high precision isotopic characterization of usgs reference materials by tims and mc icp ms the pacific centre for isotopic and geochemical research pcigr at the university of british columbia has undertaken a systematic analysis of the isotopic sr nd and pb compositions and concentrations of a broad compositional range of u s geological survey usgs reference materials including basalt bcr 1 2 bhvo 1 2 andesite agv 1 2 rhyolite rgm 1 2 syenite stm 1 2 granodiorite gsp 2 and granite g 2 3 usgs rock reference materials are geochemically well characterized but there is neither a systematic methodology nor a database for radiogenic isotopic compositions even for the widely used bcr 1 this investigation represents the first comprehensive systematic analysis of the isotopic composition and concentration of usgs reference materials and provides an important database for the isotopic community in addition the range of equipment at the pcigr including a nu instruments plasma mc icp ms a thermo finnigan triton tims and a thermo finnigan element2 hr icp ms permits an assessment and comparison of the precision and accuracy of isotopic analyses determined by both the tims and mc icp ms methods e g nd isotopic compositions for each of the reference materials 5 to 10 complete replicate analyses provide coherent isotopic results all with external precision below 30 ppm 2 sd for sr and nd isotopic compositions 27 and 24 ppm for tims and mc icp ms respectively our results also show that the first and second generation usgs reference materials have homogeneous sr and nd isotopic compositions nd isotopic compositions by mc icp ms and tims agree to within 15 ppm for all reference materials interlaboratory mc icp ms comparisons show excellent agreement for pb isotopic compositions however the reproducibility is not as good as for sr and nd a careful sequential leaching experiment of three first and second generation reference materials bcr bhvo agv indicates that the heterogeneity in pb isotopic compositions and concentrations could be directly related to contamination by the steel mortar pestle used to process the materials contamination also accounts for the high concentrations of certain other trace elements e g li mo cd sn sb w in various usgs reference materials

anthropogenic influence on sedimentation and intertidal mudflat change in san pablo bay california 1856 1983 analysis of a series of historical bathymetric surveys has revealed large changes in morphology and sedimentation from 1856 to 1983 in san pablo bay california in 1856 the morphology of the bay was complex with a broad main channel a major side channel connecting to the petaluma river and an ebb tidal delta crossing shallow parts of the bay in 1983 its morphology was simpler because all channels except the main channel had filled with sediment and erosion had planed the shallows creating a uniform gently sloping surface the timing and patterns of geomorphic change and deposition and erosion of sediment were influenced by human activities that altered sediment delivery from rivers from 1856 to 1887 high sediment delivery 14 1 10 6 m 3 yr to san francisco bay during the hydraulic gold mining period in the sierra nevada resulted in net deposition of 259 14 10 6 m 3 in san pablo bay this rapid deposition filled channels and increased intertidal mudflat area by 60 37 4 3 4 to 60 6 6 2 km 2 from 1951 to 1983 23 3 10 6 m 3 of sediment was eroded from san pablo bay as sediment delivery from the sacramento and san joaquin rivers decreased to 2 8 10 6 m 3 yr because of damming of rivers riverbank protection and altered land use intertidal mudflat area in 1983 was 31 8 3 9 km 2 similar to that in 1856 intertidal mudflat distribution in 1983 however was fairly uniform whereas most of the intertidal mudflats were in the western part of san pablo bay in 1856 sediment delivery through its affect on shallow parts of the bay was determined to be a primary control on intertidal mudflat area san pablo bay has been greatly affected by human activities and will likely continue to erode in the near term in response to a diminished sediment delivery from rivers 2007 elsevier ltd all rights reserved

late quaternary pollen record from the central california continental margin abstract a pollen record obtained from a deep sea core from the continental margin off central california contains evidence of the terrestrial floral adaptation to changing climatic conditions over the last ca 20 000 cal bp the pollen record is divided into three pollen zones two of which are late pleistocene in age glacial and transitional and the third is holocene interglacial the glacial pollen zone ca 20 000 17 000 cal bp is characterized by pinus and abies pollen reflecting environmental conditions during the last glacial maximum overlying this ca 17 000 11 600 cal bp is the transitional pollen zone containing a pollen assemblage indicative of a transitional climatic regime with species that reflect more arid environmental conditions pinus and artemisia decreasing in abundance and those reflecting moister conditions sequoia and alnus rising in abundance pediastrum and dinoflagellates are common and are attributable to increased nutrient rich coastal runoff the bolling allerod 295 256 cm ca 14 600 12 900 bp and younger dryas 256 243 cm ca 12 900 11 600 bp events occur within the transitional pollen zone as well the interglacial pollen zone ca 11 600 cal bp to present is characterized by decreasing pinus and increasing sequoia quercus and asteraceae reflecting changes in vegetation during the climatic warming of the holocene two brief dry periods are represented in this pollen zone one from 150 to 125 cm ca 8000 6400 cal bp and the other at 22 20 cm ca 800 700 cal bp they are correlated with the middle holocene dry period and the medieval climate anomaly respectively

structure and flow induced variability of the subtidal salinity field in northern san francisco bay abstract the structure of the salinity field in northern san francisco bay and how it is affected by freshwater flow are discussed two datasets are examined the first is 23 years of daily salinity data taken by the u s bureau of reclamation along the axis of northern san francisco bay the second is a set of salinity transects taken by the u s geological survey between 1988 and 1993 central to this paper is a measure of salinity intrusion x2 the distance from the golden gate bridge to where the bottom salinity is 2 psu using x2 to scale distance the authors find that for most flow conditions the mean salinity distribution of the estuary is nearly self similar with a salinity gradient in the center 70 of the region between the golden gate and x2 that is proportional to x 12 analysis of covariability of q and x2 showed a characteristic timescale of adjustment of the salinity field of approximately 2 weeks the steady state response deduced from the x2 time series implies that x2 is proportional

sediment transport on the freiston shore managed realignment site an investigation using environmental magnetism this paper presents the first attempt to use environmental magnetism to quantify sediment provenance on a managed realignment mr site mr is one technique for creating restoring intertidal habitats and improving the standard of coastal flood protection monitoring of mr sites is essential for determining how successful they are at achieving these aims and normally includes measurement of sedimentation rates through the use of accretion plates and sediment erosion tables sets one limitation of this technique is that the provenance of sediment accreting on realigned surfaces cannot readily be quantified our results demonstrate that magnetics based fingerprinting can successfully apportion sediment source contributions to created restored coastal saltmarshes with an efficiency similar to that of existing un mixing models applied to other habitats 82 87 analysis of mineral magnetic properties fd irmsoft and sirm demonstrated that the majority of sediment accreting on the freiston shore mr site lincolnshire uk is derived from established saltmarshes seaward of the breached embankment this indicates that the mr site may be growing at the expense of neighbouring saltmarshes thereby undermining the habitat creation objectives used to justify mr it is recommended that future mr monitoring programmes consider the provenance of post breach deposits to help identify any adverse impacts that wetland creation restoration may have on existing habitats further testing of environmental magnetism in coastal saltmarshes and mr sites is necessary to validate wider use of the technique

geochemical tracers of sediment sources to san francisco bay river inflow and suspended sediment flux to san francisco bay are dominated by the sacramento and san joaquin river systems suspended sediments collected from rivers within the sacramento and san joaquin drainage basinsshow distinct chemical and sr isotope signatures reflecting their distinct bedrock lithologies concentrations of sm nd k and rb and 8 7 sr 8 6 sr ratios in suspended sediments increase from north to south in sierra nevada rivers and are significantly higher in the san joaquin drainage than in the sacramento drainage we show that variations in the geochemistry of fine grained detrital sediments cored beneath the bay can be used to assess the relative contributions of suspended sediment and inflow from these two major drainages in california for the sampled intervals over the past 1850 yr the proportion of suspended sediment from the sacramento drainage relative to the san joaquin drainage ranged between 5 and 85 average value of 55 compared with a modern value of 91 the current predominance of sediment entering san francisco bay from the sacramento drainage may be the result of greater trapping of sediments by reservoirs within the san joaquin drainage basin changes in the relative proportion of sediment from the sacramento and san joaquin drainages may reflect changes in the position of the storm track over california

tracing dust sources and transport patterns using sr nd and pb isotopes continental dust transported through the atmosphere can be a tracer of atmospheric circulation and transport as well as being a source of information about climate in the dust s source area this information about the provenance of dust transported from desert areas and deposited elsewhere on the oceans and continents can be evaluated using several observational techniques satellite imagery has been used to this end in recent decades and air mass back trajectories have been calculated to trace dust deposits back to their source area another method consists of analysis of the concentration and composition of certain tracers in the dust itself and comparing them to soils and sediments from possible source areas this method has the advantage of being useable for paleo atmospheric circulation and paleo dust transport studies whereas satellite imagery and air mass back trajectories are restricted to relatively recent times we review here different kinds of isotopic tracers that have been used to trace dust provenance but special attention is focused on the use of sr nd and pb isotopes we evaluate their use in studies of both spatially as well as temporally varying continental dust source and transport

sediment transport patterns in the san francisco bay coastal system from cross validation of bedform asymmetry and modeled residual flux abstract the morphology of 45 000 bedforms from 13 multibeam bathymetry surveys was used as a proxy for identifying net bedload sediment transport directions and pathways throughout the san francisco bay estuary and adjacent outer coast the spatially averaged shape asymmetry of the bedforms reveals distinct pathways of ebb and flood transport additionally the region wide ebb oriented asymmetry of 5 suggests net seaward directed transport within the estuarine coastal system with significant seaward asymmetry at the mouth of san francisco bay 11 through the northern reaches of the bay 7 8 and among the largest bedforms 21 for 50 m this general indication for the net transport of sand to the open coast strongly suggests that anthropogenic removal of sediment from the estuary particularly along clearly defined seaward transport pathways will limit the supply of sand to chronically eroding open coast beaches the bedform asymmetry measurements significantly agree up to 76 with modeled annual residual transport directions derived from a hydrodynamically calibrated numerical model and the orientation of adjacent flow sculpted seafloor features such as mega flute structures providing a comprehensive validation of the technique the methods described in this paper to determine well defined cross validated sediment transport pathways can be applied to estuarine coastal systems globally where bedforms are present the results can inform and improve regional sediment management practices to more efficiently utilize often limited sediment resources and mitigate current and future sediment supply related impacts

the use of modeling and suspended sediment concentration measurements for quantifying net suspended sediment transport through a large tidally dominated inlet abstract sediment exchange at large energetic inlets is often difficult to quantify due complex flows massive amounts of water and sediment exchange and environmental conditions limiting long term data collection in an effort to better quantify such exchange this study investigated the use of suspended sediment concentrations ssc measured at an offsite location as a surrogate for sediment exchange at the tidally dominated golden gate inlet in san francisco ca a numerical model was calibrated and validated against water and suspended sediment flux measured during a spring neap tide cycle across the golden gate the model was then run for five months and net exchange was calculated on a tidal time scale and compared to ssc measurements at the alcatraz monitoring site located in central san francisco bay 5 km from the golden gate numerically modeled tide averaged flux across the golden gate compared well r 2 0 86 p value mckee et al 2013 this issue there was little variation from year to year exports were computed to be greatest during the wettest water year analyzed but only marginally so

