on the origin of the warm inflow to the nordic seas abstract warm and saline waters enter the nordic seas from the south as part of the warm to cold water transformation of the thermohaline circulation of the northern north atlantic one explanation for the origin of the nordic seas inflow is a shallow source hypothesis under which the inflow waters are a modification of upper ocean subtropical waters warm waters from the subtropical gyre are carried to the eastern north atlantic by the north atlantic current and branch northwards joined by poleward upper thermocline flow along the upper continental slope to provide the nordic seas inflow along this pathway the upper water column is progressively cooled and freshened by winter convection the subpolar mode water transformation process and this sets the inflow characteristics a deep source hypothesis provides an alternative explanation for the characteristics of the nordic seas inflow and the pathway delivering the waters to the inflow under this hypothesis inflow waters originate from the core of the mediterranean overflow waters in the gulf of cadiz carried northward at mid depth by the eastern boundary undercurrent in the subtropics continuing into the subpolar gyre along the eastern boundary and rising from depths near 1200m in the rockall trough to less than 600m to cross the wyville thomson ridge into the faroe shetland channel and thence to the nordic seas the deep source hypothesis focus is on lower thermocline source waters beneath the sill depth for the nordic seas inflow in contrast to the shallow source hypothesis focus of transformation of upper thermocline waters above the sill depth on the basis of regional water mass distributions geostrophic shear and direct current measurements we reject the deep source hypothesis in favor of the shallow source hypothesis rather than a flow of deep mediterranean overflow water along the eastern boundary rising from depth to feed the nordic seas the inflow is supplied directly by transformed north atlantic current waters from the same depth range as the inflow mediterranean overflow water is a constituent of the inflow but only through its contribution to defining the temperature salinity relationship of the interior of the subtropical gyre from which the north atlantic current draws its water rather than by direct northward advection of mediterranean outflow water via the eastern boundary undercurrent crossing from the subtropics into the subpolar domain instead the eastern boundary undercurrent wholly expels its transport of mediterranean overflow water into the eastern edge of the subtropical gyre creating the mid depth westward extending subtropical salinity plume for the lower thermocline isopycnal range of the core of the mediterranean overflow water measurements show that at the wyville thomson ridge the flow is southward and descending rather than northward and rising representing cold spillover from the faroese channels entraining warm upper ocean waters as the spillover plume descends and warms into the northern rockall trough no evidence is found in rockall trough northward of 54 n porcupine bank for direct advection of mediterranean overflow waters via an eastern boundary undercurrent extension and the very dilute mediterranean overflow waters in the trough reflect the interaction of the wyville thomson ridge plume descending into the trough from the north and lower thermocline waters delivered to the trough from the south

tracking the prime eddy using satellite altimetry abstract the prime cruise to the north atlantic during june july 1996 surveyed and sampled an extremely vigorous and deep reaching eddy with a significant barotropic component although it exhibited anticyclonic flow and featured a warm core at depth it had been capped at some point during its lifetime so appeared as a cold feature in the upper 500 m satellite derived sea surface temperatures sst showed it to have moved little during the few weeks prior to the cruise in this paper we discuss the origin of the prime eddy including where and when it is likely to have formed consistently large amounts of cloud cover restrict the use of sst imagery to track such features altimetry provides a better method to trace this eddy back in time and space since microwave radiation is not significantly affected by cloud cover sea level anomaly sla data from the topex poseidon and european remote sensing ers satellites were used results show that the eddy remained almost stationary in the iceland basin since first being detected in late 1995 and that it almost certainly formed locally probably as a result of an instability in the current flow around the northwest of the hatton bank comparisons between satellite slas and hydrographic estimates of sea surface elevation confirm that the eddy had a substantial barotropic flow both the altimeter data and the sea surface height derived from the acoustic doppler current profiler agree that the prime eddy had a sea surface elevation of about 20 cm and that its diameter was about 120 km

