energy transport by nonlinear internal waves wintertime stratification on oregon s continental shelf often produces a near bottom layer of densefluid that acts as an internal waveguide on which nonlinear internal waves propagate shipboard profiling and bottom lander observations capture disturbances that exhibit properties of internal solitary waves bores and gravity currents wave like pulses are highly turbulent instantaneous bed stresses are 1 n m 2 resuspending bottom sediments into the water column and raising them 30 m above the seafloor the waves cross shelf transport of fluid counters the time averaged ekman transport in the bottom boundary layer in the nonlinear internal waves we have observed the kinetic energy is roughly equal to the available potential energy and is o 0 1 mj per m of coastline the energy transported by these waves includes a nonlinear advection term huei that is negligible in linear internal waves unlike linear internal waves the pressure velocity energy flux hupi includes important contributions from nonhydrostatic effects and surface displacement it is found that statistically huei 2hupi vertical profiles indicate that up z is more important in transporting energy near the seafloor while ue z dominates farther from the bottom with the wave speed c estimated from weakly nonlinear wave theory it is verified experimentally that the total energy transported by the waves hupi huei chei the high but intermittent energyflux by the waves is in an averaged sense o 100 w per m of coastline this is similar to independent estimates of the shoreward energy flux in the semidiurnal internal tide at the shelfbreak

instability of baroclinic tidal flow in a stratified fjord abstract the taylor goldstein equation is used to investigate the stability of a baroclinic tidal flow observed in a stratified fjord the flow is analyzed at hourly intervals when turbulent dissipation measurements were made the critical gradient richardson number is often close to the miles howard limit of 0 25 but sometimes it is substantially less although during 8 of the 24 periods examined the flow is marginally stable it is either very stable or very unstable in others for the unstable flow the e folding period of the fastest growing disturbances is 83 455 s about 46 of the buoyancy period at the levels where the fastest growing disturbances have their maximum amplitude these disturbances to the flows have wavelengths about 20 72 of the water depth and have mostly a second mode structure simultaneous measurements of the flow and turbulence allow for testing of the hypothesis that the growth rates of the most unstable disturbances are related to the turbulent dissipation rates dissipati

observations of overturning in the thermocline the context of ocean mixing abstract the time sequence of events that lead to internal wave breaking and ocean turbulence is investigated data are obtained from depths 100 400 m with a repeat profiling ctd and a coded pulse doppler sonar the instruments were deployed from r p flip during february march 1995 while stationed 30 km west of point arguello california as an aspect of the marine boundary layer experiment although the water depth at the site is 1500 m both rms shear and diapycnal diffusivity as inferred from the average rate and size of overturning events increase with depth below 250 m a deep source of wave energy is implied depth time series of 6 4 m shear s 2 m strain n2 n2 where n is the buoyancy frequency 6 4 m gradient richardson number ri n2 s2 and 2 m effective strain rate the depth derivative of ctd inferred vertical velocity are obtained at 4 minute intervals over a 9 day 100 400 m domain the occurrence of overturns static instabilities of vertical scale 2 m in the observed density

the vertical structure of turbulent dissipation in shelf seas abstract the free fall fly profiler has been used to determine the variation in energy dissipation in the water column over a tidal cycle at mixed and stratified sites in the irish sea it was found that exhibits a strong m4 variation with a pronounced phase lag that increases with height above the bed in mixed conditions this m4 signal which extends throughout the water column is reasonably well reproduced by turbulent closure models of the vertical exchange in the summer stratified situation the m4 signal in is confined to about 40 m above the seabed with phase delays of more than 4 h relative to the seabed the lowest levels of dissipation 10 5 w m 3 measured in the pycnocline are significantly above the system noise level and much higher than predicted by a model using the mellor yamada level 2 closure scheme my2 0 however when allowance is made for the diffusion of tke the model my2 2 simulates the depth time distribution of dissipation in the stratified case satisfactorily if

