seawater ph pco2 and co2 3 variations in the caribbean sea over the last 130 kyr a boron isotope and b ca study of planktic foraminifera abstract here a new analytical methodology is described for measuring the isotopic composition of boron in foraminifera using multicollector inductively coupled plasma mass spectrometry mc icpms this new approach is fast 10 samples analysed in duplicate per analytical session and accurate to better than 0 25 at 95 confidence with acceptable sample size requirements 1 3 mg of carbonate a core top calibration of several common planktic and two benthic species from geographically widespread localities shows a very close agreement between the isotopic composition measured by mc icpms and the isotopic composition of b oh 4 in seawater as predicted using the recently measured isotopic equilibrium factor of 1 0272 at the depth of habitat a down core and core top investigation of boron concentration b ca ratio shows that the partition coefficient is influenced by co2 3 complicating the application of this proxy nevertheless it is demonstrated that these two proxies can be used to fully constrain the carbonate system of surface water in the caribbean sea odp site 999a over the last 130 kyr this reconstruction shows that during much of the holocene and the last interglacial period surface water at site 999a was in equilibrium with the atmosphere with respect to co2 during the intervening colder periods although the surface water pco2 was lower than the holocene it was a minor to significant source of co2 to the atmosphere possibly due to either an expansion of the eastern equatorial atlantic upwelling zone or a more local expansion of coastal upwelling in the southern caribbean such reorganisation of the oceanic carbonate system in favour of a larger source of co2 to the atmosphere from the equatorial ocean may require mechanisms responsible for lowering atmospheric co2 during glacial periods to be more efficient than previously supposed

mass flux and undertow in a surf zone abstract the mass of water carried shoreward by the breaking waves in a surf zone will in a two dimensional situation be compensated by a seaward return flow the undertow it is shown that the undertow is driven by the local difference between radiation stress and the set up pressure gradient which only balance each other in average over the depth turbulent shear stresses are required to maintain a steady situation comparison with measurements confirms the theoretical results

global biogeochemical cycle of boron 1 the global boron b cycle is primarily driven by a large flux 1 44 tg b yr through the atmosphere derived from seasalt aerosols other significant sources of atmospheric boron include emissions during the combustion of biomass 0 26 0 43 tg b yr and coal which adds 0 20 tg b yr as an anthropogenic contribution these known inputs to the atmosphere cannot account for the boron removed from the atmosphere during rainfall 3 0 tg b yr and estimated dry deposition 1 3 2 7 tg b yr in addition to atmospheric deposition rock weathering is a source of boron 0 19 tg b yr for terrestrial ecosystems and humans mine about 0 31 tg b yr from the earth s crust more than 4 8 tg b yr circulates in the biogeochemical cycle of land plants and about 0 53 0 63 tg b yr is carried from land to sea by rivers the biogeochemical cycle of boron in the sea includes 4 4 tg b yr circulating in the marine biosphere and an annual loss of 0 47 tg b yr to the oceanic crust via a variety of sedimentary processes that collectively remove only a small fraction of the total annual inputs to the oceans thus with our current understanding of the global biogeochemistry of b the atmospheric budget shows outputs inputs while the marine compartments show inputs outputs despite these uncertainties it is clear that the human perturbation of the global b cycle has more than doubled the mobilization of b from the crust and contributes significantly to the b transport in rivers

tracing the strength of the southwest monsoon using boron isotopes in the eastern arabian sea here we present the first boron isotope based pco2sw pco2 of seawater reconstruction from the eastern arabian sea using the planktic foraminifera species globigerinoides ruber our results from sediment core aas9 21 show that pco2sw varied between 160 and 300 atm during the last 23 kyr the pco2 the sea air pco2 difference is relatively small during the last glacial maximum and becomes more negative toward the holocene with the exception of a significant excess during the last deglaciation centered on the bolling allerod throughout the record pco2 is predominantly negative probably as a result of enhanced biological productivity and higher nutrient and carbon utilization during the southwest monsoon a reduction in pco2 during the last glacial maximum is therefore consistent with a reduction in the strength of this monsoon system

nonlinear and 3d effects in leaky infragravity waves abstract in this paper infragravity ig waves forced by normally and obliquely incident wave groups are studied using the quasi 3d q3d nearshore circulation model shorecirc van dongeren a r i a svendsen 1997b quasi 3 d modeling of nearshore hydrodynamics research report cacr 97 04 center for applied coastal research university of delaware newark 243 pp which includes the q3d effects the governing equations that form the basis of the model as well as the numerical model and the boundary conditions are described the model is applied to the case of leaky ig waves it is shown that the q3d terms have a significant effect on the cross shore variation of the surface elevation envelope especially around the breakpoint and in the inner surf zone the effect of wave groupiness on the temporal and spatial variation of all q3d terms is shown after which their contribution to the momentum equations is analyzed this reveals that only those q3d coefficients which appear in combination with the largest horizontal velocity shears make a significant contribution to the momentum equations as a result of the calculation of the q3d coefficients the ig wave velocity profiles can be determined this shows that in the surf zone the velocity profiles exhibit a large curvature and time variation in the cross shore direction and a small but essential depth variation in the longshore direction

p wave residuals at fiji from deep earthquakes in the tonga subduction zone a total of 47 deep earthquakes occurring between 1982 and 1985 in the tonga subduction zone were used to derive station corrections for the fiji seismograph network fsn the joint hypocenter determination jhd method was employed to relocate hypocenters using p wave arrival times at selected teleseismic and fsn stations p wave residuals for fiji show variations of more than 1 sec between southern viti levu on the one hand and northern viti levu and vanua levu on the other hand the smallest residuals are observed in southern viti levu where the oldest volcanic rocks in fiji are mapped and on the island of koro station residuals in northern viti levu vanua levu and the smaller fijian islands except for koro are on average 0 4 to 0 7 sec higher than in southern viti levu the effect of hypocentral mislocation on the observed residual variations is negligible at stations in viti levu ovalau and beqa but it may be important for stations in vanua levu koro taveuni and yasawa large p wave delays observed at some stations are probably caused by low velocity sedimentary surface layers the variations in crustal thickness that are probably not larger than 5 km would explain only a minor part of the residual differences without a better knowledge of crustal structure the contribution of lateral variations in upper mantle p velocities is difficult to assess

