abrupt change of sediment records in the southern south china sea during the last glacial period and its environment significance abstract chemical compositions of sediments at core ns07 25 6 39 945 n 113 32 936 e water depth 2006 m are analyzed to discuss abrupt change of sediment records in the southern south china sea scs during the last glacial period and its environmental implications major and trace elements experienced three significant changes which occurred at 31 9 26 1 and 18 5 ka bp respectively at 31 9 ka bp when sea surface temperature remained relatively low terrigenous sediment flux increased but biogenic activities weakened greatly at 26 1 ka bp both terrigenous sediment flux and biogenic fractions number were steady however some elemental ratios changed noticeably at that time before 26 1 ka bp core sediments with low nb ta but high zr hf ratios were mainly derived from the paleo mekong and or molengraaff rivers exposed on the sunda shelf at that time after 26 1 ka bp sediments with high nb ta but low zr hf ratios probably relate to strengthened impact of deep water current since 18 5 ka bp sea level ascended rapidly from 110 m below the present terrigenous sediment flux decreased and biogenic activities strengthened continuously probably related with the east asian monsoon evolution

sedimentary responses to sea level rise and kuroshio current intrusion since the last glacial maximum grain size and clay mineral evidence from the northern south china sea slope abstract we analyzed the terrigenous fraction of a sediment core from the northern slope of the south china sea to better understand the depositional history of the region since the last glacial maximum lgm temporal variations in the grain size and clay mineral composition revealed a complex set of overlapping controls approximately 90 of terrigenous sediment throughout the core ranged in size from 5 5 to 8 5 with the 5 25 6 25 size class being particularly sensitive to environmental changes the proportion of this fraction decreased during deglacial indicating a reduction in the supply of coarser grains due to coastline retreat as the sea level rose toward its present position the relative proportion of clay derived from taiwan increased however the mass accumulation rate of taiwan derived clay decreased suggesting a reduction in the westward bottom current intensity in contrast the relative contribution of clay from the pearl river decreased from 40 during the lgm to 5 when the sea level reached 70 m below its present position the pearl river contribution has remained consistently low throughout the holocene indicating that shore parallel circulation patterns on the shelf resembled their present configuration by 13 ka compared to taiwan and the pearl river the proportion of clay derived from the area east of pearl river epr was relatively minor and less variable a local peak in the relative contribution from this area occurred during a melt water pulse event mwp 1a suggesting that a reservoir of smectite rich clays residing in coastal bays was remobilized by this marine transgression spectral analysis of the relative contributions of the three major clay sources revealed a significant periodicity of 380 years which may reflect changes in solar insolation modulating the flux of clay minerals from taiwan and the pearl river to the deposition site on a centennial scale

upward flow of north pacific deep water in the northern south china sea as deduced from the occurrence of drift sediments 1 reflection seismic profiles show that drift sediments occur in the depth range of 1200 2800 m on the continental margin off southeast china these drift deposits were generated by upward flow near the dongsha islands of the north pacific deep water npdw which enters the south china sea via the bashi channel sill depth 2500 m this flow results in deposition of slope sediments resuspended off east and south taiwan on the slope southeast of the dongsha islands at 1200 m water depth this upward flow probably terminates and the npdw mixes with the surface water sediment ages from odp site 1144 southeast of the dongsha islands show that this process started at least 1 1 m y ago indications for mass wasting in the area of upslope water flow document the simultaneous occurrence of current and gravity controlled sedimentation processes however bottom current related drift sedimentation dominates

increased contribution of terrigenous supply from taiwan to the northern south china sea since 3 ma seismic profiles provide evidence that there has been strong transport by deep water bottom currents and drift deposition on the northern slope of the south china sea earlier geochemical studies suggest that the drift sediments originated primarily from taiwan however the transport process history and origin of the deep water bottom deposition in the northern south china sea on both glacial interglacial and tectonic time scales remain unclear here we show new high resolution records of clay minerals grain size and mass accumulation rate mar of terrigenous materials from ocean drilling program odp site 1144 together with trace element concentrations in siliciclastic sediments from odp site 1146 combined with other published data we find that the primary source for sediments at odp sites 1144 1148 since 3 ma is from taiwan and not from pearl river as previously thought before 3 ma however sediment source to odp sites 1146 and 1148 was mainly from the pearl river increased contribution of terrigenous supply from taiwan to the northern south china sea since similar to 3 ma may be related to the formation of the taiwan orogen and strengthening of deep water bottom current transport in the northern south china sea variations in clay mineralogy and sedimentology at odp site 1144 located on a sediment drift shows strong glacial interglacial cyclicity this suggests that bottom current deposition is highly dependent on sea level fluctuations which control the terrigenous supply to the deep sea c 2010 elsevier b v all rights reserved

geochemical records of taiwan sourced sediments in the south china sea linked to holocene climate changes we present a multi proxy geochemical analysis of core kng5 retrieved from the northern south china sea slope spanning the last 13 0 ka bp to assess the response of weathering and erosion processes in the southwestern taiwan river basin to climate change a provenance analysis indicates that the core sediments were primarily derived from the southwestern taiwan river and can be used to reconstruct the erosion and or weathering history of this river basin the chemical index of alteration the plagioclase index of alteration rb sr al ti principle component 1 and k al combined with terrigenous mass accumulation rates and the proportion of clay exhibit sharp excursions from 12 0 to 5 5 ka peaking at 10 0 ka which suggests strong chemical weathering and physical erosion during the early mid holocene the period of the maximum summer monsoon abrupt falling weathering trends during 5 2 and 3 5 ka bp correlate with a weaker monsoon after 3 5 ka bp a stable lower weathering trend to the present day was evident indicating the deposition of less weathered sediments in the slope when the monsoon rainfall was weakening a good correlation between our proxy records of chemical weathering and variations of the monsoon intensity in south china emphasizes that variation in monsoon intensity is most likely the primary drive of the intensity of weathering and erosion in southwestern taiwan river sediments over the last 13 0 ka bp finally we concluded that geochemical parameters can be used as reliable proxies for climate variation on a millennial centennial time scale in such areas as taiwan where weathering limited regimes exist c 2015 elsevier b v all rights reserved

the effects of diagenetic processes and fluid migration on rare earth element and organic matter distribution in seep related sediments a case study from the south china sea abstract methane seepage is an important factor governing microbial activity in marine sediments although its impact on the distribution of rare earth elements rees and organic matter in sediments is unclear here we report isotope signatures of organic 13ctoc and inorganic 13ctic carbon as well as total rees contents of core sediments collected from a well characterized seep area on the northern south china sea previous studies have identified sediments corresponding to three methane release events mres in the studied core mre i at 4 0 5 5 m mre ii at 7 4 8 2 m and mre iii at 10 0 11 5 m depth intervals increased methane flux and reducing bottom waters during mre i resulted in a higher accumulation of marine sourced organic matter as indicated by lower c n ratios and higher 13ctoc values compared with those of mres ii and iii sediments deposited during mre i have relatively low total ree contents which may be related to reduced ree adsorption on mn oxyhydroxides however the absence of ce anomaly at mre i is more likely due to the detrital input that obscures the original ce anomaly in the mre iii sediments a weak negative eu anomaly relative to that in the mre i and ii may be attributed to the reduction of eu3 to eu2 under strongly reducing conditions that caused by intense methane seepage these observations demonstrate that fluid flow may have an important effect on the distribution of both organic matter and rees in methane rich marine sediments

