mechanisms controlling the sensitivity of the atlantic thermohaline circulation to the parameterization of eddy transports in ocean gcms abstract the authors identify and describe the important dynamical mechanisms that explain the significant sensitivity of the atlantic thermohaline circulation to the parameterization of heat and salt transports by mesoscale eddies in numerical models in particular the effects of the gent mcwilliams gm scheme which has a strong flattening effect on isopycnals and a simple horizontal diffusion scheme are considered and compared two control runs one with each scheme exhibit very different circulations and density structures to analyze the dynamical reasons for the differences between the control runs a number of numerical experiments with regionally varying diffusion coefficients are carried out emphasizing the effects of different schemes in key regions the main effect of eddies in the southern ocean in nature is to shoal the subsurface isopycnal surfaces thus increasing the density of the northward inflow of relatively dense intermediate waters into the atlantic as will be seen this is more

one hundred million years of geomagnetic polarity history since 1968 absolute ages have been assigned to the late cretaceous cenozoic geomagnetic reversal time scale by fixing the ages of two or more calibration points in a composite marine magnetic anomaly profile and interpolating between or extrapolating beyond these points assuming constant spreading rates in each interval previously no more than 4 calibration points were used but it is now possible to specify 11 calibration points in addition to the 0 m y datum this improvement is based on magnetostratigraphic studies in italian pelagic limestones these studies closely tie the geomagnetic reversal sequence to the foraminiferal and coccolith zonations absolute ages of calibration points are provided by the best available dates on stage boundaries which are located from the biostratigraphic zonation the greatest changes from previous scales come in the late paleocene early eocene where the new ages are as much as 3 m y younger than in the 1977 scale of labrecque and others and as much as 1 8 m y younger than in the 1980 scale of ness and others

sensitivity of the ocean state to lee wave driven mixing abstractdiapycnal mixing plays a key role in maintaining the ocean stratification and the meridional overturning circulation moc in the ocean interior it is mainly sustained by breaking internal waves two important classes of internal waves are internal tides and lee waves generated by barotropic tides and geostrophic flows interacting with rough topography respectively currently regarding internal wave driven mixing most climate models only explicitly parameterize the local dissipation of internal tides in this study the authors explore the combined effects of internal tide and lee wave driven mixing on the ocean state a series of sensitivity experiments using the geophysical fluid dynamics laboratory cm2g ocean ice atmosphere coupled model are performed including a parameterization of lee wave driven mixing using a recent estimate for the global map of energy conversion into lee waves in addition to the tidal mixing parameterization it is shown that although the global energy input in

pacific subtropical cell response to reduced equatorial dissipation abstract equatorial turbulent diffusivities resulting from breaking gravity waves may be more than a factor of 10 less than those in the midlatitudes a coupled general circulation model with a layered isopycnal coordinate ocean is used to assess pacific climate sensitivity to a latitudinally varying background diapycnal diffusivity with extremely low values near the equator the control experiments have a minimum upper ocean diffusivity of 10 5 m2 s 1 and are initialized from present day conditions the average depth of the 26 4 interface z26 4 in the pacific increases by 140 m after 500 yr of coupled model integration this corresponds to a warming trend in the upper ocean low equatorial diffusivities reduce the z26 4 bias by 30 isopycnal surfaces are elevated from the eastern boundary up to midlatitudes by cooling in the upper several hundred meters partially compensated by freshening entrainment of intermediate water masses from below 26 4 decreases by 1 5 sv 1 sv 106 m3 s 1 m

late holocene diatom biostratigraphy and sea level changes in the southeastern beaufort sea late holocene sediments from the atkinson point area were analysed to provide quantitative reconstructions of recent sea level changes in the southeastern beaufort sea the succession of diatom assemblages in five cores revealed paleoenvironmental changes induced by the transgression of the beaufort sea during successive periods of lacustrine conditions breaching and flooding of thermokarst lakes by the sea and the landward migration of sandy spits based on radiocarbon dates and quantitative paleodepth determinations a relative sea level curve for the late holocene has been developed despite a loss of temporal precision due to old carbon contamination an envelope of sea level change has been defined for the last 2 ka bp suggesting a sea level rise in the order of 1 1 mm a 1 for the last millennium this paper presents the first sea level reconstruction inferred from a diatom based transfer function it represents an improvement over traditional methods which were limited to qualitative estimates of

volcanic ash layers in the upper cretaceous of the central apennines and a numerical age for the early campanian at montagna della maiella and at gola del furlo central apennines two discrete layers of bentonic clay are intercalated within the pelagic furlo and turbiditic pelagic limestones maiella of the upper cretaceous basinal succession of the umbrian basin scaglia facies the bentonite layers are dated by planktonic foraminifera to the globotruncanita elevata zone early campanian and by calcareous nannofossils to the aspidolithus parcus zone cc 18 they fall into the reversed interval of chron 33 detailed correlation shows the layers to be of exactly the same age the upper layer is dated by u pb on magmatic zircons to 81 67 0 21 ma an age compatible with the cretaceous time scale of obradovich the mineralogy of the bentonitic clays is almost pure montmorillonite and contrasts sharply with the clay mineral assemblage of the enclosing pelagic and turbiditic limestones which is dominated by soil derived smectite and illite in different proportions the bentonite seams are interpreted as the submarine alteration products of wind borne volcanic ashes they can be followed with only minor changes in thickness over 200 km and must be derived from distant volcanic sources and related to extreme volcanic events a possible source area is present in the dinarides where upper cretaceous subduction related magmatic rocks are widespread

the exhaust valve of the north atlantic during glacial periods climate records are marked by large amplitude oscillations believed to be a result of north atlantic na freshwater anomalies which weakened the thermohaline circulation thc and introduced instabilities such oscillations are absent from the present interglacial period with the aid of a semiglobal analytical model it is proposed that the bering strait bs acts like an exhaust valve for the above na freshwater anomalies specifically it is suggested that large instabilities in the thc are only possible during glacial periods because during these periods the bs is closed during interglacial periods when the bs the exhaust valve is open low salinity anomalies are quickly flushed out of the north atlantic by the strong southern ocean winds

