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

assimilation of satellite altimetry referenced to the new grace geoid estimate 1 currently two satellite gravimetric missions champ grace are dedicated to the improvement of our knowledge of the geoid and one goce is planned in the near future this will allow the absolute altimeter ocean height measurements to be exploited instead of only sea level variations in this paper we evaluate the impact of the grace mission on ocean data assimilation the new approach is to directly assimilate the full altimetric signal relative to the first release of a grace geoid the response of an eddy permitting ocean model of the north atlantic to the assimilation of this altimetric signal is analysed the results are compared to that obtained using the usual approach i e the assimilation of the dynamic topography derived from the addition of altimetric sea level anomalies and a mean dynamic topography estimate even if the grace mission resolution 333 km is not yet compatible with oceanographic studies at mid latitude we show that the geoid estimate can already be used with success in basin scale altimetric data assimilation problems

estimating short term changes in eustatic sea level the history of short term eustatic sea level change proposed by p r vail and his coworkers was originally based on shifts through time in the landward pinchout of seismic sequences in order to quantify the magnitude of these proposed sea level changes histories of subsidence sediment loading sediment compaction and paleowater depth are required of these accurate estimates of paleowater depth and subsidence are the most difficult to derive this approach is applied to two example data sets for one study the midway atoll we use the theoretical subsidence model of detrick et al 1981 the possible error in this model is approximately the same as the extreme differences in sea level highstands 50 100 m proposed by previous investigators the second example is from the baltimore canyon area here we estimate subsidence by an average angular tilt rate resulting estimates of sea level highstands for the past 30 ma are similar to the long term sea level estimates of kominz 1984 however the overall variation in the highstands parallels that of haq et al 1987 short term sea level falls are estimated to be similar in magnitude to those of haq et al 1987 most of these short term fluctuations are within the range of reasonable glacioeustatic fluctuations 30 100 m a correlation is found between the estimated short term changes in sea level and the miocene oxygen isotope record this correlation exists both prior to and after 14 ma however there is a 1 08 isotopic shift in the data in the middle miocene because estimated highstands are within 10 15 m of being the same magnitude before and after this shift we suggest that this shift is caused mainly by a cooling of deep waters

isotopic composition of bank margin carbonates on midway atoll amplitude constraint on post early miocene eustasy the university of hawaii9s continuously cored borehole through the midway atoll coral cap provides a record of post early miocene eustasy subaerial exposure horizons are identified by light carbon isotope signatures and in some instances by lithologic criteria sea level highstands are recorded by aggradational units of reef sediment that are bounded by these subaerial exposure horizons sea level lowstands are constrained to fall no farther than a meteoric marine diagenetic boundary observed in the core this diagenetic boundary is defined by an offset in both oxygen and carbon isotope data light isotopic composition being indicative of intermittent meteoric diagenesis these data constrain the amplitudes of three post early miocene glacio eustatic sea level falls to be no more than 32 43 and 52 m absolute sea level elevations are estimated by constructing a subsidence model for midway atoll application of this analytic approach may provide amplitude constraints on eustasy elsewhere in the geologic record

path of the north atlantic deep water in the brazil basin recent hydrographic sections and high quality historical data sets are used to determine geostrophic currents at subtropical latitudes in the western basin of the south atlantic levels of no motion are determined from water mass information and a mass balance constraint to obtain the transport field of north atlantic deep water nadw in this region the incoming nadw transport of about 20 sv from the north at 19 degrees s appears to be balanced by only one third of this transport leaving in the south and two thirds leaving to the east or northeast at the mid atlantic ridge a simple model is proposed to determine the cause of the nadw branching it is shown that potential vorticity preservation in the presence of topographic changes leads to a similar flow pattern as observed with branching near the vitoria trindade ridge and also an eastward turning of the southward western boundary current at about 28 degrees s the latitude where a balance of planetary vorticity change and stretching can be expected

heat flow on the hawaiian swell and lithospheric reheating most oceanic volcanic centres caused by hotspot activity are surrounded by sea floor that is unusually shallow for its age1 2 there is increasing evidence that swells found on older sea floor like the hawaiian swell have formed from a broad scale reheating and thinning of the lithosphere as it passes over a mantle hotspot3 4 if the formation and subsequent disappearance of these swells are controlled by thermal processes they should have an above normal heat flux we present here the results from 95 new heat flow measurements on the hawaiian swell along the older part of the swell the heat flow is 20 25 higher than the normal heat flow for crust of this age this anomaly is consistent with the observed swell uplift the shape and amplitude of the heat flow anomaly require that the reheating be largely confined to the lower half of the lithosphere

impact of the gravity field and steady state ocean circulation explorer goce mission on ocean circulation estimates 2 volume and heat fluxes across hydrographic sections of unequally spaced stations 1 accurate geoids are expected to improve our knowledge of the dynamic sea surface height ssh as a mirror of the dynamic state of the oceans the dedicated gravity field and steady state ocean circulation explorer goce mission will lead to a highly accurate geoid model with a resolution of degree and order 200 we examine the impact of this mission on the assessment of large scale oceanic mass and heat transports via its expected error characteristics we do so applying a linear box inverse model and a nonlinear section inverse model to hydrographic data and to synthetic ssh data the results are compared to those obtained when substituting the error estimates of the gravity recovery and climate experiment grace mission and the present day earth gravitational model 1996 for the box inverse model we find an average reduction in transport uncertainties of about 9 for grace geoid error covariances and about 17 for goce over the hydrography only solution in both grace and goce these average percentage improvements are significantly increased when model error is excluded summarizing our results and those of the companion parts of this study we conclude that the grace mission reduces the marine geoid uncertainties such that altimetry may become useful for the study of the steady state ocean circulation the goce mission will improve the accuracy of the circulation estimates significantly on the large scales and introduce higher accuracy on shorter wavelengths as well furthermore it will enable us to study individual ocean currents

evidence in hydrography and density fine structure for enhanced vertical mixing over the mid atlantic ridge in the western atlantic received 24 august 2001 revised 22 february 2002 accepted 25 march 2002 published 15 october 2002 1 anomalous conditions exist in the salinity oxygen and nutrient fields over the western flank of the northern hemisphere mid atlantic ridge we examine possible advective sources for this anomaly but determine that vertical mixing is the most likely cause we proceed to use knowledge gained from the brazil basin tracer release experiment in the south atlantic where microstructure and fine structure were obtained to explore the intensity spatial distribution and mechanisms of mixing in the deep ocean to interpret density fine structure from common conductivity temperature depth data in the north atlantic these data support the hypothesis that the anomalous hydrographic conditions are associated with enhanced levels of vertical mixing the inferred levels of vertical diffusivity over the northern hemisphere mid atlantic ridge are as high as in the south atlantic 1 10 10 4 m 2 s index terms 4532 oceanography physical general circulation 4536 oceanography physical hydrography 4568 oceanography physical turbulence diffusion and mixing processes keywords diapycnal mixing fine structure recirculation mid atlantic ridge mar hydrography silicate

oxygen isotopes and sea level from the time that detailed oxygen isotope records derived from foraminifera living in the constant temperature environment of the abyssal ocean became available there has been a discrepancy between the ice volume record that these records imply and that derived from the altitude of dated coral terraces around the world here we re examine the data and conclude that the temperature of the abyssal ocean has been an actively varying component of the climate system

the production of north atlantic deep water sources rates and pathways updating an earlier account by dickson et al 1990 this paper reviews the initial development phase of north atlantic deep water nadw production from the points where the dense inflows from nordic seas cross the greenland scotland ridge to the point off south greenland where the buildup of new production appears almost complete in particular three long term current meter arrays totaling 91 instruments and set at 160 km intervals south from the denmark strait sill are used to validate earlier short term arrays by others and in combination with these earlier arrays to describe the downstream evolution of mean speed depth and entrainment the variability of the overflow current in space and time and the likely contribution of the other three main constituents of nadw production at densities greater than 27 8 from the points of overflow 5 6 sv the transport within this range increases by entrainment and confluence with other contributory streams to around 13 3 sv at cape farewell while recirculating elements prevent us from determining the net southgoing transport a nadw transport of this order appears consistent with recent estimates of net abyssal flow passing south through the north and south atlantic

interannual evolution of multiple longshore sand bars in a mesotidal environment truro massachusetts usa abstract multiple longshore bars 0 30 1 5 m in amplitude are present in the nearshore zone off truro ma in cape cod bay these bars exist in a mesotidal environment with a tidal range of 3 0 m a detailed interannual investigation of these bars over a 16 year time period using orthorectified vertical aerial photography has been carried out to characterize the behavior of multiple bars forming in a mesotidal environment over a temporal scale of observation not generally achieved by direct field study this investigation reveals that the bars are dynamic over the time interval studied with offshore extents of up to 660 m and wavelengths of 45 150 m generally increasing in the seaward direction at any one location 4 to 10 bars are present with an apparent addition of bars at the southern end of the study area in addition the bars are consistently parallel to offshore bathymetric contours and comparison of more recent photographs with a 1960 image reveals a 0 5 km alongshore zone without bars that has persisted and grown since 1960 the characteristics of the truro multiple bar field are consistent with several existing theories of multiple bar formation including formation by breaking waves standing infragravity waves and edge waves the demonstrated dynamic nature of the truro multiple bar field over a long temporal scale suggests that field experiments designed to distinguish between possible formation theories may provide an explanation for the continuing modern creation and modification of this and similar multiple bar fields occurring in mesotidal environments

