well documented travel history of mesozoic pelagic chert in japan from remote ocean to subduction zone the mino tanba belt in southwest japan a segment of the cordilleran type orogenic chain of jurassic east asia is composed mainly of a middle upper jurassic subduction accretion complex in which triassic and lower jurassic bedded radiolarian cherts occur as large allochthonous units structurally interlayered with middle upper jurassic clastic rocks high resolution microfossil conodont and radiolaria research has identified very low average sedimentation rates of about 0 5 g cm 1000 yr in the chert units similar to those of modern pelagic sediments accumulated in open ocean environments judging from the low average sedimentation rate high purity of biogenic silica long duration of continuous deposition 50 m y and wide along strike extent 1000 km the bedded radiolarian cherts in the mino tanba belt are best understood as ancient pelagic sediments that accumulated in open ocean environments accordingly the alleged origin in smaller marginal basins is untenable upward lithologic change from bedded chert to overlying siliceous mudstone in the uppermost portion of chert sequences suggests the gradual landward approach of the oceanic plate toward a trench the tectonic interlayering of these cherts and coarse grained terrigenous elastics is a secondary feature that was added through duplexing underplating in the subduction zone on the basis of the primary stratigraphy and field occurrence of triassic bedded chert in the mino tanba belt newly proposed are an idealized oceanic plate stratigraphy and a generalized travel history of a cordilleran type bedded chert from its birth at a mid oceanic ridge to its demise at a subduction zone

internal tide generation by arbitrary two dimensional topography to date analytical models of internal tide generation by two dimensional ridges have considered only idealized shapes here we advance the green function approach to address the generation of internal tides by two dimensional topography of arbitrary shape employing the wentzel kramers brillouin wkb approximation to consider the impact of non uniform stratifications this allows for a more accurate analytical estimation of tidal conversion rates studies of single and double ridges reveal that the conversion rate and the nature of the radiated internal tide can be sensitive to the topographic shape particularly around criticality and when there is interference between wave fields generated by neighbouring ridges the method is then applied to the study of two important internal tide generation sites the hawaiian and luzon ridges where it captures key features of the generation process

dynamics diffusion and geomorphological significance of tidal residual eddies many shallow tidal areas show the occurrence of ebb and flood surplusses organized in cell like structures or tidal residual eddies they seem to arise from a nonlinear transfer of vorticity from the oscillating tidal field to the mean field the irregular structure of the bottom topography or the coastline acting as a catalyst to produce the necessary vorticity gradients the dynamical characteristics of the eddies assist our understanding of the geomorphology of the sea bed

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

tidal conversion at a submarine ridge the radiative flux of internal wave energy the tidal conversion powered by the oscillating flow of a uniformly stratified fluid over a two dimensional submarine ridge is computed using an integral equation method the problem is characterized by two nondimensional parameters a and b the first parameter a is the ridge half width scaled by h where h is the uniform depth of the ocean far from the ridge and is the inverse slope of internal tidal rays horizontal run over vertical rise the second parameter b i s the ridge height scaled by h two topographic profiles are considered a triangular or tent shaped ridge and a polynomial ridge with continuous topographic slope for both profiles complete coverage of the a b parameter space is obtained by reducing the problem to an integral equation which is then discretized and solved numerically it is shown that in the supercritical regime ray slopes steeper than topographic slopes the radiated power increases monotonically with b and decreases monotonically with a in the subcritical regime the radiated power has a complicated and nonmonotonic dependence on these parameters as a 0 recent results are recovered for the tidal conversion produced by a knife edge barrier it is shown analytically that the a 0 limit is regular if a 1 the reduction in tidal conversion below that at a 0 is proportional to a 2 further the knife edge model is shown to be indicative of both conversion rates and the structure of the radiated wave field over a broad region of the supercritical parameter space as a increases the topographic slopes become gentler and at a certain value of a the ridge becomes critical that is there is a single point on the flanks at which the topographic slope is equal to the slope of an internal tidal beam the conversion decreases continuously as a increases through this transition visualization of the disturbed buoyancy field shows prominent singular lines tidal beams in the case of a triangular ridge these beams originate at the crest of the triangle in the case of a supercritical polynomial ridge the beams originate at the shallowest point on the flank at which the topographic slope equals the ray slope

saturation of the internal tides and induced mixing in the abyssal ocean as part of an ongoing effort to develop a parameterization of wave induced abyssal mixing the authors derive an heuristic model for nonlinear wave breaking and energy dissipation associated with internal tides then the saturation and dissipation of internal tides for idealized and observed topography samples are investigated one of the main results is that the wave induced mixing could be more intense and more confined to the bottom than previously assumed in numerical models furthermore in this model wave breaking and mixing clearly depend on the small scales of the topography below 10 km or so which is below the current resolution of global bathymetry this motivates the use of a statistical approach to represent the unresolved topography when addressing the role of internal tides in mixing the deep ocean

