the subthermocline lens d1 part i description of water properties and velocity profiles abstract one remarkable result of the local dynamics experiment in polymode is the discovery of a large number of small energetic eddies using ctd data sofar float tracks and profiles of absolute velocity we describe one of these features the subthermocline eddy d1 the feature has an advective time scale of 1 day and its primary mode of movement is advection by the ambient flow field the eddy is resolved into a coordinate system moving with the velocity of the ambient flow which ranges from 11 16 cm s 1 its phase speed is less than 2 cm s 1 the eddy is a lens centered at 1500 db velocity profiles show the lens has no detectable signal in and above the main thermocline or below about 3000 db its subsurface velocity maximum is 28 6 cm s 1 at 1500 db 15 km from the center the radial variation of the azimuthal velocity is gaussian inside the velocity maximum but decays as e br beyond there is little evidence of the eddy beyond a radius of 25 km inside the velocity maximum the eddy is characte

detection structure and origin of extreme anomalies in a western atlantic oceanographic section abstract ten anomalous water parcels were detected in the water column of a western atlantic oceanographic section 0 5550 m 70 w 23 33 n the parcels had extreme properties lying either two standard deviations from historical mean values or estimated origins lying 2000 km from the oceanographic section detection structure and origin of the parcels were determined from analyses on isobaric and isopycnal surfaces using eight kinds of measurements temperature salinity oxygen light scattering silicate phosphate nitrate and tritium the parcels originated from seven of the major water masses comprising the north atlantic ocean as observed along the oceanographic section the parcels had the following average range characteristics vertical pressure extent 650 db 100 150 db horizontal extent 130 km 30 260 km and distance to origin 2300 km 400 5200 km a population density equaling approximately one parcel per 100 km was obtained as the number of parcels 10 divided by the length o

steady models of arctic shelf basin exchange steady state exchanges between the arctic shelves and the central basins are estimated using an inverse box model estimates based only on mass heat and salt conservation are highly uncertain and cannot determine how the shelf basin exchange is partitioned between dense overflows and surface layer exchange inclusion of 18o conservation greatly reduces the uncertainty with the 18o constraints dense water fluxes from the shelves of 0 2 0 1 sv in the canadian basin and 1 4 0 3 sv in the eurasian basin with a small o 0 1 sv surface layer transport from shelves to basins best satisfy the requirements of steady state up to 3 8 sv of shelfbreak upwelling is consistent within error bars with steady state but none is required water leaving the shelves is replaced primarily from the bering strait the barents sea inflow and runoff and not from the basin surface layer proper representation of these external sources for the shelves is important for capturing the full range of plausible steady solutions the steady state solutions identify the balances which if upset could lead to arctic change

circulation and thermohaline variability of the hanna shoal region on the northeastern chukchi sea shelf we analyzed velocity and hydrographic data from 23 moorings in the northeast chukchi sea from 2011 to 2014 in most years the eastern side of hanna shoal was strongly stratified year round while weakly stratified regions prevailed on the shelf south and west of the shoal stratification differences cause differential vertical mixing rates which in conjunction with advection of different bottom water properties resulted in seasonally varying along isobath density gradients in agreement with numerical models we find that bottom waters flow anticyclonically around the shoal whereas most of the shelf responded barotropically to wind forcing there was a strong baroclinic component to the flow field northeast of hanna shoal resulting in no net vertically integrated transport on average in contrast there is a net eastward transport from west of the shoal which implies convergence north of the shoal convergence and along isobath density gradients may foster cross shelf exchange north of hanna shoal modal analyses indicate that the shelf south of the shoal and barrow canyon responded coherently to local and remote winds whereas the wind current response around hanna shoal was less coherent barotropic topographic waves of 3 day period were generated episodically northeast of the shoal and propagate clockwise around hanna shoal but are blocked from entering barrow canyon and are possibly scattered by the horizontally sheared flow and converging isobaths on the western side of the shoal analysis of water properties on the western side of hanna shoal suggests that these include contributions from the western and southern portions of the chukchi sea

