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

easterly denitrification signal and nitrogen fixation feedback documented in the western pacific sediments 1 a sedimentary 15n record in the equatorial western pacific wp shows glacial interglacial variability from 6 2 to 11 2 during the last two climatic cycles similar to the denitrification record in the eastern tropical pacific etp contrastively a record in the south china sea scs exhibits less changes from 4 4 to 6 4 and is quite alike previously published results in marginal seas in the wp by ruling out several possible causes for the 15n variability the 15n record in the equatorial wp is interpreted as the source nitrate 15n signals advected from the etp comparison of several 15n records for the last 25 ka distributed in the wp brings out a pattern of northward decrease in 15n values and variability from the equator to off mindano and then to marginal seas supposed to be caused by the northward increase of local n2fixation therefore the less glacial interglacial changes in some 15n records in the wp could imply that the glacial decrease in subsurface 15n due to less denitrification in source waters from the etp would have been isotopically compensated by a synchronous decrease in local n2 fixation

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

the impact of the mid pleistocene transition on the composition of submerged reefs of the maui nui complex hawaii the submarine reef terraces l1 l12 of the maui nui complex mnc the islands of lanai molokai maui and kahoolawe in hawaii provide a unique opportunity to investigate the impact of climate and sea level change on coral reef growth by examining changes in reef development through the mid pleistocene transition 900 800 ka we present an analysis of the biological and sedimentary composition of the reefs that builds directly on recently published chronological and morphological data we define nine distinct limestone facies and place them in a spatial and stratigraphic context within 12 reef terraces using rov and submersible observations these include oolitic two coral reef two coralline algal nodule algal crust hemi pelagic mud bioclastic and peloidal mud facies these facies characterise environments from high energy shallow water coral reef crests to low energy non reefal deep water settings combining the bottom observations and sedimentary facies data we report a shift in the observed sedimentary facies across the submerged reefs of the mnc from dominant shallow coral reef facies on the deep reefs to coralline algae dominated exposed outcrop morphology on the shallower reefs we argue that this shift is a reflection of the change in period and amplitude of glacioeustatic sea level cycles 41 kyr and 60 70 m to 100 kyr and 120 m during the mid pleistocene transition mpt 800 ka coupled with a slowing in the subsidence rate of the complex the growth of stratigraphically thick coral reef units on the deep pre mpt reefs was due to the rapid subsidence of the substrate and the shorter smaller amplitude sea level cycles allowing re occupation and coral growth on successive cycle low stands longer larger amplitude sea level cycles after the mpt combined with greater vertical stability at this time produced conditions conducive to deep water coralline algae growth which veneered the shallower terraces additionally we compare reef development both within the mnc and between the mnc and hawaii finally we suggest that climatic forcings such as sea surface temperature and oceanographic currents may also have influenced the distribution of coral species within the sample suite e g the disappearance of the acropora genus from the maui nui complex in the middle pleistocene

drowned coralline algal dominated deposits off lanai hawaii carbonate accretion and vertical tectonics over the last 30 ka we present detailed bathymetry remotely operated vehicle rov and submersible observations and sedimentary and radiocarbon age data from carbonate deposits recovered from two submerged terraces at 150 m t1 and 230 m t2 off lanai hawaii the tops of the terraces are veneered by relatively thin b5 m in situ accumulations of coralline algal nodule coralgal nodule halimeda and a derived oolitic facies deposited in intermediate 30 60 m to deep fore reef slope settings 60 120 m the data are used to develop a sedimentary facies model that is consistent with eustatic sea level variations over the last 30 ka both nodule facies on t1 and t2 initiated growth 30 29 ka following a fall in sea level of 50 m and increase in bottom currents during the transition from marine isotope stage 3 to 2 the nodules accreted slowly throughout the last glacial maximum when sea level was relatively stable drowning occurred during the early deglaciation 17 16 ka and was marked by the complete drowning of coralline algal nodules facies on t2 and incipient drowning of coralgal facies on t1 abrupt sea level rise during the middle deglaciation perhaps associated with global meltwater pulse 1a 14 15 ka finally drowned the coralgal facies on t1 which in turn was overlain by a deep water halimeda facies or an oolitic facies derived from upslope our data indicates that lanai has experienced relatively little vertical tectonic movement over the last 30 ka using paleobathymetric data derived from the sedimentary facies age vs depth relationships and published sea level curves we estimate that lanai could be either slowly uplifting or subsiding but at rates b0 1 m kyr uplift or b0 4 m kyr subsidence over this 30 kyr period d 2005 elsevier b v all rights reserved

southern hemisphere ionosphere and plasmasphere response to the interplanetary shock event of 29 31 october 2003 1 we analyze the effects on the southern hemisphere ionosphere and plasmasphere due to the 29 31 october 2003 geomagnetic storms the so called series of halloween storms solar wind data from ace and ionospheric data from the gps global position system ground and leo low earth orbit receivers the topex poseidon altimeter the image fuv camera and the dmsp drift meter are used to understand the ionospheric dynamics as a function of the storm phase the detailed structure of the ionosphere has been obtained using tomographic reconstruction applied to data from both ground and space based gps receivers the tomographic approach using leo observations of signals received from gps satellites above the leo s horizon allows us to investigate the topside ionospheric and plasmaspheric density distribution in more detail than can be obtained using ground based gps receivers this is because with ground based receivers the higher topside ionosphere and plasmasphere contribute only a small fraction to the total electron content tec and so the measurements are dominated by the ionospheric structure at the f2 peak in contrast the australian leo satellite fedsat which has been used for this study orbits at 800 km altitude well above the f2 peak and hence the tec measured is primarily due to the upper topside ionosphere and plasmasphere this paper presents the tomographically reconstructed topside ionosphere and plasmasphere electron density distributions using leo observations the temporal and regional maps of tec and the image fuv data show that the storm that commenced on 29 october dramatically decreased the plasma density in the southern hemisphere middle and high latitudes the region remained depleted of plasma for more than 24 hours until 31 october when the second severe storm began topex poseidon data shows a daytime localized density enhancement occurred above the middle of the pacific ocean these results show large interhemispheric and longitudinally narrow storm time structure in the ionosphere and topside ionosphere plasmasphere