upper ocean currents around taiwan abstract current velocity measured by shipboard acoustic doppler current profiler sb adcp during 1991 2000 was used to study the upper ocean the composite and moored currents revealed a branch of the kuroshio that intruded steadily and persistently into the south china sea part of the intruded kuroshio flowed out of the south china sea through the northern luzon strait and re united with the main stream kuroshio the kuroshio had two velocity maximum cores southeast of taiwan but gradually combined into one as the kuroshio flowed north the kuroshio was deflected by the i lan ridge east of taiwan and the zonal running shelf break northeast of taiwan at the shelf break the kuroshio split with one branch intruding onto the shelf west of the luzon strait the kuroshio intruded into the south china sea some water flowed northward into the taiwan strait and re joined the kuroshio currents in the taiwan strait flowed primarily in a northward direction except for the southward current near the coast of mainland china north of the taiwan strait a branch of the northward flow followed the northern coast of taiwan to join the kuroshio the composite current varied consistently from season to season there was generally poor correlation between currents and local winds especially in the deep water regime remote forces were important in the currents around taiwan

three dimensional seismic characterization of a complex sediment drift in the south china sea evidence for unsteady flow regime this study describes a previously unobserved reflection seismic configuration comprising a honeycomb planform and a repeated erosion infill cross section based on high resolution three dimensional two dimensional seismic data and bathymetric data the honeycomb structures cover an area of more than 5000km 2 and are developed within the late miocene to recent deep water sediments of the north western south china sea linear erosional troughs up to 10km long and 1km wide are widely developed in this area are intimately related to the particular seismic configuration and interpreted to represent a new type of sediment drift that is caused by unsteady bottom current regimes operating since the late miocene the unsteady bottom current regimes are suggested to be triggered by irregular seabed morphologies considerable sea floor topography was generated as a direct result of tectonic movements in the area since the late miocene and this topography then influenced the pathways of strong bottom currents this study highlights that i an unsteady bottom current regime can be laterally extensive and persist for millions of years ii structurally controlled sea floor relief plays an important role in controlling the depositional pattern and iii the bottom currents were active since the late miocene flowing from the south east through the xisha guangle gateway and crossing the honeycomb structure zone this study documents a new style of drift and will help to improve current knowledge of palaeoceanography and understanding of the south china sea deep water circulation which is at present still poorly understood

grain size and geochemistry of surface sediments in northwestern continental shelf of the south china sea eighty six surface sediments collected from the northwestern continental shelf of the south china sea scs were analyzed for grain size distribution calcium carbonate organic carbon and major and trace element compositions to investigate sediment provenance and factors controlling their geochemical composition sediments from the eastern continental shelf of hainan island have higher sand and lower clay content while the samples from the nearshore hainan island have higher contents of gravel and clay calcium carbonate contents in samples show a positive correlation with water depth in northwestern shelf of scs suggesting that it is related to biological factors however the nearshore sediments have higher contents of organic carbon compared to those of the outer shelf possibly suggesting that the terrigenous organic matter usually deposited in nearshore environments such as bays and estuaries compared with the upper continental crust the samples have relatively lower contents of sio2 and al2o3 higher than those of the pearl and red river sediments the low contents of k2o and na2o in sediments from the northwestern continental shelf are consistent with intense chemical weathering in the river basin due to the seasonally hot and humid climate regime the sediments mainly consist of three components including the gravel fraction composed of calcareous debris the sand fraction composed of quartz and the silt and clay fractions mainly composed of clay minerals the content of each component depends on grain size sediment source biogenesis and hydrodynamic conditions which finally controls the chemical composition of the sediments the distributions of co al2o3 cr al2o3 and zr sc ratios for sediments in the northwestern continental shelf suggest that source rocks are mainly composed of felsic rocks rather than mafic rocks there is a distinct difference in sediment source between eastern and western shelf sediments the eastern shelf sediments are characterized by high zr sc ratios mainly derived from the pearl river while the western shelf sediments have relatively low values of zr sc indicating a main contribution possibly sourced from the red river basin terrigenous materials from hainan island usually influence the geochemistry of sediments deposited in the nearshore area

deep water bottom current evolution in the northern south china sea during the last 150 kyr evidence from sortable silt grain size and sedimentary magnetic fabric abstract deep water bottom current dwbc plays a central role in global climate relative to the atlantic due to poor preservation of marine carbonate in the pacific sediments the evolution of pacific deepwater circulation is still unclear the south china sea scs connection to the pacific through luzon strait at a depth of about 2400 m offers a unique opportunity to monitor the changes of western pacific deep water circulation we present a magnetic and grain size analysis of two sediment cores pc111 and pc83 located in xisha trough northern scs in order to reconstruct past changes of dwbc during the last 150 kyrs variations in the mean size of sortable silt are interpreted to indicate past changes of dwbc which suggest abrupt millennial scale increasing dwbc strength during heinrich stadials hs1 hs2 hs3 hs4 hs5 hs6 hs7 hs8 hs9 hs10 hs11 for past 150 kyr the flow orientation of dwbc revealed by the anisotropy of magnetic susceptibility ams are mostly nw se direction in core pc111 and core pc83 which are both parallel to the local topography combined with the published studies we suggest the increase bottom current in northern scs during the heinrich stadials hs1 to hs11 times of weak north atlantic deep water formation demonstrating the tight coupling between the atlantic and pacific oceans

