nucleation dominated crystallization of forsterite in the ubehebe peak contact aureole california the morphology and number of forsterite crystals in the ubehebe peak california contact aureole vary systematically as a function of metamorphic grade from their first appearance to as close as 150 m from the intrusive contact forsterite crystals are large 5 20 mm and have a tabular habit a c b in contrast forsterite near the contact is equigranular and much smaller 1 mm in diameter the number of crystals per mole of forsterite increases from 3 5 104 at the forsterite in isograd to more than 1 5 108 near the contact this trend is interpreted to result from an increase in the ratio of nucleation rates with respect to growth rates with proximity to the intrusion the change in morphology from tabular to equigranular is explained by kinetic surface roughening the nucleation and growth information gained from this study highlights the important role of nucleation kinetics in the crystallization of forsterite at the ubehebe peak aureole

a comparison study of zonal drift velocities measurements as seen by mf spaced antenna and hf doppler radar in the indian dip equatorial mesospheric and lower thermospheric 80 100 km region 1 the simultaneous measurements of zonal drift velocities observed in the heights of 84 98 km in the indian geomagnetic dip equatorial region by an medium frequency mf 1 98 mhz spaced antenna and a high frequency hf 18 mhz doppler radars are compared on selected few days in the solar maximum years of 1998 1999 and 2000 the agreement between the two radar measurements is found to be good below about 88 km where the neutral turbulence induced ionospheric irregularities are more predominant above 90 km however the agreement becomes poor and at the highest height of 98 km it becomes the least at this height more often the hf doppler radar shows a westward drift of about 200 m s whereas the mf spaced antenna radar values lie within 10 m s and sometimes attain maximum values of 50 m s detailed discussions are made on the possible sources of underestimation of the drift velocities measured by the mf radar and the nature of scattering irregularities that are produced because of large neutral turbulences and plasma instabilities it is suggested that these neutral and plasma turbulences particularly type ii plasma irregularities contribute in a different manner to different radar frequencies and techniques and hence very different drift velocities in the heights of 90 100 km particularly in the geomagnetic dip equatorial region discussions are also made on 1 the real atmospheric and ionospheric physical process prevailing in the 90 100 km region and 2 the technical aspects of the radars that limits them to measure only particular types of motion in this region

the influence of whitecapping waves on the vertical structure of turbulence in a shallow estuarine embayment abstract the vertical distribution of the turbulent kinetic energy dissipation rate was measured using an array of four acoustic doppler velocimeters in the shallow embayment of grizzly bay san francisco bay california owing to the combination of wind and tide forcing in this shallow system the surface and bottom boundary layers overlapped whitecapping waves were generated for a significant spectral peak steepness greater than 0 05 or above a wind speed of 3 m s 1 under conditions of whitecapping waves the turbulent kinetic energy dissipation rate in the upper portion of the water column was greatly enhanced relative to the predictions of wind stress wall layer theory instead the dissipation followed a modified deep water breaking wave scaling near the bed bottom 10 of the water column the dissipation measurements were either equal to or less than that predicted by wall layer theory stratification due to concentration gradients in suspended sediment was identified as the likely cause for t

a numerical study of circulation in a coastal reef lagoon system 1 a coupled wave circulation numerical model was used to simulate the distribution of wave energy as well as the circulation induced by wave breaking wind and tidal forcing within a coral reef system in kaneohe bay oahu hawaii modeled wave current and wave setup fields were compared with field measurements collected on the forereef reef flat and reef channels and in the lagoon over a 4 week period the predicted wave height transformation across the reef lagoon system was in good agreement with field observations using single parameter spatially uniform values to describe both wave breaking and frictional dissipation the spatial distribution of the resulting wave setup field drove a persistent wave driven flow across the reef flat that returned to the ocean through two deeper channels in the reef both the magnitude and direction of these currents were well described using a spatially uniform hydraulic roughness length scale notably the model lends support to field observations that setup within the coastally bounded lagoon was a substantial fraction of the maximum setup on the reef 60 80 which generated relatively weak cross reef wave driven flows 10 20 cm s 1 compared with reefs having mostly unbounded lagoons e g many atolls and barrier reefs numerical experiments conducted using lagrangian particle tracking revealed that residence times within kaneohe bay are extremely heterogeneous typically ranging from 1 month within its sheltered southern lagoon

wave transformation over coral reefs ocean wave attenuation on coral reefs is discussed using data obtained from a preliminary field experiment and from the seasat altimeter marked attenuation of the waves is observed the rate being consistent with existing theories of bottom friction and wave breaking decay in addition there is a significant broadening of the spectrum during propagation across reefs three dimensional effects such as refraction and defraction can also lead to substantial wave height reduction for significant distances adjacent to coral reefs as a result a matrix of such reefs provides significantly more wave attenuation than may initially be expected

laboratory observation of boundary layer flow under spilling breakers in surf zone using particle image velocimetry abstract a boundary layer flow under spilling breakers in a laboratory surf zone with a smooth bottom is investigated using a high resolution particle image velocimetry piv technique by cross correlating the images oscillatory velocity profiles within a viscous boundary layer of o 1 mm in thickness are resolved over ten points using piv measurements taken for an earlier study and the present study flow properties in the wave bottom boundary layer wbbl over the laboratory surf zone are obtained including the mean velocities turbulence intensity reynolds stresses and intermittency of coherent events the data are then used to estimate the boundary layer thickness phase variation and bottom shear stress it is found that while the time averaged mass transport inside the wbbl is onshore in the outer surf zone it changes to offshore in the inner surf zone the zero eulerian mass transport occurs at h hb 0 92 in the outer surf zone the maximum overshoot of the streamwise velocity and boundary layer thickness are not constant across the surf zone the bottom shear stress is mainly contributed by the viscous stress through mean velocity gradient while the reynolds stress is small and negligible the turbulence level is higher in the inner surf zone than that in the outer surf zone although only a slight increase of turbulent intensity is observed inside the wbbl from the outer surf zone to the inner surf zone the variation of phase inside and outside the wbbl was examined through the spatial velocity distribution it is found the phase lead is not constant and its value is significantly smaller than previous thought by analyzing instantaneous velocity and vorticity fields a remarkable number of intermittent turbulent eddies are observed to penetrate into the wbbl in the inner surf zone the size of the observed large eddies is about 0 11 to 0 16 times the local water depth its energy spectra follow the 5 3 slope in the inertial subrange and decay exponentially in the dissipation subrange

