geochemistry of laterites stability of al goethite al hematite and fe super 3 kaolinite in bauxites and ferricretes an approach to the mechanism of concretion formation

reversing bottom circulation in the somali basin two sets of direct velocity measurements were taken concurrent with hydrographic data in the bottom waters of the northern somali basin in june and september 1995 the velocities indicate a temporal flow reversal in the bottom circulation which is consistent with the changing density structure between the sections in june there is evidence of a southward deep western boundary current with a transport of 5 sv by september flow close to the boundary is northward with a transport of 2 6 sv furthermore the deep density gradient across the interior of the somali basin also changes between occupations implying a cyclonic circulation in june and anticyclonic flow in september rossby wave activity is high in this region during the southwest monsoon yet there is also evidence of a strong barotropic component to the great whirl in september which may cause the reversal in the abyssal circulation

measurements of shoaling internal waves and turbulence in an estuary 1 the shoaling of horizontally propagating internal waves may represent an important source of mixing and transport in estuaries and coastal seas including such effects in numerical models demands improvements in the understanding of several aspects of the energetics especially those relating to turbulence generation and observations are needed to build this understanding to address some of these issues in the estuarine context we undertook an intensive field program for 10 days in the summer of 2008 in the st lawrence estuary the sampling involved shore based photogrammetry ship based surveys and an array of moorings in the shoaling region that held both conventional and turbulence resolving sensors the measurements shed light on many aspects of the wave shoaling process wave arrivals were generally phase locked with the m2 tide providing hints about far field forcing in the deeper part of the study domain the waves propagated according to the predictions of linear theory in intermediate depth waters the waves traversed the field site perpendicularly to isobaths a pattern that continued as the waves transformed nonlinearly acoustic doppler velocimeters permitted inference of the turbulent energetics and two main features were studied first during a period of shoaling internal waves turbulence dissipation rates exceeded values associated with tidal shear by an order of magnitude second the evolving spectral signatures associated with a particular wave shoaling event suggest that the turbulence is at least partly locally generated overall the results of this study suggest that parameterizations of wave induced mixing could employ relatively simple dynamics in deep water but may have to handle a wide suite of turbulence generation and transport mechanisms in inshore regions

a tidal model for eastern juan de fuca strait and the southern strait of georgia a three dimensional barotropic finite element model is used to calculate the tidal flows in eastern juan de fuca strait and the southern strait of georgia the harmonics of eight constituents are computed and compared with those from previous finite difference models and those from historical tide gauge and current meter observations root mean square differences between observed and calculated sea level amplitudes are within 2 0 cm for all constituents and the phases are within 4 0 for all constituents except k2 horizontal currents from the model are found to reproduce the observed vertical variations in shear except in regions where stratification effects and internal tides exist in particular the model representation of currents at six stations in the canadian tide and current tables volume 5 is accurate the pattern of tidal residual currents has much more detail than previous coarser resolution models and numerous eddies are predicted computed energy flux fields reveal that over a 29 day period only 38 of the tidal power entering juan de fuca strait is transmitted into the southern strait of georgia and of the 39 entering haro strait 36 is dissipated within the strait itself

stability characteristics of deep water replacement in the strait of georgia abstract it has been suggested that low frequency current fluctuations in the southern strait of georgia are the result of baroclinic instability however data extracted from cyclesonde and fixed current meter moorings suggest that the conditions for baroclinic instability are highly variable in space and time it has been recently discovered that there are summertime bottom intensified gravity currents with fortnightly and monthly periods associated with the introduction of salty waters from the juan de fuca strait during periods of neap tides these currents are the dominant mechanism for deep water renewal in the strait of georgia it is argued that these currents are baroclinically unstable and that the stability characteristics are reasonably consistent with the observed structure of the low frequency current fluctuations the episodic nature of these unstable bottom flows may help to explain the spatial and temporal variability of the low frequency current fluctuations observed in the strait of geo

tidally generated turbulence over the knight inlet sill very high turbulent dissipation rates above 5 1024 wk g 21 were observed in the nonlinear internal lee waves that form each tide over a sill in knight inlet british columbia this turbulence was due to both shear instabilities and the jumplike adjustment of the wave to background flow conditions away from the sill turbulent dissipation was significantly lower 5 1027 to 5 1028 wk g 21 energy removed from the barotropic tide was estimated using a pair of tide gauges a peak of 20 mw occurred during spring tide approximately twothirds of the barotropic energy loss radiated away as internal waves while the remaining one third was lost to processes near the sill observed dissipation in the water column does not account for the near sill losses but energy lost to vortex shedding and near bottom turbulence though not measured could be large enough to close the energy budget

petrological differentiation patterns and geomorphic distribution of ferricretes in central africa geomorphic distribution and petrological differentiation patterns of ferricretes widespread on landsurfaces were studied in the dembia zemio area southeastern central african republic four types of ferricretes are distributed on high plateaux hillslopes and low plateaux the main contrast corresponds to the differentiation between ferricretes of high plateaux rich in poorly hydrated minerals hematite and kaolinite and those covering hillslopes and low plateaux richer in hydrated minerals goethite and gibbsite a principal component analysis of geochemical and mineralogical data was used to characterize the main differentiation patterns of ferricretes in relation with their petrographic facies and the geomorphic features of the landscape the distribution of secondary minerals and their relationships to trace elements within and between the ferricrete types reflects differences in weathering and erosion processes our results document that the petrological patterns and the distribution of ferricretes are related to geomorphic features depending on hydroclimatic variations that govern the landscape evolution of many tropical shields

