evolution of double diffusion convection in a felsic magma chamber abstract the onset of double diffusion convection ddc is modeled in a two dimensional case in respect to magma chambers the viscosity model for the melt takes into account the effects of temperature and concentration of the dissolved component h 2 o the upper boundary of the convecting magma chamber is assumed to be anhydrous and at constant temperature whereas the lower boundary is treated as being hydrous permeable with a temperature greater than that within the upper boundary the case of positive compositional and thermal buoyancy of melt is studied assuming a h 2 o diffusion coefficient small in comparison with thermal diffusivity the ddc has been modeled using a system of equations solved by the finite difference method on a square grid the convective pattern evolution has been studied for fixed boundary conditions as well as for cooling and degassing due to the higher viscosity in the upper zone the upper boundary layer is thicker than the lower one the variation of water concentration in this zone of the convective cell can be significant in nature the high gradient of water concentration can be responsible for the observed variations of water content in minerals crystallized from a granite melt e g biotite because of a high lewis number 100 temperature variations in the magma chamber decay much faster than the water concentration in this case the intensive convection can continue at a constant temperature due to the non zero water content in the chamber in principle the effect can be applied to the formation of magmatic bodies if the cooling and degassing system reaches a uniform temperature distribution prior to the crystallization temperature water content throughout the body may still remain variable

settling of ocean dumped dredged material townsville australia mud is dredged from the port of townsville australia and its navigation channel and is dumped offshore in typically 12 m depth there are two stages to the settling initial rapid descent as a negatively buoyant jet forming a high concentration suspension near the bottom followed by subsequent slower settling of mud flocs in calm weather mud flocs settled out of this layer in about 15 min and the suspension did not move out of the dump site in rough weather the settling of mud flocs was inhibited by wave induced turbulence and the suspension was mobile and was transported away from the dump site in quiescent waters this suspension compacted to about 8 0 of its original volume in approximately 4 days even after compaction the mud was resuspended presumably by pumping by long waves since no strong currents were observed forming a mobile 1 m thick high concentration suspension at the bottom

factors controlling the field settling velocity of cohesive sediment in estuaries abstract it has long been recognized that the suspended sediment concentration ssc is one of the major determinants for the flocculation of cohesive particles into sediment flocs in estuaries it is furthermore well known that the turbulent shear of the water significantly influences the flocculation process and the equilibrium settling velocity of flocculated sediment in a turbulent flow a vast number of authors have reported algorithms relating the median settling velocity w 50 to suspended sediment concentration however only a few studies have dealt with the impact of the turbulent shear in this paper expressed as the root mean square rms velocity gradient g in the water on the w 50 in situ there is a strong need to establish algorithms based on in situ measurements describing the dual impact of both ssc and g on the flocculation process and hence w 50 the present paper addresses this topic field settling velocities of suspended cohesive sediment have been measured in micro meso and macro tidal estuaries regression analyses between the w 50 ssc and g are presented it is shown that by including both g and ssc in the regression analyses a significant increase in the correlation of the description of w 50 and the controlling parameters from each area can be obtained a generic algorithm describing the data from all the investigated areas is suggested it works well within specific tidal areas but fails to give a generic description of the field settling velocity

double diffusive convection in magma chambers single or multiple layers an approximate set of equations applicable to double diffusive convection in magma chambers has been solved in the steady state for a range of geologically relevant parameters no evidence for the steady state existence of layered convection for conditions appropriate to magma chambers has been found at large ratios of the thermal to chemical diffusivity lewis number le the heat transport is independent of the lewis number and equal to that found for thermal convection in a single component fluid the vertical upward transport of light component varies directly with both the rayleigh and lewis numbers nuc ra0 23 le0 37

evolutionary structures in double diffusive convection in magma chambers finite amplitude solutions to subcritical time dependent double diffusive convection d d c applicable for magma chambers are obtained by a two dimensional finite element method based on stream function temperature and compositional fields grid refinement is used for resolving the disparately scaled thermal and chemical boundary layers present for large ratios of the thermal to chemical diffusivity lewis number characteristic of magmas the occurrence of layered convection depends strongly on the initial conditions of the temperature and composition it is shown that in the infinite prandtl number limit a local transition from a diffusive to a finger like regime can take place for large enough lewis numbers this time dependent finding suggests that a strict categorization of d d c into the finger and diffusive regimes requires modification in geological applications

