an experimental study of the relationship between joint spacing and layer thickness abstract two methods for measuring joint spacing are described and compared the area method is a constant for a given outcrop area and is not affected by joint distribution within that area in contrast the line method depends on the location of the linear traverse two kinds of joint sets are distinguished on bedding surfaces 1 a poorly developed set represents the early stages of development when typical joint lengths are less than typical spacing 2 a well developed set represents later stages when lengths are much greater than spacing the area method is applicable to both poorly and well developed sets whereas the line method produces inconsistent results for poorly developed joint sets surface textures on many joints indicate point fracture origins and propagation parallel to bedding whereas most numerical model studies of spacing assume linear origins and propagation perpendicular to bedding the laboratory experiments described in this paper do not suffer from these restrictions an important concept confirmed during these experiments is fracture saturation when the applied strain reaches a certain value fracture spacing stops evolving and remains nearly constant these fracture sets are well developed spacing at saturation is a function of layer thickness but is independent of strain whereas spacing before saturation varies strongly with applied strain thus plotting spacing vs thickness and comparing the slopes of lines fit to such data for poorly developed joint sets in different layers is unlikely to be a diagnostic test for differences in material properties on the other hand spacing may be a sensitive indicator of strain for layers with poorly developed joint sets assessing fracture saturation is a lirst order consideration when gathering spacing data

internal tides and tidal cycles of vertical mixing in western long island sound in estuaries tidal period variations in the rate of vertical mixing have been observed to result from various causes in liverpool bay and the york river they have been attributed to tidal straining of the along channel density gradient modulating stratification in the hudson river they arise from tidal modulation of the height of the tidal current bottom boundary layer bbl along continental shelves tidal period fluctuations in mixing have been observed to result from the dissipation of internal waves iws western long island sound wlis moored instrument records indicate that large near bottom increases in dissolved oxygen do and heat and a decrease in salt occur during the middle of the flood tide an analysis of water mass signatures indicates that the transport involved is vertical and not horizontal temperature data from a vertical thermistor array deployed in the wlis for 16 days in august 2009 clearly show a tidal cycle of iw activity creating a mean thermocline depression at midflood of approximately 25 of the water depth with individual iw thermocline depressions of as much as 50 of the water depth contemporaneous adcp measurements show increases in shear due to iws during the flood near bottom internal wave activity is maximal at and after midflood and is correlated with near bottom temperature and do tendencies at both tidal and subtidal scales we conclude that internal tides are an important vertical mixing mechanism in the wlis through both increased shear from iws and displacement of the pycnocline into the region of high shear in the bbl

observations of turbulence in a tidal beam and across a coastal ridge during a microstructure survey off california in monterey bay we found a midwater beam of strong turbulence emanating from the shelf break along the ray path of the semidiurnal m2 internal tide within the 50 m thick beam the turbulence kinetic energy dissipation rate e exceeded 10 6 w kg 1 and the diapycnal eddy diffusivity k was 0 01 m2 s 1 the beam extended 4 km off the shelf break several factors suggest that this beam of strong turbulence resulted from the breaking of semidiurnal internal tides the beam appeared to originate from the shelf break which is a potential generation site for semidiurnal internal tides the beam closely followed the ray path of the semidiurnal internal tide the average e off the shelf break varied by a factor of 100 with a semidiurnal tidal periodicity the isopycnal displacement confirmed the presence of semidiurnal internal tides processes associated with the breaking of internal tides are intermittent and sporadic at the same location we also observed equally intense turbulence in a 100 m thick layer of stratified water across the ridge of a sea fan this layer of strong turbulence was separated from the bottom and was clearly not generated by bottom friction although less well resolved in time the strong turbulence above the bottom seemed to vary with the semidiurnal tide and existed at the lee of the ridge where the isopycnal surface dipped and rebounded in a pattern resembling that of internal hydraulic jumps on the basis of the behavior of the density field we believe that the deep mixing was most likely produced by the across ridge current of internal tides the breaking of internal tides at middepth where the richardson number is close to the critical value is likely due to shear instability the presence of the coastal ridge provides an alternative pathway for converting energy from internal tides to turbulence via internal hydraulics multiplying the average e in the midwater beam by the length of the global coastline gives 31 gw only a small fraction of the estimated 360 gw dissipated globally by m2 internal tides our observations suggest that either most internal tides are generated away from shelf breaks or most internal tides generated at shelf breaks propagate away from their generation sites rather than dissipate locally and eventually contribute to pelagic mixing

hydrography and energetics of a cold subpolar fjord andvord bay western antarctic peninsula abstract fjords along the western antarctic peninsula contain rich marine ecosystems and tidewater glaciers potentially sensitive to ocean change but much is unknown about the physical oceanography of these fjords this paper presents a comprehensive description of the physical environment of andvord bay a glacial fjord located in the gerlache strait on the northern end of the peninsula measurements were collected as part of the fjordeco program between november 2015 and march 2017 including during three research cruises and from a number of fixed installations sub surface moorings time lapse cameras and automatic weather stations andvord bay is located just north of a sill in the gerlache strait this sill inhibits the direct influence of warm upper circumpolar deep water from the shelf and deep waters in the fjord are therefore relatively cold as a result glaciers in andvord bay are not subject to the substantial ocean driven retreat observed farther south on the peninsula instead mass flux from the glaciers occurs mainly through calving the influence of meltwater in andvord bay is small compared to glacial fjords in the arctic and in the south shetland islands although summer freshening is evident in the fjord near surface layer likely as a result of glacial inputs the combination of surface freshening and the absence of strong mean wind forcing in the fjord results in salinity stratification extending well into the euphotic zone providing advantageous conditions for phytoplankton blooms andvord bay is generally dynamically quiet compared to the ambient ocean with the exception of during local katabatic wind events exchange with the gerlache strait is weak although the deep waters of the fjord are replenished on an annual scale through slow lateral exchange with the outside in addition deep convection may play a role in ventilating subsurface waters in winter

a numerical model of internal tides with application to the australian north west shelf abstract a nonlinear primitive equation finite difference numerical model is applied to the problem of the generation propagation and dissipation of internal tides over a cross section of the continental slope and shelf topography of a region on the australian north west shelf the model is forced through the specification of the offshore tidal elevation and as such the full tidal field is modeled for the m2 constituent an energetic internal tide is produced in the model with results showing sensitivity to changes in both stratification and bathymetry the ratio of the slope of the internal wave characteristics to the bathymetry is generally less than or close to one producing subcritical and approximately critical conditions model results are compared to previously reported observations and show reasonable agreement in terms of wave structure propagation direction and regions of generation and energy dissipation the model shows a high degree of spatial variability in the amplitude and phase of

observations of the internal tide in monterey canyon abstract data from two shipboard experiments in 1994 designed to observe the semidiurnal internal tide in monterey canyon reveal semidiurnal currents of about 20 cm s 1 which is an order of magnitude larger than the estimated barotropic tidal currents the kinetic and potential energy evidenced by isopycnal displacements of about 50 m was greatest along paths following the characteristics calculated from linear theory these energy ray paths are oriented nearly parallel to the canyon floor and may originate from large bathymetric features beyond the mouth of monterey bay energy propagated shoreward during the april experiment itex1 whereas a standing wave that is an internal seiche was observed in october itex2 the difference is attributed to changes in stratification between the two experiments higher energy levels were present during itex1 which took place near the spring phase of the fortnightly 14 8 days cycle in sea level while itex2 occurred close to the neap phase further evide

