vertical mixing in the ocean the thermohaline circulation of the ocean results primarily from downwelling at sites in the nordic and labrador seas and upwelling throughout the rest of the ocean the latter is often described as being due to breaking internal waves here we reconcile the difference between theoretical and observed estimates of vertical mixing in the deep ocean by presenting a revised view of the thermohaline circulation which allows for additional upwelling in the southern ocean and the separation of the north atlantic deep water cell from the antarctic bottom water cell the changes also mean that much less wind and tidal energy needs to be dissipated in the deep ocean than was originally thought

flow hydrography turbulent mixing and dissipation at fieberling guyot examined with a primitive equation model 1 the extensive set of measurements previously taken at fieberling guyot provides a backdrop for model results on flow hydrography turbulent mixing and derivative variables a z level primitive equation model driven at subinertial and superinertial tidal frequencies allows the nonlinear interaction of free and topographically trapped motions to jointly determine model outcomes model residual flows mean hydrographic features topographic amplification of oscillatory currents turbulent dissipation and vertical diffusivity kv profiles are all examined in the light of the observations azimuthal residual flows are toroidal above the summit with maximum speed 20 cm s 1 diurnal flow over the summit is intensified by a factor 20 downward vertical flow as a time mean w t occurs from 150 m above the summit apex to summit rim depth with radially inward flow above the apex and radial outward flow below upward w t rings the summit at larger r the existence of the observed cold dome is shown to depend on w t in the summit circulation cell vertical current shear is concentrated in a 150 m thick cap above the summit accounting for a domed distribution of and kv with maxima of 10 7 w kg 1 and 30 cm2 s 1 respectively profiles most like the observations of kv are obtained with a subgrid scale parameterization in which the turbulent prandtl number pr depends on the shear richardson number ri

ocean current and temperature time series at brothers volcano 1 time series of currents and temperatures were acquired near surface and at depth on three moorings above brothers volcano 34 52 25 s 179 04 e 25 km west of the kermadec ridge and 300 km northeast of the north island new zealand from september 2004 to may 2005 ocean current time series were previously unavailable within 300 km of this site and few such measurements exist anywhere near magmatically or hydrothermally active volcanoes such as brothers energy in near surface currents 163 527 m depth was primarily subtidal 64 subtidal motions to 527 m depth are shown to be reasonably well correlated with geostrophic currents derived from satellite sea level anomalies although the moorings were separated laterally by only 11 km the upper current meters also recorded significant differences in m2 tidal currents indicating the presence of significant internal tides at this site below volcano summit depth 1220 m the kinetic energy of currents was primarily tidal 54 longer period currents at depth evidenced the influence of volcano topography temperature time series showed a 3 month period of sharply decreased temperature that extended in depth from 163 m to at least 1260 m advanced very high resolution radiometer avhrr sea surface temperature data show colder surface water immediately above and north of brothers over the same time period these data together with the velocity records suggest an anomalous deep cold water mass arrived and lingered over brothers for 3 months in the austral late spring and early summer of 2004 2005

