time variations of δ15n of organic nitrogen in deep western subarctic pacific sediment over the last 145 ka we present 15n data of organic nitrogen 15non from a deep western subarctic pacific wsap sediment core over the last 145 ka to remove the effect of inorganic nitrogen in on bulk nitrogen bn we used the contents of in and bn and the isotopic ratios of in 15nin and bn 15nbn the contribution of in to bn was largest 59 and 15nin had lower values than 15nbn however the large contributions of in to bn and the distinct isotopic values did not largely change any variability associated with 15non in the 15nbn thus it is possible to use 15nbn in carrying out paleoceanographic research with 15n at least in the open wsap the 15non values have been affected by long term diagenesis making the values lower with depth in the sediment but the values during less productive colder periods were generally lower compared to those during neighboring productive warmer periods the results might indicate that 15non during the less productive colder periods i e glacial periods were lower than that during the productive warmer periods i e interglacial periods previous studies have reported that the biological production in wsap where it is limited by iron at present during glacial periods was at more reduced level than during interglacials despite there being more eolian dust supply during glacial periods this indicates that the increase of biological production with enhanced iron supply derived from eolian dust during the glacial periods did not occur if this is the case and alternatively the iron input from the subsurface layer to the surface mixed layer by ventilation process is more important as suggested by recent works the variations in 15non would be explained by the variations in the fe no3 ratio in the upwelled water although 15non has been affected by long term diagenesis in the sediment the usage of this isotopic ratio provides new implication regarding the past ocean circulation in the open wsap

reconstructing the sedimentation history of the bengal delta plain by means of geochemical and stable isotopic data abstract the purpose of this study is to examine the sedimentation history of the central floodplain area of the bengal delta plain in west bengal india sediments from two boreholes were analyzed regarding lithology geochemistry and the stable isotopic composition of embedded organic matter different lithofacies were distinguished that reflect frequent changes in the prevailing sedimentary depositional environment of the study area the lowest facies comprises poorly sorted fluvial sediments composed of fine gravel to clay pointing at high transport energy and intense relocation processes this facies is considered to belong to an early holocene lowstand systems tract that followed the last glacial maximum fine to medium sands above it mark a gradual change towards a transgressive systems tract upwards increasing proportions of silt and the stable isotopic composition of embedded organic matter both indicate a gradual change from fluvial channel infill sediments towards more estuarine and marine influenced deposits youngest sediments are composed of clayey and silty overbank deposits of the hooghly river that have formed a vast low relief delta floodplain close to the surface small concretions of secondary mn oxides and fe oxyhydr oxides occur and mark the fluctuation range of the unsaturated zone these concretions are accompanied by relatively high contents of trace elements such as zn ni cu and as to sum up the outcomes of this study provide new insights into the complex sedimentation history of the barely investigated central floodplain area of west bengal

lack of enhanced preservation of organic matter in sediments under the oxygen minimum on the oman margin the impingement of oxygen minima on continental margins is widely thought to promote the accumulation of sedimentary facies enriched in well preserved organic matter it is shown here however that such a relationship does not clearly apply to the productive oman margin in the arabian sea which hosts one of the most severe oxygen minima in the oceans measurements made on the 0 1 cm depth interval from fourteen box cores collected from the outer shelf upper continental slope area off oman show that 1 1 deposited organic matter is overwhelmingly of marine origin 2 2 there is no significant correlation between the abundance of sedimentary organic carbon corg and the bottom water o2 concentration 3 3 there is no relation between the sedimentary corg n ratio and bottom water o2 4 4 there is no correlation between the hydrogen index hi of the organic matter and bottom water oxygen there are however significant correlations between the corg n ratio and the i corg cr al and zr al ratios as well as between the corg n ratio and the hydrogen index these relationships are interpreted as being the result of winnowing and attendant reworking which produce a progressive increase in the corg n ratio and a decrease in the hi and the i corg ratio as organic matter becomes progressively degraded commensurate rises in the cr al and zr al ratios result from the increased proportion of heavy minerals associated with winnowed lag deposits overall these data suggest that the bottom water oxygen concentration has little effect in governing either the distribution or the degree of preservation of organic matter on this margin thus the generally high but spatially variable corg content of the sediments on the oman margin may not reflect the occurrence of an oxygen minimum but instead be the result of a high settling flux of organic matter supported by monsoon driven upwelling and post depositional redistribution of the organic material by hydrodynamic influences

physical and geoacoustic properties of surface sediments off eastern geoje island south sea of korea abstract in order to characterize and map the surface sediments of the shelf off eastern geoje island the south sea of korea sediment texture physical and geoacoustic properties were measured and calculated on eighteen core samples collected from the study area the surface sediments are characterized by both holocene sediments mostly supplied from the nakdong river and quaternary sediments e g relict sediments due to a rising of sea level during the quaternary depending on seafloor bathymetry based on the properties analyzed the study area is divided into three different geoacoustic provinces 1 province i affected directly by the nakdong river discharge 2 province ii covered by the southern branch of the nakdong river discharge and 3 province iii dominated by relict sediments mean grain size velocity and bulk density decrease from province i 7 4 1528 m s and 1 6 g cm 3 respectively to province ii 8 1 1485 m s and 1 5 g cm 3 and then increase rather rapidly in province iii 1 4 1664 m s and 2 2 g cm 3 porosity on the other hand exhibits an opposite trend increasing from province i 64 5 to province ii 73 9 and then decreasing significantly in province iii 32 9

unchanged nitrogen isotopic composition of organic matter in the south china sea during the last climatic cycle global implications the 15n of surface and down core sediments spanning the last 20 200 kyr from the entire south china sea scs ranges only from 3 0 to 6 5 with no correlation with discernible paleoclimatic oceanographic changes detailed profiles of the uppermost sediment column including fluff samples indicate a minor diagenetic overprint of 0 3 1 2 at the sediment water interface the absence of any correlation with reconstructed glacial interglacial changes in primary production terrigenous input and or sea level related basin configuration is attributed to a complete consumption of nitrate during primary production in this marginal basin during at least the last 140 000 years this in turn implies that the 15n of the nitrate used during primary production remained approximately constant during the last climatic cycle the proposed scenario infers an unchanged nitrogen isotopic composition of the western pacific subsurface nitrate between glacial and interglacial stages as well as during terminations and thus constrains proposed changes in the oceanic n inventory

marine sediment acoustics new field and laboratory data indicate that the assumption of a constant q or equivalently an attenuation coefficient that depends on the first power of frequency is unacceptable in the case of nearly all marine sediments the fluid component of marine sediments causes various forms of viscous damping that are always frequency dependent in coarser sediments overall motion of the fluid field relative to the skeletal frame causes a strong frequency dependence that depends on permeability and the tortuosity of the intergranular pores in the finer sediments local viscous losses occur near the intergranular contacts producing a viscoelastic response similar to the squeeze film phenomenon that is well known in lubrication theory both kinds of viscous damping as well as frictional losses at the grain contacts can be included in the generalized biot model which has been used to describe the acoustical response of marine sediments in this paper we summarize recent field data which illustrate the wide spread of q values that are to be expected and present some new experimental data that demonstrate both kinds of viscous damping mentioned above finally we use the model to estimate the response of a p wave based on laboratory measurements of torsional vibrations a simple mathematical model is used to establish the connection between these two modes of motion

archaeal ammonia oxidation plays a part in late quaternary nitrogen cycling in the south china sea abstract thaumarchaeota as an ammonia oxidizing archaea aoa is crucial for modern marine nitrogen cycling however little is known about its history during the quaternary climate change here isoprenoidal glycerol dialkyl glycerol tetraethers gdgts biomarkers of thaumarchaeota were used to trace the role of aoa in the south china sea scs for the past 160 kyr the gdgt 2 3 ratio was firstly argued as an indicator of contribution of shallow thaumarchaeota cluster that is more active in ammonia oxidization ao than the deep cluster and then was used to reconstruct ao in the past the inferred ao exhibited intensification in the interglacials and moreover showed strong precessional cycles with enhancements at the precessional maxima when boreal winter insolation was the highest the aoa record varied in line with isotope record of organic nitrogen 15 norg that is modulated by the strength of diazotroph n2 fixation nf suggesting a close coupling of increased ao with enhanced nf during periods of weak east asian winter monsoon eawm and hence increase of upper water stratification ao intensification a step of a series of dissolved oxygen consuming processes is hereby hypothesized to encourage nf when the eawm weakens this result might be a reference for the future nf trend in the current situation of enhanced ocean deoxygenation due to global warming

