enhanced diapycnal mixing in the south china sea profiles of current velocity temperature and salinity were obtained in the internal wave and mixing experiment in the south china sea scs the luzon strait and the north pacific the observations are examinedforevidenceofenhanceddiapycnalmixinginthescs whichreacheso 10 23 m 2 s 21 inmagnitude resultsfrom independent casts reveal that diapycnal diffusivity in the scs andthe luzon strait is elevatedby two orders of magnitude over that of the smooth bathymetry in the north pacific which are typical of background values in an open ocean the vertical distribution of diapycnal diffusivity is nonuniform in the scs exhibiting higher values at depths greater than about 1000 m this result compares favorably with the direct microstructure measurements at four stations in the scs velocity and density profiles are combined to estimatetheinternaltideenergyfluxgeneratedintheluzonstraitanddirectedintothescs theenergyamounts to 10 gw most of which is rationalized to be the potential energy source for enhanced mixing in the scs

dynamical mechanisms for the south china sea seasonal circulation and thermohaline variabilities abstract the seasonal ocean circulation and the seasonal thermal structure in the south china sea scs were studied numerically using the princeton ocean model pom with 20 km horizontal resolution and 23 sigma levels conforming to a realistic bottom topography a 16 month control run was performed using climatological monthly mean wind stresses restoring type surface salt and heat and observational oceanic inflow outflow at the open boundaries the seasonally averaged effects of isolated forcing terms are presented and analyzed from the following experiments 1 nonlinear dynamic effects removed 2 wind effects removed and 3 open boundary inflow outflow set to zero this procedure allowed analysis of the contribution of individual parameters to the general hydrology and specific features of the scs for example coastal jets mesoscale topographic gyres and countercurrents the results show that the pom model has the capability of simulating seasonal variations of the scs circulation and thermoha

observed evidence of the anomalous south china sea western boundary current during the summers of 2010 and 2011 seven years of directly measured current data from a mooring in the xisha area of the south china sea scs together with shipboard adcp and satellite data have shown the western boundary current wbc anomaly and its vertical structure during the summers of 2010 and 2011 the observed wbc presented obvious year to year variability especially in the summer overall the summer mean velocity at the mooring site over 7 year 2007 2013 was northeastward the moored adcp showed that the northeastward velocity was particularly strong in the summer of 2010 but the increase was confined in the upper 120 m in contrast the northeastward current disappeared throughout the observed depth range from 50 to 450 m in the summer of 2011 even at the deepest observed position the monthly velocity anomalies reached 14 cm s 1 westward and 12 cm s 1 southward in the zonal and meridional directions respectively both the vietnam offshore current voc and double gyres in the western scs disappeared and the southern anticyclonic gyre expanded to strengthened the northward wbc in the summer of 2010 however in summer of 2011 the voc intensified and the northern cyclonic gyre enlarged with its northern edge reaching 18 degrees n slightly north of mooring site which weakened the northeastward wbc the observed scs circulation anomalies during 2010 and 2011 were mainly induced by the basin scale wind field anomalies associated with the 2009 2010 el nino and 2010 2011 la nina

south china sea isopycnal surface circulation this paper investigates the seasonal variabilities of the south china sea isopycnal surface circulations and of the kuroshio intrusion through the luzon strait using the u s navy s climatological temperature and salinity dataset public domain with 83 8 resolution by the p vector method the representative pattern is a persistent basin scale cyclonic circulation away from the surface and a seasonally varying circulation with a weak anticylonic gyre in the summer and a strong cyclonic gyre in the winter near the surface this pattern is consistent with a classical view of mean cyclonic circulation in large stratified lakes and semienclosed marginal seas by emery and csanady and with a recent numerical simulation using the navy s layered ocean model by metzger and hurlburt the computed monthly volume transport through the luzon strait is negative inflow all year round with a minimum value of 213 7 sv in february strongest intrusion and a maximum value of 21 4 sv in september weakest intrusion the annual mean transport is 26 5 sv intrusion

variability in the deep overflow through the heng chun ridge of the luzon strait abstractthe deep water overflow at three gaps in the heng chun ridge of the luzon strait is investigated based on long term continuous mooring observations for the first time these observations e

microstructural evolution of the serido belt ne brazil the effect of two tectonic events on development of c axis preferred orientation in quartz the polyphase evolution of the serido belt ne brazil includes d crust formation at 2 3 2 1 ga d 2 thrust tectonics at 1 9 ga and crustal reworking by d 3 strike slip shear zones at 600 ma microstructural investigations within mylonites associated with d 2 and d 3 events were used to constrain the tectono thermal evolution of the belt d 2 shear zones commenced at deeper crustal levels and high amphibolite facies conditions 600 650 degreesc through grain boundary migration subgrain rotation and operation of quartz q prism slip continued shearing and exhumation of the terrain forced the re equilibration of high t fabrics and the switching of slip systems from c prism to positive and negative a rhombs during d 3 enhancement of ductility by dissipation of heat that came from syn d 3 granites developed wide belts of amphibolite facies mylonites continued shearing uplift and cooling of the region induced d 3 shear zones to act in ductile brittle regimes marked by fracturing and development of thinner belts of greenschist facies mylonites during this event switching from a prism to a basal slip indicates a thermal path from 600 to 350 degreesc therefore microstructures and quartz c axis fabrics in polydeformed rocks from the serido belt preserve the record of two major events which includes contrasting deformation mechanisms and thermal paths c 2003 elsevier ltd all rights reserved

