cyclonic eddies in the gulf of mexico observations by underwater gliders and simulations by numerical model abstractcirculation in the gulf of mexico gom is dominated by the loop current lc and by loop current eddies lces that form at irregular multimonth intervals by separation from the lc comparatively small cyclonic eddies ces are thought to have a controlling influence on the lce including its separation from the lc because the ces are so dynamic and short lived lasting only a few weeks they have proved a challenge to observe this study addresses that challenge using underwater gliders these gliders data and satellite sea surface height ssh are used in a four dimensional variational 4dvar assimilation in the massachusetts institute of technology mit general circulation model mitgcm the model serves two purposes first the model s estimate of ocean state allows the analysis of four dimensional fields and second the model forecasts are examined to determine the value of glider data ces have a rossby number of about 0 2 implying that the effects of flow curvature cyclostrophy to

eddy resolving observation of the north pacific subtropical mode water abstracthydrographic data obtained by high resolution shipboard observations and argo profiling floats have been analyzed to study the mesoscale structure and circulation of the north pacific subtropical mode water stmw the float data show that in the late winter of 2008 stmw having a temperature of approximately 18 8 17 7 and 16 6 c formed west of 140 e at 140 150 e and east of 150 e respectively in the recirculation gyre south of the kuroshio extension after spring the newly formed stmw gradually shift southward decreasing in thickness simultaneously the stmws of 16 6 and 17 7 c are gradually stirred and then mixed in terms of properties in late fall they seem to be integrated to form a single group of stmws having a temperature centered at 17 2 c such stmw circulation in 2008 is much more turbulent than that in 2006 which was investigated in a previous study the difference between the two years is attributed to the more variable state of the kuroshio extension in 2008 associate

multicore structure of the north pacific subtropical mode water from enhanced argo observations seventeen argo profiling floats with enhanced vertical and temporal sampling were deployed in the kuroshio recirculation gyre in the western north pacific in late march 2014 the subtropical mode water stmw observed in many profiles displays a multicore structure with more than one minima in potential vorticity pv corroborated by vertical covariations in apparent oxygen utilization aou these cores are classified into four submodes according to density and aou the submode waters are typically 100 m thick in which pv varies by 1 10 10 m 1 s 1 and aou by 10 mole kg the stmw multicore structure is most frequently observed in spring gradually taken over by single core profiles into summer the seasonal evolution is suggestive of vertical mixing especially in stmw of lower density

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

quartz cemented breccias from the mid atlantic ridge samples of a high salinity hydrothermal upflow zone textural mineralogical chemical and fluid inclusion studies on a suite of quartz rich sulfide bearing greenstone breccias indicate that high salinity high fluid flow systems were recently active on the mid atlantic ridge south of the kane fracture zone these systems involved fluids with temperatures close to 300 c and salinities almost 3 times that of seawater rounded pebblelike fragments enclosed within a matrix of euhedral quartz crystals appear to have been cemented by quartz deposition from a moving fluid which attained velocities in excess of 1 m s homogenization temperatures and freezing point depression effects in fluid inclusions from texturally early and late quartz crystals indicate temporal evolution of fluid temperatures and nacl equivalent salinities from 290 c and 10 wt to 200 c and 4 7 wt during alteration and cementation of the breccias highly variable cobalt concentrations in the evolving hydrothermal solutions are indicated by fine scale oscillatory zoning in euhedral pyrite within the breccias a continuous supply of the high salinity fluids may be generated either by supercritical two phase separation at depths well below the level of inclusion entrapment or by retrograde dissolution of hydroxy chloride phases in the deeper portions of the hydrothermal system either model requires the initial temperature of the deeply circulating fluids to have been distinctly higher than 415 c and the fluid to have been cooled by conduction or by mixing with lower temperature seawater prior to entrapment within the inclusions

signature of the agulhas current in high resolution satellite derived wind fields abstract 5 years of systematic envisat advanced synthetic aperture radar asar acquisitions and 8 years of observations from the jason 2 altimeter are used to investigate the signature of the agulhas current on high resolution between 1 and 5 km satellite derived winds the satellite wind observations are analysed together with co located ocean current sea surface temperature sst and significant wave height information satellite derived winds cannot be considered current relative over the agulhas current sar and altimeter winds increase in magnitude over the agulhas current in all up down and cross current wind conditions with contributions from both the ocean surface current and sst when winds blow against the current strong accelerations in satellite winds are observed at the agulhas current s inshore front with the strongest winds observed 10 km offshore from the location of maximum sst gradient the strong sst gradient appears to drive a thermal wind with a magnitude of about 1 m s and which intensifies abates the predominant alongfront winds at the agulhas current s northern wall the sar dataset shows abnormally high increases in wind speeds during up current conditions in comparisons to the jason 2 derived winds we argue that these differences are caused by the inability of the cmod type algorithms to taken into account the wave field and provide accurate wind speed estimates in conditions where wave height exceed the expected value for a given wind speed our analysis suggests that wave current interactions in regions of strong current shear produce enhanced sea surface roughness signatures and lead to artificially high estimates of sar derived wind speeds there is future potential in using high resolution sar imagery to map strong ocean current fronts and thus improve our ability to monitor ocean surface currents from space

