circulation mixing and production of antarctic bottom water abstract the antarctic source of bottom water to the abyssal layer of the world ocean is examined as well as its large scale flow pattern and ultimate entrainment rate into the deep water above we make use of the available high quality station data in the southern ocean to construct bottom maps of neutral density and mean property maps including chlorofluorocarbon cfc for the abyssal layer underneath a selected neutral density surface the maximum density at the sill depth of drake passage is used to distinguish between the voluminous deep water mass that is a continuous component of the antarctic circumpolar current from the relatively denser bottom water originated along the antarctic continental margins based on water density antarctic bottom water aabw is defined here generically to include all volumes of non circumpolar water of antarctic origin over the shelf regime multiple localized sources of specific aabw types contribute to the abyssal layer of the adjacent antarctic basins characteristics of these dense bottom waters reflect closely those observed on the parent shelf water mass spreading paths of newly formed deep and bottom waters over the slope regime and their subsequent oceanic circulation patterns are analyzed on the basis of global property maps for the aabw layer interior mixing and interbasin exchanges of aabw are deduced from mean characteristic curves following the southern streamline of the antarctic circumpolar current outflow and mixing of aabw from the weddell sea to the argentine basin is depicted using density and cfc distributions of two zonal hydrographic lines recirculation and mixing of deep and bottom waters within the weddell gyre are also detailed using a meridional section along the greenwich meridian the strength of all localized sources of aabw combined is estimated by two independent approaches an estimate of the total production rate of aabw is calculated based on the oceanic cfc budget for the aabw layer offshore of the 2500 m isobath the sum of all downslope inputs of well ventilated bottom water types underneath the top isopycnal must account for the measured cfc content in the bottom layer the resulting total aabw production rate is about 8 sv which is a conservative figure that neglects the loss of cfc bearing waters across the top isopycnal in recent years whereas about 9 5 sv is calculated assuming a well mixed bottom layer making use of their transient nature cfc distributions at the top of the aabw layer indicate that more direct and rapid entrainment of cfc rich bottom waters below occurs over localized areas with relatively strong upwelling rates and enhanced vertical mixing a second more ad hoc but independent oceanic mass budget of the bottom layer is also constructed a typical basin wide rate of deep upwelling of 3 10 7 m s 1 requires 10 sv 1 sv 106 m3 s 1 of newly formed aabw to sink down the slope around antarctica we have also formulated a spatial distribution of deep upwelling on the isopycnal at the top of the aabw it is expressed as a combination of wind topographic and turbulent components which in turn are functions of the isopycnal depth bottom depth and bottom layer thickness this non uniform upwelling field yields about 12 sv of aabw exported across the top isopycnal fortuitously the overall average of upward speed at the top isopycnal 3 7 10 7 m s 1 compares well with previous estimates of deep upwelling in the northern basins a series of likely sites for strong vertical entrainment of aabw are clearly identified in the modeled distribution of deep upwelling consonant with the observed cfc distributions on the top isopycnal altogether regions with relatively high upwelling rates 5 10 7 m s 1 occupy only a quarter of the total areal extent of the top isopycnal but they account for as much as 45 of the total vertical transport

two basin filling boxes the convection induced by turbulent buoyant plumes in a rectangular filling box baines and turner 1969 is extended to situations where the lower depths of the box are divided into two basins by a vertical barrier the barrier restricts horizontal spreading and allows the interbasin exchange of water to occur only in the common region above the barrier height one and two plume systems are considered in the two plume case it is assumed that each of the plumes arises from an independent buoyancy source above each basin the resulting two basin circulation is characterized by different stratifications in each basin and by an overflow from one basin into the other the spreading depths of the plumes and ambient stratification depend on the barrier height relative basin sizes and in the two plume case the relative strengths of the two buoyancy fluxes these results may be of relevance to multibasin seas and oceans where the circulation produced by near surface sources of intermediate and deep water is influenced by underwater ridges