giant bauxite deposits of south china multistage formation linked to late paleozoic ice age lpia eustatic fluctuations abstract the lower carboniferous jiujialu formation bauxite deposits at zunyi northern guizhou are distinguished by their great thickness to 110 m and cyclic alternation of bauxite ore and bauxitic claystone layers these features are typical of the kazakhstan subtype of karst bauxite deposits although the genesis of this type of deposit is poorly understood here we undertook a petrological mineralogical and geochemical study of the zunyi deposit in drillcore zk5600 to gain insights into its formation history the zunyi profile contains seven bauxite cycles as recorded by petrological mineralogical and geochemical features indicating a multistage formation history each cycle is composed of a lower bauxitic claystone layer and an upper bauxite ore layer the bauxite ore is characterized by high al2o3 high al mineral diaspore and low sio2 content positive ce anomalies high cia values 90 and strong depletion of major elements indicate that the bauxite ore formed through intense chemical weathering and leaching in a well drained soil environment the bauxitic claystone is characterized by relatively lower al2o3 and higher sio2 and clay mineral mostly illite content this lithology exhibits both negative and positive ce anomalies moderate cia values 70 80 and enrichment of some elements e g fe k indicating formation through moderate chemical weathering in a poorly drained soil environment secular variations in chemical weathering intensity and soil drainage conditions were linked to regional hydrologic changes during the early carboniferous the zunyi area was located in a karstified coastal upland setting and its hydrologic system was affected by glacio eustatic fluctuations high groundwater table elevations during eustatic highstands led to formation of bauxitic claystone layers whereas low groundwater table elevations during eustatic lowstands led to formation of bauxite ore layers

variability of water properties heat and salt fluxes in the arabian sea between the onset and wane of the 1995 southwest monsoon abstract we investigate the variability of the circulation water masses heat and salt fluxes in the arabian sea over the course of the southwest monsoon two zonal sections taken along 8 30 n in 1995 as part of the indian ocean woce hydrographic program are used the first was occupied in early june at the onset of the southwest monsoon winds the second in late september at the wane of the monsoon the september section was found to be generally warmer 0 32 c and saltier 0 04 than in june despite a 50 mm drop in mean sea level therefore the common assumption that an increase in sea surface height follows an increase in heat content the hydrostatic response does not hold instead we conclude that the heat content increases due to the advection of arabian sea surface water and red sea water onto the section from the north and the drop in sea level is due to a loss of mass rather than heat from the water column there are large uncertainties involved in diagnosing the heat flux divergence across the arabian sea because the seasonal variability of the water masses and circulation in the basin mean that our data are not representative of a steady state we treat each section separately and find an oceanic heat export of 0 72 pw in june and 0 19 pw in september implying a basin cooling rate of about 0 36 pw in june and a slight heating of 0 12 pw in september in june the mass and heat balances are dominated by the ekman transport and the somali current with very flat density surfaces resulting in a small interior geostrophic transport by september the ekman transport has reduced and it is primarily the interior transport that balances a strong somali current there are two main overturning cells in june and september a shallow one of approximate magnitude 15 sv in june and 0 sv in september which reaches depths of no more than 500 m and is driven by ekman divergence at the surface and a deep cell of magnitude 1 sv representing a weak inflow and subsequent upwelling of circumpolar deep water the deep cell implies a basin averaged upwelling velocity of 3 2 10 5 cm s 1 through 2200 m

spreading of red sea overflow waters in the indian ocean as a result of its remarkably high salinity and despite its small volume input remnants of red sea water rsw have been identified in the agulhas current over 6000 km distant of their source this provided the motivation to investigate the long term mean spreading of rsw throughout the indian ocean using a comprehensive set of observations taken from the national oceanographic data center archives and from the world ocean circulation experiment hydrographic program for the indian ocean after emerging from the gulf of aden into the arabian sea rsw spreads predominantly southwestward along the african continental slope as indicated by strongly inclined isohalines across the arabian sea there is some monsoon variability so that during the winter monsoon there is more rsw present in the gulf of aden and an intensification of southward spreading along the western boundary between 12 and 5 n elsewhere the intermediate depth salinity field of the indian ocean appears relatively stationary between 5 and 10 s in the region of the south equatorial current isohalines of the rsw layer become quasi zonal across the width of the indian ocean only dipping southward toward the western boundary west of 50 e south of here there is a strong tongue of rsw spreading southward through the mozambique channel and into the agulhas current these conclusions concur with previous localized investigations of intermediate water properties using a simple mixing model the percentage of rsw throughout the indian ocean was quantified it was found that the flux of salt into the gulf of aden from the red sea is similar to that estimated to cross 32 s in the agulhas current this result implies that all the rsw which is mixed into the interior of the indian ocean may eventually be exported at the western boundary furthermore it implies that rsw is the dominant component of the salt budget for the intermediate layer and that input from the indonesian seas and via diapycnic processes are small

upwelling rebound ephemeral secondary pycnoclines and the creation of a near bottom wave guide over the monterey bay continental shelf several sequential upwelling events were observed in fall 2012 using measurements from the outer half of the continental shelf in monterey bay during which the infiltration of dense water onto the shelf created a secondary near bottom pycnocline this deep pycnocline existed in concert with the near surface pycnocline and enabled the propagation of near bottom cold semidiurnal internal tidal bores as well as energetic high frequency nonlinear internal waves of elevation iwoe the iwoe occurred within 20 m of the bottom had amplitudes of 8 24 m periods of 6 45 min and depth integrated energy fluxes up to 200 w m 1 iribarren numbers 0 03 indicate that these iwoe were nonbreaking in this region of the shelf these observations further demonstrate how regional upwelling dynamics and the resulting bulk cross margin hydrography is a first order control on the ability of internal waves at tidal and higher frequencies to propagate through continental shelf waters

