observations of the kuroshio s barotropic and baroclinic responses to basin wide wind forcing 1 observations show that the kuroshio in the east china sea ecs kuroshio responds to the large scale wind stress curl field at two time scales it is argued that these two responses are related to barotropic and baroclinic modes that reach the ecs via different waveguides variability in the ecs kuroshio is assessed by comparing satellite altimetry historical hydrography and the pacific decadal oscillation pdo index with the latter used as a proxy for the large scale wind stress curl forcing sea level difference across the ecs kuroshio is positively correlated with pdo at zero lag and negatively correlated at 7 year lag in contrast pycnocline steepness and pdo are uncorrelated at zero lag and negatively correlated at 7 year lag these signals in the ecs kuroshio considered together with wind stress curl anomalies in the open ocean are consistent with a barotropic response to the wind at zero lag the barotropic response is likely forced in the central north pacific by wind stress curl anomalies of opposite sign one of which is centered at ecs latitudes 27 n while the other sits further north this suggests that in general the absolute transport at a given latitude is not simply that predicted by the sverdrup balance along the latitude this is a consequence of waveguides that can steer the barotropic mode across latitude lines in contrast the signals that lag pdo by 7 years are consistent with a baroclinic mode which represents the ocean s time integrated response to the wind stress curl along a single latitude band between 24 n and 27 n

rapid gravitational adjustment of horizontal shear flows the evolution of a horizontal shear layer in the presence of a horizontal density gradient is explored by three dimensional numerical simulations these flows exhibit characteristics of both free shear flows and gravity currents but have complex dynamics due to strong interactions between the turbulent features of each vertical vortices produced by horizontal shear are tilted and stretched by the gravitational adjustment rapidly enhancing vorticity shear intensification at frontal convergences produces high wavenumber vertical vorticity and the slumping of the density interface produces horizontal kelvin helmholtz vortices typical of a gravity current the interaction between these instabilities promotes a rapid transition to three dimensional turbulence the flow development depends on the relative time scales of shear instability and gravitational adjustment described by a parameter gamma where the limits gamma rightarrow infty and gamma rightarrow 0 represent a pure gravity current and a pure mixing layer respectively the growth rate of three dimensional instability and the mixing increase for smaller gamma when gamma is sufficiently small there are two distinct regimes an early period of during which the interface grows rapidly followed by horizontal diffusive growth numerical results are consistent with field observations of tidal separation flows in the haro strait farmer pawlowicz jiang dyn atmos oceans vol 36 2002 pp 43 58 including the magnitude of downwelling vertical currents horizontal scales of surface vortex features and mixing rate

a new magma chamber model based on structural studies in the oman ophiolite abstract structural mapping in the mafic ultramafic transition zone and in the overlying crustal section of the oman ophiolite has revealed the importance of magmatic flow in the formation of layering in the gabbros and the mechanical coupling between this flow and the asthenospheric flow of the underlying peridotites the crustal section near the spreading axis and in particular the magma chamber are fed by two independent melts a dominant gabbroic melt episodically injected from depth and a subordinate wehrlitic crystal mixture produced by compaction of the transition zone layering in the gabbros can be partly produced by tectonic transposition of the gabbroic and wehrlitic mixtures during magmatic flow whatever its origin the layering orientation in the newly created crust does not necessarily reflect its original attitude the final orientation of the layering is determined by the attitude of the magmatic flow plane at the time it was frozen a new magma chamber model is proposed which solves some of the physical difficulties of previous models and accounts for the seismic imaging of magma chambers beneath oceanic ridges

migration of mid ocean ridge volcanic segments the propagation of small offset volcanic spreading centre segments along mid ocean ridge crests may reflect absolute motion of the plate boundary relative to the underlying mesospheric frame such a relationship could be caused by a purely vertical flow of the mantle under spreading centres and would have value in constraining past plate motions from non transform trends generated during along ridge propagation and in linking the major element variability of oceanic crust and upper mantle to the bulk composition and temperatures of mantle ascending under mid ocean ridges

subduction influence on magma supply at the east scotia ridge despite a spreading rate of 65 70 km ma 1 the east scotia ridge has along most of its length a form typically associated with slower rates of sea floor spreading this may be a consequence of cooler than normal mantle upwelling which could be a feature of back arc spreading at the northern end of the ridge recently acquired sonar data show a complex rapidly evolving pattern of extension within 100 km of the south sandwich trench new ridge segments appear to be nucleating at or near the boundary between the south american and scotia sea plates and propagating southwards supplanting older segments the most prominent of these north of 56 30 s has been propagating at a rate of approximately 60 km ma 1 for at least 1 ma and displays a morphology unique on this plate boundary a 40 km long axial high exists at the centre of this segment forming one of the shallowest sections of the east scotia ridge beneath it seismic reflection profiles reveal an axial magma chamber or amc reflector similar to those observed beneath the east pacific rise and valu fa ridge simple calculations indicate the existence here of a narrow 1 km wide body of melt at a depth of approximately 3 km beneath the sea floor from the topographic and seismic data we deduce that a localised mantle melting anomaly lies beneath this segment rates of spreading in the east scotia sea show little variation along axis hence the changes in melt supply are related to the unique tectonic setting in which the south american plate is tearing to the east perhaps allowing mantle flow around the end of the subducting slab volatiles released from the torn plate edge and entrained in the flow are a potential cause of the anomalous melting observed a southward mantle flow may have existed beneath the axis of the east scotia ridge throughout its history

topographic vorticity generation submesoscale instability and vortex street formation in the gulf stream meanders and eddies are routinely observed in the gulf stream along the south atlantic bight we analyze here the instability processes that lead to the formation of submesoscale eddies on the cyclonic side of the gulf stream at the exit of the florida straits using very high resolution realistic simulations the positive relative vorticity and potential vorticity on the cyclonic side of the gulf stream are strongly intensified in the straits due to topographic drag along the continental slope the bottom drag amplifies the cyclonic shear by generating large positive vertical vorticity values within the sloped turbulent bottom boundary layer downstream from the straits the current becomes unstable to horizontal shear instability rolls up and forms a street of submesoscale vortices the vortices expand as they propagate northward along the shelf where they can generate large vertical displacements and enhance cross shelf exchanges

duality of magmatism in the plutonic sequence of the sumail nappe oman abstract detailed field mapping of the crustal sequence in several areas of the sumail ophiolite nappe mainly in the fizh the salahi and the haylayn blocks and comparisons with other well studied areas have shown that the crustal sequence was constructed by two distinct although nearly contemporaneous magmatic series the first a gabbroic series was emplaced during the accretion stage at an oceanic spreading centre which formed the layered gabbro unit the high level isotropic gabbro unit and their by products the sheeted dyke complex and the lower extrusives fine grained homogeneous planar laminated gabbros commonly occur at the top of the layered gabbro sequence in some specific areas wadi haymiliyah and wadi rajmi these are strongly differentiated fe ti rich gabbronorites and norites which coincide with large scale discontinuities within the plutonic sequence interpreted as axial discontinuities of the spreading magma chambers the second series an ultramafic wehrlitic series is locally rooted in the upper mantle i e the impregnated dunitic transition zone this has intruded the whole crustal sequence up to the pillow lavas countless discordant and concordant wehrlitic bodies intruded the plutonic sequence making up 20 40 of it in volume we describe the various settings and forms of these intrusions which were largely underestimated in previous studies we also describe their mineralogy and textures and show with chemical and mineralogical arguments that these bodies evolved as relatively closed systems independently from each other we infer from the study of the contacts that the gabbros were still hot and consolidated just at the moment of the wehrlitic intrusion at the base of the crust however indications of immiscibility between gabbros and wehrlites are common suggesting that both magmatic series were quite contemporaneous the wehrlites are commonly isotropic and may exhibit an internal layering of the dunite wehrlite clinopyroxenite type sometimes appearing at the upper or lower margins of the intrusions in this case the ultramafic layered cumulates show lobate intrusive contacts with the adjacent layered gabbros these plagioclase free ultramafic layered cumulates therefore are not interbedded within the gabbro cumulates but actually belong to the wehrlitic intrusive series picritic dykes radiating from the uppermost intrusions can be traced up to the upper extrusives which are for the main part cogenetic with the wehrlites the time of this second magmatic event coincides with the cessation of the accretion process and with the beginning of the intraoceanic detachment of the ophiolite at the spreading centre we believe that the compressive regime that initiated the detachment acted as an efficient filter press and helped the extraction and ascent of the wehrlitic magmas towards the uppermost levels of the crust

island wakes in deep water abstract density stratification and planetary rotation distinguish three dimensional island wakes significantly from a classical fluid dynamical flow around an obstacle a numerical model is used to study the formation and evolution of flow around an idealized island in deep water i e with vertical island sides and surface intensified stratification and upstream flow focusing on wake instability coherent vortex formation and mesoscale and submesoscale eddy activity in a baseline experiment with strong vorticity generation at the island three types of instability are evident centrifugal barotropic and baroclinic sensitivities are shown to three nondimensional parameters the reynolds number re rossby number ro and burger number bu the dependence on re is similar to the classical wake in its transition to turbulence but in contrast the island wake contains coherent eddies no matter how large the re value when re is large enough the shear layer at the island is so narrow that the ver