the last glacial interglacial transition in patagonia argentina the stable isotope record of bulk sedimentary organic matter from laguna potrok aike abstract an investigation of stable isotope 13 c toc and 15 n tn and elemental parameters toc tn contents and toc tn ratios of bulk organic matter 13 c toc values toc tn contents and toc tn ratios indicate that the lake approached a new state with reduced primary productivity probably induced by unfavourable growing conditions for primary producers like strengthened winds and reduced nutrient availability the steady increase in 15 n tn values presumably suggests limitation of nitrate supply for growth of primary producers resulting from a nutrient shortage after the preceding phase with high productivity nitrate limitation and consequent decreased lacustrine primary productivity continued into the early holocene 10 970 8400 cal years bp as reflected by isotopic and elemental values

response of western pacific marginal seas to glacial cycles paleoceanographic and sedimentological features abstract this paper reviews the recent progress in late quaternary studies in five northwestern pacific marginal seas especially the south china sea as an example a series of marginal seas separate asia from the pacific ocean and significantly modify the material and energy flux linkage between land and sea during glacial cycles the sea level induced environmental signal was amplified in the marginal seas giving rise to drastic changes in areas and configurations of these seas and to reorganization of sea water circulation in basins since most of the western pacific marginal seas are influenced by monsoon circulation and some of these are located within the western pacific warm pool the glacial geographic changes have produced a profound impact on regional and global climate for example the decrease of sea area and sea surface temperature sst in the marginal seas was one of the factors responsible for the enhanced aridity of inland china during the glaciation glacial intensification of the winter monsoon and increased seasonality of sst in marginal seas might explain at least partly the apparent discrepancy between the tropical paleotemperature estimations based on terrestrial and open ocean records in this region as the western pacific marginal seas trap terrigenous material supplied by east asia the deep water sedimentation rates there can be one to two orders of magnitude higher than in the open ocean down slope sediment transport is more active when the sea level changes particularly during the deglaciation at least four types of carbonate cycles have been recognized in the western pacific marginal seas and each of those contains environmental signals from the surface and deep sea water as well as from the drainage basin

attenuation of sound in marine sediments a review with emphasis on new low frequency data in many situations the acoustic properties of the bottom are important and considerable effort has been directed at their elucidation over the whole frequency range of interest to underwater acoustics at low frequencies experimental measurement of these properties is particularly difficult and uncertainty exists in the values of some key parameters the determination of compressional and shear wave attenuation has been especially challenging and it is not surprising that debate has persisted as to the magnitude of this property and its overall dependence on frequency at low frequencies this paper attempts to examine this question through a review of the relevant literature from rock mechanics and underwater acoustics with a special emphasis on low frequency data

acoustic lance new in situ seafloor velocity profiles the acoustic lance is an instrument developed to obtain in situ compressional wave velocity and attenuation q 1 profiles for a sedimentary layer of several meters thickness at the sediment seawater interface the self contained instrument consists of ten independent recording channels with a linear array of receivers embedded in the seafloor below a broadband acoustic source it provides in situ recording of full waveforms to determine interval velocity and attenuation the system can be attached to a gravity corer or to a specially designed probe a comprehensive experiment was carried out in mid atlantic ridge sediment ponds where the lance made in situ measurements and core samples were recovered core data agree well with in situ data in one location but disagree in other locations lance data indicate that the sediment ponds have similar in situ velocity distributions with an acoustic channel much thinner than that predicted by earlier investigators

a pollen record of the last 37 ka in deep sea core 17940 from the northern slope of the south china sea this paper presents the palynological record of deep sea core 17940 from the south china sea 20 07 n 117 23 e water depth 1727 m this core is about 13 30 m long and covers the last 37 ka a total of 103 samples were counted at 10 cm intervals with a time resolution of ca 360 yr three pollen zones are recognized zone p1 14c age ca 37 0 15 0 ka b p 13 06 8 70 m is characterized by the expansion of montane conifers tsuga picea and abies and colonization by temperate grassland mainly artemisia on the exposed northern continental shelf as well as by frequent natural fires indicated by high values of charcoal concentrations this implies that the climate of this period was cool and dry frequent alternations of montane conifers and grassland dominated by artemisia indicate that oscillations of comparatively cool and humid conditions with temperate and dry conditions occurred according to the oxygen isotope data the period corresponds to stage 3 and the last glacial maximum climatic warming p2 a 8 70 7 23 m 15 0 11 3 ka b p associated with a rapid rise in sea level from ca 14 ka b p is inferred by expansion of tropical subtropical broad leaved forest with a replacement of grassland by mangroves mainly rhizophora and sonneratia this time interval may be assigned to the bolling allerod warming stage subsequently climatic cooling reflected by expansion of both montane conifers and upper montane rain forests mainly podocarpus and dacrydium during the period of ca 11 3 10 0 ka b p p2 b 7 23 6 6 m may be correlated with the younger dryas cold spell the similarity of pollen assemblages during the holocene and in the surface sediment from the northern south china sea implies that the vegetation and climate during the last 10 000 years was close to those of the present during the last 1400 years human activities are reflected in the sharp increase of dicranopteris fern spores

the isotopic composition of diatom bound nitrogen in southern ocean sediments treatment of diatom microfossils from southern ocean sediments with hot perchloric acid leaves a diatom bound n fraction which is 0 4 lower in 15n than the bulk sediment typically 3 lower in recent antarctic diatom ooze results from southern ocean surface sediments indicate that early diagenetic changes in bulk sediment n content and 15n are not reflected in diatom bound n suggesting that diatom bound n is physically protected from early diagenesis by the microfossil matrix a meridional transect of multicores from the indian sector of the southern ocean shows a northward increase in the 15n of diatom bound n suggesting that diatom bound 15n like bulk sedimentary 15n varies with nitrate utilization in the overlying surface waters the 15n of diatom bound n is 3 4 higher in glacial age antarctic sediments than in holocene sediments supporting the hypothesis previously based on bulk sediment 15n that nitrate utilization in the surface antarctic was higher during the last ice age while there are important uncertainties the inferred range of utilization changes could potentially explain the entire 80 ppm amplitude of observed glacial interglacial variations in atmospheric co2

230th normalization an essential tool for interpreting sedimentary fluxes during the late quaternary there is increasing evidence indicating that syndepositional redistribution of sediment on the seafloor by bottom currents is common and can significantly affect sediment mass accumulation rates notwithstanding its common incidence this process generally referred to as sediment focusing is often difficult to recognize if redistribution is near synchronous to deposition the stratigraphy of the sediment is not disturbed and sediment focusing can easily be overlooked ignoring it however can lead to serious misinterpretations of sedimentary fluxes particularly when past changes in export flux from the overlying water are inferred in many instances this problem can be resolved at least for sediments deposited during the late quaternary by normalizing to the flux of 230th scavenged from seawater which is nearly constant and equivalent to the known rate of production of 230th from the decay of dissolved 234u we review the principle advantages and limitations of this method notwithstanding its limitations it is clear that 230th normalization does provide a means of achieving more accurate interpretations of sedimentary fluxes and eliminates the risk of serious misinterpretations of sediment mass accumulation rates

carbon stable isotope δ13c and elemental toc tn geochemistry in saltmarsh surface sediments western brittany france a useful tool for reconstructing holocene relative sea level providing a dense network of holocene relative sea level rsl records still faces some challenges such as the paucity of microfossil assemblages within some holocene sedimentary sequences recently the isotopic 13c and elemental geochemistry total organic carbon toc total nitrogen tn and c n ratios of saltmarsh sediments has showed potential for rsl reconstruction this study presents the results of new 13c toc and tn measurements obtained on surface sediments of two marshes of the brittany region france overall the distribution of 13c toc tn and c n values shows clear dependencies with elevation sediments from above and below the high tide level show contrasting tn contents clustering analyses identified three elevation dependent groups characterized by specific values of 13c toc and tn the use of this geochemical reference for rsl reconstruction is tested on a core retrieved from one of the marshes the sea level index points obtained plot in good accordance with the microfauna based rsl positions previously obtained in the region some diagenetic losses in tn are observed between modern and holocene sediments this does not appear to be harmful to the accuracy of the rsl reconstructions but suggests that c n ratios may be unreliable palaeoenvironmental proxies in this specific context

