high resolution bathymetry of the east pacific rise axial summit trough 9 49 51 n a compilation of alvin scanning sonar and altimetry data from 1991 1995 bathymetric data acquired during six cruises to the east pacific rise crest 9 49 51 n are compiled into a single bathymetric database and used to create high resolution bathymetry maps of two geologically and biologically active areas scanning sonar and alvin altimetry were collected during 23 alvin dives to the p vent bio9 and biomarker 141 areas during 1991 95 bathymetry data were filtered edited and processed as individual dives then combined into a single database for each cruise and statistically evaluated cruise data sets were numerically and visually compared and cross correlated to known bottom features and fixed seafloor reference markers then horizontally shifted to establish a consistent database with 3 m vertical and 5 m horizontal resolutions the compiled and corrected bathymetry was used to produce bathymetric maps of two areas within the axial summit collapse trough a 2 104 m area around p and bio9 vents and a 1 1 10 m area around biomarker 141 the resulting detailed bathymetry maps reveal topography dominated by low relief volcanic constructional features and post eruptive collapse of lobate and sheet lava surfaces

evidence for large scale eddy driven gyres in the north atlantic analysis of a recent climatological database for the north atlantic has detailed an extensive large scale recirculation system in the intermediate waters of the north atlantic basin the pressure fields that define this recirculation coupled with the potential vorticity fields associated with the recirculating flow provide observational evidence for basin scale eddy driven flow in the global ocean the recirculations are intimately tied to the waters carried southward by the deep western boundary current and are therefore likely to affect the distribution of climatic anomalies in the north atlantic

sensitivity studies of the red sea eddies using adjoint method the topography data is derived from general bathymetric chart of the oceans gebco https www gebco net the open boundary conditions are extracted from the estimating the circulation and climate of the ocean ecco product https ecco jpl nasa gov products the data supporting the analysis presented here can be found at figshare https figshare com articles data for 2018jc014531r 7243184 the research reported in this manuscript is supported by king abdullah university of science and technology kaust and made use of the resources of the supercomputing laboratory and computer clusters at kaust

an oceanographic nowcast forecast system for the red sea we describe the application of a nowcast forecast system for three dimensional currents temperature and salinity to the red sea the modeling system is constructed around a high resolution 6 7 km primitive equation numerical circulation model with complete thermodynamics and an imbedded turbulence closure submodel it is coupled to near real time databases containing meteorological forecasts and remotely sensed and in situ temperature and salinity data the temperature and salinity data are ingested into the model daily using a nudged objective analysis technique because the red sea is a relatively narrow basin bounded by typically high and complex orography a single layer atmospheric boundary layer submodel has been used to increase the effective resolution of the original 40 km resolution meteorological fields by taking into account orographic steering of the low level winds in order to validate the modeling system two very complete hydrographic surveys of the red sea were undertaken and their results are described both the surveys and the modeling system nowcasts demonstrate that the circulation pattern of the red sea is variable and often composed of a series of eddies or subgyres mainly anticyclones immediately before one survey the winds tended to be along axis while just before the second they tended to be cross axis the red sea circulation was much more eddy like when the winds were cross axis by forcing the modeling system with and without orographically steered winds we were able to establish that the complex eddy structure is a response to a wind field which can be highly structured and vorticity rich because of interaction with the high and variable adjacent orography when the winds are more along axis there is less interaction with the adjacent orography and consequently there are fewer eddies in the red sea

eddies in the red sea a statistical and dynamical study sea level anomaly sla data spanning 1992 2012 were analyzed to study the statistical properties of eddies in the red sea an algorithm that identifies winding angles was employed to detect 4998 eddies propagating along 938 unique eddy tracks statistics suggest that eddies are generated across the entire red sea but that they are prevalent in certain regions a high number of eddies is found in the central basin between 18 n and 24 n more than 87 of the detected eddies have a radius ranging from 50 to 135 km both the intensity and relative vorticity scale of these eddies decrease as the eddy radii increase the averaged eddy lifespan is approximately 6 weeks aes and cyclonic eddies ces have different deformation features and those with stronger intensities are less deformed and more circular analysis of long lived eddies suggests that they are likely to appear in the central basin with aes tending to move northward in addition their eddy kinetic energy eke increases gradually throughout their lifespans the annual cycles of ces and aes differ although both exhibit significant seasonal cycles of intensity with the winter and summer peaks appearing in february and august respectively the seasonal cycle of eke is negatively correlated with stratification but positively correlated with vertical shear of horizontal velocity and eddy growth rate suggesting that the generation of baroclinic instability is responsible for the activities of eddies in the red sea

sulfur isotope evidence for microbial sulfate reduction in altered oceanic basalts at odp site 801 the subsurface biosphere in the basaltic ocean crust is potentially of major importance in affecting chemical exchange between the ocean and lithosphere alteration of the oceanic crust commonly yields secondary pyrite that is depleted in 34s relative to igneous sulfides although these 34s depleted sulfur isotope ratios may point to signatures of biological fractionation previous interpretations of sulfur isotope fractionation in altered volcanic rocks have relied on abiotic fractionation processes between intermediate sulfur species formed during basalt alteration here we report results for multiple s isotope 32s 33s 34s compositions of altered basalts at odp site 801 in the western pacific and provide evidence for microbial sulfate reduction within the volcanic oceanic crust in situ ion microprobe analyses of secondary pyrite in basement rocks show a large range of 34s values between 45 and 1 whereas bulk rock 34s analyses yield a more restricted range of 15 8 to 0 9 these low and variable 34s values together with bulk rock s concentrations ranging from 0 02 up to 1 28 are consistent with loss of magmatic primary mono sulfide and addition of secondary sulfide via microbial sulfate reduction high precision multiple sulfur isotope 32s 33s 34s analyses suggest that secondary sulfides exhibit mass dependent equilibrium fractionation relative to seawater sulfate in both 33s and 34s values these relationships are explained by bacterial sulfate reduction proceeding at very low metabolic rates the determination of the s isotope composition of bulk altered oceanic crust demonstrates that s based metabolic activity of subsurface life in oceanic basalt is widespread and can affect the global s budget at the crust seawater interface

high resolution 40ar 39ar dating of the oldest oceanic basement basalts in the western pacific basin 1 we report new 40ar 39ar ages for the oldest pacific oceanic floor at ocean drilling program site 801c in the pigafetta basin and site 1149d close to the izu bonin subduction zone in the nadezhda basin these ages were determined by applying high resolution incremental heating experiments including 15 30 heating steps to better resolve the primary argon signal from interfering alteration signatures in these low potassium ocean crust basalts combined with previous results from pringle 1992 for site 801b and 801c we arrive at a multistage history for the formation of the pigafetta ocean crust the oldest part of the pacific plate was formed at the spreading ridges at 167 4 1 4 3 4 ma n 2 2 internal absolute error offering an important calibration point on the geological reversal timescale grts since it represents the old end of the mesozoic magnetic anomalies this mid ocean ridge basalt sequence however is overlain by more tholeiites and alkali basalts that were formed 7 3 1 5 myr later around 160 1 0 6 ma n 7 2 internal error the older age group is confirmed independently by radiolarian ages ranging from late bajocian to middle bathonian 167 173 ma bartolini and larson 2001 and by profound differences in the structural characteristics of this basement section pockalny and larson 2003 thin layers comprising hydrothermal deposits separate these sequences which in addition to the difference in isotopic age show distinct major and trace element compositions this indicates that key volcanic and hydrothermal activity took place 400 600 km away from the spreading ridges on the basis of a jurassic 66 km myr half spreading rate in the pacific it remains unclear if these processes were active continuously after the initial formation of the pacific oceanic crust but all our observations seem to point to an episodic history site 1149d gives another important calibration point on the grts of 127 0 1 5 3 6 ma n 1 2 internal absolute error for anomaly m12 that is slightly younger when compared to current timescale compilations 134 2 2 1 ma gradstein et al 1995 this might suggest that the dated basalt from site 1149d does not represent the age of the ocean crust formed at its ridge axis it may also be part of the early cretaceous intraplate events that have produced dolerite sills in the pacific crust at sites 800 and 802 around 114 126 ma

collision induced post plateau volcanism evidence from a seamount on ontong java plateau abstract many seamounts on the ontong java plateau ojp occur near the stewart arch a topographic high that extends parallel to the north solomon trench along the southern margins of the plateau despite the thick sediment cover several volcanic cones with strong acoustic reflection were discovered on the submarine flank of the nuugurigia seamount from such volcanic cones basalts were successfully sampled by dredging radiometric dating of basalts and ferromanganese encrustation indicate eruption age of 20 25 ma significantly younger than the 122 ma main ojp plateau and post plateau basalts the age range coincides with the collision of the ojp with the solomon arc the nuugurigia basalts geochemically differ from any other rocks sampled on the ojp so far they are alkali basalts with elevated sr low zr and hf and enriched mantle i emi like isotopic composition parental magmas of these alkali basalts may have formed by small degree melting of peridotitic mantle impregnated with recycled pyroxenite material having enriched geochemical composition in the ojp s mantle root we conclude that small volume alkali basalts from the enriched mantle root migrated through faults or fractures caused by the collision along the stewart arch to form the seamount our results suggest that the collision of the ojp with the solomon arc played an important role in the origin of similar post plateau seamounts along the stewart arch

iron isotope fractionation during oceanic crust alteration abstract the purpose of this work is to study the mobility and budget of fe isotopes in the oceanic crust and in particular during low temperature interaction of seawater with oceanic basalt we carried out this investigation using samples from ocean drilling program odp site 801c drilled during leg 129 and leg 185 in jurassic pacific oceanic crust seaward of the mariana trench the site comprises approximately 450 m of sediment overlying a section of 500 m of basalt which includes intercalated pelagic and chemical sediments in the upper basaltic units and two low temperature 10 30 c ocherous si fe hydrothermal deposits fe was chemically separated from 70 selected samples and 57fe 54fe ratios were measured by mc icp ms isoprobe the isotopic ratios were measured relative to an internal standard solution and are reported relative to the international fe standard irmm 14 based on duplicate measurements of natural samples an external precision of 0 2 2 has been obtained the results indicate that the deep sea sediment section has a restricted range of 57fe which is close to the igneous rock value in contrast large variations are observed in the basaltic section with positive 57fe values up to 2 05 for highly altered basalts and negative values down to 2 49 for the associated alteration products and hydrothermal deposits secondary fe minerals such as fe oxyhydroxides or fe bearing clays celadonite and saponite have highly variable 57fe values that have been interpreted as resulting from the partial oxidation of fe2 leached during basalt alteration and precipitated as fe3 rich minerals in contrast altered basalts at site 801c which are depleted in fe up to 80 display an increase in 57fe values relative to fresh values which suggest a preferential leaching of light iron during alteration the apparent fractionation factor between dissolved fe2 and fe remaining in the mineral is from 0 5 to 1 3 and may be consistent with a kinetic isotope fractionation where light fe is stripped from the minerals alternatively the formation of secondary clays minerals such as celadonite during basalt alteration may incorporate preferentially the heavy fe isotopes resulting in the loss of light fe isotopes in the fluids because microbial processes within the oceanic crust are of potential importance in controlling rates of chemical reactions fe redox state and fe isotope fractionation we evaluated the possible effect of this deep biosphere on fe isotope signatures the fe isotope systematics presented in this study suggest that even though iron behavior during seafloor weathering may be mediated by microbes such as iron oxidizers 57fe variations of more than 4 may also be explained by abiotic processes further laboratory experiments are now required to distinguish between various processes of fe isotope fractionation during seafloor weathering

