coherence of western boundary pressure at the rapid wave array boundary wave adjustments or deep western boundary current advection this study investigates the coherence between ocean bottom pressure signals at the rapid climate change programme rapid west atlantic variability experiment wave array on the western north atlantic continentalslope includingthewoodsholeoceanographicinstitutionlinew highlycoherentpressuresignals propagate southwestward along the slope at speeds in excess of 128 m s 21 consistent with expectations of barotropic kelvin like waves coherent signals are also evidenced in the smaller pressure differences relative to 1000 m depth which are expected to be associated with depth dependent basinwide meridional transport variations or an overturning circulation these signals are coherent and almost in phase for all time scales from 3 6 years down to 3 months coherence is still seen at shorter time scales for which group delay estimates are consistent with a propagationspeedofabout1 m s 21 over990 kmofcontinentalslopebutwithlargeerrorboundsonthespeed this is roughly consistent with expectations for propagation of coastally trapped waves though somewhat slower than expected a comparison with both eulerian currents and lagrangianfloat measurements shows that the coherence is inconsistent with a propagation of signals by advection except possibly on time scales longer than 6 months

diatom productivity peak and increased circulation during latest quaternary alboran basin western mediterranean abstract diatoms were studied quantitatively in six latest quaternary 70 kyr b p to recent piston cores from the westernmost mediterranean the alboran basin and the atlantic region immediately to the west of the straits of gibraltar the atlantic cores completely lack diatoms in the alboran basin diatoms are common from late stage 3 27 5 kyr b p to termination ib 9 kyr b p and in recent core tops but are absent in the other latest quaternary intervals maximum accumulation of diatoms and highest abundance of species normally in sediments associated with increased productivity occurred during the latest quaternary deglaciation in the first phase of termination i 14 8 kyr b p in the modern alboran basin a region of high biological productivity occurs immediately east of the gibraltar straits this high productivity results from upwelling associated with the interaction between the atlantic inflow and the bottom topography near the spanish coast the upwelled nutrient rich waters are then advected to the east and southeast by the surficial anticyclonic gyral circulation late quaternary variations in diatom abundance are considered to reflect changes in this upwelling intensity with highest diatom abundances inferred to result from increased upwelling associated with an intensification of the anticyclonic gyral circulation highest inferred upwelling rates occurred during the first phase of latest quaternary deglaciation it is possible that an intensification of circulation within the mediterranean basin as a whole occurred from late stage 3 to mid termination i because widespread hiatus formation has been reported at this time in the straits of sicily due to an increase in the formation of intermediate waters diatoms were not preserved in other latest quaternary intervals due to insufficient productivity to counterbalance their dissolution

ekman transport along the galician coast northwest spain calculated from forecasted winds 1 ekman transport is studied close to the galician coast by means of forecasted winds provided by meteogalicia from november 2001 to october 2004 three different coastal zones are identified western coast from mino river to cape finisterre middle coast from cape finisterre to cape ortegal and northern coast from cape ortegal to cape penas in addition to existence of long term variations the periodicity of the transport signal is characterized by an annual component 365 days a seasonal fluctuation 50 to 80 days and a timescale related to passing storms 15 20 days although the periodicity of the signal is similar at the three zones owing to external meteorological forcing the ekman transport is modulated by the presence of the coast in such a way that seasonal patterns vary in intensity and direction along the coast thus the autumn winter pattern is characterized by high transport at the northern and middle coast pointing landward perpendicular to the shoreline and moderate values at the western coast pointing landward and oblique to the shoreline on the other hand the spring summer pattern is characterized by high transport at the western coast pointing seaward perpendicular to the shoreline the same orientation is observed at the middle coast although with a lower magnitude finally ekman transport at the northern coast points landward and oblique to the shoreline the different transport orientations are shown to be responsible for the upwelling probability variation along the coast

diatoms as hydrographic tracers example from bering sea sediments variations in the distribution of diatom species in surface sediments mirror distinct hydrographic regimes on the bering shelf spring salinity fronts divide the water column into four zones with different vertical structures and different productivity patterns four assemblages of diatoms can be distinguished in sediments underlying the zones

arctic ocean circulation patterns revealed by grace abstractmeasurements of ocean bottom pressure obp anomalies from the satellite mission gravity recovery and climate experiment grace complemented by information from two ocean models are used to investigate the variations and distribution of the arctic ocean mass from 2002 through 2011 the forcing and dynamics associated with the observed obp changes are explored major findings are the identification of three primary temporal spatial modes of obp variability at monthly to interannual time scales with the following characteristics mode 1 50 of the variance is a wintertime basin coherent arctic mass change forced by southerly winds through fram strait and to a lesser extent through bering strait these winds generate northward geostrophic current anomalies that increase the mass in the arctic ocean mode 2 20 reveals a mass change along the siberian shelves driven by surface ekman transport and associated with the arctic oscillation mode 3 10 reveals a mass dipole with mass decreasing

variability of upwelling off nw africa during the latest quaternary diatom evidence diatom abundance and species composition were quantitatively studied in two latest quaternary 130 ka to the present sequences from the continental margin of northwest africa off this region coastal upwelling is well developed under the influence of the ne trade winds variations in diatom abundance in these cores are inferred to represent changes caused by varying degrees of the upwelling fertility times of high productivity are marked by high relative frequencies of chaetoceros while low productivity is marked by the dominance of aulacoseira granulata upwelling increased during glacial episodes isotopic stages 2 4 and 6 relative to isotopic stages 1 and 5 during the late holocene primary productivity levels are similar to those for stage 5 but in the early holocene upwelling intensities seem to have been weaker than today the paleoproductivity reconstruction based on the diatom record is supported by paleoproductivity estimations based on the organic carbon content of the sediments sarnthein et al 1987a

the observed north atlantic meridional overturning circulation its meridional coherence and ocean bottom pressure abstractanalyses of meridional transport time series from the rapid climate change meridional overturning circulation rapid moc array at 26 n and from argo float and altimetry data at 41 n reveal that at semiannual and longer time scales the contribution from the western boundary dominates the variability of the north atlantic meridional overturning circulation moc defined as the transport in the upper 1000 m of the ocean because the variability of the western boundary contribution is associated with a geostrophic overturning it is reflected in independent estimates of transports from gradient of ocean bottom pressure obp relative to and below 1000 m on the continental slope of the western boundary at three nominal latitudes 26 39 and 42 5 n time series of western meridional transports relative to and below 1000 m derived from the obp gradient or equivalently derived from the transport shear profile exhibit approximately the same phase relationship between 26 and 39 42 5 n as the wes

assessment of geochemical and micropaleontological sedimentary parameters as proxies of surface water properties in the canary islands region abstract the canary islands region occupies a key position with respect to biogeochemical cycles with the zonal transition from oligotrophic to nutrient rich waters and the contribution of saharan dust to the particle flux we present the distribution of geochemical proxies toc carbonate 15n 13corg c n ratio and micropaleontological parameters diatoms dinoflagellates foraminifera pteropods in 80 surface sediment samples in order to characterise the influence of coastally upwelled water on the domain of the subtropical gyre results of the surface sediment analyses confirmed the high biomass gradient from the coast to the open ocean inferred from satellite data of surface chlorophyll or sst the distribution of total dinoflagellate cysts the planktic foraminifera species globigerina bulloides the diatom resting spore chaetoceros spp and toc concentration coincided well with the areas of strong filament production off cape ghir and cape yubi the warm water planktic foraminifera globigerinoides ruber white the diatom nitzschia spp and the 15n values showed the opposite trend with high values in the open ocean factor analyses on the planktic foraminifera species distribution indicated three major assemblages in the canary islands region that represent the present surface water conditions from the upwelling influenced region via a mixing area towards the subtropical gyre

a wind driven isopycnic coordinate model of the north and equatorial atlantic ocean 1 model development and supporting experiments numerical approximations to the dynamic equations are given which allow basin size ocean circulation models formulated in isopycnic coordinates to accommodate variable bottom topography and irregular coastlines emphasis is placed on computational economy through the use of a split explicit time integration scheme on the proper formulation of the advection and coriolis terms in the momentum equation in case of strongly varying layer thickness and on the correct estimation of the horizontal pressure gradient force in grid boxes truncated by steep bottom slopes the algorithms are tested in a series of two and three layer double gyre experiments in cases of steady forcing leading to a steady circulation we are able to reproduce the expected motionless final state in coordinate layers that are below the direct influence of the wind forcing this includes layers intersecting topographic obstacles a long term 25 30 year vacillation tentatively associated with the outcropping of isopycnals along the edge of the cyclonic gyre in a steadily forced model is documented the paper forms the basis for a subsequent study in which circulation features obtained in a realistic north atlantic setting will be discussed

the explosive diversification of the diatom genus chaetoceros across the eocene oligocene and oligocene miocene boundaries in the norwegian sea abstract eocene to middle miocene stratigraphic changes in species richness abundance and valve size of chaetoceros resting spores in the norwegian sea dsdp site 338 were investigated in order to understand past productivity and paleoenvironmental changes in upwelling regions as a result drastic resting spore events were recognized in a 6 myr interval across the eocene oligocene boundary eo event the oligocene miocene boundary om event and in the early middle miocene emm event the eo event was characterized by explosive diversification at both the morpho generic and specific levels an increase in abundance and a decrease in valve size from the upper eocene through the lowest oligocene the om event was defined by a two fold increase in species richness during the emm event spore abundance decreased rapidly and species richness and valve size decreased gradually these changes may indicate changes in the nutrient supply especially in upwelling regions the increased species richness suggests a change from a stable water column with a constant nutrient supply in the eocene to an unstable one with a sporadic nutrient supply by increased vertical mixing in the oligocene based on evaluation of the ecologic differences between dinoflagellate cysts and chaetoceros resting spores the role of main primary producer might have switched from dinoflagellates and or nannoplankton in the eocene to diatoms especially chaetoceros in the oligocene in the norwegian sea increased resting spore species richness during the om event may show that environmental changes such as global cooling and nutrient mixing led to a diversification of the spore producing genus chaetoceros the emm event might have been affected by changes in paleoceanographic conditions perhaps a decrease in nutrient supply this study presents the first paleoceanographic analysis using not only the total resting spore abundance but also the abundances of individual species and establishes the value of spore taxonomy and diatom analysis including spores

