the apparent paradox of abundant foramol facies in low latitudes their environmental significance and effect on platform development recent studies of low latitude carbonates from se asia and australia have revealed deposits and platform types that do not fit easily into the perceived view of warm water tropical carbonates the sediments are classified as a foramol or foralgal facies and are dominated by non framework building light dependent biota such as perforate larger benthic foraminifera coralline algae and sometimes halimeda although ancient foramol deposits are often interpreted as an indication of non tropical conditions foramol facies have long been known from the tropics yet the environmental conditions in which they form are poorly known the aims of this paper are to evaluate how these deposits are best classified and more importantly whether there are any overriding controls that influence their common development in low latitude areas and if resultant platform development is affected the deposits are all best grouped within the photozoan association james n p 1997 the cool water depositional realm in james n p clarke j a d eds cool water carbonates sepm special publication 56 1 20 an assignment synonymous with warm water conditions the facies were also found to develop in conditions of limited light or oligophoty all the platforms described are characterised by having extensive areas of oligophotic facies generally in water depths extending down from 20 m but sometimes in shallower waters platforms types vary from land attached rimmed shelves homoclinal and distally steepened ramps to isolated banks and platforms but all have extensive moderate to deep photic zone development of oligophotic facies some workers might assign these platforms to the incipiently drowned platform type read j f 1985 carbonate platform facies models american association of petroleum geologists bulletin 69 1 21 however a morphological assignment is preferred here to signify that many of the deposits did not or may not form through drowning limited light in moderate to deeper depths of the photic zone often in regions with a reduced depth euphotic high light zone is seen as key to the extensive development of these deposits and the resultant platforms these conditions are often developed in humid low latitude areas of high terrestrial runoff and therefore regions of reduced water salinity or in areas of nutrient upwelling reduced water clarity due to nutrients plankton blooms suspended particulate matter upwelling and strong currents all promote the development of oligophotic conditions and facies on a regional scale time periods of relative rises in sealevel can also promote oligophotic facies development the findings of this study have broader implications for the development of low latitude platforms beyond australasia and during time periods when non framework building oligophotic biota are dominant sediment contributors the reconstruction of past climatic conditions based on study of foramol grain assemblages requires careful study to distinguish warm water deposits from those formed in cool waters

topographically controlled fronts in the ocean and their biological influence headlands islands and reefs generate complex three dimensional secondary flows that result in physical and biological fronts mixing and diffusion processes near these reefs and headlands are quite different from these processes in the open sea and classical advection diffusion models that were developed for the open sea are not valid near shore topographically generated fronts affect the distribution of sediments and they aggregate waterborne eggs larvae and plankton this aggregation influences the distribution and density of benthic assemblages and of pelagic secondary and tertiary predators

diagnoses of vertical transport in a three dimensional finite element model of the tidal circulation around an island a three dimensional finite element model is used to investigate the formation of shallow water eddies in the wake of rattray island great barrier reef australia field measurements and visual observations show that stable eddies develop in the lee of the island at rising and falling tides the water turbidity downstream of the island suggests the existence of strong upwelling that would be responsible for carrying bed sediments tip to the sea surface we first propose to look at the upwelling velocity and then use the theory of the age to diagnose vertical transport the water age is defined as the time elapsed since particles of water left the sea bottom where the age is prescribed to be zero two versions of this diagnosis are considered although the model predicts upwelling within the eddies it is not sufficiently intense to account for vertical transport throughout the water column during the life span of the eddies as mesh resolution increases this upwelling does not intensify however strong upwelling is then resolved off the island s tips which is confirmed by the results obtained with the age this study also shows that the finite element method together with unstructured meshes performs well for representing three dimensional flow past ail island c 2006 elsevier ltd all rights reserved