some comparative marine chemistries of rhenium gold silver and molybdenum abstract four metals re au ag and mo whose dissolved forms in seawater can potentially be reduced to insoluble states have been measured in a variety of solids depositing under anoxic conditions hydrothermal sulfides coastal sediments and phosphorites for comparative purposes these elements have also been determined in ferromanganese minerals and pelagic sediments which have accumulated under oxidizing conditions rhenium appears to be a unique sentinel for identifying reducing depositional environments where enrichments of greater than three orders of magnitude above crustal concentrations are found molybdenum follows re in these sediments but mo is enriched also in those that accumulate under oxidizing conditions the reported mo crustal concentrations appear low in comparison to our measured sedimentary values gold and ag are concentrated in hydrothermal deposits and sulfides appear to be involved in the precipitation of these elements coastal sediments adjacent to a domestic outfall of los angeles california contain extraordinary high accumulations of anthropogenic au ag and pt the study seeks an understanding of the mobilities and sinks of these metals in the marine environment during the major weathering cycle further anthropogenic contributions to their sedimentary concentrations are identified

evidence of transpression along the clipperton transform implications for processes of plate boundary reorganization abstract high resolution bathymetry data of the clipperton fracture zone and focal mechanisms of recent earthquakes along the active transform provide evidence for recent and ongoing transpression along the clipperton transform structural and morphological features observed in the bathymetry data include normal and strike slip faults oriented obliquely to the strike of the transform curved trends of abyssal hills produced by simple shear of the lithosphere bordering the transform fault abyssal hills offset by obliquely trending strike slip faults on lithosphere bordering the transform and lithospheric flexure and associated volcanism near the active transform all of these features can be explained by a transpression scenario in which a counter clockwise change in spreading direction of 5 began about 0 4 0 5 ma and subjected the right stepping clipperton transform to compression a comparison of the median ridge volume to calculated estimates of the convergent volume predicted by the transpression scenario indicates that the median ridge is likely to be a product of the brittle deformation associated with transpression the convergent volume estimates suggest that larger spreading direction changes 5 do not occur instantaneously instead spreading direction changes begin slowly and accelerate to the new spreading direction once compression across the transform has ceased many of the structures observed along the clipperton transform are very similar to features observed along other known convergent transforms such as the san andreas fault in california and may have important implications for understanding continental transforms the transpression scenario also indicates that transforms are very important in constraining the rate and character of global plate motion changes

mean velocity decomposition and vertical eddy diffusivity of the pacific ocean from surface gdp drifters and 1000 m argo floats abstractwith the relatively recent development of global drifter program gdp drifters that measure the near surface ocean velocity and argo floats that can be used to derive both the intermediate ocean 1000 m velocity and the mean dynamic height of the surface relative to 1000 dbar there now exists the opportunity to directly observe the mean velocity decomposition of the ocean this study computes the mean ekman velocity by subtracting the mean referenced velocity derived from argo data from the mean surface velocity derived from gdp data this ekman velocity is slightly stronger than previous observations and shows a spatial structure consistent with a vertical eddy diffusivity that is linearly dependent on wind stress to do this analysis the author has to deal with the fact that gdp drifters often lose their drogues and a product of this research is validation of the wind slip correction applied to gdp drifters that have lost their drogues

wind driven currents in the tropical pacific abstract an analysis is made of the ensemble mean ageostrophic near surface circulation measured by 1503 lagrangian drifters drogued to 15 m depth in the tropical pacific between 1987 and 1994 it was found that the physical model of the wind driven currents in a weakly stratified upper layer in which the richardson number remains near unity accounts for 40 of the vector variance of the observations in such a model the amplitude of the current is proportional to u n f 1 2 and the depth scale of the wind driven layer is proportional to u n f 1 2 when the ageostrophic currents at 15 m depth are binned by the scaled ekman depth a net rotation of 0 87 radians was observed through the layer depth these measurements suggest that the vertical austausch coefficient of the upper ocean is proportional to u2 n ekman proposed such a model based on two reports of wind driven currents in 1905 at widely separated latitudes

on the origin of a chain of eddies in the gulf of eilat aqaba abstractthe gulf of eilat aqaba is a terminal elongated basin that exchanges water with the northern red sea via the straits of tiran this study used energy budgets of mean kinetic energy mke and eddy kinetic energy eke differentiated by a simple horizontal averaging filter instability analysis and numerical simulations to study the horizontal circulation of the gulf which is characterized by the existence of a chain of eddies along its main axis the kinetic energy is predominantly in the form of eke energy conversion between mke and eke is negligible where the main sources for both energy reservoirs are the conversions from the available potential energy ape this term is balanced by the work done by pressure at the straits in case of mke and by dissipation in the case of eke the mke balance represents the coupling between the exchange flow at the straits and the wintertime dense water formation the dense water exits through the straits while sinking adiabatically along the gulf the stro

simulating the dynamics and intensification of cyclonic loop current frontal eddies in the gulf of mexico 1 the dynamics associated with the loop current lc variability in the gulf of mexico gom are studied using a 5 year free running numerical simulation with the hybrid coordinate ocean model hycom the dynamics of major gom circulation features are represented the extension of the lc and the associated anticyclonic warm core loop current eddies lces and cyclonic loop current frontal eddies lcfes the study focuses on the dynamics of the lcfes and their role during the lces shedding which dramatically affects the gom circulation we analyze several characteristics of the lc frontal dynamics modeled lcfes have a coherent vertical structure which extends to the deep layers of the gom they may split in two separate upper and lower layer eddies deep and surface remnants from different frontal eddies are able to align to form new coherent structures lcfes intensify along the extended lc northern edge when flowing over the deep northern gom shelf slope that forms the mississippi fan through a promontory effect in which the incoming cyclone aggregates positive potential vorticity anomalies in lower layers leading to the intensification of the whole vortex structure lcfes may also expand further along the lc path by horizontal vortex merging when they are blocked between the lc and the northeast corner of the continental shelf in the gom the intensification and merging due to topographic effects explain the enlarged frontal eddies observed on the eastern side of the loop current these larger eddies further migrate along the lc front and may play a role in the shedding sequence

re os results from odp site 801 evidence for extensive re uptake during alteration of oceanic crust abstract re and os concentrations and os isotopic ratios were determined for composite samples prepared from volcanoclastics vcl and basaltic flows flo from jurassic oceanic crust ocean drilling program leg 185 site 801 in the western pacific with the aim of determining the effect of seafloor weathering on the re os budget a supercomposite sample prepared from a proportionate mixture of the various composite powders served to represent the average composition of the altered oceanic crust kelley k a plank t ludden j and staudigel h 2003 composition of altered oceanic crust at odp sites 801 and 1149 geochem geophys geosyst 4 6 8910 doi 10 1029 2002gc000435 re contents vary from 0 2 to 1 3 ng g 1 and from 2 2 to 3 1 ng g 1 in the vcl and flo composites respectively os contents vary from 0 005 to 0 047 ng g 1 in the vcl and from 0 008 to 0 027 ng g 1 in the flo composites the flo composites have much higher re os ratios and thus have more radiogenic os compositions 187os 188os 1 38 to 8 48 than the vcl composites 187os 188os 0 32 to 4 40 the vcl composite from the upper section of the crust shows evidence for substantial re loss and os uptake consistent with oxidative weathering processes however re uptake during weathering processes under more reducing conditions evident in the flo samples from throughout the section and to a lesser extent in the lower vcl samples more than compensates for this re loss in the upper vcl os concentrations were essentially unchanged by these reductive processes model age calculations suggest that re uptake continued for tens of millions of years after crust formation abundant secondary pyrite is found throughout the altered hole 801c crust in zones of restricted seawater flow and this may have accommodated an important part of the input re the re content of the supercomposite 2 2 ng g 1 is about 1 ng g 1 higher than would be expected on the basis of its yb content if the results from hole 801c are typical they suggest that the re concentration of at least the upper part of the oceanic crust may be nearly doubled during seafloor alteration such large extents of re uptake would have a significant effect on the oceanic re budget furthermore assuming that they survive passage through the subduction zone these elevated re contents would greatly decrease the proportion of subducted oceanic crust required in the source region to explain the radiogenic os compositions of many ocean island basalts

topex poseidon observations of mesoscale eddies over the subtropical countercurrent kinematic characteristics of an anticyclonic eddy and a cyclonic eddy 1 relative dynamic heights and geostrophic fields were derived from topex poseidon altimetry data and then used to track mesoscale eddies over the subtropical countercurrent stcc the radii centers vorticities shearing deformation rates stretching deformation rates divergences and center velocities of all identified eddies over the stcc were determined using a model that assumes constant velocity gradients most eddies are concentrated in a zonal band near 22 n and there is an interannual variation in the number of eddies a case study was made for a cyclonic eddy and an anticyclonic eddy with time series of eddy kinematic parameters computed both eddies survive for 220 days and propagate westward along over 22 n 24 n to reach the kuroshio current east coast of taiwan where the eddies were dissipated and in turn affected the kuroshio current in many ways sea surface temperature data and drifter data confirm the existence of these two eddies the radii of both eddies vary and their shapes are mostly elliptical during propagation the anticyclonic eddy propagated almost westward with oscillating north south components and the mean speed is 8 3 km day the cyclonic eddy moved southwestward before reaching 130 e and then moved northwestward with a mean speed of 7 6 km day the propagations of these two eddies are basically consistent with the standard theory of eddy propagation but with larger speeds the propagating direction could be altered while passing steep bottom topography or merging with the other eddies index terms 4520 oceanography physical eddies and mesoscale processes 4576 oceanography physical western boundary currents 4512 oceanography physical currents 4594 oceanography physical instruments and techniques 4556 oceanography physical sea level variations

wind stress and near surface shear in the equatorial atlantic ocean the upper ocean response to wind stress is examined using 8 months of unique near surface moored velocity temperature and salinity data at 0 n 23 w in the equatorial atlantic the effects of wind stress and shear on the time varying eddy viscosity are inferred using the surface shear stress boundary condition parameterizations of eddy viscosity as a function of wind stress and shear versus wind stress alone are then examined in principle eddy viscosity should be proportional to the inverse shear but how it is represented implicitly or explicitly can affect estimates of the near surface flow field this result may explain some discrepancies that have arisen from using parameterizations based only on wind stress to characterize the effects of turbulent momentum mixing

physical and biological characteristics of the winter summer transition in the central red sea the central red sea crs lies between two distinct hydrographic and atmospheric regimes in the southern red sea seasonal monsoon reversal regulates the exchange of water between the red sea and the indian ocean in the northern red sea intermediate and occasionally deep water are formed during winter to sustain the basin s overturning circulation highly variable mesoscale eddies and the northward flowing eastern boundary current ebc determine the physical and biogeochemical characteristics of the crs ship based and glider observations in the crs between march and june 2013 capture key features of the transition from winter to summer and depict the impact of the eddy activity on the ebc flow less saline and relatively warmer water of indian ocean origin reaches the crs via the ebc initially an anticyclonic eddy with diameter of 140km penetrating to 150m depth with maximum velocities up to 30 35 cm s 1 prevails in the crs this anticyclonic eddy appears to block or at least redirect the northward flow of the ebc dissipation of the eddy permits the near coastal northward flow of the ebc and gives place to a smaller cyclonic eddy with a diameter of about 50km penetrating to 200m depth by the end of may as the northerly winds become stronger and persistent throughout the basin characteristic of the summer southwest monsoon wind regime the ebc and its associated lower salinity water became less evident replaced by the saltier surface water that characterizes the onset of the summer stratification in the crs