size density sorting of sand size spheres during deposition from bedload transport and implications concerning hydraulic equivalence it is well known that sediment sorting according to size shape and density occurs but the exact mechanisms involved are poorly understood to assess the effects of size and density sand size spheres of two densities were transported and deposited under controlled flume conditions observations on the motion of discrete particles show that grains smaller than bed roughness grains move continuously and have the same transport velocities regardless of density for grains near and slightly larger than the roughness movement is intermittent and for a given size heavy particles move more slowly than lights for grains much larger than bed roughness grains movement is continuous over the rough surface and light and heavy grains have nearly the same transport velocities analyses of bulk sediment deposited from plane bed transport show that the size and proportion of heavies decreases and that of lights increases with distance transported for ripple bed transport however the size relations between associated light and heavy grains remains essentially unchanged with transport distance and the proportion of light and heavy grains is extremely variable these results suggest that size density sorting in plane bed transport is a function of the transportabilities identified in the discrete grain studies but that sorting in ripple bed transport is related to deposition on and recycling through the bed forms application of these findings to the concept of hydraulic equivalence implies that some indication of bed configuration may be necessary for the concept to be useful

an interpretation of magnetic signatures of subduction zones detected by magsat abstract the magnetic anomalies detected by magsat over subduction zones are related to the thermal state and the location with respect to the geomagnetic poles of the subducting oceanic lithosphere it is shown that an old about 100 m y subducting lithosphere produces about twice as strong a magnetic anomaly as that associated with a young about 40 m y one also a given subducting oceanic lithosphere produces a stronger magnetic anomaly at high geomagnetic latitudes than near the geomagnetic equator based on the thermal evolution models of the oceanic lithosphere and assuming a mean magnetic susceptibility of 13 10 3 si the pacific plate subducting along the kuril trench produces a magnetic anomaly similar to the observed one the nazca plate subducting along the peru chile trench produces a magnetic anomaly of less than 0 5 nt no distinct anomaly observed by magsat over this region

a satellite magnetic anomaly map of greenland summary a satellite magnetic anomaly map of greenland has been compiled using data from the pogo 2 4 and 6 satellites data from quiet passes have been extracted and processed into an equivalent source representation in the form of a contour map of the satellite magnetic field at an altitude of 500 km the satellite magnetic anomaly map contains some very pronounced anomalies a magnetic maximum of 8nt centred in northern greenland at approximately 79 30 n 37 w a smaller but also significant maximum over southern greenland at 61 30 n 44 w and two minima over the disko nugssuaq area of central west greenland 70 n 52 w and the scoresby sund area of central east greenland 71 n 24 w respectively a qualitative comparison with major geological features shows a good general correlation although no final conclusions should be drawn from the existing pogo data the magnetic anomaly map is also compared with the scarce existing geophysical data from this area major changes in crustal properties and or structures are indicated under the inland ice across a line connecting the disko nqugssuaq area and the scoresby sund area

seismic structure across the active subduction zone of western canada the vancouver island seismic project was conducted in 1980 to study the structure of the subducting oceanic juan de fuca plate and the overriding continental america plate the principal seismic refraction line line i was a 350 km onshore offshore profile perpendicular to the continental margin an array of 32 receivers was located on the america plate on the mainland and across vancouver island and extended offshore with three ocean bottom seismometers obs s two shots were fired at the eastern end of the line and 17 shots were located along the westernmost 100 km of the profile control for the interpretation of the onshore offshore profile was provided by a reversed refraction profile along the length of vancouver island and by a marine refraction profile recorded on the obs s modeling of the seismic structure of this complex region utilized an iterative inversion method for travel times from explosions in which shots at several locations are recorded on the same set of receivers and utilized an algorithim based on asymptotic ray theory for the calculation of synthetic seismograms through two dimensional media the major features of the refraction structural model are that 1 the oceanic lithosphere dips at 3 or less beneath the continental slope so the bend in the subducting slab occurs landward of the foot of the slope 2 the oceanic lithosphere dips at 14 16 beneath the continental shelf until it passes beneath the continental moho at 37 km depth below western vancouver island 3 an upper mantle reflector may correspond to the base of the subducting lithosphere and 4 a segment of high velocity material above the downgoing crust with velocity 7 7 km s and depth range 20 25 km may represent a remnant of subducted lithosphere perhaps detached when the subduction zone jumped westward to its present position

the influence of oceanic swell on flows over an estuarine intertidal mudflat in san francisco bay in this study we examine the role that remotely forced ocean waves play in the hydrodynamics of an intertidal estuarine mudflat the observations indicate that long period 10 20 s ocean waves are a potentially important source of near bed energy and shear stress in this environment over a two week period in february 2001 we deployed an autonomous sontek hydra system on a mudflat in central san francisco bay and measured velocity and sediment concentration approximately 10 cm from the bed using an acoustic doppler velocimeter adv and an optical backscatter sensor obs the experiment continued through wet high tide and dry low tide periods over an entire spring neap cycle and thus included the variation of near bed velocity over a range of timescales results show that during large ebb tides tidally forced flows dominate the near bed dynamics during calm conditions wind waves dominate whenever the wind direction exposes the mudflat to wind coming off the bay from the south and southwest as occurs during winter storms during periods when tidal forcing is limited and wind waves are small remotely forced ocean swells become an important energy source these motions appear in the burst samples at frequencies between 0 1 and 0 04 hz and their energy correlates well q 0 8 with ocean swell measured from a buoy offshore of san francisco spectral analysis of data shows that the average energy of ocean waves per tide varied between 2 and 15 of total energy load moreover extreme values in the distribution of ocean waves bring episodic bursts of greater energy onto the estuarine mudflat which may influence local suspension of sediments 2003 elsevier ltd all rights reserved

magnetic properties and opaque mineralogy of drilled submarine intrusive rocks summary measurements of natural remanent magnetization nrm curie temperature ferrimagnetic and paramagnetic susceptibility saturation induced and remanent magnetizations coercive forces alternating field properties and viscous magnetization are reported for 50 submarine intrusive rocks drilled during legs 30 37 and 45 of dsdp the collection includes doleritic sill rocks fresh and serpentinized cumulate gabbros and serpentinized cumulate peridotites and serpentinized lherzolites believed to have originated in layers 2b 3b and 4 respectively magnetite with a curie temperature between 520 and 580 c is the principal magnetic mineral in all samples there is no indication of maghemitization or of metamorphism to greenschist facies or above the magnetite in the doleritic and cumulate gabbros is a product of deuteric alteration of titanomagnetite and pyroxene the stable nrm is a primary trm the magnetite in the serpentinized rocks is a secondary product of serpentinization the stable nrm is a crm in most rock types the magnetite is of single domain or pseudo single domain size and soft components of nrm are small the magnetite grain size in some of the doleritic gabbros is much coarser these rocks acquire large viscous magnetizations which however are readily removed by alternating field cleaning the cleaned nrms of legs 30 and 45 rocks have approximately dipole inclinations but the nrms of most of the mutually intruded leg 37 units have been dispersed by tectonic rotations the doleritic gabbros and the serpentinized peridotites have stable directionally coherent nrms 10 3emu cm 3 in intensity their counterparts in layers 2b and 3b 4 are likely contributors to oceanic magnetic anomalies layer 3b cumulate gabbros and tectonic serpentinites in the middle and upper crust are less likely anomaly sources

comparison of sediment supply to san francisco bay from watersheds draining the bay area and the central valley of california article i nfo quantifying suspended sediment loads is important for managing the world s estuaries in the context of nav igation pollutant transport wetland restoration and coastal erosion to address these needs a comprehen sive analysis was completed on sediment supply to san francisco bay from fluvial sources suspended sediment optical backscatter velocity data near the head of the estuary and discharge data obtained from the output of a water balance model were used to generate continuous suspended sediment concentration records and compute loads to the bay from the large central valley watershed sediment loads from small tributary watersheds around the bay were determined using 235 station years of suspended sediment data from 38 watershed locations regression analysis and simple modeling over 16 years net annual suspended sediment load to the head of the estuary from its 154 000 km 2 central valley watershed varied from 0 13 to

surface and near surface sediments from the continental shelf off the russian river northern california abstract there are two basic types of detrital sediments in the study area modern and relict modern sediment consists mostly of sand on the inner shelf and silt and clay on the middle shelf the silt and clay overlie an older transgressive sand and extend northwest southeast with an average thickness of 10 m this unit pinches out toward the outer shelf where relict detrital sand dominates with some authigenic glauconite the detrital sand is much cleaner and darker than the inner shelf sand the important heavy minerals of the sand fraction for detecting sediment dispersal patterns are biotite hornblende glaucophane and glauconite biotite and hornblende are abundant in the southern parts of the study area close to point reyes beach and decrease in abundance northward and offshore glaucophane is abundant close to the russian river mouth and decreases in abundance southward glauconite is abundant on the outer shelf and decreases in abundance southward there are two sediment sources for the inner and middle shelf russian river discharge and coastal erosion particularly of beaches headlands and cliffs in the southern part of the area the sand sized sediment of the russian river is being deposited on the inner shelf between salt point to the north and bodega head to the south the russian river silt and clay are confined to the middle shelf some of this silt and clay is being transported into bodega submarine canyon the coastal material is eroded in the south and transported northward seaward and also into bodega submarine canyon

results from a detailed aeromagnetic survey across the northeast newfoundland margin part i spreading anomalies and relationship between magnetic anomalies and the ocean continent boundary abstract a detailed aeromagnetic survey carried out across the northeast newfoundland margin clearly shows the presence of sea floor spreading anomalies 25 to 34 correlation of these anomalies with synthetic profiles shows an increase in the rate of spreading soon after anomaly 27 time three fracture zones can be identified by dislocations in the magnetic anomalies their positions are confirmed on the depth to basement map of this region an eastward extension of the southernmost fracture zone at latitude 49 n matches well with the faraday fracture zone across the mid atlantic ridge and with a basement ridge known as pastouret ridge mapped off goban spur by combining the present survey data with the previously collected shipborne measurements we have also traced the westward continuation of the charlie gibbs fracture zone under the newfoundland shelf a large amplitude magnetic anomaly lies along the margin and separates two zones with different magnetic characteristics long wavelength small amplitude anomalies on the landward side and quasi lineated anomalies on the seaward side seismic data compilations show that this large anomaly coincides with the ocean continent boundary at most places north of flemish cap modelling of the magnetic anomalies indicate that the large amplitude anomaly is caused by the juxtaposition of highly magnetized oceanic crust against weakly magnetized continental crust this situation is similar to that observed across the goban spur margin which is a conjugate of the flemish cap margin the presence of highly magnetized oceanic crust landward of anomaly 34 and within the cretaceous magnetic quiet zone is attested to by the presence of similar large amplitude anomalies south of the flemish cap and goban spur regions but these do not mark the ocean continent transition