examining n cycling in the northern south china sea from n isotopic signals in nitrate and particulate phases nitrogen sources and dynamics one of the key issues in marine biogeochemical cycles remain poorly constrained in marginal seas here we examine the nitrogen cycle in the northern south china sea scs by combining data from previous reports with a new dataset of n isotopic compositions 15n of nitrate zooplankton and sinking particles average 15n in subsurface nitrate is 4 8 0 3 similar to that of sinking particles 15nsink of 4 4 through the euphotic zone ez collected by floating traps and to documented mean 4 6 for long term mooring traps at 200 m this along with oft observed shallow nitracline 100 m suggests that subsurface nitrate is the primary source of new n to support export production moreover 15nsink at the bottom of the ez resembles those of suspended particles 4 2 1 0 and zooplankton 5 4 1 0 inside the ez high similarity in 15n among various types of particles including zooplankton in different size fractions in the ez implies rapid n turnover in the ecosystem in deep waters at 2000 3000 m however additional particulate n fluxes are found due to lateral transport which contain 15n depleted particles resulting in a downward decreasing trend of 15nsink incorporation of lighter n by bacteria and selective export of picoplankton are proposed as alternative mechanisms contributing to low 15nsink in the deep waters the significant 15nsink change in the deep water column makes the scs different from most other marginal seas thus caution should be made when using sedimentary 15n to reconstruct paleo nitrogen processes

bathymetric distribution of ichnocoenoses from recent subtropical algal nodules off fraser island eastern australia abstract coralline algal nodules living on the subtropical shelf off fraser island eastern australia from the inner to the uppermost outer shelf from 28 to 117 m water depth are pervasively bioeroded five ichnogenera have been identifed as nodule borers comprising one ichnotaxon attributed to bivalves gastrochaenolites one to sponges entobia and three to polychaetes and barnacles trypanites maeandropolydora rogerella microtraces comparable to those produced by fungi algae bacteria and or sponges are also present two ichnocoenoses have been recognised the shallow water ichnocoenosis egtm occurs at 60 m and shallower depths and includes all identified ichnogenera the deep water ichnocoenosis from 68 to 117 m is characterised by trypanites and the trypanites maeandropolydora network tm ichnocoenosis with a generally higher boring density than in shallower nodules decreasing size of algal nodules and reduced thickness of the coralline thalli probably explain the decrease in diversity of ichnogenera with depth as the larger bioeroders are excluded from the ichnoassemblages lower growth rates favour higher density of bioerosion in deeper algal nodules

re assessing the nitrogen signal in continental margin sediments new insights from the high northern latitudes organic and inorganic nitrogen and their isotopic signatures were studied in continental margin sediments off spitsbergen we present evidence that land derived inorganic nitrogen strongly dilutes the particulate organic signal in coastal and fjord settings and accounts for up to 70 of the total nitrogen content spatial heterogeneity in inorganic nitrogen along the coast is less likely to be influenced by clay mineral assemblages or various substrates than by the supply of terrestrial organic matter tom within eroded soil material into selected fjords and onto the shelf the 15 n signal of the inorganic nitrogen 15 ninorg in sediments off spitsbergen seems to be appropriate to trace tom supply from various climate and ecosystem zones and elucidates the dominant transport media of terrigenous sediments to the marine realm moreover we postulate that with the study of sedimentary 15 ninorg in the atlantic arctic gateway climatically induced changes in catchment s vegetations in high northern latitudes may be reconstructed the 15 norg signal is primarily controlled by the availability of nitrate in the dominating ocean current systems and the corresponding degree of utilization of the nitrate pool in the euphotic zone not only does this new approach allow for a detailed view into the nitrogen cycle for settings with purely primary produced organic matter supply it also provides new insights into both the deposition of marine and terrestrial nitrogen and its ecosystem response to paleo climate changes

the miocene nullarbor limestone southern australia deposition on a vast subtropical epeiric platform abstract the early to middle miocene nullarbor limestone forms the vast karsted nullarbor plain in southern australia and may be the most extensive miocene carbonate deposit described to date these carbonates were deposited at southern paleolatitudes of 40 s and are interpreted to be subtropical to warm temperate in character because of the presence of certain genera of tropical coralline algae rhodoliths and articulated types large benthic foraminifera tropical molluscs zooxanthellate corals and micrite envelopes facies are dominated by skeletal grainstones and floatstones that accumulated in three interpreted paleoenvironments 1 seagrass banks upper photic zone 2 rhodolith pavements lower photic zone and 3 open seafloors lower photic to subphotic zone a decrease of tropical components from west to east across the platform implies that warm oceanic currents possibly related to a proto leeuwin current as well as a period of warm climate miocene climatic optimum resulted in subtropical deposition at southern latitudes the southern ocean extended inboard 450 km from the shelf edge during nullarbor limestone deposition but interpreted paleodepths did not extend much below the base of the photic zone a small slope angle 0 02 over a wide shelf 300 000 km2 implies deposition on an epeiric platform or epeiric ramp a miocene barrier reef was likely coeval with nullarbor limestone deposition therefore the inboard portion of the nullarbor limestone can be considered part of an extensive back reef lagoon system on a rimmed epeiric platform perhaps attaining a size similar to the modern great barrier reef system

