burial and degradation of organic carbon in louisiana shelf slope sediments abstract the primary focus of this paper is to better understand carbon burial on the louisiana continental margin using spatial scales that covered various shelf depositional areas far field and near field sediment and organic carbon inputs relative to river mouth proximity and covering a variety of sedimentation rates box cores samples were collected in july 2003 cores were collected along two depositional transects extending westward and southward from the southwest pass sw pass a key difference between the two transects sampled in this study was the greater occurrence of mobile muds derived from spillover from shallower regions along the westward 50 m isobaths the dominant mechanism for mixing in the surface active zone saz on the inner louisiana shelf was due to physical not biological forces burial efficiencies for organic carbon 57 2 91 5 and total nitrogen 44 2 86 9 ranged widely across all shelf stations lower burial efficiencies for bulk organic carbon total nitrogen and pigment biomarkers were associated with mobile muds west of southwest pass chlorophyll a concentrations were significantly higher than pheopigments at depth at the mississippi river and southwest pass stations making up 40 4 and 77 4 of total pigment concentrations in the saz and 46 2 and 63 2 in the accumulation zone az respectively these results are in agreement with earlier plant pigment studies which showed that a large fraction of the phytodetritus delivered to the inner shelf was derived from coastal and river diatoms the amount of lignin preserved with depth decreased with increasing residence time in the saz and diagenetic zone dz along the canyon transect but not along the western transect trends for lignin concentration followed previously identified surface sediment trends indicating overall lower burial of refractory terrestrial material at depth with greater distance offshore

mississippi river subaqueous delta is entering a stage of retrogradation abstract the subaqueous delta of the mississippi river the largest river system in the conterminous u s has entered a stage of retrogradation caused by multiple natural and anthropogenic activities since the 1950s the suspended sediment load of the mississippi river has decreased by 50 due primarily to the construction of 50 000 dams in the mississippi basin the impact of this decreased sediment load has been observed in subaerial environments but the impact on sedimentation and geomorphology of the subaqueous delta front has yet to be examined to identify historic trends in sedimentation patterns we compiled bathymetric datasets including historical charts industry and academic surveys and national oceanic and atmospheric administration hydrographic data collected between 1764 and 2009 the progradation rate measured at the 10 m depth contour of southwest pass which receives 69 of the suspended sediment load reaching head of passes has decreased from 67 m yr between 1874 and 1940 to 26 m yr between 1940 and 1979 with evidence of further deceleration from 1979 to 2009 at south pass and pass a loutre the delta front has entered the destructive phase with the 10 m contour retreating at rates 20 m yr at both passes since 1979 advancement of the delta front also decelerated in deeper water in some areas out to 180 m depth except locally where mudflow lobes are advancing deeper contours show a pattern of decreasing progradation rate between 1874 1940 and 1979 2005 time periods furthermore based on differences measured between available bathymetric datasets the sediment accumulation rate across the delta front decreased by 73 for the same period the retention rate of mississippi river sediment on the delta front ranged from 67 to 81 for the time periods assessed with total sediment load stored on the delta front equal to 317 54 mt yr from 1874 to 1940 145 25 mt yr from 1940 to 1979 and 87 15 mt yr from 1979 to 2005 we document for the first time that the mississippi river delta front has entered a phase of retrogradation which will likely be accelerated by future upstream activities that divert a portion of the sediment load to the upper delta for coastal protection and restoration projects the decline of the subaqueous mississippi river delta has critical implications for biogeochemical cycling subaqueous mass wasting and sediment dispersal to the coastal ocean

mud capped dredge pits an experiment of opportunity for characterizing cohesive sediment transport and slope stability in the northern gulf of mexico abstract mud capped dredge pits mcdps defined as sand borrow sites from paleo river channels with cohesive sediment capped walls are used for northern gulf of mexico ngom coastal restoration projects due to lower cost than more distal restoration resources mcdp evolution including infilling and pit wall slope stability is poorly understood in relation to sandy borrow areas we present and interpret bathymetric data from sandy point mcdp which was constructed in 2012 about 20 km northwest of southwest pass the most active mississippi river distributary in water depths of 11 m repeat bathymetric surveys show the pit is infilling 54 cm or volumetrically 200 000 m3 per year which is on the same order as seasonal scale and an order of magnitude higher than the decadal scale vertical accretion rates observed seaward of southwest pass this infilling rate is higher than predicted based solely on excavated volume when compared with other dredge pits in sandy substrate sediment starved settings mcdp infill is volumetrically dominated by far field here defined as river plume or shelf bed resuspension sediment with only 9 of pit infill from pit wall failure geomorphic comparison of sandy point mcdp walls with southwest pass mudflow gully walls shows that the mcdp is oversteepened relative to natural depression features in this setting the convergence of mcdp and mudflow gully gradients towards a common value 4 5 may represent an angle of repose in lieu of decadal scale forcings findings from this experiment of opportunity show that mcdps 1 are effective sediment traps 2 have steep but relatively laterally stable walls 3 do not represent significant risk to infrastructure in a 3 year time scale and 4 are predicted to infill within about 2 decades provided a proximal sediment source exists

using multi radiotracer techniques to better understand sedimentary dynamics of reworked muds in the changjiang river estuary and inner shelf of east china sea abstract reworked muds including mobile muds resuspended sediments and bio mixed muds are ephemeral layers in the benthic boundary of large river delta front estuaries ldes in this study multiple radiotracers 210pb 137cs 234th 7be 235u 228th 228ra 226ra and 40k were combined to evaluate the sedimentary dynamics of the mud belt on the inner shelf of the east china sea ecs adjacent to the changjiang river estuary we first categorized eight types of typical 210pb profiles in marine sediments and specified which ones could be used as possible evidence of reworked muds the types of 210pb profiles observed in previous studies and this study were then used to examine the depth distribution of reworked mud layers of the benthic boundary of ecs we found that reworked mud depth in the along shore mud belt of the inner shelf of ecs was deeper than those in the outer shelf and slope area reaching up to 150 cm deep in the changjiang river lde and up to 50 cm deep in the zhejiang fujian coast mud area sediment core tracer profiles also showed that the reworked mud layer could be further divided into several sub layers with distinct redox conditions and microbe sulfate reducing bacterial abundance srb abundance intensively fluctuated with changing redox environment and larger abundance values were usually observed in anoxic conditions based on 7be and 234th the top layer ca 2 4 cm thick was the most modern and active zone showing evidence of reworking on seasonal timescales the deeper sections of the reworked mud layer were generally modified over longer timescale years which were examined using the more long lived tracers e g 137cs 228thex and 228ra 226ra ratio we found for the first time in this region that age of the reworked layers was usually much younger than underlying accumulating burial layers we posit that this multi radionuclide approach is critical for evaluating the complex biogeochemical sediment record on delta front estuaries of large rivers subject to changing climate conditions and human impacts over the last several centuries