decadal response of global circulation to southern ocean zonal wind stress perturbation abstract a substantial component of north atlantic deep water formation may be driven by westerly wind stress over the southern ocean variability of this wind stress on decadal time scales may lead to circulation variability far from the forcing region the hybrid coordinate ocean model hycom a numerical ocean model is used to investigate the spatial patterns and the time scales associated with such wind variability the evolution of circulation and density anomalies is observed by comparing one 80 yr simulation forced in part by relatively strong southern hemisphere westerlies with a simulation driven by climatological wind the volume transport anomaly takes about 10 yr to reach near full strength in the entire southern hemisphere however in the northern hemisphere it grows for the duration of the run the southern hemisphere indo pacific volume transport anomaly is about twice the strength of that found in the atlantic in the thermocline water exits the southern westerlies belt in a broad f

paleomagnetic data from umbria italy implications for the rotation of adria and mesozoic apparent polar wander paths abstract sixteen new jurassic and cretaceous paleomagnetic sampling sites are located in northern umbria along three river valleys bosso burano sentino the late jurassic and early cretaceous data are consistent in declination but not inclination with previously published data from these valleys early jurassic data from eight sites give site mean declinations which are significantly different from the two site mean declinations of this age which were previously available comparison of the data with cretaceous and jurassic mean directions from the southern alps indicate 20 anticlockwise rotation relative to the southern alps of this part of northern umbria during neogene deformation of the umbrian fold and thrust belt if the umbrian mean directions are rotated to compensate for the tectonic rotation the early jurassic and cretaceous umbrian and southern alpine pole positions coincide closely with a recently derived african apparent polar path apwp implying that adria moved with africa since at least early jurassic times the late jurassic umbrian and southern alpine poles however are not consistent with current apwps and imply rapid apparent polar wander in both african and north american coordinates from high latitude to lower latitude between bathonian and oxfordian times

a palaeomagnetic study of apennine thrusts italy monte maiella and monte raparo abstract three separate structural blocks within the southern apennines have been sampled for palaeomagnetic investigation to constrain their original separation and movement during mid tertiary deformation the mesozoic limestones are weakly magnetic and the nrm intensity of all samples from upper and lower cretaceous limestone from the alburni platform and from upper cretaceous limestone at monte maiella were too low to yield results lower cretaceous limestone at monte maiella contained a mean magnetisation after structural correction of d 326 i 42 k 44 n 9 57 n 263 e and cretaceous limestone at monte raparo a mean of d 132 i 61 k 50 n 19 54 n 306 e the monte maiella results near the central part of the apennine thrust front are compatible with a local clockwise block rotation during deformation while monte raparo results may bear evidence of the major east west thrust motion during shortening in addition to anticlockwise block rotations already reported from the southernmost apennines

on the relationships between features of the depth latitude meridional overturning streamfunctions across global coupled climate models a comparative analysis of the state and response of the latitude depth meridional overturning streamfunctions in the climate model inter comparison project 3 cmip3 model set is presented simulated overturning strengths of the north atlantic cell tend to converge towards observational estimates the models whose simulations of the north atlantic cell are closest to observational estimates indicate a 29 5 13 decrease in the maximum intensity of that cell by 2 100 in contrast agreement with regard to the state and the response to anthropogenic radiative forcing of the global southern ocean abyssal cell is poor among the models a weak relationship between the mean state and the response of the abyssal cell can be used to constrain the reduction of the southern abyssal cell by 2 100 to 29 3 20 7 in rough agreement with the decrease predicted in the northern cell the biases across the cmip3 models in the northern deep cell and southern abyssal cell cannot be related dynamically by a buoyancy based seesaw like argument the absence or presence of characteristic relationships between the state and evolution of different features of the overturning streamfunction indicate that the main reasons for across model spread are how each model deals with subgrid scale processes and viscosity this highlights the fact that subgrid scale parameterizations and resolution improvements should be a priority of model development these factors are able to explain qualitatively the inter model differences between the northern overturning cells of the different models across model differences in the winds over the southern ocean are responsible for much of the disparity in the overturning circulation cells of the southern ocean

assessment of finescale parameterizations of deep ocean mixing in the presence of geostrophic current shear results of microstructure measurements in the antarctic circumpolar current region

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

hydraulic characterization of a fault zone from fracture distribution abstract a quantitative assessment of how faults control the migration of geofluids is critical in many areas of geosciences we integrated geological fieldwork quantitative analysis of the fractures distribution and numerical modeling to build a geometrical representation of a fault zone and to characterize its hydraulic properties our target is a fault located in the majella mountain italy we collected 21 scan lines across the fault profile in order to characterize its architecture the numerical modeling of the fracture network of the damage zones and their hydraulic parameters was performed using both commercial move and open source software dfnworks and pflotran move was used to build a representative model of the fault zone using fracture spacing as a proxy and to model the hydraulic parameters of the different fault domains dfnworks and pflotran were employed to infer the hydraulic parameters of the damage zones of the fault and then upscale these properties to an equivalent continuum domain suitable for fluid flow simulations through the whole fault zone our findings show how even in a relatively small area it is possible to describe changes in terms of hydraulic properties of a fault zone and to build models capable to represent these variations

is ocean thermohaline circulation linked to abrupt stadial interstadial transitions abstract are the abrupt stadial interstadial s is climate transitions observed in the greenland ice cores also seen in marine climate records literature which shows that the s is events have a large footprint in ocean surface marine properties encompassing the entire northern hemisphere has been reviewed whether this influence extends to the deep circulation is more equivocal on most recent evidence several of the heinrich ice rafting debris events are clearly associated with elimination of north atlantic source waters from the deep atlantic but most cores studied do not resolve the other s is events except for one new record from the bermuda rise which shows all of the major s is cycles in benthic foraminiferal deep sea corals can tell us how rapid these events are in the deep sea