tidal mixing events on the deep flanks of kaena ridge hawaii abstract a 3 month mooring deployment august november 2002 was made in 2425 m depth on the south flank of kaena ridge hawaii to examine tidal variations within 200 m of the steeply sloping bottom horizontal currents and vertical displacements inferred from temperature fluctuations are dominated by the semidiurnal internal tide with amplitudes of 0 1 m s 1 and 100 m respectively a series of temperature sensors detected tidally driven overturns with vertical scales of 100 m a thorpe scale analysis of the overturns yields a time averaged dissipation near the bottom of 1 2 10 8 w kg 1 10 100 times that at similar depths in the ocean interior 50 km from the ridge dissipation events much larger than the overall mean up to 10 6 w kg 1 occur predominantly during two phases of the semidiurnal tide 1 at peak downslope flows when the tidal stratification is minimum n 5 10 4 s 1 and 2 at the flow reversal from downslope to upslope flow when the tidal stratification is ordinarily increasi

internal tide scattering at seamounts ridges and islands 1 the scattering of mode 1 internal tides from idealized gaussian topography in a nonrotating ocean with constant and realistic stratifications is examined with a primitive equation numerical model incident mode 1 energy fluxes of 20 and 2000 w m 1 are used to examine the linear regime and a more realistic situation simulations using two dimensional or infinite ridges compare well with ray tracing methods and illustrate how the size and shape of the topography influence wave scattering the height affects energy transmission and reflection while the slope and width determine the conversion of low mode internal tides into beams or higher modes three dimensional topographic scattering is considered for seamounts finite width ridges and islands scattering from finite ridges focuses wave energy directly downstream while scattering from seamounts produces azimuthal energy dispersion scattering to higher wave modes occurs in the lee of near critical and supercritical seamounts and ridges nonlinear interactions transfer energy into the mode 1 m4 internal tide the mellor yamada level 2 5 submodel parameterizes turbulent mixing for the near critical and supercritical ridges with realistic stratification elevated mixing is found over the leading edge of the topography and along a tidal beam up to the first surface bounce a transition from a beam structure near the topography to a low mode structure farther away occurs due to an increased contribution from the mode 1 internal tide as it refracts around the topography and not due to turbulent dissipation internal tide scattering at topography leads to a loss of energy to mixing and to a redistribution of energy flux in space frequency and mode number

deep sea currents driven by breaking internal tides on the continental slope mooring data collected on the continental slope of the south china sea show that along slope deep sea bottom currents are generated when large spring internal tides internal waves with tidal frequency are observed with the maximum velocity amplitude exceeding 0 15m s the observations are consistent with predictions that near bottom breaking of internal waves can result in generation of along slope flows when these waves obliquely approach the slope a linear internal tide model in one horizontal dimension with realistic topography and stratification is used to show that the breaking of internal tides is likely due to near critical reflection on the slope combining the mooring observations and the model simulation an along slope near bottom transport of similar to 0 5sv is estimated along slope bottom flows caused by breaking internal waves potentially provide a significant way to deform continental slopes and affect deep water exchange between the marginal sea and open ocean

intrinsic nonlinearity and spectral structure of internal tides at an idealized mid atlantic bight shelf break abstractto quantify dynamical aspects of internal tide generation at the mid atlantic bight shelf break this study employs an idealized ocean model initialized by climatological summertime stratification and forced by monochromatic barotropic tidal currents at the offshore boundary the froude number of the scenario is subunity and the bathymetric slope offshore of the shelf break is supercritical a barotropic to baroclinic energy conversion rate of 335 w m 1 is found with 14 of the energy locally dissipated through turbulence and bottom friction and 18 radiated onto the shelf consistent with prior studies nonlinear effects result in additional super and subharmonic internal waves at the shelf break the subharmonic waves are subinertial evanescent and mostly trapped within a narrow beam of internal waves at the forcing frequency they likely result from nonresonant triad interaction associated with strong nonlinearity strong vertical shear associated with the subharmonic waves tends to enhanc

images of internal tides near the norwegian continental slope internal tides or internal gravity waves propagating attidal frequencies play an important role in ocean mixing butare challenging to detect and map over large spatial sectionsin the ocean s interior we present seismic images ofoceanic finestructure in the norwegian sea that demonstratethat semidiurnal m

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

pull aparts shear fractures and pressure solution vein arrays are often composed of pull aparts which are linked by shear fractures good examples of which occur in the lower jurassic limestones of somerset southwestern england such pull apart arrays have displacement distance characteristics which are similar to fault zones with maximum displacement indicated by the largest pull apart widths near the centre of the array and with displacement decreasing towards the tips pull apart arrays usually die out into enechelon or pinnate veins evidence for pressure solution along the shear fractures which connect pull aparts include their dark and braided nature their obliquity to the displacement direction the high dihedral angles often 90 between conjugate shear fractures and the dissolution of earlier structures a range of geometries occurs with varying relative amounts of veins and pressure solution being related to varying amounts of transtension or transpression there is a general trend for an increase in the angle between vein segments and the shear fractures as contraction increases there is therefore a trend for increased pressure solution on the shear fractures in more contractional arrays the concentration of insoluble material along shear fractures has important implications for the mechanics and sealing of faults

esr dating of the fossil hominid cranium from petralona cave greece the age of the hominid cranium discovered in 1960 in a limestone cave near petralona greece is a continuing cause of controversy the age of the skull which was apparently encrusted by brown calcite soon after the death of the individual concerned has been variously estimated at between 70 0001 and 700 0002 yr here we show using electron spin resonance esr measurements of the calcite encrustation and of bone fragments that the age of the petralona hominid lies between 160 000 and 240 000 yr we also demonstrate by trace element analysis that the composition of the calcite encrustation is the same as that of the very top of the travertine floor

experiments on the generation of internal waves over continental shelf topography experiments were performed to examine the generation of internal waves by a barotropic tide forcing a continuously stratified fluid over idealized continental shelf slope topography a range of responses was observed including the generation of both internal wave beams and boundary layer boluses primarily dependent on the values of both the reynolds number and the topographic steepness parameter the formation of beams required a critical bottom slope whilst for bolus formation a large vertical fluid excursion was necessary a bolus formed when the non dimensional vertical excursion parameter hn w 0 3 2 here h is the vertical excursion n is the buoyancy frequency and w 0 is the near bottom vertical velocity associated with the local depth averaged velocity we simplified the classification of the observed flow regimes using a generation parameter g defined as the ratio of a reynolds number to the topographic steepness parameter the estimated flow regime boundaries were for g g g g 400 there was no bolus observed we estimated that approximately 4 of the barotropic energy was converted to baroclinic energy when beams were generated

esr dating in quaternary geology abstract electron spin resonance esr a relatively new dating technique was first suggested by zeller et al 1967 zeller 1968 and levy 1968 it has made substantial progress in frequent applications in the last few years esr dating is based on the direct measurement of the amount of radiation induced paramagnetic electrons trapped in crystal defects these free electrons were generated by alpha beta and gamma radiation of natural radioelements e g u th k and have accumulated in the minerals over geologic time the esr age is obtained by dividing the total amount of accumulated radiation dose archaeological dose ad by the dose per year annual dose this review comprises four major parts the principles of the method the determination of the archaeological dose ad the determination of the annual dose and a compilation of datable materials several questions remain the evaluation of the ad the determination of the annual dose and particularly with respect to the nature and stability of the electron traps used for dating

simulation of barotropic and baroclinic tides off northern british columbia abstract the tidal response of northern british columbia coastal waters is studied through simulations with a three dimensional prognostic primitive equation model the model is forced at the boundaries with the leading semidiurnal and diurnal constituents and experiments with stratified and homogeneous fluid are compared the barotropic response shows good agreement with previously published studies of tides in the region a comparison with tide gauge measurements indicates that average relative rms differences between observations and the model surface elevation field are less than 5 for the largest constituents an internal tide is generated in cases where the model is initialized with a vertical stratification diagnostic calculations of the baroclinic energy flux are used to identify regions of generation and propagation of internal tidal energy with a representative summer stratification the integrated offshore flux is about 0 5 gigawatts higher than previously estimated from theoretical model