a review of nitrogen isotopic alteration in marine sediments key points use of sedimentary nitrogen isotopes is examined on average sediment 15n 14n increases approx 2 per mil during early burial isotopic alteration scales with water depth abstract nitrogen isotopes are an important tool for evaluating past biogeochemical cycling from the paleoceanographic record however bulk sedimentary nitrogen isotope ratios which can be determined routinely and at minimal cost may be altered during burial and early sedimentary diagenesis particularly outside of continental margin settings the causes and detailed mechanisms of isotopic alteration are still under investigation case studies of the mediterranean and south china seas underscore the complexities of investigating isotopic alteration in an effort to evaluate the evidence for alteration of the sedimentary n isotopic signal and try to quantify the net effect we have compiled and compared data demonstrating alteration from the published literature a 100 point comparison of sediment trap and surface sedimentary nitrogen isotope values demonstrates that at sites located off of the continental margins an increase in sediment 15n 14n occurs during early burial likely at the seafloor the extent of isotopic alteration appears to be a function of water depth depth related differences in oxygen exposure time at the seafloor are likely the dominant control on the extent of n isotopic alteration moreover the compiled data suggest that the degree of alteration is likely to be uniform through time at most sites so that bulk sedimentary isotope records likely provide a good means for evaluating relative changes in the global n cycle

testing models of past ocean chemistry using foraminifera 15n 14n previous models have attempted to explain glacial to interglacial changes in atmospheric pco2 by invoking changes in the ocean s nutrient concentration or regional changes in nutrient utilization nitrogen is limiting to primary production and has a residence time in the ocean compatible with glacial to interglacial variations but up to now there has been no geological indicator for glacial to interglacial changes in the ocean s nitrogen cycle we propose that 15n 14n ratios for the organic matrix of preserved foraminifera yield an interpretable 15n record we have developed models to study the relationship between plausible changes in the ocean s nitrogen cycle and resulting changes in the 15n 14n ratio of dissolved no3 our model results demonstrate that 15n 14n ratios exhibit excursions during periods in which the oceans are accumulating or losing nitrogen regardless of the means by which these changes occur foraminifera 15n 14n results for a pacific and an atlantic core provide evidence against wide spread glacial anoxia a consequence of many models of ocean chemistry we suggest that increasing shelf sediment denitrification upon deglaciation reduced nitrogen concentrations in the modern ocean ambiguities between the two foraminifera 15n 14n records indicate that local effects associated with changes in hydrography or ecology need to be studied further

millennial scale changes in terrestrial sediment input and holocene surface hydrography in the northern south china sea images md972146 abstract this study presents a high resolution multi proxy analysis of sediments from images core md972146 in the northern south china sea scs analyses include detailed measurements of planktonic foraminifer oxygen isotopes sediment carbonate total organic carbon toc opal and phosphorus concentrations as well as a holocene interval of planktonic foraminifer sea surface temperature sst estimates the age model of md972146 was constructed by adopting oxygen isotope stratigraphy and ams 14c dating and fine tuned further by correlation with nearby well studied sonne 17940 and hulu stalagmite isotope records the age model indicates that this record covers the past 70 000 yr from isotope stage 4 to the holocene with a nearly constant very high sedimentation rate of 50 cm kyr such sedimentation rates allow for intensive investigations of millennial scale climate variability expressed in the scs and its potential global linkages we constructed a composite terrestrial index cti for md972146 through a principal component analysis of a suite of the core proxies that are sensitive to terrestrial sediment input during the last glacial of stage 4 to stage 2 warm interstadials appear to coincide with high terrestrial sediment pulses inferred from the cti suggesting humid conditions in the scs and southern china intervals of high terrestrial input are also correlated with heinrich events suggesting an increase of eolian and possibly also of fluvial terrestrial input to the northern scs our high resolution holocene sst and salinity estimates show warm stable and humid conditions during short episodes of quasi periodic millennial scale cooling in the north atlantic superimposed on generally more humid conditions during the middle holocene 4 6 ka compared to the dry late holocene 0 4 ka the presented data provide evidence that a variety of mechanisms involving the strength of east asian summer monsoons migration of the intertropical convergence zone and processes that are analogous to those governing the el nino southern oscillation and the arctic oscillation might play important roles in modulating tropical climate during the last glacial stages and the holocene

a critical review of marine sedimentaryδ13corg pco2 estimates new palaeorecords from the south china sea and a revisit of other low latitude δ13corg pco2 records in an attempt to understand better the local biogeochemistry of the south china sea scs and to unravel the contribution of this marginal low latitude basin to changes in atmospheric co2 concentrations we analyzed the carbon isotopic composition of organic matter 13corg in four sediment cores from throughout the scs covering the last 220 kyr higher values around 19 5 to 20 5 mark glacial stages while lower values around 21 to 22 5 are characteristic of interglacials following well established procedures the 13corg records are converted to local pco2 estimates on the basis of these and other low latitude 13corg pco2 estimates from the literature we present a critical evaluation of the use of 13c of bulk sedimentary organic matter to hindcast past changes in local co2 aq three crucial pitfalls are identified 1 given the present inability to quantify precisely the time varying amount of terrigenous corg input to marine sediments absolute values of pco2 estimates based on bulk sedimentary corg are questionable 2 none of the low latitude sedimentary 13corg pco2 records shows the expected correlation between temporal changes in upwelling intensity and co2 estimates most likely due to the antagonistic influences of co2 aq and phytoplankton growth rate on 13corg 3 a detailed comparison of marine 13corg pco2 records with the vostok co2 record reveals significant differences in phasing specifically at the end of the last deglaciation and during the oxygen isotope stage 5 4 transition however in areas where equilibrium between oceanic and atmospheric co2 occurs for example the scs and the mediterranean the timing of changes in 13corg should agree with the co2 record from ice cores if 13corg is a reliable proxy for changes in co2 aq taken together the compilation of records presented here cautions the use of 13corg as an unambiguous tracer of dissolved molecular co2 in the surface ocean and calls for a re evaluation of the role of the low latitude ocean on temporal changes in atmospheric co2

evidence from chlorin nitrogen isotopes for alternating nutrient regimes in the eastern mediterranean sea abstract nitrogen isotopes of chlorins degradation products of chlorophyll reflect the isotopic composition of nutrient n utilized by marine phytoplankton communities here we show that in sediments of the eastern mediterranean pleistocene and holocene values of 15n for chlorins and total nitrogen vary in concert with a consistent offset of 5 reflecting the fractionation imparted during chlorophyll biosynthesis samples from the integrated ocean drilling program sites 964 and 969 were analyzed at a sampling resolution of 4 10 cm clustered around sapropel events 2 3 4 and 5 100 170 ka in low organic content sediments chlorin values of 0 coincident with total nitrogen values of 5 indicate that the latter reflects the original biomass and is not a consequence of diagenetic isotope enrichment in sapropel horizons the chlorin and total nitrogen values are 5 more negative 5 and 0 respectively resembling previously reported modern day water column particulates 0 we suggest that nutrient conditions in the eastern mediterranean correspond to three scenarios and that the similarity between sapropel and modern day bulk 15n is coincidental organic poor marl sediments formed under oligotrophic conditions where surface productivity resulted from upwelling of atlantic sourced nitrate sapropels were characterized by enhanced diazotrophy that was likely fueled by increased riverine p fluxes to surface waters present day conditions are dominated by anthropogenic n sources these scenarios agree with a model of sapropel formation in which stratification caused by increased fresh water inputs led to n fixation due to p n nutrient imbalance enhanced production combined with stratification promoted and maintained anoxic deep waters consequently increasing organic matter preservation such a model may be relevant to interpreting other episodes of intense organic matter deposition in past oceans

distributions and vertical variation patterns of sound speed of surface sediments in south china sea the distributions of sound speed show different characteristics in continental shelf continental slope and nansha trough the differences have closely related to the distributions of sediment physical properties in the southern south china sea according to the analysis of sound speeds and physical properties variation characteristics with buried depth the vertical variations of sound speed are closely related to sediment texture sedimentary environment transport erosion compaction consolidation etc the comparison results indicate 3 vertical variation patterns of sound speed increasing model invariant model and complicate variation model the above 3 variation models represent the vertical distribution characteristics of sound speed in different depositional environments different variation patterns have different key factors which generally contain porosity or grain size the calculated sound speeds with buckingham s theory of compressional waves in fluid like marine sediments follows the trend of measured speeds accurately c 2014 elsevier ltd all rights reserved