accumulation of transition metals and metalloids in sulfidized stromatolites of the 3 48 billion year old dresser formation pilbara craton abstract stromatolites of the 3 48 billion year old dresser formation pilbara craton western australia provide some of the oldest convincing evidence of life on earth here we augment previous evidence with a detailed investigation of the concentrations and distributions of various transition metals cr mn co ni cu zn mo se ag sn au hg and pb and metalloids as sb and te in unweathered samples of strongly sulfidized stromatolites from drill cores high resolution elemental mapping and in situ compositional analysis of sulfides pyrite and sphalerite show that these sedimentary and hydrothermally sourced elements are strongly concentrated in texturally distinctive nano porous pyrite enriched in autochthonous organic matter which forms the major petrogenetically earliest component of wrinkly laminated and digitate growth fabrics within the stromatolites repeated cyclic alternations of various transition metals and metalloids most importantly ni and zn plus the presence of disconformities and overgrowth relationships between wrinkly stromatolite laminae suggest that these element accumulations were primarily established by depositional processes during continuous stromatolite formation because transition metals and metalloids generally have strong affinities for organic matter and can play active roles in biochemical processes we interpret these element accumulations in the dresser formation stromatolites to be the result of binding to organic matter of living microbial communities and or dead biomass and perhaps also microbial utilization collectively our results show that the precise characterization of transition metal metalloid concentrations and distributions can unveil element enrichment patterns suggestive of biological activity even in some of earth s oldest stromatolites

satellite traces an ionogram signature for large scale wave structure and a precursor for equatorial spread f 1 although the source that controls day to day variability in the occurrence of equatorial plasma structure i e equatorial spread f or esf remains to be identified progress is being made there is evidence that the appearance of large scale wave structure lsws in the bottomside f layer around the time of its post sunset rise pssr is a more direct precursor of esf than the pssr itself the bulk of the evidence however is in the form of satellite f traces in ionograms which may be viewed as less than convincing because these signatures have not been shown to be causally related to lsws in this paper incoherent scatter radar and ionosonde data both collected on 24 july 1979 from the kwajalein atoll marshall islands are used to show that this is indeed the case

the dynamics of travertine dams we present a simple abstract model for travertine dam formation the simulation uses a depth averaged hydrodynamic code coupled with an empirical precipitation model where surface normal growth rate is proportional to local flow rate the dynamics of the resulting formation coarsening and migration progradation of crests is demonstrated and compared with field observations the local self enhancement of crests due to increasing flow rate in combination with lateral inhibition due to upstream drowning implies a classical pattern formation system with a characteristic dam size however this wavelength is not stable but increasing the model also reproduces crest lobes step bunching and other processes that contribute to the complex dynamics of travertine systems

vertical structure of dissipation in the nearshore abstract the vertical structure of the dissipation of turbulence kinetic energy was observed in the nearshore region 3 2 m mean water depth with a tripod of three acoustic doppler current meters off a sandy ocean beach surface and bottom boundary layer dissipation scaling concepts overlap in this region no depth limited wave breaking occurred at the tripod but wind induced whitecapping wave breaking did occur dissipation is maximum near the surface and minimum at middepth with a secondary maximum near the bed the observed dissipation does not follow a surfzone scaling nor does it follow a log layer surface or bottom boundary layer scaling at the upper two current meters dissipation follows a modified deep water breaking wave scaling vertical shear in the mean currents is negligible and shear production magnitude is much less than dissipation implying that the vertical diffusion of turbulence is important the increased near bed secondary dissipation maximum results from a decrease in the tu

julia radar studies of equatorial spread f this paper presents coherent scatter radar observations of plasma irregularities in the equatorial f region ionosphere made with the julia jicamarca unattended long term studies of the ionosphere and atmosphere radar and discusses model equations and simulations pertinent to their interpretation the data set shows that bottom type and bottomside scattering layers are prevalent throughout solar minimum equinox bottom type layers are undifferentiated and relatively weak layers confined to a narrow range of altitudes falling within regions of the ionosphere driven by the e region dynamo these layers are often precursors to large scale radar plumes as well as to bottomside layers which are broader more structured and more intense layers than the bottom type variety bottomside layers are the source of intermediate scale plasma depletions that can ascend and penetrate through to the topside fluid simulations of the collisional interchange instability suggest that dynamo theory explains why one kind of layer emerges at a given time and altitude

growth and characterization of complex mineral surfaces precipitation of mineral aggregates near the earth s surface or in subsurface fractures and cavities often produces complex microstructures and surface morphologies here we demonstrate how a simple surface normal growth sng process may produce microstructures and surface morphologies very similar to those observed in some natural carbonate systems a simple sng model was used to fit observed surfaces thus providing information about the growth history and also about the frequency and spatial distribution of nucleation events during growth the sng model can be extended to systems in which the symmetry of precipitation is broken for example by fluid flow we show how a simple modification of the sng model in which the local growth rate depends on the distance from a fluid source and the local slope or fluid flow rate produces growth structures with many similarities to natural travertine deposits

high resolution observations of 150 km echoes at jicamarca high resolution soundings of equatorial upper e region echoes at jicamarca exhibit gravity wave modulated signal intensity distributions and doppler velocities corresponding to vertical plasma drifts a gravity wave wind driven interchange instability is suggested as a possible generation mechanism of the field aligned plasma irregularities responsible for the echoes the echoes may be utilized in gravity wave studies and in zonal electric field measurements by radars with modest sensitivities

calcite precipitation instability under laminar open channel flow abstract we present a 2d numerical model for the growth of calcite from supersaturated aqueous solutions under laminar open channel flow conditions the model couples solution chemistry precipitation at solution calcite interfaces hydrodynamics diffusion and degassing the model output is compared with experimental results obtained using an oversaturated calcite solution produced by mixing cacl 2 and na 2 co 3 the precipitation rate is observed to increase when the supersaturated solution flows over an obstruction leading to a growth instability that causes the formation of terraces at relatively high flow rates the most important mechanism for this behaviour seems to be hydrodynamic advection of dissolved species either towards or away from the calcite surface depending on location relative to the obstruction which deforms the concentration gradients at lower flow rates steepening of diffusion gradients around protrusions becomes important enhanced degassing over the obstruction due to shallowing and pressure drop is not important on small scales diffusion controlled transport close to the calcite surface can lead to a fingering type growth instability which generates porous textures our results are consistent with existing diffusive boundary layer theory but for flow over non smooth surfaces simple calcite precipitation models that include empirical correlations between fluid flow rate and calcite precipitation rate are inaccurate