δ13c values of miocene pacific benthic foraminifera correlations with sea level and biological productivity 13 c 12 c ratios of miocene benthic foraminifera from 22 pacific ocean sites vary with time but are similar at almost all sites in any restricted interval 13 c values are correlated with sea levels inferred from onlap offlap curves reflecting the deposition of greater amounts of organic matter on the continental shelves during transgressions differences in 13 c between sites are correlated with local differences in biological productivity in the overlying surface waters 13 c 12 c values of benthic foraminifera show promise as indicators of marine paleoproductivity

coastal geomorphology through the looking glass abstract coastal geomorphology will gain future prominence as environmentally sound coastal zone management strategies requiring scientific information begin to supplant engineered shoreline stabilization schemes for amelioration of coastal hazards we anticipate substantial change and progress over the next two decades but we do not predict revolutionary advances in theoretical understanding of coastal geomorphic systems paradigm shifts will not occur knowledge will advance incrementally we offer predictions for specific coastal systems delineated according to scale for the surf zone we predict advances in wave shoaling theory but not for wave breaking we also predict greater understanding of turbulent processes and substantive improvements in surf zone circulation and radiation stress models very few of these improvements are expected to be incorporated in geomorphic models of coastal processes we do not envision improvements in the theory of sediment transport although some new and exciting empirical observations are probable at the beach and nearshore scale we predict the development of theoretically based two and three dimensional morphodynamical models that account for non linear time dependent feedback processes using empirically calibrated modules most of the geomorphic research effort however will be concentrated at the scale of littoral cells this scale is appropriate for coastal zone management because processes at this scale are manageable using traditional geomorphic techniques at the largest scale little advance will occur in our understanding of how coastlines evolve any empirical knowledge that is gained will accrue indirectly finally we contend that anthropogenic influences directly and indirectly will be powerful forces in steering the future of coastal geomorphology if you should suddenly feel the need for a lesson in humility try forecasting the future kleppner 1991 p 10

midlatitude equatorial dynamics of a grounded deep western boundary current part i midlatitude flow and the transition to the equatorial region abstracta comprehensive theoretical study of the nonlinear hemispheric scale midlatitude and cross equatorial steady state dynamics of a grounded deep western boundary current is given the domain considered is an idealized differentially rotating meridionally aligned basin with zonally varying parabolic bottom topography so that the model ocean shallows on both the western and eastern sides of the basin away from the equator the flow is governed by nonlinear planetary geostrophic dynamics on sloping topography in which the potential vorticity equation can be explicitly solved as the flow enters the equatorial region it speeds up and becomes increasingly nonlinear and passes through two distinguished inertial layers referred to as the intermediate and inner inertial equatorial boundary layers respectively the flow in the intermediate equatorial region is shown to accelerate and turn eastward forming a narrow equatorial jet the qualitative properties of the solution presented are consistent wi

reconstruction of tertiary progradation and clinoform development on the new jersey passive margin by 2 d backstripping we have reconstructed the oligocene to middle miocene paleobathymetry and stratigraphy of the new jersey margin using a modified backstripping technique by analyzing the geometry of the margin through time we investigate its response to fluctuating sea level changing climate and variable sediment supply during the tertiary the reconstructions reveal a change in the margin morphology from a more steeply dipping 1 300 to 1 500 carbonate ramp in the eocene to a flatter shelf with a sharp shelf edge at present this was accomplished by an increase in the terrigenous sediment supply that filled available accommodation and caused progradation across the margin we link the increase in sediment flux with climatic cooling rather than tectonic processes the progradation is evidenced by a series of clinoforms whose formation was modulated by sea level and which extend over 100 km across the shelf the height and dip of the clinoforms increased as they extended onto the deeper parts of the earlier ramp the miocene clinoform rollovers at the new jersey margin had water depths of60 130 m and are interpreted as the edge of a new continental shelf built over the older ramp sea level fall was probably insufficient to drive the miocene shorelines past the shelf breaks thus measurements of sea level amplitude based upon coastal onlap over the clinoforms are not reliable 1999 elsevier science b v all rights reserved

model data comparisons of moments of nonbreaking shoaling surface gravity waves the predictions of linear and nonlinear boussinesq shoaling wave models for nonbreaking unidirectional surface gravity waves are compared to field observations with particular emphasis on quantities that may be important for cross shore sediment transport the extensive data sets were obtained on two natural beaches span water depths between 1 and 10 m and include incident wave power spectra with narrow broad and bimodal shapes significant wave heights varied between approximately 30 and 100 cm and peak periods between approximately 8 and 18 s the evolution of total variances of sea surface elevation cross shore velocity and horizontal acceleration is modeled at least qualitatively well by both linear and nonlinear theories only the nonlinear theory predicts the increasingly asymmetric sea surface elevations and horizontal velocities pitched forward wave shapes and the weaker variation of skewness difference between crest and trough profiles which are observed to occur during shoaling the nonlinear theory also models qualitatively well the large skewed accelerations which occur during the passage of asymmetric waves

calculating the time mean oceanic general circulation and mixing coefficients from hydrographic data abstract the relation between the circulation calculated from averaged hydrographic data such as the levitus data and the actual time average circulation is examined using a ctd dataset which provides both time and space coverage of a region of the mediterranean sea the connection between eddy mixing coefficients calculated from hydrographic data and the eddy fluxes u t they are intended to parameterize is also considered an inverse model is used to calculate circulation and mixing coefficients from the time average data then the actual time averaged circulation is estimated by averaging six realizations of the instantaneous velocity field and mixing coefficients are calculated by directly parameterizing the eddy fluxes of heat and salt comparing the results obtained by the different procedures it is concluded that the horizontal time average circulation can be reliably estimated from averaged and smoothed climatological data but that it is nearly impossible to obtain physically meaningful m

three dimensional stratigraphic evolution of the miocene baltimore canyon region implications for eustatic interpretations and the systems tract model a seismic stratigraphic analysis of miocene deposits in the baltimore canyon region offshore new jersey reveals tremendous threedimensional complexity and challenges traditional approaches to sequence stratigraphic interpretation individual sequences vary dramatically in along strike thickness revealing the locations of the sediment sources within sequences the lowstand wedge thins dramatically along strike tens to hundreds of meters and is interpreted to record variable paleobathymetry along strike as indicated by sequence thickness distributions shelf break positions lithologic composition and stratigraphic relationships sequences record sediment migration and progradation across the basin through time as a result of these depositional complexities relative sea level curves interpreted from parallel dip lines vary in magnitude and amplitude across the basin development of neogene stratal patterns within the baltimore canyon region has been closely linked to glacioeustatic change our reconstructions of delta switching and progradation emphasize that miocene stratal patterns were greatly influenced by autocyclic depositional processes

on deep western boundary currents the stommel and arons 1960a b theory of the deep circulation of the world ocean does not directly address the physics of deep boundary currents in the present paper a maximally simple steady state physics for deep western boundary currents is developed and integrated into the stommel arons model this is accomplished by modifying the assumptions of the latter to include effective horizontal eddy viscous terms everywhere in the deep water including in the interior the resulting solution for the meridional velocity in a rectangular ocean on a beta plane is mathematically analogous to that of munk 1950 for the wind driven circulation in the interior the meridional velocity reduces identically to that of stommel and arons among other benefits the solution eliminates the theoretical difficulties associated with the crossing of the equator by the deep western boundary current as an initial test of the theory s consistency with observation theoretical plots of pressure and meridional velocity as a function of longitude are qualitatively compared with hydrographic sections and inferred meridional velocity fields in the eastern and western basins of the abyssal north atlantic also the theoretical profile for the meridional velocity as a function of longitude is qualitatively compared with observations of longshore velocity as a function of offshore distance in the deep western boundary current of the north atlantic deep water