induced compositional layering in a convecting fluid layer by an endothermic phase transition abstract an endothermic phase change in the presence of chemical heterogeneities can act as an efficient filter such that heavy material is sequestered below the phase change and light material is trapped above the phase change due to the fact that the endothermic phase change damps thermal convection it can act as a trap door for chemical heterogeneities ascending flows which are chemically dense will need more thermal buoyancy to rise through the transition than ascending flows whose composition is closer to the background composition likewise descending flows which are chemically light need more thermal buoyancy to sink through the transition the results of a suite of numerical calculations of two dimensional double diffusive convection in a fluid layer with an endothermic phase change suggests that if the 670 km seismic discontinuity has a steep enough clapeyron slope compositional layering may be induced and dynamically maintained by the transition furthermore these calculations also show that the phase change and compositional boundaries will approximately coincide

dynamics of the turbidity maximum in king sound tropical western australia king sound is a 100 km long embayment located in tropical northwestern australia with a spring tidal range of 11 m this is the second largest tide in the world after the bay of fundy in canada intertidal areas cover about 800 km2 the upper reaches of the sound are turbid with fine suspended sediment concentration reaching 3 kg m 3 field studies of the dynamics of water and fine sediment were carried out in the dry seasons of 1997 and 1998 the tide was a propagating wave shoaling and dissipating by friction as it entered the sound this mode of propagation generated an asymmetric tidal current with a stronger current at flood than at ebb an evaporation driven salinity maximum zone was found in the upper reaches of the sound and this was also where the turbidity maximum occurred tidal pumping by the tidal asymmetry and possibly the biological filter formed by muddy marine snow trapped the fine sediment in the upper regions of king sound wind driven waves contributed significantly to entrainment of bottom fine sediment possibly through wave pumping of the sediment and not wave induced orbital velocities field data suggest that erosion of bottom fine sediment was proportional to the sixth power of the tidal current and the third power of the wave height

10be constrains the sediment sources and sediment yields to the great barrier reef from the tropical barron river catchment queensland australia abstract estimates of long term background sediment generation rates place current and future sediment fluxes to the great barrier reef in context without reliable estimates of sediment generation rates and without identification of the sources of sediment delivered to the reef prior to european settlement c 1850 determining the necessity and effectiveness of contemporary landscape management efforts is difficult here using the 2100 km 2 barron river catchment in queensland australia as a test case we use in situ produced 10 be to derive sediment generation rate estimates and use in situ and meteoric 10 be to identify the source of that sediment which enters the coral sea near cairns previous model based calculations suggested that background sediment yields were up to an order of magnitude lower than contemporary sediment yields in contrast in situ 10 be data indicate that background 43 t km 2 y 1 and contemporary sediment yields 45 t km 2 y 1 for the barron river are similar these data suggest that the reef became established in a sediment flux similar to what it receives today since western agricultural practices increased erosion rates large amounts of sediment mobilized from hillslopes during the last century are probably stored in queensland catchments and will eventually be transported to the coast most likely in flows triggered by rare but powerful tropical cyclones that were more common before european settlement and may increase in strength as climate change warms the south pacific ocean in situ and meteoric 10 be concentrations of coral sea beach sand near cairns are similar to those in rivers on the atherton tablelands suggesting that most sediment is derived from the extensive low gradient uplands rather than the steep more rapidly eroding but beach proximal escarpment

development of an inshore fringing coral reef using textural compositional and stratigraphic data from magnetic island great barrier reef australia the stratigraphy of fringing coral reef environments and platforms provides unique insights into reef development and evolution this study used twelve sediment cores from three transects across a reef flat in nelly bay magnetic island ne australia to examine its development over the holocene the maximum thickness of the holocene reefal material based on seismic and bore log data was around 5 m and comparable to other fringing reefs in the great barrier reef gbr six different sedimentary facies were identified in the cores and two coincided with reef accretion the lower muddy sand with coral rubble and the upper siliciclastic sand with coral rubble radiocarbon and u series dates show that the nelly bay fringing reef initiated around 6300 yr bp on a gently sloping unconsolidated or weakly cemented pleistocene alluvial sedimentary facies the ages of four massive coral heads range between 5790 and 6290 calibrated c 14 yr bp were almost contemporaneous with reefal initiation indicating that conditions were favourable for reef growth around this time vertical accretion rates for the nelly bay fringing reef were on average about 0 5 mm yr over the last 6000 yr although rates were as high as 5 mm yr during initiation average lateral accretion rates varied from 98 to 120 mm yr which are comparable to rates of other fringing reefs in the region the age structure of the lower muddy sedimentary facies was consistent with the classic seaward prograding model of fringing reef development in contrast the upper siliciclastic sand with coral rubble facies was much younger in age 1100 yr bp than the models and appears to represent an erosional unconformity between the upper and lower reefal facies possibly linked to late holocene sea level fall this younger facies extends laterally across the reef flat and has no obvious prograding symmetry our integrated approach using multi proxy analyses of sediment cores from the nelly bay reef flat highlights the complex development of this reef which include changes in coral composition and rubble preservation reef evolution in response to sea level change and changes in reef accretion rates

