tide supported gravity flows on the upper delta front fraser river delta canada abstract three anomalous events aes were recorded off the fraser river canada during the freshet of 2008 and are ascribed to quasi continuous gravity flows these flows transport warm low salinity fraser river waters to the upper delta front of the fraser delta to at least 50 m water depth all flows occurred during the freshet and spring ebbing tide and were characterized by deposition of fine grained sand and silt beds with likely high water contents these sediments were susceptible to resuspension by the subsequent flood tide current producing very high near bed suspended sediment concentrations ssc with enough excess density to generate hyper concentrated flows our observations show that these episodic events result from the combination of high river discharge high ssc and strong tides and therefore are likely to occur on the delta fronts of other large tide dominated and tide influenced rivers in shallow water basins

what controls submarine channel development and the morphology of deltas entering deep water fjords river deltas and associated turbidity current systems produce some of the largest and most rapid sediment accumulations on our planet these systems bury globally significant volumes of organic carbon and determine the runout distance of potentially hazardous sediment flows and the shape of their deposits here we seek to understand the main factors that determine the morphology of turbidity current systems linked to deltas in fjords and why some locations have well developed submarine channels whilst others do not deltas and associated turbidity current systems are analysed initially in five fjord systems from british columbia in canada and then more widely this provides the basis for a general classification of delta and turbidity current system types where rivers enter relatively deep 200 m water fjord delta area is found to be strongly bimodal avalanching of coarse grained bedload delivered by steep mountainous rivers produces small gilbert type fan deltas whose steep gradient 11 25 approaches the sediment s angle of repose bigger fjord head deltas are associated with much larger and finer grained rivers these deltas have much lower gradients 1 5 10 that decrease offshore in a near exponential fashion the lengths of turbidity current channels are highly variable even in settings fed by rivers with similar discharges this may be due to resetting of channel systems by delta top channel avulsions or major offshore landslides as well as the amount and rate of sediment supplied to the delta front by rivers

which triggers produce the most erosive frequent and longest runout turbidity currents on deltas subaerial rivers and turbidity currents are the two most voluminous sediment transport processes on our planet and it is important to understand how they are linked offshore from river mouths previously it was thought that slope failures or direct plunging of river flood water hyperpycnal flow dominated the triggering of turbidity currents on delta fronts here we re analyse the most detailed time lapse monitoring yet of a submerged delta comprising 93 surveys of the squamish delta in british columbia canada we show that most turbidity currents are triggered by settling of sediment from dilute surface river plumes rather than landslides or hyperpycnal flows turbidity currents triggered by settling plumes occur frequently run out as far as landslide triggered events and cause the greatest changes to delta and lobe morphology for the first time we show that settling from surface plumes can dominate the triggering of hazardous submarine flows and offshore sediment fluxes

ancient lacustrine hyperpycnites a depositional model from a case study in the rayoso formation cretaceous of west central argentina abstract hyperpycnal flows originate when sediment laden fluvial discharges enter standing lower density water because of their excess density the flows plunge near the river mouth and continue to travel basinward as a quasi steady and fully turbulent underflow the related deposits are hyperpycnites and constitute a particular type of turbidite with poorly known facies and facies tracts although hyperpycnal flows seem to be quite common in present times their occurrence in fossil strata is poorly documented this paper addresses the characteristics and depositional processes of shallow lacustrine sandy hyperpycnites on the basis of the field analysis of well exposed lower cretaceous strata rayoso formation in the neuquen basin of west central argentina the rayoso formation is composed of clastic and minor evaporitic red beds up to 1200 m thick deposited in a shallow perennial lake of variable salinity affected by long lived hyperpycnal flows main clastic facies are composed of fine grained sandstones with climbing ripples and plane beds other common sandstone facies include massive beds and low angle cross stratification most sandstone facies are related to traction plus fallout processes and often show a vertical fluctuation between sedimentary facies originated under different traction plus fallout conditions within single beds these fluctuations are interpreted to be evidence of deposition from flow fluctuations in sustained hyperpycnal flows most beds internally show the existence of three depositional phases acceleration ap erosion plus bypass ep and deceleration dp which record the complete evolution of a single long lived hyperpycnal flow at a fixed point additionally the depositional evolution of a single long lived hyperpycnal flow with distance records initially the progressive basinward migration of the ap and ep phases and finally an overall deposition under the dp phase both in proximal and distal areas this evolution provides an adequate explanation for the basinward extension of channelized features and for the occurrence of fine grained sandstones with climbing ripples both in proximal and distal positions within the same hyperpycnal system consequently facies analysis derived from application of the bouma sequence is not valid for deposits of quasi steady hyperpycnal flows