the missing silica sink revisiting the marine sedimentary si cycle using cosmogenic 32si burial of biogenic silica bsitotal in high sedimentation rate continental margins remains highly uncertain cosmogenic 32si t1 2 140 years can be used to trace the fates of bsitotal postdeposition including as opal bsiopal and diagenetically altered opal bsialtered the latter dominantly authigenic clay bsiclay to determine the magnitude and form of bsitotal storage in coastal sediments conventional operational leaches targeting bsiopal and bsialtered including bsiclay were modified for large scale samples necessary for measurement of 32si the 32si activity was used to estimate total biogenic silica burial bsitotal bsiopal bsialtered in several depositional settings gulf of papua gulf of mexico long island sound and in the previously studied amazon guianas deltaic system in subtropical and temperate regions 32si was detected in both traditional biogenic silica leaches bsiopal and residual authigenic clays traditional bsiopal and modified operational leaches designed to target the most reactive authigenic silicates bsialtered consistently underestimate authigenic clay formation bsiclay and thus the magnitude of bsitotal burial in temperate coastal zones and subtropical deltas by 2 4 fold in tropical deltas 32si activities in the residual fraction after removal of bsiopal demonstrate rapid and almost complete alteration of initial bsiopal to new forms most likely bsiclay globally 4 5 4 9 tmol yr si may be trapped in marine nearshore deposits as rapidly formed clay bsiclay 100 of the missing silica sink in the marine silica budget

biotic and geochemical δ 18 o δ 13 c mg ca ba ca responses of globigerinoides ruber morphotypes to upper water column variations during the last deglaciation gulf of mexico abstract within the gulf of mexico gom the bryant canyon is exceptional in that rapid sedimentation sustained by high rates of terrigenous sediment delivery and surface marine productivity make this basin an excellent recorder of paleoenvironmental and paleoclimatic conditions we present a new 21 kyr record of sea surface temperature sst and local salinity changes from the nw gom core jpc 26 approximated from combined globigerinoides ruber morphotype specific 18 o and mg ca as well as ba ca which reflect the subtropical gom hydrographic dynamics and their relationship to both mississippi river discharges and climate evolution during the last deglaciation overall the reconstructed sst and sss related patterns reveal notable variations in amplitude between the analyzed morphotypes adding valuable insights to previously published g ruber w mixed gom records especially during the deglaciation bryant canyon meltwater flooding events bcdfs and associated sea surface freshening seem to be more pronounced than the sst reduction our mg ca derived sst records of both morphotypes g ruber sensu stricto s s and g ruber sensu lato s l show comparable general trends but with important sst differences t we interpret down core t as a record of changing upper water column hydrography with particular influence from the deglacial meltwater bcdfs or holocene bchfs flooding events during the warm intervals the deeper thicker and probably more seasonally persistent mixed layer led to more uniform thermal conditions for both g ruber morphotypes and therefore to a minimum t on the contrary during the cold and low salinity periods the shallower mixed layer favored more habitat divergence and caused a maximum thermal gradient in the well stratified upper water column overall this supports the notion that g ruber s s is consistently calcifying in warmer waters than g ruber s l either due to a shallower depth habitat or to a more summer weighted seasonal distribution moreover intra specific paired 13 c and ba ca differences show that g ruber s l is more sensitive to river water influence than g ruber s s due to its ability to change its depth habitat and therefore exploit optimal temperature salinity productivity stratification conditions during the low salinity events overall our observations support the current practice of treating the two g ruber morphotypes separately and further illustrate the necessity to map both their spatial and temporal distribution

the last 1000 years of natural and anthropogenic low oxygen bottom water on the louisiana shelf gulf of mexico abstract the relative abundance of three species of low oxygen tolerant benthic foraminifers the peb index in foraminiferal assemblages from sediment cores is used to trace the history of low oxygen bottom water conditions on the louisiana shelf analyses of a network of box cores indicate that the modern zone of chronic seasonal hypoxia off the mississippi delta began to develop around 1920 and was well established by 1960 the pattern of development over the last century is consistent with the interpretation that the formation of modern chronic hypoxia is related to anthropogenic activities resulting in increased transport of nutrients to the louisiana shelf the peb index in two gravity and box core pairs mrd05 4 and 05 6 indicates that low oxygen bottom water events have occurred periodically on the louisiana shelf for at least the last 1000 14 c years the pre 1900 low oxygen bottom water events are likely caused by intervals of increased mississippi river discharge and widespread wetland export the peb record in gravity cores indicates that the pre 1900 low oxygen bottom water events were not as well developed or as geographically extensive as the modern hypoxia zone we conclude that the development of low oxygen bottom water on the louisiana shelf is a natural process that has been negatively modified by human activities in the last 100 years

morphological analysis of the lake lahontan shoreline and beachfront fault scarps pershing county nevada abstract with the diffusion equation representation of landform evolution providing reference calculations quantitative comparisons between profiles of the high stand of lake lahontan presented here and profiles of the lake bonneville shoreline scarps analyzed elsewhere reveal that the two sets of scarps are nearly identical morphologically when care is exercised in the selection of profiles the lahontan high stand scarps are remarkably reproducible from one profile to the next highly suggestive evidence that the processes that have shaped and changed the shape of these landforms are correspondingly regular slope angle differences of only 2 are both discernible and interpretable features of these late quaternary landforms cut in weakly consolidated alluvium at a level of uncertainty of no more than 50 per cent the mass diffusivity of the lahontan high stand is the same as the lake bonneville shoreline 1 1 gkg 1 gkg 1 m 2 ka this result suggests that much can be learned about the ages of late quaternary fault scarps cut in weakly consolidated alluvium throughout the basin and range province from their morphology alone the beachfront fault scarps themselves truncated by lake lahontan in our study area are morphologically only slightly older 15 to 18 ka bp than the lahontan high stand 12 ka bp

234th 238u disequilibria within the california current1 profiles of dissolved and particulate sup 234 th were determined at several stations within the california current modeling of the disequilibria between the sup 234 th and sup 238 u within the surface waters provides for estimates of the residence time of dissolved thorium with respect to particle scavenging the particle residence time and the particulate sup 234 th flux exiting the surface layer the model derived first order scavenging rate constant for dissolved thorium is observed to be proportional to the rate of primary production particle residence times seem to be governed by the rate of zooplankton grazing and the types of zooplankton present model derived particulate sup 234 th fluxes are in good agreement with direct measurements by sediment traps

fluvial terrace riser degradation and determination of slip rates on strike slip faults an example from the kunlun fault china 1 the use of displaced fluvial terrace risers to determine slip rates along strike slip faults depends on knowing when risers become passive markers typically chronologic constraints from terrace deposits only place bounds on this age consequent slip rates may be highly uncertain along the kunlun fault in northeastern tibet we demonstrate that consideration of riser degradation can augment terrace chronology and improve the precision of slip rate estimates multiple offset risers and 14c age determinations from terrace treads yield a narrow range of slip rates of 4 5 0 5 m kyr at one site but permit a wide range of allowable rates 3 10 m kyr in an adjacent drainage using a locally calibrated sediment transport rate of 3 2 5 4 m2 ka we show that riser morphology at this latter site is consistent with degradation since abandonment of the upper terrace tread our analysis indicates that slip rates at this site are 5 2 m kyr

