isotopic evidence for the influence of typhoons and submarine canyons on the sourcing and transport behavior of biospheric organic carbon to the deep sea abstract export of biospheric organic carbon from land masses to the ocean plays an important role in regulating the global carbon cycle high relief islands in the western pacific are hotspots for such land to ocean carbon transport due to frequent floods and active tectonics submarine canyon systems serve as a major conduit to convey terrestrial organics into the deep sea particularly during episodic floods though the nature of ephemeral sediment transportation through such canyons remains unclear in this study we deployed a sediment trap in southwestern taiwan s gaoping submarine canyon during summer 2008 during which typhoon kalmaegi impacted the study area we investigated sources of particulate organic carbon and quantified the content of fossil organic carbon oc f and biospheric non fossil carbon ocnf during typhoon and non typhoon periods based on relations between total organic carbon toc isotopic composition 13 c 14c and nitrogen to carbon ratios n c of newly and previously reported source materials during typhoons flooding connected terrestrial rivers to the submarine canyon fresh plant debris was not found in the trap except in the hyperpycnal layer suggesting that only hyperpycnal flow is capable of entraining plant debris while segregation had occurred during non hyperpycnal periods the ocnf components in typhoon flood and trapped samples were likely sourced from aged organics buried in ancient landslides during non typhoon periods the canyon is more connected to the shelf where waves and tides cause reworking thus allowing abiotic and biotic processes to generate isotopically uniform and similarly aged ocnf for transport into the canyon therefore extreme events coupled with the submarine canyon system created an efficient method for deep sea burial of freshly produced organic rich material our results shed light on the ephemeral transport of organics within a submarine canyon system on an active tectonic margin

erosion of modern terrestrial organic matter as a major component of sediments in fjords fjords have recently been recognized as hotspots of carbon burial in this study we investigated organic carbon oc and biomarker radiocarbon values in fjord sediments from new zealand our results showed that oc was mostly modern with the most aged oc in middle reaches of fjords likely related to hydrodynamic sorting and inputs along adjacent slopes radiocarbon ages of sedimentary oc increased from north to south consistent with the fiordland regional gradients of lower fjord slopes and less rainfall our biomarker results suggested that lignin and long chain fatty acids were preferentially linked with fresh terrestrial debris and degraded soil respectively likely due to their chemical and physical properties finally we propose that fjords are a significant sink of modern oc in contrast to large lowland coastal systems as a major sink of pre aged oc overall this study indicated that radiocarbon techniques are critical in investigating carbon dynamics in coastal systems

fluid budgets at convergent plate margins implications for the extent and duration of fault zone dilation faults at convergent plate boundaries are important conduits for fluid escape and recent evidence suggests that fluid expulsion along them is both transient and heterogeneous for the nankai and barbados convergent margins we have used numerical models to investigate the long term partitioning of expelled fluids between diffuse flow and flow along connected high permeability fault conduits for a simple case of spatial heterogeneity we estimated the extent of high permeability conduits necessary to maintain a balance between incoming and expelled fluids for the case of transient expulsion we constrained the duration of elevated permeability required to balance the fluid budgets comparison of modeled and observed geochemical profiles suggests that the initiation of connected flow conduits is delayed with respect to the time of accretion into each accretionary complex and may be related to burial below a critical depth either where the overlying wedge is sufficiently thick to prevent fluid escape to the sea floor or where sediments behave brittlely

provenance and climate change inferred from sr nd pb isotopes of late quaternary sediments in the huanghe yellow river delta china we present a provenance study of core zk2 from the huanghe yellow river delta in order to assess the impacts of climate change on the sediment supplies during the last glacial interglacial cycle facies analysis and sequence stratigraphy methods are used to construct the age model sr isotopic compositions of zk2 range from 0 716389 to 0 723884 with 87sr 86sr increased with decreasing grain size nd and pb isotopic compositions display two large major excursions during marine oxygen isotope stages mis 2 and 4 with less radiogenic end and lower 208pb 204pb 207pb 204pb and 206pb 204pb values during these periods these excursions have been explained in terms of changes in the mixing proportion of sediments from the loess plateau and ordos plateau resulting from east asian monsoon intensity variations the weak summer monsoon precipitation resulted in decreased erosion of loess plateau during mis 2 4 and the middle of mis 3 meanwhile both the intensified east asian winter monsoon and the southward expansions of mu us desert significantly enhanced the eolian sand entering the huanghe therefore our results highlight the impact of monsoon variability on erosion patterns in the huanghe basin

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

sources and radiocarbon ages of organic carbon in different grain size fractions of yellow river transported particles and coastal sediments abstract the elemental toc tn and c n and carbon isotope 14c and 13c compositions of organic matter were measured in different grain size fractions of particles transported by the yellow river and surface sediments in the bohai sea and the yellow sea in the riverine particle and sediment samples high oc contents were associated with small grain size fractions consisting mainly of clay minerals the 13c and 14c values of the bulk riverine particulate organic carbon poc collected from the lijin and xiaolangdi sites were relatively constant but varied significantly 21 9 to 26 0 and 325 to 620 respectively among the different size fractions in comparison large spatial variations in 13c 20 6 to 24 5 and 14c 188 to 646 values which increased seaward due to the difference in source carbon were found for bulk toc 14c preserved in the surface sediments but no significant differences were observed among the values in the different size fractions in most sediments the different carbon isotopic values of the riverine poc and sedimentary toc reflect differences in the sources degradation and cycling time scales of the oc the yellow river exports very old 5220 295 yrs poc that is much older than the toc 2457 676 yrs preserved in the surface sediments in the bohai and yellow seas calculations using a dual isotope three end member model indicate that pre aged soil oc and ancient fossil oc represent major proportions 57 16 and 30 8 respectively of the riverine poc and that terrestrial biomass oc represents a minor proportion 13 11 the drainage environment of the river plays important roles in controlling the sources and ages of the riverine poc in contrast the toc in the grain size fractions of the surface sediments in the bohai and yellow seas is dominated by marine derived modern oc 47 13 followed by pre aged soil oc 29 9 and ancient fossil oc 25 14 the ages of the toc are determined mainly by the source input rapid sedimentation sediment minerology and decomposition of oc during early diagenesis in these large river influenced marginal seas

observational constraints on the fracture energy of subduction zone earthquakes we relate seismologically observable parameters such as radiated energy seismic moment rupture area and rupture speed to the dynamics of faulting to achieve this objective we computed the radiated energy for 23 subduction zone earthquakes recorded between 1992 and 2001 most of these earthquakes have a magnitude m w 7 5 but we also included some smaller m w 6 7 well studied subduction zone earthquakes and six crustal earthquakes we compiled static stress drop estimates for these 29 earthquakes from literature and used a slip weakening model to determine the radiation efficiency of these earthquakes we also determined the rupture speed of these earthquakes from literature from fracture mechanics fracture energy and hence radiation efficiency can be related to the rupture speed the radiation efficiencies estimated from the partitioning of energy as given by the slip weakening model are consistent with the rupture speed estimated for these earthquakes most earthquakes have radiation efficiencies between 0 25 and 1 and are hence efficient in generating seismic waves but tsunami earthquakes and two deep earthquakes the 1994 bolivia and the 1999 russia china border earthquakes have very small radiation efficiencies 0 25 and hence dissipate a large amount of energy during faulting we suggest that differences in the radiation efficiencies of different types of earthquakes could be due to fundamental differences in their rupture mechanics in deep events the energy is probably dissipated in thermal processes in the fault zone while it is possible that the morphology of the trench causes large energy dissipation during the rupture process of tsunami earthquakes

sources of tsunami and tsunamigenic earthquakes in subduction zones we classified tsunamigenic earthquakes in subduction zones into three types earth quakes at the plate interface typical interplate events earthquakes at the outer rise within the subducting slab or overlying crust intraplate events and tsunami earthquakes that generate considerably larger tsunamis than expected from seismic waves the depth range of a typical interplate earthquake source is 10 40km controlled by temperature and other geological parameters the slip distribution varies both with depth and along strike recent examples show very different temporal change of slip distribution in the aleutians and the japan trench the tsunamigenic coseismic slip of the 1957 aleutian earthquake was concentrated on an asperity located in the western half of an aftershock zone 1200km long this asperity ruptured again in the 1986 andreanof islands and 1996 delarof islands earthquakes by contrast the source of the 1994 sanriku oki earthquake corresponds to the low slip region of the previous interplate event the 1968 tokachi oki earthquake tsunamis from intraplate earthquakes within the subducting slab can be at least as large as those from interplate earthquakes tsunami hazard assessments must include such events similarity in macroseismic data from two southern kuril earthquakes illustrates difficulty in distinguishing interplate and slab events on the basis of historical data such as felt reports and tsunami heights most moment release of tsunami earthquakes occurs in a narrow region near the trench and the concentrated slip is responsible for the large tsunami numerical modeling of the 1996 peru earthquake confirms this model which has been proposed for other tsunami earthquakes including 1896 sanriku 1946 aleutian and 1992 nicaragua

recycling of graphite during himalayan erosion a geological stabilization of carbon in the crust at geological time scales the role of continental erosion in the organic carbon oc cycle is determined by the balance between recent oc burial and petrogenic oc oxidation evaluating its net effect on the concentration of carbon dioxide and dioxygen in the atmosphere requires the fate of petrogenic oc to be assessed here we report a multiscale nanometer to micrometer structural characterization of petrogenic oc in the himalayan system we show that graphitic carbon is preserved and buried in marine sediments while the less graphitized forms are oxidized during fluvial transport radiocarbon dating indicates that 30 to 50 of the carbon initially present in the himalayan rocks is conserved during the erosion cycle graphitization during metamorphism thus stabilizes carbon in the crust over geological time scales

surface area control of organic carbon accumulation in continental shelf sediments the relationship between organic carbon oc and grain size found in most continental shelf sediments is here reinterpreted in terms of the surface area of the sediments cores from many north american shelf environments show downcore decreases in oc to similar refractory background concentrations if expressed relative to the surface area of the sediments this consistent concentration is 0 86 mg oc m 2 which is equivalent in concentration to a monolayer of organic matter coating all mineral surfaces a more global collection of sediment water interface samples show that this relationship is even more extensive with exceptions occurring in areas of very high riverine sediment input organic pollution or low oxygen water columns density separations indicate that organic matter is largely adsorbed to mineral grains the microtopography of surfaces was examined with n2 sorption and most surface area was found to be inside pores of 10 nm width these data lead to a hypothesis that organic matter is protected by its location inside pores too small to allow functioning of the hydrolytic enzymes necessary for organic matter decay such protection would likely work in concert with other protection mechanisms such as humification this consistent surface area correlation with oc concentration may explain control of spatial and temporal variations in oc burial rates by sedimentation rates the pore protection hypothesis provides a causal mechanism for this observed control

transport of terrestrial organic carbon to the oceans by rivers re estimating flux and burial rates this study re estimates one important component in the global carbon cycle the modern global fluviatile organic carbon discharge and burial rates according to these results approximately 430 1012 g of terrestrial organic carbon are transported to the ocean in modern times this amount is higher than the latest estimates but takes into account new data from oceania not previously considered in global flux studies however only the minor amount of 10 or approximately 43 1012 gc year 1 is most likely buried in marine sediments this amount is similar to the burial of marine organic carbon in the coastal ocean 55 1012 gc year 1 adding both estimates gives approximately 100 1012 gc year 1 which is the value calculated by berner 1982 for terrestrial deltaic shelf sediments however the results in this study suggest that on a global scale the organic carbon content in coastal ocean sediments is not solely of terrestrial origin but a mixture of nearly equal amounts of marine and terrestrial organic carbon the major part of the terrestrial organic carbon that enters the ocean by rivers approximately 400 1012 gc year 1 seems to be either a remineralised in the ocean whereas the mechanism by which the terrestrial organic carbon is oxidised in the ocean are unknown or b is dispersed throughout the oceans and accumulates in pelagic sediments