deep sea fluid and sediment dynamics influence of hill to seamount scale seafloor topography abstract deep sea sediments play a central role in a wide range of subject areas a number of important controls on the formation of sedimentary deposits have been studied however to date the impact of submarine landscape geometry as a possible control has received comparatively little attention this seems to be particularly true for intermediate scale topographic features such as abyssal hills knolls and seamounts that can be found in many regions of the global seafloor recent estimates suggest that in the deep open oceans away from continental margins there might be as many as 25 106 abyssal hills knolls and seamounts despite this large number very little is known about how they influence environmental complexity and patchiness biogeochemical fluxes and the formation of sedimentary records this paper reviews the currently known types of fluid flow interactions with abyssal hills knolls and seamounts that could potentially influence the way sediments are formed the main types of relevant flow components are quasi steady to eddying background flow internal lee and near inertial waves barotropic and baroclinic tides and seamount trapped waves previous studies looking into systematic links between fluid dynamics and sediments at hills knolls and seamounts are reviewed finally a case study is presented which aims to combine our current knowledge and investigate whether a given combination of recent fluid flow components leaves a detectable imprint in the recent sediments on and around a short seamount the main conclusions and implications are as follows 1 topographically generated flow field geometries that are composed of a number of different prevailing fluid flow components can be reflected and detected in properties of the underlying sediments 2 tidal and other higher frequency lee wave near inertial components of deep ocean currents can be essential for locally driving total current velocities across threshold values for non deposition erosion resuspension of freshly deposited deep sea sediments moreover there is evidence suggesting that not only maximum current speeds but also intensities of higher frequency tidal and or near inertial current direction variability might control sediment dynamics and sediment formation this relativises the view that current speed is the main or even only controlling factor for sediment dynamics and sediment formation 3 when it comes to the reconstruction of paleo flows these findings imply that certain sedimentary records may well reveal more about variability in the higher frequency flow components than about variability in the basin scale net flow component that often is the focus of paleoceanographic studies 4 single core paleo records from hill seamount or similarly controlled sediment deposits may be biased due to the asymmetry of flow fields around these topographic features to arrive at unbiased paleo records for non fluid dynamic parameters the influence of the flow field geometry would have to be removed from the record first 5 it seems the mechanistic understanding of hill and seamount related flow topography interactions and their links to sediment dynamics is approaching a level that may a facilitate improved interpretation of topographically controlled sedimentary paleo records b help fill in the knowledge gap that exists for functional deep sea biodiversity at intermediate space scales and c improve predictive capabilities for exploration of economically relevant iron manganese fe mn crusts on seamounts

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

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

decay of an internal tide due to random topography in the ocean we present a theoretical and numerical study of the decay of an internal wave caused by scattering at undulating sea floor topography with an eye towards building a simple model in which the decay of internal tides in the ocean can be estimated as is well known the interactions of internal waves with irregular boundary shapes lead to a mathematically ill posed problem so care needs to be taken to extract meaningful information from this problem here we restrict the problem to two spatial dimensions and build a numerical tool that combines a real space computation based on the characteristics of the underlying partial differential equation with a spectral computation that satisfies the relevant radiation conditions our tool works for finite amplitude topography but is restricted to subcritical topography slopes detailed results are presented for the decay of the gravest vertical internal wave mode as it encounters finite stretches of either sinusoidal topography or random topography defined as a gaussian random process with a simple power spectrum a number of scaling laws are identified and a simple expression for the decay rate in terms of the power spectrum is given finally the resulting formulae are applied to an idealized model of sea floor topography in the ocean which seems to indicate that this scattering process can provide a rapid decay mechanism for internal tides however the present results are restricted to linear fluid dynamics in two spatial dimensions and to uniform stratification which restricts their direct application to the real ocean

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

ocean internal wave spectra inferred from seismic reflection transects 1 internal waves affect many important dynamical processes in the ocean but in situ observations of internal waves are infrequent and spatially sparse here we show that remote sensing of internal waves by marine seismic reflection methods can provide quantitative information on internal wave energy and its spatial variability at high lateral resolution and full ocean depth over large volumes of the ocean seismic images of the norwegian sea water column show reflections that capture snapshots of finestructure displacements due to internal waves horizontal wave number spectra derived from digitized reflection horizons in the open ocean compare favorably to the garrett munk tow spectrum of oceanic internal wave displacements spectra within 10 km laterally and 200 m vertically of the continental slope show enhanced energy likely associated with internal wave sloping boundary interactions

observations of internal tides off the coast of shandong peninsula china abstract bottom mounted platforms equipped with current profilers meters temperature salinity and turbidity sensors were deployed for about 10 days in august 2017 over an elongated deposit off the coast of shandong peninsula in order to monitor the hydrodynamics and sediment processes in the bottom boundary layer in total semidiurnal barotropic tides dominate the measured currents accounting for 90 of total variance however in the cross shore direction greater variance is associated with the semidiurnal internal tidal currents than the semidiurnal barotropic currents both the empirical orthogonal functions and normal mode analysis demonstrate that the baroclinic velocity is dominated by the mode 1 internal tides i e the current has a vertical shear with strong opposite flows near the surface and bottom while weak in the middle although the bottom slope is subcritical in most area of the deposit the ratio between the bottom slope and the slope of internal tide characteristics is greater than 0 5 suitable for local internal tide generation the internal tides generated from the deposit are especially significant considering that the shelf of the yellow sea is usually broad and flat the quantitative estimation of the water column mixing indicate that the bottom dissipation induced by the barotropic tides 6 44 10 4 m3 s 3 is greater than the internal tides 0 95 10 4 m3 s 3 and the total dissipation rate due to bottom drag is 5 49 10 4 m3 s 3 which is much greater than the interior one due to internal tides 2 69 10 4 m3 s 3 the internal tidal current alone is not energetic enough to resuspend the local fine grained sediments however in the cross shore direction the sediment flux due to internal tides is twice as much as the barotropic component resulting in a net onshore sediment flux thus highlighting the advection effect of internal tides in the coastal mass transport

