modelling shoreface profile evolution current knowledge of hydro sediment and morpho dynamics in the shoreface environment is insufficient to undertake shoreface profile evolution modelling on the basis of first physical principles we propose a simple panel type model to map observed behaviour the internal dynamics are determined by slope dependent wave induced cross shoreface transports while the external driving factors are lateral sediment supply and sea level rise this model concept is tested with reasonable success against the observed behaviour of the central holland coast considering two hindcast periods one covering the evolution over the last century the other the subboreal subatlantic evolution a limitation of this model is that the cross shoreface dynamics are solely steered by the variations of shoaling short waves since a variety of other wave and current dynamics may be expected to be present in the coastal boundary layer it may well be that the effects of the mechanisms and conditions which are not represented are hidden in the coefficients of the sediment transport formula this limits the accuracy of the coefficients as used and our findings should be considered as an order of magnitude estimate only indeed behaviour oriented modelling implies that generalization of results to arbitrary situations and conditions is not straightforward yet we expect that some of the conclusions are more generally applicable this concerns the substantiation of the assumption that the upper shoreface responds on a much smaller time scale than the lower shoreface and the idea that the shoreface profile is not always and everywhere in equilibrium with its forcing a worthwhile observation from the holland coast application is that the bottom slope effect on the transport is only important at geological time scales the profile evolution at the engineering time scales say 10 to 100 years is effectively quasi static in that there is no feedback between the long term averaged transport and the state of the profile this implies that at these smaller scales the profile changes can be predicted on the basis of a static sediment balance this does not mean that the gravitational downslope transport is unimportant as a physical phenomenon in coastal profile evolution it is only unimportant if a highly aggregated model like this is applied at relatively short time scales

morphometric classification of swell dominated embayed beaches abstract globally embayed beaches are common to hilly and mountainous coastlines they are typically characterised by two headlands that are a primary control on incident wave exposure and beach morphodynamics embayed beaches exist under a range of headland morphologies and degree of embaymentisation here we present a generalised embayment morphometric parameter e which classifies the geomorphological setting of embayed beaches based on the embayment indentation and area we apply this to 168 swell dominated embayed beaches from 6 regions using open access imagery the embayment morphometric parameter e was subjected to k means cluster analysis to identify 4 classes of embayed beaches with increasing e indicating greater headland influence and impact on incident wave exposure the classes range from 1 to 4 with increasing degree of embayment the most common is class 2 43 n 73 which represents embayed beaches that have moderate embayment indentation and headland influence there are clear trends in embayment geometry regardless of location wave climate or tidal regimes within the embayments there were 6 possible headland orientations types h1 h6 the most common 58 n 97 is when both headlands are orientated outwards from the beach h6 and may result in greater morphological beach response from less headland shadowing compared with headlands orientated inwards onto the beach h1 in summary we have developed a simple classification scheme for embayed beaches based on degree of indentation and headland orientation that can be applied to any embayed beach globally

the extreme 2013 2014 winter storms hydrodynamic forcing and coastal response along the southwest coast of england the southwest coast of england was subjected to an unusually energetic sequence of atlantic storms during the 2013 2014 winter with the 8 week period from mid december to mid february representing the most energetic period since at least 1953 a regional analysis of the hydrodynamic forcing and morphological response of these storms along the sw coast of england highlighted the importance of both storm and site specific conditions the key factor that controls the atlantic storm wave conditions along the south coast of southwest england is the storm track energetic inshore wave conditions along this coast require a relatively southward storm track which enables offshore waves to propagate up the english channel relatively unimpeded the timing of the storm in relation to the tidal stage is also important and coastal impacts along the macro tidal southwest coast of england are maximised when the peak storm waves coincide with spring high tide the role of storm surge is limited and rarely exceeds 1 m the geomorphic storm response along the southwest coast of england displayed considerable spatial variability this is mainly attributed to the embayed nature of the coastline and the associated variability in coastal orientation on west facing beaches typical of the north coast the westerly atlantic storm waves approached the coastline shore parallel and the prevailing storm response was offshore sediment transport many of these north coast beaches experienced extensive beach and dune erosion and some of the beaches were completely stripped of sediment exposing a rocky shore platform on the south coast the westerly atlantic storm waves refract and diffract to become southerly inshore storm waves and for the southeast facing beaches this results in large incident wave angles and strong eastward littoral drift many south coast beaches exhibited rotation with the western part of the beaches eroding and the eastern part accreting 2015 the authors earth surface processes and landforms published by john wiley sons ltd

evaluation of depth of closure using data from duck nc usa using 12 years of frequent high precision profiles collected on a wave dominated sandy oceanic beach to 8 m depth the characteristics and interpretation of depth of closure or the seaward limit of significant profile change is critically examined this includes evaluation of the predictive capability of d1 the seaward boundary of the littoral zone as originally defined by hallermeier 1981 hallermeier r j 1981 a profile zonation for seasonal sand beaches from wave climate coastal eng 4 253 277 depth of closure during major erosional events is usually produced by the seaward limit of offshore bar movement following the original recommendation of hallermeier 1981 d1 based on 12 h exceeded wave height and a reference depth of mean low water provides a robust limit to the observations using a 6 cm change criterion empirically the observed depth of closure is 69 of d1 although the scatter is large this scatter is partly controlled by pre event profile shape most particularly bar configuration depth of closure under accretional conditions can also be measured but it is time scale dependent as accretion is a slow steady process d1 underpredicts closure for accretional situations time interval e g annual depth of closure represents the integral effect of erosional and accretional events an important observation of the data is that depth of closure increases with time scale however the full population of time interval observations is not resolved at duck due to the measurement limit 8 m depth as time interval increases from 1 year to 8 years less cases close most non closing time interval cases coincide with the periods influenced by the most energetic wave events however time interval closures are generally deeper than the biggest event closure in the period showing that it represents more than the largest event the frequency distribution of the data suggests that most if not all of these missing data simply represent closures deeper than 8 m depth up to a 4 year time interval d1 t appears to provide a reasonable limit to the quantified observations it is an interesting result that d1 an event based approach might provide a limit to closure over periods up to 4 years as these time interval closures are generally larger than those produced by single storms therefore the general applicability of this result for more complete data sets or on rapidly evolving i e eroding or accreting coasts is uncertain the present data also suggest that on swell dominated coastlines where accretional processes are dominant d1 may underpredict closure suggesting an important limitation to this approach but as sediment would be moving onshore this may not be a practical problem therefore within the limits of the data set hallermeier s 1981 approach is found to define robust estimates of depth of closure particularly for individual erosional events this useful result is expected to find widespread application in coastal geology and engineering

mantle metasomatism above subduction zones trace element and radiogenic isotope characteristics of peridotite xenoliths from batan island philippines trace element abundances and radiogenic isotope ratios have been determined for a suite of upper mantle derived xenoliths collected from pliocene quaternary andesitic lavas on batan island northernmost philippines the xenoliths exhibit mineralogical changes and large ion lithophile enrichment indicative of metasomatism involving h2o rich fluids strontium and neodymium isotopes in the xenoliths are not totally consistent with those in host lavas but a common signature is indicated by the fact that all samples plot below the mantle array the flux of fluids in the mantle wedge probably occurred over a long period of time the flux induced large but variable changes in mineral and trace and isotopic compositions and ultimately resulted in the melting of the peridotites and production of island arc lavas

flow pattern and sediment transport in a braided river the torrent de st pierre french alps summary in order to bring some understanding on the mountain stream dynamics we report measurements of flow and sediment transport leveled in a proglacial gravel bed river the torrent de st pierre in the french alps the river exhibits a modest discharge 3 s during most of the glacier melting season a braiding plain developed thanks to the occurrence of a massive landslide providing a small and simplified study area quite similar to recent experimental studies a mass balance was established at the outlet of the braiding plain our measurements indicate that in the range of flows measured the dominating transport mode is suspension though less important bed load transport is far from being negligible dissolved load eventually appears to be very small compared to solid transport analysis of velocity profile measurements shows that in this highly turbulent and shallow stream the use of a logarithmic form fails to recover the velocity profile and to estimate the shear velocity of the flow a uniform chezy like relationship is shown to be valid for the velocity with friction a coefficient considered as constant over the range of our measurements accordingly the only relevant velocity for transport description is the average velocity coupled measurements of bed load and velocity show that bed load transport is related to the average velocity through a power law eventually a correlation between bed load transport and suspended load transport is evidenced and discussed

the impact of waves and tides on residual sand transport on a sediment poor energetic and macrotidal continental shelf 2019 the authors the energetic macrotidal shelf off south west england was used to investigate the influence of different tide and wave conditions and their interactions on regional sand transport patterns using a coupled hydrodynamic wave and sediment transport model residual currents and sediment transport patterns are important for the transport and distribution of littoral and shelf sea sediments morphological evolution of the coastal and inner continental shelf zones and coastal planning waves heavily influence sand transport across this macrotidal environment median 50 exceedance waves enhance transport in the tidal direction extreme 1 exceedance waves can reverse the dominant transport path shift the dominant transport phase from flood to ebb and activate sand transport below 120 m depth wave tide interactions encompassing radiation stresses stoke s drift enhanced bottom friction and bed shear stress refraction current induced doppler shift and wave blocking significantly and nonlinearly enhance sand transport determined by differencing transport between coupled wave only and tide only simulations a new continental shelf classification scheme is presented based on sand transport magnitude due to wave forcing tide forcing and nonlinear wave tide interactions classification changes between different wave tide conditions have implications for sand transport direction and distribution across the shelf nonlinear interactions dominate sand transport during extreme waves at springs across most of this macrotidal shelf at neaps nonlinear interactions drive a significant proportion of sand transport under median and extreme waves despite negligible tide induced transport this emphasizes the critical need to consider wave tide interactions when considering sand transport in energetic environments globally where previously tides alone or uncoupled waves have been considered

contribution of asian dust and volcanic material to the western philippine sea over the last 220 kyr as inferred from grain size and sr nd isotopes asian dust and volcanogenic materials are two major components in the northwestern pacific quantitatively distinguishing them and estimating their mass accumulation rates mars are very important for understanding regional and global climate change here we present the grain size composition of detrital sediments and the radiogenic strontium sr and neodymium nd isotopic compositions of different grain size fractions of detrital sediments that were recovered from the western philippine sea these new records show that the different grain size distributions can be associated with 1 asian dust from the western and central chinese deserts and chinese loess and 2 volcanogenic materials that were derived from the luzon islands the mars of this asian dust and volcanic materials are obtained by using weibull function fitting the mars of asian dust and volcanic materials are coupled with the glacial interglacial cycle these values are found to have been higher and more variable during the glacial period than during the interglacial period we argue that the strengthening aridity of the asian continent which is connected to solar insolation and ice volume variations from orbital eccentricity constitutes an important mechanism that drives the high mars of glacial dust in the western philippine sea the internal positive feedback of dust may be another important mechanism the significant increase in volcanic material during the glacial period was caused by sea level changes which were driven by the ice volume and solar insolation at high latitudes and by strengthened precipitation from the el nino southern oscillation enso which is driven by orbital eccentricity and precession cycles on the luzon islands