foraminiferal end in the deep north western subtropical pacific ocean tracing changes in weathering input over the last 30 000 years abstract this study focuses on the neodymium isotopic composition end of mixed planktonic foraminifera species in sediment cores collected on the north western margin of the south china sea scs and in the western equatorial pacific the aim was to identify temporal changes in the end of the upper circumpolar deep water ucdw during its northward penetration in the western subtropical pacific and to re evaluate the significance of deep water end changes at the northern margin of the scs over the past 25 kyr the past seawater end record derived from sediments of the subtropical western pacific displays a narrow range from 2 9 0 3 to 1 6 0 4 this suggests that the end of the ucdw is greatly modified during its northward penetration through the process of boundary exchange along the western volcanic margin of the south pacific and that the unradiogenic end signature of the ucdw observed in the south pacific about 6 has not been propagated beyond the equatorial pacific at least not over the last 25 kyr seawater end values obtained from the northern scs display large variations with values that are lower 6 8 0 3 to 5 6 0 2 for the last glacial period than for the late holocene 5 7 0 3 to 4 1 0 2 such glacial end cannot be attributed to a higher proportion of southern sourced water ssw as end values of the ucdw in the equatorial western pacific are more radiogenic than those observed in the scs the evolution of the seawater end values of the northern scs during the last glacial period and the last climatic transition is coeval with variations in the contribution of sediments from the pearl river the low sea level stand of the last glacial period resulted in a more proximal position of the pearl river mouth relative to core md05 2904 which a higher input of freshwater and in particular detrital sedimentary particles originating from the pearl river that partially dissolved during sinking led to a decrease in the seawater end along the north western margin of the scs enhanced rainfalls associated with intensified monsoon and more frequent typhoon activities during the early holocene climatic optimum from 9 to 7 cal kyr bp are linked to a decrease in sea surface salinity lower 18o values of planktonic foraminifera and a decrease in end values 6 2 0 3 induced by lithogenic nd input from pronounced freshwater and sediment discharge from distal rivers

three dimensional geometry and interference of fault bend folds examples from the ponga unit variscan belt nw spain abstract examples of the three dimensional geometry and interference patterns between fault bend folds occur in the ponga unit of the variscan cantabrian foreland thrust and fold belt of nw spain the ponga unit consists of several e directed thrust sheets with a cumulative displacement of 93 km which were emplaced during upper westphalian stephanian time two major lateral ramps developed in the basal thrust of the ponga unit reaching 15 and 20 km in length respectively and some 3 km in height lateral structures are also common within the hangingwall thrust sheets the three dimensional staircase trajectories of thrust faults together with the tectonic superposition of thrust sheets has produced a complex interference pattern of fault related folds most map scale folds formed as fault bend folds related to interference between frontal and lateral ramps fold geometry and size varies depending on the geometry and size of the associated thrust ramp and flat the axial traces are grouped into lateral and frontal sets which are sub parallel or sub perpendicular to the tectonic transport direction respectively corner folds form with plunging axes at the intersections of frontal and lateral ramps and generally link pairs of frontal lateral folds they have relatively short axial traces that are oblique to the tectonic transport direction fold plunge varies due to the superposition of lateral and frontal structures of a thrust fault and also depends on the geometry of subsequent thrusts in the footwall the final geometry of frontal folds in the ponga unit are not only the result of the bending mechanism but have been modified by simple shear parallel to the emplacement direction major lateral structures have been reactivated as reverse faults and are locally overturned due to post emplacement north south compression

upper layer circulation in the south china sea abstract upper layer circulation is investigated by using all available historical temperature profiles combined with climatological temperature salinity relationships in the south china sea two cyclonic eddies are revealed one is located east of vietnam called the east vietnam eddy and the other is off northwest luzon called the west luzon eddy both local ekman pumping and remotely forced basin scale circulation are important mechanisms controlling these two eddies the luzon strait transport relative to 400 db is estimated to be of the order 3 0 sv 1 sv 1 106 m3 s 1 in the mean and has a seasonal cycle dominated by the annual signal with a maximum 5 3 sv in january february and a minimum 0 2 sv in june july pressure gradients are also examined to explore the dynamics of the intrusion of waters from the pacific into the south china sea through the luzon strait

depositional characteristics and processes of alongslope currents related to a seamount on the northwestern margin of the northwest sub basin south china sea this study infers from 2d seismic data the presence of a seamount related deep water contourite depositional system located on the northwestern margin of the northwest sub basin of the south china sea alongslope aligned erosive features and contourite drifts developed in water depths between 1000 and 1500 m on the present seafloor a moat formed north of the seamount as a result of bottom current intensification after being deflected by an obstacle morphology indicating a major eastward flowing current due to the coriolis deflection an elongated mounded drift developed to the north of the moat and a modest plastered drift to the south onlapping the north side of the seamount bottom currents away from the seamount are less or minimally intensified generating contourite channels and furrows over the drift to the north of the moat combined with the known oceanographic setting the bottom currents could belong to the anticyclonic south china sea intermediate water circulation from the seismic data the architecture of contourite deposits during progressive burial of the seamount is documented the first appearance of contourite channels in seismic unit 1 is inferred to be the onset of the contourite depositional system which could be traced back to the early late miocene the following aggradational pattern of this system from the base of seismic unit 2 onwards indicates relatively enhanced and stable south china sea intermediate water circulation occurring on the northwestern margin of the northern south china sea subsequently the behaviour and depositional processes of bottom currents upstream and downstream the seamount are discussed the depositional model suggests that a complex contourite channel system will replace the former moat drift system once the seamount is buried finally our findings may provide new challenges for investigating the south china sea cenozoic palaeoceanography which are helpful to understand the sedimentary dynamic processes related to the south china sea deepwater circulation c 2014 elsevier b v all rights reserved

neotectonic regime on the passive continental margin of the northern south china sea abstract between 1989 and 1994 more than 6600 km of reflection seismic profiles were obtained in the south china sea off hong kong with the german research vessel sonne during cruises so 50b so 72a and so 95 a seismo stratigraphic interpretation of this data set leads to a new age assignment of the unconformity t0 which we place within the pleistocene both neogene unconformities t1 and t0 are generated by uplift of the dongsha rise and truncation of their overlying strata this uplift is caused by intrusion of magma into the upper crust our seismic profiles show plutons which have penetrated the sedimentary cover whereby their original stratification in the contact zone is eliminated these magmato tectonic events may be correlated to the two main collision phases between taiwan and the continental margin of east china 5 3 and 3 0 ma ago the collisional events subsequent to the nnw to wnw drift of taiwan transformed the compression into strike slip movements along the continental margin of southeastern china the accompanying stress regime is transtensional with subsidence of the cooling oceanic crust since the cessation of rifting and its consumption beneath the manila trench providing the extensional stress the strike slip movements remobilized many of the rift and drift faults providing pathways for magma ascent the tectonic framework of the northern south china sea is characterized by miocene faults trending ne sw these faults are scarce but are distributed throughout the study area pliocene faults striking ene wsw to ne sw are concentrated west of the dongsha islands and are mostly strike slip in character recent faults are generally oriented ne sw subparallel to the synrift faults they result in part from local uplifts where they are normal in character but strike slip motion also occurs most of the faults involve the basement and represent reactivated zones of weakness of the rift and drift phases