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

internal tides and ocean mixing recent satellite and in situ observations have shown that at ocean ridges and other seafloor topographic features a substantial amount of energy is transferred from the main ocean tides into internal tides in his perspective garrett explains how these internal waves with tidal periods propagate through the density stratified deep ocean and eventually break down into turbulence the resulting mixing affects ocean stratification and ocean circulation it thus influences climate as well as biological production the energy for the internal tides is derived from the rotational energy of the earth moon system changes of the length of the day and the distance to the moon

scattering of low mode internal tides at a continental shelf abstracta series of laboratory experiments are performed to investigate the scattering of low mode internal tides at a continental shelf by varying the criticality parameter and normalized topograp

petrologic study of the belgica 7904 carbonaceous chondrite hydrous alteration oxygen isotopes and relationship to cm and ci chondrites abstract seven components were separated from the belgica 7904 b7904 carbonaceous chondrite in order to learn more about the genetic relationships between the petrology hydration reactions and the oxygen isotopic compositions these components include two partially altered chondrules two phyllosilicate clasts two olivine fragments and one matrix sample the partially altered chondrules have a core rim structure cores have igneous textures and are unaltered and rims consist mainly of talc component bearing phyllosilicates and unaltered olivine clear textural evidence indicates that the phyllosilicates in the rims were produced by replacing pyroxene and plagioclase while the olivine remained unaltered during the process on the other hand the phyllosilicate clasts consist mainly of fine grained serpentine produced from olivine as well as the pyroxene and plagioclase the olivine fragments derived by disaggregation of large porphyritic olivine chondrules are unaltered the matrix sample consists mainly of fine grained phyllosilicates if the hydration reactions took place with liquid water in the parent body olivine would have produced talc component free phyllosilicates before pyroxene and plagioclase reacted this is not the case for the phyllosilicates in the chondrule rims therefore we suggest that the chondrule rims formed by hydration in the nebula prior to accretion rather than with liquid water in the parent body thermodynamic calculations show that the reactions of pyroxene and plagioclase with a gas would produce the talc component bearing phyllosilicates at temperatures higher than that at which olivine reacts to produce serpentine assuming that total gas pressure was 10 3 bars the chondrule rims may have been produced by reactions with a nebular gas having an h 2 o h 2 ratio of 0 052 at temperatures ranging from 560 to 330 k the phyllosilicate clasts where olivine also reacted may have been produced by reactions with this nebular gas at temperatures near 300 k and the matrix phyllosilicates may have been in equilibrium with the gas at temperatures higher than 250 k there is no evidence for liquid water interacting with the chondrite the cm mixing line in the three oxygen isotope plot mayeda et al 1991 which includes the separated components and whole rock composition of b7904 is explained by hydration in nebular gas ci chondrites may have formed from materials similar to the b7904 matrix by reactions with liquid water in a parent body cm chondrites have experienced two stage alteration including both hydrous reactions with a gas in the nebula and aqueous alteration with liquid water in their parent body

the role of internal tides in mixing the deep ocean abstract internal wave theory is used to examine the generation radiation and energy dissipation of internal tides in the deep ocean estimates of vertical energy flux based on a previously developed model are adjusted to account for the influence of finite depth varying stratification and two dimensional topography specific estimates of energy flux are made for midocean ridge topography weakly nonlinear theory is applied to the wave generation at idealized topography to examine finite amplitude corrections to the linear theory most internal tide energy is generated at low modes associated with spatial scales from roughly 20 to 100 km the richardson number of the radiated internal tide typically exceeds unity for these motions and so direct shear instability of the generated waves is not the dominant energy transfer mechanism it also seems that wave wave interactions are ineffective at transferring energy from the large wavelengths that dominate the energy flux instead it appears that most of