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

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

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

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

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

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

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

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

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

the paris ocean altimeter in orbit demonstrator mesoscale ocean altimetry remains a challenge in satellite remote sensing conventional nadir looking radar altimeters can make observations only along the satellite ground track and many of them are needed to sample the sea surface at the required spatial and temporal resolutions the passive reflectometry and interferometry system paris using global navigation satellite systems gnss reflected signals was proposed as a means to perform ocean altimetry along several tracks simultaneously spread over a wide swath the bandwidth limitation of the gnss signals and the large ionospheric delay at l band are however issues which deserve careful attention in the design and performance of a paris ocean altimeter this paper describes such an instrument specially conceived to fully exploit the gnss signals for best altimetric performance and to provide multifrequency observations to correct for the ionospheric delay furthermore an in orbit demonstration mission that would prove the expected altimetric accuracy suited for mesoscale ocean science is proposed

deglacial mesophotic reef demise on the great barrier reef abstract submerged reefs are important recorders of palaeo environments and sea level change and provide a substrate for modern mesophotic deep water light dependent coral communities mesophotic reefs are rarely if ever described from the fossil record and nothing is known of their long term record on great barrier reef gbr sedimentological and palaeo ecological analyses coupled with 67 14c ams and u th radiometric dates from dredged coral algae and bryozoan specimens recovered from depths of 45 to 130 m reveal two distinct generations of fossil mesophotic coral community development on the submerged shelf edge reefs of the gbr they occurred from 13 to 10 ka and 8 ka to present we identified eleven sedimentary facies representing both autochthonous in situ and allochthonous detrital genesis and their palaeo environmental settings have been interpreted based on their sedimentological characteristics biological assemblages and the distribution of similar modern biota within the dredges facies on the shelf edge represent deep sedimentary environments primarily forereef slope and open platform settings in palaeo water depths of 45 95 m two coral algal assemblages and one non coral encruster assemblage were identified 1 massive and tabular corals including porites montipora and faviids associated with lithophylloids and minor mastophoroids 2 platy and encrusting corals including porites montipora and pachyseris associated with melobesioids and sporolithon and 3 melobesiods and sporolithon with acervulinids foraminifera and bryozoans based on their modern occurrence on the gbr and coral sea and modern specimens collected in dredges these are interpreted as representing palaeo water depths of 100 m respectively the first mesophotic generation developed at modern depths of 85 130 m from 13 to 10 2 ka and exhibit a deepening succession of 100 m palaeo water depth through time the second generation developed at depths of 45 70 m on the shelf edge from 7 8 ka to present and exhibit stable environmental conditions through time the apparent hiatus that interrupted the mesophotic coral communities coincided with the timing of modern reef initiation on the gbr as well as a wide spread flux of siliciclastic sediments from the shelf to the basin for the first time we have observed the response of mesophotic reef communities to millennial scale environmental perturbations within the context of global sea level rise and environmental changes

on the dynamics of the south china sea deep circulation 1 in the south china sea scs the deep water is confined to a bowel type trench and the maximum depth is approximately 4700 m the luzon strait is the only deep connection between the scs and the pacific ocean with the deepest sill at about 2400 m in the bashi channel using the hybrid coordinate ocean model this study gives a good description of the scs deep circulation the most obvious features are basin scale cyclonic gyre and western intensification the gyre is elliptical shaped and its major axis is northeast southwest a numerical experiment is designed to investigate what could be possibly responsible for the scs deep circulation the results reveal that the deepwater overflow through the luzon strait controls over the basin scale circulation structure in the deep scs basin the driving mechanism is elucidated based on the potential vorticity pv integral constraint which means the pv inflow across the boundary is balanced by the net pv dissipation along the boundary

recent macroids on the kikai jima shelf central ryukyu islands japan sandy and gravelly carbonate sediments found off kikai jima southern japan a coral reef related island shelf represent the northernmost sub tropical carbonate deposits in the central ryukyu islands ryukyus on the kikai jima shelf at water depths of 61 to 105 m these sediments are characterized by macroid pavements since the abundance of very small and of exceptionally large macroids may indicate specific hydrodynamic controls regarding constraints on growth and taphonomy the detailed analysis of recent and fossil macroid pavements is meaningful ecologically and environmentally macroids ranging in size from ca 25 to 130 mm in diameter are spheroidal and sub spheroidal in shape and consist mainly of the encrusting foraminifer acervulina inhaerens and subordinate thin encrusting and lumpy coralline algae accessory components include bryozoans serpulids and to a lesser extent encrusting arborescent foraminifera homotrema and miniacina low sedimentation rates and occasional movement due to current action are indicated by sizes shapes and growth forms of the studied macroids the entobia gastrochaenolites trypanites maeandropolydora ichnocoenosis and the bioerosion index for coated grains introduced herein the deep water tidally induced current energy was sufficient to maintain multi directional growth spheroidal shapes of the larger macroids and to initiate macroid growth using the diverse biogenic remnants as nuclei the asymmetrical inner arrangement suggests possible periods of stability for the macroids the residence time of the coated grain in its original environment determines the size and morphology of the macroid and the selection of coating organisms the composition of the coating community is mainly a consequence of component growth rates in relation to turnover time and residence time long term studies are needed to assess the spatial and temporal resolution of present day encrusting communities across biogeographic provinces and shelf to slope regions