boundary wave communication of bottom pressure and overturning changes for the north atlantic 1 the relationship between changes in sea surface height bottom pressure and overturning is explored using isopycnal model experiments for the north atlantic changes in high latitude forcing are communicated rapidly over the basin through boundary wave propagation along the continental slope involving a hybrid mixture of kelvin and topographic rossby waves as well as spreading more slowly through advection along the western boundary this wave communication leads to coherent signals in sea surface height and bottom pressure variability extending for several thousand kilometers along the continental slope the model results are in broad agreement with altimetric diagnostics and the patterns only alter in detail with the realism of the topography the adjustment in bottom pressure is directly linked to a change in overturning since west east contrasts in bottom pressure are associated with a zonal integral in the meridional geostrophic flow correlation patterns reveal that temporal changes in overturning are primarily connected to the vertical contrast in bottom pressure across the shelf and continental slope along the western boundary

influence of a layered liquefiable soil on seismic site response using physical modeling and numerical simulation abstract in this research the seismic behavior of liquefiable sub layers and their effect on seismic ground response have been evaluated the initial patterns of seismic response along the height of a layered liquefiable soil are extracted using a series of shaking table testing the sub layers of the shaking table models were built with different densities and the models were subjected to specific record motions of varying intensity afterwards in order to use compatible constitutive model in numerical analysis a series of effective stress numerical models have been employed while the results were verified adequately with the results of the shaking table test dafalias manzari model was utilized in the current study as a suitable constitutive model the effect of depth and height of liquefiable sub layers is discussed from different perspectives as it relates to attenuation or amplification of the seismic ground surface response consequently experimental and numerical studies of this research have shown that contrary to the usual view the thicker and shallower liquefiable sub layers can effectively reduce the intensity of seismic waves and earthquake induced forces however the thinner liquefiable sublayers at greater depths could increase seismic intensity and reduce settlement

shelf fjord exchange driven by coastal trapped waves in the arctic in this article we show that the class of low frequency subinertial waves known as coastal trapped waves ctws are a significant agent of water volume exchange in a west svalbard fjord and by extension more widely along the west svalbard and east greenland margins where similar conditions prevail we show that ctws generated by weather systems passing across the sloping topography of the shelf break propagate into the fjord steered by the topography of an across shelf trough the ctws have characteristic periods of 2 days set by the passage time of weather systems phase speeds and wavelengths vary seasonally by a factor of two according to stratification winter summer values are cp 0 25 ms 1 0 5 ms 1 and 40 km 84 km ctw induced flow velocities in excess of 0 2 ms 1 at 100 m water depth are recorded observationally scaled ctw model results allow their explicit role in volume exchange to be quantified of the estimated exchange terms estuarine exchange is weakest qest 0 62 103 m3s 1 followed by barotropic tidal pumping qbt 2 5 103 m3s 1 with intermediary exchange dominating qi 2 4 104 m3s 1 oscillatory flows display greatest activity in the 1 5 day period band and ctw activity is identified as the likely source of variability in the 40 60 h period band within that band intermediary exchange driven by ctws is estimated as qictw ave 0 82 104 m3s 1 an exchange rate exceeding both barotropic and estuarine exchange estimates

productivity and paleoceanographic implications on the tore seamount iberian margin during the last 225 kyr foraminiferal evidence foraminifera counts and climatic assemblages from the tore seamount are used to approach the glacial and interglacial changes in temperature and productivity on the iberian margin over the last 225 kyr chronostratigraphy is based on globigerinoides ruber and globigerina bulloides oxygen isotopes and supported by foraminifera and carbonate stadial fluctuations foraminifera indicate cooling from late interglacial stage 5 to the beginning of termination i ti neogloboquadnna pachyderma s reflects cold conditions during glacial stages 4 2 in contrast glacial stage 6 is dominated by warmer n pachyderma d and dutertrei and a restricted arctic assemblage past sea surface temperatures confirm the general cooling reaching 4 3 c simmax 28 during stage 2 multiple productivity proxies such as organic carbon productivity related foraminifera and 13c constrain the changes observed a productivity increase occurs after interglacial stage 5 enhanced from late glacial stage 3 to ti present day satellite detected phytoplankton plumes off portugal would have accounted in the past glacial stages for the general productivity increase over the tore on top of this welldefined peaks of organic carbon and productivity related foraminifera correspond with heinrich events 1 4

late pleistocene holocene paleoenvironmental changes inferred from the diatom record of the ulleung basin east sea sea of japan abstract the diatom floral record from two piston cores 00ghp 01 and 00ghp 07 taken from the southwestern margin of the ulleung basin east sea sea of japan reveals a series of well defined changes in glacio eustatic sea level and paleoceanographic conditions during the late pleistocene holocene six assemblage zones and two barren zones in 00ghp 01 and four assemblage zones in 00ghp 07 are erected respectively on the basis of frequency of variations in and occurrences of biostratigraphically significant diatom species all assemblage zones have been strongly influenced by the tsushima warm current twc the twc has an important affect on controlling the distribution and composition of diatom flora which in turn reveal the history of the twc in this area the distribution pattern of diatoms in the diatom assemblages reveals sea surface temperature and salinity affected by the sediments type and terrigenous material input diatom temperature td values show that the site of 00ghp 01 in the ulleung basin has been influenced by a relatively enhanced twc twice during the deposition of lowermost and uppermost intervals a relatively weak twc was recorded in the middle interval since the latest pleistocene the diatom assemblages of 00ghp 07 represent an apparently continuous late quaternary record spanning the last glacial maximum bolling allerod younger dyras and holocene high abundance of a low salinity coastal water diatom paralia sulcata may reflect the influx of the east china sea water through the korean strait to the east sea sea of japan during the last glacial maximum the sea level was low enough that selected basin with shallow sills along the margin of the east sea sea of japan became isolated from the pacific ocean salinity also decreased due to increased freshwater input from rivers draining the surrounding lands the density stratified water column may have prevented vertical mixing and resulted in anoxic bottom water conditions

determining north atlantic meridional transport variability from pressure on the western boundary a model investigation 1 in this paper we investigate the possibility of determining north atlantic meridional transport variability using pressure on the western boundary focusing on the 42 n latitude of the halifax wave array we start by reviewing the theoretical foundations of this approach next we present results from a model analysis both statistical and dynamic that demonstrate the feasibility of the approach we consider how well we can quantify the meridional transport variability at 42 n given complete knowledge of bottom pressure across the basin and to what degree this quantification is degraded by first ignoring the effect of intervening topography and then by using only bottom pressure on the western boundary we find that for periods of greater than 1 year we can recover more than 90 of the variability of the main overturning cell at 42 n using only the western boundary pressure provided that we remove the depth averaged boundary pressure signal this signal arises from a basin mode of bottom pressure variability which has power at all time scales but that does not in truth have a meridional transport signal associated with it and from the geostrophic depth independent compensation of the ekman transport an additional benefit of the removal of the depth averaged pressure is that this high frequency ekman signal which is essentially noise as far as monitoring the meridional overturning circulation for climatically important changes is concerned is clearly separated from other modes

effects of spatial variability on liquefaction induced settlement and lateral spreading abstractnonlinear dynamic numerical simulations of infinite slopes are used to examine the effects of spatial variability in penetration resistances on liquefaction induced settlement and lateral spreading for gently sloping ground and to develop guidance on selecting representative properties for uniform models simulation results for models having uniform properties uniform models are compared to results for models having spatially correlated gaussian random field property distributions stochastic models results are presented for sets of stochastic model realizations and a set of ground motions scaled to a range of peak ground accelerations computed responses and ground deformations settlements and lateral displacements for these uniform and stochastic models are used to identify representative properties as a percentile of the stochastic distributions for which the uniform models produce reasonable agreement with the median of the stochastic model responses the effects of the scales of fluct

shallow marine sediment cores record climate variability and earthquake activity off lisbon portugal for the last 2000 years abstract sea surface temperature sst river discharge and biological productivity have been reconstructed from a multi proxy study of a high temporal resolution sedimentary sequence recovered from the tagus deposition center off lisbon portugal for the last 2000 years sst shows 2 c variability on a century scale that allows the identification of the medieval warm period mwp and the little ice age lia high iron fe and fine sediment deposition accompanied by high n alkane concentrations and presence of freshwater diatoms during the lia 1300 1900 ad science 292 2001 662 suggest augmented river discharge whereas higher total alkenone concentrations point to increased river induced productivity during the mwp 550 1300 ad science 292 2001 662 larger mean grain size and low values of magnetic susceptibility and concentrations of fe n alkanes and n alcohols are interpreted to reflect decreased runoff at the same time increased benthic and planktonic foraminifera abundances and presence of upwelling related diatoms point to increased oceanic productivity on the basis of the excellent match found between the negative phases of the north atlantic oscillation nao index and the intensified tagus river discharge observed for the last century it is hypothesized that the increased influx of terrigenous material during the lia reflects a negative nao like state or the occurrence of frequent extreme nao minima during the milder few centuries of the mwp stronger coastal upwelling conditions are attributed to a persistent positive nao like state or the frequent occurrence of extreme nao maxima the peak in magnetic susceptibility centered at 90 cm composite core depth ccd is interpreted as the result of the well known 1755 ad lisbon earthquake the lisbon earthquake and accompanying tsunami are estimated to have caused the loss of 39 cm of sediment 355 years of record most of the lia and the instantaneous deposition of a 19 cm sediment bed