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

accuracy assessment of global barotropic ocean tide models the accuracy of state of the art global barotropic tide models is assessed using bottom pressure data coastal tide gauges satellite altimetry various geodetic data on antarctic ice shelves and independent tracked satellite orbit perturbations tide models under review include empirical purely hydrodynamic forward and assimilative dynamical i e constrained by observations ten dominant tidal constituents in the diurnal semidiurnal and quarter diurnal bands are considered since the last major model comparison project in 1997 models have improved markedly especially in shallow water regions and also in the deep ocean the root sum square differences between tide observations and the best models for eight major constituents are approximately 0 9 5 0 and 6 5 cm for pelagic shelf and coastal conditions respectively large intermodel discrepancies occur in high latitudes but testing in those regions is impeded by the paucity of high quality in situ tide records long wavelength components of models tested by analyzing satellite laser ranging measurements suggest that several models are comparably accurate for use in precise orbit determination but analyses of grace intersatellite ranging data show that all models are still imperfect on basin and subbasin scales especially near antarctica for the m2 constituent errors in purely hydrodynamic models are now almost comparable to the 1980 era schwiderski empirical solution indicating marked advancement in dynamical modeling assessing model accuracy using tidal currents remains problematic owing to uncertainties in in situ current meter estimates and the inability to isolate the barotropic mode velocity tests against both acoustic tomography and current meters do confirm that assimilative models perform better than purely hydrodynamic models

tide model errors and grace gravimetry towards a more realistic assessment summary the manner in which errors in tide models affect monthly gravity solutions from grace satellite data is re examined we perform a complete simulation of grace gravity estimation including allowance for accelerometer calibrations and satellite state vector adjustment errors in monthly geoid estimates are for most regions of a order of 0 5 mm or roughly 1 cm of equivalent water height when smoothed over radii of 600 km in polar regions where ocean tide models are suspect errors can grow significantly larger over 2 mm in geoid height although over very localized regions errors from diurnal tides tend to cancel but they are not completely eliminated inducing geoid errors of the order of 0 3 mm the currently accepted grace total error budget is roughly an order of magnitude larger than the component arising from tide modelling errors

hyperpycnal plume formation from riverine outflows with small sediment concentrations a series of laboratory experiments has been conducted in order to elucidate the sediment induced mixing processes accompanying riverine outflows specifically the discharge of a warm fresh particle laden fluid over a relatively dense cool brine in a parameter regime analogous to recently acquired field measurements hypopycnal surface plumes were subject to a convective instability driven by some combination of heat diffusing out of the warm fresh sediment laden plume and particle settling within it convection was robust in the presence or absence of intense turbulence at sediment concentrations as low as 1 kg m 3 and took the form of millimetre scale sediment laden fingers descending from the base of the surface plume a consequence of the convective instability of the original hypopycnal plume is the generation of a hyperpycnal bottom riding flow the experiments presented here indicate that natural river outflows may thus generate hyperpycnal plumes when sediment concentrations are 40 times less than those required to render the outflow heavy relative to the oceanic ambient the resulting hyperpycnal plumes may play an important role in transporting substantial quantities of sediment to the continental slope and beyond

modeling ocean tides with and without assimilating data when reviewing the application of semiempirical and free ocean tide models to the computation of semidiurnal diurnal and long period tides it is recognized that the basin dominating features of the computed oscillation systems have in general proven to be compatible with the relevant data available in particular free tidal models moreover allow together with the results from investigations of free oscillations and of tides in idealized ocean basins to determine the dependence of tidal regimes on specific constituents of tidal dynamics e g on loading and self attraction as the computational results are not as precise as required for for example geophysical and astronomical applications a procedure has been developed permitting to utilize also the increasing amount of information from pelagic data for improving the mapping of ocean tides by numerical models using a spectral model test calculations have first been performed for an idealized ocean basin with well determined free and forced oscillation properties reference is made in detail to a realistic ocean tide model which includes loading and self attraction using a convolution integral and which permits the assimilation of data by minimizing a functional made up by the residuals of data and of equations of momentum consistent fields of sea surface elevation and currents with mass precisely conserved have been obtained for the m2 tide in the world ocean comparisons are drawn between these fields and those having been obtained by applying that free model which represents a special case of the model considering information from data the gain of the tidal oscillation system in basin wide realism due to assimilating pelagic harmonic constants is estimated and found promising