consequences of phase separation on the distribution of hydrothermal fluids at ashes vent field axial volcano juan de fuca ridge recent studies of hydrothermal fluid chemistry at the axial seamount hydrothermal emissions study ashes vent field of axial volcano indicate separation of liquid and vapor phases during the migration of fluids to the seafloor the brine phase liquid emanates from discrete sulfide chimneys while fluid which has been through vapor phase separation flows diffusely from fissures in the surrounding basalt one possible mechanism to explain this spatial segregation of the fluid phases is based on the relative permeability terms in the equations of two phase flow a qualitative model for the distribution of fluids observed at ashes is postulated in which brine phase fluids are confined within flow conduits by a surrounding relative permeability barrier while vapor phase fluids flow diffusely into the surrounding host rock

generation of submesoscale frontal eddies in the agulhas current copyright 2019 brill due to copyright restrictions the attached pdf file contains the abstract of the full text item for access to the full text item please consult the publisher s website https agupubs onlinelibrary wiley com doi full 10 1029 2019jc015229

observing subsurface changes of two anticyclonic eddies passing over the izu ogasawara ridge eddy bathymetry interactions are common in the ocean but the full evolution of the interaction is difficult to observe below the surface using 17 iridium argo floats we continually track two anticyclonic eddies aes in the north pacific that migrate westward and encounter the izu ogasawara ridge based on over 5000 argo profiles following the two aes this study presents the first detailed descriptions of changes in eddy vertical structure and diapycnal mixing as the two aes pass the ridge there we find that isopycnals dome up and the eddy diameter increases while the diapycnal mixing is enhanced to the order of 10 4 m 2 s 1 or larger in comparison with an ambient of 10 5 m 2 s 1 the enhanced mixing around the ae center in the upper 1000m appears where the underlying bathymetry is shallower than 4000m and is mainly sustained by tidally generated internal waves

mesoscale eddy effects on the subduction of north pacific mode waters mesoscale eddy effects on the subduction of north pacific mode waters are investigated by comparing observations and ocean general circulation models where eddies are either parameterized or resolved the eddy resolving models produce results closer to observations than the noneddy resolving model there are large discrepancies in subduction patterns between eddy resolving and noneddy resolving models in the noneddy resolving model subduction on a given isopycnal is limited to the cross point between the mixed layer depth mld front and the outcrop line whereas in eddy resolving models and observations subduction takes place in a broader zonally elongated band within the deep mixed layer region mesoscale eddies significantly enhance the total subduction rate helping create remarkable peaks in the volume histogram that correspond to north pacific subtropical mode water stmw and central mode water cmw eddy enhanced subduction preferentially occurs south of the winter mean outcrop with an anticyclonic eddy to the west and a cyclonic eddy to the east the outcrop line meanders south and the thermocline mld shoals eastward as eddies propagate westward the mld shoals shielding the water of low potential vorticity from the atmosphere the southward eddy flow then carries the subducted water mass into the thermocline the eddy subduction processes revealed here have important implications for designing field observations and improving models

characteristics energetics and origins of agulhas current meanders and their limited influence on ring shedding abstractthe agulhas current intermittently undergoes dramatic offshore excursions from its mean path because of the downstream passage of mesoscale solitary meanders or natal pulses new observations and analyses are presented of the variability of the current and its meanders using mooring observations from the agulhas current time series experiment act near 34 s using a new rotary eof method mesoscale meanders and smaller scale meanders are differentiated and each captured in a single mode of variance during mesoscale meanders an onshore cyclonic circulation and an offshore anticyclonic circulation act together to displace the jet offshore leading to sudden and strong positive conversion of kinetic energy from the mean flow to the meander via nonlinear interactions smaller meanders are principally represented by a single cyclonic circulation spanning the entire jet that acts to displace the jet without extracting kinetic energy from the mean flow synthesizing in situ observations with altimeter

generation of topographic waves over the continental margin abstract numerical experiments were carried out to simulate the generation of topographic waves by a gulf stream ring over the continental margin in a stratified ocean on an f plane the study was aimed at understanding the combined effect of density advection and bottom topography on the flow field the momentum equation is linear and nonlinearity is introduced in the density equation the mechanism of wave generation was investigated by turning on and off the nonlinear density advection and by changing the strength of the ring and bottom topography the results show that topographic waves are generated by advection of density in a ring over a sloping bottom the vorticity associated with the swirl velocity of a ring is less important during wave generation the strength of a ring affects the wave amplitude in the case of a strong ring self advection of density may be induced at the surface however the generation and propagation of topographic waves are independent of the strength of the ring waves