high frequency internal waves on the oregon continental shelf abstract measurements of vertical velocity by isopycnal following neutrally buoyant floats deployed on the oregon shelf during the summers of 2000 and 2001 were used to characterize internal gravity waves on the shelf using measurements of vertical velocity the average spectrum of wentzel kramers brillouin wkb scaled vertical kinetic energy has the level predicted by the garrett munk model gm79 plus a narrow m2 tidal peak and a broad high frequency peak extending from about 0 1n to n and rising a decade above gm79 the high frequency peak varies in energy coherently with time across its entire bandwidth its energy is independent of the tidal energy the energy in the continuum region between the peaks is weakly correlated with the level of the high frequency peak energy and is independent of the tidal peak energy the vertical velocity is not gaussian but is highly intermittent with a calculated kurtosis of 19 the vertical kinetic energy varies geographically low energy is found offshore and

observation of very large and steep internal waves of elevation near the massachusetts coast 1 we report on near bottom waves of elevation with amplitude nearly half the 25 m water column very steep and propagating into a sheared turbulent wave guide the waves contained trapped cores transporting parcels of water shoreward these large waves depart strongly from weakly nonlinear and weakly nonhydrostatic conditions and challenge established paradigms they can also represent an important factor in the across shore transport of plankton and contaminants

gravity currents facilitate formation of high frequency internal solitons and bores at the base of the fraser delta in the southern strait of georgia

very large subaqueous sand dunes on the upper continental slope in the south china sea generated by episodic shoaling deep water internal solitary waves abstract very large subaqueous sand dunes were discovered on the upper continental slope of the northern south china sea the dunes were observed along a single 40 km long transect southeast of 21 93 n 117 53 e on the upper continental slope in water depths of 160 m to 600 m the sand dunes are composed of fine to medium sand with amplitudes exceeding 16 m and crest to crest wavelengths exceeding 350 m the dunes apparent formation mechanism is the world s largest observed internal solitary waves which generate from tidal forcing on the luzon ridge on the east side of the south china sea propagate west across the deep basin with amplitudes regularly exceeding 100 m and dissipate extremely large amounts of energy via turbulent interaction with the continental slope suspending and redistributing the bottom sediment while subaqueous dunes are found in many locations throughout the world s oceans and coastal zones these particular dunes appear to be unique for two principal reasons their location on the upper continental slope away from the influence of shallow water tidal forcing deep basin bottom currents and topographically amplified canyon flows and their distinctive formation mechanism approximately 60 episodic extremely energetic large amplitude events each lunar cycle

intrusive gravity currents and internal gravity wave generation in stratified fluid the excitation of internal gravity waves by fluid intrusions that propagate along the interface between a uniform upper layer and a uniformly stratified lower layer is examined by way of laboratory experiments intrusions are generated using a simple lock release apparatus experiments are conducted in which the density gradient of the uniformly stratified layer the density jump across the interface and the density difference between the lock fluid and the uniform upper layer are varied in all cases the fluid intrusions travelled at a constant speed the forcing imparted by the generated internal gravity waves did not deform the intrusion head or significantly retard the intrusion s rate of forward advance for a limited range of density parameters good agreement was obtained between the experimental data and the two layer analytical theory of j y holyer h e huppert j fluid mech vol 100 1980 pp 739 767 which provides estimates for the intrusion speed and depths of penetration into the upper and lower layers internal gravity wave excitation is due to the initial collapse of the lock fluid and the forcing imparted by the head of the intrusion waves are visualized and their amplitudes measured using synthetic schlieren the vertical flux of horizontal momentum due to internal gravity wave excitation is related to measurable properties of the fluid intrusion this analysis suggests that outflows produced by tall convective storms that travel along the tropopause may excite non hydrostatic internal gravity waves in the stratosphere whose momentum flux at least during the transient generation time is comparable to that of waves generated by topographic forcing

spatial variability of turbulent mixing in the abyssal ocean ocean microstructure data show that turbulent mixing in the deep brazil basin of the south atlantic ocean is weak at all depths above smooth abyssal plains and the south american continental rise the diapycnal diffusivity there was estimated to be less than or approximately equal to 0 1 x 10 4 meters squared per second in contrast mixing rates are large throughout the water column above the rough mid atlantic ridge and the diffusivity deduced for the bottom most 150 meters exceeds 5 x 10 4 meters squared per second such patterns in vertical mixing imply that abyssal circulations have complex spatial structures that are linked to the underlying bathymetry

goethite and hematite in a climosequence in southern brazil and their application in classification of kaolinitic soils abstract the goethite hematite goethite ratio of 11 profiles of oxisols ultisols and inceptisols along a 600 km e w transect in s brazil varied systematically with climatic and soil factors the ratio increased with decreasing mean annual air temperature increasing excess moisture rainfall minus evapotranspiration increasing soil organic carbon and decreasing ph this is explained in light of the current concept of goethite and hematite formation in soils higher temperatures favor hematite whereas higher excess moisture higher organic carbon and lower ph favor goethite a basis is suggested for using goethite and hematite in the mineralogical classes at the family level of soil taxonomy