zonal circulation in the nw atlantic and caribbean from a meridional world ocean circulation experiment hydrographic section at 66 w a world ocean circulation experiment hydrographic program section along 66 w in the north atlantic was made in 1997 in addition to the usual variables hydrographic and tracer measured in woce onetime sections we made lowered acoustic doppler current profiler ladcp measurements at nearly all of the stations the section closed off a portion of the western north atlantic to the west of the line making a closed volume for constraining the circulation in addition the deep portions of the caribbean do not communicate with the rest of the basin by combining mass silica and ladcp information as constraints an inverse calculation obtained reveals a strong eastward transport in the gulf stream bounded by westward flowing water on either side within these energetic flows we see evidence for recently ventilated classical labrador sea water which has not reached the deep western boundary current north of puerto rico in any significant amounts within the caribbean our major new finding is a deep cyclonic circulation below sill depth in excess of 100 times the inflow of deep atlantic water through the major deep sill the anegada jungfern passage the signature of the deep atlantic source water is most prominent in cfcs and both a bottom and mid depth maximum are present in the caribbean to the south of puerto rico off the coast of venezuela however only the deeper cfc maximum is found for the entire section the net overturning circulation heat flux and freshwater fluxes are all consistent with expectations based on water mass formation and air sea exchanges to the west of our section but the annual mean air sea fluxes of heat and freshwater from comprehensive ocean atmosphere data sets appear somewhat too small in comparison with our single section result

dynamical pathways of antarctic bottom water in the atlantic abstract a reduced gravity model is developed to represent the flow of antarctic bottom water aabw over realistic bathymetry in an atlantic domain the dynamics are based on the steady planetary geostrophic shallow water equations including a linear bottom friction and a uniform diapycnal upwelling through the top of the model layer the model solutions are broadly consistent with observations of the distribution and transport of aabw the flows occur predominantly along potential vorticity contours which are in turn broadly oriented along bathymetric contours the characteristic weak flow across potential vorticity contours of the stommel arons model is present as a small addition to this stronger forced mode along potential vorticity contours as a consequence mass balance is maintained not by hypothesized western boundary currents as in the stommel arons model but by the interplay between topographic slope currents and interior recirculations in particular a transposition is found in the flow

storm driven cyclic beach morphodynamics of a mixed sand and gravel beach along the mid atlantic coast usa abstract the morphodynamics of a mixed sand and gravel beach in delaware were investigated based on 18 almost monthly beach profile surveys at 46 locations from 2009 to 2011 60 sediment cores and 550 surface sediment samples collected at various alongshore and cross shore transects three different atmospheric disturbances occurred within a 3 month window during the study period 1 a distal hurricane 2 an energetic winter storm and 3 nor ida a long lasting and extremely energetic event resulting from the collision of a hurricane and winter storm the storm induced beach changes and post storm recovery following each of the three storms are evaluated a distinctive beach cycle was identified consisting of a built up berm profile and depleted nearly planar storm profile the time scale of the beach cycle relates to the frequency and intensity of storm impact and duration of inter storm recovery instead of simple seasonality the initiation of post storm recovery occurs during the subsiding phase of the storm attributable to the reduction in wave height and steepness transitioning to accretionary swells the sediment characteristics of the storm deposit associated with nor ida demonstrated substantial cross shore variation ranging from sandy gravel and gravelly sand within the storm swash zone near the pre storm dune edge to well sorted medium to coarse sand seaward of the storm swash zone storm deposits along mixed sand and gravel beaches demonstrate a variety of sedimentological characteristics in addition the studied beaches lacked a sandbar under all wave conditions a new beach cycle model is proposed for the non barred mixed sand and gravel beach

sediment flux and equilibrium slopes in a barred nearshore estimates of time integrated values of total itvf and net invf sediment volume flux and the associated changes in bed elevation and local slope were determined for a crescentic outer nearshore bar in kouchibouguac bay new brunswick canada for eight discrete storm events a 100 150 m grid of depth of activity rods spaced at 10 m intervals was used to monitor sediment behaviour on the seaward slope bar crest and landward slope during the storms at which time winds incident waves and near bed oscillatory currents were measured comparisons between storm events and between these events and a longer term synthetic wave climatology were facilitated using hindcast wave parameters strong positive correlations between storm wave conditions significant height and total cumulative energy and total volume flux contrasted strongly with the zero correlation between storm wave conditions and net volume flux itvf values ranged up to 1646 m3 for the experimental grid and were found to have power function relations with significant wave height exponent 2 and cumulative wave energy exponent 0 4 values of invf ranged from 0 up to 100 m3 for the same grid indicating a balance of sediment volume in the bar form through time sediment reactivation increased linearly with decreasing depth across the seaward slope and bar crest reaching maxima of 20 cm for the two largest storms bed elevation and thus slope changes were restricted to the bar crest and upper landward slope with near zero morphological change on the seaward slope the latter represents a steady state equilibrium with null net transport of sediment under shoaling waves measurements of the asymmetry of orbital velocities close to the bed show that the energetics approach to predicting beach slope of inman and bagnold 1963 is sound gradients predicted vary from 0 01 to 0 03 for a range of angles of internal friction appropriate to the local sediment tan o 0 3 0 6 these compare favorably with the measured seaward slope of 0 015 formed under average maximum orbital velocities of 1 12 m s 1 landward and 1 09 m s 1 seaward recorded during the period of the largest storm waves

uncertainties in the mean ocean dynamic topography before the launch of the gravity field and steady state ocean circulation explorer goce 1 in anticipation of the future observations of the gravity mission gravity field and steady state ocean circulation explorer goce the present day accuracy of mean dynamic topography mdt is estimated from both observations and models a comparison of five observational estimates illustrates that rms differences in mdt vary from 4 2 to 10 5 cm after low pass filtering the fields with a hamming window with wavenumber n 120 corresponding to an effective resolution of 167 km rms differences in observational mdt reduce to 2 4 8 3 cm for n 15 1334 km differences in data sources geoid model in situ data are mostly visible in the small scale oceanic features while differences in processing filtering inverse modeling techniques are reflected at larger scales a comparison of seven different numerical ocean models demonstrates that model estimates differ mostly in western boundary currents and in the antarctic circumpolar current rms differences between modeled and observed mdt are at best 8 8 cm for n 120 and reduce to 6 4 cm for n 15 for models with data assimilation a minimal rms difference of 6 6 cm n 120 to 3 4 cm n 15 is obtained with respect to the observational mdts the reduction of differences between mdts with increasing filtering scales is smaller than expected while it is expected that goce will improve mdt estimates at small spatial scales improvement of mean sea surface estimates from satellite altimetry may be needed to improve mdt estimates at larger scales

evolution of the deep western boundary current of antarctic bottom water in the brazil basin abstract a synthesis of woce and other hydrographic data shows that the deep western boundary current of antarctic bottom water has a double core structure and that it is differentially modified during its northward transit through the brazil basin at 25 s it descends about 200 m while continuing equatorward as a paired double core current over the relatively broad sloping topography of the western region the downslope core is faster 4 6 cm s 1 versus 3 cm s 1 and is coincident with the high density core equatorward of 19 s the cores begin to diverge and by 15 s the velocity cores have separated and the high speed pattern has inverted between 13 and 11 s the colder slower flowing branch around 3 cm s 1 deepens by 350 m with a noticeable decrease in the vertical stratification of overlying water characteristics subsequently it continues to the equator toward the romanche chain fracture zones the warmer faster flowing branch around 8 cm s 1 proceeds to the equator along the continent