estimating open ocean barotropic tidal dissipation the hawaiian ridge the generalized inverse of a regional model is used to estimate barotropic tidal dissipation along the hawaiian ridge the model based on the linear shallow water equations incorporates parameterizations for the dissipation of energy via friction in the bottom boundary layer and form drag due to internal waves generated at topographic slopes sea surface height data from 364 orbit cycles of the ocean topography experiment topex poseidon satellite mission are used to perform inversions at eight diurnal and semidiurnal tidal frequencies it is estimated that the barotropic m2 tide loses energy at a rate of 19 gw of which 88 is lost within 250 km of the ridge presumably via conversion to the internal or baroclinic tide uncertainty in the assumed model error and wave drag in the forward model suggest that m2 dissipation values from 18 to 25 gw are consistent with the altimetric observations other barotropic tidal constituents are estimated to lose a total of 5 7 gw the spatial distribution of barotropic dissipation along the ridge is similar to that inferred from three dimensional primitive equation models and it is largely insensitive to details of assumed model and data errors dissipation at semidiurnal frequencies is most intense at the french frigate shoals with lesser but significant contributions at other sites diurnal tidal dissipation is concentrated to the east of the french frigate shoals at the gardner pinnacles further work with threedimensional models will be necessary to determine the fate of the energy that is removed from the barotropic tide

effects of ambient currents and waves on gravity driven sediment transport on continental shelves abstract observations from several shelf environments show that down slope gravity driven transport may constitute an important mode of suspended sediment dispersal across shelves and highlight the influence of ambient waves and currents on gravity induced sediment flux the phenomena discussed here involve high concentrations of suspended sediment mixed with seawater and thus differ in genesis from hyperpycnal plumes released directly from sediment laden rivers the field sites examined are the gulf of bohai off the mouth of the yellow river huanghe the northern california shelf off the mouth of the eel river and the louisiana shelf west of the mouths of the mississippi river off the yellow river rapid down slope transport over distances of a few km occurred when frictional resistance induced by strong along shelf currents was temporarily relaxed more prolonged down slope motion over longer distances occurred following floods of the eel river when wave and current agitation provided turbulence to sustain gravity driven transport of fluid mud on the louisiana inner shelf the down slope gravity force was much weaker but observations suggest that thin gravity flows may still have occurred in the presence of waves a simple analytical theory is developed that incorporates the influence of ambient shelf currents on gravity driven transport of suspended sediment this theory is quantitatively consistent with the observations from the three sites if the supply of easily suspended sediment is less than the capacity of ambient currents including waves to carry sediment then intense turbulence limits gravity induced sediment transport by increasing the drag at the base of the flow when ambient currents abruptly cease rapid down slope transport can then occur over short distances until the sediment settles such flows do not remain intensely turbulent because the slope of the continental shelf is too gentle to induce shear instability within the gravity flow the maximum sustained rate of gravity induced sediment transport occurs when ambient currents are strong but the supply of easily suspended sediment exceeds the resuspension capacity of the ambient currents feedback then leads to values of the gradient richardson number ri within the flow that are near the critical value of 1 4 this partially damps bottom drag but still allows the generation of sufficient turbulence to maintain sediment in suspension observations also indicate systematic relationships among ri the supply of easily suspended sediment and the bottom drag coefficient acting on the gravity flow

tides on the ross ice shelf observed with icesat 1 the ice cloud and land elevation satellite icesat provides the first opportunity for measurement of surface elevation hi over the portions of the antarctic ice shelves that are south of the european remote sensing ers satellite maximum latitude 81 5 s the dominant source of short period variability in hi is ocean tides we use crossover elevation difference hi data from the ross ice shelf ris to demonstrate icesat s ability to detect the tidal signal and to compare the accuracy of several tide models the root mean square rms value of all ris measurements of hi is 0 74 m after removing the tide using the most accurate model the rms of the residual signal in regions of optimal model performance is 0 16 0 03 m this value corresponds to an uncertainty in hi of 0 11 0 02 m we postulate that the primary sources of the residual signal are tide model errors and the inverse barometer effect