convective mixing and the thermohaline circulation abstract an idealized three dimensional model of buoyancy driven flow in a single hemisphere is used to investigate the relationship between the meridional overturning and the efficiency by which convective mixing eliminates static instability in the fast limit mixing timescale hours to weeks the meridional overturning is not rate limited by the efficiency of convective mixing if convective mixing is made less efficient the model s meridional overturning strength increases moreover the dominant downwelling occurs not at the highest surface density hence the deep ocean is relatively buoyant the numerical results are explained by the different influences of convective mixing and downward advection on the deep ocean heat budget they underscore the fundamentally three dimensional nature of the meridional overturning in addition the narrowness of deep downwelling is related to the geostrophic dynamics of deep temperature anomalies near the eastern wall the model results presented here are in con

the effect of localized mixing on the ocean circulation and time dependent climate change observations indicate that intense mixing in the ocean is localized above complex topography and near the boundaries model experiments presented here illustrate that accounting for this fact can be important in particular it is found that in the case of localized mixing the rate of overturning circulation is proportional to the net rate of generation of potential energy by the vertical mixing linked to the net downward heat diffusion rather than to the value of the mean vertical diffusivity coefficient furthermore it is shown that two climate models having the same vertical profile of diffusivity but differing in their distribution horizontally uniform versus topography boundary intensified can simulate significantly different meridional oceanic circulations vertical heat transfers and responses of simulated climate to atmospheric co2 increase this is found for relatively large o 1 0 cm 2 s 1 horizontal mean values of vertical diffusivity in the pycnocline however in cases of relatively small o 0 1 cm 2 s 1 mean diffusivity in the pycnocline the simulated integral quantities such as meridional mass and heat transports do not depend much on the details of the mixing distribution even so it is found that the deep western boundary currents are more localized near the boundaries in the case of topography boundary intensified mixing also the stratification in the deep ocean is set through the localized regions of intense vertical mixing in addition it is shown that reconciling the observed basin mean values of diffusivity in the abyssal ocean of o 10 cm 2 s 1 with realistic stratification can be problematic unless the regions of enhanced vertical mixing are localized

paleomagnetic and structural evidence for neogene block rotations in the central apennines italy magnetic fabric and paleomagnetic analyses on sedimentary sequences in several structural units in the central apennines ranging from upper cretaceous pelagic carbonates to upper miocene turbidites provide evidence for at least two distinct phases of rotation the first counterclockwise ccw rotation is well recorded in eocene oligocene sediments and does not affect the lower middle miocene sequences the second phase is clearly recorded in lower middle and upper miocene sediments and shows both ccw and clockwise cw rotations in concordance with trends of the different thrust structures we detected three domains characterized by different rotation patterns the westernmost is the southern sabina area an arcuate thrust belt which underwent a cw rotation after the early miocene the second domain is the latium abruzzi carbonate platform where a ccw rotation occurred after the late miocene the third is the marsica area that underwent a cw rotation after the late miocene the magnetic fabric analyses confirm the existence of these different structural provinces and show a strong correlation between the present day strike of the anisotropy of magnetic susceptibility magnetic lineation and the rotations recorded in miocene sediments we attribute present day variations in orientation of the compressional structures in the central apennines to differential rotations about vertical axes due to strike slip faults and out of sequence thrust activity rather than to a change in the stress field orientation we also suggest that this deformation mechanism could be common in other collisional chains around the world

relating background fractures to diagenesis and rock physical properties in a platform slope transect example of the maiella mountain central italy abstract fractured reservoirs are of prime interest as fracture networks control most of the fluid flow and or accumulation however characterizing 3d fracture patterns from subsurface data remains challenging studying fractures on outcrops is a good substitution to 1d data from subsurface exploration tools in addition outcrops allow deciphering the nature origin and conditions for fracture formation through the geodynamic history in this paper we aim at characterizing the true 3d fracture patterns and determining the genetic role of facies diagenesis and rock physical properties we targeted a platform slope transect within a carbonate reservoir analog the maiella mountain in central italy where implications for analog hydrocarbon reservoir can be discussed fracture patterns are sorted based on geometric and kinematic criteria from field measurements and petrographic analyzes on thin sections sedimentary facies pore types and rock physical properties have been characterized in order to establish the impact of early diagenesis on rock evolution diagenetic sequences have been unraveled and correlated to the fractures fracture sequences have been determined considering the cross cutting relationships and compared with burial uplift history in the two studied formations platform and slope carbonates we interpret a stage of fracturing perpendicular to bedding formed at shallow depth and occurring prior to major regional tectonic events the studied carbonates have undergone early diagenesis during fast and shallow burial conferring early brittle behavior the amount of stylolites is not correlated to burial depth but to fracture density porosity and free air p wave velocity it means that fracture development mechanical and petrophysical properties are acquired during early diagenesis both studied formations have undergone the same geodynamic history and their brittle response is different and not related to folding but to burial and early cementation deciphering the close relationship between sedimentary facies diagenetic and geodynamic history has allowed unraveling the controling factors on rock properties and therefore on fracture pattern

a primitive equation ocean circulation model using a general vertical coordinate transformation 2 application to an overflow problem the version of the ocean general circulation model of the geophysical fluid dynamics laboratory with a generalized vertical coordinate transformation introduced in part 1 is used to study the overflow of a zonal ridge in a coarse resolution grid typical for climate applications the configuration roughly resembles the greenland scotland ridge with respect to scale latitude and height of the ridge reasonable qualitative agreement with observed conditions over the iceland faroe section has been achieved especially when a deeper passage was included at the eastern end of the idealized model ridge upwelling of deep water occurs at the eastern boundary where friction and more importantly diapycnal diffusion accomplish the necessary changes in potential vorticity the overflow consists of intermediate water when the renewal time for the deep water is made much larger than that for intermediate water the meridional mass transport is most sensitive to geometric factors like the height of the ridge frictional and diapycnal processes are crucial for the potential vorticity conversion at the ridge and have a strong effect on the water mass distribution bottom friction increases the near bottom flow across f h lines resulting in a large amount of northern basin deep water south of the ridge this effect can be represented only when the frictional bottom boundary layer is adequately resolved by the numerical grid

