 0 36 g cm2 ka in the neogene ird mass accumulation rate mar maxima in the miocene and pliocene cooccur with either glacial initiation or intensification in the sub arctic the 46 25 ma ird onset in the central arctic slightly precedes the earliest evidence of ice in the antarctic and compares in timing with a 1000 ppm decrease in atmospheric concentrations of co2 the decline of pco2 in the middle eocene may have driven both poles across the temperature threshold that enabled the nucleation of glaciers on land and partial freezing of the surface arctic ocean especially during times of low insolation

intensification of northern hemisphere glaciations in the circum atlantic region 3 5 2 4 ma ice rafted detritus evidence abstract records of ice rafted detritus ird from ocean drilling program sites 644 and 907 in the nordic seas and deep sea drilling program sites 610 and 607 in the north atlantic ocean are used to determine the growth and history of northern hemisphere glaciations spanning the interval from 3 6 to 2 4 ma the records document that the initiation of large scale glaciation in the circum atlantic region occurred stepwise between 3 5 and 2 4 ma with greenland leading the other areas the first major pulse of ird occurs at 3 3 ma suggesting a distinct expansion of the greenland ice sheet progressive increases in ird occur from 3 0 ma with a synchronous ice sheet development between the greenland scandinavian and north american regions starting around 2 72 2 75 ma the regional records of ird correspond to major trends in the oxygen isotope record suggesting a tight connection between the record of global ice volume and evidence for expanding glaciers in the northern hemisphere it appears as if widespread ird distribution occurs when the global ice volume surpasses certain thresholds similar to the late quaternary situation

age constraints on the origin and growth history of a deep water coral mound in the northeast atlantic drilled during integrated ocean drilling program expedition 307 sr isotope stratigraphy provides a new age model for the first complete section drilled through a deep water coral mound the 155 m long section from challenger mound in the porcupine sea bight southwest of ireland is on miocene siliciclastics and consists entirely of sediments bearing well preserved cold water coral lophelia pertusa the 87sr 86sr values of 28 coral specimens from the mound show an upward increasing trend correspond to ages from 2 6 to 0 5 ma and identify a significant hiatus from ca 1 7 to 1 0 ma at 23 6 m below seafloor the age of the basal mound sediments coincides with the intensification of northern hemisphere glaciations that set up the modern stratification of the northeast atlantic and enabled coral growth mound growth persisted throughout glacial interglacial fluctuations reached a maximum rate 24 cm k y ca 2 0 ma and ceased at 1 7 ma unlike other buried mounds in porcupine seabight challenger mound was only partly covered during its growth interruption and growth restarted ca 1 0 ma

oxygen isotope calibration of the onset of ice rafting and history of glaciation in the north atlantic region we report here that dsdp site 552a cored with the hydraulic piston corer on the west flank of rockall bank recovered an undisturbed sequence of alternating white deep sea carbonate oozes and dark coloured layers that are rich in glacial debris oxygen isotope analysis of the sequence together with detailed nannofossil and palaeomagnetic stratigraphy shows that the first major horizon of ice rafting occurred at about 2 4 myr and was preceded by a minor pulse of ice rafting at about 2 5 myr the carbon isotope record shows that the site has been bathed by a water mass of similar characteristics to present day north atlantic deep water at least since 3 5 myr

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

neogene stratigraphy and the sedimentary and oceanographic development of the nw european atlantic margin a regional correlation of neogene stratigraphy has been attempted along and across the nw european atlantic continental margin between mid norway and sw ireland two unconformity bounded successions are recognised these are referred to as the lower and upper neogene successions and have been dated as miocene early pliocene and early pliocene holocene respectively in age their development is interpreted to reflect plate wide tectonically driven changes in the sedimentary oceanographic and latterly climatic evolution of the ne atlantic region the lower neogene succession mainly preserves a record of deep water sedimentation that indicates an expansion of contourite sediment drifts above submarine unconformities within this succession on both sides of the eastern greenland scotland ridge from the mid miocene this is interpreted to record enhanced deep water exchange through the faroe conduit deepest part of the southern gateway and can be linked to compressive inversion of the wyville thomson ridge complex thus a pervasive interconnected arctic north atlantic deep water circulation system is a neogene phenomenon the upper neogene succession records a regional change at about 4 ma in the patterns of contourite sedimentation submarine erosion new depocentres coeval with the onset of rapid seaward progradation of the continental margin by up to 100 km this build out of the shelf and slope is inferred to record a marked increase in sediment supply in response to uplift and tilting of the continental margin associated changes in deep water circulation may be part of an atlantic wide reorganisation of ocean bottom currents glacial sediments form a major component of the prograding shelf margin shelf slope sediment wedges but stratigraphic data indicate that the onset of progradation pre dates significant high latitude glaciation by at least 1 ma and expansive northern hemisphere glaciation by at least 3 ma