the foreslope hills large scale fine grained sediment waves in the strait of georgia british columbia abstract the foreslope hills are a set of 20 m high 5 km long ridges at 230 350 m water depth in the south central strait of georgia occupying a 60 km 2 area at the base of the fraser river delta foreslope they are composed of clay silt and fine sand previous authors have interpreted them as 1 a single mass slide deposit 2 mud diapirs 3 in situ rotational failures and 4 creep deformation features but collaborative evidence for these interpretations is lacking seafloor surface morphological renders derived from recent multibeam sonar bathymetry data show linear evenly spaced symmetrical ridges with ridge bifurcation resembling wave ripples but on a much larger scale detailed multichannel and single channel seismic reflection data show sinusoidal internal reflections suggesting upslope migration the ridges occur within the uppermost portion of the holocene section in a very high sedimentation rate environment consequently they are probably less than 3000 years old moored current meter records for the region show reversing currents largely oriented normal to the ridge crests averaging 10 cm s with a maximum of 50 cm s this evidence combined with increasing documentation of large scale sedimentary bedforms in slope and rise environments suggests that the foreslope hills should be re interpreted as sediment waves upslope migration is typical of many large scale fine grained sediment waves the preferred physical interpretation for the creation and maintenance of the foreslope hills as sediment waves is the lee wave model requiring a phase shift in density stratified flow as it passes over the wavy topography maximum measured bottom currents are easily strong enough to entrain silt and clay delivered to the site by turbidity currents or by sediment plume fallout from fraser river outflow either strong flood tides or severe biannual density intrusions due to their intense stratification may be susceptible to lee wave formation and the creation of sediment waves leading to the observed pattern of upslope migration

circulation hydrography and transport over the summit of axial seamount a deep volcano in the northeast pacific a numerical model of ocean flow hydrography and transport is used to extrapolate observations of currents and hydrography and infer patterns of material flux in the deep ocean around axial seamount a destination node of nsf s ocean observatories initiative s cabled array using an inverse method the model is made to approximate measured deep ocean flow around this site during a 35 day time period in the year 2002 the model is then used to extract month long mean patterns and examine smaller scale spatial and temporal variability around axial like prior observations model month long mean currents flow anti cyclonically around the seamount s summit in toroidal form with maximum speeds at 1500m depth of 10 11 cm s as a time mean the temperature salinity anomaly distribution takes the form of a cold briny dome above the summit passive tracer material continually released at the location of the ashes vent field exits the caldera primarily through its southern open end before filling the caldera once outside the caldera the tracer circles the summit in clockwise fashion fractionally re entering the caldera over lower walls at its north end while gradually bleeding southwestward during the modeled time period into the ambient ocean a second tracer release experiment using a source of only two day duration inside and near the casm vent field at the northern end of the caldera suggests a residence time of the fluid at that locale of 8 9 days

evolution of a shoaling internal solitary wavetrain 1 field observations of an internal solitary wavetrain impacting a shoaling bottom are presented measurements of the spatio temporal characteristics of the shoaling waves are given as well as estimations of the mixing they may have caused upon impact the observations are discussed in the context of numerical simulations laboratory experiments and hypotheses recently raised on the origin and evolution of internal solitary waves in coastal environments

a model study of the salish sea estuarine circulation arealistichindcastsimulationofthesalishsea whichencompasses theestuarinesystemsofpugetsound the strait ofjuan de fuca and the strait of georgia is described for the year 2006 the model shows moderate skill when compared against hydrographic velocity and sea surface height observations over tidal and subtidal time scales analysis of the velocity and salinity fields allows the structure and variability of the exchange flow to be estimated for the first time from the shelf into the farthest reaches of puget sound this study utilizes the total exchange flow formalism that calculates volume transports and salt fluxes in an isohaline framework which is then compared to previous estimates of exchange flow in the region from this analysis residence time distributions are estimated for puget sound and its major basins and are found to be markedly shorter than previous estimates the difference arises from the ability of the model and the isohaline method for flux calculations to more accurately estimate the exchange flow in addition evidence is found to support the previously observed spring neap modulation of stratification at the admiralty inlet sill however the exchange flow calculated increases at spring tides exactly opposite to the conclusion reached from an eulerian average of observations

the oman upwelling zone during 1993 1994 and 1995 abstract satellite derived sea surface temperature topex poseidon t p sea level anomalies slas model wind data and hydrographic data are used to characterize the upwelling along the oman coast during the us joint global ocean flux study us jgofs arabian sea process study asps in 1995 as well as to look at interannual variability in the upwelling over the period 1993 1995 empirical orthogonal function eof analysis of the satellite derived sea surface temperature sst at the locations of the us jgofs standard stations shows the first mode which represents a biannual variability contributes 67 of the total variance in addition the sst shows the upwelling front moving offshore with the development of southwest sw monsoon in early june 1995 reaching a maximum distance of approximately 120 km by late august 1995 finally sst shows the persistence of cold upwelling waters for nearly a month after the end of the sw monsoon within the bays along the oman coast topex poseidon slas indicate that with the onset of the sw monsoon a 30 cm drop in steric height is observed along the oman coast associated the presence of the cool upwelled waters this drop in steric height sets up a horizontal pressure gradient and results in a compensating along shore northeastward flowing geostrophic current east arabian current eac during the sw monsoon similarly the altimeter data slow an offshore decrease in steric height during the northeast ne monsoon indicating a seasonal reversal in direction of the eac with flow to the southwest subsurface temperature data indicate that the actual uplifting of isotherms associated with the upwelling can be found to a distance of approximately 260 km from the shore and to a depth of 150 200 m using along track altimetry data we estimate that for a region 260 km in offshore distance and 600 km alongshore 2 2 10 6 1 4 10 6 and 0 55 10 6 m 3 s 1 were upwelled through the 100 m level with upwelling velocities o 2 0 10 5 m s 1 during the sw monsoons of 1993 1994 and 1995 respectively the reduced upwelling in the summer of 1995 is attributed to a reduction in wind stress curl along the arabian coast when compared to 1993 and 1994