hydrodynamic forces on larvae affect their settlement on coral reefs in turbulent wave driven flow this study investigates a key aspect of how ambient flow affects the recruitment of water dispersed marine larvae onto benthic substrata the sweeping away of larvae that have landed on surfaces through a combination of field and laboratory measurements we studied how waves interact with a complex substratum to affect hydrodynamic forces encountered by microscopic larvae sitting at different positions on the bottom terrain we used larvae of the nudibranch phestilla sibogae settling onto coral reefs as the system to address this question laser doppler anemometry was utilized within a laboratory flume to measure water velocities encountered 200 m mf rom coral surfaces by microscopic larvae sitting at different locations within a reef of the branching coral porites compressa comparing wave driven flow based on conditions measured over p compressa reefs in hawaii with unidirectional flow of the same mean velocity we found that peak shear stresses along coral surfaces were 15 times greater and hydrodynamic forces on larvae were 10 times higher in wave conditions peak forces on larvae sitting on the reef top were 3 10 times greater than on larvae 5 10 cm below the reef top intermittent bursts of high velocity which occurred more often at the reef top than within it determined the settlement probability for larvae in different reef microhabitats the faster and more strongly a larva sticks to a surface the higher the probability of successful settlement using values for p sibogae adhesive strength we predict they can settle only on sheltered surfaces within reefs

spectral wave dissipation over a barrier reef 1 a 2 week field experiment was conducted to measure surface wave dissipation on a barrier reef at kaneohe bay oahu hawaii wave heights and velocities were measured at several locations on the fore reef and the reef flat which were used to estimate rates of dissipation by wave breaking and bottom friction dissipation on the reef flat was found to be dominated by friction at rates that are significantly larger than those typically observed at sandy beach sites this is attributed to the rough surface generated by the reef organisms which makes the reef highly efficient at dissipating energy by bottom friction results were compared to a spectral wave friction model which showed that the variation in frictional dissipation among the different frequency components could be described using a single hydraulic roughness length scale surveys of the bottom roughness conducted on the reef flat showed that this hydraulic roughness length was comparable to the physical roughness measured at this site on the fore reef dissipation was due to the combined effect of frictional dissipation and wave breaking however in this region the magnitude of dissipation by bottom friction was comparable to wave breaking despite the existence of a well defined surf zone there under typical wave conditions the bulk of the total wave energy incident on kaneohe bay is dissipated by bottom friction not wave breaking as is often assumed for sandy beach sites and other coral reefs

ionospheric variability over indian low latitude linked with the 2009 sudden stratospheric warming in this paper we analyze radar observations of e b drift and plasma irregularities ionosonde observations of e and f layer parameters including spread f and magnetic field observations made from indian low latitudes linked with the 2009 sudden stratospheric warming ssw event e b drift variations presented here are the first of their kind from the indian sector as far as the effect of ssw is concerned difference of magnetic fields observed from the equator and low latitude h and e b drift show linear relation and both show remarkably large positive values in the morning and negative values in the afternoon exhibiting semidiurnal behavior remarkable changing patterns in the critical frequency of f2 layer fof2 and f3 layer fof3 were observed after the occurrence of ssw large variations with quasi 16 day periodicity were observed in h fof2 and fof3 both semidiurnal and quasi 16 day wave modulation observed after the 2009 ssw event are consistent with those reported earlier we also noted quasi 6 day variations in h and fof2 soon after the ssw commencement not much reported before during the counterelectrojet events linked with the ssw event while equatorial es esq disappeared as expected there were no blanketing es esb a finding not reported and discussed earlier esb was also not formed at the off equatorial location indicating the absence of required vertical wind shear but e region plasma irregularities were observed by the ionosonde and radar with a close relationship between the two weak f region irregularities were observed in the postmidnight hours and case studies suggest the possible role of ssw related background electric field in the manifestation of postmidnight f region irregularities

tide effects on wave attenuation and wave set up on a caribbean coral reef abstract the effects of tides on wave attenuation and wave set up were investigated at great pond bay a caribbean reef located in st croix u s virgin islands measurements of wave pressure fluctuations were made at three stations across the reef profile total wave set up was measured between the forereef and the reef crest or backreef lagoon wave spectra indicate significant filtering of energy at the peak frequencies as waves traveled across the reef the energy dissipation calculations imply an average energy reduction of 62 between the forereef and reef crest mean energy reduction between the forereef and lagoon was 90 energy dissipation between the forereef and reef crest increased 15 between high and low tide and 6 between forereef and lagoon tidal reduction of water depth at the reef crest intensified wave breaking and this condition increased energy dissipation measurements of wave set up ranged from 0 8 to 1 5 cm calculations of wave set up using tait s 1972 model showed good agreement with observations

growth and development of spring towers at shiqiang yunnan province china abstract throughout the world high artesian pressures in hydrothermal areas have led to the growth of tall spring towers that have their vents at their summits the factors that control their development and formative precipitates are poorly understood because these springs irrespective of location are mostly inactive spring towers found at shiqiang yunnan province china which are up to 4 m high and 3 m in diameter are formed largely of calcite and aragonite crystal bushes euhedral calcite crystals and coated grains with alternating fe poor and fe rich zones calcite rafts and cements formed of various combinations of calcite aragonite strontianite mg si reticulate needle fiber calcite calcified and non calcified microbes diatoms and insects collectively the limestones that form the towers can be divided into 1 group a that are friable porous and form the cores of the towers and have 18 o smow values of 15 7 to 19 7 average 17 8 and 13 c pdb values of 5 1 to 6 9 average 5 9 and 2 group b that are hard and well lithified and found largely around the vents and the tower sides and have 18 o smow values of 13 0 to 22 0 average 17 6 and 13 c pdb values of 1 4 to 3 6 average 2 6 the precipitates and the isotopic values indicate that these were thermogene springs growth of the shiqiang spring towers involved 1 phase ia when precipitation of calcite and aragonite bushes formed the core of the tower and phase ib when calcite commonly fe rich was precipitated locally 2 phase ii that involved the precipitation of white cements formed of calcite aragonite strontianite and mg si reticulate coatings in cavities amid the phase i precipitates and 3 phase iii which formed probably after spring activity ceased when needle fiber calcite was precipitated and the mounds were invaded by microbes some now calcified diatoms and insects at various times during this complex history pore waters mediated dissolution of the calcite and aragonite and sometimes partial alteration of the aragonite the diverse array of precipitates depositional fabrics and diagenetic changes clearly indicate that the composition of the spring water changed frequently growth of the spring towers at shiqiang continued until there was insufficient artesian pressure to lift the water above the top of the tower vent

boundary layer turbulence and flow structure over a fringing coral reef measurements of velocity and rates of turbulence were made across a fringing coral reef in the gulf of aqaba red sea to determine the effect that the rough topography has on boundary layer mixing and flow dynamics observations were made at two fore reef sites and a nearby sandy slope the friction velocity u and drag coefficient cd were determined directly from turbulent reynolds stresses measured using acoustic doppler velocimeters values of cd for the coral substrates ranged from 0 009 to 0 015 three to five times greater than over the sandy bottom site the turbulence dissipation rate e was determined by fitting spectra of vertical velocity to the theoretical 5 3 law expected for the inertial subrange of turbulence there was a local balance between production and dissipation of turbulent kinetic energy signifying that we could estimate u from either the mean velocity profile turbulence or dissipation rate of turbulent kinetic energy estimates from all three measures agreed well with mean u uo ranging from 0 10 6 0 03 to 0 12 6 0 03 indicating that existing turbulent boundary layer flow theory can be applied to flows over the rough topography of coral reefs the bottom topography by enhancing both reef scale and local drag and mixing levels allows reef biota to more effectively exchange dissolved and particulate matter with oceanic waters