ore forming process of the huijiabao gold district southwestern guizhou province china evidence from fluid inclusions and stable isotopes abstract the huijiabao gold district is one of the major producers for carlin type gold deposits in southwestern guizhou province china including taipingdong zimudang shuiyindong bojitian and other gold deposits occurrences petrographic observation microthermometric study and laser raman spectroscopy were carried out on the fluid inclusions within representative minerals in various mineralization stages from these four gold deposits five types of fluid inclusions have been recognized in hydrothermal minerals of different ore forming stages aqueous inclusions co2 inclusions co2 h2o inclusions hydrocarbon inclusions and hydrocarbon h2o inclusions the ore forming fluids are characterized by a h2o co2 ch4 n2 system with medium to low temperature and low salinity from early mineralization stage to later ones the compositions of the ore forming fluids experienced an evolution of h2o nacl h2o nacl co2 ch4 n2 h2o nacl ch4 co2 with a slight decrease in homogenization temperature and salinity the 18o values of the main stage quartz vary from 15 2 to 24 1 while the dh2o and calculated 18oh2o values of the ore forming fluids range from 56 9 to 116 3 and from 2 12 to 12 7 respectively the 13cpdb and 18osmow values of hydrothermal calcite change in the range of 9 1 to 0 5 and 11 1 23 2 respectively stable isotopic characteristics indicate that the ore forming fluid was mainly composed of ore and hydrocarbon bearing basinal fluid the dynamic fractionation of the sulfur in the diagenetic pyrite is controlled by bacterial reduction of marine sulfates the hydrothermal sulfides and the diagenetic pyrite from the host rocks are very similar in their sulfur isotopic composition suggesting that the sulfur in the ore forming fluids was mainly derived from dissolution of diagenetic pyrite the study of fluid inclusions indicates that immiscibility of h2o nacl co2 fluids took place during the main mineralization stage and caused the precipitation and enrichment of gold

directly measured mid depth circulation in the northeastern north atlantic ocean the circulation of water masses in the northeastern north atlantic ocean has a strong influence on global climate owing to the northward transport of warm subtropical water to high latitudes but the ocean circulation at depths below the reach of satellite observations is difficult to measure and only recently have comprehensive direct observations of whole ocean basins been possible here we present quantitative maps of the absolute velocities at two levels in the northeastern north atlantic as obtained from acoustically tracked floats we find that most of the mean flow transported northward by the gulf stream system at the thermocline level about 600 m depth remains within the subpolar region and only relatively little enters the rockall trough or the nordic seas contrary to previous work our data indicate that warm saline water from the mediterranean sea reaches the high latitudes through a combination of narrow slope currents and mixing processes at both depths under investigation currents cross the mid atlantic ridge preferentially over deep gaps in the ridge demonstrating that sea floor topography can constrain even upper ocean circulation patterns

interannual thermohaline changes in the northern north atlantic 1991 1996 abstract in the period 1991 1996 the woce hydrographic section a1e ar7e between greenland and ireland was repeated five times the observed thermohaline changes altered the baroclinic structure along the eastern margin of the subpolar gyre significantly between june 1995 and august 1996 an overall increase of the temperature and thickness and a decrease of the density of the subpolar mode water spmw layer were observed accompanied by an increase of its salinity east of the reykjanes ridge and a decrease of its salinity in the irminger sea the changes were most pronounced in the iceland basin where the subarctic front retreated westwards coinciding with a strong weakening of the westerlies as determined by the north atlantic oscillation they are related to a local reduction of the ekman upwelling and the ocean to atmosphere heat flux on the one hand and to the advection of anomalies from the subtropics on the other hand the eastward spreading of the different labrador sea water lsw vintages led to a corresponding cooling of the lsw in the irminger sea and in the iceland basin in the period 1991 1996 the renewal of the lsw in the rockall trough occurred more sporadically indicating that the north atlantic current nac impedes the southward spreading of lsw in the eastern atlantic the changes in 1996 seem to have also counteracted this spreading