source mechanism of volcanic tremor low frequency 10 hz volcanic earthquakes originate at a wide range of depths and occur before during and after magmatic eruptions the characteristics of these earthquakes suggest that they are not typical tectonic events physically analogous processes occur in hydraulic fracturing of rock formations low frequency icequakes in temperate glaciers and autoresonance in hydroelectric power stations we propose that unsteady fluid flow in volcanic conduits is the common source mechanism of low frequency volcanic earthquakes tremor the fluid dynamic source mechanism explains low frequency earthquakes of arbitrary duration magnitude and depth of origin as unsteady flow is independent of physical properties of the fluid and conduit fluid transients occur in both low viscosity gases and high viscosity liquids a fluid transient analysis can be formulated as generally as is warranted by knowledge of the composition and physical properties of the fluid material properties geometry and roughness of the conduit and boundary conditions to demonstrate the analytical potential of the fluid dynamic theory we consider a single phase fluid a melt of mount hood andesite at 1250 c in which significant pressure and velocity variations occur only in the longitudinal direction further simplification of the conservation of mass and momentum equations presents an eigenvalue problem that is solved to determine the natural frequencies and associated damping of flow and pressure oscillations for a simple constant pressure reservoir conduit orifice fluid system a change in orifice size can cause the source signal duration due to a single disturbance to change from several seconds to in excess of an hour fluid kinematic viscosity 0 412 m2 s is both included and neglected in the analysis to illustrate its effect upon system damping tremor magnitude is related to the magnitude of the conduit wall motion occurring in response to oscillating fluid pressures the entire volcanic fluid system does not generally experience a transient flow condition at a given time closed end and constant pressure fluid system boundaries reflect pressure waves and isolate components of the fluid system total fluid movement may not be accurately monitored by tremor data alone since steady state and slowly changing flows are aseismic

historical changes in terrestrially derived organic carbon inputs to louisiana continental margin sediments over the past 150 years 1 major rivers and associated deltaic environments provide the dominant pathway for the input of terrestrial derived organic carbon in sediments toct to the ocean natural watershed processes and land use changes are important in dictating the amount and character of carbon being buried on continental margins seven core sites were occupied on the louisiana continental margin aboard the r v pelican in july 2003 along two major sediment transport pathways south and west of the mississippi river mouth lignin profiles in these age dated cores 210pb geochronology indicate artificial reservoir retention as a primary control on organic carbon quantity and quality reaching the margin post 1950 whereas pre 1950 sediments may reflect soil erosion due to land clearing and farming practices lignin 8 concentrations range 0 2 to 1 7 also indicate that toct delivery rates decay processes have probably remained relatively consistent from proximal to distal stations along transects the down core profile at the canyon station seems to be temporally linked and connected to inner shelf deposition suggestive of rapid cross shelf transport sources of terrestrially derived organic carbon were reflective of mixed angiosperms over the last 150 years in cores west and south of the mississippi river delta the lignin phenol vegetation index lpvi range 130 0 to 510 proved to be a sensitive indicator of source changes in these sediments and eliminated some of the variability compared to c v range 0 01 to 0 4 and s v range 0 9 to 2 1 ratios stochastic events such as hurricanes and large river floods have a measurable albeit ephemeral effect on the shelf toct record burial of toct on the river dominated louisiana continental margin is largely driven by anthropogenic land use alterations in the last 150 years land use changes in the mississippi river basin and river damming have likely affected carbon cycling and toct burial on the louisiana continental margin over a large spatial extent as observed by similar trends in cores from across and along the margin

enhanced short term sediment deposition within the nazare canyon north east atlantic abstract in january and may 1999 interface sediments were sampled within the nazare canyon a large submarine canyon that deeply indents the western iberian continental margin ne atlantic at around 39 35n excess 234th profiles were established with high resolution to calculate inventories and bioturbation coefficients a northern transect at 42 n is briefly presented as a reference for the western iberian margin synthesis of these parameters is used to examine short term deposition within the nazare canyon 234thxs was always detected with significant activities on surface in most of the samples along the reference transect and in the adjacent area surface 234th excesses are about 10 20 dpm g 1 in contrast 234thxs reaches very high levels up to 170 dpm g 1 in the canyon there is a large range of variability in inventories and bioturbation rates in relation with depth and location these results show a preferential deposition in the canyon and focus in the upper and middle part of the canyon on a monthly time scale the nazare canyon appears as a significant locus of sedimentation for the western iberian margin

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

modification of wave cut and faulting controlled landforms from a casual observation that the form of degraded fault scarps resembles the error function this investigation proceeds through an elementary diffusion equation representation of landform evolution to the application of the resulting equations to the modern topography of scarplike landforms the morphologic observations can be analyzed either in the form of one or more cross strike elevation profiles or in the form of the slope offset plot a point plot of maximum scarp slope versus scarp offset working with either or both of these data representations for nine geologic structures which range in age from 3 to 400 ka b p and in offset from 1 to 50 m we apply analytical solutions for the vertical initial value scarp the vertical continuous offset scarp and the finite slope initial value scarp the model calculations are intrinsically ambiguous yielding as the final answer only the product t in the case of the initial value problem or the product a 1 in the case of the repeated faulting problem here t is the age of a single scarp forming event 2a is the vertical slip rate and is the mass diffusivity a single profile across three sea cliffs along the santa cruz california coast is analyzed as three separate initial value problems a reasonably constrained age for the sea cliff standing above the highway 1 platform returns 11 gkg 1 gkg 1 m2 ka with this we can date the two older sea cliffs in fact we do the converse age estimates for these two older sea cliffs based on a uniform rate of uplift both yield the same as for the lower sea cliff we treat a single profile of the raymond fault in pasadena san marino in terms of the repeated faulting problem for it the uplift rate of r crook and others yields 16 gkg the very substantial preexisting offset across the raymond fault must have been buried leveled some 230 ka b p when the modern topography began to form our analysis of the lake bonneville shoreline scarps reveals a dependence of t on 2a suggestive of nonlinear modification processes this appearance is treated with the finite slope initial value scarp model to determine 1 1 gkg for the lake bonneville shoreline scarps the suggestion of m n machette that approximately 100 000 year old meter high scarps are unobservable in weakly consolidated alluvial terranes of the basin and range and rio grande rift valley provinces can be formulated as 1 gkg the coincidence between this inequality and the lake bonneville shoreline is striking and it suggests that the value of 1 gkg may be generally applicable as a good first approximation to the modification of alluvial terranes within the semiarid regions of the western united states the lake bonneville shoreline is the basis for dating four sets of fault scarps in west central utah the drum mountains fault scarps can be modeled in several different circumstances but the most likely interpretation is that these fault scarps formed as the result of a single episode of normal faulting 3 6 to 5 7 ka b p the younger age is associated with quite low initial slope angles 25 the other three sets of fault scarps show no evidence for finite initial value slopes fault scarps along the eastern base of the fish springs range are very young 3 ka b p we estimate the age of fault scarps along the western flank of the oquirrh mountains to be 32 ka b p which meets the weak geologic constraint that they be older than the lake bonneville shoreline fault scarps along the northeastern margin of the sheeprock mountains are even older 53 ka b p an intriguing consequence of our single event analysis of these scarps is that an 11 5 m offset occurred in a single earthquake