effects of strait mixing on ocean stratification the density distribution in the abyssal atlantic ocean suggests that mixing associated with overflows across deep sills may account for substantial amounts of deep mixing estimates of the strait mixing are made from published estimates of the overflows and the difference between antarctic bottom water densities across the vema channel and the romanche fracture zone to demonstrate that the strait mixing is an order of magnitude larger than the abyssal mixing estimated for a standard diffusivity of 1 times 10 ndash 4 m2 s ndash 1

structural analysis and kinematic evolution of the inverted central south celtic sea basin abstract the central south celtic sea basin shows excellent examples of tectonics and sedimentation relationships as evidenced by detailed geological interpretation of a local grid of seismic profiles these relationships together with balanced restored geological cross sections and block diagrams have been used to unravel the post variscan evolution of this part of the celtic sea basin three sedimentary mega sequences separated by two erosional surfaces have been recognized overlying a deformed palaeozoic basement in this area 1 permo triassic jurassic syn rift mega sequence sedimentation of the lowest part of this succession is strongly controlled by extensional faults whereas the rest of the sequence indicates much less fault control lateral extent of these rocks is also controlled by the disposition of the palaeozoic basement which appears as an elevation in the pembrokeshire ridge area where no sedimentation occurs 2 cretaceous post rift mega sequence 3 tertiary post rift mega sequence the cretaceous and tertiary successions are more extensive than permo triassic jurassic sediments covering the central south celtic sea basin and the pembrokeshire ridge the structural framework displayed by the syn rift and post rift sequences is very different thus the general structure beneath the jurassic cretaceous late cimmerian unconformity consists of a wsw ene trending fault system and related folds this resulted from an extensional phase which led to a sub basin compartmentalization of the area and a subsequent inversional event which caused significant reverse movement along previous extensional structures early cretaceous erosion was responsible for an important and unequal denudation the timing of the switch between extension and inversion cannot be determined due to early cretaceous erosion overlying the jurassic cretaceous unconformity cretaceous sediments are slightly deformed by broad anticlines formed during early tertiary mainly as a result of tightening of previous folds the tertiary sequence shows a subhorizontal disposition responsible for the present day smooth bathymetric relief of the south celtic sea basin

controls on the location of compressional deformation on the nw european margin the distribution of cenozoic compressional structures along the nw european margin has been compared with maps of the thickness of the crystalline crust derived from a compilation of seismic refraction interpretations and gravity modelling and with the distribution of high velocity lower crust and or partially serpentinized upper mantle detected by seismic experiments only a subset of the mapped compressional structures coincide with areas susceptible to lithospheric weakening as a result of crustal hyperextension and partial serpentinization of the upper mantle notably partially serpentinized upper mantle is well documented beneath the central part of the southern rockall basin but compressional features are sparse in that area where compressional structures have formed but the upper mantle is not serpentinized simple rheological modelling suggests an alternative weakening mechanism involving ductile lower crust and lithospheric decoupling the presence of pre existing weak zones associated with the properties of the gouge and overpressure in fault zones and local stress magnitude and orientation are important contributing factors

circulation and deep water export at the western exit of the subpolar north atlantic the current system east of the grand banks was intensely observed by world ocean circulation experiment woce array acm 6 during 1993 95 with eight moorings reaching about 500 km out from the shelf edge and covering the water column from about 400 m depth to the bottom more recently a reduced array by the institut fur meerskunde ifm at kiel germany of four moorings was deployed during 1999 2001 focusing on the deep water flow near the western continental slope both sets of moored time series each about 22 months long are combined here for a mean current boundary section and both arrays are analyzed for the variability of currents and transports a mean hydrographic section is derived from seven ship surveys and is used for geostrophic upper layer extrapolation and isopycnal subdivision of the mean transports into deep water classes the offshore part of the combined section is dominated by the deep reaching north atlantic current nac with currents still at 10 cm s 1 near the bottom and a total northward transport of about 140 sv sv 106 m3 s 1 with the details depending on the method of surface extrapolation used the mean flow along the western boundary was southward with the section mean north atlantic deep water outflow determined to be 12 sv below the 27 74 kg m 3 isopycnal however east of the deep western boundary current dwbc the deep nac carries a transport of 51 sv northward below 27 74 kg m 3 resulting in a large net northward flow in the western part of the basin from watermass signatures it is concluded that the deep nac is not a direct recirculation of dwbc water masses transport time series for the dwbc variability are derived for both arrays the variance is concentrated in the period range from 2 weeks to 2 months but there are also variations at interannual and longer periods with much of the dwbc variability being related to fluctuations and meandering of the nac a significant annual cycle is not recognizable in the combined current and transport time series of both arrays the moored array results are compared with other evidence on deep outflow and recirculation including recent models of different types and complexity