two high levels of continental waters in the southern tunisian chotts at about 90 and 150 ka uranium and thorium content and activity ratios were measured on 20 samples 19 molluscs and 1 calcareous concretion from the great chotts in southern tunisia results were studied by the isochron method and by age frequency histograms they suggest that two major flood episodes took place about 150 and 90 ka uranium activity ratios indicate a ground water supply of continental origin in agreement with biological indicators which show large variations in salinity from fresh to marine like conditions the existence of a lacustrine phase radiocarbon dated to 17 40 ka as previously suggested for the northern sahara is highly questionable

grain growth kinetics in olivine aggregates abstract grain growth kinetics were studied in hot pressed fine grained olivine aggregates experimental conditions include pressures of 0 1 mpa 300 mpa and 1 gpa and temperatures of 1473 1573 and 1673 k with or without the presence of water at the initial stage of grain growth growth of larger grains occurs rapidly consuming smaller grains which results in significant pore entrapment almost homogeneous grain size distribution is established in this process after this stage grain size distribution remains almost homogeneous in most cases it was found that the presence of water enhances the grain growth kinetics when the amount of water is limited however when the amount of water is large the water containing pores significantly inhibit the grain boundary migration therefore the enhancement of grain growth due to the presence of water is due to the role of dissolved water in olivine rather than the mass transport through water abnormal grain growth was found in some samples in these cases normal grain growth was inhibited by the presence of a significant amount of water filled pores or grains with significantly larger size than the rest occurred in the starting materials in 0 1 mpa runs significant porosity developed and the grain growth rates were significantly lower than in those at high confining pressures these results show that both water and pores have important effects on grain growth kinetics in olivine when the effects of pores or secondary phases in inhibiting grain growth are unimportant the grain growth rate in olivine is very fast growth to 100 m size will occur in 102 to 103 hours at 1500 k thus fine grain size in olivine will be maintained only for a short geological time unless the grain boundaries are effectively pinned by secondary particles

why the western pacific subtropical high has extended westward since the late 1970s the western pacific subtropical high wpsh is closely related to asian climate previous examination of changes in the wpsh found a westward extension since the late 1970s which has contributed to the inter decadal transition of east asian climate the reason for the westward extension is unknown however the present study suggests that this significant change of wpsh is partly due to the atmosphere s response to the observed indian ocean western pacific iwp warming coordinated by a european union s sixth framework programme understanding the dynamics of the coupled climate system dynamite five agcms were forced by identical idealized sea surface temperature patterns representative of the iwp warming and cooling the results of these numerical experiments suggest that the negative heating in the central and eastern tropical pacific and increased convective heating in the equatorial indian ocean maritime continent associated with iwp warming are in favor of the westward extension of wpsh the sst changes in iwp influences the walker circulation with a subsequent reduction of convections in the tropical central and eastern pacific which then forces an enso gill type response that modulates the wpsh the monsoon diabatic heating mechanism proposed by rodwell and hoskins plays a secondary reinforcing role in the westward extension of wpsh the low level equatorial flank of wpsh is interpreted as a kelvin response to monsoon condensational heating while the intensified poleward flow along the western flank of wpsh is in accord with sverdrup vorticity balance the iwp warming has led to an expansion of the south asian high in the upper troposphere as seen in the reanalysis

evolution of an oceanic anticyclone in the lee of madeira island in situ and remote sensing survey island wakes are areas of a strong eddy activity influencing the availability and transport of organic matter in the ocean which in turn impact biological productivity despite this eddy formation in the lee of north atlantic tropical islands is scarcely documented except for the canary islands moreover the occurrence of anticyclones leeward of madeira has seldom been detected during the summer of 2011 a multiplatform approach combining satellite data with in situ measurements was used to study an anticyclonic eddy generated in the lee of the madeira island the main objective was to confirm recent numerical evidence suggesting that orographically perturbed winds can induce anticyclonic eddies leeward of madeira particularly during summer months the high resolution sampling of the eddy s interior shows a strong downwelling of 100 m of the isopycnal layer below the mixed layer typical of intrathermocline eddies the 25 km radius of this anticyclonic structure exceeds the local deformation radius by a factor of 2 the vortex rossby number remained moderate ro 0 26 even if the relative core vorticity reached a finite value f 0 7 the occurrence of strong trade winds 10 15 m s 1 prior to the detection of the first surface eddy signatures july 2011 concurrent with opposite flowing geostrophic currents shows that the orographic wind forcing is the main mechanism for generating this mesoscale long lived eddy after leaving the shelter of the island the eddy traveled northwesterly following a perpendicular net ekman transport pathway at a speed of 5 km d for at least 2 months an interaction with a cyclonic partner generated in the area helped precipitate the northward trajectory this study presents the first clear evidence of a wind induced mesoscale anticyclone in the lee of madeira

friction frontogenesis and the stratification of the surface mixed layer the generation and destruction of stratification in the surface mixed layer of the ocean is understood to result from vertical turbulent transport of buoyancy and momentum driven by air sea fluxes and stresses in this paper it is shown that the magnitude and penetration of vertical fluxes are strongly modified by horizontal gradients in buoyancy and momentum a classic example is the strong restratification resulting from frontogenesis in regions of confluent flow frictional forces acting on a baroclinic current either imposed externally by a wind stress or caused by the spindown of the current itself also modify the stratification by driving ekman flows that differentially advect density ekman flow induced during spindown always tends to restratify the fluid while wind driven ekman currents will restratify or destratify the mixed layer if the wind stress has a component up or down front i e directed against or with the geostrophic shear respectively scalings are constructed for the relative importance of friction versus frontogenesis in the restratification of the mixed layer and are tested using numerical experiments of mixed layer fronts forced by both winds and a strain field the scalings suggest and the numerical experiments confirm that for wind stress magnitudes mixed layer depths and cross front density gradients typical of the ocean wind induced friction often dominates frontogenesis in the modification of the stratification of the upper ocean the experiments reveal that wind induced destratification is weaker in magnitude than restratification because the stratification generated by up front winds confines the turbulent stress to a depth shallower than the ekman layer which enhances the frictional force ekman flow and differential advection of density frictional destratification is further reduced over restratification because the stress associated with the geostrophic shear at the surface tends to compensate a down front wind stress

rapid crustal accretion and magma assimilation in the oman u a e ophiolite high precision u pb zircon geochronology of the gabbroic crust 1 new high precision u pb zircon geochronology from the oman united arab emirates u a e ophiolite provides insight into the timing and duration of magmatism and the tectonic setting during formation of the lower crust the new data come from a well preserved and exposed crustal section in the center of the wadi tayin massif single grain and grain fragment 206pb 238u dates from upper level gabbros tonalites trondhjemites and gabbroic pegmatites corrected for initial th exclusion range from 112 55 0 21 to 95 50 0 17 ma with most data clustered between 96 40 0 17 to 95 50 0 17 ma zircon dates from upper level gabbros are most consistent with the ophiolite forming at a fast spreading ridge with half rates of 50 100 km ma dates from tonalites trondhjemites and from a gabbroic pegmatite associated with a wehrlite intrusion overlap with dates from adjacent upper level gabbros suggesting that any age differences between these three magmatic series are smaller than the analytical uncertainties or intrasample variability in the dates three of the dated upper level gabbros and a single gabbroic pegmatite from the base of the crust have 1 ma intrasample variability in single grain dates suggesting assimilation of older crust during the formation or crystallization of the magmas whole rock end t of seven samples including the upper level gabbros with variable zircon dates have tightly clustered initial values ranging from end 96 ma 7 59 0 23 to 8 28 0 31 the end values are similar to those from other gabbros within the ophiolite suggesting that any assimilated material had a similar isotopic composition to primitive basaltic magmas the new dates suggest that the studied section formed at a fast spreading mid ocean ridge between 96 4 95 5 ma the large intrasample variability in zircon dates in some samples is unexpected in this setting and may be related to propagation of a younger ridge into older oceanic lithosphere