1 ma east pacific rise oceanic crust and uppermost mantle exposed by rifting in hess deep equatorial pacific ocean abstract a series of dives with the french submersible nautile has been conducted in the region of the galapagos triple junction at the tip of the cocos nazca propagator most of the dives were devoted to the study of hess deep a rift valley produced by rifting of oceanic crust created at the axis of the very fast spreading east pacific rise the dives have enabled the structures and lithologies to be assessed and confirmed earlier dredging evidence for abundant basal crust and mantle rocks on an intra rift ridge located to the north of the axis of hess deep this shows that this situation is not specific not slow spreading ridges a nearly complete and unique log of young 1 ma crust and uppermost mantle representative of very fast accretion can be reconstructed even though the section is discontinuous and highly dismembered we propose two models that can explain the exposure on the ocean floor of the deep foundation of the oceanic crust one model stresses symmetry and vertical tectonics through isostasy diapirism of serpentinized mantle another model requires a larger amount of extension and emphasizes asymmetry with denudation of the upper crust through low angle detachment faulting in both models which differ mainly in the structure at depth amagmatic extension of east pacific rise crust by the cocos nazca propagator tip results in uplift and denudation of lower crust and upper mantle

spatiotemporal variations of mesoscale eddies in the sulu sea mesoscale eddies have been observed in the sulu sea but their characteristics have not been well described this study investigates the eddy population in the sulu sea using 22 years of satellite altimeter data with high spatiotemporal resolution on average there are approximately 1 6 eddies observed in the sulu sea each day and 1 8 eddy tracks generated each month two of the main eddy genesis regions are west of negros island and the zamboanga peninsula the mean radius lifespan and propagation speed of the eddies are 76 6 km 32 days and 4 5 cm s respectively the eddy radius and amplitude are generally large in the central sulu sea but small on its margin the mean eddy kinetic energy and vorticity generally monotonically decrease from south to north consistent with the distributions of background current kinetic energy over the seasonal cycle there are more cyclonic eddies during boreal winter and they tend to have a larger amplitude and radius than the other 3 seasons while there are more anti cyclonic eddies during boreal summer and they tend to have a larger amplitude and radius than the other 3 seasons the instability of the mean current and the island gap wind jets are the two key eddy genesis mechanisms in the sulu sea

probing the pacific s oldest morb glass mantle chemistry and melting conditions during the birth of the pacific plate major element chemistry of basalt from the southern east pacific rise epr is different from that of the epr at the time of the formation of the pacific plate at 170 ma glass recovered from jurassic age 170 ma pacific ocean crust bartolini and larson geology 29 2001 735 738 at ocean drilling program hole 801c records higher fe8 10 77 wt and marginally lower na8 2 21 wt compared to the modern epr suggesting deeper melting and a temperature of initial melting that was 60 c hotter than today trace element ratios such as la sm and zr y on the other hand show remarkable similarities to the modern southern epr indicating that site 801 was not generated on a hotspot influenced ridge and that mantle composition has changed little in the pacific over the past 170 ma our results are consistent with the observation that mid ocean ridge basalts morbs older than 80 ma were derived by higher temperature melting than are modern morbs humler et al earth planet sci lett 173 1999 7 23 which may have been a consequence of the cretaceous superplume event in the pacific site 801 predates the formation of pacific oceanic plateaus and 801c basalt chemistry indicates that higher temperatures of mantle melting beneath pacific ridges preceded the initiation of the superplume f 2002 published by elsevier science b

wind driven motions in the northeast pacific as measured by lagrangian drifters abstract analysis is presented of the time dependent motion of 47 surface drifters in the northeast pacific during fall 1987 and 16 drifters in fall and winter 1989 90 the drifters were designed at 15 m depth and were designed to have wind produced slips less than 2 cm s 1 for wind speeds up to 20 m s 1 the coherence of velocity and local wind is presented for motions with periods between 1 day and 40 days for periods between 5 and 20 days drogue motion at 15 m depth is found to be highly coherent with local wind with an average phase of 70 to the right of the rotating wind vector these results differ from analyses of fgge type drifters as reported by mcnally et al and niiler in the same area a model of wind produced slip as a function of drifter design is used to provide a possible explanation of the differences a linear regression which accounts for 20 40 of the current variance gives water motion al 0 5 of wind speed and 68 to the right of the wind vector assuming an ekman type balance

intermediate zonal jets in the tropical pacific ocean observed by argo floats abstractargo float data in the tropical pacific ocean during january 2003 august 2011 are analyzed to obtain lagrangian subsurface velocities at their parking depths maps of mean zonal velocities at 1000 and 1500 m are presented at both depths a series of alternating westward and eastward zonal jets with a meridional scale of 1 5 is seen at the basin scale from 10 s to 10 n these alternating jets with mean speeds about 5 cm s 1 are clearly present in the western and central parts of the basin but weaken and disappear approaching the eastern coast they are stronger in the southern hemisphere along the equator at both 1000 and 1500 m a westward jet is seen the jets closer to the equator are remarkably zonally coherent across the basin but the jets farther poleward appear broken in several segments in the western half of the basin the 1000 m zonal jets appear to slant slightly poleward from east to west at the western boundary in the south east of solomon islands and papua new guinea the al

sources of eddy kinetic energy in the labrador sea experiments with a suite of north atlantic general circulation models are used to examine the sources of eddy kinetic energy eke in the labrador sea a high resolution model version 112 quantitatively reproduces the observed signature a particular feature of the eke in the labrador sea is its pronounced seasonal cycle with a maximum intensity in early winter as already found in earlier studies based on altimeter data in contrast to a previously advanced hypothesis the seasonally varying eddy field is not related to a forcing by high frequency wind variations but can be explained by a seasonally modulated instability of the west greenland current wgc the main source of eke in the labrador sea is an energy transfer due to reynolds interaction work barotropic instability in a confined region near cape desolation where the wgc adjusts to a change in the topographic slope geostrophic contours tend to converge upstream of cape desolation such that the topographically guided wgc narrows as well and becomes barotropically unstable the eddies spawned from the wgc instability area dominating the eke in the interior labrador sea are predominantly anticyclonic with warm and saline cores in the upper kilometer of the water column while the few cyclones originating as well from the instability area show a more depth independent structure companion experiments with a model exhibit the strength of the wgc influenced by either changes in the wind stress or heat flux forcing as a leading factor determining seasonal to interannual changes of eke in the labrador sea

deposition of osmium and other platinum group elements beneath the ultramafic hosted rainbow hydrothermal plume osmium and other platinum group elements pges have been measured in sediments accumulating directly under the rainbow hydrothermal plume at 36 deg n on the mid atlantic ridge 187os 188os and pge concentrations in the sediments of four cores taken 2 25 km from the active vent site reveal evidence of both radiogenic os scavenged from seawater and importantly unradiogenic os released by hydrothermal venting the majority of analyses n 16 yield 187os 188os ratios that fall in a narrow range 0 99 1 06 close to that of modern seawater in these samples os concentrations correlate linearly with hydrothermal v enrichments which are also derived from seawater scavenging a smaller subset of samples characterized by unusually high concentrations of ni and cr derived from ultramafic rock fragments exhibit distinctly lower 187os 188os ratios their ir content is also higher and their pge ratios are more similar to mantle material than the pge patterns of the larger set of samples dominated by seawater scavenged os although the two most proximal cores lack evidence for any similar ultramafic detritus in their surficial sediments 187os 188os ratios in these samples are also lower than that of ambient seawater suggesting they are likely to have been influenced by unradiogenic os from vent fluid incorporated into the plume samples from the most distal core by contrast exhibit 187os 188os ratios indistinguishable from that of seawater compared with background ne atlantic sediments os is enriched four fold in the seawater dominated samples while pd pt and ir are twice the background value burial fluxes of os scavenged by hydrothermal fe in these sediments are 200 400 pg cm 2 kyr 1 up to twice that found on the epr and several times the background bg of 50 pg cm 2 kyr 1 for pt burial fluxes are 1800 3000 pg cm 2 kyr 1 bg ca 1000 pg cm 2 kyr 1 and for pd 2700 4600 pg cm 2 kyr 1 bg ca 800 pg cm 2 kyr 1

summer transport estimates of the kamchatka current derived as a variational inverse of hydrophysical and surface drifter data 1 the quasistationary summer bering sea circulation is reconstructed as a variational inverse of the hydrographic and atmospheric climatologies transport estimates through the bering strait and surface drifter data our results indicate the splitting of the kamchatka current in the vicinity of the shirshov ridge this branching is in agreement with independent argo drifter observations it was also found that transport of the kamchatka current gradually increases downstream from 14 sv in the olyutorsky gulf to 24 sv in the kamchatka strait which is twice higher than previous estimates

