early and late holocene paleoenvironmental reconstruction of the pearl river estuary south china sea using foraminiferal assemblages and stable carbon isotopes abstract proxy reconstructions of estuarine evolution provide perspectives on regional to global environmental changes including relative sea level changes climatic changes and agricultural developments here we present a new benthic foraminiferal record along with 13c and c n and lithological data from a sediment core in the pearl river estuary lingding bay adjacent to the south china sea the core has relatively thick holocene sediments 40 m due to its location in the paleo valley of the pearl river the lithologic and foraminiferal record reveal an evolution in paleoenvironment from fluvial inner estuary to middle estuary between 11300 and 8100 cal a bp in response to rapid sea level rise 13c and c n data indicate high freshwater discharge from 10500 to 8100 cal a bp driven by a strong asian monsoon the middle holocene 8100 3300 cal a bp sediment is absent in the core due to subaqueous erosion resulting from the unique geomorphology of the pearl river delta in the late holocene from 3300 cal a bp to the present the lithology and foraminiferal assemblages suggest a further evolution from outer estuary middle estuary channel to middle estuary shoal resulting from deltaic progradation under stable relative sea levels in the last 2000 years 13c and c n values reveal the intensive development of agriculture coupled with the reduction of freshwater input derived from a weakening asian monsoon

worldwide initiation of holocene marine deltas by deceleration of sea level rise radiocarbon dated deltaic sequences of holocene age from different parts of the world began to accumulate within a restricted time range from about 8500 to 6500 years ago evaluation of major delta processes indicates that deceleration in sea level rise was the key factor in holocene delta formation within many deltas there is as much as a 2000 year age range between basal deposits in seaward and landward cores this age difference records the progressive landward migration of near mean sea level depositional environments during the lower to mid holocene establishment of a chronostratigraphic framework for holocene delta development provides a fundamental global baseline for distinguishing sea level change from vertical land motion by tectonism and isostasy and for evaluating rates of future marine incursion into low lying deltas

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

sedimentary evolution of the holocene subaqueous clinoform off the shandong peninsula in the yellow sea abstract a subaqueous clinoform wraps around the end of the shandong peninsula in the yellow sea the clinoform previously called the shandong mud wedge is up to 40 m thick nearshore and thins seaward its origin has been controversial since it was first noted in the 1980s for our recent investigation offshore of the northeastern shandong peninsula high resolution shallow seismic profiles covering about 1700 km were obtained and two drilling cores penetrating the clinoform were recovered we described the lithofacies characteristics identified benthic foraminifera and ostracoda measured grain size analyzed the mineral components of the cores and obtained ams 14 c dates on 28 samples to decipher the sedimentary evolution of the clinoform in response to postglacial sea level changes the shallow seismic profiles show that the clinoform comprises three units a lowermost seismic unit su 3 less than 2 3 m thick showing a retrogradational aggradational stacking pattern with subhorizontal internal reflectors a middle seismic unit su 2 up to 35 m thick showing a prograding reflection pattern with mostly seaward stepping reflectors separated by several erosive surfaces and an uppermost seismic unit su 1 maximum thickness 18 m exhibiting an aggradational reflection pattern with subparallel reflectors the three seismic units are bounded on the bottom by distinct erosion surfaces analyses of the two cores indicate that the clinoform comprises three depositional units du 1 du 2 and du 3 in descending order corresponding respectively to su 1 su 2 and su 3 the depositional units are distinguished by lithofacies characteristics and the downcore distributions of benthic foraminiferal and ostracod assemblages mineral components of the cores suggest that the clinoform s provenance is predominantly yellow river derived sediments ams 14 c dates suggest that du 3 was formed from about 11 6 to 9 6 cal kyr bp du 2 from 9 6 to 6 5 cal kyr bp and du 1 after ca 6 5 cal kyr bp some major meltwater pulse mwp events during the deglacial transgression were registered in the clinoform stratigraphy with the basal surfaces sediments of du 3 and du 2 corresponding respectively to mwp 1b ca 11 6 11 3 cal kyr bp and mwp 1c ca 9 6 9 2 cal kyr bp events and with du 2 being largely formed after the 8 4 8 2 cal kyr meltwater event rapid centennial to multidecadal scale flooding events were presumably responsible for the erosive surfaces separating the downlapping internal reflectors in su 2 the change of depositional pattern from progradational in su 2 to aggradational in su 1 is attributed to a change from strong dominantly to and fro tidal currents to the modern circulation in the bohai sea as well as to the weakening of the tidal current field during the highstand after about 6500 cal yr bp as a product of complex interactions among sediment supply sea level changes and hydrodynamic regimes the clinoform can be regarded as the distal part of the tidal depositional system in the eastern bohai sea which was largely derived from the yellow river