in situ observation of contour currents in the northern south china sea applications for deepwater sediment transport deepwater currents and related suspended sediment concentration were obtained by an acoustic doppler current profiler adcp mooring system in the northern south china sea from september 2011 to may 2013 to characterize the occurrence of contour currents and to evaluate their sediment transport capacity magnitude of the current velocity generally varied in the range of 0 2 cm s with a dominant flow direction of 250 southwestward the observed contour current defined as the along slope component of the deepwater currents has a tunnel like vertical structure with the largest velocity occurring in the middle of the tunnel and decreasing outwards both the magnitude and the depth range of the maximum velocity display evident inter seasonal variations with the strongest velocity in summer and the weakest in spring while the thickness of the contour currents was the highest in winter and the lowest in spring we also found that passing through of the deep reaching mesoscale eddies significantly affected the magnitude and direction of the contour currents the suspended sediment concentration ssc estimated from echo intensities of the adcp is the highest at the near bottom 400 g l and decreases upwards to 10 g l at water depth shallower than 1750 m high ssc is mostly observed during periods of low magnitude of the contour currents suggesting resuspension of sediment from the seafloor is not the major controlling factor of these high ssc events our observation also suggests that the major role that contour currents play is to transport sediment from the sources through keeping sediment suspended above the lower continental slope of the south china sea

tectonic and paleoceanographic conditions during the formation of ferromanganese nodules from the northern south china sea based on the high resolution geochemistry mineralogy and isotopes abstract deep water ferromanganese fe mn nodules cumulate trace elements from the underlying sediment pore water and seawater during the concentric mineral layers growth process over millions of years they can record long term tectonic movements and paleoceanographic changes to systematically ascertain paleoceanographic evolution of the deep south china sea scs since the last 3 2 ma we comprehensively investigated microstructure mineralogy geochemical element concentrations as well as sr nd and pb isotopic compositions in the fe mn nodules nearby the dongsha islands in the northern scs results indicate that these deposits were formed in a continental marginal environment by a mixture of diagenetic and hydrogenetic processes overall the studied nodules can be divided into three stages with different microstructures and chemical compositions which indicate different formation environments stage 1a is the innermost and oldest layer with a porous mottled texture and has the lowest mn fe ratio cu ni and zn which implies comparatively high oxidization conditions in contrast the mn mineralogy of stage 2 shows conditions similar to those of buserite formed under less oxidative conditions between stage 1a and 2 stage 1b represents a mixture of stage 1a and 2 and has inhomogeneous growth structures based on the nd and sr isotopic composition of the detrital phases and pb isotopes three potential terrigenous source regions including south china luzon and taiwan that discharge into the northern scs from 3 2 ma to 1 06 ma after 1 06 ma the terrigenous fraction in the fe mn deposits on the northern slope of the scs is a two end members mixture of fluvial input from taiwan islands and eolian dusts from the chinese loess our study indicates that scs bottom water variation occurred at 3 2 ma 2 1 ma and 1 06 ma respectively which could be attributed to global cooling and the influence of luzon arc forearc uplift

middle miocene mound shaped sediment packages on the slope of the xisha carbonate platforms south china sea combined result of gravity flow and bottom current deep water mound shaped sediment packages on the northern slope of the xisha carbonate platforms in the northern south china sea were analyzed by integrating high resolution multi channel seismic and drilling data the mounds are distributed in the beijiao depression of the qiongdongnan basin within the t41 t40 seismic horizons which correspond to the middle miocene mound shaped reflections were identified both in the ne sw and nw se oriented seismic profiles the mound shapes are most prominent in the center of the nw se oriented seismic profiles and the undulating tops flatten out towards the nw and se similar reflections are mostly asymmetric with steeper eastern flanks in the ne sw oriented seismic profiles and they are mostly round in shape the wave impedance from the inversion calculation is 6 8 x 10 6 kg m 2 s it is much lower than that of the reef reservoir in the lh11 1 reef oilfield paleogeographic analysis shows that the xisha uplift was dominated by tropical shallow carbonate platforms while the beijiao depression became a bathyal environment in the middle miocene drilling data confirmed that the mound shaped sediment packages are mainly composed of calcareous mudstone therefore we infer that the mound shaped sediment packages could be reef complexes or they were presumably built by combined gravity flow and bottom current c 2015 elsevier ltd all rights reserved

source to sink transport processes of fluvial sediments in the south china sea the south china sea offers an excellent case for studying source to sink transport processes of fluvial sediments among the global marginal seas this study synthesizes existing clay mineralogical and geochemical data from similar to 1500 samples from the seafloor and surrounding rivers deepwater mooring observation results and high resolution glacial cyclic clay mineralogy records from six high quality sediment cores source to sink sediment transport from the river mouth to the continental shelf and then to the abyssal basin is investigated at two time scales modern process and late quaternary glacial cycles the results firstly show the high diversity of clay mineralogical and geochemical compositions in riverbed surface sediments surrounding the south china sea e g dominant illite and chlorite in taiwan overwhelming majority of smectite in luzon dominant kaolinite in south china and similar amounts of the four clay mineral species in red and mekong river systems the formation of these fluvial sediments through chemical weathering in surrounding drainage systems is controlled principally by the east asian monsoon climate with warm temperature and high precipitation and subordinately by tectonic activity and specific lithological character the basin wide distribution of clay mineral assemblages combined with neodymium and strontium isotopic compositions reflects strong provenance control and differential settling effects the differential settling of kaolinite in slightly saline and proximal regions relative to smectite in more saline and distal regions is well demonstrated in the south china sea through combining clay mineralogical distributions on the seafloor with observed oceanic current systems the modern transport pathways can be well established e g in the northern south china sea illite and chlorite from taiwan are mainly carried by contour currents with the strong influence of mesoscale eddies high resolution sediment dynamic analysis for the late quaternary reveals different sediment transport patterns in the northern western and southern south china sea when the land sea configuration dramatically changed during glacial conditions in the north the terrigenous dispersal is mainly controlled by provenance supply and oceanic current transport in the west the clay mineral assemblage reflects variations of the prevailing surface current influenced by monsoon winds in the south the clay mineral input indicates intensive chemical weathering during interglacial periods and strengthened physical erosion during glacial periods the transport of terrigenous sediments since the last glaciation is quantitatively reconstructed through studying two deepwater sediment cores located in the northern south china sea the relative contributions from three provenances south china luzon and taiwan highlight their distinct variability over the last 28 ka implying that the southward shift of the inter tropical convergence zone itcz at 16 ka bp caused an increased sediment contribution from south china the intensified influence of the kuroshio current intrusion controls more efficient westward transport of luzon sediments and the stronger deepwater current transports taiwan sourced sediments further westward from the last glaciation to the holocene c 2015 elsevier b v all rights reserved

