local geoelectrical models of the martian subsurface for shallow groundwater detection using sounding radars received 15 february 2002 revised 20 july 2002 accepted 28 august 2002 published 6 march 2003 1 low frequency sounding radars should be able to probe the martian subsurface layers down to varying depths depending on the geoelectrical properties of the sounded sites we present in this work four frequency dependent geoelectrical models of the martian subsurface in the 1 20 mhz frequency band based on laboratory electromagnetic characterization of martian soil analogues those models correspond to local martian sites that we considered to be of particular interest in the search for water using mainly the ground penetrating radar gpr instrument of the netlander mission results and discussion are also valid for both sounding experiments marsis and sharad the four models of the martian subsurface are designed to represent terrains where recent fluviallike features suggest the presence of near subsurface ground ice and probably liquid water we performed measurements on volcanic and sedimentary materials that may be present on these sites under the appropriate geophysical conditions that may exist in those terrains we then simulated the backscattered radar echo arising from each site in the 2 mhz frequency band using the finite difference time domain fdtd algorithm in order to evaluate the instrument performances to probe the subsurface stratigraphy of each site our results confirm that the near subsurface rich iron oxide mineralogy controls the instrument performances in terms of penetration depth and signal to noise ratio in the 2 mhz frequency band we finally discuss the geophysical and geoelectrical sounding conditions that could lead to an ambiguous detection of shallow subsurface water on mars for the netlander gpr index terms 3210 mathematical geophysics modeling 1794 history of geophysics instruments and techniques 5144 physical properties of rocks wave attenuation 5109 physical properties of rocks magnetic and electrical properties keywords mars hydrology gpr sounding simulation fdtd

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

ground penetrating radar and its use in sedimentology principles problems and progress abstract ground penetrating radar gpr also referred to as ground probing radar surface penetrating radar subsurface radar georadar or impulse radar is a noninvasive geophysical technique that detects electrical discontinuities in the shallow subsurface

variability of internal tides in the laurentian channel data from three sequential stations of thermistor chains and current meters along the main axis of the lower st lawrence estuary during the summer fall period in 1978 were analyzed to help understand generation and variability of the internal tide the lagrangian or direct tracing method has been developed to compute the displacements of internal tides which can overcome limitations of the eulerian method caused by the very small vertical temperature gradients internal tides of semidiurnal frequency were observed but diurnal tides were not in both the time domain and frequency band the surface diurnal tide behaves like a standing wave rather than a progressive one due to the nonlinear interaction of the internal tide generated locally near the sill with topography quarter diurnal and higher frequency oscillations were also generated the displacement of internal tides can reach 80 40 and 30 m during spring tides respectively at station 1 and at two downstream stations 3 and 5 the internal tides propagate seaward with attenuation downstream which mainly results from changing vertical stratification conditions but may also be partly attributed to wave breaking and turbulent mixing in the upper layer and bottom and lateral friction the amplitude ratio of s2 m2 is smaller 0 2 for the baroclinic current than for the barotropic current 0 24 at station 1 but becomes larger at stations 3 and 5 this implies the presence of the narrower response frequency band of the baroclinic tide to the barotropic forcing near the generation site the progressive semidiurnal and quarter diurnal internal tides were of the poincare type which implies a three dimensional structure the nutrient pumping due to the internal tides was confirmed to occur only near the generation region of the internal tide this convergence zone of higher primary productivity is considered to be equivalent to the rotor clouds in atmospheric mountain waves

the nutrient salinity and stable oxygen isotope composition of bering and chukchi seas waters in and near the bering strait seawater nutrient salinity and oxygen 18 data collected from 1990 to 1993 in the bering and chukchi seas were used to identify potential sources of nutrients and water masses that result in formation of the arctic ocean upper halocline and its associated nutrient maximum water matching the delta sup 18 o values of the arctic ocean upper halocline and containing sufficient or a nearly sufficient nutrient and salinity concentration was collected in subsurface waters in the summer in portions of the bering sea particularly the gulf of anadyr however nutrient concentrations significantly declined in this north flowing water over the shallow continental shelf before it reached the bering strait as a consequence of biological utilization and dilution with nutrient poor and oxygen 18 depleted fresh water therefore it does not appear likely that the flow of unaltered water through the bering strait in the summer plays a critical role in the formation of the arctic ocean upper halocline the role of other mechanisms for contributing pacific derived waters to the arctic ocean nutrient maximum is considered copyright 1997 american geophysical union

on the origin of the chemical properties of the arctic ocean halocline profiles of chemical constituents in seawater above the alpha ridge in the central arctic ocean obtained during the canadian expedition to study the alpha ridge cesar support a model in which the halocline is maintained by dense saline water produced on the continental shelves within the arctic ocean by the formation of sea ice it is argued that nutrient regeneration on the continental shelves largely accounts for the nutrient maximum that has been observed in the upper halocline over a wide region of the arctic ocean and that while the bering sea and north altantic can be recognized as origins of halocline water water masses from these regions undergo sufficient changes in their chemical properties within the arctic ocean significant that they no longer retain their identity in the halocline

three dimensional double ridge internal tide resonance in luzon strait abstractthe three dimensional 3d double ridge internal tide interference in the luzon strait in the south china sea is examined by comparing 3d and two dimensional 2d realistic simulations both the 3d simulations and observations indicate the presence of 3d first mode semi diurnal standing waves in the 3 6 km deep trench in the strait as in an earlier 2d study barotropic to baroclinic energy conversion flux divergence and dissipation are greatly enhanced when semidiurnal tides dominate relative to periods dominated by diurnal tides the resonance in the 3d simulation is several times stronger than in the 2d simulations for the central strait idealized experiments indicate that in addition to ridge height the resonance is only a function of separation distance and not of the along ridge length that is the enhanced resonance in 3d is not caused by 3d standing waves or basin modes instead the difference in resonance between the 2d and 3d simulations is attributed to the topographic blocking

pyroclastic flow deposits of the 1991 eruption of volcan de colima mexico the april 16 1991 eruption of volcan de colima represents a classical example of partial dome collapse with the generation of progressively longer runout merapi type pyroclastic flows that traveled up to 4 km along the el cordoban gullies east central and west the flows filled the gullies with block and ash flow deposits up to 10 m thick of which after 7 years of erosion only remnants remained in the el cordoban west and east gullies the el cordoban central gully however provided a well preserved and incised longitudinal section of the 1991 deposits the deposits were emplaced as proximal and distal facies separated by a change in slope angle from 30 to 20 the proximal facies consists of massive clast supported flow units up to 1 m thick with andesite blocks locally supported by a matrix of coarse ash and devoid of segregation structures or grading the distal facies consists of a massive matrix supported deposit up to 8 m thick which contains dispersed andesite blocks in a fine ash matrix in the distal facies a train of blocks marks flow unit upper boundaries and although sorting is poor some grading is present thin finely stratified or dune bedded layers of fine ash material are locally present above or below units of both facies sedimentologic parameters show that the size or fraction of large pyroclasts larger than 1 decreases from proximal to distal facies as the percentage of matrix 0 to 4 increases especially immediately beyond the break in slope we propose that the propagation of the colima pyroclastic flows is critically dependent on local slope angle the presence of erodible slope debris and the decrease in grain size with distance from the vent the progressive fining is probably caused by some combination of erosion clast breakup and deposition of larger pyroclasts and is itself influenced by the slope angle in the proximal region the flows moved as granular avalanches in which interacting grains ground each other and erosion occurred to produce an overriding dilute ash cloud the maximum runout distance of the avalanches was controlled by the angle of repose of the material and the volume and grain size of source and eroded material because the slope angle is close to the repose angle for this debris granular avalanches were not able to propagate far beyond the change in slope if however an avalanche had enough mass in finer grain size fractions at least part of the flow continued beyond the break in slope and across the volcano apron propagating in a turbulent state and depositing surge layers or in an otherwise settling modified state and depositing block and ash flow layers

3 d sedimentary architecture of a quaternary gravel delta sw germany implications for hydrostratigraphy abstract this paper investigates a quaternary gilbert type gravel delta that was formed in an ice marginal environment at the end of the last glacial period outcrop sediment core and ground penetrating radar gpr studies reveal the sedimentary facies and depositional architecture of the delta that comprises three major units 1 a 2 5 m thick gravelly topset with an erosional base formed by accretion of bedload sheets in a braided river 2 an up to 40 m thick steeply inclined 13 35 foreset dominated by gravelly lithofacies being the product of cohesionless debris flows and debris falls as well as gravity slides while sandy lithofacies was deposited by traction currents and 3 a 10 20 m thick sandy bottomset comprising low density turbidites syn to postdepositional deformation of parts of the bottomset deposits largely resulted from rapid deposition of overlying gravels and differential loading of the prograding foreset beds the development of the delta was most likely controlled by a high sediment supply and lake level fluctuations the overall coarsening upward succession reflects delta progradation and aggradation into a glaciolacustrine environment outcrop sedimentology served as a direct analogue in order to characterise the three dimensional sedimentary and hydraulic architecture of the nearby gravel delta aquifer applying a multidisciplinary approach sedimentological geophysical and hydrogeological data were integrated within the 3 d modelling package gocad earth decision sciences to develop high resolution 3 d aquifer models