on the mechanical role of smectite in subduction zones smectites a group of hydrated phyllosilicate minerals are often a main component of sediments entering a subduction zone they are common in hemipelagic sediments and consist of an authigenetic component that arises from the alteration of volcanic ash intercalated in the sediment and a detrital component smectite rich strata are structurally weak retain water and are highly porous a review of sediment lithology in subduction zones around the world suggests that decollement zones may preferentially form in smectite rich horizons one consequence of this observation is that the assignment of high frictional resistance to materials in a decollement may be unwarranted at deeper structural levels smectite is transformed to illite a mechanically stronger mineral estimates of the depth of this transition coincide with the depth at which earthquakes are first detected along plate interfaces i speculate that the smectite illite transition in subduction zones may be an important component of sediment consolidation processes that trigger interplate seismicity

the rupture process and asperity distribution of three great earthquakes from long period diffracted p waves moment tensor source mechanisms for the largest twenty nine shallow earthquakes from 1981 m s 6 5 have been determined using long period rayleigh wave spectra and p wave first motions recorded by the international deployment of accelerograms ida global digital seismic network gdsn and world wide standardised seismic network wwssn these are compared with the centroid moment tensor mechanisms presented by dziewonski and woodhouse which were obtained in a contrasting manner in most cases the source is well represented by a single double couple mechanisms with good agreement of scalar moment and orientation between the two studies apparent mismatches for other cases may be interpreted in terms of source complexity we emphasise the objectivity of comparing moment tensor elements apparent discrepancies in the moment and orientation of double couple fault plane solutions are usually due to differences in the mxz and myz moment tensor elements which are poorly constrained by long period data

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

glacial interglacial changes in southern africa compound specific δ13c land plant biomarker and pollen records from southeast atlantic continental margin sediments this is part 2 of a study examining southwest african continental margin sediments from nine sites on a north south transect from the congo fan 4 s to the cape basin 30 s representing two glacial mis 2 and 6a and two interglacial stages mis 1 and 5e contents distribution patterns and molecular stable carbon isotope signatures of long chain n alkanes c27 c33 and n alkanols c22 c32 as indicators of land plant vegetation of different biosynthetic types were correlated with concentrations and distributions of pollen taxa in sediments of the same time horizons selected single pollen type data reveal details of vegetation changes but the overall picture is best illustrated by summing pollen known to predominantly derive from c4 plants or c4 plus cam plants the c4 plant signals in the biomarkers are recorded in the 13c data and in the abundances of c31 and c33n alkanes and the c32n alkanol calculated clusters of wind trajectories for austral summer and winter situations for the holocene and the last glacial maximum afford information on the source areas for the lipids and pollen and their transport pathways to the ocean this multidisciplinary approach provides clear evidence of latitudinal differences in leaf wax lipid and pollen composition with the holocene sedimentary data paralleling the current major phytogeographic zonations the northern sites congo fan area and northern angola basin get most of their terrestrial material from the congo basin and the angolan highlands dominated by c3 plants airborne particulates derived from the western and central south african hinterland dominated by deserts semideserts and savannah regions are rich in organic matter from c4 plants as can be expected from the present and glacial positions of the phytogeographic zones the carbon isotopic signatures of n alkanes and n alkanols both become isotopically more enriched in 13c from north to south in the northern part of the transect the relative importance of c4 plant indicators is higher during the glacials than in the interglacials indicating a northward extension of arid zones favoring grass vegetation in the south where grass rich vegetation merges into semidesert and desert the difference in c4 plant indicators is small

a hybrid method for calculating the radiated wave energy of deep earthquakes abstract the energy radiated as waves is a parameter vital to the understanding of earthquake rupture physics calculations of this energy however are difficult and wrought with uncertainty we developed a new hybrid method for the calculation of radiated wave energy and other key seismic parameters the method calculates these parameters in an internally consistent and objective manner allowing for robust comparison between parameters and across earthquakes in addition the method does not require deconvolution or filtering of data thus results contain all recorded high frequencies we use the method to calculate source time functions seismic moment duration and radiated wave energy for 19 recent deep depth 292 km earthquakes ranging in size from m w 6 5 to 8 2 we compute effective seismic efficiency for the three largest events the principle result is that the effective seismic efficiencies are less than 0 3 if earthquake rupture adhered to the orowan model then the average frictional stress during rupture is equal to the final shear stress on the fault plane and the seismic efficiency is 1 but since the measured seismic efficiency is less than 1 the rupture process of these large deep earthquakes partitions more energy into friction and the average frictional stress during rupture is higher than the final fault plane stress

loading and fate of particulate organic carbon from the himalaya to the ganga brahmaputra delta abstract we use the evolution of river sediment characteristics and sedimentary corg from the himalayan range to the delta to study the transport of corg in the ganga brahmaputra system and especially its fate during floodplain transit a detailed characterisation of both mineral and organic particles for a sampling set of river sediments allows taking into account the sediment heterogeneity characteristic of such large rivers we study the relationships between sediment characteristics mineralogy grain size specific area and corg content in order to evaluate the controls on corg loading contributions of c3 and c4 plants are estimated from corg stable isotopic composition 13corg we use the evolution of 13corg values from the himalayan range to the delta in order to study the fate of corg during floodplain transit ganga and brahmaputra sediments define two distinct linear relations with specific area in spite of 4 5 times higher specific area ganga sediments have similar corg content grain size and mineralogy as brahmaputra sediments indicating that specific area does not exert a primary control on corg loading the general correlation between the total corg content and al si ratio indicates that corg loading is mainly related to 1 segregation of organic particles under hydrodynamic forces in the river and 2 the ability of mineral particles to form organo mineral aggregates bed and suspended sediments have distinct 13corg values in bed sediments 13corg values are compatible with a dominant proportion of fossil corg derived from himalayan rocks erosion suspended sediments from himalayan tributaries at the outflow of the range have low 13corg values 24 8 average indicating a dominant proportion of c3 plant inputs in the brahmaputra basin 13corg values of suspended sediments are constant along the river course in the plain on the contrary suspended sediments of the ganga in bangladesh have higher 13corg values 22 4 to 20 0 consistent with a significant contribution of c4 plant derived from the floodplain our data indicate that during the plain transit more than 50 of the recent biogenic corg coming from the himalaya is oxidised and replaced by floodplain corg this renewal process likely occurs during successive deposition erosion cycles and river course avulsions in the plain

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

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

rapid postseismic transients in subduction zones from continuous gps 1 continuous gps time series from three of four recently measured large subduction earthquakes document triggered rapid postseismic fault creep representing an additional moment release upward of 25 over the weeks following their main shocks data from two mw 8 0 and mw 8 4 events constrain the postseismic centroids to lie down dip from the lower limit of coseismic faulting and show that afterslip along the primary coseismic asperities is significantly less important than triggered deep creep time series for another mw 7 7 event show 30 postseismic energy release but here we cannot differentiate between afterslip and triggered deeper creep a fourth mw 8 1 event which occurred in the broad chilean seismogenic zone shows no postseismic deformation despite coseismic offsets in excess of 1 m for the three events which are followed by postseismic deformation stress transferred to the inferred centroids at 34 60 and 36 km depths by their respective main shock asperities increased reverse shear stress by 0 5 0 8 and 0 2 bar with a comparatively small decrease in normal stress 0 01 bar constraining the coulomb stress increase required to force slip along the metastable plate interface deep triggered slip of this nature is invisible without continuous geodesy but on the basis of these earthquakes would appear to constitute an important mode of strain release from beneath the seismogenic zones of convergent margins these events captured by some of the first permanent gps networks show that deep moment release is often modulated by seismogenic rupture updip and underscore the need for continuous geodesy to fully quantify the spectrum of moment release in great earthquakes index terms 7209 seismology earthquake dynamics and mechanics 3040 marine geology and geophysics plate tectonics 8150 8155 8157 8158 8150 tectonophysics plate boundary general 3040 7230 seismology seismicity and seismotectonics keywords subduction zone earthquake postseismic moment release

the potential of leaf wax biomarkers from fluvial soil sediment sequences for paleovegetation reconstructions upper alazani river central southern greater caucasus georgia abstract leaf wax derived long chain n alkanes are increasingly used for paleovegetation reconstructions but have hardly been applied to fluvial sediments so far however such analyses could significantly enhance knowledge of the former vegetation in many regions devoid of non fluvial sediment archives therefore this exemplary study investigates potentials and challenges of n alkane biomarker analyses in a fluvial sediment paleosol sequence fsps along the upper alazani river in the central southern greater caucasus generally fsps contain two different biomarker signals a catchment signal in fluvial sediments and a local in situ signal in intercalated paleosols this allows paleovegetation reconstructions for both catchment area and sampling site however several archive related challenges exist concerning the catchment signal from fluvial sediments i this could be biased by different vegetation zones land use histories in subcatchments ii long term pedogenesis on the slopes or intermediate sediment storage in the catchment could have caused a time lag between biomarker formation and sedimentation iii taphonomic processes could have biased the preserved n alkane pattern iv there could be petrogenically inherited or in river produced n alkanes v the signal could be overprinted by post sedimentary processes concerning the local paleosol signal this could be biased by inherited catchment derived biomarkers or by taphonomic processes these factors are thoroughly discussed for the investigated fsps with respect to paleovegetation patterns our investigations gave the following results i leaf waxes in fluvial sediments deposited prior to around the pleistocene holocene transition and between ca 5 and 1 7 cal ka bp are indicative of more deciduous trees shrubs in the catchment compared with the other periods that were dominated by grasses herbs considering a possible time lag of ca 1 4 ka between biomarker formation and deposition this indicates delayed holocene reforestation in the catchment compared with western and central europe in agreement with regional pollen studies the subsequent decline of deciduous trees shrubs could be linked to human activity in the catchment during the late holocene ii leaf waxes in floodplain paleosols indicate local grass herb dominance throughout the holocene which is possibly caused by long lasting local human activity

soil organic carbon pools in the northern circumpolar permafrost region of all soils in the northern permafrost region is approximately 18 782 10 3 km 2 o r approximately 16 of the global soil area in the northern permafrost region organic soils peatlands and cryoturbated permafrost affected mineral soils have the highest mean soil organic carbon contents 32 2 69 6 kg m 2 here we report a new estimate of the carbon pools in soils of the northern permafrost region including deeper layers and pools not accounted for in previous analyses carbon pools were estimated to be 191 29 pg for the 0 30 cm depth 495 80 pg for the 0 100 cm depth and 1024 00 pg for the 0 300 cm depth our estimate for the first meter of soil alone is about double that reported for this region in previous analyses carbon pools in layers deeper than 300 cm were estimated to be 407 pg in yedoma deposits and 241 pg in deltaic deposits in total the northern permafrost region contains approximately 1672 pg of organic carbon of which approximately 1466 pg or 88 occurs in perennially frozen soils and deposits this 1672 pg of organic carbon would account for approximately 50 of the estimated global belowground organic carbon pool