compressional deformation at the ocean continent transition in the ne atlantic local zones of compressional deformation spatially coincident with the ocean continent transition occur in the ne atlantic off western iberia on the northern margin of the bay of biscay and in the southern rockall trough the deformation zones are typically broad oceanward facing monoclines several tens of kilometres in width the amount of shortening is small although the structures may also accommodate some strike slip motion deformation peaked during the mid late eocene in biscay off galicia bank and in rockall trough and in the mid miocene off western iberia these deformation pulses were contemporary with the pyrenean and betic orogenies in western europe and may have resulted from structural reorganizations within the evolving orogens driven by changes in plate motion possible mechanisms which might concentrate deformation at the ocean continent transition include slip within serpentinized peridotite underlying the transitional region and reactivation of a pre existing detachment fault within the thinned continental crust our observations may imply that rifted continental margins when reactivated can develop into new sites of plate subduction

evidence for changes in mesozoic and cenozoic oceanic circulation on the south western continental margin of ireland dsdp ipod leg 80

quantitative determination of tertiary sediment supply to the north sea basin sediment supply comprises a major family of regime variables that influence geomorphic surface grade spatial and temporal changes in total sediment supply and sediment texture gravel sand mud ratio will cause reconfiguration of depositional and erosional profiles potentially creating or influencing the sequence stratigraphic framework of the basin sequence grain volume which is defined as the volume of sedimentary grains in an individual stratigraphic sequence total sequence volume minus cement and porosity volume has been quantitatively determined for each of 16 genetic stratigraphic sequences in the north sea basin rates of total sediment supply to the basin in both time and space were then calculated sand grain volume and sand mud ratio were also calculated for each sequence these data define four principal episodes of tertiary sediment supply the most significant episode occurred in the late paleocene and was followed by secondary episodes in the eocene and oligocene a fourth neogene episode extends through the present all episodes correlate to source terrain tectonic pulses related to evolution of the north atlantic basin to intraplate stress changes associated with successive phases of the alpine orogeny or to the late cenozoic epeirogenic uplift of scandinavia the major episodes in turn contain secondary sequence to sequence variations that correspond to changes in spatial or temporal values of one or both of the supply regime variables again most changes closely reflect details within the histories of the principal tectonic phases the history of changing source area relief and resulting topographic grades and related changes in sediment yield into the basin was a principal control on north sea cenozoic sequence development source basin relief in turn was largely determined by regional tectonism

palaeocene oligocene tectonics of nw europe s u m m a r y during the palaeogene in nw europe a gallic subplate was very nearly created this plate was almost entirely bordered by plate boundaries although not of equivalent ages to the n the n atlantic began to open about 56 ma ago the alpine convergent boundary extended southwestwards to the pyrenean subduction zone on the ne side a n british pataeocene early eocene fracture dyke boundary appears to pass southeastwards across the north sea into a lutetian to burdigalian rift system there is an age disparity between the fracturing and nw dyke intrusion in britain and the fracturing and formation of the rhine graben the last dykes in britain ypresian were intruded not long before the important subsidence of the rhine graben earliest lutetian but their causes were different the british dyke fractures propagated southeastwards via the cleveland dyke towards the north sea whereas the rhine graben propagated northwards towards the zuider zee depression however the structures from both sides converged in the sole pit basin in the north sea with the result that a continuous though not coevally originated fracture system developed from nw scotland to the alps during the early tertiary there was a wide range of tectonic activity throughout nw europe fig 1 in nw britain lavas were extruded and plutonic complexes and extensive dyke swarms were intruded in the north sea tufts were deposited as a result of volcanism along the rockall faeroe rift reactivation of faults con trolled magmatism localization of gas fields devolatilization of coal and inversion of basins caused uplift deformation and erosion along the rhine graben doming subsidence and rift propagation took place in association with alka line volcanism and plutonism coevally with the meso alpine compressive deformations that oc curred in the alps faulting controlled sedimen tation patterns during inversion of basins in southern england the english channel northern france and holland old rift faults were reacti vated in the western approaches basin thrust faults formed in the southern bay of biscay contemporaneously with thrusting in the pyre nees and variscan massifs were tilted and uplifted along steep reverse faults the main tectonic activity lasted from about 60 ma to about 30 ma but it was diachronous generally earlier in the nw and later in the se the igneous activity in northern britain was related to the opening of the n atlantic in the late palaeocene but the formation of the rhine graben and the inversion of sedimentary basins in the north sea and near the english channel were caused by major orogenic events in the alpine region in the late eocene to mid oligocene frisch 1981 tectonic phenomena in the north sea provide the link between those in northern britain and those in the rhine graben the aim of this paper is to demonstrate that these movements from the atlantic and alpine sides almost fragmented the lithospheric plates of nw europe during the creation of a gallic sub block an earlier northern boundary from nw scotland to northern germany being transected by a later eastern boundary along the rhine graben