mass wasting on the mississippi river subaqueous delta abstract the mississippi river delta front mrdf is an excellent natural laboratory for studying seafloor instability and evaluating the preconditioning factors and triggering mechanisms that lead to seafloor failures the occurrence of seafloor landslides on the mrdf has been recognized since the 1950s but the bulk of research on the topic was conducted in the 1970s 80s after seafloor landslides triggered by hurricane camille damaged offshore infrastructure through these efforts it was recognized that seafloor instability features are present across the entire delta front that rapid sediment delivery from the mississippi river is a primary preconditioning factor for failures and that cyclic loading from hurricane waves is the main triggering mechanism for deep seated catastrophic events however mounting evidence shows that mrdf seafloor motion occurs even during periods of no hurricane activity which could be attributed to creep like motion of underconsolidated sediment or smaller episodic flows triggered by winter storms or mississippi river floods given the extensive spatial distribution of instabilities on the mrdf the multiple mechanisms of failure and variety of resulting morphology and the range of potential triggering mechanisms with short recurrence the mrdf is an exceptional location to assess the complex problem of seafloor landslides an improved understanding of seafloor landslides is crucial for understanding global sediment budgets and associated biogeochemical cycling as they can evacuate large volumes of sediment into deep water over short time periods additionally seafloor landslides pose a hazard to offshore infrastructure and to coastal communities through possible tsunami inundation and advancing research on preconditioning factors and triggering mechanisms would improve hazard assessments this paper presents a review and synthesis of geological and geotechnical research on the mrdf particularly with respect to seafloor landslides their occurrence geological and geotechnical controls triggering mechanisms and knowledge gaps related thereto this synthesis is conducted at times of rapidly developing technologies for studying seafloor instability and as the mrdf enters a stage of degradation characterized by reduced sediment delivery and accumulation

antarctic ice mass balance estimates from grace tidal aliasing effects 1 geophysical interpretation of grace gravity fields has provided estimates of antarctic ice mass change such analyses rely on proper consideration of ocean tidal effects through the models csr4 and fes2004 in general mis modeling of tidal constituents with aliasing period less than 30 day will not have significant impact on ice mass change however for constituents such as k1 k2 and s2 the aliasing period is sufficiently large to potentially compromise long term variability studies here we quantify tidal aliasing over antarctica by simulating grace signatures due to differences between csr4 and fes2004 and the best available circum antarctic model tpxo6 2 the s2 simulations are in close agreement with the observed s2 signal from grace simulations of ice mass change show that over 2002 2006 long term k1 and k2 aliasing is equivalent to a rate error of 4 5 1 3 km3 a of ice with csr4 but only 0 2 0 2 km3 a with fes2004 after spatial averaging and destriping k1 plus k2 mis modeling in csr4 fes2004 introduce point wise errors up to 5 2 mm a in equivalent water height over a 3 5 year period with observed mass change equivalent to less than 30 mm a of water height over much of antarctica the simulations show tidal aliasing uncertainty at the 2 3 mm a level for august 2002 january 2006 or 10 of the signal with grace release 04 the revised estimate april 2002 january 2006 of published ice volume decrease is 164 80 km3 a of ice although this value depends very much on the gia model and grace analysis approach

sediment dispersion pattern off the present huanghe yellow river subdelta and its dynamic mechanism during normal river discharge period hydrological observations were conducted synchronically along three transects in the southeast middle and northeast off the present huanghe yellow river subdelta during normal discharge approximately 200 m 3 s 1 period on august 8 13 2003 suspended sediment fluxes and dispersion patterns off the present huanghe subdelta were studied based on the hydrographic data collected in these surveys along each survey transect tidal shear fronts were identified that in combination with the tidal currents were the dominant factors controlling the pattern of sediment dispersal most of the river laden suspended sediment from the river mouth was transported via hypopycnal flow and was limited within the 5 m isobath off the mouth due to the barrier effect of the tidal shear front and the weak river flow in northern and southern areas off the subdelta the sediment fluxes at stations farther from the coast were much higher than those at the nearshore ones indicating that the river laden sediments were transported to north and south offshore via deeper water areas at both sides of the river mouth the tidal shear fronts revealed in the northern and southern nearshore areas of the subdelta jointly with tidal currents barred the sediment transport from offshore to nearshore this resulted in offshore sediment deposition on the northern and southern parts of the subaqueous subdelta rather than in the nearshore area thus forming nearshore erosion and offshore accumulation areas respectively