geographical variability of the first baroclinic rossby radius of deformation global 1 83 18 climatologies of the first baroclinic gravity wave phase speed c1 and the rossby radius of deformation l1 are computed from climatological average temperature and salinity profiles these new atlases are compared with previously published 5 83 58 coarse resolution maps of l1 for the northern hemisphere and the south atlantic and with a 1 83 18 fine resolution map of c1 for the tropical pacific it is concluded that the methods used in these earlier estimates yield values that are biased systematically low by 5 15 owing to seemingly minor computational errors geographical variations in the new high resolution maps of c1 and l1 are discussed in terms of a wkb approximation that elucidates the effects of earth rotation stratification and water depth on these quantities it is shown that the effects of temporal variations of the stratification can be neglected in the estimation of c1 and l1 at any particular location in the world ocean this is rationalized from consideration of the wkb approximation

submesoscale cyclones in the agulhas current gliders were deployed for the first time in the agulhas current region to investigate processes of interactions between western boundary currents and shelf waters continuous observations from the gliders in water depths of 100 1000 m and over a period of 1 month provide the first high resolution observations of the agulhas current s inshore front the observations collected in a nonmeandering agulhas current show the presence of submesoscale cyclonic eddies generated at the inshore boundary of the agulhas current the submesoscale cyclones are often associated with warm water plumes which extend from their western edge and exhibit strong northeastward currents these features are a result of shear instabilities and extract their energy from the mean agulhas current jet

agulhas current meanders facilitate shelf slope exchange on the eastern agulhas bank large solitary meanders are arguably the dominant mode of variability in the agulhas current observational studies have shown that these large meanders are associated with strong upwelling velocities and affect the shelf circulation for over 100 days per year here 10 year time series from two ocean general circulation models are used to create a composite picture of the agulhas current and its interactions with the shelf circulation in meandering and nonmeandering modes both models show good agreement with the size propagation speed and frequency of observed meanders these composite meanders are then used to examine the response of shelf waters to the onset of large meanders with the use of model output enabling the dynamics at depth to be explored results show a composite mean warming of up to 3 c of depth averaged temperature along the shelf edge associated with an intrusion of the current jet onto the shelf driven by an intensification of the flow along the leading edge of large meanders however this intensification of flow results in cooling of bottom waters driving cold events at the shelf break of 10 c at 100 m thus the intensification of the current jet associated with large meander events appears to drive strong up and downwelling events across the inshore front of the agulhas current facilitating shelf slope exchange

comment on consequences of phase separation on the distribution of hydrothermal fluids at ashes vent field axial volcano juan de fuca ridge by christopher g fox

variability of the kuroshio extension jet recirculation gyre and mesoscale eddies on decadal time scales abstract twelve years of sea surface height ssh data from multiple satellite altimeters are used to investigate the low frequency changes and the interconnections of the kuroshio extension ke jet its southern recirculation gyre and their mesoscale eddy field the dominant signal is characterized by the steady weakening of the ke jet recirculation gyre from 1993 to 1996 followed by a gradual strengthening after 1997 during the weakening period of 1993 96 the ke path migrated southward in general and this path migration reversed in direction during the strengthening period of the ke jet and recirculation gyre after 1997 by hindcasting the ssh signals using linear vorticity dynamics it was found that weakening strengthening in the ke jet and recirculation gyre is consistent with westward propagation of negative positive ssh anomalies generating in the eastern north pacific and strengthening during their westward propagation when the ke jet and recirculation gyre were in a weak mode during 19

submarine venting of phase separated hydrothermal fluids at axial volcano juan de fuca ridge since the discovery of high temperature venting on the east pacific rise in 19791 it has been expected2 3 because of the physical properties of sea water at pressures and temperatures encountered during submarine hydrothermal circulation4 5 that phase separated fluids would discharge from ridgecrest vents although this notion is supported by the reported large deviations in vent fluid chlorinity relative to that of sea water 40 200 6 7 by observations of venting at p t conditions clearly within the two phase region 220 bar and 420 c 8 and by fluid inclusion data9 10 unequivocal identification11 of phase separated venting fluids has remained elusive here we report observations of chloride and metal depleted gas enriched fluids from a shallow vent field on the juan de fuca ridge which confirm the expectation that phase separated effluents are delivered to the deep ocean from some sea floor venting systems