waves currents sediment flux and morphological response in a barred nearshore system abstract a shore normal array of seven bi directional electromagnetic flowmeters and nine surface piercing continuous resistance wave staffs were deployed across a multiple barred nearshore at wendake beach georgian bay canada and monitored for a complete storm cycle time integrated estimates of total itvf and net invf sediment volume flux together with bed elevation changes were determined using depth of activity rods the three bars ranging in height from 0 10 to 0 40 m accreted during the storm 0 03 m and the troughs were scoured 0 05 m sediment reactivation depths reached 0 14 m and 12 of the nearshore control volume was mobilized however the invf value for the storm was less than 1 of the control volume revealing a near balance in sediment volume in the bar system landward migration of the inner crescentic and second sinuous bars occurred in association with an alongshore migration of the bar form itself the outermost straight shore parallel bar remained fixed in location the surf zone was highly dissipative throughout the storm 3 8 10 2 192 10 2 and the wave spectrum was dominated by energy at the incident frequency spectral peaks at frequencies of the first harmonic and at one quarter that of the incident wave were associated with secondary wave generation just prior to breaking and a standing edge wave respectively the former spectral peak was within the 95 confidence band for the spectrum while the latter contributed not more than 10 to the total energy in the surface elevation spectrum even near the shoreline during the storm wave height exceeded 2 m h s and periods reached 5 s t p k orbital velocities exceeded 0 5 m s 1 u rm s and were above the threshold of motion for the medium to fine sands throughout the storm shore parallel flows in excess of 0 4 m s 1 were recorded with maxima in the troughs and minima just landward of the bar crest the rate and direction of sediment flux is best explained by the interaction of antecedent bed slopes with spatial gradients in the mean and asymmetry of the shore normal velocity field these hydrodynamic parameters represent steady flows superimposed on the dominantly oscillatory motion and assumed a characteristic spatial pattern from the storm peak through the decay period increases spatially in the magnitudes of both the mean flows and flow asymmetries cause an increasing net transport potential erosion decreases in these values spatially cause a decreasing net transport potential and thus deposition these transport potentials are increased or decreased through the gravity potential induced by the local bed slope shore parallel flow was important in explaining sediment flux and morphological change where orbital velocities mean flows and flow asymmetries were at a minimum

morphodynamics of intertidal bars in wave dominated coastal settings a review abstract intertidal bar systems are ubiquitous features on wave dominated beaches in coastal settings with a significant 1 m tidal range depending primarily on the wave conditions and the tidal range and to a lesser extent on the nearshore gradient they can assume a variety of forms slip face bars represent the most pronounced and dynamic intertidal bar morphology and are generally found on their own around the mean high tide level they usually form low on the intertidal beach after storm induced beach erosion and develop into a berm under prolonged calm wave conditions low amplitude ridges and sand waves represent multiple bar morphologies the bars occur across the entire intertidal profile and they remain present throughout the year multiple intertidal bars tend to be rather subdued and relatively static especially sand waves and their origin remains unclear the morphological response of intertidal bars to changing wave conditions is largely forced bars build up and migrate onshore under calm waves and are flattened and may migrate offshore during storms the morphological response is however significantly affected by relaxation time effects and morphological feedback particularly on beaches with multiple intertidal bars despite their morphological differences the intertidal bar types exhibit pronounced similarities in their morphodynamics sediment transport processes and morphological response are principally controlled by the tidal water levels on the beach because these together with the offshore wave energy level and the beach morphology determine the type intensity and duration of the wave processes operating on the cross shore profile it is the dominant importance of tidal water level variations and wave processes in shallow water depths swash and surf zone bores rather than wave height variability and deeper water wave processes breaking and shoaling waves that constitutes the main difference between intertidal and subtidal bar morphodynamics

nutrient mineralization rates and ratios in the eastern south atlantic the physical and biogeochemical components of nutrients and inorganic carbon distributions along woce line a14 are objectively separated by means of a constrained least squares regression analysis of the mixing of eastern south atlantic water masses contrary to previous approaches essentially devoted to the intricate south atlantic circulation this work is focused on the effects of circulation on nutrients and carbon biogeochemistry with special emphasis on the stoichiometry and the rate of mineralization processes combination of nutrient and apparent cfc age anomalies derived from the mixing analysis indicate faster mineralization rates in the equatorial 12 10 2 mol p kg 1 yr 1 and subequatorial 5 3 10 2 mol p kg 1 yr 1 than in the subtropical 4 3 10 2 mol p kg 1 yr 1 regime at the south atlantic central water sacw depth range lower rates are obtained in the antarctic intermediate water aaiw domain 3 0 10 2 mol p kg 1 yr 1 significant variation with depth of o2 c n p anomalies indicates preferential mineralization of proteins in thermocline waters as compared with the reference redfield composition

oceanic fluxes on the woce a11 section abstract the most southerly woce one time section in the south atlantic designated a11 was occupied in january 1993 the cruise track lay across the cool subantarctic zone of the circumpolar current in the west and the warm subtropical gyre in the east in this paper estimates of the flux of heat salt oxygen and other tracers across the section are presented a brief description of the distribution of physical and chemical properties is followed by a determination of the flux in the surface ekman layer direct measurements of current shear made from a shipborne adcp and estimates from cruise wind data and climatological data all yield a flux of 5 1 sv sv 106 m3 s 1 equatorward when combined with geostrophic estimates relative to a level near 3500 dbar or the bottom where shallower an initial guess for the flow field is derived this initial guess is combined with absolute currents derived from the adcp when the ship is underway unrealistic aspects of the circulation are found and we conclu

bragg reflection of ocean waves from sandbars 1 resonant bragg reflection of ocean surface waves by a field of natural shore parallel sandbars was observed in cape cod bay ma waves transmitted through the bars were reflected strongly from the steep shoreline and the observed cross shore variations in the onshore and offshore directed energy fluxes are consistent with theory for resonant bragg reflection including a 20 decay of the incident wave energy flux that is an order of magnitude greater than expected for wave orbital velocity induced bottom friction bragg reflection was observed for a range of incident wave conditions including storms when sediment transported toward and away from nodes and antinodes caused by the reflecting waves might result in growth and maintenance of the sandbars

anatomy and origin of toplap in a mixed carbonate clastic system seven rivers formation permian guadalupian guadalupe mountains new mexico usa the seven rivers formation exposed in slaughter canyon guadalupe mountains new mexico reveals complex relations between long and short term relative changes in sea level shelf configuration and sedimentation which interacted to create a distinct toplap geometry at least five sandstones diverge basinward from a prominent boundary unit marking the surface of toplap at the top of the seven rivers formation and create a series of prograding shingled clinoforms the boundary unit is a horizontal well sorted quartz arenite underlain across the shelf by peritidal carbonate or by other merging sandstones preserved palaeotopography is indicated by facies changes downdip and the presence of horizontal geopetal indicators in inclined beds near the boundary unit updip merging sandstones contain rare sedimentary structures including evaporite moulds and irregular fenestrae and are bounded above and below by peritidal carbonate with microbial laminae fenestral fabrics and mudcracks laterally downdip the sandstone bounding peritidal carbonate facies pass into subtidal carbonate facies ooid peloid fusulinid dasyclad mollusc pack and grainstone and interbedded sandstones contain sedimentary structures such as ripple marks and trough to planar cross stratification as well as ooids fusulinids and other carbonate grains toplap is interpreted to have developed by sediment bypass across a subaerially exposed shelf while sedimentation continued in still submerged areas downdip from the shelf crest and hence represents depositional toplap physical tracing of subaerial exposure surfaces suggests that the shoreline migrated up and down palaeoslope several times the vertical component of five short term shoreline migrations decreased during formation of the toplap geometry sea level rose to approximately the same position following each fall to create the toplap geometry this depositional toplap is the stratigraphic result of high frequency relative changes of sea level that combined to produce the larger scale geometry we suggest that changing amplitudes of relative sea level may play a significant role in the stratigraphic evolution of platforms and that separating short term and long term relative sea level may be ambiguous in such instances

the climatology of the north atlantic abstract data from approximately 144 000 hydrographic stations in the north atlantic have been retrieved from the national oceanic data centre and analysed to produce maps of mean pressure temperature salinity and oxygen on selected potential density surfaces for the domain bounded by 0 85 w and 0 65 n the data span the period from 1904 to 1990 with the majority of the data from the last four decades the data set for this region is 60 larger than that used in the production of levitus climatological world atlas this increase in stations coupled with smoothing scales specific to the north atlantic rather than the global ocean considerably improves the resolution of the basin s features the mean property fields and their associated standard deviations are resolved on a one degree grid with little smoothing contrasting with the levitus atlas where properties although presented on a one degree grid have been smoothed on the order of 1000km another important feature of this database is the process by which irregularly spaced data are averaged onto a regular grid in a significant departure from the levitus analysis which averaged on depth surfaces these data were averaged on potential density surfaces thus eliminating an artificial mixing of water mass properties the database is used to describe the baroclinicity of well known features such as the gulf stream the north atlantic current and the deep western boundary current and to elucidate the recirculations associated with these currents it additionally resolves several new features in the intermediate and deep north atlantic these features include the signature of a large scale deep recirculation that extends southwestward from the eastward extension of the north atlantic current to the separation point of the gulf stream near cape hatteras this recirculation which spans approximately 2000m of the water column encompasses more local recirculations and potentially mixes subpolar and subtropical waters furthermore in the upper thermocline this database reveals a coherent azores current that stretches from the gulf stream system south of the tail of the grand banks to madeira this flow is marked by divergences to the south and convergences from the north such that its downstream transport is not much changed