tides and the climate some speculations abstract the important role of tides in the mixing of the pelagic oceans has been established by recent experiments and analyses the tide potential is modulated by long period orbital modulations previously loder and garrett found evidence for the 18 6 yr lunar nodal cycle in the sea surface temperatures of shallow seas in this paper the possible role of the 41 000 yr variation of the obliquity of the ecliptic is considered the obliquity modulation of tidal mixing by a few percent and the associated modulation in the meridional overturning circulation moc may play a role comparable to the obliquity modulation of the incoming solar radiation insolation a cornerstone of the milankovic theory of ice ages this speculation involves even more than the usual number of uncertainties found in climate speculations

sediment dynamics driven by contour currents and mesoscale eddies along continental slope a case study of the northern south china sea abstract based upon 3 d seismic reflection data published drill core studies oceanographic observations and numerical modelling this study identifies a small scale contourite depositional system that is locally confined by canyons slope failures erosional terraces and erosional slopes on the jianfeng slope northern south china sea 1500 to 2300 m water depth possible oceanic driving mechanisms for the spatial heterogeneity in sedimentation and erosion within the quaternary deposits in this complex slope system are investigated numerical simulations show that the quasi steady south china sea deep water circulation which affects the study area is characterised by low velocities maximum 4 cm s with a slight modulation by tides 1 cm s this quasi steady deep water thermohaline circulation is able to keep sediment particles in suspension rather than to erode seafloor sediment the bottom hydrodynamic regime becomes energetic when mesoscale eddies horizontal scale of 10 to 100 km approach our modelling study indicates that both surface and bottom mesoscale eddies are essential to account for the spatial heterogeneity in sedimentation pattern along the northern south china sea continental slope according to simulation the eddy front contains the highest flow velocity over a mesoscale eddy cycle 45 days exceeding the threshold for resuspension of unconsolidated sediment 15 cm s as a consequence massive resuspension is produced at various sites and redistributed by sub mesoscale horizontal scale of 1 to 10 km circulations originated from an eddy topography interaction in contrast to the surrounding areas which are subject to erosional forcing for a relatively long part 7 of an eddy cycle both the locally confined drift and a further upstream large elongated mounded drift experience little erosion

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

the impacts of the luni solar oscillation on the arctic oscillation 1 the arctic oscillation ao has a major impact on climate variability in the extra tropical regions of the northern hemisphere in this study we show that specific alignments between the sun the moon and the earth known as the luni solar oscillation lso that occur at frequencies of nearly 9 and 18 years are unambiguously correlated with the ao since the mid 1960 s the occurrence of the lso peaks is predictable and as a result it improves climate predictability furthermore we hypothesize that the recent observed increase in the ao amplitude maybe due to ice melting in the arctic and sst increases at northern latitudes combined with the recent lso peaks

diurnal critical latitude and the latitude dependence of internal tides internal waves and mixing based on barcoo seamount vertical mixing is a key issue in ocean circulation modeling today mixing particularly tidal mixing is poorly represented in ocean and climate models which generally ignore critical latitude effects critical latitude is the latitude where the inertial frequency equals the tidal frequency and differs for each tidal constituent critical latitudes strongly influence generation and propagation of internal tides using a model latitude effects on tidal interactions with a seamount were examined by varying the latitude from 20 to 38 through the range of the diurnal critical latitudes the diurnal critical latitudes were found to strongly influence propagation of the diurnal internal tides the magnitude of the semidiurnal tides the energy in the harmonic and higher frequencies the barotropic mean flow and the diffusivities the strongest effects occurred between the k1 and o1 critical latitudes here the semidiurnal tides harmonics and high frequencies were enhanced barotropic mean velocities weakened energy at the harmonics and higher frequencies increased and diffusivities increased spectral techniques indicate that most of these impacts are the result of nonlinear wave wave interactions and resonant phenomena with the prominent mechanism harmonic transfers there was no evidence of parametric subharmonic instabilities the semidiurnal tides indicated a resonant response at 20 s which is near the latitude for the combined m2 and k1 tidal period 19 s