vanadium in the massive coral porites a potential proxy for historical wood clearing and burning abstract inshore coral reefs are threatened globally by decreased water quality resulting from anthropogenic land clearing and other drivers understanding the timing and rate of past native vegetation clearing and forest firing is critical for improved catchment management to protect reefs and other coastal ecosystems however commonly used coral based sediment proxies e g ba ca and y ca are controlled partly by variable precipitation and discharge rates no current marine proxy provides a temporal record of rates and areas of land clearing itself here we present a high resolution temporal record 1957 2010 of vanadium calcium v ca ratios in a porites coral colony from the southern great barrier reef gbr that correlates uniformly with historical clearance rates of woody vegetation in the local catchment despite discordant stream discharge we found that the v ca record could not be explained by terrestrial flux nutrient flux hydrocarbon pollution or upwelling and propose that the reaction between hot alkaline ash and the upper soil layer under oxidizing conditions during clearing associated burning may favour formation and desorption of soluble anionic vv species e g hvo 4 2 from soil based iron oxyhydroxides containing less mobile viii the newly soluble v components can then mobilise quickly into the earliest surface runoff and reach coastal seawater where they provide a distinct temporal record in corals that record is temporally decoupled from the sediment bound elements such as y and ba which require greater degrees of erosion to mobilise and thus better reflect particulate sediment flux the porites v ca record documented here captured the temporal effects of specific legislations aimed at regulating and conserving vegetation in the local catchment and may provide a means for evaluating catchment management practices elsewhere the new proxy also may provide records of catchment clearing and firing in prehistoric times with implications for both natural and anthropogenic fire regimes in coastal areas

flushing of bowden reef lagoon great barrier reef field and numerical studies were undertaken in 1986 and 1987 of the water circulation around and over bowden reef a 5 km long kidney shaped coral reef lagoon system in the great barrier reef in windy conditions the flushing of the lagoon was primarily due to the intrusion into the lagoon of topographically induced tidal eddies generated offshore in calm weather such eddies did not prevail and lagoon flushing was much slower the observed currents at sites a few kilometres apart in inter reefal waters have a significant horizontal shear apparently due to the complex circulation in the reef matrix under such conditions sensitivity tests demonstrate the importance of including this shear in the specification of open boundary conditions of numerical models of the hydrodynamics around reefs contrary to established practice the water circulation around a coral reef should not be modelled by assuming reefs are hydrodynamically isolated from surrounding ones little improvement appears likely in the reliability of reef scale numerical models until the inter reefal shear can be reliably incorporated in such models

the gulf of carpentaria heated torres strait and the northern great barrier reef during the 2016 mass coral bleaching event the 2015 16 enso event increased the temperature of waters surrounding northeast australia to above 30 c with large patches of water reaching 32 c for over two months which led to severe bleaching of corals of the northern great barrier reef ngbr this study provides evidence gained from remote sensing data oceanographic data and oceanographic modeling that three factors caused this excessive heating namely 1 the shutdown of the north queensland coastal current which would otherwise have flushed and cooled the northern coral sea and the ngbr through tidal mixing 2 the advection of warm 30 c water from the gulf of carpentaria eastward through torres strait and then southward over the ngbr continental shelf and 3 presumably local solar heating the eastward flux of this warm water through torres strait was driven by a mean sea level difference on either side of the strait that in turn was controlled by the wind which also generated the southward advection of this warm water onto the ngbr shelf on the ngbr shelf the residence time of this warm water was longer inshore than offshore and this may explain the observed cross shelf gradient of coral bleaching intensity the fate of the great barrier reef is thus controlled by the oceanography of surrounding seas