reinterpretation of the exposed record of the last two cycles of lake bonneville western united states a substantially modified history of the last two cycles of lake bonneville is proposed the bonneville lake cycle began prior to 26 000 yr b p the lake reached the bonneville shoreline about 16 000 yr b p poor dating control limits our knowledge of the timing of subsequent events lake level was maintained at the bonneville shoreline until about 15 000 yr b p or somewhat later when catastrophic downcutting of the outlet caused a rapid drop of 100 m the provo shoreline was formed as rates of isostatic uplift due to this unloading slowed by 13 000 yr b p the lake had fallen below the provo level and reached one close to that of great salt lake by 11 000 yr b p deposits of the little valley lake cycle are identified by their position below a marked unconformity and by amino acid ratios of their fossil gastropods the maximum level of the little valley lake was well below the bonneville shoreline based on degree of soil development and other evidence the little valley lake cycle may be equivalent in age to marine oxygenisotope stage 6 the proposed lake history has climatic implications for the region first because the fluctuations of lake bonneville and lake lahontan during the last cycle of each were apparently out of phase there may have been significant local differences in the timing and character of late pleistocene climate changes in the great basin second although the bonneville and little valley lake cycles were broadly synchronous with maximum episodes of glaciation environmental conditions necessary to generate large lakes did not exist during early wisconsin time

the use of234th 238 disequilibrium to examine the fate of particle reactive species on the yangtze continental shelf measurements of234th t1 2 24 1d in water column and seabed samples from an area near the mouth of the yangtze river people s republic of china provide the following information 1 most of the234th in waters near the mouth of the yangtze river is in particulate form and horizontal transport and sedimentation of234th bearing particles dominate the234th budget in this area a model incorporating processes in at least two dimensions is required to understand the fate of particle reactive species on the yangtze continental shelf 2 the residence times of particle reactive species with respect to scavenging range from 0 3 days nearshore to 4 0 days offshore the residence times with respect to removal to the seabed range from 0 5 day nearshore to 11 0 days offshore 3 scavenging residence times for234th decrease as the concentration of suspended particles increases the time for removal of234th to the seabed increases with distance from shore a variable which integrates such factors as scavenging rate bathymetry and frequency of resuspension

sulfur and iron diagenesis in temperate unsteady sediments of the east china sea inner shelf and a comparison with tropical mobile mud belts mmbs redox cycling of iron fe and sulfur s exerts profound influences on fates of numerous elements in coastal marine sediments in this study s and fe cycling and its geochemical expressions in the east china sea ecs inner shelf a representative of temperate mobile mud belts mmbs were characterized and compared with tropical counterparts the amazon shelf and the gulf of papua fe and s speciation consistently points to the dominance of authigenic nonsulfidized fe ii phases i e poorly crystalline clays pccs and carbonates and the prevalence of fe redox cycling in the suboxic or weakly sulfidic regimes of the ecs mmbs high contents of authigenic magnetite may be a common diagenetic expression in all mmbs compared to the tropical mmbs three main differences of diagenetic expressions in the ecs mmbs are i light 34spyrite in the ecs mmb vs characteristically heavy 34spyrite in the amazon shelf mmbs ii lower total reactive fe fetr total diagenetic fe ii and ratio of fetr to total fe in the ecs mmbs iii fe ii carbonates and pccs are equally important sinks for nonsulfidized fe ii in the ecs mmbs whereas pccs are the predominant sink in the tropical counterparts these differences are ascribable to factors including low degradability of organic matter small diffusion scales less intense chemical weathering in the drainage basin and or weaker reverse weathering in the ecs mmbs despite the differences above fe and s diagenetic expressions that characterize the prevalence of fe redox cycling in the unsteady suboxic regimes are shared by the ecs and tropical mmbs

geochemistry and deposition of 7be in river estuarine and coastal waters the atmospheric flux of cosmogenic 7be 53 3 day half life and the mode of 7be deposition in river estuarine and coastal environments have been examined the atmospheric flux of 7be commonly supports inventories ranging from 1 0 to 2 0 pci cm2 1 pci 0 037 bq beryllium 7 concentrations in water phase samples collected across salinity gradients in several estuaries along the eastern coastline of the united states range from 0 03 to 0 53 pci l and primarily reflect variations in 7be supply and sorption kinetics the major process controlling the concentration of 7be on estuarine suspended particles appears to be the length of time that these particles remain in the water column field particle to water distribution coefficients for 7be have a median value of about 4 104 but range over an order of magnitude reflecting short term variations in 7be input particle dynamics and particulate iron content rather than equilibrium sorption desorption responses to changes in water salinity or particle type residence times of 7be in the water column range from a few days in estuarine areas of rapid fine particle deposition to several weeks in high energy environments where pronounced sediment resuspension reintroduces deposited 7be back into the water column inventories of 7be in sediments range from nondetectable to 3 3 pci cm2 with the highest inventories in areas where fine particles are accumulating rapidly such sites are also major repositories for other particle reactive substances a 7be budget for the james estuary indicates that less than 5 of the expected 7be input is in the water column and that the short term estuarine trapping efficiency for atmospherically derived 7be is somewhere between 50 and 100

centers of organic carbon burial and oxidation at the land ocean interface abstract continental margin systems collectively receive and store vast amounts of organic carbon oc derived from primary productivity both on land and in the ocean thereby playing a central role in the global carbon cycle the land ocean interface is however extremely heterogeneous in terms of terrigenous input marine primary productivity sediment transport processes and depositional conditions e g such as bottom water oxygen level continental margins are also highly dynamic with processes occurring over a broad range of spatial and temporal scales the rates of oc burial and oxidation are consequently variable over both space and time hindering our ability to derive a global picture of oc cycling at the land ocean interface here we review the processes controlling the fate of organic matter in continental margin sediments with a special emphasis on hot spots and hot moments of oc burial and oxidation we present a compilation of compositional data from a set of illustrative settings including fjords small mountainous river margins large deltaic systems and upwelling areas bulk oc stable isotope and radiocarbon compositions reveal the diversity and complexity characteristic of oc buried in marginal seas this primarily relates to differences in marine and terrestrial inputs the composition of the terrestrial component e g vascular plant oc soil and petrogenic oc inputs and processes modulating the fate of oc within the marine environment e g priming this widely contrasting behavior of oc among these systems illustrates that the reactivity of oc is a product of its chemical composition and regional conditions interpreted in the context of bulk compositional data as well as that obtained on specific molecular markers e g lignin derived phenols the possibility exists to tease apart complex mixtures of terrestrial and marine inputs and to shed light on the role of the myriad of depositional and post depositional processes finally we discuss a set of hot topics that warrant further investigation such as the role of photochemistry fungi halogenation and reactive iron in dictating the fate of oc in the changing coastal ocean