the velocity and vorticity structure of the agulhas current at 32 s the full depth velocity field of the agulhas current the western boundary current of the southwest indian ocean has been directly measured using a lowered acoustic doppler current profiler ladcp fifteen combined conductivity temperature depth ctd and ladcp stations were occupied across the current at 32 s off the east coast of south africa in february march 1995 as part of the world ocean circulation experiment indian ocean program the deep velocity structure of the agulhas current was found to be very different than previously described using geostrophic estimates in particular ladcp results reveal a v shaped pattern for the level of no motion across the agulhas current and an agulhas undercurrent is observed flowing equatorward below 800 m depth directly beneath the surface core of the poleward flowing agulhas current comparisons of direct and geostrophic velocities suggest that the velocity structure of the agulhas current is essentially geostrophic below about 200 m depth where differences are generally less than estimated errors above these depths the ladcp measured shears and geostrophic shears exhibit differences and velocities can diverge shipboard adcp data support ladcp results near the surface indicating that both instruments are measuring real signals the geostrophic and ladcp measured shears are well matched away from the surface and a depth averaged fit below 200 m between them exhibits small standard deviations the geostrophic volume transport of the agulhas current as referenced to ladcp is 73 sv and is just 3 different from the direct ladcp transport estimate the most recent full depth estimate of agulhas current transport in the literature is given by toole and warren 1993 who estimate a geostrophic volume transport of 85 sv the baroclinic velocity structures from their section and from this work are similar indicating that the difference in the transport estimates is due to the choice of geostrophic reference level and ultimately to the presence of the previously unobserved agulhas undercurrent combined ctd ladcp data are very useful for potential vorticity analysis since velocity and density measurements are simultaneous and coincident the vorticity structure of the agulhas current suggests the presence of a mixing boundary at middepths similar to features observed in the gulf stream the feature appears to be associated with a sharp upturn in isopycnals coincident with the foot of the continental slope the boundary inhibits cross stream mixing of intermediate water masses and may help explain the appearance of a discrete filament of red sea water inshore of antarctic intermediate waters in the same density layer despite intense cross stream shears

mapping the agulhas current from space an assessment of asar surface current velocities 1 over 2 years of surface current information collected in the agulhas current region and derived from the doppler centroid anomalies of envisat s advanced synthetic aperture radar asar are examined the sources of errors and potential use of asar surface current velocities for oceanographic research are assessed asar surface current velocities are compared to surface drifter data and merged altimetry observations maps of sea surface temperature are used to establish the asar s capacity to capture the synoptic circulation discrepancies between observed and predicted asar velocities result predominantly from inadequate wind corrections combined with radar incidence angles below 30 occasionally observed wind induced outliers cause a bias in the estimated asar velocities but do not affect the ability of the asar to systematically image regions of strong surface current flow and shear time averaged maps of asar derived surface current velocity seem able to accurately capture the position as well as the intensity of the agulhas current the ability of the asar to pick up the smaller features of the circulation along the shelf break also shows that variability along the agulhas bank is of the same order of magnitude as that observed in the agulhas retroflection asar surface current velocities offer a very good complement to altimetry in regions where the mean dynamic topography is poorly resolved the quasi synoptic nature of asar acquisitions combined with the relatively high resolution of asar surface current velocities also make it attractive for studies of submesoscale processes and western boundary current dynamics

chemical controls on the composition of vent fluids at 13 11 n and 21 n east pacific rise six vent fields sampled at 13 11 n east pacific rise epr in may 1984 exhibit large interfield variations and a much wider range of chemical compositions than previously observed at 21 n measured ph at 25 c are acidic ranging from 3 1 to 3 7 sodium and chloride vary from 40 lower to 30 higher than seawater iron concentrations range from 2 to 10 mmol kg compared with 0 7 2 5 mmol kg at 21 n other sulfide forming metals cu zn cd and pb are generally lower at 11 13 n than at 21 n reliable temperature measurements were obtained at only two of the six vents and both were 350 5 c the vent fields at 21 n epr were resampled in august 1985 thus extending to almost 6 years the time period over which they have been monitored previous expeditions were made in november 1979 and november 1981 campbell et al this issue have shown that the chemistry of the hydrothermal fluids from these fields has been very stable over the period of repeated observation equilibrium calculations for the fluids from the fields at 13 n and 21 n using a greatly improved thermodynamic data base are described in this report they indicate that the chemistry is rock buffered and that the stability of these systems over time is a result of equilibrium control with respect to a greenschist type mineral assemblage at depth calculated high temperature ph of the fluids range from 4 1 to 4 7 with those from 13 11 n at the more acidic end of the range calculated affinities show that the fluids are close to or at saturation with respect to quartz albite muscovite smectite chlorite epidote and pyrrhotite the computations imply that lower temperature vents such as national geographic smoker ngs 273 c may have their silica concentrations controlled by equilibrium with respect to a phase other than quartz a comparison of fluid chemistry between ngs and vent 5 at 11 n suggests that the latter vent may also have a temperature 300 c while the fluid chemistry of a given field is compositionally stable the compositions themselves are unique for a particular field and cover a wide range between fields the processes controlling this variability probably include the depth of reaction i e pressure which is difficult to treat thermodynamically at present in addition increasing depth in the crust may be accompanied by decreasing permeability and hence a probable decrease in the water rock ratio it may be difficult to separate these two effects if the age differences between the fields at present unknown are of the order of decades then their temporal histories may have an important influence on their particular chemistries

