tracing tropical and intermediate waters from the south china sea to the okinawa trough and beyond 1 intermediate waters with a salinity minimum from 350 to 1350 m depths have been reported to flow out of the south china sea scs through the luzon strait this eastward flowing scs intermediate water scsiw is blocked by the northward flowing black stream kuroshio southeast of taiwan and is forced to turn to the north the scsiw subsequently enters and occupies the western half of the okinawa trough because of strong upwelling in the scs basin the scsiw contains more nutrients than does the kuroshio intermediate water in the philippine sea one of the major purposes of this note is to reconfirm that the scsiw actually does upwell onto the east china sea ecs shelf and to show that the south china sea tropical water scstw with a salinity maximum of 50 150 m in depth follows the same pathway as the scsiw and similarly occupies the western half of the okinawa trough part of these relatively nutrient rich subsurface waters upwell thereby supplying nutrients to the ecs shelves the remaining scsiw and scstw flow along with the kuroshio and can be traced as far east as 140 e south of japan this is just around the region where the oyashio joins the kuroshio to form the north pacific intermediate water

cross shelf transport of terrestrial al enhanced by the transition of northeasterly to southwesterly monsoon wind over the east china sea aluminum al is one of the key parameters of geotraces in spring 2011 we examined the distribution of dissolved al in the east china sea ecs to assess the potential passage of coastal water across the shelf to the western pacific measurement of dissolved al in coastal shelf and shelf break waters indicated decreasing concentrations with distance from the coast however the northward increase of dissolved al in the upper 100 m along the shelf break transect corresponding to the northward flow of kuroshio water along the okinawa trough from the north of taiwan to the tokara strait indicates contributions of terrestrial material the presence of an al plume indicated cross shelf transport at the subsurface at a potential density of 23 3 24 0 kg m3 this plume originates from the near bottom layer along the coast off zhejiang and fujian provinces and first moves southeastward to the north of taiwan and then northeastward to shelf break with export at 29 n 127 e we calculated the cross shelf fluxes of water and dissolved al based on simulation results of the 3 d massachusetts institute of technology general circulation model mitgcm the calculated cross shelf fluxes of al at the subsurface layer indicate that the ecs is highly efficient in pumping al rich coastal waters northward to the japan sea east sea and or eastward into the western pacific we also identified an important role of the monsoon with a change from northeasterly wind to southwesterly wind in spring on the cross shelf transport of al by use of numerical tracer experiments

geothermal heating and the properties of bottom water in cascadia basin 1 a new compilation of ctd data sheds light on the circulation and properties of bottom water within cascadia basin a relatively high salinity water mass is revealed in a region of likely bottom water inflow east of the blanco fracture zone water mass distributions and the deep geostrophic shear field are consistent with a general cyclonic circulation within the basin and suggest a northward flowing boundary current next to the deep continental slope shifts in temperature salinity relationships are consistent with a vertical transition from waters of northern origin to waters of southern origin approaching the seafloor this vertical water mass transition complicates the interpretation of temperature anomalies we redefine the temperature anomaly due to geothermal activity and the thickness of the layer influenced by seafloor heating simple heat budget calculations lead to a residence time of about one year for the bottom water shorter than suggested by previous studies

flankflux an experiment to study the nature of hydrothermal circulation in young oceanic crust the sediment buried eastern flank of the juan de fuca ridge provides a unique environment for studying the thermal nature and geochemical consequences of hydrothermal circulation in young ocean crust just 18 km east of the spreading axis where the sea floor age is 0 62 ma sediments lap onto the ridge flank and create a sharp boundary between sediment free and sediment covered igneous crust farther east beneath the nearly continuous turbidite sediment cover of cascadia basin the buried basement topography is extremely smooth in some areas and rough in others at a few isolated locations small volcanic edifices penetrate the sediment surface an initial cruise in 1978 and two subsequent cruises in 1988 and 1990 on this sedimented ridge flank have produced extensive single channel seismic coverage detailed heat flow surveys co located with seismic lines and pore fluid geochemical profiles of piston and gravity cores taken over heat flow anomalies complementary multichannel seismic reflection data w