vertical distribution and alteration of dikes in a profile through the troodos ophiolite in situ oceanic crust at intermediate depths of from one to five km is presently largely inaccessible to continuous examination and sampling except in the possibly special circumstances of major transform faults the study of ophiolites over this interval where thin sub vertical dikes are usually important may provide guidance to the nature of in situ oceanic crust at these depths the likelihood that similarities exist between in situ and ophiolitic oceanic crust has recently been strengthened by the possible identification of a dike complex below 0 8 km depth in dsdp hole 504b1 sub vertical basic dikes occur over a 4 6 km depth interval from 0 2 to 4 8 km crustal depth in a profile through the troodos cyprus ophiolite exponential growth and arctangent decay in dike density occur over 2 3 km and 1 0 km intervals respectively secondary magnetite is the dominant dike magnetic material of the dikes and associated screens these results have implications for the construction alteration history and magnetization of in situ oceanic crust at intermediate depths

equatorial carbonates an earth systems approach the hypothesis here is that an earth systems processes to products approach can be used to better develop predictive models for the recognition and assessment of under evaluated equatorial carbonate systems warm temperatures together with common clastic fresh water and nutrient influx as well as basinal settings in the equatorial tropics all have a major impact on carbonate deposition and diagenesis specific features of equatorial carbonate systems resulting from the combination of processes acting in the region include common occurrence of photoautotrophs and heterotrophs aragonitic and or calcitic dominant mineralogies lack of coated grains or aggregates common associations with clastics lack of associations with evaporites and diversity of platform types including oligophotic ones additional diagenetic characteristics include common micritization and bioerosion paucity of marine cements extensive vadose dissolution and concomitant phreatic cementation there is also significant replacement of aragonite by calcite in regions of meteoric groundwater flow common burial compaction and leaching as well as localized massive dolomitization via sea water or continental derived groundwater flow although equatorial carbonates fall into the warm water photozoan association many of the features described above are at odds with models derived from their warm water arid zone counterparts instead a range of the equatorial carbonate features show some similarities with those formed in cool waters and there have been difficulties separating carbonates from these two very different climatic regimes recommendations for the recognition of phanerozoic regional equatorial carbonate development are i a diversity of calcitic and or aragonitic photoautotrophs plus ii common elements of the heterozoan association plus iii independent for example isotopic evidence for warm temperatures 22 c additional indicators towards a humid equatorial setting are iv situation in appropriate palaeolatitudes v lack of association with sedimentary evaporites coated grain or aggregates and vi geochemical evidence for reduced marine salinity and or nutrient upwelling the aim is that this work will lead to greater awareness and understanding of equatorial carbonate systems and contribute to the development of globally predictive models to better understand past and likely future environmental change

the steens mountain oregon geomagnetic polarity transition 2 field intensity variations and discussion of reversal models we carried out an extensive paleointensity study of the 15 5 0 3 m y miocene reversed to normal polarity transition recorded in lava flows from steens mountain south central oregon one hundred eighty five samples from the collection whose paleodirectional study is reported by mankinen et al this issue were chosen for paleointensity investigations because of their low viscosity index high curie point and reversibility or near reversibility of the strong field magnetization curve versus temperature application of the thellier stepwise double heating method was very successful yielding 157 usable paleointensity estimates corresponding to 73 distinct lava flows after grouping successive lava flows that did not differ significantly in direction and intensity we obtained 51 distinguishable complete field vectors of which 10 are reversed 28 are transitional and 13 are normal the record is complex quite unlike that predicted by simple flooding or standing nondipole field models it begins with an estimated several thousand years of reversed polarity with an average intensity of 31 5 8 5 t about one third lower than the expected miocene intensity this difference is interpreted as a long term reduction of the dipole moment prior to the reversal when site directions and intensities are considered truly transitional directions and intensities appear almost at the same time at the beginning of the transition and they disappear simultaneously at the end of the reversal large deviations in declination occur during this approximately 4500 1000 year transition period that are compatible with roughly similar average magnitudes of zonal and nonzonal field components at the site the transitional intensity is generally low with an average of 10 9 4 9 t for directions more than 45 away from the dipole field and a minimum of about 5 t the root mean square of the three field components x y and z are of the same order of magnitude for the transitional field and the historical nondipole field at the site latitude however a field intensity increase to pretransitional values occurs when the field temporarily reaches normal directions which suggests that dipolar structure could have been briefly regenerated during the transition in an aborted attempt to reestablish a stationary field changes in the field vector are progressive but jerky with at least two and possibly three large swings at astonishingly high rates each of those transitional geomagnetic impulses occurs when the field intensity is low less than 10 t and is followed by an interval of directional stasis during which the magnitude of the field increases greatly for the best documented geomagnetic impulse the rapid directional change corresponds to a vectorial intensity change of 6700 2700 nt yr 1 which is about 15 50 times larger than the maximum rate of change of the nondipole field observed during the last centuries the occurrence of geomagnetic impulses seems to support reversal models assuming an increase in the level of turbulence within the liquid core during transitions the record closes with an estimated several thousand years of normal polarity with an average intensity of 46 7 20 1 t agreeing with the expected miocene value however the occurrence of rather large and apparently rapid intensity fluctuations accompanied by little change in direction suggests that the newly reestablished dipole was still somewhat unstable

spatial variations in heavy minerals and patterns of sediment sorting along the nile delta egypt abstract sand samples were collected along 34 beach profiles spanning the 240 km length of the nile delta in order to examine the sorting patterns of heavy minerals that develop during cross shore and alongshore sediment transport factor analysis of the heavy mineral contents shows that two mineral factors or groups result from sorting due to the contrasting densities and sizes of the grains one factor is dominated by augite hornblende and epidote while the second factor consists of opaques garnet zircon rutile and monazite minerals of factor 1 are of lower densities and coarser sizes and represent the grains that are selectively entrained by waves and currents in areas of beach erosion and preferentially transported to zones of beach accretion where they are deposited the higher density minerals of factor 2 tend to become concentrated in areas of beach erosion accounting for the formation of black sand placers where the erosion has been greatest the spatial distributions of these two factors reflect the grain sorting patterns of the heavy minerals which coincide with the general trends of shoreline erosion versus accretion that exist along the length of the delta there is also a distinctive pattern of cross shore sorting with factor 2 containing the denser minerals being best developed within the inner surf zone generally with a maximum at the shoreline its development corresponds to the formation of black sand concentrates on the beach face where erosion has been greatest implying that grain sorting has taken place mainly within the swash zone there is a general decrease in factor 2 relative to factor 1 toward the offshore often with oscillations that are congruent with the beach topography factor 1 with the lower density minerals is greatest over offshore bars where deposition has prevailed

a sr nd isotopic study of sand sized sediment provenance and transport for the san francisco bay coastal system abstract a diverse suite of geochemical tracers including 87sr 86sr and 143nd 144nd isotope ratios the rare earth elements rees and select trace elements were used to determine sand sized sediment provenance and transport pathways within the san francisco bay coastal system this study complements a large interdisciplinary effort barnard et al 2012 that seeks to better understand recent geomorphic change in a highly urbanized and dynamic estuarine coastal setting sand sized sediment provenance in this geologically complex system is important to estuarine resource managers and was assessed by examining the geographic distribution of this suite of geochemical tracers from the primary sources fluvial and rock throughout the bay adjacent coast and beaches due to their intrinsic geochemical nature 143nd 144nd isotopic ratios provide the most resolved picture of where sediment in this system is likely sourced and how it moves through this estuarine system into the pacific ocean for example nd isotopes confirm that the predominant source of sand sized sediment to suisun bay san pablo bay and central bay is the sierra nevada batholith via the sacramento river with lesser contributions from the napa and san joaquin rivers isotopic ratios also reveal hot spots of local sediment accumulation such as the basalt and chert deposits around the golden gate bridge and the high magnetite deposits of ocean beach sand sized sediment that exits san francisco bay accumulates on the ebb tidal delta and is in part conveyed southward by long shore currents broadly the geochemical tracers reveal a complex story of multiple sediment sources dynamic intra bay sediment mixing and reworking and eventual dilution and transport by energetic marine processes combined geochemical results provide information on sediment movement into and through san francisco bay and further our understanding of how sustained anthropogenic activities which limit sediment inputs to the system e g dike and dam construction as well as those which directly remove sediments from within the bay such as aggregate mining and dredging can have long lasting effects

an alternative approach to the identification of net sediment transport paths based on grain size trends abstract progressive changes in grain size parameters have long been linked to net sediment transport paths however the methods employed to date suffer from limitations potentially leading to serious interpretational errors which necessitate the formulation of an integrated quantitative technique the approach advocated here is a step in this direction as it eliminates some of the problems inherent in the older methods previously trend vectors were obtained by comparing the grain size parameters of only two sampling stations at a time which gives a low probability of identifying the actual transport direction in the proposed method groups of five stations comprising a central station and four satellite stations are used for each trend vector grain size parameters are first combined in such a way that bias towards any one of them is climated the resultant dimensionless numbers are then substituted for the proportional frequencies of recorded directions in conventional vector analysis the satellite stations must be located equally far from the central station on radials 90 from each other which is seldom the case an iterative trigometric technique is therefore employed to determine the combined grain size parameters at these localities conventional vector analysis adapted to the situation of using four raials instead of 10 sectors allows the calculation of a vector mean azimuth and vector magnitude

understanding processes controlling sediment transports at the mouth of a highly energetic inlet system san francisco bay ca abstract san francisco bay is one of the largest estuaries along the u s west coast and is linked to the pacific ocean through the golden gate a 100 m deep bedrock inlet a coupled wave flow and sediment transport model is used to quantify the sediment linkages between san francisco bay the golden gate and the adjacent open coast flow and sediment transport processes are investigated using an ensemble average of 24 climatologically derived wave cases and a 24 8 h representative tidal cycle the model simulations show that within the inlet flow and sediment transport is tidally dominated and driven by asymmetry of the ebb and flood tides peak ebb velocities exceed the peak flood velocities in the narrow golden gate channel as a result of flow convergence and acceleration persistent flow and sediment gyres at the headland tips are formed that limit sediment transfer from the ebb tidal delta to the inlet and into the bay the residual transport pattern in the inlet is dominated by a lateral segregation with a large ebb dominant sediment transport and flow prevailing along the deeper north side of the golden gate channel and smaller flood dominant transports along the shallow southern margin the seaward edge of the ebb tidal delta largely corresponds to the seaward extent of strong tidal flows on the ebb tidal delta both waves and tidal forcing govern flow and sediment transport wave focusing by the ebb tidal delta leads to strong patterns of sediment convergence and divergence along the adjacent ocean beach

sediment transport in the san francisco bay coastal system an overview abstract the papers in this special issue feature state of the art approaches to understanding the physical processes related to sediment transport and geomorphology of complex coastal estuarine systems here we focus on the san francisco bay coastal system extending from the lower san joaquin sacramento delta through the bay and along the adjacent outer pacific coast san francisco bay is an urbanized estuary that is impacted by numerous anthropogenic activities common to many large estuaries including a mining legacy channel dredging aggregate mining reservoirs freshwater diversion watershed modifications urban run off ship traffic exotic species introductions land reclamation and wetland restoration the golden gate strait is the sole inlet connecting the bay to the pacific ocean and serves as the conduit for a tidal flow of 8 10 9 m 3 day in addition to the transport of mud sand biogenic material nutrients and pollutants despite this physical biological and chemical connection resource management and prior research have often treated the delta bay and adjacent ocean as separate entities compartmentalized by artificial geographic or political boundaries the body of work herein presents a comprehensive analysis of system wide behavior extending a rich heritage of sediment transport research that dates back to the groundbreaking hydraulic mining impact research of g k gilbert in the early 20th century