interannual variability of south china sea winter circulation response to luzon strait transport and el nino wind the el nino wind and luzon strait transport are important factors modulating the interannual variability of the southern and northern south china sea scs winter circulation respectively the joint effect of el nino wind and westward luzon strait transport drives a dipolar gyre with an anticyclonic cyclonic circulation anomaly in the southern northern scs which enhances the cross basin current that connects the scs western boundary current with the eastern boundary of the scs around the mindoro strait and then effectively modulates the interannual variability of mindoro strait transport an extreme el nino and large luzon strait intrusion occurred in winter 2015 16 and mooring observations and remote sensing data confirmed the presence of an intense dipolar gyre this resulted in an extreme eastward cross basin current and outward scs mindoro strait transport anomaly in 2015 16

tectono thermal evolution magma emplacement and shear zone development in the caruaru area borborema province ne brazil abstract the neoproterozoic borborema province bp in northeastern brazil is characterized by a regional flat lying foliation and by abundant magmatic rocks commonly spatially associated with large transcurrent shear zones combined field micropetrographic thermobarometric and magmatic fabric studies carried out on plutons country rocks and shear zones in the eastern domain of the province the caruaru area reveal that 1 an early episode of regional deformation with a top to the ne displacement was followed by the development of conjugate strike slip shear zones 2 similar low pressure 650 c metamorphic conditions occurred during the two events 3 plutons intruded the flat lying foliation 4 magma emplacement slightly predated strain localization in transcurrent shear zones but 5 plutons underwent strike slip deformation before complete crystallization therefore regional deformation pluton emplacement and shear zone development were successive events occurring over a relatively short time span 40ar 39ar laser dating of amphibole 584 ma and biotite 545 553 ma single grains supports slow cooling 5 c ma of country rocks through the argon closure temperatures of these minerals complex sometimes discordant amphibole ages bracketed between 552 and 575 ma for shear zones may be attributed to episodic activity and or dike swarm intrusions into them which disturbed the ar system biotite ages for the shear zones 533 545 ma also imply a relatively low cooling rate these data show that the massive injection of magmas in the continental crust of the bp during the brasiliano pan african orogeny produced a long lived thermal anomaly of regional extent the 40ar 39ar ages in the caruaru area are older than in other segments of the bp with similar geological characteristics this indicates a tectono thermal history for the bp that is more complex than previously recognized with either diachronous deformation magmatism and associated low p high t metamorphism or contrasting cooling of the different domains possibly due to differential vertical movements

thermally softened continental extensional zones arcs and rifts as precursors to thickened orogenic belts abstract intra continental deformation of soft zones during continental collision requires weak continental lithosphere which is able to be shortened across considerable width during later convergence this enables significant thickening with formation of an orogenic root we have examined models with a history of lithospheric thinning by pure shear during an earlier phase of intra continental extension with associated heating geologically this situation is appropriate to intra continental rifts and back arc basins if thinning of elevated thermal structure is decoupled from the thinning of lithology then a weak soft lower crust and sub arc rift mantle result this weak structure has a favoured rheology for subsequent convergent thickening while the lithosphere is still hot these regions are associated with formation of granulites and metamorphic assemblages typical of high temperature low pressure ht lp if convergence starts while the heat input is still active then the failed rifts and arcs are shut off by lateral wedging of the hard lower crust and upper mantle of shoulder regions into the softened arc rift domain such sites are ideal for the formation and for the exhumation of metamorphic core complexes subsequent thickening during convergence leads to ht eclogites when the previous arc rift was hot and to medium t eclogites for a thickened standard geotherm these p t paths are counterclockwise and their shapes are strongly dependent on the amount of previous thinning and type of initial geotherm if the compression starts long after cessation of the extensional event and associated thermal anomaly then the geotherm of the extended area relaxes and the whole region hardens in this case no homogeneous thickening occurs and deep continental roots cannot form

emplacement setting of the granite sheeted pluton of esperanca brasiliano orogen northeastern brazil abstract anisotropy of magnetic susceptibility ams and isotopic u pb sm nd data were combined to study the emplacement setting of the granite sheets that constitute the esperanca pluton in the borborema province northeastern brazil the sheets dip moderately to the se along the contact zone between the paleoproterozoic basement rocks and early neoproterozoic orthogneisses and metasediments granite fabrics were determined mainly using ams in 136 sites distributed within the central and western part of the pluton the sheets normally have susceptibility lower than 0 35 msi but locally where a ti poor magnetite appears with titanite the susceptibility increases up to 5 msi comparison between the silicate fabric and ams showed inconsistencies between the shape of mineral and magnetic ellipsoids despite of their orientations that fit fairly well to each other ams indicated the deformation was partitioned between the lower tonalite syenogranite and upper leucogranite and coarse porphyritic granite sheets in the lower sheets the curvilinear lineation trajectory is attributed to a dominant heterogeneous pure shear event that flattened laterally the still molten tonalite and syenogranite into the regional foliation the associated microstructures are typically magmatic zircon u pb data of the syenogranite yielded a crystallization age of 592 5 ma in the upper sheets the fabric recorded a component of simple shear deformation that displaced the coarse porphyritic granite and the top gneissic host rocks to the southwest microstructures are mostly of post full crystallization type tdm model ages and nd t 0 values indicate that the magma contaminated by partial melting of the regional host rocks sheet propagation at the emplacement level would have exploited the contact zone between crustal blocks of different rheologies when the melt pressures would be able to tensionally fail the anisotropy of the host rocks