eruption styles of basalt in oceanic spreading ridges and seamounts effect of magma temperature and viscosity basalts erupted along oceanic zones of spreading and on intraplate seamounts at depths where hydroexplosions are not likely follow various styles of eruption quiet eruptions produce a variety of forms including lava lakes and sheet pillow and pavingstone lavas reactive eruptions occur instead when the lava is thermally shattered as in the formation of hyaloclastites the stresses induced in a rapidly cooling lava flow are important in determining the different lava forms with lava lakes and sheet flows resulting from low stresses pillows from higher stresses and hyaloclastites from even higher stresses which cause rupture calculations show that if we consider basaltic lavas of the same composition the intensity of the stresses induced in the cooling lava increases proportionally to the initial viscosity and inversely to the temperature and rate of discharge of the lava at eruption the viscosity is strongly dependent on the crystal liquid ratio of the magma at eruption the temperature and viscosity of the lava at eruption are related ultimately to the thermal regime of the lithosphere below viscosity tends to increase going from fast to slow spreading ridges and to intraplate seamounts within a given ridge segment temperature tends to decrease and viscosity to increase approaching a transform or overlapping boundary thus the model predicts that going from fast to slow spreading ridges i e from east pacific rise to mid atlantic ridge the probability of forming lava lakes and sheet flows decreases and the probability of forming pillow flows increases moreover within a given ridge segment the areal sheet to pillow ratio should decrease as a transform or overlapping boundary is approached sheet flows should be significant only in the earliest stages of the growth of large intraplate seamounts pillows and hyaloclastites in later stages the probability of forming hyaloclastites should be low in spreading ridges higher in intraplate seamounts recent high resolution observations on the east pacific rise the galapagos rift the mid atlantic ridge and the red sea are consistent with the model because they show that 1 the areal ratio of lava lakes and sheet flows over pillows decreases going from fast to slow spreading ridges 2 within a given ridge segment it decreases approaching a transform and 3 hyaloclastites are important on seamounts only

the annual cycle of circulation of the southwest subtropical pacific analyzed in an ocean gcm abstract an ocean gcm interpreted in light of linear models and sparse observations is used to diagnose the dynamics of the annual cycle of circulation in the western boundary current system of the southwest pacific ocean the simple structure of annual wind stress curl over the south pacific produces a large region of uniformly phased stationary thermocline depth anomalies such that the western subtropical gyre spins up and down during the year directing flow anomalies alternately toward and away from the boundary at its northern end near 10 s the response of the western boundary currents is to redistribute these anomalies northward toward the equator and southward to the subtropical gyre a redistribution that is determined principally by linear rossby processes not boundary dynamics when the subtropical gyre and south equatorial current sec are strong in the second half of the year the result is both increased equatorward transport of the new guinea coastal current and poleward transport a

physical mechanisms routing nutrients in the central red sea mesoscale eddies and boundary currents play a key role in the upper layer circulation of the red sea this study assesses the physical and biochemical characteristics of an eastern boundary current ebc and recurrent eddies in the central red sea crs using a combination of in situ and satellite observations hydrographic surveys in november 2013 autumn and in april 2014 spring in the crs 22 15 24 1 n included a total of 39 and 27 ctd stations respectively in addition high resolution hydrographic data were acquired in spring 2014 with a towed undulating vehicle scanfish in situ measurements of salinity temperature chlorophyll fluorescence colored dissolved organic matter cdom and dissolved nitrate phosphorous ratios reveal distinct water mass characteristics for the two periods an ebc observed in the upper 150 m of the water column during autumn transported low salinity and warm water from the south toward the crs patches of the low salinity water of southern origin tended to contain relatively high concentrations of chlorophyll and cdom the prominent dynamic feature observed in spring was a cyclonic anticyclonic eddy pair the cyclonic eddy was responsible for an upward nutrient flux into the euphotic zone higher chlorophyll and cdom concentrations and concomitant lower nitrate phosphorous ratios indicate the influence of the ebc in the crs at the end of the stratified summer period

seasonal overturning circulation in the red sea 1 model validation and summer circulation the overturning circulation in the red sea exhibits a distinct seasonally reversing pattern and is studied using high resolution mit general circulation model simulations in the first part of this study the vertical and horizontal structure of the summer overturning circulation and its dynamical mechanisms are presented from the model results the seasonal water exchange in the strait of bab el mandeb is successfully simulated and the structures of the intruding subsurface gulf of aden intermediate water are in good agreement with summer observations in 2011 the model results suggest that the summer overturning circulation is driven by the combined effect of the shoaling of the thermocline in the gulf of aden resulting from remote winds in the arabian sea and an upward surface slope from the red sea to the gulf of aden set up by local surface winds in the red sea in addition during late summer two processes associated respectively with latitudinally differential heating and increased salinity in the southern red sea act together to cause the reversal of the contrast of the vertical density structure and the cessation of the summer overturning circulation dynamically the subsurface northward pressure gradient force is mainly balanced by vertical viscosity resulting from the vertical shear and boundary friction in the strait of bab el mandeb unlike some previous studies the three layer summer exchange flows in the strait of bab el mandeb do not appear to be hydraulically controlled

high frequency response of wind driven currents measured by drifting buoys and altimetry over the world ocean 1 we investigate the wind driven current response over the world ocean using svp drifting buoys ers 1 and ers 2 and topex altimetry data and ecmwf wind stress fields wind driven ageostrophic currents are estimated from drifting buoys by removing altimetry deduced geostrophic currents from observed drifting velocities removing the geostrophic signal enhances the coherence with wind stress at periods longer than 10 days for superinertial periods lower than 20 days a two parameter i e angle and amplitude model is fitted to the isolated ageostrophic signal to study the upper ocean response to surface wind stress in that frequency band the model which can explain up to 30 of the variance in some areas indicates that the currents spiral to the right left of the wind with depth in the northern southern hemisphere in agreement with the ekman theory the absolute value of the angle parameter is found to exhibit significant spatial and seasonal variability the vertical eddy viscosity and the ekman layer depth as deduced from ekman theory are compared to previous results their seasonal variability is also studied model results are then used to compute the mean and standard deviation of ageostrophic currents in 5 boxes over the world ocean the equatorial divergence and the subpolar and subtropical convergence zones are well reproduced

observations of the summer red sea circulation 1 aiming at exploring and understanding the summer circulation in the red sea a cruise was conducted in the basin during the summer of 2001 involving hydrographic meteorological and direct current observations the most prominent feature characteristic of the summer circulation and exchange with the indian ocean is a temperature salinity and oxygen minimum located around a depth of 75 m at the southern end of the basin associated with gulf of aden intermediate water inflowing from the gulf of aden during the summer season as an intruding subsurface layer stirring and mixing with ambient waters lead to marked increases in temperature from 16 5 to almost 33 c and salinity from 35 7 to more than 38 psu in this layer by the time it reaches midbasin the observed circulation presents a very vigorous pattern with strong variability and intense features that extend the width of the basin a permanent cyclone detected in the northern red sea verifies previous observations and modeling studies while in the central sector of the basin a series of very strong anticyclones were observed with maximum velocities exceeding 1 m s the three layer flow pattern representative of the summer exchange between the red sea and the gulf of aden is observed in the strait of bab el mandeb in the southern part of the basin the layer flow is characterized by strong banking of the inflows and outflows against the coasts both surface and intermediate water masses involved in the summer red sea circulation present prominent spatial variability in their characteristics indicating that the eddy field and mixing processes play an important role in the summer red sea circulation

implications for crustal accretion at fast spreading ridges from observations in jurassic oceanic crust in the western pacific 1 downhole logging data and basement stratigraphy interpretations are used to determine the spreading environment and crustal accretion history of the ocean basement cored at odp hole 801c located in the jurassic magnetic quiet zone of the western pacific high resolution microresistivity data obtained with the formation microscanner are used to measure the dip of the extrusive layers and indicate a 10 30 increase in dip down the drill hole with lava flow contacts dipping back toward the original ridge axis this structural pattern and the high proportion of massive flows relative to pillow units are consistent with prevailing crustal accretion models proposed for faster spreading ridges e g 60 km m y full rate a detailed analysis of the age data basement lithology related geochemistry and structural attitudes suggest the shallowest 100 m of the drilled section e g sequences i iii were emplaced just off the ridge sequence iii or significantly farther off axis up to 5 15 m y later sequences i and ii the remainder of the drilled section e g sequences iv viii has geochemical lithological and physical trends that are assumed to be representative of crust created at faster spreading ridges the pattern of dipping lava flow contacts from this deeper section of the drill hole suggests lava flows emanating from the ridge axis are limited to 1 2 km off axis our results suggest ocean crust drilled at hole 801c was created at faster spreading rates however caution should be used when incorporating sequences i iii into geochemical reference sections for faster spreading ridges

eddy properties in the california current system 1 eddy detection and tracking algorithms are applied to both satellite altimetry and a high resolution dx 5 km climatological model solution of the u s west coast to study the properties of surface and undercurrent eddies in the california current system eddy properties show remarkable similarity in space and time and even somewhat in polarity summer and fall are the most active seasons for undercurrent eddy generation while there is less seasonal variation at surface most of the eddies have radii in the range of 25 100 km sea level anomaly amplitudes of 1 4 cm and vorticity normalized by f amplitudes of 0 025 0 2 many of the eddies formed near the coast travel considerable distance westward with speeds about 2 km day consistent with the effect anticyclones and cyclones show equatorward and poleward displacements respectively long lived surface eddies show a cyclonic dominance the subsurface california undercurrent generates more long lived anticyclones than cyclones through instabilities and topographic coastline effects in contrast surface eddies and subsurface cyclones have much more widely distributed birth sites the majority of the identified eddies have lifetimes less than a season eddies extend to 800 1500 m depth and have distinctive vertical structures for cyclones and anticyclones eddies show high nonlinearity rotation speed higher than propagation speed and hence can be efficient in transporting materials offshore

global ocean surface velocities from drifters mean variance el nino southern oscillation response and seasonal cycle 1 global near surface currents are calculated from satellite tracked drogued drifter velocities on a 0 5 0 5 latitude longitude grid using a new methodology data used at each grid point lie within a centered bin of set area with a shape defined by the variance ellipse of current fluctuations within that bin the time mean current its annual harmonic semiannual harmonic correlation with the southern oscillation index soi spatial gradients and residuals are estimated along with formal error bars for each component the time mean field resolves the major surface current systems of the world the magnitude of the variance reveals enhanced eddy kinetic energy in the western boundary current systems in equatorial regions and along the antarctic circumpolar current as well as three large eddy deserts two in the pacific and one in the atlantic the soi component is largest in the western and central tropical pacific but can also be seen in the indian ocean seasonal variations reveal details such as the gyre scale shifts in the convergence centers of the subtropical gyres and the seasonal evolution of tropical currents and eddies in the western tropical pacific ocean the results of this study are available as a monthly climatology

eddy activity in the four major upwelling systems from satellite altimetry 1992 2007 eddy activity in the four major eastern boundary upwelling systems ebus is investigated using 15 years of satellite altimetry data based on the analysis of more than 4000 long lived eddy trajectories in every ebus we show that mesoscale structures are mainly generated along the continental coasts and south of the main archipelagos and propagate westward with velocities increasing toward the equator these mesoscale eddies having radii of 70 160 km are then frequently observed along the coastal transition zones and frontal regions and some large oceanic areas are preferentially populated by cyclonic or anticyclonic eddies temporal variations of the number of newly formed eddies and the associated eddy activity index defined as the mean eddy energy density are finally examined at seasonal and interannual scales the strongest seasonal interannual respectively variations are observed in the california benguela upwelling systems the proposed indices also exhibit contrasted long term trends in each ebus which suggests that eddy activity might be sensitive to a warming climate