estimating the time of pockmark formation in the sw xisha uplift south china sea using reaction transport modeling carbon cycling and fluid seepage in marine sediments over the late quaternary were investigated at a now extinct pockmark located in a mega pockmark field in the sw xisha uplift nw south china sea measured particulate organic carbon poc content and porewater sulfate so4 2 dissolved inorganic carbon dic concentrations and 34s so4 2 distributions were used to constrain a non steady state reaction transport model and quantify poc mineralization rates as well as estimate the time when fluid flow ceased at the investigated pockmark an increase in poc content and 34s so4 2 and a decrease in sulfate concentrations in the upper ca 2m at the pockmark and a reference core implied an increase in the flux and reactivity of organic matter during the early holocene around 10kyrb p caused by enhanced primary productivity during the strengthened southwestern summer monsoon these features were simulated with the model assuming a holocene increase in poc flux and reactivity subsequently starting from an initial condition reminiscent of a modern active cold seep hydrate ridge hindcast simulations showed that fluid seepage at the pockmark ceased ca 39kyr ago this corresponds to a relative sea level high stand which is believed to be associated with gas hydrate stabilization the non steady state model presented in this contribution can also be used to constrain the time when fluid seepage ceased at other presently extinct cold seeps when suitable sediment and porewater data are available

sediment dynamics driven by contour currents and mesoscale eddies along continental slope a case study of the northern south china sea abstract based upon 3 d seismic reflection data published drill core studies oceanographic observations and numerical modelling this study identifies a small scale contourite depositional system that is locally confined by canyons slope failures erosional terraces and erosional slopes on the jianfeng slope northern south china sea 1500 to 2300 m water depth possible oceanic driving mechanisms for the spatial heterogeneity in sedimentation and erosion within the quaternary deposits in this complex slope system are investigated numerical simulations show that the quasi steady south china sea deep water circulation which affects the study area is characterised by low velocities maximum 4 cm s with a slight modulation by tides 1 cm s this quasi steady deep water thermohaline circulation is able to keep sediment particles in suspension rather than to erode seafloor sediment the bottom hydrodynamic regime becomes energetic when mesoscale eddies horizontal scale of 10 to 100 km approach our modelling study indicates that both surface and bottom mesoscale eddies are essential to account for the spatial heterogeneity in sedimentation pattern along the northern south china sea continental slope according to simulation the eddy front contains the highest flow velocity over a mesoscale eddy cycle 45 days exceeding the threshold for resuspension of unconsolidated sediment 15 cm s as a consequence massive resuspension is produced at various sites and redistributed by sub mesoscale horizontal scale of 1 to 10 km circulations originated from an eddy topography interaction in contrast to the surrounding areas which are subject to erosional forcing for a relatively long part 7 of an eddy cycle both the locally confined drift and a further upstream large elongated mounded drift experience little erosion

paleogene neogene depositional history of the middle u s atlantic continental rise mixed turbidite and contourite depositional systems abstract the construction of the middle u s atlantic continental rise from late paleogene to late pliocene time included downslope sediment gravity flows and alongslope contourite deposition some previous studies have suggested that contour following bottom currents were the dominant control on depositional patterns depositional relief from two large contourite drifts largely built in late miocene to late pliocene time continue to dominate present day lower rise morphology detailed seismic sequence mapping presented here suggests that significant turbidite fan systems also were active and are preserved in the stratigraphic section a single thick depositional sequence is mapped for oligocene to middle miocene sediments deposited when inferred fan systems off the norfolk washington canyons were reworked by bottom currents along the lower rise to form the proto hatteras outer ridge detailed mapping of three late miocene to late pliocene depositional sequences indicates that fan channel systems were active at the same time large contourite drifts were being constructed sediment delivered to the lower rise by these elongate turbidite systems undoubtedly was an important local source for construction of the hatteras outer ridge and through entrainment and resuspension was an important source for regional contourite deposition controlled by the deep western boundary undercurrent we suggest that submarine fans and current controlled sediment drifts may develop simultaneously as companion systems types of fan drift interaction include current only modification of fans transitional fan to drift and adjacent or overlapping submarine fan and sediment drift deposition

extinction of deep sea foraminifera as a result of pliocene pleistocene deep sea circulation changes in the south china sea odp sites 1143 and 1146 during the late pliocene middle pleistocene 56 species and 15 genera of elongate cylindrical benthic foraminifera disappeared from the deep sea in the south china sea odp sites 1143 and 1146 as part of the last global extinction in the deep sea this extinction group ext gp exhibited a pulsed decline in abundance and species richness mostly during glacials and often associated with periods of expansion of polar ice that resulted front increased cooling of the earth s climate since similar to 2 5 ma particularly during the mid pleistocene climate transition mpt 1 2 0 6 ma we infer that the ext gp decline in abundance and disappearance was a result of the increased glacial cooling and consequent increased ventilation of the deep sea water masses the detailed record of withdrawal of the ext gp differs between the two sites with far more disappearances occurring prior to the mpt in the deeper site 1143 2772m than in the shallower site 1146 2092 in the late pliocene and early pleistocene declines in deeper parts of the south china sea site 1143 may have resulted from enhanced glacial production of deep southern sourced water passing over the sill into the basin from the north west pacific during the mpt however the ext gp declines and disappearances were of similar timing and magnitude in both sites implying that both were influenced by the same deep water mass during glacials at this time this could have been north pacific deep water which many workers infer was formed in the northern pacific during the last glacial and may have begun forming during mpt glacials in association with the progressively enhanced cooling of the northern hemisphere c 2006 elsevier ltd all rights reserved

the importance of high horizontal resolution and accurate coastline geometry in modeling south china sea inflow as resolution is increased from 1 2 to 1 32 in pacific ocean simulations using the nrl layered ocean model marked changes are found in the kuroshio s mean pathway as it intrudes into the south china sea scs via the luzon strait with increased horizontal resolution comes a more accurate representation of the coastline geometry associated with the batan babuyan islands within the strait and a reduction in the modeled westward intrusion of the kuroshio into the scs the 1 16 model is extremely sensitive to two very small scale shoals calayan bank and a shoal north of calayan island that are resolvable at this grid spacing the exclusion of these three model gridpoints significantly alters the mean kuroshio pathway to resemble the pathway from the 1 8 model in addition excluding all islands within the luzon strait in the 1 16 model gives a deep intrusion mean pathway as found in the 1 2 model

submarine erosional troughs in the northern south china sea evidence for early miocene deepwater circulation and paleoceanographic change abstract the paleoceanography of the south china sea scs is poorly understood although recent cruises and an odp expedition leg 184 have provided a useful general framework here we report previously unrecognized multi km scale sedimentary structures consisting of coupled ridges and troughs within the early miocene strata using high resolution 3d seismic data from the northern scs margin the troughs are interpreted as linear and or arcuate erosional features which truncate the underlying strata they range in orientation from e w in the southern part of the study area to nearly ne sw in the northwestern part of the study area the spacing of erosional troughs varies from less than 0 1 km in the southern part to more than 3 km in the northern part and they are about 50 1500 m in width with a relief of 10 90 m the erosional troughs are parallel to the regional strike of the early miocene slope of the northern scs from their internal geometry context regional distribution and most importantly their orientation relative to the paleo slope gradient at the time of their formation it is argued that they formed due to the action of bottom currents linked to the broader paleo circulation regime in the basin we infer that the paleo bottom currents intruding from the pacific flowed along the northern scs slope resulting in the occurrence of localized erosional troughs as deep water masses impinged on and interacted with the sea floor topography this study provides new insights into the early miocene paleoceanography of the scs and demonstrates the utility of 3d seismic data to enhance our understanding of paleo bottom current circulation regimes

