tidal modeling of an ancient tide dominated seaway part 1 model validation and application to global early cretaceous aptian tides abstract the utility of deep time global paleotidal modeling is evaluated with a series of modeling experiments focused on the early cretaceous aptian the results from a series of paleobathymetry sensitivity experiments indicate that despite paleogeographic and paleobathymetric uncertainty appropriate use of global paleotidal models complements and enhances stratigraphic and sedimentological methods before being applied to global paleotidal modeling the imperial college ocean model icom is validated for the computation of modern global tides the icom results only deviate slightly from a state of the art published model and were achieved with considerably less computational expense and without data assimilation the results from global paleotidal modeling of the early cretaceous aptian were assessed by comparison with the published geological record icom predicts high mesotidal to macrotidal ranges on the arabian platform around india especially to the north and west along the pacific coast between north and south america northeast of australia and around southeast asia the model predicts low microtidal ranges in the proto south atlantic ocean and weddell sea a further validation test assessed the ability of the model to predict the dominant tidal constituents diurnal or semidiurnal in the aptian lower greensand seaway of southeastern england and northern france during the aptian this region was connected to the boreal proto atlantic and neotethys oceans and now preserves superbly documented tidal deposits the model predicts low microtidal ranges in the proto central atlantic ocean and boreal ocean suggesting that they had little impact on tides in the lower greensand seaway higher tidal amplitudes especially of diurnal once daily tides are predicted in the northwestern neotethys ocean suggesting that this ocean was an important source of tidal energy to the lower greensand seaway sensitivity tests to paleogeographic and paleobathymetric uncertainty indicate that the model predictions are robust the prediction of predominantly diurnal tides is supported by published analyses of large dune scale deposits in the lower greensand of southeast england

tracer transport within abyssal mixing layers abstractmixing layers near sloped topography in the abyss are thought to play a critical role in the global overturning circulation yet the behavior of passive tracers within sloping boundary laye

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

energetics of the m2 barotropic ocean tides an estimate of bottom friction dissipation from a hydrodynamic model abstract the aim of this paper is to present a detailed energy budget of the m2 ocean tides over the world ocean based on the hydrodynamic tidal solution fes94 1 which includes not only the characteristics of the sea surface tidal elevations but also of the tidal currents global and regional budgets are given the global energy input by astronomical forcing deduced from the 2 2 spherical harmonic development of the m2 sea surface elevation solution is 2 35 tw lower by 0 1 tw than for the new altimetric solutions produced recently directly from satellite observations one major feature emerging from the present analysis is that a quarter of this energy input takes place over the south atlantic ocean on the other hand ocean tides work against astronomical forcing over three areas eastern indian ocean southwest of the south american continent and around new zealand this energy is dissipated in fes94 1 by bottom friction over the main continental shelves but the outstanding feature is that 40 of the tidal energy is dissipated over the north atlantic ocean energy is thus redistributed from the areas of energy input to feed the areas of dissipation the pacific ocean the indian ocean and the south atlantic ocean receive more energy in total than they dissipate in contrast with the atlantic ocean and the arctic ocean where a large deficit must be compensated by a net influx of energy from the other basins one third of the total m2 energy input by astronomical forcing over the world ocean flows northwards through the equatorial atlantic detailed energy dissipation estimates are computed over the different areas of energy dissipation and compared to the previous estimates published in the literature

once again once again tidal friction topex poseidon t p altimetry has reopened the problem of how tidal dissipation is to be allocated there is now general agreement of a m2 dissipation by 2 5 terawatts 1 tw 1012 w based on four quite separate astronomic observational programs allowing for the bodily tide dissipation of 0 1 tw leaves 2 4 tw for ocean dissipation the traditional disposal sites since jeffreys 1920 have been in the turbulent bottom boundary layer bbl of marginal seas and the modern estimate of about 2 1 tw is in this tradition but the distribution among the shallow seas has changed radically from time to time independent estimates of energy flux into the marginal seas are not in good agreement with the bbl estimates t p altimetry has contributed to the tidal problem in two important ways the assimilation of global altimetry into laplace tidal solutions has led to accurate representations of the global tides as evidenced by the very close agreement between the astronomic measurements and the computed 2 4 tw working of the moon on the global ocean second the detection by ray and mitchum 1996 of small surface manifestation of internal tides radiating away from the hawaiian chain has led to global estimates of 0 2 to 0 4 tw of conversion of surface tides to internal tides measurements of ocean microstructure yields 0 2 tw of global dissipation by pelagic turbulence away from topography we propose that pelagic turbulence is maintained by topographic scattering of barotropic into baroclinic tidal energy via internal tides and internal waves previous estimates by baines 1974 baines 1982 of this conversion along 150 000 km of continental coastlines gave a negligible 0 02 tw evidently the important conversion takes place along mid ocean ridges the maintenance of the abyssal global stratification requires a much larger expenditure of power 2 tw versus 0 2 tw this is usually attributed to wind forcing if tidal power is to play a significant role here then the bbl estimates need to be reduced the challenge is to estimate dissipation from the energy flux divergence in the t p adjusted tidal models without prior assumptions concerning the dissipation processes