the double silica maximum in the north pacific the north pacific has two vertical silica maxima the well known intermediate maximum occurs between 2000 and 2500 m with a potential density relative to 2000 dbar of 36 90 in the northeastern pacific the deep maximum which has not been observed extensively before is found at or near the ocean bottom in the northern north pacific in a narrow latitude range maps of silica on isopycnals which intersect the intermediate and bottom maxima show that the lowest silica is found in the western tropical north pacific suggesting a route for the spread of south pacific water into the deep north pacific low silica water is found along the western boundary of the north pacific with a separate broad tongue south of hawaii the highest silica on both isopycnals is in the northeast pacific a bottom maximum in the cascadia basin in the northeastern pacific can be differentiated from both open ocean maxima four sources for the vertical maxima are considered in situ dissolution of sinking particles bottom sediment dissolution hydrothermal venting and upslope advection in the northeastern pacific because not enough is known about any of these sources only rough estimates of their contributions can be made the bottom maximum is most likely to result from bottom sediment dissolution but requires a flux larger than some current direct estimates the cascadia basin bottom maximum may result from both bottom sediment dissolution and hydrothermal venting the intermediate maximum is likely to result primarily from dissolution of sinking particles there is no quantitative estimate of the effect of possible upslope advection or enhancement of bottom fluxes due to the columbia river outflow

deep sea nutrient loss inferred from the marine dissolved n2 ar ratio 1 some estimates of the budget of bioavailable nitrogen fixed n suggest that the oceanic nitrogen cycle is grossly out of balance we use observations of dissolved n2 ar ratios along abyssal flow paths in the ocean to investigate fixed n loss by benthic denitrification one of the largest uncertainties dissolved n2 ar in the deep sea increases from the north atlantic to the north pacific at depths 3500 m this can be explained by the mixing of low n2 ar source waters from the north atlantic with high n2 ar source waters from the southern ocean benthic denitrification in sediments bathed by these abyssal waters is below the detection limit however measureable increases in n2 ar at depths of 2000 3000 m between the subtropical and subarctic north pacific regions that share the same source water must be caused by benthic denitrification the cascadia basin with high denitrification rates and connection to the open north pacific is a likely source

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

variability of the chemical hydrography at the frontal region between the east china sea and the kuroshio north east of taiwan abstract the hydrography across the frontal region between the east china sea and the okinawa trough north east of taiwan observed during the summer of 1985 and 1988 and the early spring of 1987 was governed mainly by mixing across the front and the topographically induced upwelling of the modified kuroshio water in the okinawa trough during the periodic shelfward migration of the kuroshio the location of the front relative to the shelf break seemed to be temporally variable topographically induced upwelling was evident during the summer of 1988 and the early spring of 1987 when the front was located close to the shelf break it might not have occurred in the summer of 1985 when the front was further offshore the end member composition of the upwelling water was similar in both seasons it originated from about 300 m with a temperature and salinity of 13 c and 34 4 psu it was rich in nutrients and poor in oxygen with concentrations of nitrate phosphate silicate and oxygen of 16 1 18 and 160 m respectively this upwelling water is potentially a major source of nutrients to the east china sea the deep water in the okinawa trough at temperatures below 15 c did not participate in cross shelf mixing its chemical characteristics did not change significantly from year to year

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

abyssal pathways and the double silica maximum in the northeast pacific basin causes of the double silica maximum in the deep northeast pacific basin nepb are explored using a stochastic lagrangian approach steady state advective fields and diapycnal diffusion are taken

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

germanium silicon fractionation in a river influenced continental margin the northern gulf of mexico abstract in this study we have sampled the water column and sediments of the gulf of mexico to investigate the effects of high riverine terrigenous load and sediment redox conditions on the cycling of ge and si water column ge si ratios across the gulf of mexico continental shelf range from 1 9 to 25 mol mol which is elevated compared to the global ocean value of 0 7 mol mol the ge enrichment in the gulf of mexico seawater is primarily due to anthropogenic contamination of the mississippi river which is the main ge and si source to the area and to a smaller extent due to discrimination against ge during biogenic silica bsi production ge si 1 2 1 8 mol mol especially by radiolarians and siliceous sponges ge si 0 6 1 1 mol mol most sediment pore waters ge si 0 3 4 5 mol mol and sediment incubation experiments benthic flux ge si 0 9 1 2 mol mol indicate precipitation of authigenic phases that sequester ge from pore waters non opal sink this process appears to be independent of oxidation reduction reactions and suggests that authigenic aluminosilicate formation reverse weathering may be the dominant ge sink in marine sediments compilation of previously published data shows that in continental margins non opal ge burial flux is controlled by bsi supply while in open ocean sediments it is 10 100 times lower and most likely limited by the supply of lithogenic material we provide a measurement based estimate of the global non opal ge burial flux as 4 32 mmol yr 1 encompassing the 2 16 mmol yr 1 needed to keep the global marine ge cycle at steady state