toward a revised hazard assessment at merapi volcano central java abstract of 1 1 million people living on the flanks of the active merapi volcano 440 000 are at relatively high risk in areas prone to pyroclastic flows surges and lahars for the last two centuries the activity of merapi has alternated regularly between long periods of viscous lava dome extrusion and brief explosive episodes at 8 15 year intervals which generated dome collapse pyroclastic flows and destroyed part of the pre existing domes violent explosive episodes on an average recurrence of 26 54 years have generated pyroclastic flows surges tephra falls and subsequent lahars the 61 reported eruptions since the mid 1500s killed about 7000 people the current hazard zone map of merapi pardyanto et al 1978 portrays three areas termed forbidden zone first danger zone and second danger zone based on successively declining hazards revision of the hazard map is desirable because it lacks details necessary to outline hazard zones with accuracy in particular the valleys likely to be swept by lahars and excludes some areas likely to be devastated by pyroclastic gravity currents such as the 22 november 1994 surge in addition risk maps should be developed to incorporate social technical and economic factors of vulnerability eruptive hazard assessment at merapi is based on reconstructed eruptive history on eruptive behavior and scenarios and on existing models and preliminary numerical modeling firstly the reconstructed eruptive activity in particular for the past 7000 years and from historical accounts of eruptions helps to define the extent and recurrence frequency of the most hazardous phenomena newhall et al 2000 camus et al 2000 pyroclastic flows traveled as far as 9 15 km from the source pyroclastic surges swept the flanks as far as 9 20 km away from the vent thick tephra fall buried temples in the vicinity of yogyakarta 25 km to the south and subsequent lahars spilled down the radial valleys as far as 30 km to the west and south at least one large edifice collapse has occurred in the past 7000 years newhall et al 2000 camus et al 2000 secondly four eruption scenarios are portrayed as hazardous zones on two maps and derived from the past eruptive behavior of merapi and from the most affected areas in the past thirdly simple numerical simulation based on a digital elevation model a stereo pair of spot satellite images and one 2d orthoimage helps to simulate pyroclastic and lahar flowage on the flanks and in radial valley channels and to outline areas likely to be devastated three major threats are identified 1 a collapse of the summit dome in the short to mid term that can release large volume pyroclastic flows and high energy surges towards the south southwest sector of the volcano 2 an explosive eruption much larger than any since 1930 may sweep all the flanks of merapi at least once every century 3 a potential collapse of the summit area involving the fumarolic field of gendol and part of the southern flank which can contribute to moderate scale debris avalanches and debris flows

internal tides in the northwestern south china sea observed by pressure recording inverted echo sounders abstract this study presents it observations in the northwestern scs from five pressure recording inverted echo sounders piess the vertical round trip acoustic travel times that piess measures are proportional to the vertical thermocline displacements therefore piess can be used to monitor the 1st mode internal tides piess were deployed along a section between the continental shelf break in the north and xisha islands in the south measurements show that both diurnal and semidiurnal its were stronger on the northern and southern sides of the section than those in the middle their temporal variations were coherent with local surface tides which implies locally generated its may be important complex empirical orthogonal function analysis reveals a small phase difference the south leads the north by 70 across the section for diurnal its but a significant phase difference the north leads the south by 360 for semidiurnal its these observations indicate that the dominant diurnal its propagate across the section from east to west while the semidiurnal its propagate along the section from north to south a ray tracing model was utilized to demonstrate the impact of mesoscale circulation patterns on the propagation of diurnal its from the luzon strait to the pies sites the model explains the temporal it variations which were incoherent with local surface tides the result indicates that diurnal its in the northwestern scs can be affected by its propagating from the luzon strait while semidiurnal its are primarily generated locally from the continental shelf break in the north

a conceptual model for block and ash flow basal avalanche transport and deposition based on deposit architecture of 1998 and 1994 merapi flows the 1998 block and ash flow baf deposits on the western flanks of merapi were described both immediately following emplacement and after one and two wet seasons of erosion this afforded a unique combination of data on deposit morphology and internal structure from proximal to distal reaches the deposits of the basal avalanches from individual baf events were classified into three major and two minor facies in channelised reaches primarily resulting from effects of channel confinement and slope termination reaches were classified into three facies related to preevent topography the deposit facies architecture was interpreted to understand particle transport and deposition within the framework of granular flow systematics the transport model we propose for these basal avalanches involves unsteady flow conditions generated by pulses of collapse as the source and or by development of kinetic waves during the granular flow the coarsest clasts along with low density material migrated to the wave pulse fronts within these flows whereas in bulk flow grain dispersive pressures and kinetic sieving result in coarsest clasts being buoyed to the flow top with this tendency being greatest on higher slopes greater kinetic energy and with greater flow confinement maximising particle collisions deposition begins as the flow reaches near its full extent an initial pulse or flow wave freezes rapidly from its base upward and its rear forward as it looses kinetic energy and dispersive pressure such that an upper higher energy part of the flow is still able to move downstream over the frozen base later waves or pulses then accrete progressively horizontally upslope banking up onto or overtopping earlier deposited sediment hence the overall flow freezes from its front to its tail at termination reaches in unconfined areas the overflowing upper part of flow gradually deposits from its base upward resulting in a slightly tapering sheet formed deposit marked by a front made up of wood fragments and large boulders on sudden slope breaks in termination areas piling up of sediment occurs in flat reaches producing whaleback type forms as the flows rapidly lost competence one implication of this model is that each kinetic wave or flow pulse crest developed within the basal avalanche represents a portion of greater flow depth or stage height hence development of these crests control the ability of parts of the basal avalanche to escape from confined channels and generate unexpected hazards

propagation of internal tides generated near luzon strait observations from autonomous gliders 1 the vertical isopycnal displacements associated with internal waves generated by the barotropic tidal currents in the vicinity of luzon strait are estimated using measurements collected by autonomous underwater gliders nearly 23 000 profiles from seagliders and spray gliders collected during 29 different missions since 2007 are used to estimate the amplitude and phase of the linear semidiurnal and diurnal internal waves in this energetic region particularly in the previously poorly sampled area near the eastern ridge and on the pacific side of luzon strait the mean and variability of the internal wave field in the upper 1000 m of the water column are described the phase progression of internal waves as they propagate away from their generation sites is captured directly the glider based observations are used to map the mode 1 semidiurnal and diurnal internal wave fields providing the baroclinic energy flux over a roughly 600 km 800 km region based strictly on in situ observations

the 1984 nuee ardente deposits of merapi volcano central java indonesia stratigraphy textural characteristics and transport mechanisms for many centuries merapi volcano has generated hot avalanches of blocks lapilli and ashes derived from the destruction of partially solidified viscous lava domes merapi type nuees ardentes on 15 june 1984 at least four nuees ardentes came down the southwest slope of the merapi the first and the last being responsible for more than 99 of the deposits which are now exposed the first nuee ardente a merapi type nuee ardente was produced by the destruction of the dome travelled 7 km from the crater leaving a measured deposit 2 7 m thick 4 km from the crater near its upper depositional limit regularly increasing to a maximum measured thickness of 12 m at the front of the deposit the lower contact is sharp non erosive with pines still rooted in the underlying paleosol the deposit consists of 50 ash 33 lapilli and 17 blocks with two subpopulations one rosin and one normal and is finespoor with less than 4 of fine ash d finer than 4 the deposit displays reverse population grading of both vesiculated and massive clasts and of the maximum grain size the maximum size significantly increases regularly down current over most of the exposed length of unit 1 and bed thickness increases for the entire length of the deposit the deposit of the second nuee ardente is only 6 21 cm thick and of very limited lateral extent it is a normally graded coarse to fine ash with a finespoor base the third unit consists of fines poor normally graded coarse ash exposed in low amplitude 20 40 cm 12 m wavelength dunes the deposit of the fourth nuee ardente rests in sharp erosive contact on the underlying unit increasing in thickness down flow it consists of transitional coarse and fine grained strata 6 130 c cm thick dipping 5 10 down flow the deposit made up of two subpopulations one rosin and one normal is normally graded over the entire bed but coarsegrained strata are reversely graded the relative content of vesiculated clasts increases up bed in both strata types from 12 at the base to 40 at the top the characteristics of unit 1 suggest that it accumulated from a concentrated suspension of cohesionless solids exhibiting non newtonian behavior where dispersive pressure played an important role in the suspension of the clasts units 2 and 3 were probably deposited from dilute turbulent suspensions whereas the upper unit 4 is a classic example of deposition from a high density turbulent suspension leading to the formation of multiple traction carpets driven by the overlying lower density surge the horizontal distance travelled by a hot rock avalanche may be influenced by its transport mechanism debris flows are mobile on very low slopes as low as 1 whereas grain flows even density modified grain flows require relatively high slopes more than 6 at merapi to maintain their mobility if the present merapi dome were to collapse and produce a debris flow its present volume coupled with the minimal 1 5 km vertical drop could travel a distance ranging between 15 and 30 km however if transport were by grain flow mechanisms the mass could come to rest as it reaches a 5 10 slope

reappraisal of the 1982 eruptions of el chichon volcano chiapas mexico new data from proximal deposits additional data from proximal areas enable a reconstruction of the stratigraphy and the eruptive chronology of phases iii and iv of the 1982 eruption of el chichon volcano phase iii began on 4 april at 0135 gmt with a powerful hydromagmatic explosion that generated radially fast moving 100 ms 1 pyroclastic clouds that produced a surge deposit s1 due to the sudden reduction in the confining pressure the process continued by tapping of magma from a deeper source causing a new explosion the ejected juvenile material mixed with large amounts of fragmented dome and wall rock which were dispersed laterally in several pulses as lithic rich block and ash flow f1 partial evacuation of juvenile material from the magmatic system prompted the entrance of external water to generate a series of hydromagmatic explosions that dispersed moisture rich surge clouds and small volume block and ash flows iu up to distances of 3 km from the crater the eruption continued by further decompression of the magmatic system with the ensuing emission of smaller amounts of gas rich magma which with the strong erosion of the volcanic conduit formed a lithic rich plinian column that deposited fallout layer b associated with the widening of the vent an increase in the effective density of the uprising column took place causing its collapse block and ash flows arising from the column collapse traveled along valleys as a dense laminar flow f2 in some places flow regime changes due to topographic obstacles promoted transformation into a turbulent surge s2 which attained minimum velocities of approximately 77 ms 1 near the volcano the process continued with the formation of a new column on 4 april at 1135 gmt phase iv that emplaced fall deposit c and was followed by hydromagmatic explosions which produced pyroclastic surges s3