temporal and spatial patterns of sediment deposition in the northern south china sea over the last 50 000 years abstract sediment depositional patterns along the upper continental slope of the northern south china sea scs have been studied using two sediment cores geob16601 6 20 09 07 n 116 14 38 e 1012 m water depth and geob16602 4 18 57 12 n 113 42 64 e 951 m water depth recovered during rv sonne cruise so 221 invers sediment cores were analyzed for bulk sediment element composition by x ray fluorescence xrf core scanning and clay mineral assemblage by x ray diffraction xrd the bulk sediment element and the clay mineral compositions of the two cores suggest similar depositional patterns between 50 kyr bp and 29 kyr bp and 14 kyr bp to present but a clear difference in depositional patterns during the last glacial and deglacial 29 14 kyr bp when sea level was below 90 m between 29 14 kyr bp a higher kaolinite percentage in core geob16602 4 in comparison to core geob16601 6 is interpreted to reflect a higher contribution of clay supplied by the pearl river to core site geob16602 4 in contrast core geob16601 6 received less pearl river supplied clayey material during the same period when the sea level was below 90 m during the last glacial lowstand the detrital fine grained materials supplied by the pearl river were mostly transported by coastal currents to the southwest resulting in a higher contribution of pearl river discharged material at site geob16602 4 than at site geob16601 6 we suggest that sea level induced modifications of the land ocean distribution together with changes in the palaeo physiographic conditions such as the proximity of the palaeo rivers to the individual core sites might be responsible for the different sediment depositional patterns in the study area thus the overriding control of sea level induced changes on the sediment depositional environment might mask climate related changes in sediment depositional pattern in the northern scs

different origins of seafloor undulations in a submarine canyon system northern south china sea based on their seismic character and relative location abstract high resolution 2d and 3d seismic data are used to investigate the morphology internal architecture and origin of widespread seafloor undulations in the eastern area of a submarine canyon system northern south china sea the seafloor undulations reveal similar seafloor morphologies and three different types types a b and c can be classified based on their relative locations and internal seismic characters types a and b are observed in the canyon areas whereas type c occurs in the canyon heads seismic reflections within types a and c are continuous and have an upslope migrating trend while type b seafloor undulations are separated by listric faults our analysis reveals the origins of these three different types of seafloor undulations type a seafloor undulations are sediment waves formed by turbidity currents flowing through the submarine canyons gravity driven submarine creep resulted in the formation of type b seafloor undulations type c undulations are sediment waves generated by internal waves interacting with the continental slope our results provide information about the origin of widespread seafloor undulations in other submarine canyon systems it is also of great significance to future risk assessments as the study area now is one of the most active regions for hydrocarbon exploration in se asia

sediment drifts and contourites on the continental margin off northwest britain abstract seismic reflection profiles and short cores from the continental margin off northwest britain have revealed a variety of sediment drift styles and contourite deposits preserved in the northeast rockall trough and faeroe shetland channel the sediment drifts include 1 distinctly mounded elongate drifts both single and multi crested 2 broad sheeted drift forms varying from gently domed to flat lying and 3 isolated patch drifts including moat related drifts fields of sediment waves are locally developed in association with the elongate and gently domed broad sheeted drifts the contrasting styles of the sediment drifts most probably reflect the interaction between a variable bottom current regime and the complex bathymetry of the continental margin the bulk of the mounded gently domed drifts occur in the northeast rockall trough whereas the flat lying sheet form deposits occur in the faeroe shetland channel a much narrower basin which appears to have been an area more of sediment export than drift accumulation patch drifts are present in both basins in the northeast rockall trough the along strike variation from single to multi crested elongate drifts may be a response to bottom current changes influenced by developing drift topography muddy silty muddy and sandy contourites have been recovered in sediment cores from the uppermost parts of the drift sequences on the basis of their glaciomarine origin these mid to high latitude contourites can be referred to collectively as glacigenic contourites both partial and complete contourite sequences are preserved the former consist largely of sandy mid only and top only contourites sandy contourites by their coarse grained nature and their formation under strongest bottom current flows are the most likely to be preserved in the rock record however the very large scale of sediment drifts should be borne in mind with regard to the recognition of fossil contourites in ancient successions

east asian monsoon evolution since the late miocene from the south china sea abstract the south china sea scs has become a global focus for paleoclimatic and paleoceanographic studies due to its location which makes it highly sensitive to the east asian monsoon and to pacific ocean changes we present here a refined magnetostratigraphy for the last 6 5 ma for hole u1431d which was recovered during iodp expedition 349 in the central scs magnetic analyses demonstrate that magnetite is the dominant magnetic carrier except for within a greigite bearing layer at 130 5 132 0 meters below sea floor the greigite layer coincides with the timing of intensification of northern hemisphere glaciation and records an oceanographic response to this event environmental magnetic results indicate that the east asian summer and winter monsoon were stable from 6 5 to 5 ma the summer monsoon intensified at 5 ma and then weakened gradually since 3 8 ma in contrast the winter monsoon weakened at 5 ma and has then been enhanced since 3 8 ma and more stable from 0 6 ma spectral analysis indicates that the east asian summer monsoon was driven directly by low latitude insolation changes before 3 2 ma and that it has been affected by both low latitude insolation and high latitude ice volume changes since 3 2 ma

early interglacial carbonate dilution events in the south china sea implications for strengthened typhoon activities over subtropical east asia abstract a compilation of many late quaternary marine sediment records from the northern south china sea scs continental slope confirms 15 50 reductions in sedimentary calcium carbonate concentrations between 11 0 and 8 5 ka bp in the early holocene this low carbonate event occurred at a time when the regional sea level rose from 50 m to 10 m which drowned large areas of continental shelves especially those near and within the taiwan strait this event is associated with a significant increase in bulk sedimentation rates on the upper continental slope and the relative abundance of fine grained detritus sediment provenance analyses suggest a dominant terrigenous input from taiwan and a minor contribution from luzon during the low carbonate event similar to the background terrigenous deposition in other periods of the holocene two comparable low carbonate events respectively from the beginning of marine isotope stages 5 5 and 7 3 have also been recognized pointing to similar causal factors while carbonate dissolution and carbonate accumulation rate should not have been responsible increased terrigenous input and dilution is considered as the main cause for the recurrent low carbonate events in early interglacials we further hypothesize that during early interglacials fluvial sediment discharge from taiwan and luzon intensified due to stronger typhoon activities and massive fine grained sediments from these two end members may have been transported to the northern scs continental slope via surface and deep ocean currents the conjecture of strengthened typhoon activities over east asia during the early holocene is supported by high ocean heat contents in the west pacific warm pool area with the prevailing la nina like conditions