post glacial sediment load and subsidence in coastal louisiana 1 sea level rise in the gulf of mexico has occurred at a rate of 1 8 2 2 mm yr during the 20th century or nearly the same as observed globally due to combined steric and water mass changes tide gauges in coastal louisiana however record a substantially larger rate of rise and while a number of causal mechanisms may be responsible their specific contribution is poorly understood using a realistic viscoelastic earth model detailed geologic parameters for south louisiana and new gps data we demonstrate that holocene sedimentary loading in the gulf and mississippi river delta is capable of contributing to 1 8 mm yr of subsidence over areas of 30 0 75 103 km2

morphological evolution of a mud capped dredge pit on the louisiana shelf nonlinear infilling and continuing consolidation abstract buried sandy paleo river channels on the continental shelf can be accessed through dredging for the restoration of beaches and barrier islands which are under the threat of land loss and rising sea levels however our knowledge on post dredging evolution of paleo river channels is still very limited in this study we focus on infilling rate sediment acoustic characteristics slope change and surficial morphology all of which have implications for the management of seafloor oil and gas infrastructure bathymetric data collected during nine bathymetric surveys over 13 years were used to study the long term changes of the peveto channel dredge pit which is 5 km offshore of holly beach in western louisiana usa this pit was constructed in 2003 and was completely infilled in or before 2016 initial pit infilling rates began at 214 cm year from 2003 to 2004 and then rapidly decreased to an average rate of only 33 cm year from 2006 to 2016 this corresponds volumetrically to 418 753 and 80 816 m3 year for the same intervals pit wall margins displayed small lateral migration moving

an anomaly of elf band vertical magnetic flux as a precursor of dome formation at unzen volcano and its model analysis abstract a peculiar environmental vertical magnetic flux anomaly was observed at the frequency of 223 hz which was 40 and 75 days before the 10th and 11th dome formations on unzen volcano the small but clear anomaly of order of 0 5 pt hz had appeared just on the vertical magnetic flux and never on the horizontal ones and showed in many cases an intermittent oscillations of about a half to 1 min period with almost the same size amplitudes in this paper we show a possibility that the vertical anomaly corresponds to the electromagnetic phenomena when magma passes the upper layer of aquifer under a volcano and give a simplified model which represents the phenomena and mechanism of generating the anomalous vertical magnetic flux the anomaly lasted from the end of 1992 to september 10 1994 after the termination of the appearance the unzen volcano weakened the activity and no events have been reported since then

periodic magma movement in the conduit with a barrier a model for the volcanic tremor we present a one dimensional flow model in which compressible viscous fluid runs through the dike like conduit with a barrier the barrier is assumed to open or close above or under a certain threshold pressure respectively constant flow rate at one end and a constant pressure at the other end are set as boundary conditions which mimicks the fluid flow from a reservoir to an open space the behaviour of the system depends on various parameters such as viscosity flow rate and threshold pressure for a set of parameters plausible for the magma flow in cracks the system oscillates periodically even in the existence of viscous damping spectra of the far field displacement excited by the stress due to this oscillation show a prominent frequency peak in each case the time interval during which the barrier is kept open we call the open period becomes longer as the flow rate increases this results in the elongation of peak period expected in the spectra of far field displacement the length of the open period is affected by both the flow rate and the interference of the pressure waves in the conduit generated by the previous opening closure of the barrier this model may have an important implication for volcanic tremors whose dominant frequency and continuation time change temporarily

an evaluation of mobile mud dynamics in the mississippi river deltaic region abstract large rivers are the primary interface between terrestrial and ocean environments a relatively small number of rivers account for a disproportionate amount of the freshwater and suspended materials that are delivered to the coastal ocean sediment delivery to these coastal systems plays a key role in the global carbon cycle since deltas and continental shelves are considered to be the main repositories of organic carbon in marine sediments particulate material in these environments are typically deposited and resuspended several times before permanent accumulation or transport off the shelf this sediment cycling is an important component influencing biogeochemical processes that occur in coastal environments during two cruises in april and october 2000 on the shelf adjacent to the mississippi river water and sediment samples were collected for analysis of suspended solids and particle reactive radionuclides 210 pb 137 cs 7 be and 234 th to evaluate the transport and fate of terrestrial and marine material a comparison of the distribution of these tracers provides insight about the pathways and residence times of particulate materials on the shelf inventories of these short lived radiotracers showed variations of more than two orders of magnitude indicating dramatic variations in sediment deposition between sampling events short lived radiotracers indicate that river borne materials are transported less than 30 km from the river mouth before initial deposition however seasonal variations in 7 be and 137 cs indicate significant remobilization of sediment and potential export of sediment out of the study area during the high energy e g wind wave winter months in addition depth profiles of 7 be and excess 234 th indicate sediment deposition rates between 0 8 and 3 9 cm month 1 0 4 2 1 g cm 2 month 1 at two shelf locations near river and open shelf environments these rates are much greater than those observed on decadal time scales 1 3 2 0 cm year 1 or 0 6 1 5 g cm 2 year 1 via 210 pb at the same sites this further substantiates active sediment reworking and potential export off the shelf as has been observed in other river dominated ocean margins

rapid response of the changjiang yangtze river and east china sea source to sink conveying system to human induced catchment perturbations abstract in order to investigate human impact in the changjiang east china sea source to sink conveying system we analyze the siltation and erosion state of the estuary shelf deposition systems and discuss the response intensity and timing of the depositional system of the changjiang subaqueous delta and the related changjiang distal mud results show that after the three gorges dam was put into operation in 2003 the abrupt reduction of the sediment discharge to the estuary disturbed the equilibrium between the estuary coast shelf deposition systems modifying the siltation erosion balance and seabed sediment types from the changjiang subaqueous delta to its distal mud areas the degree of response to catchment changes diminishes with a larger response lag from north to south of the distal muds influenced by dam emplacements the change of the changjiang east china sea source to sink conveying system can be divided into three stages i e pre 1950 1950 2002 and post 2003 before 1950 the source to sink system remained relatively stable between 1950 and 2002 man made fluvial impoundments created an important sink for terrigenous sediment of the upstream regions but without profound system changes in contrast after 2003 the morphodynamic patterns for the entire mid lower reaches of the changjiang river the subaqueous delta and the distal muds shifted rapidly from siltation to erosion within a short period of time furthermore the upper reaches of the river became disconnected from the source to sink conveying system and the mid lower reaches of the river together with its subaqueous delta and northern distal mud area were converted into net sediment sources as such the sink area has shrunk while the source area expanded for the changjiang east china sea source to sink conveying system