timing of crust formation deposition of supracrustal sequences and transamazonian and brasiliano metamorphism in the east pernambuco belt borborema province ne brazil implications for western gondwana assembly abstract the main structural feature of the central domain of borborema province ne brazil is a network of dextral and sinistral shear zones these shear zones rework an older regionally developed flat lying foliation in orthogneisses and supracrustal belts which in the east pernambuco belt was formed under amphibolite facies conditions this study reports la icp ms u pb zircon ages of metaigneous and metasedimentary rocks aiming to constraint the pre transcurrent tectonothermal evolution in the eastern pernambuco domain ages of 2125 7 and 2044 5 ma in a mafic layer of banded orthogneiss are interpreted as the age of the protolith of the orthogneiss and of high grade transamazonian metamorphism respectively the latter age is consistent with the occurrence of low th u metamorphic zircon xenocrysts dated at 2041 15 ma in the leucosome of a migmatitic paragneiss a granitic orthogneiss dated at 1991 5 ma reflects late to post transamazonian magmatic event a similar age 1972 8 ma was found in rounded zircon grains from a leucocratic layer of banded orthogneiss ages of detrital zircons in a paragneiss sample indicate derivation from sources with ages varying from the archean to neoproterozoic with peak ages at ca 2220 2060 1940 1200 1150 and 870 760 ma detrital zircons constrain the deposition of the supracrustal sequence to be younger than 665 ma magmatic zircons with the age of 626 15 ma are found in the leucosome of a migmatitic paragneiss and constrain the age of the brasiliano high temperature metamorphism a lower intercept age of 619 36 ma from a deformed granodiorite dated at 2097 5 ma and the crystallization age of 625 24 ma of the felsic layer of banded orthogneiss also confirm the late neoproterozoic metamorphism these results show that the present fabric in basement and supracrustal rocks was produced during the brasiliano orogeny paleoproterozoic ages reported in this study are similar to those found in other sectors of the borborema province the cameroon and nigeria provinces and the sao francisco congo craton they show the importance of the transamazonian eburnean event and suggest that these tectonic units may have been part of a larger single continental landmass likewise similarities in post transamazonian metamorphic and magmatic events in the borborema nigeria and cameroon provinces suggest that they shared a common evolution and remained in close proximity until the opening of the atlantic ocean

palaeogeographical reconstructions of the pan african brasiliano orogen closure of an oceanic domain or intracontinental convergence between major blocks abstract a reconstruction of the pan african brasiliano orogen has become possible thanks to new data from the southern pan african belt and by using published data geological mapping which included structural thermobarometric and geochemical studies in togo and neighbouring countries have enabled to define the existence of a preorogenic continental rift whose closure followed soon after its opening continental crust convergence induced an oblique collision that caused nappe stacking this involved external nappes thrust over the west african craton intermediate nappes including metabasic rocks with eclogitic assemblages and internal nappes composed of highgrade anatectic gneiss and intrusive granite and charnockite comparison with data from other regions hoggar adrar des iforas northeastern brazil nigeria central africa has led to the recognition of a pre orogenic continental rift that bordered the west africa sao francisco congo cratons in the southern part of the chain farther north in the hoggar and adrar des iforas this continental rift opened on a wider oceanic domain which involved a passive margin along the west african craton and an active margin to the east after these rifting and subduction stages continental collision followed that was dominated by strike slip movement oblique to the plate boundaries the general organization of the pan african brasiliano belt can be considered as the result of a confrontation between three major continental domains these were the west african and sao francisco congo cratons and a reworked shield composed in its inner part of polycyclic basement rocks and bounded by a fringe of monocyclic metasedimentary thrust belts that faced the cratons

internal tides in the northwestern south china sea observed by pressure recording inverted echo sounders abstract this study presents it observations in the northwestern scs from five pressure recording inverted echo sounders piess the vertical round trip acoustic travel times that piess measures are proportional to the vertical thermocline displacements therefore piess can be used to monitor the 1st mode internal tides piess were deployed along a section between the continental shelf break in the north and xisha islands in the south measurements show that both diurnal and semidiurnal its were stronger on the northern and southern sides of the section than those in the middle their temporal variations were coherent with local surface tides which implies locally generated its may be important complex empirical orthogonal function analysis reveals a small phase difference the south leads the north by 70 across the section for diurnal its but a significant phase difference the north leads the south by 360 for semidiurnal its these observations indicate that the dominant diurnal its propagate across the section from east to west while the semidiurnal its propagate along the section from north to south a ray tracing model was utilized to demonstrate the impact of mesoscale circulation patterns on the propagation of diurnal its from the luzon strait to the pies sites the model explains the temporal it variations which were incoherent with local surface tides the result indicates that diurnal its in the northwestern scs can be affected by its propagating from the luzon strait while semidiurnal its are primarily generated locally from the continental shelf break in the north