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

east pacific rise from siqueiros to orozco fracture zones along strike continuity of axial neovolcanic zone and structure and evolution of overlapping spreading centers we have used the sea beam multibeam echo sounding system to survey the east pacific rise epr from 8 20 n to 18 30 n obtaining complete coverage of the epr axial neovolcanic zone and all intervening transform faults here we focus on the epr neovolcanic zone and the definition of overlapping spreading centers ocs s between the orozco and siqueiros transform faults the neovolcanic zone is narrow 0 5 2 0 km and continuous along strike and occurs within and near a strike continuous axial summit graben the neovolcanic zone and summit graben reside along the crest of a volcanic axial high which is 2 10 km wide and which continues uninterrupted along strike for 40 140 km within 20 50 km of an intersection with a transform fault the axial neovolcanic zone narrows and deepens and within only 3 6 km of the intersection the neovolcanic zone turns sharply into the transform valley at seven locations between the siqueiros and orozco transform faults the axial neovolcanic zone is discontinuous and is laterally offset a short distance 1 15 km in contrast with a classic ridge transform ridge plate boundary however offset rise terminations overlap each other by a distance approximately 3 times greater than their offset they curve toward each other and often one merges into the other along strike separating the osc s is an elliptical overlap basin up to 600 m deep whose long axis is subparallel to the adjacent spreading centers the overlap basin is characterized by volcanic constructional edifices a key difference between these offsets and small transform faults in the atlantic is that there are no transform fault structures in the overlap basin which link the offset rise axes a continuous axial depth profile reveals a long wavelength 20 60 km undulation of the rise axis which may be associated with variations in the magmatic budget along strike the lowest points in the axial depth profile occur near transform faults and at osc s suggesting that these features are associated with along strike minima in the magmatic budget we suggest that major phases of volcanic activity propagate episodically along the axis away from centers of magmatic inflation and that osc s develop where magmatic pulses fail to meet due to misalignment of fracture systems sinuous bends in the rise axis or other heterogeneities transform faults fail to develop on fast spreading centers where the lateral offsets are small 15 km because the lithosphere is too thin and weak to maintain a classic rigid plate ridge transform fault pattern the osc geometry is unstable and evolves rapidly and the overlapping rises may propagate at rates faster than the local spreading rate one of the two osc s prevails while the other is abandoned while the locations of osc s may not be fixed relative to the rise axis they may tend to recur near the same place creating scars in older lithosphere which resemble fracture zones but whose fine scale structure is quite different there is excellent agreement between the observed structure of osc s and laboratory studies of osc s using wax models photoelastic studies of overlapping cracks and boundary element modeling of overlapping cracks seismic refraction and reflection near two osc s suggests that large offset osc s have separate magma chambers beneath the offset rise axes while small offset osc s may share a single axial magma chamber three dimensional inversion of magnetic anomalies suggests that significant petrologic anomalies may occur near some osc tips waxing and waning of overlapping magma chambers may give rise to the eruption of highly fractionated feti basalts and associated magnetic anomalies

investigation of a vine matthews magnetic lineation from a submersible the source and character of marine magnetic anomalies we report here the first attempt to map directly the boundary of a vine matthews magnetic stripe on the seafloor our objectives are to study the processes of oceanic crustal accretion as recorded in the reversal transition zone and to investigate the formation of the magnetic source of vine matthews magnetic anomalies our deep tow and alvin based magnetic studies focus on the matuyama brunhes reversal transition on the flanks of the east pacific rise near 21 n while the sea level magnetic anomalies are less than average in clarity for the east pacific rise a three dimensional inversion of deep tow data reveals a sharp strike linear polarity transition less than 1 8 km wide macdonald et al 1980a these measurements have been augmented by mounting a vertical magnetic gradiometer on alvin and making 280 reliable polarity determinations along and across the polarity transition zone even on long traverses across both sides of the boundary we find that nearly every magnetic target has the correct polarity i e the same polarity as the regional magnetic lineation this homogeneity in polarity of the magnetic lineations is surprising the magnetic polarity transition in the outcropping volcanic section is sharp and linear along strike delineated in some cases by a clear geologic contact of opposing flow fronts of different ages several weakly magnetized outcrops mapped within the transition zone may have erupted during the time in which the geomagnetic field was reversing the reversal boundary mapped on the seafloor from alvin is displaced 250 m to 500 m nw away from the spreading axis relative to the position of the average boundary as derived from inversion of the deep tow and sea level magnetic data this offset provides a means for estimating the spillover of lava flows away from the spreading axis during the time the crust was formed the combination of deep tow and alvin measurements suggests that circa 0 7 m y ago the crustal accretion zone magnetized volcanic intrusive and plutonic rocks was 2000 2800 m wide while the zone of recent volcanism alone was only 1000 2000 m wide the determination for the most recent reversal agrees well with submersible observations at the present spreading center where the zone of recent volcanism neovolcanic zone varies between 600 and 2000 m in width this very orderly picture for the formation of magnetic lineations and crustal accretion processes appears to conflict with complex deep sea drilling project dsdp magnetic results from the atlantic we suggest that the crustal generating processes and resulting magnetic structure vary significantly with spreading rate on the slow spreading mid atlantic ridge major episodes of volcanism are likely to be infrequent 104 years the magma chamber may be non steady state and the neovolcanic zone shifts or varies in width considerably this sporadic start and stop spreading process will contribute to a highly heterogeneous and complex crustal and magnetic structure as seen in dsdp holes in addition significant faulting and tilting may disrupt slow spreading crust for intermediate to fast spreading centers more frequent volcanism 50 600 years a nearly steady state magma chamber and a narrow stable neovolcanic zone will create a less complex magnetic and crustal structure both as seen from alvin and as inferred from clear sea level magnetic anomalies in the pacific

the generation and propagation of internal solitary waves in the south china sea 1 the internal wave field in the real time numerical simulation at the naval research laboratory is analyzed during april may 2007 a period of intensive field observations in the northern south china sea internal solitary waves are detected in the plots of the surface baroclinic velocity and depth integrated energy flux in each diurnal cycle an internal wave crest with eastward surface velocity arrives at a location west of the luzon strait first and is followed by two internal wave troughs of westward surface velocity in agreement with the arrival of a type b and then a type a internal solitary wave described in the literature sources of the b wave and a wave are consistent with the generation by eastward tidal currents on the western and eastern ridges in the luzon strait respectively during neap tide a b wave and an a wave switch their daily arrival times to maintain the arrival sequence of an a wave after a b wave internal waves arriving at a mooring location at the same time each day are b waves during the neap tide and a waves during the first half of the spring tide otherwise both a waves and b waves have a 1 h delay each day in their daily arrivals classification of the internal wave types based on generation gives a coherent pattern of internal wave propagation from the generation region to the continental margin in the south china sea the propagation speeds of both waves are higher than that of linear internal waves

segmentation at a fossil spreading axis the plutonic sequence of the wadi haymiliyah area haylayn block sumail nappe oman abstract wadi haymiliyah in the central part of the haylayn block offers a splendid continuous section across the crustal sequence of the sumail ophiolite the plutonic sequence of this area presents several specific features of great interest for the understanding of the structure and evolution of this ophiolite the petrological moho and the whole plutonic sequence display a subvertical attitude parallel to the mean dyke complex orientation high temperature folding occurred in the mantle sequence and in the lower crust whereas the upper crust remained unfolded and behaved as a rigid slab during this deformation resulting in a tectonic decoupling between lower and upper crust in the gabbro cumulate sequence a remarkable large scale curvature of the magmatic structures layering and lamination planes whose axis is totally discordant with the regional folds axes is interpreted as a primary magmatic feature indicating the southern ending of a magma chamber the lower crust about 2 km thick consists of a primary layered gabbroic sequence consisting of rhythmic mineral graded layers from several metres to several hundred metres thick syndepositional structures such as oblique stratification microslumps eroding mini channels and small normal faults are widespread the mineralogical composition modal variations and cryptic evolution of the whole layered sequence are described both at the megascale and on the simple cyclic scale the data support a model of crystallization of the layered sequence by open system fractionation at the floor and sides of a periodically replenished steady state magma chamber a unique feature of this cumulate sequence is the ubiquitous presence of orthopyroxene throughout the whole cumulate pile this is very unusual in the sumail crust with the exception of the wadi rajmi section in the fizh block two huge plagioclase free dunite wehrlite laccoliths about 300 m thick and numerous ultramafic sills and mushroom like bodies intrude the base of the layered sequence these ultramafic intrusions exhibit in places an internal layering and dunitic differentiation products they have sharp sinuous and lobate contacts with the gabbros which were still hot and probably not entirely consolidated at the moment of the intrusion the mineral compositions of these intrusions are much more primitive than those of the adjacent gabbros higher in the plutonic section the layered gabbros are overlain by 1 km of fine grained non layered planar laminated gabbronorites characterized by the abundance of pleochroic cumulus hypersthene the disappearance of olivine and the development of fe ti oxides and amphibole as post cumulus phases numerous occurrences of concordant coarse grained layered gabbros occur in this unit which is characterized also by a dense net of highly residual dioritic to tonalitic veins resulting in a huge magmatic breccia in the uppermost few hundred metres where the gabbronorites are brecciated by the acidic rocks hydrothermal veins are also extremely abundant in this unit which coincides with the core of the large scale curvature this unit comprising unusually fractionated rocks is interpreted as resulting from the evolution of the haymiliyah magma chamber towards a closed system fractionation due to the cutting off of source supply our interpretation of both structural and petrological data may be summarized by the following major points 1 1 the haymailiyah magma chamber was located at the southern tip of a spreading cell and was cut off from the magma supply at the end of its evolution either vertically when accretion slowed down or horizontally when it became isolated from the central part of the spreading segment we suggest that orthopyroxene bearing cumulates should be looked for all along the sumail nappe and used as markers of segmentation 2 2 early high temperature compressional deformation took place in both the mantle and crust before the intraoceanic detachment of the ophiolite the development of this compression regime activated filter pressing processes and in particular helped with the extraction of wehrlitic magmas from the upper mantle and their ascent to the uppermost levels of the crust