lagrangian time scales and eddy diffusivity at 1000 m compared to the surface in the south pacific and indian oceans abstractargo floats cannot be regarded as true lagrangian drifters because they periodically rise to the surface hence previous estimates of eddy diffusivity at depth using single particle statistics have been limited to one submerged cycle however unless the lagrangian time scale is significantly shorter than the argo cycle time this single particle calculation can have a large bias here eddy diffusivity computed from single particle statistics using argo data is compared to that computed by assuming that eulerian scales at depth are the same as at the surface and that the relationship between lagrangian and eulerian time scales derived by middleton is valid if the methods provide the same answer one can have confidence in both methods eddy diffusivity calculated from the single particle statistics shows the same spatial structure as that computed from inferred time scale but is smaller by a factor of about 2 it is suggested that this is because the deep lagrangian time scale over much of th

structure of uppermost fast spread oceanic crust exposed at the hess deep rift implications for subaxial processes at the east pacific rise the uppermost 2 km of the oceanic crust created at the fast spreading 135 mm yr 1 full rate equatorial east pacific rise epr is exposed for tens of kilometers along escarpments bounding the hess deep rift mosaics of large scale digital images from the remotely operated vehicle rov argo ii and direct observations from the submersible alvin document a degree of geological complexity and variability that is not evident from most studies of ophiolites or prevailing models of seafloor spreading dramatic variations in the thickness and internal structure are documented in both the basaltic volcanic and sheeted dike rock units these rock units are characterized by extensive faulting fine scale fracturing and rotations of coherent crustal blocks meters to tens of meters across the uppermost basaltic lavas are essentially undeformed and have overall gently inclined flow surfaces through most of the basaltic lava unit however lava flow contacts dip 20 70 w toward the epr and generally increase in dip downward in the section dikes cutting the lavas and in the underlying sheeted dike unit generally dip 90 40 e away from the epr deeper level gabbroic rocks show little evidence of the intense fracturing typical of the overlying units we interpret this upper crustal structure as the result of subaxial subsidence within 1 2 km of the epr that accommodated the thickening of the basaltic lava unit to 500 m variations in the thickness of lava and dike units and spatially related structures along the rift escarpments suggest temporal fluctuations in magma supply these results indicate that substantial brittle deformation accompanied waxing and waning volcanism during the accretion of the crustal section exposed at the hess deep rift if this type of structure is typical of uppermost oceanic crust generated at the epr these processes may be common along fast spreading mid ocean ridges

zonal surface wind jets across the red sea due to mountain gap forcing along both sides of the red sea 1 mesoscale atmospheric modeling over the red sea validated by in situ meteorological buoy data identifies two types of coastal mountain gap wind jets that frequently blow across the longitudinal axis of the red sea 1 an eastward blowing summer daily wind jet originating from the tokar gap on the sudanese red sea coast and 2 wintertime westward blowing wind jet bands along the northwestern saudi arabian coast which occur every 10 20 days and can last for several days when occurring both wind jets can attain wind speeds over 15 m s 1 and contribute significantly to monthly mean surface wind stress especially in the cross axis components which could be of importance to ocean eddy formation in the red sea the wintertime wind jets can cause significant evaporation and ocean heat loss along the northeastern red sea coast and may potentially drive deep convection in that region an initial characterization of these wind jets is presented

temporal variation of oceanic spreading and crustal production rates during the last 180 my we present a re evaluation of seafloor spreading and generation rates mainly based on a direct measurement of the remaining surfaces of oceanic crust and isochron lengths defined in the most recent isochron maps j y royer r d muller l m gahagan l a lawyer c l mayes d nurnberg j g sclater a global isochron chart tech rep 117 austin univ of tex inst for geophys 1992 r d muller w r roest j y royer l m gahagan j g sclater digital isochrons of the world s ocean floor j geophys res 102 1997 3211 3214 our evaluation of the amount of oceanic crust per unit age da dt as a function of age which can be expressed as da dt co 1 t tm is in fairly good agreement with previous determinations j g sclater b parsons c jaupart oceans and continents similarities and differences in the mechanisms of heat loss j geophys res 86 1981 11 535 11 552 d b rowley rate of plate creation and destruction 180 ma to present geol soc amer bull 114 2002 927 933 with co 2 850 0 119 km2 year 1 and tm 180 2 9 7 ma dividing these da dt by the ridge lengths l defined as the isochron length at each epoch allowed us to compute the evolution of global half spreading rates these have been roughly constant at 25 9 3 3 mm year 1 for at least the last 150 ma we propose that the global seafloor surface generation rate is roughly constant as well with a mean half value of 1 298 0 284 km2 year 1 and varying 20 with time this study corroborates the recent conclusion of rowley d b rowley rate of plate creation and destruction 180 ma to present geol soc amer bull 114 2002 927 933 of a constant generation rate since 180 ma and completely contradicts the commonly accepted idea of high seafloor spreading and surface generation rates during a large part of the cretaceous combining the oceanic surface generation rates derived here with crustal thicknesses deduced from the chemical composition of old oceanic crusts and seismic measurements e humler c h langmuir v daux depth versus age new perspectives from the chemical compositions of ancient crust earth planet sci lett 173 1999 7 23 the magmatic flux at young 0 80 ma oceanic ridges appears to be about 18 1 3 4 km3 year 1 and was possibly 15 to 30 higher during the mesozoic we propose that mantle temperature variation provides an alternative mechanism to spreading rate for the cretaceous highstand in sea level and atmospheric co2 generation

re os ages for archean molybdenite and pyrite kuittila kivisuo finland and proterozoic molybdenite kabeliai lithuania testing the chronometer in a metamorphic and metasomatic setting seven 187re 187os ages were determined for molybdenite and pyrite samples from two well dated precambrian intrusions in fennoscandia to examine the sustainability of the re os chronometer in a metamorphic and metasomatic setting using a new 187re decay constant 1 666 10 11y 1 with a much improved uncertainty 0 31 we determined replicate re os ages for molybdenite and pyrite from the kuittila and kivisuo prospects in easternmost finland and for molybdenite from the kabeliai prospect in southernmost lithuania these two localities contain some of the oldest and youngest plutonic activity in fennoscandia and are associated with newly discovered economic au mineralization ilomantsi finland and a cu mo prospect kabeliai lithuania two re os ages for vein hosted kabeliai molybdenite average 1486 5 ma in excellent agreement with a 1505 11 ma u pb zircon age for the hosting kabeliai granite pluton the slightly younger age suggests the introduction of cu mo mineralization by a later phase of the kabeliai magmatic system mean re os ages of 2778 8 ma and 2781 8 ma for kuittila and kivisuo molybdenites respectively are in reasonable agreement with a 2753 5 ma weighted mean u pb zircon age for hosting kuittila tonalite these re os ages agree well with less precise ages of 2789 290 ma for a rb sr whole rock isochron and 2771 75 ma for the average of six sm nd tdm model ages for kuittila tonalite three re os analyses of a single pyrite mineral separate from the same sample of kuittila pluton that yielded a molybdenite separate provide individual model ages of 2710 27 2777 28 and 2830 28 ma re 17 4 12 1 and 8 4 ppb respectively with a mean value of 2770 120 ma in agreement with the kuittila molybdenite age the re and 187os abundances in these three pyrite splits are highly correlated r 0 9994 and provide a 187re 187os isochron age of 2607 47 ma with an intercept of 21 ppt 187os mswd 1 1 it appears that the re os isotopic system in pyrite has been reset on the millimeter scale and that the 21 ppt 187os intercept reflects the in situ decay of 187re during the 160 to 170 m y interval from 2778 ma time of molybdenite pyrite deposition to 2607 ma time of pyrite resetting when the re os data for molybdenites from the nearby kivisuo prospect are plotted together with the kuittila molybdenite and pyrite data a well constrained five point isochron with an age of 2780 8 ma and a 187os intercept 2 4 3 8 ppt of essentially zero results mswd 1 5 we suggest that the pyrite isochron age records a regional metamorphic and or hydrothermal event possibly the time of au mineralization a proposed re os age of 2607 ma for au mineralization is in good agreement with radiometric ages by other methods that address the timing of archean au mineralization in deposits worldwide so called late au model molybdenite in contrast provides a robust re os chronometer retaining its original formation age of 2780 ma despite subsequent metamorphic disturbances in archean and proterozoic time

seasonal to interannual variability of the eddy field in the labrador sea from satellite altimetry sea level anomalies measured by the altimeters aboard the topex poseidon and ers satellites for the periods 1993 2001 and 1997 2001 respectively are used to investigate the eddy field in the subpolar north atlantic and in the labrador sea a quadratic correction of the obtained eddy kinetic energy eke with respect to significant wave height is applied that led to an increased correlation between moored and altimetric eke in the central labrador sea the mean eke field shows higher levels associated with the main currents and a strong seasonality in the labrador sea the annual cycle of the eke shows a propagation of west greenland current wgc eke into the central labrador sea with a mean southward propagation speed of about 3 cm s 1 while the eke maximum in the labrador current is well separated from the interior by local eke minima the interannual variability of the eke in the labrador sea shows distinct regional differences in the wgc region strong early winter maxima are found during 1993 and 1997 1999 in the central labrador sea maxima are found during march april 1993 1995 and 1997 variations in the annual cycle of the wgc eke are observed while there is a weak annual cycle in the wgc region during 1994 1996 with more continuous eke generation during 1997 2000 there is a strong seasonal cycle with maximum eke during january and particularly low eke during summer the propagation of wgc eke into the central labrador sea is enhanced during 1997 2000 leading to a long persistence of eke in the central labrador sea during 1993 1995 and 1997 the central labrador sea eke almost instantaneously increased during march april followed in the earlier years by a relatively fast destruction of the winterly generated eke

sulfur isotopic profile through the oceanic crust sulfur mobility and seawater crustal sulfur exchange during hydrothermal alteration measurements of the abundance of anhydrite and pyrite veins and the distribution of alteration types in oceanic basement enable estimates of global mass and isotopic fluxes of sulfur during hydrothermal alteration of oceanic crust fluxes of 2 5 10 12 g yr s 34 s 2 7 from the volcanic section to seawater and 2 1 10 12 g yr of seawater s 21 into the crust result in an insignificant change in the s content of altered ocean crust these are clearly second order fluxes compared to the riverine input of s to the oceans and the output of sedimentary pyrite most of the anhydrite that forms in the high temperature axial convection cell must later be dissolved at lower temperatures during off axis circulation the mean 34 s of altered oceanic basement is 0 9 only slightly changed from the primary value of 0 1 unless s is preferentially mobilized from 34 s rich sulfide deposits or mineralized zones subduction of altered basaltic crust is unlikely to be the source of high 34 s values of arc volcanic rocks 4 but could contribute to isotopic heterogeneities of s in the mantle