mass wasting on the mississippi river subaqueous delta abstract the mississippi river delta front mrdf is an excellent natural laboratory for studying seafloor instability and evaluating the preconditioning factors and triggering mechanisms that lead to seafloor failures the occurrence of seafloor landslides on the mrdf has been recognized since the 1950s but the bulk of research on the topic was conducted in the 1970s 80s after seafloor landslides triggered by hurricane camille damaged offshore infrastructure through these efforts it was recognized that seafloor instability features are present across the entire delta front that rapid sediment delivery from the mississippi river is a primary preconditioning factor for failures and that cyclic loading from hurricane waves is the main triggering mechanism for deep seated catastrophic events however mounting evidence shows that mrdf seafloor motion occurs even during periods of no hurricane activity which could be attributed to creep like motion of underconsolidated sediment or smaller episodic flows triggered by winter storms or mississippi river floods given the extensive spatial distribution of instabilities on the mrdf the multiple mechanisms of failure and variety of resulting morphology and the range of potential triggering mechanisms with short recurrence the mrdf is an exceptional location to assess the complex problem of seafloor landslides an improved understanding of seafloor landslides is crucial for understanding global sediment budgets and associated biogeochemical cycling as they can evacuate large volumes of sediment into deep water over short time periods additionally seafloor landslides pose a hazard to offshore infrastructure and to coastal communities through possible tsunami inundation and advancing research on preconditioning factors and triggering mechanisms would improve hazard assessments this paper presents a review and synthesis of geological and geotechnical research on the mrdf particularly with respect to seafloor landslides their occurrence geological and geotechnical controls triggering mechanisms and knowledge gaps related thereto this synthesis is conducted at times of rapidly developing technologies for studying seafloor instability and as the mrdf enters a stage of degradation characterized by reduced sediment delivery and accumulation

distribution of fluid muds on the amazon continental shelf abstract a comprehensive study of suspended sediment transport on the amazon shelf was conducted as part of the amasseds project a multidisciplinary amazon shelf sediment study to understand the link between physical processes and the fate of amazon river sediment a small instrumented tripod was used to measure the fluid flow and suspended sediment characteristics throughout the water column on varying time scales e g semidiurnal fortnightly seasonal dense nearbed suspensions or fluid muds suspended sediment concentration 10 g l on the order of a few meters in thickness were found on the inner and middle shelf covering an area ranging from 5 700 km2 during falling and low river discharge to 10 000 km2 during rising and high discharge fluid muds generally observed in the region of bottom salinity fronts extend across the topset beds to the foreset beds during rising and high discharge salinity and temperature anomalies frequently observed in fluid muds imply that often the muds do not result from erosion and resuspension from the seabed but from trapping processes at the bottom salinity front and transport across the shelf the vertical structure of fluid mud varies in space and tune variability close to the river mouth is predominantly fortnightly related to the location and structure of the bottom salinity front on the open shelf the variability appears to be related to seasonal differences in river and sediment discharge and the location of the bottom salinity front the total suspended sediment inventory on the shelf during the season of high discharge is approximately equal to the annual sediment discharge from the river 1 2 109 tons yr and 90 of that inventory is within fluid mud suspended sediment transport on the shelf is dominated by fluid mud

size distributions of coastal ocean suspended particulate inorganic matter amorphous silica and clay minerals and their dynamics particulate inorganic matter pim is a key component in estuarine and coastal systems and plays a critical role in trace metal cycling better understanding of coastal dynamics and biogeochemistry requires improved quantification of pim in terms of its concentration size distribution and mineral species composition the angular pattern of light scattering contains detailed information about the size and composition of particles these volume scattering functions vsfs were measured in mobile bay alabama usa a dynamic pim dominated coastal environment from measured vsfs we determined through inversion the particle size distributions psds of major components of pim amorphous silica and clay minerals an innovation here is the extension of our reported psds significantly into the submicron range the psds of autochthonous amorphous silica exhibit two unique features a peak centered at about 0 8 m between 0 2 and 4 m and a very broad shoulder essentially extending from 4 m to 100 m with an active and steady particle source from blooming diatoms the shapes of amorphous silica psds for sizes 10 m inside the bay likely due to wind induced resuspension of larger frustules that have settled compared to autochthonous amorphous silica the allochthonous clay minerals are denser and exhibit relatively narrower psds with peaks located between 1 and 4 m preferential settling of larger mineral particles as well as the smaller but denser illite component further narrowed the size distributions of clay minerals as they were being transported outside the bay the derived psds also indicated a very dynamic situation in mobile bay relative to the cold weather front that passed through during the experiment with northerly winds of speeds up to 15 m s 1 both amorphous silica and clay minerals showed a dramatic increase in concentration and broadening in size distribution outside the exit of the barrier islands indicative of wind induced resuspension and subsequent advection of particles out of mobile bay while collectively recognized as the pim amorphous silica and clay minerals as shown in this study possess very different size distributions considering how differences in psds and the associated particle areas will effect differences in sorption desorption properties of these components the results also demonstrate the potential of applying vsf inversion in studying biogeochemistry in the estuarine coastal ocean system

seasonal variations in 7be activity in the sediments of cape lookout bight north carolina abstract short term sediment accumulation rates were determined using activity distributions of 7be in the surficial sediments of a station a 1 in cape lookout bight north carolina usa this semienclosed coastal marine basin is characterized by high annual accumulation rates protected from high energy conditions by its geomorphology the relatively quiescent waters of the bight s interior cause it to act as an efficient settling trap for fine grained sediment lack of bioturbation in the surface sediments allowed for variations in depth integrated activity profiles of 7be to be interpreted as short term accumulation events beryllium 7 inventories exhibited seasonal cyclicity with inaxima occurring during spring february through june the inventory of 7be ranged from 5 8 to 32 6 dpm cin 2 and was always well in excess of the atmospherically supported value x 3 8 dpm cm 2 n 15 accumulation rates calculated froin 7be activity profiles indicate that the delivery of particulate matter to the sediments of cape lookout bight is not constant throughout an annual cycle the highest monthly accumulation rates appeared to be associated with north northeast storm activity inputs were generally highest during late winter early spring when storm frequency is greatest short term accumulation rates derived from this study agree with 210pb rates calculated for a ten year period of accumulation the annual sediment accumulation rates for each of the two years over which the study was conducted was found to be 4 8 0 8 g cm 2y 1 and 3 7 1 2g cm 2y 1