the progressive intensification of northern hemisphere glaciation as seen from the north pacific ocean drilling project odp site 882 50 22 n 167 36 e provides the first high resolution grape density magnetic susceptibility carbonate opal and foraminifera planktonic and benthic stable isotopes records between 3 2 and 2 4 ma in the northwest pacific we observed a dramatic increase in ice rafting debris at site 882 at 2 75 ma which is coeval with that found in the norwegian sea suggesting that the eurasian arctic and northeast asia were significantly glaciated from 2 75 ma onwards prior to 2 75 ma planktonic foraminifera 18o records indicate a warming or freshening trend of 4 c or 2 over 80 ka if this is interpreted as a warm pre glacial pliocene north pacific it may have provided the additional moisture required to initially build up the northern hemisphere continental ice sheet the dramatic drop in sea surface temperatures sst 7 5 c at 2 75 ma ended this suggested period of enhanced sst and thus the proposed moisture pump moreover at 2 79 and 2 73 ma opal mass accumulation rates mar decrease in two steps by five fold and is accompanied by a more gradual long term decrease in caco3 mars evidence from the southern ocean odp site 704 indicates that just prior to 2 6 ma there is a massive increase in opal mars the opposite to what is found in the north pacific this indicates that the intensification of northern hemisphere glaciation was accompanied by a major reorganisation of global oceanic chemical budget possibly caused by changes in deep ocean circulation the initiation of northern hemisphere glaciation occurred in the late miocene with a significant build up of ice on southern greenland however the progressive intensification did not occur until 3 5 3 ma when the greenland ice sheet expanded to include northern greenland following this stage we suggest that the eurasian arctic and northeast asia glaciated at 2 75 ma approximately 100 ka before the glaciation of alaska 2 65 ma and 200 ka before the glaciation of the north east american continent 2 54 ma

implications of quartz grain microtextures for onset eocene oligocene glaciation in prydz bay odp site 1166 antarctica abstract this paper presents the results of the scanning electron microscopic sem analysis of quartz grains from a selection of samples at site 1166 ocean drilling program leg 188 drilled site 1166 on the prydz bay continental shelf antarctica to document onset and fluctuations of east antarctic glaciation this site recovered upper pliocene holocene glacial sediments directly above cretaceous through lower oligocene sediments recording the transition from preglacial to early glacial conditions sem analysis of quartz grains at site 1166 was used to characterize the glacial and preglacial sediments by their diagnostic textures angular edges edge abrasion as well as arcuate to straight steps are the most frequent features in glacial deposits the highest frequency of grains with round edges is present in middle late eocene fluvio deltaic sands however angular outlines fractured plates with subparallel linear fractures and edge abrasion indicating glacier influence are also present preglacial carbonaceous mudstone and laminated gray claystone show distinctive high relief quartz grains and some chemical weathering on grain surfaces the results of the microtextural analysis of quartz grains are used to verify some critical periods of ice sheet evolution such as the transition from the east antarctic preglacial to glacial conditions on the continental shelf from middle late eocene to late eocene early oligocene time

scanning electron micrographs of quartz sand grains from cold environments examined using fourier shape analysis abstract the use of grain shape to identify sedimentary environments assumes that grain morphology reflects environmental history scanning electron microscopy permits detailed examination of quartz sand grain surface morphology particle shape from gross form to surface texture is quantified using closed form fourier analysis of whole grain outlines from micrographs of 158 quartz sand grains representing subglacial transport and subaerial weathering in cold environments mean harmonic amplitude spectra and roughness coefficients are calculated and three problems are investigated yielding the following results findings are preliminary due to the relatively small number of grains analyzed 1 two dimensional particle micrographs are a suitable surrogate for three dimensional grain roundness a d texture 2 the particle size of a sand grain sample affects its roundness and texture and only samples of similar size range should be compared 3 fourier shape analysis distinguishes significant differences between basal and englacial grains the latter being more angular and rough in texture this finding is relevant to the definition of debris transport paths through glaciers the technique may also prove useful in the interpretation of marine sediments from cold regions and pre quaternary diamictites of controversial or unknown origin

flux of ice rafted detritus from sea ice in the fram strait abstract a three year particle flux record from the eastern fram strait between greenland and svalbard revealed a rather untypical seasonal flux pattern compared to other particle flux studies from the nordic seas in the eastern fram strait this pattern is characterised by a sudden four to six fold increase of the particle flux in january when no daylight is available to support any biological productivity comparison with sea ice distribution maps led to the conclusion that the sudden increase in the flux is due to ice rafted detritus released from sea ice which originated from the svalbard archipelago and from the northern barents sea detailed grain size analyses of the silt fraction indicated the 10 m fraction of the lithogenic matter to be clearly enriched due to ird input even more important is the observation that lithogenic material 40 m occurs exclusively during the ice rafting event and therefore appears to be a suitable indicator for ird transported on sea ice thus in addition to coarse ird e g 500 m which is mainly derived from icebergs the analysis of fine ird 40 m in deep sea sediments can be used to reconstruct paleo sea ice extensions

inferring maximum geostrophic current velocities in the norwegian greenland sea from settling velocity measurements of sediment surface samples methods application and results abstract critical shear velocities and geostrophic current velocities were calculated from measured grain sizes and settling velocities using a shields type threshold curve of particle movement and assuming bedload transport for particles that were found to be transported by currents because this reconstruction of the current velocities is based on the coarsest transported component that could be recognized in the sediment the resulting current velocities represent a maximum flow speed that was effective during deposition of sediment the shape of the settling velocity distributions identifies the dominant type of deposition that controlled the accumulation of sediment residual well sorted or low energy depositional the resulting pattern of reconstructed maximum geostrophic current velocities in the norwegian greenland sea reflects the known features of present day thermohaline circulation which is influenced by the bathymetry at many places reconstructed current velocities are higher in areas where the cross section of meridional flows is restricted by topographic barriers the distribution of the depositional characters shows that residual and well sorted sediment types are generally associated with higher current velocities in areas of strong geostrophic currents e g fram strait and east greenland continental slope the low energy depositional sediment type is widespread in the basins of the eastern norwegian greenland sea where lower reconstructed maximum current velocities occur the high reconstructed velocities on the spitsbergen bank can be attributed to the disturbance from storm waves in shallower water depths