a primitive alkali basaltic stratovolcano and associated eruptive centres northwestern spitsbergen volcanology and tectonic significance abstract three quaternary volcanic centres sverrefjell sigurdfjell and halvdanpiggen in northwestern spitsbergen formed by off ridge alkali basaltic volcanism associated with nearby ocean floor spreading and subsequent tectonism the sverrefjell volcano is a unique stratovolcano constructed of primitive alkali basaltic pyroclastics with subordinate lavas about 15 20 vol of this volcanic and the other centres comprises a wide variety of upper mantle and lower crustal xenoliths a new estimate of the age of the sverrefjell volcano places the time of formation at a minimum of 100 000 250 000 years ago earlier than previous estimates the occurrence of interbedded pillow lavas and pahoehoe flows at all levels of sverrefjell suggests that the volcano grew concurrently with the rise of the surrounding glaciers basaltic sequences occurring as nearby mountain cappings represent earlier volcanism 2 5 11 5 ma also probably a result of thermal disturbance related to nearby ocean floor spreading geothermobarometry calculations on xenoliths from the three quaternary localities define a very high geotherm consistent with their location near the yermak hot spot and provide a good datum point for the geothermal gradient adjacent to such a thermal anomaly

wave set up on coral reefs 2 set up on reefs with various profiles abstract all available laboratory data for wave set up on two dimensional reef profiles of various shapes have been compared with data from an idealised horizontal reef with a steep reef face gourlay 1996 the data is generally well represented by a relationship between the relative set up parameter gh r t o and the submergence parameter g h r h r h o and the relative set up on reef profiles of natural form is found to be less than that observed on the idealised horizontal reef the important influences of reef rim slope and variable water depths on the reef top have been investigated and some methods for allowing for them are suggested comparison of data for irregular waves with that for regular waves has led to the development of a simple method for estimating the effects of wave groups upon the magnitude of the steady state mean wave set up gh r the results of the analyses are applied to the determination of wave set up and its effects at three specific coral reef sites

field observations of wave driven water level gradients across a coral reef flat 1 field measurements of still water surface elevations were obtained across a narrow leeward reef flat on lady elliot island great barrier reef australia in june 2003 stilling wells were deployed from the reef crest landward to the island beach and waves and mean water levels were monitored over both rising and falling tides during low to moderate wave energy conditions wave setup of up to 13 8 cm above still water level occurred in the presence of incident waves of 0 4 m yielding maximum water surface slopes greater than 6 results show that the magnitude of wave setup varies both temporally and spatially across the reef with changing water depth setup is dominant on the reef edge at low tide evolving into a dual setup system at both the reef edge and shoreline at midtide and finally a dominant shoreline setup at high tide on lady elliot island the dual setup system is considered to result from spatial differences in transformation and breaking of swell and wind waves at midtide stages the presence of a dual setup system across a reef flat has not been previously identified in field or modeling studies and has potentially significant implications for reefal current development sediment transport and the stability of reef island shorelines

on the co seismic ionospheric disturbances cids in the rapid run ionosonde observations over allahabad following mw 7 8 nepal earthquake on april 25 2015

wave generated flow on coral reefs an analysis for two dimensional horizontal reef tops with steep faces waves breaking on the seaward rim of a coral reef generate a flow of water from the exposed side of the reef to the sheltered side and or to either channels through the reef rim or lower sections of the latter this wave generated flow is driven by the water surface gradient resulting from the wave set up created by the breaking waves this paper reviews previous approaches to modelling wave generated flows across coral reefs and discusses the influence of reef morphology and roughness upon these flows laboratory measurements upon a two dimensional horizontal reef platform with a steep reef face provide the basis for extending a previous theoretical analysis for wave set up on a reef in the absence of a flow gourlay m r 1996b wave set up on coral reefs 2 set up on reefs with various profiles coastal engineering 28 1755 to include the interaction between a unidirectional flow and the wave set up the laboratory model results are then used to demonstrate that there are two basic reef top flow regimes reef top control and reef rim control using open channel flow theory analytical relationships are derived for the reef top current velocity in terms of the offreef wave conditions the reef top water depth and the physical characteristics of the reef top topography the wave set up and wave generated flow relationships are found to predict experimental values with reasonable accuracy in most cases the analytical relationships are used to investigate wave generated flows into a boat harbour channel on heron reef in the southern great barrier reef c 2005 elsevier b v all rights reserved

wave driven flow over shallow reefs long term 1 month observations of waves and currents over a natural reef are presented which show a strong correlation between offshore rms incident wave height and cross reef currents at subtidal frequencies the energy spectrum of the cross reef currents shows a significant peak at twice the semidiurnal tidal frequency while the spectrum of sea surface elevation over the reef flat shows no corresponding peak furthermore experimental results reported by gourlay 1993 show setup over the reef occurs in the absence of a beach and the cross reef transport decreases with an increase in the sea surface slope across the reef flat due to an increase in setup at the top of the reef face analytic solutions for flow forced by wave breaking over an idealized reef explain the above features of cross reef flows in the absence of a beach through the surf zone on the reef face the cross reef gradient in the radiation stress due to wave breaking is partitioned between balancing an offshore pressure gradient associated with setup over the reef and forcing a mean flow across the reef over the reef flat where the depth is constant there is no forcing due to wave breaking and the flow is driven by a pressure gradient which results from the setup through the surf zone the magnitude of the setup through the surf zone is such that the transport across the reef flat matches the transport through the surf zone which is forced by the gradient in the radiation stress solutions are presented for general reef geometry defined by the reef width and slope of the seaward reef face and incident wave forcing defined by the depth at the breakpoint and the depth of water over the reef as the depth over the reef goes to zero the solutions converge to the plane beach solutions described by longuet higgins and stewart 1964 wave setup is maximized and the cross reef transport is zero in other cases the relative magnitudes of the setup and the cross reef transport depend on the geometry of the reef and the incident wave forcing

presunrise spread f at fortaleza at fortaleza brazil in the equatorial zone about 400 km south of the magnetic equator a presunrise secondary maximum of spread f occurrence is observed during sunspot minimum and in particular during december solstice the spread f takes the form of patches of irregularities that are convecting eastwards at 50 m s 1 most of the patches are collocated with bottomside bulges of the ionosphere our measurements indicate that these bottomside bulges are unstable due to a gradient drift instability that is slowly growing and produces the spread f the bulges themselves seem to be evidence of a rayleigh taylor instability process