tectonics and magma genesis in the northern north fiji basin abstract the north fiji basin is a complex back arc basin in which active seafloor spreading is occurring along two north south ridge systems lithospheric extension is also taking place along segments of the east west trending fiji fracture zone and south pandora ridge the fiji fracture zone is clearly a transform fault but the south pandora ridge is more difficult to interpret some characteristics are consistent with a slow spreading ridge whereas others suggest a transform fault basalts recovered on the south pandora ridge are enriched in high field strength and large ion lithophile elements and many of them resemble ocean island tholeiites or transitional alkali basalts the south pandora ridge is an enigmatic tectonic feature and the geochemistry morphology and seismicity are best explained in terms of a model involving slow spreading ridge segments within a broad transform domain at its southern end the central ridge of the north fiji basin has a bathymetric profile normally associated with fast spreading steady state mid ocean ridges and the basalts recovered on this part of the ridge are moderately evolved normal mid ocean ridge basalts morb in contrast the northern end of the ridge has a complex topography dominated by a series of deep linear troughs and grabens and basalts recovered from the floors of these troughs vary widely in chemistry from normal morbs to transitional basalts that are comparatively enriched in large ion lithophile and high field strength elements the central ridge appears to be propagating northwards into old north fiji basin crust and the northern extension of the ridge is an incipient spreading locus in the very earliest stages of development in areas of the basin where fast spreading large scale mantle upwelling leads to extensive melting of asthenosphere derived depleted mantle morb like compositions dominate the erupted rocks in contrast areas of slow or incipient spreading and other tectonic settings where a transient thermal disturvance occurs are characterized by basaltic magmatism that shows relative enrichment in large ion lithophile and high field strength minor and trace elements mixing of morb and enriched end member components either at source or as magmas gives rise to a spectrum of compositions that can be related to a range of tectonic environments in the back arc setting

slip partitioning along major convergent plate boundaries along plate boundaries characterized by oblique convergence earthquake slip vectors are commonly rotated toward the normal of the trench with respect to predicted plate motion vectors consequently relative plate motion along such convergent margins must be partitioned between displacements along the thrust plate interface and deformation within the forearc and back arc regions the deformation behind the trench may take the form of strike slip motion back arc extension or some combination of both we observe from our analysis of the harvard moment tensor catalog that convergent arcs characterized by back arc spreading specifically the marianas and new hebrides are characterized by a large degree of slip partitioning however the observed rates directions and location of back arc spreading are not sufficient to account for degree of partitioning observed along the respective arcs implying that the oblique component of subduction is also accommodated in part by shearing of the overriding plate in the case of the sumatran arc where partitioning is accommodated by strike slip faulting in the overriding plate the degree of partitioning is similar to that observed along the marianas but the result is viewed with caution because it is based on a predicted plate motion vector that is based on locally derived earthquake slip vectors in the case of the alaskan aleutian arc where back arc spreading is also absent the degree of partitioning is less and rotation of slip vectors toward the trench normal appears to increase linearly as a function of the obliquity of convergence if partitioning in the alaskan aleutian arc is accommodated by strike slip faulting within the upper plate the positive relationship between obliquity of convergence and the rotation of earthquake slip vectors to the trench normal may reflect that either 1 the ratio of the depth extent of strike slip faults behind the trench z s to the subduction thrust z t increases westward along the arc 2 the dip of the subduction thrust increases westward along the arc or 3 the strength of the subduction thrust decreases westward along the arc

boron isotope based seasonal paleo ph reconstruction for the southeast atlantic a multispecies approach using habitat preference of planktonic foraminifera abstract the boron isotopic composition of planktonic foraminiferal shell calcite 11 b cc provides valuable information on the ph of ambient water at the time of calcification hence 11 b cc of fossil surface dwelling planktonic foraminifera can be used to reconstruct ancient aqueous p co 2 if information on a second carbonate system parameter temperature and salinity is available however ph and p co 2 of surface waters may vary seasonally largely due to changes in temperature dic and alkalinity as also the shell fluxes of planktonic foraminifera show species specific seasonal patterns that are linked to intra annual changes in temperature it is obvious that 11 b cc of a certain species reflects the ph and thus p co 2 biased towards a specific time period within a year this is important to consider for the interpretation of fossil 11 b cc records that may mirror seasonal ph signals here we present new multi collector inductively coupled mass spectrometry mc icpms 11 b cc coretop data for the planktonic foraminifera species globigerina bulloides globigerinoides ruber trilobatus sacculifer and orbulina universa and compare them with 11 b borate derived from seasonally resolved carbonate system parameters we show that the inferred season adjusted 11 b cc 11 b borate relationships are similar to existing calibrations and can be combined with published 11 b cc field and culture data to augment paleo ph calibrations to test the applicability of these calibrations we used a core drilled on the walvis ridge in the southeast atlantic spanning the last 330 000 years to reconstruct changes in surface water p co 2 the reconstruction based on g bulloides which reflects the austral spring season was shown to yield values that closely resemble the vostok ice core data indicating that surface water p co 2 was close to equilibrium with the atmosphere during the cooler spring season in contrast p co 2 estimated from 11 b cc of o universa t sacculifer and g ruber that predominantly lived during the warmer seasons exhibits up to 50 ppmv higher values than the vostok ice core data this is probably due to the higher austral summer and fall temperatures as shown by mg ca to be on average 4 c higher than during the cooler spring season accounting for an increase in p co 2 of 4 per 1 c our results demonstrate that paleo ph estimates based on 11 b cc contain a significant seasonal signal reflecting the habitat preference of the recording foraminifera species

core top calibration of b ca in pacific ocean neogloboquadrina incompta and globigerina bulloides as a surface water carbonate system proxy abstract practical methods for reconstructing past ocean carbonate chemistry are needed to study past periods of ocean acidification and improve understanding of the marine carbonate system s role in the global climate cycles planktic foraminiferal b ca may fill this role but requires better understanding and improved proxy calibrations we used pacific ocean core top sediments to generate new calibrations of the b ca proxy for past carbonate system parameters in two upwelling subpolar species of asymbiotic planktic foraminifera globigerina bulloides and neogloboquadrina incompta both species show significant positive correlation of b ca with calcite saturation calcite and carbonate ion concentration co 3 2 across a broad range of environmental conditions this suggests a calcification rate control on b ca incorporation as calcite regulates calcification rate in agreement with recent inorganic calcite studies this is also consistent with a surface entrapment model of trace element incorporation into caco3 in neither species is b ca significantly correlated with ph suggesting that ph does not directly regulate boron incorporation and that calculation of ph directly from foraminiferal b ca is not suitable correlations between b ca and b oh 4 b oh 4 hco3 and b oh 4 dic are weaker than with calcite boron partition coefficients k d b ca solid b oh 4 hco 3 seawater show little or no correlation with co32 or temperature and vary widely providing no support for application of kd to calculate carbonate system parameters from b ca we also discuss potential effects of depth related dissolution temperature and salinity on b ca these empirical calibrations linking foraminiferal calcite b ca with calcite provide a strong tool for reconstructing the past ocean carbonate system and improve our understanding of the proxy s geochemical basis