crossing of the equator by the deep western boundary current in the western atlantic ocean abstract property distributions and geostrophic shear from a hydrographic section near 37 w in the atlantic ocean show the deep western boundary current dwbc in the north atlantic deep water nadw established against the western boundary of the brazil basin immediately south of the equator between 2 and 5 s the dwbc thus has directly crossed the equator to the south atlantic following the east southeast trend of the continental slope isobaths the estimated dwbc transport of nadw is 35 106 m3 s 1 similar to other estimates from the tropics discussed here these large dwbc transports are opposed by flow of deep water to the north atlantic immediately offshore of the dwbc with as much as two thirds of the dwbc transport being returned as these recirculations one recirculation center is the guiana basin north of the equator but extends at least a few hundred kilometers south of the equator another is visible at 11 s in the brazil basin the degree of connection of these two observed recirculatio

testing eustatic curves based on baltimore canyon neogene stratigraphy an example application of basin fill simulation basin fill simulation techniques provide scientists in both research and exploration with an important new tool the researcher obtains a tool for investigating the interaction of the major controls on basin scale stratigraphy subsidence sediment supply and eustasy the explorationist gains a tool for better understanding the hydrocarbon potential of an area through integrating data from various sources and testing an interpretation for spatial and temporal consistency as a result a researcher or explorationist may be able to refine a basin interpretation to a degree that might not have been possible if he or she had considered only a present day rendering of the basin basin modeling can be divided into three major categories structural stratigraphic and rock fluid properties evolution structural and stratigraphic modeling can be conducted back through time using backstripping techniques all three types of modeling can be conducted forward through time using simulation techniques several modeling systems combine backstripping procedures to obtain basin geometries with forward simulation to predict rock and fluid properties each category of basin modeling has its advantages and limitations when used together these techniques complement one another in this paper we illustrate the benefits of combining stratigraphic modeling techniques by presenting a research oriented case study involving the neogene sediments of the baltimore canyon trough offshore new jersey we designed this case study to evaluate several published sea level curves stratigraphic backstripping and simulation techniques were used to model a dip oriented cross section for which present day stratigraphy is well documented each sea level curve was used in a separate modeling run comparing presently accepted and modeled stratigraphic patterns allowed us to draw conclusions about the different eustatic curves in the final section we present several ways in which basin fill simulation can address exploration problems

oligocene sea level falls recorded in mid pacific atoll and archipelagic apron settings drilling results from mid pacific atoll and archipelagic apron sites in the line islands and marshall islands provinces lead to the conclusion that oligocene sea level falls detected in atlantic passive margin sequences are also recorded in a mid plate tectonic setting in the pacific basin the mid pacific sea level falls are recorded by a the presence of distinct coarse grained graded beds of turbidite origin rich in reef derived skeletal debris of oligocene eocene and cretaceous age that were redeposited in deep water archipelagic apron carbonate sequences of middle and late oligocene age now flanking the atolls and b a marked stratigraphic hiatus and solution unconformity in the subsurface of enewetak atoll which dates an oligocene period of atoll emergence correlative with both the deposition of the turbidites and the coastal offlap events discerned in atlantic passive margins correlation of the subsidence path of enewetak atoll with the development of the oligocene solution unconformity shows that ca 30 ma sea level was as much as 100 m lower than at present

the climatological distribution of potential vorticity over the abyssal ocean climatological maps of the large scale potential vorticity field q along isopycnals are diagnosed for the abyssal waters over the global ocean the inferred patterns of q vary with density the basin and hemisphere at middepths the distribution of q is controlled by the background planetary vorticity gradient on deeper isopycnals there are regions where q contours deviate from latitude circles and even regions of nearly uniform q these different regimes appear to be robust features over the interior of ocean basins as the standard error is found to be relatively small there the nearly uniform q occurs in the deep waters of the north pacific and possibly in the bottom waters of the western north atlantic and north pacific the nearly uniform q has a low magnitude in each case as well as a relatively low variability for the deep waters of the north pacific this nearly uniform q signal appears to be formed when a single water mass enters the basin from a low latitude source

a lagrangian numerical investigation of the origins and fates of the salinity maximum water in the atlantic the origins and fates of the atlantic salinity maximum water smw formed through excess evaporation in the tropics and subtropics of both hemispheres are studied using monthly mean outputs of a numerical simulation of the world ocean climatological circulation after defining formation domains from the surface salinity field and the vertical stratification a lagrangian technique is used to estimate the formation rates and main pathways in each hemisphere and the role of this water in the framework of the warm water return flow of the meridional overturning cell formation rates around 9 and 11 sv are found in the southern and northern hemispheres respectively while the export of the southern smw from its formation area is realized by the western boundary currents that of the northern smw mainly results from interior subduction equatorward of the formation regions a fraction of each smw variety is entrained in the subtropical cells that connect the subtropics to the equatorial region poleward of them both varieties are seen to feed the regions of subtropical mode water stmw formation around 35 of latitude in both hemispheres the bulk of the transport associated with each variety eventually turns northward this amounts to 6 sv of southern smw gathered in the north brazil undercurrent nbuc and 10 sv of northern smw found in the gulf stream at 35 n of which 8 sv have gone through the caribbean sea of the 13 4 sv northward transport of the meridional overturning cell estimated by the model at 47 n more than 50 6 9 sv is found to have transited through at least one of the smw regions this gives an indication of the likely important role of smw formation in the observed northward salinity increase of the upper atlantic ocean

circulation of the north atlantic ocean from altimetry and the gravity recovery and climate experiment geoid 1 we discuss the ocean circulation derived from the temporally averaged sea surface height which is referenced to the recently released geoid from the gravity recovery and climate experiment grace mission grace gravity model 02 ggm02 the creation of a precise independent geoid allows for the calculation of the reference gravitational potential undulation surface which is associated with the resting ocean surface height this reference height is then removed from the temporally averaged sea surface height leaving the dynamic ocean topography at its most basic level the dynamic ocean topography can be related to the ocean s surface circulation through geostrophy this has previously been impracticable because of large uncertainties in previous estimates of the earth s geoid prior geoids included the temporally averaged sea surface from altimeters as a proxy for the geoid and therefore were unsuitable for calculations of the ocean s circulation geoid undulations are calculated from the grace geoid and compared to those from the nasa goddard space flight center and national imagery and mapping agency joint earth geopotential model egm96 geoid error estimates are made to assess the accuracy of the new geoid the deep ocean pressure field is also estimated by combining the calculated dynamic ocean topography with hydrography finally the derived circulation is compared to independent observations of the circulation from sea surface drifters and subsurface floats it is shown that the ggm02 geoid is significantly more accurate for use in estimating the ocean s circulation

persistent sand bars explained by geodynamic effects 1 the persistent nature of intertidal sand bars has been the subject of much speculation concerning the hydrodynamic mechanisms involved but its origin remains enigmatic here we introduce salient geophysics in contrast to the physics of fluids above the sediments the geophysical evidence combined with theoretical modeling and analysis demonstrates that the geodynamic processes ensuing during exposure periods have a profound impact yielding the persistent nature of the intertidal bars under severe hydrodynamic forcing which would otherwise lead to unstable bar behavior the feedback between the effects of the dynamics of suction i e negative pore water pressure relative to atmospheric air pressure and sediment transport and morphology is found to play a crucial role in the intertidal bar morphodynamics our finding may fundamentally alter the current perspective leading to a new level of understanding of sediment transport and bar behavior at waterfronts that are ubiquitous in rivers estuaries and coastal seas

beach morphodynamics in a strong wind bay a low energy environment abstract the morphodynamic behaviour of a multibarred beach in a fetch limited strong wind bay seaford beach se australia was examined during both high and low energy conditions and considered in the context of a definition of low energy provided in the literature measurements of nearshore waves currents and morphology revealed a bimodal behaviour under initial low energy conditions the beach exhibited a low tide terrace state and waves and currents were of very low magnitude during subsequent high energy conditions the beach demonstrated dynamic behaviour through the formation of a transitional transverse bar and rip rhythmic bar and beach and migration of the middle bar with the morphology remaining in an arrested high energy state during intervening low energy periods although broadly conforming to the morphodynamic model the beach did exhibit some distinct characteristics attributable to its fetch limited location limited progression through the morphodynamic model and the importance of wind direction and magnitude in governing morphodynamic behaviour furthermore rip currents were not significant in driving beach change through intermediate states the presence of infragravity energy in the storm wave spectra a dissipative multibarred surf zone dynamic inner and middle bars and the attainment of a transitional transverse bar and rip rhythmic bar and beach state during rising wave conditions underline seaford beach as bimodal exhibiting process and morphologic features of both higher and lower energy beaches as an example of a beach in a strong wind bay seaford illustrates that not all fetch limited beaches are low energy furthermore the presence of infragravity energy in a highly fetch limited environment indicates that infragravity energy may occur commonly in fetch limited environments that are subject to periodic strong winds a process that has remained largely unrecognised