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

a knowledge data framework and geospatial fuzzy logic based approach to model and predict structural complexity abstract prediction of structural complexity for geohazard and subsurface resource applications requires constraining and interpreting data that are often ambiguous or lack key information moreover structural complexity is a subjective term requiring context for quantification recognizing this a new knowledge data framework and a geospatial fuzzy logic method is developed to represent and predict structural complexity in the subsurface a conceptual model for known structural complexity serves as a basis for associating geospatial representations with types of damage zones a second conceptual model for zones of structural complexity facilitates its prediction notably in areas with limited explicit structural data for each conceptual model a fuzzy logic inference model is developed to incorporate geospatial data and estimate structural complexity potential this approach is demonstrated using several public geospatial datasets within the state of oklahoma explicit fault and earthquake location data were integrated using a fuzzy model of known structural complexity to train topographic lithologic and geophysical proxy datasets applied to a fuzzy model to predict structural complexity and evaluated with receiver operating characteristic analyses and error classification the final model output displayed in maps and cross sections offers comparison with interpreted structural data for validation together these results demonstrate the effectiveness and limitations of the new approach as a screening tool for predicting structurally complex areas

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

deep sea temperature and ice volume changes across the pliocene pleistocene climate transitions earth has undergone profound changes since the late pliocene which led to the development 2 7 million years ago ma and intensification 0 9 ma of large scale northern hemisphere ice sheets recorded as transitions in the benthic foraminiferal oxygen isotope 18ob record here we present an orbitally resolved record of deep ocean temperature derived from benthic foraminiferal magnesium calcium ratios from the north atlantic which shows that temperature variations are a substantial portion of the global 18ob signal the record shows two distinct cooling events associated with the late pliocene lpt 2 5 to 3 ma and mid pleistocene mpt 1 2 to 0 85 ma climate transitions whereas the lpt increase in ice volume is attributed directly to global cooling the shift to 100 000 year cycles at the mpt is more likely to be a response to an additional change in ice sheet dynamics

distinction between sortable silts and aggregated particles in muddy intertidal sediments of the east frisian wadden sea southern north sea abstract in muddy sediments the distinction between sortable silt and aggregated silty clay is important for the understanding of fine particle dynamics because both have different hydraulic properties the wadden sea of the southern north sea is severely depleted in fine grained sediments mainly due to high energy levels along the diked coastline as a result muddy sediments are restricted to a narrow belt along the diked mainland shore in the present study the mechanism by which this mud is deposited and how floc deposition and break up are reflected in the size distribution has been investigated for this purpose surficial sediments from four intertidal nearshore transects were monitored and repeatedly sampled in the course of two years high resolution grain size analyses were performed by an automated settling tube and a sedigraph particle analyser for the sand and mud fractions respectively the grain size frequency distributions of the fine fractions demonstrate that the wadden sea muds are composed of two subpopulations a well sorted coarse silt and an unsorted silty clay population a depletion of grain size around 8 m 7 phi demarcates the grain size boundary between the two populations suggesting that the finer mud population

clay mineral fluctuations and surface textural analysis of quartz grains in pliocene quaternary marine sediments from wilkes land continental rise east antarctica paleoenvironmental significance abstract pliocene quaternary marine sediments from wilkes land continental rise were investigated using clay mineral analysis and quartz grain surface texture observations the studied piston cores were collected during a geophysical and geological survey in the framework of the italian and australian wega project the cores were collected along two transects crossing the channel mound system that characterizes the wilkes land continental rise massive and laminated facies were recognized in these sedimentary sequences the clay mineral assemblages are dominated by illite smectite and chlorite occur in intermediate amounts whereas kaolinite is scarce illite derives from the hinterland of the mertz and ninnis glaciers smectite and kaolinite derive from the ross sea area and they are transported by westward marine bottom currents chlorite is derived both from the adjacent continent and from the victoria land different concentrations of individual clay minerals in the massive and laminated facies are controlled by the interplay between different source areas and the main sedimentary processes glacial and eolian quartz grains prevail in the massive units indicating short transportation and rapid deposition from melting ices with no further significant transport action by marine currents in the laminated facies the high amount of quartz grains affected by high energy subaqueous transport features are related both to turbiditic processes and to bottom current transport

glacimarine slope sedimentation contourite drifts and bottom current pathways on the barra fan uk north atlantic margin the sedimentary record of a 30 m core md95 2006 from the barra fan in the eastern rockall trough has been correlated with high resolution seismic profiles obtained across sediment drifts and large mass flow deposits a series of sediment drifts featuring upslope migrating wavy bedforms has been identified with deposition focussed along topographic steps created by glacigenic debrite lobes the most extensive drift accumulation termed the barra fan drift is observed on the distal fringe of the fan where an 80 m thick sequence of aggrading to migrating sediment waves onlap a mega debrite scarp prior to 26 ka 14c yr and during the late glacial to holocene transition silty muddy contourites were deposited by the northward flowing deep northern boundary current between 26 and 18 ka and around 14 ka contourite deposition was replaced by distal glacimarine sedimentation featuring thin bedded sandy turbidites that were triggered during shelf edge advances of the british ice sheet during the last glacial period sediments accumulated at rates of more than 40 cm ka as a consequence of the high flux of sediments from the shelf margin and winnowing of exposed mass flow deposits by along slope currents in contrast the holocene is represented by a condensed interval of silty sandy mud due to vigorous bottom circulation and a low terrigenous sediment supply seismic seafloor signatures suggest that the present morphology of the barra fan is shaped by two pathways of bottom currents probably both related to the deep northern boundary current one branch of this water mass follows the lower slope causing pronounced erosion on the distal part of the barra fan drift while the other is directed across the debrite topography of the fan bulge