the late holocene gargano subaqueous delta adriatic shelf sediment pathways and supply fluctuations the gargano subaqueous delta formed on the eastern and southeastern sides of the gargano promontory in the western adriatic this subaqueous deposit represents the southernmost portion of the late holocene highstand systems tract hst growing along the western side of the adriatic as an extensive wedge of deltaic and shallow marine mud the late holocene hst rests above a regional downlap surface that marks the time of maximum landward shift of the shoreline attained around 5 5 cal kyr bp at the end of the late pleistocene holocene sea level rise high resolution seismic stratigraphic and tephra correlation indicate the presence of a thin basal unit recording condensed deposition between 5 5 and 3 7 cal kyr bp over much of the basin above this unit sediment accumulation rates increased to high values as much as 1 5 cm yr 1 reflecting the stabilisation of relative sea level and the forcing from high frequency climatic or anthropogenic changes affecting river dynamics the late holocene mud wedge of which the gargano subaqueous delta is a significant component reaches up to 35 m in thickness and has a volume of ca 180 km3 the shore parallel thickness distribution of the mud wedge reflects the dominant oceanographic regime of the basin and the asymmetric location of the mostly western sediment sources with a combined modern delivery of 51 7 106 t yr 1 of mean suspended load in sections perpendicular to the coast the late holocene mud wedge appears composed of forestepping clinoforms with gently dipping foresets typically 0 5 the gargano subaqueous delta is characterised by a submarine topset in water depths shallower than 25 28 m and accounts for about 1 7th of the total volume of the late holocene mud wedge despite the absence of direct river supply to the gargano area in the area of maximum interaction between shore parallel currents and basin morphology progradation occurs onto a flat and barren bedrock outcrop in about 50 80 m water depth the rapid transition from a thickness of 30 m of late holocene mud to nil is a good indication of the role of southward flowing bottom hugging shelf currents in causing the redistribution of sediment along the adriatic inner shelf additional evidence of this regime comes from 1 the most recent sigmoid defined at seismic stratigraphic scale deposited since the onset of the little ice age showing a shore parallel thickness distribution and a main depocentre to the southeast of the gargano promontory 2 the maximum values of sediment accumulation rates over the last century documented by 210pb measurements defining a narrow shore parallel belt immediately seaward of the depocentre of the most recent sigmoid the gargano subaqueous delta grows from the outbuilding of progressively younger progradational sigmoids that tend to parallel the previous ones the gargano subaqueous delta differs from other documented late holocene subaqueous deltas because its growth reflects 1 sediment transport dominated by bottom currents sub parallel to the strike of the composing clinoforms 2 a complex supply regime including the po delta 350 km to the north and several coalescing apennine rivers acting as line source 3 several alternating intervals of enhanced outbuilding and condensed deposition and 4 an in phase growth of the most recent sigmoid with the major progradation of the po delta during the little ice age

sedimentary facies of the tide dominated paleo changjiang yangtze estuary during the last transgression abstract a large estuary was formed by marine inundation of the paleo changjiang yangtze incised valley during the transgression after the last glacial maximum this paper presents the sedimentary facies and architecture of the estuary fill based on the analysis of three sediment cores cm97 js98 and hq98 obtained from the present changjiang delta plain estuary fill deposits showing an upward fining succession were grouped into five depositional facies tidal river distributary channel muddy intertidal to subtidal flats transgressive lag and estuary front based on sedimentary textures lithology and physical sedimentary structures sand mud couplets are common in these deposits indicating that tides played a significant role in producing these sedimentary structures and that the estuary type was tide dominated some of the successive sand mud couplets probably recorded neap spring cycles as well as semidiurnal tidal cycles the nature of the estuary was very different from other representative tide dominated estuaries in sediment facies its distribution and sediment source for estuarine fill unlike the other estuaries that receive sediments mainly from the sea the paleo changjiang estuarine fill deposits were supplied largely from the river this difference would also have a great influence on the sedimentological and morphological component in the estuary the sediment distribution of the estuary showed fining seaward and estuary mouth sand bodies fed by marine source sand were absent the architecture model of tide dominated estuaries should be divided into two types by the degree of fluvial sediment supply the paleo changjiang estuary shows a good example for an estuary of large rivers

offshore quaternary sediments and their engineering significance in hong kong yim w w s 1994 offshore quaternary sediments and their engineering significance in hong kong in e f j de mulder editor engineering geology of quaternary deposits eng geol 37 31 50 investigation works undertaken for coastal engineering projects in hong kong has provided abundant information on the quaternary sedimentary sequence beneath the sea floor although the significance of such information may not have been realized at the time of these projects valuable lessons have often been learnt afterwards some examples of the important engineering applications concerning offshore quaternary sediments include 1 the provision of information on water movement sediment transport and sedimentation rates during the holocene period 2 the identification of exploitable offshore sand and gravel resources 3 the interpretation of marine geophysical data through the availability of reliable borehole descriptions 4 the enhancement of engineering soil testing results and their interpretation 5 the prediction of rates of long term ground settlement in coastal land reclaimations 6 the selection of offshore sites for waste disposal 7 the reduction in cost of coastal engineering projects through choosing the most cost effective site 8 the provision of baseline data to assist environmental impact assessment a new geological model is proposed for the offshore quaternary sedimentary sequence of hong kong the engineering properties of the sediments are found to be closely related to the palaco environmental changes

net sediment transport patterns over the bohai strait based on grain size trend analysis grain size trend analysis indicates two distinct characteristics of sediment transport in bohai strait eastward transport dominates the western area and along the coast of the shangdong peninsula this result supports the previous work which indicated that the yellow river sediments are transported from the bohai sea to the yellow sea through the south channel of bohai strait and dispersed into the southern yellow sea along the coast of shangdong peninsula in the central eastern bohai strait net deposition is taking place as indicated by the convergence of the grain size trends this result is consistent with current circulation pattern on bohai strait and the interpretation of strata disclosed by seismic reflection profile this study supports the use of grain size trend analysis for large scale areas on the continental shelf