a subsurface pathway for low potential vorticity transport from the central north pacific toward taiwan island 1 analysis of the simple ocean data assimilation product reveals that the central north pacific 28 n 35 n 150 e 170 w is one of the main formation regions for low potential vorticity water of density between 25 4 and 25 8 it is found that the low potential vorticity water is transported from the central north pacific toward the east of taiwan island along a subsurface pathway following the subtropical gyre circulation and it takes approximately 12 years propagation of pycnocline thickness anomalies is detected along the pathway in association with the decadal variability of the subduction rate

a role of eddies in formation and transport of north pacific subtropical mode water 1 hydrographic data acquired during 2001 by argo profiling floats deployed in the kuroshio recirculation region are used to verify the inference that mesoscale eddies prevailing in the recirculation region play an important role in the formation and transport of north pacific subtropical mode water npstmw that is the deeper winter mixed layer is formed preferentially where the thermocline is deeper in association with anticyclonic eddies in the succeeding seasons mesoscale eddies retain npstmw during their southwestward movement from the npstmw formation region so that anticylonic eddies contribute substantially to the npstmw transportation the spatial distributions of the mixed layer depth in winter and the npstmw thickness in the succeeding seasons based on the float data suggest that they are affected by mesoscale eddies the float data also provide the statistical relations of these quantities against the thermocline depth which are consistent with our inference

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

discrete and diffuse heat transfer atashes vent field axial volcano juan de fuca ridge abstract heat fluxes of discrete and diffuse components of hydrothermal discharge are estimated from submersible measurement in the ashes vent field located in the caldera of axial volcano on the central juan de fuca ridge the discrete component comprises discharge from individual vents and the diffuse component comprises seepage from large areas of the seafloor the investigation centered on the high temperature portion of the field a 100 100 m area of fractured lobate and sheet lava flows encompassing discrete discharge 326 c from seven individual vents and diffuse flow from intervening areas a total of 4 4 2 10 6 w was estimated for the discrete heat flux based on measurements of effluent temperature flow rate and orifice diameter at all the known individual vents by d s v alvin in september 1987 a total of 15 75 10 6 w was calculated with a standard plume model for the diffuse flux based on a grid of temperature measurements at altitudes of 1 m and 20 m above the study area using a 1 m long vertical array of temperature sensors mounted at the front of alvin s instrument platform the study indicates that 1 the diffuse component rises separately from the discrete component of hydrothermal discharge and is laterally advected by a prevailing current below the discrete component and that 2 the diffuse component of convective heat flux is approximately an order of magnitude greater than the discrete component in the high temperature portion of the ashes vent field

observations of the subtropical mode water evolution from the kuroshio extension system study abstract properties and seasonal evolution of north pacific ocean subtropical mode water stmw within and south of the kuroshio extension recirculation gyre are analyzed from profiling float data and additional hydrographic and shipboard adcp measurements taken during 2004 the presence of an enhanced recirculation gyre and relatively low mesoscale eddy variability rendered this year favorable for the formation of stmw within the recirculation gyre stmw formed from late winter convection that reached depths greater than 450 m near the center of the gyre the lower boundary of stmw corresponding to 25 5 kg m 3 was set by the maximum depth of the late winter mixed layer properties within the deep portions of the stmw layer remained largely unchanged as the season progressed in contrast the upper boundary of the stmw layer eroded steadily as the seasonal thermocline deepened from late april to august vertical eddy diffusivity responsible for this erosion was estimated from a budget analysis of

assessing the accuracy of satellite derived ocean currents by comparing observed and virtual buoys in the greater agulhas region abstract in this study we assess the accuracy of a combined geostrophic and ekman current product globcurrent that estimates ocean currents at 15 m depth by coupling it to a synthetic particle tracking tool and comparing the virtual trajectories to those of surface drifting buoys drogued at 15 m in the greater agulhas current region the velocities from a total of 1041 drifters are compared and evaluated to the synthetic particle derived velocities for the period 1993 2015 on average the globcurrent underestimates the velocity in the greater agulhas current by approximately 27 the underestimation ranges from 4 to 64 in different regions with the smallest error found in the agulhas retroflection region and the highest in the benguela upwelling system furthermore we compare the time taken for the separation between the virtual and real drifters to reach 35 km the mean separation time was found to be 78 h with the shortest time 35 h found in the agulhas current and the longest time 116 h located in the agulhas return current deploying 10 000 virtual drifters in a 1 1 box within the southern agulhas current shows a convergence of trajectories towards the core of the current while higher divergence is evident in the agulhas retroflection to evaluate the utility of this synthetic particle tracking tool coupled with globcurrent in open ocean search and rescue operations two test cases are examined 1 a capsized catamaran spotted south of cape recife and recovered 5 days later south of cape agulhas and 2 a drifter trajectory in the same region the comparison suggests that the globcurrent forced synthetic particle tracking tool is not appropriate for predicting the trajectory of a capsized catamaran that does not have the same drift characteristics as a surface drifting buoy drogued to 15 m