observations of internal wave reflection off sloping bottoms current and temperature spectra exhibit intensification and polarization near sloping bottoms over a band of frequencies centered at the local internal wave critical frequency examples are drawn from a variety of island seamount and continental slope observations waves propagating down from mid depth change energy density wave number and azimuth when they reflect off the bottom providing a natural perturbation to the deep ocean interior internal wave spectrum deviations from linear theory are interpreted as evidence for dissipation through subsequent shear instability and or nonlinear interaction topographic features appear likely to be energy sinks for internal wave energy

internal tides and turbulence along the 3000 m isobath of the hawaiian ridge full depth velocity and density profiles taken along the 3000 m isobath characterize the semidiurnal internal tide and bottom intensified turbulence along the hawaiian ridge observations reveal baroclinic energy fluxes of 21 5k w m 1 radiating from french frigate shoals 17 2 5 kw m 1 from kauai channel west of oahu and 13 3 5 kw m 1 from west of nihoa island weaker fluxes of 1 4 2k w m 1 radiate from the region near necker island and east of nihoa island observed off ridge energy fluxes generally agree to within a factor of 2 with those produced by a tidally forced numerical model average turbulent diapycnal diffusivity k is 0 5 1 10 4 m 2 s 1 above 2000 m increasing exponentially to 20 10 4 m 2 s 1 near the bottom microstructure values agree well with those inferred from a finescale internal wave based parameterization a linear relationship between the vertically integrated energy flux and vertically integrated turbulent dissipation rate implies that dissipative length scales for the radiating internal tide exceed 1000 km

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

numerical study on tidal mixing along the shelf break in the green belt in the southeastern bering sea 1 tidal mixing and its associated iron and nutrients flux from a subsurface layer along the shelf break has been considered as one of the key processes to maintain the high summertime biological productivity in the green belt in the southeastern bering sea in the present study tidal mixing near the shelf break is examined with a three dimensional high resolution numerical model to quantify the enhanced mixing and to reveal the underlying physical mechanisms based on the different characteristics of diurnal and semidiurnal internal waves strong turbulent mixing with energy dissipation rates of over 1 10 8 w kg is reproduced along the green belt in the numerical model forced by barotropic diurnal and or semidiurnal tides at open boundaries the energy dissipation off the shelf break near the sea surface is enhanced due to the semidiurnal internal waves whereas the dissipation near the bottom of the shelf break is enhanced by the diurnal topographically trapped waves an additional experiment with stratification representative of winter conditions shows a significant influence of stratification on the energy dissipation off the shelf break due to the change in features of both diurnal and semidiurnal internal waves low mode semidiurnal baroclinic energy flux from the aleutian passes is shown to increase the energy dissipation along the shelf slope between pribilof and zhemchug canyons these results suggest that the strong vertical mixing along the shelf break induced by the diurnal and semidiurnal tides both play important roles in maintaining the iron and nutrients supply along the green belt

temporal variability of the standing internal tide in the browse basin western australia 1 we have investigated the seasonal evolution of the internal tide using a yearlong mooring record in the browse basin on the australian north west shelf using a modal harmonic decomposition technique we studied the modulation of the semi diurnal kinetic energy potential energy energy flux group velocity and sea surface height anomaly for different internal wave modes a very coherent and energetic locally generated internal tide dominated the mooring record during spring tide periods relationships amongst the wave variables suggest that the interaction of multiple waves formed a standing wave pattern to assist in explaining the seasonal variability of this standing wave pattern we used an analytical model of internal wave generation and propagation in a double shelf system representative of the area to highlight the effects of changes in the stratification and barotropic forcing a comparison of the low mode wave energy indicated that the analytical solution overestimated the observed wave energy by a factor of two and failed to detect an apparent seasonal shift in the conversion rate we discuss potential mechanisms for this discrepancy

measurements of the turbulent energy dissipation rate e and an evaluation of the dispersion process of the changjiang diluted water in the east china sea 1 the large amount of fresh water discharged from changjiang spreads over the east china sea continental shelf as low salinity water particularly in the summer season to understand the primary production in the east china sea it is necessary to clarify the dispersion process of the changjiang diluted water cdw since the high production area appears to cover the cdw in this study the dispersion process of the cdw was evaluated through the estimation of the turbulent energy dissipation rate e in the cdw and calculation of the divergence in the cdw using satellite tracked drifters a large value of e was observed just above the bottom and in the surface layer whose magnitude was sometimes greater than 10 7 w kg 1 on the other hand a small value of e less than 10 8 w kg 1 was found just beneath the cdw the small value of e leads to a small value of the vertical eddy diffusivity of less than 10 5 m 2 s 1 the vertical advection of the bottom water is likely to be a major process for increasing the salinity since the horizontal diffusion would not play a significant role if the usual magnitude of the horizontal diffusivity is assumed calculation of divergence in the surface layer using the drifters data also suggests that upward velocity of o 10 5 m s 1 over the cdw area is expected the vertical transport from the bottom layer could increase the salinity of the cdw and also carry the nutrients into the euphotic zone resulting in biological production

stress fields about strike slip faults inferred from stylolites and tension gashes abstract in general the long axis of the tension gashes and stylolitic columns developed in limestones during a single phase of compressional deformation occur parallel to the direction of the maximum compressive stress 1 this is the case in the languedoc for structures developed in the jurassic limestones during the n s pyrenean compression exceptionnally however these microstructures turn in direction and become oblique even orthogonal one to the other probably as a consequence of a variation in intensity and direction of the stress field at the end of a microfault this mechanism also occurs in a larger scale structure involving segments of pre tectonic joints that act as en echelon microfaults in a brittle kink band equivalent to a peculiar type of potential wrench fault

observations of the semidiurnal internal tide on the southern california slope and shelf 1 we give a detailed description of the semidiurnal band current and temperature variability observed during the internal waves on the continental margin iwaves field experiments of 1996 and 1997 off of mission beach california this variability was dominated by the internal tide and the structure of the internal tide on the slope and shelfbreak region was different from that on the narrow shelf on the slope and shelfbreak the internal tide was dominated by alongshore propagating coastal trapped waves in this region semidiurnal band currents were predominantly oriented in the alongshore direction in the lower half of the water column at a water depth h of 350 m current and temperature variability were consonant with a short wavelength 8 km bottom trapped wave propagating in the alongshore direction to the north in the upper 120 m of the water column above the depth of the shelfbreak slope and shelfbreak currents were highly coherent with a zero phase lag that is there was no phase propagation in the cross shore direction on the narrow 10 km shelf cross shore currents u were much more energetic than on the slope and had the structure of a mode one internal wave the alongshore currents v decreased monotonically from the surface to the bottom of the water column with a phase that did not change with depth the near bottom u signal propagated toward the coast during all mooring deployments faster in the summer than in the fall the near bottom u and mid column temperature relative phase was neither consistent with a purely progressive nor a purely standing mode one internal wave we conclude that the internal tide on the shelf was partially reflected