overlapping spreading centres 3 d inversion of the magnetic field at 9 03 n on the east pacific rise summary overlapping spreading centres oscs represent a new type of plate boundary interaction in which en echelon rise segments overlap significantly and are not joined by a transform fault a three dimensional fourier inversion of the magnetic field was performed on an overlapping spreading centre to remove the effects of topography and ridge orientation a magnetic high exists at the tip of one of the two ridge segments forward modelling suggests that the anomalous magnetic field cannot be attributed to the effects of topography alone the inversion reveals the existence of a magnetization high at the tip of the eastern spreading centre maximum magnetization values are consistent with ones obtained in other high amplitude zones in the pacific as well as with the measured magnetization of samples dredged in the same areas we suggest that the magnetization high over the eastern ridge tip of the 9 03 n osc is associated with highly evolved basalts enriched in iron and titanium such enrichment may be caused by enhanced crystal fractionation within an axial magma chamber which is intermittent and occasionally freezes as the eastern spreading axis propagates into older lithosphere

sub mesoscale ocean vortex trains in the luzon strait 1 this study uses the argos satellite tracked surface drifter trajectory data and envisat european satellite asar advanced synthetic aperture radar images to illustrate the ocean vortex trains ovt in the luzon strait two cases that occurred in the northwest of babuyan island are observed the first train of three cyclonic vortices showed up on drifter trajectories from 20 to 20 5 n and from 120 to 121 e and the second consisting of five pairs of cyclonic anticyclonic vortices occurred on the upstream side of the first one from 19 5 to 20 0 n and from 121 0 to 122 0 e and showed up on the asar images acquired on 19 november 2006 the total length of the vortex train axis reaches about 250 km all vortices propagate northwestward 315 tn the mean angular velocity is 2 07 0 18 10 5 s 1 theoretical models of ocean vortex radar image derived from radar imaging theories are used to extract dynamical parameters from asar imagery signatures which include the distance between two consecutive vortices and that between two rows of vortices of 22 6 1 9 km and 8 2 1 2 km respectively the maximum rotational velocity radius as 4 70 km and the vortex rotational angular velocity 3 10 5s 1 dynamical analyses give the mean velocity of the current of 0 65 ms 1 and the propagation velocity of the vortex 0 58 ms 1 the vortex shedding rate is estimated as 2 57 10 5 s 1 the reynolds number is estimated as 50 to 500 for the individual vortex and the vortex train the rossby numbers are o 0 4 and o 0 5 respectively implying that both vortex and vortex train observed in the luzon strait have a sub mesoscale nature this study also reveals a strong current with an average surface current velocity of around 0 7 ms 1 and the direction of around 315 tn flowing directly from the pacific to scs passing through the southern luzon strait the mean flow velocity can be calculated using methods developed in this study and ovt dynamical models this information may provide more insight to the circulation systems in the area including the origin of kuroshio

trains of large kelvin helmholtz billows observed in the kuroshio above a seamount trains of large kelvin helmholtz kh billows within the kuroshio current at 230 m depth off southeastern taiwan and above a seamount were observed by shipboard instruments the trains of large kh billows were present in a strong shear band along the 0 55 m s 1 isotach within the kuroshio core they are presumably produced by flow interactions with the rapidly changing topography each individual billow resembling a cat s eye had a horizontal length scale of 200 m a vertical scale of 100 m and a timescale of 7 min near the local buoyancy frequency overturns were observed frequently in the billow cores and the upper eyelids the turbulent kinetic energy dissipation rates estimated using the thorpe scale had an average value of o 10 4 w kg 1 and a maximum value of o 10 3 w kg 1 the turbulence mixing induced by the kh billows may exchange kuroshio water with the surrounding water masses

eddy kuroshio interactions local and remote effects quasi geostrophic mesoscale eddies regularly impinge on the kuroshio in the western north pacific but the processes underlying the evolution of these eddy kuroshio interactions have not yet been thoroughly investigated in the literature here this interaction is examined with results from a semi idealized three dimensional numerical model and observations from four pressure sensor equipped inverted echo sounders piess in a zonal section east of taiwan and satellite altimeters both the observations and numerical simulations suggest that during the interaction of a cyclonic eddy with the kuroshio the circular eddy is deformed into an elliptic shape with the major axis in the northwest southeast direction before being dissipated the poleward velocity and associated kuroshio transport decrease and the sea level and pycnocline slopes across the kuroshio weaken in contrast for an anticyclonic eddy during the eddy kuroshio interaction variations in the velocity sea level and isopycnal depth are reversed the circular eddy is also deformed to an ellipse but with the major axis parallel to the kuroshio the model results also demonstrate that the velocity field is modified first and consequently the ssh and isopycnal depth evolve during the interaction furthermore due to the combined effect of impingement latitude and realistic topography some eddy kuroshio interactions east of taiwan are found to have remote effects both in the luzon strait and on the east china sea shelf northeast of taiwan

monsoons and the dynamics of deserts the existence of subtropical deserts such as the sahara has often been attributed to the annual mean zonal mean hadley circulation which shows strong descent in the subtropics however the zonal mean hadley circulation shows considerable evolution over the course of the year with very strong subtropical descent during winter but practically no zonal mean subtropical descent during summer when rainfall over the eastern sahara and the mediterranean is least charney 1975 proposed a biosphere albedo feedback mechanism whereby local anthropogenic effects related to over grazing could affect the radiative balance enhancing summertime diabatic descent and leading to desertification of the subtropics in general the present study which uses an idealized model suggests a monsoon desert mechanism for desertification whereby remote diabatic heating in the asian monsoon region can induce a rossby wave pattern to the west integral with the rossby wave solution is a warm thermal structure that interacts with air on the southern flank of the mid latitude westerlies causing it to descend this adiabatic descent is localized over the eastern sahara and mediterranean and over the kyzylkum desert to the south east of the aral sea by the mountains of north africa and south west asia trajectories indicate that the monsoon desert mechanism does not represent a simple walker type overturning cell instead the descending air is seen to be mainly of mid latitude origin it is speculated that the monsoon forced adiabatic descent may result in clear air and therefore a local diabatic enhancement which effectively doubles the strength of descent with this mechanism desertification can be forced by remote changes in monsoon strength rather than by local effects this conclusion is supported by the observed dramatic strengthening of descent over the mediterranean and east sahara during the onset of the asian monsoon and on the longer timescale by relating prehistoric lake levels to milankovitch monsoon forcing the latter may help to explain the perceived discrepancies between the palaeoclimate of the eastern sahara and the strength of a tropic wide monsoon the monsoon desert mechanism may not be confined to the asian monsoon alone and the existence of other monsoon climate regions over the globe may in a similar way explain the observed summertime strengthening of the oceanic sub tropical anticyclones and the existence of western continental deserts and mediterranean type climate regions

uranium series dated authigenic carbonates and acheulian sites in southern egypt field investigations in southern egypt have yielded acheulian artifacts in situ in authigenic carbonate deposits caco 3 cemented alluvium along the edges of nowaggraded paleovalleys wadi arid and wadi safsaf uranium series dating of 25 carbonate samples from various localities as far apart as 70 kilometers indicates that widespread carbonate deposition occurred about 45 141 and 212 ka thousand years ago most of the carbonate appears to have been precipitated from groundwater which suggests that these three episodes of deposition may be related to late pleistocene humid climates that facilitated human settlement in this now hyperarid region carbonate cements from sediments containing acheulian artifacts provide a minimum age of 212 ka for early occupation of the paleovalleys

a last interglacial fauna from the eastern sahara abstract recent work on the middle paleolithic at bir tarfawi in the hyperarid eastern sahara

the death of an accretion zone as evidenced by the magmatic history of the sumail ophiolite oman abstract the ophiolitic crustal sequence of the salahi block in the northern part of oman shows a complex magmatic history the oceanic accretion episode led to the formation of a main plutonic sequence consisting of layered cumulates isotropic gabbros a sheeted dike complex and a first tholeiitic lava series v1 depleted in compatible elements the second magmatic episode immediately following the accretion stage is illustrated by predominantly ultrabasic intrusions crosscutting the main plutonic sequence and by a second volcanic suite v2 directly linked as can be seen from field evidence to more differentiated high level intrusive plutons this volcanic unit includes very primitive members and is in general characterized by depletion in incompatible elements a third volcanic event v3 exhibiting a transitional character enriched in lree s caps the ophiolite these v3 lavas are separated from the v2 unit by a 15 m thick pelagic sedimentary section a geotectonic evolution of the sumail ophiolite is proposed on the basis of field mineralogical and geochemical data after the oceanic accretion phase that gave birth to the main ophiolitic sequence a second stage melting of the upper mantle is suggested to explain the genesis of the second magmatic episode such a model accounts well for the depleted character of the v2 lavas the compression linked to the beginning of the intra oceanic detachment allows the extraction from the mantle of these second stage melts which are then emplaced in the crust and partly extruded the v3 volcanism postdates the intraoceanic detachment of the ophiolite but precedes its obduction onto the arabian continental margin it is interpreted as an intraplate seamount type magmatism