meridional overturning circulation in the south china sea envisioned from the high resolution global reanalysis data glba0 08 the pattern of meridional overturning circulation moc in the south china sea scs is studied using a numerical lagrangian tracing method with the hycom ncoda global 1 12 degrees analysis glba0 08 data the scs moc has a sandwich structure which consists of a layer of stronger clockwise circulation above 500 m depth a counterclockwise layer in the mid layer between 500 and 1000 m depth and a weaker clockwise layer below 1000 m the deep below 1000 m depth clockwise layer is divided into three cells namely the deep southern moc cell dsmoc the deep middle moc cell dmmoc and the unclosed deep northern moc cell dnmoc the inflow through the luzon strait is the main source for the scs mocs the upper layer luzon strait inflow dominates the upper scs moc structure but has relatively less contribution to the dnmoc whereas the deep layer luzon strait inflow mainly influences the dnmoc and it mostly rises near 18 degrees n the inflow through the taiwan strait mainly contributes to the upper layer moc moreover inflows from the mindoro and karimata straits contribute negatively to the upper moc but play a significant role on the dsmoc the backward integration of lagrangian trajectories further validates that the scs deep water comes not only from the deep inflow but also from the entrainment of the middle and upper layer inflow through the luzon strait in the scs basin there are three northwest southeast tilted zones where tracers upwell which correspond to the three deep moc cells one possible mechanism for these upwelling zones is the interaction between the continental slope trapped waves and the westward planetary rossby waves

deep south china sea circulation 1 the analysis of an updated monthly climatology of observed temperature and salinity from the u s navy generalized digital environment model reveals a basin scale cyclonic circulation over the deep south china sea scs the cyclonic circulation lies from about 2400 m to the bottom the boundary current transport of the cyclonic circulation is around 3 0 sv our results suggest that the cyclonic circulation is mainly forced by the luzon overflow with bottom topography playing an important role the structures of potential temperature salinity and potential density in the deep scs are consistent with the existence of the cyclonic circulation specifically low salinity water is found in the interior region west of luzon island and surrounded by saline pacific water in boundary current regions to the north west and southwest our results show the potential density distribution and the corresponding cyclonic circulation in deep scs are primarily controlled by salinity variations in the deep basin

biogenic silica in surface sediments of the south china sea controlling factors and paleoenvironmental implications abstract we mapped the spatial distribution of biogenic silica bsi based on a total of 355 surface sediment samples from the south china sea to provide a basin wide bsi data set for paleoenvironmental reconstruction in the region the results show that bsi relative abundance calcium carbonate percentage siliceous test total abundance grain size and sediment magnetic susceptibility all show distinct spatial distribution patterns that are affected by environmental drivers the gradual increase in bsi from the continental shelf to the abyssal plain suggests that decreased dilution of terrigenous sediments plays a greater role in bsi preservation than does increasing dilution by caco3 decreasing productivity or siliceous dissolution the bsi correlation is weak for diatom abundance but relatively good for radiolarians confirming that radiolarians are the primary contributor to bsi fluxes in the low latitude south china sea in contrast increased dissolution results in a decrease in caco3 with increasing water depth reflecting the different preservation patterns of these two biogenic components correlation analysis also reveals a positive correlation between bsi and fine grain size perhaps reflecting the ability of clay minerals to protect bsi from dissolution volcanic ash and glass also can retard dissolution by increasing the pore water saturation of sio2 in abyssal basin sediments

impact of tidal mixing on water mass transformation and circulation in the south china sea abstractusing a high resolution regional ocean model the impact of tidal mixing on water mass transformation and circulation in the south china sea scs is investigated through a set of numerical experiments with different configurations of tide induced diapycnal diffusivity the results show that including tidal mixing in both the luzon strait ls and scs has significant impact on the ls transport and the intermediate deep layer circulation in the scs basin analysis of the density field indicates that tidal mixing in both the ls and scs are essential for sustaining a consistent density gradient and thus a persistent outward directed baroclinic pressure gradient both between the western pacific and ls and between the ls and scs basin so as to maintain the strong deep water transport through the ls further analysis of water mass properties suggests that tidal mixing in the deep scs would strengthen the horizontal density gradient intensify the basin scale cyclonic circulation induce more vigorous o

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

transports and tidal current estimates in the taiwan strait from shipboard adcp observations 1999 2001 tidal and mean flows in the taiwan strait are obtained from analysis of 2 5 years 1999 2001 of shipboard adcp data using a spatial least squares technique the average tidal current amplitude is 0 46 ms 1 the maximum amplitude is 0 80 ms 1 at the northeast and southeast entrances and the minimum amplitude is 0 20 ms 1 in the middle of the strait the tidal current ellipses derived from the shipboard adcp data compare well with the predictions of a high resolution regional tidal model for the mean currents the average velocity is about 0 40 ms 1 the mean transport through the strait is northward into the east china sea at 1 8 sv the transport is related to the along strait wind by a simple regression transport sv 2 42 0 12 wind ms 1 using this empirical formula the maximum seasonal transport is in summer about 2 7 sv the minimum transport is in winter at 0 9 sv and the mean transport is 1 8 sv for comparison this result indicates that the seasonal amplitude is almost identical to the classical estimate by wyrtki physical oceanography of the southeast asian waters scientific results of marine investigations of the south china sea and gulf of thailand 1959 1961 naga report 2 scripps institute of oceanography 195 pp based on the mass balance in the south china sea while the mean is close to the recent estimate by isobe continental shelf research 19 1999 195 based on the mass balance in the east china sea 2003 elsevier science b v all rights reserved