effects of seawater ph and biomineralization on the boron isotopic composition of deep sea bamboo corals abstract the ocean is currently absorbing excess carbon from anthropogenic emissions leading to reduced seawater ph termed ocean acidification instrumental records of ocean acidification are unavailable from well ventilated areas of the deep ocean necessitating proxy records to improve spatio temporal understanding on the rate and magnitude of deep ocean acidification here we investigate boron carbon and oxygen isotopes on live collected deep sea bamboo corals genus keratoisis from a phtot range of 7 5 8 1 these analyses are used to explore the potential for using bamboo coral skeletons as archives of past deep sea ph and to trace anthropogenic acidification in the subsurface north atlantic ocean 850 2000 m water depth boron isotope ratios of the most recently secreted calcite of bamboo coral skeletons are close to the calculated isotopic composition of borate anion in seawater 11bborate for north atlantic corals and 1 2 higher than 11bborate for pacific corals within individual coral skeletons carbon and oxygen isotopes correlate positively and linearly a feature associated with vital effects during coral calcification 11b variability of 0 5 2 is observed within single specimens which exceeds the expected anthropogenic trend in modern north atlantic corals 11b values are generally elevated in pacific corals relative to 11bborate which may reflect ph driven physiological processes aiding coral calcification in environments unfavorable for calcite precipitation elevated 11b values are also observed proximal to the central axis in multiple atlantic and pacific specimens relative to 11bborate which might reflect ontogenetic variability in calcification rates although the observed boron isotope variability is too large to resolve the present anthropogenic ocean acidification signal at the studied depths in the north atlantic 0 03 0 07 ph units ph changes 0 1 units might still be reconstructed using 11b measurements in bamboo corals

seismicity and crustal structure of the fiji platform southwest pacific data from a telemetered seismic network in fiji provide new constraints on the crustal structure and active deformation within and around the fiji platform an unusual fragmented arc complex situated within the pacific indo australian plate boundary seismic refraction data indicate that crustal thickness in fiji is typical of island arcs averaging about 15 20 km with relatively low midcrustal seismic velocities vp 6 0 km s characteristic of felsic arc related rocks the anticipated higher velocity lower crustal layer is either thin or absent mantle velocity beneath the platform is low 7 6 km s in the same range as that observed beneath the neighboring marginal basins and island arcs the record of crustal seismicity based on historical teleseismic and microearthquake catalogs indicates significant activity both within and along the boundaries of the fiji platform earthquakes located along the edges of the platform are associated with major zones of back arc deformation of the north fiji and lau basins the fiji fracture zone to the north the hunter fracture zone to the south and a deformed zone in the eastern portion of the north fiji basin to the west earthquakes within the platform intraplate events occur more sporadically than those along its margins areas of significant intraplate activity include the taveuni northeastem vanua levu area koro sea the baravi basin and central and south eastern viti levu earthquake depths within the platform are concentrated in the upper 13 16 km of lithosphere as in other areas of extensional strike slip tectonics in fiji however the seismicity apparently extends through the entire crustal section the large 1953 intraplate suva earthquake ms 6 75 was caused by strike slip faulting under the same east west extensional stress field that is deforming the north fiji and lau basins microearthquakes within and around the island of viti levu appear to occur as a result of the same stresses these earthquakes occur in discrete nests that are tightly clustered in space and time they are related to late cenozoic faults that cut the mio pliocene rocks of viti levu the characteristics of its crustal structure the anomalous mantle velocity and the active deformation within the fiji platform distinguish it from microcontinental blocks that have been observed elsewhere the seismicity and focal mechanisms within the fiji platform demonstrate that it is not technically isolated from the active deformational processes that pervade the neighboring arcs and back arc basins

the universal ratio of boron to chlorinity for the north pacific and north atlantic oceans abstract we report seawater boron concentration mg kg 1 and chlorinity values measured in seawater samples n 139 collected at various depths in the north pacific and north atlantic oceans and the east japan sea located in the western temperate north pacific our results indicate that variations in seawater boron concentration are strongly coupled to variations in chlorinity and salinity yielding a mean boron to chlorinity ratio of 0 2414 0 0009 mg kg 1 1 boron to salinity ratio 0 1336 0 0005 mg kg 1 1 this ratio was surprisingly universal throughout the water column in the three marine basins and across widely different ocean surface regimes but differs from the generally accepted ratio of 0 232 0 005 mg kg 1 1 determined by uppstrom 1974 which was based on only 20 measurements at four sites in the tropical pacific ocean in converting total alkalinity to carbonate alkalinity and vice versa for thermodynamic calculations the difference between these two ratios leads to a difference of 5 mol kg 1 in estimates for ocean surface waters where the contribution of borate to total alkalinity is typically greatest we suggest the use of the new boron to chlorinity ratio for predicting seawater boron concentrations using chlorinity or salinity data

the offshore morpho structure and tsunami sources of the viti levu seismic zone southeast viti levu fiji abstract new high resolution seabat 8160 multibeam bathymetry data reveal in detail the complex offshore morphology over part of the viti levu seismic zone vlsz in southeast viti levu the mapped seafloor is scarred by a complex network of linear submarine canyons and numerous submarine slides the submarine canyons are morphologic expressions of graben structures in the underlying basement rock submarine canyon faults are continuous with nearshore shelf faults and onshore fault controlled valleys and structural lineaments together these define continuous onshore offshore fault zones which combined form a structurally complex fault mesh of composite origin we attribute the development of the principal fault sets in the fault mesh to progressive distributed faulting in response to anticlockwise tectonic block rotations within the fiji platform during the neogene low occurrence of large earthquakes and a diffused pattern of seismicity currently observed in the vlsz may reflect complex coseismic faulting through the fault mesh the abundance of submarine slides over the vlsz which typically occur on the outer barrier reef edge as well as the submarine canyon heads and walls and mid slope imply that seismic shaking may be an important factor for triggering slope failure morphometric analysis and empirical modelling of the slides show that slides triggered in shallow water depths within 5 km of the coastline at the outer barrier reef edge and submarine canyon heads produce the largest near field tsunami amplitudes we interpret that such slides represent a significant local tsunami hazard