quantifying the north pacific silica plume 1 new hydrostations plus a comprehensive compilation of existing data have allowed us to characterize the dissolved silica plume located at midwater depths in the north pacific the north pacific silica plume is a global scale anomaly extending from the north american continental margin in the east to beyond the hawaii emperor seamount chain in the west inventory of the plume between 2000 and 3000 m depth indicates that it contains 164 tmols 164 1012 mols of anomalous dissolved silica and is maintained by a horizontal flux of approximately 1 5 tmols yr from the east the source region of this plume has been previously suggested to be cascadia basin in the ne pacific biochemical and geothermal processes within this small region can produce approximately one third of the required flux but the majority of silica contained within the north pacific plume may originate in crustal fluid venting from the warm upper basement aquifer that underlies the easternmost pacific plate

flow of formation water in the jurassic of the paris basin and its and discussion effects the jurassic of the paris basin is a major target for oil and geothermal exploitation interpretation of data from numerous wells reveals that the spatial distribution of fluid and reservoir parameters is heterogeneous with correlated anomalies for temperature and geochemistry the multidisciplinary approach used to describe these typical characteristics shows that hydrodynamics provides the key to explain observed deviations from the usual correlations with depth as a consequence of the coupling between hydrodynamics and fluid properties the analysis of induced effects is a calibration criterion which can be used to improve the numerical simulation of the regional flow path compared to the results of the constant density approach the new computer flow scheme both gravity and density driven is more consistent with the thermal and chemical anomalies observed the refined analysis including density effects confirms the existence of a confined area and a mixing zone around paris previously identified by geochemical investigations

spring of no kuroshio intrusion in the southern taiwan strait 1 the taiwan strait connects the east china sea ecs to the south china sea scs typically in spring the water in the scs and a branch of the kuroshio occupy the eastern part of the strait while the china coastal waters including a large contribution from the changjiang yangtze river occupy the western part during spring 2008 when the taiwan strait was under the influence of la nina and according to field observations the kuroshio branch did not contribute much to the waters in the southern taiwan strait a numerical model verifies this observation the china coastal waters also seem to have had less effect than in typical years since the scs waters contain more nutrients than the kuroshio branch more nutrients may be transported from the scs to the ecs in a la nina spring than at other times

downwelling then upwelling again of the upwelled kuroshio water in the southern east china sea 1 as has been well known for several decades the subsurface kuroshio waters upwell onto the east china sea when the kuroshio impinges on the continental shelf northeast of taiwan based on hydrological and geochemical data our previous study demonstrated that the upwelled kuroshio waters downwell then upwell again northwest of taiwan in august a subsequent effort attributed this complex phenomenon to varying vorticity or the rossby number at the study area which encompasses two strong currents i e the kuroshio and the taiwan warm current moreover downwelling favorable winds coincided with the observation period this study demonstrates that the above phenomenon does not occur in the northern taiwan strait but appears to surface outside of the strait during all seasons in general downwelling of previously upwelled kuroshio waters from the east brings down waters from the surface explaining why the recipient bottom waters show a horizontal maximum temperature but a minimum salinity t and no3 no2 the downwelled waters subsequently upwell again since the recipient near surface waters arise from the depth there exists a horizontal minimum in temperature but a maximum salinity t and no3 no2 is found however whether wind patterns play a critical role in generating these vertical water movements remains unclear

hydrothermal helium plumes in the pacific ocean hydrothermal activity along the global mid ocean ridge system and at active seamounts introduces a 3 he rich signal into the deep ocean basins which can be used to trace patterns of ocean circulation and mixing this hydrothermal helium signal is especially strong in the pacific ocean where the spreading rate of the ridges is the greatest in several areas of the pacific the hydrothermal activity is of sufficient strength to produce intense helium plumes which clearly define the regional circulation among these are 1 a pair of helium plumes at 2500 m depth which extend westward from the east pacific rise at 10 n and 15 s into the interior of the pacific basin 2 a helium plume at 2000 m depth extending southwest from sources on the juan de fuca ridge in the northeast pacific and 3 a plume at 1100 m depth emanating from loihi seamount at 20 n which extends eastward from hawaii to the coast of mexico the flow field implied by the helium distribution appears to be in reasonable agreement with reid s 1997 steric height analysis for the pacific

chemistry of hydrothermal solutions from the southern juan de fuca ridge fluids from three vent fields on the southern juan de fuca ridge were sampled in september 1984 using the dsrv alvin the fluids are uniquely high in both chloride which ranges up to twice the seawater value and in metal content simple vapor liquid phase separation could not have produced both the high chlorinity and gas concentrations observed in these fluids the cause of the elevated chlorinity can not be uniquely identified but may be the result of either or a combination of two processes 1 subsurface formation of a degassed brine and subsequent mixing of a small amount of this brine with a hydrothermal seawater which has not undergone a phase separation and 2 dissolution of a chloride rich phase combined with a possible small loss of gas during sampling procedures although measured temperatures were all less than 300 sup 0 c quartz geothermometry suggests that the fluids have equilibrated at greater than 340 sup 0 c quartz geobarometry is also in agreement with geophysical estimates of depth to the local magma chamber copyright american geophysical union 1987