nuees ardentes of 22 november 1994 at merapi volcano java indonesia nuees ardentes associated with dome collapse on 22 november 1994 at merapi volcano traveled to the south southwest as far as 6 5 km and collectively accumulated roughly 2 5 3 million cubic meters of deposits the damaged area comprises 9 5 km2 and is covered by two nuee ardente facies a conventional merapi type valley fill block and ash flow facies and a pyroclastic surge facies the proximal deposits reflect the accumulation of dozens of nuees ardentes with many subsidiary flow units the distal deposits are more simply organized as only a few individual events reached to distances 3 5 km the stratigraphic relationships north of turgo hill indicate that the surge deposits are a facies of particularly mobile nuees ardentes that also deposited channeled block and ash flow facies they further suggest that the surge facies beyond the channel margins correlate laterally with a finer grained sublayer locally developed at the base of the block and ash flow facies eyewitness reports suggest that the emplacement of the block and ash flow facies in the distal part of the boyong river may have followed by a short time interval the destruction and deposition of the surge facies at turgo village the stratigraphy is in accord with the eyewitness reports the surge facies was emplaced by a dilute surge current detached from the same dome collapse nuee ardente that as a separate flow unit subsequently emplaced the distal block and ash deposit in the boyong valley the detachment occurred at higher elevations likely at or above the slope break at about 2000 m elevation this flow separation enabled the surge current to shortcut over the landscape and to emplace its deposit even as the block and ash flow continued its tortuous southward movement in the boyong channel dome collapse nuee ardente activity formed the bulk of the eruption which was accompanied by virtually no significant vertical summit explosive activity

the shaping of continental slopes by internal tides the angles of energy propagation of semidiurnal internal tides may determine the average gradient of continental slopes in ocean basins 2 to 4 degrees intensification of near bottom water velocities and bottom shear stresses caused by reflection of semi diurnal internal tides affects sedimentation patterns and bottom gradients as indicated by recent studies of continental slopes off northern california and new jersey estimates of bottom shear velocities caused by semi diurnal internal tides are high enough to inhibit deposition of fine grained sediment onto the slopes

remote sensing evidence for baroclinic tide origin of internal solitary waves in the northeastern south china sea 1 evidence for baroclinic tide origin of internal solitary waves isws in the northeastern south china sea is presented based on 116 internal wave packets observed in satellite images from 1995 to 2001 these wave packets can be divided into two types a single wave isw packet containing only one isw with without an oscillating tail and a multiple wave isw packet composed of a group of rank ordered isws all of the 22 single wave isw packets occur in the deep water zone it is suggested that the isws instead of being generated by the lee wave mechanism are developed by nonlinear steepening of the baroclinic tides which are produced by the strong tidal currents flowing over a ridge in luzon strait this suggestion is verified by an ers 2 sar image which records such an evolution process from a baroclinic tide to a single isw in its spatial domain

observations of parametric subharmonic instability of the diurnal internal tide in the south china sea 1 shipboard observations are presented that suggest the occurrence of parametric subharmonic instability psi of diurnal k1 and o1 internal tides at critical latitudes of 14 52 n and 13 44 n respectively in a transect spanning 12 5 18 n depth mean shear squared shows sharp peaks at 14 52 n elevated relative to that at 15 n by a factor of ten and at 13 44 n by a factor of 7 wind speed measured from the ship and quikscat scatterometer during and before the transect was 10 m s 1 at these latitudes eight hour time series about 1 6 of an inertial period of shear and isopycnal depth at 14 52 n are sufficient to associate the elevated shear with alternating clockwise rotating layers analogous to those observed at the m2 critical latitude of 28 8 n

longitudinal structure of pyroclastic flow deposits revealed by gpr survey at merapi volcano java indonesia abstract in 2006 merapi volcano indonesia erupted for a few months producing several block and ash flows reaching a maximum distance of 7 5 km from the main vent during the eruption we conducted a survey on those flow deposits in the gendol valley at kaliadem village about 4 5 km from the merapi submit using a ground penetrating radar gpr the upper deposit was studied in its distal reaches whereas the one below was studied in its medial reaches the field study was carried out with a commercial ramac gpr coupled with 100 mhz antennas and the data treatment conducted with reflex software from this survey we determined both deposits local 1 thickness reaching a maximum of 15 m and 2 internal architecture this last one is governed by long reflecting horizons extending over 20 to 30 m that delimit layers showing progradation patterns in their distal reaches within these layers we could also observe an internal architecture of still unknown origin the layers are interpreted as the result of the flow pulses that progressively deposited downstream ward by progradation however the interpretation of those gpr profiles is a bit hazardous because of the absence of outcrops and we can only proceed by analogy with other studies nevertheless despite numerous limitations gpr is a helpful tool to understand pyroclastic deposits structure when no visual observations are available

the proximal facies of the tosu pyroclastic flow deposit erupted from aso caldera japan the tosu pyroclastic flow deposit a low aspect ratio ignimbrite lari has widely distributed breccia facies around aso caldera japan the proximal facies 9 34 km away from the source consists of 3 different lithofacies from bottom to top a lithic enriched and fines depleted fd facies a lithic enriched li facies with an ash matrix and a fines and pumice enriched ni facies modes of emplacement of fd li and ni are interpreted as ground layer 2b lithic concentration zone and normal ignimbrite respectively these stratigraphic components in the tosu originated from the flow head fd and the flow body li and ni and were generated by a single column collapse event remarkably thick fd and li in contrast to thin ni suggest that due to high mobility most ash and punice fragments in the tosu were carried and deposited as ni in the distal area heavier components were selectively deposited as fd and li in the proximal area the rate of falloff of lithic clast size in the tosu shows an inflection at 20 km from the source in a survey of well documented pyroclastic flows the inflection distance of a lari is generally greater than that of a high aspect ratio ignimbrite so that the eruption of the former is probably more intense than the latter

energetics of barotropic and baroclinic tides in the monterey bay area abstracta detailed energy analysis of the barotropic and baroclinic m2 tides in the monterey bay area is performed the authors first derive a theoretical framework for analyzing internal tide energetics based on the complete form of the barotropic and baroclinic energy equations which include the full nonlinear and nonhydrostatic energy flux contributions as well as an improved evaluation of the available potential energy this approach is implemented in the stanford unstructured nonhydrostatic terrain following adaptive navier stokes simulator suntans results from three dimensional high resolution suntans simulations are analyzed to estimate the tidal energy partitioning among generation radiation and dissipation a 200 km 230 km domain including all typical topographic features in this region is used to represent the monterey bay area of the 152 mw energy lost from the barotropic tide approximately 133 mw 88 is converted into baroclinic energy through internal tide generation and 42 56

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

varieties of shallow temperature maximum waters in the western canadian basin of the arctic ocean the properties and spreading pathways of shallow temperature maximum waters stms in the western canadian basin are investigated using ctd and mooring data obtained in 1997 98 as part of the sheba surface heat budget of the arctic ocean drift experiment and available historical data three distinct varieties of stm are recognized on the basis of salinity range 1 surface mixed layer water smlw with s 32 psu these stms carry sufficient heat within the upper layers of the ocean to significantly affect the rates of ice cover and decay for example during the winter of 1997 98 anomalously warm stm 0 c originating from ecsw was observed to spread northwards along the northwind ridge and chukchi plateau where the maximum reduction of the ice covers was subsequently observed in late summer 1998 maslanik et al 1999 regional climate variability and ice cover in the western canadian basin are thus affected not only by anomalous atmospheric circulation patterns but also by the circulation of upper ocean water masses

crumbling of dacite dome lava and generation of pyroclastic flows at unzen volcano recent modelling of volcanic eruptions has shown that the efficiency of subsurface degassing of magmas determines whether magma erupts explosively or effuses quietly1 2 slow uprise of magma is often accompanied by effective degassing leading to the extrusion of lava flows and domes although lava dome extrusion is one of the less explosive modes of eruption it is often accompanied by explosive pyroclastic activities3 5 the 1991 eruption of unzen volcano provided an opportunity to observe at close range several types of small scale pyroclastic flow glowing avalanches originating from lava domes most of the pyroclastic flows are of merapi type caused by blocks falling from a collapsing dome others are of pelean type originating in an explosion from the side of a dome the lavas apparently show variable degrees of self explosivity we suggest that variable degrees of degassing of the magma produced a wide range of excess pore pressures in the extruded lava domes resulting in both merapi type and pelean type pyroclastic flows from the domes

surface manifestation of internal tides generated near hawaii analysis of topex poseidon satellite altimetry reveals short wavelength fluctuations in the ocean surface tide that are attributable to internal tides a significant fraction of the semidiurnal internal tide generated at the hawaiian ridge is evidently phase locked to the astronomical potential and can modulate the amplitude of the surface tide by 5 cm the internal tide is thus easily mapped along satellite groundtracks and it is found to be spatially coherent over great distances with waves propagating well over 1000 km from the hawaiian ridge before decaying below noise level both first and second baroclinic modes are observed in both the m 2 lunar and s 2 solar tides the high space time coherence is in sharp contrast to what is often inferred from current meter observations but it confirms recent speculations from an acoustic experiment north of hawaii