significance of the paralia sulcata fossil record in palaeoenvironmental reconstructions of the se asia marginal seas over the last glacial cycle

mesoscale distribution patterns of diatoms in surface sediments as tracers of coastal upwelling of the galician shelf nw iberian peninsula abstract diatom distribution on continental shelf sediments from the upwelling area off galicia nw iberian peninsula has been determined in 78 surface sediment samples three well defined biofacies with a close relationship to upwelling influence along the coast have been distinguished from both the absolute diatom abundances in the sediments and assemblage diatom composition based on multivariate statistics rias baixas and the shelf areas south and north to cape finisterre chaetoceros resting spores as well as highest absolute diatom content in the sediments are recorded in the highly productive rias baixas where most of the primary production is due to intense upwelling phenomena the western shelf south of cape finisterre is characterized by thalassionema nitzschioides and thalassiosira cf leptopus both taxa reflect a minor influence of upwelling conditions and productivity related to more persistent nutrient input due to coastal outwelling rather than upwelling minor and patchy upwelling conditions as well as lower productivity in the northern shelf are characterized by the lowest absolute diatom content in the sediments and the important increase in relative abundance of the resistant paralia sulcata caution must be taken in the interpretation of paralia sulcata dominated biofacies in downcore studies since a juxtaposition of discontinuous upwelling conditions and dissolution effects may be the factors responsible for the relative increase on the taxon in the sediments the obtained results show the extent and limitations of fossil diatom distribution in surface sediments as tracers of regional coastal upwelling conditions in continental shelves where the existence of extensive areas of relict sediments and transported diatoms may mask the present day upwelling signal of the photic zone

diatom assemblages as upwelling indicators in surface sediments off portugal abstract diatom abundance and assemblage composition have been determined for 169 surface sediment samples from the portuguese margin an area where seasonal upwelling occurs each year from april to october absolute diatom abundance distribution patterns reflect the more intense and or persistent and more homogeneous upwelling north of the nazare canyon the position of the inner upwelling front south of lisbon and the eastern continuation of the coastal upwelling jet along the algarve coast distribution patterns of species and of ecologically defined groups meroplanktonic oceanic freshwater and marine benthic support the hypothesis that diatom species and assemblages are good indicators of the changing character of the upwelling system small species of the genus thalassiosira occur in areas of persistent upwelling where availability of nutrients is more constant and or higher paralia sulcata ehr cleve is an abundant species whose mean cell diameter increases as nutrient availability decreases resting spores mainly of chaetoceros ehrenberg record the position of the zone where higher variability occurs the inner upwelling front

leaky slope waves and sea level unusual consequences of the beta effect along western boundaries with bottom topography and dissipation abstractcoastal trapped waves ctws carry the ocean s response to changes in forcing along boundaries and are important mechanisms in the context of coastal sea level and the meridional overturnin

centrifuge modeling of prefabricated vertical drains for liquefaction remediation drainage methods for liquefaction remediation have been in use since the 1970s and have traditionally included stone columns gravel drains and more recently prefabricated vertical drains this paper presents the results from a dynamic centrifuge test designed to evaluate the performance of a liquefiable site treated with prefabricated vertical drains the centrifuge model consisted of gently sloping untreated and treated liquefiable soil deposits overlain by a clay crust the model was subjected to multiple shaking events that included both recorded earthquake acceleration time histories and sinusoidal input motions comparisons of deformations and excess pore water pressures in the untreated and treated areas showed that drains were effective in expediting the dissipation of excess pore water pressures and reducing deformations however depending on the characteristics of the input ground motion the peak excess pore pressures in the treated area were not always substantially smaller than in the untr

identifying the roles of the ocean and atmosphere in creating a rapid equatorial response to a southern ocean anomaly recent research has identified a rapid ocean response mechanism to salinity anomalies in the southern ocean using an idealised ocean model here we examine the relative importance of the ocean and atmosphere in creating an equatorial response to a southern ocean anomaly using a coupled climate model with realistic bottom topography and land relief two rapid teleconnections are produced from a high latitude anomaly an equatorial ocean response can be seen after 30 days the mechanism producing this response is shown to rely on barotropic and baroclinic oceanic wave propagation a second atmospheric response is seen in the northern hemisphere nh high latitudes driven by atmospheric rossby waves the ocean quickly responds to the atmospheric signal above it resulting in sea surface temperature anomalies at nh high latitudes

increased upwelling off portugal during the last glaciation diatom evidence abstract quantitative studies have been carried out on opaline microfossils and diatom assemblage composition and preservation in two latest quarternary 100 ka to p d cores from the continental slope of portugal the sites are located in an area of modern summer coastal upwelling created by northerly trade winds the spatial patterns and intensity of this upwelling system are accurately recorded by the diatom abundances and taxonomic composition in the surface sediments the diatom record in these sequences indicates that coastal upwelling intensity was similar to present day during late holocene interglacial stage 3 and late stage 5 higher during stage 2 and lower in the early holocene paleoproductivity estimates are consistent with the diatom accumulation rates from stage 3 to the recent this indicates that both the diatom and the organic carbon content of the sediments mainly reflect the biological productivity in the euphotic zone

the sea level budget along the northwest atlantic coast gia mass changes and large scale ocean dynamics sea level rise and decadal variability along the northwestern coast of the north atlantic ocean are studied in a self consistent framework that takes into account the effects of solid earth deformation and geoid changes due to large scale mass redistribution processes observations of sea and land level changes from tide gauges and gps are compared to the cumulative effect of gia present day mass redistribution and ocean dynamics over a 50 year period 1965 2014 gia explains the majority of the observed sea level and land motion trends as well as almost all interstation variability present day mass redistribution resulting from ice melt and land hydrology causes both land uplift and sea level rise in the region we find a strong correlation between decadal steric variability in the subpolar gyre and coastal sea level which is likely caused by variability in the labrador sea that is propagated southward the steric signal explains the majority of the observed decadal sea level variability and shows an upward trend and a significant acceleration which are also found along the coast the sum of all contributors explains the observed trends in both sea level rise and vertical land motion in the region as well as the decadal variability the sum of contributors also explains the observed acceleration within confidence intervals the sea level acceleration coincides with an accelerating density decrease at high latitudes

wind driven upwelling in the vicinity of cape finisterre spain observations and numerical simulations of upwelling along the galician coast of spain during april 1982 are presented in situ measurements include shipboard determinations of hydrographic and biological parameters from a grid of stations covering the continental shelf from cape finisterre to ria de vigo sea level data from vigo and la coruna and wind stress estimates derived from the ship winds and from surface pressure charts sea surface temperature information and pigment concentration information have been obtained from a sequence of satellite images from the noaa 7 advanced very high resolution radiometer and the nimbus 7 coastal zone color scanner respectively since the cape finisterre sector of the iberian peninsula is characterized by an abrupt change in coastline orientation wind driven upwelling can occur in that region over a 270 range of wind direction these data document the evolution of upwelling and the resultant coastal circulation in response to two wind events that occurred over a 10 day period salient features of the circulation include a southward coastal jet and a northward flow further offshore along the western coast numerical simulations of the coastal currents the vertical excursion of a density interface from a static equilibrium position and coastal sea level are conducted using a wind patch characterized by constant direction and negative curl the simulations show that during these wind events the greatest upwelling will occur either at cape finisterre or along the northern coast as was observed in this case and as has been reported by others it is suggested on the basis of the analysis of the sea level records and on the numerical simulations that wave disturbances propagate northward along the coast at a speed of 120 160 km day finally it is speculated that much of the organic material formed during upwelling events north of the cape finisterre is advected out to sea northwest of the cape

the biogeography of major diatom taxa in southern ocean sediments 2 open ocean related species diatoms from 228 southern ocean core top sediment samples were examined to determine the geographic distributions of 32 major diatom species taxa preserved in the sediments of three zonally distinct regions sea ice open ocean and the tropical subtropical in the first of three papers 14 species taxa occurring in the region where sea ice covers the ocean surface on an annual basis are geographically documented comparisons are drawn between the diatom abundances on the sea floor sea ice parameters annual duration and concentration in february and september and february sea surface temperature such parameters are commonly used in reconstructing past oceanographic conditions in the sea ice and open ocean zones analysis of the geographic patterns and sea surface parameter correlations reveals species specific distributions regulated primarily by sea ice coverage and sea surface temperature which support the use of diatom remains for the estimation of these past seasurface environmental parameters comparison with reliable accounts of the 14 species from the sediments or plankton also provides the first glimpses into species specific ecology and habitat linkages d 2005 elsevier b v all rights reserved

a numerical model study of the effects of interannual time scale wave propagation on the predictability of the atlantic meridional overturning circulation we investigate processes leading to uncertainty in forecasts of the atlantic meridional overturning circulation amoc a climate model is used to supply initial conditions for ensemble simulations in which members initially have identical ocean states but perturbed atmosphere states baroclinic transports diverge on interannual timescales even though the ocean is not eddy permitting interannual fluctuations of the model amoc in the subtropical gyre are caused by westward propagating rossby waves divergence of the predicted amoc with time occurs because the waves develop different phases in different ensemble members predominantly due to differences in eastern boundary windstress curl these windstress fluctuations communicate with interior ocean transports via modifications to the vertical velocity and the vortex stretching term dw dz consequently errors propagate westwards resulting in longer predictability times in the interior ocean compared with the eastern boundary another source of divergence is transport anomalies propagating along the gulf stream and other boundary currents the propagation mechanism seems to be predominantly advection by mean currents and we show that the arrival of westward propagating waves can trigger development of these anomalies the mean state of the amoc has a small effect on interannual predictability in the subtropical gyre most likely because eastern boundary windstress curl predictability is not strongly dependent on the state of the amoc in the subtropics eastern boundary windstress curl was more predictable at 45 degree sign n when the amoc was in a strongly decreasing state but unlike at 30 degree sign n no mechanism was found linking windstress curl fluctuations with deep transports