structure and petrology of peridotites clues to their geodynamic environment the first part of this paper is a review on the main mineralogical petrological and structural criteria which can be used to unravel the history of the various types of mantle peridotites met at the earth s surface these criteria are applied in the second part to show that most peridotites share a common history which is that of an asthenospheric uprise followed by specific fates corresponding to their lithospheric history the unifying concept is that of adiabatic ascent rate related to rifting and spreading rates rates lower than 0 5 cm yr in continental graben correspond to departure from adiabatic conditions at depths greater than 30 km this inhibits further melt extraction with as consequences a limited melt extraction and comparatively fertile spinel lherzolites as residue higher rates probably not exceeding 1 cm yr correspond to oceanic rifts with the main melt extraction completed around 15 km generating a thin oceanic crust and plagioclase lherzolites as residue finally rates greater than 1 2 cm yr correspond to oceanic ridges with melt being extracted at moho depth thus generating a 6 km thick crust and leaving depleted harzburgites as residue thus examination of the peridotite type and associated crustal formations give some clue to trace back the environment of origin this conclusion must however be tempered by the fact that the spreading rate envisioned here as the principal controlling parameter can change with space and time in a given environment mantle diapirism rifting seafloor spreading crust generation

overlapping rift zones at the 5 5 s offset of the east pacific rise a seabeam and magnetometer survey of the pacific nazca plate boundary around 5 5 s mapped a nontransform offset whose geology and kinematics seem typical of a whole class of structures formed where fast spreading rises are laterally offset for distances less than the width of a subaxial magma chamber though the spreading center is abruptly displaced by 15 km right laterally there is no trace of strike slip faulting instead the ends of two 100 km long axial volcanic ridges veer 15 toward each other and overlap for more than 20 km in this overlapping region between 5 22 s and 5 32 s accretion of the upper oceanic crust by dike injection and eruption is partitioned between two adjacent and parallel rift zones with oblique and one sided spreading a continuous but dog legged magma chamber is inferred to underlie both rift zones and an intervening 9 km wide volcano studded basin a strong magnetic signature from the crust which accreted around this oblique chamber identifies the trace of the offset on the adjacent rise flank in the past 0 5 106 years the southern axial ridge has propagated north at 40 mm yr 55 of the spreading half rate

kuroshio induced wake in the lee of green island off taiwan 1 the wake of green island was investigated in the alongshore flowing kuroshio east of taiwan where current speeds range from 1 to 1 5 ms 1 vertical profiling with shipboard lowered acoustic doppler current profiler and conductivity temperature depth profiler revealed sizable anomalies in flow and water characteristics in the lee of green island two different stages of wake evolution were observed from two shipboard surveys in the first stage a recirculation developed leeward of the island followed by a wavy wave like tail that resembled a weak vortex street in the second stage a cold eddy probably originating from the leeward side of the island showed up 14 km downstream of the island the wake water was colder saltier higher in chlorophyll a concentration and produced isopycnal doming up to 60 m in the recirculation area the relative vorticity either positive or negative was 10 times of planetary vorticity and the horizontal divergence or convergence was o 10 4 s 1 on average flow divergence and convergence in the wake were expected to form upwelling and downwelling zones producing a vertical circulation that vertically displaces isotherms high inverse richardson number produced by strong vertical shear of horizontal currents was associated with intense overturning events in the wake high vertical shear of horizontal currents drove the mixing the dissipation rate of turbulent kinetic energy in the overturn regions is o 10 7 10 5 w kg 1 the corresponding eddy diffusivity is o 10 3 10 1 m2 s 1 the wake water properties are vertically diffused via upwelling and turbulence and can be delivered downstream through eddy shedding or advection the extent of downstream influence remains to be investigated

complexity of the crustal sequence in the northern oman ophiolite fizh and southern aswad blocks the effect of early slicing abstract on the basis of detailed mapping of the fizh and southern aswad blocks in northern oman the complexity of the crustal sequence is shown lateral facies variations are at least as important as vertical ones and no section can be reconstructed as a stratigraphic section sharp and transitional moho boundaries alternate over a distance of 10 km the important residual mantle crust transition zones are root zones for intrusive wehrlites and cause doming in the moho fractures facilitating the penetration of seawater in the upper crustal parts dikes and lavas show intense hydrothermal alteration and can be related to shear zones in the lower parts of the crustal sequence and occasionally be followed into the peridotites intrusive wehrlites reach as high into the crust as the base of the dike complex and occasionally even the lavas they follow fault zones or n s to nw se directions recrystallization of isotropic gabbro occurs in the vicinity of the wehrlites the geometry observed is not compatible with an oceanic transform zone it may indicate the location of an overlapping spreading centre although too little is known of the deeper structures to confirm this there was certainly an important reaction to the early compression at the oceanic spreading ridge prior to final consolidation confirming an earlier model of the setting

changes in direction of seafloor spreading revisited rotation and propagation have both been proposed as mechanisms by which spreading centers can reorient following changes in direction of seafloor spreading the rotation hypothesis predicts a smooth asymmetric fanning of magnetic anomaly and abyssal hill orientations whereas the propagation hypothesis predicts that the orientation changes will occur at abrupt discontinuities which are either failed rifts or pseudofaults to test between these hypotheses we conducted a detailed sea beam magnetics seismic reflection survey of the area where the direction of pacific farallon spreading changed between anomalies 24 and 22 just north of the major bend in the surveyor fracture zone the change in trend of seafloor fabric is abrupt supporting the rift propagation hypothesis for spreading center reorientation

downstream evolution of the kuroshio s time varying transport and velocity structure observations from two companion field programs origins of the kuroshio and mindanao currents okmc and observations of kuroshio transport variability oktv are used here to examine the kuroshio s temporal and spatial evolution kuroshio strength and velocity structure were measured between june 2012 and november 2014 with pressure sensor equipped inverted echo sounders piess and upward looking acoustic doppler current profilers adcps deployed across the current northeast of luzon philippines and east of taiwan with an eight month overlap in the two arrays deployment periods the time mean net i e integrated from the surface to the bottom absolute transport increases downstream from 7 3 sv 4 4 sv standard error northeast of luzon to 13 7 sv 3 6 sv east of taiwan the observed downstream increase is consistent with the return flow predicted by the simple sverdrup relation and the mean wind stress curl field over the north pacific despite the complicated bathymetry and gaps along the north pacific western boundary northeast of luzon the kuroshio bounded by the 0 m s 1 isotach is shallower than 750 dbar while east of taiwan areas of positive flow reach to the seafloor 3000 m both arrays indicate a deep counterflow beneath the poleward flowing kuroshio 10 3 2 3 sv by luzon and 12 5 1 2 sv east of taiwan time varying transports and velocities indicate the strong influence at both sections of westward propagating eddies from the ocean interior topography associated with the ridges east of taiwan also influences the mean and time varying velocity structure there this article is protected by copyright all rights reserved

some simple analytical solutions to the problem of forced equatorial long waves this paper describes some simple time dependent analytical solutions to the problem of a sudden switch on of heating localized about the equator the equations used are the shallow water equations on the plane under the long wave approximation it is shown that with a reasonable amount of dissipation it can take several days for a steady state response to be established in the early stages the circulation differs considerably from that of the steady state the long time scale for the adjustment process has implications in numerical weather prediction since it implies that if the initial data are not in balance with the model s forcing it may take several days for a balance to be established by which time the quasi stationary tropical flow may have been irrevocably changed

submesoscale cold filaments in the gulf stream abstracta set of realistic very high resolution simulations is made for the gulf stream region using the oceanic model regional oceanic modeling system roms to study the life cycle of the intense submesoscale cold filaments that form on the subtropical gyre interior wall of the gulf stream the surface buoyancy gradients and ageostrophic secondary circulations intensify in response to the mesoscale strain field as predicted by the theory of filamentogenesis it can be understood in terms of a dual frontogenetic process along the lines understood for a single front there is however a stronger secondary circulation due to the amplification at the center of a cold filament filament dynamics in the presence of a mixed layer are not adequately described by the classical thermal wind balance the effect of vertical mixing of momentum due to turbulence in the surface layer is of the same order of magnitude as the pressure gradient and coriolis force and contributes equally to a so called turbulent therm

correlated oceanic and continental records demonstrate past climate and hydrology of north africa 0 140 ka analysis of pollen and dinocysts in a core from the eastern atlantic core v22 196 lat 13 degree 50 n long 18 degree 57 w provides the first continuous record of paleoclimate and paleohydrology for the latest climatic cycle during interglacial intervals increases in pollen input from humid vegetation zones are correlative with high dinocyst productivity this data shows a close coincidence of northward extensions of sudanian and guinean vegetation zones in north africa and increases in fresh water input into the atlantic direct evidence indicates positive hydroclimatic phases at 135 125 103 80 47 and 12 10 ka coincident with widespread continental records of high lake levels that confirm the validity of the u th chronology