accuracy assessment of recent ocean tide models over 20 global ocean tide models have been developed since 1994 primarily as a consequence of analysis of the precise altimetric measurements from topex poseidon and as a result of parallel developments in numerical tidal modeling and data assimilation this paper provides an accuracy assessment of 10 such tide models and discusses their benefits in many fields including geodesy oceanography and geophysics a variety of tests indicate that all these tide models agree within 2 3 cm in the deep ocean and they represent a significant improvement over the classical schwiderski 1980 model by approximately 5 cm rms as a result two tide models were selected for the reprocessing of topex poseidon geophysical data records in late 1995 current ocean tide models allow an improved observation of deep ocean surface dynamic topography using satellite altimetry other significant contributions include theft applications in an improved orbit computation for topex poseidon and other geodetic satellites to yield accurate predictions of earth rotation excitations and improved estimates of ocean loading corrections for geodetic observatories and to allow better separation of astronomical tides from phenomena with meteorological and geophysical origins the largest differences between these tide models occur in shallow waters indicating that the current models are still problematic in these areas future improvement of global tide models is anticipated with additional high quality altimeter data and with advances in numerical techniques to assimilate data into high resolution hydrodynamic models

internal swell generation the spatial distribution of energy flux from the wind to mixed layer near inertial motions the energy flux from the wind to inertial mixed layer motions is computed for all oceans from 50 8 st o 508n for the years 1996 99 the wind stress t is computed from 6 h 2 58 resolution ncep ncar global reanalysis surface winds the inertial mixed layer response ui and the energy flux p5 t ui are computed using a slab model the validity of the reanalysis winds and the slab model is demonstrated by direct comparison with wind and adcp velocity records from ndbc buoys at latitudes 508 the inertial response is too fast to be resolved by the reanalysis wind 6 h output interval midlatitude storms produce the greatest fluxes resulting in broad maxima near 40 8 latitude during each hemisphere s winter concentrated in the western portion of each basin northern hemisphere fluxes exceed those in the southern hemisphere by about 50 the global mean energy flux from 1996 to 1999 and 508 st o 508n is 0 98 6 0 08 3 1023 wm 22 for a total power of 0 29 tw 1 tw 5 1012 w this total is the same order of magnitude as recent estimates of the global power input to baroclinic m2 tidal motions suggesting that windgenerated near inertial waves may play an important role in the global energy balance

residual ocean tide signals from satellite altimetry grace gravity fields and hydrodynamic modelling summary improvements of a global state of the art ocean tide model are identified and quantified by applying three independent approaches namely i empirical ocean tide analysis of multimission altimeter data ii evaluation of grace data and gravity field models and iii high resolution hydrodynamic modelling although these approaches have different capabilities to sense ocean tides they obtain results which are basically consistent one with each other the analysis of altimeter data clearly identifies significant residual amplitudes over shallow water for all major diurnal and semidiurnal constituents and the non linear tide m4 grace data and the time series of monthly gravity field models exhibit on a larger scale residual ocean tide signals over much the same areas the analysis of dynamic residuals of hydrodynamic modelling with data assimilation proves the validity of linear dynamics in the deep ocean and shows correlation of dynamic residuals with energy dissipation in these areas

southwestern barents sea margin late mesozoic sedimentary basins and crustal extension abstract the deep sedimentary basins of the southwestern barents sea were formed in response to several late mesozoic early cenozoic tectonic events within the north atlantic rift zone which culminated with continental breakup and formation of a mainly sheared margin in early tertiary times due to deteriorating data quality the development of the margin bordering sorvestsnaget basin is not well known to improve on this we use both seismic interpretation and gravity modelling to estimate the depth to the middle jurassic mj sequence boundary which marks the onset of mesozoic rifting the horizon represents a first order contrast in seismic velocity and density and the gravity field correlates well with its depth of burial only one seismic line enables tracing of the mj from surrounding areas into the sorvestsnaget basin down to a depth of at least 17 km in the northeastern part of the basin the deep basin is reflected in a general thinning of the crust from 30 36 km within the barents sea to 20 24 km in the margin area the gravity modelling show that the middle jurassic lower cretaceous sequences are of comparable thicknesses in the tromso and sorvestsnaget basins however adjacent to the rifted margin segment the deep northern part of the sorvestsnaget basin is affected by additional large late cretaceous normal faulting and subsidence these faults also caused additional structuring of the intrabasinal veslemoy high post middle jurassic crustal thinning in the southwestern barents sea shows maximum cumulative values exceeding 4 within the tromso and the northern sorvestsnaget basins the corresponding crustal extension is estimated to 70 85 km in a west to northwest direction there is no uniform increase in crustal thinning toward the continent ocean boundary which we attribute to the transform origin of the margin however there is a gradual migration of tectonic activity toward the incipient margin as the time of continental breakup was approached

large scale circulation with locally enhanced vertical mixing abstract the influence of localized regions of intensified vertical mixing on the stratification and circulation in a large scale ocean model is investigated with idealized numerical experiments numerical solutions are obtained of a closed basin single hemisphere ocean model based on the planetary geostrophic equations mesoscale eddy effects are minimized and vertical mixing at the turbulent microscale is represented by a vertical diffusivity solutions with uniform are contrasted with a localized mixing solution in which increases by two orders of magnitude from its interior value 0 2 10 4 m2 s 1 in a region 500 km wide adjacent to the vertical eastern boundary when is uniform the stratification beneath the ventilated thermocline is characterized by a single vertical scale in contrast the localized vertical mixing supports a deep diffusive thermocline with two distinct vertical scales an internal boundary layer centered at the base of the ventilated thermocline roughly 1000 m