depth distribution of moment release in underthrusting earthquakes at subduction zones we present a global analysis of the depth distribution of moment release along the thrust contact at subduction zones using data from harvard s centroid moment tensor catalogue substantial regional variations in the depth distribution of moment release are observed a significant correlation exists between the depth of maximum moment release and the convergence rate of subducting lithosphere and the sediment thickness at the trench subduction zones with fast convergence rates and thick sediment accumulations concentrate moment release at greater depths than subduction zones with slow convergence rates and little sediment accumulation the correlation between the convergence rate of oceanic lithosphere and the depth distribution of moment release may be best explained by differences in the thermal structure of the plate interface subduction zones with fast convergence velocities transport cold material to greater depths than subduction zones with slow convergence velocities the colder temperature of the deep portions of the thrust contact at subduction zones with fast convergence velocities allows seismic failure to occur at greater depth than possible in subduction zones with slow convergence velocities as has been demonstrated in intraplate environments our observations in interplate thrust settings support the idea that temperature is the most important factor controlling the maximum depth of seismic failure in subduction zones with thick sediment accumulations the stable sliding properties of unconsolidated sediments may be responsible for the low levels of shallow moment release

the effect of seamount subduction on seismic coupling it has long been speculated that the subduction of seamounts may have profound mechanical consequences particularly on the generation of large subduction zone earthquakes we consider this problem as a special case of the seismic coupling model of scholz and campos the model predicts that the subduction of a large seamount will increase the normal stress across the subduction interface and hence will enhance seismic coupling in the case of coupled arcs this increased coupling will result in a large increase in the recurrence intervals of earthquakes such events will therefore appear rare in the instrumental record as is observed for decoupled arcs the subduction of a large seamount should cause them to become locally coupled three of the latter localities have been found with satellite altimetry data two on the tonga kermadec trench and one on the izu bonin trench the diagnostic feature is a shallowing or obstruction of the trench axis adjacent to a chain or group of large seamounts on the subducting plate in each case the small to moderate plate interface seismicity typical of decoupled seismic zones is almost completely absent in a 100 200 km arc segment indicating that the subduction zone is locally locked as predicted by the model the occurrence of large interplate earthquakes at both tonga sites confirms that they are seismically coupled

rupture process of large earthquakes in the northern mexico subduction zone the cocos plate subducts beneath north america at the mexico trench the northernmost segment of this trench between the orozco and rivera fracture zones has ruptured in a sequence of five large earthquakes from 1973 to 1985 the jan 30 1973 colima event m s 7 5 at the northern end of the segment near rivera fracture zone the mar 14 1979 petatlan event m s 7 6 at the southern end of the segment on the orozco fracture zone the oct 25 1981 playa azul event m s 7 3 in the middle of the michoacan gap the sept 19 1985 michoacan mainshock m s 8 1 and the sept 21 1985 michoacan aftershock m s 7 6 that reruptured part of the petatlan zone body wave inversion for the rupture process of these earthquakes finds the best earthquake depth focal mechanism overall source time function and seismic moment for each earthquake in addition we have determined spatial concentrations of seismic moment release for the colima earthquake and the michoacan mainshock and aftershock these spatial concentrations of slip are interpreted as asperities and the resultant asperity distribution for mexico is compared to other subduction zones the body wave inversion technique also determines the moment tensor rate functions but there is no evidence for statistically significant changes in the moment tensor during rupture for any of the five earthquakes an appendix describes the moment tensor rate functions methodology in detail

the origin of n alkanes in santa monica basin surface sediment a model based on compound specific δ14c and δ13c data 14c and 13c values were measured for individual long chain n alkanes c24 33 from santa monica basin sediments the data were then simulated using a three component mixing model designed to represent the contributions of different sources the three selected end members were petroleum modern plant wax and shale derived alkanes the model was optimized to fit the data and to determine the fractional contribution of each component the results indicated that petroleum accounted for 12 of the alkanes in 0 2 5 cm sediment and 5 in 2 5 7 5 cm sediment modern plant waxes contributed 80 0 2 5 cm and 87 2 5 7 5 cm and the remaining 8 of each sample was attributed to the shale source the 14c concentration of the modern terrestrial end member was also determined from the model 14c values of 235 for the 0 2 5 cm post bomb horizon and 0 for the 2 5 7 5 cm pre bomb horizon indicate that plant leaf waxes have a continental residence time of decades in the southern california region

sources of organic matter in changjiang yangtze river bed sediments preliminary insights from organic geochemical proxies insight into the content and composition of organic carbon oc in river systems contributes to our understanding of the global carbon cycle the changjiang yangtze river plays a significant role in global carbon and hydrological cycles as it is an important supplier of sediment nutrients and oc to the east china sea to provide a preliminary insight into the source of oc transported by the changjiang we analyzed bulk grain size organic carbon content 13c and molecular lignin phenols branched and isoprenoid gdgts characteristics of organic matter in bed sediments at eight locations along the river the 13c values and lignin phenol composition indicate that the oc originates from a mixture of primarily soils and plants comparison between branched gdgt br gdgt distributions in riverbed sediments and those in the different soil types in the drainage basin indicate that the br gdgt signal in the upper reaches is largely derived from soils from the qinghai tibet plateau downstream changes in br gdgt distributions can be linked to subsequent input of local soil material the observed variation in br gdgt composition along the river implies that a portion of the oc may be oxidized or replaced by the local input during transit although the relationship between 13c and lignin phenol composition indicates that the contribution of phytoplankton is limited comparison of gdgt ratios gdgt 0 crenarchaeol iso gdgts br gdgts bit index for the sediments and surrounding soils indicates that at least part of the iso gdgts has an aquatic origin overall the downstream evolution of br gdgts in the changjiang implies that their use as paleoclimate proxy in downcore applications will likely yield a local rather than a basin integrated continental climate record

freshwater radiocarbon reservoir age in the lower yellow river floodplain during the late holocene the radiocarbon concentration of the dissolved inorganic carbon dic pool of most freshwater bodies such as lakes and rivers tends to be depleted with respect to that of the contemporaneous atmosp

organic geochemistry of surface sediments from the huanghe estuary and adjacent bohai sea china abstract surface sediment samples collected in may 1985 in the huanghe river and in the bohai sea and in the estuary mixing zone between river and marine waters were analyzed for fatty acids and aliphatic hydrocarbons sediments are characterized by low organic contents 0 06 0 39 of dry sediment total fatty acid concentrations vary from 2 9 to 18 1 g g 1 dry sediment lower values are found in the mixing zone whereas higher ones are observed in the marine area the spatial distribution of the relative importance of high molecular weight compounds c24 confirms that significant amounts of continental derived material are deposited in the mixing zone the presence of substantial amounts of unsaturated fatty acids such as n c20 5 and n c22 6 indicates well preserved organic matter from both phytoplankton and zooplankton sediments from both river and mixing zone show low and equal concentrations of microbial molecular markers from 0 09 to 0 74 g g 1 sum of iso and anteiso c15 c17 fatty acids marine sediments are characterized by much higher amounts of microbial organic material evidenced by high microbial marker concentrations reaching values up to 1 39 g g 1 total non aromatic hydrocarbons account for 1 9 4 3 of dry sediment representing from 0 08 to 0 34 of the organic carbon these concentrations are low compared to those of other estuarine sediments n alkane distribution patterns support a predominant origin from terrestrial plants cpi 3 1 7 9 some riverine and marine sediments show a predominance of n c17 indicating contributions from freshwater and marine planktons the analytical results indicate some contamination of the marine environment by petroleum products

controls on the age of vascular plant biomarkers in black sea sediments abstract transfer of organic carbon oc from the terrestrial to the oceanic carbon pool is largely driven by riverine and aeolian transport before transport however terrigenous organic matter can be retained in intermediate terrestrial reservoirs such as soils using compound specific radiocarbon analysis of terrigenous biomarkers their average terrestrial residence time can be evaluated here we show compound specific radiocarbon 14c ages of terrigenous biomarkers and bulk 14c ages accompanied by geochemical proxy data from core top samples collected along transects in front of several river mouths in the black sea 14c ages of long chain n alkanes long chain n fatty acids and total organic carbon toc are highest in front of the river mouths correlating well with bit branched and isoprenoid tetraether indices which indicates contribution of pre aged soil derived terrigenous organic matter the radiocarbon ages decrease further offshore towards locations where organic matter is dominated by marine production and aeolian input potentially contributes terrigenous organic matter average terrestrial residence times of vascular plant biomarkers deduced from n c29 31 alkanes and n c28 30 fatty acids ages from stations directly in front of the river mouths range from 900 70 years to 4400 170 years these average residence times correlate with size and topography in climatically similar catchments whereas the climatic regime appears to control continental carbon turnover times in morphologically similar drainage areas of the black sea catchment along transect data imply petrogenic contribution of n c29 31 alkanes and input via different terrigenous biomarker transport modes i e riverine and aeolian resulting in aged biomarkers at offshore core locations because n c29 31 alkanes show contributions from petrogenic sources n c28 30 fatty acids likely provide better estimates of average terrestrial residence times of vascular plant biomarkers moreover sedimentary n c28 and n c30 fatty acids appear clearly much less influenced by autochthonous sources than n c24 and n c26 fatty acids as indicated by increasing radiocarbon ages with increasing chain length and are thus more representative as vascular plant biomarkers

landscape analysis of the huang he headwaters ne tibetan plateau patterns of glacial and fluvial erosion the large scale geomorphology of the huang he yellow river headwaters centered around the bayan har shan 5267 m asl in the northeastern part of the tibetan plateau is dominated by an uplifted

radiated seismic energy and earthquake source duration variations from teleseismic source time functions for shallow subduction zone thrust earthquakes 1 earthquake source time functions deconvolved from teleseismic broadband p wave recordings are used to examine rupture variations for 417 underthrusting earthquakes located on the interplate interface in circum pacific subduction zones moment scaled duration of significant moment release varies with depth with longer duration events occurring in the shallowest 20 km of the megathrusts the source time functions are also used to estimate radiated seismic energy two estimates are obtained a simple scaled triangle substitution for the moment release history provides a minimum estimate while integration of the time function shape provides an estimate limited only by the bandwidth of the teleseismic deconvolutions while these energy calculations underestimate total energy they enable systematic comparisons of rupture process within and between subduction zones we do not find significant depth dependence for radiated energy overall but some regions do show mild trends of increasing energy seismic moment ratios e mo with increasing source depth that correspond to rupture duration variations in those regions the observations of longer rupture duration at shallow depth with moderate e mo may be due to heterogeneous friction and structural features on the shallow plate interface index terms 7215 seismology earthquake parameters 7230 seismology seismicity and seismotectonics 8164 tectonophysics stresses crust and lithosphere keywords radiated energy shallow subduction source parameters