deep currents in the central subarctic pacific ocean abstract sections of closely spaced ctd stations along longs 165 w 175 w and 175 e in combination with 14 month current records from the central longitude define two deep nearly zonal currants with speed increasing upward in the subarctic pacific one flows eastward above the aleutian rise and aleutian trench and appears to be a concentration of geostrophic flow forced by the bottom topography the other flows westward along the aleutian island arc and is the northern boundary current predicted by deep circulation theory both currents reach to the sea surface the boundary current being simply the deep part of the alaskan stream the current records were too few to permit better than rough estimates of volume transports but to the extent that they could be combined with thermal wind calculations they suggest at 175 w 1 a transport of 28 106 m3 s 1 for the alaskan stream of whch 5 106 m3 s 1 was found below 1500 m and 2 a transport of around 20 1o6 m3 s 1 for the eastward jet of wh

evolution of a deep water ferromanganese nodule in the south china sea in response to pacific deep water circulation and continental weathering during the plio pleistocene abstract the south china sea scs is connected to the west pacific through a deep channel in the luzon strait thus the scs deep water is sensitive to the evolution of pacific ocean circulation which significantly influences the global climate system geochemical data pb isotope and redox sensitive elements data and magnetic data were determined for a fe mn nodule obtained from jiaolong seamount in the central scs these records reflect interactions between changes in ice sheets deep pacific circulation and weathering inputs to the deep scs during the pliocene and quaternary our results show that the scs deep water environment can be divided into three major stages stages 1 3 stage 1 4 8 1 4 ma was characterized by a well oxygenated pacific deep water pdw and lower dust inputs then moderate stable deep water ventilation and greater inputs of asian dust occurred during stage 2 1 4 0 9 ma during stage 3

hydrothermal venting and geothermal heating in cascadia basin observations in cascadia basin on the eastern flank of the northern juan de fuca ridge reveal significant bottom water modification as a result of regional conductive heating and local hydrothermal venting seafloor conductive heating occurs throughout the sedimented basin while hydrothermal fluid discharge is confined to small 1 km2 isolated igneous basement outcrops in the northern sector of the plateaulike basin the vertical fluxes of heat and mass associated with these seafloor processes lead to the formation of a 250 to 350 m thick geothermal boundary layer characterized by anomalously high temperature reduced vertical stability and high dissolved silicate concentration using a basinwide average lithospheric heat flux of 0 3 w m 2 and the observed thermal anomaly structure of the water column we obtain a mean residence time of 1 to 2 years for the deep water over cascadia basin detailed water property data collected in 1992 and 1993 within the immediate vicinity of three isolated igneous basement outcrops in the north central sector of the basin indicate that local bottom water heating arises from low temperature venting through the summit and flanks of the outcrops near the smallest edifice especially well defined layers of anomalously warm particle laden water were found within 20 m of the outcrop summit depth of 2610 m maximum anomalies of temperature light attenuation coefficient and dissolved silicate concentration in the layers were 0 040 c 0 015 m 1 and 5 mol l 1 respectively we estimate the local heat flux fo from the smallest outcrop to be 2 4 0 8 u 109 w where u m s 1 is the mean horizontal current at the venting depth for reasonable mean currents in the range 10 3 to 10 2 m s 1 we find fo 0 2 to 2 4 107 w assuming that the depressed conductive heat flow of 0 05 w m 2 observed through the sedimented seafloor surrounding the smallest outcrop reflects the advective loss of heat through the outcrop the radial distance over which crustal fluids must collect heat and converge on the outcrop is about 10 km

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

large variability of the kuroshio at 23 75 n east of taiwan synoptic features of the kuroshio at 23 75 n were quantified using nine ship based surveys between september 2012 and september 2014 the new ship based data set provides an unprecedented view of the kuroshio east of taiwan and suggest tremendous variability in its velocity hydrography volume heat and salt transports and water masses the kuroshio maximum velocity varied in 0 7 1 4 m s 1 the core current width delineated with the limit v 0 2 m s 1 ranged from 85 to 135 km and the thickness varied from 400 to 600 m a dual velocity maximum in the kuroshio core current though unexpected was observed in three of nine cruises the kuroshio core transport integrated from the directly measured velocity varied between 10 46 and 22 92 sv 1 sv 106 m3 s 1 the corresponding heat transport referenced to 0 c was 0 838 1 793 1015 w and the salt transport was 345 0 775 9 106 kg s 1 the geostrophic transport estimated using the thermal wind relation with the observed hydrographic data and reference velocity at 900 m is comparable to the directly measured kuroshio transport during most of the surveys suggesting the directly measured velocity is mostly in geostrophic balance