magnetic susceptibility study of late quaternary inner continental shelf sediments in the hong kong sar china abstract four cores of inner continental shelf sediment from the hong kong special administrative region sar have been measured for magnetic susceptibility in all the cores the upper part of marine isotope stage mis 1 down to about 3 m below seabed show abruptly elevated but highly variable levels of magnetic susceptibility attributable mainly to shipping contamination over the past 160 years the uncontaminated lower mis 1 deposits show a consistently low magnetic susceptibility above a sharp increase at the holocene pleistocene boundary this increase is accounted for by the presence of eroded palaeosol fragments enriched in iron oxides and hydroxides acid sulphate soil development during mis 2 4 on the sub aerially exposed inner continental shelf covered by mis 5 deposits is responsible for the formation of palaeosols the timing is therefore the opposite of palaeosols within terrestrial loess sequences in that they were formed during the last glacial period seventeen uncorrected conventional and accelerator mass spectrometry ams radiocarbon dates of mud and shell samples from the cores indicated that the palaeosols were formed before about 9130 yr bp to 19 430 yr bp

a review on the provenance discrimination of sediments in the yellow sea the yellow sea has been extensively studied for the understanding of dispersal patterns and limits of sediments from neighboring countries including china and korea although sedimentological mineralogical and geochemical approaches have been tried to solve the problems especially including the identification of sediment sources in and around the yellow sea the published results are not enough for understanding them suggestions on sediment origins budgets sediment accumulation rates mineralogical and geochemical compositions are not coincident to each other and sometimes even controversial for example conflicts on the distribution patterns of smectite and calcium carbonate the provenance of the southeastern yellow sea mud and sedimentation rates in there the ratios of v al and mn al in korea and china river sediments the origin of ba and pb in sandy sediments of the northeastern yellow sea and so on various geochemical indicators from the literature for the provenance discrimination in the yellow sea are reviewed here in depth and corresponding discussions are described separately research topics for the future study also are suggested for the proper access to the understanding of the origin and dispersal patterns of the yellow sea sediments especially focusing on the geochemical approaches d 2003 elsevier science b v all rights reserved

sediment dynamic processes of the yuehu inlet system shandong peninsula china in order to investigate the sediment dynamic behavior of the yuehu a small inlet system characterized by abundant sediment supply and rapid sediment infilling measurements and sampling were undertaken to obtain data sets of tidal water levels current velocities suspended sediment concentrations grain size parameters deposition rates and organic carbon contents sediment budget and the time velocity asymmetry patterns of the inlet system were analyzed the results show that the deposition rates are relatively high within the tidal basin the total sediment flux cannot be balanced by the input from the open sea the aerosol and biological production rather the material from land which has been intensified by agricultural activities over the past several decades represents a major component for the balance thus the denudation rate must be reduced to protect the yuehu as a natural reserve furthermore it is found from the present study that the yuehu inlet system exhibits all of the four time velocity asymmetry patterns with varied frequencies of occurrence compared with the two asymmetry patterns identified for larger inlet systems such phenomena are partly due to the adjustment of entrance channel geometry this behavior may be representative of the small tidal inlets at their late stage of morphological evolution and therefore may be utilized to prolong the lifespan of small inlet systems c 2003 elsevier ltd all rights reserved

holocene development of the yellow river s subaqueous delta north yellow sea high resolution seismic profiles from the north yellow sea reveal a 20 40 m thick subaqueous clinoform delta that wraps around the eastern end of the shandong peninsula extending into the south yellow sea this complex sigmoidal oblique clinoform containing an estimated 400 km 3 of sediment overlies prominent relict transgressive surfaces the nearshore topset of the clinoform 50 m contain less than 1 m of holocene sediment with low sedimentation rates 1 mm year in contrast to other clinoforms the shandong clinoform appears to be a compound subaqueous deltaic system with what we interpret to be proximal and distal phases of clinoform development the underlying proximal sequence formed proximally between f11 and 9 2 ka in response to a temporary pause in the rapid postglacial sea level rise after the meltwater pulse 1b mwp 1b and increased discharge from the yellow river to the north yellow sea due to intensification of the summer monsoon a flooding surface appears to separate the proximal and distal phases corresponding to the next rapid sea level rise 9 5 9 2 ka bp mwp 1c since 9 2 ka bp an overlying distal sedimentary sequence has accumulated reflecting the backstepping and shifting river mouth westward to the gulf of bohai some inputs from coastal erosion and nearby small streams may be locally important along shore transport cross shelf advection and upwelling in the north yellow sea have reworked post lgm sediment and have helped maintain the morphology of the clinoform in the shandong mud wedge d 2004 elsevier b v all rights reserved