surface manifestation of internal tides in the deep ocean observations from altimetry and island gauges the sea surface height signatures of internal tides in the deep ocean amounting to a few centimeters or less are studied using two complementary measurement types satellite altimetry and island tide gauges altimetry can detect internal tides that maintain coherence with the astronomical forcing island gauges can monitor temporal variability which in some circumstances is due to internal tides varying in response to changes in the oceanic medium this latter mechanism is at work at hilo and other stations on the northern coasts of the hawaiian islands by detecting spatially coherent low frequency internal tide modulations the tide gauges along with inverted echo sounders at sea suggest that the mean internal tide is also spatially coherent satellite altimetry confirms this at hawaii and in many other places topex poseidon altimetry detects mean surface waves spatially coherent and propagating great distances 1000 km before decaying below background noise when temporal variability is small the altimetry plus information on ocean density sets useful constraints on energy fluxes into internal tides at the hawaiian ridge 15 gw of tidal power is being converted from barotropic to first mode baroclinic motion examples elsewhere warn that a simplistic interpretation of the altimetry without regard to variability noise or in situ information may be highly misleading with such uncertainties extension of the hawaiian results into a usefully realistic estimate of the global internal tide energy balance appears premature at this time

internal tide generation at the continental shelf modeled using a modal decomposition two dimensional results abstract stratified flow over topography is studied with oceanic applications in mind a model is developed for a fluid with arbitrary vertical stratification and a free surface flowing over three dimensional topography of arbitrary size and steepness with background rotation in the linear hydrostatic regime the model uses an expansion of the flow fields in terms of a set of basis functions which efficiently capture the vertical dependence of the flow the horizontal structure may then be found by solving a set of coupled partial differential equations in two horizontal directions and time subject to simple boundary conditions in some cases these equations may be solved analytically but in general simple numerical procedures are required using this formulation the internal tide generated by a time periodic barotropic tidal flow over a continental shelf and slope is calculated in various idealized configurations the topography and fluid motion are taken to be independent of one coordinate di

a possible link between the geomagnetic field and catastrophic climate at the paleocene eocene thermal maximum we report high precision records of a magnetic reversal event at the paleocene eocene thermal maximum petm a cataclysmic global warming event initiated at 55 0 ma this event is confirmed by both an antipodal shift in direction and a reduction in magnetic intensity during the lower and upper transitions and it is seen at additional sites indicating that the characteristic remanent magnetization chrm was primarily acquired by earth s magnetic field during sedimentation this major fluctuation of earth s magnetic field intensity is interpreted to have been linked to the petm and to have eventually facilitated the reversal this paleocene eocene magnetic reversal pemr lasted for 53 ka from 54 964 to 54 911 ma but finally recovered to an original polarity this suggests a possible coupling between earth s core magnetofluid dynamo sphere and the atmosphere hydrosphere during an abrupt catastrophic climate event

spatial variability of turbulent mixing in the abyssal ocean ocean microstructure data show that turbulent mixing in the deep brazil basin of the south atlantic ocean is weak at all depths above smooth abyssal plains and the south american continental rise the diapycnal diffusivity there was estimated to be less than or approximately equal to 0 1 x 10 4 meters squared per second in contrast mixing rates are large throughout the water column above the rough mid atlantic ridge and the diffusivity deduced for the bottom most 150 meters exceeds 5 x 10 4 meters squared per second such patterns in vertical mixing imply that abyssal circulations have complex spatial structures that are linked to the underlying bathymetry

systematic bias in baroclinic energy estimates in shelf seas abstracta simple model of an internal wave advected by an oscillating barotropic flow suggests flaws in standard approaches to estimating properties of the internal tide when the m2 barotropic tidal current amplitude is of similar size to the phase speed of the m2 baroclinic tide spectral and harmonic analysis techniques lead to erroneous estimates of the amplitude phase and energy in the m2 internal tide in general harmonic fits and bandpass or low pass filters that attempt to isolate the lowest m2 harmonic significantly underestimate the strength of m2 baroclinic energy fluxes in shelf seas baroclinic energy flux estimates may show artificial spatial variability giving the illusion of sources and sinks of energy where none are actually present analysis of previously published estimates of baroclinic energy fluxes in the celtic sea suggests this mechanism may lead to values being 25 60 too low

the global ocean flux of particulate organic carbon areal distribution and magnitude the magnitude and distribution of the particulate organic carbon poc rain rate to the seafloor in the atlantic pacific and indian ocean basins between 61 n and 61 s has been estimated from benthic oxygen flux estimates for water depths 1000 m only the calculation utilizes the extensive data sets of sedimentary organic carbon caco3 and accumulation rate to extrapolate between individual benthic flux measurement sites using an empirically derived correlation between the seafloor oxygen flux and these parameters the poc flux through the 1000 m depth horizon was then estimated from published correlations between sediment trap determined fluxes and water depth total oxygen utilization in the deep ocean is estimated to be 1 2 1014 mol o2 yr 1 a value that agrees well with previous estimates which were based on surface water primary productivity sediment trap and depth relationships and with deep water respiration rates estimated from apparant oxygen utilization aou 14c relationships on the basis of the derived global ocean flux distribution it is concluded that 1 dissolved organic carbon doc inputs are not required to account for estimated deep water respiration rates 2 the majority of the poc input to the deep ocean occurs within 30 of the equator 3 the proportion of primary production that reaches the deep sea does not vary greatly with latitude 4 gyre and continental margin regions contribute roughly equally to the deep poc flux with a relatively minor contribution from the equatorial divergence region 5 of the estimated 7 2 1013 mol c yr 1 of poc that sinks below the 1000 m depth horizon 45 3 3 1013 mol c yr 1 reaches the seafloor where it is oxidized 6 when normalized to basin area average deep flux rates in the atlantic and pacific are similar while highest rates are observed in the indian ocean and 7 the results can be fully reconciled only if the benthic flux of doc is significantly less than the benthic o2 flux