nutrient supply and biological response to wind induced mixing inertial motion internal waves and currents in the northern chukchi sea a fixed point observation station was set up in the northern chukchi sea during autumn 2013 and for about 2 weeks conductivity temperature depth ctd water samplings 6 h and microstructure turbulence measurements 2 to 3 times a day were performed this enabled us to estimate vertical nutrient fluxes and the impact of different types of turbulent mixing on biological activity there have been no such fixed point observations in this region where incoming low salinity water from the pacific ocean river water and sea ice meltwater promote a strong pycnocline halocline that stabilizes the water column previous studies have suggested that because of the strong pycnocline wind induced ocean mixing could not change the stratification to impact biological activity however the present study indicates that a combined effect of an uplifted pycnocline accompanied by wind induced inertial motion and turbulent mixing caused by intense gale force winds 10 m s 1 did result in increases in upward nutrient fluxes primary productivity and phytoplankton biomass particularly large phytoplankton such as diatoms convective mixing associated with internal waves around the pycnocline also increased the upward nutrient fluxes and might have an impact on biological activity there for diatom production at the fixed point observation station it was essential that silicate was supplied from a subsurface silicate maximum a new feature that we identified during autumn in the northern chukchi sea water mass distributions obtained from wide area observations suggest that the subsurface silicate maximum water was possibly derived from the ventilated halocline in the canada basin

generation of block and ash flows during the 1990 1995 eruption of unzen volcano japan processes generating block and ash flows by gravitational dome collapse merapi type pyroclastic flow were observed in detail during the 1990 1995 eruption of unzen volcano japan two different types were identified by analysis of video records and observations during helicopter flights most of the block and ash flows erupted during the 1991 1993 exogenous dome growth stage initially involved crack propagation due to cooling and flowage of the dome lava lobes the mass around the crack became unstable locally decreasing in tensile strength finally a slab separated from the lobe front fragmented progressively from the base to the top within a few seconds and became a block and ash flow rock falls immediately followed in response to local instability of the lobe front clasts in these rock falls fragmented and merged with the preceding flow in contrast block and ash flows during the endogenous dome growth stage in 1994 were generated due to local bulge of the dome unstable lava blocks collapsed and subsequently fragmented to produce block and ash flows

global m 2 internal tide and its seasonal variability from high resolution ocean circulation and tide modeling 1 the present study describes a model simulation where ocean tide dynamics are simulated simultaneously with the ocean circulation the model is forced by a lunisolar tidal forcing described by ephemerides and by daily climatological wind stress heat and fresh water fluxes the horizontal resolution is about 0 1 and thus the model implicitly resolves meso scale eddies and internal waves in this model simulation the global m2 barotropic to baroclinic tidal energy conversion amounts to 1 2 tw we show global maps of the surface signature of the m2 baroclinic tide and compare it with an estimate obtained from 19 years of satellite altimeter data further the simulated seasonality in the low mode internal tide field is presented and as an example the physical mechanisms causing the non stationarity of the internal tide generated in luzon strait are discussed in general this study reveals the impact of inter annual changes of the solar radiative forcing and wind forced ocean circulation on the generation and propagation of the low mode internal tides the model is able to simulate non stationary signals in the internal tide field on global scales which have important implications for future satellite altimeter missions citation muller m j y cherniawsky m g g foreman and j s von storch 2012 global m2 internal tide and its seasonal variability from highresolution ocean circulation and tide modeling geophys res lett 39 l19607 doi 10 1029 2012gl053320

historical eruptions of merapi volcano central java indonesia 1768 1998 abstract information on merapi eruptive activity is scattered and much is remotely located a concise and well documented summary of this activity has been long needed to assist researchers and hazard mitigation efforts and the aim of this paper is to synthesize information from the mid 1700s to the present a descriptive chronology is given with an abbreviated chronology in a table that summarizes events by year assigns preliminary volcanic explosivity index vei ratings and hartmann classifications and provides key references the history of volcano monitoring is also outlined the study reveals that a major difference in eruption style exists between the twentieth and nineteenth centuries although the periodicity between larger events seems about the same during the twentieth century activity has comprised mainly the effusive growth of viscous lava domes and lava tongues with occasional gravitational collapses of parts of oversteepened domes to produce the nuees ardentes commonly defined as merapi type in the 1800s however explosive eruptions of relatively large size occurred to vei 4 and some associated fountain collapse nuees ardentes were larger and farther reaching than any produced in the twentieth century these events may also be regarded as typical eruptions for merapi the nineteenth century activity is consistent with the long term pattern of one relatively large event every one or two centuries based on the long term eruptive record deduced by others from volcanic stratigraphy it is uncertain whether or not a recurrence time model continues to apply to merapi but if so merapi could soon be due for another large event and its occurrence with only modest or inadequately appreciated precursors could lead to a disaster unprecedented in merapi s history because the area around the volcano is now much more densely populated

model estimates of m2 internal tide energetics at the hawaiian ridge 1 a primitive equation model is used to examine the structure and energetics of m 2 internal tides generated at the hawaiian ridge recent estimates based on altimeter data suggest that 20 gw of barotropic tidal dissipation occurs at the ridge with conversion to internal tides believed to be the dominant dissipation mechanism the model simulates an internal tide that accounts for 9 7 gw of radiated energy away from the ridge in the northeast and southwest directions the strongest generation occurs at three sites where enhanced barotropic currents flow across elongated topographic features the depth integrated baroclinic energy flux and energy densities at these sites are on the order of 10 4 w m 1 and 10 4 j m 2 respectively a modal decomposition indicates that 62 of the outgoing energy flux is accounted for by the first internal mode 15 is accounted for by the second mode and less than 5 is accounted for by each subsequent higher mode the tidal dissipation due to bottom friction along the ridge is estimated to be 0 1 gw the level of turbulent dissipation near the ridge owing to tidal energy conversion remains to be determined to assess fully the barotropic baroclinic energy budget

bomb rich basaltic pyroclastic flow deposit from nakadake aso volcano southwestern japan abstract a bomb rich basaltic pyroclastic flow deposit the izumikawa pyroclastic flow deposit occurs at the northeastern foot of nakadake volcano which is the only active central cone of aso caldera southwestern japan the pyroclastic flow deposit covers a fan shaped area of about 1 9 km2 and the bulk volume is estimated at 9 4 106 m3 the deposit is poorly sorted and consists of subangular faceted clasts and spherical cauliflower bombs set in a sandy non cohesive matrix the deposit forms two different facies a black reversely graded lower unit and a reddish gray reversely graded upper unit the cauliflower bombs which have slightly vesiculated crusts 1 0 1 5 cm thick and denser interiors are more abundant in the lower unit than in the upper unit the presence of cauliflower bombs suggests that the izumikawa pyroclastic flow was generated by an explosion at the source lava lake or conduit which was filled with mixture of solidified and molten lavas we propose the term bomb and ash flow deposit to describe this type of deposit the age of the izumikawa pyroclastic flow deposit was estimated at ca 19 cal ka based on a 14c age obtained from charred wood fragments in the deposit although all recent activity of nakadake has been ash eruptions strombolian eruptions and phreatomagmatic explosions the izumikawa pyroclastic flow deposit underscores the hazard of bomb rich pyroclastic flows that rush down the flanks of the volcano

the formation and fate of internal waves in the south china sea internal oceanic waves are subsurface gravity waves that can be enormous and travel thousands of kilometres before breaking but they are difficult to study here observations of such waves in the south china sea reveal their formation mechanism extreme turbulence relationship to the kuroshio current and energy budget internal waves are the underwater version of more familiar surface waves they can be enormous and travel thousands of kilometres before breaking the south china sea is known to be home to the largest internal waves in the world s oceans but their size generation mechanisms and role in the regional energy budget are unknown matthew alford and colleagues now present the results from the iwise observational campaign and reveal that internal waves more than 200 metres high break in the south china sea and create turbulence that is orders of magnitude larger than in the open ocean and that wave formation is influenced by the kuroshio current these results now allow for a complete energy budget of the south china sea and for a more accurate incorporation of internal waves into climate models internal gravity waves the subsurface analogue of the familiar surface gravity waves that break on beaches are ubiquitous in the ocean because of their strong vertical and horizontal currents and the turbulent mixing caused by their breaking they affect a panoply of ocean processes such as the supply of nutrients for photosynthesis1 sediment and pollutant transport2 and acoustic transmission3 they also pose hazards for man made structures in the ocean4 generated primarily by the wind and the tides internal waves can travel thousands of kilometres from their sources before breaking5 making it challenging to observe them and to include them in numerical climate models which are sensitive to their effects6 7 for over a decade studies8 9 10 11 have targeted the south china sea where the oceans most powerful known internal waves are generated in the luzon strait and steepen dramatically as they propagate west confusion has persisted regarding their mechanism of generation variability and energy budget however owing to the lack of in situ data from the luzon strait where extreme flow conditions make measurements difficult here we use new observations and numerical models to 1 show that the waves begin as sinusoidal disturbances rather than arising from sharp hydraulic phenomena 2 reveal the existence of 200 metre high breaking internal waves in the region of generation that give rise to turbulence levels 10 000 times that in the open ocean 3 determine that the kuroshio western boundary current noticeably refracts the internal wave field emanating from the luzon strait and 4 demonstrate a factor of two agreement between modelled and observed energy fluxes which allows us to produce an observationally supported energy budget of the region together these findings give a cradle to grave picture of internal waves on a basin scale which will support further improvements of their representation in numerical climate predictions

turbulent dissipation on the margins of the south china sea 1 measurements of turbulence along the continental slope shelfbreak and shelf of the northern south china sea are presented from a 10 day measurement program during april 2005 the shelfbreak region was characterized by a deep stratification that appears to be typical of the late winter monsoon this appears to shift the wave field at the shelfbreak from the soliton like depression anomalies observed in previous years to a more complex wave field supporting high frequency waves in both upper and lower depth intervals of the water column on average 30 of the depth integrated turbulent dissipation occurs within 10 m of the bottom where baroclinic energy is preferentially dissipated dissipation levels reaching 50 mw m2 are an order of magnitude larger than those attainable through frictional dissipation of the local barotropic tide and an order of magnitude larger than levels typical in the open ocean