radiocarbon dating and the reconstruction of late quaternary sea level changes in hong kong abstract radiocarbon dating is used widely for the reconstruction of late quaternary sea level changes in the present study eight case studies in hong kong have been chosen to highlight the difficulty in obtaining reliable radiocarbon dates pre holocene radiocarbon dates exceeding about 8100 yr bp have been found to show a young age bias a shell sample dated by two separate radiocarbon laboratories gave last interstadial ages differing by almost 9500 years while an oxygen isotope stage 5e age was obtained using uranium series dating other evidence including stratigraphy have shown that only the last interglacial age is acceptable the young age bias is attributed mainly to the post depositional introduction of young carbon into the sample for the reconstruction of sea level changes it is essential to select samples immediately above of the base of the holocene transgressive unit in offshore boreholes and excavations to satisfy the criteria of rapid burial these samples should preferably include mud plant matter and shells to facilitate interpretation furthermore as many samples as possible from a range of water depth down to about 130 m below the present sea level should be dated to reduce error introduced by counting statistics so the true signal of sea level changes can be reflected

variations in the transport distribution and budget of 210pb in sediment over the estuarine and inner shelf areas of the east china sea due to changjiang catchment changes

a census of eddy activities in the south china sea during 1993 2007 1 numerous mesoscale eddies occur each year in the south china sea scs but their statistical characteristics are still not well documented a pacific basin wide three dimensional physical biogeochemical model has been developed and the result in the scs subdomain is used to quantify the eddy activities during the period of 1993 2007 the modeled results are compared with a merged and gridded satellite product of sea level anomaly by using the same eddy identification and tracking method on average there are about 32 9 2 4 eddies predicted by the model and 32 8 3 4 eddies observed by satellite each year and about 52 of them are cyclonic eddies the radius of these eddies ranges from about 46 5 to 223 5 km with a mean value of 87 4 km more than 70 of the eddies have a radius smaller than 100 km the mean area covered by these eddies each year is around 160 170 km2 equivalent to 9 8 of the scs area with water depths greater than 1000 m linear relationships are found between eddy lifetime and eddy magnitude and between eddy vertical extent and eddy magnitude showing that strong eddies usually last longer and penetrate deeper than weak ones interannual variations in eddy numbers and the total eddy occupied area indicate that eddy activities in the scs do not directly correspond to the el nino southern oscillation events the wind stress curls are thought to be an important but not the only mechanism of eddy genesis in the scs

past environmental and circulation changes in the south china sea input from the magnetic properties of deep sea sediments abstract the south china sea located at the transition between the pacific and the indian ocean receives every year mainly during the rain season enormous amounts of river sediments originating from the erosion weathering of rocks in the catchment basins at sea these sediments are carried by different water masses to their deposition site and they constitute a unique archive for past environmental studies in this region the magnetic fraction of deep sea sediments though forming a minority in volume provides incredibly valuable information for paleoceanographic reconstructions as long as its provenance and source to sink processes are well constrained after a brief description of the climatic sedimentological and oceanographic context of the south china sea scs a review of the information available so far in the literature about the magnetic properties of scs sediments is presented it shows a large variety of interpretations conclusions that finally results in a rather unclear picture because in such a context the characterization of the sediment at the source is critical the magnetic properties recently obtained from a set of samples from rivers and marine surface sediments are summarized to describe the present day situation they are then used to interpret paleorecords from a set of seven marine cores distributed from the southern to the northern basins at different water depths and all covering at least the last climatic cycle the results reported here for the first time suggest that the magnetic mineralogy remains rather stable in time on land and that its time and spatial distribution at sea is an interplay of changes in sea level and deep sea circulation during low sea level periods bottom deep sea circulation is weak and the deposited sediment originates from the proximal rivers on the contrary during high sea level the circulation is enhanced transporting more sediment most likely from taiwan and luzon to the northwestern part of the scs and also in smaller proportion to the southern basin where it mixes with the local river borne sediment by comparing the two longest records we observe that this pattern is repeated over the last 900 ka superimposed to the 100 kyr cyclicity we also observe a longer term evolution with a maximum in the bottom current strength around 500 ka coinciding with global changes in the deep ocean circulation and carbon cycle these new results based on a wide spectrum of magnetic properties of numerous marine sedimentary cores from the scs show that the magnetic fraction yields important insights into past changes of the sedimentary pathways in particular the dynamic of the deep sea circulation depending on the global climatic context

holocene delta evolution and sediment flux of the pearl river southern china delta progradation and sediment flux of the pearl river delta prd southern china during the holocene are presented based on analyses of borehole data on the delta plain results indicate that the delta prograded into the drowned valley because of early holocene inundation from 9 to 6 cal ka bp as sea level rise decelerated the sea level reached its present level at about 6 cal ka bp and as a consequence a large portion of the drowned valley was covered by the estuary with more than 160 rock islands and platforms the scattered landmasses promoted active deposition and acted as deposition nuclei during deltaic evolution consequently apart from exhibiting a general tendency towards progression prd development occurred less regularly over time and space because of deposition around island boundaries during the last 2 ka mainly because of significantly increased human activities which have trapped sediments in the encircled tidal flats along the front of delta plains the shoreline has advanced rapidly estimated sediment fluxes for the three periods 9 6 6 2 and 2 0 cal ka bp based on the sediment volume analysis were 17 25 22 30 and 44 58 million t a 1 respectively copyright c 2016 john wiley sons ltd