influence of lateral particle advection and organic matter degradation on sediment accumulation and stable nitrogen isotope ratios along a productivity gradient in the canary islands region abstract we compare total and biogenic particle fluxes and stable nitrogen isotope ratios 15n at three mooring sites along a productivity gradient in the canary islands region with surface sediment accumulation rates and sedimentary 15n higher particle fluxes and sediment accumulation rates and lower 15n were observed in the upwelling influenced eastern boundary region ebc compared to the oligotrophic sites north of gran canaria european station for time series in the ocean canary islands estoc and north of la palma lp the impact of organic matter degradation and lateral particle advection on sediment accumulation was quantified with respect to the multi year flux record at the estoc remineralisation of organic matter in the water column and at the sediment surface resulted in an organic carbon preservation of about 0 8 and total nitrogen preservation of about 0 4 of the estimated export production higher total and carbonate fluxes and accumulation rates in the lower traps and surface sediment compared to the upper traps indicated that at least 50 of the particulate matter at the estoc was derived from allochthonous sources low 15n values in the lower traps of the estoc and lp point to a source region influenced by coastal upwelling we conclude from this study that the reconstruction of export production or nutrient regimes from sedimentary records in regions with strong productivity gradients might be biased due to the mixture of particles originating from autochthonous and allochthonous sources this could result in an imprint of high productivity signatures on sedimentation processes in oligotrophic regions

geoacoustic provinces of the south sea shelf off korea abstract in order to characterize geoacoustic provinces of the south sea shelf of korea sediment texture physical and geoacoustic properties p wave velocity were measured and calculated based on approximately 350 core samples collected from the study area the empirical relationship between mean grain size and velocity suggested by hamilton was used for calculation of p wave velocity the inner shelf sediments of the south sea are characterized by holocene muddy sediments derived from nearby rivers i e mostly supplied from nakdong and seomjin rivers near the korean shore whereas the outer shelf areas are dominated by quaternary sediments e g relict sediments due to a rising of sea level during the quaternary depending on seafloor bathymetry in this study the seafloor of the south sea shelf is differentiated into 4 provinces based on sediment properties esp mean grain size and velocity province i consisted of muddy sediments affected directly by the nakdong and seomjin rivers discharge province ii was covered by the sediments transported from two rivers province iii is marked by mixed holocene fine materials and coarse pleistocene materials province iv is dominated by relict sediments characterized by pleistocene coarse sandy materials mean grain size velocity and wet bulk density increase from province i 7 4o 1515 m s and 1 52 g cm 3 respectively through province ii 5 4o 1597 m s and 1 69 g cm 3 to province iii 2 9o 1766 m s and 2 0 g cm 3 porosity on the other hand exhibits an opposite trend decreasing from province i 71 3 to province ii 60 3 and decreasing significantly in province iii 44 6 province iv is characterized by the highest velocity 1979 m s average and the coarsest material 2 1o nevertheless the values of physical properties such as wet bulk density porosity and density lie between province ii and iii

beware intercepts interpreting compositional ratios in multi component sediments and sedimentary rocks the corganic ntotal ratio and the hydrogen index hi are commonly used to describe the bulk composition the sources and the post depositional alteration of sedimentary organic matter data from modern sediments and sedimentary rocks frequently show significant intercepts and strong linear relationships in plots of corganic vs ntotal and of s2 vs corganic for many different data sets demonstrating that the ratios are not constant across the range of organic matter contents the presence of such intercepts whose causes are well understood means that changes in corganic ntotal and hi as corganic changes cannot be used to infer different organic matter sources and or post depositional alteration or degrees of organic matter preservation of different sediment fractions moreover the strong linear regressions in such x y plots imply that the organic fraction of sediments and sedimentary rocks in any given setting or stratigraphic section generally has a uniform composition

nitrogen isotope variations in santa barbara basin sediments implications for denitrification in the eastern tropical north pacific during the last 50 000 years nitrogen isotope variations preserved in santa barbara basin sediments are used to evaluate changes in denitrification in the eastern tropical north pacific etnp during the last 50 000 years a significant component of the subsurface waters 100 400 m that presently fill the santa barbara basin is derived from the low oxygen denitrifying zone in the etnp and the nitrate in these waters has a 15n value of 8 9 during the last glacial the 15n values of santa barbara basin sediments were typically 6 7 indicating decreased denitrification in the etnp and a better oxygenated intermediate water mass in the santa barbara basin at this time this reduced denitrification during the last glacial would have increased the pool of fixed nitrogen and may have contributed to the higher productivity previously reported for various regions of the global ocean during this period at the onset of deglaciation sediment 15n values increase by more than 2 indicating increased denitrification in the etnp during younger dryas time 15n values decreased by 3 and record a brief return to better ventilated conditions in the subsurface waters of the etnp this is followed by an increase in 15n to over 9 at 10 000 years ago indicating intense denitrification at the beginning of the holocene

nitrogen isotope and chlorin paleoproductivity records from the northern south china sea remote vs local forcing of millennial and orbital scale variability abstract variations in nitrogen isotopic composition 15n and total chlorin accumulation rate ar are employed as proxies to reconstruct oceanic nitrate inventory the balance between denitrification and n fixation and paleoproductivity in a rapidly accumulating sediment drift deposit beneath the western pacific warm pool for the last 145 kyr subsurface and deep waters of the northern south china sea scs are sourced from the shallow kuroshio current kc and pacific intermediate water respectively their relative importance in determining sedimentary 15n and paleoproductivity have been altered by changes in equatorial circulation summer and winter monsoon intensity and relative sea level the location and basin configuration of the marginal scs renders it especially sensitive to such changes assuming complete annual nitrate utilization low 15n values during glacial stages are interpreted as a reflection of reduced remote denitrification in the eastern tropical north pacific etnp source waters while much of marine isotope stage mis 3 and the last interglacial were characterized by high denitrification however intervals of anomalously low 15n values are interpreted as reflecting the contribution from regional n fixation in west pacific surface waters transmitted to the site by the shallow kc unusually the holocene is characterized by declining 15n values and an inverse correlation with organic matter content since ca 8 2 ka millennial scale variations during mis 3 indicate higher frequency variations in both etnp denitrification and local n fixation which may be coherent with a hemispheric response to dansgaard oeschger events recorded at high latitudes for much of the last 145 kyr paleoproductivity was decoupled from 15n and instead seems to reflect the extent of the global nitrate inventory stimulated by elevated dust fertilization and regional mixed layer deepening associated with the relative intensity of the se asian winter monsoon despite evaluation of possible conflicting influences on the record of each proxy we interpret our data as clear evidence of glacial interglacial changes in marine nutrient inventory across the whole of the north pacific with a corresponding biogeochemical response and important implications for global co2 drawdown via an invigorated biological pump the relative importance of local regional and global contributions to our records appears to be strongly modulated by relative sea level controlling trans and extra basinal circulation in the scs

organic carbon and nitrogen contents and their isotopic compositions in surficial sediments from the east china sea shelf and the southern okinawa trough abstract the southern okinawa trough has been noted as an important depocenter for the particulate organic matter from the east china sea shelf in order to determine the major sources of sedimentary organic matter in the southern okinawa trough we analyzed surficial sediments from the east china sea shelf and the southern okinawa trough for organic carbon and nitrogen contents and their isotopic compositions in the decarbonated fraction distributions of total organic carbon content 13corg and nitrogen content all show a similar spatial pattern resembling the distribution of fine grained sediments the coastal belt of elevated organic carbon content extends southward from the changjiang mouth and veers offshore towards the southern okinawa trough just north of taiwan implying a pathway for channeling fine grained sediments from the inner shelf to the depocenter this distribution pattern is consistent with the shelf circulation the isotope compositions 13corg 15n of sediments from the southern okinawa trough fall between those of riverine particulate organic matter and the mid outer shelf sediments but overlap with those of the inner shelf sediments in addition the previously reported 13corg values of sinking particles collected by sediment traps in the southern okinawa trough are also close to those of the inner shelf sediments especially during high flux conditions therefore the isotopic evidence strongly supports the notion that a major fraction of the sedimentary organic matter in the southern okinawa trough may originate from the inner shelf