buoyancy forcing by turbulence above rough topography in the abyssal brazil basin abstract observations of turbulent dissipation above rough bathymetry in the abyssal brazil basin are presented relative to regions with smooth bathymetry dissipation is markedly enhanced above rough topography of the mid atlantic ridge with levels above bathymetric slopes exceeding levels observed over crests and canyon floors furthermore mixing levels in rough areas are modulated by the spring neap tidal cycle internal waves generated by barotropic tidal flow over topography are the likely mechanism for supplying the energy needed to support the observed turbulent dissipation a model of the spatial and temporal patterns in the turbulent dissipation rate is used to constrain the diapycnal advection in an inverse calculation for the circulation in an area of rough bathymetry this inverse model uses both beta spiral and integrated forms of the advective budgets for heat mass and vorticity and contains sufficient information to resolve the full three dimensional flow the inverse model solution re

the generation of internal tides at the hawaiian ridge previous analyses of altimeter and acoustic data indicate that the hawaiian ridge is a significant generation site for semidiurnal m2 period internal waves owing to tidal flow over topography such waves likely play an important role connecting the dissipation of tidal energy to ocean mixing here a primitive equation numerical model with realistic stratification bathymetry and tidal forcing is used to simulate the generation of these waves in a manner consistent with altimeter sea surface observations the highest amplitude waves originate at three generation sites located at both the island and seamount portions of the chain these sites have in common both enhanced flows across ridge shaped topography and maxima in model calculated body force which couples barotropic and baroclinic motions the model vertical structure suggests the presence of multiple dynamical modes within 100 km of the ridge and not just the lowest modes that have been detected at the sea surface

an introduction to the physical oceanography of six seamounts in the southwest indian ocean exploratory surveys of six seamounts in the southwest indian ocean provide a description of physical processes induced by seamounts along the southwest indian ridge mean currents 15 25 cm s 1 in the vicinity of each seamount were dominated by mesoscale eddies the dominant seamount driven process was the generation of internal tides by the barotropic tide interacting with the seamount crests this led to enhanced shear in the vicinity of the crests resulting in mixing where stratification was weak for example in the core of an anticyclonic mesoscale eddy or where there had been a winter mixed layer tidally driven up and downwelling was observed at the seabed with associated variability in bottom temperature of up to 3 c over a tidal cycle vertical displacement of isopycnals by internal tidal waves reached 200 m peak to trough fluorescence in the surface eutrophic layer could thus extend down to the seamount crest on each tidal cycle apparently spatial variations in short conductivity temperature depth sections across each seamount were probably aliased temporal variations from the strong tidal signal evidence for taylor caps or other potential trapped circulations at the seamount crest was weak most likely because currents associated with mesoscale eddies were too strong to allow their formation

latitudinal distribution of mixing rate caused by the m2 internal tide abstract ten years of ocean topography experiment topex poseidon tidal data and an energy balance relation are used to estimate the mixing rate caused by m2 internal tides in the upper ocean the results indicate that latitudinal distribution of the mixing rate has a generally symmetrical structure with respect to the equator the maxima are distributed around 28 9 n and 28 9 s and can be as high as 3 8 10 5 m2 s 1 in the pacific 5 10 5 m2 s 1 in the atlantic and 3 7 10 5 m2 s 1 in the indian oceans the minimum which is only 10 of those at 28 9 is located near the equator the data imply that midlatitudes are the key regions for internal tide mixing

lagrangian analysis of the meridional overturning circulation in an idealized ocean basin the lagrangian ocean model is used as a tool to simulate the response of the basin scale overturning circulation to spatially variable diapycnal mixing in an idealized ocean basin the model explicitly calculates the positions velocities and tracer properties of water parcels owing to its lagrangian formulation numerical diffusion is completely eliminated and water parcel pathways and water mass ages can be quantified within the framework of the discrete advective transit time distribution to illustrate the ventilation pathways simulated trajectories were tracked backward in time from the interior ocean to the surface mixed layer where the water parcel was last in contact with the atmosphere this new diagnostic has been applied to examine the response of the meridional overturning circulation to highly localized diapycnal mixing through sensitivity experiments in particular the focus is on three simulations the first holds vertical diffusivity uniform in the second the vertical diffusivity is confined within an equatorial box and the third simulation has a diffusivity pattern based on idealized hurricane induced mixing domain integrated deep ventilation rates and heat transport are similar between the first two cases however locally enhanced mixing yields about 30 younger water mass age in the tropical thermocline due to intense localized upwelling in the third simulation a slower ventilation rate of deep waters is found to be due to the lack of abyssal mixing these results are interpreted using the classical theories of abyssal circulation highlighting the strong sensitivity of the ventilation pathways to the spatial distribution of diapycnal mixing