infaunal holothurian distributions and their traces in the fraser river delta front and prodelta british columbia canada abstract holothurians sea cucumbers constitute one of the largest and most abundant infaunal groups inhabiting the fraser river delta front 0 to 150 m water depth and prodelta greater than 150 m water depth the spatial distribution and density of animals reveal their preferred substrate grain sizes and their tolerance or sensitivity to various stress factors including salinity fluctuations available food resources sedimentation rate and pollution in the delta front below 25 m water depth below storm wave base holothurians are asymmetrically distributed with respect to the main distributary channel population densities primarily reflect asymmetry in grain size distributions across the delta front holothurians are absent or occur in low density in the sand dominated southern delta front sdf whereas the mud dominated northern delta front ndf is more heavily colonized sedimentation rate and nutrient content are equally important in holothurian distribution population densities of certain holothurians show significant increase where there are moderate sedimentation rates 2 4 cm yr 1 and river derived nutrient supply several subsurface traces and their surface expressions are attributed to holothurians subsurface traces include diminutive and robust artichnus thalassinoides and u shaped bio deformation structures on the sediment surface bio topographic structures such as mounds and funnel shaped depressions are produced by the activity of sea cucumbers of the holothurian generated traces only artichnus can conclusively be attributed to sea cucumbers based on the distributions of the trace makers of artichnus we hypothesize that in the rock record this trace fossil can be used as evidence of stable euhaline salinity conditions and sediment deposition and colonization below storm wave base artichnus occurs mainly in mud dominated 55 mud substrates

ocean tidal solutions in antarctica from grace inter satellite tracking data 1 long wavelength components of the oceanic tides surrounding antarctica are estimated directly from three years of grace satellite to satellite ranging measurements an inversion is performed for the major constituents m2 o1 and s2 with k1 excluded because of inadequate phase sampling the tides are parameterized as localized average mass anomalies over areas approximately 3002 km2 other parameters including satellite state adjustments are estimated simultaneously with the tides qualitative comparison of our solutions with in situ tide measurements shows agreement in spatial pattern clearly indicating regions where our adopted prior model is inadequate to exploit these solutions follow on work must assimilate these long wavelength components into a high resolution numerical tidal model

propagation of the overtide m4 through the deep atlantic ocean 1 the nonlinear overtide m4 is generated in shallow waters and is generally no more than a few mm amplitude in the deep ocean such small periodic waves can now be mapped empirically by analyzing the long 15 year time series of topex poseidon and jason 1 satellite altimetry in a few locations of the deep atlantic m4 amplitudes reach nearly 10 mm confirming recent modeling efforts by lyard and colleagues these relatively large amplitudes evidently represent a complex interference pattern of free waves radiating from a few shallow sources especially the patagonian shelf they form approximately a standing wave resonance in the gulf of guinea

correcting grace gravity fields for ocean tide effects 1 the grace mission will be launch in early 2002 and will map the earth s gravity fields and its variations with unprecedented accuracy during its 5 year lifetime unless ocean tide signals and their load upon the solid earth are removed from the grace data their long period aliases obscure more subtle climate signals which grace aims at the difference between two existing ocean tide models can be used as an estimate of current tidal model error for the m2 s2 k1 and o1 constituents when compared with the expected accuracy of the grace system both expressed as spherical harmonic degree variances we find that the current ocean tide models are not accurate enough to correct grace data at harmonic degrees lower that 35 the accumulated tidal errors may affect the grace data up to harmonic degree 56 furthermore the atmospheric radiation tides may cause significant errors in the ocean tide model if altimetry corrected for inverted barometer effects was used in its derivation to study the temporal characteristics of the ocean tidal constituents when sampled by grace approximate alias frequencies were derived assuming a sampling of half a sidereal day those results show that the ocean tide errors will not cancel in the grace monthly averaged temporal gravity fields the s2 and the k2 terms have alias frequencies much longer than 30 days so they remain almost unreduced in the monthly averages

cyclone driven deep sea injection of freshwater and heat by hyperpycnal flow in the subtropics china 973 program 2009cb421200 program of introducing talents of discipline to universities b07034 academia sinica thematic program afobi taiwan nsc 98 2116 m 001 005

a preliminary tidal analysis of topex poseidon altimetry approximately 12 months of data from the topex poseidon satellite altimeter mission are analyzed for the major short period oceanic tides a harmonic analysis is performed on data captured within bins defined on a deep ocean grid which owing to tidal aliasing considerations must have a relatively coarse spatial resolution our analysis is in terms of corrections to the schwiderski and cartwright ray models and it confirms many of the schwiderski differences previously reported by cartwright and ray our differences with respect to the geosat based cartwright and ray model form a sectorial pattern in m2 with high low differences separated roughly 180 in longitude we suggest that these sectorial errors were most likely induced by geosat s relatively large orbit error comparisons to independent data validate the improved topex poseidon solutions in situ ground truth shows m2 rms differences of 4 10cm schwiderski 3 86cm cartwright and ray 2 63cm this paper global rates of energy dissipation confirm earlier estimates for m2 and show improved agreement with satellite tracking studies for k1 and s2 these preliminary exercises confirm that topex poseidon should result in a new generation of improved global tidal models