circulation of the pacific ocean seen in a global ocean model ocean circulation and climate advanced modelling project occam this paper compares observations made in the pacific ocean and the 8 12 year climatology of a global numerical model meridional mass and heat transports and their divergences are calculated and zonal averages compared with the air sea exchange values of doney et al 1998 with mixed success the large scale distribution of sea surface height and near surface currents are shown to be well reproduced by the model but their variance is underestimated severely so in areas of weak variability synoptic wind forcing enhances the latter though only slightly while higher model resolution improves agreement in areas of strong variability model mean transports in the east australian current in the vitiaz strait and in the kuroshio exceed measurements by 10 0 18 sv respectively and variability is underestimated by factors between 2 and 4 near 1000 m and in strong currents the flow is overestimated but over most of the ocean model output does not match either the magnitude or the spatial variability of the observations in contrast the inflow of bottom water and its spreading path throughout both south and north pacific is well described good agreement is found with measured transport through the samoan passage but at 32 s east of the tonga kermadec ridge the model yields only 60 of the observed value the sverdrup balance is shown to hold widely in the model interior utilizing the complete depth integrated vorticity equation it is found that bottom pressure torques balance the advection of planetary vorticity in both surface and bottom intensified western boundary currents

dynamics of the long period tides abstract the long period tides are a tool for understanding oceanic motions at low frequencies and large scales here we review observations and theory of the fortnightly monthly and pole tide constitutents observations have been plagued by low signal to noise ratios and theory by the complex lateral geometry and great sensitivity to bottom slopes a new spectral element model is used to compute the oceanic response to tidal forcing at 2 week and monthly periods the general response is that of a heavily damped q 5 system with both the energy input from the moon and the dissipation strongly localized in space the high dissipation result is probably generally applicable to all low frequency barotropic oceanic motions over much of the ocean the response has both the character of a large scale and a superposed rossby wave like character thus vindicating two apparently conflicting earlier interpretations to the extent that free waves are excited they are consistent with their being dominated by rossby and topographic rossby wave components although gravity modes are also necessarily excited to some degree in general a modal representation is not very helpful the most active regions are the southern ocean and the western and northern north atlantic these results are stable to changes in geometry topography and tide period on a global average basis the dynamical response of mm is closer to equilibrium than is mf

energetics of barotropic and baroclinic tides in the monterey bay area abstracta detailed energy analysis of the barotropic and baroclinic m2 tides in the monterey bay area is performed the authors first derive a theoretical framework for analyzing internal tide energetics based on the complete form of the barotropic and baroclinic energy equations which include the full nonlinear and nonhydrostatic energy flux contributions as well as an improved evaluation of the available potential energy this approach is implemented in the stanford unstructured nonhydrostatic terrain following adaptive navier stokes simulator suntans results from three dimensional high resolution suntans simulations are analyzed to estimate the tidal energy partitioning among generation radiation and dissipation a 200 km 230 km domain including all typical topographic features in this region is used to represent the monterey bay area of the 152 mw energy lost from the barotropic tide approximately 133 mw 88 is converted into baroclinic energy through internal tide generation and 42 56

from tides to mixing along the hawaiian ridge the cascade from tides to turbulence has been hypothesized to serve as a major energy pathway for ocean mixing we investigated this cascade along the hawaiian ridge using observations and numerical models a divergence of internal tidal energy flux observed at the ridge agrees with the predictions of internal tide models large internal tidal waves with peak to peak amplitudes of up to 300 meters occur on the ridge internal wave energy is enhanced and turbulent dissipation in the region near the ridge is 10 times larger than open ocean values given these major elements in the tides to turbulence cascade an energy budget approaches closure

abyssal water carbon 14 distribution and the age of the world oceans the carbon 14 distribution in the abyssal waters of the world oceans indicates replacement times for pacific indian and atlantic ocean deep waters more than 1500 meters deep of approximately 510 250 and 275 years respectively the deep waters of the entire world ocean are replaced on average every 500 years

tidal conversion by supercritical topography calculations are presented of the rate of energy conversion of the barotropic tide into internal gravity waves above topography on the ocean floor the ocean is treated as infinitely deep and the topography consists of periodic obstructions a green function method is used to construct the scattered wavefield the calculations extend the previous results of balmforth et al for subcritical topography wherein waves propagate along rays whose slopes exceed that of the topography everywhere by allowing the obstacles to be arbitrarily steep or supercritical so waves propagate at shallower angles than the topographic slopes and are scattered both up and down a complicated pattern is found for the dependence of energy conversion on e the ratio of maximum topographic slope to wave slope and the ratio of obstacle amplitude and separation this results from a sequence of constructive and destructive interferences between scattered waves that has implications for computing tidal conversion rates for the global ocean