summer circulation and temperature structure of lake kinneret a three dimensional lake model driven by wind stress and heat flux fields derived from an atmospheric model is applied to lake kinneret israel the summer wind field over the lake has a strong diurnal and large spatial variation due to complex terrain surrounding the lake the sharp temperature contrast between the arid land and the lake and due to the penetration of the mediterranean sea breeze msb into the lake area the daily mean wind curl field which is predominantly determined by the penetration of the msb is responsible for the generation of three lake gyres one of them dominates most of the lake and rotates counterclockwise it is flanked to the north and to the south by two smaller ones that rotate clockwise during the summer the diurnal variation of the wind over the lake is repeated daily due to consistent forcing conditions during that season numerical tests show that the rectified flow induced by the diurnal winds plays a minor role in the lake circulation the thermocline oscillation which was believed to be the free propagation of internal kelvin waves mainly responds to the surface elevation set up by the time dependent winds and it appears that no systematic counterclockwise propagating waves with large thermocline displacements exist in the lake the intense msb over the lake in the late afternoon pushes the heated surface water toward the east forcing the deep cooler water to be advected westward and creating strong mixing over the shallow western shore this results in higher temperature off the eastern shore and lower temperature off the western shore however a strong mean flow is constantly eliminating the temperature difference by counterclockwise transfer of the western cooler water eastward the results are in good agreement with available observations

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

the east ridge system 28 5 32 s east pacific rise implications for overlapping spreading center development abstract we report here on geophysical data from the east ridge and surrounding areas of the large offset overlapping spreading centers oscs that accommodate pacific nazca opening between 28 5 and 32 s the east ridge overlaps and is offset from the west ridge system by 120 km forming the largest known pair of oscs in this area spreading rates reach the fastest currently active on earth of 149 mm yr although the east ridge is composed of 4 morphologically defined segments separated by 3 small oscs other geophysical characteristics imply 1 upwelling segment all the active ridge segments in this area including the propagating tips of the east and west ridges form relative topographic highs with respect to the flanking sea floor however identified abandoned ridge tips form deeps we interpret these data in terms of a model in which the propagating segment represents an overshoot of a surficial rupture of the brittle lithospheric layer only partially coupled to the diverging flow of a more broadly distributed ductile deformation zone ddz surrounding the steady state ridges and crossing the offset between the oscs the topographic high of the propagating segment may be maintained primarily by along axis melt migration from the stable spreading segments rather than by direct upwelling from beneath the ridge the large overlapping ridges are inherently unstable and continued extension causes the overlapping axes to become offset from the stably spreading segments cut off from the supply of melt and replaced by a new set the failed rift tips for a period of time overlie the broad ddz and preferentially undergo continued extension and subsidence the ddz surrounding the ridge axes may be very broad in this area because of the very fast spreading rate creating a very thin lithosphere susceptible to perturbation by relatively small mantle heterogeneities advected near the ridge axis leading to the formation of the smaller oscs observed

mixed layer instabilities and restratification abstract the restratification of the oceanic surface mixed layer that results from lateral gradients in the surface density field is studied the lateral gradients are shown to be unstable to ageostrophic baroclinic instabilities and slump from the horizontal to the vertical these instabilities which are referred to as mixed layer instabilities mlis differ from instabilities in the ocean interior because of the weak surface stratification spatial scales are o 1 10 km and growth time scales are on the order of a day linear stability analysis and fully nonlinear simulations are used to study mlis and their impact on mixed layer restratification the main result is that mlis are a leading order process in the ml heat budget acting to constantly restratify the surface ocean climate and regional ocean models do not resolve the scales associated with mlis and are likely to underestimate the rate of ml restratification and consequently suffer from a bias in sea surface temperatures and ml depths in a

a model simulation of the summer circulation from the eastern mediterranean past lake kinneret in the jordan valley abstract a model is described for the representation and study of air flow from the eastern mediterranean on the west side of the model s domain past lake kinneret in the jordan valley about 210 m below msl and beyond to the east on the east side of the model in the summer months the primary purpose of the model is to improve our understanding of two striking features of the meteorology of the lake area in summer 1 the almost daily development of strong winds and an associated storm on the lake in the afternoon and 2 a nearly 50 drop in wind speed across the lake from the western to the eastern shore over a distance of only 10 km again in the afternoon the model is two dimensional it uses the sigma coordinate system and is thus hydrostatic the horizontal grid distance is 4 km it has 10 levels in the vertical between the surface and the top at 750 mb the first level in the vertical is 10 m above the surface and each of the higher levels is at an attitude that is approximately twice the

how islands stir and fertilize the upper ocean 1 large differences between the upstream and lee side flow characteristics of an isolated island in the kuroshio have been identified from a three dimensional velocity survey and from vertical profiles of fine and micro structure in the island wake the relative vorticity is o 10f the horizontal current divergence indicates upwelling of o 0 01 m s 1 and the rate of dissipation of kinetic energy is o 10 4 w kg 1 isopycnal surfaces shoal by 60 m on the lee side and surface nitrate concentration increases seven fold flow blockage by the island and the izu ogasawara ridge on its flanks induces horizontal and vertical flow separation the associated lateral and vertical shear drive the upwelling and the vertical mixing in the wake and produces a very pronounced island mass effect

epr microplates a model for the oman ophiolite structural mapping in the southern half of the oman ophiolite has revealed a palaeoridge organization with similarities to an epr microplate forming in superfast spreading conditions a nw trending propagator was rapidly opening in a lithosphere no more than 1 myr older and itself created in a ne sw ridge system the nw trending propagator underlined by small mantle diapirs was active or dying when detached as part of a future ophiolite local thrusting of the future ophiolite was also initiated very early between 1 and 5 myr after ridge accretion it was accompanied by a 40 rotation within this time lapse such an activity supports the comparison of the oman palaeoridge system with an oceanic microplate and provides evidence to suggest the existence of thrusts at active microplates

plate boundary reorganization at a large offset rapidly propagating rift the existence of rapidly spinning microplates along the southern east pacific rise has been documented by geophysical swath mapping surveys1 6 and their evolution has been successfully described by an edge driven kinematic model7 but the mechanism by which such microplates originate remains unknown proposed mechanisms1 10 have generally involved rift propagation11 possibly driven by hotspots or changes in direction of sea floor spreading here we present geophysical data collected over the earth s fastest spreading centre the pacific nazca ridge between the easter and juan fernandez microplates fig 1 which reveal a large offset propagating rift presently reorganizing the plate boundary geometry a recent episode of rapid duelling propagation of the historically failing spreading centre in this system has created a 120 120 km overlap zone between dual active spreading centres which may be the initial stage of formation of a new microplate

mesoscale to submesoscale transition in the california current system part i flow structure eddy flux and observational tests in computational simulations of an idealized subtropical eastern boundary upwelling current system similar to the california current a submesoscale transition occurs in the eddy variability as the horizontal grid scale is reduced to o 1 km this first paper in a series of three describes the transition in terms of the emergent flow structure and the associated time averaged eddy fluxes in addition to the mesoscale eddies that arise from a primary instability of the alongshore wind driven currents significant energy is transferred into submesoscale fronts and vortices in the upper ocean the submesoscale arises through surface frontogenesis growing off upwelled cold filaments that are pulled offshore and strained in between the mesoscale eddy centers in turn some submesoscale fronts become unstable and develop submesoscale meanders and fragment into roll up vortices associated with this phenomenon are a large vertical vorticity and rossby number a large vertical velocity relatively flat horizontal spectra contrary to the prevailing view of mesoscale dynamics a large vertical buoyancy flux acting to restratify the upper ocean a submesoscale energy conversion from potential to kinetic a significant spatial and temporal intermittency in the upper ocean and material exchanges between the surface boundary layer and pycnocline comparison with available observations indicates that submesoscale fronts and instabilities occur widely in the upper ocean with characteristics similar to the simulations

atmospheric methane ratio and environmental change in the sahara an sahel during the last 130 kyrs abstract the comparison of the vostok ch 4 curve over the last 130 ka with the dated succession of humid arid phases in the 6 500 000 km 2 area between 13 n and 27 n in africa shows that they roughly co vary we propose those past ecological changes in vast tropical areas as one of the factors that contributted to the global increase decrease of the methane production

structure and variability of internal tides in luzon strait abstractthe luzon strait is the generation region for strong internal tides that radiate westward into the south china sea and eastward into the western pacific intrusions of the kuroshio and strong mesoscale variability in the luzon strait can influence their generation and propagation here the authors use eight moorings and two numerical models to investigate these relationships by quantifying the coherence of the diurnal and semidiurnal internal tides in the luzon strait this study finds that the level of coherence of internal tide generation energy and energy flux is quite variable depending on the specific location within the luzon strait large scale spatial patterns in internal tide pressure and velocity exist across the region shaped by the bathymetry mean flow and stratification internal tide coherence is lower 30 near large gradients in this pattern predominantly along the eastern ridge which are shifted by the variable kuroshio and mesoscale fields at other locations within t