simulating sediment transport processes in san pablo bay using coupled hydrodynamic wave and sediment transport models abstract san pablo bay is a tidal sub embayment of the san francisco estuary which is dominated by broad shallow shoals bisected by a deep channel under the conceptual model of sediment transport in san pablo bay proposed by krone 1979 sediment typically enters san pablo bay during large winter and spring flows and is redistributed during summer conditions through wind wave resuspension and transport by tidal currents numerical simulations of sediment resuspension due to wind waves and the subsequent transport of this sediment by tidal currents show that sediment concentrations and fluxes throughout the channel shoal system result from a complex temporal and spatial interaction of the waves and tides the three dimensional untrim san francisco bay delta model was coupled with the simulating waves nearshore swan wave model and the sedimorph morphological model to develop a three dimensional 3d hydrodynamic wind wave and sediment transport model of san francisco bay and the sacramento san joaquin delta the coupled model was validated using water level velocity wind waves and suspended sediment data collected in san pablo bay and then used to quantify the spatial and temporal variability of sediment fluxes on the extensive shoals in san pablo bay under a range of tidal and wind conditions the model validation shows this modeling system can accurately predict hydrodynamics waves and suspended sediment concentration in san pablo bay the predicted bottom orbital velocities are elevated across the shoals during large wave events regardless of tidal stage but near low tide orbital velocities are increased even under low to moderate waves sediment fluxes between the shoals and the deeper channel are highest during spring tides and are elevated for up to a week following wave events even though the greatest influence of the wave event occurs abruptly

magnetic mineral transport and sorting in the swash zone northern lake erie canada a combined field and laboratory study in northern lake erie has provided new insights into the origin and dynamics of heavy mineral placer deposits on beaches consisting primarily of non magnetic sediment work was conducted on the cross shore and longshore transport of heavy magnetic minerals using magnetic susceptibility and fluorescent paints to trace the movement in the field of samples of magnetic magnetite and non magnetic quartz and calcite grains respectively laboratory experiments examined how the burial of small dense magnetic minerals is affected by the grain size of the non magnetic host material and how grain burial affects magnetic susceptibility measurements at the surface the field experiments demonstrated that the magnetic mineral tracers were buried rapidly beneath coarser non magnetic grains under low to moderate wave conditions and subsequently were unable to move in the longshore or cross shore directions the laboratory experiments showed that the magnetic susceptibility rapidly decreased with the rate and depth of burial of the magnetic minerals and that magnetic grain burial was most effective beneath coarser rather than finer non magnetic sand and for the latter sediments under less rather than more energetic conditions the results imply that magnetic mineral concentrations develop in this area through magnetic grain burial under fairly mild conditions and subsequent settling exposure and concentration in the upper swash zone during more energetic periods when the non magnetic grains are eroded it is probably during these erosional periods when the magnetic minerals are exposed in fairly homogeneous deposits that longshore and cross shore transport takes place

basement structure and sediment distribution in northwest atlantic ocean we have interpreted all available single channel and multichannel seismic reflection profiles to produce maps of structure contours on basement and isopachs of sediment thickness in the northwestern atlantic ocean including the labrador and irminger basins where appropriate we have modified and incorporated existing charts into the compilation contours are in meters derived by applying velocity regression equations based on sonobuoy results this gives a more accurate representation of geologic relations than is possible in reflection time mapping major structural relations and sediment distribution for the mid atlantic ridge mid labrador sea ridge davis strait and adjacent greenland and eastern canadian continental margins are clearly defined in the maps observ d basement structure is in good agreement with that expected from current plate kinematic models of the region the sediment thickness patterns are controlled by interaction of such factors as age of underlying oceanic crust crustal tectonic history structural trends in basement locations of sediment sources and nature of the sedimentary processes delivering sediment to the basins

determination of sediment provenance by unmixing the mineralogy of source area sediments the sedunmix program abstract along the margins of areas such as greenland and baffin bay sediment composition reflects a complex mixture of sources associated with the transport of sediment in sea ice icebergs melt water and turbidite plumes similar situations arise in many contexts associated with sediment transport and with the mixing of sediments from different source areas the question is can contributions from discrete sediment bedrock sources be distinguished in a mixed sediment by using mineralogy and if so how accurately to solve this problem four end member source sediments were mixed in various proportions to form eleven artificial mixtures two of the end member sediments are felsic and the other two have more mafic compositions end member and mixed sediment mineralogies were measured for the

using nd sr isotopes and rare earth elements to study sediment provenance of the modern radial sand ridges in the southwestern yellow sea abstract the radial sand ridges rsrs in the southwestern yellow sea off the jiangsu coast east china have been intensively studied at least since 1975 despite decades of studies the provenance of the rsr sediments remains uncertain in this study the nd sr isotopic and ree geochemical compositions of residual sediments i e the acid insoluble fractions were investigated to determine the provenance of the rsr sediments the nd isotopic composition paas normalized ree patterns and characteristic parameters e g sm nd la sm n gd yb n were merely associated with source rocks but not with particle sorting while the sr isotopic composition and ree contents of residual sediments were affected by particle sorting in addition to source rocks the onshore rsr sediments originated mainly from mixing of the fine grained sediments from various parts of the offshore rsr in terms of ree geochemical and isotopic analyses isotopic and ree geochemical comparison further reveals that the rsrs off the jiangsu coast were fed chiefly by the dispersal of surface sediments from the yangtze river mouth surface sediments from the yangtze river mouth were directly dispersed to the rsrs along the jiangsu coast and significantly affected the seaward part of the offshore rsr and the old yellow river delta area by a northward branch of the changjiang diluted freshwater plume only minor quantities of surface sediments from the modern yellow river mouth were introduced into the rsrs by the jiangsu coastal current and mainly contaminated the landward part of the offshore rsr area our findings highlighted the potential of the nd isotopes with ree geochemistry to trace the provenance of coastal sediments

an assessment of long wavelength magnetic anomalies over canada the reliability of the long wavelength portion 300 km of the magnetic field over canada as represented by the national aeromagnetic anomaly database compiled by the geological survey of canada gsc is assessed by comparison with two independent data sets a high altitude country wide survey carried out by the former earth physics branch epb and data from the magsat and pogo satellite missions the different altitudes at which each data set was measured 300 m 4 km and 400 km and their different resolution and time span of observations allow a determination of the integrity of selected wavelength bands in each data set the upward continued epb and magsat pogo fields compare well for wavelengths of 300 2500 km the gsc data show significant differences to the former indicating that the levelling and merging of several hundred individual surveys has degraded the longer wavelength components of the magnetic field replacing the gsc wavelength components 300 km with those from the epb field

geochemical and mineralogical characterization of surficial sediments from the northern rias implications for sediment provenance and impact of the source rocks abstract a multidisciplinary study of the elemental geochemistry and mineralogical characteristics of the marine surficial sediment in the northern rias nw iberian peninsula has been carried out the linkages between the marine sediment composition and their potential sources were examined the influence of the river borne sediments is only detected in the innermost part of the three rias regional variations of the mineral assemblages are governed by the source rock composition of the different geological complexes and the relative source rock contribution controlled by the continental hydrology mineralogical composition of the ortigueira ria and adjacent shelf surficial sediments are mainly made up of mafic and ultramafic rocks of the cape ortegal complex indicated by the high content of mg mn and chrysotile and riebeckite minerals in areas nearby ortegal complex the imprint of heavy minerals present in the surrounding rocks has also been recorded barqueiro and viveiro rias bed sediments are influenced by granitic and metamorphic rocks from the ollo de sapo complex as revealed by the high contribution of muscovite and quartz mining activities in the continental domain left strong imprints on marine surficial sediments pyrite content is high in the innermost areas of the ortigueira ria since this mineral is exploited in the mera river basin whereas high muscovite percentages characterize the viveiro ria owing to the abundance of granitic rocks and its exploitation in the landro river basin quartz content is high nearby cape estaca de bares induced by the presence of an important excavation of this material

the influence of particle size variations on the magnetic properties of sediments from the north eastern irish sea this paper considers the magnetic properties of a range of recent and contemporary sediments from the north eastern part of the irish sea principal component ordinations of the results show a close link between magnetic property variations and particle size the magnetic properties of a subset of samples particles sized by a combination of sieving and pipette analysis confirm that variations in ferrimagnetic magnetite grain size parallel those in particle size despite the fact that the magnetic grains in the fine grades have diameters 1 2 orders of magnitude smaller than those of the particle size fraction in which they occur this is best explained by postulating that the fine magnetic grains occur in the clay fraction but are present in declining concentrations in the coarser grades up to 4o as an artefact of the pipette method most samples have a biomodal distribution of magnetic minerals with a coarse mode associated with heavy minerals in the sands or coarse silts and a fine mode in the clays magnetic susceptibility x and saturation isothermal remanent magnetization sirm largely pick out the coarse mode where present anhysteretic remanent magnetization arm largely picks out the fine mode the results open up the possibility of normalizing samples from these environments for particle size and more specifically clay content by means of arm or arm x values the most likely source for the uniform and almost exclusive stable single domain magnetite which dominates the magnetic properties of the clays is thought to be bacterial magnetosomes the measurements as a whole do not appear to hold much promise for discriminating sediment source types

the impact of the 2009 10 el nino modoki on u s west coast beaches 1 high resolution beach morphology data collected along much of the u s west coast are synthesized to evaluate the coastal impacts of the 2009 10 el nino coastal change observations were collected as part of five beach monitoring programs that span between 5 and 13 years in duration in california regional wave and water level data show that the environmental forcing during the 2009 10 winter was similar to the last significant el nino of 1997 98 producing the largest seasonal shoreline retreat and or most landward shoreline position since monitoring began in contrast the 2009 10 el nino did not produce anomalously high mean winter wave energy in the pacific northwest oregon and washington although the highest 5 of the winter wave energy measurements were comparable to 1997 98 and two significant non el nino winters the increase in extreme waves in the 2009 10 winter was coupled with elevated water levels and a more southerly wave approach than the long term mean resulting in greater shoreline retreat than during 1997 98 including anomalously high shoreline retreat immediately north of jetties tidal inlets and rocky headlands the morphodynamic response observed throughout the u s west coast during the 2009 10 el nino is principally linked to the el nino modoki phenomena where the warm sea surface temperature sst anomaly is focused in the central equatorial pacific as opposed to the eastern pacific during a classic el nino featuring a more temporally persistent sst anomaly that results in longer periods of elevated wave energy but lower coastal water levels