boundary mixing in lakes 2 combined effects of shear and convectively induced turbulence on basin scale mixing a detailed comparison of results from a numerical three dimensional hydrostatic lake model with high resolution observations of the vertical structure of the turbulent bottom boundary layer bbl in a medium size lake lake alpnach switzerland is provided the focus of this study is on the shear induced generation and destruction of stratification in the bbl that may ultimately lead to unstable layers convection the model was shown to provide a reliable description of the internal seiching dynamics as well as the local bbl properties including the generation of shear induced convection in two data sets from 2003 and 2007 basin scale mixing parameters inferred from the simulations are closely connected to the seiching motions with the hypolimnetic mixing reacting almost immediately to the variable wind forcing and seiching activity during upslope flow the bbl becomes convectively turbulent causing low mixing efficiency on a basin scale whereas during downslope flow the bbl is restratifying and shear induced turbulence is weak but leads to a higher mixing efficiency the overall deep water mixing efficiency varied in the range of 5 to 10 in this system dominated by turbulent boundary processes

distribution and behavior of dissolved hydrogen sulfide in hydrothermal plumes through the deep ocean hydrothermal plumes disperse high concentrations of key chemical tracers including he 3 ch4 mn fe h2s etc this paper focuses on the distribution and behavior of total dissolved sulfide sulfide hereafter in hydrothermal plumes to show that its plume concentration decreases to subnanomolar a few kilometers from the vents we also report on sulfide removal rates determined at in situ conditions we observe that they are two orders of magnitude greater than for open ocean seawater consistent with sulfide being detected only in the vicinity of hydrothermal vents from our observations we infer that the sole presence of sulfide in hydrothermal plumes locates active venting at thekilometer scale

ocean acoustic reverberation tomography seismic wide angle imaging using ship towed acoustic sources and networks of ocean bottom seismographs is a common technique for exploring earth structure beneath the oceans in these studies the recorded data are dominated by acoustic waves propagating as reverberations in the water column for surveys with a small receiver spacing e g 10 km the acoustic wave field densely samples properties of the water column over the width of the receiver array a method referred to as ocean acoustic reverberation tomography is developed that uses the travel times of direct and reflected waves to image ocean acoustic structure reverberation tomography offers an alternative approach for determining the structure of the oceans and advancing the understanding of ocean heat content and mixing processes the technique has the potential for revealing small scale ocean thermal structure over the entire vertical height of the water column and along long survey profiles or across three dimensional volumes of the ocea

the maintenance of the subsurface chlorophyll maximum in the stratified western irish sea the diapycnal flux of nitrate from the deep water provides a limit on new production in the subsurface chlorophyll maximum scm during summer in stratified shelf seas here we estimate the diapycnal nitrate flux into the scm in the stratified western irish sea swis sampling took place immediately before neap tides when winds were light so flux estimates reported provide a lower limit to nitrate supply to the scm measurements of turbulent kinetic energy dissipation chlorophyll a and nitrate were used to estimate the flux of nitrate and chlorophyll through the scm turbulent dissipation was low in the scm 10 9 to 10 7 m2 s 3 driving a correspondingly low nitrate flux into the scm 0 31 mmol m 2 d 1 the thermocline was marginally stable throughout sampling and thus the addition of shear would likely result in shear instabilities and mixing we show that although the swis is documented as having an energetic internal tide at this time there was a low level of dissipation within the thermocline we argue that the internal tide sets up background shear which results in marginal stability the addition of extra shear through the passage of nonlinear internal waves and or the wind can trigger instability and mixing we extrapolate our flux estimate over the summer and show that the nitrate flux is insufficient to sustain the documented summer production estimates for the swis this suggests that episodic events are likely to be important for nitrate fluxes or even largely responsible for the nitrate flux that sustains the scm

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