borobudur a basin under volcanic influence 361 000 years bp to present abstract borobudur basin is located in central java indonesia 30 km to the north of yogyakarta city the basin is famous for its unesco world heritage temple and for one of the world s most active volcanoes merapi located to the east of borobudur basin merapi is one of the three andesitic volcanoes that surround the basin merapi merbabu and sumbing volcanoes therefore volcanic activity has strongly influenced the evolution of borobudur basin the object of this contribution is to present the evolution of borobudur basin over the last 161 000 years in the light of volcanic influence the methodology and tools developed for this research span over different areas of expertise from geochemistry geology and geomorphology to remote sensing gis and archeology results highlight the following points 1 two major volcanic events deposited volcaniclastic materials up to tens of meters thick 119 000 years bp and 31 000 years bp in the southern part of the borobudur basin the second volcanic event could correspond to the collapse of the older ancient merapi camus et al 2000 or proto merapi stage newhall et al 2000 2 there is no trace in the borobudur basin of a large debris avalanche 3 there are several generations of paleolakes in the borobudur basin the latest one has shrunk until historical times corroborating the theory of newhall et al 2000 and murwanto et al 2004 that borobudur temple was standing by a water body most of these paleolakes were impounded following volcanic events paleolakes most probably originated from the blockage of the hydrographic network by volcanic material 4 borobudur temple was never buried under volcanic material during historic times

the breaking and scattering of the internal tide on a continental slope abstracta strong internal tide is generated in the luzon strait that radiates westward to impact the continental shelf of the south china sea mooring data in 1500 m depth on the continental slope show a fortnightly averaged incoming tidal flux of 12 kw m 1 and a mooring on a broad plateau on the slope finds a similar flux as an upper bound of this 5 5 kw m 1 is in the diurnal tide and 3 5 kw m 1 is in the semidiurnal tide with the remainder in higher frequency motions turbulence dissipation may be as high as 3 kw m 1 local generation is estimated from a linear model to be less than 1 kw m 1 the continental slope is supercritical with respect to the diurnal tide implying that there may be significant back reflection into the basin comparing the low mode energy of a horizontal standing wave at the mooring to the energy flux indicates that perhaps one third of the incoming diurnal tidal energy is reflected conversely the slope is subcritical with respect to the semidiurnal tide and the observed

energy flux and dissipation in luzon strait two tales of two ridges abstractinternal tide generation propagation and dissipation are investigated in luzon strait a system of two quasi parallel ridges situated between taiwan and the philippines two profiling moorings deployed for about 20 days and a set of nineteen 36 h lowered adcp ctd time series stations allowed separate measurement of diurnal and semidiurnal internal tide signals measurements were concentrated on a northern line where the ridge spacing was approximately equal to the mode 1 wavelength for semidiurnal motions and a southern line where the spacing was approximately two thirds that the authors contrast the two sites to emphasize the potential importance of resonance between generation sites throughout luzon strait baroclinic energy energy fluxes and turbulent dissipation were some of the strongest ever measured peak to peak baroclinic velocity and vertical displacements often exceeded 2 m s 1 and 300 m respectively energy fluxes exceeding 60 kw m 1 were measured at spring tide at the wester

freshwater budget of the canada basin arctic ocean from salinity δ18o and nutrients 1 the contribution of freshwater components e g meteoric sea ice and pacific water in the canada basin is quantified using salinity 18o and nutrient data collected in 2003 and 2004 the penetration depth of sea ice meltwater is limited to the upper 30 m and brine rejected during sea ice formation is observed from 30 to 250 m depth the fraction of meteoric water is high in the upper 50 m and decreases with depth pacific water entering via bering strait is the main source of freshwater below 50 m depth bering strait throughflow which transports pacific water with salinity 32 5 together with meteoric water supplied upstream of the bering strait contributes up to 75 of freshwater input 3200 km3 a 1 to the canada basin the mean residence time of pacific water in the canada basin is estimated to be 11 years precipitation and river runoff from both north american and eurasian continents add 800 km3 a 1 and sea ice formation removes 900 km3 a 1 0 6 m a 1 of fresh water the export of ice and liquid fresh water from the canada basin contributes 40 of the freshwater flux from the arctic ocean to the north atlantic ocean

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

large scale internal structure of the sanbongi fan towada volcano japan putting the theory to the test using gpr on volcaniclastic deposits abstract the towada caldera volcano is located between the prefectures of aomori and akita northeast honshu island japan the caldera today filled by a lake has produced 15 000 years ago a complex eruption emplacing an ignimbrite topped by the lake outburst flood deposit through which the present oirase river erodes this flood deposit has shaped the geomorphologic feature named sanbongi fan on which towada city extends this flood event hypothesis is mainly based on sedimentological and geomorphological evidences of floods mainly from outcrops retrieved from the sanbongi fan area because of the lack of extended outcrops typical of the japanese environment the present paper has therefore put the theory to the test using gpr ground penetrating radar radargram extending along a 640 m length the gpr used for the survey was a pulse ekko pro with 50 mhz antennas and the software reflex was used to process the data the radargrams have displayed a sole unit which the gpr could not penetrate it can be interpreted as the ignimbrite on top of this deposit a series of subhorizontal layers with the alternation between a backset and a foreset extends between 5 m and 3 m depth above 3 m the units are regular and subhorizontal the deposit is also characterized by the extensive presence of boulders which are located along three bands 1 on top of the ignimbrite 2 in the units deposited by the outburst flood between 3 and 5 m depths 3 and in the units close to the surface although part of these punctual elements are most certainly anthropogenic compared with the outcrops the present research confirms that the material located above the ignimbrite material have been deposited by the outburst flood creating large sheet patterns which have transported boulders these sheets display backset and foreset patterns depending on the position of the deposit indicating flow pulsation or surges under a high energy flow condition

boundary crossing and non linear theory in earth system sciences a proof of concept based on tsunami and post eruption scenarios on java island indonesia although volcanic eruptions are well known to be the trigger of some weather and climatic changes land cover changes by pyroclastic flows and lahars do not get this recognition neither do major hazards such as tsunami these two earth processes are even lesser considered as being able to modify other earth processes they are not directly connected to such as landslides or river discharge in non connected basins more than a hundred kilometres away in this contribution the authors argue that these ideas are mainly driven by the process of being educated in a single academic discipline and once put to the test interactions and retroactions between earth processes and atmospheric processes are far more reaching than commonly thought for this study the site of java island indonesia was chosen to conduct 1 an analysis of a major tsunami impact in the same area as the 2006 java tsunami and 2 an analysis of the post eruption impacts of merapi volcano after a major eruption excluding any ejecta in the atmosphere for the sake of the demonstration the atmospheric feedback simulations were conducted using the regional climate model regcm 4 with calibration from weather stations in java island as a result both simulations have proven that large scale deposits of pyroclasts not introducing the ejectas sent in the atmosphere and tsunamis can have outstanding impacts on the atmospheric situation and the bio geomorphologic evolution of the landscape in the following weeks to months interestingly enough these impacts are not limited to the area impacted by the earth process and the effect are not linear in time as they work following thresholds these rainfalls tele impacts are important enough to in turn modify earth surface processes in areas remote from the original phenomenon this system acts in the same manner as a famous butterfly in africa that could trigger a hurricane on the other side of the atlantic ocean copyright 2012 john wiley sons ltd

denitrification in continental shelf sediments has major impact on the oceanic nitrogen budget denitrification rates in sediments within the oxygen deficient waters off mexico and from the gulf of maine were investigated on the basis of interstitial nutrient profiles nitrate fluxes into the sediments were calculated from gradients across the sediment water interface and vertical molecular diffusion coefficients and averaged 0 151 mexico and 0 0920 gulf of maine pmol no 3 cm 2 s 1 these are minimum values since these gradients may have been underestimated in the gulf of maine bottom water irrigation by macrobenthos increases the nitrate supply well above this estimate in addition only 15 22 of the expected ammonium is present in gulf of maine sediments perhaps because of removal by a rapid coupling of nitrification with denitrification this large apparent loss of the regenerated ammonium appears to be ubiquitous in shelf sediments with oxygenated bottom water the global denitrification rate in continental shelf sediments was reassessed to be 50 tg n yr 1 1 tg 1012 g demonstrating that sediments are an important sink for oceanic nitrogen globally current nitrogen losses from the oceans may exceed inputs by 60 90 tg n yr 1 over the glacial interglacial cycle the global sedimentary denitrification rate probably varied commensurately with the changing continental shelf area an oscillating oceanic nitrogen budget over these time scales could occur given the sequence of 1 scouring and dumping of terrestrial nitrogen into the oceans during glacial advance 2 removal of oceanic combined nitrogen to the atmosphere by denitrification following glacial retreat and 3 reincorporation of this n into terrestrial biomass during the interglacial period

characterization of volcanic deposits with ground penetrating radar field based studies of surficial volcanic deposits are commonly complicated by a combination of poor exposure and rapid lateral variations controlled by unknown paleotopography the potential of ground penetrating radar gpr as an aid to volcanological studies is shown using data collected from traverses over four well exposed recent volcanic deposits in western canada the deposits comprise a pumice airfall deposit 3 4 m thick a basalt lava flow 3 6 m thick a pyroclastic flow deposit 15 m thick and an internally stratified pumice talus deposit 60 m thick results show that gpr is effective in delineating major stratigraphic contacts and hence can be used to map unexposed deposits different volcanic deposits also exhibit different radar stratigraphic character suggesting that deposit type may be determined from radar images in addition large blocks within the pyroclastic deposits are detected as distinctive point diffractor patterns in the profiles showing that the technique has potential for providing important grain size information in coarse poorly sorted deposits laboratory measurements of dielectric constant k are reported for samples of the main rock types and are compared with values of k for the bulk deposit as inferred from the field data the laboratory values differ significantly from the field values of k these results suggest that the effectiveness of gpr at any site can be substantially improved by initial calibration of well exposed locations