geochemical characteristics and the provenance of sediments in the bransfield strait west antarctica abstract the bransfield basin is a quaternary marginal basin separating the south shetland islands from the antarctic peninsula we analyzed major trace and rare earth element chemistries and the nd sr and pb isotopic compositions for six piston core sediments from the western and eastern bransfield basins to determine the sediment provenance and factors controlling the composition of the sediments the bransfield sediments have chemical characteristics similar to sediments deposited in a tectonically active setting where the source rocks are predominated by igneous rocks of intermediate to mafic composition low k and high cn in the a cn k diagram low la sc low th sc and lower lree hree than average shale the low chemical alteration index of the sediments about 45 on average suggests the effect of weathering on the sediment composition was minimal the source rocks of the bransfield sediments are mostly composed of mesozoic to tertiary arc volcanic and plutonic rocks in the antarctic peninsula and the south shetland islands meanwhile contributions from other rock types in the northern antarctic peninsula region such as the trinity peninsula group or scotia metamorphic complex seem to be negligible the bransfield sediments can be divided into three distinct compositional groups group i sediments have a lower la yb and a less prominent negative eu anomaly than group ii sediments they are also characterized by negative ce anomalies group i sediments have been derived mainly from the south shetland islands whereas group ii sediments which are more widespread than group i sediments in the bransfield strait have been derived mainly from the antarctic peninsula group iii sediments which are very low in la yb with the lowest 87 sr 86 sr and the highest 143 nd 144 nd values have been derived from deception island the composition of the bransfield sediments is largely controlled by the composition of nearby source rocks the distribution of sediments is further modified by the current and topography of the basin

spreading rate dependent magnetization of the oceanic lithosphere inferred from the anomalous skewness of marine magnetic anomalies summary the anomalous skewness of marine magnetic anomalies decreases with increasing spreading rate and becomes negligible above a spreading rate of about 50 km myr i previous magnetization models of the oceanic lithosphere fail to explain this observation we propose a new model in which the magnetic structure of the oceanic lithosphere is dependent on spreading rate anomalous skewness measurements for anomalies 33 reversed and 25 reversed at various spreading rates are in agreement with a magnetization model in which layer 3 and the uppermost mantle bear a similar saturation magnetization and the ratio of layer 3 over layer 2a saturation magnetizations varies linearly from about 0 4 at a spreading rate of 10kmmyr to about 0 at 55kmmyr i for spreading rates higher than 55 km myr layer 3 and uppermost mantle magnetizations are negligible recent advances concerning accretionary processes at mid ocean ridges suggest that the combined effect of variations with spreading rate of magma fractionation alteration of layer 2a and serpentinization of layer 3 and the uppermost mantle may account for the proposed variation of magnetization with spreading rate

geochemical constraints on the provenance of surface sediments of radial sand ridges off the jiangsu coastal zone east china abstract the jiang harbor centered radial sand ranges rsrs off the jiangsu coast are the largest in the yellow sea however the provenance of the rsrs remains controversial in this study we compare major and trace element geochemistry together with grain size and main mineral composition in carbonate free sediments from rsrs and potential sources onshore and offshore rsr sediments have different grain size characteristics onshore rsr sediments have mean grain sizes of 2 tio 2 li and partly in cs zn and some high field strength elements y zr nb pb and th while depleted in other elements offshore rsr sediments are complicated in geochemical compositions some of them have very high contents of high field strength elements and others are similar to onshore rsr sediments onshore and offshore rsr sediments have different controlling factors of geochemical compositions onshore rsr sediments are influenced by clay size minerals whereas offshore sediments are controlled by heavy minerals the identification of zr nb and ti zr vs k rb shows that onshore and offshore rsrs seem to have similar sources their differences in grain size are a result of hydrodynamic sorting the identification of elemental ratios reveals that sources of rsr sediments are variable in space and time and the inputs of the chinese rivers especially the old yellow river and the yangtze river are still dominant but the effect of the korean field cannot be neglected our findings also demonstrate the potential of elemental ratios such as zr nb and k rb as tracer pairs for provenance of sediments in the yellow sea

initial scalar magnetic anomaly map from magsat a scalar magnetic anomaly map between 50 geographic latitude was derived from magsat data acquired during the november 1979 to june 1980 mission lifetime separation of anomaly fields from core and external fields was accomplished utilizing techniques developed for pogo data mayhew 1979 langel et al 1980 comparison with a similar map from pogo data shows that the basic anomaly patterns are essentially reproducible except in a few regions such as the atlantic and pacific at latitudes south of 15 increased resolution due to a lower measurement altitude is evident in the magsat map

rare earth elements as provenance indicators in north australian estuarine and coastal marine sediments rare earth elements ree in three grain size fractions of clay dominated estuarine and coastal sediments from the north australian coastline have been investigated for use as potential provenance indicators comparisons of data based on instrumental neutron activation analysis and inductively coupled plasma mass spectrometry revealed that hf digestions of zircon bearing samples resulted in unsatisfactory recovery of ree instead a relatively simple fast and safe partial digestion using hclo4 hno3 was used to extract ree mainly from clay minerals while excluding extraction of ree from zircons a comparison with published data for primary rock units within river catchments showed that the main ree systematics has been preserved in downstream clay rich sediments analysis of variance of la gd paas la yb paas and eu eu paas ratios in five areas showed that the 63 m fraction possessed the greatest discriminating power all five areas could be distinguished from each other at highly significant levels based on one or more of these ratios

magnetic anomaly map of north america data presented on the magnetic anomaly map in the continental areas have largely been derived from published map sources however these maps for the most part have been digitized and subjected to various processing steps in preparation for compositing the marine areas of the map consist mostly of digital data track except in the gulf of mexico caribbean sea and the continental shelf areas of alaska where the data were obtained from digitized maps

changes in surfzone morphodynamics driven by multi decadal contraction of a large ebb tidal delta abstract the impact of multi decadal large scale deflation 76 million m 3 of sediment loss and contraction 1 km of a 150 km 2 ebb tidal delta on hydrodynamics and sediment transport at adjacent ocean beach in san francisco ca usa is examined using a coupled wave and circulation model the model is forced with representative wave and tidal conditions using recent 2005 and historic 1956 ebb tidal delta bathymetry data sets comparison of the simulations indicates that along north south trending ocean beach the contraction and deflation of the ebb tidal delta have resulted in significant differences in the flow and sediment dynamics between 1956 and 2005 the transverse bar the shallow attachment point of the ebb tidal delta to the shoreline migrated northward 1 km toward the inlet while a persistent alongshore flow and transport divergence point migrated south by 500 m such that these features now overlap a reduction in tidal prism and sediment supply over the last century has resulted in a net decrease in offshore tidal current generated sediment transport at the mouth of san francisco bay and a relative increase in onshore directed wave driven transport toward the inlet accounting for the observed contraction of the ebb tidal delta alongshore migration of the transverse bar and alongshore flow divergence have resulted in an increasing proportion of onshore migrating sediment from the ebb tidal delta to be transported north along the beach in 2005 versus south in 1956 the northerly migrating sediment is then trapped by pt lobos a rocky headland at the northern extreme of the beach consistent with the observed shoreline accretion in this area conversely alongshore migration of the transverse bar and divergence point has decreased the sediment supply to southern ocean beach consistent with the observed erosion of the shoreline in this area this study illustrates the utility of applying a high resolution coupled circulation wave model for understanding coastal response to large scale bathymetric changes over multi decadal timescales common to many coastal systems adjacent to urbanized estuaries and watersheds worldwide

geochemistry of surface sediments from the mid oceanic kolbeinsey ridge north of iceland in order to assess recent submarine volcanic contributions to the sediments from the active kolbeinsey ridge surface samples were analyzed chemically the contribution of major and trace elements studied differ within the study area a statistical analysis of the geochemical variables using factor analysis and cluster method allows to distinguish possible sample groups cluster method identifies three distinct sediment groups located in different areas of sedimentation group 1 is characterized by highest contents of fe2o3 v co ni cu and zn demonstrating the input of volcaniclastic material group 2 comprises high values of caco3 cao and sr representing biogenic carbonate group 3 is characterized by the elements k rb cs la and pb indicating the terrigenous component the absolute percentage of the volcanic biogenic and terrigenous components in the bulk sediments was calculated by using a normative sediment method the highest volcanic component 60 on a carbonate free basis is found on the ridge crest the biogenic component is highest 10 30 in the eastern part of the spar fracture zone influenced by the east iceland current samples from the western and southeastern region of the study area contain more than 90 of terrigenous component which appears to be mainly controlled by input of ice rafted debris

small scale features in the earth s magnetic field observed by magsat a spherical harmonic expansion to degree and order 29 is derived using a selected magnetically quiet sample of magsat data global maps representing the contribution due to terms of the expansion above n 13 at 400 km altitude are compared with previously published residual anomaly maps and shown to be similar even in polar regions an expansion with such a high degree and order displays all but the sharpest features seen by the satellite and gives a more consistent picture of the high order field structure at a constant altitude than do component maps derived independently the appendix is available with the entire article on microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document b83 008 2 50 payment must accompany order

mineralogical and isotopic evidence for the sediment provenance of the western south yellow sea since mis 3 and implications for paleoenvironmental evolution abstract changing sediment provenance and related paleoenvironmental evolution since marine isotope stages mis 3 have been investigated based on accelerator mass spectrometry ams 14c and optically stimulated luminescence osl dating of core csdp 01 recovered from the western south yellow sea sys based on our results sea level fluctuations and monsoonal climate variations are identified as the principal factors driving these changes sea level fluctuations determined the accommodation space in the shelf area while the monsoonal climate controlled the sediment supply capacity from river to sea mineral and sr nd isotopic records reveal the major contribution of the paleo changjiang river yangtze river to the study core area during the early mid mis 3 which likely defined the northern limit of the paleo changjiang delta at that time high sediment supply and limited accommodation space led to the development of sediment fed systems on the sys shelf resulting in a high preservation potential for thick stacking and overlapping deltaic sediments along with deltaic progradation core sediment provenance gradually transformed from the paleo changjiang river to the paleo huanghe river yellow river near the late mis 3 implying that the paleo huanghe river likely emptied into the sys and built a large delta during the mis 3 interval a strong summer monsoon during the early mis 1 interval was favorable for the changjiang to deliver abundant sediments to the study core area a weak summer monsoon during the mid late mis 1 when the coastline had retreated to nearly its present day position decreased the changjiang and huanghe supply to the study area low sediment supply and sufficient accommodation space gave rise to the development of sediment starved systems during this period nd values fluctuated between the changjiang and huanghe sources at that time suggesting that sea bed erosion materials are the main sediment contribution to the study area in general sedimentary evolution in the western sys since mis 3 is a good example of river sea interaction in the marginal seas of southeast asia in which sea level and monsoonal climate changes should play an important role