diverse origins and pre depositional histories of organic matter in contemporary chinese marginal sea sediments abstract marginal seas are estimated to account for up to 90 of organic carbon oc burial in marine sediments and thus play an important role in global carbon cycle however comprehensive assessments of carbon budgets for marginal sea systems are challenging due to their inherent complexity with spatial and temporal variability in carbon inputs and dispersal processes we examine the bohai sea and yellow sea bs ys in order to further our understanding of sedimentary oc delivery translocation and accumulation in a shallow marginal sea system bulk properties and the content and isotopic compositions 14c 13c of source specific plant wax n alkyl lipid biomarkers were determined for a suite of surficial sediment samples variable 13c values 25 1 to 28 5 and contemporary radiocarbon ages of short chain n fatty acids fas c16 c18 reflect modern autochthonous marine and or fresh terrestrial plant input in contrast extremely depleted 14c values 932 to 979 of short chain n alkanes c16 c18 suggest a predominant input from sedimentary rocks petrogenic oc or petroleum abundance weighted average 13c and 14c values of long chain leaf wax lipids c26 28 30 n fas c24 26 28 n alkanols c27 29 31 n alkanes are 29 1 1 1 to 30 2 0 3 and 286 150 to 442 119 respectively illustrating that terrestrial oc delivery is dominated by pre aged 3000 5000 14c yrs c3 vegetation sources a coupled carbon isotopic mixing model based on the bulk and compound specific biomarker 13c and 14c values is used to partition the bs ys sedimentary oc into three components that reflect both origins and transport processes for all sampling sites 31 64 is modern contemporary oc 24 49 is pre aged terrestrial oc and 7 26 is fossil oc the latter likely derived from both physical erosion of ancient sedimentary rocks and fossil fuel sources pre aged soil oc is most prominent in front of the modern and old huanghe yellow river delta 48 and 49 and fossil oc is most significant north of the old huanghe mouth 26 significant pre aged soil contributions 33 are also evident for sites further offshore where transport and deposition of eolian dust supply may be important for the three major deposition areas of the bs ys system bohai basin sub aqueous huanghe delta and central south ys basin we estimate that about 3 02 mt yr of refractory plant derived pre aged soil oc and 0 98 mt yr of 14c depleted fossil oc accumulates in surface sediments corresponding to 35 and 11 of sediment toc respectively compared with estimates for fluxes from corresponding sources the burial efficiency is close to 100 for pre aged soil oc and 70 for fossil oc implying efficient oc burial in delta and shelf environments re burial of these two pools of terrigenous oc only affects carbon cycling on millennial and longer timescales respectively and exerts little influence on the modern carbon cycle

seismic energy release in mexican subduction zone earthquakes we estimated radiated seismic energy es from 18 shallow thrust mexican subduction zone earthquakes 4 1022 m 1 1 1028 dyne cm 11 h 37 km using digital accelerograms from the guerrero accelerograph array and neglecting stations with large site effects es is computed by integrating squared velocity spectra after applying geometrical spreading and q corrections we discarded epicentral recordings for the largest michoacan event we find that log es m 4 152 0 275 which gives a median value of es m and apparent stress a of 7 1 10 5 and 24 bars respectively the median es m value is in accordance with gutenberg and richter s g r 1956 formula for es in which es m 5 10 5 is implicit worldwide es m data where es is computed from local records mostly fall between 5 10 5 and 5 10 4 for events with m 1022 dyne cm on the other hand es m values generally lie between 5 10 6 and 5 10 5 if es is estimated from teleseismic records especially anomalous are the es m data from kikuchi and fukao 1988 for large and great earthquakes which fall near 5 10 6 thus while es from local data suggests that the g r relation seldom overestimates seismic energy release the teleseismic data point to the contrary the cause of this discrepancy may lie in the difficulty of resolving incoherent radiation from the fault and inappropriate choice of t in the analysis of teleseismic data

river sediment discharge to the oceans present day controls and global budgets empirical relationships between river sediment yields and a large number of hydroclimatic biological and geomorphological parameters are investigated at the global scale for a set of 60 major world river basins the environmental characteristics were extracted from various global computer data sets and natural river sediment fluxes were taken from the literature it is found that sediment yields can be best correlated by forming the products of hydroclimatic and geomorphological factors that is runoff intensity basin slope an index characterizing rock hardness and an index characterizing rainfall variability over the year the best parameter combination varies to some extent when the rivers are grouped according to their average climatic situation but it is always a combination of the above mentioned parameters that yields the most significant models in arid climates however regression coefficients are greater than in humid climates indicating that erodibility is much greater than in arid climates when extrapolated to the total continental area on the basis of the corresponding data sets the empirical models result in a total sediment flux of about 16 gigatons discharged to the oceans every year which is in good agreement with previous estimates derived from compilations of world wide river data consequently two global maps are proposed showing the spatial distributions of river sediment yields on the continents as well as the inputs of these sediments to the oceans in a grid point scale by far most of the sediments originate from the young orogenic belts of the continents mainly due to a combination of steep morphologies and high runoff intensities

the provenance of vegetation and environmental signatures encoded in vascular plant biomarkers carried by the ganges brahmaputra rivers organic matter carried by rivers and deposited in continental and marine sediments contains valuable information on past environmental conditions and their impact on the terrestrial biosphere in order to use sedimentary records to reconstruct past environmental conditions on the continents such as vegetation cover and type or precipitation intensity we need to understand the provenance of the organic signatures and how they are transferred and potentially modified by fluvial transport to the sedimentary reservoir in particular we need to understand how environmental conditions are imprinted in the composition of riverine particulate organic carbon here we investigate the stable carbon and hydrogen isotopic signatures of vascular plant leaf wax biomarkers in the modern day ganges and brahmaputra river complex one of the largest fluvial systems on earth the distribution of n alkanes and n alkanoic acids in ganges brahmaputra river sediments suggests that vascular plant inputs are consistently a significant component of the organic carbon pool molecular 13c measurements reveal that c3 vegetation inputs delivered by the himalayan rivers are partly degraded and replaced by mixed c3 c4 vegetation input in the floodplain the hydrogen isotopic composition of long chain c24 n alkanoic acids in combination with their stable c isotopic composition provides constraints on the isotopic composition of the environmental water used by higher plants within the drainage basin calculated compositions compare well with the depleted d isotopic ratios of the river water during the summer monsoon suggesting that h isotopic compositions of long chain alkanoic acids are a valuable proxy for the composition of summer monsoon moisture in the ganges brahmaputra basin detailed studies of the isotopic anatomy of modern river systems are critical for informed interpretation of marine sedimentary records in river influenced continental margins

an apparent mechanism dependence of radiated seismic energy we develop an extension to the method of boatwright and choy 1986 for determining the radiated seismic energy es that accounts for factors that bias the estimate we apply our technique to 204 events worldwide during the period 1992 1999 and find that the apparent stress is on average largest for strike slip events 0 70 mpa while for reverse and normal events it is significantly smaller 0 15 and 0 25 mpa respectively these results support the mechanism dependence of es reported by choy and boatwright 1995 although we find that once likely sources of bias are accounted for the mechanism dependence is not as strong as found previously the source of the mechanism dependence is unclear but one possibility is that it reflects a mechanism dependent difference in the stress drop this hypothesis is suggested by the scaling of slip with width in large strike slip earthquakes and makes two predictions which could be used to test it the first is that the discrepancy should disappear for the very largest dip slip earthquakes as the length of the fault greatly exceeds the downdip extent the second is that the discrepancy ought to disappear for smaller earthquakes the first can not yet be tested due to a lack of recent very large dip slip earthquakes the second is supported by the lack of mechanism dependence to es for smaller earthquakes an alternative hypothesis is that the apparent mechanism dependence could result if faults are opaque during rupture blocking seismic radiation across them brune 1996 this could cause radiated seismic energy to be trapped preferentially in the crust near the source volume for dipping faults there remains however a large discrepancy between estimates of es obtained from teleseismic versus regional data this discrepancy indicates a problem with teleseismic and or regional estimates of the seismic energy and must be resolved before a definite conclusion can be drawn

carbon isotopic evidence for the origin of macromolecular aliphatic structures in kerogen abstract this study describes compound specific stable carbon isotopic analyses of aliphatic hydrocarbon products from flash pyrolysis 800 c 20 s of kerogens representing a range of depositional environments marine estuarine lacustrine and ages recent to ordovician the carbon isotopic measurements were obtained using isotope ratio monitoring gas chromatography mass spectrometry irmgc ms for the major aliphatic pyrolysis products n hydrocarbons acyclic isoprenoids and hopanoids while isotopic compositions of n hydrocarbons varied substantially between samples average values ranged from 35 to 14 0 00 values of n alkenes and n alkanes generated from a given sample generally ranged over less than 3 0 00 this isotopic uniformity implies a common origin for n hydrocarbons probably from thermal dissociation of biopolymers supporting the concept of selective preservation of highly resistant aliphatic structures in kerogens there are notable exceptions to this general relationship in which either mixed biopolymeric sources e g guttenberg fm or minor contributions from aliphatic biopolymers e g monterey must be inferred in several cases average n hydrocarbon values also closely match the corresponding total organic carbon toc value indicating that the n hydrocarbons in these samples are derived from structurally important or at least isotopically representative constituents of the kerogen in other samples significant discrepancies were observed between the values for these products and 13ctoc in these cases the presence of additional components not yielding hydrocarbons on pyrolysis is indicated isotopic compositions of isoprenoid hydrocarbons varied non systematically relative to those of n hydrocarbons whereas hopanoid hydrocarbons were consistently depleted in 13c relative to both toc and n hydrocarbons with values as low as 50 0 00

periodic slow earthquakes from the cascadia subduction zone continuous geodetic measurements from convergent margins have shown that deep transient creep events can release large amounts of strain energy without detectable seismic shaking and they are thus known as slow or silent earthquakes because subduction zones generate the largest earthquakes

temporal variability in composition and fluxes of yellow river particulate organic matter this study examines temporal variations of the abundance and carbon isotopic characteristics of particulate organic carbon poc and specific source compounds in the context of hydrological variability in the yellow river the content and bulk carbon isotopic characteristics 13c and 14c of poc were relatively uniform over the hydrologic seasonal cycle we attribute these temporally invariant geochemical characteristics to the dominant contribution of loess material to the suspended particulate matter spm in contrast molecular level signals revealed that hydrologic conditions exert a significant influence on the proportional contributions of petrogenic and especially fresh plant derived oc while pre aged soil oc is mobilized via deeper erosion processes e g gully erosion mudslides and is independent of hydrodynamics and surface runoff a coupled biomarker isotope mixing model was applied to estimate the time varying supply of contemporary modern biomass pre aged soil and fossil oc components to chinese marginal seas from the yellow river we found that natural e g precipitation and human induced e g water and sediment regulation variations in hydrological regime strongly influence the flux with the magnitude of the corresponding annual fluxes of poc ranging between 0 343 0 122 mt yr 1 and 0 581 0 213 mt yr 1 but less strongly infleunce proportions of the different oc constituents inter annual differences in pre aged soil and fossil oc fluxes imply that extreme climate events e g floods modulate the exhumation and export of old carbon to the ocean but the oc homogeneity in the pre aged mineral soil dominated watersheds facilitates robust predictions in terms of oc transport dynamics in the past sediment cores and in the future

widespread dispersal and aging of organic carbon in shallow marginal seas the occurrence of pre aged organic carbon oc in continental margin surface sediments is a commonly observed phenomenon yet the nature sources and causes of this aged oc remain largely undetermined for many continental shelf settings here we present the results of an extensive survey of the abundance and radiocarbon content of oc in surface sediments from the northern chinese marginal seas pre aged oc is associated with both coarser 63 m and finer 63 m sedimentary components measurements on specific grain size fractions reveal that it is especially prevalent within the 20 63 m fraction of inner shelf sediments we suggest that organic matter associated with this sortable silt fraction is subject to protracted entrainment in resuspension deposition loops during which it ages is modified and is laterally dispersed most likely via entrainment within benthic nepheloid layers this finding highlights the complex dynamics and predepositional history of organic matter accumulating in continental shelf sediments with implications for our understanding of carbon cycling on continental shelves development of regional carbon budgets and interpretation of sedimentary records