gpr derived architecture of a lahar generated fan at cotopaxi volcano ecuador the internal geometry of volcaniclastic fans produced by aggradation during lahar events is difficult to examine in modern settings because of the frequent lack of three dimensional exposures this makes it challenging to i reconstruct the spatial and temporal evolution of such fans and ii interpret observed facies stratigraphy in the context of lahar flow dynamics from proximal to distal fan reaches this research therefore presents the results of a ground penetrating radar gpr survey of the rumipamba fan at the mouth of the burrohuaycu quebrada on the southwestern flank of cotopaxi volcano a survey grid consisting of 50 individual gpr profiles representing a total length of 19 4 km was constructed covering most of the 4 km2 large fan surface all gpr profiles were collected using a pulseekko 100 with a 400 v transmitter fan sediments consist of sandy and gravelly lahar deposits alternating with volcanic fallout including ash and pumice lapilli at times reworked by fluvial processes deposits could be ground truthed to a depth of 3 m whereas gpr penetration depth reaches 15 m data interpretation was based on classification into 15 distinct radar facies characterized by the nature of their bounding surfaces and or internal features cross referenced where possible with shallow exposures three main facies were identified parallel irregular and clinoform erosional contacts were distinguished from aggradational ones vertical channel fill and lateral accretion flow parallel versus flow transverse and proximal distal variations in deposit architecture were featured the results of this study confirm the existence of two major channel systems in the northern and southern extremities of the fan and the more recent formation of a smaller central fan channel system deposit architecture is complex and facies chronologies illustrate that lahars have affected the entire survey area

variability of internal tides and near inertial waves on the continental slope of the northwestern south china sea structure and variability of internal tides it and near inertial waves niw on the continental slope of the northwestern south china sea were investigated based on 9 month moored current observations from autumn to early summer in 2008 and 2009 the diurnal it kinetic energy dominant over that of semidiurnal tides is found to exhibit apparent seasonal variability strongest in summer and weakest in winter whereas the semidiurnal variance remained nearly uniform throughout the observation period moreover the diurnal it were more coherent i e phase locked to the astronomical forcing than the semidiurnal constituents coherent diurnal variance accounts for about 40 of diurnal motions but semidiurnal tides contain a much smaller fraction 10 of coherent motions further analysis demonstrates that the diurnal it are dominated by the first mode whereas the semidiurnal tides show a variable multimodal structure the second mode is dominant in summer and comparable to the first mode in spring and autumn but the first mode predominates in winter multimodal semidiurnal it are more influenced by varying stratification structures and background currents and thus exhibit highly incoherent and intermittent behavior which may wash out seasonal variability during their long propagation from the generation source the observed niw are seasonally independent and comparable to the semidiurnal motions during the passage of typhoon hagupit however the niw became the most energetic component of the inertia gravity waveband motions niw energy and shear were significantly enhanced and exceeded tidal counterparts by a factor of 2 to 3 in the upper layer

sources of dissolved inorganic carbon to the canada basin halocline a multitracer study we examine the dissolved inorganic carbon maximum in the canada basin halocline using a suite of geochemical tracers to gain insight into the factors that contribute to the persistence of this feature hydrographic and geochemical samples were collected in the upper 500 m of the southwestern canada basin water column in the summer of 2008 and fall of 2009 these observations were used to identify conservative and nonconservative processes that contribute dissolved inorganic carbon to halocline source waters including shelf sediment organic matter remineralization air sea gas exchange and sea ice brine export our results indicate that the remineralization of organic matter that occurs along the bering and chukchi sea shelves is the overwhelming contributor of dissolved inorganic carbon to pacific winter water that occupies the middle halocline in the southwestern canada basin nonconservative contributions from air sea exchange and sea ice brine are not significant the broad salinity range associated with the dic maximum compared to the narrow salinity range of the nutrient maximum is due to mixing between pacific and atlantic water and not abiotic addition of dic

significant dissipation of tidal energy in the deep ocean inferred from satellite altimeter data how and where the ocean tides dissipate their energy are long standing questions1 that have consequences ranging from the history of the moon2 to the mixing of the oceans3 historically the principal sink of tidal energy has been thought to be bottom friction in shallow seas4 5 there has long been suggestive evidence6 7 however that tidal dissipation also occurs in the open ocean through the scattering by ocean bottom topography of surface tides into internal waves but estimates of the magnitude of this possible sink have varied widely3 8 9 10 11 here we use satellite altimeter data from topex poseidon to map empirically the tidal energy dissipation we show that approximately 1012 watts that is 1 tw representing 25 30 of the total dissipation occurs in the deep ocean generally near areas of rough topography of the estimated 2 tw of mixing energy required to maintain the large scale thermohaline circulation of the ocean12 one half could therefore be provided by the tides with the other half coming from action13 on the surface of the ocean

subsurface structure of a maar diatreme and associated tuff ring from a high resolution geophysical survey rattlesnake crater arizona abstract geophysical survey techniques including gravity magnetics and ground penetrating radar were utilized to study the diatreme and tuff ring at rattlesnake crater a maar in the san francisco volcanic field of northern arizona significant magnetic anomalies 1600 nt and a positive gravity anomaly 1 4 mgal are associated with the maar joint modeling of magnetic and gravity data indicate that the diatreme that underlies rattlesnake crater has volume of 0 8 1 km 3 and extends to at least 800 m depth the modeled diatreme comprises at least two zones of variable density and magnetization including a low density highly magnetized unit near the center of the diatreme interpreted to be a pyroclastic unit emplaced at sufficiently high temperature and containing sufficient juvenile fraction to acquire thermal remanent magnetization magnetic anomalies and ground penetrating radar gpr imaging demonstrate that the bedded pyroclastic deposits of the tuff ring also carry high magnetization likely produced by energetic emplacement of hot pyroclastic density currents gpr profiles on the tuff ring reveal long 100 m wavelength undulations in bedding planes elsewhere comparable bedforms have been interpreted as base surge deposits inflated by air entrainment from eruption column collapse interpretation of these geophysical data suggests that rattlesnake crater produced highly energetic phreatomagmatic activity that gave way to less explosive activity as the eruption progressed the positive gravity anomaly associated with the maar crater is interpreted to be caused by coherent bodies within the diatreme and possibly lava ponding on the crater floor these dense magnetized bodies have excess mass of 2 4 10 10 kg and occupy approximately 5 of the diatreme by volume magnetic anomalies on the crater floor are elongate nw se suggesting that the eruption may have been triggered by the interaction of ascending magma with water in fractures of this orientation gpr imaging of the tuff ring also suggests that substantial land slip may have occurred on the western rim perhaps causing part of the tuff ring to collapse into the crater strong radar reflections indicative of well developed weathering horizons are present as well the techniques employed at rattlesnake crater demonstrate the value of combining multiple geophysical techniques in areas where exposures are limited and invasive exploration is not an option

ground penetrating radar for high resolution mapping of soil and rock stratigraphy ground penetrating radar is a technique which offers a new way of viewing shallow soil and rock conditions the need to better understanding overburden conditions for activities such as geochemical sampling geotechnical investigations and placer exploration as well as the factors controlling groundwater flow has generated an increasing demand for techniques which can image the subsurface with higher resolution than previously possible the areas of application for ground penetrating radar are diverse the method has been used successfully to map ice thickness water depth in lakes bedrock depth soil stratigraphy and water table depth it is also used to delineate rock fabric detect voids and identify karst features the effective application of the radar for the high resolution definition of soil stratigraphy and fractures in bedrock is highlighted the basic principles and practices involved in acquiring high quality radar data in the field are illustrated by selected case histories one example demonstrates how radar has been used to map the bedrock and delineate soil horizons to a depth of more than 20 m two case histories show how radar has been used to map fractures and changes of rock type to 40 m range from inside a mine another case history demonstrates how radar has also been used to detect and map the extent of groundwater contamination the corroboration of the radar results by borehole investigations demonstrates the power and utility of the high resolution radar method as an aid for interpolation and extrapolation of the information obtained with conventional coring programmes with the advent of new instrumentation and field procedures the routine application of the radar method is becoming economically viable and the method will see expanded use in the future

numerical treatment of cross shelf open boundaries in a barotropic coastal ocean model abstract using a barotropic coastal ocean model with a straight coastline and uniform cross shelf bottom slope seven different cross shelf open boundary conditions four of which are applied in either implicit or explicit form are compared in three numerical experiments 1 a mound of water is allowed to collapse and radiate waves toward the open boundaries 2 a uniform alongshelf wind stress is applied at zero time over the entire shelf and held constant for the duration of the experiment 3 a uniform cross shelf wind stress is applied at zero time over the entire shelf and held constant for the duration of the experiment the boundary condition which is most transparent to waves consists of a sponge at the outer edge of the model domain with an orlanski radiation condition at the outer edge of the sponge several open boundary conditions perform adequately in the wind stress experiments but the orlanski radiation condition alone without a sponge appears to give the best total performance of thes

use of ammonium and other nitrogen tracers to investigate the spreading of shelf waters in the western arctic halocline 1 the contribution of nutrient regeneration in summer to the nutrient maximum associated with bering sea winter water bsww is estimated from the ammonium data which was obtained in the outer shelf region of the chukchi sea for the first time by the r v mirai in 2002 the contribution rate reaches 20 30 which is larger than the rate studied earlier inside the chukchi shelf such bsww influenced by the regeneration spreads to the chukchi shelf slope up to the isobath of 3000 m however was not found in the canada basin the ammonium and a nitrogen deficit are also useful tracers to study the spreading of shelf waters that are less saline than bsww in the canada basin a small amount of ammonium 2 m was observed east of the northwind ridge this small amount of ammonium would be associated with the spreading of eastern chukchi summer water via the barrow canyon around the chukchi borderland a prominent nitrogen deficit layer was found it would be accompanied by western chukchi summer water via the hope valley herald valley channel the water flows into the chukchi abyssal plain and then spreads eastward to the west of the northwind ridge with the decrease of nitrogen deficit signal