seismic structure beneath the tonga arc and lau back arc basin determined from joint vp vp vs tomography the tonga arc and associated lau basin exhibit many geologically important processes that link subduction and mantle flow with plate separation and crustal production we create seismic tomograms of the tonga lau region by jointly inverting for vp and vp vs structure using data from the labatts ocean bottom seismograph experiment and several island deployments to better constrain dynamic processes in the mantle wedge jointly using p and s data can help distinguish between the various mechanisms responsible for seismic velocity anomalies such as temperature and the presence of melt and or volatiles because high attenuation in the wedge limits the s wave data set we focus on 2 d inversions beneath the linear obs array where resolution is best and also parameterize the solution in terms of the vp vs ratio as expected the subducting slab has fast vp and vs and a low vp vs ratio consistent with the cold downgoing plate the central lau spreading center clsc exhibits stronger anomalies in vp vs than in vp with the anomalies larger than would be predicted purely by temperature variations the clsc anomaly extends 100 km to the west of the axis suggesting a broad region of melt production driven by passive upwelling from plate separation rather than active upwelling mechanisms the anomaly is asymmetric about the axis suggesting that slab induced corner flow possibly influences mantle dynamics several hundred kilometers away from the arc there is a strong anomaly beneath the volcanic arc that gradually deepens as it trends toward the back arc likely outlining a hydrated region of melt production that feeds the volcanic front hydration possibly continues throughout the wedge to at least 400 km depth the lau ridge exhibits a thicker lithosphere relative to the rest of the basin while the fiji platform likely has a thinner lithosphere than the lau ridge from more recent extension there is also a reasonable likelihood of a small degree of partial melt in the uppermost mantle beneath the platform

evolution of waves and currents over a submerged laboratory shoal abstract the vertically integrated effect of interaction between waves and wave induced currents on wave transformation over a submerged elliptic shoal was investigated based on numerical simulations of the vincent and briggs experiment vincent c l briggs m j 1989 refraction diffraction of irregular waves over a mound journal of waterway port coastal and ocean engineering 115 2 pp 269 284 the numerical simulations were performed using two numerical wave current model systems one a combination of the wave model swan and the current model shorecirc and the other a combination of the wave model ref dif and the same current model a time dependent phase resolving wave and current model funwave was also utilized to simulate the experiment in the simulations the developed wave induced currents defocused waves behind the shoal and brought on a wave shadow zone that showed relatively low wave height distributions for the breaking case of monochromatic waves the wave heights computed using funwave showed good agreement with the measurements and the resulting wave induced currents showed a jet like velocity distribution in transverse direction and the computed results of the two model combinations agreed better with the measurements than the computed results obtained by neglecting wave current interaction however it was found that for the case in which transverse interference pattern caused by refracted waves was strong ref dif shorecirc did not correctly evaluate radiation stresses the gradients of which generate wave induced currents swan shorecirc which cannot deal with the interference patterns predicted a jet like wave induced current for breaking random wave cases the computed results of the two model combinations and funwave agreed well with the measurements the agreements indicate that it is necessary to take into account the effect of wave induced current on wave refraction when wave breaking occurs over a submerged shoal

a new boron isotope ph calibration for orbulina universa with implications for understanding and accounting for vital effects boron isotope ratios as measured in planktic foraminifera can be a useful tracer of past ocean ph and hence help to discern the concentration of co2 in the ancient atmosphere however different species of planktic foraminifera demonstrate different patterns of boron isotope variation with ambient seawater ph therefore when applying the proxy to questions in the geological past species specific calibrations are preferable beyond the evolutionary history of a calibrated species we must rely on our understanding of the causes of the observed vital effects in the modern ocean and the applicability of that understanding to extinct species here we present a new open ocean calibration of the planktic foraminifera orbulina universa measured via multi collector inductively coupled mass spectrometry mc icpms unlike other symbiont bearing foraminifera o universa record a 11b 11b and hence ph that is lower than its surrounding seawater but with a ph sensitivity roughly equal to that of aqueous borate ion we discuss the significance of this for application of the boron isotope proxy in deep time with recommendations for best practice and future research directions

active tectonism within the fiji platform southwest pacific new observational data on the velocity structure seismicity and state of stress of the large submarine platform that includes the fiji islands demonstrate that the platform is an active participant in the pervasive regional deformation of the pacific indian australian plate boundary refraction data collected within the fiji platform demonstrate that its crustal thickness 15 25 km and seismic velocity structure are comparable to those of active island arcs uppermost mantle velocity beneath the platform is anomalously low 7 55 km s in the same range as that observed beneath the neighboring marginal basins and island arcs shallow seismicity is observed both within and along the boundaries of the fiji platform moderate to large earthquakes within the platform occur more sporadically than those along its margins these intraplate events are separated by long periods of quiescence earthquake depths within the platform are concentrated in the upper 13 16 km as in other areas of extensional strike slip tectonics both the large 1953 suva earthquake m s 6 75 and microearthquakes within and around the island of viti levu occur by strike slip faulting under the same stress field that is deforming the north fiji and lau basins the low upper mantle velocities presence of widespread seismicity and neogene volcanism and state of stress of the fiji platform contradict the notion of a stable land mass surrounded by zones of deformation in the neighboring back arc basins

in situ geological and geochemical study of an active hydrothermal site on the north fiji basin ridge abstract in june 1989 a diving cruise by the submersiblenautile was carried out on the north fiji basin spreading ridge the objective of the cruise was a geological and geochemical study of the active spreading axis and associated hydrothermal processes this operation was the third cruise of the french japanese starmer project following the two cruises of the r v kaiyo in 1987 and 1988 six dives along the spreading axis between 16 58 s and 17 00s show that the axial graben consists of alternating n15 trending horsts and grabens extinct hydrothermal sites have been observed all along the graben these consist of fossil chimneys oxide staining and dead shells at 16 59 s an active chimney has been discovered and called the white lady because of its almost exclusively anhydrite composition this chimney expels a peculiar water characterized by low chlorinity and a 285 c maximum temperature in the northern extremity of the n15 axis a wide fossil hydrothermal site has been explored and sampled it is located in an area cut by n15 n140 and n60 trending faults and fissures