soil organic matter as an important contributor to late quaternary sediments of the tropical west african continental margin the contribution of soil organic matter som to continental margins is largely ignored in studies on the carbon budget of marine sediments detailed geochemical investigations of late quaternary sediments 245 0 ka from the niger and congo deep sea fans however reveal that corg ntot ratios and isotopic signatures of bulk organic matter 13corg in both fans are essentially determined by the supply of various types of som from the river catchments thus providing a fundamentally different interpretation of established proxies in marine sciences on the niger fan increased corg ntot and 13corg up to 17 were driven by generally nitrogen poor but 13c enriched terrigenous plant debris and som from c4 c3 vegetation entisol domains grass and tree savannah on young sandy soils supplied during arid climate conditions opposite humid climates supported drainage of c3 c4 vegetation alfisol ultisol domains forest and tree savannah on older developed clay bearing soils that resulted in lower corg ntot and 13corg 20 in the niger fan record sediments from the congo fan contain a thermally stable organic fraction that is absent on the niger fan this distinct organic fraction relates to strongly degraded som of old and highly developed kaolinite rich ferallitic soils oxisols that cover large areas of the congo river basin reduced supply of this nitrogen rich and 12c depleted som during arid climates is compensated by an elevated input of marine om from the high productive congo up welling area this climate driven interplay of marine productivity and fluvial som supply explains the significantly smaller variability and generally lower values of corg ntot and 13corg for the congo fan records this study emphasizes that ignoring the presence of som results in a severe underestimation of the terrigenous organic fraction leading to erroneous paleoenvironmental interpretations at least for continental margin records furthermore burial of som in marine sediments needs more systematic investigation combining marine and continental sciences to assess its global relevance for long term sequestration of atmospheric co2

chemical weathering in the upper huang he yellow river draining the eastern qinghai tibet plateau we examined the fluvial geochemistry of the huang he yellow river in its headwaters to determine natural chemical weathering rates on the northeastern qinghai tibet plateau where anthropogenic impact is considered small qualitative treatment of the major element composition demonstrates the dominance of carbonate and evaporite dissolution most samples are supersaturated with respect to calcite dolomite and atmospheric co2 with moderate 0 710 0 715 87 sr 86 sr ratios while six out of 21 total samples have especially high concentrations of na ca mg cl and so4 from weathering of evaporites we used inversion model calculations to apportion the total dissolved cations to rain evaporite carbonate and silicate origin the samples are either carbonate or evaporite dominated but the relative contributions of the four sources vary widely among samples net co2 consumption rates by silicate weathering 6 120 10 3 mol km 2 yr are low and have a relative uncertainty of 40 we extended the inversion model calculation to literature data for rivers draining orogenic zones worldwide the ganges brahmaputra draining the himalayan front has higher co2 consumption rates 110 570 10 3 mol km 2 yr and more radiogenic 87 sr 86 sr 0 715 1 24 than the upper huang he but the rivers at higher latitudes are similar to or lower than the upper huang he in co2 uptake by silicate weathering in these orogenic zones silicate weathering rates are only weakly coupled with temperature and become independent of runoff above 800 mm yr copyright 2005 elsevier ltd

erosion and sediment yields as influenced by coupled eolian and fluvial processes the yellow river china based on data from the middle yellow river a model of erosion and sediment yield is proposed to describe coupled eolian and fluvial processes in a transitional zone from and to sub humid climates and to explain rapid erosion and a high sediment yield in the zone in the study area wind action predominates from march to june which erodes weathered bedrock and transports eolian sand to gullies river channels and floodplains in the following summer especially from july to september rainstorm runoff in gullies and river channels transports large quantities of fine loessic material in the form of hyperconcentrated flow as a result most of the previously stored eolian sand and material supplied by mass wasting of loess can be transported to the major tributaries and the main stream of the yellow river resulting in the high specific sediment yield there exists all optimal grain size composition which maximizes suspended sediment concentration in the study area resulted from the combined wind water processes c 2005 elsevier b v all rights reserved

randomly interstratified illite vermiculite from weathering of illite in red earth sediments in xuancheng southeastern china abstract mixed layer illite vermiculite i v clays of the xuancheng red earth were investigated using x ray diffraction xrd fourier transform infrared ftir spectrometer and high resolution transmission electron microscopy hrtem methods the xrd results indicated that the mixed layer i v clays were characterized by the broad 10 14 a peak with a maximum intensity at 12 a in air dried sample which decomposed into two peaks at 10 a and 14 a peaks respectively after ethylene glycol treatment after k saturation the 14 a peak changed to 10 a which reverted back to 14 a after saturation with mg 2 with a notable decrease in intensity of the 10 a peak the broad 10 14 a peak collapsed to 10 a on heating to 400 c these suggested that the broad 10 14 a peak resulted from randomly interstratified illite vermiculite clays together with discrete illite and also vermiculite hrtem observation showed that straight 10 a illite layers were interstratified with 12 a vermiculite layers suggesting that transformation of illite to vermiculite involves an exchange of k by hydrated cations associated with a swelling of the illite the 060 spacing of i v clay is 1 50 a indicating a dioctahedral precursor of illite and thus reinforcing the transformation from illite to vermiculite ftir analysis suggested that most band positions of vermiculite and illite in mixed layer i v did not change in comparison with those of the discrete clay species indicating that the basic crystal structure of mixed layer illite vermiculite remains the same as the discrete clays the interlayer cations in the interlayer region of vermiculite layers of the i v clays are mainly ca and minor mg al and fe the abundant ca makes the i v clays to behave like i s on glycolated and thermal treatment while the mg al and fe complex ions in the interlayer region cause the vermiculite layer to lose its expandability and to behave like chlorite the mixed layer i v clays were widely formed in late quaternary alluvial fans in subtropical to tropical areas where the sediments experienced synchronous pedogenic modification the syndepositional pedogenesis process leads to an incomplete transformation of illite to vermiculite and causes the formation of metastable intermediates of mixed layer illite vermiculite

a new look at old carbon in active margin sediments recent studies suggest that as much as half of the organic carbon oc undergoing burial in the sediments of tectonically active continental margins may be the product of fossil shale weathering these estimates rely on the assumption that vascular plant detritus spends little time sequestered in intermediate reservoirs such as soils freshwater sediments and river deltas and thus only minimally contributes to the extraneously old 14c ages of total organic matter often observed on adjacent shelves here we test this paradigm by measuring the 14c and 13c values of individual higher plant wax fatty acids as well as the 13c values of extractable alkanes isolated from the eel river margin california the isotopic signatures of the long chain fatty acids indicate that vascular plant material has been sequestered for several thousand years before deposition a coupled molecular isotope mass balance used to reassess the sedimentary carbon budget indicates that the fossil component is less abundant than previously estimated with pre aged terrestrial material instead composing a considerable proportion of all organic matter if these findings are characteristic of other continental margins proximal to small mountainous rivers then the importance of petrogenic oc burial in marine sediments may need to be reevaluated 2009 the geological society of america

10be in chinese loess we report a first series of10be measurements on chinese loess covering the last 750 000 years the10be concentration shows a tendency to decrease with increasing grain size leaching experiments with acid solutions show that10be is strongly bound to particles and therefore mobility due to dissolution can be excluded the10be record in loess shows features similar to those observed in 180 records from deep sea sediments which strongly reflect climatic variations this allows one to correlate the10be loess records with 180 deep sea records and to establish a time scale based on this time scale accumulation rates of loess and10be fluxes can be calculated these reveal generally higher values for cold arid and windy periods than for warm humid and calmer intervals

contribution of inherent organic carbon to the bulk δ13c signal in loess deposits from the arid western chinese loess plateau the isotopic composition of total organic carbon toc in loess deposits has been widely used to reconstruct palaeovegetation and palaeoclimate for terrestrial ecosystems the possible significance of the distribution and contribution of organic carbon from dust source regions to loess toc remains unclear but may potentially affect interpretation of stable carbon isotope distributions in loess records with respect to local vegetation two loess profiles from arid areas in china with sparse vegetation coverage have been investigated after removing the surface loess affected by recent farming we detected a narrow range of carbon isotope 13c values from 21 4 to 20 in the lanzhou area and from 21 5 to 19 7 in the xining area the values are inconsistent with that of the established vegetation in these areas where c3 plants are dominant in contrast the 13c values of the loess toc closely resemble those from dust sources together with data from loess toc and magnetic susceptibility we demonstrate that the isotopic composition of loess toc in arid areas was largely controlled by the carbon isotope composition of the dust source with only a minor contribution from local native vegetation the results suggest that background carbon isotopic signals should be taken into account when interpreting carbon isotope compositions of loess deposits in arid areas

the 1992 nicaragua earthquake a slow tsunami earthquake associated with subducted sediments the 1992 nicaragua earthquake was a tsunami earthquake that is it generated tsunamis disproportionately large for its surface wave magnitude m s the moment magnitude m w determined from long period 250 s surface waves was 7 6 significantly larger than the 20 s m s of 7 this m s m w disparity is also characteristic of tsunami earthquakes the nicaragua earthquake is the first tsunami earthquake to be captured by modern broadband seismic networks allowing us to present here seismograms of sufficiently high quality to make inferences about the rupture mechanisms we conclude that the nicaragua earthquake was a slow thrust earthquake which occurred on the subduction interface between the cocos and north american plates and because of the absence of sediments on the trench floor offshore of nicaragua the slip propagated up dip all the way to the ocean bottom exciting large tsunamis the occurrence of slip on a plate interface filled with soft subducted sediments caused the rupture process to be slower than in ordinary subduction zone thrust earthquakes our results reinforce the idea that tsunami warning systems using long period 100 s waves are necessary to reduce the hazard from this type of earthquake

sources and abundances of leaf waxes in aerosols in central europe abstract atmospheric transport is an understudied mechanism for leaf wax hydrogen isotope applications that contributes to mobilizing and depositing these compounds on the surface of the earth while previous efforts have identified the importance of atmospheric leaf wax deposition in remote marine locations the processes are not well constrained on land in temperate latitudes where lakes are common and sedimentary leaf wax hydrogen isotope values are an attractive tool for understanding past precipitation changes this work presents results from a field study that was conducted in 2010 and 2011 at hainich national park germany in order to evaluate the quantity and sources of leaf waxes in the atmosphere aerosols were sampled at approximately weekly intervals inside the forest canopy and n alkane distributions and hydrogen isotope values were compared with those from major tree species surrounding the sampling site despite sampling in what was expected to be a major production center the distribution and hydrogen isotope values of atmospheric n alkanes bore little resemblance to those of the local vegetation comparison with local meteorological data and to 10 day and 36 h back air mass trajectories indicated shifting effects of winds and temperature and that mesoscale transport processes were more important than long range mechanisms back trajectories also highlighted source effects with easterly winds coinciding with relatively lower leaf wax hydrogen isotope values from more continental regions these results suggest that leaf wax aerosols average over spatial scales that exceed typical surface catchment areas for small lake systems even in forested areas yet that the area over which these compounds are derived is still relatively regional depositional fluxes were also estimated in order to assess the potential importance of atmospheric transport to sedimentary archives although difficult to constrain these estimates suggest that atmospheric deposition may be non negligible for lake systems in cases where inputs from rivers or surface runoff are limited together these observations provide new insights on how leaf waxes from different sources are integrated during aeolian transport and the spatial scales over which these processes occur