influence of abyssal mixing on the multilayer circulation in the south china sea abstractby parameterizing the abyssal mixing as the exchange velocity entrainment detrainment between the middle and deep layers of the south china sea scs its effects on the multilayer circul

evaluation of hycom in the kuroshio extension region using new metrics 1 a high resolution 0 08 at equator hybrid coordinate ocean model hycom simulation is evaluated using observations for the period 1993 2003 for a western pacific region containing the kuroshio extension ke 25 45 n and 135 180 e comparisons are made for the ke path and strength and for the upper ocean heat budget the mean strength and path agree well with observations except near the ke separation point where the jet is as much as 2 of latitude too far south however the model path variations are considerably more energetic than observed and this likely obscures the observed tendency for weaker meandering when the ke is strong the model accurately reproduces seasonal variations of upper ocean heat content but the long period about 10 yr variations of heat content and ke strength clearly differ in the region upstream of 150 e the long period variations in model ssh do not show the same relationship to wind forcing that is seen in the observations and in a low resolution ocean model simulation the hycom upper ocean heat budget is similar to a diagnostic heat budget inferred from observations in that the dominant contribution is from lateral fluxes advection however advection fluctuations again primarily in the upstream region are much larger in the model this evaluation of hycom shows realistic mean quantities and realistic variations away from the separation region however an overly energetic jet upstream of 150 e can obscure the longer period variability and its contribution to the upper ocean heat budget

kuroshio intrusion and the circulation in the south china sea 1 the princeton ocean model is used to study the circulation in the south china sea scs and its seasonal transition kuroshio enters leaves the scs through the southern northern portion of the luzon strait the annually averaged net volume flux through the luzon strait is 2 sv into the scs with seasonal reversals the inflow season is from may to january with the maximum intrusion of kuroshio water reaching the western scs during fall in compensation of summertime surface offshore transport associated with coastal upwelling from february to april the net transport reverses from the scs to the pacific the intruded kuroshio often forms an anticyclonic current loop west of the luzon strait the current loop separates near the dongsha islands with the northward branch continuously feeding the south china sea warm current scswc near the shelf break and the westward branch becoming the south china sea branch of kuroshio on the slope which is most apparent in the fall the scswc appears from december to february on the seaward side of the shelf break flowing eastward against the prevailing wind diagnosis shows that the onshore ekman transport due to northeasterly monsoon generates upwelling when moving upslope and the particular distributions of the density and sea level associated with the cross shelf motion supports the scswc

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

facies model on the modern isolated carbonate platform in the xisha archipelago south china sea abstract the xuande atoll with a discontinuous reef rim caused by platform drowning is a typical ellipse isolated platform on the northern slope of the south china sea based on the data of drilling holes the analysis of surface sediments and high resolution acoustic data six sedimentary facies are identified in the xuande atoll including reef outer slope reef front reef flat aeolianite sand island back reef slope and lagoon facies map shows that the elevated reef rimmed margins with islands are more noticeable on the windward of the platform with an elevated and discontinuous reef rimmed margin as well as coarse grained sediment in the interior platform xuande can serve as a case of a leaky bucket atoll which is characterized by initially drowning scenarios the facies architecture of the xuande atoll is evidently influenced by complex and interacting parameters including antecedent topography sea level wind driven currents water depth and tectonic subsidence different controlling factors exist in the drowning of the windward and leeward sides of the platform margin the study of modern depositional settings in the xuande atoll will provide insight on predictions for ancient carbonate provinces

seasonal variability of the meridional overturning circulation in the south china sea and its connection with inter ocean transport based on soda2 2 4

proterozoic history of the borborema province ne brazil correlations with neighboring cratons and pan african belts and implications for the evolution of western gondwana 1 geological and geochronological correlations between borborema province ne brazil and neighboring cratons and brasiliano pan african belts indicate that the amazonian west african and sao francisco congo cratons and the basement of the araguaia borborema nigerian and cameroon provinces were part of the atlantica supercontinent this continent was established at the end of the transamazonian eburnean cycle 2 0 ga and apart from ubiquitous taphrogenesis in the 1 8 1 7 ga interval remained largely unaffected for the following 1 ga around 1 ga an important magmatic event in borborema province correlates with rifting episodes and anorogenic magmatism in the sao francisco congo and amazonian cratons these events are interpreted as failed attempts to break up atlantica which at this time may have been part of the larger rodinia supercontinent renewed extensional conditions in borborema province during the middle and late neoproterozoic are attributed to far field stresses transmitted to the interior of atlantica by outwardly dipping subduction zones that encircled its northern present day coordinates portion the rarity of petrotectonic assemblages typical of subduction zone environments indicates that extension did not evolve enough to form large oceans basins and thus that the borborema province essentially includes reworked intracontinental domains regional deformation and metamorphism starting at 650 640 ma and shear zone development beginning at 590 595 ma were continuously developed through time and were synchronous throughout most of the borborema araguaia cameroon and nigerian provinces postorogenic conditions were reached 540 530 myr ago while active deformation was still occurring in other belts that accreted around atlantica to form western gondwana