sediment dynamics of a sandy contourite the sedimentary context of the darwin cold water coral mounds northern rockall trough grainsize mineralogy and current meter data from the northern rockall trough are presented in order to characterise the sandy contourite that forms the sedimentary environment of the darwin cold water coral mounds and to investigate the impact of this environment on the mound build up large clusters of small cold water coral mounds 75 m across and 5 m high have been found southwest of the wyville thomson ridge at 900 1 100 m water depth their present day sedimentary environment consists of a subtly sorted sandy contourite elongated ne sw roughly parallel to the contours critical erosional and depositional current speeds were calculated and trends in both the quartz feldspar and foraminifera fractions of the sands show a bi directional fining from bedload erosion dominated sands in the ne to suspension deposition dominated sediments in the sw and towards the s downslope this is caused by a gradual reduction in governing current speed linked to a reduction in slope gradient and by the increasing distance from the current core in the downslope direction no specific characteristics were found distinguishing the mound sediments from the surrounding sands they fit in the overall spatial pattern some mound cores show hints of a fining upward trend overall the mound build up process is interpreted as a result of sediment baffling

cenozoic alongslope processes and sedimentation on the nw european atlantic margin based on studies of sediment accumulations deposited from and erode by alongslope flowing ocean currents on the european continental margin from porcupine ireland to lofoten norway the evolution of the cenozoic paleocirculation was reconstructed as part of the stratagem project there is evidence of ocean current controlled erosion and deposition in the rockall trough in the faeroe shetland channel and on the voring plateau since the late eocene although the circulation pattern remains ambiguous the late palaeogene flow in the rockall trough was almost probably driven by southerly derived tethyan outflow water the extent and strength of any northerly derived flow is uncertain from the early neogene early mid miocene there was a massive regional expansion of contourite drift development both in the north atlantic and in the norwegian greenland sea this was most probably related to the development of the faroe conduit the opening of the fram strait and the general subsidence of the greenland scotland ridge these may have combined to cause a considerable acceleration in the exchange and overflow of deep waters between the arctic and atlantic oceans an early late neogene late early pliocene regional erosional event has been ascribed to a vigorous pulse of bottom current activity most probably the result of a global reorganisation of ocean currents associated with the closure of the central american seaway during the late neogene contourites and sediment drifts developed in deep water basins between units of glacigenic sediments as well as infill of several paleo slide scars these sediments were derived from areas of bottom current erosion as well as from the development of plio pleistocene prograding sediment wedges incorporating the extensive sediment supply derived from shelf wide ice sheets presently a profound winnowing prevails along the shelf and upper slope due to the inflowing currents of atlantic water depocentres of sediments derived from the winnowing are located locally in lower slope embayments and in slide scars

pliocene pleistocene ice rafting history and cyclicity in the nordic seas during the last 3 5 myr a continuous 3 5 myr ird record was produced from ocean drilling program odp site 907 a timescale based on magnetic polarity chrons oxygen isotope stratigraphy for the last 1myr and orbital tuning was developed the record documents a stepwise inception of large scale glacial cycles in the nordic seas region the first being a marked expansion of the greenland ice sheet at 3 3 ma a second step occurred at 2 74 ma by an expansion of large scale ice sheets in the northern hemisphere ice sheet variability around the nordic seas was tightly coupled to global ice volume over the past 3 3 myr between 3 and 1 ma most of the variance of the ird signal is in the 41 kyr band whereas the last 1 myr is characterized by stronger 100 kyr variance the gamma ray porosity evaluator grape density record is closely linked with ird variations and documents sub orbital variability resembling the late quaternary heinrich bond cycles

the evolution of the porcupine and rockall basins offshore ireland the geological template for carbonate mound development the margins of the deep water sedimentary basins west of ireland contain a number of large clusters provinces of spectacular carbonate mounds and build ups these basins have a complex development history involving the interplay of rift tectonics thermal subsidence igneous activity and oceanographic variations the porcupine and rockall basins both rest upon thin continental crust the consequence of major rift episodes in permo triassic late jurassic and early cretaceous times phases of volcanism occurred in the early cretaceous and especially in the early cenozoic fluid flow within the basins is likely to have been controlled by the overall basin geometry and by the distribution and linkage of permeable strata with fault systems stratal surfaces and unconformities a number of regional unconformities controlled by both basin tectonic and regional oceanographic effects can be mapped and correlated throughout the porcupine and rockall basins the youngest of these unconformities c10 early pliocene can be traced throughout much of the nw european atlantic margin it forms the horizon on which virtually all the carbonate mounds in the basins develop suggesting a geologically instantaneous mound nucleation and growth event although the control on their development is uncertain the mound clusters show a spatial association with lithified strata buried contourite and deltaic deposits slope failure features and with the basin margins analysis of these relationships points to a combination of geological and oceanographic processes controlling mound initiation and growth

sources and modes of terrigenous sediment input to the chilean continental slope abstract physical chemical and mineralogical properties of a set of surface sediment samples collected along the chilean continental slope 21 44 s are used to characterise present day sedimentation patterns and sediment provenance on the chilean margin despite the presence of several exceptional latitudinal gradients in relief oceanography tectonic evolution volcanic activity and onshore geology the present day input of terrigenous sediments to the chilean continental margin appears to be mainly controlled by precipitation gradients and source rock composition in the hinterland general trends in grain size denote a southward decrease in median grain size of the terrigenous corganic caco3 and opal free fraction which is interpreted as a shift from aeolian to fluvial sedimentation this interpretation is supported by previous observations of southward increasing bulk sedimentation rates north south trends in sediment bulk chemistry are best recognised in the iron fe and titanium ti vs potassium k and aluminium al ratios of the sediments that most likely reflect the contribution of source rocks from the andean volcanic arc these ratios are high in the northernmost part abruptly decrease at 25 s and then more or less constantly increase southwards to a maximum at 40 s