tidally forced internal waves and overturns observed on a slope results from home abstract tidal mixing over a slope was explored using moored time series observations on kaena ridge extending northwest from oahu hawaii during the survey component of the hawaii ocean mixing experiment home a mooring was instrumented to sample the velocity and density field of the lower 500 m of the water column to look for indirect evidence of tidally induced mixing and was deployed on a slope in 1453 m water depth for 2 months beginning in november 2000 the semidiurnal barotropic tidal currents at this site have a significant cross ridge component favorable for exciting an internal tidal response a large amplitude response is expected given that the slope of the topography 4 5 is nearly the same as the slope of the internal wave group velocity at semidiurnal frequency density overturns were inferred from temperature profiles measured every 2 min the number and strength of the overturns are greater in the 200 m nearest the bottom with overturns exceeding 24 m present at any depth nearly

intense variable mixing near the head of monterey submarine canyon abstract a microstructure survey near the head of monterey submarine canyon the first in a canyon confirmed earlier inferences that coastal submarine canyons are sites of intense mixing the data collected during two weeks in august 1997 showed turbulent kinetic energy dissipation and diapycnal diffusivity up to 103 times higher than in the open ocean dissipation and diapycnal diffusivity within 10 km of the canyon head were among the highest observed anywhere e 1 1 10 6 w kg 1 k 1 0 10 2 m2 s 1 mixing occurred mainly in an on axis stratified turbulent layer with thickness and intensity increasing from neap to spring tide strain spectra showed a gentler than k 1z rolloff suggesting that critical reflection and scattering may push energy into high wavenumbers dissipation dependence on shear appears to be much weaker in the canyon than in the open ocean with indications that the dependence maybe as low as e s coastal canyons may account for a small but significant fraction of the int

methodology for a regional tidal model evaluation with application to central california abstract observations from disparate observational assets including tide gauges moorings and high frequency hf radars were used to depict the tidal variability and to evaluate model tidal simulations for a region off central california including the monterey bay for this study the hydrodynamic model was forced only with tides derived from a large scale model for the northeast pacific ocean homogeneous density and initially horizontally uniform density stratification cases were considered the model successfully reproduced tidal sea surface height variations within the model domain as determined by comparisons with sea level or bottom pressure measured at six locations to achieve tidal currents with realistic amplitudes as determined from hf radar and moored measurements it was found that barotropic velocity as well as sea level from the large scale regional tidal model must be included in specifying the open boundary condition however even with such forcing the model with homogeneous density field under predicted the semidiurnal and diurnal barotropic currents as estimated from depth averaged currents measured at 11 locations in the diurnal frequency band the observed surface and nearshore depth averaged currents are likely influenced by meteorological forcing which was not included in the model the hf radar measured surface tidal currents both semidiurnal and diurnal are consistent from year to year and between the winter season and the entire year semidiurnal surface tidal currents derived from year long hf radar measurements do not resemble either the modeled or measured barotropic current fields rather they exhibit amplitudes and small scale spatial variability indicative of the presence of internal tides thus indicating that model derived barotropic tidal currents cannot be validated over large spatial extents using long time series of hf radar derived surface currents with initially horizontally uniform vertical density stratification the model produced surface currents with spatial variability and amplitude range comparable to what was derived from hf radar surface current measurements but the point by point comparisons are not impressive for this region of complex topography likewise the subsurface current comparisons performed at four deepwater locations show considerable model data differences possible reasons for these disparities include the effects of atmospheric forcing spatially and temporally varying stratification remotely generated coastally trapped waves and remotely generated internal tides

recent developments in the study of ocean turbulence abstract this review describes the changes in the understanding of turbulence and mixing in the upper layers of the ocean the abyssal ocean and in continental shelf seas that have come in the past 25 years largely through advances in instruments and methodology

orthogonal cross joints do they imply a regional stress rotation abstract orthogonal cross joints extend across intervals between systematic joints in brittle sedimentary strata and abut the systematic joints at about 90 angles these joints typically form a ladder like pattern if viewed on a bedding surface a common interpretation is that orthogonal cross joints define the orientation of the regional stress field during their formation least compressive stress perpendicular to the joints it follows that they indicate a rotation of regional principal stresses by 90 after the formation of the systematic joints using a three dimensional boundary element code poly3d we considered a simple geologic case of vertical systematic fractures developing in horizontal strata under a triaxial remote load with the maximum principal tensile stress being horizontal and perpendicular to the strike of the fractures the intermediate principal stress being horizontal and parallel to the strike of the fractures and the least principal tensile stress i e maximum compressive stress being vertical the results show that the local maximum principal stress is first perpendicular and then parallel to the strike of the systematic fractures as the ratio of fracture spacing to height changes from greater than to less than a critical value when the horizontal remote principal stress ratio the ratio of the intermediate remote principal stress to the maximum remote principal stress under the sign convention of positive for tensile stresses is greater than a threshold value 0 2 thus the fracturing process changes from infilling of systematic fractures to the formation of orthogonal cross fractures this provides an alternative mechanism for the formation of orthogonal cross joints that does not require a systematic rotation of the regional stress field by 90 the critical spacing to height ratio for the local principal stress switch is independent of the least remote principal stress i e overburden it increases nonlinearly with increasing ratio of the horizontal remote principal stresses and decreases nonlinearly with increasing poisson s ratio of the material

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

three dimensional numerical simulation of m2 internal tides in the east china sea the east china sea and adjacent seas are one of the most significant generation regions of the m 2 internal tide in the world s oceans in the present study we investigate the distribution and energetics of the m 2 internal tide around the continental shelf edge in the east china sea using a three dimensional numerical model the numerical experiment shows that m 2 internal tides are effectively generated over prominent topographic features such as the subsurface ridges in the bashi luzon and tokara straits the ridges along the ryukyu island chain and the continental shelf slope in the east china sea the former particularly so all of these topographic features are characterized by steep slopes at the depth of the thermocline onto which the m 2 barotropic tide is almost normally incident the m 2 internal tides propagating away from these multiple source regions interfere with each other to create a complicated wave pattern it is found that the calculated pattern of the m 2 internal tide agrees well with topex poseidon altimeter observations the conversion rate from m 2 barotropic to baroclinic energy over the whole analyzed model domain is estimated to be 35 gw roughly 10 of the energy in the m 2 surface tide incident on the prominent topographic features is converted to the m 2 internal tide although about half of the m 2 internal tidal energy is subject to local dissipation in close proximity to the generation sites

global baroclinic tides an approximate estimate of the energy in the first mode m2 baroclinic tide has been made from satellite observations results based on topex poseidon t p precision altimetry indicate that the internal tide patterns are similar to those expected from mid ocean topographic features in the global oceans both the orthotide and harmonic analyses indicate that the total energy in global m2 baroclinic tide is approximately 50 pj for a variety of reasons m2 is the only component that can be obtained reliably from altimetric measurements even then the energy value may be an underestimate and the energy flux the dissipation rate cannot be deduced from altimetry since it is the tidal currents flowing over mid ocean topographic features that are responsible for generating internal tides a model calibrated by m2 observations is a plausible alternative currents from a high resolution 15 barotropic tidal model have therefore been used to obtain an estimate of both the energy and the dissipation rate in m2 s2 and k1 baroclinic tides a simple model of baroclinic tide generation has been used and the unknown constant in this model has been selected to yield a total energy of 50 pj in the first mode m2 baroclinic tide based on this calibration the total energy is 8 pj in s2 first mode baroclinic tide and 15 pj in k1 the total in all first mode baroclinic tides is 90 pj about 16 of the total energy 580 pj in barotropic tides the model results also suggest that about 360 gw of tidal energy are dissipated in m2 baroclinic tides alone and 520 gw are dissipated in all first mode baroclinic tides the latter value is approximately 15 of the power input into barotropic ocean tides 3490 gw by the lunisolar tidal forces we have preferred to be conservative and hence these are likely to be underestimates especially since the altimetric tracks do not often intersect mid ocean topographic features at optimum angles while these values are very much within the range of earlier estimates in literature they should be regarded as still uncertain to perhaps a factor of two the dissipation rate could be anywhere from 400 gw to 800 gw the most likely value being about 600 gw the small signal to noise ratio involved in altimetric measurements of the surface manifestation of internal tides and potential contamination by mesoscale signals are serious problems in situ measurements at least a few locations underneath altimetric tracks are essential for confirmation and or refinement of these preliminary estimates hopefully these very first estimates of the energy and dissipation rate in global baroclinic tides though rather crude will serve as a catalyst for a better estimation in the future since internal tides are likely to be a prominent source of mixing in the deep oceans and important to thermocline maintenance