provenance structure and formation of the mud wedge along inner continental shelf of the east china sea a synthesis of the yangtze dispersal system surficial grain size and down core clay mineralogical data show that sediment along the inner most part of the continental shelf in east china sea is mainly derived from the yangtze river changjiang spanning from the yangtze mouth 33 degrees n similar to 1000 km southward to the southwestern corner of the taiwan strait 24 degrees n high resolution chirp seismic profiles reveal an elongated mud wedge extending along the inner shelf with a northern depocenter on the modern yangtze delta and a southern depocenter at 27 5 degrees n four distinct acoustic units are delineated within the mud wedge from bottom up unit i late pleistocene mainly valley fills unit ii formed by transgressions thin strata unit iii 11 2 kyr bp downlapping strata and unit iv 2 0 kyr bp flat and opaque strata incised valleys up to 15 m deep are filled by flat lying or inclined strata in unit i the thin 3 m and acoustically transparent unit ii is only seen between 30 and 26 degrees n in water depths between 40 and 90 m separated by acoustically opaque strata or unconformities units iii and iv are widely distributed during the past 11 kyr yangtze sediment accumulation has been unsteady showing two high and one low accumulation rate periods the high accumulation period at 5 8 kyr bp may be related to maximum east asian summer monsoon precipitation in the yangtze basin the other high accumulation period 0 2 kyr bp probably reflects intensive human activities in the river s watershed the low accumulation rate period at 2 5 kyr bp which is seen in both northern and southern yangtze depocenters is probably related to low river discharge and or intensified taiwan warm current and china coastal current c 2011 elsevier b v all rights reserved

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

a 2400 yr record of natural events and anthropogenic impacts in intercorrelated terrestrial and marine sediment cores waipaoa sedimentary system new zealand the waipaoa sedimentary system spans 100 km from terrestrial upland to continental rise alluvial buffering has little effect on sediment flux at the outlet of this mesoscale dispersal system and hinterland to margin transport is accomplished rapidly because of this synergy the floodplain and shelf depocenters are sensitive to changes in sediment production in the hinterland and natural and anthropogenically forced changes in sediment source dynamics that occur at several temporal and spatial scales leave distinctive signals in the stratigraphic record manifested as variations in sediment properties these signals appear in intercorrelated sediment cores from a headwater riparian storage area and the major terrestrial and marine repositories for sediment discharged during the past 2 4 k y the signals represent the landscape response to vegetation and land use change short term fluctuations in climate that affect surface properties and processes and extreme storms and subduction thrust earthquakes extreme storms are the minimum geomorphologically effective event preserved in the sediment records lower magnitude storms that are integral components of the prevailing hydrometeorological regime create high frequency fluctuations in sediment properties and collectively contribute to event sequences of 100 yr duration events and event sequences comprise a hierarchy of temporally sensitive phenomena the impacts of which are conditioned by frequency and magnitude by contrast vegetation disturbance is a spatially sensitive phenomenon that directly impacts sediment source areas and lowers the threshold of landscape sensitivity to erosion for this reason the taupo eruption of 1 718 ka and the piecemeal vegetation changes that occurred after the arrival of polynesian settlers also generated strong depositional signals after european colonization deforestation of the hinterland altered landscape sensitivity and precipitated the transition to an erosional regime that impacted sediment production and dispersal across the entire magnitude frequency spectrum of events regulating sediment delivery to and transport in stream channels no other perturbation had such a profound impact on the late holocene depositional record

modeling the growth limit of the changjiang delta river deltas grow in response to sediment discharge from the land it is not clear however whether or not there is a limit for such growth conceptual geometric models are used in this paper in association with the principle of mass conservation in an attempt to answer this question preliminary analyses of the changjiang delta indicate that delta growth is constrained by a number of factors the original topography bathymetry sediment supply sediment retention in the estuary sea level rise ground subsidence the quantity of sediment supply per unit area and the sediment retention index for the subaqueous delta decrease as the delta progrades towards deeper water resulting in a decreasing rate of growth the limit of growth is reached when the index approaches zero i e the shoreline reaches the shelf edge if the combined effect of sea level rise and ground subsidence is considered together with decrease in the sediment discharge from land the limit is reached at an earlier stage for the changjiang delta the model output using hypothesized sediment retention index estimates implies that the delta growth will reach its limit in the near future this will occur sooner if the sediment output of the river is reduced to 60 of its original level in response to the upstream basin changes further knowledge however is required of the retention index together with the information on future changes in river input and the character of the sediments in order to improve the accuracy of the simulations

enhanced silicate weathering of tropical shelf sediments exposed during glacial lowstands a sink for atmospheric co2 atmospheric co2 and global climate are closely coupled since 800 ka co2 concentrations have been up to 50 higher during interglacial compared to glacial periods because of its dependence on temperature humidity and erosion rates chemical weathering of exposed silicate minerals was suggested to have dampened these cyclic variations of atmospheric composition cooler and drier conditions and lower non glacial erosion rates suppressed in situ chemical weathering rates during glacial periods however using systematic variations in major element geochemistry sr nd isotopes and clay mineral records from ocean drilling program sites 1143 and 1144 in the south china sea spanning the last 1 1 ma we show that sediment deposited during glacial periods was more weathered than sediment delivered during interglacials we attribute this to subaerial exposure and weathering of unconsolidated shelf sediments during glacial sealevel lowstands our estimates suggest that enhanced silicate weathering of tropical shelf sediments exposed during glacial lowstands can account for 9 of the carbon dioxide removed from the atmosphere during the glacial and thus represent a significant part of the observed glacial interglacial variation of 80 ppmv as a result if similar magnitudes can be identified in other tropical shelf slope systems the effects of increased sediment exposure and subsequent silicate weathering during lowstands could have potentially enhanced the drawdown of atmospheric co2 during cold stages of the quaternary this in turn would have caused an intensification of glacial cycles