the fate of diatom valves in the subantarctic and polar frontal zones of the southern ocean sediment trap versus surface sediment assemblages abstract an array of deep ocean sediment traps was initiated in 1997 within the australian sector of the southern ocean and serviced annually for over a decade the subantarctic site is ongoing as part of the southern ocean time series here we expand on previous findings obtained from the shallow traps 1000 m depth in the polar frontal zone pfz and subantarctic zone saz by examining the chemical composition and diatom assemblages collected by sediment traps deployed at bathypelagic depths in the pfz 1500 m depth years 1997 1998 1999 2000 and 2003 2004 and saz 2000 and 3800 m year 1999 2000 additionally the diatom assemblages of the surface sediments below the traps were analyzed to document how the seasonal signal is recorded in the sedimentary record analysis of the changes of the bsi poc ratios with depth at both sites confirms previous work suggesting that the decoupling between si and c cycles in the southern ocean is not different from other biogeochemical provinces of the world s ocean comparison of the seasonal flux pattern registered by the traps indicates that the diatom assemblages in the sediments of the antarctic zone and pfz mainly represent the summer period in contrast the assemblages found in the sediments of the saz are a reflection of the spring and summer months a period characterized by a larger variability in chemical and physical parameters the strong correlation between the poc fluxes and the relative abundance of a group of diatom species mainly pseudo nitzschia and small fragilariopsis in the pfz traps suggest that there is an intimate relationship between the development of these species and the poc pulses to the deepest layers of the water column in this region interestingly analysis of the diatom assemblages in the surface sediments reveals that the strong dissolution in the sediment water interface removed the signal of these carbon sinkers from the sedimentary record leaving the sediment assemblage enriched in heavily silicified species

diatom distributions in northern north pacific surface sediments and their relationship to modern environmental variables abstract the quantitative analysis of diatom assemblages preserved in 52 samples from the bellingshausen and the amundsen seas provides the first comprehensive view on the distribution of diatoms in surface sediments of the eastern and central pacific sector of the southern ocean on a latitudinal transect along 120 w diatom valve accumulation rates ar reach maximum values 8 10 108 valves m 2 yr 1 in a zone extending over ca 900 km between the antarctic polar front and the maximum average winter sea ice extent and exceed those ars obtained from an eastern transect along 90 w by one order of magnitude lowest diatom concentrations 1 3 106 valves g 1 were encountered in sediments of the sea ice zone affected by winter and summer sea ice the accumulation rate pattern of the most abundant diatom fragilariopsis kerguelensis 50 abundance in 47 samples mirrors the pattern of the total diatom valve ar and the biogenic silica bsi ar making f kerguelensis the major contributor to the bsi preserved at the sea floor relative abundances of diatom species and species groups were statistically compared with a selection of environmental variables such as the mean summer sea surface temperature and salinity mean annual surface nutrient concentration nitrate phosphate silicon mean annual water column stratification mixed layer depth in summer and mean summer and winter sea ice concentrations polynomial canonical redundancy analysis rda revealed the biogeographic distribution of diatom species had the strongest relationship with summer sea surface temperature ssst out of the nine tested environmental variables this relationship accounted for 69 6 of the total variance of the diatom distribution with 29 7 explained by the first gradient significantly correlated to ssst with r2 0 941 and 15 6 explained by the second gradient correlated to both summer and winter sea ice and silicon concentration azpeitia tabularis hemidiscus cuneiformis and roperia tesselata were associated with warmer water conditions 4 c whereas fragilariopsis curta f separanda f rhombica and thalassiosira gracilis were correlated with cold ssst confirming these environmental relationships is crucial for the development of reference data sets used in quantitative estimations of palaeoclimatic and palaeoceanographic conditions with statistical methods this new data set represents the first modernised treatment of diatom remains from the se pacific ocean and generally supports the use of a circum polar database for the determination of summer sst sea ice and potentially biogenic silica distribution of the southern ocean back into the late quaternary

construction of the adjoint mit ocean general circulation model and application to atlantic heat transport sensitivity we first describe the principles and practical considerations behind the computer generation of the adjoint to the massachusetts institute of technology ocean general circulation model gcm using r giering s software tool tangent linear and adjoint model compiler tamc the tamc s recipe for fortran line by line generation of adjoint code is explained by interpreting an adjoint model strictly as the operator that gives the sensitivity of the output of a model to its input then the sensitivity of 1993 annual mean heat transport across 29on in the atlantic to the hydrography on january 1 1993 is calculated from a global solution of the gcm the kinematic sensitivity to initial temperature variations is isolated showing how the latter would influence heat transport if they did not affect the density and hence the flow over 1 year the heat transport at 29on is influenced kinematically from regions up to 20 o upstream in the western boundary current and up to 5 o upstream in the interior in contrast the dynamical influences of initial temperature and salinity perturbations spread from as far as the rim of the labrador sea to the 29on section along the western boundary the sensitivities calculated with the adjoint compare excellently to those from a perturbation calculation with the dynamical model perturbations in initial interior salinity influence meridional overturning and heat transport when they have propagated to the western boundary and can thus influence the integrated east west density difference our results support the notion that boundary monitoring of meridional mass and heat transports is feasible

variability in the deep western boundary current local versus remote forcing 1 horizontal velocity temperature and salinity measurements from the line w array for the period 2004 2008 show large changes in the water mass structure and circulation of the deep western boundary current dwbc fluctuations in the flow with periods from 10 to 60 days are bottom intensified signals most likely associated with topographic rossby waves trw a fraction 15 of the dwbc transport variability is caused by gulf stream rings and meanders these flow anomalies are surface intensified and fluctuate at frequencies lower than the trw interannual variability in the velocity field appears to be related to changes in the hydrographic properties the dominant mode of variability is characterized by an overall freshening cooling a potential vorticity pv increase in the deep labrador sea water dlsw and a pv decrease in the overflow water ow the variability in the flow associated with these property changes is not spatially homogeneous offshore water depths larger than 3500 m changes in the velocity are in phase with pv changes in the ow a decrease in the ow pv is accompanied by an increase in the southward negative transport conversely variations of the inshore flow are in phase with changes in the dlsw pv increasing pv and decreasing transport this trend true for most of the record reverses after the winter of 2007 2008 a sudden decrease of the dlsw pv is observed with a corresponding intensification of the flow in the inner dwbc as well as a northward shift in the gulf stream axis

siliceous sedimentary record of the last 280 kyr in the canary basin nw africa abstract siliceous microfossils were quantified in four sedimentary sequences off northwest africa in order to disclose the productivity story of the last 280 kyr three sediment cores retrieved along an e w profile at about 29 n geob4240 geob4241 and geob4242 and one core geob4216 from the highly productive area off cape ghir in the canary island region at 29 n along all but the most offshore sequences geob4242 coincidence of high diatom accumulation rates dar and high abundances of chaetoceros spores the upwelling related species indicate glacial stages isotope stages is 4 and 2 as more productive than the interglacial intervals is5 and holocene the dar in the coastal area of the canary basin during is2 is of the same order of magnitude 10 8 valves cm 2 kyr 1 reported for cape blanc and one order of magnitude higher than reported for the iberian margin the deviation observed between the offshore higher dar at is3 and 6 and the coastal diatom records higher dar at is2 and 4 may be a reflection of local productivity generated by wind input of nutrients and advection from coastal sources the occurrence of dar spikes at the timing of some heinrich events seems to support the hypothesis of productivity maxima associated with the presence of meltwater off nw africa as previously proposed by other authors

diatoms in southeast pacific surface sediments reflect environmental properties abstract diatom abundance and assemblage composition determined for 47 surface sediment samples from the southeast pacific 50 s 15 n combined with existing data for the peru and chile margins demonstrate responses to regional temperature upwelling and productivity high diatom abundances valves g mark the eastern equatorial pacific upwelling and the coastal upwelling areas in particular the upwelling centers off peru freshwater diatoms reflect the low salinity tongue off the chilean fjords diatom species composition distinguishes between coastal and eastern equatorial pacific upwelling conditions and records sea surface temperatures q mode factor analysis defines five floral assemblages factors 1 and 4 determined by the genus chaetoceros f1 and thalassionema f4 reflect coastal and equatorial upwelling conditions respectively factors 2 and 3 characterized by the genus thalassiosira and azpetia nodulifera can be associated with el nino conditions a 5th factor described by paralia sulcata records a near shore upwelling center off point concepcion central chile statistical transfer functions relate diatom species percentages to sea surface temperature and productivity with error estimates of 0 9 c and 23 gc m 2 yr respectively and provide new tools for estimating past temperature and productivity along the west coast of south america

opposing decadal changes for the north atlantic meridional overturning circulation hydrographic properties of the north atlantic ocean have changed significantly over the past decades a combination of changes in seawater density calculated from observed properties of sea water and a numerical ocean model reveals that the strength of the meridional overturning circulation has changed in different directions in the subpolar and subtropical basins respectively

reconstructing the meridional overturning circulation from boundary densities and the zonal wind stress numerical models are used to test whether the meridional overturning circulation moc can be reconstructed from boundary densities and the wind stress in idealized model setups without topography the strength as well as the temporal and spatial variability of the moc cell can largely be reproduced from boundary densities and the zonal wind stress with added slopes along the meridional boundaries most of the depth averaged flow is missed and neither strength nor spatial structure of the moc is well reproduced however the temporal evolution of both moc and its estimate are similar in an eddy permitting model with realistic bottom topography the contribution of the depth averaged meridional flow to the moc is captured at some places while it is missed at others nevertheless boundary densities and the zonal wind stress allow the leading modes of the temporal and spatial moc variability to be reproduced on seasonal time scales most of the moc variability is due to the wind stress but changes in the boundary density affect the moc as well on interannual time scales the moc variability largely reflects changes in the boundary density generally the moc reconstructions are accurate when bottom velocities are small an assumption made in the reconstruction approach the results are relevant for estimates of both the modern and the past moc in the real ocean boundary densities can be obtained from measurements of temperature conductivity and pressure in the water column whereas past seawater densities have left their imprint in sea sediments