merapi volcano java indonesia and merapi type nuee ardente a particular nuee ardente type merapi type avalanche nuee has been defined at the merapi volcano because of its prominent role in the recent activity of the volcano gravity plays a significant role during the eruption

transverse architecture of lahar terraces inferred from radargrams preliminary results from semeru volcano indonesia semeru volcano is the highest mountain of java indonesia and a vulcanian explosion occurs every 15 minutes on average since 1967 thus a constantly renewed stock of material and the heavy monsoon rainfall 3700 mm yr 1 at 1500 m above sea level a s l provide a perfect setting for the study of lahars and their deposits hence we examined the architecture of lahars terraces 9 5 km from the summit in the curah lengkong valley we first used ground penetrating radar gpr over vertical exposures of the lahars cut bank terraces this allowed us to better understand transversal radargrams across terraces which are not visually accessible in the field preliminary results from a single radargram are very instructive since 1 they prove that the lateral architecture does not correspond to that observed from banks only 2 we could observe the presence of lenses and stratigraphic discontinuities 3 the setting of the various units can also help reconstruct deposition processes and the chronology of different units in order to finalize these preliminary results we however need to perform multiple gpr radargrams and provide a complete set of results copyright 2010 john wiley sons ltd

long range propagation and associated variability of internal tides in the south china sea the variability of internal tides during their generation and long range propagation in the south china sea scs is investigated by driving a high resolution numerical model the present study clarifies the notably different processes of generation propagation and dissipation between diurnal and semidiurnal internal tides internal tides in the scs originate from multiple source sites among which the luzon strait is dominant and contributes approximately 90 and 74 of the baroclinic energy for m2 and k1 respectively to the west of the luzon strait local generation of k1 internal tides inside the scs is more energetic than the m2 tides diurnal and semidiurnal internal tides from the luzon strait radiate into the scs in a north south asymmetry but with different patterns because of the complex two ridge system the tidal beams can travel across the deep basin and finally arrive at the vietnam coast and nansha island more than 1000 1500 km away during propagation m2 internal tides maintain a southwestward direction whereas k1 exhibit complicated wave fields because of the superposition of waves from local sources and island scattering effects after significant dissipation within the luzon strait the remaining energy travels into the scs and reduces by more than 90 over a distance of 1000 km inside the scs the k1 internal tides with long crests and flat beam angles are more influenced by seafloor topographical features and thus undergo apparent dissipation along the entire path whereas the prominent dissipation of m2 internal tides only occurs after their arrival at zhongsha island this article is protected by copyright all rights reserved

block and ash flow deposition a conceptual model from a gpr survey on pyroclastic flow deposits at merapi volcano indonesia in 2006 a series of block and ash flows swept the southwestern and southern flanks of merapi volcano java indonesia in the k gendol valley near the village of kaliadem we conducted a gpr survey on the most distal lobe of the june 14th second block and ash flow deposit for this 100 m long transect we used a commercial gpr ramac mounted with 100 mhz antennas we measured the topography with a synchronized gps and a laser rangefinder back at the laboratory we processed the dataset with the software reflex data of the subsurface reveals a series of layers separated by strong reflective horizons these horizons are the manifestation of intercalations of fine materials in between more coarse layers the architecture of these layers presents progradation retrogradation and aggradation patterns that we relate to the block and ash flow deposition process based on these observations we proposed a relative chronology of the deposition and a simple conceptual model of the deposition the model show that the block and ash flow can deposit either long close to horizontal single layers or shorter layers that imbricate themselves following different patterns progradation retrogradation or aggradation nevertheless we remained cautious since we only studied a very short portion of the deposit and similar experiences need to be repeated moreover there are reflections in the radargram that we could not identify and further studies need to be conducted

insights into lahar deposition processes in the curah lengkong semeru volcano indonesia using photogrammetry based geospatial analysis near surface geophysics and cfd modelling abstract semeru volcano is an active stratovolcano located in east java indonesia where historic lava flows occasional pyroclastic flows and vulcanian explosions on average every 5 min to 15 min generate a stock of material that is remobilized by lahars mostly occurring during the rainy season between october and march every year several lahars flow down the curah lengkong valley on the south east flank of the volcano where numerous lahar studies have been conducted in the present contribution the objective was to study the spatial distribution of boulder size clasts and try to understand how this distribution relates to the valley morphology and to the dynamic and deposition dynamic of lahars to achieve this objective the method relies on a combination of 1 aerial photogrammetry derived geospatial data on boulders distribution 2 ground penetrating radar data collected along a 2 km series of transects and 3 a cfd model of flow to analyse the results from the deposits results show that

gpr investigation of tephra fallout cerro negro volcano nicaragua a method for constraining parameters used in tephra sedimentation models most tephra fallout models rely on the advection diffusion equation to forecast sedimentation and hence volcanic hazards here we test the application of the advection diffusion equation to tephra sedimentation using data collected on the proximal 350 to 1 200 m from the vent to medial greater than 1 200 m from the vent tephra blanket of a basaltic cinder cone cerro negro volcano located in nicaragua our understanding of tephra depositional processes at this volcano is significantly improved by combination of sample pit data in the medial zone and high resolution ground penetrating radar gpr data collected in the near vent and proximal zones if the advection diffusion equation applies then the thickness of individual tephra deposits should have gaussian crosswind profiles and exponential decay with distance away from the vent at cerro negro steady trade winds coupled with brief eruptions of relatively low energy vei 2 3 create relatively simple deposits gpr data were collected along three crosswind profiles at distances of 700 1 600 m from the vent sample pits were used to estimate thickness of the 1992 tephra deposit up to 13 km from the vent horizons identified in proximal gpr profiles exhibit gaussian distributions with a high degree of statistical confidence with diffusion coefficients of 500 m2 s 1 estimated for the deposits confirming that the advection diffusion equation is capable of modeling sedimentation in the proximal zone the thinning trend downwind of the vent decreases exponentially from the cone base 350 m to 1 200 m from the vent beyond this distance deposit overthickening occurs identified in both gpr and sample pit datasets the combined data reveal three depositional regimes 1 a near vent region on the cone itself where fallout remobilizes in granular flows upon deposition 2 a proximal zone in which particles fall from a height of less than 2 km and 3 a medial zone in which particles fall from 4 to 7 km and the deposit is thicker than expected based on thinning trends observed in the proximal zone of the deposit this overthickening of the tephra blanket defining the transition from proximal to medial depositional facies is indicative of transition from sedimentation dominated by fallout from plume margins to that dominated by fallout from the buoyant eruption cloud a feature of deposits previously identified in larger volume eruptions we interpret this change to represent a change in diffusion law occurring at total particle fall times the fall time threshold of numerical models of 400 s thus the detailed gpr profiles and pit data collected at cerro negro help to validate current numerical models of tephra sedimentation

impact of an unusually large warm core eddy on distributions of nutrients and phytoplankton in the southwestern canada basin during late summer early fall 2010 1 recent freshening of the arctic ocean due to melting of sea ice and enhanced ekman pumping has deepened the nutricline over the canada basin and reduced nutrient concentrations in the euphotic zone cold core eddies frequently transport nutrient rich shelf water to the canada basin but the eddies are much deeper than the euphotic zone because warm core eddies appear near the surface or at a depth range shallower than that of the cold core eddies they may play a crucial role in determining nutrient distributions in the euphotic zone and hence may affect primary production during late summer early fall 2010 we conducted detailed surveys of a warm core eddy which was unusually large 100 km in diameter we suggest that this warm core eddy which contained high ammonium shelf water could supply ammonium to the euphotic zone in the southwestern canada basin and may sustain 30 higher biomass of picophytoplankton 2 m than that in the surrounding water in the basin the role of warm core eddies in supplying nutrients to the euphotic zone and controlling phytoplankton distributions seems to be more important than previously because the recent deepening of the nutricline in the canada basin has decreased the nutrient supply to the euphotic zone

detection of welding in pyroclastic flows with ground penetrating radar insights from field and forward modeling data abstract we investigate the potential of ground penetrating radar gpr as a tool to delineate welded portions of pyroclastic flows by testing interpretations of field gpr data with numerical modeling specifically we test the hypothesis that regions of changing porosity with depth and regions of constant porosity are characterized by distinct signals in radargrams we model the propagation of electromagnetic waves through pyroclastic flow deposits with vertical variations in porosity the actual profiles are gradational but are represented in our models by a series of 1 cm thick homogeneous layers each layered porosity profile is converted into a layered k profile using an empirical law relating k to of dry volcanic rocks that is based on laboratory measurements the resulting synthetic traces indicate that moderate gradational changes in welding produce multiple low amplitude crests and troughs rather than strong individual reflections the lower the peak frequency of the source wavelet the greater the amplitude of the signal generated and thus the greater the potential signal to noise ratio extremely high rates of change in porosity with depth produce distinct strong reflections densely welded or unwelded portions where porosity is relatively constant produce sections of zero amplitude these preliminary results suggest that gpr can be used to map the effects of welding in pyroclastic flows specifically characteristic radar signals can be used to identify zones of changing degree of welding and zones of relatively constant degree of welding

propagation of low mode internal waves through the ocean abstract the baroclinic tides play a significant role in the energy budget of the abyssal ocean although the basic principles of generation and propagation are known a clear understanding of these phenomena in the complex ocean environment is only now emerging to advance this effort a ray model is developed that quantifies the effects of spatially variable topography stratification and planetary vorticity on the horizontal propagation of internal gravity modes the objective is to identify baroclinic shoals where wave energy is spatially concentrated and enhanced dissipation might be expected the model is then extended to investigate the propagation of internal waves through a barotropic mesoscale current field the refraction of tidally generated internal waves at the hawaiian ridge is examined using an ensemble of mesoscale background realizations derived from weekly ocean topography experiment topex poseidon altimetric measurements the path of mode 1 is only slightly affected by typical cur