gravity recovery and climate experiment grace alias error from ocean tides 1 gravity recovery and climate experiment grace is able to observe interannual and longer period mass redistribution driven by climate changes however alias errors due to inaccurate ocean tide models may contaminate these signals to quantify this problem we estimate alias contamination due to expected errors in eight tidal constituents q1 o1 p1 k1 n2 m2 s2 and k2 for the period august 2002 to february 2006 differences between got00 2 and tpxo6 2 tide models are used as estimates of tide model errors the alias estimate is based on an approximate method employing least squares fits of spherical harmonics to potential differences between the two grace satellites results from this method are similar to previous estimates confirming this is a useful and efficient way to study the alias problem new findings are 1 the period of the m2 tide alias is about 140 d much longer than the predicted period 13 5 d because of monthly sampling of the 13 5 d period 2 there are two alias periods for k1 one about 90 d and one longer than 7 years and 3 the slow decay in the grace orbit causes tide component aliases to differ from pure frequencies as the orbit evolves we also find that aliases can contaminate in both space and time and thus may affect estimates of mass changes over land finally we compare the simulated s2 alias with the estimated s2 alias in grace data they are similar but our approximate method appears to overestimate alias error over high latitude oceans and along certain coastlines while underestimating error over low latitude oceans

upslope migrating bedforms in a proglacial sandur delta cyclic steps from river derived underflows abstract backstepping cross strata on steep foresets of a gilbert type proglacial fluviodeltaic system are ascribed to cyclic steps and other associated supercritical bedforms they provide insight into how sandur river flows transition into the marine realm these sedimentary structures are located on steep foresets up to 17 with corresponding top lying flat based topsets in an upper pleistocene delta on the north shore of the gulf of st lawrence quebec canada packages of backstepping cross strata of sand and gravel lying in the lower part of the delta front outcrop are organized in 10 20 m spaced pseudo foresets with a mean slope of 11 12 seawards backstepping strata include frequent internal erosion surfaces that onlap upslope on pseudo foresets and are interpreted as cyclic steps narrow deep and asymmetrical scours and upslope climbing cross beds are interpreted as chutes and pools and antidunes respectively very shallow 15 m depositional paleo bathymetry is inferred from the preservation of the delta brink the well organized stratal pattern in cyclic step to antidune deposits indicates relatively steady and uniform flow patterns there is insufficient distance for a headscarp large enough to transform to the volume of observed accreted sands or for a flow transformation from a gravitational collapse to net depositional cyclic steps these deposits are sandier than the topsets beds and are thus not derived from them but rather correspond to topset erosional surfaces the development of cyclic steps from hyperpycnal flows was likely enhanced by tidal drawdown processes the resulting sediment laden supercritical flows plunged inertially and evolved into an underflow that generated the cyclic steps on the upper foresets the cyclic steps have a high aspect ratio and represent an end member of coarse grained sediment deposited on steep slopes in contrast to low gradient low aspect ratio muddy deposits

the accuracy of surface elevations in forward global barotropic and baroclinic tide models abstract this paper examines the accuracy of surface elevations in a forward global numerical model of 10 tidal constituents both one layer and two layer simulations are performed as far as the authors are aware the two layer simulations and the simulations in a companion paper deep sea research ii 51 2004 3043 represent the first published global numerical solutions for baroclinic tides self consistent forward solutions for the global tide are achieved with a convergent iteration procedure for the self attraction and loading term energies are too large and elevation accuracies are poor unless substantial abyssal drag is present reasonably accurate tidal elevations can be obtained with a spatially uniform bulk drag c d or horizontal viscosity k h but only if these are inordinately large more plausible schemes concentrate drag over rough topography the topographic drag scheme used here is based on an exact analytical solution for arbitrary small amplitude terrain and supplemented by dimensional analysis to account for drag due to flow splitting and low level turbulence as well as that due to breaking of radiating waves the scheme is augmented by a multiplicative factor tuned to minimize elevation discrepancies with respect to the topex poseidon t p constrained got99 2 model the multiplicative factor may account for undersampled small spatial scales in bathymetric datasets an optimally tuned multi constituent one layer simulation has an rms elevation discrepancy of 9 54 cm with respect to got99 2 in waters deeper than 1000 m and over latitudes covered by t p 66 n to 66 s the surface elevation discrepancy decreases to 8 90 cm 92 percent of the height variance captured in the optimally tuned two layer solution the improvement in accuracy is not due to the direct surface elevation signature of internal tides which is of small amplitude but to a shift in the barotropic tide induced by baroclinicity elevations are also more accurate in the two layer model when pelagic tide gauges are used as the benchmark and when the t p constrained tpxo6 2 model is used as a benchmark in deep waters south of 66 s for antarctic diurnal tides the improvement in forward model elevation accuracy with baroclinicity is substantial the optimal multiplicative factor in the two layer case is nearly the same as in the one layer case against initial expectations that the explicit resolution of low mode conversion would allow less parameterized drag in the optimally tuned two layer m 2 solution local values of the ratio of temporally averaged squared upper layer speed to squared lower layer speed often exceed 10