impact of glacial interglacial sea level change on the ocean nitrogen cycle the continental shelves are the most biologically dynamic regions of the ocean and they are extensive worldwide especially in the western north pacific their area has varied dramatically over the glacial interglacial cycles of the last million years but the effects of this variation on ocean biological and chemical processes remain poorly understood conversion of nitrate to n2 by denitrification in sediments accounts for half or more of the removal of biologically available nitrogen fixed n from the ocean the emergence of continental shelves during ice ages and their flooding during interglacials have been hypothesized to drive changes in sedimentary denitrification denitrification leads to the occurrence of phosphorus bearing n depleted surface waters which encourages n2 fixation the dominant n input to the ocean an 860 000 y record of foraminifera shell bound n isotopes from the south china sea indicates that n2 fixation covaried with sea level the n2 fixation changes are best explained as a response to changes in regional excess phosphorus supply due to sea level driven variations in shallow sediment denitrification associated with the cyclic drowning and emergence of the continental shelves this hypothesis is consistent with a glacial ocean that hosted globally lower rates of fixed n input and loss and a longer residence time for oceanic fixed n a sluggish ocean n budget during ice ages in addition this work provides a clear sign of sea level driven glacial interglacial oscillations in biogeochemical fluxes at and near the ocean margins with implications for coastal organisms and ecosystems

acoustic properties of coral sands waikiki hawaii an in situ experimental study of variations of compressional wave speed and attenuation with depth in natural coral sands has been made offshore of oahu hawaii in situ data were collected at a center frequency of 7 5 khz compressional wave speed averages around 1620 m s and attenuation expressed as qp 1 the reciprocal of the quality factor decreases from 0 04 at the seafloor to 0 01 at 2 m depth very little change in compressional wave speed is seen to 9 m below the seafloor coral sand sound speeds are lower than those reported elsewhere for quartz sand waveforms recorded over the upper 9 m below the seafloor exhibit virtually no peak broadening suggesting that scattering contributes little to the in situ attenuation the relationship of attenuation to frequency in the coral sands agrees with hamilton s observations of attenuation in other sediments although the coral sand attenuation is slightly higher than in other sediments the coral sand relationship between attenuation and porosity also a

geochemistry of the surface sediments of the sulu and south china seas abstract the chemical and mineralogical composition of the surface sediments of the sulu sea a deep hydrographically restricted basin in the indonesian archipelago and the neighbouring area of the south china sea have been examined the aim of the study was to characterize the geochemistry of the sediments of the isolated oxygen deficient basin and to compare them with sediments at equivalent water depths outside the basin as a prelude to a further study of the response of the composition of the sediments to oceanographic changes including possible anoxia during the last glacial maximum the concentrations of most of the chemical constituents in the surface sediments along four transects change markedly with water depth in the sulu sea ss and the south china sea scs thus caco 3 decreases from around 60 by weight in the shallowest samples 800 1000 m to around a few percent in the deepest sample at 4203 m in the scs where the ccd lies at around 4000 m in the ss however the ccd lies much deeper so that the caco 3 contents are still approximately 40 at 4500 m depth organic c also decreases with depth in both basins from values of around 1 2 in the shallowest samples to less than 1 in the deepest samples the ratios of si mg na k co cr cu ni pb rb y zr and zn to al all decrease with increasing water depth because of the change in mineralogy and sediment texture with water depth the p al is higher in shallower water in both areas because of the higher abundance of detrital phosphorite or phosphatized limestone in these sediments the sr al ratio is also higher in shallower water reflecting the supply of aragonitic shell debris from the shallow banks and shelves around the basin the ba al ratio has a maximum at 2000 m depth in the scs due to higher primary production in overlying surface waters whereas it is uniformly low in the ss manganese is also enriched at intermediate water depths in both the ss and the scs because of the presence of oxyhydroxides and this also produces a slight enrichment in mo in the same samples because of their association in this authigenic phase the concentration of i and the i c organic ratio decreases with water depth in both areas due to the higher abundance of fresh marine organic matter at the shallow water sites which scavenges proportionally more i from sea water finally the 13 c organic values tend to decrease irregularly with increasing water depth probably reflecting a higher contribution of terrestrial organic matter in deeper water a discriminant analysis of the full data set reveals that compared with the scs samples the oxygen deficient ss sediments have higher caco 3 contents lower n and s contents and lower i c organic ba al fe al k al pb al rb al ti al v al y al and zn al ratios these contrasts are brought about by the different depths of the ccd differences in the nature of the organic matter and different types of aluminosilicate detritus in the two areas although the i c organic ratios are slightly but significantly lower in the ss which may be due to the low dissolved oxygen contents of the waters of this basin the mn and mo contents and other minor elements that respond significantly to ambient bottom water oxygen levels are not significantly different in the ss and the scs moreover the organic c contents are also indistinguishable in the two areas hence the low bottom water oxygen levels in the ss do not lead to higher organic carbon contents in the surface sediments the composition of sediments in contact with waters having even lower oxygen concentrations should be evaluated in order to conduct a more definitive test of the effect of low oxygen conditions on carbon preservation comparison of glacial interglacial sediment sections from this area must take particular care to separate the effects of source variations on those potentially caused by low oxygen levels

the seasonal variation of the intrusion of the philippine sea water into the south china sea the seasonal variation of the intrusion of the philippine sea water into the south china sea was studied by analyzing the historical hydrographic station data in the northern south china sea and the philippine sea water masses at 150 200 and 250 m were classified by discriminant analysis according to their temperature salinity characteristics at each depth most water in the study region was classified into two groups representing the philippine sea water and the south china sea water respectively the geographic distribution of water masses in the south china sea shows that the philippine sea water was present along the continental margin south of china between october and january a westward current in the northern south china sea in winter was inferred from the distribution of the intrusion water

isotopic composition and speciation of sedimentary nitrogen and carbon in the okinawa trough over the past 30 ka total organic carbon to total nitrogen ratios c n and their isotopic compositions 13ctoc and 15ntn are oft applied proxies to discern terrigenous from marine sourced organics and to unravel ancient environmental information in high depositional asian marginal seas the inclusion of n bearing minerals in the bulk sediment dilutes or masks signals sought after in 15n and 13c analyses thus leading to incorrect and even contradictory interpretations we used koh kobr to separate operationally defined total organic matter into oxidizable labile and residual fractions for content and isotope measurements in a sediment core in the okinawa trough significant amounts of carbon and nitrogen existed in the residual phase in which the c n ratio was 9 resembling most documented sedimentary bulk c n ratios in the china marginal seas the residual carbon which was included in operationally defined total organic carbon toc displayed a 13c range 22 7 to 18 9 mean 20 7 similar to the oft used marine end member after removing the interference from the residual fraction we found that the temporal pattern of 13cloc loc denotes labile organic carbon was more variable the residual nitrogen content was associated with illite suggesting a terrestrial origin additionally 15n in the residual fraction likely reflected the climatic controls e g precipitation on lithogenic source materials further studies are required to explore the controlling factors for carbon and nitrogen isotopic speciation and to retrieve the information locked in the residual fraction

deep sea pollen from the south china sea pleistocene indicators of east asian monsoon abstract a high resolution pollen record sampling interval averages 820 years has been obtained from odp site 1144 water depth 2037 m northern south china sea the 504 m sequence in composition length covers the last 1 03 million years according to micropaleontological and isotopic stratigraphy the pollen assemblages are characterized by high proportions of pinus and herb pollen and by their frequent alternations based on these alternations 29 pollen zones have been recognized that are closely correlated to the marine oxygen isotope stages mis 1 29 pinus dominant pollen zones correspond to interglacial periods with lighter 18o values while herb marked ones relate to the heavier 18o stages assigned to glacials judging from the pollen data the exposed northern continental shelf of the south china sea during the glacials was covered by grassland and the extensive northern shelf has formed only since mis 6 ca 150 ka probably as a result of tectonic subsidence tree pollen influx values are indicative of winter monsoon which began to intensify 600 ka ago the summer monsoon variations can be approximated by the fern percentage within the total pollen and spore abundance and the result shows high values in general occurring at interglacials with the maxima at mis 15 5e and 1 the relatively high fern percentage with smaller amplitude in variations before 600 ka might suggest more stable humid conditions before the intensification of winter monsoon