quantitative mineralogy of bauxite profiles in se guinea bissau abstract in the south eastern part of guinea bissau extensive highly weathered ferrallitic mantles occur within different geomorphological levels these weathered layers are usually capped by petroplinthite frequently they are of economic interest due to their enrichment in alumina they represent the remnants of a mezo cainozoic african planation surface one hundred auger drill samples from one geomorphological structure bowal were submitted to a specially developed method of quantification of the mineral phases previously detected in the representative specimens of the batch the method consisted of computing the mineralogical composition from the principal chemical component analyses al 2 o 3 sio 2 fe 2 o 3 tio 2 h 2 o combined with dta tg studies and thermodifferential x ray diffraction studies in addition the samples from available core drillings which reached the parent rocks were investigated by means of xrd and optical microscopy two groups of bauxites developed on dolerite and shale yield the same mineral paragenese the differences of mean al 2 o 3 and fe 2 o 3 content in both groups are expressed entirely by differences of concentration of gibbsite and goethite which reflect mobility of aluminium and iron in solutions circulating through the system of open large pores boehmite and hematite would tend to crystallize from oversaturated solutions in confined environment of fine pores

the volume transport of the somali current during the 1995 southwest monsoon abstract during the summer monsoon of 1995 two hydrographic and direct velocity sections were occupied over the continental shelf and slope off the coast of somalia in order to capture the flux of the western boundary current the first section was in early june just after the onset of the monsoon winds when no current was observed instead there was an anticyclonic eddy at the boundary with a small net northward transport of 3 5 1 5 sv the second section was occupied in mid september when a strong somali current was evident the resulting snapshot represents the only direct velocity section of the jet structure as it flows along the western boundary the strength of the somali current was 37 5 sv this is in general agreement with previous observations given the temporal variability of the current and represents a peak value according to contemporary model simulations the somali current of september extended far into shallow coastal waters of less than 200 m depth with speeds over 150 cm s 1 resulting in a considerable transport of 14 sv over the shelf northward flow of more than 10 cm s 1 penetrated to over 2000 m depth along the continental slope so that the subthermocline flux contributes another 13 sv to the total volume transport model simulations and satellite images of sea surface height illustrate that the somali current system exhibits large spatial variability on short timescales and thus differences in measured transports owe as much maybe more to the changing path of the current as to variability in its strength

the generation and trapping of solitary waves over topography observations of tidal flow over a sill show that upstream solitary wave generation occurred in conjunction with the downstream movement of a streamline bifurcation over the obstacle crest solitary waves appeared upstream of the bifurcation riding on the surface stratification shear flow instabilities on the plunging interface were also evident and may contribute to wave generation through subharmonic interaction nonlinear waves generated downstream of an internal control became trapped in the supercritical flow

joint canada u s ocean wave investigation project an overview of the georgia strait experiment an overview of the georgia strait experiment joint canada u s ocean wave investigation project or jowip 1983 is presented containing a list of participants objectives procedures and main results jowip was designed to provide quantitative comparisons between surface measurements and remote sar imagery of internal waves and narrow v surface ship wakes first order bragg modeling gives factor of 3 accuracy for l band internal wave modulation the composite model and possibly nonlinear surface wave internal wave interaction theory are required at x band narrow v wakes were imaged in dabob bay washington under low wind conditions at l band surface slopes in the kelvin wakes are not large enough to produce specular reflections even at a radar incidence angle of 23 modulations along the v arms are strongly evident and have the same wavelength as the transverse kelvin wake component these results and others are described in detail in other papers in this same issue

a new analytical model for internal solitons in the ocean abstract a new model for tidally generated internal solitons in the ocean is advanced based on a little known asymptotic analytical solution to the weakly nonlinear korteweg de vries equation the solution has many of the properties observed in oceanic internal solitary waves solitons it has been adapted to simulate the dynamics of stratified fluid flow driven by tidal forcing at continental shelves and sills and the adaptation describes the canonical behavior of such solitary wave trains it is shown that the solitons are positioned at the leading edge of an internal tidal bore on the shelf and that the distance between successive packets of solitons constitutes the internal tidal wavelength a future paper will apply the model to field observations from four geographical regions

estuarine versus transient flow regimes in juan de fuca strait 1 residual currents in juan de fuca strait are observed to switch between two fundamental states estuarine and transient the estuarine regime which prevails roughly 90 of the time in summer and 55 of the time in winter has a fortnightly modulated three layer structure characterized by strong 50 cm s 1 outflow above 60 15 m depth moderate 25 cm s 1 inflow between 60 and 125 m depth and weak 10 cm s 1 inflow below 125 10 m depth rotation increases the upper layer depth by 40 m on the northern side of the channel and upwelling favorable coastal winds augment inflow in the bottom layer by as much as 5 cm s 1 rotation combined with modulation of the estuarine currents by tidal mixing in the eastern strait leads to fortnightly variability in the along channel velocity and cross channel positioning of the core flow regions transient flows which occur roughly 10 of the time in summer and 45 of the time in winter are rapidly evolving horizontally and vertically sheared reversals in the estuarine circulation generated during poleward wind events along the outer coast major events can persist for several weeks force a net inward transport and give rise to an o 10 km wide surface intensified o 100 cm s 1 inflow along the southern olympic peninsula boundary of the strait this olympic peninsula countercurrent is typically accompanied by an abrupt decrease in salinity indicating that it is a buoyancy flow originating with low density water on the northern washington shelf

