mariana trough basalts mtb trace element and srnd isotopic evidence for mixing between morb like and arc like melts abstract mariana trough basalt mtb glasses from zones of of active seafloor volcanism have incompatible trace element compositions which are intermediate between normal morb and basaltic rocks from the active northern mariana island arc miab the chemical variation is observed in trace elemental abundances and ratios such as lil lil and lil hfs mtb glasses with high lil hfs and ba sm ratios and low k rb k ba and sm nd ratios have more enriched sr and nd isotopic compositions comparison of the sr nd isotopic compositions of mtb and miab suggests that the source region within the mantle wedge is heterogeneous the diverse trace element and isotopic compositions of mtb glasses both within and between dredge sites near 18 n imply small scale source heterogeneity correlation between sm nd and143nd 144nd of the mtb glasses is interpreted as due to recent binary mixing rather than closed system evolution of a common homogeneous source mixing of melts at or near the source region between a mantle component with long term lree and lil element depletion morb like and a relatively enriched component with lower integrated143nd 144nd arc like is suggested by trends of the mtb data on ratio ratio ratio element and element element plots

the thermal history of ascending magma diapirs and the thermal and physical evolution of magmatic conduits abstract if over millions of years the positions of island arc volcanoes remain fixed relative to their source regions magma bodies must repeatedly traverse a path through the lithospheric mantle the repeated passage of such bodies thermally and chemically modifies the adjacent mantle for diapirs with radii of 3 6 km ascending at 4 10 8 to 2 10 7 m s 60 000 to 900 000 years are required to establish a magmatic conduit to crustal depths during this period wall rock temperatures increase 200 400 c below 60 km and 400 750 c between 60 and 20 km the solidification of large volumes of magma within the mantle also provides a mechanism for the introduction of kilometer scale chemical and isotopic heterogeneities into the lithospheric mantle because the crystallization sequences of magmas ascending at different stages of conduit development vary conduit thermal and physical evolution also influences magmatic differentiation these differences in crystallization sequence result from the different p t trajectories followed by individual magmatic diapirs crystal fractionation of successive diapirs with or without concurrent wall rock assimilation can therefore generate different liquid lines of descent as successive magma bodies chemically react with their wall rock and solidify at various depths the mantle also changes in composition from peridotite toward basalt depending on the stage of conduit development assimilation of wall rock could therefore yield variable magmatic differentiation trends for successive magma bodies the degree of contamination may decline as the conduit and its margin evolve physically lithospheric conduit evolution has several important ramifications for geochemical modelling first since magma ascent from source regions to crustal depths is unlikely to be isochemical radiogenic and incompatible element ratios may not always reflect characteristics of the magma source region second the earliest stage of arc magmatism e g submarine volcanism is unlikely to reflect the processes of arc magma generation rather this phase of volcanism records the interaction between ascending magma and unmodified mantle the characteristics of primary arc magmas are likely to be understood only through examining more highly developed volcanic centers supplied by mature magmatic conduits

mantle contamination under akagi volcano japan as inferred from combined sr o isotope relationships the northeast japan arc is associated with westward subduction of the pacific plate beneath the eurasian plate at the southernmost region of the arc the philippine sea plate subducts northward into the mantle wedge between the eurasian plate and the pacific slab akagi volcano located at this region yields volcanic rocks with combined sr o isotope relationships which are explained in terms of the mixing of the mantle material from the mantle wedge and deep ocean and or continent derived sediments conveyed with the subducting philippine sea plate this implys that the philippine sea plate continues to the location just under akagi volcano although the seismic philippine sea plate does not reach just under the volcano

efficient sequestration of terrigenous organic carbon in the new britain trench abstract the fate of terrigenous organic carbon octerr in the ocean remains an enigma for four decades hadal trenches the deepest ocean realm 6 11 km deep were recently proposed to be oc depocenters but whether and how much octerr was sequestrated there remain elusive here we conducted comprehensive analyses for four sediment cores from the new britain trench nbt close to papua new guinea to assess source translocation and burial of oc the bulk and molecular radiocarbon data suggest that the nbt landward slope and axis sediments mainly receive young and biogenic rather than petrogenic oc the three endmember mixing model based on 14c 13c and oc contents reveals that sediments of the nbt axis 8225 m comprise relatively high oc contents 0 66 0 08 of which biogenic octerr accounts for 62 10 the high proportion of biogenic octerr was attributed to the selective translocation of octerr enriched coarse particles and rapid delivery of sediments supported by unique v shape feature of the trench in contrast the sediment oc at the oceanward slope is primarily of a marine origin suggesting that octerr was efficiently trapped in the trench bottom it is estimated that the burial rate is 2 75 0 32 g c m 2 yr 1 for oc and 1 69 0 41 g c m 2 yr 1 for octerr in the nbt given a fact that many trenches are close to the landmasses we propose that the hadal trenches may contribute significantly to the burial of octerr in the ocean

across shelf variations in bed roughness bed stress and sediment suspension on the northern california shelf abstract field measurements of bed micromorphology roughness benthic flow bed stress and suspended sediment flux were made on the northern california continental shelf in connection with the strataform program a sediment profiling camera and side scan sonar were used to observe bed features in december 1995 biogenic roughness with 2 cm relief prevailed at both sites bottom boundary layer tripods were deployed on the 60 m and 70 m isobaths over the period 5 january to 7 march 1996 during which time two high energy events occurred skin friction shear stresses were subcritical under average conditions but appreciably exceeded the threshold for sediment suspension during storms for those high energy events near bed suspended sediment concentrations reached 2 g l at 60 m 15 cm above bed and 1g l at 70 m 27 cm above bed and suspended sediment induced stratification significantly affected bed stress estimates at those times increases in current shear were accompanied by increases in suspended sediment concentration gradients causing the gradient richardson number within the log layer to remain near the critical value of 1 4 this suggests suppression of turbulence by sediment induced stratification the abundance of under consolidated fine sediment on the shelf to the north of the eel river mouth presumably allows increases in stress to be accompanied by progressive increases in suspended sediment concentration within the log layer to maintain the critical richardson number this contrasts to situations where bed armoring limits the total amount of fine sediment in suspension applications of a wave current boundary layer model with stratification effects included reduces estimates of current friction velocities by u c about 24 relative to results from fitting the von karman prantdl equation without stratification the model suggests that the total wave current friction velocity u cw reached 3 0 cm s at 70 m and 3 5 cm s at 60 m depth integrated across shelf suspended sediment fluxes were seaward at the 60 m isobath and near zero to weakly landward at the 70 m isobath during high energy periods implying flux convergence this is consistent with the conclusions of other strataform investigators that rapid long term accumulation of mud is occurring on the mid shelf

oxygen and strontium isotopic investigations of subduction zone volcanism the case of the volcano arc and the marianas island arc abstract recent fresh volcanic rocks of the intra oceanic mariana and volcano arcs were analyzed for o and sr isotopic compositions in order to determine the source of these magmas fresh non arc volcanic rocks from the regions surrounding the mariana volcano arcs and some dsdp sediments were also analyzed for comparison the oxygen isotopic ratios of the arc lavas 5 5 6 8 exhibited a small inter island variation that cannot be entirely explained by fractional crystallization the sr isotopic composition of the arc lavas is remarkably uniform 0 70332 0 70394 for the marianas three models are considered in order to explain the observed isotopic characteristics 1 bulk mixing and melting of morb type mantle with a subducted sediments and b subducted oceanic crust excluding sediments 2 melting of a mixture of sediment derived fluids and morb type mantle and 3 melting of a mixture of sediment derived fluids and oceanic island or hot spot type mantle the last model fits the data best the conclusion that very small and variable amounts of sediment derived fluid 1 are required to explain the observed inter island o isotopic variation is consistent with that of other workers who used different isotopic and trace element methods the generation of magmas in the mariana volcano arcs involves very little sediment and the source region of mariana lavas is isotopically indistinguishable from that of hot spot basalts

response of the north atlantic dynamic sea level and circulation to greenland meltwater and climate change in an eddy permitting ocean model the response of the north atlantic dynamic sea surface height ssh and ocean circulation to greenland ice sheet gris meltwater fluxes is investigated using a high resolution model the model is forced with either present day like or projected warmer climate conditions in general the impact of meltwater on the north atlantic ssh and ocean circulation depends on the surface climate in the two major regions of deep water formation the labrador sea and the nordic seas the basin mean ssh increases with the increase of the gris meltwater flux this ssh increase correlates with the decline of the atlantic meridional overturning circulation amoc however while in the labrador sea the warming forcing and gris meltwater input lead to sea level rise in the nordic seas these two forcings have an opposite influence on the convective mixing and basin mean ssh relative to the global mean the warming leads to less sea ice cover in the nordic seas which favours stronger surface heat loss and deep mixing lowering the ssh and generally increasing the transport of the east greenland current in the labrador sea the increased ssh and weaker deep convection are reflected in the decreased transport of the labrador current lc which closes the subpolar gyre in the west among the two major components of the lc transport the thermohaline and bottom transports the former is less sensitive to the gris meltwater fluxes under the warmer climate the ssh difference across the lc which is a component of the bottom velocity correlates with the long term mean amoc rate