the isotopic composition of particulate organic carbon in mountain rivers of taiwan small rivers draining mountain islands are important in the transfer of terrestrial particulate organic carbon poc to the oceans this input has implications for the geochemical stratigraphic record we have investigated the stable isotopic composition of poc 13corg in rivers draining the mountains of taiwan in 15 rivers the suspended load has a mean 13corg that ranges from 28 1 0 8 to 22 0 0 2 on average 37 samples per river over the interval of our study to investigate this variability we have supplemented suspended load data with measurements of poc in bedrock and river bed materials and constraints on the composition of the terrestrial biomass fossil poc in bedrock has a range in 13corg from 25 4 1 5 to 19 7 2 3 between the major geological formations using coupled 13corg and n c we have found evidence in the suspended load for mixing of fossil poc with non fossil poc from the biosphere in two rivers outside the taiwan central range anthropogenic land use appears to influence 13corg resulting in more variable and lower values than elsewhere in all other catchments we have found that 5 variability in 13corg is not controlled by the variable composition of the biomass but instead by heterogeneous fossil poc in order to quantify the fraction of suspended load poc derived from non fossil sources fnf as well as the isotopic composition of fossil poc 13cfossil carried by rivers we adapt an end member mixing model river suspended sediments and bed sediments indicate that mixing of fossil poc results in a negative trend between n c and 13corg that is distinct from the addition of non fossil poc collapsing multiple fossil poc end members onto a single mixing trend as an independent test of the model fnf reproduces the fraction modern fmod in our samples determined from 14c measurements to within 0 09 at the 95 confidence level over the sampling period the mean fnf of suspended load poc was low 0 29 0 02 n 459 in agreement with observations from other mountain rivers where physical erosion rates are high and fossil poc enters river channels the mean 13cfossil in suspended poc varied between 25 2 0 5 and 20 2 0 6 from catchment to catchment this variability is primarily controlled by the distribution of the major geological formations it also covers entirely the range of 13corg found in marine sediments which is commonly thought to derive from mixing between marine and terrigenous poc if land sourced poc is preserved in marine sediments then changes in the bulk 13corg observed offshore taiwan could instead be explained by changes in the onshore provenance of sediment the range in 13corg of fossil organic matter in sedimentary rocks exposed at the surface is large and given the importance of these rocks as a source of clastic sediment to the oceans care should be taken in accounting for fossil poc in marine deposits supplied by active mountain belts

variation in stable carbon isotope ratios of individual hydrocarbons as a function of artificial maturity abstract this paper reports isotopic variations in n alkanes isoprenoids and terpenoids from different source rock types as a function of maturity by analysis of these compounds in hydrous pyrolysis products and oil at high pyrolysis temperatures n alkanes isoprenoids and terpenoids in the pyrolysis products become depleted in 12 c the most marked depletion occurs in the terpenoids particularly in the c 29 c 31 hopanes these compounds are isopically very light in the immature unheated samples of the lacustrine green river shale tertiary and a guatemalan carbonate source rock there is a marked depletion in 12 c at 330 c and higher pyrolysis temperatures for these two samples moderately mature samples of the toarcian paris basin shale and a jurassic coal from the hammerfest basin showed less or no 12 c depletion fairly uniform values were recorded for the hopanes in pyrolysates of all samples heated at temperatures of 350 c and above the isotopic composition of n alkanes and isoprenoids are fairly similar to the hopanes in samples pyrolysed at the higher temperatures it appears therefore that with increasing maturity n alkanes isoprenoids and terpenoids become fairly similar in their carbon isotopic composition the isotopic compositions within the different compound groups in the different source rocks are sufficiently different for this technique to be used in source rock oil correlation

the brittle ductile transition in porous sedimentary rocks geological implications for accretionary wedge aseismicity abstract thrusting earthquakes in subduction zones generally occur along only part of the plate boundary with motion along the shallowest part of the plate boundary occurring ascismically the maximum size of subduction boundary thrust earthquakes depends strongly upon the down dip width of the seismogenic zone the single most uncertain factor in determining that width is the location of the up dip limit of the zone the seismic front which depends upon the mechanical state of the sedimentary rocks in the plate boundary zone in order to come to a better understanding of the seismic potential of sediments in a subduction zone we carried out a series of triaxial experiments on berea and kayenta sandstones based on our experimental data a brittle ductile transition map was constructed showing that both porosity and effective pressure are important factors controlling the transition from brittle to macroscopically ductile behavior in porous rocks in the brittle field a sample fails by shear localization on one slip plane accompanied by strain softening and dilatancy whereas in the ductile field a sample deforms homogeneously with a constant yield stress or slight hardening by comparing such a map with the estimated porosity profile of an accretionary wedge the likely nature and rough location of the boundary between brittle and ductile behavior can be inferred if the sediments along a plate boundary are too young and undercompacted to be capable of brittle shear localization then their deformation is likely to be aseismic in this way it may be possible for even a very broad fore arcs to produce no great earthquakes however great earthquakes are to be expected at margins that have large zones of plate contact along which many sediments are compacted and well lithified such rocks are expected to be capable of shear localization and brittle failure with the potential for stick slip behavior

oxidation of petrogenic organic carbon in the amazon floodplain as a source of atmospheric co2 the two long term sources of atmospheric carbon are co2 degassing from metamorphic and volcanic activity and oxidation of organic carbon oc contained in sedimentary rocks or petrogenic organic carbon ocpetro the latter fl ux is still poorly constrained in this study we report particulate organic carbon content and 14c activity measurements in amazon river sediments which allow for estimates of the ocpetro content of these sediments a large decrease of ocpetro content in riverine sediments is observed from the outlet of the andes to the mouth of the large tributaries this loss reveals oxidation of ocpetro during transfer of sediments in the floodplain and results in an escape of 0 25 mt c yr to the atmosphere which is on the same order of magnitude as the co2 consumption by silicate weathering in the same area raman microspectroscopy investigations show that graphite is the most stable phase with respect to this oxidation process these results emphasize the significance of ocpetrooxidation in large river floodplains in the global carbon cycle

multiple plant wax compounds record differential sources and ecosystem structure in large river catchments abstract the concentrations distributions and stable carbon isotopes 13c of plant waxes carried by fluvial suspended sediments contain valuable information about terrestrial ecosystem characteristics to properly interpret past changes recorded in sedimentary archives it is crucial to understand the sources and variability of exported plant waxes in modern systems on seasonal to inter annual timescales to determine such variability we present concentrations and 13c compositions of three compound classes n alkanes n alcohols n alkanoic acids in a 34 month time series of suspended sediments from the outflow of the congo river we show that exported plant dominated n alkanes c25 c35 represent a mixture of c3 and c4 end members each with distinct molecular distributions as evidenced by an 8 1 0 7 1 standard deviation spread in 13c values across chain lengths and weak correlations between individual homologue concentrations r 0 52 0 94 in contrast plant dominated n alcohols c26 c36 and n alkanoic acids c26 c36 exhibit stronger positive correlations r 0 70 0 99 between homologue concentrations and depleted 13c values individual homologues average 31 3 and 30 8 respectively with lower 13c variability across chain lengths 2 6 0 6 and 2 0 1 1 respectively all individual plant wax lipids show little temporal 13c variability throughout the time series 1 0 9 indicating that their stable carbon isotopes are not a sensitive tracer for temporal changes in plant wax source in the congo basin on seasonal to inter annual timescales carbon normalized concentrations and relative abundances of n alcohols 19 58 of total plant wax lipids and n alkanoic acids 26 76 respond rapidly to seasonal changes in runoff indicating that they are mostly derived from a recently entrained local source in contrast a lack of correlation with discharge and low stable relative abundances 5 16 indicate that n alkanes better represent a catchment integrated signal with minimal response to discharge seasonality comparison to published data on other large watersheds indicates that this phenomenon is not limited to the congo river and that analysis of multiple plant wax lipid classes and chain lengths can be used to better resolve local vs distal ecosystem structure in river catchments

the remineralization of sedimentary organic carbon in different sedimentary regimes of the yellow and east china seas abstract we investigated the remineralization of sedimentary organic carbon soc at 12 sites in east china sea mobile muds ecsmms and south yellow sea central mud deposits sysmds using a time sequence sediment incubation experiment we examined pore water dissolved inorganic carbon dic dissolved organic carbon doc fluorescent dissolved organic matter fdom dissolved inorganic nitrogen din nutrients nh4 no3 and no2 redox sensitive elements fe2 and mn2 and major anions so42 and cl in incubated sediments to better constrain controlling mechanisms of soc remineralization under different sedimentary regimes lower dic production rates in sysmds 2 36 3 13 mmol m 2 d 1 than those in ecsmms 2 94 13 5 mmol m 2 d 1 were mainly attributed to cold bottom water masses and a relatively stable sedimentary environment in sys higher dic production rates were observed mostly at offshore sites of ecsmms that had relatively enriched 13c of soc which indicated preferential degradation of labile soc of marine origin when compared with tropical mobile muds higher bottom water temperatures thicker mobile muds and large inputs of reactive terrestrial oc resulted in more intense remineralization of soc in amazon mobile muds than in ecsmms lower ratios of doc dic production rates in ecsmms 0 11 0 72 were likely indicative of efficient transformation of oc and largely due to sulfate reduction a rapid increase in marine protein like fdom components during the incubation indicated that less stable marine soc was preferentially converted to doc and then to dic our soc budget indicates that 16 8 of soc was decomposed in sediments of ecsmms but only about 5 4 of soc was decomposed in sysmds suggesting lower soc preservation efficiency in mobile muds than distal muds

mobilization and export of millennial aged organic carbon by the yellow river a combined carbon isotope 13c and 14c study was carried out to investigate the sources and fate of organic carbon oc transported by the yellow river and preserved in the sediments of the bohai and yellow seas in 2015 the yellow river delivered 3 14 1010 g c and 4 12 1010 g c of dissolved organic carbon doc and particulate organic carbon poc to the bohai sea carbon isotope signatures revealed that the yellow river transports millennial aged doc and poc during all seasons the values of 13c doc ranged from 24 7 to 28 8 in the river basin and 21 0 to 27 0 in the lower reach the 14c ages of doc were 415 1690 yr before present bp in the river basin and they were relatively constant seasonally 1320 1690 yr bp in the lower reach of the river in comparison poc 13c values in the river were less variable 22 8 to 25 0 but much older in both the river basin 4960 1690 yr bp and in the lower reach 4040 1050 yr bp calculations using a dual isotopic three end member model revealed that biomass oc derived from c3 plants was the major source of riverine doc contributing 65 8 and 52 2 in the river basin and lower reach seasonally pre aged soil oc and fossil oc from weathering contributed 21 42 and 6 14 of the doc respectively in contrast pre aged soil oc and fossil oc contributed 60 70 and 17 27 of poc and biomass oc contributed a minor fraction 13 7 of riverine poc our results further revealed that aged riverine poc had a major influence on oc preservation in the delta and coastal sediments of the bohai and yellow seas the age of oc in surface sediments varied widely 1610 8275 yr due to the influence of yellow river input pre aged soil oc and fossil oc each contributed 32 8 and 22 14 of oc preserved in the sediments we estimate that about 0 27 mt yr 1 and 0 07 mt yr 1 of pre aged soil oc and fossil oc accumulate in the surface sediments from poc delivered by the modern yellow river and 0 013 mt yr 1 and 0 002 mt yr 1 of pre aged soil oc and fossil oc enters the coastal doc cycle from riverine doc the millennial aged oc delivered to coastal seas by the yellow river therefore has profound impacts not only on carbon cycling and the carbon budget in the marginal sea but also on coastal ecosystems and biogeochemical processes