wave breaking hydrodynamics within coral reef systems and the effect of changing relative sea level this paper considers the hydrodynamics of wave driven flow across a coral reef and the resultant flushing of its lagoon current depth coefficients are introduced that describe the fractional change of across reef and lagoonal current with change in the relative local sea level i e the depth of water over the reef flat the coefficients are derived from an analytical hydrodynamic model and compared with data from two reefs the first is ningaloo reef in northwest australia which is a typical barrier reef with a narrow coastal lagoon and the second is kaneohe bay in oahu hawaii where the reef is both unusually deep and wide the current depth coefficients are shown to be sensitive to the form of the frictional law on the reef flat and can be deduced from measurements of the astronomical tidal currents in the lagoon both quadratic and linear friction laws are considered for the reef flat and good agreement obtained with a linear law based on the high frequency motion due to surface gravity waves

modeling flow in coral communities with and without waves a synthesis of porous media and canopy flow approaches both canopy flow and porous media theories have been developed independent of one another to predict flow through submerged porous structures these approaches are very similar albeit with some key differences in how canopy resistance forces are parameterized canopy models provide a means of parameterizing the shear stresses that occur at the top of the canopy whereas porous media models can often provide a simpler and more tractable way of parameterizing turbulent form drag based on simple morphological metrics and empirical relationships already in the hydrology literature we developed a set of equations combining aspects of both models and applied this hybridized model to predict the flow structure within an experimental canopy formed by the branching coral porites compressa using model parameter values obtained from the literature results from the model predictions agreed well with direct measurements of flow speed and flow forces derived from particle image velocimetry under conditions of both unidirectional and wave driven oscillatory flow

wave transformation on a coral reef wave transformation of regular waves was measured in a laboratory model of a fringing reef with a steep face and an outer reef top slope gradually decreasing in the landward direction data was obtained for various wave conditions and water levels a nonlinearity parameter fco g1 25ho 0 5t2 5 hc 1 75 based upon one proposed by swart and loubser 1979 is proposed as a suitable parameter for classifying wave transformation regimes on this reef in particular when fco 150 waves plunge on the reef edge and the amount of wave energy reaching a shore or structure is small 16 when fin co 100 waves spill on the reef top but the greater part of their energy is transmitted over the reef top the maximum values of the wave height to water depth ratio on the reef top were found to be consistent with nelson s analyses for laboratory and field data which indicate that the maximum stable wave height to depth ratio h d on a horizontal bottom never exceeds 0 55 for shallow water waves fc 500 the experimental data confirms that the maximum value of h d decreases when fc decreases but that it also increases when the bottom slope increases

mass transfer limitation of nutrient uptake by a wave dominated reef flat community maximum rates of phosphate nitrate and ammonium uptake by a reef flat community were estimated from rates of frictional dissipation that were calculated from the attenuation of waves propagating over the kaneohe bay barrier reef flat time averaged flow speeds across the entire study area ranged from 0 08 to 0 22 m s 21 observed decreases in wave energy fluxes and near bottom orbital velocities gave a mean estimate for the bottom friction coefficient cf of 0 22 6 0 03 friction coefficients were used to estimate nutrient mass transfer coefficients of 5 9md 21 for phosphate and 9 16 m d 21 for ammonium and nitrate wave heights offshore of kaneohe bay were also used to estimate an annual phosphate mass transfer coefficient of 8 6 2md that was determined from measured changes in phosphate concentrations across the reef flat we conclude that rates of phosphate uptake by the kaneohe bay barrier reef flat community are occurring near the limits of mass transfer net primary production is a major pathway by which mass and energy flow into coral reef ecosystems the uptake of dissolved nutrients is often the rate limiting step for net pri mary production in marine ecosystems thus a knowledge of the kinetics of nutrient uptake by coral reef communities is necessary for assessing how nutrient loading rates change in response to natural or anthropogenic increases in nutrient concentrations bilger and atkinson 1992 proposed that nutrient uptake by shallow reef communities was limited by mass transfer the physical transfer of nutrients across con centration boundary layers covering the surfaces of reef au totrophs these authors used mass transfer correlations for rough surfaces taken from the engineering literature to cor relate maximum rates of nutrient uptake with the frictional characteristics of experimental reef communities subse quent studies demonstrated the ability of such mass transfer correlations to predict nutrient uptake kinetics for experi mental reef communities within closed recirculating flumes atkinson and bilger 1992 bilger and atkinson 1995 thomas and atkinson 1997 and a large experimental me socosm atkinson et al 2001 the results of these studies made it clear that shallow water reef communities are ca pable of taking up nutrients from the water column at rates that are limited by mass transfer however it had not yet been demonstrated whether in situ rates of nutrient uptake

peculiar features of ionospheric f 3 layer during prolonged solar minimum 2007 2009 we present the seasonal and local time occurrence of ionospheric f 3 layer over tirunelveli geographic longitude 77 8 e geographic latitude 8 7 n dip 0 7 during extremely low and prolonged solar activity period 2007 2009 canadian advanced digital ionosonde observations from this station are used in the present study we find that the occurrence of f 3 layer is nearly 3 times higher during 2009 48 as compared to that during 2007 16 the increase of this order just within the low solar activity period is unusual in earlier studies similar increase in f3 occurrence has been reported when solar activity changes from high f10 7 182 t o low f10 7 72 the other important feature is the presence of postnoon f3 layers which are observed dominantly during summer solstice of 2009 such occurrence of postnoon f3 layers was nearly absent during summer solstice of the previous solar minimum 1996 over nearby dip equatorial station trivandrum we take equatorial electrojet eej as a proxy for eastward electric field it is noticed that the eej strength and the maximum rate of change of eej are higher for f3 days as compared to those on non f3 days we find that the peak occurrence of prenoon f3 layer closely coincides with the time of maximum rate of change of eej it is in general accordance with the theory proposed by balan et al 1998 that suggests the formation of f3 through vertically upward e b drift in presence of equatorward neutral wind the present study reveals that the rate of change of eastward electric field de dt as well plays an important role in the formation of f3 layer