discrete eddies in the northern north atlantic as observed by looping rafos floats abstract rafos float trajectories near the 27 5 density level were analyzed to investigate discrete eddies in the northern north atlantic with the objective of determining their geographical distribution and characteristics floats that made two or more consecutive loops in the same direction loopers were considered to have been in an eddy overall 15 24 float years of the float data were in loopers one hundred and eight loopers were identified in 96 different eddies roughly half of the eddies were cyclonic 49 and half were anticyclonic 51 although the percentages varied in different regions a few eddies were quasi stationary for long times one for over a year in the iceland basin and many others clearly translated often in the direction of the general circulation as observed by non looping floats several floats were trapped in eddies in the vicinity of the north atlantic current just upstream west of the charlie gibbs 52 n and faraday 50 n fracture zones which seem to be preferred routes for flow crossing the mid atlantic ridge five floats looped in four anticyclones that translated southwestward away from the eastern boundary near the goban spur 47 50 n these could have been weak meddies forming from remnants of warm salty mediterranean water advected northward along the eastern boundary

a census of meddies tracked by floats recent subsurface float measurements in 27 mediterranean water eddies meddies in the atlantic are grouped together to reveal new information about the pathways of these energetic eddies and how they are often modified and possibly destroyed by collisions with seamounts twenty meddies were tracked in the iberian basin west of portugal seven in the canary basin during february 1994 14 meddies were simultaneously observed 11 of them in the iberian basin most 69 of the newly formed meddies in the iberian basin translated southwestward into the vicinity of the horseshoe seamounts and probably collided with them some meddies 31 passed around the northern side of the seamounts and translated southwestward at a typical velocity of 2 0 cm s into the canary basin some meddies observed there were estimated to be up to 5 yr old four meddies in the canary basin collided with the great meteor seamounts and three meddies were inferred to have been destroyed by the collision overall an estimated 90 of meddies collided with major seamounts the mean time from meddy formation to a collision with a major seamount was estimated to be around 1 7 yr combined with the estimated meddy formation rate of 17 meddies yr from previous work this suggests that around 29 meddies co exist in the north atlantic therefore during february 1994 we observed about half of the population of meddies

diatoms as an aid in identifying late holocene tsunami deposits diatoms bacillariophyta help identify the onshore deposits of tsunamis from earthquakes on the cascadia subduction zone along the pacific coast of oregon washington and british columbia and on faults high in the north american plate in the puget sound area of washington at the copalis river washington diatom analyses suggest that a tsunami deposit about 300 calendric years old 300 yr bp originated from sandy shoals of the lower estuary rather than nearby beaches or coastal dunes at cultus bay and west point washington well preserved benthic estuarine diatoms in sand sheets overlying tidal marsh peat indicate that the deposits came from intertidal or nearshore areas of puget sound on an abruptly uplifted mudflat at the landward end of hood canal at lynch cove washington tidal flat diatoms refute the possibility of a terrestrial source for the sand diatoms in 300 yr bp tsunami deposits on the niawiakum river washington confirm that the sand in these deposits had a marine source and help

the north atlantic current and surrounding waters at the crossroads the north atlantic current is a well defined western boundary current that flows north along the east side of the grand banks from 40 to 51 n where it turns sharply to the east and begins its journey across the ocean the current is unique in transporting warm tropical waters to much higher latitudes than any other western boundary current and thus plays a crucial role in ameliorating the climate of the european subcontinent the north atlantic current originates in the gulf stream when the latter curves north around the southeast newfoundland rise a major submarine ridge that stretches se from the grand banks a well defined front delineates the path of the current as long as it flows north as a western boundary current after the current turns east in the north it broadens into a widening band of eastward drift without a sharp or permanent front in the sense of the eastward flowing gulf stream after it separates from cape hatteras the north atlantic current transports more than 40 sv 1 sv 106 m s 1 in the south and about 20 sv by the time it flows east across the mid atlantic ridge the currents along the northward flowing front are quite swift with typical maximum average speeds in the upper 300 m near 1 m s 1 2 knots the current meanders almost as wildly as a snaking river but unlike steep meanders in the gulf stream these meanders appear to be stable and with one exception have not been observed to break off to form pools of warm and or cold waters as frequently occurs in the gulf stream the meanders appear to be induced by major topographic features along the path of the current namely the southeast newfoundland rise the newfoundland seamounts and flemish cap strong recirculations develop on the concave side of the meanders one of these the mann eddy at the first meander crest of the north atlantic current should be regarded as a permanent feature of the north atlantic circulation other meanders also contain recirculations that can persist for months under certain conditions these can merge together to form an extended sw flow recirculation just east of the north atlantic current