overview of the multi layer circulation in the south china sea abstract the south china sea scs is a semi enclosed ocean basin with its sole deepwater renewal channel in the northeast the luzon strait connected to the northwestern pacific the circulation in the scs is endowed with a distinctive multi layer structure which is influenced by the seasonally reversing southeast asian monsoon at the surface modulated kuroshio intrusion in the upper layer and enhanced diapycnal mixing and persistent luzon strait deepwater overflow in the deep layer after being diapycnally mixed by energetic internal tides internal waves and mesoscale eddies waters entering the scs in the upper and deep layers through the luzon strait are returned to the northwestern pacific in the intermediate layer this inflow outflow inflow structure in vertical induces net inflows of potential vorticity in the upper and deep layers and a net outflow of potential vorticity in the intermediate layer of the luzon strait which are believed to be closely related with the circulation structure in the scs a sandwiched circulation in the scs namely anticyclonic in the intermediate layer and cyclonic in the upper and deeper layers was recently reported but controversial issues still remain on its spatial pattern and temporal variability to ascertain this sandwiched circulation and reveal its driving mechanism is of much scientific interest to the on going discussion on the scs circulation and its role in regional climate different from previous review articles focusing on eddies or circulation in a specific layer or area we overview the full depth circulation of the scs layer by layer and outline its possible forcing mechanisms and furthermore provide perspectives for further investigation

a comparison of different tl techniques on loess samples from rheindahlen f r g abstract 9 tl samples of the loess profile rheindahlen lower rhine area germany covering the time span of the last 300 ka were studied systematic investigation was carried out using different filters and preheating procedures ed determinations were done by the additive dose and the regeneration method the annual dose was determined by aas alpha counting naa and gamma spectrometry in the laboratory and in the field the results show that the weichselian loess is datable whereas no tl age differentiation between loesses of stage 6 and stage 8 is possible if the accumulated dose ed is in the 600 gy region every apparent tl age between 100 and 300 ka can be obtained this leads to the conclusion that in rheindahlen no reliable tl ages are available for loess deposits underneath the eemian soil stage 5e

energetics of a global ocean circulation model compared to observations 1 the majority of the eddy kinetic energy eke in the ocean is found on scales of 50 km to 500 km encompassed by mesoscale eddies and the meanders and rings of the boundary currents mesoscale eddies play a critical role in the dynamics of the ocean circulation with instabilities of the strong mean currents generating eddies in the upper ocean interactions between eddies transfer energy from the upper ocean to the deep ocean where eddies interact with bottom topography to generate abyssal mean flows and eddies transfer momentum back to the mean currents the kinetic energy in a global hybrid coordinate ocean circulation model hycom is compared with long term observations from surface drifters geostrophic currents from satellite altimetry subsurface floats and deep current meter moorings hycom configured at 1 12 5 9 km typical of the present generation of high resolution models is deficient in eke in both the upper and abyssal ocean depths greater than 3000 m by 21 and 24 respectively compared to surface drifting buoys and deep current meters increasing the model resolution to 1 25 4 4 km or injecting mesoscale eddies through the assimilation of surface observations in a 1 12 5 model increases the surface and the abyssal eke to levels consistent with the observations in these models the surface abyssal eke is increased by 23 51 and 15 46 for the higher resolution or data assimilative models respectively compared to the 1 12 5 non assimilative model while data assimilation increases the eke in both the upper and abyssal ocean the kinetic energy of the mean flow in the upper ocean is decreased in the data assimilative hindcast

thermal modelling in low pressure high temperature metamorphic belts abstract low pressure high temperature metamorphic belts occur throughout the world they display a characteristic metamorphic style which has remained unchanged with time they are found in disparate tectonic settings including magmatic arcs regions of extension regions of thickened crust in continent continent collision zones and accretionary wedges they are commonly characterized by an abundance of granitoid plutons pressures of metamorphism are primarily less than or equal to that of the aluminosilicate triple point approximately 4 kbar while temperatures are in the range 500 750 c with rare exceptions inferred ptt paths are nearly isobaric and recrystallization was rapid and prograde metamorphic thermal gradients are commonly in the range 60 150 c km these conditions necessitate the presence of a large component of advective heat transfer and or anomalously high basal heat flow during metamorphism the large magmatic fluxes associated with the formation of magmatic arcs provide an adequate heat source for low pressure metamorphism lpm lithospheric extension is likely to produce lpm only if the degree of thinning is large 3 and there is additional heat from magmas the generation of lpm by crustal thickening requires either a large component of advective heating by magmas anomalously high basal heat flow or pre thickening lithospheric extension lpm in this environment must necessarily be accompanied by plutonic activity advection of heat by aqueous fluids may provide a significant contribution to the thermal budget but acting along is unlikely to produce lpm regional lpm induced by advective sources rarely occurs along a geotherm which increases monotonically with depth or synchronously across the region at a given depth it occurs over time as a series of overlapping temporally separate and spatially localized thermal events

rossby wave coastal kelvin wave interaction in the extratropics part i low frequency adjustment in a closed basin abstract the interaction of open and coastal oceans in a midlatitude ocean basin is investigated in light of rossby and coastal kelvin waves the basinwide pressure adjustment to an initial rossby wave packet is studied both analytically and numerically with the focus on the low frequency modulation of the resulting coastal kelvin wave it is shown that the incoming mass is redistributed by coastal kelvin waves as well as eastern boundary planetary waves while the incoming energy is lost mostly to short rossby waves at the western boundary the amplitude of the kelvin wave is determined by two mass redistribution processes a fast process due to the coastal kelvin wave along the ocean boundary and a slow process due to the eastern boundary planetary wave in the interior ocean the amplitude of the kelvin wave is smaller than that of the incident planetary wave because the initial mass of the rossby wave is spread to the entire basin in a midlatitude ocean basin the slow eastern boundary planetary wave