garnets within geode like serpentinite veins implications for element transport hydrogen production and life supporting environment formation geochemical micro environments within serpentinizing systems can abiotically synthesize hydrocarbons and provide the ingredients required to support life observations of organic matter in microgeode like hydrogarnets found in mid atlantic ridge serpentinites suggest these garnets possibly represent unique nests for the colonization of microbial ecosystems within the oceanic lithosphere however little is known about the mineralogical and geochemical processes that allow such unique environments to form here we present work on outcrop scale vein networks from an ultramafic massif in norway that contain massive amounts of spherulitic garnets andradite which help to constrain such processes vein andradite spherulites are associated with polyhedral serpentine brucite ni fe alloy awaruite and magnetite indicative of low temperature 200 c alteration under low fo2 and low asio2 aq geochemical conditions together with the outcrop and micro scale analysis geochemical reaction path modeling shows that there was limited mass transport and fluid flow over a large scale once opened the veins remained isolated closed system forming non equilibrium microenvironments that allowed upon a threshold supersaturation the rapid crystallization seconds to weeks of spherulitic andradite the presence of polyhedral serpentine spheres indicates that veins were initially filled with a gel like protoserpentine phase in addition massive fe oxidation associated with andradite formation could have generated as much as 600 mmol h2 aq per 100 cm3 vein although no carboneous matter was detected the vein networks fulfill the reported geochemical criteria required to generate abiogenic hydrocarbons and support microbial communities thus systems similar to those investigated here are of prime interest when searching for life supporting environments within the deep subsurface

wave set up on coral reefs 1 set up and wave generated flow on an idealised two dimensional horizontal reef wave set up may be significant in determining water levels on coral reefs particularly in microtidal environments and hence is an important factor for the design of reef top structures and for the stability of reef top islands laboratory experiments have been made on a two dimensional model of an idealised horizontal reef under two different conditions corresponding to a fringing reef or closed lagoon situation and a platform reef or open lagoon situation both wave set up on the reef top and the wave generated flow across the reef were measured and related to wave and tide level conditions all other factors being the same wave set up is greatest at low tide levels whereas wave generated flow is greater at higher tide levels the magnitude of the set up on a platform reef with a wave generated flow is less than on a fringing reef without any net flow by an amount equal to the velocity head of the flow across the reef dimensionless parameters ghrt o and q gho3 are found to be functions of relative submergence parameters hrho or r hr ho for values of ghr hr ho 1 waves break on the reef top and radiation stress theory can be used to calculate set up for ghr hr ho 0 7 waves break on the reef face and set up is determined by broadcrested weir control at the reef edge the symbols are defined as follows g is gravitational acceleration hr is still water depth over horizontal reef top ho is offreef wave height equivalent deep water value q is discharge per unit length of reef edge t is wave period and ghr is maximum wave set up on reef top

field study of wave attenuation on an offshore coral reef a major field experiment was conducted which obtained measurements of the attenuation and transformation of short gravity waves as they cross the windward edge of an offshore coral reef water level data were collected for over 3000 individual time series during a wide range of environmental conditions at the innermost measurement site which is located on the horizontal reef flat after the completion of wave breaking the upper bound of significant and maximum wave heights is limited to less than 40 and 60 of the reef flat water depth respectively as with significant wave height both the shape and energy level of the reef flat spectra are strongly affected by changes in reef flat water depth for higher tide levels the spectra on the reef flat closely mimic the corresponding incident spectra however the attenuation is greater for both lower frequencies and higher energy portions of the spectra this causes the reef flat spectra to be broader than those measured windward of the reef at lower water levels considerable energy losses due to wave breaking and bottom friction occur most of the energy loss comes from the vicinity of the spectral peak and energy shifts to harmonics of the peak of the spectrum can be seen

radiocarbon evidence for the timing and rate of island development beach rock formation and phosphatization at lady elliot island queensland australia abstract lady elliot island great barrier reef is a coral cay constructed from near concentric shingle ridges composed of coral tridacna shells and bioclastic sand bound by guano derived phosphatic cement radiocarbon dating of individual tridacna samples is used to investigate the evolution of the island and place constraints on the variations in storminess of the last 3200 years a shallow platform reef existed at lady elliot since at least 6500 yrs b p shortly before 3200 yrs b p island growth by shingle progradation commenced and proceeded to the present at a rather uniform lateral rate 60 m ka 1 to leeward and 90 m ka 1 windward phosphatization may have occurred continuously or episodically at any time throughout the last 3200 years the youngest cemented ridge top is less than 770 years whereas at the base of uncemented ridges phosphatization is a modern 1950 a d process similarly low level beach rock has continued to form within the last 25 years a significant period of instability occurred less than 500 years ago during which marine erosion truncated the southwestern extremity of lady elliot island formed an eastern spit and stranded high level beach rock however the radiocarbon ages of tridacna samples from shingle ridges from lady elliot and curacoa islands are uniformly distributed kolmogorov smirnov test throughout the last 4000 years we interpret this to indicate no significant variation in ridge forming processes or fluctuation in average storminess during this interval

vertical exb drifts from radar and c nofs observations in the indian and indonesian sectors consistency of observations and model in this paper we analyze vertical exb drifts obtained from the doppler shifts of the daytime 150 km radar echoes from two radar stations located off the magnetic equator namely gadanki in india and kototabang in indonesia and compare those with corresponding coupled ion neutral dynamics investigation cindi observations onboard the c nofs satellite and the scherliess fejer model in an effort to understand to what extent the low latitude vertical exb drifts of the 150 km region represent the f region vertical exb drifts the radar observations were made during 9 16 lt in january june july and december 2009 a detailed comparison reveals that vertical exb drifts observed by the radars at both locations agree well with those of cindi and differ remarkably from those of the model importantly the model and observed drifts show large disagreement when the observed drifts are either large or downward further while the cindi as well as the radar observations from the two longitudes are found to agree with each other on the average they differ remarkably on several occasions when compared on a one to one basis the observed difference in detail is due to measurements made in different volumes linked with latitudinal and or longitudinal differences and underlines the role of neutral dynamics linked with tides and gravity waves in the two longitude sectors on the respective vertical exb drifts the results presented here are the first of their kind and are expected to have wider applications in furthering our understanding on fine scale longitudinal variabilities in the ionosphere in general and ionospheric electrodynamics in the indian and indonesian sectors in particular

basin scale and travertine dam scale controls on fluvial travertine jiuzhaigou southwestern china article travertine deposition in fluvialsystemsbuildsdamsandotherformsthatcreatediversityingeomorphicprocesses morphology and associated wetland ecosystems in jiuzhaigou natural reserve sichuan province china we in vestigate the relation between contemporary fluvial travertine morphology slope and water chemistry at the fluvial system scale and at the local scale of large individual dams in order to address two fundamental questions first what factors determine the spatial distribution of such large valley spanning or primary travertine dams second what factors govern smaller but distinctive travertine dams and other secondary travertine morphology present on the sloping downstream side of primary travertine dams through remote sensing analysis and field work we recognize two factors as paramount in controlling spatial distribution of primary fluvial travertine dams watershed scalestepsinthelongitudinalprofile and waterchemistry based on a proxy for dissolved calcite in the steep jiuzhaigou watershed hillslope erosion processes that contribute large boulders to the channel influ ence the majority of the primary dams however two valley spanning primary dams pearl shoals and norilang lakes appear to be dominated by travertine precipitation the submerged upstream sides of these two dams are nearly vertical with heights 30 m slope varies with position along the longitudinalprofilesoverthedownstream sides of these two primary dams because the profile shapes are convex with downstream dam profile lengths 500 m flow encounters secondary travertine morphology organized as an array of travertine bedforms that vary with local channel slope along the convex profiles the secondary travertine bedforms include sequences of repeating patterns including smaller dams that impound correspondingly small waterbodies morphologic differ ences between two types of secondary dams are quantified on the basisof their relative size spacing and the slope on which they form increasing slope is correlated with a decrease in height of secondary travertine bedforms according to a power law where y 0 0053x