modeling tides in monterey bay california abstract in the process of developing a tide permitting coastal ocean forecasting system tidal signals are added to an oceanic general circulation model for monterey bay california the model which is configured from the regional ocean modeling system roms has three one way nested domains with the finest resolution of 1 6 km in the horizontal direction and 32 levels in the vertical direction in present research the tidal simulation of the system is validated against tide gauges adcp current observations high frequency radar surface current observations and compared with the output from two barotropic tidal models the results indicate that the barotropic tides from the model compare well with observations in terms of sea surface height with discrepancies in amplitude of less than 10 of the amplitude of the most energetic m 2 constituent however the discrepancy for the barotropic tidal currents can reach 30 among models with similar accuracy in sea surface height the generation and propagation of baroclinic tides associated with the monterey submarine canyon are qualitatively reproduced by the model with weaker strength the surface tidal current simulation is improved especially in terms of magnitude when the model has a more realistic stratification through changes in both barotropic and baroclinic tidal currents

global observations of open ocean mode 1 m2internal tides abstracta global map of open ocean mode 1 m2 internal tides is constructed using sea surface height ssh measurements from multiple satellite altimeters during 1992 2012 representing a 20 yr coherent internal tide field a two dimensional plane wave fit method is employed to 1 suppress mesoscale contamination by extracting internal tides with both spatial and temporal coherence and 2 separately resolve multiple internal tidal waves global maps of amplitude phase energy and flux of mode 1 m2 internal tides are presented the m2 internal tides are mainly generated over topographic features including continental slopes midocean ridges and seamounts internal tidal beams of 100 300 km width are observed to propagate hundreds to thousands of kilometers multiwave interference of some degree is widespread because of the m2 internal tide s numerous generation sites and long range propagation the m2 internal tide propagates across the critical latitudes for parametric subharmonic instability 28 8 s n

the role of turbulent mixing in the modified shelf water overflows that produce cape darnley bottom water the mixing process associated with modified shelf water msw overflows that eventually mix to form cape darnley bottom water cdbw was investigated by hydrographic and microstructure observations off the cape darnley polynya cdp east antarctica in january 2009 closely spaced microstructure observations revealed that msw properties varied considerably within a distance of 4 km across the shelf edge near the bottom the rate of turbulent kinetic energy dissipation was enhanced to values greater than 10 7 w kg 1 and the vertical scale of the bottom boundary layer bbl was on the order of 10 m the observed bbl around the shelf edge was characterized by strong vertical mixing with turbulent eddy diffusivities of o 10 3 10 2 m2 s 1 a geostrophically balanced density current which resulted from the presence of msw over the continental shelf is considered the primary energy source for the turbulent mixing in the bbl this turbulent mixing transforms the overflowing msw through mixing with ambient water masses specifically with the overlying modified circumpolar deep water the bbl is also thought to partly contribute to the gradual descent of msw down the continental slope through bottom ekman transport we conclude that turbulent mixing primarily caused by a density current plays an important role in cdbw formation by modifying the msw overflowing from the cdp

comparison of tl esr and 14c dates of speleothems abstract a series of speleothems from the magurska mi tusia and kasprowa niznia caves tatra mts s poland have been dated using the 14c tl and esr methods a method proposed by t goslar and h hercman was used to consider radioactive disequilibrium in the uranium series for dose rate calculation a total of 17 samples were dated a direct comparison of 14c dates with corresponding tl and esr dates was possible for 8 samples while simultaneous tl and esr dates were available for 6 samples there was general agreement in both groups the results obtained were used to set up time boundaries on the last glaciation of the tatra mts and to reconstruct climatic changes in this area during the last 100 ka

internal hydraulic flows on the continental shelf high drag states over a small bank observations of currents hydrography and turbulence provide unambiguous evidence for hydraulic control of flow over an isolated three dimensional topographic feature on oregon s continental shelf the flow becomes critical at the crest of the bank forming a strong supercritical downslope flow in the lower layer farther downstream internal hydraulic jumps form as the bottom flow becomes subcritical as a consequence turbulence is greatly enhanced in the bottom boundary layer in the sheared interface above the swiftly flowing bottom current and in the internal hydraulic jump the dissipation rate of turbulent energy is consistent with the mean energy removal rate for a hydraulic jump in an idealized two layer flow this enhanced turbulence constitutes a high drag state of the flow in which the form drag introduced by the topography exerts significant influence on the flow around it and mixing is increased 102 103 times the background values

barotropic and baroclinic m2 tides in the monterey bay region abstract a high resolution 250 m primitive equation model is used to simulate the depth averaged and baroclinic m2 tides in the monterey bay region the model shows a high level of skill in comparisons with sea level observations adcp current observations within the submarine canyon are reasonably well reproduced the modeled depth averaged currents have a complex spatial pattern with magnitudes in excess of 0 1 m s 1 near moss landing during the second half of flood ebb tide the flow is into out of the bay through the canyon but out of into the bay over the shelf regions this depth averaged flow pattern is not evident in a diagnostic run implying a feedback between the internal tides and the pressure gradient in the bay the depth integrated baroclinic total minus depth averaged energy fluxes show a complex beamlike pattern due to the interaction of energy from multiple sources the beams have magnitudes up to 1 kw m 1 interspersed with regions of near zero depth integrated flux energy en

horizontal distribution and characteristics of shear layers in the seasonal thermocline abstract high resolution velocity shear ctd and microstructure measurements were made simultaneously from the research submarine dolphin in monterey bay in october 1984 during three consecutive dives the dolphin cycled between the surface and 110 m along predetermined tracks 10 miles northwest of monterey inside the seasonal thermocline the vertical velocity shear appeared to be concentrated in layers 10 m thick extending several kilometers horizontally the thickness of the shear layers is consistent with the typical size of turbulent patches encountered in the seasonal thermocline in contrast no large shear layers were observed below a 50 m depth the depth levels at which the shear layers were observed were nearly constant throughout each dive suggesting that the shear layers with some unknown degree of intermittency might extend horizontally over several square kilometers the shear vector inside the seasonal themocline at t 25 5 rotated 360 over an inertial period but did appear to