characterization of sediment trapped by macroalgae on a hawaiian reef flat abstract reef researchers studying community shifts in the balance between corals and fleshy macroalgae have noted that algae are often covered with sediment this study characterizes sediment trapping by macroalgae within a hawaiian reef habitat and constrains the controls on this process sediment laden macroalgae were sampled and macroalgal cover was assessed on a wide 1 km reef flat off south central molokai macroalgae trapped a mean of 1 26 0 91 sd grams of sediment per gram of dry weight biomass and that sediment was dominantly terrigenous mud 59 by weight it was determined that biomass as a proxy for algal size and morphology were not strict controls on the sediment trapping process over 300 metric tons of sediment were estimated to be retained by macroalgae across 5 75 km 2 of reef flat 54 g m 2 suggesting that this process is an important component of sediment budgets in addition understanding the character of sediment trapped by macroalgae may help constrain suspended sediment flux and has implications for nutrient dynamics in reef flat environments

reactive dispersion of stable isotopes by mineral reaction during metamorphism abstract the process of reactive dispersion is introduced whereby reaction in one chemical system imparts hydrodynamic dispersion to another apparently unrelated reactive transport system reactive dispersion is illustrated with a one dimensional finite difference model for coupled heat flow fluid flow mineral reaction and oxygen isotopic exchange during contact metamorphism of siliceous dolomite infiltration driven decarbonation reactions impart isotopic heterogeneity to an initially homogeneous system the effect on fluid composition is explored using a breakthrough curve that tracks fluid composition through time the corresponding effects on rock composition are illustrated with plots of isotopic alteration vs distance reactive dispersion is especially efficient during infiltration of h 2 o into carbonate rocks because 18 o is strongly fractionated between co 2 and h 2 o and because mineral reactions may buffer the co 2 h 2 o content of fluid the spatially heterogeneous isotopic alteration predicted to develop during decarbonation reactions in a homogeneous protolith is similar in magnitude and distribution to that observed downstream of the isotopic depletion front in contact metamorphic aureoles

the effect of hydrobia ulvae and microphytobenthos on cohesive sediment dynamics on an intertidal mudflat described by means of numerical modelling previous investigations have documented spatial and temporal variations in the erosion threshold erosion rate and suspended sediment settling characteristics on an intertidal mudflat in a microtidal coastal plain estuary in the danish wadden sea the differences seem to be very much controlled by the effects of benthic biology rather than by physical parameters in order to test to what extend biology may interact with the dynamics of fine grained sediment in an entire estuarine system these results have been transformed into four different sets of erodibility and settling characteristics which have been used as input to the 2d hydrodynamic numerical model mike 21 mt the model was used to investigate the effect that differences in the benthic communities may have on the net deposition the model included computation of hydrodynamics wave fields and cohesive sediment dynamics based on the modelling results presented it is suggested that the benthic biological activity affects the net sedimentation pattern at the investigated site the modelling results suggest that the presence of large numbers of the destabilising mudsnail hydrobia ulvae results in higher net accumulation on the intertidal mudflat investigated in contrast biofilms may change net deposition by decreasing erosion suspended sediment concentration and consequently the resulting settling flux of the suspended material this study suggests that a numerical hydrodynamic model in combination with a fieldwork based set up of a cohesive sediment transport model may be used to describe and explain net sediment dynamics in a shallow coastal plain estuary