seabed erodibility variations on the louisiana continental shelf before and after the 2011 mississippi river flood abstract erodibility is critical to the sediment resuspension process but has not been measured systematically in large river dominated muddy continental shelves before during early summer of 2011 the mississippi river experienced a major flood event this flood provided a unique opportunity to examine how shelf seabed erodibility responded to a large river flood and the ultimate fate of flood deposition is important to geological and biogeochemical processes e g stratal formation carbon sequestration a total of 106 sediment cores were collected on the louisiana shelf during five cruises in 2010 and 2011 and a new dataset was used to evaluate the response of the seabed to the recent conditions the localized flood deposit was mainly within tens of kilometers of river sources and little sediment accumulated on the middle louisiana shelf seabed erodibility was measured using a dual core gust erosion microcosm system the erodibility of sediment collected in april 2011 exceeded that for august 2010 and august 2011 the springtime increase in erodibility seemed to be related to the recent presence of energetic waves that mobilized the seabed erodibility was highest on the inner shelf southwest of atchafalaya bay intermediate on the middle shelf lowest in the mississippi canyon and highly variable on the mississippi subaqueous delta these spatial patterns were influenced by proximity to river sources flood deposit thicknesses intensity of wave driven bed stresses and bioturbation the flood deposit thickness itself however was not sufficient to explain all the spatial variations of erodibility after the peak of the mississippi flood comparing values to published data the depth varying erodibility on the louisiana shelf was close to the low erodibility level for the york river of virginia and similar to the data collected from baltimore harbor in maryland and the main stem of upper chesapeake bay our findings promote understanding of the resuspension of fluffy organic rich layer at the water sediment interface which influences sediment oxygen demand on the louisiana shelf this dataset is also valuable to observational and modeling studies of large river sediment dispersal systems worldwide

concepts of sediment deposition and accumulation applied to the continental shelf near the mouth of the yangtze river a fundamental understanding of how sedimentary strata form requires distinction between deposition and accumulation of particles deposition refers to the temporary emplacement of particles on the seabed accumulation is the net sum of many episodes of sediment deposition and removal the difference between rates of deposition and accumulation affects the ability of an environment to record sedimentary events radionuclide profiles of 234 th and 210 pb within the seabed can be used to determine 100 day deposition rates and 100 yr accumulation rates respectively on the continental shelf near the mouth of the yangtze river short term deposition rates are about 4 4 cm month whereas accumulation rates integrated over a century are an order of magnitude less about 5 4 cm yr

seabed dynamics of the inner amazon continental shelf temporal and spatial variability of surficial strata the continental shelf southeast and northwest of the amazon river mouth is overlain by a sediment layer of about a meter in thickness characterized by 210pb profiles consisting of one or more segments with nearly uniform excess activity uniform 210pb activity profiles in shelf environments commonly are a result of intense biological reworking of sediments however biological activity is minimal in this area hence this surficial layer sl is a result either of physical reworking of the sediments or of rapid possibly episodic deposition of sediment factors controlling the formation of the sl were examined during the amasseds project between august 1989 and october 1991 primarily using 210pb t1 2 22 3 yr activity profiles and x radiography the thickness and character of the sl were assessed at four locations reoccupied during four seasonal periods corresponding to various riverine and oceanographic conditions e g discharge stage wind stress one of these stations was reoccupied during semidiurnal and fortnightly periods additionally replicate sediment cores were obtained at stations in order to assess small scale spatial variability of geochemical and sedimentological characteristics in the seabed the sl thicknesses in replicate sediment cores obtained at each site were found to vary within 5 cm normalized thickness of the sl decreased by an average of 17 cm between august 1989 and february 1990 a period of increasing wind stress during falling to rising river discharge the sl thickness subsequently increased slightly 8 cm from february to may 1990 and increased again 27 cm between may 1990 and october 1991 the maximum sl thicknesses were observed in october a period of low wind stress and minimal river input suggesting that the observed seasonal changes are dictated by oceanographic conditions as well as by sediment discharge variations in sl thickness are reflected by changes in suspended sediment mostly as fluid muds as the highest suspended sediment inventories and most extensive fluid muds are observed during the period when sl thickness is at a minimum although a significant sl was present during all of the sampling periods changes in the character of 210pb profiles at two of the stations suggest that substantial perhaps complete removal and redeposition of the sl occurred some time between february and may preserved strata i e below the sl is characterized by greater evidence of bioturbation and increased sand content but otherwise is similar to that of the sl long term preservation of strata is thought to occur through episodic suspension and redeposition of the sl with net accumulation of decimeter thick hiatus bounded layers

wind and tide induced resuspension of sediment and microphytobenthos from tidal flats in the ems estuary the resuspension of microphytobenthos mainly benthic diatoms and mud 55 pm fraction from tidal flats was studied in the ems estuary netherlands germany of which 50 is covered by intertidal areas mud and microphytobenthos are resuspended simultaneously from the tidal flats in the estuary the concentrations of these parameters in the main channels of the estuary are strongly affected by erosion due to wind induced waves and by settlement during calm weather conditions the resuspension of mud can be described as a linear function of the effective windspeed which is defined as the windspeed averaged over three high water 6 h bracketing high water periods preceding sampling the resuspended fraction of microphytobenthos from the top 0 5 cm layer of sediment can also be described as a linear function of the effective windspeed our data indicate that for this estuary the proper quantification of resuspension of mud and microphytobenthos requires consideration of relatively large areas

evidence of recent flood deposits within a distal shelf depocenter and implications for terrestrial carbon preservation in non deltaic shelf settings abstract extreme episodic events have the capacity to transport large amounts of terrestrial material to the coastal ocean while estuaries and deltas are typically thought to trap most of this material some escapes these coastal features and is transported to distal depocenters along the continental shelf distal shelf depocenters can act as the ultimate sink for event deposits yet event sedimentation and the impact of terrestrial carbon burial within these shelf deposits remains understudied therefore this study investigated event sedimentation within the texas mud blanket tmb a distal shelf depocenter of the brazos river located in the northwestern gulf of mexico using a core that was collected from the tmb during a months long elevated discharge event in late 2015 to early 2016 we applied a multi proxy approach to delineate the event deposit we utilized physical sediment properties fabric texture and bulk density radioisotopes 7be and 210pb and organic geochemical properties 13c c n and lignin phenols to identify a 10 cm event layer at the surface of the core within this 10 cm layer we also distinguished two sub layers associated with separate extreme discharge periods in the winter and spring respectively using these event layer characteristics we identified three other earlier potential event deposits in the core that we have attributed to events in 2010 2007 and 2000 2001 from these results this study has demonstrated that the tmb may be an archive for event deposits over multi decadal time periods in particular the transition from periods of prolonged drought to extreme wetness associated with the brazos river this event dominated sedimentation regime can enhance long term carbon burial potentially increasing current estimates of carbon burial significantly in the tmb and other similar distal shelf depocenters ultimately this study highlights the potential for distal shelf depocenters as organic carbon burial hotspots and postulates that this role may expand in the future as climate change increases the intensity and frequency of extreme events