thermal origin of the hawaiian swell heat flow evidence and thermal models the lithospheric reheating hypothesis for the origin of the hawaiian swell has been tested by heat flow measurements along the swell between hawaii and midway ninety five measurements at eight carefully selected sites show that the heat flux on the swell increases systematically from near normal values 52 2 mw m 2 near hawaii to values near midway 59 2 mw m 2 about 20 25 higher than normal for lithosphere of that age 110 m y this heat flow pattern is qualitatively consistent with a deep seated thermal anomaly created in a lithospheric plate moving across a fixed heat source modeling of the heat flow and bathymetry data on the hawaiian swell strongly suggest that the swell is caused by a rapid heating within 40 to 50 km depth of normal 90 m y old lithosphere over a relatively broad 500 1000 km region near hawaii this model is also consistent with gravity and geoid anomalies associated with the swell which require a low density region in the lower lithosphere and with flexure studies of seamounts in the hawaiian chain which indicate that the rigidity of the lithosphere is not significantly reduced by the reheating appendices a c are available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document j82 005 1 00 payment must accompany order

miocene stable isotope record a detailed deep pacific ocean study and its paleoclimatic implications deep sea drilling project site 289 in the western equatorial pacific has yielded an extremely detailed record of the carbon and oxygen isotopic changes in the miocene deep ocean the isotopic record reflects major changes in paleoclimate and paleoceanography probably dominated by a major phase of antarctic ice cap growth the transition from a relatively unglaciated world to one similar to today occurred between 16 5 x 10 6 and 13 x 10 6 years before the present with the greatest change occurring between approximately 14 8 x 10 6 and 14 0 x 10 6 years before the present

zonal circulation across 52 w in the north atlantic 1 in july august 1997 a hydrographic acoustic doppler current profiler adcp tracer section was occupied along 52 w in the north atlantic as part of the world ocean circulation experiment hydrographic program underway and lowered adcp ladcp data have been used to reference geostrophic velocities calculated from the hydrographic data additional small velocity adjustments provided by an inverse model constraining mass and silicate transports in 17 neutral density layers yield the absolute zonal velocity field for 52 w we find a vigorous circulation throughout the entire section with an unusually strong gulf stream 169 sv and southern deep western boundary current dwbc 64 sv at the time of the cruise at the northern boundary on the west side of the grand banks of newfoundland we find the westward flowing labrador current 8 6 sv whose continuity from the labrador sea east of our section has been disputed directly to the south we identify the slopewater current 12 5 sv eastward and northern dwbc 12 5 sv westward strong departures from strictly zonal flow in the interior which are found in the ladcp data make it difficult to diagnose the circulation there isolated deep property extrema in the southern portion associated with alternating bands of eastward and westward flow are consistent with the idea that the rough topography of the mid atlantic ridge directly east of our section causes enhanced mixing of antarctic bottom water properties into overlying waters with distinctly different properties we calculate heat and freshwater fluxes crossing 52 w that exceed estimates based on air sea exchanges by a factor of 1 7

nearshore water motion and mean flows in a multiple parallel bar system abstract measurements of surface waves and nearshore water motion were made with wave staffs and electromagnetic currentmeters across the straight outer bars of a multiple parallel bar system at wasaga beach georgian bay ontario three sets of experiments were carried out between 1983 and 1985 and this paper examines the characteristics of spatial and temporal variations in incident waves and mean flows incident wave spectra during storms are typical of fetch limited conditions with a prominent peak in the wind wave frequency and a sharp cut off towards lower frequencies there is little evidence of significant energy at infragravity frequencies mean flows perpendicular to the shoreline during storms measured at 0 1 m above the bed are offshore with speeds of 0 04 0 10 m s 1 during moderate storms and 0 25 m s 1 during intense fall storms longshore currents are relatively weak and their direction closely follows changes in the incident wind angle about shore perpendicular there is no evidence of rip cell development and offshore return flow occurs as an undertow uniformly alongshore forming a simple two dimensional net circulation pattern the presence of the undertow very close to the bed is an important control on the direction of suspended sediment transport and thus in maintaining the equilibrium of the nearshore bars

estimating a mean ocean state from hydrography and sea surface height data with a nonlinear inverse section model twin experiments with a synthetic dataset the recovery of the oceanic flow field from in situ data is one of the oldest problems of modern oceanography in this study a stationary nonlinear inverse model is used to estimate a mean geostrophic flow field from hydrographic data along a hydrographic section the model is augmented to improve these estimates with measurements of the absolute sea surface height by satellite altimetry measurements of the absolute sea surface height include estimates of an equipotential surface the geoid compared to oceanographic measurements the geoid is known only to low accuracy and spatial resolution which restricts the use of sea surface height data to applications of large scale phenomena of the circulation dedicated satellite missions that are designed for high precision high resolution geoid models are planned and or in preparation this study which relies on twin experiments assesses the important contribution of improved geoid models to estimating the mean flow field along a hydrographic section when the sea surface height data are weighted according to the error estimates of the future highly accurate geoid models grace gravity recovery and climate experiment and goce gravity field and steady state ocean circulation explorer integrated fluxes of mass and temperature can be determined with an accuracy that is improved over the case with no sea surface height data by up to 55 with the error estimates of the currently best geoid model egm96 the reduction of the estimated flux errors does not exceed 18

spatial and temporal variations in spectra of storm waves across a barred nearshore abstract wave staffs and electromagnetic current meters were deployed on a profile across a two bar system at wendake beach southern georgian bay this paper examines spatial and temporal changes in the characteristics of wave form and the spectra of surface elevation and on offshore current motion during one storm non linear effects of wave shoaling and breaking across the bars result in the appearance of secondary waves and both the wave and on offshore current spectra have significant harmonic peaks during most of the storm significant low frequency energy occurs only during the peak of the storm while the peak frequency remains constant across the bar system the proportion of energy in the primary peak is greatest in the troughs and lowest over the bar crests and there are similar changes in the proportion of energy in the first harmonic however in both surface elevation spectra and on offshore current spectra the greatest proportion of energy is found in frequencies related to the incident wind waves

tidal data inversion interpolation and inference initial efforts in applying inverse methods to studies of ocean tides have focused on making the best use of a small number of observations to map tidal fields in a large area as such inversion can be viewed as an objective analysis scheme which uses a dynamically appropriate spatial covariance derived from the shallow water equations to interpolate and smooth a sparse data set data from recent altimetry missions are not sparsely distributed relative to tidal wavelengths in the open ocean apparently reducing the need for complicated dynamically based interpolation schemes altimetric data sets are also quite large making application of rigorous inversion methods to global tidal modeling a challenging computational problem we describe here a new iterative solution scheme which allows us for the first time to fit the full set of topex poseidon cross over differences the resulting solution tpxo 3 fits validation tide gauges significantly better than previous inverse solutions tpxo 3 also reduces residual cross over variances relative to other recent inverse and empirical solutions particularly in shallow water where improvements are dramatic with the new solution approach very significant improvements in global tidal models should be possible in shallow areas and in the vicinity of complex bathymetry where high accuracy tidal modeling remains a challenging problem with the recent improvements in the definition of tidal elevations in the open ocean it should now also be possible to resolve some long unanswered questions about tidal energetics and dynamics inverse methods provide a natural framework for addressing these issues and making inferences about tidal dynamics in particular by bringing data and dynamics together in a single solution we can rigorously test the consistency of the two we present results of global and local inversions which suggest that over elongated bathymetric features oriented perpendicular to tidal flows energy dissipation in the open ocean is significantly enhanced presumably due to conversion of barotropic tidal motions into baroclinic modes for the m2 tide our preliminary results suggest that perhaps as much as 0 5 tw of energy is dissipated in this manner however due to the simplified linear dynamics and limited spatial resolution used for our inversion there are significant uncertainties associated with these results a more careful application of inverse methods to make more rigorous inferences about tidal energetics including use of more reasonable prior dynamics and the highest possible spatial resolution should allow for closure of the tidal energy budget within the next few years