wet season fine sediment dynamics on the inner shelf of the great barrier reef fine sediment dynamics were recorded in february 2007 in coastal waters of the great barrier reef during a moderate flood of the tully river an estuarine circulation prevailed on the inner continental shelf with a surface seaward velocity peaking at 0 1 m s 1 and a near bottom landward flow peaking at 0 05 m s 1 much of the riverine mud originating from eroded soils was exported onto a 10 km wide coastal strip during the rising stage of the river flood in the first flush in coastal waters suspended sediment concentration peaked at 0 2 kg m 3 near the surface and 0 4 kg m 3 at 10 m depth during calm weather and 0 5 kg m 3 near the surface and 2 kg m 3 at 10 m depth during strong winds when bottom sediment was resuspended diurnal irradiance at 4 m depth was almost zero for 10 days the sedimentation rate averaged 254 33 g m 2 d 1 over the 28 day study period and concentrations of dissolved and particulate nutrients originating from the river were high the observed low irradiance would have prevented coral photosynthesis while the sedimentation rate would have been lethal to some juvenile corals the mud may ultimately be minnowed out over long periods however flushing of the mud occurs at time scales much longer than the flood event and the mud is likely to affect coral physiology for significant periods after the flood has subsided the data show the need to better control erosion on farmed land for the conservation of coral reefs on the inner shelf of the great barrier reef

overturn and evolution of a crystallized magma ocean a numerical parameter study for mars 1 early in the history of terrestrial planets the fractional crystallization of a magma ocean can lead to a mantle stratification characterized by a progressive enrichment in heavy elements from the core mantle boundary to the surface such configuration is gravitationally unstable it causes mantle overturn and the formation of a stable chemical layering using simulations of thermo chemical convection we analyzed the consequences of overturn and subsequent layering on mantle dynamics assuming mars scaling parameters we found that the time needed to achieve chemical homogenization via convective mixing scales exponentially with the buoyancy ratio inline image which measures the relative importance of chemical to thermal buoyancy in addition when using a strongly temperature dependent viscosity the formation of a stagnant lid prevents the uppermost crystallized layers from sinking into the mantle in order to obtain their subduction an yielding mechanism must be invoked 2 in the context of mars evolution our results suggest that complete chemical mixing is unlikely to take place within time scales comparable with the planet s age magma ocean freezing could be thus responsible for the long term preservation of compositional heterogeneities as required by meteoritic evidence the lack of a surface highly enriched in incompatible elements and of a high density lid is difficult to reconcile with a stagnant lid regime operating throughout mars history an episode of surface mobilization induced by compositional overturn can resolve this difficulty provided that inline image is large enough too large buoyancy ratios however tend to suppress convective heat transport rendering it problematic to explain the late volcanic history of mars

radial fluid flow and reaction during contact metamorphism radial fluid flow in cylindrical and spherical contact metamorphic aureoles produces alteration patterns that are distinctly different from those predicted for cartesian one dimensional flow the combined effects of flow focusing and decreasing reactive rock volume during inward flow result in more alteration and steeper alteration versus distance profiles applied to contact metamorphism cartesian models overestimate by as much as an order of magnitude the time integrated fluid fluxes necessary to produce observed alteration by inward fluid flow outward radial flow is less efficient than cartesian flow because reactive rock volume increases and fluid flux is defocused cartesian models tend to underestimate the quantity of magmatic fluid required to produce alteration by outward flow

a model for the interior structure evolution and differentiation of callisto abstract the recently measured dimensionless moment of inertia moi factor for callisto of 0 3549 0 0042 anderson et al 2001 icarus 153 157 161 poses a problem its value cannot be explained by a model in which callisto is completely differentiated into an ice shell above a rock shell and an iron core such as its neighboring satellite ganymede nor can it be explained by a model of a homogeneous undifferentiated ice rock satellite we show that callisto may be incompletely differentiated into an outer ice rock shell in which the volumetric rock concentration is close to the primordial one at the surface and decreases approximately linearly with depth an ice mantle mostly depleted of rock and an about 1800 km rock ice core in which the rock concentration is close to the close packing limit the ice rock shell thickness depends on uncertain rheology parameters and the heat flow and can be roughly 50 to 150 km thick we show that if callisto accreted from a mix of metal bearing rock and ice and if the average size of the rocks was of the order of meters to tens of meters then callisto may have experienced a gradual but still incomplete unmixing of the two components an ocean in callisto at a depth of 100 200 km is difficult to obtain if the ice is pure h2o and if the ice rock lithosphere is 100 km or more thick a water ocean is more plausible for ice contaminated by ammonia methane or salts or for pure h2o at a depth of 400 600 km