heavy mineral analysis for assessing the provenance of sandy sediment in the san francisco bay coastal system abstract heavy or high specific gravity minerals make up a small but diagnostic component of sediment that is well suited for determining the provenance and distribution of sediment transported through estuarine and coastal systems worldwide by this means we see that surficial sand sized sediment in the san francisco bay coastal system comes primarily from the sierra nevada and associated terranes by way of the sacramento and san joaquin rivers and is transported with little dilution through the san francisco bay and out the golden gate heavy minerals document a slight change from the strictly sierran sacramento mineralogy at the confluence of the two rivers to a composition that includes minor amounts of chert and other franciscan complex components west of carquinez strait between carquinez strait and the san francisco bar sierran sediment is intermingled with franciscan modified sierran sediment the latter continues out the gate and turns southward towards beaches of the san francisco peninsula the sierran sediment also fans out from the san francisco bar to merge with a sierran province on the shelf in the gulf of the farallones beach sand sized sediment from the russian river is transported southward to point reyes where it spreads out to define a franciscan sediment province on the shelf but does not continue southward to contribute to the sediment in the golden gate area

bedrock geology of the san francisco bay area a local sediment source for bay and coastal systems abstract local watersheds may contribute over half of the sediment load coming into san francisco bay today the bedrock underlying these watersheds is the ultimate source for most of this sediment this paper outlines the geologic history of this bedrock which records the complex tectonic history of the san francisco bay area over the last 200 ma the jurassic to eocene franciscan complex in the bay area is the most widespread bedrock the local franciscan can be broken into nine tectonic terranes that represent pieces of seafloor that were accreted to the north american margin in over a 100 myr period of subduction each terrane has a unique age range sequence of seafloor rocks and metamorphic history the franciscan rocks were thrust eastward under the great valley complex the great valley complex reflects a forearc basin comprised of jurassic ocean crust the coast range ophiolite and overlying jurassic and cretaceous turbidite dominated sedimentary rocks of the great valley group by the beginning of the cenozoic era shallowing of the angle of subduction along the continental margin led to uplift and infilling of the forearc basin to shelf depth recorded at this time are sedimentary sequences governed by eustatic sealevel changes and evidence of the first unroofing of franciscan rocks marine sedimentary rocks dominate the region through the miocene and unconformities within the early tertiary sedimentary record reflect periods of tectonic activity and uplift middle to late miocene sedimentary rocks are extensively deposited throughout the bay area in the late miocene the mendocino triple junction passed northward through the area and transform tectonism commenced a slab window developed behind the triple junction resulted in volcanic activity that produced the sonoma volcanics in the north bay and volcanics of the east bay hills by pliocene time terrestrial sedimentary rocks were being deposited in many parts of the bay area faulting associated with the san andreas system led to the development of small basins the displacement of local bedrock blocks and the transport of the salinian complex from the southern sierra to the western margin of the bay area the modern topography of the region started emerging by about 6 ma to 4 ma when compression across the san andreas system increased and uplift of the coast ranges began the first estuarine influence in san francisco bay is recorded in 600 ka rocks about the same time as the modern sacramento river system started flowing through the san francisco estuary valley today s local san francisco bay watershed is comprised of numerous small stream systems around the bay with headwaters in the surrounding hills and mountains active tectonism produces relief in these watersheds of typically 500 m or more with the ridgelines typically supported by more resistant bedrock units steep topography leads to rapid bedrock erosion particularly of the finer grained sedimentary rocks landslides provide a significant portion of the sediment carried by the streams and several of the bedrock units are more prone to landslides particularly the central and novato quarry terranes of the franciscan complex and finer grained units of both the great valley group and tertiary rocks many of the larger streams have dammed reservoirs that trap much of their sediment load before it can reach the bay

strontium and neodymium isotopic signatures indicate the provenance and depositional process of loams intercalated in coastal dune sand western japan abstract isotopic analyses of strontium and neodymium suggest that layers of loam intercalated in dune sand on the japan sea coast at tottori western japan consist of a mixture of asian dust from china and locally derived sediment an outcrop exposure shows a succession of late pleistocene dune sand a lower loam layer daisen kurayoshi pumice dkp 50 55 ka or older an upper loam aira tn tuff ca 30 ka and holocene dune sand in ascending order bulk samples of the loam layers show an upward increase in 87 sr 86 sr suggesting that the contribution of asian dust increases upward the sr isotopic values also suggest a greater contribution of asian dust in the silt fraction than in the bulk sample asian dust transported by westerly jet from the taklamakan or gobi desert is the main constituent of the upper part of the lower loam of which isotopic values of silicate portion is isotopically identical to those of desert sand in china 87 sr 86 sr 0 717 0 719 e nd 9 5 to 9 4 in contrast the sr and nd isotopic values of dkp 87 sr 86 sr 0 705 e nd 2 6 to 0 6 are close to those of the volcanic rocks of mt daisen which is regarded as the source of the tephra the isotopic signature suggests that asian dust also have contributed to the upper part of the upper loam layer the upward increase of 87 sr 86 sr within each of the loam layers suggests that the contribution of asian dust increased as the proportion of reworked deposits from the underlying layer dune sand or dkp decreased by burial in contrast 87 sr 86 sr in dkp shows little vertical change suggesting very rapid deposition without entrainment of the underlying lower loam layer

sub weekly to interannual variability of a high energy shoreline abstract sixty one global positioning system gps sub aerial beach surveys were completed at 7 km long ocean beach san francisco ca usa between april 2004 and march 2009 the five year time series contains over 1 million beach elevation measurements and documents detailed changes in beach morphology over a variety of spatial temporal and physical forcing scales results show that seasonal processes dominate at ocean beach with the seasonal increase and decrease in wave height being the primary driver of shoreline change storm events while capable of causing large short term changes in the shoreline did not singularly account for a large percentage of the overall observed change empirical orthogonal function eof analysis shows that the first two modes account for approximately three quarters of the variance in the data set and are represented by the seasonal onshore offshore movement of sediment 60 and the multi year trend of shoreline rotation 14 the longer term trend of shoreline rotation appears to be related to larger scale bathymetric change an eof based decomposition technique is developed that is capable of estimating the shoreline position to within one standard deviation of the range of shoreline positions observed at most locations along the beach the foundation of the model is the observed relationship between the temporal amplitudes of the first eof mode and seasonally averaged offshore wave height as well as the linear trend of shoreline rotation this technique while not truly predictive because of the requirement of real time wave data is useful because it can predict shoreline position to within reasonable confidence given the absence of field data once the model is developed at a particular site

magnetization of the oceanic crust beneath the labrador sea the aeromagnetic anomalies of the oceanic crust northeast of newfoundland canada are strongly skewed with an anomalous skewness of 33 52 with respect to the anomalies calculated using the standard sea floor spreading model this paper examines the possibility that the anomalous skewness is on account of an oceanic crust with a thermo viscous remanent magnetization where unlike the standard model the lower crust is magnetic the thermo viscous remanent magnetization of the lower crust beneath the labrador sea has dominant contributions to broad scale marine magnetic anomalies and to the negative magsat anomaly of the sea

variations in magnetization intensity and low temperature titanomagnetite oxidation of ocean floor basalts the remanent magnetization of the oceanic crust exhibits a systematic long term variation which correlates with the amplitudes of marine magnetic anomalies after a sharp initial decrease of natural remanent magnetization intensity a minimum is reached at 20myr followed by a gradual increase up to ages of 120 myr the progressive sea floor alteration of the magnetic minerals carrying the crustal magnetism is proposed as a cause for this behaviour

selective transport of palynomorphs in marine turbiditic deposits an example from the ascension monterey canyon system offshore central california abstract the pollen assemblage of a deep sea core 15g collected at lower bathyal depths 3491 m on a levee of monterey canyon off central california was investigated to gain insights into the delivery processes of terrigenous material to submarine fans and the effect this transport has on the palynological record thirty two samples were obtained down the length of the core 19 from hemipelagic and mixed mud deposits considered to be the background record and 13 others from displaced flow deposits the pollen record obtained from the background samples documents variations in the terrestrial flora as it adapted to changing climatic conditions over the last 19 000 cal yrs bp a q mode cluster analysis defined three pollen zones a glacial pollen zone ca 20 000 17 000 cal yr bp an overlying transitional pollen zone ca 17 000 11 500 cal yr bp and an interglacial pollen zone ca 11 500 cal yr bp to present another q mode cluster analysis of both the background mud and flow deposits also defined these three pollen zones but four of the 13 turbiditic deposits were assigned to pollen zones older than expected by their stratigraphic position this was due to these samples containing statistically significant fewer palynomorphs than the background muds as well as being enriched 10 35 in some cases in hydraulically efficient pinus pollen a selective bias in the pollen assemblage such as demonstrated here may result in incorrect interpretations e g climatic shifts or environmental perturbations based on the floral record indicating turbiditic deposits should be avoided in marine palynological studies particularly in the case of fine grained flow deposits that may not be visually distinct granulometry and grain size frequency distribution curves may not be enough to identify these biased deposits determining the relative abundance and source of displaced shallow water benthic foraminifera entrained in these sediments serves as an excellent additional tool to do so

thermoviscous remanent magnetization of oceanic lithosphere inferred from its thermal evolution remanent magnetization patterns of the oceanic lithosphere determined on the basis of the thermal evolution of the lithosphere while taking into account both thermal and viscous magnetizations give rise to magnetic anomalies similar to those observed by magsat over the cretaceous quiet zones of the atlantic ocean and by marine magnetic surveys over anomaly 33 viscous magnetization acquired during a given core field polarity period is not removed completely by that acquired in the next period of opposite polarity because of cooling of the lithosphere and the strong temperature dependence of viscous magnetization the magnetization pattern of layer 2a resembles that of the standard seafloor spreading magnetic model consisting of normally and reversely magnetized zones separated by vertical boundaries and produces symmetric magnetic anomalies the magnetization pattern of the middle crust is similar to that of layer 2a for high magnetic blocking temperature models but it is slightly skewed with respect to layer 2a for low magnetic blocking temperature models the magnetization pattern of the lower crust is strongly skewed relative to that of layer 2a and has diffuse boundaries with pronounced slopes between normally and reversely magnetized zones it produces magnetic anomalies with appreciable skewness suggesting that observed skewness of marine magnetic anomaly 33 arises from the magnetization of this layer the magnetization pattern of the upper mantle is appreciably skewed and almost devoid of small scale variations it produces strongly skewed magnetic anomalies at satellite altitudes which may explain the observed skewness of magsat anomalies over the cretaceous quiet zones of the atlantic ocean

the demagnetization temperature necessary to remove viscous remanent magnetization recent experimental studies have shown that the temperature necessary to demagnetize viscous remanent magnetization vrm in magnetite bearing rocks is significantly higher than predicted by standard neel single domain theory the walton time temperature equation which has been invoked by some to explain the enhanced thermal stability actually relates intensities of vrms acquired at different temperatures rather than describing the unblocking of a previously acquired vrm we show that the low field approximation lfa used in all previous formulations which predicts equal vrm acquisition and decay rates is not valid for a magnetite assemblage in the earth s field a medium field approximation mfa predicts significantly faster vrm acquisition and therefore greater thermal stability in decay for the larger particles in the assemblage conventional theory does apply to red bed acquisition decay experiments since the lfa is valid for hematite