the modified bruun rule extended for landward transport article i nfo the bruun rule bruun 1954 1962 provides a relationship between sea level rise and shoreline retreat and has been widely applied by the engineering and scientific communities to interpret shoreline changes and to plan for possible future increases in sea level rise rates the bruun rule assumes that all sand removed from the upper profile is deposited offshore as sea level rises although overwash during storms and landward aeolian transport clearly indicate otherwise herein we examine processes associated with sandy beach evolution in response to relative sea level rise and propose a modified form of the bruun rule that considers the full range of parsing cross shore transport from completely seaward to completely landward depending on the prevailing storm and surge conditions and whether there is a surplus or deficit of sand in the profile with respect to the equilibrium beach profile a methodology is proposed that more appropriately represents the long term processes and beach response however an improved quantitative understanding of landward transport is required for optimal application of the proposed method published by elsevier b v

seismological evidence for a low velocity layer within the subducted slab of southern taiwan abstract a thin low velocity layer that continues from the surface down to at least 135 km depth has been detected within the subducted slab through the analysis of a three component short period set of digital data from seismic stations in southern taiwan two distinct phases in the first few seconds of the p waves generated by nine intermediate depth earthquakes are observed at one station taw located just at the intermediate up dip of the wadati benioff zone detailed analyses of these phases show the faster one is a refracted wave from the moho of the subducting plate while the subsequent phase is the direct wave propagated within the subducting crust these two distinct phases are not observed at any other stations even at station hen which is only 20 km from the plate boundary these phenomena suggest that the intermediate depth earthquakes occurred in the low velocity layer of the subducting crust and that the thickness of the low velocity layer is less than 15 km the continuity of such a thin low velocity layer down to at least 135 km is hard to explain by the metastable persistence of dry gabbro at depths less than 60 km instead however the low velocity layer might be largely attributed to the metastable persistence of hydro phases and or fluid produced by a series of dehydration reactions during subduction

sr isotopic and trace element variations in oligocene to recent igneous rocks from the philippine island arc evidence for recent enrichment in the sub philippine mantle oligocene miocene plutonic rocks from the philippine island arc are characterized by uniform87sr 86sr isotopic ratios of 0 7035 0 7039 in contrast volcanics erupted in the past 5 ma in central luzon marinduque and mindoro have higher radiogenic sr 0 7042 0 7054 and show regional variations in their sr isotopic compositions volcanics of the pliocene recent bicol volcanic chain of southern luzon have87sr 86sr in the same range 0 7034 0 7040 as the mid tertiary plutonics increases in radiogenic sr are coupled with increases in rb sr ba and th abundances in the central luzon mindoro marinduque volcanic belt while no such correlation exists for the mid tertiary plutonics we consider the low values observed for mid tertiary plutonics and bicol volcanics to be controlled by fluids released from the subducting philippine sea plate basalt that have87sr 86sr of the same range sr isotopic compositions of the volcanics in the northern part of the central luzon volcanic belt may be controlled by fluids generated from the subducted south china sea crust the highest values of radiogenic sr 0 7051 0 7054 and highest lil abundances which are observed in the southern part of the central luzon volcanic arc appear to be the result of source contamination by slivers of the continental crust of the north palawan mindoro terrane that collided with the philippine arc in the miocene

a geophysical study of the manila trench luzon philippines 1 crustal structure gravity and regional tectonic evolution the manila trench subduction zone is an active convergent plate margin between the south china sea and the northern philippines the trench trends northerly and is associated with a volcanic arc an east dipping benioff zone beneath luzon and a well developed fore arc basin system the luzon trough fore arc basins lie landward of the manila trench and contain up to 4 5 km of cenozoic sediments offscraping and accretion of turbidite sediments deposited in the manila trench have resulted in the upbuilding and outbuilding of an accretionary prism which forms the seaward margin of the fore arc basin system the uplifted zambales ophiolite and its offshore extension form the landward side of the fore arc basin multichannel seismic reflection profiles reveal that folding and thrust faulting of trench strata occur at the base of the trench slope the major structural decollement at the manila trench usually forms near the unconformity separating the hemipelagic sediments from the turbidite sediments subduction and perhaps underplating of the basal hemipelagic trench sediments accompany the deformation and accretion of the overlying clastic deposits faulting and uplift occur within a narrow zone of the fore arc where seamounts associated with the relict spreading center of the south china sea basin have presumably been subducted north of lingayan gulf the fore arc is disrupted by active fault systems that trend north and northwest offshore from the luzon central valley and from the southern cordillera central based on regional geological and tectonic observations we infer that subduction probably began at the manila trench in late oligocene to middle miocene time the long term average convergence rate at the manila trench is estimated to be between 10 and 20 mm yr and may be slowing in the north owing to the collision of taiwan with eurasia

multi annual embayment sediment dynamics involving headland bypassing and sediment exchange across the depth of closure abstract predicting the future behavior of beach and nearshore systems requires an accurate delineation and understanding of coastal cell boundaries sediment transport pathways and sediment sources and sinks unfortunately there is a paucity of field datasets on beach and nearshore morphological change that extend fully from the top of the dunes to beyond the depth of closure to enable quantification of the sediment budget here for the first time we employ a total sediment budget approach examining a sandy and embayed beach located in the north coast of sw england to investigate inter and multi annual embayment scale sediment dynamics over a 10 year period that includes extreme storm erosion and post storm recovery we demonstrate that despite the deeply embayed nature of the beach the shoreline orientation roughly parallel to the dominant wave direction and the overwhelmingly cross shore forcing of the inter tidal beach volume the system is neither closed nor balanced the very significant net changes in the recorded sediment volume from dune top to depth of closure 14 5 m odn representing a loss of c 100 m3 m 1 during the extreme storm period and a gain of c 200 m3 m 1 during the recovery period indicate that significant sediment transport occurs seaward of the base of the terminating headlands and beyond the morphological depth of closure the results further indicate that the inter tidal region is partly uncoupled from the sub tidal region with the former region dominated by cross shore sediment fluxes whereas the subtidal region is also significantly affected by longshore sediment fluxes a conceptual model is presented that balances the observed volume changes with inferred fluxes forced by variations in total and alongshore wave power this study contradicts the general assumption that when sediment exits the inter tidal it rests undisturbed in the sub tidal waiting for a period of low moderate energy to bring it onshore the large sediment volumetric variations across the lower shoreface depth of 5 20 m which are of the same order of magnitude as but uncorrelated with those occurring in the inter tidal region are suggestive of an energetic longshore transport system across this deeper region it is possible that this transport system extends along the whole north coast of sw england and this finding may lead to a shift in understanding of sediment budgets along exposed and macrotidal embayments globally

depth of closure over large regions using airborne bathymetric lidar abstract the depth at which significant bathymetric change can be expected is an important morphological factor for science and engineering on sandy coastlines although most depth of closure studies have been conducted on a limited number of sites the great quantity of airborne lidar bathymetry data collected over the past decade allows for a much wider study region here we present depth of closure analysis over 600 km of sandy coastline using the joint airborne lidar bathymetry technical center of expertise jalbtcx dataset improved closure predictions resulted when both extreme waves as represented by the 12 hour exceedance significant wave height over a given time interval and more typical storm waves as represented by the 99 significant wave height were jointly considered in contrast to some other studies wave steepness terms were found to be negligible consideration of error terms in least squares closure predictions was used to develop relations with different degrees of conservatism e g to provide closure depth exceeded by only 10 of observations results are presented for four closure criteria root mean square depth changes h close 20 30 cm and relative depth changes h close h 0 02 0 04 further improvements in accuracy may occur once decadal wave hindcasts include storm surge variations in water levels and have increased nearshore resolution

cenozoic plate interaction of the australia and philippine sea plates hit and run tectonics abstract recent studies in northwest new guinea have shown the presence of at least two marginal basins of different age both of which formed in back arc settings the older basin opened between the middle jurassic and early cretaceous a remnant of which is now preserved as the new guinea ophiolite its obduction started at 40 ma and it was finally emplaced on the australian margin at 30 ma the younger basin was active during the oligocene to middle miocene and was obducted in the early pliocene studies of the western edge of the philippine sea also reveal an important deformation of the philippine arc in the oligocene which hitherto has remained unexplained using information from these systems paleomagnetic results kinematic reconstructions and geochemistry of the supra subduction ophiolite we present a plate model to explain the region s eo oligocene development we suggest that an extensive portion of oceanic crust extended the australian plate a considerable distance north of the australian craton as australia began its steady 7 8 cm year northward drift in the early eocene this lithosphere was subducted thus the portion of the philippine sea plate carrying the taiwan philippine arc to its present site may have actually been in contact with the ophiolite now in new guinea and obduction led to deformation of the philippine sea plate itself neogene plate kinematics transported the deformed belt in contact with the sunda block in the late miocene and pliocene this interpretation has implications for the origin for the philippine sea plate and the potential incorporation of continental fragments against its boundaries

new methodology for describing the equilibrium beach profile applied to the valencia s beaches abstract mathematical models used for the understanding of coastal seabed morphology play a key role in beach nourishment projects these projects have become the fundamental strategy for coastal maintenance during the last few years accordingly the accuracy of these models is vital to optimize the costs of coastal regeneration projects planning of such interventions requires methodologies that do not generate uncertainties in their interpretation a study and comparison of mathematical simulation models of the coastline is carried out in this paper as well as elements that are part of the model that are a source of uncertainty the equilibrium profile ep and the offshore limit corresponding to the depth of closure doc have been analyzed taking into account different timescale ranges the results have thus been compared using data sets from three different periods which are identified as present past and future accuracy in data collection for the beach profiles and the definition of the median grain size calculation using collected samples are the two main factors that have been taken into account in this paper these data can generate high uncertainties and can produce a lack of accuracy in nourishment projects together they can generate excessive costs due to possible excess or shortage of sand used for the nourishment the main goal of this paper is the development of a new methodology to increase the accuracy of the existing equilibrium beach profile models providing an improvement to the inputs used in such models and in the fitting of the formulae used to obtain seabed shape this new methodology has been applied and tested on valencia s beaches