storms modify baroclinic energy fluxes in a seasonally stratified shelf sea inertial tidal interaction observations made near the celtic sea shelf edge are used to investigate the interaction between wind generated near inertial oscillations and the semidiurnal internal tide linear baroclinic energy fluxes within the near inertial f and semidiurnal m2 wave bands are calculated from measurements of velocity and density structure at two moorings located 40 km from the internal tidal generation zone over the 2 week deployment period the semidiurnal tide drove 28 48 w m 1 of energy directly on shelf little spring neap variability could be detected horizontal near inertial energy fluxes were an order of magnitude weaker but nonlinear interaction between the vertical shear of inertial oscillations and the vertical velocity associated with the semidiurnal internal tide led to a 25 43 increase in positive on shelf energy flux the phase relationship between f and m2 determines whether this nonlinear interaction enhances or dampens the linear tidal component of the flux and introduces a 2 day counter clockwise beating to the energy transport two very clear contrasting regimes of a tidally and b inertially driven shear and energy flux are captured in the observations

strong inertial currents and marginal internal wave stability in the central north sea solar insolation stabilizes the water column and suppresses vertical exchange observations from the central north sea clearly show that increased heating in summer is accompanied by enhanced de stabilizing vertical current differences shear surprisingly to such extent that the equilibrium state is marginally stable under calm weather conditions the shear is predominantly generated by near inertial motions while the internal wave spectrum primarily results from nonlinear interaction between the dominating tidal and near inertial motions in terms of the associated enhanced vertical mixing across the largest vertical temperature gradients shelf seas are not different from the abyssal ocean despite the proximity to energy sources near boundaries in the former by the lack of sufficiently strong wind and tidal mixing this internal mixing is considered to be responsible for the diapycnal transport of nutrients leading to the observed increase in near surface values and triggering the late summer phytoplankton bloom

internal wave mixing in the baltic sea near inertial waves in the absence of tides 1 the dynamics of near inertial motions and their relation to mixing is investigated here with an extensive data set including turbulence and high resolution velocity observations from two cruises conducted in 2008 summer and 2010 winter in the bornholm basin of the baltic sea in the absence of tides it is found that the basin scale energetics are governed by inertial oscillations and low mode near inertial wave motions that are generated near the lateral slopes of the basin these motions are shown to be associated with persistent narrow shear bands strongly correlated with bands of enhanced dissipation rates that are the major source of mixing inside the permanent halocline of the basin in spite of different stratification near inertial wave structure and atmospheric forcing during summer and winter conditions respectively the observed dissipation rates were found to scale with local shear and stratification in a nearly identical way this scaling was different from the gregg henyey type models used for the open ocean but largely consistent with the mackinnon gregg scaling developed for the continental shelf

topographically induced drag and mixing at a small bank on the continental shelf recent turbulence measurements over a small bank on the continental shelf off oregon reveal a previously undetected site for intense mixing of the coastal ocean the flow is hydraulically controlled and turbulence diffusivities over the bank are more than 100 times greater than estimates made on the shelf away from topography the total drag exerted by the bank on the flow field is a combination of bottom friction plus form drag analogous to mountain drag and is comparable to the coriolis force this drag is sufficient to decelerate the flow over the bank in a matter of hours

the physical oceanography of jones bank a mixing hotspot in the celtic sea abstract new measurements are presented of the currents and hydrography at jones bank in the celtic sea these measurements collected during the summer of 2008 identify a highly energetic internal wavefield generated by the local interaction of seasonally stratified flow with topography observations close to the bank crest reveal internal waves of up to 40 m amplitude approaching 50 of the local water depth these waves occur during spring periods and are predominantly associated with off bank tidal flow we provide evidence that these waves are the result of hydraulic control of the tidal currents which result in supercritical flow in the bottom mixed layer bml on the upper slopes of the bank the waning tide produces a transition from super to subcritical flow identifiable as a regular hydraulic jump on the bank slope microstructure measurements identify a turbulent bore associated with such jumps that increases bml turbulence by several orders of magnitude and produces a regular burst of enhanced mixing at the base of the ever present thermocline additional mixing in the surface mixed layer is provided during gale force conditions during the first of the two spring tides observed occurring at the start of our three week measurement period the average thermocline mixing rate during stormy spring tide conditions is 1 9 1 0 95 10 3 m 2 s 1 driven by both surface mixing and hydraulic jumps during the later calm spring period the average thermocline mixing rate is 3 3 1 7 10 4 m 2 s 1 dominated by jump associated events by comparison the intervening neap tide period produces no hydraulic jumps and is characterised by relatively calm weather a strong shear layer is however maintained during this quiet period sufficient to enhance thermocline turbulence by a factor 1000 above background levels a short lived peak in thermocline turbulence during the neap period produces diapycnal mixing as high as 1 6 10 2 m 2 s 1 however a more representative background thermocline mixing rate is 2 8 0 6 10 5 m 2 s 1