western extension of the iberian european plate boundary during the early cenozoic pyrenean convergence a new model abstract a dense seismic net work allows of drawing the western prolongation of the northern boundary of the iberian plate this early cenozoic deformed boundary is disrupted by two prominent nw se transform faults a kinematic reconstruction with a nw late cretaceous lower eocene motion of the iberian plate is proposed the azores biscay rise is interpreted as a short lived subduction zone whereas king s trough could be a transform fault

structure and development of porcupine seabight sedimentary basin offshore southwest ireland the porcupine basin is a deep sedimentary basin on the continental margin west of ireland all available geologic and geophysical data have been used to interpret the history of the basin it contains up to 8 km of cretaceous and younger sediments underlain by an unknown thickness of jurassic and triassic rock gravity and magnetic anomaly models have been used to investigate the nature of the crust beneath the porcupine basin these models suggest a thinned continental crust rather than the oceanic crust previously proposed by some authors although the nature of a narrow zone of crust 10 km thick in the central southern basin cannot be determined conclusively a high amplitude elongate gravity high associated with a negative magnetic anomaly in the axis of the n rthern porcupine seabight correlates with a volcanic ridge probably of early cretaceous age seen on seismic reflection profiles regional geologic and geophysical studies show that the porcupine basin was originally structured in the early mesozoic as part of a complex northeast to north northeast trending intracontinental rift system extending from the grand banks of newfoundland to the present northwest europe continental shelf the basin can be divided into a sequence of segments bounded by north northeast trending normal faults and northwest trending strike slip faults the degree of extension within the basin decreases northward across each strike slip fault accounting for the overall northward narrowing of the basin the early mesozoic rift fabric of the porcupine basin was reactivated during the early cretaceous when the basin became caught up in the northwest trending rift that later evolved into the n rth atlantic this second phase of extension led to subsidence and the accumulation of extreme thicknesses of cretaceous and younger sediments

topographic control of oceanic flows in deep passages and straits saddle points between neighboring deep ocean basins are the sites of unidirectional flow from one basin to the next depending on the source of bottom water flow in these sites appears to be topographically controlled so the interface between the bottom water and the water above adjusts itself to permit bottom water flow from the basin that contains a source of bottom water into the next examples in the atlantic include flow in the romanche fracture zone the vema channel the ceara abyssal plain the anegada jungfern passage and the discovery gap but there are many more theoretical predictions of volume flux using a method that requires only conductivity temperature depth data archives and detailed knowledge of bathymetry near the saddle point are compared with volume flux estimates using current meters and or geostrophic estimates for seven cases the ratio of prediction to volume flux estimate ranges from 1 0 to 2 7 some ocean straits that separate adjacent seas are also found to critically control bidirectional flows between basins theory of the influence of rotation on such critical flows is reviewed predictions of volume flux in eight cases are compared with ocean estimates of volume flux from traditional methods