a statistical study of midlatitude spread f at wallops island virginia 1 an ionosonde study using data from wallops island virginia 37 95 n 284 53 e 67 5 dip angle over a full solar cycle from 1996 to 2006 has been conducted a pattern recognition algorithm is used to analyze these ionograms in order to determine the statistics of midlatitude spread f an ionogram displays spread f both horizontally and vertically which are defined as range and frequency spread f respectively range and frequency spreading can occur either simultaneously or separately seasonal and solar cycle variations have been studied using the data set both are significant and are somewhat different for range and frequency spread f correlations of spread f duration with f 10 7 kp and ae are investigated the results provide insights into causative sources for both types of midlatitude spread f

characteristics of the equatorial plasma drifts as obtained by using canadian doppler ionosonde over southern tip of india we present here characteristics of the doppler drift measurements over tirunelveli 8 73 n 77 70 e dip 0 5 n an equatorial site over southern india using doppler interferometry technique of canadian ionosonde three dimensional bulk motions of the scatterers as reflected from the ionosphere are derived by using doppler interferometry technique at selected frequencies using spaced receivers arranged in magnetic e w and n s directions after having compared with lowell s digisonde drifts at trivandrum we studied the temporal and seasonal variabilities of quiet time drifts for the year 2012 the observations showed higher vertical drifts during post sunset in the equinox followed by winter and summer seasons the comparison of doppler vertical drifts with the drifts obtained from a virtual height and b fejer drift model suggests that doppler vertical drifts are relatively higher as compared to the drifts obtained from model and virtual height methods further it is seen that vertical drifts exhibited equinoctial asymmetry in prereversal enhancement quite similar to such asymmetry observed in the spread f in the ionograms and gps l band scintillations the zonal drifts on the other hand showed westward during daytime with mean drifts of 150 200 m s and correlated well with equatorial electrojet strength indicating the role of e region dynamo during daytime while they are eastward during nighttime with mean drifts of 100 m s resembling f region dynamo process also zonal drifts showed large westward prior to the spread f onset during autumn equinox than vernal equinox suggesting strong zonal shears which might cause equinoctial asymmetry in spread f

factors controlling tufa deposition in natural waters at waterfall sites abstract study on calcite precipitation has major implications for both the hydrochemical evolutions of river systems and the global carbon cycle the precipitation of calcite generally requires the water to be 5 10 times supersaturated with respect to calcite which is usually achieved by the removal of co2 formation of waterfall tufa has been often simply described as the result of water turbulence in fast flowing water in this paper the formation mechanisms of waterfall tufa are discussed and a series of laboratory experiments are designed to simulate the hydrological conditions at waterfall sites the influences of the air water interface the water flow velocity and the solid water interface on co2 outgassing and calcite precipitation are compared and evaluated quantitatively the results show that the principal cause of waterfall tufa formation is the enhanced inorganic carbon dioxide outgassing resulted from the sudden hydrological changes occurring at waterfall sites rather than organisms evaporation or the solid water interface the air water interface area and the water flow velocity are greatly increased at waterfall sites as a result of the aeration effect low pressure effect and jet flow effect which greatly accelerate co2 outgassing inorganic co2 outgassing drives the waters to become highly supersaturated with respect to calcite and consequently results in much calcite deposition the solid water interface is less important as the air water interface in affecting calcite precipitation at waterfall sites field measurements showed that conductivity ca2 and hco3 concentrations along tianhe creek and hot creek decrease downstream while ph rises field observations also showed that tufa deposition occurred mainly at waterfall sites

radar and satellite global equatorial f region vertical drift model we present the first global empirical model for the quiet time f region equatorial vertical drifts based on combined incoherent scatter radar observations at jicamarca and ion drift meter observations on board the atmospheric explorer e satellite this analytical model based on products of cubic b splines and with nearly conservative electric fields describes the diurnal and seasonal variations of the equatorial vertical drifts for a continuous range of all longitudes and solar flux values our results indicate that during solar minimum the evening prereversal velocity enhancement exhibits only small longitudinal variations during equinox with amplitudes of about 15 20 m s is observed only in the american sector during december solstice with amplitudes of about 5 10 m s and is absent at all longitudes during june solstice the solar minimum evening reversal times are fairly independent of longitude except during december solstice during solar maximum the evening upward vertical drifts and reversal times exhibit large longitudinal variations particularly during the solstices in this case for a solar flux index of 180 the june solstice evening peak drifts maximize in the pacific region with drift amplitudes of up to 35 m s whereas the december solstice velocities maximize in the american sector with comparable magnitudes the equinoctial peak velocities vary between about 35 and 45 m s the morning reversal times and the daytime drifts exhibit only small variations with the phase of the solar cycle the daytime drifts have largest amplitudes between about 0900 and 1100 lt with typical values of 25 30 m s we also show that our model results are in good agreement with other equatorial ground based observations over india brazil and kwajalein

ionogram signatures of large scale wave structure and their relation to equatorial spread f 1 observations of signatures of the large scale wave structure lsws and subsequent development of equatorial spread f esf by using data from a newly installed digital ionosonde at trivandrum 8 5 n 77 e 0 5 n magnetic dip latitude are presented the lsws signatures are observed using the ionograms with echo directions the satellite traces are shown as echoes from oblique directions when an upwelling associated with lsws is not directly over the ionosonde location when an upwelling is centered overhead and the radius of curvature of the isodensity contours matches the height of reflection signals from various directions can add in phase to enhance the ionospheric reflection coefficient and produce another ionogram signature referred to as multireflected echoes mres it is also shown that the generation of esf is related to the presence of lsws the skymaps also show the presence of small scale wave structures in the bottomsidefregion the investigation also indicates that the range spread f rsf occurs because of the reflections from the embedded smaller scale structures within the large scale upwelling