mixing in seasonally stratified shelf seas a shifting paradigm although continental shelf seas make up a relatively small fraction ca 7 of the world ocean s surface they are thought to contribute significantly 20 50 of the total to the open ocean carbon dioxide storage through processes collectively known as the shelf sea pump the global significance of these processes is determined by the vertical mixing which drives the net co 2 drawdown which can occur only in stratified water in this paper we focus on identifying the processes that are responsible for mixing across the thermocline in seasonally stratified shelf seas we present evidence that shear instability and internal wave breaking are largely responsible for thermocline mixing a clear development from the first order paradigm for the water column structure in continental shelf seas the levels of dissipation observed are quantitatively consistent with the observed dissipation rates of the internal tide and near inertial oscillations it is perhaps because these processes make such a small contribution to the total energy dissipated in shelf seas that they are not well represented in current state of the art numerical models of continental shelf seas the results thus present a clear challenge to oceanographic models

near inertial waves on the new england shelf the role of evolving stratification turbulent dissipation and bottom drag abstract energetic variable near inertial internal waves were observed on the springtime new england shelf as part of the coastal mixing and optics cmo project surface warming and freshwater advection tripled the average stratification during a 3 week observational period in april may 1997 the wave field was dominated by near inertial internal waves generated by passing storms wave evolution was controlled by a balance among wind stress bottom drag and turbulent dissipation as the stratification evolved the vertical structure of these near inertial waves switched from mode 1 to mode 2 with associated changes in the magnitude and location of wave shear the growth of mode 2 waves was attributable to a combination of changing wind stress forcing and a nonlinear coupling between the first and second vertical modes through quadratic bottom stress to explore both forcing mechanisms an open ocean mixed layer model is adapted to the continental shelf in this model surface wind stress and bottom stre

an investigation of internal mixing in a seasonally stratified shelf sea the shelf sea seasonal thermocline is a critical interface within the marine environment separating the euphotic zone from nutrient rich deep water fluxes across the thermocline therefore represent a key biogeochemical pathway in this paper we quantify the rate of mixing across the seasonal thermocline for a location in the celtic sea and investigate the processes responsible for driving thermocline fluxes profiles of the rate of dissipation of turbulent kinetic energy e show enhanced dissipation within the thermocline region similar to 6 x 10 5 w m 3 the diffusivity implied by these measurements is similar to 0 5 cm 2 s 1 similar to previous shelf sea studies and is sufficient to explain the observed warming of the deep water suggesting that vertical mixing is the dominant control on water column structure two potential sources of mixing energy are identified the internal tide and near inertial waves the mechanism of energy transfer from the candidate mixing mechanisms to turbulence is not clear thermocline dissipation rates were found to have no richardson number dependence but scaled positively with n 2 and s 2 in agreement with a previous turbulence parameterization application of this model to our data does a good job of capturing the mean characteristics of the observed heating flux across the thermocline although none of the short term fluctuations in mixing were reproduced

observations of the internal tide and associated mixing across the malin shelf 1 an energetic internal tide was observed at two contrasting shelf continental sites to the west of scotland the first site was 5 km shoreward of the continental shelf break and the second was 45 km directly to the east of the first site each site was instrumented with a seabed mounted acoustic doppler current profiler and thermistor chain for a 2 week period in july 1996 when thermal stratification was well developed in addition to the measurements of the evolution of the water column structure and flow field two series of measurements of the rate of dissipation of turbulent kinetic energy were made at each of the sites the barotropic tide was found to contain an unusually strong diurnal component thought to be due to a coastally trapped wave as a result there is a significant diurnal component to the baroclinic energy spectra significant peaks are also present in the baroclinic energy spectra at interaction frequencies between the main semidiurnal m2 and diurnal k1 tidal constituents at both sites observations of profiles of the rate of dissipation of turbulent kinetic energy show a significant proportion of the measured rate of dissipation took place within the thermocline close to the shelf edge detailed observations of a hydraulic jump and nonlinear internal waves are analyzed to show significantly stronger mixing at this site characterized by diffusion coefficients of 1 6 and 6 1 10 4 m2 s 1 than at the site farther onshore where the diffusion coefficient is estimated to be 0 7 10 4 m2 s 1