a numerical investigation of the dynamics and structure of hyperpycnal river plumes on sloping continental shelves 1 a 3 d hydrodynamic model regional ocean modeling system is used to investigate the dynamics and structure of hyperpycnal river plumes over sloping continental shelves the focus is on the plume s response to varying slopes and settling velocities ws the idealized model is configured to represent small mountainous river systems during a flood event a hyperpycnal sediment concentration of 60 g l is specified at the river mouth such that the sediment freshwater mixture is denser than the seawater causing the plumes to traverse the shelves as undercurrents a realistic range of shelf slope of 0 001 0 03 is chosen the settling velocity is varied based on river s carrying capacity the model derived velocity profiles and the entrainment rate compare favorably against prior laboratory experiments both cross shore and alongshore momentum balances are primarily between gravitational forcing and bottom friction but the coriolis deflection is significant at the plume core in the alongshore momentum budget i e ekman balance as the slope increases and settling velocity decreases hyperpycnal plumes transition from depositional to autosuspending regime an estimate of critical slope governed by a dimensionless parameter ws3 qb qb is buoyancy input reasonably captures the regime transition in the depositional regime the plume s runout cross shore penetration scales with advective distance increasing slopes and discharge enhance the gravitational forcing and plume velocity leading to an increase in runout in contrast increasing settling velocity shortens the vertical settling time thereby reducing the plume s horizontal footprint for the range of parameters considered the runout of depositional plumes is confined within 15 km from the mouth whereas the penetration of autosuspending plumes is essentially unlimited

measurement of size and settling velocity of suspended aggregates on the northern california continental shelf abstract a high resolution video camera attached to a miniature sediment trap was used to make time lapse images of suspended aggregates settling through the water column the video trap system was placed 2 m above the seabed in the strataform study area off eureka california and was programmed to take a 7 second time sequence of settling particles every 6 h over a 4 month period the camera field of view within the trap is 15 mm and the minimum particle resolution is approximately 130 m data analysis was carried out with a video frame grabber and digital imaging software to determine the particle size shape and settling velocity results of the first deployment of this system september 1995 show that particle sizes elliptical nominal diameter determined from the video images ranged from 130 to 740 m with a modal size of 300 m the average form factor ratio of short to long semi axis of the aggregates was 0 71 measured settling velocities varied from 0 09 to 8 13 mm s in terms of weight percent or mass the median size of the aggregate distribution is 600 m analysis of settled particles collected from the sediment trap shows disaggregated or component grains ranging from 1 0 to 63 m with a modal size of 26 m and a median size of 11 m additionally an analysis was carried out to separate the relative importance of particle shape and excess density on settling velocity and these results were compared to observations using the equations for settling velocity of spheres and prolate spheroids and substituting published relationships for size versus excess density into these equations the settling velocity for combinations of shape and excess density has been calculated results show that differences between sphere and prolate spheroid with major axis both parallel and perpendicular to flow approximations caused less than a 13 difference in computed settling velocity in contrast the various size excess density relationships used to compute settling velocity caused order of magnitude deviations from measured values in all cases however the approximations of settling velocity for aggregates provide a significantly better fit to data than approximations based on disaggregated sediment size distribution

nd and sr isotopic compositions of lavas from the northern mariana and southern volcano arcs implications for the origin of island arc melts nd and sr isotopic data are reported for lavas from 23 submarine and 3 subaerial volcanoes in the northern mariana and southern volcano arcs values of end range from 2 4 to 9 5 whereas 87sr 86sr ranges from 0 70319 to 0 70392 these vary systematically between and sometimes within arc segments the nd and sr isotopic compositions fall in the field of ocean island basalt oib and extend along the mantle array lavas from the volcano arc mariana central island province and the southern part of the northern seamount province have end to 10 and 87sr 86sr 0 7032 to 0 7039 these are often slightly displaced toward higher 87sr 86sr at similar end in contrast those lavas from the northern part of the mariana northern seamount province as far north as iwo jima show oib isotopic characteristics with end and 87sr 86sr 0 7035 to 0 7039 plots of 87sr 86sr and end versus ba la and la yb n support a model in which melts from the mariana and volcano arcs are derived by mixing of oib type mantle or melts therefrom and a metasomatized morb type mantle or melts therefrom an alternate interpretation is that anomalous trends on the plots of nd and sr isotopic composition versus incompatible element ratios found in some s nsp lavas suggest that the addition of a sedimentary component may be locally superimposed on the two component mixing of mantle end members

linking late pleistocene alpine glacial erosion and continental margin sedimentation insights from 40ar 39ar dating of silt sized sediment canterbury basin new zealand abstract quaternary climatic and eustatic cycles in mid latitude regions have led to more extensive alpine glaciations and continental shelf progradation respectively however the glacial influence on sediment fluxes to the ocean creating continental margin strata is poorly documented this contribution analyzes the provenance of fine sediment accumulating on the continental shelf during the late pleistocene to evaluate the influence of glacial cycles on sediment erosion and routing to the continental shelf taking advantage of the contrasting bedrock ages exposed across the southern alps new zealand we perform 40 ar 39 ar incremental heating on the bulk silt size sediment from three drill sites of iodp expedition 317 canterbury basin new zealand the results suggest that a large proportion of sediment accumulating on the continental shelf results from erosion within the main divide fault zone of the southern alps sediment 40 ar 39 ar age fluctuations over this time period suggest that bedrock with various 40 ar 39 ar cooling ages has been differentially eroded in the upper waitaki river catchment and mixed in the waitaki canterbury sediment routing system across shelf variations in sediment 40 ar 39 ar age reflect changing modes of sediment dispersal on the continental shelf fluvial material likely derived from the main drainage divide zone preferentially accumulates in the middle continental shelf whereas material representing erosion of older bedrock torlesse terrane located lower in the drainage basin is dispersed uniformly across the shelf the age signature of the muddy sediment accumulating on the continental shelf reflects late pleistocene landscape evolution of the southern alps and its influence on sediment dispersal to the continental shelf

unzipping of the volcano arc japan abstract a working hypothesis for the recent evolution of the southern volcano arc japan is presented which calls upon a northward progressing sundering of the arc in response to a northward propagating back arc basin extensional regime this model appears to explain several localized and recent changes in the tectonic and magrnatic evolution of the volcano arc most important among these changes is the unusual composition of iwo jima volcanic rocks this contrasts with normal arc tholeiites typical of the rest of the izu volcano mariana and other primitive arcs in having alkaline tendencies high concentrations of light ree and other incompatible elements and relatively high silica contents in spite of such fractionated characteristics these lavas appear to be very early manifestations of a new volcanic and tectonic cycle in the southern volcano arc these alkaline characteristics and indications of strong regional uplift are consistent with the recent development of an early stage of inter arc basin rifting in the southern volcano arc new bathymetric data are presented in support of this model which indicate 1 1 structural elements of the mariana trough extend north to the southern volcano arc 2 2 both the mariana trough and frontal arc shoal rapidly northwards as the volcano arc is approached 3 3 rugged bathymetry associated with the rifted mariana trough is replaced just south of iwo jima by the development of a huge dome 50 75 km diameter centered around iwo jima such uplifted domes are the immediate precursors of rifts in other environments and it appears that a similar situation may now exist in the southern volcano arc the present distribution of unrifted volcano arc to the north and rifted mariana arc to the south is interpreted not as a stable tectonic configuration but as representing a tectonic snapshot of an arc in the process of being rifted to form a back arc basin

petrology of mariana trough and lau basin basalts the crust of actively opening back arc basins has close chemical and mineralogic similarities to normal mid ocean ridge basalts n morb but some subtle but distinctive differences exist these are largely due to differences in volatiles fe oxidation ratio abundances of large ion lithophile elements lil and some high field strength hfs elements isotope data for sr pb nd he and o are variable but broadly are morb like we present data contrasting mariana trough mtb and lau basin basalts lbb showing how they differ in certain trace element and isotopic signatures and compare both to n morb relative to n morb and lbb the mtb are enriched in alkalis alkaline earths light rare earth elements ree h2o and fe fe even for primitive samples while having morb type he 3 4 7 8 to 8 4 ra sr 87 86 mean 0 70293 and nd e 10 2 the lau basin is zoned with a central area having n morb characteristics for h2o lil ree nd e 8 1 to 9 0 and o but a depletion in hfs elements sr is more radiogenic mean 87 86 0 70347 and 3he 4he 3 4 7 2 to 11 0 ra is high relative to n morb the lau basin has a zone bordering the adjacent island arcs which is like mtb in both back arc basins relatively primitive unfractionated basalts with mg 100 mg fe 62 are found which resemble postulated primitive n morb calculated parental magmas obtained by adding xenocrystic olivine plot near or on 3 and 4 phase boundaries at 1 1 5 gpa for the ol di si system low p fractional crystallization and magma mixing explain most of the observed rock types possible explanations for differences between mtb and lbb include differences in the extent of previous melting episodes of their mantle sources and effects of source metasomatism through dehydration and partial melting of subducted lithosphere the long and complex history of mariana trough mantle sources led to a metasomatized mantle which gives rise to the distinctive mtb in contrast the lau basin is dominated by basalts derived from a source depleted in volatiles lil and hfs elements a previous melting history is implied mixing with a mantle component enriched in 87sr and 3he may be due to mantle counterflow driven by the subduction process