structural framework and tectono stratigraphic evolution of the porcupine seabight basin offshore western ireland abstract the porcupine seabight basin is an intra cratonic rift basin which evolved through recurrent episodes of lithospheric stretching structure contour and isopach maps presented here have been constructed following the interpretation of approx 10 000 km of seismic data together with all the available well data this integrated database has allowed the tectono stratigraphic history of the basin to be traced in detail from its earliest inception the basin was initially formed during the carboniferous when up to 3 7 km of autuno carboniferous sediments were deposited on a caledonian and hercynian structured basement late permian and early mesozoic sediments at least 1 km thick are preserved in contiguous grabens and their presence is also inferred within localized sub basins late liassic crustal doming heralded the onset of the final rifting episode and in the north promoted severe erosion and a rapid discharge of clastic sediments rapid subsidence block faulting and magmatism accompanied the deposition of up to 3 5 km of middle upper jurassic sediments in asymmetrical sub basins the transition from stretching to passive subsidence across the jurassic cretaceous boundary in combination with localized inversion abrupt eustatic and environmental changes generated a basin wide unconformity the rift drift transition in the adjacent proto atlantic rift system is recorded in the porcupine seabight basin by voluminous volcanism and a late lower cretaceous unconformity cretaceous sediments are strongly transgressive and up to 6 km thick these were superseded during the early palaeogene by several regressive transgressive cycles before the arrival of an upper slope fauna in the mid middle eocene cenozoic sediments are up to 4 km thick and record the interplay between 1 the location of the basin pn the pyrenean alpine foreland superimposed on the periphery of the icelandic plume and 2 its development as a marginal atlantic shelf region the former is thought to be responsible for eo oligocene faulting subsidence and igneous activity in the north east part of the basin and the latter for unconformities and a change in the style of sedimentation principally due to oceanic circulation changes

when do marginal seas and topographic sills modify the ocean density structure 1 we ask what effect marginal seas at high latitudes have on the abyssal densities and stratification of the oceans although marginal seas are not necessary for the formation of dense abyssal waters topographic sills tend to restrict exchange flows and increase density differences laboratory experiments with a steady state large scale overturning circulation forced by a gradient in surface temperatures or heat fluxes show that a marginal sea and topographic sill influence the abyssal density when the sill depth is less than twice the oceanic thermocline depth the overflow over shallow sills interacts directly with the surrounding thermocline stratification decreasing the abyssal density relative to an ocean with no marginal sea and increasing the density difference between the sea and the ocean experiments show that the effect of the sill depends on the surface boundary conditions and indicate a larger response for conditions approaching a prescribed distribution of temperature rather than of heat flux application of the results to the north atlantic circulation suggests that the greenland scotland ridge is shallow enough to lead to a significant reduction of the density of north atlantic deep water and this is consistent with the conclusions from an analysis of water mass properties the greenland scotland ridge is therefore likely to have a significant effect on the density structure and heat transport in the global oceans

rift zone development around a plume related magma centre on the isle of skye scotland a model for stress inversions using the example of the isle of skye in scotland we investigate the influence of pressure variations in upper crustal magma reservoirs on the development of rift type normal faulting around central volcanoes the regional synmagmatic stress regime is of strike slip type in scotland during the lower tertiary during a prolonged period of overall high pressure in the skye magma reservoir gabbro intrusion stage crustal extension results from the injection of basaltic dykes parallel to the trend of the far field maximum stress during a subsequent period of pressure decrease in the reservoir granites intrusion stage normal faults trending parallel to the dykes are initiated these faults tilt the upper crustal blocks along with the former dyke swarm and associated lava pile finite element modelling shows that a decrease of magma pressure in a circular cavity may lead as in skye to a change from a regional strike slip to a local rift type normal stress regime