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

formation and growth of normal faults in carbonates within a compressive environment normal faults were initiated and grew through hierarchical formation of pressure solution structures and their subsequent shearing in cretaceous carbonates in the leading thrust front of maiella mountain italy through mapping in the field we have documented the detailed architecture of faults with increasing slip values from a few millimeters to 50 m and have identified pretilting structural elements and four stages of fault development each stage representing addition of a new structural element the result is a conceptual model that begins with pretilting structures bed parallel and bed perpendicular solution surfaces that were reactivated in shear upon tilting of the beds at the frontal limb of the maiella anticline slip on mechanical layer boundaries and on bed perpendicular solution surfaces resulted in oblique solution surfaces linkage of solution surfaces and fragmentation of rock oblique zones of fragmented rock in adjacent mechanical layers linked to form a continuous breccia and facilitated fault growth these normal faults formed through mechanical processes strictly in a compressional regime

observations of tidal internal wave beams at kauai channel hawaii abstract to observe the across ridge structure of internal tides density and velocity were measured using seasoar and a doppler sonar over the upper 400 600 m of the ocean extending 152 km on each side of the hawaiian ridge at kauai channel eighteen sections were completed in about 18 days with sampling intentionally detuned from the lunar semidiurnal m2 tide so that averaging over all sections was equivalent to phase averaging the m2 tide velocity and displacement variance and several covariances involving velocity and displacement showed one m2 internal wave beam on each side of the ridge and reflection of the beams off of the surface theoretical ray slopes aligned with the observed beams and originated from the sides of the ridge energy flux was in agreement with internal wave generation at the ridge inferred turbulent dissipation was elevated relative to open ocean values near tidal beams energy flux was larger than total dissipation almost everywhere across the ridge internal wave energy fl

global mapping of diapycnal diffusivity in the deep ocean based on the results of expendable current profiler xcp surveys 1 based on the results of the extensive xcp surveys in the north pacific we first examine the empirical relationship between the estimated diapycnal diffusivity in the thermocline and the numerically predicted available energy density of the semidiurnal internal tide major energy source for diapycnal diffusivity at each location the diapycnal diffusivity is estimated by applying the parameterization of gregg 1989 to the fine scale vertical shear of horizontal velocity measured by xcp next the numerically predicted energy density of the semidiurnal internal tide at each longitude and latitude in the world s oceans is incorporated into the resulting empirical relationship to obtain the global distribution of diapycnal diffusivity in the thermocline this model predicts that strong diapycnal mixing mixing hotspot is limited to the prominent topographic features at latitudes between 20 and 30

mixing on the black sea shelf north of the bosphorus microstructure observations over the black sea shelf and slope north of the bosphorus reveal a very small turbulent diapycnal diffusivity k 10 6 m s 1 in the cold intermediate water during late summer when winds are at their seasonal minimum recent modeling by oguz et al 1998 shows that only with such low diffusivity can the observed separation between dissolved oxygen o2 and hydrogen sulfide h2s be maintained the measurements also provide a reference for mixing over continental shelves where tides are negligible and when winds are light

sources of baroclinic tidal energy in the gaoping submarine canyon off southwestern taiwan 1 a three dimensional model driven by tidal constituents o1 k1 m2 and s2 was adopted to evaluate the sources of baroclinic tidal energy in the gaoping submarine canyon gpsc off southwestern taiwan the model domain covered the probable primary generation sites including the luzon strait ls and the southeastern taiwan strait ts the simulated baroclinic tides agreed with the observations of tidal current velocity isotherm vertical displacement and baroclinic tidal energy flux fbc in the gpsc the depth integrated seven day averaged fbc computed from the model result was 2 2 kw m 1 in the gpsc and the corresponding area integrated fbc reached 189 4 mw the results obtained from the model suggest that the baroclinic tides lead to strong turbulent mixing near the canyon head with a vertical diffusivity of 3 5 10 3 m2 s 1 baroclinic tidal energy in the gpsc is mainly generated on the western ridge in the ls and on the steep topography in the southeastern ts the local generation of baroclinic energy only accounts for 4 4 of the total value the other 95 6 of the baroclinic tidal energy is remotely generated at the ls and the southeastern ts of which 31 9 and 8 8 are directly emanated respectively into the gpsc the northwestward and southeastward baroclinic energy beams radiating from the ls and the southeastern ts respectively meet each other and form internal partial standing tides outside the gpsc the transverse baroclinic energy from the internal partial standing tides accounts for the remaining 54 9 of the baroclinic tidal energy in the gpsc

observations of enhanced diapycnal mixing near the hawaiian ridge profiles of potential density obtained from ctd casts at two stations at different distances from the hawaiian ridge are examined for evidence of diapycnal turbulent mixing as indicated by density inversions and internalwave vertical strain results from independent casts are used to produce ensemble averaged vertical distributions for the number of inversions and the thorpe scale both parameters were found to be higher over the slope of the topography at 2500 m depth than in the deep ocean 110 km to the north thorpe scale based estimates of the rate of dissipation of turbulent kinetic energy and turbulent vertical diffusivity are elevated by an order of magnitude over the slope relative to deep ocean background levels the vertical distributions of these mixing parameters are nonuniform and exhibit signs of locally enhanced dissipation possibly due to internal tides generated at the ridge at the deep station turbulence is at background levels from the surface down to 2000 m below this a localized zone of enhanced mixing is observed within which the dissipation rate is o 1029 w kg21 and turbulent diffusivity is greater than o 1024 m2 s 21 perhaps due to an internal tide ray originating at the ridge the full depth topographical enhancement of mixing near the ridge also appears in the vertical strain field estimates of dissipation rate and turbulent diffusivity based on an internal wave wave interaction model give results similar to direct thorpe scale methods except in weakly stratified environments where both methods are subject to uncertainty near the topography the variation in mixing intensity observed between casts is sensitive to sporadic large mixing events which are triggered by internal waves associated with the spring tide the upper portion of the water column stronger stratification is more responsive to the tide than the deep regions

propagation and dissipation of the internal tide in upper monterey canyon 1 submarine canyons are sites of intense turbulence and mixing monterey canyon cuts into the continental shelf off california and is defined by its sinuous nature temperature salinity and current velocity measurements were made over 21 days in april 2009 with a depth cycling towed body to understand internal tide propagation and dissipation through the canyon bends cross canyon transects reveal complex flow patterns that follow large scale bathymetry on scales greater than 5 km changes in thalweg direction deflect baroclinic energy flux but the bends in the measurement region are too sharp for the flux to follow the thalweg ridges that form the bends in the canyon act as obstacles to the flow and turbulent dissipation rates greater than 1 10 5 m2 s 3 were observed on their flanks especially at the largest meander the gooseneck the canyon integrated baroclinic energy flux increased from 2 7 mw at the most western section to 3 7 mw at the gooseneck ridge which has a nearly critical bottom slope with respect to the semidiurnal baroclinic tide on the western side baroclinic energy flux was 50 less on the eastern side of the ridge while measured dissipation near the gooseneck meander was sufficient to explain the flux divergence turbulence near the gooseneck may have been undersampled between the gooseneck ridge and the most eastern cross canyon transect dissipation may account for the decrease in the energy flux though a local energy balance does not hold the energy budget is balanced over the larger scale of the measurement region east of the gooseneck ridge

observations of boundary mixing over the continental slope observations of mixing over the continental slope using a towed body reveal a great lateral extent several kilometers of continuously turbulent fluid within a few hundred meters of the boundary at depth 1600 m the largest turbulent dissipation rates were observed ove ra5k mhorizontal region near a slope critical to the m2 internal tide over a submarine landslide perpendicular to the continental slope enhanced mixing extended at least 600 m above the boundary increasing toward the bottom the resulting vertical divergence of the heat flux near the bottom implies that fluid there must be replenished intermediate nepheloid layers detected optically contained fluid with u s properties distinct from their surroundings it is suggested that intermediate nepheloid layers are interior signitures of the boundary layer detachment required by the near bottom flux divergance