the impact of abyssal mixing parameterizations in an ocean general circulation model a parameterization of vertical diffusivity in ocean general circulation models has been implemented in the ocean model component of the community climate system model ccsm the parameterization represents the dynamics of the mixing in the abyssal ocean arising from the breaking of internal waves generated by the tides forcing stratified flow over rough topography this parameterization is explored over a range of parameters and compared to the more traditional ad hoc specification of the vertical diffusivity diapycnal mixing in the ocean is thought to be one of the primary controls on the meridional overturning circulation and the poleward heat transport by the ocean when compared to the traditional approach with uniform mixing the new mixing parameterization has a noticeable impact on the meridional overturning circulation while the upper limb of the meridional overturning circulation appears to be only weakly impacted by the transition to the new parameterization the deep meridional overturning circulation is significantly strengthened by the change the poleward ocean heat transport does not appear to be strongly affected by the mixing in the abyssal ocean for reasonable parameter ranges the transport of the antarctic circumpolar current through the drake passage is related to the amount of mixing in the deep ocean the new parameterization is found to be energetically consistent with the known constraints on the ocean energy budget

meridional density gradients do not control the atlantic overturning circulation a wide body of modeling and theoretical scaling studies support the concept that changes to the atlantic meridional overturning circulation amoc whether forced by winds or buoyancy fluxes can be understood in terms of a simple causative relation between the amoc and an appropriately defined meridional density gradient mdg the mdg is supposed to translate directly into a meridional pressure gradient here two sets of experiments are performed using a modular ocean model coupled to an energy moisture balance model in which the positive amoc mdg relation breaks down in the first suite of seven model integrations it is found that increasing winds in the southern ocean cause an increase in overturning while the surface density difference between the equator and north atlantic drops in the second suite of eight model integrations the equation of state is manipulated so that the density is calculated at the model temperature plus an artificial increment dt that ranges from 238 to 98c an increase in dt results in increased sensitivity of density to temperature gradients the amoc in these model integrations drops as the mdg increases regardless of whether the density difference is computed at the surface or averaged over the upper ocean traditional scaling analysis can only produce this weaker amoc if the scale depth decreases enough to compensate for the stronger mdg five estimates of the depth scale are evaluated and it is found that the changes in the amoc can be derived from scaling analysis when using the depth of the maximum overturning circulation or estimates thereof but not from the pycnocline depth these two depth scales are commonly assumed to be the same in theoretical models of the amoc it is suggested that the correlation between the mdg and amoc breaks down in these model integrations because the depth and strength of the amoc is influenced strongly by remote forcing such as southern ocean winds and antarctic bottom water formation

biogeochemical cycling in the global ocean 1 a new analytical model with continuous vertical resolution and high latitude dynamics a new simple analytical model of ocean chemistry is presented which includes continuous vertical resolution high latitude dynamics air sea exchange and sea ice cover in this high latitude exchange interior diffusion advection hilda model ocean physics are represented by four parameters k and w an eddy diffusion coefficient and a deep upwelling velocity in the stratified interior q a rate of lateral exchange between the interior and a well mixed deep polar ocean and u an exchange velocity between surface and deep layers in the polar ocean first estimates are made of ice free and ice covered areas at high latitudes surface temperatures and air sea exchange velocities from available data then values of the physical parameters are estimated from simultaneous least mean square fits of model solutions for temperature t and abiotic carbon 14 14c to interior profiles of t and 14c and surface layer 14c values all derived from available data best fit values for k w q and u are 3 2 10 5 m2 s 1 2 0 10 8 m s 1 7 5 10 11 s 1 and 1 9 10 6 m s 1 respectively these results are interpreted in terms of modes of ocean circulation and mixing and compared with results from other simplier and more complex models in parts 2 and 3 of this series these values for k w q and u are taken as inputs for studying phosphorus oxygen and carbon cycling in the global ocean with the hilda model

vertical mixing and cabbeling in layered models abstract a consistent scheme for vertical mixing in layered numerical models is derived in this paper the fact that the vertical coordinate density depends on the properties being transported namely salinity and potential temperature renders the inclusion of vertical mixing in layered models a subtle problem the approach the authors have taken is based upon the entrainment into a layer being proportional to the turbulent activity in that layer across each interface there are then two entrainment velocities one upward velocity that is the entrainment of fluid into the layer above the interface and one downward velocity being the entrainment velocity into the layer below the interface this double entrainment accounts for both the diffusive and the advective consequences of turbulent mixing the proposed scheme works without approximation for a nonlinear equation of state and can readily handle the production of density caused by cabbeling several examples are given

solution of a model for the oceanic pycnocline depth scaling of overturning strength and meridional pressure difference 1 we present an analysis of the model by gnanadesikan 1999 for the pycnocline depth in the ocean an analytic solution for the overturning strength as a function of the meridional pressure difference is derived and used to discuss their mutual scaling we show that scaling occurs only in two unphysical regimes of the model in the absence of the southern ocean so processes i e for a northern overturning cell the volume transport is proportional to the square root of the pressure difference linear scaling is seen when the overturning is restricted entirely to the so i e when no northern downwelling exists for comparison we present simulations with the coupled climate model climber 3 which show linear scaling over a large regime of pressure differences in the north atlantic na we conclude that the pycnocline model is not able to reproducethelinearscalingbetweenitstwocentralvariables pressure and volume transport index terms 4532 oceanography physical general circulation 4203 oceanography general analytical modeling 4267 oceanography general paleoceanography citation levermann a and a griesel 2004 solution of a model for the oceanic pycnocline depth scalingofoverturningstrengthandmeridionalpressuredifference