bar generating cross shore flow mechanisms on a beach random waves normally incident on a dissipative beach induce a variety of cross shore flows such as asymmetric oscillatory flow wave grouping induced long wave flow breaking induced turbulent flow and momentum decay induced undertow these flows are identified analyzed and hindcasted in a set of laboratory experiments with the aim of revealing the role of each of the flow mechanisms in the two dimensional case of bar generation on a beach

bar formation due to wave groups and associated long waves abstract field observations reveal that waves propagating onto a beach from deeper water have a grouped structure associated with this pattern of alternating high and low waves is a long wave forced by radiation stress variations due to the changing short wave height as the wave groups propagate onshore the relationship between the variation in the short wave height and the long wave motion is complicated by breaking of the short waves reflection of the long wave and the generation of a free long wave by time variation of the breakpoint position nevertheless there may still be a fixed phase relation between the short wave envelope and the long wave motion at any particular location resulting in a net transport of sediment over the timescale of the short wave groups this transport arises from sediment grains mobilised by short waves and moved by the long wave motion model predictions of wave group propagation onto a beach and the associated long wave motions are presented which suggest that sediment transport due to short wave long wave coupling may result in the formation of a bar within the inner surf zone and the possibility of additional bars further offshore outside the surf zone this mechanism for bar formation may provide a new framework for understanding bar morphodynamics

combination of topex poseidon data with a hydrographic inversion for determination of the oceanic general circulation and its relation to geoid accuracy summary a global estimate of the absolute oceanic general circulation from a geostrophic inversion of in situ hydrographic data is tested against and then combined with an estimate obtained from topex poseidon altimetric data and a geoid model computed using the jgm 3 gravity field solution within the quantitative uncertainties of both the hydrographic inversion and the geoid estimate the two estimates derived by very different methods are consistent when the in situ inversion is combined with the altimetry geoid scheme using a recursive inverse procedure a new solution fully consistent with both hydrography and altimetry is found there is however little reduction in the uncertainties of the calculated ocean circulation and its mass and heat fluxes because the best available geoid estimate remains noisy relative to the purely oceano graphic inferences the conclusion drawn from this is that the comparatively large errors present in the existing geoid models now limit the ability of satellite altimeter data to improve directly the general ocean circulation models derived from in situ measurements because improvements in the geoid could be realized through a dedicated spaceborne gravity recovery mission the impact of hypothetical much better future geoid estimates on the circulation uncertainty is also quantified showing significant hypothetical reductions in the uncertainties of oceanic transport calculations full ocean general circulation models could better exploit both existing oceanographic data and future gravity mission data but their present use is severely limited by the inability to quantify their error budgets

diatoms of the fortuna basin southeast spain evidence for the intra messinian inundation the fortuna basin in southeast spain part of the betic strait was one of the connecting pathways between the atlantic ocean and the mediterranean sea during the late miocene the basin contains a remarkable record of messinian marine sediments two well laminated marly diatomaceous sections were examined the 1 m thick el fenazar section f section and the 36 m thick rio chicamo diatomite member rcd section both sections are intercalated with gypsum horizons the diatoms in the rio chicamo diatomite suggest an atlantic origin and strong coastal upwelling associated with high productivity on the basis of event stratigraphy the diatomites correlate to the intra messinian inundation of the mediterranean sea during the messinian salinity crisis four biostratigraphically useful species nitzchia jouseae thalassiosira oestrupii t praeoestrupii denticulopsis hustedtii and asterolampra acutiloba occur in the west pacific between 5 35 and 4 5 ma lower reversed gilbert chron this interpretation places the subsequent upper evaporite deposition into the lower reversed gilbert chron our results indicate 1 the existence of a marine connection between the atlantic ocean and the mediterranean sea through the betic strait southeast spain during the messinian salinity crisis 2 a possible earlier first appearance of nitzchia jouseae in the betic strait compared to the atlantic and pacific oceans according to the stratigraphy of the fortuna basin and 3 the probability that many of the tripolilike and younger diatomites in the mediterranean are local deposits and diachronous with each other

tectonic subsidence flexure and global changes of sea level tectonic models for the evolution of passive continental margins predict that following rifting sediments should progressively onlap basement at the edge of a margin as the lithosphere cools and increases its flexural rigidity with age the pattern of modelled onlap is strikingly similar to that used by vail and colleagues to estimate sea level rise through geological time this similarity suggests that major portions of stratigraphical sequences at margins may have a tectonic rather than eustatic control the patterns of onlap used by vail and colleagues may be widespread however because several widely separated passive margins rifted at similar times but they are unlikely to be worldwide

eddies of newly formed upper labrador sea water a new type of submesoscale eddy has been observed south of the labrador sea during late winter embedded in equatorward flow along the western boundary the eddy radius is 20 km with a weak dynamic signature swirl speed of 0 5 cm s the center of the eddy is characterized by weak stratification elevated concentrations of oxygen and anthropogenic tracers and low tracer ages all indicative of newly ventilated water strong lateral intrusions distort the shape of the feature the water mass contained in the eddy is not classical labrador sea water from the central labrador sea but is significantly fresher and hence lighter it is of the correct density to be the source of the high chlorofluorocarbon layer of the shallow deep western boundary current observed further south and hence is termed upper labrador sea water using a combination of hydrographic data sets along the western boundary to implement a simple lateral diffusion model it is shown that such eddies decay of the order of several months and are difficult to observe equatorward of the grand banks of newfoundland this is in contrast to deeper lenses of classical labrador sea water which persist further equatorward tracer derived ages of the upper labrador sea water eddy range from 3 to 5 years much older than the lifetime deduced from their lateral diffusion a simple convection model of tracer age shows that this age discrepancy is caused by gas exchange being unable to maintain equilibrium between the deep convecting mixed layer and the atmosphere during formation

nearshore bar formation by non linear wave processes a comparison of model results and field data abstract analogue wave records and associated wave spectra from field measurements of wave transformation across two nearshore bar systems in georgian bay ontario show considerable growth of energy in the higher harmonics in addition there appears to be a regular spatial pattern of energy transfer between the peak frequency and the first higher harmonics with a length dimension equal to the spacing between the bars the characteristic peak period of moderate and severe storm waves affecting the two beaches 4 0 and 7 0 s and the mean nearshore slopes 0 005 and 0 01 are used as input to a mathematical model which describes the non linear evolution of a shallow water wave and the interaction between the first and second harmonics in the model the mass transport velocities associated with the primary wave and the second harmonic are used to calculate net sediment flux across a two dimensional profile model predictions of bar number and spacing starting with an initially planar slope correlate well with the field measurements for the two sets of wave conditions and mean slopes in addition the model is able to predict profile changes reflecting seasonal changes in wave climate

float trajectories in the deep western boundary current and deep equatorial jets of the tropical atlantic abstract fourteen neutrally buoyant sofar floats at a nominal depth of 1800 m were tracked acoustically for 3 7 yr in the vicinity of the western boundary and the equator of the atlantic ocean the trajectories revealed a swift narrow southward flowing deep western boundary current dwbc extending from 7n across the equator two floats crossed the equator in the dwbc and went to 10s two other floats left the dwbc and drifted eastward in the equatorial band 3s 3n three floats entered the dwbc from the equatorial current system and drifted southward these results suggest that at times the dwbc flows directly southward across the equator with a mean velocity of 8 9 cm s averaged over long distances 2800 km at other times dwbc water is diverted eastward near the equator for long periods 2 3 yr which can reduce the mean along boundary velocity to 1 2 cm s this is much less than the instantaneous along boundary velocities in the dwbc which are often above 25 cm s and occasionally exceed 50 cm s mean eastward flowing jets were observed near 2n and 2s bounding a mean westward jet centered on the equator 1s 1n the southern jet at 2s coincides with a cfc rich plume centered south of the equator the cfc plume is inferred to have been advected by the southern jet across the atlantic and into the gulf of guinea