carbonate budget of a cold water coral mound challenger mound iodp exp 307 abstract cold water coral ecosystems represent a worldwide distributed carbonate factory which is so far not considered in global carbonate budget estimations the herein presented study evaluates the carbonate budget of a complete cold water coral mound sequence from challenger mound belgica mound province porcupine seabight sw offshore ireland drilled during iodp expedition 307 reaching back to the late pliocene versus background sediment derived calcite dominated carbonate cores from adjacent drift deposits were examined for comparison studies challenger mound which developed in a fast growth phase unit m1 2 7 to 1 6 ma and a slower growth phase or mound decline unit m2 0 8 ma until today separated by a so called mound crisis displays increased carbonate accumulation rates for both phases 17 3 g cm 2 ka for unit m1 and 5 7 g cm 2 ka for unit m2 compared to adjacent drift deposits but only about 33 to 40 wt of the carbonate is derived from corals bulk sedimentation rates of on and off mound deposits suggest a decline of challenger mound since the onset of drift deposition in the area about 1 2 ma ago yet total carbonate accumulation rates as well as hemipelagic background sediment derived carbonate accumulation rates from challenger mound unit m2 still exceed the carbonate accumulation rates of the adjacent drift deposits the selective enrichment of background sediment derived carbonate by a factor of 2 0 in a cwc mound is herein observed for the first time this might be caused by the different hydrodynamic behaviour and slower settlement of marine fluff rich in calcareous detritus compared to siliciclastic sediments and its effective baffling by the coral framework and or the active catch of the calcareous plankton by the corals the carbonate accumulation rates of challenger mound are about 4 to 12 of the carbonate accumulation rates of tropical shallow water reefs but exceeds the carbonate accumulation rates of continental slopes by a factor of 3 9 to 11 8 the carbonate production for the entire belgica mound province is estimated with 3 2 10 3 t a for unit m1 and 1 0 10 3 t a for unit m2

ocean circulation and iceberg discharge in the glacial north atlantic inferences from unmixing of sediment size distributions variability in iceberg discharge and deep ocean circulation in the north atlantic during the last glacial period is inferred from the grain size distribution and trace elemental composition of terrigenous sediments in a deep sea core taken on reykjanes ridge south of iceland end member modeling of the grain size distributions is used to unmix the signals of varying bottom current speed and iceberg discharge the size distribution within the silt fraction appears to be influenced by both factors based on th sc la relationship we established that during the ice rafted detritus events continental material of likely greenlandic origin increased to 87 and that bottom current derived material contains to 40 mid oceanic ridge fines probably of icelandic origin our results have important implications for the use of silt grain size as an indicator for paleocurrent speed in the glacial north atlantic we show that reconstructions of variations in bottom current speed based on the raw grain size data are opposite to inferences from the unmixed record the latter indicates that deep water convection decreased during periods of enhanced iceberg discharge which is in general agreement with paleoceanographic reconstructions of the north atlantic

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

high resolution bathymetry of the eastern slope of the porcupine seabight the topography of the eastern margin of the porcupine seabight was surveyed in june 2000 utilizing swath bathymetry the survey was carried out during rv polarstern cruise ant xvii 4 as part of the geomound project the main objective was to map and investigate the seafloor topography of this region the investigated area contains a variability of morphological features such as deep sea channels and giant mounds the survey was planned and realized on the basis of existing data so as to guarantee the complete coverage of the margin in order to achieve a resolution of the final digital terrain model dtm that meets the project demands data processing was adjusted accordingly the grid spacing of the dtm was set to 50 m and an accuracy better than 1 of the water depth was achieved for 96 of the soundings

therese mound a case study of coral bank development in the belgica mound province porcupine seabight high resolution seismic profiles swath bathymetry side scan sonar data and video imageries are analysed in this detailed study of five carbonate mounds from the belgica mound province with special emphasis on the well surveyed therese mound the selected mounds are located in the deepest part of the belgica mound province at water depths of 950 m seismic data illustrate that the underlying geology is characterised by drift sedimentation in a general northerly flowing current regime sigmoidal sediment bodies create local slope breaks on the most recent local erosional surface which act as the mound base no preferential mound substratum is observed neither is there any indication for deep geological controls on coral bank development seismic evidence suggests that the start up of the coral bank development was shortly after a major erosional event of late pliocene quaternary age the coral bank geometry has been clearly affected by the local topography of this erosional base and the prevailing current regime the summits of the coral banks are relatively flat and the flanks are steepest on their upper slopes deposition of the encased drift sequence has been influenced by the coral bank topography sediment waves are formed besides the coral banks and are the most pronounced bedforms these seabed structures are probably induced by bottom current up to 1 m s large sediment waves are colonised by living corals and might represent the initial phase of coral bank development the biological facies distribution of the coral banks illustrate a living coral cap on the summit and upper slope and a decline of living coral populations toward the lower flanks the data suggest that the development of the coral banks in this area is clearly an interaction between biological growth processes and drift deposition both influenced by the local topography and current regime