central water vortices of the eastern north atlantic abstract a set of 102 high resolution hydrographic lines mostly xbt lines in the eastern north atlantic is used to study baroclinic vortices dynamically intensified within the central water layer first for the sake of comparison with recent results from altimetry spatial statistics of the main thermocline dynamic height are computed the dynamic height wavenumber spectrum slope close to k 3 at wavelengths shorter than 300 km and the decrease with latitude of eddy scales deduced from its autocorrelation function are found to be consistent with previous local altimetric results then using a criterion of local temperature anomaly relative to the large scale trend along each line 162 central water mesoscale vortices are detected their distribution is heterogeneous vortices of different size sign and intensity being found in most places they have a mean apparent diameter chord along the line of 110 50 km it is estimated that a range of 100 145 central water vortices coexist at the same t

north atlantic surface circulation during the 1990 s observed with satellite tracked drifters a new compilation of lagrangian velocity observations describes the state of the north atlantic surface circulation during the 1990s gridded fields of velocity and eddy kinetic energy eke are constructed from trajectories of more than 1500 15 m drogued satellite tracked surface drifters in service between january 1990 and december 1999 this time period overlaps a coordinated field study of circulation and variability in the north atlantic completed between 1996 2000 as part of the world ocean circulation experiment we describe the construction of a self consistent drifter climatology present decadal mean quasi eulerian velocity and eke fields computed on a 1 grid and compare these results with contemporary satellite measurements detailed discussion of the inferred surface circulation is focused on three regions 1 the gulf stream and north atlantic current 2 the labrador sea and subpolar gyre and 3 the caribbean sea the swiftest drifter motions were found in the equatorial region and along the tropical subtropical and subpolar western boundaries the maximum instantaneous speed determined from a single quality controlled and filtered drifter observation was 273 cm s 1 in the gulf stream southeast of cape cod the highest eke value in the north atlantic 2790 cm2 s 2 was found in the gulf stream just downstream of the new england seamounts over most of the atlantic basin drifter derived eke values were found to be o 100 cm2 s 2 higher than corresponding values derived from satellite altimetry in the labrador sea a region of sharply elevated eke appears to be geographically related to the localized ejection of drifters and by extension mass and kinetic energy from the energetic west greenland current between 60 and 62 n when compared to drifter measurements made in the late 1970s our results suggest but do not statistically confirm an enhancement and slight northward shift of the zonal gulf stream extension such a shift is consistent in sign with expectations based on observed interdecadal variations in wind stress and subtropical gyre potential energy associated with the north atlantic oscillation

characteristics of intermediate water flow in the benguela current as measured with rafos floats abstract seven floats not launched in rings crossed over the mid atlantic ridge in the benguela extension with a mean westward velocity of around 2 cm s between 22s and 35s two agulhas rings crossed over the mid atlantic ridge with a mean velocity of 5 7 cm s toward 285 this implies they translated at around 3 8 cm s through the background velocity field near 750 m the boundaries of the benguela current extension were clearly defined from the observations at 750 m the benguela extension was bounded on the south by 35s and the north by an eastward current located between 18s and 21s other recent float measurements suggest that this eastward current originates near the trindade ridge close to the western boundary and extends across most of the south atlantic limiting the benguela extension from flowing north of around 20s the westward transport of the benguela extension was estimated to be 15 sv by integrating the mean westward velocities from 22s to 35s and multiplying by the 500 m estimated thickness of intermediate water roughly 1 5 sv of this are transported by the 3 agulhas rings that cross the mid atlantic ridge each year as observed with altimetry this value of the benguela extension transport is the first one to have been obtained from long term two year observations and across the full width of the benguela extension