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

sediment cd and mo accumulation in the oxygen minimum zone off western baja california linked to global climate over the past 52 kyr 1 concentrations of organic carbon orgc cadmium cd and molybdenum mo were measured in two sediment cores raised from depths of 430 and 700 m within the oxygen minimum zone omz off southern baja california at a temporal resolution of 0 5 kyr over the past 52 kyr these records are supplemented with diffuse spectral reflectance dsr measurements obtained on board ship soon after collection at a resolution of 0 05 kyr in the core from 700 m depth a component extracted from the dsr data and the three geochemical proxies generally vary in concert with each other and over a wide range 4 22 orgc 1 40 mg kg cd 5 120 mg kg mo intervals of increased orgc cd and mo accumulation generally correspond to warm periods recorded in the oxygen isotopic composition of greenland ice with the exception of the bolling allerod which is only weakly expressed off baja california concentrations of the biogenic proxies are higher in the core from 430 m depth but erratic sediment accumulation before 15 ka precludes dating of the older intervals that are laminated and contain elevated orgc cd and mo concentrations the new data provide further evidence of an intimate teleconnection between global climate and the intensity of the omz and or productivity along the western margin of north america on the basis of a comparison with cd and mo records collected elsewhere in the region we conclude that productivity may actually have varied off southern baja california by no more than a factor of 2 over the past 52 kyr

ionospheric calibration of radar altimeters using gps tomography we compare tec measurements from the nasa radar altimeter and doris instrument on board topex poseidon with gps tec estimates and evaluate different gps data analysis strategies we verify that global tomographic gps analysis using a voxel grid is well suited for ionospheric calibration of altimeters we show that a 1 day fit of 20 second averaged nra ionospheric correction data versus gps tomographic tec data has a bias of 3 4 tecu and a root mean square deviation of 3 2 tecu tomographic inversion using simulated data from the parametrized ionospheric model highlights the strong correlation between gps bias constants electronic densities at the highest layer and unmodeled protonospheric tec this suggests that gps tec estimates at the topex poseidon altitude are more accurate if the bias constants are estimated and if a layer above topex poseidon is added to the grid

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

contrasting facies patterns in subtropical and temperate continental slope sediments inferences from east australian late quaternary records abstract studies of latest quaternary continental slope sediments at two localities on the east australian margin have revealed markedly different responses to late quaternary sea level fluctuations offshore of noosa in the sub tropics the sediment is predominantly a mixture of fine metastable carbonate siliciclastic material and pelagic carbonate important features of the stratigraphy include a siliciclastic dominated facies deposited relatively slowly during the last glacial lowstand sedimentation rate 8 cm ka and a calcareous facies rich in metastable carbonate deposited more rapidly during the late post glacial transgression sedimentation rates 15 24 cm ka highstand and transgressive sedimentation rates are greater than lowstand rates by a factor of 2 5 6 due to increased shelf carbonate productivity after flooding of the mid shelf off sydney in temperate latitudes continental slope sediment is largely a mixture of fine siliciclastic material and pelagic carbonate mean sedimentation rates range from 2 to 5 cm ka over the last four oxygen isotope stages with mean glacial interstadial rates higher than holocene rates by a factor of 1 36 this largely reflects the transfer of siliciclastic mud from the shelf to the slope during sea level regression in both localities facies changes on the slope are not related to specific sea level states e g lowstand facies transgressive facies etc but reflect instead the interaction of changing sea level with shelf morphology

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

platforms of the nicaraguan rise examples of the sensitivity of carbonate sedimentation to excess trophic resources the nicaraguan rise is an active tectonic structure in the western caribbean carbonate accumulation on its platforms has not kept pace with relative holocene sea level rise despite a tropical location remote from terrigenous sedimentation trophic resources apparently exceed levels favoring coral reef development because sponge algal communities dominate the drowning western platforms in contrast to mixed coral algal benthos on pedro bank and well developed coral reefs along the north coast of jamaica concentrations of biotic pigments in sea surface waters show a corresponding west east gradient oceanic waters flowing over the western banks carry nearly twice as much biotic pigment as oceanic waters north of jamaica sources enriching the western caribbean are terrestrial runoff upwelling off northern south america and topographic upwelling over the nicaraguan rise that relatively modest levels of trophic resources can suppress coral reef development holds important implications for understanding carbonate platform drownings in the geologic record

classification of the australian continental shelf based on predicted sediment threshold exceedance from tidal currents and swell waves abstract estimates of significant wave height and period together with tidal current speed over a semi lunar cycle were used to predict the area on the australian continental shelf over which unconsolidated sediment was mobilised threshold exceedance these sediment entraining processes were examined independently to quantify their relative importance on the continental shelf using observed grain size data mobilisation from swell waves occurred on 31 and tidal currents on 41 of the continental shelf swell wave energy is sufficient to mobilise fine sand 0 1 mm diameter to a water depth of 142 m on the otway shelf near the western entrance to bass strait tidal currents in king sound northwest shelf are capable of mobilising large areas of medium sand 0 35 mm diameter 100 of the time superimposing the distribution of threshold exceedance by wave and tidal currents indicates that there are areas on the shelf where either wave induced or tidal currents dominate some areas where waves and tides are of relatively equal importance and still other areas where neither is significant we define six shelf regions of relative wave and tidal energy zero no mobility waves only wave dominated mixed tide dominated and tides only our results provide a predictive process based understanding of the shelf sedimentary system that has applications to marine engineering projects and to regional studies of pollution dispersal and accumulation where significant shelf sediment mobilisation is a factor

an assessment and calibration of formulations for bagnold s bedload equation abstract bagnold s bedload equation in the form q u ucr 3 has frequently been employed to predict sediment mass transport rates in tidal flows and to assist with the interpretation of ancient tidal deposits however physical considerations suggest that the form q u2 u2cr u is more correct this latter formulation is therefore calibrated with experimental data and the coefficient of proportionality is shown to be strongly dependent on the sediment grain size