comment on sr nd isotope composition and clay mineral assemblages in eolian dust from the central philippine sea over the last 600 kyr implications for the transport mechanism of asian dust by seo et al against xu et al 2016 who argued that east asian desert ead dust that traveled on east asian winter monsoon winds dominates over central asian desert cad dust in the philippine sea with presentation of additional data we reconfirm seo et al s 2014 conclusion that cad dust carried on the prevailing westerlies and trade winds dominates over ead dust in overall dust budget of the central philippine sea the relative contribution of dust from eads and cads using clay mineral composition should be evaluated with elimination of mineralogical contribution from the volcanic end member which is enriched in kaolinite and overestimate the contribution of ead dust

andesite and dacite genesis via contrasting processes the geology and geochemistry of el valle volcano panama the easternmost stratovolcano along the central american arc is el valle volcano panama several andesitic and dacitic lava flows which range in age 5 10 ma are termed the old group after a long period of quiescence approximately 3 4 ma volcanic activity resumed approximately 1 55 ma with the emplacement of dacitic domes and the deposition of dacitic pyroclastic flows 0 9 0 2 ma these are referred to as the young group all of the samples analyzed are calc alkaline andesites and dacites the mineralogy of the two groups is distinct two pyroxenes occur in the old group rocks but are commonly absent in the young group in contrast amphibole has been found only in the young group samples several disequilibrium features have been observed in the minerals e g oscillatory zoning within clinopyroxenes these disequilibrium textures appear to be more prevalent among the old as compared with the young group samples and are most likely the result of magma mixing assimilation and or polybaric crystallization mass balance fractionation models for major and trace elements were successful in relating samples from the old group but failed to show a relationship among the young group rocks or between the old and young group volcanics we believe that the old group volcanics were derived through differentiation processes from basaltic magmas generated within the mantlewedge the young group however does not appear to be related to more primitive magmas by differentiation the young group samples cannot be related by fractionation including realistic amounts of amphibole distinctive geochemical features of the young group including la yb ratios 15 yb 1 sr y 150 and y 6 suggest that these rocks were derived from the partial melting of the subducted lithosphere these characteristics can be explained by the partial melting of a source with residual garnet and amphibole dacitic material with the geochemical characteristics of subducted lithosphere melting is generated apparently only where relatively hot crust is subducted based on recent work the young dacite genesis at el valle volcano is related to the subduction of relatively hot lithosphere

across shelf benthic transports on the inner shelf of the middle atlantic bight during the halloween storm of 1991 instrumented bottom boundary layer tripods were deployed on the inner shelf at depths of 13 m and 8 m off the u s army corps of engineers field research facility at duck north carolina usa over a two week period that included the severe and prolonged halloween storm of late october 1991 the storm persisted for five days and generated waves with heights and periods of up to 6 m and 22 s although the instrumentation was destroyed current profile and suspended sediment concentration profile data were recovered from the 13 m site wind driven mean along shelf currents at 1 24 m above the bed attained speeds of nearly 0 5 m s 1 across shelf flows primarily seaward directed had speeds varying from 0 05 to 0 15 m s 1 these seaward flows intensified in association with groups of high waves total mean current and skin friction bed shear stresses were increased relative to moderate energy values by more than an order of magnitude notably the highest shear stresses occurred in association with high long period swell during the late phase of the storm after winds had turned offshore creating shoreward mean flows near the bed suspended sediment concentrations exceeded 1 g 1 1 throughout the lower meter of the water column and at elevations well above the top of the wave boundary layer net across shelf suspended sediment fluxes were strongly dominated by mean flows cospectral analyses show that important but secondary roles were also played by infragravity oscillations and by wave orbital velocities

analysis of the scale of errors in nearshore bathymetric data most studies of nearshore hydrodynamics sediment transport and morphology focus on bathymetric variability within a narrow band of spatial and temporal scales typically these studies rely on bathymetry estimates derived from field observations consisting of discrete samples in space and time with varying degrees of measurement error sampling limitations which result in aliasing and measurement errors can significantly contaminate variability at resolved scales and may lead to large errors in the representation of the scales of interest using a spectral analysis interpolation errors were analyzed for three different nearshore bathymetric data sets each of which targeted a different range of spatial scales bathymetric features that were unresolved or poorly resolved e g beach cusps introduced the potential for contamination in two of the data sets this contamination was significantly reduced using an appropriate scale controlled interpolation method leading to more accurate representations of the actual bathymetry an additional benefit of using scale controlled interpolation is that interpolation errors may be estimated independently of actual observations which allows one to design bathymetric sampling strategies that ensure that dominant scales are either resolved or largely removed finally interpolation errors corresponding to a particular sample design can be used to determine which interpolated values contribute usefully to a band limited analysis of bathymetric variability

modes of cross shore sediment transport on the shoreface of the middle atlantic bight the mechanisms responsible for onshore and offshore sediment fluxes across the shoreface zone seaward of the surf zone were examined in a 3 year field study the study was conducted in the southern part of the middle atlantic bight in the depth region 7 17 m using instrumented tripods supporting electromagnetic current meters pressure sensors suspended sediment concentration sensors and sonar altimeters the observations embraced fairweather moderate energy swell dominated and storm conditions cross shore mean flows ranged from near zero during fairweather to 20 cm s 1 during the storm oscillatory flows were on the order of 10 cm s 1 during fairweather and 100 cm s 1 during the storm suspended sediment concentrations at about 10 cm above the bed were 5 kg m 3 during the storm three methods were applied to evaluate the relative importance of incident waves long period oscillations mean flows and gravity in effecting shoreward or seaward sediment flux 1 an energetics transport model was applied to instantaneous near bottom velocity data 2 higher moments of near bottom flows were estimated and compared and 3 suspended sediment fluxes were estimated directly from the instantaneous products of cross shore velocity and suspended sediment concentration the results show that measurable contributions were made by all four of the processes most significantly mean flows were seen to dominate and cause offshore fluxes during the storm and to contribute significantly to onshore and offshore flux during fairweather and moderate energy incident waves were in all cases the major source of bed shear stress but also caused shoreward as well as seaward net sediment advection low frequency effects involving wave groups and long period waves made secondary contributions to cross shore sediment flux contrary to expectations low frequency fluxes were just as often shoreward as seaward whereas cross correlations between suspended sediment concentration and the instantaneous near bottom current speed were high and in phase under storm conditions they were weak and out of phase during fairweather conditions this suggests that simple energetics models are probably inadequate for predicting fairweather transport of suspended sediment

significance of slab derived partial melts and aqueous fluids for the genesis of tholeiitic and calc alkaline island arc basalts evidence from mt arayat philippines abstract mt arayat an inactive stratovolcano is located behind the volcanic front of the bataan segment of the taiwan luzon arc in the central valley of luzon the philippines volcanism in this arc segment results from subduction of south china sea basin crust along the manila trench eruption products of mt arayat comprise pyroclastics and porphyritic basalt and andesite lavas of high k calc alkaline affinity compared to typical oceanic island arc volcanics the basalts display slightly elevated abundances of ta and nb relative to zr and hf and of ta nb zr hf and light rare earth elements lree s relative to y and heavy rare earths hree s their ree distribution suggests mixing between high hree low lree hree and low hree high lree hree components the latter suggesting the presence of residual garnet in the source region of mt arayat basalts enrichment of lree s relative to hree s is typical of calc alkaline and high k calc alkaline island arc basalts but is usually missing or small in island arc tholeiites lree enrichment is often attributed to a metasomatizing aqueous fluid generated during dehydration of the subducted slab for this model to be applicable extremely low abundances in the fluid of agents like f oh and or co2 3 which form hard complexes with the ree s are a prerequisite due to the temperature dependence of the eu 3 eu 2 redox potential divalent eu predominates in aqueous fluids of low complex forming capacity in the subduction zone environment whereas the other ree s with the possible exception of yb are still trivalent a lree enriched aqueous fluid generated by slab dehydration should therfore display a positive eu anomaly however lree enriched island arc basalts generally do not show positive eu anomalies implying that this lree enrichment is unlikely to result from ree transfer by an aqueous fluid instead a model is favoured which assumes contributions from both slab derived aqueous fluids and partial melts in the source region for island arc tholeiites the mantle wedge is only affected by a lile enriched aqueous fluid whereas the source region for calc alkaline and high k calc alkaline basalts is additionally metasomatized by small volumes of melt generated by small degrees of partial melting of the subducted slab with garnet as a residual phase these lree enriched partial melts may react with the depleted peridotite of the mantle wedge to produce domains of refertilized garnet peridotite subsequent partial melting produces calc alkaline melts whose trace element compositions display signatures of both depleted peridotite and more fertile garnet peridotite

tectonic and paleoceanographic conditions during the formation of ferromanganese nodules from the northern south china sea based on the high resolution geochemistry mineralogy and isotopes abstract deep water ferromanganese fe mn nodules cumulate trace elements from the underlying sediment pore water and seawater during the concentric mineral layers growth process over millions of years they can record long term tectonic movements and paleoceanographic changes to systematically ascertain paleoceanographic evolution of the deep south china sea scs since the last 3 2 ma we comprehensively investigated microstructure mineralogy geochemical element concentrations as well as sr nd and pb isotopic compositions in the fe mn nodules nearby the dongsha islands in the northern scs results indicate that these deposits were formed in a continental marginal environment by a mixture of diagenetic and hydrogenetic processes overall the studied nodules can be divided into three stages with different microstructures and chemical compositions which indicate different formation environments stage 1a is the innermost and oldest layer with a porous mottled texture and has the lowest mn fe ratio cu ni and zn which implies comparatively high oxidization conditions in contrast the mn mineralogy of stage 2 shows conditions similar to those of buserite formed under less oxidative conditions between stage 1a and 2 stage 1b represents a mixture of stage 1a and 2 and has inhomogeneous growth structures based on the nd and sr isotopic composition of the detrital phases and pb isotopes three potential terrigenous source regions including south china luzon and taiwan that discharge into the northern scs from 3 2 ma to 1 06 ma after 1 06 ma the terrigenous fraction in the fe mn deposits on the northern slope of the scs is a two end members mixture of fluvial input from taiwan islands and eolian dusts from the chinese loess our study indicates that scs bottom water variation occurred at 3 2 ma 2 1 ma and 1 06 ma respectively which could be attributed to global cooling and the influence of luzon arc forearc uplift

geologic and paleomagnetic evidence for a possible miocene collision in western panay central philippines the palawan metamorphic terrane represented by paleozoic basement on the northwestern tip of panay central philippines collided with the remainder of the island between late oligocene and middle miocene time subduction continued north and south of the collision zone along the manila and negros trenches respectively evidence for the collision is 1 the juxtaposition along a major fault of old melange terrane against highly metamorphosed paleozoic continental sediments similar to those exposed on palawan island itself and 2 miocene thrusting in the melange terrane oriented parallel to the suture paleomagnetic studies show that since the early miocene the island of panay has rotated 20 clockwise declination 20 9 inclination 22 1 for six sites whereas the northern philippines has rotated counterclockwise these contrasting rotations are consistent with a collision of the philippine arc with a northeastward converging palawan block