seasonal to interannual variations in the intensity and central position of the surface kuroshio east of taiwan 1 seasonal and interannual changes of surface kuroshio intensity and central position east of taiwan during 1993 2012 are investigated by quantitatively analyzing the satellite altimetry product the kuroshio moves inshore offshore off northeast of taiwan in winter summer whereas it has an offshore inshore path off southeast of taiwan in winter summer the seasonal change of heat flux over the east china sea shelf is found to cause the seasonality of the kuroshio central position off northeast of taiwan whereas the seasonal kuroshio movement off southeast of taiwan is found to be induced by the combined effect of the kuroshio changes through the luzon strait and the eastern luzon island in contrast to this y dependent path changes the kuroshio becomes weaker stronger as a whole east of taiwan in winter summer on the interannual time scales the kuroshio throughout the eastern coast of taiwan intensifies and has a concurrent offshore path during the periods of 1995 1997 and 2004 2007 the relative intensity of cyclonic eddies to anticyclonic eddies off eastern taiwan are found to contribute to these interannual kuroshio changes

kinematics of mantle flow beneath a fossil overlapping spreading center the wuqbah massif case oman ophiolite the wuqbah massif central oman ophiolite comprises a well preserved 2 km thick crustal unit over a 6 8 km thick mantle sequence the mantle comprises harzburgites and few dunites cut by various types of dykes with the exception of basal and late fault zones peridotites display granoblastic and porphyroclastic textures acquired by high temperature plastic deformation they locally suffered important recrystallization as shown by neoblastic shapes and arrangements macroscopically the peridotites have well defined foliations and lineations whose features allow the massif to divide into three structural domains it comprises a n110 trending central zone that suffered an anticlockwise rotation with an upwelling zone in its southwestern part bound between two ns areas sheared in right lateral conditions this peculiar geometry is thought to reflect an overlapping spreading center osc where the east and west bordering zones would define the trace in the mantle of two ridge segment terminations and the oblique n110 central zone the axial part of the overlap area it is proposed that the northward migration of the southwest branch and its concomitant ew spreading caused the deformation and rotation of the overlap zone in our osc model flow in the mantle would be continuous from one spreading center branch to the other being curved in the overlap area to accommodate the offset the mantle flow would therefore be more and more decoupled with the brittle crust when approaching the overlap zone where extensional tectonics can occur we consider that some mantle upwelling is possible due to its specific location in between two ridge segments and over the main mantle flow the distance between the two ridge axes is 15 km which means that this paleo osc can be ranked in the class of intermediate oscs illustrating a third order ridge segmentation at the scale of the ophiolite the wuqbah osc is located northwest of a major domain marked by the presence of a nw se trending propagating ridge responsible for the formation of a new oceanic crust it is suggested that the wuqbah osc formed earlier and underlines the trace of a ridge that had later migrated to the east

energetics of eddy mean flow interactions in the gulf stream region a detailed energetics analysis of the gulf stream gs and associated eddies is performed using a highresolution multidecadal regional ocean model simulation the energy equations for the time mean and timevaryingflowsarederivedasatheoreticalframeworkfortheanalysis theeddy meanflowenergycomponents and their conversions show complex spatial distributions in the along coast region the cross stream and cross bump variations are seen in the eddy mean flow energy conversions whereas in the off coast region a mixed positive negative conversion pattern is observed the local variations of the eddy mean flow interaction are influenced by the varying bottom topography when considering the domain averaged energetics theeddy meanflowinteractionshowssignificantalong streamvariability upstreamofcapehatteras the energy is mainly transferred from the mean flow to the eddy field through barotropic and baroclinic instabilities upon separating from the coast the gs becomes highly unstable and both energy conversions intensify when the gs flows into the off coast region an inverse conversion from the eddy field to the mean flow dominates the power transfer for the entire gs region the mean current is intrinsically unstable and transfers 28 26gw of kinetic energy and 26 80gw of available potential energy to the eddy field the mesoscaleeddykineticenergyisgeneratedbymixedbarotropicandbaroclinicinstabilities contributing28 26 and 9 15gw respectively beyond directly supplying the barotropic pathway mean kinetic energy also provides 11 55gw of power to mean available potential energy and subsequently facilitates the baroclinic instability pathway

sensitivity of climate to late cenozoic uplift in southern asia and the american west numerical experiments experiments with general circulation models with no mountains half mountains and full modern mountains show the sensitivity of atmospheric circulation patterns to progressive amounts of uplift the experiments were motivated by geologic evidence for large kilometer scale uplift in the late cenozoic in southern asia and the american west particularly within the last 10 m y in january the amplitude of the mid latitude upper tropospheric planetary waves increased with uplift and the low level winds were progressively blocked or diverted around the topographic features in july the progressive uplift caused monsoonlike circulations to develop in the vicinity of the colorado and tibetan plateaus atmospheric heating rates midtroposphere vertical motion and upper tropospheric planetary wave amplitudes varied approximately linearly with progressive uplift these results suggest that geologically recent kilometer scale uplift may have had climatic consequences comparable in magnitude and pattern to those of earlier stages of uplift comparison of the simulated climatic effects of uplift with the geologic evidence for late cenozoic climatic change especially for the last 10 m y is given in accompanying papers

the base of a sheeted dyke complex oman ophiolite implications for magma chambers at oceanic spreading axes the sheeted dyke complex in the maydan syncline area of the oman ophiolite was formed during a single sea floor spreading episode in some areas individual dykes from this sheeted dyke complex have been seen to root in the high level gabbro and others are truncated by high level gabbro diorite and trondhjemite however elsewhere dykes penetrate laterally into the layered part of the plutonic sequence this situation suggests that active magma chambers and zones of dyke injection were discontinuous along the spreading axis at any one time

a pleistocene lacustrine episode in southeastern libya fossiliferous lacustrine deposits of middle pleistocene age have been found in central fezzan libya 1 on each side of the east west depressions of the wadi shati south of the precambrian qarqaf anticline1 8 they represent the shoreline of a former brackish water lake fig 1 which some 130 000 yr bp covered an area about 100km long and 10 20 km wide at present the area may be classified as hyperarid since 1978 a collaborative study of the fossil assemblages has been undertaken it included macro and micropalaeontological determination th u dating stable isotope and chemical analyses in parallel with sedimentological and archaeological studies of the sites here we consider the th u dating and the isotopic palaeohydrology of the lacustrine episode

modulation of kuroshio transport by mesoscale eddies at the luzon strait entrance measurements of kuroshio current velocity at the entrance to luzon strait along 18 75 n were made with an array of six moorings during june 2012 to june 2013 strong positive relative vorticity of the order of the planetary vorticity f was observed on the western flank of the kuroshio in the upper 150 m on the eastern flank the negative vorticity observed was about an order of magnitude smaller than f kuroshio transport near its origin is computed from direct measurements for the first time kuroshio transport has an annual mean of 15 sv with a standard deviation of 3 sv it is modulated strongly by impinging westward propagating eddies which are identified by an improved eddy detection method and tracked back to the interior ocean eight kuroshio transport anomalies 5 sv are identified seven are explained by the westward propagating eddies cyclonic anticyclonic eddies decrease increase the zonal sea level anomaly sla slope and reduce enhance kuroshio transport large transport anomalies of 10 sv within o 10 days are associated with the pairs of cyclonic and anticyclonic eddies the observed kuroshio transport was strongly correlated with the sla slope correlation 0 9 analysis of sla slope data at the entrance to luzon strait over the period 1992 2013 reveals a seasonal cycle with a positive anomaly i e an enhanced kuroshio transport in winter and spring and a negative anomaly in summer and fall eddy induced vorticity near the kuroshio has a similar seasonal cycle suggesting that seasonal variation of the kuroshio transport near its origin is modulated by the seasonal variation of the impinging mesoscale eddies

the kuroshio east of taiwan moored transport observations from the woce pcm 1 array observations from the woce pcm 1 moored current meter array east of taiwan for the period september 1994 to may 1996 are used to derive estimates of the kuroshio transport at the entrance to the east china sea three different methods of calculating the kuroshio transport are employed and compared these methods include 1 a direct method that uses conventional interpolation of the measured currents and extrapolation to the surface and bottom to estimate the current structure 2 a dynamic height method in which moored temperature measurements from moorings on opposite sides of the channel are used to estimate dynamic height differences across the current and spatially averaged baroclinic transport profiles and 3 an adjusted geostrophic method in which all moored temperature measurements within the array are used to estimate a relative geostrophic velocity field that is referenced and adjusted by the available direct current measurements the first two methods are largely independent and are shown to produce very similar transport results the latter two methods are particularly useful in situations where direct current measurements may have marginal resolution for accurate transport estimates these methods should be generally applicable in other settings and illustrate the benefits of including a dynamic height measuring capability as a backup for conventional direct transport calculations the mean transport of the kuroshio over the 20 month duration of the experiment ranges from 20 7 to 22 1 sv 1 sv 106 m3 s 1 for the three methods or within 1 3 sv of each other the overall mean transport for the kuroshio is estimated to be 21 5 sv with an uncertainty of 2 5 sv all methods show a similar range of variability of 10 sv with dominant timescales of several months fluctuations in the transport are shown to have a robust vertical structure with over 90 of the transport variance explained by a single vertical mode the moored transports are used to determine the relationship between kuroshio transport and sea level difference between taiwan and the southern ryukyu islands allowing for long term monitoring of the kuroshio inflow to the east china sea