spatial variability of sea level rise in twenty first century projections abstract a set of state of the science climate models are used to investigate global sea level rise slr patterns induced by ocean dynamics in twenty first century climate projections the identified robust features include bipolar and bihemisphere seesaws in the basin wide slr dipole patterns in the north atlantic and north pacific and a beltlike pattern in the southern ocean the physical and dynamical mechanisms that cause these patterns are investigated in detail using version 2 1 of the geophysical fluid dynamics laboratory gfdl coupled model cm2 1 under the intergovernmental panel on climate change s ipcc special report on emissions scenarios sres a1b scenario the steric sea level changes relative to the global mean the local part in different ocean basins are attributed to differential heating and salinity changes of various ocean layers and associated physical processes as a result of these changes water tends to move from the ocean interior to continental shelves in the north at

reversed north atlantic gyre dynamics in present and glacial climates the dynamics of the north atlantic subpolar gyre spg are assessed under present and glacial boundary conditions by investigating the spg sensitivity to surface wind stress changes in a coupled climate model to this end the gyre transport is decomposed in ekman thermohaline and bottom transports surface wind stress variations are found to play an important indirect role in spg dynamics through their effect on water mass densities our results suggest the existence of two dynamically distinct regimes of the spg depending on the absence or presence of deep water formation dwf in the nordic seas and a vigorous greenland scotland ridge gsr overflow in the first regime the gsr overflow is weak and the spg strength increases with wind stress as a result of enhanced outcropping of isopycnals in the centre of the spg as soon as a vigorous gsr overflow is established its associated positive density anomalies on the southern gsr slope reduce the spg strength this has implications for past glacial abrupt climate changes insofar as these can be explained through latitudinal shifts in north atlantic dwf sites and strengthening of the north atlantic current regardless of the ultimate trigger an abrupt shift of dwf into the nordic seas could result both in a drastic reduction of the spg strength and a sudden reversal in its sensitivity to wind stress variations our results could provide insight into changes in the horizontal ocean circulation during abrupt glacial climate changes which have been largely neglected up to now in model studies

temporal and spatial variability of the sediment grain size distribution on the eel shelf the flood layer of 1995 abstract sediment grain size characteristics observed on the eel shelf have been analyzed using a wet sieving technique that minimizes breakage of aggregates at several sites on the 70 m isobath north of the river where a 1995 flood layer attained a maximum thickness of about 9 cm replicate box cores were collected on seven cruises during february 1995 to january 1997 these samples provide a unique opportunity to follow the evolution of a flood layer over a two year period as it was modified and gradually buried one month after the flood a layer of tan colored high porosity sediment with up to 96 of its particles in the size range of 0 20 m had accumulated on the central part of the shelf 7 30 km north of the river and principally between the 50 m and 90 m isobaths substantial coarsening of this layer occurred between february 1995 and may 1995 particularly along the southern and the landward edge of the deposit in water depths of

sorted bed forms as self organized patterns 1 model development 1 here we present a modified version of the exploratory numerical model originally presented by murray and thieler 2004 and use it to further investigate the development of sorted bed forms on the inner continental shelf the new version of the model is based on widely accepted parameterizations for hydrodynamics and sediment transport that are more detailed and empirically tested than the parameterizations used in the original model the shallow water wave equations are replaced by the general equations and changes in water depth related to morphological development are accounted for this model reproduces the main results of the previous one supporting the hypothesis that sorted bed forms are a self organized pattern and develop as a result of a coupling between bed composition and sediment flux the sensitivity of the model predictions evaluated in terms of the geometry of the sorted bed forms and their growth rate with respect to external forcing variables and internal model parameterizations shows increasing decreasing sorted bed form spacing height with increasing wave height and period the opposite occurs for increasing water depths more complicated behavior is observed when the ratio fine to coarse sediment diameter or the percentage of fine and coarse material is varied the shape of the suspended sediment and current profiles and the formulation used to predict the geometry of wave generated ripples can significantly affect or even inhibit growth rates of sorted bed forms results from a sensitivity analysis show that there are deficiencies in the description of small scale processes that limit the ability to quantitatively predict sorted bed form evolution highlighting gaps in our knowledge of sediment transport over mixed grain beds that need to be filled

constraints on the evolution of the japan sea based on 40ar 39ar ages and sr isotopic ratios for volcanic rocks of the yamato seamount chain in the japan sea 40 ar 39 ar and sr isotope analyses were performed on basalts and andesites dredged from the yamato seamount chain in the japan sea the 40 ar 39 ar plateau ages range from about 11 to 17 ma though most samples show ages between 10 and 14 ma the seamounts seem to have formed within a period of a few million years although some of them might have formed earlier based on the present results together with previously reported radiometric age data it is thought that the yamato basin formed during some period prior to 17 ma and probably later than around 25 ma taking into account the radiometric age data on rocks from the japan basin it is conjectured that the opening of the japan sea might have started almost at this time or a little earlier the observed 87 sr 86 sr ratios range from 0 70357 to 0 70388 suggesting incorporation of some time integrated components enriched in incompatible elements such as continental crustal materials this may indicate that in the japan sea area at least the yamato basin had not developed enough to show the characteristics of typical n type morb source materials without being affected by pre existing continental crustal materials

depositional processes on an ancient and modern muddy shelf northern california the modern eel river shelf and analogous pleistocene rio dell formation in northern california provide an ideal opportunity to combine the advantages of studying a modern environment with those of studying an ancient sequence and thereby enables further understanding of muddy shelf processes the modern shelf is the site of accumulation of a thick deposit of holocene mud both large scale sediment distribution patterns and small scale stratigraphy on the shelf indicate that river floods play an important role in sediment accumulation even on a high energy storm dominated coast the major factors in preservation of this flood signature are the cohesive behaviour of fine grained sediments and episodically rapid rates of sediment input the rio dell formation includes approximately 400 m of mostly fine grained shelf deposits that accumulated offshore from a palaeo eel river mouth the shelf sediments comprise four depositional sequences sequence 1 records progradation from outer to inner shelf depths facies trends closely resemble across shelf trends on the modern shelf suggesting that processes were similar detailed examination of these deposits provides insight into the nature and role of various processes on both the ancient and modern shelf muddy facies of the rio dell sequence are characterized by bioturbated clayey silts interbedded with event layers of several types clay rich silt layers are interpreted as flood deposits and physically stratified coarse silt layers are interpreted to record transport and deposition of coarse silt on the midshelf during storms sediment transport calculations and consideration of grain size distributions of bioturbated sediments which form the bulk of the rio dell sequence suggest that these sediments are the result of biological homogenization of the fine grained flood deposits and of the coarser grained storm deposits the results of this study in general indicate that fine grained shelf deposits do preserve a distinguishable if subtle record of depositional processes

sediment dynamics during wet and dry storm events on the tet inner shelf sw gulf of lions abstract the importance of short term processes such as floods and storms on sediment delivery and reworking on the tet inner shelf was investigated the tet inner shelf is a small event dominated system located in the south western part of the gulf of lions the expected sedimentary scenario in this environment is that fluvial sediment should be deposited on the prodelta and later dispersed around the shelf and slope by wave and current reworking during storms this paper investigates differences in inner shelf sediment dynamics between storm events occurring during usual river discharges and those occurring during river floods waves current velocities near bottom water turbidity bottom sediment grain size and sea floor erosion accretion were concurrently measured at 28 m water depth on the tet inner shelf from november 2003 to march 2004 two major storms took place on 4 december 2003 and 21 february 2004 and two moderate storms occurred on 8 december 2003 and 14 march 2004 the two major storms displayed similar wave characteristics maximum significant wave height h s 7 m peak period t p 12 s and wave direction around 90 the main environmental differences during the two major storm events correspond to the amount of sediment discharged from the tet river about 2 10 4 t of sediment was delivered by the river during the 4 december flood wet storm and less than 5 10 2 t during the 21 february storm dry storm sediment dynamics were quite similar during the storm events resuspension caused by waves and sediment advection towards the southeast due to near bottom shelf currents were the dominant sedimentary processes the result was a bottom sediment erosion of several centimetres at the study site during both the wet and dry events the main differences between the wet and dry events arose after the storm immediately after the peak of the wet storm sediment supplied by the tet river and probably from other rivers was deposited around the river mouth a few days later during a moderate storm this unconsolidated sediment was resuspended transported offshore and deposited on the inner shelf in contrast a moderate storm which occurred some days after the dry february storm caused bottom erosion on the inner shelf because no fresh sediment was available on the shallower area the results from this study indicate that the tet inner shelf at 28 m water depth is mainly a bypass zone for sediment that is transported s se towards the middle outer shelf and slope although ephemeral sediment deposits may be favoured by the sediment supplied from flood events sediment transport across the shelf from the river to the slope follows a complex multi step pattern that needs to be addressed using a multi event approach