recent enrichment in the source region of arc magmas from luzon island philippines sr and nd isotopic evidence luzon the philippines is wedged between east and west directed subducting slabs westward subduction has resulted in pre miocene igneous rocks from northern luzon characterized by 87 sr 86 sr and 143 nd 144 nd ratios typical of intra oceanic arcs where sediment involvement is minor in addition pliocene to holocene volcanic eruptions of sr and nd isotopic signatures similar to those of the pre miocene rocks have developed along the bicol arc in southern luzon these rocks are also associated with the westward subduction in contrast pliocene to holocene volcanoes have been generated by eastward subduction along the western coast of central luzon the bataan arc in the north and the mindoro arc in the south and are significantly higher in radiogenic sr and lower in radiogenic nd than the rocks discussed above the pre miocene and bicol arc isotopic characteristics appear to reflect the mixing of small amounts of products from the philippine sea crust with the mantle wedge magmas erupted along the bataan and mindoro arcs may reflect that larger amounts of sediment are available for subduction in the south china sea rocks containing the highest radiogenic sr and lowest radiogenic nd values so far noted in philippine igneous rocks occur in the mindoro arc and may have been contaminated by slivers of the continental mindoro north palawan terrane which apparently had been carried down to mantle depths after the collision of this terrane and the arc in the miocene these interpretations imply that nd and by inference other rare earth elements can migrate from the subducted slab to the mantle wedge thus variable nd isotopic ratios in island arc magmas e g sunda and lesser antilles arcs may not be a primary feature of the mantle wedge but a consequence of variations in the release of nd from the subducted slab

miocene to recent calc alkalic volcanism in eastern taiwan k ar ages and petrography abstract k ar radiometric datings are presented for volcanic rocks from the coastal range of taiwan and from lanhsu and lutao islands the samples involved are basalts andesites and dacites which show the main petrological and geochemical characteristics of island arc magmas the k ar data show that volcanic activity occurred from early miocene to early pliocene times in the coastal range and in lanhsu island and during pliocene times ca 1 3 4 3 ma in lutao island the geological significance of early and middle miocene ages is discussed with respect to hydrothermal metasomatic alterations which have affected most of the samples a significant increase in incompatible elements e g k and sr is shown to have occurred during pliocene to recent times and is exemplified by the compositions of the lanhsu and lutao volcanic rocks the origin of these chemical variations is related to the magmatic effects of crustal thickening linked to the transition from subduction to collision regimes

modern sedimentation on the shoreface and inner continental shelf at wrightsville beach north carolina u s a abstract the geologic framework and surficial morphology of the shoreface and inner continental shelf off the wrightsville beach north carolina barrier island were mapped using high resolution sidescan sonar bathymetric and seismic reflection surveying techniques a suite of over 200 diver vibracores and extensive seafloor observations by divers the inner shelf is a sediment starved active surface of marine erosion modern sediments where present form a patchy veneer over tertiary and quaternary units the lithology of the underlying units exerts a primary control on the distribution texture and composition of surficial sediments as well as inner shelf bathymetry the shoreface is dominated by a linear cross shore morphology of rippled scour depressions rsds extending from just seaward of the surf zone onto the inner shelf on the upper shoreface the rsds are incised up to 1 m below surrounding areas of fine sand and have an asymmetric cross section that is steeper sided to the north on the inner shelf the rsds have a similar but more subdued cross sectional profile the depressions are floored primarily by shell hash and quartz gravel vibracore data show a thick up to 1 5 m sequence of rsd sediments that unconformably overlies ancient coastal lithosomes in this sediment starved inner shelf setting rippled scour depressions probably form initially on preexisting coarse sediment substrates such as modern lag deposits of paleofluvial channel lithosomes or ancient tidal inlet thalwegs interannual observations of seafloor morphologic change and the longer term record contained in vibracores suggest that the present seafloor morphology is either relatively stable or represents a recurring preferential morphologic state to which the seafloor returns after storm induced perturbations the apparent stability is interpreted to be the result of interactions at several scales that contribute to a repeating self reinforcing pattern of forcing and sedimentary response which ultimately causes the rsds to be maintained as sediment starved bedforms responding to both along shore and across shore flows sediment accumulation from over 30 years of extensive beach nourishment at wrightsville beach appears to have exceeded the local shoreface accommodation space resulting in the leaking of beach and shoreface sediment to the inner shelf a macroscopically identifiable beach nourishment sediment on the shoreface and inner shelf was used to identify the decadal scale pattern of sediment dispersal the nourishment sediment is present in a seaward thinning wedge that extends from the beach over a kilometer onto the inner shelf to waters depths of 14 m this wedge is best developed offshore of the shoreline segment that has received the greatest volume of beach nourishment

modelling of embayed beach equilibrium planform and rotation signal abstract embayed beaches are highly attractive sandy beaches bounded laterally by rigid boundaries which deeply affect equilibrium beach planform and shoreline dynamics we use lx shore a state of the art shoreline change model coupled with a spectral wave model to address embayed beach shoreline dynamics driven by longshore sediment transport processes the model is applied to different idealized embayed beach configurations including variations in headland lengths the model simulates a large range of equilibrium embayed beach planforms and associated spatial and temporal modes of shoreline variability for short headlands enabling occasional headland sand bypassing both embayed beach curvature and maximum erosion at the upwave side of the embayment increases with increasing headland length beach curvature also increases with increasing headland length for headlands long enough to prevent any headland sand bypassing in contrast at the same time embayed beach becomes increasingly curved and symmetric with maximum localised erosion within the embayment decreasing in intensity when there is no headland sand bypassing rotation signal decreases in amplitude and becomes increasingly symmetric with increasing headland length the modal time invariant directional spreading of incident waves is critical to embayed beach behaviour with the envelope and variance of cross shore shoreline change and time averaged shoreline curvature all increasing with decreasing modal directional spreading embayed beach rotation characteristic timescale increases with increasing embayed beach length while the narrower the embayment the smaller the cross shore amplitude of shoreline variability our simulations provide new insight into the influence of embayment characteristics and incident wave conditions on equilibrium planform and shoreline dynamics of embayed beaches this work also implies that the degree of potential headland sand bypassing should be taken into account for modelling of beach rotational dynamics and embayed beach dynamic planform configuration

an example of trondhjemite petrogenesis the blakes ferry pluton alabama u s a abstract the blakes ferry pluton is a calc alkaline pluton that is exposed in southwestern randolph county alabama u s a the petrogenesis of the blakes ferry pluton has been a controversy for almost 15 years a petrogenetically coherent model is presented however as a result of new mineral analyses and the examination of previous analytical data crystal fractionation of plagioclase has been substantiated based on mass balance calculations assimilation crystal fractionation modelling and mixing calculations suggest that the biotite muscovite sphene rich schlieren observed within the blakes ferry pluton are remnants of partially assimilated metasedimentary rock furthermore the biotite chemistry of the blakes ferry pluton is quite similar to that of the biotites in the wedowee schists which are the host rock to the blakes ferry intrusion the above indicates the assimilation mixing of the wedowee metasediments occurred toward the end of plagioclase fractionation the blakes ferry pluton has both l and s type characteristics interpreted as inherited from the source melting of an igneous rock with subsequent assimilation of the metasediments surrounding the pluton the elkahatchee quartz diorite a large older tonalitic intrusive near the blakes ferry pluton has been ruled out as a potential source rock contrary to previous interpretations crystal fractionation of a more mafic magma e g gabbro to generate the blakes ferry melt also does not seem plausible because the associated sequence of differentiated products are not observed in the region based on ree modelling and experimental work the only plausible source is the partial melting of a morb with a hornblende quartz eclogite residual the most likely source for the partial melting of a morb is in a subduction related environment several researchers have proposed an arc setting for associated rocks within the same structural and metamorphic block that the blakes ferry poluton is situated this suggests that the necessary setting for the partial melting of morb was present in the region the partial melting of approximately 28 morb coupled with the generation of 72 hornblende quartz eclogite residual in a subduction zone is envisioned the density differences between the trondhjemitic melt and the surrounding mantle generated the ascent of the magma plagioclase fractionation via filter pressing probably occurred during ascent the magma stalled in the wedowee metasediments because the density contrasts no longer existed between melt and surrounding rocks assimilation and further fractional crystallization took place as the magma cooled to become the trondhjemitic schlieren rich body observed in the field today

the application of neodymium isotope as a chronostratigraphic tool in north pacific sediments it has been suggested that dust generation was closely linked to the development of global ice sheets and or cooling this feature has allowed asian dust to be a potential chronostratigraphic tool in north pacific ocean npo sediments the orbital scale age control in npo sediments is usually established by adjusting the benthic foraminiferal 18o to the global 18o stack lr04 however it would become difficult if the sediments did not contain enough foraminifera this study investigates sr and nd isotopes trace elements mineralogy and grain size of the operationally defined aeolian dust oded extracted from the sediments recovered at ocean drilling program odp site 1209b on the shatsky rise in the npo covering the past five glacial interglacial cycles the geochemical results show that the oded at site 1209b is actually a mixture of asian dust and volcanic ash the variation of nd isotope mimics the cycles of glacial interglacial ice sheets as revealed by the global benthic foraminifera s oxygen isotope stack lr04 over the past 500 ka the low high nd values corresponded with the cool warm periods we propose that nd variation reflects the evolving aeolian dust in site 1209 sediments the excellent agreement between nd values at site 1209b and lr04 stack over the past 500 ka allows establishing the orbital timescale age control by tuning nd to the lr04 curve we thus propose that nd isotope provides a chronostratigraphic technique in npo sediments especially for sediments with a limited amount of foraminifera

morphodynamic characteristics and classification of beaches in england and wales abstract the use of beach classification models has become widespread in literature in recent years beach classification models that recognise distinct modal beach states in response to environmental conditions are most widely used these models were developed largely in high energy micro to meso tidal sandy environments and subsequent attention has focussed on extending their use into other beach environments here the applicability of these traditional beach classification models to the highly diverse coastline of england and wales was assessed through collection of detailed morphodynamic characteristics of 92 beaches yielding a comprehensive multi variate data set containing morphological sedimentological and hydrodynamic information the complex and diverse study region incorporates beach morphology covering the full spectrum from reflective to dissipative and non barred to multi barred cluster analysis supplemented by mds ordination resulted in the identification of 9 distinct beach types traditional morphodynamic indices and rtr were found to be effective in discriminating between beach groups providing some support for the beach state models derived using information from australian beaches it was found that absolute wave energy wave power is important as well in controlling beach type for intermediate beaches a wave energy flux p h 2 t value of 3 kw m 1 was found to differentiate between beaches with p 3 kw m 1 and without p 1 three dimensional bar rip morphology a key component controlling recreational beach hazard levels observations presented here inform a beach classification model to be used as the basis for a national beach risk assessment programme beach classification models based on environmental parameters are by necessity simplifications and should be used as tools for understanding morphodynamic systems rather than beach type prediction