low temperature alteration of mesozoic oceanic crust ocean drilling program leg 185 1 basalts drilled from the mesozoic crust at ocean drilling program odp sites 801 and 1149 during leg 185 have been affected by a succession of submarine variably oxidative alteration processes by cold seawater the low temperature alteration resulted in various combinations of secondary minerals both as replacements of igneous phases and as void and crack fillings mg smectite calcite celadonite and fe oxyhydroxide are the dominant secondary minerals quartz chalcedony and phillipsite are always very minor phases that fill open spaces the rocks generally exhibit concentric haloes 0 5 to 1 cm in thickness around gray inner cores and usually adjacent to exposed surfaces color zonations result from the abundance of various secondary mineral assemblages present in each zone the green rocks are dominated by celadonitic phyllosilicates whereas the dusky red haloes are characterized by abundant iddingsite and fe oxyhydroxides replacing the fine clinopyroxene finally mg smectite calcite are the most common secondary phases in the inner gray cores the most unusual effects of the low temperature alteration of the study rocks are the pervasive pale green to gray green color and the relatively abundant dusky red haloes surrounding inner reddish gray cores alteration of mesozoic crust cored during leg 185 is comparable with low temperature alteration of 310 m thick uppermost volcanic section of the 5 9 my old crust of hole 504b except the renewed precipitation of calcite in veins the aging of oceanic crust does not depend on time probably because it occurs during the first few millions of years after the accretion and ceases when the crust is sealed off

hydrothermal alteration of a 1 km section through the upper oceanic crust deep sea drilling project hole 504b mineralogy chemistry and evolution of seawater basalt interactions deep sea drilling project hole 504b penetrates 1076 m into oceanic layer 2 and is the first hole to pass through the transition from pillow basalts altered at low temperatures into hydrothermally metamorphosed sheeted dikes alteration of the crust at site 504 occurred in four stages related to the movement of the crust away from the spreading axis 1 dikes reacted with seawater 200 300 c in the upwelling zone of an axial convection cell at the spreading axis resulting in the formation of greenschist facies parageneses in veins and host rocks mixing of the upwelling hydrothermal fluids with seawater circulating in the overlying more permeable pillow section occurred in the upper part of the lithologic transition zone causing a steep temperature gradient at the base of the pillow section secondary minerals formed in the lower pillow section from the resultant reducing mixed fluids at temperatures of around 100 c at the same time the initial effects of seafloor weathering began in the upper 320 m of the pillow section at low temperatures 50 c and under conditions of open circulation of oxidizing seawater 2 following refracturing of the dikes a second stage of axial upwelling occurred hydrothermal fluids 200 380 c were probably similar to those presently sampled from spreading ridges on the seafloor mixing of these fluids with seawater in the lithologic transition zone caused deposition of quartz epidote and sulfides in veins and formation of a sulfide rich stockworklike zone within this transition zone alteration of the pillow section proceeded under the prior conditions with the effects of seafloor weathering extending progressively downward into the crust 3 seawater recharge penetrated to depths of at least 1075 5 m subbasement and deposited anhydrite locally in veins 4 off axis alteration of the dikes was characterized by formation of zeolites calcite and prehnite in veins and host rocks from more highly evolved and lower temperature 100 250 c fluids alteration in the upper pillow section evolved from seafloor weathering conditions to more reducing and rock dominated as cracks in the basalt were sealed with secondary minerals and the basement was covered with a layer of sediment zeolites and calcite were the last phases to form throughout the pillow section sealing of the crust to convective cooling also allowed conductive reheating of the crust from below calculations of seawater crustal chemical fluxes from whole rock data are complicated by the low recovery and heterogeneity of alteration effects but indicate that basalt seawater interactions are a sink for seawater mg and k and a source for si and ca

dynamically balanced absolute sea level of the global ocean derived from near surface velocity observations 1 the 1992 2002 time mean absolute sea level distribution of the global ocean is computed for the first time from observations of near surface velocity for this computation we use the near surface horizontal momentum balance the velocity observed by drifters is used to compute the coriolis force and the force due to acceleration of water parcels the anomaly of horizontal pressure gradient is derived from satellite altimetry and corrects the temporal bias in drifter data distribution ncep reanalysis winds are used to compute the force due to ekman currents the mean sea level gradient force which closes the momentum balance is integrated for mean sea level we find that our computation agrees within uncertainties with the sea level computed from the geostrophic hydrostatic momentum balance using historical mean density except in the antarctic circumpolar current a consistent horizontally and vertically dynamically balanced near surface global pressure field has now been derived from observations

ancient depleted mantle as a source of boninites in the izu bonin mariana arc evidence from os isotopes in cr spinel and magnetite abstract boninite is a volcanic rock derived from shallow melting of highly depleted hydrous mantle fluxed with water from subducted slabs the eruption of boninite early in the history of the izu bonin mariana ibm arc 48 45 ma suggests generation by melting of upper mantle material that was relatively unmodified by subducted components thus the boninite composition should largely reflect that of the sub arc mantle for better understanding of the mantle sources of nascent arc settings and the contributions of different components to arc melts we analyzed os isotope ratios 187os 188os of bulk rocks and mineral separates euhedral cr spinel from boninites and euhedral cr spinel magnetite mixtures from tholeiites younger than 45 ma that erupted after boninites from the bonin islands and guam the age corrected initial os isotope ratios of the whole rock samples 0 1179 0 2050 were more radiogenic and variable than those of the mineral separates possibly because of contamination with crustal materials during magma ascent or alteration after emplacement the age corrected os isotope ratios of euhedral cr spinel in boninite from the bonin islands 0 1187 0 1254 and from guam 0 1220 0 1269 are unradiogenic relative to primitive mantle and those of the cr spinel magnetite mixtures from the tholeiites from the bonin islands are similar to or slightly more radiogenic 0 1224 0 1382 the most depleted os isotope ratio of the cr spinel from boninite yielded a model re depletion trd age of 1 4 ga suggesting that the mantle source of the boninite experienced melt extraction prior to 1 4 ga the source of the boninites is interpreted to be mostly highly depleted mantle with a small contribution of slab flux arising from altered oceanic crust that has radiogenic os components with or without contributions from components with relatively unradiogenic os such as volcaniclastics of oceanic island basalt affiliation or very young mid ocean ridge basalt

stability of the sargasso sea subtropical frontal zone abstract recent studies suggest that eddy properties are significantly influenced by the mean current shear associated with the western sargasso sea subtropical frontal zone sfz between 19 and 34 n the mean density structure is characterized by three layers separated by a climatologically permanent upper seasonal thermocline that shoals and a lower main thermocline that deepens toward the north the thermoclines are separated by the wedge shaped southern part of the subtropical mode water pool the sfz is evident as a zonal band between about 26 and 32 n where subtropical frontogenesis between the westerlies and trades enhances the slope of the mean seasonal thermocline classical linear as well as more recent nonlinear stability theories predict that the mean sfz flow should be unstable the linear eigenvalue problem suggests that the most unstable perturbations have wavelengths between 150 and 200 km analysis of a channel version of the miami isopycnic coordinate primitive equation numeri

three dimensional structure and temporal evolution of submesoscale thermohaline intrusions in the north pacific subtropical frontal zone abstract four instances of persistent intrusive deformation of the north pacific subtropical front were tagged individually by a lagrangian float and tracked for several days each feature was mapped in three dimensions using repeat towed observations referenced to the float isohaline surface deformations in the frontal zone included sheetlike folds elongated in the alongfront direction and narrow tongues extending across the front all deformations appeared as protrusions of relatively cold and fresh water across the front no corresponding features of the opposite sign or isolated lenslike structures were observed the sheets were o 10 m thick protruded about 10 km into the warm saline side of the front and were coherent for 10 30 km along the front having about the same thickness and cross frontal extent as the sheets tongues extended less than 5 km along the front all of the intrusions persisted as long as they were followed several days to one week their structures evolved on both inertial

baroclinic tides simulation in the red sea comparison to observations and basic characteristics the author would like to thank james h churchill larry pratt and jim thomas for the discussions and help the topography data are derived from general bathymetric chart of the oceans gebco https www gebco net the initial salinity and temperature is extracted from world ocean atlas 2009 woa09 https www nodc noaa gov oc5 woa09 pr woa09 html the barotropic tidal boundary currents and the spatial distribution of elevation amplitudes and phases are derived from tpxo 7 2 inverse model http volkov oce orst edu tides global html the mitgcm model output data files sea level data from gauges and mooring data can be found at figshare https figshare com projects data for b2018jc013970 bc redsea 57407 the research reported in this manuscript was supported by king abdullah university of science and technology this research made use of the resources from the supercomputing laboratory and or computer clusters at king abdullah university of science and technology

observational evidence for a southern hemisphere oceanic supergyre 1 a high resolution hydrographic atlas resolves the narrow boundary flow of the western pacific gyre and its pathway around tasmania southern australia and into the indian ocean basin this confirms recent model descriptions of a southern hemisphere supergyre a nested system of subtropical gyres the observations show that the gyre flow is squeezed into a narrow band between tasmania and the antarctic circumpolar current the residue of east australian current transport turns westward around tasmania and leaks into the indian ocean while there is also a limited form of gyre connection between the indian and atlantic systems south of africa with a mean outflow of agulhas current water into the atlantic basin these gyre circulations remain far more discrete the gyre coupling and the east australian current in particular provide the mechanism by which sub antarctic mode water and antarctic intermediate water are distributed between the ocean basins

global observations of large oceanic eddies 1 ten years of sea surface height ssh fields constructed from the merged topex poseidon t p and ers 1 2 altimeter datasets are analyzed to investigate mesoscale variability in the global ocean the higher resolution of the merged dataset reveals that more than 50 of the variability over much of the world ocean is accounted for by eddies with amplitudes of 5 25 cm and diameters of 100 200 km these eddies propagate nearly due west at approximately the phase speed of nondispersive baroclinic rossby waves with preferences for slight poleward and equatorward deflection of cyclonic and anticyclonic eddies respectively the vast majority of the eddies are found to be nonlinear