arc dynamics and tectonic history of fiji based on stress and kinematic analysis of dikes and faults of the tavua volcano viti levu island fiji 1 stress analysis of dikes and kinematic analysis of faults within the tavua volcano of viti levu fiji indicate an apparent migration of the causative maximum principal stress axis 1 from nw toward north between 5 0 and 3 9 ma the dikes and faults are part of successive structural and magmatic events at the arc scale we present data on the chronological succession of stress indicators in the tavua volcano based on overprinting relationships and published geochronology which also equate with a counterclockwise rotation of fiji assuming an approximately constant n s regional compressive stress orientation during this time the latter interpretation is consistent with paleomagnetism studies that require substantial counterclockwise rotation of the fiji platform since fragmentation of the formerly continuous outer melanesian arc during the latest miocene to earliest pliocene the stress data suggest that the fiji platform has undergone an 50 rotation since 5 ma given that rotation apparently stopped at 3 ma then particularly fast rotation of 25 myr 1 occurred from 5 ma to 3 ma recent seismicity data indicate the platform is currently subject to n s compression the history of late miocene and pliocene events in the region can be related to the consequences arising from collision of an island arc with an oceanic plateau

height limits in top down and bottom up wave environments this paper isolates two environments or processes in which maximum stable wave heights can be attained in water of constant depth in top down environments the maximum stable wave height compatible with the depth is approached from above while in bottom up environments it is approached from below the analyses of field data from these two environments are compared in water of constant depth the individual waves in naturally occurring bottom up wave trains are shown to conform to the same upper height limit criteria as naturally occurring top down wave trains that limit being the same function developed from monochromatic laboratory waves however important differences are found in the shallow and transitional wave content of the wave populations generated by the two different processes

boron sr o and h isotope geochemistry of groundwaters from mt etna sicily hydrologic implications combined b o h and sr isotopic studies of groundwaters from mt etna provide new constraints on their origin and the consequences of fluid rock interaction within this hydrologic system variations in d 18 o 29 7 to 27 2 and d d 262 to 223 mainly lie along the regional meteoric water line and suggest that most waters originated as local precipitation however small shifts in d 18 o and variable 87 sr 86 sr 0 70355 to 0 70879 and d 11 b 25 2 to 125 8 indicate that subsequent interactions occurred between the fluids and local rocks high b cl ratios in all samples seemingly preclude direct involvement of seawater in the hydrologic system despite the proximity to the coast and in some samples elevated 87 sr 86 sr and d 11 b two general end member water types are recognized on the basis of their chemistry these apparently are produced by interactions of local meteoric waters with the dominant reservoir rocks either basaltic lavas of etna or the underlying sediments respectively high d 11 b in the sediment hosted end member points to a significant marine carbonate contribution subsequent mixing between these or similar end members produced a range of intermediate composition groundwaters certain anomalous water compositions require the presence locally of a distinct component with high b and moderate d 11 b ca 110 but relatively low 87 sr 86 sr an anthropogenic source for this component is plausible one unusual sample has b and sr isotopic compositions similar to the other volcanic rock hosted waters but anomalously high cl content that likely reflects local magmatic outgassing near this sampling locality in general this study indicates that groundwater b and sr isotopic compositions are rock dominated these data provide useful constraints on the origin and evolution of groundwaters copyright 2000 elsevier science ltd

p wave velocity anomalies between the tonga subducting slab and the overlying mantle beneath the lau basin during a 3 week period in november december 1984 nine ocean bottom seismograph obs stations were operating in the lau basin concurrently with a land based station in the tongan island of vava u vav data from two intermediate depth 200 km 400 km earthquakes in the tonga benioff zone allowed the p wave velocity contrast between the subducting slab and the overlying mantle beneath the lau basin to be determined based on relative residuals obs vav and on three dimensional ray tracing a p wave velocity contrast of 7 is inferred this is an average contrast for depths above 400 km the standard error of the estimates is of the order of 2 the data are consistent with a hot upper mantle beneath the lau basin where temperatures are close to the solidus temperature but they do not necessarily require the presence of partial melt in the asthenosphere beneath the lau basin

basalts of the north fiji basin the generation of back arc basin magmas by mixing of depleted and enriched mantle sources active spreading ridges in the north fiji basin range from well developed stable ridges where largescale mantle upwelling is in progress to proto ridges where spreading is incipient south of 17 s where the central ridge of the north fiji basin has a bathymetric profile normally expected of a fast spreading steadystate mid ocean ridge basalts are evolved n type morbs north of 17 s where the central ridge is propagating northward into old north fiji basin crust and spreading is in the initial stages two types of basalt have been recovered n type morbs from this northern arm of the central ridge are believed to be samples of older north fiji basin crust basalts with transitional alkalic chemistry up to 0 5 ne in the norm and characterized by strong relative enrichments in rb ba k nb la ce sr p zr and ti are believed to be associated with incipient rifting among the latter group are compositions that are intermediate between transitional alkalic types and morbs and these are geochemically similar to the back arc basin babb magma type defined by sinton and fryer 1987 from a study of mariana back arc basin basalts dredges along the south pandora ridge a transform zone characterized by short spreading segments are dominated by basalts that are enriched in large ion lithophile and high field strength minor and trace elements and compositions range from types resembling ocean island tholeiites to transitional alkalic varieties basalts from rotuma are regarded as alkalic end members of the south pandora ridge magmatic spectrum in areas of the north fiji basin where relatively fast spreading must be accompanied by largescale asthenospheric upwelling depleted n type morbs dominate whereas in areas of slow mantle upwelling or where some other tectonic effect e g a transform fault causes a transient thermal disturbance within the lithosphere or upper asthenosphere enriched alkalic magmas either dominate or make a significant and noticeable contribution to the overall chemical characteristics of basalts being erupted the morbs have a depleted asthenospheric source and the alkalic component is believed to derive from an enriched lithospheric or shallow asthenospheric source the babb magma type may simply be part of the spectrum of mixed magmas that can occur in the transitional tectonic settings represented by the early development of most back arc basins

wave height variation across beaches of arbitrary profile an intuitive expression for the spatial change in energy flux associated with waves breaking in the surf zone is developed using shallow water linear wave theory analytical solutions for wave height transformation due to shoaling and breaking on a flat shelf a plane slope and an equilibrium beach profile are derived and then compared to laboratory data with favorable results the effect of beach slope on wave decay is included explicitly while wave steepness effects are included implicitly by specification of the incipient conditions set down set up in the mean water level bottom friction losses and bottom profiles of arbitrary shape are introduced and solutions are obtained numerically the model is calibrated and verified using laboratory data with very good results for the wave decay but not so favorable results for set up a test run on a prototype scale profile containing two bar and trough systems demonstrates the model s ability to describe the shoaling breaking and wave re forming process commonly observed in nature bottom friction is found to play a negligible role in wave decay in the surf zone when compared to shoaling and breaking