scarp degraded by linear diffusion inverse solution for age under the assumption that landforms unaffected by drainage channels are degraded according to the linear diffusion equation a procedure is developed to invert a scarp profile to find its diffusion age diffusion age having dimension length 2 is the product of diffusivity times chronological age the second moment of scarp slope grows linearly with age this fact together with an assumption about initial scarp shape allows the inverse determination of diffusion age age found assuming a vertical initial scarp is termed apparent age any nonvertical initial scarp profile has a nonzero initial apparent age true diffusion age differs from apparent age by a fraction of scarp offset squared the inverse procedure applied to synthetic data yields the following rules of thumb evidence of initial scarp shape has been lost when apparent age reaches twice its initial value if a scarp is formed by two events the inversion gives their offset weighted mean age with an error that is a fraction of offset squared a scarp that appears to have been formed by one event may have been formed by two with an interval between them as large as apparent age after scarps of two fault traces have diffused to appear as one the error in inferred age may be as large as half the apparent age variation of apparent age along strike would indicate multiple fault traces the simplicity of scarp profile measurement and this inversion makes profile analysis attractive if linearity of the flow law time for a free face to be reduced to the angle of repose and variation of diffusivity with climate and material could be established profile analysis would become a reliable dating technique

historical reconstruction of organic carbon decay and preservation in sediments on the east china sea shelf 1 sediment cores were collected from the east china sea inner shelf in 2010 to study the decay and preservation of organic carbon oc the highest sediment mass accumulation rate 0 61 0 20 g cm 2 yr 1 derived from 210pb was found near the river mouth and decreased alongshore to the south 0 17 0 004 g cm 2 yr 1 and in an offshore direction 0 31 0 08 g cm 2 yr 1 average total oc content was higher at inner shelf stations 0 52 than those offshore 0 38 the 13c was more depleted at nearshore 23 49 to 21 97 than offshore 22 49 to 21 60 stations principal component analysis indicated that terrestrial oc as indicated by lignin phenols 8 values was preserved in sediment closer to the coast 0 22 0 44 while offshore sediment was more composed of lignin poor 0 12 0 24 degraded oc that was likely hydrodynamically sorted marine derived oc as indicated by plant pigments was significantly more abundant in the sediment mixed layer than the underlying accumulation layer historical flooding events were detected in 8 profiles in two of the six cores located at midshelf stations despite the magnitude of the 2010 flood in east china we did not see any signature of this event with the chemical biomarker in these two cores this may suggest that reduced sediment loading due to recent dam construction may have greatly decoupled river inputs with sediment loading to shelf sediment the total oc standing stock since 1900 was approximately 1 62 1 15 kg c m 2 about one tenth of all the middle and lower lakes in the changjiang catchment basin this work further supports the need for more research to better understand how the reduced inputs of fluvial input of sediments from chinese rivers due to river diversions and dams affect carbon cycling in the east china sea

radiocarbon derived sedimentation rates in the gulf of mexico abstract sedimentation rates were determined for the northern gulf of mexico margin sediments at water depths ranging from 770 to 3560 m using radiocarbon determinations of organic matter resulting sedimentation rates ranged from 3 to 15 cm kyr decreasing with increasing water depth these rates agree with long term sedimentation rates estimated previously using stratigraphic methods and with estimates of sediment delivery rates by the mississippi river to the northern gulf of mexico but are generally higher by 1 2 orders of magnitude than those estimated by 210pbxs methods near surface slope sediments from 2737 m water depth in the mississippi river fan were much older than the rest they had minimum 14c ages of 16 27 kyr and 13c values ranging from 24 to 26 5 indicating a terrestrial origin of organic matter the sediments from this site were thus likely deposited by episodic mass wasting of slope sediment through the canyon delineating the previously suggested main pathway of sediment and clay movement to abyssal gulf sediments

the behavior of particle reactive tracers in a high turbidity environment 234th and 210pb on the amazon continental shelf excess 234th and 210pb seabed inventories were measured in cores collected from the amazon continental shelf to examine particle scavenging and seabed dynamics typical excess 210pb inventories range from 100 to 300 dpm cm 2 and the total excess 210pb inventory for the amazon shelf was determined to be 2 7 1017 dpm the 210pb measurements indicate that particle reactive species are scavenged not only from the amazon river but also from the lateral advection of offshore water in order to sustain the 210pb inventories the volume of water supplied by the lateral advection from offshore must be approximately five to ten times the water discharge of the amazon river this lateral advection supplies about 67 of the total excess 210pb to the amazon continental shelf with relatively small contributions from riverine input 31 atmospheric fallout 2 3 and in situ production 0 1 the 234th inventories were measured on four cruises which occurred during periods of differing river discharge wind stress and flow rates of the north brazil current the 234th excess seabed inventories show large spatial and seasonal variability with a range from 0 to 22 dpm cm 2 ratios of predicted 234th inventories over observed 234th inventories indicate that a large portion of the inventories on the inner and mid shelf occur in the fluid mud layer or the suspended sediments the 234th excess seabed inventories are controlled by resuspension cycling the inventories between the water column and the seabed 210pb and 234th excess seabed inventories are compared directly using corrections for the different time scales and offshore concentrations this approach indicates that for most of the shelf the inventories of the shorter term tracer 234th are less than predicted by the inventories of the longer term tracer 210pb there are two explanations for this trend the first is that a larger portion of the 234th inventory occurs in the fluid muds or the water column relative to 210pb the second is that the supply of offshore water scavenging efficiency and or deposition have been lower over the two year study period relative to the last one hundred years

mobile mud dynamics in the east china sea elucidated using 210pb 137cs 7be and 234th as tracers mobile mud mm which has fine grain size distribution 90 clay silt and 2 5 in south inshore indicates that the sediment focusing resulted in the increased mass flux the residence time of mm is estimated as 3 6 years both by mass balance of mm and 210pbex in mm

lateral offsets and revised dates of large prehistoric earthquakes at pallett creek southern california recent excavation and new radiocarbon dates of sediments at pallett creek are the basis for new conclusions regarding the late holocene history of the san andreas fault systematic dissection of a 50 m long 15 m wide 5 m deep volume of earth centered on the fault enables documentation in three dimensions of fault patterns lateral offsets and vertical deformation associated with large earthquakes of the past the excavations expose evidence for 12 earthquakes that occurred between about 260 and 1857 a d with an average recurrence interval of about 145 years prehistoric slip events that occurred in 1720 50 1550 70 1350 50 1080 65 and 845 75 a d have lateral offsets that are comparable to those of the most recent great earthquake of 1857 thus all of these events represent earthquakes of large magnitude the lateral offsets of two other events in 935 85 and 1015 100 a d are an order of magnitude smaller and may be interpreted in several ways with regard to the size of these events the new data constrain the average recurrence interval for large earthquakes at this site to between 145 and 200 years but suggest a monotonic decrease in individual intervals to below this range during the past 900 years on the basis of these data the probability of a large earthquake with surficial fault rupture at this site is between 0 2 and 5 during 1984 and 7 and 60 by the year 2000