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

palaeocurrent reconstruction sediment and thorium focussing on the iberian margin over the last 140 ka sedimentological data in particular sediment grain size from core md95 2040 2465 m water depth and a nearby core omii 9k 1833 m water depth presently under the influence of lower north atlantic deep water and deep intermediate water respectively have been used to reconstruct changes in the vigour of near bottom water flow on the iberian margin the pattern of the palaeocurrent index indicates faster flow during the warm periods and slower in cold this also holds in the younger dryas but there is an added effect of brief collapse of the circulation in termination 1b due to meltwater input the cold periods are generally characterised by elevated clay percentage terrigenous material 2 m diameter and overall sediment accumulation fluxes in comparison warm periods of higher flow have lower depositional flux and a tendency to silt terrigenous material 2 63 m dominance consistent with the higher flow speed and suppression of clay deposition this is in contrast with a recent 230thxs based study of two cores md95 2040 and 2039 j thomson et al earth planet sci lett 165 1999 255 270 which concluded that increased glacial sediment and th focussing was caused by stronger currents the crucial factor is that the controlling speed is that of the flow at the depositional site rather than that of the erosional or transporting flow to the site high glacial maximum fluxes of carbonate 6 g cm 2 ka 1 are largely composed of fine 63 m non coccolith material suggesting a significant detrital component it is proposed that the sediment and th arrive on the lower slope via different routes sediment down slope in bottom nepheloid layers and turbidity currents th scavenged from the water column by organic matter and are rapidly mixed on the bed removal of this material from a large area and its deposition in a small one adjacent to oporto seamount together with a small amount of direct down slope supply accounts for the properties of the deposits allowance for erroneous fluxes due to possible coring expansion stretching of the upper part of md95 2040 does not invalidate these conclusions

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

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

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

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

comparison of laser grain size analysis with pipette and sieve analysis a solution for the underestimation of the clay fraction classically the grain size of soil and sediment samples is determined by the sieve method for the coarse fractions and by the pipette method based on the stokes sedimentation rates for the fine fractions results from the two methods are compared with results from laser diffraction size analysis which is based on the forward scattering of monochromatic coherent light from a point of view of laboratory efficiency the laser sizing technique is far superior accuracy and reproducibility are shown by measurements on certified materials it appears that laser grain size measurements of certified materials correspond very well with the certificated measurements tests were also done on a set of randomly selected sediments of fluvial aeolian and lacustrine origin except for the 2 m clay fraction there is a coarsening of the mean diameter of one to two size classes 0 25 caused by the non sphericity of the particles the platy form of the clay particles induces considerable differences eight size classes between pipette and laser measurements the 2 m grain size defined by the pipette method corresponds with a grain size of 8 m defined by the laser particle sizer for the studied sediments using a higher grain size level for the clay fraction when laser analysis is applied enables workers in the geological and environmental field to compare classical pipette analysis with a laser sizing technique

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

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

origin glacial interglacial responses and controlling factors of a cold water coral mound in ne atlantic 1 recent deep ocean exploration has revealed unexpectedly widespread and diverse coral ecosystems in deep water on continental shelves slopes seamounts and ridge systems around the world origin and growth history of these cold water coral mounds are poorly known owing to a lack of complete stratigraphic sections through them here we show high resolution oxygen isotope records of planktic foraminifers from the base to the top of challenger mound southwest of ireland which was drilled during integrated ocean drilling program expedition 307 challenger mound began to grow during isotope stage 92 2 24 million years ago ma immediately after the onset of northern hemisphere glaciation and the initiation of modern stratification in the northeast atlantic mound initiation was likely due to reintroduction of mediterranean outflow water mow and ensuing development of a density gradient with overlying northeastern atlantic water neaw where organic matter was prone to be stagnated and fueled the coral ecosystem coral growth continued for 11 glacial interglacial cycles until isotopic stage 72 1 82 ma with glacial siliciclastic input from the continental margin after a long hiatus that separates the lower mound and the upper mound coral growth restored for a short time in isotope stages 19 18 0 8 0 7 ma in which sediments were either eroded or not deposited during a full glacial stage the development pattern of the water mass interface between mow and neaw might have changed because of the fluctuations of the mow production which is responsible for the amplitude in ice volume oscillations from the low amplitude 41 ka cycles for the lower mound to the high amplitude 100 ka cycles for the upper mound the average sedimentation and caco3 production rates of the lower mound were evaluated 27 cm ka and 31 1 g cm2 ka respectively

the relationship of heinrich events and their european precursors over the past 60 ka bp a multi proxy ice rafted debris provenance study in the north east atlantic high resolution multi proxy records of ice rafted debris ird flux and provenance in the ne atlantic detail the development variability and decline of marine margins of the last glacial circum north atlantic ice sheets coupled lithological identification sr and nd isotopic composition and 40ar 39ar ages of individual hornblende grains reduce ambiguity as to ird potential source region allowing clear differentiation between laurentide lis icelandic and british bis ice sheet sources the icelandic and bis are collectively referred to as the nw european ice sheet nweis a step wise increase in the flux of ird to the core site at 26 5 ka bp documents bis advance and glaciation of ireland millennial scale variability of the bis at a 2 ka periodicity is inferred through clusters of pulsed ird fluxes throughout the late glacial 26 5 10 ka bp combination of these european ird events and the 7 ka periodicity of lis instability is thought to account for quasi synchronicity of the nweis and lis ird pulses at heinrich event h 2 and h1 previously suggested to represent the possible involvement of the nweis in the initiation of h events furthermore the lack of extensive nweis marine margin is inferred prior to h3 31 5 ka bp such that no european precursor event is associated with either h5 or h4 this suggests that precursor events were not directly implicated in the collapse of the lis and the persistent instabilities of the bis that are clustered at a 2 ka periodicity are incompatible with the concept that both h events and their precursors are independent responses to a common underlying trigger