multi reflected echoes another ionogram signature of large scale wave structure 1 one or more steeply sloped traces have been found in evening ionograms taken from the kwajalein atoll 4 3 n dip latitude during july 1979 their resemblance to the normal f trace suggests that they are echoes that have undergone a large number of reflections from the f layer these multi reflected echoes mres are interpreted in terms of focusing produced by curved isodensity contours in the bottomside f layer which appear to be associated with large scale wave structure lsws that develops in the bottomside f layer mres appear to be another signature for lsws together with satellite traces that appear later in time closer to the onset of plasma structure referred to as equatorial spread f mres are interesting because they display for the data set examined a strong preference to occur during the post sunset rise of the f layer which includes e region sunset how this finding affects our understanding of lsws is discussed

magnetospheric disturbance induced equatorial plasma bubble development and dynamics a case study in brazilian sector 1 equatorial ionospheric plasma bubble irregularity development and dynamics during the major magnetospheric storm of 26 august 1998 are investigated using the data collected by a multistation and multi instrument diagnostic network operated at equatorial and low latitude sites in brazil and auroral electrojet activity au al imf and dst indices a magnetospheric disturbance onset in the morning of 26 august 1998 was initiated by a solar wind shock and associated imf bz polarity reversals and ssc that were soon followed by a succession of substorm like auroral electrojet ae intensifications and dst development an imf bz southward turning and associated ae intensifications in the brazilian dusk sector produced intense prompt penetration eastward electric field that caused large f region vertical drift and consequently the developments of intense postsunset equatorial anomaly and a series of intense plasma bubbles the latter event lasting the entire night as observed by digital ionosondes at sao luis 2 33 s 315 8 e dip angle 5 and fortaleza 3 9 s 321 55 w dip angle 9 and an all sky imager two scanning photometers and a digisonde at the low latitude site cachoeira paulista 22 6 s 315 e dip angle 28 a notable aspect of the dynamics of the bubbles was their initially very low eastward drift velocity which turned into steadily increasing westward velocity that lasted till early morning hours the results show for the first time a relationship between the zonal drift velocities of optically observed large scale bubbles tens to hundreds of kilometers and that of the smaller scale kilometer sizes structures as observed by a digital ionosonde the results point to the dominant role of a disturbance dynamo associated westward thermospheric wind to maintain the plasma irregularity drift increasingly westward going into postmidnight hours as an important finding the results further show that significant contribution to the westward plasma bubble irregularity drift normally attributed to disturbance dynamo effect could arise from prompt penetration disturbance zonal electric field in the course of a disturbance sequence lasting several hours such effect is attributed to hall electric field arising from the primary disturbance zonal electric field under enhanced nighttime ionospheric conductivities produced possibly by storm associated particle precipitation in the brazilian longitude sector in agreement with recent evidences abdu et al 1998b

dissipation of wave energy and turbulence in a shallow coral reef lagoon received 6 april 2011 revised 14 november 2011 accepted 3 january 2012 published 10 march 2012 1 simultaneous in situ measurements of waves currents and turbulence are presented to describe dissipation rates of wave energy and turbulent kinetic energy in the windward coral reef lagoon system at lady elliot island lei australia the dissipation of wave energy in the lagoon is tidally modulated and strongly correlates with frictional dissipation due to the presence of the extremely rough bottom boundary the observed turbulent kinetic energy tke dissipation rate in this wave dominated lagoon is much larger than recently reported values for unidirectional flows over natural fringing coral reefs the correlation between the wave dissipation and is examined the average rate of dissipation induced by the rough turbulent flow was estimated directly from the observed coupled with both a depth integrated approach and with a bottom boundary layer scaling rates of tke dissipation estimated using the two approaches approximate well within a factor of 1 5 to 2 4 to the surface wave energy dissipation rate the wave dissipation and friction factor in the lagoon can be described by a spectral wave frictional model with a bottom roughness length scale that is approximately constant across the lagoon we also present estimates of dissipation induced by the canopy drag force of the coral heads the dissipation in this case is enhanced and becomes more significant for the total energy dissipation when the water depth in the lagoon is comparable to the height of the coral heads

abiotic versus biotic controls on the development of the fairmont hot springs carbonate deposit british columbia canada the relict fairmont hot springs deposit formed largely of carbonates covers an area of 0ae 5k m 2 and is up to 16 m thick the triangle shaped discharge apron which broadens down valley is divided into a proximal part with beds dipping at 10 and a distal part with beds dipping at 10 to 15 the deposit is formed of the 1 basal macrophyte 2 lower carbonate 3 middle clastic 4 upper carbonate and 5 upper clastic sequences two charcoal samples embedded in the lower carbonate sequence yielded dates of 8690 90 and 8270 70 cal yr bp indicating that much of the deposit formed post glacially during the early to mid holocene deposit aggradation ceased in the mid to late holocene when the fairmont creek valley was incised the lower and upper carbonate sequences which are the thickest sequences are composed of nearly equal parts of travertine abiotic and tufa biotic with feather dendrite travertine radiating dendrite travertine and stromatolite tufa dominating competition between calcite precipitation rates and biotic growth rates controlled the distribution of tufa and travertine across the discharge apron calcite and biotic growth rates were controlled largely by flow velocity across the apron which in turn was controlled by topography and regular fluctuations in spring water discharge volume during times of high spring discharge slow sheet flow over the proximal part of the apron promoted stromatolite growth whereas fast turbulent flow on the distal part of the apron induced rapid feather dendrite formation during times of low spring discharge quiescent shallow evaporative pools conducive to radiating dendrite formation formed on the proximal part of the apron whereas slow flow on the distal part promoted stromatolite growth facies with high calcite supersaturation experienced rapid abiotic dendrite growth that precluded most biotic growth

study of equinoctial asymmetry in the equatorial spread f esf irregularities over indian region using multi instrument observations in the descending phase of solar cycle 23 1 in this paper we present the results of a morphological study of equatorial spread f esf irregularities over indian region based mainly on observations of 1 amplitude scintillations on gps l band signal and rate of tec index roti obtained using a network of gps receivers and 2 amplitude scintillations on a vhf signal using spaced receivers at tirunelveli an equatorial station occurrence of both amplitude scintillations on the gps l1 signal and occurrence of significant roti recorded at several stations has been investigated the latitudinal extent of l band scintillations shows that their strength is weak over the dip equator but stronger over equatorial ionization anomaly eia region preferentially during vernal equinox we find an equinoctial asymmetry in both the occurrence of scintillations and roti wherein their occurrence is greater in the vernal equinox than in the autumn equinox attempts have been made to understand the asymmetry in latitudinal extent using maximum cross correlation ci of intensity fluctuations obtained from the vhf spaced receivers observations the observations suggest that occurrence of ci less than 0 5 is more in the vernal equinox than in the autumn equinox suggesting that the maximum height of the equatorial plasma bubbles epbs during vernal equinox may be higher than that during autumn equinox timed guvi retrieved peak electron density during the same period also indicates that background electron density is higher and more symmetric during vernal equinox than autumn equinox hence our results suggest that background electron density may be playing a vital role in creating the equinoctial asymmetry