regional heat flow variations across the sedimented juan de fuca ridge eastern flank constraints on lithospheric cooling and lateral hydrothermal heat transport seafloor heat flow has been estimated continuously along a transect on the sedimented eastern flank of the juan de fuca ridge to provide constraints on the scale and rate of lateral heat and fluid transport in the upper igneous crust and on the total flux from the young lithosphere beneath the profile extends from 20 km east of the ridge axis where turbidite sediments lap onto the oceanic crust at an age of less than 1 ma and ends 110 km east of the axis over 3 6 ma crust estimated heat flow is derived from the combination of the depth to igneous basement determined from seismic reflection profiles and basement temperatures measured in nine ocean drilling program boreholes along the transect the strategy is based on the knowledge that in this young area upper basement temperatures are locally homogenized by vigorous hydrothermal circulation and hence vary smoothly between drilling sites at the young end of the transect near the region of extensive outcrop heat flow is only 15 of that predicted for lithosphere of this age heat flow increases systematically to the east reaching the full predicted level about 20 km from the point of sediment basement onlap the anomaly can be accounted for by mixing and or eastward flow of cool water in the upper igneous crust beneath the sediment at a darcian rate of the order of 1 m yr a geochemical signature of fresh seawater in basement is observed many tens of kilometers farther to the east although the thermal signature is no longer present along the remainder of the transect the heat flow conforms very well to that predicted by simple boundary layer cooling theory once the thermal effects of rapid sedimentation on this ridge flank are accounted for

evidence for a major change in silicon cycling in the subarctic north pacific at 2 73 ma the initiation of northern hemisphere glaciation in the subarctic north pacific at 2 73 ma was marked by an abrupt cessation of high opaline accumulation considered to result from an increased stratification of the water column that should have led to higher utilization of nutrients in the surface ocean we present a new stable si isotope based record of si utilization that is hard to reconcile with this model a drop in 30si 28si by 0 4 at 2 73 ma is coincident with an increase in bulk n isotope composition the contrasting utilization records cannot have been both caused by a hydrographic change alone excluding a change in the si n export ratio these results either imply a relative increase in silicic acid supplied to the surface waters or a change in its si isotope composition while it is impossible to distinguish between these two possibilities both imply a regional or global change in the si biogeochemical cycle potentially caused by an enhanced storage of si in the underlying deep waters of the pacific

deconvolving the controls on the deep ocean s silicon stable isotope distribution abstract we trace the marine biogeochemical silicon si cycle using the stable isotope composition of si dissolved in seawater expressed as 30 si open ocean 30 si observations indicate a surprisingly strong influence of the physical circulation on the large scale marine si distribution here we present an ocean general circulation model simulation that deconvolves the physical and biogeochemical controls on the 30 si distribution in the deep oceanic interior by parsing dissolved si into its preformed and regenerated components we separate the influence of deep water formation and circulation from the effects of biogeochemical cycling related to opal dissolution at depth we show that the systematic meridional 30 si gradient observed in the deep atlantic ocean is primarily determined by the preformed component of si whose distribution in the interior is controlled solely by the circulation we also demonstrate that the 30 si value of the regenerated component of si in the global deep ocean is dominantly set by oceanic regions where opal export fluxes to the deep ocean are large i e primarily in the southern ocean s opal belt the global importance of this regionally dynamic si cycling helps explain the observed strong physical control on the oceanic 30 si distribution since most of the regenerated si present within the deep atlantic and indo pacific oceans is in fact transported into these basins by deep waters flowing northward from the southern ocean our results thus provide a mechanistic explanation for the observed 30 si distribution that emphasizes the dominant importance of the southern ocean in the marine si cycle

silica and germanium in pacific ocean hydrothermal vents and plumes dissolved silica si and inorganic germanium ge concentrations were measured in hydrothermal fluids from black smoker vents on the east pacific rise 21 n epr and the southern juan de fuca ridge 45 n sjdfr north and south cleft sites axial volcano these typically display end member concentrations ranging from 16 to 23 mm si and 150 to 280 nm ge and end member ge si ratios clustering between 8 and 14 10 6 more than 10 fold greater than the ratio entering the ocean via rivers 0 54 10 6 and being recycled in seawater 0 7 10 6 excess concentrations of dissolved si and ge above oceanic background are observed in mid water hydrothermal plumes over mid ocean ridge mor spreading centers on the southern epr sepr 10 20 s and the sjdfr the largest si and ge concentration anomalies occur over the north cleft segment of the sjdfr these are a factor of three greater than anomalies over the sepr 10 20 s excess ge correlates with excess3he in plumes at a ge 3he molar ratio of about 1 104 approximately the same ratio as in black smokers these observations combined with low abundances of ge in femn rich metalliferous sediments suggest that ge and si behave conservatively in mid ocean ridge hydrothermal plumes a simple ocean si and ge balance constrained by the global river silica flux and ge si ratios in hydrothermal vents rivers and biogenic silica suggests that the global hydrothermal silica flux is about 1 4 1011 mole yr 1 much lower than that estimated from3he either 1 70 80 of the ge flux to the ocean is removed in as yet undiscovered sinks not opal or 2 only 10 of the mantle to ocean3he and heat fluxes is associated with mor hydrothermal convection through the 350 c isotherm 90 is off ridge or 3 the oceanic ge si 3he and87sr86sr balances today are far from steady state