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

near boundary mixing above the flanks of a midlatitude seamount fine scale velocity and density profile data with concurrent turbulent velocity and temperature dissipation estimates obtained above the flanks of fieberling guyot a seamount in the eastern north pacific ocean are examined for evidence of near bottom boundary mixing fine scale shear and strain spectral levels were elevated over the flanks of the seamount in a 500 m thick stratified layer above the bottom the velocity shear was horizontally isotropic clockwise and counterclockwise with depth shear spectral levels were comparable and no significant correlation between shear and strain was observed above the steepest bottom slopes near the seamount summit rim excess vertical strain relative to shear was observed as compared to the background internal wave field suggesting the presence of high frequency internal waves these signals may have been the product of wave reflections from the steep flanks of the seamount and or wave generation from tidal currents flowing over the rough bottom associated with the enhanced shears and strains were more frequent occurrences of low 10 m richardson number events increased overturning scales and larger estimated turbulent eddy diffusivity relative to observations 15 km or more from the seamount in particular turbulent diffusivity estimates increased from o 0 1 10 4 m2 s 1 in the ocean interior to 1 5 10 4 m2 s 1 within 500 m vertically 1 3 km horizontally of the seamount flank a simple geometric scaling argument suggests that boundary mixing of this intensity has relevance to the large scale circulation at abyssal depths where a large fraction of the ocean waters is in close proximity to the bottom

turbulent mixing and exchange with interior waters on sloping boundaries abstractmicrostructure measurements along the axes of monterey and soquel submarine canyons reveal 200 300 m thick well stratified turbulent near bottom layers with average turbulent kinetic energy dissipation rates e 4 10 8 w kg 1 and eddy diffusivities k 16 10 4 m2 s 1 assuming mixing efficiency 0 2 to at least thalweg depths of 1200 m turbulent dissipation rates are an order of magnitude lower in overlying waters whereas buoyancy frequencies are only 25 higher well mixed bottom boundary layer thicknesses hn are an order of magnitude thinner than the stratified turbulent layer hn he because well stratified turbulent layers are commonly observed above slopes arguments that mixing efficiency should be reduced on sloping boundaries do not hold in cases of energetic internal wave generation or interaction with topography an advective diffusive balance is used to infer velocities and transports predicting horizontal upslope flows of 10 50 m day 1 extrapolating this estimate globa

semidiurnal tidal currents in the deep ocean near the east pacific rise between 9 and 10 n spatial and temporal variations of the semidiurnal tidal currents especially the baroclinic components in the deep ocean near a segment of the east pacific rise epr are examined using observations from a set of current meter moorings over the ridge crest the baroclinic semidiurnal tidal current is dominated by the zonal component and is coherent along the observed ridge segment in the direction across the ridge crest the baroclinic semidiurnal tidal current is not coherent and its magnitude decreases away from the ridge crest vertically the baroclinic semidiurnal tidal current covaries in a few hundred meters near the seafloor both the semidiurnal kinetic energy ke and shear show significant subinertial temporal variations by comparing with background forcings the author found that the subinertial variation of the semidiurnal tides over the ridge crest is related to both the spring neap cycles and the eddy induced low frequency flows in the deep ocean particularly their cross ridge components the observation that the baroclinic tidal currents at the axial stations flowing perpendicularly to the ridge crest suggests that the baroclinic semidiurnal tides at the axial stations are generated locally it is therefore probable that the subinertial variation of the baroclinic semidiurnal tides near the epr is due to the eddy modulated internal tide generation since the mesoscale eddies in the eastern tropical pacific vary with the state of the climate the observed eddy modulated internal tide generation connects climate change and variability to the physical and biogeochemical dynamics in the deep ocean and implies an unexplored feedback mechanism potentially affecting the climate system

interfering paths of deformation and development of arcs in the fold and thrust belt of the central apennines italy in the foreland fold and thrust belt of the central apennines the major thrust sheets design systems of arcs interfering with noncoaxial trends localization of shortening by thrusting and shearing appears to be controlled by the squeezing of low competence basinal units marche gran sasso monte picca and monte genzana in between the rigid blocks of the lazio abruzzi and adriatic carbonate platforms the geometrical interlocking has been resolved by differential rotations of the superposed thrust sheets as also substantiated by paleomagnetic data the structural analysis and the age of the syntectonic siliciclastic deposits suggest an irregular sequencing of superposed contractional and extensional events during late miocene middle pliocene times interfering kinematic paths characterize the arcuate belts where slip partitioning has adjusted the coeval deformation of the noncoaxially arranged tectonic units in the arcuate gran sasso monte picca thrust belt out of sequence thrusting displacement transfer on high angle strike slip faults and growth of high angle normal faults behind the most rotated blocks have resulted in the back and forth superposition of contractional and extensional structures in adjacent domains our kinematic reconstruction of the central apennines indicates that it is impossible to perform the retrodeformation of tectonic events by assuming a regular outward progression of deformation pulses in such a strongly arcuate belt the irregular trajectories of the displacement field and the complex overprinting relations between different sets of structures reflect the kinematic accommodation of blocks with contrasting rigidity and are not fitted easily within a regionally smoothed stress field

spatially broad observations of internal waves in the upper ocean at the hawaiian ridge abstract the density and current structure at the hawaiian ridge was observed using seasoar and doppler sonar during a survey extending from oahu to brooks banks across and along ridge changes in internal wave statistics in the upper ocean within 200 km of the ridge are investigated internal waves with trough to crest amplitude as large as 60 m and horizontal wavelength of about 50 km are observed repeatedly in across ridge sections of potential density within 150 km of the ridge kinetic and potential energy density exceed open ocean values with maxima about 10 times garrett munk levels in the kauai channel kc the kinetic energy density is largest along an m2 internal tide ray the ray originates at the northern edge of the ridge peak at a large across ridge change in topographic slope and terminates at the ocean surface about 30 40 km south of the ridge peak kinetic and potential energy density are larger on the south side of the ridge at kc the side with larger topographic slope energy densi

semidiurnal internal tide in jasin observations and simulation temperature was observed in the upper 80 m by moored thermistor chains at three locations in rockall channel west of scotland isotherms were interpolated and a 1 week period of exceptionally energetic tidal oscillations was analyzed the moored array horizontal separations ranging from 6 to 20 km was used as an antenna to determine the dominant horizontal wavelength and direction of propagation of the internal tide within the array rockall bank 100 km to the southeast was identified as the source of the internal tide the semidiurnal internal tide generated by the interaction of the surface tide with rockall bank was simulated by use of a model due to prinsenberg and rattray the model predicts generation of the internal tide at the shelf break and propagation seaward as energetic beams which lie along internal wave characteristics some energy is trapped near the surface in association with the pycnocline there is substantial structure in the velocity and vertical displacement fields most of the total energy of the internal tide is in the first vertical mode however at particular depths vertical modes as high as 4 horizontal wavelengths of 25 km dominate the high degree of spatial variability in the modeled internal tide illustrates the potential for error when basing a description of the tide on sparse observations there is good agreement between the modeled vertical displacements and the 1 week period of energetic oscillations of isotherm depth observed at the moorings in addition there is good agreement between the model and the tidal velocity variance measured during the same week at depths ranging from 10 to 1000 m and distances ranging from 50 to 130 km from rockall bank richardson numbers associated with the vertical shear of the modeled internal tide range down to values less than 2

numerical simulation of internal tides and the resulting energetics within monterey bay and the surrounding area 1 we use a three dimensional nonhydrostatic unstructured grid code to simulate internal tides within monterey bay the predicted water surface barotropic and baroclinic velocities and internal tides in the greater coastal region agree with observations the agreement is due to the use of a high resolution mesh alongshore prescription of the barotropic m2 tidal velocities and specification of initial conditions consistent with field data results of depth integrated m2 period averaged energy flux and energy flux divergence are presented in order to identify locations of significant internal wave generation and dissipation based on the results there is a domain wide power surplus of 52 mw due to internal tides that is available for pelagic mixing yet isolated bathymetric features such as monterey submarine canyon and smooth ridge are net dissipative with dissipation rates of 8 3 and 1 5 mw respectively