quantification of diffusive benthic fluxes of nitrate phosphate and silicate in the southern atlantic ocean pore water data from surface sediments and bottom water data at 180 locations were used to create distribution maps of diffusive benthic release rates of nitrate phosphate and silicate in the southern atlantic ocean for water depths 1000 m geostatistical methods of variogram analysis and kriging were used for data interpolation since benthic fluxes are controlled by organic matter degradation and dissolution processes and therefore by the supply of organic matter to the sediment surface the distribution pattern of all investigated constituents should reflect a general coupling to surface water productivity this seems to be true for the most part of the oligotrophic central south atlantic and the upwelling area off southwest africa striking regional differences in this regard however exist for the eastern equatorial region where unexpectedly low fluxes were calculated and the argentine basin where benthic fluxes are very high the argentine basin obviously receives a higher input of degradable dissolvable material whereas in the eastern equatorial region the low benthic fluxes are possibly due to intense nutrient recycling within the water column estimated fluxes vary considerably over the entire region no3 10 180 mmol m 2 yr 1 po4 2 11 mmol m 2 yr 1 and si 0 0 65 mol m 2 yr 1 areas of highest release rates are the continental margins off southwest africa and off argentina the investigated area comprises a total of approximately 32 106 km2 between 8 n and 40 50 s our estimations reveal benthic release rates of 1 55 l012 mol no3 yr 1 3 5 l010 mol po4 yr 1 and 2 1 1012 mol si yr 1 open ocean areas with middle to low fluxes contribute about 70 80 of the total estimated fluxes the release of phosphate is probably underestimated because of core recovery artifacts and is therefore based on the assumption that fluxes are not lower than 0 25 mmol m 2 yr 1 at any location of the studied area the investigated area represents about one tenth of the world deep ocean without the arctic ocean assuming the south atlantic to be representative we calculate annual global release rates of 15 l012 mol no3 32 l010 mol po4 and 20 1012 mol si if our estimates are correct about 4 6 of silicate 3 4 of nitrate and 1 of phosphate annually produced in the surface waters are remineralized in surface sediments from water depths 1000 m

radon 222 in the benthic boundary layer a detailed survey of radon 222 and temperature profiles of the benthic boundary layer in the hatteras abyssal plain shows a strong correlation between the structure of both the apparent vertical diffusivities estimated from radon 222 are of the order of 50 cm2 s 1 in the mixed layer and of the order of 1 cm 2 s 1 above it one profile appears to have been taken in a frontal zone where isotherms dip sharply into the sediments this is the only profile where there is significant penetration of radon above the mixed layer several other profiles suggest that the temperature may take longer than several radon half lives to adjust to new mixing and advection regimes in such cases one often sees considerable structure in the radon profile within the region where the potential temperature is well mixed

semi diurnal and diurnal tidal dissipation from topex poseidon altimetry 1 tidal energy dissipation is estimated for eight semi diurnal and diurnal constituents using a global inverse solution constrained by topex poseidon altimeter data very similar spatial patterns are obtained for all semi diurnal constituents with about one third of the total dissipation occurring in the deep ocean over rough topography maps for diurnal constituents are also similar amongst themselves but quite different from the semi diurnal results for diurnals a smaller fraction of dissipation roughly 10 occurs in the deep ocean much of the difference can be explained by the very different spatial pattern of diurnal and semi diurnal tidal currents the lack of free internal waves at frequencies poleward of 30 at diurnal frequencies also probably plays a role limiting the effectiveness of baroclinic conversion as an energy sink for barotropic diurnal tides

estimates of m2 tidal energy dissipation from topex poseidon altimeter data most of the tidal energy dissipation in the ocean occurs in shallow seas as has long been recognized however recent work has suggested that a significant fraction of the dissipation perhaps 1 tw or more occurs in the deep ocean this paper builds further evidence for that conclusion more than 6 years of data from the topex poseidon satellite altimeter are used to map the tidal dissipation rate throughout the world ocean the dissipation rate is estimated as a balance between the rate of working by tidal forces and the energy flux divergence computed using currents derived by least squares fitting of the altimeter data and the shallow water equations such calculations require dynamical assumptions in particular about the nature of dissipation to assess sensitivity of dissipation estimates to input assumptions a large suite of tidal inversions based on a wide range of drag parameterizations and employing both real and synthetic altimeter data are compared these experiments and monte carlo error fields from a generalized inverse model are used to establish error uncertainties for the dissipation estimates owing to the tight constraints on tidal elevation fields provided by the altimeter area integrals of the energy balance are remarkably insensitive to required dynamical assumptions tidal energy dissipation is estimated for all major shallow seas excluding individual polar seas and compared with previous model and data based estimates dissipation in the open ocean is significantly enhanced around major bathymetric features in a manner consistent with simple theories for the generation of baroclinic tides

topographically induced mixing around a shallow seamount measurements of the rate of dissipation of kinetic energy around a shallow seamount in the eastern north pacific show that mixing there is 100 to 10 000 times as large as that far away from the seamount if such values are typical of other seamounts mixing across density surfaces in the ocean occurs mainly at their boundaries and topographically induced mixing may help to explain the discrepancy between the observed intensity of mixing in the interior of the oceans and that required to satisfy models of ocean circulation