decadal variation and trends in subsurface salinity from 1960 to 2012 in the northern south china sea observations suggest that subsurface waters in the northern south china sea nscs exhibited substantial low frequency variability with a striking decadal change in the southern limit of the 34 6 psu isohaline long term freshening of the subsurface waters started in 1960 was followed by salinification from 1975 and freshening occurred again from 1993 to 2012 the linear trends were 0 0076 0 0100 and 0 0078 psu yr respectively an analysis of the subsurface salinity budget reveals that the main underlying contributors to subsurface salinity are horizontal advection and vertical entrainment in particular advection driven by the luzon strait transport and vertical entrainment from the mixed layer are the key factors controlling variations on subsurface salinity diagnosis of the salinity budget further suggests that entrainment from the mixed layer played a more important role in the freshening periods than in the salinifying period

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

lagrangian decomposition of the deacon cell the meridional overturning cells in the southern ocean are decomposed by lagrangian tracing using velocity and density fields simulated with an ocean general circulation model particular emphasis is given to the deacon cell the flow is divided into four major components 1 water circling around antarctica in the antarctic circumpolar current acc 2 water leaving the acc toward the north into the three world oceans 3 water coming from the north and joining the acc mainly consisting of north atlantic deep water nadw and 4 interocean exchange between the three world oceans without circling around antarctica the deacon cell has an amplitude of 20 sv of which 6 sv can be explained by the the east west tilt of the acc 5 sv by the east west tilt of the subtropical gyre and the remaining 9 sv by the differences of the slope and depth of the southward transport of nadw and its return flow as less dense water the diabatic or cross isopycnal deacon cell is only 2 sv

obliquely convergent tectonics and granite emplacement in the trans saharan belt of eastern nigeria a synthesis abstract the eastern nigeria terrane belongs to the 3000 km long trans saharan belt which was formed in the neoproterozoic between 750 and 500 ma by continental collision between the converging west african craton congo craton and east saharan block the study area consists mostly of gneisses and migmatites that underwent granulite facies metamorphism 800 c 800 mpa in contrast with western nigeria and cameroon no basement cover relationship has been identified which is in agreement with a monocyclic metamorphic history around 640 ma the area underwent a nappe tectonics with eastward displacement emplacement of bt ms granites and granulite facies peak later on around 615 ma nappes were towards the north numerous hbl bt granite plutons were emplaced around 585 ma during north south strike slip regional deformation the anisotropy of magnetic susceptibility fabric helps in defining strain localization along narrow north south to nne ssw vertical shear zones during the exhumation history exhumation of the terrane assessed using u pb ar ar and rb sr methods was presumably slow with uplift rates around 0 2 0 5 mm year preliminary estimates of contemporaneous horizontal movements suggest that they were one order of magnitude larger

moderate overthickening of thinned sialic crust and the origin of granitic magmatism and regional metamorphism in low p high t terranes formation of low pressure p high temperature t metamorphic terranes by homogeneous shortening and thickening of tectonically thinned sialic crust and overlying sedimentary basins at geologically reasonable strain rates avoids the shortcomings of hypotheses linking the characteristically high geothermal gradients to doubling of normal thickness crust crustal extension alone intrusion of granitoids or extensive basic magmatism on the basis of geological and p t constraints from the archean slave province the p t histories of three points in a hypothetical block of crust are presented in p t p distance and p time diagrams the relations between the rock that ends up at the surface base of the basin base of the crust isotherms and depth determine the type of metamorphism and the degree of partial melting required to produce abundant granitoids this simple qualitative framework can account for the characteristic features of low p high t metamorphic terranes and reconcile those who believe granites are the cause of the metamorphism with those who favor the contrary

deepwater circulation variation in the south china sea since the last glacial maximum deepwater circulation plays a central role in global climate compared with the atlantic the pacific deepwater circulation s history remains unclear the luzon overflow a branch of the north pacific deep water determines the ventilation rate of the south china sea scs basin sedimentary magnetic properties in the scs reflect millennial scale fluctuations in deep current intensity and orientation the data suggest a slightly stronger current at the last glacial maximum compared to the holocene but the most striking increase in deep current occurred during heinrich stadial 1 h1 and to a lesser extent during the younger dryas yd results of a transient deglacial experiment suggest that the northeastern current strengthening at the entrance of the scs during h1 and the yd times of weak north atlantic deep water formation could be linked to enhanced formation of north pacific deep water

on the driving processes of the atlantic meridional overturning circulation because of its relevance for the global climate the atlantic meridional overturning circulation amoc has been a major research focus for many years yet the question of which physical mechanisms ultimately drive the amoc in the sense of providing its energy supply remains a matter of controversy here we review both observational data and model results concerning the two main candidates vertical mixing processes in the ocean s interior and wind induced ekman upwelling in the southern ocean in distinction to the energy source we also discuss the role of surface heat and freshwater fluxes which influence the volume transport of the meridional overturning circulation and shape its spatial circulation pattern without actually supplying energy to the overturning itself in steady state we conclude that both wind driven upwelling and vertical mixing are likely contributing to driving the observed circulation to quantify their respective contributions future research needs to address some open questions which we outline