seismic liquefaction lateral spreading and flow slides a numerical investigation into void redistribution experience from past earthquakes indicates that seismically induced large lateral spreads and flow slides in alluvial sand deposits have taken place in coastal and river areas in many parts of the world the ground slope in these slides was often not very steep gentler than a few percent recent research indicates that the presence of low permeability silt or clay sublayers within the sand deposits is responsible for this behaviour such layers form a barrier to upward flow of water associated with earthquake generated pore pressures this causes an accumulation of pore water at the base of the layers resulting in greatly reduced strength and possible slope instability this paper uses an effective stress coupled stress flow dynamic analyses procedure to demonstrate the effects of a low permeability barrier layer on ground deformations from an earthquake event the analyses show that an expansion zone develops at the base of barrier layers in stratified soil deposits under seismic loading which can grea

coherent sea level fluctuations along the global continental slope signals in sea level or more properly sub surface pressure ssp sea level corrected for the inverse barometer effect are expected to propagate rapidly along the continental slope due to the effect of sloping topography on wave modes resulting in strongly correlated ssp over long distances observations of such correlations around the arctic and antarctic are briefly reviewed and then extended using satellite altimetry to the rest of the global continental slope it is shown that such long distance correlations are common especially in extra tropical regions simple correlations from altimetry cannot however establish the wave speed or whether waves are responsible for the correlations as opposed to large scale coherence in the forcing a case study around south america is used to highlight some of the complications and is found to strengthen the case for the importance of wave modes in such long distance ssp coherence although more detailed in situ data are required to resolve the cause of the correlations

north atlantic meridional overturning circulation variations from grace ocean bottom pressure anomalies concerns about north atlantic meridional overturning circulation namoc changes imply the need for a continuous large scale observation capability to detect changes on interannual to decadal time scales here we present the first measurements of lower north atlantic deep water lnadw transport changes using only time variable gravity observations from gravity recovery and climate experiment grace satellites from 2003 until now improved monthly gravity field retrievals allow the detection of north atlantic interannual bottom pressure anomalies and lnadw transport estimates that are in good agreement with those from the rapid climate change meridional overturning circulation and heatflux array rapid mocha concurrent with the observed amoc transport anomalies from late 2009 through early 2010 grace measured ocean bottom pressures changes in the 3000 5000 m deep western north atlantic on the order of 20 mm h2o 200 pa implying a southward volume transport anomaly in that layer of approximately 5 5 sverdrup our results highlight the efficacy of space gravimetry for observing amoc variations to evaluate latitudinal coherency and long term variability

paleoproductivity variations related to climatic conditions in the alboran sea western mediterranean during the last glacial interglacial transition the diatom record the present study addresses the analysis of changes in marine primary productivity derived from climatic variability over the last 30 000 yr the study area is the alboran sea this is the westernmost basin of the mediterranean sea and was a very sensitive area to changes in sea levels and atmospheric configuration during the last glacial interglacial transition we report the results from four sediment cores recovered in both the western and eastern alboran basins this allowed us to monitor the w e evolution of the hydrological structures the study is mainly based on the diatom record although total organic carbon toc isotopes and uk 0 37 sst were also used to gain further information paleoceanographic conditions favoured high paleoproductivity rates during the last glacial maximum although this occurred at termination 1a and during the younger dryas event yd increasing towards the easternmost sites during these periods meteorological conditions with increased westerlies intensified the flow to the east driving an eastward migration of the western anticyclonic gyre a possible displacement of the north alboran upwelling system is also considered the major component of the diatom assemblage during the yd are the resting spores of leptocylindrus danicus which suggest the presence of cooler and less saline surface waters the opposite behaviour between planktonic and benthic proxies in addition to the high toc values allows us to infer a phase of reduced deep water renewal between 16 5 and 9 cal ky bp fresh water diatoms and opal phytoliths were used as indicators of aridity and humid land conditions respectively during the glacial period and until 14 cal ky bp we observed a gradual climatic deterioration accompanied by a loss of grass belts climatic conditions were warmer and moister during the bolling allerod while the yd was dry the re establishment of vegetation belts and replenishment of lakes was observed at 8 cal ky bp q 2001 elsevier science b v all rights reserved

radionuclide dates and foraminiferal accumulation rates examples from submarine canyons abstract caesium 137 an anthropogenic radionuclide has been present in the global environment for the past 40 years and may be detected in sediment using non destructive gamma spectrometry 137cs peaks can be used to date layers within core material the effect of bioturbation upon the dating results has been considered using x radiography of the core material recent sedimentary material from submarine canyons cutting the portuguese continental margin has been dated using 137cs and this information used in conjunction with foraminiferal assemblage data has allowed benthic and planktic foraminiferal test accumulation rates to be calculated benthic foraminiferal accumulation rates range from 55 to 687 tests yr 10 cm2 and planktic rates range from 51 to 1338 tests yr 10 cm2 at water depths of 385 to 3400 accumulation rates have been calculated for selected genera and brizalina has the highest overall value

climate change and coastal hydrographic response along the atlantic iberian margin tagus prodelta and muros ria during the last two millennia the tagus prodelta w portugal and the muros ro a nw spain are areas of high deposition rates registering high resolution palaeoclimatic records for western iberia we compare the climatic conditions of the two areas over the last two millennia based on proxies of temperature sea surface temperatures and oxygen isotopes continental input grain size iron and magnetic susceptibility and productivity inorganic and organic carbon carbon isotopes benthic foraminifera and diatoms biogeochemical changes in the tagus prodelta reflect widely recognized north atlantic climatic periods encompassing the roman period ad 0 350 the dark ages ad 400 700 the mediaeval warm period mwp ad 800 1200 and the little ice age lia ad 1300 1750 the atmospheric north atlantic oscillation nao drives the tagus prodelta multidecadal long term variability in precipitation river input during cold periods negative nao and marine upwelling during warmer periods positive nao a scheme that is reversed in the galician region the muros ro a shows only local hydrodynamics until ad 1150 including a suboxic event in the inner ro a around ad 500 700 since ad 1150 atlantic warm upwelled waters have ventilated the outer ro a but only reach the inner ro a at ad 1750 the twentieth century records are also interpreted as a reflex of the inverse nao mode in both areas resulting in amplification of the lia biogeochemical water conditions centennial scale solar activity appears to be another important forcing mechanism or the only one if solar activity drives the nao and bond cycles behind changes in the hydrography of the tagus prodelta and primary production bottom ventilation and organic carbon degradation in the muros ro a

interaction of a coastal kelvin wave with the mean state in the gulf stream separation area the interaction of a coastal kelvin wave with the mean state in the gulf stream separation area is studied using a hierarchy of numerical models including both low and high resolution 2 5 layer models and a coarse resolution ocean general circulation model ogcm in a simple configuration when the kelvin front reaches the separation area in the low resolution 2 5 layer model an anomaly of opposite sign emerges and remains in the upper layer of the separation area the mechanism leading to its buildup is the following the variations of thickness in the active midlayer due to the propagation of the kelvin wave induce current variations that act as a source of thickness anomalies for the upper layer negative feedback this source term is proportional to the mean vorticity gradient the latter therefore must be large enough to obtain a significant response which explains why this phenomenon occurs only in the separation area the anomaly remains in the separation area because the advection by the mean zonal current is balanced by the current anomalies due to the variations of thickness in the surface layer a very similar response is obtained in the high resolution case and with the ogcm thus the mechanism leading to this evolution seems also largely independent of the model however in the ogcm the surface current is sufficiently strong to advect the anomaly in the surface layers above 200 m depth note finally that these anomalies do not prevent the kelvin waves from pursuing their travel southward and then eastward toward the eastern boundary where rossby waves are radiated numerous recent results based on this adjustment mechanism therefore would be robust

mid depth oxygen drawdown during heinrich events evidence from benthic foraminiferal community structure trace fossil tiering and benthic δ13c at the portuguese margin abstract the distribution of trace fossils and benthic foraminiferal assemblages in two sediment cores from 2160 m water depth at the northern and 1100 m at the southern portuguese continental margin was used to reconstruct the bottom water oxygenation during the last 40 ka emphasis was given to the heinrich events during which enhanced meltwater flux associated with the iceberg surges reduced or even halted deep water formation in the north atlantic condensed trace fossil tiering structures and high proportions of low oxygen tolerant benthic foraminifera suggest a major drawdown of bottom water oxygenation during heinrich events using the benthic foraminiferal oxygenation index bfoi of kaiho 1991 1994 that links benthic foraminiferal communities to ambient bottom water oxygenation we extracted apparent oxygen concentrations from benthic assemblages bfoi values suggest low oxic conditions during heinrich events 1 and 4 with mean oxygen levels of 2 6 to 2 8 ml l 1 and high oxic conditions with 4 1 ml l 1 during heinrich event 2 at the shallower site high proportions of low oxygen tolerant foraminiferal species and bfoi minima are recorded a few centimetres below the maximum concentrations of ice rafted debris indicating that the original microhabitat depth of dysoxic species is preserved beneath the heinrich layers even though bioturbation continued during the events trace fossil tiering calibrated with the redox boundary in low oxic environments and dysoxic ichnotaxa commonly associated with black shales indicate oxygen levels lower than those implied by the bfoi oxygenation estimates derived from trace fossil tiering denote low oxic conditions during h1 13 3 ka with oxygen concentrations slightly above 1 ml l 1 and dysoxic conditions during h2 20 6 ka h3 27 ka and h4 33 5 ka with oxygen concentrations between 0 1 and 1 ml l 1 during the younger dryas bottom waters likely were low oxic negative excursions of benthic carbon isotope values provide independent control on the oxygen drawdown during heinrich events considering a bottom water oxygenation of 6 1 to 6 5 ml l 1 during the last glacial the benthic 13 c minima reveal an oxygen depletion to values between 3 4 and 5 0 ml l 1 during h1 through h4 at the shallower core site differences between estimates from benthic 13 c bfoi and trace fossil tiering suggest that benthic foraminiferal communities are rather robust to oxygen depletion if the level does not fall below 3 ml l 1 whereas burrowing organisms react sensitively to depth variations of the redox boundary in near surface sediments due to even small changes of bottom water oxygenation