atlantic pycnocline theory scrutinized using a coupled climate model simulations with changed southern ocean wind stress oceanic vertical mixing surface freshwater forcing and global warming confirm the basic equations of gnanadesikan s 1999 theory for the atlantic one vertical scale the pycnocline depth d contributes inversely proportional to low latitudinal upwelling and linearly to southern ocean eddy transport the maximum atlantic overturning is confirmed to be quadratic in d but is also shown to be linear in a meridional density difference our simulations strongly suggest that the theory needs to be complemented by a dynamical equation for since changes in both d and are significant and mutually independent while under global warming d varies strongly and is practically constant the situation is reversed for altered surface freshwater fluxes similarly variations in the meridional length scale of southern ocean outcropping require a dynamical equation in order to capture the fundamental behavior of the atlantic meridional overturning circulation

location of potential energy sources and the export of dense water from the atlantic ocean the export of dense water from the atlantic and into the indo pacific oceans and heat transport in the opposite direction is traditionally attributed to the fact that dense water forms in the atlantic but not the pacific evidence from two models presented here suggests this is an incomplete explanation it is found that dense water export from the atlantic depends on a poten tial energy pe sink associated with dense water downwelling in the at lantic that is not balanced by a pe source within the atlantic therefore increasing the atlantic pe source reduces dense atlantic water export tide models suggest that the atlantic pe source may have been much higher at the last glacial maximum this could have significantly reduced dense wa ter export from the atlantic ocean even if atlantic overturning was stronger than it is today

magnetic and sequence stratigraphy of redeposited upper cretaceous limestones in the montagna della maiella abruzzi italy abstract the carbonate platform margin of the montagna della maiella in the abruzzi region of central italy has a complex history of sedimentation consisting of aggradational and progradational episodes along the shelf margin and pelagic deposition in the basin a paleomagnetic study at 12 regionally distributed limestone sites of late cretaceous to miocene age in the maiella anticline was unable to define stable magnetic directions at most sites largely due to the weakness of the magnetizations at the few usable sites inclinations agreed with reference values based on an african polar wander path declinations were inconsistent indicating local tectonic rotations both normal and reversed polarities were preserved at some sites a magnetostratigraphic section consisting of 280 samples spaced at 1 1 5 m intervals was sampled along a profile in the valle delle tre grotte near the village of pennapiedimonte sequence stratigraphy based on two dimensional analysis of outcrops formed the stratigraphic framework for the magnetostratigraphic study rock magnetic analyses showed that magnetite is the dominant ferromagnetic mineral in the limestones both alternating field and thermal demagnetization were satisfactory in defining two main components in the weak magnetizations a component with low coercivity low unblocking temperature and normal polarity was close in direction to the present axial dipole field direction at the site a higher coercivity higher unblocking temperature component with both polarities was interpreted as the characteristic remanent magnetization chrm although the mean directions of samples with normal and reversed polarity are not exactly antipodal a stratigraphic sequence of magnetozones is very clearly defined the pennapiedimonte magnetostratigraphy correlates well with late cretaceous chrons c30r to c34n in the established polarity timescale numerical ages can thus be allocated to the reversals correlation to the gubbio section allows paleontological dates for the reversal sequence to be inferred the correlations allow more precise dating of formational and sequence boundaries and a better evaluation of stratigraphic hiatuses in particular the boundary between the tre grotte formation supersequence 1 turonian to middle campanian and the orfento formation supersequence 2 upper campanian to upper maastrichtian is shown to be associated with a significant hiatus spanning most of the middle campanian g ventricosa zone likewise the absence of chron c29r at the top of the orfento formation ss2 documents non deposition during the latest maastrichtian or

global abyssal mixing inferred from lowered adcp shear and ctd strain profiles abstract internal wave wave interaction theories and observations support a parameterization for the turbulent dissipation rate e and eddy diffusivity k that depends on internal wave shear vz2 and strain z2 variances its latest incarnation is applied to about 3500 lowered adcp ctd profiles from the indian pacific north atlantic and southern oceans inferred diffusivities k are functions of latitude and depth ranging from 0 03 10 4 m2 s 1 within 2 of the equator to 0 4 0 5 10 4 m2 s 1 at 50 70 diffusivities k also increase with depth in tropical and subtropical waters diffusivities below 4500 m depth exhibit a peak of 0 7 10 4 m2 s 1 between 20 and 30 latitudes where semidiurnal parametric subharmonic instability is expected to be active turbulence is highly heterogeneous though the bulk of the vertically integrated dissipation e is contributed from the main pycnocline hotspots in e show some correlation with small scale bottom roughness and near bottom flow at sites where st

mixing variability in the southern ocean a key remaining challenge in oceanography is the understanding and parameterization of small scale mixing evidence suggests that topographic features play a significant role in enhancing mixing in the southern ocean this study uses 914 high resolution hydrographic profiles from novel em apex profiling floats to investigate turbulent mixing north of the kerguelen plateau a major topographic feature in the southern ocean a shear strain finescale parameterization is applied to estimate diapycnal diffusivity in the upper 1600m of the ocean the indirectestimates of mixing match direct microstructure profiler observations made simultaneously it is found that mixing intensities have strong spatial and temporal variability ranging from o 10 26 t oo 10 23 m 2 s 21 this study identifies topographic roughness current speed and wind speed as the main factors controlling mixing intensity additionally the authors find strong regional variability in mixing dynamics and enhanced mixing in the antarctic circumpolar current frontal region this enhanced mixing is attributed to dissipating internal waves generated by the interaction of the antarctic circumpolar currentandthetopographyofthekerguelenplateau extendingthemixingobservationsfromthekerguelen region to the entire southern ocean this study infers a large water mass transformation rate of 17 sverdrups sv 1sv 10 6 m 3 s 21 across the boundary of antarctic intermediate water and upper circumpolar deep water in the antarctic circumpolar current this work suggests that the contribution of mixing to the southern ocean overturning circulation budget is particularly significant in fronts