nonlinear physics of double diffusive convection in geological systems double diffusive convection d d c is a nonlinear fluid dynamical phenomenon driven by thermal and compositional effects on the density we discuss the nature of subcritical finite amplitude double diffusive convection for infinite prandtl number and large lewis number le which have applications in magma chambers and at the d layer at the core mantle boundary cmb numerical solutions by two dimensional finite element method are presented to portray the nature of time dependent d d c in both the diffusive and the finger regimes the compositional heterogeneities at the cmb are far more complex than the local thermal structure because of the largele and may have important implications for the scattering of seismic waves off the cmb the effects of increasing the buoyancy ratior are to suppress time dependent d d c even at highra in narrow slots shear heating instabilities can be triggered in the finger regime by the abrupt overturn of the compositional interface this phenomenon may occur in tall magma chambers with low dissipation numbers of of order 0 0 01

modis imagery of turbid plumes in san diego coastal waters during rainstorm events abstract data of normalized water leaving radiance nlw obtained from the moderate resolution imaging spectroradiometer modis on the aqua satellite at spatial resolution of 250 m band 1 centered at 645 nm and 500 m band 4 at 555 nm are used to study turbid plumes in coastal waters of southern california during rainstorm events in winter of 2004 2005 our study area includes san diego coastal waters which extend approximately 25 km offshore between point loma and 10 km south of the us mexican border these waters are influenced by terrigenous input of particulate and dissolved materials from san diego and tijuana watersheds and non point sources along the shore optimum threshold values of satellite derived normalized water leaving radiances at both wavebands were established for distinguishing the plume from ambient ocean waters these threshold values were determined by searching for a maximum correlation between the estimates of satellite derived plume area calculated using a broad range of nlw values and the environmental variables characterizing rainfall river discharge wind and tides a correlation analysis involving the amount of precipitated water accumulated during a storm event over the san diego and tijuana watersheds was selected as the basis for final determinations of the optimum threshold nlwthr and subsequent calculations of the plume area by applying this method to a sequence of modis imagery we demonstrate the spatial extent and evolution of the plume during rainstorm events under various conditions of precipitation river discharge wind forcing and coastal currents

wave induced water motion and the functional implications for coral reef fish assemblages using a functional approach we quantified water motion and the distribution of fish swimming modes across five habitat zones and four exposure regimes commonly found on coral reefs there were major spatial variations in net flow velocity 7 4 43 2 cm s21 and rates of flow direction change 0 06 0 66 hz among habitats of different depth water motion within the shallow crest and flat habitats appeared to be largely wave driven with rates of flow direction change 0 63 0 66 hz corresponding with approximately double the wave periodicity 0 31 0 36 hz and relatively little contribution 14 16 from drift flow velocities a similar variation in water motion was found among reefs of different exposure with the highest and lowest velocities recorded in the exposed and sheltered locations respectively exposed and oblique reef crests displayed greater temporal variation in wave height and water motion 24 4 59 5 cm s21 net velocities when compared with the relatively static conditions in sheltered 6 2 12 6 cm s21 and lagoonal sites 17 1 25 3 cm s21 we examined the distribution and functional structure of seven coral reef fish families 156 species across the full range of water motion variation on these reefs pectoral swimming fishes were the most abundant group predominating in areas with high levels of water motion pectoral caudal and caudal swimming fishes displayed the opposite trend we suggest that these differences are the result of an interaction between water motion and the biomechanical and energetic attributes associated with each swimming mode

transition to chaos and implications for time scales of magma hybridization during mixing processes in magma chambers abstract in this contribution numerical simulations of magma mixing are carried out with the aim of understanding the physico chemical conditions that trigger the development of chaotic mixing dynamics in detail the mixing process is simulated in a magma chamber where a less evolved magma underplates a more evolved magma the chaoticity of this system is quantitatively estimated via computed finite time lyapunov exponents it is shown that magma chamber dynamics are strongly controlled by the rayleigh number ra whereas other parameters such as buoyancy ratio and viscosity ratio play a subordinate role results indicate that magma chambers with ra of the order of 10 6 are dominated by non chaotic behaviour increasing ra shifts the system towards an increasing chaotic state and in particular above ra 10 7 chaotic dynamics are fully developed in the magma chamber estimates of possible time scales of hybridization of magmas during chaotic mixing suggest for example that a blob of mafic magma with an initial diameter of 100 m within a magma chamber with a width of 1000 m is stretched to a filament like structure with a thickness of 15 m after 320 years and after 1900 years its thickness is reduced to 4 0 mm using typical chemical diffusion coefficients for magmas of the order of 10 14 m 2 s it can be calculated that a 4 0 mm thick filament would homogenize by diffusion in 10 years such homogenization time scales are orders of magnitude lower that typical life times estimated for magma chambers even in the volcanic environment indicating that fast hybridization of magmas can be rapidly achieved when chaotic dynamics govern the evolution of the magmatic system