exchange through the strait of gibraltar to measure the exchange between the atlantic and mediterranean through the strait of gibraltar an array of current meter moorings was deployed for a year in the strait during 1985 1986 a novel aspect of these measurements is the inclusion of conductivity as well as temperature and pressure sensors on each current meter so that the salinity of the flows could be monitored continuously these salinity measurements determine the water mass characteristics of the flows crossing the sill they allow definition of the 37 psu isohaline as the interface between inflowing fresher atlantic water and outflowing saltier mediterranean water and they enable time series to be developed for the depth of this interface for the upper layer inflow and for the lower layer outflow from these measurements the time averaged outflow of mediterranean water is estimated to be 0 68sv 1sv 1 106m3s 1 and the outflow salinity transport defined to be the outflow times the salinity excess above a basic atlantic water salinity of 36 1 psu is estimated to be 1 50 103m3s 1 1sv 1psu 1 103m3s 1 equivalent to a net evaporation over the mediterranean basin of 52cm y 1 extrapolated measurements of the inflow from current meters generally deployed below 100m depth yield an estimate for the time averaged inflow of 0 93sv which is believed to be unrealistically high in view of the better measured outflow and net evaporation thus a more realistic estimate of the inflow is 0 72sv equal to the sum of the outflow and net evaporation as required by the mass budget for the mediterranean sea such estimates of the exchange are smaller by almost a factor of 2 than previous values for the exchange by lacombe and richez 1982 the exchange across the gibraltar sill is found to be due in nearly equal parts to the mean currents and to the tidal fluctuations the mean currents are smaller than had been expected reaching a peak value of only about 60 cm s 1 in the deep outflow over the sill the tidal exchange is due to a strong correlation over the tidal period between the depth of the interface and the strength of the inflowing currents for the m2 tide at the sill the amplitude of the interface depth is 51 m and the amplitude of the tidal currents is 1 2m s 1 furthermore the inflow and interface depth have similar phases as a consequence the upper layer is deep on the inflowing tide so that a large slug of atlantic water crosses the sill into the mediterranean on the outflowing tide the interface is shallow so that a large slug of mediterranean water crosses the sill into the atlantic similar processes occur for the s2 o1 and k1 tides though the amplitude are smaller in this manner tidal oscillations lead to a time averaged exchange of water masses across the gibraltar sill the inflow and outflow defined to be the instantaneous transports above and below the 37psu isohaline interface exhibit m2 tidal amplitudes of 2 3 sv and 1 3sv respectively thus the tides are large enough to reverse the mean upper layer inflow and lower layer outflow daily averaged inflow and outflow transports exhibit low frequency fluctuations with standard deviations of 0 37sv and 0 22sv respectively such low frequency fluctuations have been shown previously to be associated with barotropic flows through the strait of gibraltar compensating for sea level variations over the mediterranean due to atmospheric pressure fluctuations candela winant and bryden 1989 finally from these measurements there appear to be little fortnightly or annual period fluctuations in the exchange through the strait of gibraltar

intense mixing of the faroe bank channel overflow 1 the continuous swift flow of cold water across the sill of the faroe bank channel the deepest passage from the nordic seas to the north atlantic ocean forms a bottom attached dense plume overflow the amount and distribution of entrainment and mixing that the overflow encounters during its descent influence the ventilation of the deep north atlantic however remain poorly known due to lack of direct measurements using the first direct turbulence measurements we describe the dynamic properties and mixing of the overflow plume as it descends toward the iceland basin the vigorously turbulent plume is associated with intense mixing and enhanced turbulent dissipation near the bottom and at the plume ambient interface but with a quiescent core our measurements show a pronounced transverse circulation consistent with rotating plume dynamics a strong lateral variability in entrainment velocity and a vertical structure composed of order 100 m thick stratified interface and comparably thick well mixed bottom boundary layer with significant transport and entrainment

submaximal exchange between a convectively forced basin and a large reservoir if a sill enclosed basin connected to a large reservoir is suddenly subjected to a de stabilizing surface buoyancy flux it will first mix vertically by turbulent convection before the resulting lateral buoyancy gradient generates a horizontal exchange flow across the sill we present a study which examines the unsteady adjustment of such a basin under continued steady forcing it is shown through theoretical development and laboratory experimentation that two consecutive unsteady regimes characterized by different dynamic balances are traversed as the flow approaches a steady state once established the exchange flow is controlled at the sill crest where it is hydraulically critical in the absence of a lateral contraction the single control at the sill crest allows a range of submaximal exchange states with the flow at the sill being dependent not only on the forcing and geometrical parameters but also on mixing conditions within the basin which are in turn dependent on the sill exchange the sill basin system is therefore strongly coupled although it remains isolated from the external reservoir conditions by a region of internally supercritical flow results from the laboratory experiments are used to demonstrate the link between the forcing and the exchange flow at the sill steady state measurements of the interior mean velocity and buoyancy fields are also compared with previous analytical models