dynamics and evolution of a northern meddy abstract a meddy was discovered in april 1997 off the northwestern corner of spain near 45 n 11 30 w it was tracked during 18 months with lagrangian floats and deep drogued buoys and several cruises were set to collect further hydrological and lowered adcp measurements on it the meddy named ulla was a one core lens with maximum values of temperature and salinity of 11 5 c and 36 17 psu near 1000 m depth yielding anomalies above 2 5 c and 0 5 psu compared to its environment its rotation frequency was close to 1 loop every 5 days the maximum azimuthal velocities of 15 20 cm s 1 were reached near a 15 km radius the meddy had a wide remote influence notably up to the surface and was associated with a total azimuthal volume transport of around 10 sv sv 106 m3 s 1 of which around 2 sv was trapped in the core a widening of the radial structure with decreasing depth was notable in august 1997 meddy ulla was significantly elliptic for most of the time and depending on the periods the main el

eddy kinetic energy of the north atlantic subpolar gyre from satellite altimetry the surface eddy kinetic energy field of the north atlantic subpolar gyre 40 65 n 5 60 w is studied using the altimetric satellites geosat 1987 1988 and ers 1 1992 1993 this is on the whole an area of low eddy activity previous studies of the north atlantic have usually concentrated on the highly variable gulf stream system we review what is known of the surface circulation of the region we confirm that there is a close relationship between the eddy kinetic energy and the mean currents and that it is strongly constrained by the topography the eddy field occurs in deep water and follows the contours particularly around the flemish cap high eddy kinetic energy is seen on the flanks of topography and is higher where the slope is steeper this is particularly clear on both east and west flanks of the rockall plateau interannual changes in the currents are revealed by the differences between the geosat and ers 1 eddy kinetic energy maps in some years 1988 and 1992 1993 the northern core of the north atlantic current nac usually assumed to be tied to the charlie gibbs fracture zone 52 n is considerably weaker and may not exist at all while in 1987 there is a distinct core here in 1988 and 1992 1993 the main eddy region shifts farther to the south to about 49 n in 1988 and 50 n in 1992 1993 in 1987 there is also a current core even farther south centered at about 47 n implying that in that year the nac is arranged into two distinct branches

pathways of cross frontal exchange in the north atlantic current the north atlantic current nac forms part of the boundary between the subtropical and subpolar gyres in the north atlantic ocean the current has topographically controlled stationary meanders that appear to grow and decay a region east of the current in the newfoundland basin contains water of mixed subpolar subtropical properties suggesting that there is exchange across the nac this study considers data from isopycnal rafos floats launched in the nac region from 1993 to 1995 we use the rafos data to define the frontal zone as a pressure range where the jet is most likely to be found this definition requires a latitudinal dependence as the nac shoals to the north floats shallower and deeper than this range are defined to be on the subpolar and subtropical side respectively these definitions are used to estimate mixing that occurs between the current and its surroundings and to estimate the relative quantity of exchange of water parcels between the two gyres only small quantities of mass exchange from one gyre to the other are found but there is a distinct asymmetry leading to a mean flux from the subpolar to subtropical sides we also find that floats spend significant time in the frontal region and are frequently exchanged between fast and slow moving waters particularly at the meander extrema diffusion while in the jet leads to eddy cross frontal exchange which is important for the exchange of properties across the nac