intermediate depth circulation of the indian and south pacific oceans measured by autonomous floats as part of the world ocean circulation experiment 306 autonomous floats were deployed in the tropical and south pacific ocean and 228 were deployed in the indian ocean to observe the basinwide circulation near 900 m depth mean velocities seasonal variability and lateral eddy diffusivity from the resultant 2583 float years of data are presented area averages local function fits and a novel application of objective mapping are used to estimate the mean circulation patterns of mean circulation resemble those at the surface in both basins well developed subtropical gyres twice as strong in the indian ocean as in the pacific feed western boundary currents tropical gyres are separated by eastward flow along the equator in both hemispheres of both basins although the indian subcontinent splits the north indian tropical gyre the antarctic circumpolar current acc and west wind drifts are prominent in both basins generally tending slightly southward but deviating to the north behind the del cano kerguelen and campbell plateaus and of course south america remarkably the eastern boundaries of the southern subtropical gyres in all three basins apparently occur in the ocean interior away from land the indian ocean s subtropical gyre and perhaps part of the south atlantic s reaches east to a retroflection just upstream of the campbell plateau south of new zealand seasonal variability at 900 m is focused around the equator with weaker variability found near certain bathymetric features there is a remarkable agreement between the observed seasonable variability and that predicted by the jet propulsion laboratory jpl estimating the circulation and climate of the ocean ecco data assimilating numerical model aside from seasonal effects eddy variability is greatest along the equator in tropical and subtropical western basins and along the acc integrals of velocity across regional passages tasman sea mozambique channel provide useful reference for hydrographic analyses of transport across whole ocean basins however the uncertainty associated with the appropriate continuity relation for horizontal flow e g geostrophy vs nondivergence is comparable to the mean flow

seasonal overturning circulation in the red sea 2 winter circulation author posting 0american geophysical union 2014 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in journal of geophysical research oceans 119 2014 2263 2289 doi 10 1002 2013jc009331

seasonal modulations in the eddy field of the south pacific ocean abstract decade long satellite altimeter data from the ocean topography experiment topex poseidon and european remote sensing satellite 1 and 2 ers 1 2 missions are analyzed to investigate the eddy signals in the south pacific ocean high eddy kinetic energy eke bands with well defined annual cycles are detected along the eastward flowing surface currents of the south tropical countercurrent stcc between 21 29 s and the south equatorial countercurrent secc centered near 9 s overriding the westward flowing south equatorial current sec the stcc layer has the sign of its mean potential vorticity gradient opposite to that in the sec layer subjecting the vertically sheared stcc sec system to baroclinic instability in austral winter the stcc sec system is baroclinically more unstable than in other seasons because of the large vertical shear and weak stratification this seasonal variation in the intensity of baroclinic instability is responsible for the seasonal modulation of the stcc s eke fi

effects of increased horizontal resolution in a simulation of the north atlantic ocean global mean and eddy fields from a four year experiment with a 1 6 1 5 horizontal resolution implementation of the cme north atlantic model are presented the time averaged wind driven and thermohaline circulation in the model is compared to the results of a 1 3 2 5 model run in very similar configuration in general the higher resolution results are found to confirm that the resolution of previous cme experiments is sufficient to describe many features of the large scale circulation and water mass distribution quite well while the increased resolution does not lead to large changes in the mean flow patterns the variability in the model is enhanced significantly on the other hand however not all aspects of the circulation have improved with resolution the azores current frontal zone with its variability in the eastern basin is still represented very poorly particular attention is also directed toward the unrealistic stationary anticyclones north of cape hatteras and in the gulf of mexico

instability of the north pacific subtropical countercurrent abstractthe north pacific subtropical countercurrent stcc has a weak eastward velocity near the surface but the region is populated with eddies studies have shown that the stcc is baroclinically unstable with a peak growth rate of 0 015 day 1 in march and the 60 day growth time has been used to explain the peak eddy kinetic energy eke in may observed from satellites it is argued here that this growth time from previously published normal mode instability analyses is too slow growth rates calculated from an initial value problem without the normal mode assumption are found to be 1 5 to 2 times faster and at shorter wavelengths due to the existence of i nonmodal solutions and ii sea surface temperature front in the mixed layer in winter at interannual time scales it is shown that because of rapid surface adjustments the stcc geostrophic shear hence also the instability growth is approximately in phase with surface forcing leading to eke modulation that peaks approximately 10 months later

eddy processes in semienclosed seas a case study for the black sea abstract the enclosed boundaries and small scales of some seas lead to the formation of specific physical balances which motivates the oceanographic interest in studying the dynamics of semienclosed ocean basins the focus in the paper is on the specific appearances of eddy processes when the basin scales and the ones of the topographic features are comparable with the baroclinic radius of deformation the black sea is used as a test basin eddy variability is analyzed using simulation results and compared with existing observations the bryan cox model with horizontal resolution 1 10 and 1 6 is forced with annual mean wind stress data buoyancy flux at the sea surface is proportional to the deviation of the model density from the annual mean climatological data sensitivity studies on different forcing and on the topographic control are carried out synoptic periods are estimated to be about 0 5 yr eddies form in the eastern black sea and propagate westward with a speed of about 3 cm s 1 t

highly siderophile element systematics of the 3 3 ga weltevreden komatiites south africa implications for early earth history highly siderophile element hse os ir ru pt pd and re abundances re os isotopic systematics and major minor and lithophile trace element abundances are determined for a suite of remarkably fresh komatiites from the weltevreden formation fm of the barberton greenstone belt south africa the komatiite lavas examined are calculated to have contained ca 31 mgo upon emplacement and are among the most mgo rich lavas ever erupted onto earth s surface based on the partitioning behavior of v indicating reduced conditions of magma formation as well as the low calculated h2o abundance of 0 02 in the mantle source anhydrous melting for the weltevreden fm komatiites is inferred the high calculated liquidus temperatures of the emplaced komatiite lavas of ca 1600 c require an unusually hot 1800 c mantle source 100 c hotter than the ambient contemporaneous mantle these observations are most consistent with formation of the weltevreden komatiites via deep 530 km melting in a mantle plume the re os isotopic data for twelve whole rock samples and an olivine separate define a precise re os isochron age of 3266 8 ma 2 mean and an initial 187os 188os of 0 10440 5 187os 0 13 0 05 the re os data coupled with the relatively high calculated hse abundances in the mantle source totaling 80 of those in modern primitive mantle pm estimates indicate that at least some portions of the deep early archean mantle evolved with essentially chondritic re os and absolute hse abundances that are typical of the sources of late archean komatiites if the hse budget of the terrestrial mantle was established via late accretion of several large planetesimals following the cessation of major chemical interaction between the core and the mantle our data indicate that by 3 3 ga these materials were well homogenized within the mantle domains sampled by the weltevreden komatiites and by inference within the mantle as a whole

rhenium osmium isotope systematics and platinum group element concentrations in oceanic crust knowledge of the 187 os 188 os ratio as well as the inventories of rhenium and platinum group elements pge in oceanic crust allows quantification of the proportion of recycled oceanic crust in oceanic basalt sources our knowledge is limited by the availability of well characterized sections of oceanic crust specifically of the plutonic lower portion that has not been drilled in situ to the moho here we report new data for plutonic rocks that compose the bottom 4680 m of an ocean crust section from the oman ophiolite major and trace element data as well as mineral analyses indicate that oman gabbros are primitive cumulates from melts similar to typical mid oceanic ridge basalt the mean weighted composition of this section re 427 pg g os 55 pg g ir 182 pg g pd 2846 pg g pt 4151 pg g initial 187 os 188 os 0 142 indicates significantly higher os and lower re concentrations than previously analyzed partial sections of ocean crust that lack cumulate lower crust deep sea drilling project ocean drilling program dsdp odp hole 504b odp hole 735b emphasizing that the lower cumulate oceanic crust dominates the os budget of oceanic crust analyses of mineral grain size fractions indicate that rhenium pge and lead are enriched in the sulfur rich fine fraction this corroborates the notion that small accessory phases and the melt migration processes affecting them control these elements budgets distributions and susceptibilities to alteration the re os pge inventories of a hypothetical 6 5 km thick composite section that consists of 1825 m of dsdp hole 504b like upper oceanic crust and 4680 m of oman like lower ocean crust re 736 pg g os 45 pg g ir 133 pg g pd 2122 pg g pt 2072 pg g initial 187 os 188 os 0 146 provide a new comprehensive assessment of oceanic crust composition upon recycling and mixing with reasonable proportions of mantle peridotite this composite requires at least 2 g y to develop sufficiently radiogenic 187 os 188 os to generate high himu 238 u 204 pb basalts

mesoscale eddies off peru in altimeter records identification algorithms and eddy spatio temporal patterns relatively little is known about coherent vortices in the eastern south pacific along the peruvian coast even with regard to basic facts about their frequency of occurrence longevity and structure this study addresses these issues with nearly 15 years of relatively high resolution satellite altimetry measurements we first compare two distinct automated methods for eddy identification the objective validation protocol shows that the rarely used geometrical or winding angle method based on the curvature of the streamline functions is more accurate than the commonly used okubo weiss algorithm which defines a vortex as a simple connected region with values of okubo weiss parameter weaker than a given threshold we then investigate vortices off peru using more than 20 000 mesoscale eddies identified by the winding angle method coherent eddies characterized by a high ratio of vorticity to deformation rate are typically formed along the coast and propagate westward at 3 6 cm s 1 the vortices have a mean radius of 80 km increasing northward and are most frequently observed off of chimbote 9s and south of san juan 15s the mean eddy lifetime is about 1 month but if eddies survive at least 2 months the probability for surviving an additional week or month is constant at 90 or 67 anticyclonic eddies tend to propagate northwestward whereas cyclonic vortices migrate southwestward in general cyclones and anticyclones are similar except for eddies surviving at least 6 months in this case after a similar 3 4 months of radius and amplitude growth amplitudes or sizes decay particularly rapidly for anticyclonic or cyclonic eddies in terms of intensity cyclonic eddies show a rapid decay during the first 3 months before arriving at a quasi constant value whereas anticyclones exhibit steady decline finally eddy temporal variations were examined at seasonal and interannual scales in the coastal region favorable to the formation of energetic mesoscale structures on seasonal scales eddy activity is maximal in fall and minimum in spring at interannual scales the eddy activity index was maximal during the strong el nino of 1997 1998 but another strong maximum of eddy activity also occurred late in 2004 these temporal variations are probably associated with the intensification of the upwelling thermal front and with the passage of coastal trapped waves which generate baroclinic instabilities further investigation of the mechanisms involved on the eddy genesis is needed