observations and analysis of the horizontal structure of a tidal jet at deep scour holes scour in the vicinity of a hydraulic structure may compromise its geotechnical stability or that of nearby structures much fundamental research has been dedicated to the understanding and prediction of these processes in order to enable the efficient design of mitigation measures while most of these efforts consider laterally uniform flows nonuniformity is the rule rather than the exception this study presents field observations near the storm surge barrier in the eastern scheldt estuary the netherlands where significant scour holes have developed the tidal flow through this semi open barrier exhibits characteristics of a shallow jet a pronounced contraction of this jet toward the nearby scour hole during particular stages of the tidal cycle is revealed attributed to potential vorticity conservation the depth averaged vertical vorticity increases proportionally to the depth increase measurements show a vertically uniform velocity profile in the scour hole that is attributed to a reduction of the adverse pressure gradient due to the contraction that suppresses boundary layer separation from the upstream slope of the scour hole a positive feedback mechanism is thus revealed lateral velocity gradients lead to relatively high near bed velocities in the scour hole which enhances erosion causing an even stronger horizontal contraction maintaining the scouring potential if the upstream flow field is laterally uniform observed around slack tide horizontal contraction does not occur and the boundary layer separates from the upstream slope the scour depth will then tend to an equilibrium the results infer the importance of the nonuniformity of the horizontal flow field

mesoscale circulation features of the great barrier reef region inferred from noaa satellite imagery abstract the commissioning of a noaa satellite receiving station at townsville in north queensland in 1988 greatly expanded the a vhrr coverage of the northeast australian region to include the entire great barrier reef system and marginal seas selected imagery from this and a southern station installed previously at aspendale victoria provide a valuable new perspective on oceanographic phenomena occurring in this ecologically significant region this perspective could not be attained using conventional ship board and in situ oceanographic sampling techniques a rich spectrum of mesoscale oceanographic features is revealed in the analyzed imagery and various features such as western boundary current meanders frontal shear waves eddies and jets are described the temporal and spatial variability of these features appears strongly linked to that of the larger scale coral sea current circulation several of the features identified are unique to the region others resemble features observed in other western boundary current systems but are significantly modified by the complex regional topography and by the presence of the great barrier reef gbr evidence has been found for a number of processes which have significant implications for the origin and maintenance of gbr ecosystems including shelf edge exchange processes stratified slope water intrusions onto the shelf and boundary layer mixing around reefs such processes provide a mechanism for injection of cool nutrient rich waters into the reef matrix the imagery provides a clear picture of a well organized but spatially complex frontal system existing in the southern coral sea which is associated with enhanced commercial and recreational fishing activity in the region the avhrr imagery has thus proven to be a valuable tool for spatial mapping of oceanographic features throughout the gbr region for hypothesis formation in dynamical and modeling studies and for ship board reconnaissance operations

successive phases of holocene reef flat development evidence from the mid to outer great barrier reef a re examination of 46 recently published u th reef flat ages from heron and one tree reefs in the southern great barrier reef gbr identified several distinct holocene reef growth phases with a clear 2 3 kyr hiatus in lateral reef accretion from 3 9 ka to 1 5 ka an analysis of all available published radiocarbon reef flat ages 165 from 27 other mid outer platform reefs revealed a similar hiatus between 3 6 ka and 1 6 ka for the northern south central and southern gbr however no hiatus in reef flat growth was observed in reefs from the central gbr with ages ranging from 7 6 ka to 0 9 ka increased upwelling turbidity and cyclone activity in response to increased sea surface temperature sst s precipitation and el nino southern oscillation variability have been ruled out as possible mechanisms of reef turn off for the mid outer platform reefs rather a fall 0 5 m in relative sea level at 4 3 5 ka is the most likely explanation for why reefs in the northern and southern regions turned off during this time greater hydro isostatic adjustment of the central gbr and long term subsidence of the halifax basin may have provided greater vertical accommodation for the mid outer reefs of the central gbr thus allowing these reefs to continue to accrete vertically despite a fall in sea level 4 3 5 ka further evidence for greater subsidence in this region includes the lack of senile reefs and dominance of incipient and juvenile reefs in the central gbr this suggests that these reefs approached sea level considerably later than the northern and southern reefs consistent with their deeper antecedent substrates thus these results not only provide important information about possible reef flat demise in response to natural environmental factors but also provide insights into regional subsidence that affected relative sea level along the east australian margin during the holocene