suspended particulate layers and internal waves over the southern monterey bay continental shelf an important control on shelf mud belts 1 physical and optical measurements taken over the mud belt on the southern continental shelf of monterey bay california documented the frequent occurrence of suspended particulate matter features the majority of which were detached from the seafloor centered 9 33 m above the bed in fall 2011 an automated profiling mooring and fixed instrumentation including a thermistor chain and upward looking acoustic doppler current profiler were deployed at 70 m depth for 5 weeks and from 12 to 16 october a long range autonomous underwater vehicle performed across shelf transects individual spm events were uncorrelated with local bed shear stress caused by surface waves and bottom currents nearly half of all observed spm layers occurred during 1 week of the study 9 16 october 2011 and were advected past the fixed profiling mooring by the onshore phase of semidiurnal internal tide bottom currents at the start of the 9 16 october period we observed intense near bed vertical velocities capable of lifting particulates into the middle of the water column this updraft event appears to have been associated with nonlinear adjustment of high amplitude internal tides over the mid and outer shelf these findings suggest that nonlinear internal tidal motions can erode material over the outer shelf and that once suspended this spm can then be transported shoreward to the middle and shallow sections of the mud belt this represents a fundamental broadening of our understanding of how shelf mud belts may be built up and sustained

the dynamics of double monsoon onsets abstract double monsoon onset develops when the strong convection in the bay of bengal is accompanied by the monsoonlike circulation and appears in the indian ocean in early may which is about 3 weeks earlier than the climatological date of the onset 1 jun the initial bogus onset is followed by the flow weakening or reversal and clear sky and dry conditions over the monsoon region the best example of such a phenomenon is the development of the summer monsoon in 1995 when monsoonlike perturbations that appeared in mid may disappeared by the end of the month and were followed by a heat wave in india delaying onset of the monsoon the climatology of double onsets is analyzed and it is shown that they are associated with delay of the monsoon rainfall over india this analysis indicates that the development of bogus onsets depends on the timing of intraseasonal oscillation in the indian ocean and the propagation of convective episodes into the western pacific there is evidence that an sst evolution

mesoscale eddies coastal upwelling and the upper ocean heat budget in the arabian sea estimation of the terms in the upper ocean heat budget from a moored array in the central arabian sea shows periods when a rough balance between the temperature trend and the horizontal advection of heat exists altimetry and sea surface temperature imagery are used to demonstrate that these episodes of strong horizontal advection are associated with mesoscale features during the wintertime northeast ne monsoon these are capped off mesoscale eddy features generated during the previous summertime southwest sw monsoon and have little horizontal transport of heat within the mixed layer during the sw monsoon the major contribution is strong offshore export of coastally upwelled water in a filament with a strong surface presence temperature and salinity properties from the moored array and a seasoar survey during the formation of the coastal filament confirm the offshore transport of the upwelled water mass to the site of the moored array more than 600 km offshore estimates of the filament section heat flux are several percent of the total estimated heat flux due to upwelling along the arabian peninsula and remote sensing data show that similar mesoscale variability along the coast is enhanced during the sw monsoon this points to the importance of mesoscale modulated transports in not only the observed heat budget at the moored array but in the overall upper ocean heat budget in the arabian sea

ferricrete biochemical degradation on the rainforest savannas boundary of central african republic in southeastern central african republic the lateritic weathering mantles are capped by 2 to 5 m thick ferricretes which previously formed under a seasonal tropical climate the actual humid tropical climatic conditions result in the biophysical disaggregation of the ferricretes everywhere the forest develop that lead to a soil formation composed of ferricrete relicts and ferruginous nodules embedded in a soft bioturbated micro aggregated clay ferruginous matrix the potential effect of the biological activity e g termites on the soil and vegetation dynamics and therefore on the evolution of the previous consolidated ferricrete is discussed following its mechanical disaggregation by the forest tree roots the ferricrete underwent a chemical degradation under the combined effect of hydration and redox conditions which result from the biodegradation and oxidation of the organic matter the transformation of the ferricrete into a soft bioturbated micro aggregated clay ferruginous soil matrix implies the hematite dissolution and the kaolinite transformation into gibbsite which may characterize a late bauxitization secondary gibbsitization of kaolinite of previous ferricrete profiles linked to a late quaternary environmental climate and vegetation change however the geochemical and mineralogical patterns of the matrix not only reflect the geochemistry of the parental ferricrete but also depend on the physical transfers of quartz and heavy minerals from the lower horizons of the profile hence the use of geochemical indexes such as ti and or zr for mass balance calculations in the lateritic weathering profiles is precluded because these supposedly inert chemical elements are not simply accumulated by in situ chemical weathering process

mineralogy and geochemical dispersion in lateritic soil profiles of northern nigeria abstract six lateritic soil profiles overlying metasedimentary and crystalline basement rocks of northern nigeria have been investigated in order to study the mineralogical and geochemical relationships between bedrock and weathering products a total of 96 samples have been collected including 26 from exposed quarry and road cut faces and 70 from auger holes to a depth of 8 m two selective leaching methods cold extraction with 0 1 m hci and hot extraction with aqua regia have been applied to the m fraction and up to sixteen elements determined by aas conclusions are based largely on the auger hole samples where element distributions have not been modified by subaerial exposure quartz is the dominant mineral in the upper part of the soil profile while kaolinite increases strongly with depth at the base of some profiles mica is also abundant elements are distributed through the soil profile according to their association with clays iron oxides and to a lesser extent carbonates while intercalations of lateritic crusts obscure general trends with depth dispersion and accumulation processes appear to be similar within each profile in spite of the intensive weathering and secondary accumulation processes characteristic of the savanna belt the lateritic soils within surface sampling depth appear to retain a geochemical imprint of the underlying bedrock criteria and potential problems in the application of soil geochemistry to bedrock mapping are discussed