agulhas eddies a synoptic view using geosat erm data abstract warm core rings formed in the agulhas retroflection transfer water from the indian ocean to the south atlantic in an attempt to measure the strength of this exchange a combination of satellite altimeter and hydrographic data are used to examine agulhas eddy paths and decay rates in the south atlantic because the surface dynamic height of a warm core eddy is higher than surrounding waters the rings are visible in satellite altimeter measurements over 20 agulhas eddies have been tracked from maps of anomalous sea surface height ssh derived from the geosat exact repeat mission erm dataset the correlation r2 of dynamic height referenced to 2000 dbar and anomaly ssh for one coincidentally sampled area is 97 within an agulhas eddy dropping to a fraction of that outside of it indicating that the ssh anomaly signal is a reliable measure for strong features like agulhas eddies the sizes and distribution of the agulhas eddies in the erm record compare favorably with those in recent hydrogr

westward motion of mesoscale eddies abstract since the pioneering work of nof the determination of the westward drift of mesoscale eddies under the planetary beta effect has been a recurrent theme in mesoscale oceanography and several different formulae have been proposed in the literature here recpatiulation is sought and within the confines of a single layer model a generalized formula is derived although it is similar to nof s the present formula is established from a modified definition and with fewer assumptions it also recaptiulates all other formulae for the one layer model and applies to a wide variety of situations including cases when the vortex develops a wake of rossby waves or undergoes axismmetrization following the derivation of the formula a physical interpretation clarifies the migration mechanism which can be divided between a self induced propulsion and a reaction from the displaced ambient fluid numerical simulations with primitive and geostrophic equations validate the formula for a variety of length sc

a long lived eddy in the iceland basin 1998 a survey was made of a large 100 km eddy in the iceland basin in june 1998 in situ observations from a shallow undulating conductivity temperature depth profiler and vessel mounted acoustic doppler current profiler were used to generate sea surface height along two topex poseidon tracks comparisons were made with the altimetric measurements to arrive at an estimate of the sea surface height for 6 years of topex poseidon altimeter data the 3 month track of a drifting buoy was used to estimate the location of the center of the eddy comparison with the altimetric sea surface height showed that the position of the eddy correlated well with an elevated sea surface signal of 25 30 cm having identified this signal as a characteristic signature of eddies inspection of the 6 year record revealed other similar features whose presence and longevity varied considerably the presence or absence of eddies appeared to link with the large scale variability of the subpolar gyre when the gyre expanded e g 1993 1994 the north atlantic current tended to follow a southerly route and eddies in the iceland basin were few and weak especially compared to periods when the gyre contracted e g 1992 1993 and 1996 1998 and the north atlantic current turned through the iceland basin then saltier water from the eastern north atlantic extended westward into the iceland basin and into large long lived eddies

a census of eddies observed in north atlantic sofar float data abstract sofar floats that looped in discrete eddies were studied in order to map and describe the distribution and characteristics of eddies in the north atlantic one hundred eighteen individual looping float trajectories loopers were identified each consisting of two or more consecutive loops each looper was interpreted to be in a discrete eddy and its characteristics were estimated from the float trajectory the highest percentage of loopers occured at 700m in the newfoundland basin where roughly half of the float data were in loopers mostly cyclones in the gulf stream region approximately 20 of the float data recorded at 700m were in loopers again mostly cyclones overall 21 of 700m data and 6 of 2000m data were in loopers the fastest swirl speeds 40cm s 1 were in cyclones south of the gulf stream most of which were in gulf stream rings but numerous swift 35cm s 1 anticyclones were found there too swirl velocity decreased with depth to roughly half as swift at 2000m as at 700m for three eddies in the sargasso sea measured simultaneously with floats at these two depths in the western north atlantic the average swirl velocity of cyclones and anticyclones was the same translation velocity of eddies was generally westward to southwestward at a few cm s 1 the mean translation velocity of 39 eddies in the sargasso sea was u bar 2 8 0 4 cm s 1 v bar 0 4 0 4 cm s 1 many of these were located just south of the gulf stream in the region of its recirculation and were probably advected by a westward current there near the gulf stream and along its extension in the newfoundland basin eddies were often advected downstream with speeds up to 15 20cm s 1 and eddy trajectories were often complicated south of 30 n and near the western boundary 700m eddies were advected northwestward and 1300m and 2000m eddies southeastward by boundary currents there numerous energetic anticyclones were observed south of the gulf stream one was tracked for 430 days and its properties well measured the formation of these eddies has not been documented but they are inferred to have formed near and by the gulf stream and to consist of a thick layer of 18 c water lying above a depression in the thermocline analogous anticyclones were observed in the newfoundland basin seaward of the gulf stream extension there