distribution of biologic anthropogenic and volcanic constituents as a proxy for sediment transport in the san francisco bay coastal system abstract although conventional sediment parameters mean grain size sorting and skewness and provenance have typically been used to infer sediment transport pathways most freshwater brackish and marine environments are also characterized by abundant sediment constituents of biological and possibly anthropogenic and volcanic origin that can provide additional insight into local sedimentary processes the biota will be spatially distributed according to its response to environmental parameters such as water temperature salinity dissolved oxygen organic carbon content grain size and intensity of currents and tidal flow whereas the presence of anthropogenic and volcanic constituents will reflect proximity to source areas and whether they are fluvially or aerially transported because each of these constituents have a unique environmental signature they are a more precise proxy for that source area than the conventional sedimentary process indicators this san francisco bay coastal system study demonstrates that by applying a multi proxy approach the primary sites of sediment transport can be identified many of these sites are far from where the constituents originated showing that sediment transport is widespread in the region although not often used identifying and interpreting the distribution of naturally occurring and allochthonous biologic anthropogenic and volcanic sediment constituents is a powerful tool to aid in the investigation of sediment transport pathways in other coastal systems

sand sources and transport pathways for the san francisco bay coastal system based on x ray diffraction mineralogy abstract the mineralogical compositions of 119 samples collected from throughout the san francisco bay coastal system including bayfloor and seafloor area beaches cliff outcrops and major drainages were determined using x ray diffraction xrd comparison of the mineral concentrations and application of statistical cluster analysis of xrd spectra allowed for the determination of provenances and transport pathways the use of xrd mineral identifications provides semi quantitative compositions needed for comparisons of beach and offshore sands with potential cliff and river sources but the innovative cluster analysis of xrd diffraction spectra provides a unique visualization of how groups of samples within the san francisco bay coastal system are related so that sand sized sediment transport pathways can be inferred the main vector for sediment transport as defined by the xrd analysis is from san francisco bay to the outer coast where the sand then accumulates on the ebb tidal delta and also moves alongshore this mineralogical link defines a critical pathway because large volumes of sediment have been removed from the bay over the last century via channel dredging aggregate mining and borrow pit mining with comparable volumes of erosion from the ebb tidal delta over the same period in addition to high rates of shoreline retreat along the adjacent open coast beaches therefore while previously only a temporal relationship was established the transport pathway defined by mineralogical and geochemical tracers support the link between anthropogenic activities in the bay and widespread erosion outside the bay the xrd results also establish the regional and local importance of sediment derived from cliff erosion as well as both proximal and distal fluvial sources this research is an important contribution to a broader provenance study aimed at identifying the driving forces for widespread geomorphic change in a heavily urbanized coastal estuarine system

sub tidal benthic habitats of central san francisco bay and offshore golden gate area a review abstract deep water potential estuarine and marine benthic habitat types were defined from a variety of new and interpreted data sets in central san francisco bay and offshore golden gate area including multibeam echosounder mbes side scan sonar and bottom grab samples potential estuarine benthic habitats identified for the first time range from hard bedrock outcrops on island and mainland flanks and some bay floor regions to soft very dynamic bedforms consisting of sediment waves and ripples soft sediment ranges from mud and sand to bimodal two or more grain sizes sediment of gravel pebbles and cobbles in addition considerable anthropogenic features i e pipelines bridge abutments dredged channels dump sites were distinguished of the 52 potential benthic habitat types mapped compressed to 14 types for this paper 24 were of unconsolidated sediment with five of these comprised of dynamic bedforms or sediment waves and dunes five of mixed soft over hard substrate type six of hard substrate or rock outcrop 13 of anthropogenically disturbed areas and four hard anthropogenic features rock outcrops and rubble are considered the primary habitat type for rockfish sebastes spp lingcod ophiodon elongatus and in shallow water for herring clupea pallasii spawning dynamic bedforms such as sand waves are considered potential foraging habitat for juvenile lingcod may be sub tidal habitat for the pacific sand lance ammodytes hexapterus forage fish and possibly resting habitat for migratory fishes such as sturgeon acipenser medirostris the potential marine benthic habitats identified in san francisco bay are not unlike those found in other estuaries around the world and this study should contribute significant information that will be of interest to scientists managers and fishers investigating and utilizing bay and estuarine resources as described in the many papers of this special issue the understanding of the interrelationship of geology and ecology is critical to the identification of essential habitats and the sustainability of a healthy ecosystem

net sediment transport patterns inferred from grain size trends based upon definition of transport vectors reply abstract a new approach to the analysis of the grain size trends associated with net sediment transport directions in shallow marine environments is developed here two specific trends modified from mclaren and bowles 1985 on the basis of a literature review are used to define a grid of trend vectors such vectors are filtered and transformed into transport vectors it is suggested that an ordered pattern of the transport vectors represents net transport paths the orderliness of the derived pattern is examined on the basis of a significance test using the average length of the transport vectors as a criterion both the filtering operation and the significance test procedure are based upon the assumption that the trend vectors which are not associated with net transport have the same probability of being in any direction the technique is applied to data from yangpu harbour southern china the technique can be applied to inner continental shelf and coastal environments for such an analysis the area under investigation should be sampled at an interval large enough to reflect the real grain size trends resulting from net sediment transport but small compared with the dimensions of the sedimentary environment the time scale of the results depends upon the sampling depth applicability of the technique is likely to be somewhat limited where the environment is highly variable over short distances furthermore due to its statistical character the analysis may fail to identify net transport patterns

comment on magnetization of the oceanic crust thermoremanent magnetization or chemical remanent magnetization by c a raymond and j l labrecque

rare earth major and trace elements in chert from the franciscan complex and monterey group california assessing ree sources to fine grained marine sediments abstract rare earth element ree major and trace element analyses of 77 samples from the mesozoic franciscan complex and miocene monterey group of california usa indicate that magnitudes of the ce anomaly ce ce and total ree abundances sree in these rocks are controlled dominantly by a the amount of included metalliferous material b the amount of direct terrigenous input and c the overall burial rate the relative importance of these individual processes varies across an ocean basin in such a way that ree relative fractionations and sree correspond with its depositional environment our conclusions are supported by an extensive review of published ree data from various river coastal open ocean and ridge influenced waters as well as terrigenous pelagic and metalliferous sediment the chert sequences record deposition in spreading ridge open ocean basin and continental margin environments the relative importance of metalliferous and terrigenous influences and the role of scavenging from seawater may be estimated from a sample s inferred depositional distance km from the spreading ridge the major element chemistry and the stratigraphie context the ce ce values are low 0 29 in the vicinity of spreading ridges and trend to successively higher 1 values with decreasing metalliferous and increasing terrigenous influences other ree indicators ree lu n la n eu eu also respond to metalliferous and terrigenous influences near the spreading ridge chert ree appears determined by burial rate while shale ree responds to metalliferous abundance in open ocean and continental margin environments ree is controlled by sediment exposure time and therefore is related inversely to burial rate ree data are consistent with the major elements fe2o3 mno and al2o3 in reflecting the respective metalliferous and terrigenous sources p2o5 and cao do not vary with ce ce in any environment but cao shows a weak negative correlation with ree trace element trends e g v cr cu ge si rb sr y th u in general can similarly be accounted for in the context of depositional position relative to metalliferous and terrigenous inputs rees in chert appear less affected by post depositional processes than either major or trace elements indicating that rees are better tools for paleoceanographic or tectonic reconstructions that are based on chert chemistry this work complements recent efforts to elucidate the factors determining large scale ree distributions in marine sediments and has direct bearing on previous attempts to use the ce anomaly in older rocks and sediments as a recorder of secular variations and anoxic events in the overlying water column

anthropogenic influences on shoreline and nearshore evolution in the san francisco bay coastal system abstract analysis of four historical bathymetric surveys over a 132 year period has revealed significant changes to the morphology of the san francisco bar an ebb tidal delta at the mouth of san francisco bay estuary from 1873 to 2005 the san francisco bar vertically eroded an average of 80 cm over a 125 km 2 area which equates to a total volume loss of 100 52 million m 3 of fine to coarse grained sand comparison of the surveys indicates the entire ebb tidal delta contracted radially with the crest moving landward an average of 1 km long term erosion of the ebb tidal delta is hypothesized to be due to a reduction in the tidal prism of san francisco bay and a decrease in coastal sediment supply both as a result of anthropogenic activities prior research indicates that the tidal prism of the estuary was reduced by 9 from filling diking and sedimentation compilation of historical records dating back to 1900 reveals that a minimum of 200 million m 3 of sediment has been permanently removed from the san francisco bay coastal system through dredging aggregate mining and borrow pit mining of this total 54 million m 3 of sand sized or coarser sediment was removed from central san francisco bay with grain sizes comparable to the ebb tidal delta and its direct connection to the bay mouth removal of sediments from central san francisco bay may limit the sand supply to the delta and open coast beaches swan wave modeling illustrates that changes to the morphology of the san francisco bar have altered the alongshore wave energy distribution at adjacent ocean beach and thus may be a significant factor in a persistent beach erosion hot spot occurring in the area shoreline change analyses show that the sandy shoreline in the shadow of the ebb tidal delta experienced long term 1850s 1890s to 2002 and short term 1960s 1980s to 2002 accretion while the adjacent sandy shoreline exposed to open ocean waves experienced long term and short term erosion therefore the recently observed accelerating rates of bay sediment removal ebb tidal delta erosion and open coast beach erosion are all correlated temporally

geochemistry of surface sediments off the southern and western coasts of korea abstract the continental shelf off the southern and western side of the korean peninsula is part of a modern epicontinental sea and is an effective sediment trap for clastic material derived from china and korea we have analyzed 179 surface sediment samples from this shelf for al fe na k mg ca ti p mn sr ba v cr co ni cu zn organic carbon and calcium carbonate in order to determine the geochemical characteristics of these sediments results showed a wide range of element contents which are mainly related to the textural variability of sediments exceptions to this were found in the contents of ca k sr and ba the ca and sr contents were largely determined by the amounts of carbonate present the k content on the other hand appeared to be influenced by both the contents of illite and feldspar and ba of potassium feldspar for muds i e sediments deposited under present day conditions it is possible to distinguish those in the central yellow sea from those in the keum estuary the former are characterized by high contents of fe na k mg ca and v and the latter by high contents of mn ba and co these differences become more apparent when these elements are normalized relative to al in order to minimize grain size effects the distribution of v al ratios is different from that of other elements the highest v al values occur in muds from the central yellow sea derived from the huanghe the yellow river in china whereas the highest values of mn al are found in the nearshore area adjacent to the korean peninsula based on these results it is suggested that the sources of fine sediments in the yellow and south seas can be distinguished from the geochemical characteristics of the surface sediments in the yellow sea two different sources of fine grained sediments can be seen the huanghe and the keum river the former is characterized by higher v contents and the latter by higher mn contents using the v al ratio as an end member component of the two source materials the dispersal patterns of the fine sediments 6o were also derived

comment on tectonic rotations in extensional regimes and their paleomagnetic consequences for ocean basalts by kenneth l verosub and eldridge m moores deviate significantly from expected values vetosub and moores 1981 sought to account for what appear to be sys tematic departures of mean inclination at several dsdp base ment sites in terms of tectonic rotations along listtic normal faults such rotations about horizontal axes perpendicular to the extension direction and typically amounting to 30o 50 o