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

an application of scanning electron microscopy of quartz sand surface textures to the environmental diagnosis of neogene carbonate sediments finestrat basin south east spain the finestrat basin 25 km ne of alicante contains a poorly understood sequence of neogene sediments that lack an indigenous fauna study of the surface textures of euhedral quartz grains probably derived by first cycle weathering from an underlying triassic mudstone diapir provides new data on the depositional environment of the basin the possible influence of alluvial fans is recorded by mechanical breakage features in these non glaciated sediments the distribution and abundance of chemical etch pits suggest their diagenetic origin following non marine deposition while the density and abundance of mechanically induced v shaped pits seems typical of fluvial and low energy littoral environments the presence of silica precipitated during transport such as silica globules suggests a silica rich transport medium and a depositional environment that was not highly alkaline in combination with independent sedimentological evidence these data suggest that the sediments collected in a lake after derivation by rivers and alluvial fans from the diapir it is concluded that the abundance and superposition of features must be noted for each grain in order to yield useful results and that the mechanisms acting on each grain be deduced before attempting to identify specific environments

exploring the structure of the mid pleistocene revolution with advanced methods of time series analysis the mid pleistocene climate transition is a complex global change leading to late pleistocene ice ages with increased mean ice volume and dominant 100 ka cycle a thorough understanding of this transition demands quantitative investigations in the time and frequency domains and in the stochastic domain three methods of time series analysis are presented which have been adapted for this purpose they are tested by means of predefined artificial time series and applied to benthic oxygen isotope d18o records which serve as ice volume indicator results are as follows a the time dependent mean shows an increase of 0 35 vs pdb from 942 to 892 ka b evolutionary spectral analysis reveals an abrupt in crease of 100 ka cycle amplitude at approximately 650 ka c probability density function exhibits a bifur cation behavior at approximately 725 ka these find ings point to a multiple transition from a more linear climate system to a strong nonlinear system the signif icant lead of the transition in mean in relation to the 100 ka amplitude change and bifurcation is left open for explanation

muddled or mixed inferring palaeoclimate from size distributions of deep sea clastics abstract one of the outstanding problems of palaeoclimate reconstruction from physico chemical properties of terrigenous deep sea sediments stems from the fact that most basin fills are mixtures of sediment populations derived from different sources and transported to the site of deposition by different mechanisms conventional approaches to palaeoclimate reconstruction from deep sea sediments do not distinguish between provenance and dispersal related variations and therefore often fail to recognise the true significance of variations in sediment properties we formulate a set of requirements that each proposed palaeo environmental indicator should fulfil and focus on the intrinsic coupling between grain size and chemical composition a critical review of past achievements in grain size analysis serves to introduce a conceptual model of spatio temporal grain size variation based on dynamic populations each dynamic population results from a characteristic combination of production and transport mechanisms that corresponds to a distinct subpopulation in the data analysed the mathematical statistical representation of the conceptual model can be obtained by means of the end member modelling algorithm emma applications of the model to several ocean basins are discussed as well as methods to examine the validity of grain size based palaeoclimate reconstructions palaeoclimate reconstructions of a high and low latitude basin illustrate the common degree of complexity of deep sea grain size records

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

surface textures of turbidite sand grains laurentian fan and sohm abyssal plain surface textures of quartz grains have been examined from five samples from the laurentian fan and sohm abyssal plain representing varied transport distances and power of the depositing turbidity current the grains retain their primary irregular shape derived from glacial erosion and glacial surface textures are preserved in dish shaped depressions these features have been superimposed by a slight rounding of edges and an abundance of collision induced markings particularly mechanical v forms the most intense current modification of this sort occurs in mid wisconsinan or earlier sands that have been transported over 1000 km to the distal sohm abyssal plain by turbidity currents collision textures probably develop during grain flow on the steep continental slope delicate resedimented shelf foraminifera are preserved in the same turbidites and most have been transported exclusively in suspension

grain surface textures of late wisconsinan sands from the canadian beaufort shelf abstract a semiquantitative analysis of quartz grain surface textures is used to interpret the transport history of sands from beaufort sea drillcores within a sample up to six types of grain are recognized a highly angular grains with fresh conchoidal fractures b angular grains with conchoidal fractures modified by solution precipitation and edge abrasion c irregularly shaped rounded grains with mechanical v marks and linear grooves d well rounded grains with dish shaped concavities and upturned plates and e type c and d grains with large fresh fractured surfaces although most grams probably have glacial origins only types a and b have surface features indicative of glacial processes other grains show modification by high energy subaqueous transport type c probably in a littoral environment or by wind action type d later fracturing of the grains type e may have occurred in the littoral zone or by frost action the relative proportions of each grain type are used tentatively to distinguish sands deposited in fluvial or channel mouth environments from sands of the littoral zone of a wave dominated delta the presence of aeolian grains in several assemblages provides evidence for a drier environment in the yukon mackenzie delta region during the late wisconsinan

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

changes in sedimentation patterns of the nordic seas region across the mid pleistocene sediment core data from a site in the central nordic seas suggest that during the mid pleistocene revolution mpr this region has experienced a systematic change in its overall oceanographic and climatic conditions first distinct changes occur around 1 ma and reveal the beginning of a shift in climate periodicity from stronger 41 ka cycles towards a dominant 100 ka cyclicity most pronounced are the changes at the study region between about 700 and 420 ka when parallel to the evolution of large 100 ka cycles a distinct decrease in the input of magnetic particles is observed also for this interval an intensification of glacial conditions is indicated by a marked increase in the accumulation rates of ice rafted debris ird during marine isotope stages 16 and 12 the observed mid pleistocene changes were likely due to a gradual shift from a more zonal behavior of the coupled ocean atmosphere system at high northern latitudes prior to the mpr to more meridionality thereafter a shift that affected both the patterns of ocean circulation and ice drift in the nordic seas region accordingly the subsequent mpr related changes of these two climate parameters should be responsible for the decrease in the concentration of magnetic particles at the study site after 700 ka with the mid pleistocene strengthening of the nordic heat pump the mode of deep water production and the flow of bottom currents changed at high northern latitudes which led to an increased export of magnetic particles from basaltic source regions around greenland and iceland into the subpolar north atlantic consequently less magnetic material was deposited in the nordic seas than before the mpr when water mass exchange between the nordic seas and the north atlantic was more restricted in addition the large late pleistocene expansions of glacial ice caps on the eastern margin of the nordic seas led to a major change in the composition of ird material in the study area with more material originating from the scandinavian and barents sea shelf regions which ultimately caused a dilution of the magnetic signal