controls of local geology and cross shore longshore processes on embayed beach shoreline variability 10 shoreline variability along the 3 6 km long narrabeen beach embayment in se australia is 11 investigated over a 5 year period we apply the one line shoreline change model lx shore 12 which couples longshore and cross shore processes and can handle complex shoreline 13 planforms non erodible emerged headlands and submerged rocky features the model 14 skilfully reproduces the three dominant modes of shoreline variability which are by 15 decreasing order of variance cross shore migration rotation and a third mode possibly 16 related to breathing model results confirm previous observations that longshore processes 17 primarily contribute to the rotation and third modes on the timescales of months to seasons 18 while cross shore processes control the shoreline migration on shorter timescales from hours 19 storms to months additional simulations simplifying progressively the bathymetry show 20 how the inherent geology strongly modulates the spatial modes of shoreline variability the 21 offshore central rocky outcrop is found to limit the rotation in contrast the submerged rocky 22 platforms that extend from the headlands enhance the shoreline rotation mode and increase 23 alongshore variability of the cross shore migration mode owing to increased alongshore 24 variability in wave exposure offshore wave transformation across large scale submerged 25 rocky features and headland shape are therefore critical to contemporary shoreline dynamics 26 2

interpretation of open system petrogenetic processes phase equilibria constraints on magma evolution we have used a computer model traces to simulate low pressure differentiation of natural basaltic magmas in an attempt to investigate the chemical dynamics of open system magmatic processes our results in the form of simulated liquid lines of descent and the calculated equilibrium mineralogy were determined for perfect fractional crystallization fractionation paired with recharge and eruption prf fractionation paired with assimilation afc and fractionation paired with recharge eruption and assimilation fear these simulations were calculated in an attempt to assess the effects of combinations of petrogenetic processes on major and trace element evolution of natural systems and to test techniques that have been used to decipher the relative roles of these processes if the results of prf calculations are interpreted in terms of a mass balance based fractionation model e g bryan et al 1969 it is possible to generate low residuals even if one assumes that fractional crystallization was the only active process in effect the chemical consequences of recharge are invisible to mass balance models pearce element ratio analyses however can effectively discern the effects of prf versus simple fractionation the fractionating mineral proportions and therefore bulk distribution coefficients d of a differentiating system are dependent on the recharge or assimilation rate comparison of the results of simulations assuming constant d with the results calculated by traces show that the steady state liquid concentrations of some elements can differ by a factor of 2 to 5 if the prf simulation is periodic with episodes of mixing separated by intervals of fractionation parallel liquidus mineral control lines are produced most of these control lines do not project back to the parental composition this must be an important consideration when attempting to calculate a potential parental magma for any natural suite where magma chamber recharge has occurred most basaltic magmas cannot evolve to high silica compositions without magnetite fractionation small amounts of rhyolite assimilation assimilation fractionation 0 1 however can drive evolving basalts to more silica rich compositions if mass balance models are used to interpret these synthetic afc data low residuals are obtained if magnetite is added to the crystallizing assemblage this approach works even for cases where magnetite was not a fractionating phase thus the mass balance results are mathematically correct but are geologically irrelevant

dynamics of longshore bars this paper presents empirical predictive expressions describing the cross shore movement of linear nearshore bars based on intensive analysis of survey data from duck north carolina the analysis centers on 300 beach profile surveys taken at approximately 2 week intervals for the continuous period from 1981 to 1989 together with accurate measurements of the wave conditions the geometry and dynamics of bars derived from the surveys are related to wave characteristics and criteria previously developed by the authors to predict beach erosion and accretion are found to be applicable to bar movement if a multiplicative empirical coefficient in each criterion is modified the results indicate that onshore movement of bars is more probable than previously estimated the implication is that linear bars formed of dredged material are more likely to move onshore to nourish the surf zone and beach than previously thought

seasonal variations in the siliciclastic fluxes to the western philippine sea and their impacts on seawater end values inferred from 1 year of in situ observations above benham rise

age geochemical and isotopic variations in volcanic rocks from the coastal range of taiwan implications for magma generation in the northern luzon arc abstract this paper reports the first systematic analysis of age and geochemical variations in volcanic rocks from the coastal range of taiwan the northern luzon arc the rocks recovered from four main volcanoes vary from low k tholeiitic to medium k calc alkaline basalts to dacites the rocks are typical of arc magmatic products exhibiting enrichment in the large ion lithophile elements and depletion in the high field strength elements our new 40ar 39ar age data constrain the youngest eruption time in each of the four volcanoes i e from north to south at 7 2 ma yuemei 4 2 ma chimei 6 2 ma chengkuang ao and 8 5 ma tuluanshan respectively these data indicate that volcanism in the northern luzon arc did not cease progressively from north to south as previously alleged the high and broadly uniform nd isotope ratios end 10 1 to 8 8 and trace element characteristics of the rocks suggest a principal magma source from the depleted mantle wedge their overall geochemical variations are ascribed to magma chamber processes the effects of magmatic differentiation and crustal contamination differ among each volcano most likely owing to the discrepancy of residence time in individual magma chambers consequently we propose a binary mixing model for the magma generation that involves arc magmas sourced from the depleted mantle wedge and up to 5 crustal contamination with a continental fragment split off from the eurasian margin

storm and fair weather wave base a relevant distinction surface waves are an important mechanism for the redistribution of sediment on shallow marine shelves and are commonly interpreted as comprising two distinct populations fairweather waves and storm waves the latter of which are generally thought to penetrate to greater water depths here we used 2 3 10 6 spectral density estimates for the surface ocean collected between 1996 and 2008 from 32 buoys in the caribbean the gulf of mexico and the western atlantic to test the hypothesis that surface waves in the modern ocean comprise two size modes although distinct wave size classes occur in some individual measurements and over the time scales of some individual storms time averaged frequency distributions of wave size are unimodal thus there is no empirical basis for presupposing a distinct bimodal separation in the size of fair weather and storm waves or in the manifestation of such differences in stratigraphic successions instead there is a continuously increasing probability that a wave will reach the bottom with decreasing water depth and a separate probability that describes the hydrodynamic state of the sediment water interface wave size does however exhibit signifi cant geographic bimodality locations in the relatively protected gulf of mexico and caribbean regions have modal wavelengths that are 50 m less than waves at locations along the western atlantic time integrated estimates of the depth of wave penetration provide empirical constraints on the paleo water depths of ancient sedimentary deposits and highlight differences between sheltered shelf environments such as those that characterized many ancient epeiric seas and open ocean facing narrow continental shelves

an assessment of 40ar39ar dating for the whole rock volcanic samples from the luzon arc near taiwan from electron microprobe petrographic and image analyses of samples from the northern tip of the luzon arc the effects of various alteration reactions phenocryst and groundmass assemblages on the whole rock 40ar39ar step heating spectra have been delineated the alteration of primary hornblende to an assemblage of zoisite chlorite sphene the palagonitization of glass and the crystallization of phillipsite tends to cause discordant 40ar39ar dates in the low temperature steps of the age spectra discordant 40ar39ar dates in the high temperature steps appear to result from degassing of inherited or trapped 40ar from coarse grained phenocrysts samples in which most of the k resides in groundmass plagioclase tend to yield meaningful plateau dates whereas samples in which most of the k resides primarily in palagonitized glass tend to yield meaningless plateau and isochron dates substantial loss of 39ar 13 40 occurred from irradiated samples prior to 40ar39ar step heating analysis which appears to be correlated with the abundance of groundmass and the degree of alteration this argon loss is attributed to thermally induced argon diffusion from the fine grained groundmass plagioclase glass and alteration phases during the pre step heating bakeout

nearshore sediment pathways and potential sediment budgets in embayed settings over a multi annual timescale abstract embayed beaches constitute a large proportion of the world s rocky coastlines but there is a paucity of studies focusing on the longshore sediment exchange between embayed beaches separated by rocky stretches of coast here we investigate the nearshore sediment transport dynamics along a 15 km stretch of the embayed coastline of north cornwall sw england using delft3d numerical simulations coupled wave and tide are conducted to compute major circulation modes and sediment fluxes including order of magnitude for sediment bypassing between bays for a wide range of modal and extreme wave conditions results indicate that extreme events cause i multi embayment circulation and mega rip formation where an alongshore current is deflected offshore 0 7 m s 1 at 20 m depth in the down wave sectors ii large bypassing rates 103 104 m3 day 1 bypassing and iii exchanges extending to depths that exceed the base of the headlands accretionary phases over moderate high swell periods were associated with clockwise intra embayment circulation with simulated currents inducing redistribution towards the south in the long embayments 103 m3 day 1 longshore this circulation mode is combined with significant bypassing rates around the shallower and wider headlands 102 103 m3 day 1 predictions of sediment fluxes along the lower shoreface are based on the correlation between the modelled sediment fluxes and offshore wave conditions r 0 92 providing insights into the potential sediment budget over multi annual timescales hindcasted yearly bypassing rates around the headlands range between 103 and 105 m3 y 1 under an assumption of unlimited sediment supply with the bulk of the transport occurring mainly during high energy events hence the magnitude of the computed potential sediment fluxes presented here has implications for coastal evolution at longer timescales 10 years especially along sediment starved coastlines

role of waves and tides on depth of closure and potential for headland bypassing abstract depth of closure is a fundamental concept used to define the seaward extent of a morphodynamically active shoreface at a particular temporal scale the estimation of this limit in relation to the depth in front of the bounding headlands along embayed coastlines allows questioning whether embayments often deemed closed sediment cells experience more headland bypassing than expected wave based parameterisations developed for microtidal beaches are most widely used to estimate closure depth however a re evaluation of the concept for shorefaces influenced by geological control presence of headlands and or bedrock and strong tidal currents is appropriate here we use the macrotidal embayed and high energy coastline of sw england to identify the active nearshore limits with a multi method approach that includes observations of shoreface morphology and sedimentology offshore inshore wave formulations and bed shear stress computations we identify the basal limit of significant i e 0 14 m morphological change depth of closure doc and a maximum depth of extreme bed activity and sediment transport depth of transport dot observations of doc correspond closely to the values predicted by existing formulations based on inshore wave conditions 10 15 m for the study area relative to mean low water spring water level in this case the computed dot represented by the upper plane bed transition attained under extreme conditions exceeds 30 m depth in the study area the significant implication is that even though many headlands appear sufficiently prominent to suggest a closed boundary between adjacent embayments significant wave and tide driven sediment transport is likely to occur beyond the headland base during extreme events especially at low water levels the maximum depth for significant sediment transport dot was computed across a broad wave current parameter space further highlighting that tidal currents can increase this closure depth estimate by 10 m along macrotidal coastlines representing a 30 increase compared to tideless settings this work illustrates the importance of tidal currents in depth of closure calculations and challenges the notion that embayed beaches are generally closed cells as headland bypassing may be more wide spread than commonly assumed along exposed coastlines globally