nitrogen isotopic composition of sediments from the eastern tethys during oceanic anoxic event 2 abstract low nitrogen isotopic compositions 15n have been reported in deposits from the proto north atlantic and western tethys during oceanic anoxic event 2 oae2 at the cenomanian turonian c t transition it has been proposed that the low 15n values may have resulted from enhancement of n2 fixation and or incomplete assimilation of the upwelled ammonium due to expansion of anoxic euxinic conditions however few 15n measurements are available for the sediments from the eastern tethys and the pacific and therefore the global significance of the n cycle and its environmental implications remains to be tested here we present 15n data from oae2 deposits in the gongzha section in the tingri area of southern tibet which was located on the southern margin of the eastern tethys during the mid cretaceous the 15n data reveal a large perturbation of the n cycle during oae2 the pronounced negative shift in 15n prior to oae2 as well as the persistent low 15n values during oae2 imply the significant contribution of n2 fixation the changes in the marine n cycle suggest that the expansion of an anoxic environment may also have occurred in the southern continental margin areas of eastern tethys the coincidence of the marine faunal turnover and the perturbation of the n cycle suggests that the expansion of anoxic water masses may have played an important role in the extinction of marine organisms across the c t boundary in eastern tethys

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

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

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

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

quiet and perturbed ionospheric representation according to the electron content from gps signals 1 signals from global positioning system gps satellites received at the surface of the earth have passed through the terrestrial atmosphere and are therefore affected by refraction in the ionosphere a large number of permanent dual frequencies gps tracking stations have been built up in the last years and their data have proved to be suitable to study the ionosphere the main goal of this paper is to assess the capability of these observations to continuously and routinely monitor the ionosphere at a global scale the interest was focused on retrieving the coefficients of a spherical harmonics expansion that describe the global distribution of the vertical total electron content vtec from the gps signal to test our results we compare them with other gps derived results with vtec values computed with the international reference ionosphere iri 95 model and with direct vtec determinations provided by topex poseidon satellite a large set of global vtec maps with a time resolution of 2 hours was used to describe the evolution of this ionospheric variable at quiet geomagnetic periods during the year 1997 the outstanding features of the vtec during the 15 may 1997 geomagnetic storm have also been studied the results show that our method is able to identify large scale features and seasonal variations of the vtec in quiet conditions as well as its variations during a large geomagnetic storm

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

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

carbonate sedimentation on subtropical shelves around lord howe island and balls pyramid southwest pacific abstract lord howe island and balls pyramid are mid oceanic basaltic islands 20 km apart in the tasman sea subaerial carbonates dating back at least 350 ka and a holocene fringing reef occur on lord howe island no reefs or subaerial carbonate deposits occur on balls pyramid both islands sit near the centre of wide shelves that are on average 40 50 m deep with a distinct break of slope between 70 and 100 m depth the lord howe shelf is characterised by a discontinuous drowned ridge which rises to 30 m depth and is located between the mid shelf and shelf edge it is composed of limestone and is interpreted as a fossil reef being veneered by holocene coralline algae early to middle holocene branching coral gravel is found in the lee of the fossil reef indicating limited give up reef growth during the postglacial transgression the surface sediments across the shelf are calcareous except in close proximity to the island where volcanic content is significant coralline algae represent the dominant grain type with minor amounts of coral bryozoans halimeda and foraminifera are common however they are not volumetrically important rhodoliths and molluscs occur near the shelf edge and appear to have accumulated at times of lower sea level these subtropical shelves are mid oceanic examples of the transition between tropical and temperate carbonate sedimentation they indicate the potential for carbonate production on broad planated shelves outside reef forming seas

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

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

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

evaluation of the topex poseidon dual frequency ionosphere correction the nasa altimeter on board topex poseidon exploits the difference in the delays of the ku and c band radar pulses to estimate an ionosphere correction to the range measurement the dependence of the ionosphere correction on ocean and satellite parameters is less than 1 cm the standard deviation of the 1 s averaged ionosphere correction depends on the height of the ocean waves and ranges from 5 to 14 mm the accuracy of the ionosphere correction is better than 1 cm at the 1 confidence level the ionosphere correction should be averaged over 140 km 20 s along track in order to minimize its noise without sacrificing its accuracy ionosphere models must achieve an independent sample spacing of 900 km or less in order to allow a single frequency altimeter to have an ionosphere correction comparable in accuracy to that of the nasa dual frequency altimeter

a study of the kuroshio s seasonal variabilities using an altimetric gravimetric geoid and topex poseidon altimeter data the first year of topex poseidon t p altimeter data were used to study the seasonal variabilities of the kuroshio current the intercomparison between the t p and gauge sea levels at selected tide gauge stations around taiwan shows that the two have a correlation of about 0 9 at the immediate vicinity of the deep ocean and both show an annual cycle with an amplitude of 15 cm a 3 3 geoid for the western pacific was constructed by least squares collocation using gravity anomalies and sea surface gradients derived from seasat geosat ers 1 and t p altimetry to account for the oceanographic signal in the altimeter data we derived a covariance function for the gradients of the sea surface topography sst based on a global averaging concept and a spherical harmonic expansion of the levitus sst to degree 50 the accuracy of the geoid ranges from 5 to 40 cm the sst values derived from the geoid and the data along t p s descending tracks were fitted to the hyperbolic functions in a two step procedure to find the kuroshio s seasonal axes and the parameters that describe its characteristics the mean variabilities in the kuroshio s path maximum velocity baroclinic transport and width are 22 km 19 cm 8 sv and 27 km respectively the averaged percentage variability of all quantities is 25 all the variabilities are relatively large near the northeast coast of taiwan and the starting point of the kuroshio extension the large scale circulations over the western pacific were obtained by median filtering the sst at the 1334 km spatial scale the pacific s subtropical gyre is clearly visible and it shows different features over the four seasons and its kinetic energy shows possible correlations with the determined parameters over the south china sea a warm ring with a radius of 300 400 km and a center at 15 n 113 e was detected in the spring and summer