disentangling marine soil and plant organic carbon contributions to continental margin sediments a multi proxy approach in a 20 000 year sediment record from the congo deep sea fan abstract a 20 kyr long sediment sequence from the congo deep sea fan core geob 6518 1 one of the world s largest deep sea river fans has been analysed for bulk and molecular proxies in order to reconstruct the marine soil and plant organic carbon oc contributions to these sediments since the last glacial maximum the bulk proxies applied c n ratio and 13 c org ranged from 10 to 12 5 and from 24 5 to 21 vpdb respectively as molecular proxies concentrations of marine derived alkenones and terrestrial derived odd numbered n alkanes were used which varied between 0 2 and 4 g g dry weight sediment in addition the branched vs isoprenoid tetraether bit index a proxy for soil organic matter input was used which varied from 0 3 to 0 5 in this core application of binary mixing models based on the different individual proxies showed estimates for terrestrial oc input varying by up to 50 due to the heterogeneous nature of the oc application of a three end member mixing model using the 13 c org content the c n ratio and the bit index enabled the distinction of soil and plant organic matter as separate contributors to the sedimentary oc pool the results show that marine oc accounts for 20 to 40 of the total oc present in the deep sea fan sediments over the last 20 kyr and that soil oc accounts for about half 45 on average of the oc present this suggests that soil oc represents the majority of the terrestrial oc delivered to the fan sediments accumulation rates of the plant and soil oc fractions over the last 20 kyr varied by a factor of up to 5 and are strongly related to sediment accumulation rates they showed an increase starting at ca 17 kyr bp a decline during the younger dryas peak values during the early holocene and lower values in the late holocene this pattern matches with reconstructions of past central african humidity and congo river discharge from the same core and revealed that central african precipitation patterns exert a dominant control on terrestrial oc deposition in the congo deep sea fan marine oc accumulation rates are only weakly related to sediment accumulation rates and vary only little over time compared to the terrigenous fractions these variations are likely a result of enhanced preservation during times of higher sedimentation rates and of relative small fluctuations in primary production due to wind driven upwelling

pre aged soil organic carbon as a major component of the yellow river suspended load regional significance and global relevance abstract large rivers connect the continents and the oceans and corresponding material fluxes have a global impact on marine biogeochemistry the yellow river transports vast quantities of suspended sediments to the ocean yet the nature of the particulate organic carbon poc carried by this system is not well known the focus of this study is to characterize the sources composition and age of suspended poc collected near the terminus of this river system focusing on the abundance and carbon isotopic composition 13c and 14c of specific biomarkers the concentrations of vascular plant wax lipids long chain c24 n alkanes n fatty acids and poc co varied with total suspended solid tss concentrations indicating that both were controlled by the overall terrestrial sediment flux poc exhibited relatively uniform 13c values 23 8 to 24 2 and old radiocarbon ages 4000 4640 yr however different biomarkers exhibited a wide range of 14c ages short chain c16 c18 fatty acid 14c ages were variable but generally the youngest organic components from 502 yr to modern suggesting they reflect recently biosynthesized material lignin phenol 14c ages were also variable and relatively young 1070 yr to modern suggesting rapid export of carbon from terrestrial primary production in contrast long chain plant wax lipids display relatively uniform and significantly older 14c ages 1500 1800 yr likely reflecting inputs of pre aged mineral associated soil oc from the yellow river drainage basin even carbon numbered n alkanes yielded the oldest 14c ages up to 26 000 yr revealing the presence of fossil petrogenic oc two isotopic mass balance approaches were explored to quantitively apportion different oc sources in yellow river suspended sediments results indicate that the dominant component of poc 53 57 is substantially pre aged 1510 1770 yr and likely sourced from the extensive loess paleosol deposits outcropping within the drainage basin of the remaining poc between 10 and 31 is fossil in origin 26 000 yr resulting from the physical erosion of ancient sedimentary rock and input of fossil fuel residues from anthropogenic activity and 16 33 is modern carbon derived from terrestrial and aquatic productivity these findings have implications both regarding the provenance and vintage of organic matter signatures emanating from the yellow river basin and similar catchments containing extensive paleosol sequences as well as for the reactivity and fate of this poc upon supply to adjacent marginal seas

on relating apparent stress to the stress causing earthquake fault slip apparent stress a is defined as where is the average shear stress loading the fault plane to cause slip and is the seismic efficiency defined as ea w where ea is the energy radiated seismically and w is the total energy released by the earthquake the results of a recent study in which apparent stresses of mining induced earthquakes were compared to those measured for laboratory stick slip friction events led to the hypothesis that this hypothesis is tested here against a substantially augmented data set of earthquakes for which can be estimated mostly from in situ stress measurements for comparison with a the expanded data set which includes earthquakes artificially triggered at a depth of 9 km in the german kontinentales tiefbohrprogramm der bundesrepublik deutschland ktb borehole and natural tectonic earthquakes covers a broad range of hypocentral depths rock types pore pressures and tectonic settings nonetheless over 14 orders of magnitude in seismic moment apparent stresses exhibit distinct upper bounds defined by a maximum seismic efficiency of 0 06 consistent with the hypothesis proposed before this behavior of a and can be expressed in terms of two parameters measured for stick slip friction events in the laboratory the ratio of the static to the dynamic coefficient of friction and the fault slip overshoot typical values for these two parameters yield seismic efficiencies of 0 06 in contrast to efficiencies for laboratory events for which is always near 0 06 those for earthquakes tend to be less than this bounding value because ea for earthquakes is usually underestimated due to factors such as band limited recording thus upper bounds on appear to be controlled by just a few fundamental aspects of frictional stick slip behavior that are common to shallow earthquakes everywhere estimates of from measurements of a for suites of earthquakes using are found to be comparable in magnitude to estimates of shear stress on the basis of extrapolating in situ stress data to seismogenic depths

climate regulates the erosional carbon export from the terrestrial biosphere erosion drives the export of particulate organic carbon from the terrestrial biosphere pocbiosphere and its delivery to rivers the carbon transfer is globally significant and can result in drawdown of atmospheric carbon dioxide co2 if the eroded pocbiosphere escapes degradation during river transfer and sedimentary deposition despite this recognition we lack a global perspective on how the tectonic and climatic factors which govern physical erosion regulate pocbiosphere discharge obscuring linkages between mountain building climate and co2 drawdown to fill this deficit geochemical 13c 14c and c n hydrometric water discharge suspended sediment concentration and geomorphic slope measurements are combined from 33 globally distributed forested mountain catchments radiocarbon activity is used to account for rock derived organic carbon and reveals that pocbiosphere eroded from mountain forests is mostly 1300 14c years old annual pocbiosphere yields are positively correlated with suspended sediment yields confirming results from taiwan and a recent global analysis and are high in catchments with the steepest slopes based on these relationships and the global distribution of slope angles 3 arc second it is suggested that topography steeper than 10 16 of the continental area may contribute 40 of global pocbiosphere erosional flux climate is shown to regulate pocbiosphere discharge by mountain rivers by controlling hydrologically driven erosion processes in catchments where discharge measurements are available 8 of the 33 a significant relationship exists between daily runoff mm day 1 and pocbiosphere concentration mg l 1 r 0 53 p 0 0001 the relationship can be described by a single power law and suggests a high connectivity between forested hillslopes and mountain river channels as a result annual pocbiosphere yields are significantly correlated with mean annual runoff r 0 64 p 0 0001 a shear stress pocbiosphere erosion model is proposed which can explain the patterns in the data the model allows the climate sensitivity of this carbon flux to be assessed for the first time for a 1 increase in annual runoff pocbiosphere discharge is predicted to increase by 4 in steeper catchments pocbiosphere discharge increases more rapidly with an increase in annual runoff for comparison a 1 increase in annual runoff is predicted to increase carbon transfers by silicate weathering solute fluxes in mountains by 0 4 0 7 depending on the fate of the eroded pocbiosphere river export of pocbiosphere from mountains may act as an important negative feedback on rising atmospheric co2 and increased global temperature erosion of carbon from the terrestrial biosphere links mountain building and climate to the geological evolution of atmospheric co2 while the carbon fluxes are sensitive to predicted changes in runoff over the coming century

differences in radiocarbon ages among molluscan shells plant materials and total organic carbon an example from the paleo changjiang incised valley fill china abstract radiocarbon dating of samples from the cm97 cores of late pleistocene to holocene sediments in the paleo changjiang incised valley china was performed and age differences among molluscan shells wood and other plant materials and bulk total organic carbon toc were evaluated the incised valley fill consists of fluvial estuarine and deltaic deposits in ascending order in the dating results samples of wood and other plant materials yielded similar ages to molluscan shell samples in contrast in samples from estuarine and deltaic sediments radiocarbon ages of toc were systematically older by up to 6500 calibrated years than those of molluscan shells this result suggests that the paleo changjiang river transported aged terrigenous organic matter to its mouth the magnitude of the age offset increased upward within the transgressive estuarine sediments and the largest offset 4500 calibrated years on average was observed in the prodelta sediments deposited after the maximum transgression grain size the c n ratio 13c values and the sediment accumulation rate of the incised valley fill sediments and the paleo water depth indicated a weak terrestrial influence and a strong marine influence in the prodelta sediments therefore the large age offsets in the prodelta sediments likely reflect reworking and resuspension in a strongly tide dominated setting of sediments deposited earlier on the inner shelf resulting in the supply of both fine grained resuspended sediments and old organic carbon to the prodelta in addition to the supply of terrigenous organic carbon from the paleo changjiang river the upward deepening increase of the age offset in the estuarine sediments supports this interpretation the magnitude of the age offset in the past prodelta sediments was comparable to the old radiocarbon ages of the surface sediments in the present prodelta to inner shelf area this result suggests that the supply dispersal recycling and burial of terrestrial organic carbon on the inner shelf has been mostly stable during the past 8000 years

the updip and downdip limits to great subduction earthquakes thermal and structural models of cascadia south alaska sw japan and chile this study examines thermal and structural controls of the updip and downdip rupture limits of great subduction thrust earthquakes data on past great earthquake seismic limits have been compiled for four continental subduction zones cascadia sw japan south alaska and chile these limits have then been compared to the predictions of several models for what constrains great earthquake rupture temperatures on the subduction thrusts have been estimated by finite element numerical models the landward limits of the observed updip aseismic zones correspond to the position where the thrust temperature reaches about 100 c that is depths of about 2 to 10 km for the subduction zones studied this temperature agrees with the dehydration of stable sliding smectite clays to illite chlorite the temperatures in this region are controlled mainly by the thickness of sediment on the incoming crust and by the crustal age and thus heat flow the downdip limits correspond to the depth on the thrust where either 1 the temperature reaches about 350 c which corresponds to thermally activated stable sliding behavior for crustal rocks with a transition to 450 c or 2 about 40 km depth if 350 c is reached at greater depth depths of about 40 km approximately correspond to the intersection of the thrust with the continental forearc moho and this downdip limit may be a consequence of stable sliding serpentinite or talc and other hydrated forearc mantle rocks the primary temperature controls on the downdip region are the age of the subducting oceanic plate and the thrust dip profile secondary control comes from the thickness of incoming sediment the convergence rate and the radioactive heat generation in the overlying forearc the 100 c updip limit occurs near the trench for young subducting plates with a thick sediment section such as cascadia 6 8 ma and up to 80 km landward for older oceanic crust such as south alaska 50 ma the 350 c downdip thermal limit is applicable for young oceanic plates e g cascadia and nankai whereas the forearc mantle limit applies for older plates e g south alaska and chile except near the chile rise for the margins studied that have experienced great earthquakes there is generally good agreement between the postulated thermal and moho limits and the rupture or seismogenic zone as defined by the distribution of aftershocks and by waveform tsunami and dislocation modeling the downdip limit of the interseismic locked zone from dislocation modeling is also in agreement with these limits