secular effects of oceanic tidal dissipation on the moon s orbit and the earth s rotation the earth and moon are considered as a two body system in gravitational isolation from the sun and other planets the lunar orbit is taken as circular and the solid earth is assumed to be a rigid sphere with no tidal deformation so that there are no precessional torques other than those arising from the tidally deformed ocean numerical solutions to laplace s tidal equations with dissipation by linear bottom friction are used to obtain ocean wide distributions of tidal amplitude for two idealized continentalities a single circular continent spherical cap centered at the north pole and a single spherical cap centered on the equator calculations are made for two different values of the frictional resistance coefficient thus giving rise to four sets of solutions the computed tidal amplitudes are used to calculate the oceanic tidal torque which in turn is used to integrate the orbital equations backward in time for solution of the two body problem the coriolis parameter and the tidal frequencies change with time thus requiring that the tidal equations be solved several times during the course of each orbital integration in this manner the earth s rotational and the moon s orbital histories are determined on a geologic time scale for each of the four models the calculated position of the lunar orbit at 4 5 billion years ago is found to range from 38 to 53 earth radii in the four models and corresponds to a sidereal month of 330 to 550 hours the sidereal day would have been 12 to 18 hours with a relative inclination of 3 to 22 between the terrestrial and lunar poles these results are in sharp contrast to those from previous studies of the earth moon system most of which indicated a roche limit approach of the two bodies roughly 1 to 2 billion years ago and presented therefore a time scale difficulty in theories of lunar origin this contrast arises mainly from the fact that previous modelers avoided solution of laplace s tidal equations by prescribing a constant frictional phase lag angle between the angular position of the moon and the major axis of the second degree harmonic of the tidally deformed surface of the earth the amount of phase lag was established from the present astronomically deduced rate of tidal dissipation but this precluded dynamic variations in tidal torque over geologic time which are critical for determination of the orbital time scale the present rate of oceanic tidal dissipation is evidently anomalously high because of the near resonance of the oceanic response in both frequency and shape to the tidal forcing for the earth and moon to have evolved to their present separation from a distance of less than about 35 earth radii solely on the basis of oceanic tidal dissipation would have required the m2 response to have been near resonance for a significant portion of geologic history a rather implausible scenario the calculations reported here show that on the contrary frictional coupling between the earth and moon was much weaker than at present throughout most of the orbital history and consequently the moon s closest approach could not have been as small as 35 earth radii although idealized continentalities were used in these calculations the general conclusion of a weaker frictional coupling in the past is believed to be relatively insensitive to the continental configuration this is because at faster paleorotation the semidiurnal tidal frequencies would be resonant only with smaller scale normal modes of the ocean rather than with global scale modes as at present the time scale difficulty heretofore present in models of orbital evolution is thereby eliminated it should be noted that the orbital history developed here supports the theory of binary planetary accretion for lunar origin as opposed to fission or tidal capture

evidence for enhanced mixing over rough topography in the abyssal ocean the overturning circulation of the ocean plays an important role in modulating the earth s climate but whereas the mechanisms for the vertical transport of water into the deep ocean deep water formation at high latitudes and horizontal transport in ocean currents have been largely identified it is not clear how the compensating vertical transport of water from the depths to the surface is accomplished turbulent mixing across surfaces of constant density is the only viable mechanism for reducing the density of the water and enabling it to rise however measurements of the internal wave field the main source of energy for mixing and of turbulent dissipation rates have typically implied diffusivities across surfaces of equal density of only approximately 0 1 cm2 s 1 too small to account for the return flow here we report measurements of tracer dispersion and turbulent energy dissipation in the brazil basin that reveal diffusivities of 2 4 cm2 s 1 at a depth of 500 m above abyssal hills on the flank of the mid atlantic ridge and approximately 10 cm2 s 1 nearer the bottom this amount of mixing probably driven by breaking internal waves that are generated by tidal currents flowing over the rough bathymetry may be large enough to close the buoyancy budget for the brazil basin and suggests a mechanism for closing the global overturning circulation

internal wave induced dispersion and mixing on a sloping boundary 1 a fluorescent dye tracer was released in a stratified water column above a sloping boundary revealing profound dispersive asymmetry initially the dye spread symmetrically in the vertical until the deeper portion became influenced by the bottom boundary layer bbl the shallower portion then spread rapidly up slope in a thin boundary layer influenced by highly non linear isopycnal distortions the deeper down slope portion of dye subsequently became detached from the boundary and intruded into the basin interior in three distinct layers along isopycnal surfaces the intrusions result from the gravitational collapse of mixing patches created by baroclinic flow over an irregular boundary the vertical separation of the layers matches the inverse topographic wavenumber up slope displacement of the dye is consistent with an advective diffusive balance near the sloping boundary controlled by slope angle and roughness horizontal diffusivities increased from 1 4 m2s 1 to 18 4 m2s 1 during the 4 day experiment

a mechanism for local dissipation of internal tides generated at rough topography abstract fine and micro structure observations indicate that turbulent mixing is enhanced within o 1 km above rough topography enhanced mixing is associated with internal wave breaking and in many regions of the ocean has been linked to the breaking and dissipation of internal tides the generation and dissipation of internal tides are explored in this study using a high resolution two dimensional nonhydrostatic numerical model which explicitly resolves the instabilities leading to wave breaking configured in an idealized domain with a realistic multiscale topography and flow characteristics the control simulation chosen to represent the brazil basin region produces a vertical profile of energy dissipation and temporal characteristics of finescale motions that are consistent with observations results suggest that a significant fraction of mixing in the bottom o 1 km of the ocean is sustained by the transfer of energy from the large scale internal tides to smaller scale internal waves by nonlin

a topex poseidon global tidal model tpxo 2 and barotropic tidal currents determined from long range acoustic transmissions abstract tidal currents derived from the tpxo 2 global tidal model of egbert bennett and foreman are compared with those determined from long range reciprocal acoustic transmissions amplitudes and phases of tidal constituents in the western north atlantic are derived from acoustic data obtained in 1991 1992 using a pentagonal array of transceivers small spatially coherent differences between the measured and modeled tidal harmonic constants mostly result from smoothing assumptions made in the model and errors caused in the model currents by complicated topography to the southwest of the acoustical array acoustically measured harmonic constants amplitude phase of m2 tidal vorticity 3 8 10 9s 1 210 310 agree with those derived from the tpxo 2 model 2 5 10 9s 1 250 300 whereas harmonic constants of about 1 2 10 9s 1 350 360 are theoretically expected from the equations of motion harmonic constants in the north pacific ocean are determined using acoustic data from a triangular transceiver array deployed in 1987 these constants are consistent with those given by the tpxo 2 tidal model within the uncertainties tidal current harmonic constants determined from current meters do not generally provide a critical test of tidal models the tidal currents have been estimated to high accuracy using long range reciprocal acoustic transmissions these estimates will be useful constraints on future global tidal models