strontium and oxygen isotopic variations in mesozoic and tertiary plutons of central idaho regional variations in initial 87sr 86sr ratios r i of mesozoic plutons in central idaho locate the edge of precambrian continental crust at the boundary between the late paleozoic mesozoic accreted terranes and precambrian sialic crust in western idaho the r i values increase abruptly but continuously from less than 0 704 in the accreted terranes to greater than 0 708 across a narrow 5 to 15 km zone characterized by elongate lens shaped highly deformed plutons and schistose metasedimentary and metavolcanic units the chemical and petrologic character of the plutons changes concomitantly from ocean arc type diorite tonalite trondhjemite units to a weakly peraluminous calcic to calcalkalic tonalite granodiorite granite suite the idaho batholith plutons in both suites yield late cretaceous ages but permian through early cretaceous bodies are confined to the accreted terranes and early tertiary intrusions are restricted to areas underlain by precambrian crust the two major terranes were juxtaposed between 75 and 130 m y ago probably between 80 and 95 m y oxygen and strontium isotopic ratios and rb and sr concentrations of the plutonic rocks document a significant upper crustal contribution to the magmas that intrude precambrian crust magmas intruding the arc terranes were derived from the upper mantle subducted oceanic lithosphere and may have been modified by anatexis of earlier island arc volcanic and sedimentary units plutons near the edge of precambrian sialic crust represent simple mixtures of the precambrian wall rocks with melts derived from the upper mantle or subducted oceanic lithosphere with r i of 0 7035 rb sr varies linearly with r i producing pseudoisochrons with apparent ages close to the age of the wall rocks measured 18o values of the wall rocks are less than those required for the assimilated end member by sr o covariation in the plutons however indicating that wall rock 18o was reduced significantly by exchange with circulating fluids metasedimentary rocks of the belt supergroup are similarly affected near the batholith documenting a systematic depletion in 18o as much as 50 km from the margin of the batholith plutons of the bitterroot lobe of the idaho batholith are remote from the accreted terranes and represent mixtures of precambrian wall rocks with melts dominated by continental lower crust r i 0 708 rather than mantle pseudoisochrons resulting from these data are actually mixing lines that yield apparent ages less than the true age of the wall rocks and meaningless ri assimilation fractional crystallization models permit only insignificant amounts of crystal fractionation during anatexis and mixing for the majority of plutons of the region

submarine arc volcanism in the southern mariana arc as an ophiolite analogue supra subduction zone ssz ophiolites are being recognized more and more frequently in the geologic record submarine volcanism in intra oceanic arcs is one tectonic setting in which such ophiolites might form the southern seamount province of the mariana arc represents the best documented example of an active intra oceanic submarine arc which can serve as a modern analogue for some ssz ophiolites the southern seamount province comprises nine submarine volcanoes at least seven of which are active or dormant these edifices have erupted plagioclase clinopyroxene olivine phyric basalts andesites dacites and dacitic pumices these lavas are similar to those of the subaerial edifices in the central marianas sio2 49 70 tio2 0 4 1 3 mgo 1 2 5 9 ba 140 450 ppm 87sr 86sr 0 70346 0 70354 but are somewhat more enriched in the light rare earth elements the geochemical characteristics of subaerial mariana arc lavas are preserved in the submarine lavas and the ssp lavas are slightly enriched in incompatible elements relative to those of the subaerial edifices we are ignorant of the composition of any lavas erupted between the principal edifices which may be expected to dominate the volcanic section of ssz ophiolites nevertheless the characteristic high ratio lil hfsc low ti ni and cr and diagnostic mineral compositions calcic plagioclase relatively fe rich olivine are likely to be preserved in unaltered submarine arc lavas the mariana active arc is built on back arc or thinned frontal arc crust and any ophiolite formed from such an arc is likely to exhibit complex intrusive and eruptive relationships of plutonic hypabyssal and volcanic rocks of back arc frontal arc and active arc origin such complicated intrusive relationships if preserved in structurally disrupted ophiolites will make it difficult to reconstruct the geologic history of an ssz ophiolite

modern accumulation rates and a sediment budget for the eel shelf a flood dominated depositional environment the northern california continental margin is periodically impacted by geologically significant storms which have a marked influence on terrigenous sediment supply flood deposition and long term accumulation of fine grained sediment on the eel shelf accumulation of eel river muds on the adjacent shelf was investigated using 210pb and 137cs geochronologies in order to understand the fate of sediment discharged by the eel river and to relate patterns of net sediment accumulation 100 yr time scale to sediment dynamics 210pb data demonstrate that modern accumulation of river mud occurs from the 50 m isobath seaward across shelf accumulation rates decrease from maximum mid shelf values of 0 6 1 7 g cm 2 yr 1 to values of 0 2 0 4 g cm 2 yr 1 at the shelf break with a spatially weighted mean of 0 5 g cm 2 yr 1 0 4 cm yr for the entire shelf 210pbxs sediment depth profiles from the region of highest accumulation rate are characterized by subsurface intervals of low and uniform activity which are produced by flood deposition in some cores particular 210pbxs activity intervals may be associated with major eel river floods of 1955 1964 and 1974 it is postulated that because of the coincidence of high river flow events and southerly winds during cyclonic winter storms net northward transport allows for preferential deposition of fine grained sediment north of the river mouth over the past 100 years fluvial sediment input combined with marine dispersal processes have produced a mid shelf depocenter evident by both the spatial distribution of 210pb accumulation rates and by clay rich flood layers partially preserved in shelf deposits a fine grained sediment budget for the dispersal system based on hydrological data and 210pb geochronologies demonstrates that a maximum of 20 3 109 kg yr of the mean annual supply of fluvial mud 14 109 kg yr is trapped on the shelf the results of this study demonstrate that 1 short term sedimentation processes associated with floods can influence sediment accumulation on longer time scales and 2 a major fraction of fine grained sediment supplied to tectonically active margins by flood prone mountainous rivers bypasses narrow continental shelves

from gullies to mountain belts a review of sediment budgets at various scales this paper reviews the state of the art in the concept as well as in the application of sediment budgets in sedimentary research sediments are a product of mass dispersal at the earth surface and take part in global cycles sediment budgets aim at quantifying this mass transfer based on the principle of mass conservation and are the key to determine ancient fluxes of solid matter at the earth surface this involves fundamental questions about the interplay of uplift climate and denudation in mountain belts and transfer of sediments from the continents to the oceans as well as applied issues such as soil and gully erosion reservoir siltation and coastal protection first after introducing basic concepts relevant scales and methodologies the different components of quaternary routing systems from erosion in headwaters river systems glacial and paraglacial systems lakes deltas estuaries coasts shelves epicontinental seas and deep sea fans are discussed in terms of their sediment budget most suitable are sedimentologically closed or semi closed depositional environments e g alluvial fans lakes deltas and deep sea fans in a second step the dynamics of passive active and collisional tectonic settings and sediment budgets in related sedimentary basins are explored and new concepts of sediment portioning at large geodynamic scales are introduced ancient routing systems are more or less incomplete and may be intensively fragmented or destroyed in active tectonic settings in terms of sedimentary basin types rifts intracontinental and epicontinental settings are preferred objects of sediment budgets because of their persistence and relatively simple overall sedimentary architecture however closing basins such as foreland forearc retroarc piggy back and wedge top basins may provide excellent snapshots of orogenic sediment fluxes in a third step the large long lived routing systems of the amazon the ganges brahmaputra and the rhine are reviewed for each system estimates of either sediment volumes mass or sediment fluxes of continental and marine subsystems have been compiled in order to receive a complete routing in terms of mass conservation for specific time periods since the late glacial maximum as well as the cenozoic following lessons can be taken from these case studies i depositional centers and fluxes show strong shifts in space and time and call for caution when simply looking at subsystems ii the response times of these large systems are within the milankovich time interval thus lower than predicted from diffusion models iii cyclic routing of sediments in continental basins is much more dominated by climate human control than by eustacy and iv at long time scales ultimate sinks win over intermittent storage it is concluded from this review that the quantitative understanding of global sediment cycling over historic and geologic time and its response to allogenic forcing is still in its infancy and further research is needed towards a holistic view of sediment routing systems at various temporal and spatial scales and their coupling with global biogeochemical cycles this includes i to better determine response times of large routing systems by linking quaternary with cenozoic sediment budgets and continental with marine sub systems ii to combine advanced provenance techniques with sediment budgets in order to reconstruct ancient systems iii to study sediment partitioning at the basin scale iv to reconcile continental supply dominated sequence stratigraphy with the eustatic dominated marine concept and iv to account for non actualism of ancient systems with respect to their erosion and transport mode in particular during glaciations and pronounced arid intervals glacial and eolian sediment routing may cross over hydrologic boundaries of drainage basins thus challenging the principle of mass conservation

relationships between grain size and organic carbon 14c heterogeneity in continental margin sediments abstract the deposition and long term burial of sedimentary organic matter om on continental margins comprises a fundamental component of the global carbon cycle a key unknown in interpretation of carbon isotope records of sedimentary om is the extent to which om accumulating in continental shelf and slope sediments is influenced by dispersal and redistribution processes here we present results from an extensive survey of organic carbon oc characteristics of grain size fractions ranging from 14 c values defined here as h 14 to argue that the hydrodynamic processes amplify overall 14c heterogeneity within corresponding bulk sediment samples the magnitude and footprint of this heterogeneity carries implications for our understanding of carbon cycling in shallow marginal seas