internal tide reflection and turbulent mixing on the continental slope abstract observations of turbulence internal waves and subinertial flow were made over a steep corrugated continental slope off virginia during may june 1998 at semidiurnal frequencies a convergence of low mode onshore energy flux is approximately balanced by a divergence of high wavenumber offshore energy flux this conversion occurs in a region where the continental slope is nearly critical with respect to the semidiurnal tide it is suggested that elevated near bottom mixing k 10 3 m2 s 1 observed offshore of the supercritical continental slope arises from the reflection of a remotely generated low mode m2 internal tide based on the observed turbulent kinetic energy dissipation rate the high wavenumber internal tide decays on time scales o 1 day no evidence for internal lee wave generation by flow over the slope s corrugations or internal tide generation at the shelf break was found at this site

sustained full water column observations of internal waves and mixing near mendocino escarpment abstract the relative strength and spatiotemporal structure of near inertial waves niw and internal tides it are examined in the context of recent moored observations made 19 km south of mendocino escarpment an abrupt ridge step feature in the eastern pacific in addition to strong internal tide generation steps and ridges give rise to the possibility of shadowing wherein near inertial energy is prevented from reaching depths beneath a characteristic intersecting the ridge top a combination of two moored profilers and a long range acoustic doppler current profiler adcp yielded velocity and shear measurements from 100 to 3640 m 60 m above bottom and isopycnal depth strain and overturn inferred turbulence dissipation rate from 1000 to 3640 m sampling intervals 20 min in the upper 1000 m and 1 5 h below that were fast enough to minimize aliasing of higher frequency internal wave motions the 67 day long record is easily sufficient to isolate niw and it via bandpass filtering and to capture

tl and esr dating of speleothems and radioactive disequilibrium in the uranium series abstract dating of speleothems by tl and esr is seriously complicated by radioactive disequilibria in the uranium series this paper presents a simple method which takes into consideration the u series disequilibria in the case where the annual dose is determined by gamma scintillation spectrometry the method described is based on the concept of an appropriately defined laboratory age and enables direct reading of the age of a sample from the curve the gh plot independently of the results of measurements

desert paleoenvironmental data from cave speleothems with examples from the chihuahuan somali chalbi and kalahari deserts abstract pollen bearing lake bog and spring sediments are relatively scarce in many arid and semiarid regions of the world and few are dateable beyond the 14c range we have obtained pollen spectra from speleothems collected from caves in the somali chalbi and kalahari deserts suggesting that these deposits may be an important future source of desert paleovegetation data as cave speleothems can be dated by the 230th 234u method to c 350 000 yr b p and by the tl and esr methods potentially to 1 m y b p and can sometimes give paleotemperature and paleohydrologic data they could provide a first glimpse of desert paleoenvironments during isotope stages 4 9 ages of speleothems from the chihuahuan kalahari and somali chalbi deserts suggest that there was more available moisture in the southwestern u s a and in northwestern bostwana during glacials and interstadials of the last c 300 000 years but that wetter conditions in the horn of africa corresponded with interglacials and perhaps to a lesser extent with interstadials pollen from three northern somalia speleothems indicate more mesic conditions in the horn of africa at 10 000 11 800 and 176 500 yr b p while speleothem pollen spectra from matupi cave in northeastern zaire presently surrounded by tropical rainforest suggest a savanna grassland at this cave c 14 000 yr b p

esr ages of middle pleistocene corals from the ryukyu islands abstract electron spin resonance ages of 11 corals from the lower part of the ryukyu group japan can be classified into two groups about 600 000 and 800 000 yr the result indicates that the lower part of the ryukyu group is correlated to at least two of the oxygen isotope stages 15 17 19 21 and 23 lowermost part of the ryukyu group was probably deposited during a large transgression and may be correlated worldwide

semidiurnal baroclinic wave momentum fluxes at kaena ridge hawaii abstractkaena ridge hawaii is a site of energetic conversion of the semidiurnal barotropic tide diffuse baroclinic wave beams emanate from the critical slope regions near the ridge crest directed upward and southward from the north flank of the ridge and upward and northward from the south flank here the momentum fluxes associated with generation at the ridge are estimated continuous vertical profiles of density and velocity from 80 to 800 m were obtained from the research platform floating instrument platform flip over the southern edge of the ridge as an aspect of the hawaii ocean mixing experiment data are used to estimate the reynolds stress eulerian buoyancy flux and the combined eliassen palm flux in the semidiurnal band an upward southward stress maximum of 0 5 10 4 m2 s 2 appears at depths of 300 500 m generally consistent with beam like behavior a strong off ridge buoyancy flux 0 3 10 4 m2 s 3 combines with large along ridge reynolds stresses to form an eliassen palm flux

internal wave reflection and mixing at fieberling guyot the structure of internal wave reflection off a sloping bottom on the steep flank of a tall north pacific ocean seamount is observed in year long moored array records to differ substantially from the form predicted by linear theory although linear theory accounts for several qualitative features of the process this study documents new features of wave reflection as described below wave reflection is detectable as far as 750 m above the bottom motions are dominated by a single empirical mode whose phase structure obeys linear internal wave dispersion but whose amplitude decays with a scale comparable to the wavenumber while the dominant mode has scales appropriate to the reflection of a first baroclinic mode wave incident from the open ocean its decay from the bottom is such that current vectors in the vertical plane rotate clockwise in time when viewed with shallow water to the right this flow resembles the lower half of the deepest cell pattern predicted by linear reflection from a uniform slope at the local internal wave critical frequency the dominant mode has nearly a vanishing wavenumber rather than the infinite wavenumber predicted by linear reflection reflected waves are aligned parallel to the bottom slope measured on wave spatial scales rather than shorter ones wave reflection causes large frequent density overturns implying mixing the rate and strength of these overturns imply a local vertical eddy viscosity of 2 6 10 4 m2 s over the bottom few hundred meters the contribution of bottom intensified mixing to the open deep ocean is roughly equivalent to that found in situ although reflection from gentler slopes or at lower latitude may produce greater contribution from internal wave reflection induced mixing

offshore detachment process of the low salinity water around changjiang bank in the east china sea abstract a patchlike structure of low salinity water detached from the chanjiang diluted water cdw is frequently observed in the east china sea ecs in this study the offshore detachment process of cdw into the ecs is examined using a three dimensional numerical model the model results show that low salinity water is detached from the cdw plume by the intense tide induced vertical mixing during the spring tide period when the tidal current becomes stronger during the spring tide thickness of the bottom mixed layer in the sloping bottom around changjiang bank reaches the mean water depth implying that the stratification is completely destroyed in the entire water column as a result the offshore detachment of cdw occurs in the sloping side of the bank where the tidal energy dissipation is strong enough to overcome the buoyancy effect during this period on the other hand the surface stratification is retrieved during the neap tide period because the tidal current becomes substantially weaker

internal tide radiation from mendocino escarpment abstract strong semidiurnal internal tides are observed near mendocino escarpment in full depth profile time series of velocity temperature and salinity velocity and density profiles are combined to estimate the internal tide energy flux divergence of this flux demonstrates that its source is the barotropic tide interacting with the escarpment a baroclinic energy flux of 7 kw m 1 radiates from the escarpment corresponding to 3 of the 220 kw m 1 fluxing poleward in the surface tide energy and energy flux are concentrated in packets that emanate from the flanks of the ridge surmounting the escarpment and one site 90 km north of the escarpment coherent beamlike structure along semidiurnal ray paths remains identifiable until the first surface reflection beyond the first surface reflection north of the escarpment the energy flux drops by 2 kw m 1 and beams are no longer discernible turbulence as inferred from finescale parameterizations is elevated by over two orders of magnitude relative to th