coastal upwelling in the canary island region spatial variability reflected by the surface sediment diatom record abstract modern diatom and c org distribution patterns were investigated in 39 surface sediment samples of the canary region in order to quantitatively determine the influence of coastal upwelling and saharan dust on the flux of these sedimentary components high diatom abundance in surface sediments 2 10 6 valves g 1 dry sediment as well as the dominance of the assemblages by spores of chaetoceros which is a genus related to upwelling conditions reflect the stronger coastal upwelling conditions occurring at cape ghir off the nw african coast further offshore total diatom abundance decreases one order of magnitude 1 10 5 valves g 1 dry sediment and the assemblages are dominated by oceanic species of the genus nitzschia and fresh water diatoms mainly the genera aulacoseira which is known to be a component of saharan dust this association suggest that offshore diatom concentrations may be generated by dust input from desert regions even though the sediments are expected to preserve only a mixed and averaged oceanographic signal characteristic biogeographic patterns of a phytoplankton community occurring across a gradient of turbulence and nutrient availability are recorded in surface sediments off cape ghir this is seen in the subsequent maximum abundances of the genera thalassiosira chaetoceros and rhizosolenia

high resolution diatom stratigraphy of quaternary sediments from the scotia sea upper quaternary pelagic and hemipelagic sediments from the scotia sea and south scotia ridge range from diatom ooze to diatom bearing mud diatom content increases northwards and at most sites diatom rich and diatom poor sediments alternate downcore on a scale of metres a local stratigraphy is based on relative abundance of six prominent diatom taxa eucampia antarctica rhizosolenia spp thalassiosira spp chaetoceros spores nitzschia kerguelensis and othernitzschia species and one silicoflagellate species distephanus speculum these stratigraphic units defined using diatoms are correlated with radiolarian abundance stratigraphy cycladophora davisiana and with palaeomagnetic stratigraphy information from modern environments phytoplankton and sediment trap studies indicates that changes in diatom species composition are related to n s movement of the winter ice edge and of the antarctic convergence

evaluation of simulation models of lateral spread sites treated with prefabricated vertical drains abstractfinite element analyses are performed of centrifuge tests consisting of untreated and drain treated lateral spread sites with the goal of evaluating the ability of numerical simulations to predict the response of sites improved with prefabricated vertical drains finite element models of varying complexity are analyzed a two dimensional model of the full centrifuge test a three dimensional unit cell model around a single drain and a two dimensional unit cell model all the finite element models predict pore pressures consistent with the centrifuge tests the deformation responses of the finite element models show that unit cell analyses produce significantly larger deformations than those observed in the centrifuge this result is caused by the fact that the centrifuge test geometry is not well represented by the infinite slope condition assumed in a unit cell the full two dimensional model predicts deformations that are more consistent with those of the centrifuge because it can capture the

monitoring the atlantic meridional overturning circulation the rapid climate change programme rapid has established a prototype system to continuously observe the strength and structure of the atlantic meridional overturning circulation moc at 26 5 n here we provide a detailed description of the rapid moc monitoring array and how it has evolved during the first four deployment years as well as an overview of the main findings so far the rapid moc monitoring array measures 1 gulf stream transport through florida strait by cable and repeat direct velocity measurements 2 ekman transports by satellite scatterometer measurements 3 deep western boundary currents by direct velocity measurements 4 the basin wide interior baroclinic circulation from moorings measuring vertical profiles of density at the boundaries and on either side of the mid atlantic ridge and 5 barotropic fluctuations using bottom pressure recorders the array became operational in late march 2004 and is expected to continue until at least 2014 the first 4 years of observations april 2004 april 2008 have provided an unprecedented insight into the moc structure and variability we show that the zonally integrated meridional flow tends to conserve mass with the fluctuations of the different transport components largely compensating at periods longer than 10 days we take this as experimental confirmation of the monitoring strategy which was initially tested in numerical models the moc at 26 5 n is characterised by a large variability even on timescales as short as weeks to months the mean maximum moc transport for the first 4 years of observations is 18 7 sv with a standard deviation of 4 8 sv the mechanisms causing the moc variability are not yet fully understood part of the observed moc variability consists of a seasonal cycle which can be linked to the seasonal variability of the wind stress curl close to the african coast close to the western boundary fluctuations in the gulf stream and in the north atlantic deep water nadw coincide with bottom pressure variations at the western margin thus suggesting a barotropic compensation ongoing and future research will put these local transport variations into a wider spatial and climatic context

diatom taphocoenoses in the coastal upwelling area off south west africa abstract the diatom floral composition of 124 sediment samples from the south east atlantic records the influence of coastal upwelling on sediment composition off south west africa inner shelf samples between 19 and 24 s are rich in diatom valves and the patterns of diatom species distribution in these samples are related to the coastal upwelling process comparison with recent phytoplankton data shows that the sediment assemblages preserve many of the important species of the diatom biocoenoses including chaetoceros resting spores delphineis karstenii thalassiosira eccentrica and thalassionema nitzschioides delphineis karstenii a pioneer species in enriched coastal water occurs nearshore and chaetoreros resting spores are widespread with highest relative abundance values in some more offshore samples the abundance of the thalassiosira eccentrica group and of thalassionema nitzschioides in sediment samples in and near walvis bay reflects the recurrence of intense upwelling off this part of the coast an abundance of large centric species has been reported in hydrological conditions characteristic of newly upwelled waters and correspondingly actinocyclus octonarius and some large coscinodiscus species occur in the sediments in nearshore patches or belts

the impact of resolution on the adjustment and decadal variability of the atlantic meridional overturning circulation in a coupled climate model variations in the atlantic meridional overturning circulation moc exert an important influence on climate particularly on decadal time scales simulation of the moc in coupled climate models is compromised to a degree that is unknown by their lack of fidelity in resolving some of the key processes involved there is an overarching need to increase the resolution and fidelity of climate models but also to assess how increases in resolution influence the simulation of key phenomena such as the moc in this study we investigate the impact of significantly increasing the ocean and atmosphere resolution of a coupled climate model on the simulation of moc variability by comparing high and low resolution versions of the same model in both versions decadal variability of the moc is closely linked to density anomalies that propagate from the labrador sea southward along the deep western boundary we demonstrate that the moc adjustment proceeds more rapidly in the higher resolution model due the increased speed of western boundary waves however the response of the atlantic sea surface temperatures to moc variations is relatively robust in pattern if not in magnitude across the two resolutions the moc also excites a coupled ocean atmosphere response in the tropical atlantic in both model versions in the higher resolution model but not the lower resolution model there is evidence of a significant response in the extratropical atmosphere over the north atlantic 6 years after a maximum in the moc in both models there is evidence of a weak negative feedback on deep density anomalies in the labrador sea and hence on the moc with a time scale of approximately ten years our results highlight the need for further work to understand the decadal variability of the moc and its simulation in climate models

palaeoproductivity changes and upwelling variability in the galicia mud patch during the last 5000 years geochemical and microfloral evidence theholocenepalaeoclimatichistoryofthegaliciancontinentalshelfhasbeeninvestigatedthrough theanalysesofdiatomremains othersiliceouscompounds biogenicsilica bsi andmetalscontentinamul tiproxyapproachtoagravitycorerecoveredfromthegaliciamudpatch nwiberianpeninsula coveringthe last 5000 years downcore changes in diatom assemblages composition and abundance reflect changes in diatomproductionrelatedtolong short termvariationsinclimate regionaloceanography upwellingstrength and river influx off the coast of nw spain and portugal palaeoclimatic variability was related to the relative strengths and position of the azores high and iceland low pressure cells metals and microflora fluctuations are interpreted as changes in the riverine influence and upwelling intensity paced by oceanographic atmos pheric and climatic changes lack of diatoms between 4700 3300 and 1800 1200 cal yr bp could be linked to early diagenetic processes taking place in the sediment after burial biogenic barium baexcess metals and diatomassemblages showageneralincreaseofmarineproductivityforthelast1200cal yrbp between800 and500cal yrbphighproductionofthemicrofloraistriggeredbyinfluxofriver derivednutrientsundercon ditionsofswwindsandstormsresultingfromanaonegative likephase thebiosiliceousandgeochemical signatures of sediments from the last 500 cal yr bp indicate conditions of enhanced upwelling and increased

peruvian coastal upwelling late quaternary productivity changes revealed by diatoms a transfer function pdu 1 relating modern marine diatom sediment surface assemblages to a 10 year averaged surface water primary productivity map spanning a range of 0 1 1 0 g c m2 day is used to interpret downcore variation in productivity at three sites site 680 681 and 686 of odp leg 112 off peru variation in coastal upwelling determined by the transfer function method and by qualitative assessment using smear slides from each site were staked into one composite record for the last 400 000 years this record revealed the following productivity at 11 and 13 5 s was highly variable during the last 400 000 years with the strongest coastal upwelling phases occurring during the following oxygen isotope stages middle of 1 upper part of 3 lower part of 5 the 67 and 78 transition lower part of 8 upper and lower part of 9 and middle part of 11 significant decreases in upwelling occurred during the following oxygen isotope stages lower part of 1 4 upper part of 5 upper part of 7 upper part of 9 the 1011 transition and the upper part of 11 the overall decreases and increases in paleoproductivity are not in phase with the general glacial interglacial cycles the variability of coastal upwelling is more complex and largest swings in the magnitude of paleoproductivity seem to occur across oxygen isotope stage boundaries the periods of highest paleoproductivity are characterized by excellent diatom assemblage preservation high abundance of skeletonema and delphineis and varved or finely laminated sediments periods when paleoproductivity was weaker on the other hand are characterized by bioturbated sediments poor diatom preservation and high abundance of azpeitzia coscinodiscus nodulifer and pseudoeunotia doliolus

