mean stream coordinates structure of the subantarctic front temperature salinity and absolute velocity 1 the mean synoptic structure of the northern strongest branch of the antarctic circumpolar current southwest of tasmania at the subantarctic front saf is estimated by a stream coordinates analysis of data from overlapping arrays of inverted echo sounders iess and horizontal electric field recorders deployed during the 1995 1997 sub antarctic flux and dynamics experiment the stream coordinates are derived from a daily objective mapping of the temperature field obtained from combining the ies travel time measurements with an empirical look up table constructed from the extensive hydrography acquired during woce full water column stream coordinates sections of temperature salinity and absolute velocity are presented and compared with prior observations the along stream current has a single peak with surface velocities reaching about 50 cm s 1 the vertical structure of the along stream velocity is roughly consistent with a combined external and first internal normal mode description that is adapted to the buoyancy frequency as it varies across the front although there are some significant differences the cross stream structure of along stream velocity is very nearly symmetric about the jet axis but the lateral shear magnitude is slightly larger on the cold side of the saf separating the baroclinic and barotropic currents reveals that the saf currents are diffluent primarily baroclinically in the cross stream direction baroclinic cross stream diffluence of approximately 0 23 sv per km sv 106 m3 s 1 or about 16 sv per degree of longitude at 51 s the 2 year mean total saf transport is 75 sv for a 220 km width the barotropic contribution is small 8 sv but not negligible

the structure and transport of the gulf stream at 73 w abstract between september 1980 and may 1983 16 sections of temperature and velocity were obtained with the pegasus instrument along a transect crossing the gulf stream at 73 w the mean temperature and velocity fields of the upper 2000 meters were calculated the transport above 2000 meters calculated from the sections had a mean of 87 8 17 3 106 m3 s 1 a comparison with mass flux measurements obtained by previous investigators at cape fear indicated that the addition to the transport of the stream in the region was uniform with depth above 800 meters the mean inflow measured at the pegasus line was found to be uniform above 800 meters and to decrese substantially below this depth the increase in transport at the line estimated from the mean cross stream velocity field was 15 4 5 8 106 m3 s 1 per 100 km downstream distance the temporal fluctuation of the pegasus transport measurements was consistent with an annual cycle with a maximum in april the mean eddy kinetic energy at the surface

bottom temperatures in drake passage abstractlong time series of bottom temperatures in the southern ocean are rare the cdrake array with over 40 current and pressure recording inverted echo sounders moored across drake passage to monitor the antarctic circumpolar current acc variability and transport measured temperature at 1 and 50 m above the seafloor at depths 3500 m and at the southern continental margin the 4 yr dataset provided an opportunity to examine the temporal and spatial scales of bottom temperature variability high variability was observed ranges were 0 5 0 9 c in the northern passage and 0 3 0 6 c in the southern passage standard deviations in the two regions were 0 1 0 15 c and 0 05 c respectively meandering of the acc with its deep reaching thermocline accounted for up to 50 of the observed bottom temperature variance northern passage temperatures spaced less than 40 km apart were correlated with each other while those in the southern portion separated by 60 70 km were not a gap in the west scotia

satellite observations of an annual cycle in the agulhas current 1 ocean models show an annual cycle in the agulhas current transport which has not yet been confirmed in analyses of in situ or satellite observations a cross stream coordinate approach is used to study the variability of the agulhas current from 18 years of along track altimetry and merged altimetry and close to 7 years of high frequency sea surface temperature sst observations while the position and width of the agulhas current s dynamical core do not display an annual cycle the geostrophic current speed at the current s core exhibits distinct seasonal variations with a stronger flow observed in austral summer the annual cycle dominates the frequency spectra of the current s core geostrophic velocities

instruments and methods using distributed temperature sensors to monitor an antarctic ice shelf and sub ice shelf cavity monitoring of ice shelf and sub ice shelf ocean temperatures represents an important component in understanding ice sheet stability continuous monitoring is challenging due to difficult surface access difficulties in penetrating the ice shelf and the need for long term operation of non recoverable sensors we aim to develop rapid lightweight drilling and near continuous fiber optic temperature monitoring methods to meet these challenges during november 2011 two instrumented moorings were installed within and below the mcmurdo ice shelf a sub region of the ross ice shelf antarctica at windless bight we used a combination of ice coring for the upper portion of each shelf borehole and hot point drilling for penetration into the ocean the boreholes provided temporary access to the ice shelf cavity into which distributed temperature sensing dts fiber optic cables and conventional pressure temperature transducers were installed the dts moorings provided near continuous in time and depth observations of ice and ocean temperatures to a depth of almost 800 m beneath the ice shelf surface data received document the presence of near freezing water throughout the cavity from november through january followed by an influx of warmer water reaching 150 m beneath the ice shelf base during february and march the observations demonstrate prospects for achieving much higher spatial sampling of temperature than more conventional oceanographic moorings

