internal waves across the pacific 1 the long range propagation of the semidiurnal internal tide northward from the hawaiian ridge and its susceptibility to parametric subharmonic instability psi at the critical latitude c 28 8 n were examined in spring 2006 with intensive shipboard and moored observations spanning 25 37 n along a tidal beam velocity and shear at c were dominated by intense vertically standing inertially rotating bands of several hundred meters vertical wavelength these occurred in bursts following spring tide contrasting sharply with the downward propagating wind generated features seen at other latitudes these marginally stable layers which have inverse 16 meter richardson number ri16 1 0 7 are interpreted as the inertial waves resulting from psi of the internal tide elevated near inertial energy and parameterized diapycnal diffusivity and reduced asymmetry in upgoing downgoing energy were also observed at and equatorward of c yet simultaneous moored measurements of semidiurnal energy flux and 1 km deep velocity sections measured from the ship indicate that the internal tide propagates at least to 37 n with no detectable energy loss or phase discontinuity at c our observations indicate that psi occurs in the ocean with sufficient intensity to substantially alter the inertial shear field at and equatorward of c but that it does not appreciably disrupt the propagation of the tide at our location

redistribution of energy available for ocean mixing by long range propagation of internal waves ocean mixing which affects pollutant dispersal marine productivity and global climate1 largely results from the breaking of internal gravity waves disturbances propagating along the ocean s internal stratification a global map of internal wave dissipation would be useful in improving climate models but would require knowledge of the sources of internal gravity waves and their propagation towards this goal i present here computations of horizontal internal wave propagation from 60 historical moorings and relate them to the source terms of internal waves as computed previously2 3 analysis of the two most energetic frequency ranges near inertial frequencies and semidiurnal tidal frequencies reveals that the fluxes in both frequency bands are of the order of 1 kw m 1 that is 15 50 of the energy input and are directed away from their respective source regions however the energy flux due to near inertial waves is stronger in winter whereas the tidal fluxes are uniform throughout the year both varieties of internal waves can thus significantly affect the space time distribution of energy available for global mixing

parameterizing tidal dissipation over rough topography the traditional model of tidal dissipation is based on a frictional bottom boundary layer in which the work done by bottom drag is proportional to a drag coefficient and the velocity cubed however away from shallow coastal regions the tidal velocities are small and the work done by the bottom boundary layer can account for only weak levels of dissipation in the deep ocean the energy flux carried by internal waves generated over rough topography dominates the energy transfer away from barotropic flow a parameterization for the internal wave drag over rough topography is included as a dissipative mechanism in a model for the barotropic tides model results suggest that the inclusion of this dissipation mechanism improves hydro dynamical models of the ocean tide it also substantially increases the amount of modeled tidal dissipation in the deep ocean bringing dissipation levels there into agreement with recent estimates from topex poseidon altimetry data

mid pleistocene acheulean like stone technology of the bose basin south china stone artifacts from the bose basin south china are associated with tektites dated to 803 000 3000 years ago and represent the oldest known large cutting tools lcts in east asia bose toolmaking is compatible with mode 2 acheulean technologies in africa in its targeted manufacture and biased spatial distribution of lcts large scale flaking and high flake scar counts acheulean like tools in the mid pleistocene of south china imply that mode 2 technical advances were manifested in east asia contemporaneously with handaxe technology in africa and western eurasia bose lithic technology is associated with a tektite airfall and forest burning

new altimetric estimates of mode 1 m2 internal tides in the central north pacific ocean abstract new estimates of mode 1 m2 internal tide energy flux are computed from an extended ocean topography experiment topex poseidon t p altimeter dataset that includes both the original and tandem tracks improving spatial resolution over previous estimates from o 500 km to o 250 km additionally a new technique is developed that allows separate resolution of northward and southward components half wavelength features previously seen in unseparated estimates are shown to be due to the superposition of northward and southward wave trains the new technique and higher spatial resolution afford a new view of mode 1 m2 internal tides in the central north pacific ocean as with all altimetric estimates only the coherent or phase locked signals are detectable owing to the long repeat period of the tracks emanating from specific generation sites consistent with predictions from numerical models internal tidal beams 1 are as narrow as 200 km and 2 propagate a longer distance than previously observ