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

powerful unconfined turbidity current captured by cabled observatory on the fraser river delta slope british columbia canada turbidity currents are one of the main sediment transport processes on earth yet are notoriously difficult to monitor directly this article presents the first direct and high bandwidth observation of a turbidity current using a cabled sea floor observatory on 5 june 2012 a platform on ocean networks canada located in 107 m of water on the fraser river delta slope was displaced downslope and severed from its data cable the platform weighed ca 1000 kg in water the event took place during high river discharge high tides and rapid sediment accumulation on adjacent upslope areas of the sea floor data recorded as it tumbled downslope allow a reconstruction of the flow which is inferred to have been an unconfined turbidity current lines of evidence indicate that the flow came in as a bed hugging wedge and built up to between 1 m and 4 m in height as the head passed through comparison with laboratory data suggest that the flow was initially supercritical while the adjacent slope offset to the north clearly exhibits change over an annual resurvey period the bathymetry directly at the event location show no resolvable change over a period from seven months before the event to one month after sediment cores collected after the event were pervasively biototurbated and they contain no obvious deposit connected with this event the remarkable aspects of this research follow the flow was powerful enough to carry a 1 tonne platform and sever a heavily armoured cable the current occurred on the unchannelized open slope this powerful event failed to cause discernible seabed elevation change the flow was triggered by tidal conditions the event was detected by a purpose designed cabled observatory thus providing high bandwidth data and also alerting researchers in real time to mount follow on investigations

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

the periodic growth increments of biological shells and the orbital parameters of earth moon system periodic increments in the growth of organismal shells and fossils in the intertidal zone were studied by light microscopy scanning electron microscopy and chemical composition analyses the results were used to calculate the orbital parameters of the earth moon system from the ordovician to quaternary period the annual semi annual biweekly 14 day daily and subdaily growth rhythms were identified on the surface of shells the periodic changes in the growth increments of shells and the rhythmic variations of microelements in fossils and organisms were reliable indicators of environmental changes there were 415 69 days for an annual period in ordovician 407 1 days in devonian 400 51 days in carboniferous permian 393 98 days in tertiary 374 13 days in triassic and 367 4 days in quaternary the data collected and calculated from these growth increments show that from the ordovician to the quaternary period the rate of earth s rotation has been slowing down and that the distance from the earth to the moon has been increasing while the rate of lunar retreat has been decreasing

grace observations of m2 and s2 ocean tides underneath the filchner ronne and larsen ice shelves antarctica 1 by processing the grace satellite to satellite tracking data and estimating the temporal gravity fields regionally over the southern polar region with a 5 day interval we observed m2 and s2 ocean tides underneath the filchner ronne and larsen ice shelves antarctica based on the predicted aliased periods we extracted the m2 and s2 signals from the time series of 5 daily mean grace regional gravity estimates the grace observations agreed well with the predicted tides from the fes2004 and cats02 01 models after smoothing the models to the commensurate spatial resolution as grace overall the grace and the models agreed within 10 20 difference in the tidal amplitude and 20 in phase for both m2 and s2 our results suggest that grace provides valuable observations of ocean tides with a spatial resolution as short as 300 km over the remote area lacking of quality observations such as the antarctica ice shelves

hyperpycnal sediment discharge from semiarid southern california rivers implications for coastal sediment budgets southern california rivers discharge hyperpycnal river density greater than ocean density concentrations of suspended sediment 40 g l according to buoyancy theory during flood events mostly during el nino southern oscillation enso conditions because hyperpycnal river discharge commonly occurs during brief periods hours to occasionally days mean daily flow statistics often do not reveal the magnitude of these events hyperpycnal events are particularly important in rivers draining the transverse range and account for 75 of the cumulative sediment load discharged by the santa clara river over the past 50 yr these events are highly pulsed totaling only 30 days 0 15 of the total 50 yr period observations of the fate of sediment discharge although rare are consistent with hyperpycnal river dynamics and the high likelihood of turbidity currents during these events we suggest that much of the sediment load initially bypasses the littoral circulation cells and is directly deposited on the adjacent continental shelf thus potentially representing a loss of immediate beach sand supply during particularly exceptional events 100 yr recurrence intervals flood underflows may extend past the shelf and escape to offshore basins