a cretaceous carbonate delta drift in the montagna della maiella italy the upper cretaceous campanian maastrichtian bioclastic wedge of the orfento formation in the montagna della maiella italy is compared to newly discovered contourite drifts in the maldives like the drift deposits in the maldives the orfento formation fills a channel and builds a miocene delta shaped and mounded sedimentary body in the basin that is similar in size to the approximately 350 km2 large coarse grained bioclastic miocene delta drifts in the maldives the composition of the bioclastic wedge of the orfento formation is also exclusively bioclastic debris sourced from the shallow water areas and reworked clasts of the orfento formation itself in the near mud free succession age diagnostic fossils are sparse the deposi tional textures vary from wackestone to float rudstone and breccia conglom erates but rocks with grainstone and rudstone textures are the most common facies in the channel lensoid convex upward breccias cross cut ting channelized beds and thick grainstone lobes with abundant scours indi cate alternating erosion and deposition from a high energy current in the basin the mounded sedimentary body contains lobes with a divergent progradational geometry the lobes are built by decametre thick composite megabeds consisting of sigmoidal clinoforms that typically have a channel ized topset a grainy foreset and a fine grained bottomset with abundant irregular angular clasts up to 30 m thick channels filled with intraforma tional breccias and coarse grainstones pinch out downslope between the megabeds in the distal portion of the wedge stacked grainstone beds with foresets and reworked intraclasts document continuous sediment reworking and migration the bioclastic wedge of the orfento formation has been vari ously interpreted as a succession of sea level controlled slope deposits a shoaling shoreface complex or a carbonate tidal delta current controlled delta drifts in the maldives however offer a new interpretation because of their similarity in architecture and composition these similarities include i a feeder channel opening into the basin ii an excavation moat at the exit of the channel iii an overall mounded geometry with an apex that is in shallower water depth than the source channel iv progradation of stacked lobes v channels that pinch out in a basinward direction and vi smaller channelized intervals that are arranged in a radial pattern as a result the upper cretaceous campanian maastrichtian bioclastic wedge of the orfento formation in the montagna della maiella italy is here interpreted as a carbonate delta drift

robustness of multiple equilibria in the global ocean circulation 1 in an idealized atlantic pacific ocean model we study the steady state solutions versus freshwater input in the northern north atlantic we find that four different states the conveyor c the southern sinking ss the northern sinking ns and the inverse conveyor ic appear as two disconnected branches of solutions where the c is connected with the ss and the ns with the ic we argue that the latter has the intriguing consequence that the parameter volume for which multiple steady states exist is greatly increased

determination of diapycnal diffusion rates in the upper thermocline in the north atlantic ocean using sulfur hexafluoride 1 the apparent diapycnal diffusivity below the wind driven surface mixed layer of the ocean was determined in an anticyclonic eddy in the eastern north atlantic using sulfur hexafluoride sf6 tracer data collected in june 1998 in this tracer experiment the downward penetration of sf6 was measured for 3 weeks following the deliberate injection of sf6 in the surface mixed layer the resulting data were used to constrain the one dimensional fickian diffusion model to estimate the diapycnal diffusivity the model also includes the lateral diffusion component so that it can more accurately represent the time evolution of the sf6 concentrations along the isopycnal surface this affects the estimation of the diapycnal diffusivity for the upper thermocline immediately below the surface mixed layer we estimated the diapycnal diffusivity for the 3 week period as 0 3 0 2 cm2 s 1 at a buoyancy frequency of 8 2 cph

anomalous southward intrusions of the oyashio east of japan 2 two layer numerical model anomalous southward intrusions of the oyashio along the japanese coast in the northwestern pacific occur from winter to late spring with cold sea surface temperatures exerting various influences on the temperature in japan and on aquaculture a two layer numerical model is employed to examine the interannual response of the ocean to the observed wind stress change over 1961 1987 with special reference to the occurrence of the anomalous southward oyashio intrusion since 1971 anomalous southward oyashio intrusions were observed in winter of 1974 1981 1984 and 1986 and the significant southward shift of the oyashio is well simulated in these years because the observed southward latitude of no wind stress curl in the north pacific and the sverdrup transport show clear simultaneous correlation with the calculated southernmost latitude of the subarctic circulation the anomalous southward intrusion of the oyashio is found to be essentially due to the barotropic response of the ocean to the change in the wind stress characterized by the southward development of the enhanced aleutian low the model also shows that a baroclinic response from the eastern boundary is mainly confined to a region east of 140 w and an uplift of the interface in a central area of the subarctic circulation is also formed by the divergence of the surface ekman layer in winter of the anomalous southward oyashio intrusion the calculated upper layer thickness south of the subarctic circulation has a clear positive simultaneous correlation with the observed southernmost latitude of the oyashio defined by the 5 c isotherm at a depth of 100 m which has been used as an index however the observed southernmost latitude of the oyashio follows the observed latitude of no wind stress curl and the sverdrup transport by 2 4 months while the calculated southernmost latitude of the subarctic circulation shows simultaneous correlation with no wind stress curl and the sverdrup transport from this it is pointed out that the observed southernmost latitude of the oyashio defined by the 5 c isotherm at a depth of 100 m lags by 2 4 months the barotropic response of the ocean which appears in the surface pressure fields and upper layer velocity