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

the systematics and significance of coralline red algae in the rhodolith sequence of the amedee 4 drill core southwest new caledonia abstract the mode of early settlement and development of the new caledonian barrier reefs is interpreted based on the study of a thick rhodolith sequence found at a depth of 126 5 m near the base of the amedee 4 drill core this sequence lies immediately above bedrock and consists of successive reef sequences which belong to the last interglacial stages of the quaternary the rhodolith sequence relates to the pioneer stage of the barrier reef development based largely on the corallinaceae taxonomy growth forms and the composition of floristic and faunistic associations in combination with sedimentological data a thick 12 3 m rhodolith sequence from 116 2 to 128 5 m depth can be subdivided into six distinct units the algal assemblage includes ten taxa which are found in present day coral reef environments i e 8 non geniculated species lithophyllum kotschyanum l pustulatum l tamiense hydrolithon reinboldii lithoporella melobesoides mesophyllum funafutiense m mesomorphum an unidentified melobesoideae one geniculated species amphiroa fragillissima and the green alga halimeda by reference to the biozonation depth range and water energy setting of their modern counterparts the different fossil assemblages can be used to reconstruct the conditions of deposition in the early reef stages the occurrence and shapes of concentrated rhodoliths indicate a development related to active growing phases fairweather periods and as well as to erosion and reworking events caused by storms at water depths less than 40 m thus forming a stabilised substrate upon blocks and debris of substrate as a result a large carbonate platform formed a similar stratal sequence can be observed in the australian great barrier reef it strongly supports our hypothesis that calcareous algae have played a significant role in reefal substrate stabilisation and building of barrier reefs

satellite altimetry the marine geoid and the oceanic general circulation for technical reasons the general circulation of the ocean has historically been treated as a steady laminar flow field the recent availability of extremely highaccuracy and high precision satellite altimetry has provided a graphic demonstration that the ocean is actually a rapidly time evolving turbulent flow field to render the observations quantitatively useful for oceanographic purposes has required order of magnitude improvements in a number of fields including orbit dynamics gravity field estimation and atmospheric variability with five years of very high quality data now available the nature of oceanic variability on all space and time scales is emerging including new findings about such diverse and important phenomena as mixing coefficients the frequency wavenumber spectrum and turbulent cascades because the surface elevation is both a cause and consequence of motions deep within the water column oceanographers soon will be able to provide general circulation numerical models tested against and then combined with the altimeter data these will be complete three dimensional timeevolving estimates of the ocean circulation permitting greatly improved estimates of oceanic heat carbon and other property fluxes

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

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

analysis of tec measurements above active seismic regions abstract ionospheric perturbations by natural geophysical activity such as volcanic eruptions and earthquakes have been studied since the great alaskan earthquake in 1964 measurements made from the ground show a variation of the critical frequency of the ionosphere layers before and after the shock in this paper we present an experimental investigation of the electron density variations before earthquakes when the low altitude satellite topex poseidon is above active seismic regions fluctuations in the integrated electron density or tec total electron content between the satellite and the ground are measured to correct the altimetry measurement the satellite was launched on august 10 1992 and an analysis of the tec fluctuations above the main earthquakes ms 5 is performed up to the end of 1995 due to different constraints the number of earthquakes considered in this study is only 706 increases as well as decreases of tec are observed above some epicentres three events are detailed and a statistical study is performed with the doris data the corresponding number of tec perturbations correlated in space and in time up to 48 h before these earthquakes is 238 i e 34 of the cases a comparison is made with tec data randomly selected during the lifetime of the satellite and ionospheric perturbations are observed in 16 of the cases this study indicates that it is possible to use tec measurements to survey these phenomena

the eocene storm dominated foralgal ramp of the western pyrenees urbasa andia formation an analogue of future shallow marine carbonate systems abstract if the ongoing phenomenon of global warming prevails three main consequences are expected in tropical seas a higher sea level a reduction in coral reefs and more intense cyclones what will shallow marine carbonate systems be like insights can be gained from the pyrenean urbasa andia formation a transgressive heterozoan like foralgal larger foraminiferal and red algal ramp that formed in middle eocene times a greenhouse interval characterized by high atmospheric co 2 content firstly the evolution of future tropical shallow marine systems subject to a sea level rise is very likely to be similar to that seen in the backstepping architecture of the urbasa andia formation secondly eocene larger foraminifers rose when the paleocene eocene hyperthermal event caused a decline in corals in tropical seas coral reefs are again among the ecosystems that are likely to be particularly affected by current global warming it is therefore probable that future shallow marine tropical ecosystems will be devoid of platform margin coral reefs heterozoan ramps being far more common thirdly strong storm influence was common on the urbasa andia carbonate ramp the most distinctive feature being a distal dune field that was formed below storm wave base by high energy return currents similar features also characterize other eocene carbonate ramps furthermore numerical simulations highlighted the effect of strong tropical cyclones during the equable climate of the eocene together this information supports the hypothesis that tropical cyclone activity may increase under future greenhouse conditions taking everything into account the transgressive storm dominated foralgal ramp represented by the urbasa andia formation can be used as a virtual analogue of future shallow marine carbonate sedimentary environments developed under greenhouse conditions