instability and focusing of internal tides in the deep ocean received 18 december 2006 and in revised form 7 april 2007 the interaction of tidal currents with sea floor topography results in the radiation of internal gravity waves into the ocean interior these waves are called internal tides and their dissipation due to nonlinear wave breaking and concomitant threedimensional turbulence could play an important role in the mixing of the abyssal ocean and hence in controlling the large scale ocean circulation as part of on going work aimed at providing a theory for the vertical distribution of wave breaking over sea floor topography in this paper we investigate the instability of internal tides in a very simple linear model that helps us to relate the formation of unstable regions to simple features in the sea floor topography for two dimensional tides over one dimensional topography we find that the formation of overturning instabilities is closely linked to the singularities in the topography shape and that it is possible to have stable waves at the sea floor and unstable waves in the ocean interior above for three dimensional tides over two dimensional topography there is in addition an effect of geometric focusing of wave energy into localized regions of high wave amplitude and we investigate this focusing effect in simple examples overall we find that the distribution of unstable wave breaking regions can be highly non uniform even for very simple idealized topography shapes

forcing of oceanic mean flows by dissipating internal tides we present a theoretical and numerical study of the effective mean force exerted on an oceanic mean flow due to the presence of small amplitude internal waves that are forced by the oscillatory flow of a barotropic tide over undulating topography and are also subject to dissipation this extends the classic lee wave drag problem of atmospheric wave mean interaction theory to a more complicated oceanographic setting because now the steady lee waves are replaced by oscillatory internal tides and most importantly because now the three dimensional oceanic mean flow is defined by time averaging over the fast tidal cycles rather than by the zonal averaging familiar from atmospheric theory although the details of our computation are quite different we recover the main action at a distance result from the atmospheric setting namely that the effective mean force that is felt by the mean flow is located in regions of wave dissipation and not necessarily near the topographic wave source specifically we derive an explicit expression for the effective mean force at leading order using a perturbation series in small wave amplitude within the framework of generalized lagrangian mean theory discuss in detail the range of situations in which a strong secularly growing mean flow response can be expected and then compute the effective mean force numerically in a number of idealized examples with simple topographies

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

radiation and dissipation of internal waves generated by geostrophic motions impinging on small scale topography application to the southern ocean abstract recent estimates from observations and inverse models indicate that turbulent mixing associated with internal wave breaking is enhanced above rough topography in the southern ocean in most regions of the ocean abyssal mixing has been primarily associated with radiation and breaking of internal tides in this study it is shown that abyssal mixing in the southern ocean can be sustained by internal waves generated by geostrophic motions that dominate abyssal flows in this region theory and fully nonlinear numerical simulations are used to estimate the internal wave radiation and dissipation from lowered acoustic doppler current profiler ladcp ctd and topography data from two regions in the southern ocean drake passage and the southeast pacific the results show that radiation and dissipation of internal waves generated by geostrophic motions reproduce the magnitude and distribution of dissipation previously inferred from finescale measurements in the region suggesting that it is one of the

reconstructed oceanic plate stratigraphy of the ino formation in the ino district kochi prefecture central shikoku japan abstract the ino formation which has been regarded as a member of the kurosegawa terrane is distributed in the ino district central shikoku japan it is composed of metamorphosed and unmetamorphosed rocks radiolarians in the late triassic to early jurassic strata are found in the unmetamorphosed components the late triassic radiolarians were collected from chert and siliceous mudstone the early jurassic radiolarians are discriminated from the siliceous mudstone and mudstone samples based on chronological data and findings from previous studies the oceanic plate stratigraphy ops of the unmetamorphosed part of the ino formation is reconstructed as follows late carboniferous to late triassic or earliest jurassic bedded chert late triassic late carnian to early jurassic siliceous mudstone and early jurassic mudstone in ascending order based on this observation it is confirmed that the unmetamorphosed part of the ino formation is an early jurassic accretionary complex its origin can be attributed to the chichibu terrane the reconstructed ops of the unmetamorphosed part of the ino formation is possibly correlated to the yusugawa sumaizuku and kamiyoshida units of the northern chichibu terrane or the unknown oldest unit of the southern chichibu terrane