formation and transformation processes of iron duricrust systems in tropical humid environment abstract formation and transformation processes of iron duricrust developed under tropical humid conditions in the southeastern part of the central african republic have been investigated in terms of geomorphological petrological and geochemical pathways the study of five typical weathering profiles of the most extensive iron duricrust system now known in the world indicates that saprolitization and ferruginization are sequentially involved in such processes as reflected by kaolinite gibbsite and hematite goethite replacements alkali earths rare earths metals and elements belonging to chemically inert minerals segregate during saprolite and iron duricrust formation and degradation mass balance calculations performed on a typical weathering system enable us to quantify net mass element transfers deriving from lateritic weathering processes volumetric change collapse or dilation as well as al and ti clearly discriminate between the saprolitization and ferruginization processes saprolite development preserves the geochemical inheritance of parent rocks whereas ferruginization depletes it and mostly reflects through mineralogical pathways pedoclimatic conditions and global climatic changes the global iron duricrust system of the southern part of central africa derived from previous hematite rich crust and not from ancient bauxites as it is generally believed for iron crusts formed on west african shields

a river mouth submarine channel and failure complex fraser delta canada abstract high resolution seismic and side scan sonar surveying combined with coring of the fraser delta slope seaward of the main fluvial distributary has revealed a complex suite of morphologic units which include undisturbed delta slope sediments shallow rotational slides relict and active slope channels debris accumulations and ponded turbidites sediment transport through the main submarine channel is thought to be primarily by debris flows rather than by turbidity currents although this is a seismically active region the instability related features described here are probably due primarily to rapid sediment deposition on the upper delta slope at the river mouth

near bed solibores over the continental slope in the faeroe shetland channel abstract on two occasions within a 12 day measurement period in the faeroe shetland channel strongly nonlinear wave trains were observed at the sea bed propagating up the continental slope in water depths 450 m the events were separated by a period of 4 days and whilst resembling in appearance a density current running up a slope are termed solibores displaying the properties of both turbulent internal bores and nonlinear internal solitary waves isw each solibore displays a steep leading edge followed by a train of nonlinear waves with amplitudes of o 10 m and periods of 5 20 min wave induced particle velocities are consistent with isw whilst a zone of strong horizontal convergence at the leading edge of the solibores causes the formation of a rotor with flow in the opposite sense to a forward overturning surface wave in both cases upward vertical velocities 10 cm s 1 are immediately followed by a return downward flow of equal magnitude a ctd and microstructure transect conducted during the passage of the first solibore illustrates its behaviour as an up slope intrusion of cold dense water with concurrent rates of turbulent dissipation e of o 10 7 w kg 1 and resulting in short term maximum vertical diffusivities kz of o 10 1 m2 s 1 in the long term however kz 140 days which again indicate intermittency in periods of enhanced sediment flux the solibores are consistent with the results of numerical and laboratory experiments on hydraulic jumps resulting from shoaling isw the influence of the slope is proposed to be the reason for their slightly different forms and effects on sediment transport thus the first solibore propagating directly up the slope is proposed to result from an overturning hydraulic jump caused by kinematic instabilities and which subsequently forms a horizontal density intrusion the second solibore represents a dispersive wave train due its oblique direction of propagation which reduces the effective bottom slope allowing dispersion to balance nonlinear effects and prohibiting overturning

coastal trapped waves alongshore pressure gradients and the california undercurrent abstractthe california undercurrent cuc a poleward flowing feature over the continental slope is a key transport pathway along the west coast of north america and an important component of regional upwelling dynamics this study examines the poleward undercurrent and alongshore pressure gradients in the northern california current system ccs where local wind stress forcing is relatively weak the dynamics of the undercurrent are compared in the primitive equation navy coastal ocean model and a linear coastal trapped wave model both models are validated using hydrographic data and current meter observations in the core of the undercurrent in the northern ccs in the linear model variability in the predominantly equatorward wind stress along the u s west coast produces episodic reversals to poleward flow over the northern ccs slope during summer however reproducing the persistence of the undercurrent during late summer requires additional incoming energy from sea level variability applied south

footprints of obliquely incident internal solitary waves and internal tides near the shelf break in the northern south china sea a mooring system and two sites of bottom currents were deployed over the slope and near the shelf break on the propagating paths of internal solitary waves isws west off dongsha atoll in the northern south china sea data indicated that energetic isws obliquely shoaled onto the shelf west off dongsha atoll in an approximately 290 degrees direction causing strong reversing currents some exceeding 80 cm s near the bottom two types of sandwaves and short scour channels are discernible on the seafloor near the shelf break which have reasonable correlations with the obliquely incident isws and internal tides type 1 sandwaves featured by isws at the depths of 130 150 m have flat crests interacting with the isobaths at an angle of nearly 45 degrees which slightly incline and migrate upslope type 2 sandwaves are associated with internal tides which have crests parallel to the isobaths and distinctly incline and migrate downslope short channels are parallel to the depth contours and truncate the strata which could be formed and maintained by along slope currents that are probably produced by the obliquely isws on a large gradient gamma 0 8 degrees the isws can move coarse grains or suspend fine grains but do not change the long term trend of sediment transport on the seabed with larger gradients gamma c 1 which is dominated by internal tides these features are likely widespread near the shelf break in the northern south china sea and other seas but are limited on mild slopes where isws do not break