chemical and biological impacts of ocean acidification along the west coast of north america abstract the continental shelf region off the west coast of north america is seasonally exposed to water with a low aragonite saturation state by coastal upwelling of co2 rich waters to date the spatial and temporal distribution of anthropogenic co2 canth within the co2 rich waters is largely unknown here we adapt the multiple linear regression approach to utilize the go ship repeat hydrography data from the northeast pacific to establish an annually updated relationship between canth and potential density this relationship was then used with the noaa ocean acidification program west coast ocean acidification wcoa cruise data sets from 2007 2011 2012 and 2013 to determine the spatial variations of canth in the upwelled water our results show large spatial differences in canth in surface waters along the coast with the lowest values 37 55 mol kg 1 in strong upwelling regions off southern oregon and northern california and higher values 51 63 mol kg 1 to the north and south of this region coastal dissolved inorganic carbon concentrations are also elevated due to a natural remineralized component cbio which represents carbon accumulated through net respiration in the seawater that has not yet degassed to the atmosphere average surface canth is almost twice the surface remineralized component in contrast canth is only about one third and one fifth of the remineralized component at 50 m and 100 m depth respectively uptake of canth has caused the aragonite saturation horizon to shoal by approximately 30 50 m since the preindustrial period so that undersaturated waters are well within the regions of the continental shelf that affect the shell dissolution of living pteropods our data show that the most severe biological impacts occur in the nearshore waters where corrosive waters are closest to the surface since the pre industrial times pteropod shell dissolution has on average increased approximately 19 26 in both nearshore and offshore waters

b ca in planktonic foraminifera as a proxy for surface seawater ph boron isotope systematics indicate that boron incorporation into foraminiferal caco3 is determined by the partition coefficient k d frac left rm b rm ca right rm caco3 left rm b left rm oh right 4 rm hco 3 right rm seawater and b oh 4 hco3 seawater providing in principle a method to estimate seawater ph and pco2 we have measured b ca ratios in globigerina bulloides and globorotalia inflata for a series of core tops from the north atlantic and the southern ocean and in globigerinoides ruber white from ocean drilling program odp site 668b on the sierra leone rise in the eastern equatorial atlantic b ca ratios in these species of planktonic foraminifera seem unaffected by dissolution on the seafloor k d shows a strong species specific dependence on calcification temperature which can be corrected for using the mg ca temperature proxy a preliminary study of g inflata from southern ocean sediment core chat 16k suggests that temperature corrected b ca was 30 higher during the last glacial correspondingly ph was 0 15 units higher and aqueous pco2 was 95 atm lower at this site at the last glacial maximum the covariation between reconstructed pco2 and the atmospheric pco2 from the vostok ice core demonstrates the feasibility of using b ca in planktonic foraminifera for reconstructing past variations in ph and pco2

crust and upper mantle heterogeneities in the southwest pacific from surface wave phase velocity analysis abstract direct earthquake to station rayleigh and love wave data observed on high gain broadband records are analyzed in order to improve the lateral resolution of the uppermost mantle in the southwest pacific region we used data of nine permanent geoscope and iris stations located in the southern hemisphere and nine other stations as part of two temporary networks the first one installed in new caledonia and vanuatu hereafter named cavascope network by orstom and the eost from louis pasteur university in strasbourg france and the second one installed in the fiji tonga and niue islands hereafter named spase network by washington university in st louis usa in order to collect more significant details on the surficial structures we included the analysis of short period waves down to 8 s a multiple frequency filtering technique has been used to recover phase velocities of rayleigh and love waves for selected earthquakes with magnitude greater than 5 5 and with known centroid moment tensor cmt about 1100 well distributed seismograms have been processed in the period range 8 100 s and corrections for topography and water depth have been applied to the observed phase velocities the geographical distribution of phase velocity anomalies have then been computed using the tomographic method developed by montagner montagner j p 1986a regional three dimensional structures using long period surface waves ann geophys 4 b3 283 294 due to a poor knowledge of dense well distributed crustal thickness values and corresponding velocity models we did not perform or speculate on the construction of an s wave 3d velocity model therefore we limited this study to the interpretation of the phase velocity distribution the location of phase velocity anomalies are well determined and the deviations are discussed within the framework of the geological context and compared with other tomographic models at long periods from 40 s to 100 s our results agree well with most of previous studies the tomographic imaging shows a large contrast between low and high phase velocities along the solomon new hebrides and fiji tonga trenches the lowest phase velocity anomalies are distributed beneath northern and southern fiji basins and the lau basin corresponding to the volume situated just above the dipping slabs whereas the highest values are displayed beneath the pacific plate and the eastern part of indian plate downgoing under the north fiji basin at shorter periods our results show that the phase velocity distributions are well correlated with the large structural crustal domains the use of local temporary broadband stations in the central part of the studied area gives us the opportunity to observe surface waves showing well dispersed trains allowing extended velocity measurements down to 8 s although aliasing due to multipaths become important the continental regions eastern australia new guinea fiji islands and new zealand show low velocities which are likely due to thick continental crust whereas the tasmanian d entrecasteaux and the northern and southern fiji basins are characterized by higher velocities suggesting thinner oceanic crust additional analysis including the anisotropic case and s wave velocity inversion with depth is in progress

examination of the influence of several factors on longshore current computation with random waves abstract influence of various factors affecting the longshore currents induced by obliquely incident random waves is examined through numerical calculation seven numerical models for random wave breaking process are found to yield large differences in the wave heights in the surf zone and longshore current velocities the turbulent eddy viscosity formulation by larson and kraus larson m and kraus n c 1991 numerical model of longshore current for bar and trough beaches j waterway port coastal and ocean eng asce 117 4 pp 326 347 functions almost equal to that by battjes battjes j a 1975 modeling of turbulence in the surf zone proc symp modeling techniques pp 1050 1061 but the formulation by longuet higgins longuet higgins m s 1970 longshore current generated by obliquely incident sea waves 1 and 2 j geophys res 75 33 pp 6779 6801 produces excessive diffusion of longshore currents into the offshore zone the generation and decay process of the surface roller is indispensable in the longshore current analysis the random wave transformation model called pegbis parabolic equation with gradational breaker index for spectral waves by goda goda y 2004 a 2 d random wave transformation model with gradational breaker index coastal engineering journal jsce and world scientific 46 1 pp 1 38 produced good agreement with several laboratory and field data of longshore currents