deepwater overflow through luzon strait 1 this study examines water property distributions in the deep south china sea and adjoining pacific ocean using all available hydrographic data our analysis reveals that below about 1500 m there is a persistent baroclinic pressure gradient driving flow from the pacific into the south china sea through luzon strait applying hydraulic theory with assumptions of zero potential vorticity and flat bottom to the luzon strait yields a transport estimate of 2 5 sv 1 sv 106 m3 s 1 some implications of this result include 1 a residence time of less than 30 years in the deep south china sea 2 a mean diapycnal diffusivity as large as 10 3 m2 s 1 and 3 an abyssal upwelling rate of about 3 10 6 m s 1 these quantities are consistent with residence times based on oxygen consumption rates the fact that all of the inflowing water must warm up before leaving the basin implies that this marginal sea contributes to the water mass transformations that drive the meridional overturning circulation in the north pacific density distributions within the south china sea basin suggest a cyclonic deep boundary current system as might be expected for an overflow driven abyssal circulation

thorium 230 normalized particle flux and sediment focusing in the panama basin region during the last 30 000 years 1 application of the 230 th normalization method to estimate sediment burial fluxes in six cores from the eastern equatorial pacific eep reveals that bulk sediment and organic carbon fluxes display a coherent regional pattern during the holocene that is consistent with modern oceanographic conditions in contrast with estimates of bulk mass accumulation rates mars derived from core chronologies two nearby sites less than 10 km apart which have different mars show nearly identical 230 th normalized bulk fluxes focusing factors derived from the 230 th data at the foot of the carnegie ridge in the panama basin are 2 in the holocene implying that lateral sediment addition is significant in this part of the basin new geochemical data and existing literature provide evidence for a hydrothermal source of sediment in the southern part of the panama basin and for downslope transport from the top of the carnegie ridge the compilation of core records suggests that sediment focusing is spatially and temporally variable in the eep during oxygen isotope stage 2 ois 2 from 13 27 ka bp focusing appears even higher compared to the holocene at most sites similar to earlier findings in the eastern and central equatorial pacific the magnitude of the glacial increase in focusing factors however is strongly dependent on the accuracy of age models we offer two possible explanations for the increase in glacial focusing compared to the holocene the first one is that the apparent increase in lateral sediment redistribution is partly or even largely an artifact of insufficient age control in the eep while the second explanation which assumes that the observed increase is real involves enhanced deep sea tidal current flow during periods of low sea level stand

isotopic constraints on glacial interglacial changes in the oceanic nitrogen budget early deglacial maximum in nitrate 15 n 14 n in suboxic zones and no significant glacialto late holocene change in global ocean nitrate 15 n 14 n consistent with the work of brandes and devol 2002 we find that the steady state 15 n 14 n of oceanic nitrate is controlled primarily by the fraction of total denitrification that occurs in the water column therefore a deglacial peak in the ratio of water column to sediment denitrification caused by either a strong feedback between water column denitrification and the n reservoir or by an increase in sediment denitrification due to sea level rise can explain the observed deglacial 15 n 14 n maximum in sediments underlying water column denitrification zones the total denitrification rate and the mean ocean nitrate concentration are also important determinants of steady state nitrate 15 n 14 n for this reason modeling a realistic deglacial 15 n 14 n maximum further requires that the combined negative feedbacks from n2 fixation and denitrification are relatively strong and n losses are relatively small our results suggest that the glacial oceanic n inventory was at most 30 greater than today s and probably less than 10 greater index terms 4267 oceanography general paleoceanography 4805 oceanography biological and chemical biogeochemical cycles 1615 4845 oceanography biological and chemical nutrients and nutrient cycling 4870 oceanography biological and chemical stable isotopes keywords feedback nitrogen isotopes paleoceanography

elevated foraminifera bound nitrogen isotopic composition during the last ice age in the south china sea and its global and regional implications 1 we report a new foraminifera bound d 15 n fb d 15 n record from the south china sea scs extending back to 42 ka this record shows a 1 2 glacial to interglacial d 15 n decrease with a deglacial d 15 n maximum similar to that observed in many bulk sedimentary d 15 n records and in a caribbean fb d 15 n record the glacial to interglacial d 15 n decrease is smaller than in the caribbean record indicating that at least half of the caribbean d 15 n decrease into the holocene was regional not global supporting the interpretation of a holocene increase in atlantic nitrogen fixation at the same time the glacial to interglacial d 15 n decrease observed in the scs may also be explained as a regional signal of increasing nitrogen fixation into the holocene other aspects of the scs record suggest an effect of physical circulation on fb d 15 n fb d 15 n starts to increase toward its deglacial maximum before the last ice age ends and it continues to decrease through the later holocene in contrast to the more pure glacial deglacial interglacial steps in the caribbean record these changes have parallels in other pacific d 15 n records precessionally driven east asian monsoon records and the slow holocene warming of scs surface waters in addition the scs record exhibits two one point high d 15 n spikes in multiple foraminiferal species that coincide with apparent hydrographic events thinning or weakening of the thermocline in the late glacial and early holocene as well as during the noted events may have yielded a higher d 15 n for thermocline nitrate and thus a higher fb d 15 n

asynchronous alkenone and foraminifera records from the benguela upwelling system abstract radiocarbon stratigraphy is an essential tool for high resolution paleoceanographic studies age models based on radiocarbon ages of foraminifera are commonly applied to a wide range of geochemical studies including the investigation of temporal leads and lags the critical assumption is that temporal coupling between foraminifera and other sediment constituents including specific molecular organic compounds biomarkers of marine phytoplankton e g alkenones is maintained in the sediments to test this critical assumption in the benguela upwelling area we have determined radiocarbon ages of total c37 c39 alkenones in 20 samples from two gravity cores and three multicorer cores the cores were retrieved from the continental shelf and slope off namibia and samples were taken from holocene deglacial and last glacial maximum core sections the alkenone radiocarbon ages were compared to those of planktic foraminifera total organic carbon fatty acids and fine grained carbonates from the same samples interestingly the ages of alkenones were 1000 to 4500 yr older than those of foraminifera in all samples such age differences may be the result of different processes bioturbation associated with grain size effects lateral advection of recycled material and redeposition of sediment on upper continental slopes due to currents or tidal movement are examples for such processes based on the results of this study the age offsets between foraminifera and alkenones in sediments from the upper continental slope off namibia most probably do not result from particle selective bioturbation processes resuspension of organic particles in response to tidal movement of bottom waters with velocities up to 25 cm s recorded near the core sites is the more likely explanation our results imply that age control established using radiocarbon measurements of foraminifera may be inadequate for the interpretation of alkenone based proxy data observed temporal leads and lags between foraminifera based data and data derived from alkenone measurements may therefore be secondary signals i e the result of processes associated with particle settling and biological activity

on the sedimentological origin of down core variations of bulk sedimentary nitrogen isotope ratios 1 the bulk sedimentary nitrogen isotopic composition of two cores from nearby sites on the northern slope of the south china sea site 17940 and ocean drilling program odp site 1144 differs by up to 2 during the last glacial period given their close proximity both core sites are located in the same biogeographic zone and nutrient regime and it is thus unlikely that this offset is due to a true gradient in surface ocean conditions in an attempt to resolve this offset we have investigated the possible effects of two sedimentological parameters that can affect bulk sedimentary 15n namely the variable contribution of inorganic n to bulk n in the sediment and the grain size dependence of bulk 15n we find that neither effect singly or in combination is sufficient to explain the significant 15n offset between the two down core records by elimination the most likely explanation for the observed discrepancy is a different origin of both the organic and inorganic nitrogen at each site this study adds to the growing body of evidence highlighting the complex nature and origin of the sedimentary components in sediment drifts such as odp site 1144

plio quaternary sedimentation processes and neotectonics of the northern continental margin of the south china sea abstract analyses of over 6600 km of reflection seismic profiles on the northern continental margin of the south china sea permit the recognition of four quaternary high frequency type 1 sequences of the 4th order deposited during the past ca 690 kyr at the present day shelf edge only lowstand systems tracts characterised by a prograding clinoformal internal reflection pattern are preserved the prograding complexes can be considered as regressive units accumulated during relative sea level falls they exhibit internal discontinuities which might point to minor sea level fluctuations of the 5th order a preliminary regional relative sea level curve for the past 630 kyr is established using the present positions of the delta fronts mapped the neotectonics curve derived by subtracting eustatic sea level changes from the relative sea level curve shows that the depths of the delta fronts today are controlled primarily by regional tectonic movements and the global sea level our seismo stratigraphic interpretation documents that the area off hong kong and around the dongsha islands experienced two uplift episodes during the past 5 ma namely at the miocene pliocene boundary and at the end of the lower middle pleistocene respectively these uplift events which are centred on the dongsha rise led to its subaerial exposure and to the erosion of the pliocene and most of the pleistocene strata the change from thermal subsidence of the continental margin initiated at the end of the drift phase to the phase of magmato tectonic uplift was caused by a reorientation of the tectonic regime the recent depositional environment on the northern continental margin of the south china sea is dominated by sediment accumulation within the inner shelf and the zhujiang pearl river estuary the outer shelf and upper slope especially around the dongsha islands are characterised by bypass of terrigenous material the sedimentary column in the deepsea basin has a thickness of more than 2 km and comprises 14 depositional units starting with terrestrial rift deposits it overlies oceanic as well as transitional crust