coarse grained terrigenous sediment deposition on continental rise drifts a record of plio pleistocene glaciation on the antarctic peninsula sediment drifts on the continental rise are located proximal to the western side of the antarctic peninsula and recorded changes in glacial volume and thermal regime over the last ca 15 m y at ocean drilling program odp site 1101 leg 178 which recovered sediments back to 3 1 ma glacial interglacial cyclicity was identified based on the biogenic component and sedimentary structures observed in x radiographs magnetic susceptibility and lithofacies descriptions glacial intervals are dominated by fine grained laminated mud and interglacial units consist of bioturbated muds enriched in biogenic components from 2 2 to 0 76 ma planktonic foraminifera and calcareous nannofossils dominate in the interglacials suggesting a shift of the antarctic polar front apf to the south near the drifts prior to 2 2 ma cyclicity cannot be identified and diatoms dominate the biogenic component and high percent opal suggests warmer conditions south of the apf and reduced sea ice over the drifts analyses of the coarse grained terrigenous fraction pebbles and coarse sand from sites 1096 and 1101 record glaciers at sea level releasing iceberg rafted debris ird throughout the last 3 1 m y analyses of quartz sand grains in ird with the scanning electron microscope sem show an abrupt change in the frequency of occurrence of microtextures at similar to 1 35 ma during the late pliocene to early pleistocene the population of quartz grains included completely weathered grains and a low frequency of crushing and abrasion suggesting that glaciers were small and did not inundate the topography debris shed from mountain peaks was transported supraglacially or englacially allowing weathered grains to pass through the glacier unmodified during glacial periods from 1 35 0 76 ma glaciers expanded in size the hid flux was very high and dropstones have diverse lithologies conditions resembling those at the last glacial maximum lgm have been episodically present on the antarctic peninsula since similar to 0 76 ma quartz sand grains show high relief fracture and abrasion common under thick ice and the ird flux is low with a more restricted range of dropstone lithologies

a 300 kyr record of aridity and wind strength in southwestern africa inferences from grain size distributions of sediments on walvis ridge se atlantic abstract the terrigenous fraction of sediments recovered from walvis ridge se atlantic ocean reveals a history of southwestern african climate of the last 300 kyr end member modelling of a data set of grain size distributions n 428 results in three end members the two coarsest end members are interpreted as eolian dust the third end member as hemipelagic mud the ratio of the two eolian end members reflects the eolian grain size and is attributed to the intensity of the se trade winds trade winds were intensified during glacials compared to interglacials changes in the ratio of the two eolian end members over the hemipelagic one are interpreted as variations in southwestern african aridity late quaternary southwestern african climate was relatively arid during the interglacial stages and relatively humid during the glacial stages owing to meridional shifts in the atmospheric circulation system during glacials the polar front shifted equatorward resulting in a northward displacement of the zone of westerlies causing increased rainfall in southwestern africa the equatorward shift of the polar front is coupled with an increase of the meridional pressure gradient leading to enhanced atmospheric circulation and increased trade wind intensity

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

sortable silt and fine sediment size composition slicing parameters for palaeocurrent speed and palaeoceanography fine sediment size 63 ixm is best measured by a sedimentation technique which records the whole size distribution repeated size measurement with intermediate steps of removal of components by dissolution allows inference of the size distribution of the removed component as well as the residue in this way the size of the biogenic and lithogenic noncarbonate fractions can be determined observations of many size distributions suggest a minimum in grain size frequency curves at 8 to 10 ixm the dynamics of sediment erosion deposition and aggregate breakup suggest that fine sediment behavior is dominantly cohesive below 10 1xm grain size and noncohesive above that size thus silt coarser than 10 ixm displays size sorting in response to hydrodynamlc processes and its properties may be used to infer current speed silt that is f mer than 10 ixm behaves in the same way as clay 2 xm useful parameters of the distribution are the 10 63 ixm mean size and the percentage 10 63 ixm in the fine fraction we cannot use size distributions to distinguish the nature of the currents therefore to infer water mass advection speeds i e the mean kinetic energy of the flow ku regions of high eddy kinetic energy ke must be avoided at the present such abyssal regions lie under the high surface k e of major current systems gulf stream kuroshio agulhas antarctic circmpolar current and brazil falldand currents in the argenthe basin this is probably a satisfactory guide for the pleistocene with regard to the carbonate subfraction of the size spectrum size modes due to both cocco iths and foramlnlferal fragments can be recognized and analyzed with the boundary between them again at about 10 lm the flux of less than 10 lm carbonate at pelagic sites above the lysocline is another candidate for a productivity indicator

continental ice in greenland during the eocene and oligocene the eocene and oligocene epochs approximately 55 to 23 million years ago comprise a critical phase in earth history an array of geological records supported by climate modelling indicates a profound shift in global climate during this interval from a state that was largely free of polar ice caps to one in which ice sheets on antarctica approached their modern size however the early glaciation history of the northern hemisphere is a subject of controversy here we report stratigraphically extensive ice rafted debris including macroscopic dropstones in late eocene to early oligocene sediments from the norwegian greenland sea that were deposited between about 38 and 30 million years ago our data indicate sediment rafting by glacial ice rather than sea ice and point to east greenland as the likely source records of this type from one site alone cannot be used to determine the extent of ice involved however our data suggest the existence of at least isolated glaciers on greenland about 20 million years earlier than previously documented at a time when temperatures and atmospheric carbon dioxide concentrations were substantially higher