boron calcium ratios in globigerinoides ruber from the arabian sea implications for controls on boron incorporation abstract culture and downcore studies have been used to argue that b ca ratios in planktic foraminifera are correlated with seawater ph and may record seawater borate bicarbonate ratios although other factors may also control b ca specimens of globigerinoides ruber from the ocean drilling program odp site 723a western arabian sea and core aas9 21 eastern arabian sea from the last 22 kyr were analysed for b ca 18 o and mg ca b ca was compared to reconstructed salinity and sea surface temperature sst records to gain insight into the processes controlling the incorporation of boron in both cores b ca and mg ca are positively correlated which suggests that temperature governs the incorporation of boron in g ruber to some extent higher b ca ratios at the site affected by upwelling odp 723a than in the non upwelling region core aas9 21 and a positive correlation between b ca and shell size in g ruber are observed we observe no significant correlation between b ca in g ruber and salinity ph or dissolved inorganic carbon dic in either the western or eastern arabian sea which throws considerable doubt on the utility of b ca ratios as a ph or pco 2 proxy

the geochemistry of young volcanism throughout western panama and southeastern costa rica an overview oblique aseismic subduction below western panama and southeastern costa rica has produced recent arc related volcanism the aseismicity is probably related to the subduction of relatively hot oceanic lithosphere the volcanism throughout this region over the past 2 ma has been quite distinct consisting of felsic magmas andesites to rhyolites but mainly dacites with geochemical signatures suggesting a metamorphosed basaltic source it is believed that the subduction of young oceanic crust sets up conditions under which the slab melts rather than the overlying mantle wedge rocks with slab melt geochemistries and associated with young subducted crust have been termed adakites elsewhere the young adakite melts are sometimes associated with a few rare young high nb basalts but there is no obvious genetic link between them through differentiation high nb basalts may also be derived from the partial melting of the subducted oceanic crust high nb basalt migmatites have been found with pegmatites of adakite compositions in the exposed subduction terrain of the catalina schist california alternatively the high nb basalts may be partial melts of phlogopite rich mantle that has previously reacted with adakite magmas eruption of adakites and high nb basalts was preceded by a 2 3 ma period of relative quiescence prior to this there was a 7 ma period of calc alkaline volcanism typical of the present day magmatism associated with a distinct benioff zone found throughout the central american arc the abrupt transition in volcanism with time from an early calc alkaline sequence to a later adakite high nb basalt sequence may record a change in the tectonic setting of western panama and southeastern costa rica over the past 12 ma

field observations of shear waves in the surf zone 1 alongshore propagating meanders of the mean alongshore current in the surf zone called shear waves have periods of a few minutes and wavelengths of a few hundred meters here shear wave properties are estimated with arrays of current meters deployed for 4 months within 300 m of the shoreline of a sandy beach shear wave velocity fluctuations are approximately horizontally isotropic with root mean square values between 10 and 40 of the mean 3 hour averaged alongshore current v cross shore variations of the time averaged shear wave momentum flux are consistent with shear wave energy generation close to shore where the breaking wave driven mean alongshore current v and current shear vx are strong and with shear wave energy dissipation and transfer back to the mean flow farther offshore where v and vx are weak in case studies where v is a narrow jet near the shoreline the observed strong decay of shear wave energy levels seaward of the jet and the cross shore and alongshore structure of shear waves within the jet are similar to predictions based on the linearly unstable modes of the observed v shear wave energy levels also are high in a marginally unstable case with a strong but weakly sheared v

surf zone longshore currents and random waves field data and models abstract analytic and numerical models for longshore currents generated by obliquely incident random waves am compared with field observations five days of observations were selected during which the waves were narrow banded in both frequency and direction in keeping with model assumptions the extensive measurements included radiation stress and wave directional spectra in 9 m depth and a closely spaced array of current and pressure sensors on a line perpendicular to shore the longshore current models are based on balancing the gradient of the radiation stress with the alongshore bed shear and reynold s stresses assuming stationary wave conditions and straight and parallel bottom contours the spatial variation of wave height required to determine the gradient of the radiation stress is modeled using linear random wave theory given hrms in 9 m depth the model predicts hrms at shoreward locations with an average error of less than 9 using a nonlinear bottom shear stress formulation and the meas

geological structure of the central spreading system north fiji basin abstract seabeam mapping single channel and multichannel seismic profiling sonobuoy obsh refraction measurements and geomagnetic anomaly observations obtained during the cruises kaiyo87 and 88 in the north fiji basin reveal the detailed structure and history of jumps of young spreading systems currently active spreading systems north northwest and south southwest of a triple junction at about 17 s 174 e where active hydrothermal activity was discovered during kaiyo88 jumped to their present positions possibly in the late quaternary the spreading ridge south southwest of the triple junction which is oriented n15 20 e has a 0 7 3 5 km wide axial graben and a 15 35 km wide trapezoidal morphological profile it cuts into a wide n40 60 e oriented graben whose side walls themselves sharply cut previously formed structures including a high seamount which is now separated into three highs

numerical simulation of nearshore circulation on field topography under random wave environment abstract in order to investigate surf zone hydrodynamics through two dimensional numerical simulations of nearshore circulation under random wave environment a nearshore circulation model shorecirc and a random wave model swan were combined and utilized using this combined model a numerical simulation of the october 2 1997 sandyduck field experiment was performed for this simulation field topography and an input offshore spectrum were constructed using observed data sets synchronized with the experiment the wave breaking model in swan was modified by using breaker parameters varied according to bottom slope the simulation results were compared with the experimental data which revealed a well developed longshore current as well as with results using other combinations which were shorecirc and its original monochromatic wave driver and shorecirc and the default of swan the results from the novel combined model agreed well with the experimental data the results of the present simulation also indicate that alongshore field topography influences shear fluctuation of longshore currents