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

the rare earth element geochemistry of surface sediments in four transects in the south china sea and its geological significance seventy five samples of surface sediment were collected from four transects in the south china sea scs for analyses of rare earth element ree geochemistry total ree abundance ree in the scs varies from 45 to 195 ppm average 128 ppm lower than that of the upper continental crust the spatial distribution of ree is strongly dependent upon the geographical location and depositional environment low ree concentrations are observed on the continental slope e g xisha and nansha islands while high ree concentrations are present in the deep basin sediments on the slope are also characterized by lower lree hree la yb n eu eu and ce ce ratios relative to deep basin sediments there is a positive correlation between al2o3 and ree and a negative correlation between cao and ree conversely the relatively insignificant fe mn oxide accumulation in the scs suggests that manganese nodules do not make a significant contribution to the bulk ree composition of sediments therefore the sediment ree geochemistry is mainly controlled by terrigenous and biogenic sources biogenic carbonate has a diluting effect on ree concentrations but a significant influence on lree hree ce ce and la yb n values is found only in sediments with especially high biogenic carbonate levels the ree geochemistry of scs surface sediments indicates that their source is mainly post archean felsic rocks in the eastern sub basin the relatively low lree hree ratios and high eu eu values of the sediments indicate that significant terrigenous materials are derived from young volcanic rocks e g rocks in the luzon arc

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

bottom current controlled sedimentation and mass wasting in the northwestern sea of okhotsk abstract quaternary sedimentation in the northwestern sea of okhotsk where tidal and thermohaline currents are active was studied using 8443 km of high resolution air gun profiles from four cruises it is characterized by 1 bottom current controlled processes which lead to widespread deposition of contourite drifts and sediment waves on the north okhotsk continental margin and the northernmost sakhalin slope as well as to erosion and sediment reworking on the northern sakhalin shelf 2 mass wasting triggered probably by shallow earthquakes by gas hydrate instability during sea level lowstands leading to slumps and debris flows in the western derugin basin 3 deposition of the fluvial load of the river amur which results in sediment drift bodies and prograding lowstand wedges during glacial periods and to contourite drifts and a fan during interglacial times and 4 ice rafted detritus and hemipelagic sedimentation interrupted by episodic turbidity current activity especially in the derugin basin and its northern eastern and southern flanks

compositions of foraminifera rich turbidite sediments from the shenhu area on the northern slope of the south china sea implication for the presence of deep water bottom currents abstract the sediments in gravity core dh 1 collected from shenhu area on the northern slope of the south china sea are composed of two dark grey clay silt layers a1 and a3 and two foraminifera rich layers a2 and a4 a1 is the top layer and a4 is the bottom layer major and trace metal contents along with grain size and mineralogic data suggest that these silt layers represent background hemipelagic sedimentation unlike silt layers the intervening foraminifera rich layera4 exhibits a fining upward trend is distal turbidite grain size cm diagram and the sharp contacts between the foraminifera rich layer a2 and the upper and lower layers suggest layer a2 is the result of depositional interaction between turbidite and bottom currents ams 14c dating of planktonic foraminifera indicate the age of the turbidite in a2 is between15 3 ka and 22 6 ka we hypothesize that turbidite formation in this period was related to the increase supply of terrigenous matter since the last glacial maximum the rapid deposition of each turbidite led to reduced rates of oxygen diffusion into the sediment allowing anoxic conditions develop in sediments and fostering u enrichment 3 1 g g in foraminifera rich layer a4b in contrast decrease concentration of u and u mo ratios in foraminifera rich layera2 which is possibly due to u remobilization as a consequence of downward penetration of the oxidation front from the oxygen rich bottom currents these new data suggest that authigenic u was quite sensitive to the inflow of bottom currents and u mo ratios may indicate the depositional environmental change in relation to the bottom current action on the turbidite

detrital fine grained sediment contribution from taiwan to the northern south china sea and its relation to regional ocean circulation article i nfo results of clay mineralogy in 140 samples collected in major rivers and lakes in southwestern taiwan and on the seafloor off taiwan in the northeastern south china sea scs combined with clay mineral records of the pearl river drainage basin rivers in luzon and the south china shelf and slope are used to semi quantitatively evaluate the detrital fine grained sediment contribution of taiwan to the northern scs the clay mineral assemblage of the taiwan sourced sediments consists dominantly of illite average 56 and chlorite 41 with very scarce kaolinite and smectite their respective distribution from the rivers and lakes to the seafloor off taiwan does not show obvious basin wide differences linear correlations of illite chemistry index with illite crystallinity and of illite crystallinity with kaolinite present two end members of provenances the pearl river and taiwan for the south china shelf and slope assuming that kaolinite in the northern scs is provided completely from the pearl river the contribution of taiwan in clay minerals is evaluated as 29 to the south china shelf and 23 to the south china slope respectively accordingly the contribution of the pearl river to the south china shelf and slope is 52 and 31 respectively the luzon arc accounts for the rest of clay mineral components for the northern scs mainly by providing smectite the bashi strait crossed branches of the southward deep north pacific deep water and the northward surface kuroshio current in the western pacific may transport taiwan sourced suspended sediments westwards to the northern scs

the morphologies and genesis of mega pockmarks near the xisha uplift south china sea pockmarks are normally regarded to be manifestations of fluids escape through the seabed kilometer wide depressions here called mega pockmarks occur as widespread features near the xisha uplift northern south china sea most of the pockmarks observed in this area are multi kilometers and much larger than normal pockmarks reported worldwide the maximum diameter observed is 3210 m and the maximum depth observed is 165 2 m based on multibeam data and 2d seismic data the pockmarks are circular elliptical and crescentic in plan view seismic profiles show that the genesis of pockmarks is related to fluid gas and or pore water escape according to the fluids pathways the pockmarks fall into four types 1 gas chimney related 2 depositional boundary related 3 gas chimney and inclined structure fault related 4 inclined structure related bottom currents are strong and complex in the study area the multibeam data and seismic profiles indicate that they may play an important role on extension maintenance and shaping of pockmarks the research of the study area is in its initial stage and the identification of these features as indicators of fluid flow is probably useful for hydrocarbon exploration c 2011 elsevier ltd all rights reserved