an intense acoustic scattering layer at the top of a mid ocean ridge hydrothermal plume we have used a tethered oceanic profiling package consisting of a conductivity temperature depth ctd sensor transmissometer and acoustic doppler current profiler adcp to investigate the plume emanating from a known hydrothermal vent site at a depth of 2200 m near the crest of endeavour ridge in the northeast pacific ocean acoustic profiles obtained in august 1988 about 3 km to the southwest of the vent site revealed the presence of an intense scattering layer centered at approximately 1870 m depth near the top of the neutrally buoyant portion of the plume peak intensity anomalies in the 100 m thick scattering layer ranged from 10 to 15 db and were of comparable magnitude to upper ocean values observed in the euphotic zone below the top of the plume backscatter intensities were significantly below background levels we speculate that the strong backscatter layer consists of highly mobile macrozooplankton which congregate near the top of the plume to take advantage of the increased concentrations of nutrients originating with vertical buoyant transport of chemosynthetic bacteria and fine grain particles from the vent site at the same time the animals are able to avoid toxic levels of hydrothermally derived metals and sulfur inherent to the main body of the plume

the epigenetic replacement of kaolinite by hematite in laterite petrographic evidence and the mechanisms involved abstract this paper describes the petrographical and mineralogical transformations accompanying the accumulation of iron oxides within the deep mottled layer of a laterite from burkina faso in this layer the proportions of purple red hematitic spots or nodules which form at the expense of volumes occupied by a soft microporous kaolinite plasma increase as the surface of the soil is approached the antagonism between hematite and kaolinite was observed at different levels in all cases from the border to the core of the hematitic domains kaolinite experiences corrosion soon followed by complete destruction at this later stage hemalite crystals are organized into thin lamellar structures showing clearly the shapes of former kaolinite platelets a mechanism explaining coincidence of the accumulation of hematite with the destruction of kaolinite is proposed we postulate that in the deep layers of laterites fed by fe 2 solutions the protons necessary to dissolve kaolinite are generated by a reaction similar to the oxidation hydrolysis step of ferrolysis in the mottled layer of this laterite therefore the progressive building up of a high concentration of iron appears to be the result of two closely related processes i e the precipitation of iron oxides from solution and the concommitant dissolution of kaolinite

geochemical study of laterites of the jamnagar district gujarat india implications on parent rock mineralogy and tectonics abstract the laterite deposits occur in a linear stretch along the northern arabian sea coast in the jamnagar and porbandar districts of gujarat state india these deposits are characterised by presence of gibbsite kaoline calcite quartz anatase natroalunite goethite and hematite and relicts of mafic minerals and plagioclase on the basis of petro mineralogy and geochemistry these deposits are grouped as aluminous laterites fe2o3 1 45 3 84 av 3 13 al2o3 39 31 57 24 av 45 80 and laterites fe2o3 9 84 32 21 av 25 13 al2o3 34 74 49 59 av 41 27 the major trace and ree characteristics of laterites indicate that these were formed in situ by the alteration of parent rocks of trachytic andesitic composition and the process of bauxitisation followed the path of destruction of kaolinite and deferruginisation the correlation patterns of several trace and rare earth elements and their preferential enrichment have indicated that there is an influence of precursor rock on the distribution of trace elements the jamnagar laterite deposits occur as capping over the deccan trap basaltic lava flows and pyroclasic deposits lateritisation prevailed during palaeocene age when india was separated from the seychelles and passing over the equator during this time climate morphology and drainage conditions were favourable for lateritisation that result in the formation of jamnagar and other laterite deposits within the deccan province flood basaltic provinces of deccan columbia north australia and hawaii appear good location for hosting laterite deposits due to their wide areal extent small geological time span and uniform chemical composition however comparison of the major flood basaltic provinces of the world has indicated that their palaeopositions along with palaeoclimate morphology and drainage are equally important factors for facilitating lateritisation

direct breaking of the internal tide near topography kaena ridge hawaii abstract barotropic to baroclinic conversion and attendant phenomena were recently examined at the kaena ridge as an aspect of the hawaii ocean mixing experiment two distinct mixing processes appear to be at work in the waters above the 1100 m deep ridge crest at middepths above 400 m mixing events resemble their open ocean counterparts there is no apparent modulation of mixing rates with the fortnightly cycle and they are well modeled by standard open ocean parameterizations nearer to the topography there is quasi deterministic breaking associated with each baroclinic crest passage large amplitude small scale internal waves are triggered by tidal forcing consistent with lee wave formation at the ridge break these waves have vertical wavelengths on the order of 400 m during spring tides the waves are nonlinear and exhibit convective instabilities on their leading edge dissipation rates exceed those predicted by the open ocean parameterizations by up to a factor of 100 with the disparity in

trace elements and their relation to the mineral phases in the lateritic bauxites from southeast guinea bissau abstract fourteen trace elements sr ba la ca mg cu zn v ni co mn ga cr zr were determined in 120 auger and core drill samples from one bauxite plateau situated in the se part of guinea bissau following the quantitative determination of minerals identified in the samples all geochemical and mineralogical data were statistically treated the use of several statistical tools enabled us to identify two distinct populations of samples which were found to be related to the shale and dolerite parent rocks respectively the dispersion patterns of the elements mn zr la zn cu cr and ni yield strong contrasts between these two populations bauxites developed on devonian shales were found to contain more cr and ni than bauxites derived from cretaceous dolerites which were richer in cr and ni it is postulated that the difference in duration of the bauxitization processes which affected the two parent bedrocks and or the different resistance to weathering of the primary mineral host phases in the two rock types are responsible for this inversion r mode factor analysis revealed the conspicuous affinity of the mn zn ni cu co mg group and v to goethite gibbsite boehmite and anatase were found to be associated with resistate trace elements like zr and to a lesser extent cr gibbsite also reveals a certain affinity to more mobile strongly depleted elements like sr and ba the study proved the existence of numerous statistically significant correlations between the trace elements like the groups zr ti zn cu ni co mn and sr ba la