internal tides around the hawaiian ridge estimated from multisatellite altimetry 1 satellite altimetric sea surface height anomaly ssha data from geosat follow on gfo and european remote sensing ers as well as topex poseidon t p are merged to estimate m2 internal tides around the hawaiian ridge with higher spatial resolution than possible with single satellite altimetry the new estimates are compared with numerical model runs along track analyses show that m2 internal tides can be resolved from both 8 years of gfo and 15 5 years of ers ssha data comparisons at crossover points reveal that the m2 estimates from t p gfo and ers agree well multisatellite altimetry improves spatial resolution due to its denser ground tracks thus m2 internal tides can be plane wave fitted in 120 km 120 km regions compared to previous single satellite estimates in 4 lon 3 lat or 250 km 250 km regions in such small fitting regions the weaker and smaller scale mode 2 m2 internal tides can also be estimated the higher spatial resolution leads to a clearer view of the m2 internal tide field around the hawaiian ridge discrete generation sites and internal tidal beams are clearly distinguishable and consistent with the numerical model runs more importantly multisatellite altimetry produces larger m2 internal tidal energy fluxes which agree better with model results than previous single satellite estimates this study confirms that previous altimetric underestimates are partly due to the more widely spaced ground tracks and consequently larger fitting region multisatellite altimetry largely overcomes this limitation

surface manifestation of internal tides in the deep ocean observations from altimetry and island gauges the sea surface height signatures of internal tides in the deep ocean amounting to a few centimeters or less are studied using two complementary measurement types satellite altimetry and island tide gauges altimetry can detect internal tides that maintain coherence with the astronomical forcing island gauges can monitor temporal variability which in some circumstances is due to internal tides varying in response to changes in the oceanic medium this latter mechanism is at work at hilo and other stations on the northern coasts of the hawaiian islands by detecting spatially coherent low frequency internal tide modulations the tide gauges along with inverted echo sounders at sea suggest that the mean internal tide is also spatially coherent satellite altimetry confirms this at hawaii and in many other places topex poseidon altimetry detects mean surface waves spatially coherent and propagating great distances 1000 km before decaying below background noise when temporal variability is small the altimetry plus information on ocean density sets useful constraints on energy fluxes into internal tides at the hawaiian ridge 15 gw of tidal power is being converted from barotropic to first mode baroclinic motion examples elsewhere warn that a simplistic interpretation of the altimetry without regard to variability noise or in situ information may be highly misleading with such uncertainties extension of the hawaiian results into a usefully realistic estimate of the global internal tide energy balance appears premature at this time

flood deposits penecontemporaneous with 0 8 ma tektite fall in ne thailand impact induced environmental effects abstract although a crater is not yet identified the australasian tektite strewn field provides evidence that a major impact cratering event took place in the southeast asian region at 0 8 ma just prior to the brunhes matuyama geomagnetic polarity reversal paleomagnetic evidence including reversed polarity in mud lens closely associated with in situ tektites suggests that tektite bearing flood deposits near ban ta chang and chum phuang in northeast thailand are penecontemporaneous with the impact event the deposits include abundant organic debris including whole tree trunks and mammal bones that preserved due to reducing conditions which are also responsible for the presence of abundant iron sulphides sedimentological observations suggest a series of major flood events that are out of character with the modern meandering river system to which they are related the deposits are consistent with the effects of regional deforestation increased run off and erosion and other environmental disruptions expected in the aftermath of a major impact event

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

reduced mixing from the breaking of internal waves in equatorial waters in the oceans heat salt and nutrients are redistributed much more easily within water masses of uniform density than across surfaces separating waters of different densities but the magnitude and distribution of mixing across density surfaces are also important for the earth s climate as well as the concentrations of organisms most of this mixing occurs where internal waves break overturning the density stratification of the ocean and creating patches of turbulence predictions of the rate at which internal waves dissipate were confirmed earlier at mid latitudes here we present observations of temperature and velocity fluctuations in the pacific and atlantic oceans between 42 degrees n and 2 degrees s to extend that result to equatorial regions we find a strong latitude dependence of dissipation in accordance with the predictions in our observations dissipation rates and accompanying mixing across density surfaces near the equator are less than 10 of those at mid latitudes for a similar background of internal waves reduced mixing close to the equator will have to be taken into account in numerical simulations of ocean dynamics for example in climate change experiments