mesoscale eddies of the arctic ocean subsurface baroclinic eddies in the arctic ocean have a diameter of 10 20 km and are confined in depth between 50 and 300m during the arctic ice dynamics joint experiment aidjex in the central beaufort sea between march 1975 and may 1976 extensive information on eddy characteristics statistics and behavior was collected from four manned drifting ice camps during this 14 month period 146 eddies were encountered of which 19 were found to be repeated crossings making a total of 127 separate eddies observed during this period on the basis of the 1975 1976 aidjex data set it is concluded that eddies are 1 prevalent in the amerasia basin of the arctic ocean and in particular the beaufort sea where they may occupy up to a quarter of the available surface area 2 located in the depth range of 50 300 m although a few deeper eddies are also present 3 the second largest producers 32 of kinetic energy found within the upper 200 m of the beaufort sea and 4 predominantly anticyclonic in rotational tendency these eddies apparently originate north of point barrow alaska as a result of instability in the eastward flowing alaskan coastal current and transfer seasonally varying water properties from the chukchi sea and alaskan shelf into the arctic ocean they appear to translate in response to barotropic forcing over short time scales and over longer time periods move with the mean geostrophic field the season of formation for an eddy may be identified by the anomalous thermal properties still residing in its core

the structure dynamics and origin of a small scale lens of water in the western north atlantic thermocline abstract a small scale isolated anticyclonically rotating lens of water was observed in the western north atlantic thermocline during the polymode local dynamics experiment using a combination of sofar float hydrographic nutrient and moored current and temperature data we deduce that the lens was about 20 km across with a thickness not greater than 300 m centered on 750 m that its shape was not dissimilar to that of a vertical radial gaussian eddy and that at its center the lens had strong anomalies of salinity dissolved oxygen nitrate and vortex stretching the water mass properties within the eddy are not inconsistent with an origin for the feature near 15 n 54 w several thousand kilometers from where it was observed in the western north atlantic although an unambiguous origin cannot be discerned from the data if such features are not uncommon they may be an important mechanism for large scale mixing of water properties in the ocean

evaluation of shelf basin interaction in the western arctic by use of short lived radium isotopes the importance of mesoscale processes shelf basin exchange in the western arctic was evaluated by use of water column analyses of 228 ra 226 ra ratios and the first measurements of the short lived 224 ra t1 2 3 64 d in the arctic during the 2002 shelf basin interaction sbi program excess 224 ra was detected over the shelf but was not found seaward of the shelf break similarly the 228 ra 226 ra ratio dropped rapidly from the shelf across the shelf break consequently the model age gradient elapsed time since shelf residence northward across the chukchi shelf increased from 1 5 years nearshore to approximately 14 years in surface waters sampled off shelf at the southern margin of the beaufort gyre this steep gradient is consistent with very slow exchange between the chukchi shelf and the beaufort gyre whereby bering strait inflow is constrained by the earth s rotation to follow local isobaths and does not easily move into deeper water the strong dynamic control inhibiting water that enters the system through bering strait from flowing north across isobaths also would lead to a long recirculation time of river water emptied into the beaufort gyre possible mechanisms that can generate cross shelf currents that break the topographic constraint to follow isobaths and thereby transport water and associated properties off the shelves include wind induced upwelling downwelling meandering jets and eddies evidence of such a process was found during the icex project in the beaufort sea in april 2003 when excess 224 ra was measured over 200 km from any shelf source this required an ne offshore flow of 40 cm s 1 assuming that the source water derives from the mouth of barrow canyon a weak northeastward flow was measured using an ladcp within the upper 300 m of the ocean but was of lower speed than required by the 224 raxs at the time of the icex occupation

observations of small eddies in the beaufort sea the horizontal and vertical variations of velocity temperature density and turbulent kinetic energy dissipation in the central beaufort sea were measured with helicopter borne expendable current profilers and conductivity temperature depth units almost all velocity differences larger than 0 05 m s 1 could be consistently interpreted as being due to nearly circular eddies with a diameter of 10 20km a thickness of 50 500 m peak velocities of 0 07 0 3 m s 1 and little expression at the top of the ocean four such eddies were found two anticyclones were found and accurately sampled two cyclones were found but were only poorly sampled both were beneath and close to one of the anticyclones relative vorticity could be computed for two anticyclones and one cyclone within experimental error the two anticyclones and all historical beaufort sea anticyclones had a relative vorticity of and thus zero potential vorticity at the center the cyclone had a central relative vorticity of about 0 5 and thus a different value of potential vorticity than the surrounding fluid one anticyclonic eddy b was sampled seven times over a period of 23 days its measured velocity and density fields were in approximate gradient wind balance its central core contained values of temperature nitrate and silicate that were different from those outside the core at the same density it moved eastward at about 0 02 m s 1 through the surrounding fluid measurements of turbulent kinetic energy dissipation were almost always less than the noise level of the instrument about 10 9 w kg 1 corresponding to a mean dissipation much less than this and a minimum decay time due to turbulence much longer than 0 3 year the nondimensional strength rossby number and shape burger number of anticylcone b are very similar to those of other beaufort sea anticyclones and similar to those of small mid latitude eddies each of the eddies observed here was centered on a temperature maximum associated with one of the warm water masses that advect into the arctic ocean the two anticyclones were centered on temperature maxima originating in the pacific ocean whereas the two cyclones were centered on temperature maxima from the atlantic ocean this is consistent with the hypothesis that the eddies are formed as these water masses enter the arctic ocean