geodynamic evolution of the taiwan luzon mindoro belt since the late eocene abstract the structural framework of the taiwan luzon mindoro belt or festoon is described following three major transects the luzon transect with active subduction and active island arc the taiwan transect with active collision the mindoro transect with active subduction and inactive collision based on this geological study and on available geophysical data a model for the geodynamic evolution of this portion of the philippine sea and eurasia plates boundary is proposed in a succession of reconstructions between the late eocene and the present the major geodynamic events are 1 1 beginning of the opening of the south china sea s c s in lower oligocene times contemporaneous with obduction of the zambales and angat ophiolites on luzon 2 2 subduction of a mesozoic oceanic basin along the proto manila trench from the upper oligocene to the lower miocene 3 3 obduction of the south china sea oceanic crust onto the chinese and reed bank calamian passive margins in middle miocene time 14 15 ma related to a major kinematic reorganization end of opening of the s c s 4 4 beginning of collision between the luzon microblock and the two margins of the s c s in the upper miocene 7 ma collision is still active in taiwan whereas it stopped in mindoro during the pliocene

millennial scale evolution of elemental ratios in bulk sediments from the western philippine sea and implications for chemical weathering in luzon since the last glacial maximum abstract to reconstruct the chemical weathering history in luzon philippines since the last glacial maximum lgm major and trace elements ti al fe k ba rb v sc cr and th and grain size were determined for core md06 3054 as well as the bulk and detrital fractions of three core top samples from the western philippine sea wps in combination with previously published sr nd isotopes our new results indicate that ti normalized elemental ratios in the study samples were not controlled by the quantity of biogenic authigenic or diagenetic materials sediment provenance or grain size instead variations in ti normalized elemental ratios mainly reflect changes in chemical weathering intensity with lower values representing stronger chemical weathering in luzon to assess long term integrated chemical weathering patterns we defined a stacked chemical weathering index scwi based on all elemental ratios in the study core downcore scwi records indicate that sediments deposited during the lgm underwent a degree of chemical weathering equal to that during the holocene and sediments deposited during the last deglaciation exhibit rapid changes in chemical weathering with higher intensity during the heinrich event 1 h1 and younger dryas yd and lower intensity during the bolling allerod b a in the wps these observations are in excellent agreement with chemical weathering proxies such as the k al ratios and chemical index of alteration when applied to the same core we infer that persistent sea level lowstand and induced reworking of poorly consolidated sediments on the eastern luzon continental shelf during the lgm accounted for equal or slightly stronger chemical weathering for the lgm sediments relative to the holocene sediments rainfall rather than air temperature in luzon was responsible for the rapid changes in chemical weathering during the last deglaciation with higher precipitation generating stronger chemical weathering during the h1 and yd than during the b a our observations combined with existing data suggest that strong weathering of marine sediments during colder intervals of the middle late quaternary is likely to be a general feature of the tropical west pacific although the mechanism that underlies this phenomenon remains controversial

subduction of the south china sea axial ridge below luzon philippines abstract the scarborough seamount chain present at the axis of the extinct south china sea spreading center is being subducted obliquely along the manila trench a detailed seabeam survey of this convergent zone reveals that the fabric of the ridge is characterized by n60 e trending normal faults and n130 e transform faults this ridge can be traced into the forearc area this could be interpreted as the result of underplating of ridge fragments which are accreted to the upper plate

the initial morphological response of the sand engine a process based modelling study abstract sand nourishments are presently widely applied to maintain or enhance coastal safety and beach width over the last decades global sand nourishment volumes have increased greatly and the demand for nourishments is anticipated to increase further in coming decades due to sea level rise with the increase in nourishment size and the request for more complex nourishment shapes an adequate prediction of the morphodynamic evolution is of major importance yet neither the skill of current state of the art models for such predictions nor the primary drivers that control the evolution are known this article presents the results of a detailed numerical modelling study undertaken to examine the model skill and the processes governing the initial morphological response of the sand engine and the adjacent coastline the process based model delft3d is used to hindcast the first year after completion of the mega nourishment the model reproduces measured water levels velocities and nearshore waves well the prediction of the morphological evolution is consistent with the measured evolution during the study period with brier skill scores in the excellent range the model results clearly indicate that the sand eroded from the main peninsular section of the sand engine is deposited along adjacent north and south coastlines accreting up to 6 km of coastline within just one year analysis of model results further show that the erosional behaviour of the sand engine is linearly dependent on the cumulative wave energy of individual high energy wave events with the duration of a storm event being more dominant than the maximum wave height occurring during the storm the integrated erosion volume due to the 12 events with the highest cumulative wave energy density accounts for about 60 of the total eroded volume of the peninsula indicating that the less energetic wave events with a higher probability of occurrence are also important for the initial response of the sand engine a structured model experiment using the verified delft3d model indicates that wave forcing dominates the initial morphological response of the sand engine accounting for approximately 75 of the total erosion volume in the first year the vertical tide is the second most important factor accounting for nearly 17 of the total erosion volume with surge wind and horizontal tide playing only a minor role

the rare earth element geochemistry of surface sediments in four transects in the south china sea and its geological significance seventy five samples of surface sediment were collected from four transects in the south china sea scs for analyses of rare earth element ree geochemistry total ree abundance ree in the scs varies from 45 to 195 ppm average 128 ppm lower than that of the upper continental crust the spatial distribution of ree is strongly dependent upon the geographical location and depositional environment low ree concentrations are observed on the continental slope e g xisha and nansha islands while high ree concentrations are present in the deep basin sediments on the slope are also characterized by lower lree hree la yb n eu eu and ce ce ratios relative to deep basin sediments there is a positive correlation between al2o3 and ree and a negative correlation between cao and ree conversely the relatively insignificant fe mn oxide accumulation in the scs suggests that manganese nodules do not make a significant contribution to the bulk ree composition of sediments therefore the sediment ree geochemistry is mainly controlled by terrigenous and biogenic sources biogenic carbonate has a diluting effect on ree concentrations but a significant influence on lree hree ce ce and la yb n values is found only in sediments with especially high biogenic carbonate levels the ree geochemistry of scs surface sediments indicates that their source is mainly post archean felsic rocks in the eastern sub basin the relatively low lree hree ratios and high eu eu values of the sediments indicate that significant terrigenous materials are derived from young volcanic rocks e g rocks in the luzon arc

geochemistry and tectonic setting of the luzon arc philippines miocene 10 ma to recent volcanism is associated with eastward subduction along the manila trench for some 1 200 km from the coastal range in taiwan south to min doro we suggest calling this the luzon arc there are five distinct segments along this arc mindoro bataan northern luzon babuyan and taiwan the bataan and mindoro segments in the south are separated by a northeast southwest zone of volcanoes the northern luzon segment consists of pliocene to pleistocene necks and plugs that run along the entire western section of northern luzon the babuyan segment 10 ma to recent is made up of a larger number of active volcanoes than are other segments of the luzon arc the taiwan segment is composed entirely of extinct volcanoes in the coastal range and on the islands of lanhsu and lutao late miocene to 1 8 ma the nature of volcanism throughout the luzon are is clearly subduction related with calc alkaline affinities high th la ratios and negative nb ta and ti anomalies the earliest phase of volcanism so far recorded 10 ma however is tholeiitic island of calayan in the babuyan segment with mid oceanic ridge basalt like morb like tight rare earth element and large ion lithophile element concentrations and low th u ratios there are clear differences in sr and nd isotopic ratios among the samples from the luzon are samples from the southern segments mindoro through bataan fall within the mantle array with higher sr and lower nd isotopic values than those of morb pb isotope data indicate sediment involvement the isotopic values have been interpreted to result from source contamination by slab derived fluids bataan segment and by subducted crustal material from collision of the mindoro palawan terrane mindoro segment with the manila trench in contrast babuyan segment samples north have unusual island arc nd and sr isotopic ratios that fall below the mantle array they appear to be the result of sediment source contaminants or a unique mantle composition incorporation of sediments analyzed from eastern china and taiwan into a morb type mantle can explain the nd and sr isotopic ratios of the babuyan segment

reply to comment by xu et al on sr nd isotope composition and clay mineral assemblages in eolian dust from the central philippine sea over the last 600 kyr implications for the transport mechanism of asian dust by seo et al against xu et al 2016 who argued that east asian desert ead dust that traveled on east asian winter monsoon winds dominates over central asian desert cad dust in the philippine sea with presentation of additional data we reconfirm seo et al s 2014 conclusion that cad dust carried on the prevailing westerlies and trade winds dominates over ead dust in overall dust budget of the central philippine sea the relative contribution of dust from eads and cads using clay mineral composition should be evaluated with elimination of mineralogical contribution from the volcanic end member which is enriched in kaolinite and overestimate the contribution of ead dust