climatic and geomorphic drivers of plant organic matter transport in the arun river e nepal fixation of atmospheric co2 in terrestrial vegetation and subsequent export and deposition of terrestrial plant organic matter in marine sediments is an important component of the global carbon cycle yet it is difficult to quantify this is partly due to the lack of understanding of relevant processes and mechanisms responsible for organic matter transport throughout a landscape here we present a new approach to identify terrestrial plant organic matter source areas quantify contributions and ascertain the role of ecologic climatic and geomorphic controls on plant wax export in the arun river catchment spanning the world s largest elevation gradient from 205 to 8848 m asl in eastern nepal our approach takes advantage of the distinct stable hydrogen isotopic composition expressed as d d values of plant wax n alkanes produced along this gradient transported in river waters and deposited in flood deposits alongside the arun river and its tributaries in mainstem flood deposits we found that plant wax n alkanes were mostly derived from the lower elevations constituting only a small fraction 15 of the catchment informed by remote sensing data we tested four differently weighted isotopic mixing models that quantify sourcing of tributary plant derived organic matter along the arun and compare it to our field observations the weighting parameters included catchment area net primary productivity npp and annual rainfall amount as well as catchment relief as erosion proxy when weighted by catchment area the isotopic mixing model could not explain field observations on plant wax d d values along the arun which is not surprising because the large arid tibetan plateau is not expected to be a major source weighting areal contributions by annual rainfall and npp captured field observations within model prediction errors suggesting that plant productivity may influence source strength however weighting by a combination of rainfall and catchment relief also captured the observed d d value pattern suggesting dominantly erosive control we conclude that tributaries at the southern himalayan front with high rainfall high productivity high relief and high erosion rates dominate plant wax exports from the catchment

do trench sediments affect great earthquake occurrence in subduction zones seismic energy release is dominated by the underthrusting earthquakes in subduction zones and this energy release is further concentrated in a few subduction zones while some subduction zones are characterized by the occurrence of great earthquakes others are relatively aseismic this variation in maximum earthquake size between subduction zones is one of the most important features of global seismicity previous work has shown that the variation in maximum earthquake size is correlated with the variation in two other subduction zone properties age of the subducting lithosphere and convergence rate these two properties do not explain all the variance in maximum earthquake size i propose that a third subduction zone property trench sediments explains part of the remaining variance in maximum earthquake size subduction zones are divided into two groups 1 those with excess trench sediments and 2 those with horst and graben structure at the trench thirteen of the 19 largest subduction zone events including the three largest occur in zones with excess trench sediments about half the zones with excess trench sediments are characterized by great earthquake occurrence most of the other zones with excess trench sediments but without great earthquakes are predicted to have small earthquakes by the age rate correlation two notable exceptions are the oregon washington and middle america zones overall the presence of excess trench sediments appears to enhance great earthquake occurrence one speculative physical mechanism that connects trench sediments and earthquake size is that excess trench sediments are associated with the subduction of a coherent sedimentary layer which at elevated temperature and pressure forms a homogeneous and strong contact zone between the plates

compound specific d h ratios and molecular distributions of higher plant leaf waxes as novel paleoenvironmental indicators in the chinese loess plateau abstract we measured d h ratios of individual long chain leaf wax n alkanes isolated from a loess profile spanning the last 130 ka from xifeng china the d values show large variation 140 to 200 for the past 130 ka and are highly correlated with changes in magnetic susceptibility ms an accepted proxy for past monsoon circulation in the chinese loess plateau peaks in high d values 140 to 160 coincide with low ms values for loess sections formed under relatively dry conditions marine isotope stages miss 2 and 4 whereas peaks in low d values 190 to 200 coincide with high ms values for paleosol sections formed under relatively wet conditions miss 1 3 and 5 we attribute the isotopic variations to the combined effects of varying aridity which controls the soil and leaf water evaporation and temperature and monsoon intensity which alter the d h ratios of precipitation we also discovered a strong negative correlation between the molecular distributions ratios of c31 c29 and c31 c27 n alkanes and the d values of n alkanes based on studies of modern plants and the xifeng loess sequence the complex relationship between ms and monsoon circulation has been difficult to understand mechanistically however the climatic controls on the d h ratios of individual long chain n alkanes and c31 c29 n alkane ratios can be readily demonstrated and calibrated from modern plants and surface soils therefore these new molecular and isotopic proxies have potential as quantitative proxies for paleoenvironmental reconstruction in the chinese loess plateau

origin and dispersal of recent clay minerals in the yellow sea abstract the clay minerals in the by considering the clay minerals supplied by rivers in china the old and present day huanghe river and korea the keum and yeongsan to the yellow sea continental shelf and the spatial variation in the distribution of clay minerals in the yellow sea this study indicates that the provenance of the cysm may be closely related to the old and present day huanghe river system whereas the clay minerals in the seysm seem to be largely associated with the keum and yeongsan rivers in addition smectite may be suggested as an important clay mineral in differentiating between cysm and seysm and understanding the sources of these two mud categories

long term storage and age biased export of fluvial organic carbon field evidence from west iceland terrestrial organic carbon oc plays an important role in the carbon cycle but questions remain regarding the controls and timescale s over which atmospheric co remains sequestered as particulate oc poc motivated by observations that terrestrial poc is physically stored within soils and other shallow sedimentary deposits we examined the role that sediment storage plays in the terrestrial oc cycle specifically we tested the hypothesis that sediment storage impacts the age of terrestrial poc we focused on the efri haukadalsa river catchment in iceland as it lacks ancient sedimentary bedrock that would otherwise bias radiocarbon based determinations of poc storage duration by supplying pre aged petrogenic poc our radiocarbon measurements of riverine suspended sediments and deposits implicated millennial scale storage times comparison between the sample types suspended and deposits suggested an age offset between transported suspended sediments and stored deposits poc at the time of sampling which is predicted by theory for the sediment age distribution in floodplains we also observed that poc in suspended sediments is younger than the predicted mean storage duration generated from independent geomorphological data which suggested an additional role for oc cycling consistent with this we observed interparticle heterogeneity in the composition of poc by imaging our samples at the microscale using x ray absorption spectroscopy specifically we found that particles within individual samples differed in their sulfur oxidation state which is indicative of multiple origins and or diagenetic histories altogether our results support recent coupled sediment storage and oc cycling models and indicate that the physical drivers of sediment storage are important factors controlling the cadence of carbon cycling

chemical and isotopic characterization of size fractionated organic matter from cryoturbated tundra soils northern alaska 1 recent studies indicate a second layer of organic matter often accumulates in the lower active layer and upper permafrost in arctic tundra soils as a result of cryoturbation in this study cryoturbated organic matter was characterized using a combination of physical size fractionation and modern analytical techniques for elemental composition c and n stable isotopes 13c and 15n radiocarbon content 14c and molecular fingerprinting pyrolysis gas chromatography mass spectrometry py gc ms the results indicated that cryoturbated organic matter could be highly bioavailable soil organic matter som associated with fine sand particles was considered to be the organic carbon pool most sensitive to the changing climate more organic matter is stabilized on clay minerals in arctic tundra soils compared to those in temperate and tropical soils the bioavailable soluble organic matter extracted from cryoturbated soil was found to have significant long term effects on carbon cycling the similar molecular composition between cryoturbated and surface soil organic matter suggests that the vegetation cover has not significantly changed since the early holocene furthermore the som quality in moist acidic tundra was found to be higher than that of wet nonacidic tundra with thawing permafrost and a deepening of the active layer cryotrubated organic matter could reenter the biogeochemical cycles in the arctic resulting in a positive feedback to climate change

loss of organic matter from riverine particles in deltas abstract in order to examine the transport and burial of terrigenous organic matter along the coastal zones of large river systems we assessed organic matter dynamics in coupled river delta systems using mineral surface area as a conservative tracer for discharged riverine particulate organic matter pom most pom in the rivers studied n 6 is tightly associated with suspended mineral material e g it is sorbed to mineral surfaces average organic loadings in the amazon river 0 67 0 14 mg c m 2 the river for which we have the largest dataset are approximately twice that of sedimentary minerals from the amazon delta 0 35 mg c m 2 stable carbon isotope analysis indicate that approximately two thirds of the total carbon on the deltaic particles is terrestrial the combined surface normalized isotope distinguished estimate is that 70 of the amazon fluvial pom is not buried in the delta consistent with other independent evidence aller et al 1996 losses of terrestrial pom have also been quantified for the river delta systems of columbia in the usa fly in new guinea and huange he in china if the losses of riverine pom observed in these river delta systems are representative of rivers worldwide then the surface constrained analyses point toward a global loss of fluvial pom in delta regions of 0 1 x 1015 g c y 1

tsunami earthquakes as transient phenomena 1 recent modeling of tsunami waveforms caused by tsunami earthquakes indicates that fault slip occurred along the subduction boundary close to the trench axis on the other hand it is well known that seismicity is generally very low within ca 50 km from the trench axis and this has been attributed to the stable frictional sliding properties of the subducted unconsolidated sediments this makes tsunamigenic slip near the trench difficult to explain in order to solve this dilemma i propose that transition from stable sliding to nearly zero friction with a velocity weakening property occurs as a result of areal increase of zones of elevated fluid pressure which may make fairly rapid seismic slip possible following the breakage of asperities at normal seismogenic depths this transition can be identified as seismic reflections with negative polarities which may help to rate hazards for a coming large tsunami earthquake

a silent slip event on the deeper cascadia subduction interface continuous global positioning system sites in southwestern british columbia canada and northwestern washington state usa have been moving landward as a result of the locked state of the cascadia subduction fault offshore in the summer of 1999 a cluster of seven sites briefly reversed their direction of motion no seismicity was associated with this event the sudden displacements are best explained by 2 centimeters of aseismic slip over a 50 kilometer by 300 kilometer area on the subduction interface downdip from the seismogenic zone a rupture equivalent to an earthquake of moment magnitude 6 7 this provides evidence that slip of the hotter plastic part of the subduction interface and hence stress loading of the megathrust earthquake zone can occur in discrete pulses

influence of depth focal mechanism and tectonic setting on the shape and duration of earthquake source time functions source time functions of 255 moderate to great earthquakes obtained from inversions of teleseismic body waves by tanioka and ruff 1997 and coworkers were compared in a systematic way they were scaled to remove the effect of moment and to allow the direct comparison and averaging of time function shape as well as duration time function durations picked by tanioka and ruff 1997 are proportional to the cube root of seismic moment if moments from the harvard centroid moment tensor catalog are used the average duration of scaled time functions is shorter and the average shape has a more abrupt termination for deeper events than shallower ones with a distinct change occurring at 40 km depth the complexity of the time functions as quantified by the number of subevents appears to decrease below 40 km depth furthermore among events shallower than 40 km the average duration of scaled time functions is shorter and their average shape has a more abrupt termination 1 for events with strike slip focal mechanisms compared to thrust events and 2 for the few thrust events associated with an intraplate setting compared to the majority associated with an interplate subduction boundary in each of these cases events in more technically and seismically active settings have a longer duration and a more gradual termination this can be interpreted in terms of lower stress drops and or slower rupture velocities at active plate boundaries suggesting that fault rheology depends on slip rate and may evolve as total fault slip accumulates furthermore differences in average time function shape and duration associated with different subduction zones suggest that differences exist in the rheology on the plate boundaries at the various subduction zones supporting data table is available via web browser or via anonymous ftp from ftp kosmos agu org directory append username anonymous password guest subdirectories in the ftp site are arranged by paper number information on seraching and submitting electronic supplements is found at http www agu org pubs esupp about html