clay mineral distribution in surface sediments of the northeastern south china sea and surrounding fluvial drainage basins source and transport clay mineralogy of surface samples throughout the northeastern south china sea scs and surrounding fluvial drainage basins has been investigated to reveal source and transport of detrital fine grained sediments three characteristic end members in clay mineral compositions were observed from three major provenances respectively major kaolinite and moderate illite and chlorite from the pearl river predominant illite and chlorite from taiwan and principal smectite from the luzon arc system the transport of four clay mineral species in the northeastern scs is influenced by various mechanisms smectite derived from the luzon arc system is transported mainly by surface current with significant influence of the kuroshio intrusion illite and chlorite from taiwan are mainly carried by deep water current while kaolinite from the pearl river is affected obviously by the westward guangdong coastal current and longshore current a westerly tongue shaped distribution of high contents of illite and chlorite mainly from taiwan on the eastern shelf may result from the westward guangdong coastal current during the winter the results suggest that clay mineral assemblages in the northeastern scs are mainly controlled by provenance supply and current transport and their downcore records do not bear contemporaneous paleoclimatic features the implication of clay minerals for proxies of the late quaternary east asian monsoon evolution is realized through both the provenance supply and current transport processes c 2010 elsevier b v all rights reserved

a giant submarine creep zone as a precursor of large scale slope instability offshore the dongsha islands south china sea a giant submarine creep zone exceeding 800 km2 on the continental slope offshore the dongsha islands south china sea is investigated using bathymetric and 3d seismic data tied to borehole information the submarine creep zone is identified as a wide area of seafloor undulations with ridges and troughs the troughs form nw and wnw trending elongated depressions separating distinct seafloor ridges which are parallel or sub parallel to the continental slope the troughs are 0 8 4 7 km long and 0 4 to 2 1 km wide the ridges have wavelengths of 1 4 km and vertical relief of 10 30 m slope strata are characterised by the presence of vertically stacked ridges and troughs at different stratigraphic depths but remaining relatively stationary in their position the interpreted ridges and troughs are associated with large scale submarine creep and the troughs can be divided into three types based on their different internal characters and formation processes the large scale listric faults trending downslope below mtd 1 and horizon t0 may be the potential glide planes for the submarine creep movement high sedimentation rates local fault activity and the frequent earthquakes recorded on the margin are considered as the main factors controlling the formation of this giant submarine creep zone our results are important to the understanding of sediment instability on continental slopes as a the interpreted submarine creep is young or even active at present and b areas of creeping may evolve into large scale slope instabilities as recorded by similar large scale events in the past

holocene changes in biome size and tropical cyclone activity around the northern south china sea abstract the south china sea scs characterized by a large continental shelf is located at the edge of the asian monsoon domain in this study two marine sediment cores from the northern scs nscs continental slope were investigated to construct composite vegetation and precipitation isotopic composition records based on the 13c and d values of plant wax n alkanes throughout the holocene last 11 200 years i e 11 2 ka the composite 13cwax record indicates an overall predominance of c3 vegetation over the last 11 2 ka before 8 ka bp higher 13cwax values are attributed to preferential wax input from grassland and wetland biomes on the exposed continental shelf after the inundation of the shelf by eustatic sea level rise until ca 8 ka bp grassland and wetland biomes suffered a major size reduction and arboreal vegetation became better represented in the 13cwax record the composite temperature corrected dwax t record suggests that moisture source variability drove precipitation isotopic composition changes during the holocene lower dwax t values before 8 3 ka bp are interpreted as a larger moisture contribution by pacific ocean tropical cyclones whereas higher dwax t values after 8 5 ka bp are interpreted as a larger moisture contribution from the indian ocean summer monsoon higher incidence of tropical cyclones in the nscs during the early holocene was related to a temporary westward shift of the western pacific warm pool and enhanced insolation over the northern hemisphere both external and internal forcing mechanisms regulated moisture source changes in east asia during the holocene

discovery of the southwest dongsha island mud volcanoes amid the northern margin of the south china sea abstract the dongsha basin circling dongsha island that is amid the northern margin of the south china sea is characterized by thin 0 5 km cenozoic sediments veneering on thick up to 5 km mesozoic strata recently several geophysical and geological surveys including multiple channel reflection seismic sub bottom profiling and benthic dredging have been conducted on the slope southwest to the dongsha island where the water depth varies from 400 m to 2000 m a novel discovery is numerous submarine mud volcanoes of various sizes over there typically 50 200 m high and 0 5 5 km wide geophysical profiles document their unusual features e g roughly undulating seafloor high amplitude seabed reflectivity foggy hyperbolic diffractions up to 50 m in water column above seabed and internal reflection chaos and wipe out down to 2 3 km level or deeper below the seabed benthic dredging from the mud volcanoes gives abundant faunas of high diversity e g scleractinian stony coral gorgonian black coral thiophil tubeworm glass sponge bryozoan etc indicating booming chemosynthetic community among which the lophelia pertusa like coral and the euretidae like glass sponges are the first reports in the south china sea concomitantly with them there are also abundant authigenic carbonate nodules and slabs raw brecciated and breccias with bio clasts congregation besides there coexist massive mudflows and allogenic coarse grained quartz feldspar and tourmaline most likely brought out by mud volcanism geochemical analysis of the bottom water samples give dissolved methane concentration up to 4 times higher than the background average these results lend comprehensive evidences for the ongoing and historical mud volcanism the escaping methane gas is inferred to source mainly from the mesozoic strata occupying a large province of the deep water slope ca 1000 km 2 or more the mud volcanoes is prospective for gas hydrate and natural gas for the dongsha basin

the influence of oceanographic processes on contourite features a multidisciplinary study of the northern south china sea abstract this study examines how multiscale oceanographic processes interact with the seafloor to influence the development of contourite features in northern part of the south china sea the multidisciplinary approach used in this study combines physical oceanographic monitoring numerical simulation multibeam echosounding seismic reflection profiling and sediment core interpretation the contourites detected and interpreted herein include depositional drifts and sediment waves erosional channels moats and furrows and mixed erosional and depositional features terraces and irregular depressions this study finds that climatic variation influences the intensity of quasi steady along slope regional water circulation which in turn influences the long term development of primary 10 100 km contourite depositional systems energetic but intermittent oceanographic processes such as eddies and internal waves generate smaller secondary features within the contourite depositional systems resulting in a complex local seafloor morphology westward to south westward migrating mesoscale eddies locally enhance regional water mass circulation and trigger sub mesoscale flows which can generate 1 10 km irregular depressions along their paths westward propagating internal solitary waves form sedimentary waves with the aid of numerical modelling results a sedimentary model is proposed to explain how oceanographic processes influence sedimentary processes and determine a hierarchy of associated feature formation this model can help advance understanding of how bottom currents influence sedimentary processes along continental margins and abyssal plains

observations of the kaiser effect under multiaxial stress states implications for its use in determining in situ stress experimental tests of the kaiser effect the stress history dependence of acoustic emission production show that interactions between principal stresses cannot be ignored as is commonly done when trying to use the kaiser effect to determine in situ stress experimental results obtained under multiaxial stress states are explained in terms of a qualitative model the results show that the commonly used technique of loading uniaxially along various directions to determine stress history must be reevaluated as it cannot be justified in terms of the laboratory experiments one possible resolution of the conflict between laboratory and field results is that the kaiser effect phenomenon observed in cores retrieved from the earth is not the same phenomenon as is observed in rock loaded under laboratory conditions

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