the geochemistry and tectonic setting of the northern section of the luzon arc the philippines and taiwan abstract the luzon arc consists of a 1200 km chain of stratovolcanoes and volcanic necks stretching from mindoro 13 n to the coastal range of taiwan 24 n this study is concerned with three of the five major segments along the arc the northern luzon babuyan and taiwan segments the late tertiary to quaternary volcanics of these segments are primarily andesitic but range in composition from basalt to rhyolite and are typical arc volcanics porphyritic plagioclase textures primarily calc alkaline with a few tholeiitic volcanic centers low tio 2 concentrations and low high field strength element hfse to large ion lithophile element lile ratios there is a large range in k 2 o and other liles from low k tholeiites to high k calc alkaline suites calayan island and mt tabungon volcanic substratum of mt cagua volcanics in the babuyan segment and most rocks from the taiwan coastal range are low k tholeiites e g nearly flat ree patterns low lree and lile concentrations and low th u ratios the dominant calc alkaline series ranges from medium k to high k rocks the high k calc alkaline rocks are mainly young and are found on batan and lutao islands when the low k tholeiitic and medium and high k calc alkaline rocks are associated in the same region the low k rocks are usually older there is a general relationship between k 2 o and other lile concentrations and k ar radiometric dates to some extent 87 sr 86 sr ratios also increase with time throughout the arc there is a correlation between latitude and 87 sr 86 sr and a positive correlation between 87 sr 86 sr and la sm cn an increase in both these geochemical parameters has been associated with an increase in the input of continental crustal material in other arc regions the lowest 87 sr 86 sr ratios found along the entire luzon arc the samples from baguio are equivalent to those found in samples from mid tertiary plutons from northern luzon and the bicol arc both groups of rocks are associated with westward subduction along the philippine trench where presumably deep oceanic sediments with little or no continental crustal component have been subducted the absence of continental crust below the arc in the northern luzon and babuyan segments has been suggested by several groups of researchers this together with the fact that metasomatized ultramafic nodules probably of mantle origin in disequilibrium with their batan host lavas but with similar 87 sr 86 sr and la sm cn ratios to the host rocks suggests that upper level assimilation afc processes does not appear to be the major influence on the geochemical signatures a collision zone between the upper crustal block of eastern china and taiwan and the manila trench has been recorded in the northern section of the arc taiwan sediments have also been shown to decrease in thickness along the south china sea basin nearly parallel to the manila trench from north to south the sediment source region is most probably taiwan and perhaps eastern china this latitudinal in variation sediment thickness may explain the crustal signature related to both geochemical and age parameters we suggest that this crustal input has taken place via subduction of sediment rich in a crustal component

hydrodynamic and geologic influence of event dependent depth of closure along the south florida atlantic coast this study develops a method to identify the depth of closure using airborne laser bathymetric data and compares the measured depth of closure to calculated depth of closures and subaqueous geomorphic units airborne laser data sets were collected before and after the 2004 hurricane season along 100 km of beaches in palm beach broward and miami dade counties in southeast florida wave and geologic hardgrounds play different roles in determining the depth of closure from north to south in the study area calculated depths of closure in terms of event dependent wave data are compatible with measured depths of closure in the northern part of the study area in this region diabathic channels that are hydrodynamically formed morphosedimentary features generally coincide with the measured depth of closure indicating that the depth of closure in the northern study area is mainly controlled by storm wave energy in contrast for the southern part of the study area the calculated depth of closure is on average greater than that measured in the southern region hardgrounds coincide with the locations of measured depth of closure suggesting geological control

a double island arc between taiwan and luzon consequence of ridge subduction analysis of geomorphological geochronological geochemical and geophysical features in the segment of the taiwan luzon arc between taiwan and luzon the bashi segment allows the recognition of a double arc structure the two volcanic chains are separated by 50 km just north of luzon 18 n and converge near 20 n islets in the western chain are older and largely composed of volcanic rocks of miocene to pliocene age they all show low relief lateritic platforms and wave cut terraces and are covered by massive recrystallized limestone in contrast all active volcanoes in this segment of the taiwan luzon arc belong to the eastern chain where most islets are quaternary in age the volcanoes have well developed cone shapes and well preserved deposits of near vent facies magmas of the eastern chain have higher ksi la n la yb n and lowerend than their counterparts at the same latitude in the western chain therefore the magmas erupted in the eastern chain were derived from more enriched mantle sources than the magmas erupted in the western chain moreover the available seismological data seem to suggest an abrupt increase of the dip angle from 30 at 18 n to 80 at 20 n thus the double arc structure is located in the region where the benioff zone suddenly changes in analogy with the lesser antilles arc we propose a geodynamic model in which the double arc in the bashi strait is the tectonic manifestation of the subduction of the aseismic scarborough seamount chain the extinct mid ocean ridge of the south china sea before that ridge reached the manila trench the western chain was the volcanic front when the ridge reached the subduction zone at 5 4 ma its buoyancy temporarily interrupted the subduction thus causing a time gap in magmatic activity furthermore this ridge arc collision was probably also responsible for regional uplift causing extensive sub aerial weathering and erosion as well as massive reef formation in the western chain when subduction started again the dip angle became shallower in response to the extra buoyancy of the downgoing ridge if the depth of magma generation remained constant the shallower dip angle would have naturally led to an eastward shift of the volcanic front thus producing the younger eastern chain moreover we speculate that the abrupt change of the dip angle may have torn the downgoing slab thus allowing more enriched continental lithospheric material to invade the mantle wedge from the northwest thus imprinting a geochemically more enriched signature on the magmas of the eastern chain

exploring shoreface dynamics and a mechanistic explanation for a morphodynamic depth of closure using energetics based formulations for wave driven sediment transport we develop a robust methodology for estimating the morphodynamic evolution of a cross shore sandy coastal profile in our approach wave driven cross shore sediment flux depends on three components two onshore directed terms wave asymmetry and wave streaming and an offshore directed slope term in contrast with previous work which applies shallow water wave assumptions across the transitional zone of the lower shoreface we use linear airy wave theory the cross shore sediment transport formulation defines a dynamic equilibrium profile and by perturbing about this steady state profile we present an advection diffusion formula for profile evolution morphodynamic peclet analysis suggests that the shoreface is diffusionally dominated using this depth dependent characteristic diffusivity timescale we distinguish a morphodynamic depth of closure for a given time envelope even though wave driven sediment transport can and will occur at depths deeper than this morphodynamic closure depth the rate of morphologic bed changes in response to shoreline change becomes asymptotically slow linear wave theory suggests a shallower shoreface depth of closure and much sharper break in processes than shallow water wave assumptions analyzing hindcasted wave data using a weighted frequency magnitude approach we determine representative wave conditions for selected sites along the u s coastline computed equilibrium profiles and depths of closure demonstrate reasonable similarities except where inheritance is strong the methodology espoused in this paper can be used to better understand the morphodynamics at the lower shoreface transition with relative ease across a variety of sites and with varied sediment transport equations

grain size distributions on high energy sandy beaches and their relation to wave dissipation grain size and sorting represent two key parameters when characterising sediments or modelling beach morphology and sediment transport traditionally an average value for grain size or sorting is often assumed for the entire area determined from only a few sediment samples ignoring any spatial or temporal variability in sediment characteristics this contribution uses a data set of physical surface sediment samples from 53 beach locations around the south west peninsula of the united kingdom in addition to bi monthly high spatial resolution mean 240 samples digital grain size surveys from a high energy oceanic sandy beach perranporth north cornwall systematic spatial variations in grain size and sorting were consistently observed in the seaward direction across the intertidal zone of sandy beaches with grain sizes coarsening and sorting improving by up to 51 7 and 64 3 respectively this variability was deterministically related to the time averaged antecedent adjusted energy dissipated by breaking waves with the observed maximum grain sizes and sorting values correlating with the location of peak wave energy dissipation r2 0 998 p 0 01 this article is protected by copyright all rights reserved

strontium lead and zinc isotopes in marine cores as tracers of sedimentary provenance a case study around taiwan orogen abstract the active collision zone around taiwan orogen receives a variety of sedimentary inputs including terrigenous flux from taiwan and chinese rivers oceanic currents and atmospheric dust in order to determine the present day respective contributions of these different sources we analysed the pb and sr isotopic compositions of late quaternary sediments accumulated offshore east taiwan samples from the taiwan coastal range andesites sandstones conglomerate and peinan river terraces and suspended loads have also been analysed to constrain the mean taiwan isotopic signature mixing lines between the different sources of material indicate that the core located in the okinawa trough represents a mixture of about 60 of taiwan 30 of chinese loess and 10 of yangtze river contributions the southernmost core located close to luzon arc is influenced by taiwan 60 and volcanic material 40 the sr and pb isotopic compositions of samples cored in the manila trench and in the huatung basin are strongly influenced by the taiwan signature while the ryukyu trench core samples point to significant but variable contributions of chinese loess and yangtze river this work also reports zn isotopic variations in the silicate fraction of these marine core samples the overall variation in zn isotopic compositions expressed as 66zn is greater than 0 3 per mil for an analytical precision of 0 05 the zn isotopic signal for most of the marine core samples is similar to the literature data measured on sedimentary material except for the manila trench core samples and the older sample from the huatung basin they present values heavier by 0 2 0 3 close to those obtained on all taiwan rocks and peinan river particulates these results show 1 the particular characteristics of taiwan zn isotopic compositions on a large scale and 2 the possible use of zn isotopes as a tracer of material sources

bathyal records of enhanced silicate erosion and weathering on the exposed luzon shelf during glacial lowstands and their significance for atmospheric co2 sink abstract we present a new high resolution multiproxy data set of mass accumulation rates sr nd isotopes as well as major and trace elements for the siliciclastic sediment fraction from international marine global change study core md06 3052 located on the continental slope of the western philippine sea we integrate our new data with published grain sizes and sea surface temperatures from the same core as well as with equatorial pacific sea level and east asian summer monsoon precipitation in order to constrain at high resolution changes in physical erosion and chemical weathering intensities on luzon and sediment source to sink processes we assess the potential significance of chemical weathering of arc silicates in regulating global atmospheric co2 since 156 kyr bp sr nd isotopes show that the siliciclastic sediments were dominantly sourced from volcanic rocks exposed on luzon 68 100 with a lesser contribution from asian dust 0 32 different indices indicate that stronger physical erosion and chemical weathering occurred during marine isotope stage mis 6 130 156 kyr bp as well as in the latter stage of mis 3 and mis 2 14 40 kyr bp the large sea level lowstands and associated significant exposure of continental shelf in the western philippine sea during these two cold periods should favor physical erosion and chemical weathering of unconsolidated sediments on the exposed shelf furthermore we notice the relatively good coherence between chemical weathering intensities on luzon and global atmospheric co2 concentrations over these cold intervals we suggest that strengthening of chemical weathering of silicates on luzon and other tropical arcs within 20 of the equator during the quaternary glacial sea level lowstands may significantly contribute to the lowering of atmospheric co2 concentrations during ice ages we estimate that a significant fraction up to 16 i e 8 ppmv of all atmospheric co2 ultimately sequestered by silicate weathering may be processed through an area corresponding to only 1 of the exorheic drainage area worldwide