thermohaline circulation in the deep south china sea basin inferred from oxygen distributions 1 on the basis of the historical oxygen data available distributions of dissolved oxygen were analyzed in detail to investigate the thermohaline circulation in the south china sea scs the analyses confirmed the existence of a layer of minimal oxygen content at intermediate depths of the basin which shows a low oxygen 1 6 ml l 1 core in the southern basin with water ages shorter than 100 years after entering the scs and which appears isolated from its counterpart of the western philippine sea north to the core along the northern slope there is a band of oxygen rich water in both upper and intermediate layers above 700 m the band can be attributed to the intrusion of high oxygen water through the luzon strait while vertical flux appears to be responsible between 700 and 1500 m the oxygen distribution provides additional evidence for a sandwiched vertical structure in transports through the luzon strait with outflows in the intermediate layer and inflows above and below while the abyssal water of the scs is being replenished by the deep inflows an abrupt change of water properties was observed in both upper and intermediate layers across the luzon strait suggesting possible domination of local vertical mixing over horizontal spreading of inflows in the northern scs a four cell conceptual model was proposed for the thermohaline circulation which consists of a three layer cross basin exchange cell in the luzon strait an active ventilation cell in the upper and intermediate layers along the northern slope an abyssal replenishment cell in the deep and a cyclonic recirculation cell in the interior basin

progress on the formation dynamics of the layered circulation in the south china sea abstract in the south china sea scs an alternating cyclonic anticyclonic cyclonic cac circulation is recognized in the upper middle deep layers based on the principle of stokes theorem the cac circulation is driven extrinsically by the east asia monsoonal winds a vertical sandwich like inflow outflow inflow through luzon strait ls and intrinsically by the slope current topography interaction the understandings on the formation mechanisms of cac circulation have been achieved based on different principles and the physically solid interpretation on the cac circulation need to be further clarified in this paper we review different dynamic perspectives from recent researches that describe the combined effects of surface wind forcing lateral external forcing and the intrinsic coupling among different layers our aim is to obtain a consistent understanding of the dynamics of the circulation in the scs the cac circulation forms largely from the planetary vorticity flux that is extrinsically induced by the inflow outflow inflow through ls which is predominantly balanced by the interaction between the cac flow and bottom topography inside basin the vertical motion dynamically links the circulation in three layers and its spatial pattern has a strong impact on the basin circulation particularly in the middle and deep layers vertical coupling of the layers occurs mainly over the slope because of the cross slope motion due to interaction between strong slope current and topography the internal layered circulation and intensified mixing in turn affect and maintain the layered current structure in ls based on the review of the forcing mechanisms we offer perspectives for further investigations

three dimensional pathways of water masses in the south china sea a modeling study we conduct a numerical eulerian analysis on the lagrangian characteristics of south china sea scs water masses this is the first study to investigate the water pathway and residence time in response to time dependent three dimensional basin circulation in the scs the circulation of the scs is largely determined by westward intrusions of the northwestern pacific waters in the upper layer 0 750 m and deep layer 1500 m and by an eastward extrusion in the intermediate layer 750 1500 m through luzon strait ls the waters in these three layers are interlinked to sustain the three dimensional circulation in the scs the upper intrusive waters flow cyclonically and have a residence time of 3 years before they subduct into a deeper layer or exit the scs through surrounding straits the intrusive denser waters in the deep layer flow along the northern slope and reside for 25 years in the northern basin north of 13 n where a strong subduction occurs a cyclonic circulation exists in the deep layer in the southern basin south of 13 n where a subduction of intermediate waters occurs over its eastern side and a deep upwelling exists over its western side the water in the deep southern basin has a residence time of 40 years the upwelled deep waters and the subducted waters from the upper layer form the intermediate water where waters circulate anti cyclonically towards ls and have a longest residence time 42 years these findings are supported by the spatial variation in the observed potential density variance

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

an updated examination of the luzon strait transport 1 despite numerous previous estimates of luzon strait transport lst we attempt an update using a fine resolution model with these improvements the circulation in and around luzon strait shows up rather realistically intrusion of a kuroshio meander into the south china sea scs is seasonally varying the lst especially in the upper ocean caused by a small difference between the large meander inflow and outflow is also seasonally varying and subject to large standard deviation the annual mean lst is estimated to be westward 4 0 5 1 sv along 120 75 e we have also conducted process of elimination experiments to assess the relative importance of open ocean inflow outflow wind stress and surface heat flux in regulating lst and its seasonality the east asian monsoon winds stand out as the predominant forcing without it the upper ocean lst changes from westward to eastward ranging up to 4 sv and with misaligned seasonality triggering an inflow from the mindoro strait to the scs to replenish the water mass loss discounting monsoon winds sea level in the sulu sea is generally higher because it receives the indonesian throughflow before the scs which causes an inflow from the sulu sea to the scs on the other hand the annual mean wind from the northeast invites outflow from the scs to the sulu sea or inflow from the luzon strait weighing the two competing factors together we see the cessation of northeast monsoon as a condition favorable for the luzon strait outflow or the mindoro strait inflow