tidal jets nutrient upwelling and their influence on the productivity of the alga halimeda in the ribbon reefs great barrier reef abstract a field experiment was carried out to study water circulation and benthic biological productivity near a passage through the ribbon reefs in the northern great barrier reef of australia the currents through the passage were phase locked with the tide during rising tides strong currents through the passage generated localized upwelling on the upper continental slope enriching the depleted surface waters in nutrients particularly nitrate and phosphate simultaneously on the shelf side of the passage a tidal jet vortex pair system developed which separated from the ribbon reefs so that the coral reefs themselves received little of the upwelled water this was propagated as a bottom trapped layer towards the meadows of the calcareous alga halimeda situated several kilometres inshore of the reefs halimeda can accumulate nutrients particularly nitrate from the relatively low concentrations available from the upwelling events the quantity of nitrogen upwelled was more than sufficient to supply the total nitrogen requirements of the halimeda vegetation a tidal jet also formed offshore from the reef passage during falling tides and the coral covered offshore side of the ribbon reefs may be sustained by the subsequent vertical turbulent entrainment into the jet of deep nutrient rich water immediately offshore from the reef passages these processes require a continuous barrier reef with only narrow passages several kilometers apart numerical models successfully reproduce the observations of jet driven upwelling and of the dynamics of the tidal jet vortex pair system the model predictions are very sensitive to the details of the bathymetry of reef passages as such data are presently unavailable it is not yet possible to use these models to calculate the jet driven nutrient upwelling for the whole great barrier reef

deep tow magnetic anomaly study of the pacific jurassic quiet zone and implications for the geomagnetic polarity reversal timescale and geomagnetic field behavior 1 the jurassic quiet zone jqz is a region of low amplitude magnetic anomalies whose distinctive character may be related to geomagnetic field behavior we collected deep tow magnetic profiles in pigafetta basin western pacific where previous deep tow data partially covered the jqz sequence our goals were to extend the survey through the jqz examine anomaly correlations and refine a preliminary geomagnetic polarity timescale gpts model we collected a series of closely spaced profiles over anomaly m34 and ocean drilling program hole 801c to examine anomaly correlation in detail one profile in between previous profiles and two long profiles extending the survey deeper into the jqz anomaly features can be readily correlated except in a region of low amplitude short wavelength anomalies in the middle of the survey area low amplitude zone or laz the small multiprofile surveys demonstrate anomaly linearity implying that surrounding anomalies are also linear and likely result from crustal recording of geomagnetic field changes we constructed a gpts model assuming that most anomalies result from polarity reversals the polarity timescale is similar to the polarity sequences from previous studies but its global significance is uncertain because of problems correlating anomalies in the laz and the ambiguous nature of the small jqz anomalies overall anomaly amplitude decreases with age into the laz and then increases again implying low geomagnetic field strength perhaps related to a rapidly reversing field other factors that may contribute to the laz are interference of anomalies over narrow crustal polarity zones and poorly understood local tectonic complexities

milankovitch climatic origin of mid cretaceous black shale rhythms in central italy the earth s orbital variations reflected in pleistocene ice volume were also recorded in non glacial times carbonate production in pelagic mid cretaceous sediments quantified by calcium carbonate and optical densitometry time series reflects the orbital eccentricity and precessional cycles minimal eccentricity brought deep sea anoxia most of the sedimentary variability of this 100 myr old sequence lies within the milankovitch orbital frequency band