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

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

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

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

tide influenced high energy environments and rhodolith associated carbonate deposition on the outer shelf and slope off the miyako islands southern ryukyu island arc japan sediments distributed off the miyako islands southern ryukyus japan include rhodoliths larger foraminifera cycloclypeus and or bryozoan dominated carbonates of low mud content on the outer insular shelf and planktonic foraminiferal mud free carbonate sand on the slopes sidescan sonograms show large scale 2 d subaqueous dunes in the deeper shelf sediments which suggest a nw se flow direction sea bottom photographs of the slope sediments to depths of 1000 m show small scale 2 d or 3 d ripples those sedimentologic features suggest the existence of relatively high speed currents on both the shelf and slope in the area current direction and velocity have been directly measured to clarify the origin and character of the current governing the area where the rhodoliths large foraminifera are distributed the results of measurements carried out at 14 stations at depth ranges of 14 to 799 m show that the direction and velocity of the currents on the shelf and slope change semi diurnally at most shelf stations the currents at high tide are to the north northwest i e from the pacific ocean to the east china sea conversely the currents at low tide are to the south southeast from the east china sea to the pacific ocean on the slope current movements are to the west at high tide and to the east at low tide it is concluded therefore that the currents on the shelf and slopes are tidally related current speed is small in protected areas and is high on the open shelf and shelf slopes the ryukyu island arc interrupts the tidal northwestern and southeastern flow this interaction probably develops substantial turbulence and topography induced upwelling and therefore forms a natural site for the formation of mud free and or coarse sediments with rhodoliths and large formainifera

observations of the ionospheric response to the 15 december 2006 geomagnetic storm long duration positive storm effect 1 the long duration positive ionospheric storm effect that occurred on 15 december 2006 is investigated using a combination of ground based global positioning system gps total electron content tec topex and jason 1 tec and topside ionosphere plasmasphere tec gps radio occultation and tiny ionospheric photometer tip observations from the constellation observing system for meteorology ionosphere and climate cosmic satellites this multi instrument approach provides a unique view of the ionospheric positive storm effect by revealing the storm time response in different altitude regions the ground based gps tec topex jason 1 tec and topside ionosphere plasmasphere tec all reveal significant enhancements at low latitudes to midlatitudes over the pacific ocean region during the initial portions of the storm main phase from 0000 0400 universal time ut on 15 december at low latitudes the topside ionosphere plasmasphere tec increase represents greater than 50 of the tec enhancement that is observed by ground based gps receivers moreover electron density profiles obtained using the technique of gps radio occultation demonstrate that the f layer peak height increased by greater than 100 km during this time period the effects of soft particle precipitation are also apparent in the cosmic observations of topside ionosphere plasmasphere tec the positive storm effects over the pacific ocean region remain present in the equatorial ionization anomaly crest regions beyond 1200 ut on 15 december this long lasting positive storm effect is most apparent in ground based gps tec and cosmic tip observations while only a small increase in the topside ionosphere plasmasphere tec after 0400 ut is observed this indicates that the long lasting positive storm effect occurs predominantly at f region altitudes and furthermore that refilling of the topside ionosphere and plasmasphere is not the primary mechanism for producing the long lasting positive storm phase during this event the observations suggest that the enhanced eastward electric field and equatorward neutral wind are likely to play a significant role in the generation of long lasting positive storm effects

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

influence of sediment transport dynamics and ocean floor morphology on benthic foraminifera offshore fraser island australia abstract the extensive longshore sediment transport system along the se margin of australia transports yearly 500 000 m 3 of sand from the gold coast of southern queensland north towards fraser island fraser island which consists of 203 km 3 of quartz sand is presently not increasing in size and north of the island quartz sand is replaced by carbonate sand recent multibeam sonar seafloor imagery and sediment analysis has established that the transported sand is being diverted by strong ebb tidal flow over the continental shelf edge onto the tasman abyssal plain through a series of active gullies that incised the continental slope foraminiferal distribution patterns on the shelf and slope are closely linked to the variable ocean floor morphology and associated physical processes in sample locations outside the continental slope gullies areas unaffected by downslope sediment transport foraminiferal assemblages gradually change in accordance with bathymetric zones and their prevailing ecological parameters species diversity evenness the proportion of infaunal species and the abundance of agglutinated taxa all increase with depth assemblages within gullies of the clastic sand transport route are significantly different estuarine and shelf species are transported over the shelf break and mix with typical slope species along the transport path resulting in continued high species diversities as the sediment and faunal load enters the abyssal plain a faunal portion continues to travel within the capricorn sea valley to over 4000 m depth the erosional nature of gullies results in reduction of agglutinated species subtle topographic features such as ridges or levees within the canyon and deep sea valley act as protection from the main erosional sand transport pathway and support the presence of fragile and erect suspension feeders foraminiferal distribution patterns would have received an entirely different biofacies interpretation without linking them to ocean floor processes as revealed through multibeam sonar imagery