lagrangian observations of meddy formation during a mediterranean undercurrent seeding experiment mediterranean eddies meddies play an important role in maintaining the temperature and salinity distributions in the north atlantic but relatively little is known about their early life histories including where how often and by what mechanism they form a major field program called a mediterranean undercurrent seeding experiment has been carried out to directly observe meddy formation and the spreading pathways of mediterranean water into the north atlantic between may 1993 and march 1994 49 rafos floats were deployed sequentially in the mediterranean undercurrent south of portugal and tracked acoustically for up to 11 months the float deployments were accompanied by high resolution xbt sections across the undercurrent nine meddy formation events were observed in the float trajectories six near cape st vincent at the southwestern corner of the iberian peninsula and three near the estremadura promontory along the western portuguese continental slope meddy formation thus occurs where the continental slope turns sharply to the right when facing in the downstream direction of the undercurrent after conditionally sampling the float dataset to identify floats that were well seeded in the undercurrent the authors have estimated a meddy formation rate of 15 20 meddies per year the timescale for meddy formation at cape st vincent was found to be 3 7 days shorter than previous estimates based on the volume of larger meddies meddies were observed to form most frequently when the speed of the mediterranean undercurrent was relatively fast the meddy formation process at cape st vincent resembles the conceptual model of e a d asaro whereby anticyclonically rotating eddies are formed by separation of a frictional boundary layer with negative relative vorticity at a sharp corner comparison of the relative vorticity in the anticyclonic shear zone of the undercurrent and that of the newly formed meddies shows that much of the anticyclonic relative vorticity in meddies can be accounted for by the horizontal shear in the undercurrent this confirms earlier work suggesting that the classical mechanism for the generation of submesoscale coherent vortices by collapse and geostrophic adjustment of a weakly stratified fluid injected into a stratified ocean may not be the principle mechanism at work in the formation of meddies at cape st vincent

generation of submesoscale vortices a new mechanism small scale intense vortices composed of water with anomalous values of quasi conservative tracers have been observed in many oceans they are particularly numerous in the beaufort gyre of the arctic ocean possible mechanisms responsible for the generation of these features are examined conservation of temperature salinity and nutrients requires that beaufort sea vortices be created from water that flows into the arctic ocean from the pacific ocean across the broad shallow chukchi sea much of this water passes through barrow canyon near point barrow alaska observations in the canyon show the generation of vortices of approximately the same size as those observed in the beaufort sea barrow canyon is therefore a likely site for the generation of beaufort sea vortices most observed beaufort sea vortices have a central potential vorticity near zero because of a relative vorticity close to their chukchi sea source water is typically stratified with little relative vorticity so that its potential vorticity is nonzero a key step in the generation of the vortices is therefore the reduction of the potential vorticity of chukchi sea water to nearly zero it is proposed that this occurs through the action of frictional torques occurring as the chukchi sea water flows through barrow canyon rather than througji the action of vertical mixing because this flow is driven by a downstream pressure gradient it is concentrated on the right hand wall of the canyon by the coriolis force the frictional torques thus preferentially reduce the potential vorticity of the fluid anticyclonic vortices are therefore preferentially generated it is suggested that a similar scenario may play a role in the generation of submesoscale vortices containing water from the mediterranean and labrador seas