quantifying the relative importance of flow regulation and grain size regulation of suspended sediment transport α and tracking changes in grain size of bed sediment β to predict changes in sediment transport it is essential to know whether transport is regulated mainly by changes in flow or by changes in grain size of sediment on the bed in flows where changes in suspended sediment transport are regulated purely by changes in flow grain size of bed sediment is constant increases in flow strength cause increases in both concentration and grain size of sediment in suspension because stronger flows are able to suspend more sediment and coarser grains under this constraint of constant grain size of bed sediment concentration and median diameter of suspended sediment are positively correlated in contrast where transport is regulated purely by changes in grain size of sediment on the bed concentration and median diameter of suspended sediment are negatively correlated because increasing the median diameter of the bed sediment causes the concentration to decrease while causing the median grain size in suspension to increase where both flow strength and grain size on the bed are free to vary the relation between concentration and grain size in suspension can be used to quantify the importance of grain size regulation relative to flow regulation of sediment transport a measure defined as to predict sediment transport in systems that are regulated dominantly by changes in grain size on the bed it is more useful to measure sediment input events or changes in grain size on the bed than to measure changes in flow more commonly grain size of bed sediment may be secondary to flow in regulating transport but may nevertheless be important the relative coarseness of bed sediment can be measured directly or like can be calculated from measurements of concentration and grain size of suspended sediment

strontium and carbon isotope stratigraphy of the llandovery early silurian implications for tectonics and weathering abstract a high resolution 87sr 86sr curve and paired 13c carbonate organic data set is generated for the llandovery series from the ikla drill core in estonia a 13c carbonate curve is also presented from the pancake range in nevada observed 87sr 86sr values in the ikla drill core are at a minimum in the early llandovery rhuddanian stage 0 7079 to 0 7080 and then trend to more radiogenic ratios in the basal part of the telychian stage an 87sr 86sr high near 0 7084 is observed in the telychian at the top of the studied section the range of values is in general agreement with the data from previous sample sets of brachiopods and conodonts recovered from localities in north america and europe that record a rising trend in the 87sr 86sr ratio throughout the llandovery from approximately 0 7080 to 0 7084 the major increase in the 87sr 86sr ratio during the late llandovery may be due to weathering of radiogenic source rocks that were uplifted during early silurian continent continent collisions the sr rise potentially coincides with the occurrence of an unusually thick sequence of k bentonite beds representing large magnitude ash falls in the early telychian a previously documented negative 13c excursion in marine carbonates in the lower telychian interval of the ikla core is quasi synchronous with the increase in 87sr 86sr our new organic matter 13c data from the ikla core confirm that this negative 13c carbonate excursion is not a result of diagenesis furthermore a negative 13c excursion in carbonates from the early telychian portion of the pancake range section in nevada seems to confirm the global scope of this carbon cycle perturbation

shoreface ravinement evolution tracked by repeat geophysical surveys following hurricane ike bolivar peninsula texas 2008 2013 we have investigated the impact of hurricane ike on the shoreface of the bolivar peninsula texas using three nearsurface marine geophysical surveys during a five year span following the storm which made landfall in september of 2008 multibeam bathymetry sidescan backscatter and chirp subbottom reflection data were collected during each survey the first survey in november 2008 discovered the presence of an erosional landward facing scarp across a broad of the barrier spit shoreface at approximately 3 5 m water depth the erosion incised into a shallow reflection horizon interpreted as the holocene shoreface ravinement exposing lag deposits that were truncated at the scarp and forming a thin high backscatter anomaly up to 1 0 m of material was excavated shoreward of the scarp including up to 0 5 m of shoreface sand above the shoreface ravinement and another 0 5 m of indeterminate

sedimentation and self weight consolidation constitutive equations and numerical modelling the solution of the mass balance equation for sedimentation and consolidation in sediment suspensions requires closure equations for the parameters diffusivity permeability and effective stress experimental data for non cohesive and cohesive materials are discussed new semi empirical relations which are a better approximation of reality are proposed the non uniqueness for cohesive sediments is explained in terms of differences in aggregation history the numerical implementation of the unifying theory for sedimentation and consolidation faces some serious problems particularly the discontinuities require the addition of artificial diffusivity to create the necessary damping to avoid overshoot induced oscillations improved stability is obtained using a special finite element technique the model is validated with several data sets and proves to predict the right behaviour and density profile evolution for both non cohesive and cohesive sediments the remaining differences between measured and comp

observations of event scale sedimentary dynamics with an instrumented bottom boundary layer tripod abstract a new approach to examine event scale sedimentation is described that establishes a direct connection between water column signals and changes in the seabed the po river italy shelf is a good case study due to the dominant impact of winter storm events on sediment transport and the availability of coincident measurements necessary for the analysis repeated deployments of an instrumented bottom boundary layer tripod at this site have produced a nearly continuous record of sediment transport over 2 5 y sediment cores were collected every 3 mo during this time and seabed inventories of 7 be half life 53 3 d were used to determine net sediment deposition or erosion during each deployment comparison of these values with the net elevation change obtained from the tripod altimeter shows good agreement varying from 2 cm deposition to 1 cm erosion the altimeter s use is extended to quantify the net seabed change that results from individual storm induced sediment resuspension events lasting from days to weeks within each event analysis of the altimeter record has proved challenging likely due to changes in sediment porosity that occur during a storm event however net erosion and deposition that occurs over an event can be evaluated and was found to be

the drivers of projected north atlantic sea level change sea level change predicted by the cmip5 atmosphere ocean general circulation models aogcms is not spatially homogeneous in particular the sea level change in the north atlantic is usually characterised by a meridional dipole pattern with higher sea level rise north of 40 n and lower to the south the spread among models is also high in that region here we evaluate the role of surface buoyancy fluxes by carrying out simulations with the famous low resolution aogcm forced by surface freshwater and heat flux changes from co2 forced climate change experiments with cmip5 aogcms and by a standard idealised surface freshwater flux applied in the north atlantic both kinds of buoyancy flux change lead to the formation of the sea level dipole pattern although the effect of the heat flux has a greater magnitude and is the main cause of the spread of results among the cmip5 models by using passive tracers in famous to distinguish between additional and redistributed buoyancy we show that the enhanced sea level rise north of 40 n is mainly due to the direct steric effect the reduction of sea water density caused by adding heat or freshwater locally the surface buoyancy forcing also causes a weakening of the atlantic meridional overturning circulation and the consequent reduction of the northward ocean heat transport imposes a negative tendency on sea level rise producing the reduced rise south of 40 n however unlike previous authors we find that this indirect effect of buoyancy forcing is generally less important than the direct one except in a narrow band along the east coast of the us where it plays a major role and leads to sea level rise as found by previous authors

time series measurements of macrobenthos abundance and sediment bioturbation intensity on a flood dominated shelf abstract four 70 m stations on the continental shelf offshore from the eel river northern california were occupied at roughly four month intervals between february 1995 and march 1998 and in august 1999 at each of the stations profiles of excess 234 th were used to quantify sediment bioturbation intensity in addition at two of the stations macrofaunal abundance species composition and functional groupings were quantified during the study period the eel river displayed a range of hydrological conditions with historically significant floods in january 1995 and january 1997 return periods of 15 and 40 y respectively relatively low flows during the winters of 1995 1996 and 1998 1999 and an el nino year characterized by moderate but frequent discharges in 1997 1998 the january 1995 and 1997 floods deposited 3 7 cm of fine grained high porosity sediment with high c n ratios and a terrestrial organic carbon signature at the study sites the following general questions are addressed herein 1 how do macrofaunal abundance species composition and functional groupings vary over time 2 does the sediment deposition following the january 1997 flood constitute a major disturbance to the eel shelf macrobenthos 3 how does sediment bioturbation intensity vary in time space and what are the main factors controlling this variation the eel shelf macrofauna is strongly dominated by subsurface deposit feeding polychaetes with anomalously low abundances of surface deposit feeders and virtually no suspension feeders among the community dominants the abundance data revealed a clear seasonal pattern with peak density 4 5 10 4 m 2 in the fall and a factor of two lower density in the late winter spring 2 10 4 m 2 within this seasonal context there was little evidence for extraordinary mortality caused by the january 1997 flood in that overall wintertime mortality and the mortality of most community dominants during a year 1995 1996 when there was no flood deposition were comparable to the mortality observed following the january 1997 flood in contrast the depth distribution of the macrofauna revealed a distinctive post flood pattern whereby a majority 55 70 of individuals were temporarily found at depths 4 cm this pattern suggests an active response by the resident fauna to sediment deposition and supports the idea that the floods did not cause a widespread disturbance although there may not be clear evidence for short term flood effects the overall species composition and functional groupings do imply that the sedimentary environment high sediment accumulation rates and abundant terrestrial organic matter has had a long term influence on the eel shelf macrofauna model fits to 75 profiles of excess 234 th show that in general the data are consistent with a steady state biodiffusive model the resultant mixing intensities ranged from 3 to 325 cm 2 y 1 with averages standard deviation of 35 33 24 19 37 35 and22 9 cm 2 y 1 at stations c70 i70 l70 and o70 respectively the average biodiffusivity for all stations and times was 29 25 cm 2 y 1 n 62 due to the large amount of variability which is consistent with other continental margin studies it was not possible to detect significant spatial or temporal variability although there is a hint of higher mixing intensities during the late summer early fall the period of maximal carbon flux to the seabed correlations between total macrofaunal abundance and mixing intensity are notably poor whereas a slightly better correlation r 2 0 22 was obtained between the abundance of large animals and bioturbation intensity by explicitly considering organic carbon flux or some measure of seabed food resources and the abundance of larger organisms it may be possible to predict bioturbation intensity better in future studies although the pervasive small scale variability detected on the eel river shelf warrants in depth theoretical and experimental consideration