multidecadal variability of the overturning circulation in presence of eddy turbulence at low resolution idealized ocean circulation models forced by prescribed differential surface heat fluxes show spontaneous multidecadal variability depending critically on eddy diffusivity coefficients the existence of this critical threshold in the range of observational estimates legitimates some doubt on the relevance of such intrinsic oscillations in the real ocean through a series of numerical simulations with increasing resolution up to eddy resolving ones 10 km and various diapycnal diffusivities this multidecadal variability proves a generic ubiquitous feature at least in model versions with a flat bottom the mean circulation largely changes in the process of refining the horizontal grid along with the associated implicit viscosity and diffusivity and the spatial structure of the variability is largely modified but there is no clear influence of the resolution on the main oscillation period the interdecadal variability appears even more robust to low vertical diffusivity and overturning when mesoscale eddies are resolved the mechanism previously proposed for these oscillations involving westward propagating baroclinically unstable rossby waves in the subpolar region and its feedback on the mean circulation appears unaffected by mesoscale turbulence and is simply displaced following the polar front

paleomagnetism of the umbrian marches orogenic belt abstract the eower cretaceous maiolica formation was investigated in a regional paleomagnetic study in order to clarify the role of the umbrian marches region in western mediterranean tectonics this area has been considered as a semi autonomous microplate by some authors and as an allochthonous overthrust block by others oroclinal bending has been inferred from earlier paleomagnetic results of the scaglia formation in spite of weak natural remanent magnetizations nrm stable characteristic remanent magnetization chrm directions were defined for 31 sites the site mean directions are well grouped d 306 i 37 95 5 but are not uniform fisher statistics are therefore not applicable the nonuniformity of directions is partially due to regional and local variations but is not related to the orientation of the fold axes as suggested by several authors it is possible that the umbrian marches region has suffered thrust decollement on the underlying triassic evaporites during the late tertiary orogeny but this was not accompanied by large scale translation or rotation relative to the assumed autochthonous parts of the adriatic promontory

a thermal oscillation under a restorative forcing summary the authors report an interdecadal oscillation in a wind and thermally driven ocean general circulation model ogcm the oscillation is tantalizing in that it occursunder a relatively strong thermal damping 26 3 w m 2k examinations involving a two dimensional ogcm a simple thermal flip flop model and a three dimensional ogcm with and without the nonlinear effect of temperature in the state equation of sea water demonstrate that the oscillation is not driven by mechanisms such as the so called convective oscillator or the advective overshooting oscillator instead the oscillation is associated with the propagation of modelled long rossby waves with westward phase velocity it is found that the north south basin extent of the ogcm is an important factor a larger northsouth basin extent is conducive to the generation of thermal wind flows crucial for initiating the propagation of disturbances the geophysical relevance of these results is discussed

microstructure measurements in the mid depth waters of the north pacific 1 microstructure measurements from the surface down to maximum depths of 2000 m were carried out at 28 locations in the interior of the north pacific special attention was directed to the diapycnal diffusivities k in the significant generation regions of the semidiurnal internal tide such as the aleutian ridge the hawaiian ridge and the izu ogasawara ridge in the profiles obtained near the aleutian ridge only a few turbulent patches with 10 9 wkg 1 were detected and k was generally less than 10 5 m2s 1 in the profiles obtained near the hawaiian ridge many turbulent patches with 10 9 wkg 1 were observed although k was generally of the order of 10 5 m2s 1 along the izu ogasawara trough running in parallel with the izu ogasawara ridge in contrast remarkably intense turbulent mixing 10 8 wkg 1 k 10 4 10 3 m2s 1 was common throughout the observed water depth

differential compaction as a control on depositional architectures across the maiella carbonate platform margin central apennines italy abstract the role of differential compaction as a control in the creation of accommodation and on compaction modified depositional features and stratal geometries across the maiella platform margin has been investigated through a combined analysis of seismic scale outcrops porosity evaluation and modeling geologic evolution and large exposures make the platform margin of the maiella an ideal place to investigate the effects of differential compaction a high relief cemented carbonate platform a deep basin filled with highly compactable deposits and a prograding grain rich succession sealing morphologic differences across the platform margin represent suitable features for promoting differential compaction stratal relationships across the platform margin exhibit evidence of differential compaction induced effects such as basinward divergence and thickening of strata updip pinch out of wedge shaped stratal packages and an anticline hinge porosity analysis and modeling indicate that through progressive loading mechanical and chemical processes act in concert to destroy most of the depositional porosity mechanical compaction appears to have played the greatest part in the total budget of compaction however chemical compaction seems to have played a prominent role in the formation of geometrically consistent depositional profiles during progradation due to differential compaction across the platform margin a compaction hinge formed concomitantly with the beginning of progradation producing a basin facing monocline characterized by the progressive steepening of basinward stratal dips the resulting compaction induced stratal deformation together with sea level changes controls the distribution and depositional timing of wedge shaped stratal packages during late cretaceous and paleocene and the distribution of coral algal reef buildups during the late eocene early oligocene the development of the compaction hinge usually follows the progressive increase of loading but a decrease in compaction dissipation may be caused by overburdening of compactable deposits this will cause a delayed compaction induced subsidence whose effects will be produced after deposition i e during loading interruption this mechanism is thought to have an important role in the timing of compaction induced subsidence throughout the end of cretaceous and the early tertiary and it is considered together with sea level as the main controlling process of the occurrence and distribution of downslope sediments during a long lasting period of platform emersion

on the driving processes of the atlantic meridional overturning circulation because of its relevance for the global climate the atlantic meridional overturning circulation amoc has been a major research focus for many years yet the question of which physical mechanisms ultimately drive the amoc in the sense of providing its energy supply remains a matter of controversy here we review both observational data and model results concerning the two main candidates vertical mixing processes in the ocean s interior and wind induced ekman upwelling in the southern ocean in distinction to the energy source we also discuss the role of surface heat and freshwater fluxes which influence the volume transport of the meridional overturning circulation and shape its spatial circulation pattern without actually supplying energy to the overturning itself in steady state we conclude that both wind driven upwelling and vertical mixing are likely contributing to driving the observed circulation to quantify their respective contributions future research needs to address some open questions which we outline