intraseasonal to seasonal variability of the intermediate waters along the kuroshio path east of taiwan the variability of the intermediate water iw east of luzon and taiwan is investigated using data acquired from moored instrumented lines and shipboard hydrographic and current velocity surveys the iw is defined as the water mass with a local salinity minimum along the kuroshio path an empirical formula is developed to estimate the iw salinity minimum east of taiwan using temperature measurements around 580 m depth properties of the iw east of taiwan vary greatly as a result of variable contributions from three water masses including the high salinity south china sea intermediate water scsiw the low salinity north pacific intermediate water npiw and the intermediate salinity kuroshio intermediate water kiw our analysis concludes that npiw is predominantly found east of taiwan and the northward transport of kiw from northeast of luzon to east of taiwan is not a steady process concurrent mooring measurements at these two locations enable us to correlate the variations of the layer thickness of the kuroshio near its origin klto northeast of luzon to the nature of the iw east of taiwan when the kuroshio is deep i e large klto kiw is transported northward across the luzon strait where its salinity increases presumably due to turbulence mixing with scsiw this modified kiw is then transported to the east of taiwan when the kuroshio is shallow i e small klto the kiw transport east of luzon is nil or southward east of taiwan npiw feeds in below the kuroshio and is transported northward beyond the i lan ridge

deepwater redox changes in the southern okinawa trough since the last glacial maximum abstract in this study rare earth element ree was treated as a paleo redox proxy to investigate the changes of depositional environment in the southern okinawa trough since the last glacial maximum the acid leachable fraction leachate of the sediments recovered from the odp site 1202b is dominated by biogenic and authigenic components while detrital contamination is minor the significant enrichment of middle ree suggests a large contribution from authigenic mn oxyhydroxides and cerium ce anomaly can indicate deepwater redox change the ree parameters including ce anomaly in the leachate exhibit remarkable and abrupt changes in the early holocene 9 5 ka and during lgm 20 ka an increase of ce anomaly at 28 22 ka implies the suboxic deepwater condition probably caused by increased primary productivity weak positive ce anomalies during the last glacial maximum and deglaciation suggest an oxic depositional environment responding to the enhanced deepwater ventilation with the advection of the north pacific intermediate water and or south china sea intermediate water into the trough a decrease of ce anomaly in the early holocene might be caused by the intrusion and strengthening of the kuroshio current in the trough that enhanced the water stratification and induced a gradual development of suboxic depositional condition furthermore an abrupt change of chemical composition at ca 4 ka probably indicates a decrease of dissolved oxygen in deepwater and a weakening of ventilation in the okinawa trough this study suggests that ree proxy can provide new insights into the linkage among surface current deepwater circulation and sediment record in the continental margin where terrigenous input dominates

the circulation in the upper and middle layers of the luzon strait during spring 2002 1 on the basis of current measurements at the mooring station and hydrographic and wind data obtained in the luzon strait during spring 2002 the numerical calculation and comparison of circulation were implemented by the aid of a diagnostic model with a modified inverse method during the observation period the directions of subtidal current at the mooring station are mostly northwestward or northward at depths of 200 and 500 m different from those at a depth of 800 m at depths above 400 m most of the kuroshio bypasses the south china sea scs near the luzon strait however both the observed and modeled results show part of the kuroshio flows westward to intrude into the area around the continental slope south of china and the net westward volume transport across the longitudinal section of 120 33 e is about 0 82 106 m3 s 1 in the upper layers from the sea surface to 400 m level at depths below 400 m the directions of flow east of 120 57 e are mostly eastward and the net eastward volume transport across the longitudinal sections of 121 09 e and 121 15 e both are about 2 4 106 m3 s 1 in the middle layers between 500 m and 1200 m this indicates the scs water with a higher oxygen concentration flows eastward into the eastern side of the luzon strait in the middle layer comparison between the observed and modeled results shows they agree basically with each other