deposits associated with the 1990 1995 eruption of unzen volcano japan abstract the 1990 1995 eruption of unzen volcano in japan was characterized by lava dome growth and block and ash flows triggered by dome collapse the repeated dome collapse events produced block and ash flow ash cloud surge and fine grained ash fall deposits block and ash flow deposits which are confined to valleys are massive to reversely graded very poorly sorted and contain non vesiculated to poorly vesiculated blocks up to 10 m across the deposits often display finer grained basal parts coarse clast depleted flow units which have intermediate grain size distribution between main flow and surge deposits occur as marginal part of block and ash flow deposits ash cloud surge deposits which spread more widely are finer grained and better sorted than block and ash flow deposits ash fall deposits which were derived from ash clouds of block and ash flows and were dispersed around the volcano are very fine grained and are as well sorted as the surge deposits lahars resulting from remobilization of pyroclastic debris devastated the base of the volcano and their deposits are moderately fines depleted and occasionally display two different lahar facies debris flow and hyperconcentrated flow units

welded block and ash flow deposits from mount meager british columbia canada abstract the 2360 years b p eruption of mount meager british columbia produced a succession of rarely observed welded block and ash flow deposits and non welded equivalents we report on these rhyodacitic block and ash flow deposits by describing the deposits documenting the nature of the welding process and establishing the origins of these pyroclastic deposits variations in welding intensity are tracked by image analysis of field texture maps petrographic study of shard morphology and measurements of sample density and porosity pyroclast oblateness from image analysis of texture maps provides a qualitative record of welding intensity but underestimates the amount of compactional e g volume strain when compared to estimates from physical property measurements e g density porosity unconsolidated deposits have an average matrix porosity of 41 38 45 and clasts have an average porosity of 32 24 40 in unconsolidated deposits isolated porosity is pervasive 50 m shortening of the thickest deposit from 162 m to the current 112 m the pyroclastic flow deposits result from accumulation in a narrow confined river valley the accumulation was sufficiently rapid to keep the deposits above their glass transition temperature thereby allowing the succession to weld as a single cooling unit the nature and distribution of isolated porosity in the juvenile clasts of rhyodacite suggest an explosive rather than effusive origin for these block and ash flow deposits that may be analogous to some vulcanian eruption triggered dome collapse processes observed at soufriere hills volcano montserrat rather than gravitational collapse

sole marks at the base of the late pleistocene abrigo ignimbrite tenerife implications for transport and depositional processes at the base of pyroclastic flows sole marks which are common in turbidites have been observed as casts at the base of the abrigo ignimbrite on tenerife canary islands they have been engraved by pebble to cobble sized lithic tools in a soft cohesive fine grained substrate the casts range from long parallel groove marks often with the tool embedded at their termination to short elongate impact marks and are useful as a flow direction marker they were formed from a highly energetic pyroclastic flow pulse and were almost immediately infilled with ash after rapid waning of flow large lithic tools which formed groove marks were held in place under high gas and grain dynamic pressures and moved forward by their own momentum and the drag force exerted by a highly concentrated granular flow impact marks were formed by smaller lithic tools which had more freedom of movement within the agitated chaotic flow scour structures on the lee side of stationary lithic tools may have formed by local turbulence in their wake

internal tide radiation from the luzon strait the m2 k1 and o1 internal tides originating in the luzon strait are investigated using the sea surface height measurements by multiple satellites ers 2 envisat topex poseidon jason 1 2 and geosat follow on a plane wave fit method is used to resolve multiple internal tides in arbitrary horizontal directions the luzon strait is an energetic internal tide generation site and radiates internal tides both westward into the south china sea scs and eastward into the western pacific wp in the scs the k1 and o1 internal tides propagate over 1600 km reaching the vietnam coast in the wp they propagate over 2500 km and arrive to the mariana ridge and guam the k1 and o1 internal tides refract toward the equator during propagation the m2 internal tides in the scs bifurcate into two beams the northwestward beam is coincident with the frequent occurrence of internal solitary waves in this region implying their causative relation the phase speeds inferred from the altimetric along beam propagation agree with the theoretical values due to the influence of the earth s rotation the k1 and o1 phase speeds decrease remarkably from high to low latitudes for the diurnal internal tides the eastward radiation is about 50 greater than the westward radiation for m2 the westward radiation is about two times the eastward radiation the altimetric energy fluxes are about 50 of those in numerical model simulations

shoaling of the nutricline with an increase in near freezing temperature water in the makarov basin 1 the water mass changes in the makarov basin and adjacent areas associated with the recent loss of arctic sea ice had not been studied in detail we combined data obtained from multiple cruises in these regions and used chemical tracers to investigate the spatial and temporal changes in water masses our data show that a previously present temperature maximum water has disappeared from the makarov basin and chukchi abyssal plain due to enhanced cooling and convection in the east siberian sea in addition a large volume of water has formed by cooling and convection and is flowing into the makarov basin producing a temperature minimum with relatively high nutrients and resulting in a shoaling of the nutricline this temperature minimum water likely originated from the eastern part of the east siberian sea where significant open water areas appeared after 2005 in the freeze up season the water mass boundary between this temperature minimum water and the pacific origin temperature minimum water shifted westward from the chukchi plateau in the early 2000s to the mendeleyev ridge in the late 2000s probably owing to a westward flow of the enhanced beaufort gyre associated with recent sea ice loss in the canada basin although the shoaling of the nutricline in the makarov basin could increase phytoplankton production such production could decrease in the southern makarov basin because a large amount of sea ice meltwater covers that region and might decrease the nutrient supply from the subsurface layer

evolution of nonlinear internal waves in the east and south china seas synthetic aperture radar sar images from ers i have been used to study the characteristics of internal waves northeast and south of taiwan in the east china sea and east of hainan island in the south china sea rank ordered packets of internal solitons propagating shoreward from the edge of the continental shelf were observed in the sar images on the basis of the assumption of a semidiurnal tidal origin the wave speed can be estimated and is consistent with the internal wave theory by using the sar images and hydrographic data internal waves of elevation have been identified in shallow water by a thicker mixed layer as compared with the bottom layer on the continental shelf the generation mechanism includes the influences of the tide and the kuroshio intrusion across the continental shelf for the formations of elevation internal waves the effects of water depth on the evolution of solitons and wave packets are modeled by the nonlinear kortweg devries kdv type equation and linked to satellite image observations the numerical calculations of internal wave evolution on the continental shelf have been performed and compared with the sar observations for a case of depression waves in deep water the solitons first disintegrate into dispersive wave trains and then evolve to a packet of elevation waves in the shallow water area after they pass through a turning point of approximately equal layer depths that has been observed in the sar image and simulated by the numerical model the importance of the dissipation effect in the coastal area is also discussed and demonstrated

effects of remote generation sites on model estimates ofm2internal tides in the philippine sea abstractthis study investigates the impact of remotely generated internal tides on model estimates of barotropic to baroclinic tidal conversion for two generation sites bounding the philippine sea the luzon strait and the mariana island arc a primitive equation model is used to characterize the internal tides generated by the principal semidiurnal tide m2 over a domain encompassing the two generation sites energetic internal tides are generated at the luzon strait where nearly 17 gw of barotropic tide energy is converted to baroclinic energy of which 44 4 78 gw is radiated eastward into the philippine sea from the mariana arc baroclinic energy propagates westward into the philippine sea as a result of 3 82 gw of barotropic to baroclinic energy conversion simulations that focus on each generation site without influence of the other are performed and comparisons show that remotely generated internal tides have a significant effect on local conversion at the two sites total conversion is greate

numerical and analytical estimates of m2 tidal conversion at steep oceanic ridges abstract numerical calculations of the rate at which energy is converted from the external to internal tides at steep oceanic ridges are compared with estimates from analytic theories the numerical calculations are performed using a hydrostatic primitive equation ocean model that uses a generalized s coordinate system as the vertical coordinate the model regional ocean modeling system roms estimates of conversion compare well with inviscid and nondiffusive theory in the sub and supercritical regimes and are insensitive to the strength of viscosity and diffusivity in the supercritical regime the nondissipative analytic solution is singular all along the internal tide beams because of dissipation the roms solutions are nonsingular although the density gradients are strongly enhanced along the beams the agreement between model and theory indicates that the prominent singularities in the inviscid solution do not compromise the estimates of tidal conversion and that the linearization used in derivi

an updated examination of the luzon strait transport 1 despite numerous previous estimates of luzon strait transport lst we attempt an update using a fine resolution model with these improvements the circulation in and around luzon strait shows up rather realistically intrusion of a kuroshio meander into the south china sea scs is seasonally varying the lst especially in the upper ocean caused by a small difference between the large meander inflow and outflow is also seasonally varying and subject to large standard deviation the annual mean lst is estimated to be westward 4 0 5 1 sv along 120 75 e we have also conducted process of elimination experiments to assess the relative importance of open ocean inflow outflow wind stress and surface heat flux in regulating lst and its seasonality the east asian monsoon winds stand out as the predominant forcing without it the upper ocean lst changes from westward to eastward ranging up to 4 sv and with misaligned seasonality triggering an inflow from the mindoro strait to the scs to replenish the water mass loss discounting monsoon winds sea level in the sulu sea is generally higher because it receives the indonesian throughflow before the scs which causes an inflow from the sulu sea to the scs on the other hand the annual mean wind from the northeast invites outflow from the scs to the sulu sea or inflow from the luzon strait weighing the two competing factors together we see the cessation of northeast monsoon as a condition favorable for the luzon strait outflow or the mindoro strait inflow