tidally driven vorticity diurnal shear and turbulence atop fieberling seamount abstract fine and microstructure profiles collected over fieberling seamount at 32 26 n in the eastern north pacific reveal a variety of intensified baroclinic motions driven by astronomical diurnal tides the forced response consists of three phenomena coexisting in a layer 200 m thick above the summit plain i an anticyclonic vortex cap of core relative vorticity 0 5f ii diurnal fluctuations of 15 cm s 1 amplitude and 200 m vertical wavelength and iii turbulence levels corresponding to an eddy diffusivity e 10 10 4 m2 s 1 the vortex cannot be explained by taylor proudman dynamics because of its 0 3fn2 negative potential vorticity anomaly the 0 3f fortnightly cycle in the vortex s strength suggests that it is at least partially maintained against dissipative erosion by tidal rectification the diurnal motions are slightly subinertial turning clockwise in time and counterclockwise with depth over the summit plain they also exhibit a fortnightly cycle in their amplitude pointing to

flow and mixing around a small seamount on kaena ridge hawaii abstract microstructure observations over a small seamount on the kaena ridge hawaii showed asymmetry in the along and across ridge directions the 400 m high seamount is on the southern edge of the ridge centered at 21 43 49 n 158 38 48 w 42 km northwest of oahu a 1 km resolution numerical simulation shows that the flow within the depth range of the seamount tends to be accelerated around the seamount rather than going up and over it the flow patterns however are more complicated than for an isolated seamount because of the influence of the 3000 m high kaena ridge comparison with the numerical simulations indicates that the across ridge asymmetry in which dissipation on the north northeastern side of the seamount was higher and more concentrated toward the bed than on the south southwestern side is consistent with an m2 tidal beam generated at the northern edge of the ridge the along ridge asymmetry with higher dissipation on the east southeastern flank than on the west northwestern fla

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

on the momentum flux of internal tides abstractthe action of the barotropic tide over seafloor topography is the major source of internal waves at the bottom of the ocean this internal tide has long been recognized to play an important

radiation and dissipation of internal waves generated by geostrophic motions impinging on small scale topography theory abstract observations and inverse models suggest that small scale turbulent mixing is enhanced in the southern ocean in regions above rough topography the enhancement extends o 1 km above the topography suggesting that mixing is supported by the breaking of gravity waves radiated from the ocean bottom in this study it is shown that the observed mixing rates can be sustained by internal waves generated by geostrophic motions flowing over bottom topography weakly nonlinear theory is used to describe the internal wave generation and the feedback of the waves on the zonally averaged flow vigorous inertial oscillations are driven at the ocean bottom by waves generated at steep topography the wave radiation and dissipation at equilibrium is therefore the result of both geostrophic flow and inertial oscillations differing substantially from the classical lee wave problem the theoretical predictions are tested versus two dimensional high resolution numerical simulations with parameters representative of

recognizing oib and morb in accretionary complexes a new approach based on ocean plate stratigraphy petrology and geochemistry abstract we present a new approach for recognizing the origin of accreted basaltic rocks based on ocean plate stratigraphy ops and on the petrology and geochemistry of basalts from mid oceanic ridges morb and oceanic islands oib using examples from four accretionary complexes ac in sw japan akiyoshi mino tamba chichibu and shimanto the key to the problem is the model of ops which includes an association of igneous and sedimentary rocks that form on an oceanic plate during its travel from a mid oceanic ridge to a subduction zone we propose the reconstruction of the tectonic settings of basalts according to their relationships with associated ops sediments their petrogenesis and their geochemical features five types of ops are recognized in the accretionary complexes of sw japan 1 sandstone shale 2 sandstone shale and chert 3 sandstone shale chert and morb 4 sandstone shale chert morb and gabbro peridotite 5 seamount ops including oib cap carbonates slope clastics and basal shale chert the alkaline tholeiitic or calc alkaline composition of basaltic melts which are typical of oceanic islands mid oceanic ridges and island arcs respectively can be identified by the sequence in crystallization of their major phenocrysts i e olivine ol clinopyroxene cpx and plagioclase pl and by their compositions alkaline and calc alkaline mafic lavas are characterized by an ol cpx pl succession whereas tholeiitic melts by their ol pl cpx succession titanium rich minerals e g ti augite kaersutite ti biotite are typical of alkaline lavas the application of geochemistry based tectonic discrimination diagrams is also a powerful tool if not supported by geological and petrological data may result in confusion due to magma contamination post magmatic alteration and secular change of mantle thermal conditions we propose that a direct comparison of normalized multi element patterns and key binary plots from older volcanic rocks with their modern analogues provides a more viable and reliable method of basalt discrimination our ops petrology geochemistry method allows us to confirm the above conclusions that the lavas of the akiyoshi mino tamba and southern chichibu ac formed in oceanic islands because they are associated with seamount ops sediments crystallized from ol to cpx and pl contain ti augite and kaersutite and are enriched in tio2 lree and nb in this paper we present geochemical data from the inuyama basalts of the mino tamba ac and from the toba complex in the huge mikabu greenstone belt of the chichibu ac the inuyama basalts are in contact with jurassic pelagic cherts but their geochemical features are confusing they contain phenocrysts of ol ti augite and kaersutite and therefore probably formed in seamounts the toba volcanic rocks are a part of the huge ophiolite belt they have flat to slightly lree enriched ree patterns are characterized by an ol cpx succession of phenocrysts and they plot in the oib field in binary plots suggesting they formed in an oceanic plateau