the potential role of ridge flank hydrothermal systems on oceanic germanium and silicon balances abstract sediment pore water samples and warm spring fluids from three ridge flank hydrothermal systems 40 75 c were analyzed for ge si and mg to quantify the contribution of these systems to oceanic ge and si balances these warm hydrothermal fluids have elevated concentrations of ge and si relative to bottom seawater indicating that these systems are net sources of ge and si to the oceans end member ge si molar ratios range from 12 to 34 mol mol which is similar to but elevated relative to the average ratio from high temperature 350 c midocean ridge hydrothermal systems the source for this ge and si is suggested to be a combination of seawater reaction with basalt and diffusive exchange with overlying basal pore waters which are in pseudo equilibrium with amorphous silica because the ge si molar ratio in both basalt and sediment is much less than those measured in the dissolved phase a net preferential removal of si relative to ge must occur within basaltic basement as suggested for high temperature hydrothermal systems we suggest that this removal mechanism is likely a consequence of quartz precipitation and the formation of secondary clays i e smectite we estimate that ridge flank hydrothermal systems likely provide 10 of the ge and si fluxes to the oceans

the barotropic response of the subpolar north pacific to stochastic wind forcing in a recent observational study koblinsky et al 1989 attempted to demonstrate that the topographic sverdrup balance can account for mesoscale current fluctuations with periods between 10 and 100 days in the abyssal north pacific however the topographic sverdrup balance proved difficult to verify systematically over the north pacific in this paper the conditions required to obtain the topographic sverdrup balance are investigated through numerical experiments with a stochastically forced barotropic quasi geostrophic numerical model of the subpolar north pacific in the numerical experiments the topographic sverdrup balance emerges from area averages of the terms in the vorticity equation but only for periods longer than about 40 days when the averages are taken over 4 4 region this period increases when averages are taken over progressively smaller regions an examination of vorticity balances at individual points along sections through the model domain indicates that the topographic sverdrup balance is not obtained at individual points even for very long period motions the possibility of verifying topographic sverdrup dynamics with oceanic data is considered it is argued that topographically generated small scales in the velocity field reduce the likelihood that the topographic sverdrup balance can be systematically observed in velocity measurements from individual current meter moorings the results suggest that the vorticity balance is complex and that topographic sverdrup dynamics cannot be expected to provide an adequate explanation for the seasonal modulation of the abyssal eddy kinetic energy that is observed with moored instrumentation in the north pacific

sources and biological fractionation of silicon isotopes in the eastern equatorial pacific abstract silicon isotopes in dissolved silicic acid were measured in the upper four kilometers between 4 n and 3 s latitude at 110 w longitude in the eastern equatorial pacific silicon isotopes became progressively heavier with silicic acid depletion of surface water as expected from biological fractionation the value of e estimated by applying a steady state isotope fractionation model to data from all stations between 4 n and 3 s was 0 77 0 12 std err when the analysis was restricted to those stations whose temperature and salinity profiles indicated that they were directly influenced by upwelling of the equatorial undercurrent euc the resulting value of e was 1 08 0 27 std err similar to the value established in culture studies 1 1 when the non steady state rayleigh model was applied to the same restricted data set the resulting value of e was significantly more positive 0 61 0 16 std err to the extent that the equatorial system approximates a steady state these results support a value of 1 1 for the fractionation factor for isotopes of si in the sea without the assumption of steady state the value of e can only be constrained to be between 0 6 and 1 1 silicic acid in equatorial pacific deep water below 2000 m had a near constant 30 si of 1 32 0 05 that value is significantly more positive than obtained for north pacific deep water at similar depths at stations to the northwest of our study area 0 9 1 0 and it is slightly less positive than new measures of the 30 si of silicic acid from the silicic acid plume centered over the cascadia basin in the northeast pacific si oh 4 180 m 30 si 1 46 0 12 sd n 4 we show that the data from the equator and cascadia basin fit a general trend of increasing 30 si oh 4 with increasing silicic acid concentration in the deep sea but that the isotope values from the northeast pacific are anomalously light the observed level of variation in the silicon isotope composition of deep waters from this single ocean basin is considerably larger than that predicted by current models based on fractionation during opal formation with no isotope effect during dissolution confirmation of such high variability in deep water 30 si oh 4 within individual ocean basins will require reassessment of the mechanisms controlling the distribution of isotopes of silicon in the sea