petrogenesis of a tholeiite boninite sequence from ayios mamas troodos ophiolite evidence for splitting of a volcanic arc lavas and intrusives from ayios mamas at the western end of the limassol forest complex south of the arakapas fault belt troodos comprise three groups a a basal sequence of pillow lavas intruded by dikes and sills with the phenocryst assemblage plag cpx mt ol b a middle sequence of pillows and massive flows cpx plag ol and c an upper sequence mostly of pillows and breccia ol opx cpx sp the lower group is tholeiitic and the upper two groups boninitic group c whole rock and glass mg numbers exceed 72 and range up to 78 with corresponding olivine compositions of fo92 they are strongly depleted in high field strength elements and on the basis of cr y variation and major element mass balances are interpreted to reflect partial melting of a basalt depleted cpx harzburgite source group a tholeiites in contrast are interpreted to derive from a more fertile lherzolite source magmaphile and compatible trace element variation is best modelled after an open magma system involving periodic replenishment tapping and fractionation although neither tholeiites nor boninites represent steady state compositions the boninites belong to a cao rich sio2 poor variant resembling those from guam but contrasting with those from bonin and cape vogel morb normalized enrichment of low field strength elements k sr ba and rb in all groups indicates subduction derived source contamination it is proposed that the ayios mamas section reflects splitting of a volcanic arc prior to back arc spreading in an environment analogous to that of the present day andaman sea

non uniform across shelf variations in thickness grain size and frequency of turbidites in a transgressive outer shelf the middle pleistocene kakinokidai formation boso peninsula japan abstract across shelf variations in thickness grain size and frequency of sandstone beds in a transgressive outer shelf succession were investigated from the middle pleistocene ca 0 7 ma kakinokidai formation on the boso peninsula japan the transgressive deposits are generally muddy and contain slumps and slump scars the intercalated sandstone beds are interpreted to have been formed from turbidity currents as a response to erosion and resuspension of sandridge complex deposits in the southwestern upslope area during storm events mapping of volcanic ash beds and a transgressive surface in the base of the formation permits detailed bed by bed correlation of the outer shelf sandstone beds although overall thickness grain size and frequency of sandstone beds decrease in the downslope direction some sandstone beds locally thin out and coarsen in association with slump scars in the surrounding muddy deposits these sandstone beds subsequently thicken and fine and finally thin out in the farther downslope area in addition to the local thinning of sandstone beds the frequency of sandstone beds first decreases and then increases in the farther offshore direction from this evidence we concluded that these non uniform patterns of across outer shelf variations in thickness grain size and frequency of sandstone beds were caused by the local increases in flow speeds and subsequent expansion and reduced speeds of turbidity currents along with a local increase in the seafloor gradient that was induced by the development of slump scars in the transgressive outer shelf floor these physiographic features in the outer shelf are interpreted not to have permitted monotonous downslope thinning and fining of sandstone beds compared with the bed shape models of depletive turbidity currents and with the proximality trend of shelf sandstones from modern and ancient highstand stage shelf systems

early muddy deposits along the gulf of lions shoreline a key for a better understanding of land to sea transfer of sediments and associated pollutant fluxes large quantities of sediment introduced by rivers especially during flood events lead to the formation of prodeltaic structures characterized by fine grained deposits in the proximal area of the shelf according to their mean grain size it is largely admitted in the literature that these deposits mainly stand below the storm wave base in the gulf of lions nw mediterranean however our data show that these muddy sediments also exist above the storm wave limit in the uppermost unit of the holocene prism the purpose of this work is therefore to draw a detailed sedimentological and geochemical portrait of these units and to discuss the processes involved in the sedimentation and remobilization of these sediments our results show that the fine particles accumulate earlier in the inner shelf in front of the nearby rivers in association with the chemical elements which are commonly associated with this grain size fraction e g organic carbon radionuclides and heavy metals this accumulation probably mainly occurs during storm and flood events the early deposits are then exposed to resuspension events and can actively participate to the distribution of fine grained sediment in the entire margin by advective transfers via the benthic nepheloid layer these fine grained nearshore prodeltas are a common feature of the mediterranean deltaic systems and mark the frontal processes that occur at the continent sea interface of non tidal seas our results especially point out the potential use of heavy metals as markers of the tracking of riverine sediments which is naturally an important condition when evaluating the ultimate fate of land derived pollutants in the marine realm but also more fundamental studies on the understanding of sedimentological processes and reconstruction of margin stratigraphies should consider these deposits as functional units for the distribution of platform sediments

calculating shoreline erosion potential using nearshore stratigraphy and sediment volume outer banks north carolina 1 despite the acknowledged influence of coastal geological framework on the behavior of beaches and barrier islands and a wealth of geological and bathymetric observations from the inner shelf quantitatively connecting those observations to shoreline behavior has been difficult nearshore geologic and morphologic variability described by recent research is not well represented by conventional geologic parameters such as mean grain size and shoreface slope used in most shoreline change models we propose that total nearshore sediment volume as calculated to a continuous seismic reflection surface provides a flexible and robust metric for use in the prediction of shoreline change this method of determining the volume of sediment in the nearshore accounts for three dimensional sandbar morphologies and heterogeneous seafloor sediments the decadal scale shoreline change rate for northeastern north carolina is significantly correlated to the volume of sediment in the nearshore when a geologically defined base is used in volume determinations suggesting that the shallow stratigraphic framework of transgressive coasts is an important influence on decadal shoreline behavior nearshore sediment volume was overestimated when an arbitrary depth constant baseline was used and was not correlated to decadal shoreline change this implies that a volume metric which accounts for both framework geology and variable seafloor morphology better represents the geologic character of the shoreface and may help to improve existing models of shoreline change an empirical model of regional shoreline erosion potential demonstrates the importance of incorporating nearshore sediment volume shallow framework geology and surface morphology when predicting seasonal to decadal shoreline evolution

sediment resuspension characteristics in baltimore harbor maryland abstract critical bed shear stress for sediment resuspension and sediment erosion rate were measured in situ at sites from inner to outer baltimore harbor using the vims sea carousel clay mineral contents and biological conditions were almost the same at the four study sites the experimental results indicated that the erosion rate increased from the outer harbor toward the inner harbor with a maximum difference of about 10 times at an excess bed shear stress of 0 1 pa the measured critical bed shear stress strongly depended on the existence of a fluff layer it was approximately 0 05 pa if a fluff layer existed and increases to about 0 1 pa in the absence of a fluff layer

across shelf sediment transport interactions between suspended sediment and bed sediment 1 we use a two dimensional time dependent sediment transport model to quantify across shelf transport deposition and sorting during wave driven resuspension events characteristic of those that dominate sediment transport on many continental shelves decreases in wave orbital velocities as water depth increases and the resulting cross shelf gradient in bed shear stress favor a net offshore transport of sediment on wide flat shelves slopes 0 1 percnt these gradients are low and the depth to which the seabed is reworked depends mainly on bottom shear stress and local sediment availability on narrow steep shelves slopes 0 5 percnt however the gradient in bottom stress generates significant cross shelf suspended sediment flux gradients that create regions of net erosion and deposition while the magnitude of waves generally determines the water depth to which sediment can be resuspended erosional and depositional patterns on narrow shelves are sensitive to cross shelf gradients in wave energy nonlocal sediment availability and the direction and magnitude of the cross shelf current during energetic waves cross shelf divergence of suspended sediment flux can create a coarsened erosional area on the inner shelf that abuts a region of fine grained sediment deposition on the mid to outer shelf if currents are strongly shoreward however flux divergence leads to erosion over the entire shelf

long term coordinated changes in the convective activity of the north atlantic the north atlantic is a peculiarly convective ocean the convective renewal of intermediate and deep waters in the labrador sea and greenland iceland sea both contribute significantly to the production and export of north atlantic deep water thus helping to drive the global thermohaline circulation while the formation and spreading of 18 degree water at shallow to intermediate depths off the us eastern seaboard is a major element in the circulation and hydrographic character of the west atlantic for as long as time series of adequate precision have been available to us it has been apparent that the intensity of convection at each of these sites and the hydrographic character of their products have been subject to major interannual change as shown by aagaard 1968 clarke et al 1990 and meincke et al 1992 for the greenland sea in the ows bravo record from the labrador sea eg lazier 1980 et seq and at the panulirus hydrostation s site in the northern sargasso off bermuda eg jenkins 1982 talley and raymer 1982 this paper reviews the recent history of these changes showing that the major convective centres of the greenland and labrador seas are currently at opposite convective extrema in our postwar record with vertical exchange at the former site limited to 1000 m or so but with labrador sea convection reaching deeper than previously observed to over 2300 m as a result greenland sea deep water has become progressively warmer and more saline since the early 70 s due to increased horizontal exchange with the arctic ocean through fram strait while the labrador sea water has become progressively colder and fresher over the same period through increased vertical exchange most recently convection has become deep enough there to reach into the more saline nadw which underlies it so that cooler but now saltier and denser lsw has resulted