postglacial sediment deposition along a mixed carbonate siliciclastic margin new constraints from the drowned shelf edge reefs of the great barrier reef australia a seismic stratigraphy analysis was conducted at two sites hydrographers and noggin passages separated by about 540 km on the shelf edge of the central great barrier reef gbr australia we used recently available seismic and bathymetry data and a new synthesis of downhole logs and lithological petrophysical and radiometric data from cores recovered by the integrated ocean drilling program expedition 325 great barrier reef environmental changes we compared the stratigraphy of both sites identifying a full depositional sequence with deposits from at least 28 ka bp to 7 ka bp bounded by two marine flooding surfaces within this sequence each systems tract is represented by unique depositional features characteristic of the shelf edge systems despite the broad environmental and geomorphic similarities between the two sites differences in postglacial reef development were remarkable these contrasts can be explained as a result of 1 local antecedent substrate variations and 2 the interplay of shelf physiography with late quaternary sea level fluctuations which favoured changes in biological production and sediment flux as the palaeo shoreline evolved from linear to complex during intermediate sea levels during these intermediate sea levels the northern estuarine coast and its steep substrate at shelf edge locations contrasted strongly with the protected palaeo lagoons and the extensive gentle marginal terraces found at the southern central gbr this setting enhanced the regional differences in sediment transport and reef development through the last transgression the conceptual model presented here provides a broader depositional framework and improves the understanding of the main processes controlling the spatial and temporal depositional patterns on the shelf edge of mixed siliciclastic carbonate margins

m sequence geomagnetic polarity time scale mhtc12 that steadies global spreading rates and incorporates astrochronology constraints 1 geomagnetic polarity time scales gptss have been constructed by interpolating between dated marine magnetic anomalies assuming uniformly varying spreading rates a strategy to obtain an optimal gpts is to minimize spreading rate fluctuations in many ridge systems however this has been possible only for a few spreading centers we describe here a monte carlo sampling method that overcomes this limitation and improves gpts accuracy by incorporating information on polarity chron durations estimated from astrochronology the sampling generates a large ensemble of gptss that simultaneously agree with radiometric age constraints minimize the global variation in spreading rates and fit polarity chron durations estimated by astrochronology a key feature is the inclusion and propagation of data uncertainties which weigh how each piece of information affects the resulting time scale the average of the sampled ensemble gives a reference gpts and the variance of the ensemble measures the time scale uncertainty we apply the method to construct mhtc12 an improved version of the m sequence gpts late jurassic early cretaceous 160 120 ma this gpts minimizes the variation in spreading rates in a global data set of magnetic lineations from the western pacific north atlantic and indian ocean nw of australia and it also accounts for the duration of five polarity chrons established from astrochronology cm0r through cm3r this gpts can be updated by repeating the monte carlo sampling with additional data that may become available in the future

transient tidal circulation and momentum balances at a shallow inlet an analysis of transient momentum balances is carried out to elucidate circulation dynamics and exchange mechanisms at shallow barotropic tidal inlets circulation is computed using a depth integrated fully nonlinear time stepping finite element model with variably spaced grids having horizontal resolution down to 50 m velocity and elevation fields from the model are used to directly evaluate the contribution of each term in the momentum equations to the overall momentum balance a transformation of the x y momentum terms into an s n coordinate system is used to simplify the interpretation of the dynamics and provide vivid illustrations of the forces and resulting accelerations in the flow the analysis is conducted for an idealized inlet and contrasted with a highly detailed model of beaufort inlet north carolina results show that momentum balances in the immediate vicinity of these inlets vary significantly in time and space and oscillate between two dynamical states near maximum ebb or flood the alongstream momentum balances are dominated by advective acceleration pressure gradient and bottom friction cross stream balances are dominated by centrifugal acceleration and pressure gradients near slack balances more closely follow linear wave dynamics with local accelerations balancing pressure gradients and to a lesser degree coriolis comparisons between the idealized inlet and beaufort inlet show broad similarities in these momentum balances however natural inlet geometry and bottom topography as well as the tidal transmission characteristics of the sounds behind beaufort inlet produce strong asymmetries moreover momentum balances are highly localized often with subkilometer length scales the dynamics are used to explain the physical mechanisms for inlet exchange in particular the results indicate that the cross stream dynamics generate a wall along the length of an inlet during the stronger phases of the tide the wall is established by opposing cross inlet pressure gradients and centrifugal forces and it poses a significant barrier to cross inlet exchange during the stronger phases of the tide but is absent near slack