kimberlite emplacement temperatures from conodont geothermometry abstract kimberlites are mantle derived ultramafic rocks preserved in volcanic and sub volcanic edifices and are the main primary source of diamonds the temperatures of formation transport eruption and deposition remain poorly constrained despite their importance for understanding the petrological and thermodynamic properties of kimberlite magmas and styles of volcanic eruption here we present measured values of colour alteration indices cai for conodonts recovered from 76 paleozoic carbonate xenoliths found within 11 pipes from the chidliak kimberlite field on baffin island nunavut canada the dataset comprises the largest range of cai values 1 5 to 8 and the highest cai values reported to date for kimberlite hosted xenoliths thermal models for cooling of the chidliak kimberlite pipes and synchronous heating of conodont bearing xenoliths indicate time windows of 10 20 000 h and for these short time windows the measured cai values indicate heating of the xenoliths to temperatures of 225 to 925 c we equate these temperatures with the minimum temperatures of the conduit filling kimberlite deposit i e emplacement temperature t e the majority of the xenoliths record cai values of between 5 and 6 5 suggesting heating of xenoliths to temperatures of 460 c 735 c the highest cai values are consistent with being heated to 700 c 925 c and establish the minimum conditions for welding or formation of clastogenic kimberlite deposits lastly we use t e variations within and between individual pipes in conjunction with the geology of the conduit filling deposits to constrain the styles of explosive volcanic eruption

migration of reaction and isotopic fronts in infiltration zones assessments of fluid flux in metamorphic terrains abstract criteria are presented for recognising fluid infiltration driven reactions in metamorphic rocks and quantifying the associated fractionations of oxygen and carbon isotopic compositions in medium or high grade metamorphic rocks with local equilibrium between fluid and solid phases reactions or isotopic changes driven by infiltrating fluid are expected to migrate as relatively sharp fronts with limited diffusive broadening fluid leaving such reaction fronts is compositionally buffered by the reacting phases in suitably reactive rocks a series of reaction fronts will develop each driven by infiltration of fluid buffered by the upstream reaction knowledge of the spatial arrangement of such fronts allows calculation of the time integrated fluid fluxes total fluid volume per unit area distinctive stable isotope fractionations are predicted adjacent to infiltration driven reactions with the distribution and magnitude of the fractionation effects dependent upon the relative velocities of the reaction and isotopic fronts the various possibilities are illustrated by reference to a hypothetical infiltration driven decarbonation reaction the calculated isotopic fractionations do not in general resemble those predicted by the open or closed system water rock ratio calculations

implications of geochemical fronts in the notch peak contact metamorphic aureole utah usa abstract the geochemistry of the notch peak contact metamorphic aureole was examined to determine the dominant source of fluid attendant on metamorphism and to estimate fluid fluxes progressive metamorphism of calc silicate rocks is defined by phlogopite diopside and wollastonite isograds mineral assemblages at wollastonite and diopside grades indicate water rich conditions during decarbonation reactions near the intrusion the rocks are highly fractured in both the horizontal and the vertical direction the 18o values of most unmetamorphosed through diopside grade rocks range from 16 3 to 20 2 whereas in the wollastonite zone and near a pre intrusion fault the values approach the 9 5 value of the granitic stock coincident with the zone of18o depletion are zones of ba and zn enrichment consideration of solubilities of these elements in magmatic fluids and of published mineral water distribution coefficients indicates that these elements were advected from the magma model 18o profiles for up temperature flow of formation water assuming variable damko hler numbers and both static and variable thermal gradients fit poorly most data and do not reproduce the broadened front in the observed profile in contrast model profiles for radial one dimensional flow of magmatic water with variable damko hler number under static or variable thermal gradients fit the data well although the model isotopic front remains less distended that the one observed the integrated radial flux of magmatic water indicated by the position of the isotopic front is 1 8 107 mol m 2 additional broadening of the observed front and the scatter of the data suggest diffusion or hydrodynamic dispersion of oxygen regression of the data indicates an effective porosity of 12 in the inner aureole during fluid flow the porosity was largely fracture controlled and resulted from decarbonation sustained exsolution of water from the magma and up to 30 reaction produced volume loss in the high grade rocks the coincidence of the ba zn and 18o fronts suggests that bulk of the magmatic water flow was confined to the wollastontie zone the exception is the proximity of the fault where fluids emanating from an underlying part of the intrusion may also have flowed upward through lower grade rocks