morphodynamics of nearshore rhythmic sandbars in a mixed energy environment sw france 2 physical forcing analysis abstract the morphology and migration of rhythmic intertidal ridge and runnel systems and subtidal crescentic bars that border the southwest coast of france were characterized using in situ surveys and maps obtained by remote sensing methods the period from 1986 to 2000 was investigated a total of 35 km of coast was mapped this data set shows several specificities the origin of which are examined in the present report using hydrodynamic data a complete analysis of the influence of wave climate on both the shape and the movements of these rhythmic sedimentary patterns was performed in addition swan and morphodyn coupled numerical models were used to provide quantification of both wave breaking and longshore currents for wave parameters that were representative of the mean values and of the energetic conditions this study demonstrated the short time response of intertidal systems to the wave forcing when the offshore significant wave height h s was lower than 2 5 m regular coastal ridge and runnel systems developed in the intertidal zone and migrated in the longshore drift direction at a rate of 1 7 3 1 m day 1 by contrast the ridge and runnel system morphology abruptly changed when the h s exceeded 2 5 m and after the storm the typical ridge and runnel rhythmic topography was recovered within 5 9 days the crescentic bars which had a convex seaward shape were affected by waves with h s values greater than 3 m slightly less for short waves depending on the wave orientation the crescentic bars moved in the longshore drift direction at a rate that reached 1 m day 1 the data suggested a slight negative correlation between the mean alongshore length of the crescentic bar and the mean h s finally it seemed that increasing the wave obliquity with respect to the coast resulted in the flattening of the crescentic bars thus coupling spot and in situ mapping to hydrodynamic records allow the characterization of coastal morphology and dynamics with time and space samplings that are particularly well adapted to the little studied alongshore morphodynamics this approach should improve the difficult parameterization of morphodynamic models in high energy environments

miocene equatorial and southwest pacific paleoceanography from stable isotope evidence abstract stable isotope results from seven miocene deep sea drilling projects in the equatorial and southwest pacific ocean previously correlated using carbon isotope stratigraphy have been examined discussed and interpreted in terms of the development of the miocene pacific ocean the most obvious features of the benthonic foraminiferal stable isotopic records are a major increase in 18o 1 0 during the middle miocene a series of long term oscillations 2 3 my of amplitude 0 5 0 75 and a decrease in 13c values 0 5 1 0 during the latest miocene planktonic foraminiferal 18o records show different trends for high and low latitude regions in the equatorial pacific planktonic 18o values actually decrease during the miocene whereas in the higher southern latitudes planktonic 18o values become more positive in response to cooling surface waters planktonic 13c records show opposite trends to 18o with the high latitude values becoming more negative relative to the tropical regions the development of the miocene pacific ocean in terms of its vertical and horizontal thermal structure and isotopic composition is well illustrated by examining changes in the isotopic difference between planktonic and benthonic foraminifera 18ob p benthonic planktonic is a measure of the thermal structure of the water column 18oph pl high latitude low latitude planktonic values is a measure of the latitudinal temperature gradient 13cb p is an indirect measure of nutrient concentrations in the water column and 13cph pl measures differences in surface water nutrient concentrations between high and low latitude 18ob p increases during the miocene with the greatest increase occurring in the middel miocene at about 14 ma by the latest miocene the isotopic gradient at site 289 in the equatorial pacific approaches the present day isotopic gradient about 4 5 an increase in 18oph pl during the miocene suggests that the latitudinal temperature gradient increased by about 6 c to a value of 12 c in the latest miocene between sites 289 equator and 281 subantarctic 13cb p and 13cph pl values are relatively constant through the early miocene but begin to increase during the middle miocene bottom water 13c values respond similarly at all sites but surface water 13c values exhibit different trends because higher latitude values begin to decrease this decrease perhaps suggests that phosphate concentrations may have increased due to increased upwelling as the circum antarctic circulation system evolved its present day characteristics the isotopic data compiled in this paper suggest that the southwest pacific was responding uniformly to some global or at least pacific wide control during the early miocene in the middle miocene the response became more complex as the low and high latitudes began to show independent trends the changes in the thermal vertical and latitudinal structure probably occurred in respons to the build up of the east antarctic ice sheet intensification of bottom water circulation and an increase in zonal circulation in surface waters in the southern hemisphere the changes in 13c vertical and latitudinal gradients are due to some complex interaction of sea level continental hypsometry climate and biological processes coupled with oceanic circulation changes a strong correlation between estimated sea level changes and 13c values suggests that transgressions and regressions play a critical role in controlling the flux of oxidized organic carbon enriched in12c from the continental shelves and epicontinental seas to the open ocean

deep cross equatorial flow in the atlantic measured with sofar floats neutrally buoyant sofar floats at nominal depths of 800 1800 and 3300 m were tracked for 21 months in the vicinity of tropical boundary currents in the atlantic near 6 n and at several sites near 11 n as well as along the equator trajectories at 1800 m show a swift 50 cm s narrow 100 km wide southward flowing deep western boundary current dwbc extending from 7 n to the equator the average transport per unit depth in the dwbc was estimated to be 13 8 103 m2 s coupling this value with mean velocities measured in the dwbc by current meters gave a volume transport of 15 106 m3 s between depths of 900 m and 2800 m approximately 6 106 m3 s recirculated northward between the dwbc and the mid atlantic ridge leaving 9 106 m3 s as cross equatorial transport no obvious dwbc nor swift equatorial current was observed by the 3300 m floats a low mean velocity at this depth lay between f 11 and higher velocity cores above and below the 1800 m trajectories also suggest that at times february march 1989 the north atlantic deep water in the dwbc turned eastward and flowed along the equator and at other times august september 1990 the dwbc crossed the equator and continued southward the velocity near the equator calculated by grouping floats in a box along the equator was eastward at 4 1 cm s from february 1989 to february 1990 and westward at 4 6 cm s from march 1990 to november 1990 thus the amount of cross equatorial flow in the dwbc appeared to be linked to low frequency variability of the structure of the equatorial current system floats in antarctic intermediate water at 800 m revealed a northwestward western boundary current although flow patterns were complicated three floats that significantly contributed to the northwestward flow looped in anticyclonic eddies that translated up the coast at 8 cm s six 800 m floats drifted eastward along the equator between 5 s and 6 n at a mean velocity of 11 cm s one reached 5 w in the gulf of guinea suggesting that the equatorial currents at this depth extended at least 35 40 along the equator three of these floats reversed direction near the end of the tracking period

changes in erosion and ocean circulation recorded in the hf isotopic compositions of north atlantic and indian ocean ferromanganese crusts abstract high resolution hf isotopic records are presented for hydrogenetic fe mn crusts from the north atlantic and indian oceans bm1969 from the western north atlantic has previously been shown to record systematically decreasing nd isotopic compositions from about 60 to 4 ma at which time both show a rapid decrease to unradiogenic nd composition thought to be related to the increasing influence of nadw or glaciation in the northern hemisphere during the oligocene north atlantic hf became progressively less radiogenic until in the mid miocene 15 ma it reached 1 it then shifted gradually back to an hf value of 3 at 4 ma since when it has decreased rapidly to about 1 at the present day the observed shifts in the hf isotopic composition were probably caused by variation in intensity of erosion as glaciation progressed in the northern hemisphere ferromanganese crusts ss663 and 109d are from about 5500 m depth in the indian ocean and are now separated by 2300 km across the mid indian ridge they display similar trends in hf isotopic composition from 20 to 5 ma with the more northern crust having a composition that is consistently more radiogenic by 2 hf units paradoxically during the last 20 ma the hf isotopic compositions of the two crusts have converged despite increased separation and subsidence relative to the ridge a correlatable negative excursion at 5 ma in the two records may reflect a short term increase in erosion caused by the activation of the himalayan main central thrust changes to unradiogenic hf in the central indian ocean after 5 ma may alternatively have been caused by the expanding influence of nadw into the mid indian basin via circum antarctic deep water or a reduction of pacific flow through the indonesian gateway in either case these results illustrate the utility of the hf isotope system as a tracer of paleoceanographic changes capable of responding to subtle changes in erosional regime not readily resolved using other isotope systems

bars bumps and holes models for the generation of complex beach topography in shallow water any two waves of the same frequency are shown to produce complex patterns of drift velocity above the sea bed if the longshore components hi h of the wave numbers of the two waves are different these steady flow patterns exhibit a longshore periodicity of wave number hi h irrespective of whether the waves propagate in the same direction say hi he positive or in opposite directions he negative the interaction of two edge wave modes is examined in detail the drift velocities are calculated and a simple sediment transport model is used to predict the beach topography that would be in equilibrium with these flow patterns as expected crescentic sand bars are produced by the special case of standing edge waves hi h intriguingly for all other cases a combination of complex transverse bars plus meandering or straight offshore bars result patterns that are surprisingly reminiscent of many published descriptions of complex rhythmic topography the extension of the model to three or more waves produces topography that appears to be very irregular although the pattern should repeat over sufficiently long distances along the beach even with only three waves these distances may be very large compared to the scale of the bars