microstructure measurements in the mid depth waters of the north pacific 1 microstructure measurements from the surface down to maximum depths of 2000 m were carried out at 28 locations in the interior of the north pacific special attention was directed to the diapycnal diffusivities k in the significant generation regions of the semidiurnal internal tide such as the aleutian ridge the hawaiian ridge and the izu ogasawara ridge in the profiles obtained near the aleutian ridge only a few turbulent patches with 10 9 wkg 1 were detected and k was generally less than 10 5 m2s 1 in the profiles obtained near the hawaiian ridge many turbulent patches with 10 9 wkg 1 were observed although k was generally of the order of 10 5 m2s 1 along the izu ogasawara trough running in parallel with the izu ogasawara ridge in contrast remarkably intense turbulent mixing 10 8 wkg 1 k 10 4 10 3 m2s 1 was common throughout the observed water depth

evolution of the north pacific subtropical mode water in anticyclonic eddies anticyclonic eddies aes trap and transport the north pacific subtropical mode water stmw but the evolution of the stmw trapped in aes has not been fully studied due to the lack of eddy tracking subsurface observations here we analyze profiles from special designed argo floats that follow two stmw trapping aes for more than a year the enhanced daily sampling by these argo floats swirling around the eddies enables an unprecedented investigation into the structure and evolution of the trapped stmw in the aes the upper lower thermocline domes up concaves downward and this lens shaped double thermocline encompasses the thick stmw within the eddy core the lighter stmw 25 0 25 2 trapped in aes dissipates quickly after the formation in winter because of the deepening seasonal thermocline but the denser stmw 25 2 25 4 remains largely unchanged except when the ae passes across the izu ridge the enhanced diapycnal mixing over the ridge weakens the denser stmw appreciably while many aes decay upon hitting the ridge some pass through a bathymetric gap between the hachijojima and bonin islands forming a cross ridge pathway for stmw transport by contrast the north pacific intermediate water npiw underneath is deeper than the eddy trapping depth 600 m and hence left behind east of the izu ridge in argo climatology the shallow stmw 400 m intrudes through the gap westward because of the eddy transport while the npiw 800 m is blocked by the izu ridge

geochemistry of hydrothermal fluids from axial seamount hydrothermal emissions study vent field juan de fuca ridge subseafloor boiling and subsequent fluid rock interaction hydrothermal fluids collected from the ashes vent field in 1986 1987 and 1988 exhibit a very wide range of chemical composition over a small area 60 m in diameter compositions range from a 300 c gas enriched 285 mmol kg co2 low chlorinity 33 of seawater fluid to a 328 c relatively gas depleted 50 mmol kg co2 high chlorinity 116 of seawater fluid the entire range of measured compositions at ashes is best explained by a single hydrothermal fluid undergoing phase separation while rising through the ocean crust followed by partial segregation of the vapor and brine phases other mechanisms proposed to produce chlorinity variations in hydrothermal fluids precipitation dissolution of a chloride bearing mineral or crustal hydration cannot produce the covariation of chlorinity and gas content observed at ashes there is good agreement of the measured fluid compositions with compositions generated by a simple model of phase separation in which gases are partitioned according to henry s law and all salt remains in the liquid phase significant enrichments in silica lithium and boron in the low chlorinity fluids over levels predicted by the model are attributed to fluid rock interaction in the upflow zone depletions in iron and calcium suggest that these elements have been removed by iron sulfide and anhydrite precipitation at some time in the history of the low chlorinity fluids the distribution of low and high chlorinity venting is consistent with mechanisms of phase segregation based on differential buoyancy or relative permeability the relatively shallow depth of the seafloor 1540 m and the observed chemistry of ashes fluids are consistent with phase separation in the sub critical or near critical region