tidally induced upwelling by the great barrier reef the great barrier reef is similar to some other coral reefs in growing right up to the edge of the shelf in a region of nutrient poor surface water but large tides it is suggested that the resultant strong tidal currents suck in nutrient rich water from the depth where the tidal flow speed drops to the fastest internal wave speed the nutrients could encourage the reef to grow vigorously at the edge of the shelf some observations in cook s passage 14 32 s 145 34 e were made to test the concept and are encouraging

siderophile element systematics of iab complex iron meteorites new insights into the formation of an enigmatic group siderophile trace element abundances and the 187re 187os isotopic systematics of the metal phases of 58 iab complex iron meteorites were determined in order to investigate formation processes and how meteorites within chemical subgroups may be related close adherence of 187re 187os isotopic data of most iab iron meteorites to a primordial isochron indicates that the siderophile elements of most members of the complex remained closed to elemental disturbance soon after formation minor presumably late stage open system behavior however is observed in some members of the slm slh shl and shh subgroups the new siderophile element abundance data are consistent with the findings of prior studies suggesting that the iab subgroups cannot be related to one another by any known crystallization process equilibrium crystallization coupled with crystal segregation solid liquid mixing and subsequent fractional crystallization can account for the siderophile element variations among meteorites within the iab main group mg the data for the slm subgroup are consistent with equilibrium crystallization combined with crystal segregation and mixing by contrast the limited fractionation of siderophile elements within the sll subgroup is consistent with metal extraction from a chondritic source with little subsequent processing the limited data for the other subgroups were insufficient to draw robust conclusions about crystallization processes involved in their formation collectively multiple formational processes are represented in the iab complex and modeling results suggest that fractional crystallization within the mg may have been a more significant process than has been previously recognized

observation of internal tidal currents in the kaoping canyon off southwestern taiwan abstract internal tidal currents and associated water mass displacements were investigated during multiple cruises in the kaoping submarine canyon off southwestern taiwan observations from both moored and shipboard acoustic doppler current profilers and hydrographic casts were conducted along the canyon the velocity data showed that in the lower layer the major axis of the tidal currents aligned with the orientation of the canyon and currents moved up canyon during flood and down canyon during ebb the vertical phase shift and amplitude of the currents indicated that the semidiurnal internal tide dominated with intensity increasing with depth toward the canyon head tidal energy was channeled from the shelf landward with a beamlike internal wave guided by bottom topography the estimated phase velocity was 1 4 1 7 m s 1 based on normal mode analysis and the phase lag between sampling stations empirical orthogonal function analysis of hydrographic profiles confirmed that the first mode m 2 internal tide explained 70 of the total variance the strong convergence of internal tidal currents near the canyon head during flood may play an important role in the daily migration of cherry shrimps which burrow along the canyon wall

revised pacific m anomaly geomagnetic polarity timescale summary the current m anomaly geomagnetic polarity timescale gpts is mainly based on the hawaiian magnetic lineations in the pacific ocean m anomaly gpts studies to date have relied on a small number of magnetic profiles a situation that is not ideal because any one profile contains an uncertain amount of geologic noise that perturbs the magnetic field signal compiling a polarity sequence from a larger array of magnetic profiles is desirable to provide greater consistency and repeatability we present a new compilation of the m anomaly gpts constructed from polarity models derived from magnetic profiles crossing the three lineation sets hawaiian japanese and phoenix in the western pacific polarity reversal boundary locations were estimated with a combination of inverse and forward modelling of the magnetic profiles separate gpts were established for each of the three pacific lineation sets to allow examination of variability among the different lineation sets and these were also combined to give a composite timescale owing to a paucity of reliable direct dates of the m anomalies on ocean crust the composite model was time calibrated with only two ages one at each end of the sequence these two dates are 125 0 ma for the base of m0r and 155 7 ma for the base of m26r relative polarity block widths from the three lineation sets are similar indicating a consistent pacific wide spreading regime the new gpts model shows slightly different spacings of polarity blocks as compared with previous gpts with less variation in block width it appears that the greater polarity chron irregularity in older models is mostly an artifact of modelling a small number of magnetic profiles the greater averaging of polarity chron boundaries in our model gives a gpts that is statistically more robust than prior gpts models and a superior foundation for late jurassic early cretaceous geomagnetic and chronologic studies