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

tidal effects on ecosystem variability in the chesapeake bay from modis aqua abstract eight year ocean color observations between 2002 and 2009 from the moderate resolution imaging spectroradiometer modis onboard the satellite aqua are used to quantitatively assess the tidal effects on variability of ocean s optical biological and biogeochemical properties in the chesapeake bay we demonstrate that tidal variation in the lower chesapeake bay is one of the important ocean processes that drive significant changes of the ocean s optical and biogeochemical properties normalized water leaving radiance spectra nlw water diffuse attenuation coefficient at the wavelength of 490 nm kd 490 and total suspended sediment tss concentration show significant tidal variations in the lower chesapeake bay indeed in the lower bay region kd 490 increases from 0 9 m 1 under low tidal current conditions at 0 10 0 15 m s to 1 35 m 1 under high tidal current conditions at 0 45 0 50 m s while chlorophyll a concentration in the lower bay region decreases slightly with an increase of the tidal current tide driven variability in kd 490 and tss in the lower bay is similar to and slightly larger than the seasonal variability in the region on the other hand different from the variability in the lower bay the tidal effects on the ecosystem are small and negligible in the middle and a large part of upper chesapeake bay regions

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

entrainment and distribution of different sand sizes under water waves abstract analysis of the bed sediment and suspended sediment collected at different elevations over wave ripples shows that for grain sizes larger than 0 5 mm the likelihood of entrainment into suspension decreases with increasing grain size whereas for the finer material diameter smaller than 0 5 mm the amount of suspended material is proportional to the amount available in the bed material the concentration profiles for individual sieve fractions very similar upwards from about 4 cm above the ripple crest so that the grain size distribution for suspended sand above this level varies very little with elevation all of this taken together indicates that the finer material that goes into suspension is not going to be sorted whereas the coarsest material will be singled out

estimates of m2 tidal energy dissipation from topex poseidon altimeter data most of the tidal energy dissipation in the ocean occurs in shallow seas as has long been recognized however recent work has suggested that a significant fraction of the dissipation perhaps 1 tw or more occurs in the deep ocean this paper builds further evidence for that conclusion more than 6 years of data from the topex poseidon satellite altimeter are used to map the tidal dissipation rate throughout the world ocean the dissipation rate is estimated as a balance between the rate of working by tidal forces and the energy flux divergence computed using currents derived by least squares fitting of the altimeter data and the shallow water equations such calculations require dynamical assumptions in particular about the nature of dissipation to assess sensitivity of dissipation estimates to input assumptions a large suite of tidal inversions based on a wide range of drag parameterizations and employing both real and synthetic altimeter data are compared these experiments and monte carlo error fields from a generalized inverse model are used to establish error uncertainties for the dissipation estimates owing to the tight constraints on tidal elevation fields provided by the altimeter area integrals of the energy balance are remarkably insensitive to required dynamical assumptions tidal energy dissipation is estimated for all major shallow seas excluding individual polar seas and compared with previous model and data based estimates dissipation in the open ocean is significantly enhanced around major bathymetric features in a manner consistent with simple theories for the generation of baroclinic tides

accelerated ice discharge from the antarctic peninsula following the collapse of larsen b ice shelf acceleration exceeds 27 km 3 per year and ice is thinning at rates of tens of meters per year we attribute this abrupt evolution of the glaciers to the removal of the buttressing ice shelf the magnitude of the glacier changes illustrates the importance of ice shelves on ice sheet mass balance and contribution to sea level change index terms 1827 hydrology glaciology 1863 1863 hydrology snow and ice 1827 3349 meteorology and atmospheric dynamics polar meteorology 6924 radio science interferometry 9310 information related to geographic region antarctica citation rignot e g casassa p gogineni w krabill a rivera and r thomas 2004 accelerated ice discharge from the antarctic peninsula following the collapse of larsen b ice shelf geophys res lett 31 l18401 doi 10 1029 2004gl020697

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

estimates of m2 internal tide energy fluxes along the margin of northwestern pacific using topex poseidon altimeter data 1 topex poseidon altimeter data from october 1992 to june 2002 are used to calculate the energy flux of m2 internal tides along the margin of northwestern pacific this arc borderline of the pacific basin is characterized by sharp changes in bottom topography which constitute good boundary conditions for internal tidal energy concentration we extract baroclinic tides that yield energy transmission from temporarily coherent internal tide signals in the altimeter data we use the field measurements of current velocities in the south china sea scs to test the method the results show that satellite derived m2 tide components agree with the field data very well computation results indicate that the maximum energy flux of m2 internal tides 3 kw m 1 appears in the ryukyu trench the total energy flux of m2 internal tides along the margin of northwestern pacific is about 15gw