late pleistocene nutrients and sea surface productivity in the south china sea a record of teleconnections with northern hemisphere events surface nutrient variations during the last 200 000 years have been reconstructed based on the cd ca ratios in the tests of planktonic foraminifera neogloboquadrina dutertrei and the biogenic opal content from two gravity cores retrieved from the northern and northwestern parts of the south china sea scs the cd ca ratios obtained from n dutertrei in recent sediments from fourteen box cores distributed over the scs basin reflect present nutrient levels in the overlying surface waters areas with relatively high cd ca values in the surface sediments are in the region of high chlorophyll a in the northern south china sea near the dongsha islands consistent with previous observation high values of cd ca found in sediments east of vietnam and east of the nansha islands may be a result of increased nutrients due to local upwelling induced by the summer monsoon core 17940 2 raised from the northern continental slope of the scs exhibits exceptional high sedimentation rates 25 85 cm kyr for the last 35 kyr the cd ca ratios in this core are relatively higher during the periods of late d 18 o stage 3 and the mid holocene core 17950 2 with an average sedimentation rate of 5 cm kyr offers a continuous long record back to d 18 o stage 7 in general cd ca values in the downcore records are higher during interglacials and progressively increase as the interglacials proceed values peak around the times of optimum climate conditions and correlate with periods of increased opal wt correlations in the interval of overlap between the two records support the interpretation that variations in cd ca ratios in core 17940 2 are not an individual signal but can be replicated of special interest in this study is the tentative correlation between cd ca peaks in the scs record and the timing of iceberg discharge events heinrich events in the north atlantic mass accumulation rate mar of opal data from core 17950 2 indicate high surface productivity during glacial intervals corresponding to oxygen isotope stages 6 4 and 2 the increase in surface productivity during glacials from the northern scs is contemporaneous with an intensified winter monsoon as recorded by the terrestrial loess deposits the agreement with wind strength recorded in the loess plateau from mainland china supports the

stable nitrogen isotope analysis of the upper devonian palynomorph tasmanites abstract bulk samples are commonly used in stable n isotope studies to infer climate changes however due to uncertainties in the composition of bulk samples the inconsistency of diagenetic alteration and the variation of dominant oceanic features such as n fixation and denitrification the isolation of specific sedimentary n fractions has become a crucial step to understanding the nitrogen cycle this paper describes the extraction techniques and the stable nitrogen isotope analysis on a nano ea irms of the palynomorph tasmanites spp 80 200 m found in upper devonian famennian black shales from kentucky usa tasmanites is a widely occurring and long ranging prasinophyte unicellular green algae genus palynomorphs such as tasmanites are highly resistant to most forms of decay it is therefore suggested that the 15n signature of this palynomorph may be a useful unaltered indicator of baseline isotopic change in future palaeoclimate studies the greatly reduced sample size accepted by the nano ea irms makes this technique a viable complement to bulk sediment analyses the results using the nano ea irms demonstrate that the 15n signature of the bulk organic samples differ significantly from that of the isolated tasmanites spp three distinct isotopic relationships were observed from the three different sample localities these include parallel changes in the 15n values of bulk samples and extracted tasmanites spp variation in the 15n of bulk samples with no corresponding change recorded in tasmanites spp and opposing 15n changes recorded between the bulk samples and the extracted tasmanites spp this inconsistent isotopic variation further emphasises the complexity of the nitrogen cycle possible explanations for the observed variation include changes in the rate of n fixation and denitrification due to climate change incomplete nitrification and variation in the bulk organic content

on the significance of sea level variations and shelf paleo morphology in governing sedimentation in the southern south china sea during the last deglaciation abstract deglacial sedimentation on the outer sunda shelf the shelf margin and slope shows a close correlation with the stages of flooding of the emerged shelf it is mainly controlled by the relationship between shelf paleo physiography and changes in sea level and sediment supply based on the sedimentological and geochemical variability at five sites along a transect across the outer shelf and the continental slope covering the last 20 000 years four intervals of significant depositional changes are identified the first reorganization in the sedimentation regime which was established during sea level lowstand is associated with the drowning of the lower course of the north sunda river between 16 5 and 14 5 ka during and following the rapid rise in sea level at 14 5 14 ka sedimentation on the slope is characterized by an accelerated decrease in the supply of terrigenous material associated with the flooding of the middle part of the paleo valley this abrupt change in sedimentation is followed by a period of gradual decrease of terrigenous supply to the slope when the surrounding plains of the river valley were flooded 14 8 5 ka the final change occurred between ca 8 5 and 6 ka when the coastline reached its modern position and modern sedimentary patterns are established this change probably marks the end of reworking by transgression given the synchroneity of sedimentological changes along the transect across the sunda shelf and into the deep sea with the environmental shifts on the central shelf sedimentation on the margin and slope appears to be mainly controlled by the interrelationship of sea level shelf paleo physiography and sediment supply moreover the records display lateral changes through time associated with stages of the deglacial transgression which mask any potential sedimentological variability due to changes in precipitation vegetation or atmospheric circulation this fact cautions the interpretation of near shore sedimentary records as unequivocal recorders of local climate change e g se asian monsoon and highlights the need to include variations in shelf physiography and sea level in future paleoceanographic studies

investigating the history of east asian monsoon and climate during the last glacial interglacial period 0 140 000 years mineralogy and geochemistry of odp sites 1143 and 1144 south china sea abstract monsoon climate is an important component of the global climatic system a comprehensive understanding of its variability over glacial interglacial time scales as well as of its effects on the continent and in the ocean is required to decipher links between climate continental weathering and productivity a detailed multiproxy study including bulk and clay mineralogy grain size analysis phosphorus geochemistry sedex extraction organic matter characterization and nitrogen stable isotopes was carried out on samples from odp sites 1143 and 1144 leg 184 south china sea covering the past 140 000 years we tentatively reconstruct the complex sedimentation and climatic history of the region during the last glacial interglacial cycle when sea level variations linked to the growth and melting of ice caps interact with monsoon variability during interglacial periods of high sea level summer monsoon was strong and humid and warm climate characterized the adjacent continent and islands clay minerals bear signals of chemical weathering during these intervals high calcite and reactive phosphorus mass accumulation rates mars indicate high productivity especially in the southern region of the basin during glacial intervals strong winter monsoon provided enhanced detrital input from the continent as indicated by high detrital mar glacial low sea level resulted in erosion of sediments from the exposed sunda shelf to the south and clay mineral variations indicate that warm and humid conditions still prevailed in the southern tropical areas enhanced supply of nutrients from the continent both by river and eolian input maintained high primary productivity reduced circulation during these periods possibly induced active remobilization of nutrients such as phosphorus from the sediments intense and short cold periods recorded during glacial and interglacial stages correlate with loess records in china and marine climatic records in the north atlantic confirming a teleconnection between low and high latitude climate variability

spatial and temporal offsets between proxy records in a sediment drift chronologies for late quaternary marine sediment records are usually based on radiocarbon ages of planktonic foraminifera signals carried by other sedimentary components measured in parallel can provide complementary paleoclimate information a key premise is that microfossils and other indicators within a given sediment horizon are of equal age we show here that haptophyte derived alkenones isolated from bermuda rise drift sediments are up to 7000 years older than coexisting planktonic foraminifera this temporal offset which is apparently due to lateral transport of alkenones on fine grained particles from the nova scotian margin markedly influences molecular estimates of sea surface temperatures more broadly the observation raises questions about both the temporal and the geographic fidelity of paleoenvironmental records encoded by readily transported components of sediments