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

modern fine grained sedimentation spatial variability and environmental controls on an inner pericontinental shelf hong kong abstract fine grained sediments in hong kong form part of an extensive cover that extends from nearshore locations to the mid continental shelf this featureless mud blanket is associated with sediment inputs from the pearl river and has generally been considered to be homogeneous in its characteristics however detailed sedimentological and geochemical analyses have revealed that the superficial deposits show systematic spatial variations that reflect contrasts in deposition between the pearl river estuary to the west and fully marine conditions to the east results indicate significant differences in particle size accumulation rates biogenic silica organic carbon content c n ratios and stable carbon and nitrogen isotopes that reflect location with respect to the pearl river delta calcium carbonate content varies widely tending to be higher close to land major controls over spatial variability include rainfall patterns and the supply of estuarine suspended particulate matter the effects of palaeotopography and modern water depth resuspension induced by monsoon winds and typhoons and human impacts on the sea floor

provenance of heavy mineral deposits on the northwestern shelf of the south china sea evidence from single mineral chemistry abstract a study of heavy mineral geochemistry has been carried out in order to examine the potential sources of heavy mineral deposits within surficial sediment on the northwestern shelf of the south china sea tourmaline amphibole and garnet from six samples near the coast and eleven samples on the shelf were analyzed by an electron microprobe chemical varieties of tourmaline and amphibole indicate that the pearl river is the main supplier of sandy sediments on the eastern shelf within a 100 km radius west of the paleo deltas sandy sediments on the western shelf are mainly sourced from the jian river and the wanquan river heavy mineral placers on the middle and outer shelves are mainly derived from reworking of the paleo pearl river deltas heavy mineral placers in the west are mainly sourced from the small rivers and are distributed in the sandy deposits near the coasts this study demonstrates that the occurrence of heavy mineral placers on wide continental shelf is mainly determined by the sediment supply and marine processes during transgressions

late quaternary environmental changes in hong kong abstract the offshore quaternary deposits of hong kong include a wide range of clastic sediments that accumulated in a variety of settings including lacustrine channel overbank coastal and marine environments detailed studies of the sedimentology and diatoms of several long continuously sampled cores combined with seismic reflection profiles has enabled the reconstruction of late pleistocene and holocene palaeoenvironments in hong kong the quaternary sediments comprise several informal seismic units that are separated by marine planation tidal scour and fluvial erosion surfaces seismic unit 1 represents pre quaternary bedrock and weathered bedrock which is separated from a complex assemblage of pleistocene channel floodplain backswamp and lacustrine deposits seismic unit 2 by a major erosion surface u1 sediments that represent the basal part of unit 2 have been dated at about 248 000 yr b p well preserved laminations at several horizons suggest periodic deposition and probably seasonal flooding the presence of kaolin indicates strong chemical weathering and warm humid conditions at the time of deposition seismic unit 3 consists of marine mud that unconformably overlies a fluvial erosion surface fe1 cut into deposits represented by seismic unit 2 the sediments comprising unit 3 are tentatively correlated with oxygen isotope stage 5e and high sea levels at about 128 000 105 000 yr b p a marine planation surface r1 terminates unit 3 and is overlain by coastal and nearshore deposits comprising seismic unit 4 at about 95 000 to 80 000 yr b p this phase of marine deposition was terminated by a major fall in sea level that caused widespread fluvial incision across hong kong and produced surface fe2 a subsequent rise in sea level after about 18 000 yr b p led to deposition of a complex succession of marine sediments and erosion surfaces initially homogeneous mud seismic unit 5a was laid down tidal currents perhaps related to base level changes then caused incision and the formation of surface ts1 at several localities further shallow marine mud comprising unit 5b was laid down between about 9500 and 8000 yr b p a planar erosion surface r2 with local palaeosols and minor incision cuts across earlier deposits the overlying seismic unit 5c represents diatomaceous marine mud and a basal sand at one coring site these sediments have been divided into five major diatom zones that reflect changes in salinity and sea level modern sea level was attained by about 6000 yr b p in broad terms the late quaternary record is one of two periods of marine flooding separated by a major regressive episode with no evidence of older quaternary marine sediments being present

sediment accumulation rates in subpolar fjords impact of post little ice age glaciers retreat billefjorden svalbard abstract the little ice age 1600 1900 ad and 20th century sediment accumulation rates in billefjorden a subpolar fjord on svalbard were reconstructed by applying 210 pb 137 cs and ams 14 c datings the modern sediment accumulation rate decreases from more than 0 39 cm y 1 at the fjord head to 0 08 cm y 1 close to the fjord mouth however during the little ice age the sediments accumulated at a much lower rate of 0 02 cm y 1 in the central fjord basin this difference is most likely related to the rapid retreat of glaciers during the 20th century when most of them withdrew up to 2 km the post little ice age increases in temperature and a negative glacier mass balance resulted in a larger meltwater discharge transferring substantial amounts of sediments released from the glaciers as well as those eroded from previously stored unconsolidated glacial sediments a comparison of data from the subpolar fjords of svalbard suggests that the increase in the sediment accumulation rate is a common trend and further increases might be expected if climate warming continues the properties of the fjord sediments grain size ird coarse fraction composition clay mineralogy from the little ice age and the 20th century showed no distinct differences the change in the accumulation rate may be the most evident sedimentary record of this climatic change