upwelling of arctic pycnocline associated with shear motion of sea ice 1 high resolution radar imagery shows that the dynamic response of winter sea ice to gradients in large scale surface wind stress is often localized along quasi linear fractures hundreds of kilometers long relative shearing motion across these narrow fractures can exceed 10 cm s 1 in one event recorded during the drift of the sheba ice camp we observed an intense zone of pycnocline upwelling 14 m associated with significant shear motion near the camp while upward turbulent heat flux in the ocean boundary layer reached nearly 400 w m 2 an order of magnitude greater than at any other time during the year long drift we attribute the upwelling to ekman pumping associated with concentrated ice shear over the entire arctic ocean sea ice cover this process could be responsible for significant heat exchange between the cold surface layer and warmer subsurface water at the ubiquitous fractures resulting from large scale atmosphere ice interactions

characterizing the eddy field in the arctic ocean halocline ice tethered profilers itp deployed in the arctic ocean between 2004 and 2013 have provided detailed temperature and salinity measurements of an assortment of halocline eddies a total of 127 mesoscale eddies have been detected 95 of which were anticyclones the majority of which had anomalously cold cores these cold core anticyclonic eddies were observed in the beaufort gyre region canadian water eddies and the vicinity of the transpolar drift stream eurasian water eddies an arctic wide calculation of the first baroclinic rossby deformation radius rd has been made using itp data coupled with climatology rd 13 km in the canadian water and 8 km in the eurasian water the observed eddies are found to have scales comparable to rd halocline eddies are in cyclogeostrophic balance and can be described by a rankine vortex with maximum azimuthal speeds between 0 05 and 0 4 m s the relationship between radius and thickness for the eddies is consistent with adjustment to the ambient stratification eddies may be divided into four groups each characterized by distinct core depths and core temperature and salinity properties suggesting multiple source regions and enabling speculation of varying formation mechanisms

a numerical study on the successive formation of meddy like lenses 1 we present a process study on the sustaining mechanism of lens formation using a series of numerical experiments of a density current over a sloping bottom with a cape along the coastline water parcels in the bottom density current are shed into the offshore region leading to periodic formation of anticyclonic lenses as part of baroclinic dipolar vortices the cyclonic partner is more prominent at the surface and the coupled vortices are carried by the mean current established in the offshore region parameter dependence of dipole generation is examined which suggests that the background current is necessary for the detached eddies to be coherent in the downstream direction and for shedding events to repeat nof and pichevin 1996 it is also shown that the density mixing of the bottom current provides criteria for cyclogenesis at the sea surface a detailed analysis is given by a five layer model forced by a water mass source sink which reproduces the baroclinic dipolar vortices similar to those observed in the preceding z coordinate model we find that the dipole generation is due to the finite amplitude divergence convergence of the baroclinic current passing the cape stern and chassignet 2000 the overall analyses suggest three necessary conditions for successive eddy formation 1 a localized variation in the coastline causing the finite amplitude disturbance 2 mixing of mediterranean water with the surrounding fluids leading to anticyclonic rotation of meddies as well as cyclogenesis at the surface and 3 background currents that advect the detached vortices out of the source region index terms 4255 oceanography general numerical modeling 4219 oceanography general continental shelf processes 4520 oceanography physical eddies and mesoscale processes 4528 oceanography physical fronts and jets keywords eddy shedding dense water plume numerical simulation