a 220 000 year climatic record for the east equatorial atlantic ocean and equatorial africa evidence from diatoms and opal phytoliths in the zaire congo deep sea fan accumulation rates of microfossil associations are independent of each other and in addition to percentages give indispensable information about the significance of micropaleontological data marine diatoms reveal that coastal upwelling in the zaire fan region was strong during glacial stages and weaker during interglacial stages oceanic upwelling was intense in stages 6 and 2 and at the stage 5d 5c transition but not in stage 4 the benguela current did not penetrate into the gulf of guinea during the last 220 000 years the phfd index based on the contribution of freshwater diatoms and phytoliths is a measure of aridity in equatorial africa the production in the low salinity river plume was high in the most humid periods on land and low when the continent was arid on the long term nutrient supply of the zaire river to the ocean was probably larger in humid than in arid periods periods of strong seasonal variability in river fluxes and coastal upwelling coincide with arid intervals except in the very humid interval with strong seasonal contrasts 35 000 20 000 years b p

siliceous phytoplankton response to a middle eocene warming event recorded in the tropical atlantic demerara rise odp site 1260a abstract the middle eocene diatom and silicoflagellate record of odp site 1260a demerara rise is studied quantitatively in order to throw light on the changes that siliceous phytoplankton communities experienced during a middle eocene warming event that occurred between 44 0 and 42 0 ma both pianka s overlap index calculated per couple of successive samples and cluster analysis point to a number of significant turnover events highlighted by changes in the structure of floristic communities the pre warming flora dominated by cosmopolitan species of the diatom genus triceratium is replaced during the warming interval by a new and more diverse assemblage dominated by paralia sulcata an indicator of high productivity and two endemic tropical species of the genus hemiaulus the critical warming interval is characterized by a steady increase in biogenic silica and a comparable increase in excess ba both reflecting an increase in productivity in general it appears that high productivity not only increased the flux of biogenic silica but also sustained a higher diversity in the siliceous phytoplankton communities the microflora preserved above the critical interval is once again of low diversity and dominated by various species of the diatom genus hemiaulus all assemblages in the studied material are characterized by the total absence of continental and benthic diatoms and the relative abundance of neritic forms suggesting a transitional depositional environment between the neritic and the oceanic realms

finite element modelling of vertical drains beneath embankments on soft ground a methodology is described for modelling vertical drains in plane strain finite element analyses of embankments on soft ground this includes the use of a suitably formulated drainage element to represent each drain criteria for matching the effect of a single drain in axisymmetric and plane strain analyses are developed on the basis of a widely accepted theory matching can be achieved by adjusting the geometry drain spacing and or the permeability of the soil the finite element analysis and matching procedure are validated by comparison with theoretical results the effects of both finite drain permeability well resistance and smear are modelled satisfactorily une methode est deacute acute crite pour simuler des drains verticaux dans une analyse aux elements finis a deformations planes de remblais sur sols mous ceci inclut l utilisation d un element de drainage formule de facon adequate pour representer chaque drain des criteres pour representer l effet d un drain unique dans les analyses axisy

at the land s end marine resources and the importance of fluctuations in the coastline in the prehistoric hunter gatherer economy of portugal abstract this paper focuses on the importance of aquatic resources in economy and subsistence strategies during the middle and upper palaeolithic of portugal modern theoretical biases in archaeology have led to a marginalization of marine resources and a dismissal of their use by palaeolithic hunter gatherers geological and archaeological data show that changes in the position of the coastline had a direct impact on the visibility of marine resources in the archaeological record marine regressions and transgressions have significantly altered the record of pleistocene coastal settlement using recent studies on changes in upwelling intensity during the last glacial we offer a new perspective on palaeolithic hunter gatherer economy that emphasizes the importance of the coast as a focus of subsistence and settlement

distribution of diatoms coccolithophores and planktic foraminifers along a trophic gradient during sw monsoon in the arabian sea the distribution of diatoms coccolithophores and planktic foraminifers mirrored the hydrographic and trophic conditions of the surface ocean 0 100 m across the upwelling area off the oman coast to the central arabian sea during may june 1997 and july august 1995 the number of diatoms was increased in waters with local temperature minimum and enhanced nutrient concentration nitrate phosphate silicate caused by upwelling vegetative cells of chaetoceros dominated the diatom assemblage in the coastal upwelling area towards the more nutrient depleted and stratified surface waters to the southeast the number of diatoms decreased coccolithophore and planktic foraminiferal numbers increased and floral and faunal composition changed in particular the transition between the eutrophic upwelling region off oman and the oligotrophic central arabian sea was marked by moderate nutrient concentration and high coccolithophore and foraminifer numbers florisphaera profunda previously often referred as a lower photic zone species was frequent in water depths as shallow as 20 m and at high nutrient concentration up to 14 mol no3 l 1 and 1 2 mol po4 l 1 to the oligotrophic southeast of the divergence cell densities of coccolithophores declined and umbellosphaera irregularis prevailed throughout the water column down to 100 m depth in general total coccolithophore numbers were limited by nutrient threshold concentration with low numbers 70 103 cells l 1 at low no3 and po4 the components of the complex microplankton succession diatoms coccoliths and planktic foraminifers and possibly others should ideally be used as a combined paleoceanographic proxy consequently models on plankton ecology should be resolved at least for the seasonality to account for the bias of paleoceanographic transfer calculations

decadal predictions of the cooling and freshening of the north atlantic in the 1960s and the role of ocean circulation in the 1960s north atlantic sea surface temperatures sst cooled rapidly the magnitude of the cooling was largest in the north atlantic subpolar gyre spg and was coincident with a rapid freshening of the spg here we analyze hindcasts of the 1960s north atlantic cooling made with the uk met office s decadal prediction system depresys which is initialised using observations it is shown that depresys captures with a lead time of several years the observed cooling and freshening of the north atlantic spg depresys also captures changes in sst over the wider north atlantic and surface climate impacts over the wider region such as changes in atmospheric circulation in winter and sea ice extent we show that initialisation of an anomalously weak atlantic meridional overturning circulation amoc and hence weak northward heat transport is crucial for depresys to predict the magnitude of the observed cooling such an anomalously weak amoc is not captured when ocean observations are not assimilated i e it is not a forced response in this model the freshening of the spg is also dominated by ocean salt transport changes in depresys in particular the simulation of advective freshwater anomalies analogous to the great salinity anomaly were key therefore depresys suggests that ocean dynamics played an important role in the cooling of the north atlantic in the 1960s and that this event was predictable

simulations of a centrifuge test with lateral spreading and void redistribution effects abstractnumerical simulations of a centrifuge test in which dissipation patterns lateral spreading and shear strain localization were measured and recorded are performed for validation of the numerical modeling approach and insight on the deformation mechanisms the constitutive model calibration process is performed based on available laboratory data and is described in detail the model container and construction sequence are simulated to provide good approximations of the boundary conditions and initial stress distributions two approaches for simulating successive shaking events are presented and compared the key observations and mechanisms from the centrifuge test namely 1 the dynamic response and onset of liquefaction 2 the amount and pattern of surface deformation 3 the patterns of pore pressure dissipation and void ratio redistribution and 4 the difference in response between a sand profile treated and not treated with liquefaction drains are all reasonably captured and bounded b

detection of the fast kelvin wave teleconnection due to el nino southern oscillation previous analyses of the ocean state along the western american coast have often indicated unexpectedly slow and limited propagation of coastally trapped kelvin waves associated with the e1 nifio southern oscillation in contrast theoretical and numerical ocean models demonstrate that these kelvin waves are a rapid and long range teleconnection between the low and high latitude pacific ocean strongly impacting both the surface coastal currents and nutrient upwelling sea level variations along the western coast of north america are reexamined under the assumption that tropically forced kelvin waves are produced in bursts of several months duration a cross correlation analysis restricted to mid 1982 to mid 1983 is performed between galapagos island and stations along western central and north america a coastally trapped kelvin wave is revealed to propagate at a speed of 2 3 m s from the tropical pacific to the aleutian island chain the observed phase speed agrees with the estimated speed of a kelvin wave based on the average density profile of the ocean near the coast weakere1 nifio events in 1986 1987 and 1991 1992 appear to contain a combination of this remotsignal and local wind forcing the wave propagation speed calculated from the spectrhl phase is shown to be sensitive to the presence of other noise processes in the observations this is demonstrated through an analysis of a synthetic sea level data set that contains many of the essential features of the real sea level data a relatively small level of red noise can give a 100 expected error in the estimated propagation speed this suggests a new explanation for this important inconsistency within dynamical oceanography

a theory for the surface atlantic response to thermohaline variability abstract the response of the upper warm limb of the thermohaline circulation in the north atlantic to a rapid change in deep water formation at high latitudes is investigated using a reduced gravity ocean model changes in deep water formation rate initiate kelvin waves that propagate along the western boundary to the equator on a timescale of months the response in the north atlantic is therefore rapid the southern hemisphere response is much slower limited by a mechanism here termed the ldquo uatorial buffer since to leading order the flow is in geostrophic balance the pressure anomaly decreases in magnitude as the kelvin wave moves equatorward where the coriolis parameter is lower together with the lack of sustained pressure gradients along the eastern boundary this limits the size of the pressure field response in the southern hemisphere interior adjustment is by the westward propagation of rossby waves but only a small fraction of the change in thermohaline circulation strength is commun