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

internal tide generation along the south scotia ridge abstract the generation of semidiurnal internal tides along the south scotia ridge ssr the boundary between the northern weddell sea and the scotia sea is investigated using a fully three dimensional primitive equation numerical model the sensitivity of the model to changes in horizontal and vertical grid spacing stratification and choice of bathymetric data set is discussed the highest resolution model 1 16 1 25 41 levels with realistic stratification produces an average along ridge lateral baroclinic m2 energy flux magnitude j m2 160 w m 1 for the section of the ssr between the tip of the antarctic peninsula and the south orkney plateau this value is 10 to time averaged open water fraction thus baroclinic tides may play a significant role in setting mean heat and freshwater exchange and ice formation in the northern weddell sea

indirect evidence for substantial damping of low mode internal tides in the open ocean a global high resolution ocean circulation model forced by atmospheric fields and the m2 tidal constituent is used to explore plausible scenarios for the damping of low mode internal tides the plausibility of different damping scenarios is tested by comparing the modeled barotropic tides with tpxo8 a highly accurate satellite altimetry constrained tide model and by comparing the modeled coherent baroclinic tide amplitudes against along track altimetry five scenarios are tested 1 a topographic internal wave drag argued here to represent the breaking of unresolved high vertical modes applied to the bottom flow default configuration 2 a wave drag applied to the barotropic flow 3 absence of wave drag 4 a substantial increase in quadratic bottom friction along the continental shelves with wave drag turned off and 5 application of wave drag to the barotropic flow at the same time that quadratic bottom friction is substantially increased along the shelves of the scenarios tested here the default configuration 1 yields the most accurate tides in all other scenarios 2 5 the lack of damping on open ocean baroclinic motions yields baroclinic tides that are too energetic and travel too far from their sources despite the presence of a vigorous mesoscale eddy field which can scatter and decohere internal tides in the model the barotropic tides are also less accurate in the absence of an open ocean damping on barotropic motions that is in scenarios 3 and 4 the results presented here suggest that low mode internal tides experience substantial damping in the open ocean

biogeochemical evidence of vigorous mixing in the abyssal ocean the metabolic activities of biological communities living at the abyssal seabed create a strong source of nutrients and a sink for oxygen if the published estimates of vertical mixing based on instantaneous microstructure measurements are correct near to the abyssal seabed away from rough topographic features there should be enhanced concentrations of nitrate and phosphate and depletion of oxygen recent data on the vertical concentration profiles of inorganic nutrients and oxygen over the bottom 1000 m of the water column world ocean circulation experiment woce provide no such evidence it is concluded that the effective vertical mixing rates are much more vigorous than previously indicated and may even be higher than estimates of average basin scale rates based on temperature and salinity distributions we propose that the enhanced mixing associated with rough topography influences the entire volume of the abyssal ocean on short time scales e g one month one year

significant dissipation of tidal energy in the deep ocean inferred from satellite altimeter data how and where the ocean tides dissipate their energy are long standing questions1 that have consequences ranging from the history of the moon2 to the mixing of the oceans3 historically the principal sink of tidal energy has been thought to be bottom friction in shallow seas4 5 there has long been suggestive evidence6 7 however that tidal dissipation also occurs in the open ocean through the scattering by ocean bottom topography of surface tides into internal waves but estimates of the magnitude of this possible sink have varied widely3 8 9 10 11 here we use satellite altimeter data from topex poseidon to map empirically the tidal energy dissipation we show that approximately 1012 watts that is 1 tw representing 25 30 of the total dissipation occurs in the deep ocean generally near areas of rough topography of the estimated 2 tw of mixing energy required to maintain the large scale thermohaline circulation of the ocean12 one half could therefore be provided by the tides with the other half coming from action13 on the surface of the ocean

ocean tidal heating in icy satellites with solid shells abstract as a long term energy source tidal heating in subsurface oceans of icy satellites can influence their thermal rotational and orbital evolution and the sustainability of oceans we present a new theoretical treatment for tidal heating in thin subsurface oceans with overlying incompressible elastic shells of arbitrary thickness the stabilizing effect of an overlying shell damps ocean tides reducing tidal heating this effect is more pronounced on enceladus than on europa because the effective rigidity on a small body like enceladus is larger for the range of likely shell and ocean thicknesses of enceladus and europa the thin shell approximation of beuthe 2016 is generally accurate to less than about 4 explaining enceladus endogenic power radiated from the south polar terrain by ocean tidal heating requires ocean and shell thicknesses that are significantly smaller than the values inferred from gravity and topography constraints the time averaged surface distribution of ocean tidal heating is distinct from that due to dissipation in the solid shell with higher dissipation near the equator and poles for eccentricity and obliquity forcing respectively this can lead to unique horizontal shell thickness variations if the shell is conductive the surface displacement driven by eccentricity and obliquity forcing can have a phase lag relative to the forcing tidal potential due to the delayed ocean response for europa and enceladus eccentricity forcing generally produces greater tidal amplitudes due to the large eccentricity values relative to the obliquity values despite the small obliquity values obliquity forcing generally produces larger phase lags due to the generation of rossby haurwitz waves if europa s shell and ocean are respectively 10 and 100 km thick the tide amplitude and phase lag are 26 5 m and