impact of nonlinear waves on the dissipation of internal tidal energy at a shelf break the vertical and temporal structure of the dissipation of turbulent kinetic energy within the internal tide at a location 5 km shoreward of the shelf break on the malin shelf has been determined using a combination of the free falling light yo yo profiler and acoustic doppler current profilers two distinct internal wave regimes were encountered period i in which large amplitude high frequency nonlinear internal waves niws occurred around neap tides and period ii in which the internal wave spectral continuum was not dominated by any particular frequency band around spring tides empirical orthogonal function analysis shows that for the low frequency waves 76 of the variance was described by mode 1 rising to 95 for the high frequency waves during period i the dissipation and vertical mixing were characterized by the niws and 70 of the dissipation occurred in the bottom boundary layer during period ii the depth integrated dissipation was more evenly distributed throughout the tidal cycle whereas vertical mixing was greatly enhanced during a single hour long episode of elevated thermocline dissipation coincident with weakened stratification during both periods i and ii 30 of the total measured dissipation occurred within the thermocline when averaged over 12 4 hours the remainder occurred within the bottom boundary layer bbl tidal average values for depth integrated dissipation and vertical eddy diffusivity for period i ii were 1 1 10 2 w m 2 4 0 10 2 w m 2 and 5 cm2 s 1 12 cm2 s 1 respectively decay rates and internal damping are discussed and vertical heat fluxes are estimated observed dissipation rates are compared with a simple model for bbl dissipation

sedimentary and oceanographic responses to early neogene compression on the nw european margin the lower neogene stratigraphy of the nw european atlantic margin from the voring to the porcupine basins is interpreted to record a discrete phase of compressional tectonism that spanned at least 8 ma from the earliest to the early mid miocene this compressional tectonism may be coeval with a local reorganisation of the ne atlantic plate system with the transfer of the jan mayen micro plate from greenland to europe the compressional tectonics has resulted in a number of stratigraphic sequences of complex character bounded by regional base neogene and intra miocene unconformities these are traceable across a range of depths and record distortion of the basin margins and changes in deep water circulation patterns this episode of compressional tectonics has also resulted in the creation of a number of anticlinal domes along the norwegian faroese and uk atlantic margins the stratigraphic and structural evidence are interpreted to record two stages in the development of the margin the first being characterised by a prolonged period of regional flexure in response to the build up of compressive stresses the second stage is the development of anticlinal structures that led to a rapid release of stress in the wyville thomson faroes region compressional deformation influenced the creation of the present day deep water conduit of the faroe bank channel which is interpreted to be an early neogene syncline together the faroe bank and faroe shetland channels represent the deepest water passageway across the greenland scotland ridge the early neogene development of this conduit is considered to mark the onset of deep water exchange across this oceanic gateway

internal tides in monterey submarine canyon abstract the m2 internal tide in monterey submarine canyon is simulated using a modified version of the princeton ocean model most of the internal tide energy entering the canyon is generated to the south on sur slope and at the head of carmel canyon the internal tide is topographically steered around the large canyon meanders depth integrated baroclinic energy fluxes are up canyon and largest near the canyon axis up to 1 5 kw m 1 at the mouth of the upper canyon and increasing to over 4 kw m 1 around monterey and san gregorio meanders the up canyon energy flux is bottom intensified suggesting that topographic focusing occurs net along canyon energy flux decreases almost monotonically from 9 mw at the canyon mouth to 1 mw at gooseneck meander implying that high levels of internal tide dissipation occur the depth integrated energy flux across the 200 m isobath is order 10 w m 1 along the majority of the canyon rim but increases by over an order of magnitude near the canyon head where internal ti

geochemistry of the amazon 1 precipitation chemistry and the marine contribution to the dissolved load at the time of peak discharge analyses of precipitation and surface water are used to estimate the fluxes of marine cyclic salts through that part of the amazon river system draining past obidos 80 of the basin at the time of peak discharge in june amazon precipitation chemistry can be devided into two principal components marine and terrestrial the marine component determined from analyses of marine rain consists of na k mg ca and cl in approximately sea salt proportions with s doubly enriched the excess sulfur is probably derived from gas phase inputs the terrestrial component makes an important contribution of k ca s and n much of which can be related to biological emissions the emission of reduced sulfur in the marine and terrestrial environment and nitrogen in the terrestrial environment is responsible for a natural acid rain in the amazon region with a ph from 4 7 to 5 7 this is about one tenth the acidity of polluted urban rain the chloride content of lowland rivers which drain regions lacking significant geologic sources of chloride shows a systematic decrease in chloride with increasing distance from the ocean this trend is used to define the cyclic salt background for amazonian surface waters cyclic salts in general make only a minor contribution relative to terrestrial inputs to the chemistry of amazon basin rivers even those draining intensely weathered terrains an estimated 17 6 cl 6 9 na 1 3 mg 3 6 s 0 4 k and 0 1 ca of the dissolved load at obidos during peak discharge is cyclic