large amplitude leaky island generated internal waves around palau micronesia three years of temperature data along two transects extending to 90 m depth at palau micronesia show twice a day thermocline vertical displacements of commonly 50 100 m and on one occasion 270 m the internal wave occurred at a number of frequencies there were a number of spectral peaks at diurnal and semi diurnal frequencies as well as intermediate and sub inertial frequencies less so at the inertial frequency at palau the waves generally did not travel around the island because there was no coherence between internal waves on either side of the island the internal waves at a site 30 km offshore were out of phase with those on the island slopes suggesting that the waves were generated on the island slope and then radiated away palau island was thus a source of internal wave energy for the surrounding ocean a numerical model suggests that the tidal and low frequency currents flowing around the island form internal waves with maximum wave amplitude on the island slope and that these waves radiate away from the island the model also suggests that the headland at the southern tip of palau prevents the internal waves to rotate around the island the large temperature fluctuations commonly daily fluctuations 10 c peaking at 20 c appear responsible for generating a thermal stress responsible for a biologically depauperate biological community on the island slopes at depths between 60 and 120 m depth

high resolution unstructured meshes for hydrodynamic models of the great barrier reef australia accuracy and mesh generation are key issues for the high resolution hydrodynamic modelling of the whole great barrier reef our objective is to generate suitable unstructured grids that can resolve topological and dynamical features like tidal jets and recirculation eddies in the wake of islands a new strategy is suggested to refine the mesh in areas of interest taking into account the bathymetric field and an approximated distance to islands and reefs such a distance is obtained by solving an elliptic differential operator with specific boundary conditions meshes produced illustrate both the validity and the efficiency of the adaptive strategy selection of refinement and geometrical parameters is discussed

river plumes coral reefs and mixing in the gulf of papua and the northern great barrier reef abstract the mean annual freshwater discharge in the gulf of papua principally from the fly kikori and purari rivers is estimated to be 13000 m 3 s 1 water from these rivers forms a low salinity surface layer in the gulf where it has a residence time of about two months and flows generally eastward a small fraction of this water intrudes through bligh entrance on the great barrier reef continental shelf horizontal patchiness and mixing of these intruding waters with shelf waters are considerably enhanced by secondary circulation wakes around coral reefs the wakes shapes visible in enhanced landsat imagery are similar to those around cylinders and plates in laboratory experiments at low reynolds numbers topographically enhanced mixing may explain why the cross shelf gradients of temperature and of the structure of fish communities are smaller in the northern region than in the central region of the great barrier reef

surface current patterns in front of the venice lagoon abstract surface patterns of the low frequency current in a 20 30 km region in front of the venice lagoon were analysed from a 13 month long hf radar data set surface circulation was related to prevalent wind regimes in the area and to the tidal flow through the lagoon inlet three different categories of wind forcing were defined bora ne wind sirocco se wind and finally the category containing all other wind directions and calms winds lower than 3 m sec mean flow and vorticity spatial distributions were discussed for different wind conditions the coastal area about 5 km wide is characterized by a flow field with maximum vorticity outside the coastal boundary layer the interior flow is part of the adriatic basin wide cyclonic circulation two counter rotating vortices of the dimension of about 4 5 km were evidenced in the average flow field in front of the lagoon inlet malamocco inlet in all situations except for the bora the vortex pair is probably associated with the tidal flow through the inlet the bora wind induces a strong southward coastal jet detached from the coast by about 5 km homogenizing the flow and eliminating the dipole the average coastal flow pattern in calm wind conditions was also analysed as a function of the strong inflow outflow currents in the inlet 0 7 m s 1 from the lagoon inlet in both cases the vorticity pattern is similar with the negative vorticity to the left of the inlet and positive to the right looking seaward