gulf stream fluctuations and meanders over the onslow bay upper continental slope abstract gulf stream fluctuations observed over the 200 and 400 m isobaths off onslow bay north carolina have a prominent weekly time scale the principal fluctuations observed during the 4 month winter experiment are consistent with webster s 1961a description of downstream propagating skewed lateral meanders of the gulf stream over the upper continental slope the subtidal velocity fluctuations were highly coherent over the vertical extent 120 m and over the horizontal extent 64 km of our array the implied downstream propagation speed was 30 km day 1 for the weekly period meanders concurrent satellite images of a sea surface temperature sst meander pattern indicate that subsurface temperature salinity velocity and relative vorticity maxima occurred as meander crests shoreward sst front excursions passed over the experiment site the meandering currents were not coherent with nearby wind stress or coastal sea level fluctuations eddy flux estimates indicate energy conversion from the f

effects of mesoscale eddies on subduction and distribution of subtropical mode water in an eddy resolving ogcm of the western north pacific abstract the effects of mesoscale eddies on the subduction and distribution of the north pacific subtropical mode water stmw are investigated using an eddy resolving ocean general circulation model ogcm first the subduction rate is calculated and the contribution of eddies to the subduction of stmw is estimated it is found that eddy subduction significantly contributes to the total subduction of stmw second eddy thickness transport and diapycnal flux are directly diagnosed to investigate the large scale eddy induced transport process of stmw the large southward eddy thickness transport in the stmw core density is consistent with eddy subduction the eddy transport on the isopycnal surface of stmw is directed down the thickness gradient and traverses the mean flow the meridional eddy transport streamfunction indicates two eddy circulation cells south of 30 n associated with the circulation of stmw these cells flatten density surfaces similar to the effect of the gent and mcwilliams gm schem

effect of mesoscale eddies on subtropical mode water variability from the kuroshio extension system study kess abstract forty eight profiling floats have been deployed in the kuroshio extension ke region since may 2004 as part of the kuroshio extension system study kess project by combining the float temperature salinity measurements with satellite altimetry data this study investigates the role played by mesoscale eddies in controlling the property changes in north pacific subtropical mode water stmw following a 3 yr period of low eddy activity in 2002 04 the ke showed a transition to a high eddy kinetic energy state in 2005 this transition is the result of delayed oceanic response to the 2002 shift in the basin scale surface wind forcing in connection with the pacific decadal oscillation the high eddy kinetic energy state of the ke is characterized by successive shedding of strong cold core rings into the recirculation gyre resulting from the interaction of the ke jet with the shatsky rise or the preexisting cutoff rings by transporting northern origin high potential vorticity pv ke water into t

submesoscale dynamics of a gulf stream frontal eddy in the south atlantic bight abstractfrontal eddies are commonly observed and understood as the product of an instability of the gulf stream along the southeastern u s seaboard here the authors study the dynamics of a simulated gulf stream frontal eddy in the south atlantic bight including its structure propagation and emergent submesoscale interior and neighboring substructure at very high resolution dx 150 m a rich submesoscale structure is revealed inside the frontal eddy meander induced frontogenesis sharpens the gradients and forms very sharp fronts between the eddy and the adjacent gulf stream the strong straining increases the velocity shear and suppresses the development of barotropic instability on the upstream face of the meander trough barotropic instability of the sheared flow develops from small amplitude perturbations when the straining weakens at the trough small scale meandering perturbations evolve into rolled up submesoscale vortices that are advected back into the interior of the frontal eddy the d

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

relationships between lava types seafloor morphology and the occurrence of hydrothermal venting in the ashes vent field of axial volcano deep towed and submersible photographic surveys within the caldera of axial volcano have been integrated with high resolution bathymetry to produce a geological map of the most active vent field axial seamount hydrothermal expeditions ashes in the caldera the ashes vent field encompasses an approximately 200 m 1200 m area of active venting which is located adjacent to the southwest caldera wall locations for over 2000 photographs in and near the vent field were determined using a seafloor transponder network then each photograph was described utilizing a classification system which provides detailed information concerning lava type hydrothermal activity sediment cover geological structure and biology resulting data were entered into a digital data base and computer generated maps were created that portray spatial relationships between selected geological variables in general the entire ashes field is characterized by pervasive low temperature venting the most vigorous venting is concentrated in an approximately 80 m 80 m area where there are several high temperature vents including some which are producing high temperature vapor phase fluids derived from a boiling hydrothermal system lava types within the ashes vent field are grouped into three distinct morphologies 1 smooth flat surfaced ropy and whorled sheet flows 2 lobate flows and 3 jumbled sheet flows the most intense hydrothermal venting is concentrated in the smooth sheet flows and the lobate flows the location of the ashes field is mainly attributable to faulting which defines the southwest caldera wall but the concentration of intense venting appears to be related also to the spatial distribution of lava types in the vent field and their contrasting permeabilities other structural trends of faults and fissures within the field also influence the location of individual vents