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

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

critical bed shear stress and threshold of motion of maerl biogenic gravel abstract a determination of the critical bed shear stress of maerl is a prerequisite for quantifying its mobility rate of erosion and deposition in conservation management the critical bed shear stress for incipient motion has been determined for the first time for samples from biogenic free living maerl beds in three contrasting environments open marine intertidal and beach in galway bay west of ireland the bed shear stress was determined using two methods law of the wall and turbulent kinetic energy in a rotating annular flume and in a linear flume the velocity profile of flowing water above a bed of natural maerl grains was measured in four runs of progressively increasing flow velocity until the flow exceeded the critical shear stress of grains on the bed the critical shields parameter and the mobility number are estimated and compared with the equivalent curves for natural quartz sand the critical shields parameters for the maerl particles from all three environments fall below the shields curve along with a previously reported correlation between maerl grain shape and settling velocity these results suggest that the highly irregular shapes also allow maerl grains to be mobilised more easily than quartz grains with the same sieve diameter the intertidal beds with the roughest particles exhibit the greatest critical shear stress because the particle thalli interlock and resist entrainment in samples with a high percentage of maerl and low percentage of siliciclastic sand the lower density lower settling velocity and lower critical bed shear stress of maerl results in its preferential transport over the siliciclastic sediment at velocities 10 cm s 1 higher than the threshold velocity of grain motion rarely documented subaqueous maerl dunes formed in the annular flume

estimation of annual bedload flux in a macrotidal estuary bristol channel u k sedimentological data from the bristol channel indicate that mutually evasive ebb and flood dominant zones of net bedload transport are present to test this hypothesis long term observations of currents from the channel are combined with empirical formulae to estimate annual bedload transport rates under the combined influence of tidal currents and surface wind waves extrapolating these values over the ebb and flood dominant zones sand flux to the upper part of the channel is estimated at about 64 105 t yr 1 with supply and removal being of nearly equal magnitude such patterns of sand and water movement may be typical of tidally dominated estuaries and embayments

pumice rafting and faunal dispersion during 2001 2002 in the southwest pacific record of a dacitic submarine explosive eruption from tonga a new influx of sea rafted pumice reached the eastern coast of australia in october 2002 approximately 1 year after a felsic shallow marine explosive eruption at a previously unknown volcano 0403 091 along the tofua volcanic arc tonga the eruption produced floating pumice rafts that first became stranded in fiji in november 2001 approximately i month after the eruption strandings of sea rafted pumice along shorelines have been the only record of products from this submarine explosive eruption at the remote submerged volcano computed drift trajectories of the sea rafted pumice using numerical models of southwest pacific surface wind fields and ocean currents indicate two cyclonic systems disturbed the drift of pumice to eastern australia as well as the importance of the combined wave and direct wind effect on pumice trajectory pumice became stranded along at least two thirds 2000 km of the coastline of eastern australia being deposited on beaches during a sustained period of fresh onshore winds typical amounts of pumice initially stranded on beaches were 500 4000 individual clasts per in and a minimum volume estimate of pumice that arrived to eastern australia is 1 25 x 10 5 m 3 pumice was beached below maximum tidal storm surge levels and was quickly reworked back into the ocean such that the concentration of beached pumice rapidly dissipated within weeks of the initial stranding and little record of this stranding event now exists most stranded pumice clasts ranged in size from 2 to 5 cm in diameter the largest measured clasts were 10 cm in australia and 20 cm in fiji the pumice has a low phenocryst content 3500 km and period of pumice floatation greater than or equal to1 year confirm the importance of sea rafted pumice as a long distance dispersal mechanism for marine organisms including marine pests and harmful invasive species billions of individual rafting pumice clasts can be generated in a single small volume eruption such as observed here and the geological implications for the transport of sessile taxa over large distances are significant an avenue for future research is to examine whether speciation events and volcanicity are linked the periodic development of globalism for some taxa e g corals gastropods bryozoa may correlate in time and or space with voluminous silicic igneous events capable of producing 10 6 km 3 of silicic pumice rich pyroclastic material and emplaced into ocean basins c 2004 elsevier b v all rights reserved

sand and rhodolith gravel entrainment on the mid to outer shelf under a western boundary current fraser island continental shelf eastern australia abstract carbonate sediments on the east australian continental shelf off fraser island represent a transition from the warm water tropical carbonate deposits in the north i e the great barrier reef to cool water temperate carbonate deposits in the south on the outer shelf in 40 140 m water depth these deposits are characterised by pebble to cobble sized rhodoliths current meter data obtained from this area demonstrates that near bed southward flowing currents of up to 130 cm s occur episodically to depths of over 70 m these current events may last for several days and are probably related to intrusions of the east australian current a western boundary current onto the shelf flume experiments on different size classes of rhodoliths suggests that the threshold speed referenced to 100 cm above the bed u 100 cr for 10 mm diameter rhodoliths is of the order of 45 cm s whereas u 100 cr for 50 mm diameter rhodoliths is of the order of 80 cm s therefore the shelf currents measured are competent to initiate rhodolith movement percentage exceedence of these threshold speeds ranges from 1 to 10 surface waves also generate nearbed oscillatory flows which when combined with the steady current are considered to be important in initiating movement of the rhodoliths

mobility of maerl siliciclastic mixtures impact of waves currents and storm events abstract maerl beds are free living non geniculate coralline algae habitats which form biogenic reefs with high micro scale complexity supporting a diversity and abundance of rare epifauna and epiflora these habitats are highly mobile in shallow marine environments where substantial maerl beds co exist with siliciclastic sediment exemplified by our study site of galway bay coupled hydrodynamic wave sediment transport models have been used to explore the transport patterns of maerl siliciclastic sediment during calm summer conditions and severe winter storms the sediment distribution is strongly influenced by storm waves even in water depths greater than 100 m maerl is present at the periphery of wave induced residual current gyres during storm conditions a combined wave current sediment mobility index during storm conditions shows correlation with multibeam backscatter and surficial sediment distribution a combined wave current mobilization frequency index during storm conditions acts as a physical surrogate for the presence of maerl siliciclastic mixtures in galway bay both indices can provide useful integrated oceanographic and sediment information to complement coupled numerical hydrodynamic sediment transport and erosion deposition models

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

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

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

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

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

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