influence of intermediate water in the western okinawa trough by the outflow from the south china sea although the kuroshio and the south china sea scs waters flow in and out of the luzon strait near surface the scs water mainly flows out of the scs at mid depth between 350 and 1350 m in all seasons and years that we studied the eastward flowing scs intermediate water is blocked by and joins the northward flowing kuroshio at about 122 e thus the kuroshio intermediate water kiw is composed of the west philippine sea wps proper water on the east centered at 600 m depth because the ridge east of taiwan separating the okinawa trough from the wps is mostly shallower than 600 m the eastern portion of the kiw is largely blocked by the ridge and is forced to turn eastward this water does not enter the okinawa trough freely until it reaches a deep gap in the ryukyu ridge farther north subsequently forming the eastern portion of the intermediate water in the trough the western portion of the kiw is the mixed water of scs and wps the nutrient rich scs intermediate water centered at 500 m is less influenced by the ridge and is able to flow into the okinawa trough the scs intermediate water thus retains its signature in the southern and western okinawa trough upwells onto the east china sea shelf and becomes a major source of nutrients to the shelf water

distribution of exchangeable fixed organic and total nitrogen in interbedded turbiditic pelagic sediments of the madeira abyssal plain eastern north atlantic abstract nitrogen compounds in the interbedded turbiditic pelagic sediments of the madeira abyssal plain from hereon map have been divided in separate extracted fractions such as exchangeable nitrogen nex fixed nitrogen nfix and organic nitrogen norg nex is found to be directly proportional to the amount of organic matter corg in the sediment and is not related to the amount of ammonium in the porewater only at a relatively low corg content is the nex determined by the mineralogy of the sediment the norg as determined from norg ntot nfix nex is strongly related with corg the nfix content and the n fix al ratio for organic rich sediments are high compared with other sediments and have not changed upon post depositional oxidation of the organic matter post depositional oxidation of organic matter through oxygen does lead to a decrease in the c n ratio of the remaining organic matter in the organic rich turbidites the c n ratio calculated for the organic matter that has been decomposed through oxygen is similar to that calculated through stoichiometric modelling for decomposition under reducing circumstances c n ratios of 17 and 18 respectively this implies that for the sediments of the map the c n ratio is identical for organic matter decomposed under oxygenated and under reducing conditions

organic matter in river influenced continental margin sediments the land ocean and climate linkage at the late quaternary congo fan odp site 1075 1 late quaternary sections 1 2 ma of odp site 1075 from the congo deep sea fan are investigated to reconstruct variations of terrigenous organic matter supply to the eastern equatorial atlantic to characterize the organic matter om with regard to marine and terrigenous amounts we used elemental analysis c n s stable carbon isotopes bulk 13corg rock eval pyrolysis and terrigenous biomarkers lignin phenols from cuo oxidation the records of total organic carbon toc contents corg ntot ratios bulk om degradation rates corg corg and the ratios of hydrocarbons hc from low mature versus hc from high mature om lm hm reveal pronounced cyclic changes in om abundance preservation and reactivity that are closely related to the precessional controlled record of insolation and thus to variations in upwelling intensity and fluvial run off primary productivity off the congo is stimulated by both enhanced nutrient supply in response to trade induced upwelling during arid african climates insolation minima and fluvial nutrient delivery during humid stages following insolation maxima especially due to the contribution of dissolved silica that is taken up preferably by diatoms however results stemming from a multiparameter approach reveal that the fluvial supply of degraded om and black carbon bc associated with fine grained sediments from soil erosion is a decisive factor for the preservation of marine om and in addition significantly influences the geochemical signature of bulk and terrigenous om riverine and eolian supply of c4 plant matter as well as enhanced concentrations of bc during arid and arid to humid transitional climate stages may lead to a severe underestimation of terrigenous organic carbon if its amount is calculated from bulk isotopic ratios using binary end member models during the humid stages it is the massive supply of 13c enriched soil om with low corg ntot ratios that may suggest a mainly marine composition of bulk om in fact terrigenous om governs bulk om geochemical signatures in the sediments of the congo deep sea fan a result that is contradictory to earlier studies especially to the conventional interpretation of the bulk 13corg signal

control of turbidity currents in reservoirs by solid and permeable obstacles turbidity currents are often the main process for the transport and deposition of the sediments in narrow alpine reservoirs these underwater avalanches with high concentration of suspended sediments follow the thalweg of the lake to the deepest area near the dam where the sediments can affect the operation of the bottom outlet and the intake structures to control the sedimentation within the reservoir the effects of solid and permeable obstacles on the turbidity current were investigated with physical experiments and numerical simulations in the physical experiments the velocity distributions as well as the spatial and temporal evolution of the deposits were measured the investigated measures were also simulated by means of a two dimensional numerical model based on the flow solver cfx 4 4 the investigations showed that turbidity currents can be influenced effectively by properly designed constructive measures based on the results of the physical experiments and numerical simulations some design recommendations for solid and permeable obstacles are proposed

attenuation of millennial scale events by bioturbation in marine sediments the discovery of large millennial scale oscillations 1 10 kyr period in climate records from ice cores and marine sediments in the north atlantic has motivated the search to understand their cause and evaluate the geographic extent of this variability one uncertainty in comparing marine geologic records of millennial scale variability is the extent to which mixing of sediment by organisms at the seafloor bioturbation may attenuate millennial scale events in the stratigraphic record evidence of attenuation of millennial variability can be found in cores with sedimentation rates in the range of 5 15 cm kyr modeling the attenuation of a hypothetical input time series similar to gisp2 using a moderate level of mixing provides estimates of attenuation as a function of sedimentation rate the amplitude of a 4 kyr duration event is reduced by 50 for sedimentation rates10 cm kyr and reduced by 20 for sedimentation rates of 20 cm kyr minimal attenuation 5 is achieved only when the sedimentation rate exceeds 50 cm kyr for a 4 kyr duration event and 70 cm kyr for a 2 kyr duration event the intensity of mixing plays a role in determining how much attenuation occurs the amplitude of a 4 kyr duration event in a 10 cm kyr core is reduced by 75 under strong mixing or reduced by 25 under weak mixing this study indicates that the original amplitude of dansgaard oeschger do millennial scale events observed during the last glacial may be twice the observed amplitude for cores with sedimentation rates 10 20 cm kyr that have experienced moderate bioturbation regional comparisons of the amplitude of millennial scale variability will require cores with weak mixing or sedimentation rates exceeding 50 cm kyr in order to avoid biased estimates of the amplitude of millennial scale 4 kyr duration variability

northward intrusion of antarctic intermediate water in the western pacific abstract the northward intrusion of antarctic intermediate water aaiw is examined using historical data combined with synoptic observations from a repeated hydrographic section in the western pacific ocean the results of this analysis suggest that aaiw is traced as a salinity minimum to only about 15 n via the new guinea coastal undercurrent and the mindanao undercurrent there is no northward extension of aaiw farther to the north along the western boundary although relatively high oxygen water does exist in the okinawa trough it is connected with high oxygen water in the south china sea scs through the luzon strait but not from the south as an extension of aaiw local circulation seems to play an essential role in localizing the oxygen maximum in the scs evidence exists to suggest that high oxygen water enters the scs as part of the pacific deep water around the still depth 2000 m of the luzon strait from there part of it upwells and is entrained into shallower isopycnal surfaces by vertica

an evaluation of 14c age relationships between co occurring foraminifera alkenones and total organic carbon in continental margin sediments 1 radiocarbon age relationships between co occurring planktic foraminifera alkenones and total organic carbon in sediments from the continental margins of southern chile northwest africa and the south china sea were compared with published results from the namibian margin age relationships between the sediment components are site specific and relatively constant over time similar to the namibian slope where alkenones have been reported to be 1000 4500 years older than co occurring foraminifera alkenones were significantly similar to 1000 years older than co occurring foraminifera in the chilean margin sediments in contrast alkenones and foraminifera were of similar age within 2 sigma error or better in the nw african and south china sea sediments total organic matter and alkenone ages were similar off namibia age difference toc alkenones 200 700 years chile 100 450 years and nw africa 360 770 years suggesting minor contributions of preaged terrigenous material in the south china sea total organic carbon is significantly 2000 3000 years older owing to greater inputs of preaged terrigenous material age offsets between alkenones and planktic foraminifera are attributed to lateral advection of organic matter physical characteristics of the depositional setting such as seafloor morphology shelf width and sediment composition may control the age of co occurring sediment components in particular offsets between alkenones and foraminifera appear to be greatest in deposition centers in morphologic depressions aging of organic matter is promoted by transport age offsets are correlated with organic richness suggesting that formation of organic aggregates is a key process