estimating suspended solids concentrations from backscatter intensity measured by acoustic doppler current profiler in san francisco bay california abstract the estimation of mass concentration of suspended solids is one of the properties needed to understand the characteristics of sediment transport in bays and estuaries however useful measurements or estimates of this property are often problematic when employing the usual methods of determination from collected water samples or optical sensors analysis of water samples tends to undersample the highly variable character of suspended solids and optical sensors often become useless from biological fouling in highly productive regions acoustic sensors such as acoustic doppler current profilers that are now routinely used to measure water velocity have been shown to hold promise as a means of quantitatively estimating suspended solids from acoustic backscatter intensity a parameter used in velocity measurement to further evaluate application of this technique using commercially available instruments profiles of suspended solids concentrations are estimated from acoustic backscatter intensity recorded by 1200 and 2400 khz broadband acoustic doppler current profilers located at two sites in san francisco bay california adcp backscatter intensity is calibrated using optical backscatterance data from an instrument located at a depth close to the adcp transducers in addition to losses from spherical spreading and water absorption calculations of acoustic transmission losses account for attenuation from suspended sediment and correction for nonspherical spreading in the near field of the acoustic transducer acoustic estimates of suspended solids consisting of cohesive and noncohesive sediments are found to agree within about 8 10 of the total range of concentration to those values estimated by a second optical backscatterance sensor located at a depth further from the adcp transducers the success of this approach using commercially available doppler profilers provides promise that this technique might be appropriate and useful under certain conditions in spite of some theoretical limitations of the method

magnetization of the oceanic crust thermoremanent magnetization of chemical remanent magnetization we propose a model in which chemical remanent magnetization crm acquired within the first 20 m y of crustal evolution may account for 80 of the bulk natural remanent magnetization of older basalts the crm of the crust is acquired as the original thermoremanent magnetization trm is lost through low temperature alteration the crm intensity and direction are controlled by the posternplacement polarity history this model explains several independent observations concerning the magnetization of the oceanic crust the model accounts for amplitude and skewness discrepancies observed in both the intermediate wavelength satellite field and the short wavelength sea surface magnetic anomaly pattern it also explains the decay of magnetization away from the spreading axis and the enhanced magnetization of the cretaceous quiet zones while predicting other systematic variations with age in the bulk magnetization of the oceanic crust the model also explains discrepancies in the anomaly skewness parameter observed for anomalies of cretaceous age further our study indicates varying rates of trm decay in very young crust which depicts the advance of low temperature alteration through the magnetized layer

integration of bed characteristics geochemical tracers current measurements and numerical modeling for assessing the provenance of beach sand in the san francisco bay coastal system abstract over 150 million m3 of sand sized sediment has disappeared from the central region of the san francisco bay coastal system during the last half century this enormous loss may reflect numerous anthropogenic influences such as watershed damming bay fill development aggregate mining and dredging the reduction in bay sediment also appears to be linked to a reduction in sediment supply and recent widespread erosion of adjacent beaches wetlands and submarine environments a unique multi faceted provenance study was performed to definitively establish the primary sources sinks and transport pathways of beach sized sand in the region thereby identifying the activities and processes that directly limit supply to the outer coast this integrative program is based on comprehensive surficial sediment sampling of the san francisco bay coastal system including the seabed bay floor area beaches adjacent rock units and major drainages analyses of sample morphometrics and biological composition e g foraminifera were then integrated with a suite of tracers including 87sr 86sr and 143nd 144nd isotopes rare earth elements semi quantitative x ray diffraction mineralogy and heavy minerals and with process based numerical modeling in situ current measurements and bedform asymmetry to robustly determine the provenance of beach sized sand in the region

coefficients for sea surface wind stress heat flux and wind profiles as a function of wind speed and temperature surface layer coefficients for wind profiles wind stress and heat flux in typical open sea conditions are briefly reviewed businger dyer flux gradient relationships and a charnock wind stress formula fit the empirical data and are dimensionally consistent these have been solved by an iterative method and the results are presented in a tabular form suitable for climatological calculations from marine wind and temperature data

harmonic analysis of tides and tidal currents in south san francisco bay california abstract water level observations from tide stations and current observations from current meter moorings in south san francisco bay south bay california have been harmonically analysed at each tide station 13 harmonic constituents have been computed by a least squares regression without inference tides in south bay are typically mixed there is a phase lag of approximately 1 h and an amplification of 1 5 from north to south for a mean semi diurnal tide because most of the current meter records are between 14 and 29 days only the five most important harmonics have been solved for east west and north south velocity components the eccentricity of tidal current ellipse is generally very small which indicates that the tidal current in south bay is strongly bidirectional the analyses further show that the principal direction and the magnitude of tidal current are well correlated with the basin bathymetry patterns of eulerian residual circulation deduced from the current meter data show an anticlockwise gyre to the west and a clockwise gyre to the east of the main channel in the summer months due to the prevailing westerly wind opposite trends have been observed during winter when the wind was variable

thermoremanent magnetization of the oceanic lithosphere inferred from a thermal evolution model implications for the source of marine magnetic anomalies abstract thermoremanent magnetization models of the oceanic crust and the uppermost part of the oceanic mantle are derived on the basis of a typical thermal evolution model of the oceanic lithosphere using different magnetic blocking temperature ranges the magnetization of the basaltic layer 2a has a similar pattern but with a lower intensity to that of the standard sea floor spreading magnetic model however the magnetization patterns of the lower crust and upper mantle are skewed so that in a given polarity period the total magnetization of a lithospheric column which is created early in the period is greater than that of a column which is created later in the period magnetic anomalies of the magnetization models are calculated at sea level and at magsat elevation for slow moderate and fast sea floor spreading velocities although the magnetization models are derived based on purely physical reasoning without using any a priori information about the observed marine and magsat magnetic anomalies they do yield magnetic anomalies which are similar to the observed anomalies the models explain several features of the marine and magsat anomalies the anomalous skewness of marine magnetic anomalies is explained in terms of the magnetization of the oceanic lower crust the magnetization of the oceanic upper mantle may account for the anomalous skewness observed over the cretaceous quiet zones in the atlantic ocean the skewness of the magnetic anomalies calculated at sea level decreases with the increase in the sea floor spreading velocity

tectonic rotations in extensional regimes and their paleomagnetic consequences for oceanic basalts paleomagnetic samples of many deep sea drilling project dsdp basalts have shallower inclinations than would be inferred from the paleolatitude at which the basalts were extruded at mid ocean ridges rather than arising from peculiarities of the geomagnetic field the anomalous magnetic directions may result from tectonic rotations along the listric normal faults which often characterize extensional tectonic regimes several lines of evidence support this conclusion observations of the basin and range province an extensional tectonic regime occurring in continental crust observations of the troodos complex cyprus an oceanic extensional tectonic regime now exposed on land and analysis of possible fault patterns associated with the magma chambers postulated to occur at some mid oceanic ridges the tectonic rotations resulting from movement along the listric normal faults occur about a horizontal axis generally perpendicular to the extension direction and typically amount to 30 to 50 although rotations as large as 70 to 90 are not uncommon the paleomagnetic consequences of these rotations can be calculated for dsdp basalts if the original strike and latitude of a ridge are known at four dsdp sites for which adequate data are available namely sites 319 332 410 and 417 rotations ranging from 50 to 70 are required to explain the paleomagnetic results if the original strike and location of the ridge are not known as is the case for most of the older parts of the pacific ocean the paleomagnetic data and the inferred rotation determine a relationship between possible ridge strikes and locations this information combined with a similar but independent relationship derived from the marine magnetic anomalies puts severe constraints on the original strike and location of the ridge

subtidal sea level and current variations in the northern reach of san francisco bay abstract analyses of sea level and current meter data using digital filters and a variety of statistical methods show a variety of phenomena related to non local coastal forcing and local tidal forcing in the northern reach of san francisco bay a partially mixed estuary low frequency variations in sea level are dominated by non local variations in coastal sea level and also show a smaller influence from tidally induced fortnightly sea level variations low frequency currents demonstrate a gravitational circulation which is modified by changes in tidal current speed over the spring neap tidal cycle transients in gravitational circulation induce internal oscillations with periods of two to four days

band limited global scalar magnetic anomaly map of the earth derived from magsat data the magnetometer satellite magsat data are separated into two distinct sets the dawn and the dusk sets the two sets are analyzed independently because of the dawn dusk asymmetry of the external magnetic field components of the data two scalar magnetic anomaly maps the dawn and the dusk maps are derived using the spherical harmonic expressions of the respective data set the significant correlation of the two maps in the harmonic range of 18 41 indicates the repeatability of the magsat data in these harmonics the shortest repeatable wavelength is about 920 km a band limited global scalar magnetic anomaly map is derived at about 410 km altitude by arithmetic averaging of the dawn and the dusk maps the map is then downward continued to about 10 km altitude the downward continued magnetic anomalies are relatively more localized the main features of the anomalies are as follows 1 continents have relatively stronger magnetic anomalies than oceans especially the younger oceans 2 many circum pacific subduction zones have magnetic signatures and 3 there is no overall correlation between anomalies and major shields

sand wave migration predictor based on shape information 1 migration of offshore seabed waves which endangers the stability of pipelines and communication cables is hard to measure the migration rates are small compared to the measurement errors here sandwave migration rates are determined from the change in the crest position deduced from long time series of bathymetric echo sounding data the crests are identified as local extremes in a bathymetric profile after low pass filtering this approach is applied to both two dimensional data and to profiles along pipelines a consistent migration rate of several meters per year is found a strong correlation between the sandwave shape and the migration rate is translated in a migration predictor the predictor assumes that the sandwaves migrate in the direction of the steepest slope following a quadratic relation with the asymmetry furthermore it is included that longer waves travel faster but higher waves travel slower the predictor is calibrated against data from nine areas and validated using three additional areas an error analysis using markers shows that the error of the predictor is small compared to the noise in the individual crest position observations

sand waves and sediment transport around the end of a tidal sand bank two detailed surveys have been made of the north western end of the haisborough sand off the norfolk coast using echosounder 3 5 khz reflection profiler and side scan sonar asymmetrical sand waves indicate north westerly sand movement on the southern side and south easterly sand movement on the steeper northern side of the bank secondary superimposed megaripples which are probably better indicators of sediment movement give evidence of a cross bank component between the north westerly and south easterly facing sand waves on the tip of the bank there is a zone of symmetrical sand waves these are usually taken to indicate zero net transport but in this case the oblique orientation of megaripples in their troughs indicates transport parallel to the sand wave crests this suggests the route by which sand travels around the end of the bank to form a roughly closed circulation sediment textural parameters support the notion that sand is winnowed from the foot of the bank on both sides and is transported to the middle with an overall net transport from the south to the north analysis of charts dating back to 1886 shows that the bank is stable within the error limits of position fixing though that could allow more than 0 25 km shift to the north east in 100 years to pass undetected a box model is drawn up for the estimated sediment fluxes around the end of the bank and implications for residence times and circulation rates are drawn from it