internal tides as a major process in amazon continental shelf fine sediment transport abstract the description of hydrodynamics associated with the extensive reef system on the shelf break adjacent to the amazon river is still a challenge for ocean sciences despite the discharge of more than one billion tons of cohesive sediment per year the outer continental shelf of the world s largest river presents very low concentrations of suspended sediment near the bottom and an absence of modern fine sediment deposits nearly one hundred kilometers before the shelf break the offshore limit of the subaqueous delta consists of a sigmoidal clinoform standing between 40 and 70 m in depth a depositional feature that cannot be explained solely by estuarine like gravitational circulation this paper aims to test the hypothesis that internal tides have a major role in the control of offshore fine sediment transport for that we implement a set of tridimensional non hydrostatic and high resolution up to 2 m vertical and 2 km horizontal delft3d models the experiments showed that even disregarding river plume buoyancy wind drag superficial waves and ocean currents the exclusive interaction between barotropic tidal currents bathymetry and the stratification structure of the ocean is capable of generating asymmetrical current patterns compatible with modern deposition the maximum shelf slope and the relative depth between the outer shelf and the pycnocline represent the main factors influencing the generation and shoreward propagation of internal tides over time spring neap cycles are eventually capable of reverting cross shore subtidal transport tendencies while seasonal variability in ocean stratification modulates the intensity of baroclinic processes

thermocline mixing in summer stratified continental shelf seas 1 a key process in the shelf sea pumping of co2 to the open ocean is vertical mixing in the summer stratified zones of continental shelf seas here we present measurements of profiles of the rate of dissipation of turbulent kinetic energy from which vertical mixing is inferred for several locations in the summer stratified zones of the nw european shelf seas at both sites we find significant thermocline mixing with 20 of the observed turbulent dissipation taking place within the thermocline we then present evidence to demonstrate that the thermocline mixing is a result of shear instability within the thermocline this is contrary to the conventional view that vertical mixing in shelf seas is largely driven by boundary shear stresses

temporal variability of diapycnal mixing in shag rocks passage diapycnal mixing rates in the oceans have been shown to have a great deal of spatial variability but the temporal variability has been little studied here results are presented from a method developed to calculate diapycnal diffusivity from moored acoustic doppler current profiler adcp velocity shear profiles an 18 month time series of diffusivity is presented from data taken by a longranger adcp moored at 2400 m depth 600 m above the seafloor in shag rocks passage a deep passage in the north scotia ridge southern ocean the polar front is constrained to pass through this passage and the strong currents and complex topography are expected to result in enhanced mixing the spatial distribution of diffusivity in shag rocks passage deduced from lowered adcp shear is consistent with published values for similar regions with diffusivity possibly as large as 90 3 10 24 m 2 s 21 near the seafloor decreasing to the expected background level of 0 1 3 10 24 m 2 s 21 in areas away from topography the moored adcp profiles spanned a depth range of 2400 1800 m thus the moored time series was obtained from a region of moderately enhanced diffusivity the diffusivity time series has a median of 3 3 3 10 24 m 2 s 21 and a range from 0 5 3 10 24 to 57 3 10 24 m 2 s 21 there is no significant signal at annual or semiannual periods but there is evidence of signals at periods of approximately 14 days likely due to the spring neap tidal cycle and at periods of 3 8 and 2 6 days most likely due to topographically trappedwaves propagating around the local seamount using the observed stratification and an axisymmetric seamount of similar dimensions to the one west of the mooring in a model of baroclinic topographically trapped waves produces periods of 3 8 and 2 6 days in agreement with the signals observed the diffusivity is anticorrelated with the rotary coefficient indicating that stronger mixing occurs during times of upward energy propagation which suggests that mixing occurs due to the breaking of internal waves generated at topography