the impact of the mediterranean outflow water mow on benthic foraminiferal assemblages and surface sediments at the southern portuguese continental margin benthic foraminifera and surface sediments were analyzed from 23 box core and core top samples from 250 to 3600 m depth at the southern portuguese continental margin between 37 and 38 n this area is affected by the mow which flows northwards along the slope between 600 and 1500 m waterdepth sediment structures grain size distribution and clay mineral assemblages of surface sediments indicate active winnowing in the upper part of the mow and deposition of the fine fraction near its lower boundary r mode cluster analyses of foraminiferal census data from the 250 m fraction revealed four associations the shelf edge association occurs on glauconitic shelf and upper slope sands down to 268 m the upper slope association is recognized between 498 and 1300 m where sand silt clays to clayey silts are encountered the lower slope association is found between 1405 and 2985 m and differs markedly from assemblages below 3000 m deep water association where the near surface sediments are soft hemipelagic clays the boundary layer association shows no significant depth limits but abundance maxima both in the density interface above the mow and in the interval of decreasing turbulence below it the boundaries of the shelf edge and upper slope association correspond to these hydrographic boundary layers whereas the boundary between lower slope and deep water assemblage is related to threshold values of nutrient flux to the benthic community examination of hard substrates reveals 27 different species of epibenthic foraminifera six of these the epibenthos group were found attached to elevated substrates only within the mow above the mow elevated substrates were inhabited by different species whilst below the mow they were not used by any epibenthic foraminifers evidently the hydrodynamic environment of the mow current provides an ecological niche which is efficiently used by opportunistic suspension feeders the epibenthos group is more abundant in the middle part of the study area between 37 20 and 37 40 n where the sand content of surface sediments is also higher both indicate an enhanced sediment water interaction in this area which results from an obstruction of the mow flow by the principes d avis basement spur

benthic pelagic coupling and postdepositional processes as revealed by the distribution of opal in sediments the case of the ria de vigo nw iberian peninsula opal concentrations in dry bulk sediment were measured in 43 sampling stations in the ria de vigo at 0e1 1e2 4e5 10e11 and 14e15 cm sediment depths the amount of opal was correlated with the biogenic silicon flux to the sediment obtained by means of a box model the biosiliceous flux to the sediment annual mean is in good agreement with the content of opal found in the uppermost oxic layer revealing that pelagic primary production is the main factor controlling the biogenic silica content in surface sediments this correlation is illustrated by the equation opal wt 0 103bsif 0 414 r 2 0 95 where bsif is the biogenic silicon flux to the sediment in g si m 2 year 1 in the innermost part of the ria i e san simon inlet the content of opal is higher than predicted by the equation since other biogenic silica sources to the sediment may be involved as benthic diatoms proliferation or freshwater diatoms input elevated percentages recorded in the inner ria in the subsuperficial sediment respond to the establishment of suboxiceanoxic conditions that enhance the preservation of opal the input of faecal pellets to the surface sediment derived from mussel rafts also controls the opal distribution and concentration in the ria 2006 elsevier ltd all rights reserved

temporal variability of the atlantic meridional overturning circulation at 26 5 n the vigor of atlantic meridional overturning circulation moc is thought to be vulnerable to global warming but its short term temporal variability is unknown so changes inferred from sparse observations on the decadal time scale of recent climate change are uncertain we combine continuous measurements of the moc beginning in 2004 using the purposefully designed transatlantic rapid climate change array of moored instruments deployed along 26 5 n with time series of gulf stream transport and surface layer ekman transport to quantify its intra annual variability the year long average overturning is 18 7 5 6 sverdrups sv range 4 0 to 34 9 sv where 1 sv a flow of ocean water of 106 cubic meters per second interannual changes in the overturning can be monitored with a resolution of 1 5 sv

numerical and centrifuge modeling of seismic soil foundation structure interaction on liquefiable ground abstractthe effective mitigation of the liquefaction hazard requires an improved understanding of the consequences of liquefaction in terms of ground shaking permanent displacement and building performance in this paper results from centrifuge experiments of a shallow founded structure on liquefiable sand are used to evaluate the predictive capabilities of a state of the art numerical tool solid fluid fully coupled 3d nonlinear numerical simulations were performed using the pdmy02 soil model implemented in a software modeling domain the numerical model captured excess pore pressures and accelerations well in the free field but largely underestimated volumetric settlements due to loss of water during shaking this was associated with the drastic increase in soil hydraulic conductivity when approaching liquefaction which was not taken into account numerically as well as the underestimation of soil volumetric compressibility the contribution of volumetric strains to total building settlement was

on enso coastal currents and sea levels abstract sea level measurements along the western coast of the americas have shown that there is a strong signal at enso frequencies approximately 2 2 yr 1 to 2 5 yr 1 that propagates poleward at about 40 to 90 cm s 1 this enso sea level signal must be associated with enso coastal currents but because adequate interannual current time series are unavailable the structure and strength of these currents are not known coastal enso currents must be fundamentally affected by bottom topography and bottom friction but previous theory has not taken these effects into account a near boundary numerical model with realistic bottom friction stratification and shelf and slope topography was therefore constructed to study enso coastal flow i at enso frequencies previous results for models with no bottom topography and no bottom friction suggest that sea level should not propagate poleward with realistic bottom friction and bottom topography coastal sea level propagates poleward at speeds similar to tho

diatom record of late quaternary climatic change in the eastern equatorial atlantic and tropical africa over the last 160 000 years diatom productivity in the equatorial atlantic has been high during glacial stages 2 4 and 6 and moderate during parts of substages 5b and 5d approximately 96 000 and 117 000 years b p productivity of diatoms is particularly low in substage 5e and in the middle of stage 1 higher productivity implies more vigorous trade winds during glacial intervals leading to stronger upwelling and enhanced lateral advection of surface waters the influence of the benguela current near the equator was strongest during stage 2 a separate regime of coastal upwelling may have existed in the gulf of guinea at this time upwelling and advection may not always respond to the same forcing as sea surface temperature results support the hypothesis that ethmodiscus rex oozes result from high diatom productivity runoff from the zaire and niger rivers was highest at the stage 2 1 transition and just prior to the stage 6 5 transition due to intensification of the african monsoon several other times of increased runoff are indicated periods of increased surface water circulation in the eastern equatorial atlantic appear to correspond to times of aridity in tropical africa conversely intervals of decreased circulation in the eastern equatorial atlantic coincide with times of humidity in tropical africa precessional forcing of continental climate is suggested however precessional forcing of surface ocean circulation can be neither confirmed nor refuted based on the records examined here influx of antarctic bottom water to the eastern equatorial atlantic has been insignificant throughout the last 160 000 years

the last 100 000 years palaeoenvironmental changes inferred from the diatom assemblages of core md012404 from the okinawa trough east china sea the diatom assemblage records preserved in a sedimentary core md012404 retrieved from the okinawa trough in the east china sea ecs imply palaeoenvironmental changes of the last 100 ka our statistical analyses of diatom species abundance data indicate that the assemblages dominate open ocean and warm water coastal water and freshwater masses in the ecs these proxy species were used to infer the long term variation in surface hydrological conditions and palaeoclimate cycles of ca 23 ka observed in the relative abundance of the tychopelagic species paralia sulcata indicate that the increases in precipitation driven by solar insolation might have controlled the diatom assemblages in the ecs the diatom records also indicate relatively low abundances of tropical tychopelagic and freshwater species during millennial scale cold events such as the younger dryas and heinrich events which have been well expressed in the high latitude northern hemisphere climate the floral patterns are interpreted as synchronous cooling and more saline sea surface conditions in the ecs caused by the enhanced asian winter monsoon during the northern hemisphere cold events the higher abundances of tropical species during deglaciation and the holocene might have been linked to gradual increases in the inflow of the kuroshio into the okinawa trough the records also suggest a temporary reduction in tropical species from 5 to 3 ka corresponding to the pulleniatina minimum event during which the warm water planktic foraminifer pulleniatina obliquiloculata was rare copyright 2009 john wiley sons ltd

millennial scale coccolithophore paleoproductivity and surface water changes between 445 and 360 ka marine isotope stages 12 11 in the northeast atlantic abstract a high resolution coccolithophore study was carried out in order to improve the understanding of the paleoceanographic evolution and changes in paleoproductivity occurring off the iberian margin im between 445 and 360 ka i e during late marine isotope stage 12 to 11 coccolithophore assemblages allowed reconstructing surface water changes characterized by millennial scale oscillations 1 5 kyr cycles involving portugal or iberian poleward currents pc and ipc prevalence changes in paleoproductivity possibly related to the upwelling of eastern north atlantic central waters enacw of sub tropical enacwst or sub polar origin enacwsp were also recognized this study also permitted detecting abrupt events stadial interstadial type oscillations and revealed that changes in paleoproductivity are related to opposite dynamics during glacial and interglacial stages with the reversed setting being established during the deglaciation furthermore a possible control of half and fourth precessional cycle components on the occurrence of abrupt changes within the assemblages structure during the deglaciation is proposed on the basis of wavelet analysis results applied to selected taxa

permeability and stiffness of sands at very low effective stresses loose saturated sandy soils may undergo liquefaction under cyclic loading generating positive excess pore pressures due to their contractile nature and inability to dissipate pore pressures rapidly during earthquake loading these liquefied soils have a near zero effective stress state and hence have very low strength and stiffness causing severe damage to structures founded upon them the duration for which this near zero effective stress state persists is a function of the rate of reconsolidation of the liquefied soil which in turn is a function of the permeability and stiffness of the soil at this very low effective stress existing literature based on observation of physical model tests suggests that the consolidation coefficient cv associated with this reconsolidation of liquefied sand is significantly lower than that of the same soil at moderate stress levels in this paper the results of a series of novel fluidisation tests in which permeability k and coefficient of consolidation cv were indep