the building blocks of continental crust evidence for a major change in the tectonic setting of continental growth at the end of the archean abstract oceanic arcs are commonly cited as primary building blocks of continents yet modern oceanic arcs are mostly subducted also lithosphere buoyancy considerations show that oceanic arcs even those with a felsic component should readily subduct with the exception of the arabian nubian orogen terranes in post archean accretionary orogens comprise 50 produced in continental arcs felsic igneous rocks in oceanic arcs are depleted in incompatible elements compared to average continental crust and to felsic igneous rocks from continental arcs they have lower th yb nb yb sr y and la yb ratios reflecting shallow mantle sources in which garnet did not exist in the restite during melting the bottom line of these geochemical differences is that post archean continental crust does not begin life in oceanic arcs on the other hand the remarkable similarity of incompatible element distributions in granitoids and felsic volcanics from continental arcs is consistent with continental crust being produced in continental arcs during the archean however oceanic arcs may have been thicker due to higher degrees of melting in the mantle and oceanic lithosphere would be more buoyant these arcs may have accreted to each other and to oceanic plateaus a process that eventually led to the production of archean continental crust after the archean oceanic crust was thinner due to cooling of the mantle and less melt production at ocean ridges hence oceanic lithosphere is more subductable widespread propagation of plate tectonics in the late archean may have led not only to rapid production of continental crust but to a change in the primary site of production of continental crust from accreted oceanic arcs and oceanic plateaus in the archean to primarily continental arcs thereafter

hydrodynamic and sedimentary responses to two contrasting winter storms on the inner shelf of the northern gulf of mexico abstract results are presented from the deployment of three bottom mounted instrumentation systems in water depths of 6 9 m on the sandy inner shelf of louisiana usa the 61 day deployment included nine cold front passages that were associated with large increases in wind speed two of the most energetic cold front passages were characterized by distinct meteorological hydrodynamic bottom boundary layer and sedimentary responses and may potentially be treated as end member types on a continuum of regional cold front passages arctic surges ac storms have a very weak pre frontal phase followed by a fairly powerful post frontal phase when northeasterly winds dominate migrating cyclones mc storms are dominated by a strong low pressure cell and have fairly strong southerly winds prior to the frontal passage followed by strong northwesterly winds on the basis of measurements taken during this study ac storms are expected to have a lower average significant wave height than mc storms and are dominated by short period southerly waves subsequent to the frontal passage currents are weak and northerly during the pre frontal phase but become very strong and southwesterly following the passage sediment transport rate during as storms was not as high as during mc storms and the mean and overall direction tended to be southwesterly to westerly with low frequency flows producing easterly transport and wind wave flows producing southeasterly transport mc storms had the most energetic waves of any storm type with peaks in significant wave height occurring during both the pre and post frontal phases the wave field during mc storms tended to be more complex than during as storms with an energetic northerly swell band gradually giving way to a southerly sea band as the post frontal phase progressed currents during mc storms were moderate and northerly during the pre frontal phase but became much stronger and southeasterly during the post frontal phase shear velocity was high during both the pre and post frontal phases of the storm although sediment transport was highest following the frontal passage mean and overall sediment transport was directed southeasterly during mc storms with low frequency and wind wave flows producing northerly transport in summary the data sets presented here are unique and offer insight into the morphosedimentary dynamics of mid latitude micro tidal coasts during extratropical storms

how human activities affect the fine sediment distribution in the dutch coastal zone seabed abstract the fine sediment distribution in the seabed is an important indicator for the ecological functioning of shallow coastal seas in this paper we investigate the processes and conditions that determine the fine sediment distribution in the dutch coastal zone surficial seabed while also assessing the response of the system to human interventions an extensive sediment dataset collected in the dutch coastal zone from 2006 to 2014 is presented these data are used to map the distribution of fines in the seabed of the dcz at unique spatiotemporal scales for the entire dutch coastal zone the distribution of fines generally agrees well with previous studies the recent extension of the port of rotterdam the maasvlakte 2 reclamation was found to locally change the distribution of fines in the sand mining pit and directly south of the reclamation fines percentages in the seabed increased by more than 10 we developed a conceptual framework to analyse the distribution of fines and how it is affected by human interventions three components are distinguished within this framework 1 sources of fines 2 transport pathways and 3 accumulation potential these components are determined both qualitatively and quantitatively based on high resolution bathymetric and hydrodynamic model data the distinction between the three components makes it possible to unravel the contributions of different human interventions to the changes in the fines distribution in the case of maasvlakte 2 the local increase of fines percentage in the seabed could thus be attributed to a temporary additional source of fines and enhanced accumulation potential the high spatiotemporal resolution of the new sediment dataset proved crucial to enable development and testing of the framework to evaluate the impact of large engineering works on the spatial distribution of fines

movable bed roughness in unsteady oscillatory flow a model to predict the roughness in unsteady oscillatory flows over movable noncohesive beds is presented the roughness over movable beds is shown to be a function of the boundary shear stress rather than a fixed geometrical scale as is the case for fully rough turbulent boundary shear flows over immobile beds the model partitions the roughness into two distinct contributions these two contributions are due to the form drag around individual bed forms and to the near bed sediment transport the form drag over the bed forms is treated explicitly as a function of the boundary geometry and shear stress the ripples are predicted as a function of the local skin friction and a semiempirical expression is derived using standard law of the wall arguments which gives the ripple or form roughness as a function of the boundary geometry the ripple roughness is found to be proportional to the product of the ripple steepness and height favorable comparison of the form drag model with the results of bagnold s 1946 fixed ripple study is found the value of z0 associated with intense sediment transport in oscillatory flow over a flat bed is determined from carstens et al s 1969 experiments this value is found to be 7 or 8 grain diameters an expression is derived for the roughness associated with the maximum thickness of a near bottom sediment transporting layer consistent with owen s 1964 roughness hypothesis for saltation of uniform grains in air at large values of the boundary shear stress relative to the critical value for initial sediment motion the derived expression is similar to the results of smith and mclean s 1977 unidirectional flow approach modified for oscillatory flow the total roughness model is found to compare favorably with carstens et al s 1969 data in contrast to smith and mclean s 1977 steady flow findings the results here show that when ripples are present they account for a significant portion of the boundary roughness

a 2 ma record of explosive volcanism in southwestern luzon implications for the timing of subducted slab steepening 1 new chemical and isotopic analyses of the tephra layers plus deep sea tephrostratigraphic record from two cores from either side of luzon island philippines have allowed the identification of two periods of explosive volcanic activity originating from the macolod corridor in the southwestern part of the luzon the first period extended from prior to 1355 ka to 1977 ka and the second period extended from 478 ka to the present separated by a period of relative quiescence the time intervals between large explosive eruption events in each period were 31 15 ka and 156 52 ka respectively combined with published chronological and geochemical data from onshore volcanic deposits the tephrostratigraphic record shows that the locus of large explosive eruptions has migrated southwestward from the northeastern section to the middle and southwestern sections of the macolod corridor the period of relative quiescence is characterized by monogenetic volcanism in the central section of the corridor the migration of active volcanism across the southwestern part of luzon during the quaternary is used to infer the evolution of the subducting south china sea crust the period of relative quiescence represents a period of adjustment of the subducted slab by steepening which began around 1355 ka or shortly thereafter and finished at around 478 ka

the western central luzon volcanic arc the philippines two arcs divided by rifting abstract the western central luzon arc is apparently a complex zone of volcanism and tectonism the volcanoes of the northern segment of the arc the bataan arc ba fall along two semi parallel lineaments the western bataan lineament wbl and the eastern bataan lineament ebl this northern segment is cut off from the southern extension of the arc by a ne sw cross arc zone of volcanism the macolod corridor mc the volcanoes of the southern segment of the arc mindoro arc ma fall along two parallel lineaments the western mindoro lineament wml and the eastern mindoro lineament eml samples collected from the mc ebl and ma are alkali and lil enriched compared with the wbl the enrichment of the ebl is believed to be the result of the release of smaller amounts of hydrous rich fluids within the mantle below the ebl than below the wbl this process generated smaller degrees of partial melting below the ebl as compared to the wbl which resulted in the higher concentrations of lil elements in the ebl magmas as compared to the wbl magmas the alkali and lil enriched nature of the mc is believed to be the result of small degrees of partial melting during rifting the enriched nature of the ma is thought to be due to slivers of crustal material from the palawan mindoro block being incorporated into the mantle during subduction this region has the highest radiogenic sr values found in the philippines the mc may represent a pull apart rift zone between the philippine and west luzon shear zones and the transform between the manila and philippine trenches

accreted terranes in the northern part of the philippine archipelago the philippine archipelago consists of a complex array of ophiolites continental fragments and island arc elements that can be identified as accreted terranes similar to those increasingly recognized as components of orogenic zones the northern philippines including luzon mindoro and nearby smaller islands can be divided into at least six of these tectonic elements from west to east across central luzon there are the neogene accretionary prism of the west luzon arc the eocene zambales ophiolite the cretaceous angat ophiolite and a late cretaceous early paleogene volcanic arc built on an older metamorphic basement this arc terrane is repeated by offset along the philippine fault to the south the western luzon terranes are juxtaposed against the metamorphic basement block of mindoro which itself is colliding with the north palawan microcontinental fragment the ophiolites appear to have originated in back arc basins rather than in oceanic plateaus and the metamorphic belts have protoliths indicating deformation along active margins perhaps deep within accretionary prisms the philippine terranes are interpreted as fragments that originated within the complex pacific eurasian plate boundary rather than as intra pacific basin units these terranes have been assembling at least since the oligocene by strike slip and convergent displacements strike slip displacement either along transcurrent faults or as a component of convergence played a very important if not dominant role in this assembly most terranes identified in the northern philippine appear to be plate fragments with attached crust and upper mantle their characteristics contrast with those usually interpreted for terranes in the north american cordillera where near orthogonal convergence and shallow dipping terrane sutures are favored

quantitative estimates of asian dust input to the western philippine sea in the mid late quaternary and its potential significance for paleoenvironment we present a new high resolution multiproxy data set of sr nd isotopes rare earth element soluble iron and total organic carbon data from international marine global change study core md06 3047 located in the western philippine sea we integrate our new data with published clay mineralogy rare earth element chemistry thermocline depth and delta c 13 differences between benthic and planktonic foraminifera in order to quantitatively constrain asian dust input to the basin we explore the relationship between philippine sea and high latitude pacific eolian fluxes as well as its significance for marine productivity and atmospheric co2 during the mid late quaternary three different indices indicate that asian dust contributes between similar to 15 and similar to 50 to the detrital fraction of the sediments eolian dust flux in core md06 3047 is similar to that in the polar southern pacific sediment coherent changes for most dust flux maximum minimum indicate that dust generation in interhemispheric source areas might have a common response to climatic variation over the mid late quaternary furthermore we note relatively good coherence between asian dust input soluble iron concentration local marine productivity and even global atmospheric co2 concentration over the entire study interval this suggests that dust borne iron fertilization of marine phytoplankton might have been a periodic process operating at glacial interglacial time scales over the past 700 ka we suggest that strengthening of the biological pump in the philippine sea and elsewhere in the tropical western pacific during the mid late quaternary glacial periods may contribute to the lowering of atmospheric co2 concentrations during ice ages