importance of wave induced bed liquefaction in the fine sediment budget of cleveland bay great barrier reef data from a three year long field study of fine sediment dynamics in cleveland bay show that wave induced liquefaction of the fine sediment bed on the seafloor in shallow water was the main process causing bed erosion under small waves during tradewinds and that shear induced erosion prevailed during cyclonic conditions these data were used to verify a model of fine sediment dynamics that calculates sediment resuspension by both excess shear stress and wave induced liquefaction of the bed for present land use conditions the amount of riverine sediments settling on the bay may exceed by 50 75 the amount of sediment exported from the bay sediment is thus accumulating in the bay on an annual basis which in turn may degrade the fringing coral reefs for those years when a tropical cyclone impacted the bay there may be a net sediment outflow from the bay during the dry tradewind season fine sediment was progressively winnowed out of the shallow reefal waters

high temperature metamorphism and the role of magmatic heat sources at the rogaland anorthosite complex in southwestern norway the rogaland complex covers 1000 km in southwestern norway and consists mainly of anorthosite massifs and the layered bjerkreim sokndal lopolith bsl these rocks intrude charnockitic migmatites containing intercalated marbles and garnetiferous migmatites high temperature mineral isograds pigeonite osumilite and orthopyroxene in the metamorphic basement are subparallel to and increase in grade towards the intrusive complex p t estimates from the country rocks show a roughly linear increase in temperature towards the bsl consistent with the distribution of isograds the peak p t conditions at 20 and 2 5 km from the contact at 5 kbar range from 700 to 41000 c field relations and age determinations link the high t metamorphism and the magmatism the two dimensional thermal modelling indicates that heat from a single magmatic cooling unit is not sufficient to produce the array of isograds and the peak metamorphic temperatures two magmatic episodes separated by 3myr however can account for the high temperature metamorphism in this model the emplacement and crystallization of the anorthosite produces a regional thermal gradient from 750 to 600 c after a brief hiatus a second smaller body bsl provides an additional thermal input that results in an array of high temperature isograds and country rock temperatures 41000 c

modelling of suspended sediment transport in coastal areas under waves and currents abstract a coupled hydrodynamic suspended sediment transport model including waves and currents was developed four models a nested grid circulation model 2 d and 3 d a refraction diffraction dissipation wave propagation model a wave current bottom boundary layer model and a quasi 3 d suspended sediment concentration ssc model are integrated the model system has been applied to cleveland bay australia to study ssc in january and march 1993 when two high ssc events 100 mg l 1 were observed during an intensive field monitoring programme the swell has been found to be the dominant suspension mechanism and thus an important factor of high ssc in the bay the model was able to predict the high ssc events in january and march 1993 a net deposition rate in cleveland bay was estimated to be about 0 1 mm year 1 a figure consistent with geological evidence

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

importance of biologically mediated removal of fine sediments from the fly river plume papua new guinea abstract a freshwater plume from the fly river papua new guinea stretched to the south west over a distance of more than 150 km from the estuary towards torres strait the highly turbid freshwater was mixed with the relatively clear water of the gulf of papua producing a sharp boundary around 23 salinity sediment concentrations were typically more than 50 mg l 1 inside the turbid water mass and were rapidly reduced to a few milligrams per litre in the area where salinity was still as low as 26 the area had relatively high levels of phytoplankton 1 g chl l 1 resulting in rapid depletion of nitrate and phosphate biological as well as physico chemical flocculation processes seemed responsible for the rapid removal of sediments from the plume settling particles collected near the estuary consisted largely of fine sediments bound loosely by flocculant organic matter and contained very few plankton and their remains further away from the estuary however settling particles were dominated by colonies of phytoplankton fecal pellets and macroscopic aggregates of apparently biological origin fine sediments were found firmly attached to or embedded in these settling particles the area of high biological activities in the plume probably functions as a barrier limiting a further offshore transport of sediments