chalk porosity and tertiary uplift western approaches trough sw uk and nw french continental shelves porosities have been derived from sonic logs for the cenomanian maastrichtian chalk of 22 hydrocarbon exploration wells in the western approaches trough although the burial depth of the chalk studied ranges from 40 1500 m below sea bed porosities are all within the range 0 45 the most deeply buried chalk sequences exhibit close to normal porosity depth relations for offshore chalks abnormally low porosities in the remainder of the wells result from burial at greater depth than that presently observed low porosities were preserved during tertiary alpine related uplift of the area for a given well the magnitude of uplift not reversed by subsequent subsidence apparent uplift equals the displacement of its porosity depth relation from the normal relation along the depth axis apparent uplift in the western approaches trough ranges from 0 1 3 km in the western approaches trough chalk porosity data provide evidence of more widespread tertiary uplift than do seismic reflection records alpine related compression and uplift fault bounded basin inversion is apparent only on seismic records in the southern part of the trough brittany and south west channel basins whereas chalk porosity data suggest regional uplift occurred throughout the trough and adjacent highs chalk porosity data were also used to quantify tertiary uplift in the cleethorpes l well of the east midlands shelf the resultant value of 1 1km is considerably greater than that previously derived from shale sonic velocities approximately 0 3 km and slightly less than that based on apatite fission track analysis 1 3 1 7 km

large scale relief development related to quaternary tectonic uplift of a proterozoic paleozoic basement the armorican massif nw france the topography of basements located in intraplate domains has often been interpreted in terms of planation theory by examining the remnants of paleosurfaces in this paper we address the significance of the present day drainage networks that erode such topographies by looking at the relief development on the armorican massif basement northwestern france using digital elevation model dem analysis the topography of this massif is characterized by large scale 250 km relief variations that define high elevation domains heds these domains control the pattern of drainage networks by setting the location of the main drainage divides and the polarity of the regional slopes large scale relief is strongly associated with the existence of scarps along inherited fault zones suggesting that relief development is mainly controlled by tectonics through fault reactivation a surface evolution study shows that drainage networks developed during the quaternary which corresponds to the timing of the tectonic activity which also led to relief development the study of quaternary fluvial erosion through a new method for measuring incision shows that the drainage basins of the heds record greater amounts of base level fall during quaternary times this implies that differential uplift is responsible for the large scale relief development of the armorican massif during the quaternary our study suggests that as seen in active settings the topography of basements corresponds to a dynamic signal between tectonics and erosional processes which can be used for example in the study of intraplate deformation

faroe bank channel overflow 1995 2005 abstract the faroe bank channel fbc is the deepest passage across the greenland scotland ridge and there is continuous overflow of dense water through the channel which provides a substantial contribution to the global thermohaline circulation since november 1995 acoustic doppler current profilers adcps have been moored at the sill of the channel continuously except for short annual servicing periods in addition to this ctd sections have regularly been occupied across the channel and instruments recording temperature and salinity have been moored for short periods these observations demonstrate that the channel due to its small width can be monitored fairly well with only one adcp mooring and they allow the generation of a time series of overflow volume flux for the 1995 2005 period the kinematic overflow flux defined solely from the velocity field was found to have an average value of 2 1 0 2 sv with a seasonal and with inter annual variations of approximately 10 amplitude but with no discernible trend for the whole period the average flux of water with potential density exceeding 27 8 kg m 3 was found to be 1 9 0 3 sv with average properties 0 25 c s 34 93 28 01 kg m 3 for this period no evidence was found for a weakening overflow flux but the salinity of the fbc overflow especially the warmer parts has increased substantially during the period which implies an increased average density on the order of 0 01 kg m 3 previous observations of a helical cross channel circulation are confirmed and may explain the thin pycnocline layer but shear instability induces intensive mixing that puts a lower limit on the layer thickness critical control at one point of the sill cross section rather than friction seems to govern the overflow dynamics and simple layered models can explain much of the observed features as well as the seasonal variation but potential vorticity as defined for a single overflow layer is not conserved a previously suggested 1950 2000 weakening of the fbc overflow which was partly based on a subset of the data presented here is not supported by the full dataset