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

sediment retention at the changjiang sub aqueous delta over a 57 year period in response to catchment changes the growth of a river delta system is controlled mainly by fluvial sediment discharge and sediment retention in the deltaic areas in the present study we attempt to define a sediment retention index r and its relation to the deposition rate of the delta based upon two assumptions that the amount of the sediment that escapes from the deltaic areas qe is stationary with minor fluctuations and that there is a linear relationship between the deposition rate averaged over the sub aqueous delta dav and the deposition rate at accretion sites within the delta dr the changes in the accretion erosion patterns of the changjiang sub aqueous delta during the period of 1951 2007 in response to river sediment discharge changes are analyzed the results show that the sediment retention index can be related to the deposition rate of the sub aqueous delta the spatial temporal distribution pattern of the deposition rate reveals the behaviour of sediment retention of a delta system for the changjiang sub aqueous delta fluvial sediment discharge data together with pb 210 based deposition rates provide useful information on sediment retention changes in the sediment retention index and the accretion erosion patterns of the sub aqueous delta have taken place in response to river input changes in order to improve our understanding of the processes associated with estuarine sediment retention sediment cores with sufficient spatial coverage may be collected and analyzed to establish accurate qe r and dav dr relationships in combination with numerical modeling of sediment transport these relationships form a basis for the analysis of sediment retention mechanisms

clay mineralogy of the riverine sediments of hainan island south china sea implications for weathering and provenance abstract clay mineralogy of 54 fluvial samples collected from 20 major rivers on hainan island are investigated in order to determine compositional changes of clay minerals and to assess the weathering processes the clay mineral assemblages consist dominantly of kaolinite 31 66 with a lesser abundance of chlorite 22 44 and illite 4 33 and a trace amount of smectite 0 15 fluvial sediments from the east and northwest of hainan island are characterized by a higher kaolinite content and illite chemical index and poorer illite crystallinity than those from southwest hainan only minor smectite mean of 7 occurs in the sediments from west hainan smectite is total lacking in east hainan compared with the adjacent basins hainan island is characterized by moderate to intensive chemical weathering with strong hydrolysis our results suggest that rainfall is the principal factor controlling the intensity of chemical weathering on hainan island with more intense chemical weathering occurring in eastern and northwestern hainan another practical implication of this study is that it provides a missing end member hainan island in the provenance discrimination study focused on the northern south china sea scs hainan fine grained sediments likely play an important role in providing clay minerals to the northern scs carried by the south china sea warm current scswc during the summer

predicting the terrestrial flux of sediment to the global ocean a planetary perspective a new model for predicting the long term flux of sediment from river basins to the coastal ocean is applied to a global data set of 340 river basins the model is based on relief basin area or averaged discharge and basin averaged temperature basinaveraged temperature is determined from basin location latitude longitude and the lapse rate across the basin relief hypsometric approximation the sediment flux model incorporates climate through basin temperature and hydrologic runoff solutions are provided for each of the major hemispheric climate regions polar temperate and tropic the model successfully predicts the pre anthropogenic flux of sediment to within the uncertainties associated with the global observations within a factor of two for 75 of rivers that range across five orders of magnitude in basin area and discharge most of the problem rivers are associated with low observational loads often smaller rivers where anthropogenic impacts are often magnified and temporal variability is high model predictions provide a baseline for researchers 1 to question the quality of observational data where available and disagreement is greatest 2 to examine a river basin for unusually large anthropogenic influences i e causes of erosion or causes of hinterland sediment retention and 3 to uncover secondary factors not addressed by our model lithology lakes the model provides a powerful tool to address the impact of paleo climate fluctuations warmer colder wetter drier on the impact of sediment flux to the coastal ocean d 2003 elsevier b v all rights reserved

a unique yellow river derived distal subaqueous delta in the yellow sea abstract newly acquired high resolution chirp sonar profiles reveal a unique yellow river derived alongshore distributed bidirectional landward and seaward across shelf transported omega shaped distal subaqueous deltaic lobe deposited around the eastern tip of the shandong peninsula in the yellow sea this clinoform deposit directly overlies the postglacial transgressive surface featured by convex up seafloor morphology up to 40 m thick locally radiocarbon 14 dates from the underlain pre holocene and transgressive sediments indicate this distal lobe has formed since the middle holocene highstand under a relatively stable sea level this along shelf distributed distal clinoform has been deposited mainly by the resuspended yellow river sediments carried down by the coastal current interacting with the local waves tides and upwelling collectively over the past 7000 years nearly 30 of the yellow river derived sediment has been re suspended and transported out of the bohai sea into the yellow sea overall the yellow river derived sediment could reach the 80 m water depth in the central south yellow sea about 700 km from the river mouth in contrast a very small fraction of the modern riverine sediment could escape the outer shelf or reach the okinawa trough