initiation of turbidity currents outcrop evidence for eocene hyperpycnal flow turbidites abstract the most widely used although not as widely documented explanation for initiation of turbidites is the conversion of catastrophic sediment failures into turbidites such instantaneous sediment failures generate short lived surge type flows that deposit turbidite beds described as bouma sequences in this communication we present data from the eocene central basin of spitsbergen that shows turbidite systems that are volumetrically dominated by thick ungraded and laminated sandy turbidite beds deposited by gradual aggradation from sustained flows sustained flows are long lived and more or less continuous they can be generated by a variety of mechanisms e g 1 instability during volcanic eruptions and the consequent remobilisation of unconsolidated material 2 seismically triggered subaerial sliding within the drainage 3 storm surges 4 retrogressive slope failure 5 breaching and 6 hyperpycnal flows our database shows that in the eocene central basin the sustained flows were generated by hyperpycnal flows i e by direct river effluent the hyperpycnal flow turbidites have been recognized on the basis of 1 physical connection between fluvial and turbidite channels at the shelf edge 2 abundance of thick turbidite sandstone beds 3 sand prone nature of the turbidite systems 4 downslope changes of individual thick sandy turbidite beds and their collapsed pinch out segments 5 great abundance of continental material leaves coal fragments in turbidite beds 6 low abundance of associated slumped or debris flow beds and 7 the occurrence of turbidites in systematically accreted shelf margins these features strongly suggest that hyperpycnal flow generated by direct river effluent deposited significant number of turbidite beds in the documented slope and basin floor turbidite successions we also argue that the hyperpycnal flows are preferentially fed into the deepwater slopes beyond the shelf edge during the falling stage and lowstand of relative sea level the turbidite beds were studied in the context of seismic scale 1 15 km dip oriented outcrops by measuring detailed vertical sections following individual beds and packages of beds downslope for distances over 5 km lateral mapping and helicopter taken photomosaics

shallow water tides in the northwest european shelf region from topex poseidon altimetry during recent years the accurate measurements from the topex poseidon satellite have improved global ocean tide models considerably however these global ocean tide models are still not accurate enough on the continental shelves for detailed oceanographic studies the need for increasing accuracy in shelf regions calls for inclusion of more than just semidiurnal and diurnal constituents in future global ocean tide models this is because a considerable part of the tidal variability on the shelves is caused by shallow water constituents one example is the m4 constituent which exceeds 50 cm at several locations on the northwest european shelf so far topex poseidon has not been considered for resolving these constituents mainly owing to its coarse ground track resolution reliable empirical estimates of several major shallow water constituents can be obtained from topex poseidon by combining along track and crossover observations estimates of the major shallow water constituents for the northwest european shelf m4 m6 and ms4 are presented in this study and compared with tide gauges and existing hydrodynamic models

oceanic tides from geosat altimetry direct tidal analysis of the altimetry from the geosat exact repeat mission s first year is used to derive estimates of the diurnal and semidiurnal oceanic tides the geoid is removed by collinear differences at 34 1 day separation and the orbit error is reduced by subtracting a slowly modulated 1 cycle revolution term a sequence of independent analyses at grid areas of 1 latitude 1 5 longitude using orthotide functions ensures complete definition of the diurnal and semidiurnal species global admittance maps for m2 and s2 within the latitudes 58 n and 59 s compare well with ground truth at 66 open ocean sites maps of differences between geosat and the naval surface weapons center model show important areas of the order of 10 15 cm the integral for the global power input from the moon gives 2 51 tw m2 0 44 tw s2 lower than many previous estimates but in agreement with figures deduced from a recent analysis of satellite orbits

accuracy assessment of ocean tide models around antarctica 1 accurate ocean tide models for the circum antarctic seas are required to remove unwanted signals from floating ice elevation and space borne time variable gravity measurements e g grace we present accuracy assessments for several global csr4 fes2004 fes99 got00 2 nao 99b tpxo6 2 and antarctic cada00 10 and cats02 01 ocean tide models using coastal and pelagic tide gauges gravimetric data and gps records of ice shelf surface elevation the accuracies of csr4 and nao 99b are poor in the ice shelf regions the optimum model for the entire circum antarctic seas is tpxo6 2 with a root mean square deviation of 5 7 cm 40 lower than the next best model fes2004 the main exception is the filchner ronne ice shelf where cada00 10 and cats02 01 most accurately represent observations from two sites near the rutford ice stream grounding line