small water property transporting eddies statistical outliers in the hydrographic data of the polymode local dynamics experiment abstract hydrographic measurements from the polymode local dynamics experiment lde 31 n 69 5 w may july 1978 are examined for highly anomalous outlying observations of salinity oxygen and vortex stretching on isopycnal surfaces the methodology which defines outliers in the observations is based on examination of gaps in histograms of these water properties on each isopycnal these outliers are indicative of vertically confined over 20 2000 m sub mesoscale eddies diameters of 25 50 km at the lde site evidence for 31 eddies is found at the lde site over the two months of the experiment these features are described individually and characterized by their core water properly signal and dynamical structure eighteen features are found to be anticyclonic lenslike structure eight have no detectable dynamic signal and only four are characterized by cyclonic circulation the work establishes that sub mesoscale eddies in a small portion of the western north atlantic exhibit a variety of distinct wat

isolated waves and eddies in a shallow water model abstract a shallow water beta channel model was used to carry out numerical experiments with cyclonic and anticyclonic disturbances of various strengths the model is inviscid so fluid elements conserve potential vorticity q when unforced regions of closed q contours correspond to lagrangian material eddies all fluid within a lagrangian eddy travels with the eddy in contrast to regions of closed height contours motion is wavelike for very weak disturbances maximum particle speed u long planetary wave speed the height field disperses like a group of linear rossby waves and tracers have small oscillatory mainly north south displacements with very little scatter when u the planetary q field is sufficiently distorted for small lagrangian eddies to appear very small eddies are simply bodily advected by the linear wave field small eddies are to some extent self propelling they move westward and north cyclone or south anticyclone moving fluid elements towards their rest latit

observations of internal gravity waves under the arctic pack ice internal gravity waves measured under the arctic pack ice were strikingly different from measurements at lower latitudes the total wave energy integrated over the internal wave frequency band was lower by a factor of 0 03 0 07 and the spectral slope at high frequency was nearly 1 in contrast to the 2 observed at lower latitudes this result has implications for theoretical investigations of the generation evolution and destruction of internal waves and is also important for other processes such as the propagation of sound and the wave induced turbulent diffusion of heat plankton and chemical tracers

on the origin of eddies discovered during the polymode local dynamics experiment abstract the intensive hydrographic survey conducted in 1978 as part of the polymode local dynamics experiment lde revealed a large number of anomalous water parcels at various depths near 31 n 70 w in the sargasso sea from analyses of the mean water properties in the lde survey lindstrom and taft have prepared a census of discrete features that have statistically significant anomalies of salinity oxygen or potential vorticity the present analysis utilizes the climatological annual mean north atlantic dataset compiled by levitus to identify the large scale distribution of salinity and oxygen on specific potential density surfaces this technique has revealed distinct geographic origins for the majority of the 23 lde features analyzed nine shallow features residing between 25 8 and 26 4 sigma theta were found to have varied origins two from the eastern atlantic three from the gulf stream two from the central sargasso sea and two were indeterminate with the available data four of six upper th

modeling the formation and fate of the near surface temperature maximum in the canadian basin of the arctic ocean 1 a numerical model is used to investigate the time and space extent of the near surface temperature maximum nstm of the canadian basin of the arctic ocean over the years 2000 2009 the nstm is formed from local summertime absorption of solar radiation which in some circumstances descends through the fall and early winter to form a warm subsurface layer just below the winter mixed layer we find that winter survival of this layer is confined largely to the beaufort gyre of the canadian basin where ekman convergence and downwelling push the summer warm layer down below the winter mixing depth in recent years summer stratification has increased downwelling has accelerated and the nstm has warmed as the sea ice cover in the beaufort gyre has thinned the result is a strengthening nstm which contained enough heat by the end of winter 2007 2008 to melt about 20 cm of sea ice northwest of alaska the model also simulates a second deeper temperature maximum layer that forms from advection of saltier summer pacific water however this layer is difficult to adequately resolve and maintain given the model s resolution

changes to the near surface waters in the canada basin arctic ocean from 1993 2009 a basin in transition 1 increased sea ice melt and decreased surface albedo have changed the near surface water mass structure of the canada basin from 1993 2009 the near surface temperature maximum nstm and remnant of the previous winter s mixed layer rwml warmed by about 1 5 c and 0 5 c and freshened by about 4 and 2 practical salinity units respectively results from a 1 d model suggest rwml warming can be explained by heat diffusion from both the nstm and pacific summer water psw the same model predicts salinization of the rwml whereas freshening was observed this suggests that changes to the rwml are from both diffusion and the accumulation of freshwater the rwml s salinity was associated with distance from the center of the beaufort gyre the rwml at stations inside the gyre was on average 1 9 salinity units fresher than at stations outside in addition the salinity of psw in the canada basin defined by its local temperature maximum freshened from about 30 32 in 1993 to 28 32 in 2008 order of magnitude calculations suggest that neither changes in psw source waters nor changes in advection pathways of psw explain this freshening our model suggests that salt diffused from psw to the freshening rwml this diffusion increased and freshened the psw salinity range as the rwml freshened these results show that surface effects through warming and ice melt are felt to at least the depth of psw observations from 2009 show the appearance of a third temperature maximum from an as yet unknown source