model data comparisons of shear waves in the nearshore 1 observations of shear waves alongshore propagating meanders of the mean alongshore current with periods of a few minutes and alongshore wavelengths of a few hundred meters are compared with model predictions based on numerical solutions of the nonlinear shallow water equations the model after ozkan haller and kirby 1999 assumes alongshore homogeneity and temporally steady wave forcing and neglects wave current interactions eddy mixing and spatial variation of the nonlinear bottom drag coefficient although the shapes of observed and modeled shear wave velocity spectra differ and root mean square velocity fluctuations agree only to within a factor of about 3 aspects of the cross shore structure of the observed 0 5 1 0 m above the seafloor and modeled vertically integrated shear waves are qualitatively similar within the surf zone where the mean alongshore current v is strong and shear waves are energetic observed and modeled shear wave alongshore phase speeds agree and are close to both v and clin the phase speed of linearly unstable modes consistent with previous results farther offshore where v is weak and observed and modeled shear wave energy levels decay rapidly modeled and observed c diverge from clin and are close to the weak alongshore current v the simulations suggest that the alongshore advection of eddies shed from the strong sheared flow closer to shore may contribute to the offshore decrease in shear wave phase speeds similar to the observations the modeled cross and alongshore shear wave velocity fluctuations have approximately equal magnitude and the modeled vorticity changes sign across the surf zone

alteration of the oceanic crust implications for geochemical cycles of lithium and boron abstract fresh tholeiitic basalt glass has been reacted with seawater at 150 c water rock mass ratio of 10 and fresh diabase has been reacted with a na k ca cl fluid at 375 c water rock mass ratios of 1 2 and 5 to understand better the role of temperature basalt composition and water rock mass ratio on the direction and magnitude of b and li exchange during basalt alteration at 150 c slight but nevertheless significant amounts of b and li were removed from seawater and incorporated into a dominantly smectite alteration phase at 375 c however b and li were leached from basalt b behaved as a soluble element and attained concentrations in solution limited only by the b concentration in basalt and the water rock mass ratio li however was less mobile for example at water rock mass ratios of 1 2 and 5 the percent of li leached from basalt was 58 70 and 92 respectively this suggests some mineralogic control on li mobility during hydrothermal alteration of basalt especially at low water rock mass ratios in general these results as well as those for b are consistent with the temperature dependent chemistry of altered seafloor basalt and the chemistry of ridge crest hydrothermal fluids based on the distribution and chemistry of products of seafloor weathering low 150 c and high temperature hydrothermal alteration of basalt and the chemistry of ridge crest hydrothermal fluids it was estimated that alteration of the oceanic crust is a li source for seawater this is not true for b however since the hot spring flux estimated for b is balanced by low temperature basalt alteration these data coupled with b and li flux estimates for other processes e g continental weathering clay mineral adsorption authigenic silicate formation and formation of siliceous skeletal material yield new insight into the b and li geochemical cycles calculations performed here indicate relatively good agreement between the magnitude of b and li sources and sinks the geochemical cycle of b however may be affected by serpentinization of mantle derived peridotite in oceanic fracture zones serpentinites are conspicuously enriched in b and if the b source for these rocks is seawater then an additional b sink exists which must be integrated into the b geochemical cycle however until more data are available in terms of areal extent of serpentinization serpentite chemistry and isotopic composition the importance of b in these rocks with respect to the b geochemical cycle remains speculative at best

diffuse back arc deformation in the southwestern pacific earthquake distribution and focal mechanisms from the lau and north fiji back arc basins indicate a diffuse and shear dominated system of deformation at odds with traditional plate tectonic models of lithospheric accretion in back arc basins the entire back arc region between the tonga and new hebrides arcs is more realistically modelled as a giant internally deformed pull apart basin formed along a left step in the transform boundary between the pacific and indo australian plates

effects of wave current interaction on shear instabilities of longshore currents 1 we examine the effects of wave current interaction on the dynamics of instabilities of the surf zone longshore current we utilize coupled models for the simulation of the incident waves and the wave induced nearshore circulation the coupling between the models occurs through radiation stress gradient terms accounting for the generation of nearshore circulation and through wave current interaction terms leading to the modification of the wave field by the generated circulation field simulations are carried out with a realistic barred beach configuration and obliquely incident waves for two frictional regimes the results show that the shear instabilities of the longshore current have a significantly altered finite amplitude behavior when wave current interaction effects are included for beaches with relatively high frictional damping the primary effects are a reduction of the offshore extent of the motions and a delay of the onset of instabilities in addition the energy content of the motions within two surf zone widths is reduced the propagation speed increases and tendency to form offshore directed jets is reduced the horizontal mixing induced by the instabilities is also reduced when wavecurrent interaction is considered leading to a larger peak mean longshore current and a larger offshore current shear these effects appear to be primarily linked to a feedback mechanism whereby the incident wave field gains energy at locations of offshore directed currents for more energetic shear instability fields that occur when frictional damping is small this feedback affects the propagation speed and energy content of the instabilities near and onshore of the current peak only minimally however the offshore extent of the motions and the tendency to shed vortices offshore are still reduced a reduction in the mixing due to the instabilities is evident offshore of the current peak hence the mean longshore current profile is only affected offshore of the current peak the inclusion of wave current interaction significantly affects the shear instability signature observed in the shoreline runup for either frictional regime these results indicate that the energy content and frequency extent of the shoreline response is increased markedly due to the wavecurrent interaction process this effect appears to be related to variations in the forcing of the circulation that arise due to the refraction of the incident waves around offshore directed features of the circulation index terms 4255 oceanography general numerical modeling 4512 oceanography physical currents 4546 oceanography physical nearshore processes

numerical modeling of infragravity wave response during delilah 1 the nearshore circulation model shorecirc is applied to simulate the infragravity wave conditions at two intervals during the 1990 delilah campaign at duck n c the model has been extended to solve the energy equation for random short waves on the timescale of the wave groups which acts as a wave driver for the long wave model to simulate the wave conditions an algorithm has been derived which synthesizes a directional offshore wavefield from measured data including the bound directional low frequency components the model data comparison shows that the mean short wave transformation and mean longshore current are predicted well the structure of the infragravity spectrum as measured in the nearshore array is correctly represented albeit that the energy levels are underpredicted in most locations the 2 d frequency longshore wavenumber spectra show that the infragravity wave energy consists mostly of edge waves and that the computations qualitatively resemble the measurements it is shown that for 1 day bar trapped edge waves are present the model is also used to show that the influence of the longshore variability is small for this particular beach and that the directional spreading in the offshore wave field is critical in predicting the nearshore infragravity wave conditions correctly edge waves which propagate against the current are generated by the directionally broad short wave forcing and to a lesser extent by back scattering the nonlinear terms are relatively unimportant for the prediction of the infragravity wave climate the cross shore gradient of the onshore directed radiation stress is the most important of the forcing terms