mesoscale eddies in the south china sea mean properties spatiotemporal variability and impact on thermohaline structure we investigated mean properties and the spatiotemporal variability of eddies in the south china sea scs by analyzing more than 7000 eddies corresponding to 827 eddy tracks identified using the winding angle method and 17 years of satellite altimetry data eddies are mainly generated in a northeast southwest direction and southwest of luzon strait there is no significant difference between the numbers of two types of eddies anticyclonic and cyclonic in most regions the mean radius and lifetime of eddies are 132 km and 8 8 weeks respectively both depending on where the eddies are formed anticyclonic and cyclonic eddies tend to deform during their lifetimes in different ways furthermore eddy propagation and evolution characteristics are examined in the northern scs eddies mainly propagate southwestward along the continental slope with velocities of 5 0 9 0 cm s 1 while in the central scs eddies tend to move with slight divergence but still in a quasi westward direction with velocities of 2 0 6 4 cm s 1 eddy propagation in the western basin to the east of vietnam is quite random with no uniform propagate direction investigation of 38 long lived eddies shows that eddies have a swift growing phase during the first 12 weeks and then a slow decaying phase that affects the eddy radii and eddy energy densities nevertheless vorticity has less variability in addition the effect of eddies on the thermocline and halocline is analyzed using 763 argo temperature profile data cyclonic eddies drive the thermocline shallower and thinner and significantly strengthen the thermocline intensity whereas anticyclonic eddies cause the thermocline to deepen and thicken and weaken the thermocline intensity to a certain degree the halocline impacted by cyclonic eddies is also shallower and thinner than that impacted by anticyclonic eddies finally eddy temporal variations are examined at seasonal and interannual scales eddy activity is sensitive to the wind stress curl and in the northern scs it is also related with the strength of the background flows

precise re os ages of organic rich mudrocks and the os isotope composition of jurassic seawater rhenium and osmium isotope and abundance data have been obtained on precisely located samples from three suites of immature organic rich mudrocks from jurassic coastal outcrops in england the data provide accurate whole rock ages of 207 12 ma 181 13 ma and 155 4 3 ma for suites of hettangian toarcian exaratum subzone and kimmeridgian sensu anglico wheatleyensis subzone samples these new re os ages are indistinguishable within the assigned analytical uncertainties from interpolated depositional ages estimated from published geological timescales and establish the importance of the re os dating technique for chronostratigraphic studies early diagenetic pyrite nodules possess levels of re and os which are 1 2 orders of magnitude lower than in the enclosing organic rich mudrocks indicating that these elements had already been removed from sediment pore waters at the time of nodule formation thus the re os isotope system in these organic rich mudrocks has been closed since or from very soon after the time of sediment deposition because most of the re 98 and os 95 99 8 in the mudrocks is shown to be hydrogenous the 187os 188os i of the samples is interpreted to be that of contemporaneous seawater the data thereby provide the first estimates of the os isotope composition of jurassic seawater during the earliest jurassic hettangian the seawater 187os 188os ratio was extremely unradiogenic 0 15 it had increased to 0 8 at the end of the early jurassic toarcian 20 ma later while in the late jurassic kimmeridgian the seawater 187os 188os ratio was 0 59 the most likely explanation for the unradiogenic os isotope composition of hettangian seawater is that the contribution of unradiogenic os to the oceans from the hydrothermal alteration of oceanic crust greatly exceeded the input of radiogenic os from the continents at that time this interpretation is in line with observations suggesting that global weathering rates were low in the hettangian and that increased hydrothermal and volcanic activity preceded the break up of pangea the re os ratios of hettangian mudrocks and by inference of contemporaneous seawater are similar to those of mudrocks deposited at later times during the jurassic and argues against the unradiogenic os in hettangian seawater being derived from extraterrestrial meteoritic sources

new cnes cls09 global mean dynamic topography computed from the combination of grace data altimetry and in situ measurements 1 an accurate knowledge of the ocean mean dynamic topography mdt is mandatory for the optimal use of altimetric data including their assimilation into operational ocean forecasting systems a new global 1 4 resolution mdt was computed for the 1993 1999 time period with improved data and methodology compared to the previous rio05 mdt field first a large scale mdt is obtained from the cls01 altimetric mean sea surface and a recent geoid model computed from 4 5 years of grace gravity recovery and climate experiment data altimetric sea level anomalies and in situ measurements are then combined to compute synthetic estimates of the mdt and the corresponding mean currents while the rio05 mdt was based on 10 years of in situ dynamic heights and drifting buoy velocities the new field benefits from an enlarged data set of in situ measurements ranging from 1993 to 2008 and includes all hydrological profiles from the argo array moreover the processing of the in situ data has been updated a new ekman model was developed to extract the geostrophic velocity component from the drifting buoy measurements the handling of hydrologic measurements has also been revisited compared to the previous rio05 solution the new global mdt resolves much stronger gradients in western boundary currents with mean velocities being doubled in some places moreover in comparison to several other recent mdt estimates we find that the new cnes cls09 mdt is in better agreement with independent in situ observations

pacific microplate and the pangea supercontinent in the early to middle jurassic new biostratigraphic data based on radiolarians recovered from deep within the oceanic crustal section of ocean drilling program hole 801c in the western pacific along with existing radiometric information date this oceanic crust as late bajocian early bathonian 170 165 ma the overlying basal sediments at hole 801c are essentially identical in age middle bathonian 164 162 ma to the basal sediments at deep sea drilling program hole 534a in the central atlantic we estimate the time of formation of the pacific plate as 175 170 ma and the time of initial separation of the pangea supercontinent in the central atlantic as 190 180 ma we also identify a time of extensive subduction zone magmatism 175 159 ma at the eastern and western edges of pangea we suggest that the initial plate separation of pangea increased subduction rates at its outer margins and altered the plate boundaries in the pacific superocean leading to formation of the pacific plate

the geochemical cycle of rhenium a reconnaissance rhenium re is one of a suite of elements including uranium and molybdenum that display conservative behavior in seawater and are enriched in anoxic sediments the decay of187re to187os provides a geochronometer in ancient sedimentary rocks and gives rise to os isotopic variations in nature in order to better characterize its sources to seawater re was measured in three major rivers amazon orinoco ganges brahmaputra and some of their tributaries re concentrations span four orders of magnitude from 0 02 to 400 pmol kg with the highest concentrations found in rivers draining black shales in the venezuelan andes mainstream re levels in the three rivers are between 1 and 10 pmol kg with a flux weighted average of 2 3 pmol kg the residence time for re in the oceans is estimated to be 750 000 yr with respect to river inputs re profiles from the atlantic and pacific oceans confirm that re behaves conservatively in seawater with no significant uptake onto particles and or recycling within the water column this is also true in the anoxic water column of the black sea re removal into anoxic sediments occurs at or below the sediment water interface as demonstrated in sediment pore waters from chesapeake bay in oxic sediments re is not cycled with manganese oxides and it is not enriched in very slowly accumulating pelagic sediments with a large hydrogenous iron and manganese component or in manganese nodules burial of re in anoxic sediments which accumulate on 0 3 of the ocean floor removes approximately 50 of the riverine re flux to the oceans hence oceanic re concentrations may be very sensitive to changes in the area of anoxic sedimentation

average circulation seasonal cycle and mesoscale dynamics of the peru current system a modeling approach h isolines the pccc appears to be directly forced by the cyclonic wind stress curl the model is able to produce the upwelling front the cold water tongue which extends toward the equator and the equatorial front as described in the literature model seasonal changes in sst and ssh are compared to measurements for the central pcs model eke is 10 to 30 lower than the observations the model eddy diameters follow a strong equatorward increase the injection length scales derived from the energy spectra strongly correlate to the rossby radius of deformation confirming the predominant role of baroclinic instability at 3 s the model solution appears to switch from a turbulent oceanic regime to an equatorial regime dominated by zonal currents

quantifying and interpreting striations in a subtropical gyre a spectral perspective abstractthe amplitude origin and direction of striations in the subtropical gyre are investigated using simulated and analytical multidimensional spectra striations defined as banded structures in the low frequency motions account for a noticeable percentage of zonal velocity variability in the east north pacific enp 25 42 n 150 130 w and central north pacific cnp 10 22 n 132 e 162 w regions in an eddying global ocean model thus they likely are nonnegligible in mixing and transport processes striations in the enp region are nonzonal and are embedded in the nonzonal gyre flow whereas striations in the cnp region are more zonal as are the mean gyre flows an idealized 1 5 layer model shows the gyre flow partially determines their directions which qualitatively resemble those in the global eddying model in the linear limit structures are quasi stationary frequency 0 linear rossby waves and the gyre flow influences the direction by influencing the nature of the zero rossby wave f

structure of an eddy measured with drifters drifters are used to measure the structure of an eddy on western bank scotian shelf over a 5 day period a regression method that uses both the temporal and spatial structure of flow field observations is presented and used to analyze this eddy the eddy has vorticity 1 9 10 5 s 1 with divergence stretching deformation and shearing deformation smaller by more than an order of magnitude the eddy is centered on the crest of western bank the motion residual to the eddy had a slab like part that moved all points on a plane in a circle without rotation this latter type of motion can cause substantial error when vorticity and other eddy properties are estimated using methods that operate on a single drifter track the eulerian statistics of residual motion show correlations greater than 0 5 are restricted to spatial separations less than 2 km and temporal lags less than 3 h but motion directed along the vector separating two velocity measurements has a significant eulerian correlation for timescales of more than 40 hours and length scales of order 5 km transverse motion is positively correlated over lesser scales much cluster distortion results from subtidal frequency motion that has spatial scales that are seldom coherent over drifter separation scales greater than 2 3 km the long lagrangian timescale is inconsistent with a description of horizontal mixing in terms of an eddy diffusion coefficient rather we might picture drifters being dispersed by slowly evolving narrow streams of current that have larger spatial scales along their axis than across their axis

mapping mesoscale variability of the azores current using topex poseidon and ers 1 altimetry together with hydrographic and lagrangian measurements the semaphore mesoscale air sea experiment was conducted in the azores madeira region from july to november 1993 topex poseidon tip and ers 1 were flying simultaneously at that time the main purposes of this paper are to evaluate the estimation of the oceanic mesoscale circulation from the two different sets of altimetric data tip and ers 1 and to compare the results with in situ measurements provided by the semaphore hydrographic surveys and smface drifters three expendable bathytermograph conductivity temperature depth surveys in a 500 km2 box and a set of 47 lagrangian surface drifters drogued at 150m comparisons are carried out through the maps obtained by objective analysis ti om the four data sets the mapping accuracy of tip ers i tip and ers 1 combined and in situ data is investigated as weii as the sensitivity of the mapping to the correlation functions used there is a good qualitative agreement between altimetric maps and corresponding drifter and hydrographic maps for the three hydrographic surveys correlations are about 0 8 and the regression fit is about 0 6 0 7 the lower values are clue to the smooth climatology used to reference the altimetric maps the correlation for time differences is better with regression lines not significantly different from i especiaily when ers 1 and tip are combined tip mapping is almost as good as ers 1 mapping which was rather unexpected since the ers 1 space time sampling is better suited for the mesoscale this may reflect the fact that the signal mapped by the hydrography and drifters does not contain the high frequency wavenumber components tip and ers 1 combined provide better results although the improvement is not as large as expected probaply for the same reason