tectono stratigraphy and low grade metamorphism of late permian and early jurassic accretionary complexes within the kurosegawa belt southwest japan implications for mechanisms of crustal displacement within active continental margin abstract we characterize the tectono stratigraphic architecture and low grade metamorphism of the accretionary complex preserved in the kurosegawa belt of the kitagawa district in eastern shikoku southwest japan in order to understand its internal structure tectono metamorphic evolution and assessments of displacement of continental fragments within the complex we report the first ever documented occurrence of an early jurassic radiolarian assemblage within the accretionary complex of the kurosegawa belt that has been previously classified as the late permian accretionary complex thus providing a revised age interpretation for these rocks the accretionary complex is subdivided into four distinct tectono stratigraphic units late permian melange and phyllite units and early jurassic melange and sandstone units the stratigraphy of these four units is structurally repeated due to an e w striking steeply dipping regional fault we characterized low grade metamorphism of the accretionary complex via illite crystallinity and raman spectroscopy of carbonaceous material the estimated pattern of low grade metamorphism showed pronounced variability within the complex and revealed no discernible spatial trends the primary thermal structure in these rocks was overprinted by later tectonic events based on geological and thermal structure we conclude that continental fragments within the kurosegawa belt were structurally translated into both the late permian and early jurassic accretionary complexes which comprise a highly deformed zone affected by strike slip tectonics during the early cretaceous different models have been proposed to explain the initial structural evolution of the kurosegawa belt i e micro continent collision and klippe tectonic models even if we presuppose either model the available geological evidence requires a new interpretation whereby primary geological structures are overprinted and reconfigured by later tectonic events

longshore current dislocation on barred beaches 1 we present a numerical investigation of longshore currents driven by breaking waves on barred beaches alongshore inhomogeneity in the wave envelope or bathymetry leads to the generation of strong dipolar structures when the waves are breaking the dynamics of these structures transfer momentum from the bar of the beach into the trough this study is pursued using a new model that allows long simulation times and realistic wave amplitudes we study two idealized settings that are expected to produce current dislocation as observed in field experiments in one setting the current maximum is dislocated in the other the current is diffused but the maximum is not shifted

particle transport induced by internal wave beam streaming in lateral boundary layers quantifying the physical mechanisms responsible for the transport of sediments nutrients and pollutants in the abyssal sea is a long standing problem with internal waves regularly invoked as the relevant mechanism for particle advection near the sea bottom this study focuses on internal wave induced particle transport in the vicinity of almost vertical walls we report a series of laboratory experiments revealing that particles sinking slowly through a monochromatic internal wave beam experience significant horizontal advection extending the theoretical analysis by beckebanze et al j fluid mech vol 841 2018 pp 614 635 we attribute the observed particle advection to a peculiar and previously unrecognized streaming mechanism in the stratified boundary layer originating at the lateral walls this vertical boundary layer streaming mechanism is most efficient for significantly inclined wave beams when vertical and horizontal velocity components are of comparable magnitude we find good agreement between our theoretical prediction and experimental results

response of glacial lake outburst floods to climate change in the yarkant river basin on northern slope of karakoram mountains china based on the glacial flood events and climate change in the yarkant river basin during the past 50 years the study investigated the long term change of temperature and precipitation the characteristics of glacial floods the origin of sudden flood release the suggested flood mechanism of glacial lakes and the relationship between glacial floods and climate change results showed that there was an obvious increase in the temperature of the basin since 1987 specifically in the mountainous area the significantly increasing temperature in the summer and autumn seasons accelerated the melting rate of glaciers and caused glacial lake burst sudden flood release occurred frequently the frequency of glacial lake outburst floods was 0 4 times a during the period 1959 1986 and increased to 0 7 times a during 1997 2006 peak discharge also increased there were seven floods with peak discharge over 4000 m 3 s from 1959 2006 and three occurred after 1997 the increasing frequency and magnitude of glacial outburst floods mirrored the effect of climate warming on glaciers c 2010 elsevier ltd and inqua all rights reserved