a multi scale model of the hydrodynamics of the whole great barrier reef an unstructured mesh parallel hydrodynamic model of the whole great barrier reef is presented this model simultaneously simulates most scales of motion it allows interactions between small and large scale processes the depth averaged equations of motion are discretized in space by means of a mixed finite element formulation while the time marching procedure is based on a third order explicit adams bashforth scheme the mesh is made up of triangles their size and shape can be modified easily so as to resolve a wide range of scales of motion from those of the regional flows to those of the eddies or tidal jets that develop in the vicinity of reefs and islands the forcings are the surface wind stress the tides and the inflow from the coral sea east australian current coral sea coastal current the latter two forcings being applied along the open boundaries of the computational domain the numerical results compare favourably with observations of both longshore currents and the local perturbations due to narrow reef passages comparisons are also performed with the simulations of a three dimensional model applied to a small domain centered on rattray island showing that both models produce similar horizontal flow fields for a structured mesh model to yield results of the same accuracy there is no doubt that the computational cost would be much higher

island wakes in shallow coastal waters rattray island northeast australia is 1 5 km long 300 m wide and lies in well mixed water approximately 25 m deep its long axis is inclined at about 60 into the direction of the dominant semidiurnal tidal current the length of the wake in the lee of the island as documented by aerial photographs and satellite imagery appears to equal that of the wake behind a flat plate in a two dimensional flow at a reynolds number of about 10 however current metering drogues measurements and temperature mapping indicate internal wake velocities much greater than would be consistent with such a simple low reynolds number model further estimates of the turbulent eddy coefficient suggest an effective reynolds number more in the vicinity of 103 to reconcile these observational differences and to explain the observed upwelling in the core of the wake an ekman pumping model is proposed it is postulated that the ekman benthic boundary layer driven by rotation in the wake allows the vertical vorticity introduced into the water at the tip of the island at the point of separation to be negated by the vorticity of opposite sign introduced at the bottom further it is shown that a large fraction of the kinetic energy of the upstream flow facing the island is used to drive the wake eddies leading to the conclusions that the trapping of water in the lee of islands greatly increases head losses on continental shelves with numerous islands coral reefs and rock outcrops

acoustic doppler current profiler measurements of the velocity field of an ebb tidal jet a broadband acoustic doppler current profiler was used to measure the velocity field of the ebb tidal jet formed at the entrance to the otago harbour south island new zealand four separate surveys were conducted where various sets of transects were run continuously over a 13 hour period producing time series of velocity profiles with 1 hour sampling over a grid with an across jet resolution of 20 m and an along jet resolution of 150 m the velocity field of the ebb tidal jet is phase locked to the tidal response of the harbor making it possible to combine the data from separate tidal cycle surveys to produce synoptic maps of the depth averaged velocity field the spatial structure of the ebb tidal jet at the time of peak flow exhibits many features of a classical plane jet there is a strong asymmetry between the ebb and flood flow structures the ebb flow extends beyond 2 km from the entrance while the flood flow is limited to within 600 m of the coast the flow along the jet axis becomes pulse like in time with distance from the entrance the pulse that develops propagates way from the entrance at a speed slower than the advective speed of the ebb jet the formation of a propagating eddy observed along the eastern side of the jet suggests that this momentum pulse may be associated with the pair of separation eddies generated by the accelerating ebb tidal flow