isolating the role of mesoscale eddies in mixing of a passive tracer in an eddy resolving model 1 this study examines the role of mesoscale eddies in distribution of chlorofluorocarbon cfc in a numerical model of the north atlantic our main conclusions are based on a comparison of two eddy resolving experiments one with and one without eddy advection of cfc the cfc distributions in these two experiments exhibit substantial differences within the subpolar gyre in particular in the presence of eddies the horizontal distribution of cfc in the upper 1000 m is more uniform and the cfc concentration is lower in the lower 1500 m our analysis demonstrates that these basin wide differences are caused by the interactions of eddy advection with convection and mean advection in several isolated locations the corresponding eddy flux divergence terms are spatially non uniform in magnitude their effects are often nonlocal and sometimes work against the spreading of cfc being carried out by the mean advection these conclusions are further confirmed by a third experiment in which the eddy advection was replaced by a down gradient diffusive parameterization our results demonstrate that advection by mesoscale eddies is crucial to the mixing of atmospheric gasses into the ocean and outline difficulties in representing eddies by the down gradient diffusion

geothermal heating and its influence on the meridional overturning circulation the effect of geothermal heating on the meridional overturning circulation is examined using an idealized coarse resolution ocean general circulation model this heating is parameterized as a spatially uniform heat flux of 50 mw m 2 through the flat ocean floor in contrast with previous studies that have considered an isolated hotspot or a series of plumes along the mid atlantic ridge the equilibrated response is largely advective a deep perturbation of the meridional overturning cell on the order of several sv is produced connecting with an upper level circulation at high latitudes allowing the additional heat to be released to the atmosphere rising motion in the perturbation deep cell is concentrated near the equator the upward penetration of this cell is limited by the thermocline analogous to the role of the stratosphere in limiting the upward penetration of convective plumes in the atmosphere the magnitude of the advective response is inversely proportional to the deep stratification with a weaker background meridional overturning circulation and a less stratified abyss the overturning maximum of the perturbation deep cell is increased this advective response also cools the low latitude thermocline the qualitative behavior is similar in both a single hemisphere and double hemisphere configuration the anomalous circulation driven by geothermal fluxes is more substantial than previously thought we are able to understand the structure and strength of the response in the idealized geometry and further extend these ideas to explain the results of adcroft et al 2001 where the impact of geothermal heating was examined using a global configuration

a basinwide estimate of vertical mixing in the upper pycnocline spreading of bomb tritium in the north pacific ocean abstract the vertical diffusivity kv in the upper half kilometer of the north pacific subtropical pycnocline is estimated from observations of the spreading rate of anthropogenic tritium the calculation is based on approximately 300 ocean tritium profiles made since tritium was introduced to the atmosphere via bomb testing in the 1960s the data coverage does not permit detailed mapping of tritium penetration especially in the sparsely sampled western pacific for this reason and to minimize advective effects the spreading rate is averaged within the closed streamlines of the subtropical gyre spanning 5 n to 40 n the result kv 1 5 0 7 10 5 m2 s 1 is consistent with inferences from microstructure and purposefully released tracer measurements in the north atlantic confirming that the spatially averaged rate of mixing in the upper pycnocline is substantially lower than the canonical munk estimate for the lower pycnocline

depositional geometries and facies associations in an upper cretaceous prograding carbonate platform margin orfento supersequence maiella italy abstract although progradation of platform margins is a well documented process its timing with respect to sea level cycles is controversial this outcrop study was designed to test the relation between prograding stratal patterns and sea level cycles using a sequence stratigraphic analysis and direct investigation of the sedimentological facies associations the upper campanian maastriehtian orfento supersequence in the maiella platform margin is an outstanding outcrop example of a large scale prograding carbonate wedge composed of smaller scale vertically and laterally stacked sequences the evolution of the orfento supersequence was characterized by an initial phase of aggradation followed by progradation at the scale of the supersequence basinal aggradation preceded progradation of hallower water facies because excess relief had to be buried prior to progradation seven depositional facies were distinguished on the basis of depositional geometries stratal patterns and sedimentary features these facies record different depositional environments on a low angle ramp ranging from deep water pelagic wackestones to wave dominated upper shoreface grainstones facies distributions record the overall transition from pelagic sediments turbidites and megabreccias into progressively shallower water shoreface complexes the prograding units consist of shingled offlapping sigmoidal complexes composed of rudstones and grainstones deposited in shallow wave dominated environments and their deeper water equivalents sigmoidal sequences are separated by erosive unconformities which bring upper shoreface facies into direct contact with underlying lower shoreface or outer shelf facies indicating a sea level fall forced regression meteoric diagenesis associated with the unconformities also supports lowering of relative sea level depositional facies patterns within sequences record a relative rise and highstand of sea level repetitive downward shifts bring the shoreline successively farther basinward indicating long term lowering of sea level during the late stages of progradation producing downstepping progradation our data suggest that changes in relative sea level acting on a low angle ramp control the overall architecture of sequence distribution whereas changes in sediment supply con rol changes in facies association within each sequence

parameter sensitivity of primitive equation ocean general circulation models abstract experiments with a low resolution primitive equation ocean general circulation model with idealized basin geometry and surface forcing have been carried out in order to identify the processes controlling the climatically important aspects of the circulation emphasis was placed on the sensitivity of the model solutions to the magnitude of the vertical diffusivity scaling arguments suggest and the numerical experiments confirm that the solutions are most sensitive to the magnitudes of the wind stress curl and the vertical diffusivity for small vertical diffusivity wind forcing dominates the solution the vertical scale of the thermocline is set by the strength of the ekman pumping and there is a multiple gyre circulation in the upper layers for large vertical diffusivity diabatic surface forcing dominates the solution vertical diffusion controls the vertical scale of the thermocline and there is a single large anticyclonic gyre in the upper layers both the meridionally and zonally inte