evaporation from lake kinneret israel during hot summer days summary the relationships between the evaporation from a medium size 168 7 km 2 lake kinneret northern israel and its governing synoptic factors are well demonstrated during the summer of 2010 during july august the daily temperature of the air and water surface were 2 4 c higher the daily wind over the lake was 80 weaker and the evaporation from the lake was 5 lower than the long term july august mean in this study we explore the impact of the regional and local synoptic scale atmospheric conditions on the evaporation from the lake during exceptionally hot days in the mid summer months july august the factors that were found to be correlated with the lake evaporation are the temperatures at 850 hpa negative and 500 hpa positive the sea level pressure difference between northern egypt and armenia positive and the height of the marine inversion positive synoptic analysis indicates that two conditions are responsible for the reduction of the mediterranean sea breeze msb during exceptionally hot days and consequently to the reduction of evaporation from the lake first the weakening of the permanent synoptic etesian winds which otherwise supports the inland penetration of the msb and second the descent of the marine inversion to a height below the topographic ridge of the galilee mountains upwind of the study area which blocks the marine sea breeze from reaching lake kinneret

turbulent mixing within the kuroshio in the tokara strait turbulent mixing and background current were observed using a microstructure profiler and acoustic doppler current profilers in the tokara strait where many seamounts and small islands exist within the route of the kuroshio in the east china sea vertical structure and water properties of the kuroshio were greatly modified downstream from shallow seamounts in the lee of a seamount crest at 200 m depth the modification made the flow tend to shear instability and the vertical eddy diffusivity is enhanced by nearly 100 times that of the upstream site to k o 10 3 o 10 2 m2 s 1 a one dimensional diffusion model using the observed eddy diffusivity reproduced the observed downstream evolution of the temperature salinity profile however the estimated diffusion time scale is at least 10 times longer than the observed advection time scale this suggests that the eddy diffusivity reaches to o 10 1 m2 s 1 in the vicinity of the seamount at a site away from the abrupt topography eddy diffusivity was also elevated to o 10 3 m2 s 1 and was associated with shear instability presumably induced by the kuroshio shear and near inertial internal wave shear our study suggests that a better prediction of current water mass properties and nutrients within the kuroshio requires accurate understanding and parameterization of flow topography interaction such as internal hydraulics the associated internal wave processes and turbulent mixing processes

observations of island wakes at high rossby numbers evolution of submesoscale vortices and free shear layers abstractoceanic vortex evolution on the lee side of taiwan s green island 7 km in diameter where the kuroshio flows at a speed of 1 1 5 m s 1 is observationally examined and compared to theori

glider observations of a mesoscale oceanic island wake abstractin this study a 2 yr time series of velocity profiles to 1000 m from meridional glider surveys is used to characterize the wake in the lee of a large island in the western tropical north p

rapid emplacement of the oman ophiolite thermal and geochronologic constraints in understanding of ophiolite emplacement requires knowledge of the elapsed time between igneous crystallization and intraoceanic thrusting and the rate and duration of that thrusting hornblende 4oar 39ar ages demonstrate that the igneous oceanic crust in oman crystallized and cooled to 825 k in 1 2 m y hornblende ages from metamorphic rocks and from cross cutting dikes require that the basal metamorphic thrust fault beneath the ophiolite also cooled below 825 k in 1 2 m y motion along the sole thrust accounted for 200 km of displacement at a rate of 100 200 mm yr on the basis of age relationships and thermal considerations we favor a two stage model for the initial stages of samall ophiolite emplacement intraoceanic thrusting over 2 m y old lithosphere at 150 km m y parallel to a spreading ridge for 1 2 m y followed by equally rapid and brief thrusting over cold and old lithosphere preservation of the samail ophiolite is a direct result of its young age and positive buoyancy at the time of ocean closure and we propose that all ophiolites that originated near spreading centers and were emplaced onto continents were young at the time of intraoceanic thrusting

evidence from earthquakes for bookshelf faulting at large non transform ridge offsets migrating non transform offsets which occur along mid ocean ridges when a propagating segment gradually elongates and takes over spreading from a neighbouring doomed rift segment1 3 represent a significant modification of the plate tectonic paradigm4 the migrating offset zone between the two spreading segments is clearly a locus of significant deformation but the mechanism of this deformation has been controversial here we use the source parameters and locations of earthquakes at such offsets to discriminate between previously proposed models2 4 7 earthquakes at large non transform offsets at medium and fast spreading rates show strike slip mechanisms with nodal planes rotated relative to the expected transform fault orientation one set of nodal planes presumably corresponding to the fault planes is parallel to curved sea floor lineaments which show increased rotation as a function of position in the deforming zone a bookshelf faulting model in which initially ridge parallel faults are rotated by simple shear is consistent with the observed lineament orientations focal mechanisms and earthquake distributions

mixing characteristics and compositional differences in mantle derived melts beneath spreading axes evidence from cyclically layered rocks in the ophiolite of north oman within the ophiolite of north oman interlayered gabbros and peridotites form a unit up to 3 5 km thick between pervasively foliated harzburgites and dunites of mantle origin and isotropic gabbros and plagiogranites spatial and chemical relationships within this sequence require the existence of a large reservoir 20 km wide 3 5 km high of tholeiitic magma that was periodically replenished by mantle derived picritic to tholeiitic melts during the spreading process cyclicity in the appearance of minerals during cooling of the magma is marked by the repetition of stratigraphies in the layered rocks within these cyclic units basal peridotites with magnesian olivines and pyroxenes are abruptly overlain by gabbros with less magnesian mafic phases this abrupt discontinuity is explained by density stratification set up at the base of the chamber whenever a picritic melt influx occurs by virtue of its greater density than tholeiitic magma sparks et al 1979 any picritic magma emplaced into the base of the tholeiitic magma reservoir would spread out along the floor of the chamber with only limited mixing taking place across the liquid liquid interface cooling of this basal layer by contact with the cooler overlying magma would result in the precipitation of olivine chrome spinel pyroxene from the picritic liquid this process would continue until the now more evolved input liquids were incorporated into the tholeiitic magma resevoir the precipitation of a gabbroic layer would then take place until a new magma input occurred to repeat the cycle variable thicknesses of the cyclic units different liquid lines of descent and various entry points within the liquid line of descent represented by the lowermost layered rocks reveal that the input liquids varied in volume primary composition and the extent and nature of prefractionation in the mantle liquids expelled from the chamber as lavas and dykes are shown to be more fractionated than liquids precipitating the layered rocks and are considered to have undergone additional fractionation within a zone of underplated gabbro and plagiogranite beneath the dyke swarm the existence of a large magma reservoir supports earlier interpretations based on age tilton et al 1981 and geochemical data pearce 1980 that the oman ophiolite is an analogue for fast spreading ridges

along strike variation of the sheeted dike complex in the oman ophiolite insights into subaxial ridge segment structures and the magma plumbing system 1 along strike variations of the 60 km long sheeted dike complex in the northern oman ophiolite were studied in order to understand the shallow magma plumbing system beneath the fossil fast spreading ridge the presence of numerous dikes intruding into the layered gabbro defines the northern end of the paleoridge segment at wadi fizh the postulated segment center is located at wadi thuqbah which has a thicker mono transition zone than elsewhere along the fossil segment aphyric dikes predominate in the sheeted dikes of which 99 are simple while multiple and composite dikes are few the thickness of 1511 dikes ranges from 13 m with an average thickness of 71 3 cm restored dike trends in the 30 km long northern half of the dike complex display the ns trending north domain and nne ns trending south domain bordered at the south of wadi bani umar al gharbi in the domain boundary dikes gradually change strikes or are mutually intrusive dike thickens northward with the largest peak along wadi fizh at the northern end of the paleoridge segment and a small peak at wadi bani umar al gharbi most dikes have a bulk mg of 55 66 which overlaps the majority of morb less common highly evolved dikes with mg 34 40 characterize the north domain thicker dikes 3 m tend to have high mg while thinner dikes 2 m are highly variable in mg the regional variations of the dike trends and the whole rock compositions can be explained by the secular variation in the structures of the paleoridge segment comparable to a third order segment of the present mid ocean ridge system spanning a few tens of thousands of years initially the segment long melt lens developed along the paleoridge axis which fed long and thick dikes with high mg with decreasing supply of magma the melt lens split up into the north and south smaller lenses bordered by a deval that fed thinner dikes intruding into the former thick dikes cut off of the northern melt lens from the magma source changed the melt composition to highly evolved low mg magmas which subsequently intruded as short evolved dikes meanwhile the main melt lens in the segment center continued feeding the high mg dikes which were maintained by the larger melt lens size and intermittent magma supply from deep magma chambers