determining continuous basins across conjugate margins the east orphan porcupine and galicia interior basins of the southern north atlantic ocean abstract the east orphan porcupine and galicia interior basins are several of the most promising basins for hydrocarbon exploration along the rifted continental margins of the southern north atlantic ocean despite having formed at similar geological times the basins exhibit fundamental differences in symmetry crustal thickness sedimentary cover thickness and amount of extension interpretation of seismic reflection and well data was integrated with published 3d grids of depth to basement and moho proxy depth to interpret and restore select seismic reflection lines publicly available kinematic evolution models were also integrated to evaluate and compare the restored seismic reflection lines in a more global regional context interpretation of five seismo stratigraphic units and three tectonostratigraphic megasequences along the east orphan porcupine and galicia interior basins reveals similar seismic character for each unit and comparable tectonic history the structural restoration of the selected lines indicates that evolution sedimentary cover thickness faulting style crustal structure and kinematic evolution of the east orphan and porcupine basins differ significantly a variable and asymmetrical crustal structure is found in the east orphan basin contrasting with the elongated and symmetric porcupine and galicia interior basins rift domain maps of the three basins reveal that they are each underlain by hyperextended crust with possible exhumed mantle in the centre of the porcupine basin based on a holistic analysis of the results obtained the linkage between the east orphan and the porcupine basins seems implausible but rather a contemporaneous relationship is interpreted moreover a potential connection between the galicia interior basin and the porcupine basin during the early to late jurassic is proposed such scenarios imply an oblique and synchronous rifting evolution around the bay of biscay triple junction of the southern north atlantic

eocene deformation on the continental margin sw of the british isles two narrow e w trending zones of late eocene compressional deformation one on the northern margin of the bay of biscay the other in the southern porcupine seabight are described both appear to follow pre existing geological lineaments the deformation is related to the nw movement of iberia between latest cretaceous and late eocene time

early tertiary structural inversion in the stord basin norwegian north sea the stord basin is an east sloping extensional basin that lies to the east of the viking graben in norwegian waters of the northern north sea the basin formed by extension with normal faulting beginning in triassic time and continuing episodically into the middle and late jurassic seismic reflection profiles show that the normal faults which affect the sedimentary section are steeply dipping and approximately planar some of these faults were reactivated in the early tertiary this reactivation reversed earlier accumulated normal displacement and created relative structural highs out of previous structural lows the most obvious evidence of fault reactivation and structural inversion is the presence of hanging wall folds that parallel the strike of reactivated faults the inverted structures of the stord basin are part of a widespread field of early tertiary inverted structures in north west europe we suggest that these structures formed in response to horizontal compression that resulted from the interaction of stress fields set up by alpine continent continent collision and the early opening history of the north atlantic ocean

the flux of dense cold overflow water southeast of iceland abstract from the period commencing midsummer 1990 and lasting for 13 months 13 current meters were deployed on seven moorings at depths between 1000 and 2300 m southeast of iceland 63 09 n 17 18 w to 61 44 n 15 24 w the purpose of the array designated woce acm8 was to measure the overflow of dense water downstream of the source in the faeroe bank channel and downstream of any sources on the iceland faeroe ridge in the depth range 1300 2100 m three of the moorings showed a bottom intensified current that was persistent and directed to the southwest at the other moorings the current was erratic and weak the records were combined to form a transport time series for water denser than 0 27 8 kg m 3 in the direction 240 a mean value of 3 2 0 5 sv was found with considerable variability near a period of seven days but there was no convincing evidence for a seasonal signal the amount of pure norwegian sea water present in the overflow was estimated at 1 6 0 15 sv close to previous determina