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

oceanography mixing with latitude measurements over a range of latitudes support a theory relating ocean turbulence to internal waves the upshot should be easier mapping of ocean mixing and eventually better climate models

time variable refraction of the internal tide at the hawaiian ridge abstractthe interaction of the dominant semidiurnal m2 internal tide with the large scale subtidal flow is examined in an ocean model by propagating the tide through an ensemble of background fields in a domain centered on the hawaiian ridge the background fields are taken from the simple ocean data assimilation soda ocean analysis at 2 month intervals from 1992 through 2001 tides are computed with the primitive equation z coordinate harmonic analysis of tides pez hat model by 14 day integrations using soda initial conditions and m2 tidal forcing variability of the tide is found to occur primarily as the result of propagation through the nonstationary background fields rather than via generation site variability generation of incoherent tidal variability is mapped and shown to occur mostly in association with waves generated at french frigate shoals scattering near the musicians seamounts to the north of the ridge the phase coherent internal tide loses energy at a domain average rate of 2 mw m

estimates of internal tide energy fluxes from topex poseidon altimetry central north pacific energy fluxes for first mode m2 internal tides are deduced throughout the central north pacific ocean from topex poseidon satellite altimeter data temporally coherent internal tide signals in the altimetry combined with climatological hydrographic data determine the tidal displacements pressures and currents at depth which yield power transmission rates for a variety of reasons the deduced rates should be considered lower bounds internal tides are found to emanate from several large bathymetric structures especially the hawaiian ridge where the integrated flux amounts to about 6 gigawatts internal tides are generated at the aleutian trench near 172 w and propagate southwards nearly 2000 km

high mixing rates in the abyssal southern ocean mixing of water masses from the deep ocean to the layers above can be estimated from considerations of continuity in the global ocean overturning circulation but averaged over ocean basins diffusivity has been observed to be too small to account for the global upward flux of water and high mixing intensities have only been found in the restricted areas close to sills and narrow gaps here we present observations from the scotia sea a deep ocean basin between the antarctic peninsula and the tip of south america showing a high intensity of mixing that is unprecedented over such a large area using a budget calculation over the whole basin we find a diffusivity of 39 plus minus 10 x 104 m2 s 1 averaged over an area of 7 x 105 km2 the scotia sea is a basin with a rough topography situated just east of the drake passage where the strong flow of the antarctic circumpolar current is constricted in width the high basin wide mixing intensity in this area of the southern ocean may help resolve the question of where the abyssal water masses are mixed towards the surface

time varying parametric subharmonic instability from repeat ctd surveys in the northwestern pacific ocean 1 time varying diapycnal diffusivity signals are estimated using the fine scale parameterization method from high resolution ctd data along three repeat sections in the northwestern pacific ocean indicative of the parametric subharmonic instability psi locally elevated diapycnal mixing is detected alongallthree sections within the 25 29 n band where bottom topography is relatively featureless due to their proximity to the semidiurnal internal tide generation sites the two sections along 137 e have a time mean diffusivity value 2 5 10 5 m2 s 1 in the 300 2 000 m upper ocean in contrast it is 1 2 10 5 m2 s 1along the 165 e section the time varying diffusivity along both sections is dominated by signals whose vertical structure resembles the local first dynamic normal mode profile at the 137 e site of 25 29 n the local spring neap modulated semidiurnal tidal current is found to lead the ctd derived diffusivity time series by 6 days and can alter the diffusivity level by 0 24 10 5 m2 s 1 similarly the concurrent surface wind work is found to modify the diffusivity level by 0 35 10 5 m2 s 1 the combined spring neap tide and wind work forcing explains 47 of the observed time varying diffusivity signals

latitudinal dependence of diapycnal diffusivity in the thermocline estimated using a finescale parameterization 1 the spatial distribution of diapycnal diffusivity in the thermocline over a large area in the interior of the north pacific is obtained by incorporating the finescale vertical shear of horizontal velocity measured by expendable current profilers into the empirical formula proposed by gregg 1989 it is clearly shown that diapycnal diffusivity in the north pacific strongly depends on the latitude for example the estimated diapycnal diffusivities near the hawaiian ridge and the izu ogasawara ridge exceed 10 4 m2 s 1 whereas those near the aleutian ridge and the emperor seamounts are of the order of 0 1 10 4 m2 s 1 even though the available semidiurnal internal tidal energy is similar among all of these prominent topographic features the observed results are consistent with the numerical prediction that the cascade of internal tidal energy down to dissipation scales is dominated by parametric subharmonic instability which is expected to occur only below 30 n