gulf stream dynamics along the southeastern u s seaboard abstractthe gulf stream strongly interacts with the topography along the southeastern u s seaboard between the straits of florida and cape hatteras the dynamics of the gulf stream in this region is investigated with a set of realistic very high resolution simulations using the regional ocean modeling system roms the mean path is strongly influenced by the topography and in particular the charleston bump there are significant local pressure anomalies and topographic form stresses exerted by the bump that retard the mean flow and steer the mean current pathway seaward the topography provides through bottom pressure torque the positive input of barotropic vorticity necessary to balance the meridional transport of fluid and close the gyre scale vorticity balance the effect of the topography on the development of meanders and eddies is studied by computing energy budgets of the eddies and the mean flow the baroclinic instability is stabilized by the slope everywhere except past the bump the flow

observations of the vertical and temporal evolution of a natal pulse along the eastern agulhas bank this study re investigates the work of lutjeharms et al 2001 2003 who documented the properties of a natal pulse using isopycnal lagrangian floats we combined lagrangian analyses and eulerian maps derived from objective analysis to better describe the evolution of a natal pulse along three density surfaces referred to as the surface satellite observed shallow isopycnal 1026 8 kg m 3 and deep isopycnal 1027 2 kg m 3 layer our observations show that this natal pulse extended to a depth of 1000m and was associated with cyclonic relative vorticity values of about 6 5 to 8 5x10 5 s 1 in the surface and shallow layer and 4x10 5 s 1 in the deep layer this natal pulse contributed to cross shelf exchange through the offshore advection of eastern agulhas bank water near the surface onshore advection of south indian central water and or indian equatorial water in the shallow layer and antarctic intermediate water in the deep layer sea surface temperature maps showed that the downstream progression of the natal pulse along the 3000m isobath was related to a readjustment of its rotation axis this readjustment advected eastern agulhas bank water into the natal pulse eddy and triggered a sst cooling of about 3 c in the cyclonic area the importance of a warm recirculating agulhas plume originating from the natal pulse was highlighted this warm water plume extended to a depth of 700m and was associated with onshore velocities exceeding those experienced within the natal pulse eddy by a factor of two our observations indicate that the june july 1998 natal pulse and its associated plumes enhanced cross shelf exchanges this article is protected by copyright all rights reserved

new perspectives on natal pulses from satellite observations 1 more than 6 years of high frequency sea surface temperature sst imagery are used to follow perturbations at the inshore front of the agulhas current between the northern natal bight and port elizabeth selected case studies as well as a front detection algorithm applied to the sst data provide some new insights into the dynamics of natal pulses and the variability of the northern agulhas current over the measurement period the path of the agulhas current s inshore front does not exhibit any seasonality instead large excursions in the agulhas current s inshore front are dominated by the intermittent passage of offshore cyclonic meanders from the natal bight and port edward regions to port elizabeth sst imagery reveals that as they progress downstream natal pulses interact with the topography to form secondary offshore meanders which propagate in the lee of the original perturbation over time these secondary meanders dissipate remerge with the original natal pulse or detach from the agulhas current fluctuations in the agulhas current inshore path do not display the same frequency characteristics at all transects from the northern natal bight to port edward both the size and frequency of natal pulses increases while south of port edward the number of natal pulses decreases at port elizabeth the number of natal pulses observed is lower in comparison to previous estimates with an average of 1 6 natal pulses per year

submesoscale coherent vortices in the gulf stream seismic images and glider sections of the gulf stream front along the u s eastern seaboard capture deep lens shaped submesoscale features these features have radii of 5 20 km thicknesses of 150 300 m and are located at depths greater than 500 m these are typical signatures of anticyclonic submesoscale coherent vortices a submesoscale resolving realistic simulation which reproduces submesoscale coherent vortices with the same characteristics is used to analyze their generation mechanism submesoscale coherent vortices are primarily generated where the gulf stream meets the charleston bump a deep topographic feature due to the frictional effects and intense mixing in the wake of the topography these submesoscale coherent vortices can transport waters from the charleston bump s thick bottom mixed layer over long distances and spread them within the subtropical gyre their net effect on heat and salt distribution remains to be quantified plain language summary the interior of the ocean is populated by small scale coherent vortices which redistribute water properties on the scale of basins these structures are very difficult to observe they have no surface signature and small dimensions on the order of 1 50 km such that they are missed by satellites and sampled only by chance furthermore climate scale ocean models do not resolve these type of motions and do not take into account their impacts for the large scale transport and distribution of heat nutrients and other materials understanding and parameterizing these phenomena within models is critical for a better prediction of climate here we present new observations of submesoscale coherent vortices from seismic images and glider sections in the region of the gulf stream we use a numerical model at very high resolution to reproduce vortices with the same characteristics and to analyze their generation mechanism these vortices are generated where the gulf stream interacts with a deep topographic feature called the charleston bump due to frictional effects and intense mixing in the wake of the topography these vortices transport waters from the charleston bump s thick bottom mixed layer and act to spread them all around the subtropical gyre