on the transport modes of fine sediment in the wave boundary layer due to resuspension deposition a turbulence resolving numerical investigation previous field observations revealed that the wave boundary layer is one of the main conduits delivering fine sediments from the nearshore to continental shelves recently a series of turbulence resolving simulations further demonstrated the existence of a range of flow regimes due to different degrees of sediment induced density stratification controlled by the sediment availability in this study we investigate the scenario in which sediment availability is governed by the resuspension deposition from to the bed specifically we focus on how the critical shear stress of erosion and the settling velocity can determine the modes of transport simulations reveal that at a given wave intensity which is associated with more energetic muddy shelves and a settling velocity of about 0 5 mm s three transport modes ranging from the well mixed transport mode i two layer like transport with the formation of lutocline mode ii and laminarized transport mode iii are obtained as the critical shear stress of erosion reduces moreover reductions in the settling velocity also yield similar transitions of transport modes we also demonstrate that the onset of laminarization can be well explained by the reduction of wave averaged bottom stress to about 0 39 pa due to attenuated turbulence by sediments a 2 d parametric map is proposed to characterize the transition from one transport mode to another as a function of the critical shear stress and the settling velocity at a fixed wave intensity

historical evolution of the columbia river littoral cell abstract this paper details the historical coastal evolution of the columbia river littoral cell in the pacific northwest of the united states geological data from a d 1700 and records leading up to the late 1800s provide insights to the natural system dynamics prior to significant human intervention most notably jetty construction between 1885 and 1917 all reliable surveys charts and aerial photos are used to quantify decadal scale changes at the three estuary entrances and four sub cells of the littoral cell shoreline bathymetric and topographic change over three historical intervals 1870s 1920s 1920s 1950s and 1950s 1990s are integrated to provide an understanding of sediment sharing relationships among the littoral cell components regional morphological change data are developed for alongshore segments of approximately 5 km enabling comparisons of shoreline change to upper shoreface and barrier volume change within common compartments the construction of entrance jetties at the columbia river 1885 1917 and grays harbor 1898 1916 has profoundly affected the evolution of the littoral cell and has accentuated the morphological coupling between the inlets ebb tidal deltas shorefaces and barriers the jetties induced erosion of the inlets and offshore migration of ebb tidal deltas the change in boundary conditions at the entrances enabled waves to rework the flanks of ebb tidal deltas and supply enormous quantities of sand to the adjacent coasts over several decades the initial sand pulses have been dispersed alongshore up to tens of kilometers from the estuary entrances winter waves and coastal currents produce net northward sediment transport across the shoreface while summer conditions tend to induce onshore sediment transport and accumulation of the upper shoreface and barriers at relatively high rates historical shoreline progradation rates since jetty construction are approximately double the late prehistoric rates between 1700 and the 1870s erosion rates of the mid to lower shoreface to the south of the jettied estuary entrances have typically been greater than the accumulation rates of the upper shoreface and barrier suggesting that the lower shoreface has been an important source of littoral sediments over decadal and longer time scales until recent decades sediment supply from the ebb tidal delta flanks and lower shoreface has largely masked the decline in columbia river sediment supply resulting from flow regulation and dredging disposal practices with the contemporary onset and expansion of coastal erosion adjacent to the jettied estuary entrances proper management of dredged sediment is imperative to mitigate the effects of a declining sediment budget

classifying seabed sediment type using simulated tidal induced bed shear stress abstract an ability to estimate the large scale spatial variability of seabed sediment type in the absence of extensive observational data is valuable for many applications in some physical e g morphodynamic models knowledge of seabed sediment type is important for inputting spatially varying bed roughness and in biological studies an ability to estimate the distribution of seabed sediment benefits habitat mapping e g scallop dredging although shelf sea sediment motion is complex driven by a combination of tidal currents waves and wind driven currents in many tidally energetic seas such as the irish sea long term seabed sediment transport is dominated by tidal currents we compare observations of seabed sediment grain size from 242 irish sea seabed samples with simulated tidal induced bed shear stress from a three dimensional tidal model roms to quantitatively define the relationship between observed grain size and simulated bed shear stress with focus on the median grain size of well sorted seabed sediment samples we present predictive maps of the distribution of seabed sediment classes in the irish sea ranging from mud to gravel when compared with the distribution of well sorted sediment classifications mud sand and gravel from the british geological survey digital seabed sediment map of irish sea sediments digsbs250 this grain size tidal current proxy gstcp correctly estimates the observed seabed sediment classification in over 73 of the area

alkali and alkaline earth element geochemistry of los humeros caldera puebla mexico abstract results of the measurements of alkali k rb and cs and alkaline earth ba and sr elements on seven pre caldera and twenty post caldera samples of los humeros volcanics pliocene to recent are described these data are interpreted in terms of the known solid liquid partition coefficients it appears that fractional crystallization is a dominant petrogenetic process and is controlled by the observed modal phases namely plagioclase olivine and clinopyroxene in decreasing importance and perhaps in addition biotite and titanomagnetite in the later stages of the differentiation sequence the available major element chemistry and mass balance calculations support these conclusions sr and nd isotopic data further suggest that these magmas were generated in the underlying mantle fractionated in a shallow level magma chamber and underwent very insignificant sialic contamination before eruption

flood dispersal and deposition by near bed gravitational sediment flows and oceanographic transport a numerical modeling study of the eel river shelf northern california 1 a large flood of the eel river northern california created a thick sediment deposit between water depths of 50 and 70 m in january 1997 the freshwater plume however confined sediment delivery to water depths shallower than 30 m mechanisms proposed to explain the apparent cross shelf transport include dispersal by oceanographic currents resuspension by energetic waves and gravitationally forced transport of a thin layer of fluidized mud field observations indicate that these processes were all active but cannot determine their relative significance or whether these mechanisms alone explain the location size and timing of deposition approximately 30 of the sediment delivered by the eel river is accounted for in the midshelf mud bed and inner shelf but the fate of the remaining 70 is uncertain a three dimensional hydrodynamic model was used to examine potential mechanisms of sediment transport on the eel river shelf the model includes suspended sediment transport and was modified to account for a thin near bed layer of fluidized mud it was used to simulate flood dispersal on the eel river shelf to compare the relative importance of transport within the near bed fluid mud layer to suspended sediment transport and to evaluate sediment budgets for floods settling properties of fine grained sediment both within the flood plume and the fluid mud layer critically impact depositional patterns to a lesser degree wind driven ocean currents influence the volume of sediment that escapes the shelf and wave magnitude affects the cross shelf location of flood deposits though dilute suspension accounts for a large fraction of total flux cross shelf transport by gravitational forcing appears necessary to produce a midshelf mud deposit similar in volume location and timing to those seen offshore of the eel river

sediment dispersal in the northwestern adriatic sea 1 sediment dispersal in the adriatic sea was evaluated using coupled three dimensional circulation and sediment transport models representing conditions from autumn 2002 through spring 2003 the calculations accounted for fluvial sources resuspension by waves and currents and suspended transport sediment fluxes peaked during southwestward bora wind conditions that produced energetic waves and strengthened the western adriatic coastal current transport along the western adriatic continental shelf was nearly always to the south except during brief periods when northward sirocco winds reduced the coastal current much of the modeled fluvial sediment deposition was near river mouths such as the po subaqueous delta nearly all po sediment remained in the northern adriatic material from rivers that drain the apennine mountains traveled farther before deposition than po sediment because it was modeled with a lower settling velocity fluvial sediment delivered to areas with high average bed shear stress was more highly dispersed than material delivered to more quiescent areas modeled depositional patterns were similar to observed patterns that have developed over longer timescales specifically modeled po sediment accumulation was thickest near the river mouth with a very thin deposit extending to the northeast consistent with patterns of modern sediment texture in the northern adriatic sediment resuspended from the bed and delivered by apennine rivers was preferentially deposited on the northern side of the gargano peninsula in the location of thick holocene accumulation deposition here was highest during bora winds when convergences in current velocities and off shelf flux enhanced delivery of material to the midshelf

response of a strongly eddying global ocean to north atlantic freshwater perturbations abstractthe strongly eddying version of the parallel ocean program pop is used in two 45 yr simulations to investigate the response of the atlantic meridional overturning circulation amoc to strongly enhanced freshwater input due to greenland melting with an integrated flux of 0 5 sverdrups sv 1 sv 106 m3 s 1 for comparison a similar set of experiments is performed using a noneddying version of pop the aim is to identify the signature of the salt advection feedback in the two configurations for this reason surface salinity is not restored in these experiments the freshwater input leads to a quantitatively comparable reduction of the overturning strength in the two models to examine the importance of transient effects in the relation between amoc strength and density distribution the results of the eddy resolving model are related to water mass transformation theory the freshwater forcing leads to a reduction of the rate of light to dense water conversion in the north atlantic but there