tidally driven processes leading to near field turbulence in a channel at the crest of the mendocino escarpment abstractin situ observations of tidally driven turbulence were obtained in a small channel that transects the crest of the mendocino ridge a site of mixed diurnal and semidiurnal tides diurnal tides are subinertial at this latitude and once per day a trapped tide leads to large flows through the channel giving rise to tidal excursion lengths comparable to the width of the ridge crest during these times energetic turbulence is observed in the channel with overturns spanning almost half of the full water depth a high resolution nonhydrostatic 2 5 dimensional simulation is used to interpret the observations in terms of the advection of a breaking tidal lee wave that extends from the ridge crest to the surface and the subsequent development of a hydraulic jump on the flanks of the ridge modeled dissipation rates show that turbulence is strongest on the flanks of the ridge and that local dissipation accounts for 28 of the energy converted from the barotropic tide into baroclinic motion

influence of water column anoxia on the elemental fractionation of carbon and phosphorus during sediment diagenesis abstract organic carbon oxidation and benthic total phosphorus flux measurements from sites covering a range of bottom water oxygen concentrations have been compiled the data show that p regeneration relative to carbon oxidation is much more extensive in sediments overlain by oxygen depleted waters these results are consistent with studies showing that low oxygen bottom water concentrations correlate with reduced total phosphorus burial efficiencies and enhanced organic carbon burial efficiencies based on these observations a positive feedback is proposed between water column anoxia enhanced benthic phosphorus regeneration and marine productivity this feedback may help explain the widespread accumulation of organic rich marine sediments from anoxic waters observed in the geologic record

high mixing rates in the abyssal southern ocean mixing of water masses from the deep ocean to the layers above can be estimated from considerations of continuity in the global ocean overturning circulation but averaged over ocean basins diffusivity has been observed to be too small to account for the global upward flux of water and high mixing intensities have only been found in the restricted areas close to sills and narrow gaps here we present observations from the scotia sea a deep ocean basin between the antarctic peninsula and the tip of south america showing a high intensity of mixing that is unprecedented over such a large area using a budget calculation over the whole basin we find a diffusivity of 39 plus minus 10 x 104 m2 s 1 averaged over an area of 7 x 105 km2 the scotia sea is a basin with a rough topography situated just east of the drake passage where the strong flow of the antarctic circumpolar current is constricted in width the high basin wide mixing intensity in this area of the southern ocean may help resolve the question of where the abyssal water masses are mixed towards the surface

orbitally forced sedimentary rhythms in the stratigraphic record is there room for tidal forcing the imprint of orbital cycles which result from the varying eccentricity of the earth s orbit and changes in the orientation of its axis have been recognised throughout the phanerozoic rock record variations in insolation and their effect on climate are generally considered to be the sole transfer mechanism between the orbital variables and cyclic sedimentary successions common oceanographic principles however show that the ocean tide also responds to variations in the orbital parameters the ocean tide has not yet been considered to be a valid additional transfer mechanism for the orbital variations in geological studies of milankovitch cycles in sedimentary successions the insolation paradigm offers satisfying explanations and the role of long term variations of the ocean tide has not yet been appreciated variations in the ocean tide related to changing eccentricity at present 0 0165 theoretical maximum 0 0728 affect a variety of oceanographic and sedimentary processes in addition to the widely accepted paradigm of orbitally forced insolation changes the tidal transfer of orbital signals may explain certain less well understood aspects of orbitally induced cycles in the stratigraphic record related to ocean mixing organic productivity and tidal processes in shallow seas and deep water variations of the ocean tide in relation to the 18 6 year lunar nodal cycle which has no insolation counterpart by which they may be obscured indeed show that these relatively small variations can produce significant effects in sedimentary environments that are sensitive to variations in the strength of the ocean tide in analogy with the 18 6 year lunar nodal cycle orbital variations of the tide on milankovitch time scales are likely to have affected sedimentary systems in the past

actinium 227 as a deep sea tracer sources distribution and applications abstractactinium is one of the rarest naturally occurring elements on earth we measured its longest lived isotope 227ac half life 21 77 years for the first time in the water column of the southeast pacific the central arctic the antarctic circumpolar current acc and the weddell gyre besides the profile in the southeast pacific which confirms earlier findings about the role of diapycnal mixing for 227ac distribution we found three other different types of vertical profiles these profiles point to a prominent role of advection for 227ac distribution especially in the southern ocean depending on the type of profile found 227ac is proposed as a tracer for different oceanographic questions in the southern ocean up to 4 93 0 32 dpm m 3 227acex 227ac in excess of its progenitor 231pa are found close to the sea floor which are the highest concentrations ever observed in the ocean close to the sea surface in the weddell gyre wg 0 46 0 05 dpm m 3 227acex are detected we use 227acex there to determine the upwelling velocity in the eastern weddell gyre to be about 55 m y 1 in the acc upper and lower circumpolar deep water ucdw and lcdw are found to differ clearly in their 227acex activity high 227acex activities are therefore a promising tracer for recent inputs of lcdw to the sea surface which may help to understand the role of deep upwelling for iron inputs into antarctic surface waters the expected release of 227ac is compared with 228ra to make sure that the large near surface excess in the water column of the southern ocean is not due to lateral inputs by isopycnal mixing results of a model indicate that the 227ac 228ra flux ratio is about 50 times lower on shelves than in the deep sea data from the central arctic and from a transect across the acc confirm that 228ra and 227acex differ strongly in their sources the first measurements of 227ac on suspended matter less than 1 7 of total 227ac close to the sea floor indicate that the particle reactivity of 227ac is negligible in the open ocean in agreement with earlier findings nozaki 1984 despite the extremely low concentrations of 227ac new measurement techniques moore and arnold 1996 point to a comfortable and comparably simple determination of 227ac in the future finally 227acex may become a widely used deep sea specific tracer