eddy kinetic energy in the arctic ocean from a global simulation with a 1 km arctic simulating arctic ocean mesoscale eddies in ocean circulation models presents a great challenge because of their small size this study employs an unstructured mesh ocean sea ice model to conduct a decadal scale global simulation with a 1 km arctic it provides a basinwide overview of arctic eddy energetics increasing model resolution from 4 to 1 km increases arctic eddy kinetic energy eke and total kinetic energy tke by about 40 and 15 respectively eke is the highest along main currents over topography slopes where strong conversion from available potential energy to eke takes place it is high in halocline with a maximum typically centered in the depth range of 70 110 m and in the atlantic water layer of the eurasian basin as well the seasonal variability of eke along the continental slopes of southern canada and eastern eurasian basins is similar stronger in fall and weaker in spring

effects of ambient stratification and shelfbreak topography on offshore transport of dense water on continental shelves the transport of dense water offshore from an idealized coastal polynya is examined using a primitive equation numerical model first the prior scaling of the equilibrium density of water produced within the polynya is extended to include the effects of linear bottom slope next ambient linear stratification is added the equilibrium density is modified slightly by the density at the bottom at the initial time next shelfbreak topography is included with both weak and strong ambient stratification for the case of weak stratification dense water carried to the shelfbreak within eddies moves rapidly downslope and is trapped near the bottom the along shelf scale of the dense water cascading down the slope is set by the diameter of the dense water eddies that form along the periphery of the coastal polynya for the case of strong stratification dense water is carried offshore across the shelfbreak at an intermediate depth injecting water originally within the polynya across the shelf and over the continental slope a bottom trapped current flowing near the shelfbreak in the direction of coastal trapped wave propagation also forms these results suggest that water formed within coastal polynyas over arctic shelves may be capable of ventilating the continental slope regions and possibly central basins of the arctic ocean via eddy fluxes

large lenses of highly saline mediterranean water isolated compact anticyclonic eddies or salt lenses were found in the canary basin hydrographic surveys of three such lenses show large anomalies of salinity and temperature 0 8 2 5 c they are centered at 1100 m have a vertical extent of up to 900 m and radii of 50 km current meter records indicate anticyclonic velocities up to 29 cm s 1 fine structure with vertical scales of 20 m and less possibly due to intrusive decay appears at the outer edges of the lenses whereas the centers are free of such structure the probability of finding a salt lens at any station in the canary basin is fairly high 0 08

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

evidence for a lava lake on mt michael volcano saunders island south sandwich islands from landsat sentinel 2 and aster satellite imagery abstract mt michael is an active stratovolcano on saunders island in the south sandwich islands a remote oceanic island arc in the southern atlantic ocean bordering the southern ocean the arc contains the only active volcanoes in the south georgia and south sandwich islands british overseas territory yet little is known of their activity despite lava lakes being extremely rare with only a few global examples previous analyses of satellite avhrr imagery of mt michael in the 1990s showed persistent thermal anomalies not associated with magma overflowing the crater this suggested the existence of a lava lake inside mt michael s crater however their study relied on 1 km resolution imagery and there have been no long term investigations to determine if this is a persistent feature in situ observations of mt michael are extremely difficult given the location we used landsat sentinel 2 and aster satellite data to monitor activity and detect thermal anomalies within the crater persistent volcanic plumes and eruptions were identified throughout the thirty year period studied on all 15 occasions that a suitable satellite image was available a thermal anomaly within the crater was detected in the high transmissivity shortwave infrared bands swir centred on 1 65 m and 2 2 m pixel integrated surface temperatures over the crater floor yield temperatures of 284 419 c comparable to lava lakes elsewhere unmixing these temperatures using the dual band method reveals a molten lava component at basaltic temperatures 989 1279 c among a cooler crust this is the first evidence for a lava lake within mt michael from data that can resolve the crater floor and the first evidence for magmatic temperatures as thermal anomalies were detected in all images showing the crater we suggest that the lava lake is a common and persistent feature