esmeralda bank geochemistry of an active submarine volcano in the mariana island arc esmeralda bank is the southernmost active volcano in the izu volcano mariana arc this submarine volcano is one of the most active vents in the western pacific it has a total volume of about 27 km3 rising to within 30 m of sea level two dredge hauls from esmeralda recovered fresh nearly aphyric vesicular basalts and basaltic andesites and minor basaltic vitrophyre these samples reflect uniform yet unusual major and trace element chemistries mean abundances of tio2 1 3 and feo 12 6 are higher and cao 9 2 and al2o3 15 1 are lower than rocks of similar silica content from other active mariana arc volcanoes mean incompatible element ratios k rb 488 and k ba 29 of esmeralda rocks are indistinguishable from those of other mariana arc volcanoes on a ti zr plot esmeralda samples plot in the field of oceanic basalts while other mariana arc volcanic rocks plot in the field for island arcs

ocean change around greenland under a warming climate the impact of climate warming on the ocean near greenland is investigated with a high resolution coupled global climate model the ocean around greenland exhibits a strong warming in response to a four times increase of present day atmospheric co 2 levels the signal is intensified in the intermediate layer and regionally strongest in the greenland sea the projected changes in temperature are driven by changes affecting the large scale ocean circulation rather than changes of the local atmospheric heat forcing the ocean conditions examined here provide a background for the water masses in contact with the outlet glaciers around the greenland coast the future warming of the warm subtropical origin layer could thus lead to enhanced ice sheet melting although the signal could be mitigated by other effects including an enhanced stratification of the surface fresh layer applying a simple parameterization to estimate the change in melt rate along the greenland coast we find that ice sheet melting increases everywhere in response to the change in water mass properties although the melt rate changes show large variations in space the largest melting acceleration is found on the east coast between fram strait and denmark strait where both the parameterization applied to present day conditions and observations suggest moderate melting up to now these model results caution that the greenland ice sheet mass balance should be monitored everywhere and not only where melting occurs at the moment

sediment transport events on the northern california continental shelf abstract a long term monitoring tripod has been maintained in 60 m water depth at the northern end of the strataform study site on the northern california continental shelf as part of this ongoing study tripod data for 1 year beginning 24 september 1995 are used to provide a sediment transport analysis on an event by event basis the objective of this paper is to highlight the energetic nature of this shelf region in terms of the frequency duration and magnitude of sediment suspension events and the associated particle flux analyses are based on measurements from two current meters and two optical backscatterance sensors located at 30 and 100 cm above the bed data from these instruments and a pressure sensor were averaged over 7 5 min every hour during the year of record 41 distinct sediment suspension events occurred i e sustained suspended sediment concentrations greater than 20 mg l above background level at 100 cm above bed suspended sediment events were associated with significant wave activity tidal currents and river discharge the average duration of a sediment suspension event was 3 1 days and varied from 0 7 to 8 days during events mean suspended sediment concentrations of 110 mg l were observed with peak hourly observations exceeding 1000 mg l concentrations between events averaged 35 mg l the overall sediment flux for the period of record was directed seaward and southward the distribution and magnitude of sediment suspension events and particle flux showed a strong seasonality for example of the sediment transport during events 98 of the net along shelf and 73 of the net across shelf sediment transport occurred in the winter three major winter storms could account for 72 of the total along shelf transport but only 10 of the across shelf transport the across shelf flux was more evenly distributed over the year and occurred as a result of mean currents and very low frequency seaward flows associated with mesoscale circulation patterns

two stable equilibria of the atlantic subpolar gyre the cyclonic circulation of the atlantic subpolar gyre is a key mechanism for north atlantic climate variability on a wide range of time scales it is generally accepted that it is driven by both cyclonic winds and buoyancy forcing yet the individual importance and dynamical interactions of the two contributions remain unclear the authors propose a simplified four box model representing the convective basin of the labrador sea and its shallow and deep boundary current system the western subpolar gyre convective heat loss drives a baroclinicflow of relatively light water around the dense center eddy salt flux from the boundary current to the center increases with a stronger circulation favors the formation of dense waters and thereby sustains a strong baroclinic flow approximately 10 25 of the total in contrast when the baroclinic flow is not active surface waters may be too fresh to convect and a buoyancy driven circulation cannot develop this situation corresponds to a second stable circulation mode a hysteresis is found for variations in surface freshwater flux and the salinity of the near surface boundary current an analytical solution is presented and analyzed

strontium isotopes from circum pacific intra oceanic island arcs and marginal basins regional variations and implications for magmagenesis circum pacific intra oceanic island arc lavas have a mean 87 sr 86 sr of 70355 associated marginal basins have a mean 87 sr 86 sr of 70311 significant hemispheric variations are noted for both island arcs and back arc basins in the north pacific mean 87 sr 86 sr for island arcs 70335 and back arc basins 70287 is less radiogenic than counterparts in the south pacific 70374 70336 this hemispheric variation is not related to the age of sea floor being subducted therefore partial fusion of sediments and or altered crust are not likely to be responsible back arc basin magmas are generally depleted in radiogenic strontium relative to those of the associated arc but arc basin systems are enriched or depleted systematically arcs around the western pacific show regional variations similar to that observed for alkali basalts of the pacific basin both show enrichments in radiogenic strontium near samoa and become progressively depleted away from it least radiogenic samples from continental margin volcanics indicate their sources are more radiogenic in the southern circum pacific these regional variations in 87 sr 86 sr in island arc and marginal basin systems suggest that 1 regional isotopic variations noted for the mantle beneath the pacific basin are maintained across convergent plate boundaries 2 the source regions of marginal basin basalts are isotopically similar to that of mid ocean ridge basalts while those of island arcs are similar to those of intra plate ocean island basalts 3 the sources of island arcs and marginal basin magmas lie in the mantle

estimates of suspended sediment flux and bedform activity on the inner portion of the eel continental shelf energetic waves strong bottom currents and relatively high rates of sediment discharge from the eel river combined to produce large amounts of suspended sediment transport on the inner continental shelf near the eel river during the winter of 1995 1996 bottom boundary layer bbl measurements at a depth of 50 m using the geoprobe tripod showed that the strongest near bottom flows combined wave and current speeds of over 1 m s and highest sediment concentrations exceeding 2 g l at 1 2 m above the bed occurred during two storms one in december 1995 and the other in february 1996 discharge from the eel river during these storms was estimated at between 2 and 4 103 m3 s suspended sediment flux ssf was measured 1 2 m above the bed and calculated throughout the bbl by applying the tripod data to a shelf sediment transport model these results showed initially northward along shelf ssf during the storms followed by abrupt and persistent southward reversals along shelf flux was more pronounced during and after the december storm than in february across shelf ssf over the entire measurement period was decidedly seaward this seaward transport could be responsible for surficial deposits of recent sediment on the outer shelf and upper continental slope in this region sediment ripples and larger bedforms were observed in the very fine to fine sand at 50 m depth using a sector scanning sonar mounted on the tripod ripple wavelengths estimated from the sonar images were about 9 cm which compared favorably with photographs of the bottom taken with a camera mounted on the tripod the ripple patterns were stable during periods of low combined wave current bottom stresses but changed significantly during high stress events such as the february storm two different sonic altimeters recorded changes in bed elevation of 10 to 20 cm during the periods of measurement these changes are thought to have been caused principally by the migration of low amplitude long wavelength sand waves into the measurement area

rb sr study of metavolcanic rocks from the la ronge and flin flon domains northern saskatchewan two whole rock suites of metavolcanic rocks from separate volcanic belts of the churchill province in northern saskatchewan have been dated by rb sr samples from the amisk group of the flin flon snow lake domain provide an isochron date of 1784 44 ma suites from the waddy lake and devil lake areas of the la ronge lynn lake domain yield isochron dates of 1814 26 and 1854 100 ma respectively all are regarded as minima for but close approximations to emplacement ages the maximum crustal age of any suite cannot greatly exceed 1850 ma previous rb sr and u pb isotopic dates together with these new determinations confirm the contemporaneous existence of two volcanic arcs active during the late aphebian 1875 1784 ma in the churchill province low initial 87 sr 86 sr ratios 0 7017 0 7022 are consistent with a petrochemically inferred subduction related origin for the volcanic rocks with no closed system reworking of archean crust and a linear evolution of 87 sr 86 sr ratio in the magmatic arc mantle source region from 4 55 ga to the present

helium isotopes and tectonics in southern italy geodynamic evolution of southern italy can be understood within the framework of the mediterranean alpine system subduction of a plate along the sicily calabrian forearc under the tyrrhenian sea has been suggested by many geophysicists although it is not yet confirmed and remains somewhat controversial helium isotope ratios provide useful information on the geotectonic structure of the region the authors report here the sup 3 h sup 4 he ratios of terrestrial gas samples from southern italy the observed sup 3 he sup 4 he ratios are relatively high in the eolian volcanic arc region and low in the other areas dichotomous explanations are presented firstly volcanic arc forearc hypothesis suggests the subduction along the sicily calabrian forearc secondly horizontal transport hypothesis is described based on the relationship between the ratios and radial distance from the recent spreading basin in southern tyrrhenian sea