sedimentary responses to holocene sea level change in a shallow marine environment of southern china abstract this study has examined how the sedimentary processes in the prevalent non deltaic coastal marine environments along the southeast coast of china have responded to sea level change and other environmental drivers during the holocene three sediment cores collected from a shallow marine embayment of the lantau island hong kong on the northern coast of the south china sea were analyzed the results of particle size total organic carbon content organic carbon and nitrogen ratios organic carbon stable isotope ratios abundance of alkenones and radiocarbon dating of these cores have helped reconstruct the sedimentary history of this site this history shares the similarity in sedimentary processes within the deltaic environment for the early holocene because palaeo incised channels exist in both environments the first 1500 years of deposition involved rapid channel infill caused by the rapidly rising sea level and strong monsoon driven discharge this was followed by a period of decelerated sedimentation under strong marine influence as the sea flooded the wide accommodation space in the subsequent two millennia major differences between the two environmental settings occur in the past 7000 years vertical accretion was seen in the non deltaic coastal environment whilst lateral shoreline advance was the dominant process in the deltaic basin the progressively slowing down in sedimentation rate in the non deltaic site during the middle and late holocene was caused by the reduced monsoon discharge intensified disturbance from tropical cyclone activity and coastal currents

net sediment transport patterns inferred from grain size trends based upon definition of transport vectors reply abstract a new approach to the analysis of the grain size trends associated with net sediment transport directions in shallow marine environments is developed here two specific trends modified from mclaren and bowles 1985 on the basis of a literature review are used to define a grid of trend vectors such vectors are filtered and transformed into transport vectors it is suggested that an ordered pattern of the transport vectors represents net transport paths the orderliness of the derived pattern is examined on the basis of a significance test using the average length of the transport vectors as a criterion both the filtering operation and the significance test procedure are based upon the assumption that the trend vectors which are not associated with net transport have the same probability of being in any direction the technique is applied to data from yangpu harbour southern china the technique can be applied to inner continental shelf and coastal environments for such an analysis the area under investigation should be sampled at an interval large enough to reflect the real grain size trends resulting from net sediment transport but small compared with the dimensions of the sedimentary environment the time scale of the results depends upon the sampling depth applicability of the technique is likely to be somewhat limited where the environment is highly variable over short distances furthermore due to its statistical character the analysis may fail to identify net transport patterns

bayesian geoacoustic inversion using wind driven ambient noise this paper applies bayesian inversion to bottom loss data derived from wind driven ambient noise measurements from a vertical line array to quantify the information content constraining seabed geoacoustic parameters the inversion utilizes a previously proposed ray based representation of the ambient noise field as a forward model for fast computations of bottom loss data for a layered seabed this model considers the effect of the array s finite aperture in the estimation of bottom loss and is extended to include the wind speed as the driving mechanism for the ambient noise field the strength of this field relative to other unwanted noise mechanisms defines a signal to noise ratio which is included in the inversion as a frequency dependent parameter the wind speed is found to have a strong impact on the resolution of seabed geoacoustic parameters as quantified by marginal probability distributions from bayesian inversion of simulated data the inversion method is also applied to experimental data coll

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

distal mud deposits associated with the pearl river over the northwestern continental shelf of the south china sea abstract continental shelf mud deposits represent an important archive of the holocene earth history such deposits are usually associated with large rivers that transport a large quantity of suspended sediment the pearl river has formed a distal shore parallel holocene mud deposit on the northwestern continental shelf of the south china sea investigations into its spatial distribution and evolutionary history are necessary for an improved understanding of such sedimentary systems seabed sediment sampling in situ tidal cycle measurements seismic survey and the associated data analyses reveal that the distal mud deposit associated with the pearl river occupies an area of approximately 8 87 10 3 km 2 with a modern deposition rate of 1 27 to 5 66 mm yr 1 evidence from sediment balance environmentally sensitive components sediment transport processes and regional shelf circulation patterns indicates that the pearl river is a major sediment source for the mud deposit this distal mud deposit represents an initial stage of its development the fining upward pattern and the negative skewness values in the layer are indicative of the pearl river influence and the 210 pb age is younger than 10 2 yr the main body of the holocene deposit of the region is not related directly to the modern pearl river sediment for most of the holocene periods the pearl river has been trapping the sediment to fill its extensive estuarine waters and therefore the formation of the distal mud is a recent event a regional characteristic is that the timing of the formation of distal muds associated with large rivers depends on the estuarine morphological evolution and the quantity of sediment discharge

holocene evolution of mud depocentres on a high energy low accumulation shelf nw iberia the high energy low accumulation nw iberian shelf features three confined holocene mud depocentres here we show that the evolution of such depocentres follows successive steps the flooding of inner shelf zones and river catchment areas by the late deglacial sea level rise provided the precondition for shelf mud deposition following this the holocene deceleration of the sea level rise caused a rapid refill of the accommodation space within river valleys subsequently the export of major amounts of fines was initiated the initial onset and loci of shelf mud deposition were related to deposition favouring conditions in mid shelf position or to the presence of morphological highs which act as sediment traps by providing protection against stronger hydrodynamic energy the detailed reconstruction of the holocene depocentre evolution shows for the first time that the expansion of such shelf mud deposits cannot only occur by linear growth off the associated sediment source rather they might develop around centres that are fully disconnected from the source of original sediment supply and expand later into specific directions based on these differences and on the connection of the individual mud depocentres to the material source we propose a conceptual subdivision of the group mid shelf mud depocentres