the influence of water mass mixing on the dissolved si isotope composition in the eastern equatorial pacific silicon isotopes are a powerful tool to investigate the cycling of dissolved silicon si in this study the distribution of the si isotope composition of dissolved silicic acid 30si oh 4 was analyzed in the water column of the eastern equatorial pacific eep where one of the globally largest oxygen minimum zones omzs is located samples were collected at 7 stations along two meridional transects from the equator to 14 s at 85 50 w and 82 00 w off the ecuadorian and peruvian coast surface waters show a large range in isotope compositions 30si oh 4 2 2 to 4 4 with the highest values found at the southernmost station at 14 s this station also revealed the most depleted silicic acid concentrations 0 2 mol kg which is a function of the high degree of si utilization by diatoms and admixture with waters from highly productive areas samples within the upper water column and the omz at oxygen concentrations below 10 mol kg are characterized by a large range in 30si oh 4 which mainly reflects advection and mixing of different water masses even though the highly dynamic hydrographic system of the upwelling area off peru does not allow the identification of clear si isotope signals for distinct water masses therefore we cannot rule out that also dissolution processes have an influence on the 30si oh 4 signature in the subsurface water column deep water masses 2000 m in the study area show a mean 30si oh 4 of 1 2 0 2 which is in agreement with previous studies from the eastern and central pacific comparison of the new deep water data of this study and previously published data from the central pacific and southern ocean reveal substantially higher 30si oh 4 values than deep water signatures from the north pacific as there is no clear correlation between 30si oh 4 and silicic acid concentrations in the entire data set the distribution of 30si oh 4 signatures in deep waters of the pacific is considered to be mainly a consequence of the mixing of several end member water masses with distinct si isotope signatures including lower circumpolar deep water lcdw and north pacific deep water npdw

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

the tug of war between the west philippine sea and south china sea tropical waters and intermediate waters in the okinawa trough kuroshio subsurface waters are the major source of nutrients to the east china sea continental shelf a major fishing ground these subsurface waters are heavily affected by the south china sea scs tropical and intermediate waters which contain more nutrients than the tropical smax and intermediate smin waters from the west philippine sea wps a front was found to separate these waters from the scs and wps the reported front in the okinawa trough however was identified based only on one time data from a single cross section here historical hydrographic data between march 1950 and december 2011 are analyzed a vertical front tilted toward the west is found in all seasons in all years in the okinawa trough in winter the presence of the scs tropical water is the most prominent it is the weakest in autumn as for intermediate waters smin the wps and scs intermediate waters show much weaker seasonality compared with tropical waters although in summer the wps intermediate water contribution is slightly larger than during other times

the thermal environment of cascadia basin 1 located adjacent to the ne pacific convergent boundary cascadia basin has a global impact well beyond its small geographic size composed of young oceanic crust formed at the juan de fuca ridge igneous rocks underlying the basin are partially insulated from cooling of their initial heat of formation by a thick layer of pelagic and turbidite sediments derived from the adjacent north american margin the igneous seafloor is eventually consumed at the cascadia subduction zone where interactions between the approaching oceanic crust and the north american continental margin are partially controlled by the thermal environment within cascadia basin basement topographic relief varies dramatically and sediments have a wide range of thickness and physical properties this variation produces regional differences in heat flow and basement temperatures for seafloor even of similar age previous studies proposed a north south thermal gradient within cascadia basin with high geothermal flux and crustal temperatures measured in the heavily sedimented northern portion near vancouver island and lower than average heat flux and basement temperatures predicted for the central and southern portions of the basin if confirmed this prediction has implications for processes associated with the cascadia subduction zone including the location of the locked zone of the megathrust fault although existing archival geophysical data in the central and southern basin are sparse nonuniformly distributed and derived from a wide range of historical sources a substantial n s geothermal gradient appears to be confirmed by our present compilation of combined water column and heat flow measurements

heat flow across cascadia basin near 47 n 128 w some 200 previously unreported heat flow measurements were made along a flow line crossing the juan de fuca ridge crest near 47 n all but one of the multipenetration stations were on the east flank of the ridge in the thickly sedimented cascadia basin the accuracy of individual penetrations remains low due to the poor penetrability of the basin turbidites but the multiplicity of the measurements provides a statistical estimate of precision at most stations the raw heat flow means of the multipenetration stations do not decrease regularly with increasing distance from the spreading center the lowest measurements are near 70 km from the ridge crest well onto the turbidite sediment fill of the basin a basement outcrop near these measurement sites appears to cause the low heat flow by ventilating hydrothermal circulation beneath the sediments in the eastern part of the basin the sedimentation correction to the observed heat flow becomes significant and if the filling of the basin occurred mostly in the pleistocene the correction brings those measurements close to the theoretical heat flow of cooling lithosphere extrapolated basement temperatures reach nearly 200 c beneath the eastern basin a region where the magnetic anomalies become noticeably weaker than those closer to the ridge they do not however disappear entirely as might be expected from some laboratory measurements of blocking temperature