internal tides in the northwestern south china sea observed by pressure recording inverted echo sounders abstract this study presents it observations in the northwestern scs from five pressure recording inverted echo sounders piess the vertical round trip acoustic travel times that piess measures are proportional to the vertical thermocline displacements therefore piess can be used to monitor the 1st mode internal tides piess were deployed along a section between the continental shelf break in the north and xisha islands in the south measurements show that both diurnal and semidiurnal its were stronger on the northern and southern sides of the section than those in the middle their temporal variations were coherent with local surface tides which implies locally generated its may be important complex empirical orthogonal function analysis reveals a small phase difference the south leads the north by 70 across the section for diurnal its but a significant phase difference the north leads the south by 360 for semidiurnal its these observations indicate that the dominant diurnal its propagate across the section from east to west while the semidiurnal its propagate along the section from north to south a ray tracing model was utilized to demonstrate the impact of mesoscale circulation patterns on the propagation of diurnal its from the luzon strait to the pies sites the model explains the temporal it variations which were incoherent with local surface tides the result indicates that diurnal its in the northwestern scs can be affected by its propagating from the luzon strait while semidiurnal its are primarily generated locally from the continental shelf break in the north

temporal variability of the meridional overturning circulation at 34 5 s results from two pilot boundary arrays in the south atlantic data from two boundary arrays deployed along 34 5 s are combined to produce the first continuous in situ time series observations of the basin wide meridional overturning circulation moc in the south atlantic daily estimates of the moc between march 2009 and december 2010 range between 3 sv and 39 sv 1 sv 106 m3 s 1 after a 10 day low pass filter is applied much of the variability in this 20 month record occurs at periods shorter than 100 days approximately two thirds of the moc variability is due to changes in the geostrophic baroclinic plus barotropic volume transport with the remainder associated with the direct wind forced ekman transport when low pass filtered to match previously published analyses in the north atlantic the observed temporal standard deviation at 34 5 s matches or somewhat exceeds that observed by time series observations at 16 n 26 5 n and 41 n for periods shorter than 20 days the basin wide moc variations are most strongly influenced by ekman flows while at periods between 20 and 90 days the geostrophic flows tend to exert slightly more control over the total transport variability of the moc the geostrophic shear variations are roughly equally controlled by density variations on the western and eastern boundaries at all time scales captured in the record the observed time mean moc vertical structure and temporal variability agree well with the limited independent observations available for confirmation

an altimetry based gravest empirical mode south of africa 1 development and validation 1 hydrographic transects of the antarctic circumpolar current acc south of africa are projected into baroclinic stream function space parameterized by pressure and dynamic height this produces a two dimensional gravest empirical mode gem that captures more than 97 of the total density and temperature variance in the acc domain weekly maps of absolute dynamic topography data derived from satellite altimetry are combined with the gem to obtain a 16 year time series of temperature and salinity fields the time series of thermohaline fields are compared with independent in situ observations the residuals decrease sharply below the thermocline and through the entire water column the mean root mean square rms error is 0 15c 0 02 and 0 02 kg m 3 for temperature salinity and density respectively the positions of acc fronts are followed in time using satellite altimetry data these locations correspond to both the observed and gem based positions the available temperature and salinity information allow one to calculate the baroclinic zonal velocity field between the surface and 2500 dbar this is compared with velocity measurements from repeat hydrographic transects at the goodhope line the net accumulated transports of the acc derived from these different methods are within 1 3 sv of each other similarly gem produced cross sectional velocities at 300 dbar compare closely to the observed data with the rms difference not exceeding 0 03 m s 1 the continuous time series of thermohaline fields described here are further exploited to understand the dynamic nature of the acc fronts in the region and which is given by swart and speich 2010

long term observations of north atlantic current transport at the gateway between western and eastern atlantic in the western north atlantic warm and saline water is brought by the north atlantic current nac from the subtropics into the subpolar gyre four inverted echo sounders with high precision pressure sensors pies were moored between 47 40 n and 52 30 n to study the main pathways of the nac from the western into the eastern basin the array configuration that forms three segments northern central and southern allows partitioning of the nac and some assessment of nac flow paths through the different mid atlantic ridge fracture zones we exploit the correlation between the nac transport measured between 2006 and 2010 and the geostrophic velocity from altimeter data to extend the time series of nac transports to the period from 1992 to 2013 the mean nac transport over the entire 21 years is 27 5 sv consisting of 60 warm water of subtropical origin and 40 subpolar water we did not find a significant trend in the total transport time series but individual segments had opposing trends leading to a more focused nac in the central subsection and decreasing transports in the southern and northern segments the spectral analysis exhibits several significant peaks the two most prominent are around 120 days identified as the time scale of meanders and eddies and at 4 9 years most likely related to the nao transport composites for the years of highest and lowest nao indices showed a significantly higher transport 2 9 sv during strong nao years mainly in the southern segment

distribution and circulation of labrador sea water abstract labrador sea water is the final product of the cyclonic circulation of subpolar mode water in the open northern north atlantic mccartney and talley 1982 the temperature and salinity of the convectively formed subpolar mode water decrease from 14 7 c 36 08 to 3 4 c 34 88 on account of the cumulative effects of excess precipitation and cooling the coldest mode water is labrador sea water which spreads at mid depths and is found throughout the north atlantic ocean north of 40 n and along its western boundary to 18 n a vertical minimum in potential vorticity is used as the primary tracer for labrador sea water labrador sea water is advected in three main directions out of the labrador sea 1 northeastward into the irminger sea 2 southeastward across the atlantic beneath the north atlantic current and 3 southward past newfoundland with the labrador current and thence westward into the slope water region crossing under the gulf stream off cape hatteras the labrador sea water core is

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

observed ocean bottom temperature variability at four sites in the northwestern argentine basin evidence of decadal deep abyssal warming amidst hourly to interannual variability during 2009 2019

diapycnal mixing in the southern ocean diagnosed using the dimes tracer and realistic velocity fields in this work we use realistic isopycnal velocities with a 3 d eddy diffusivity to advect and diffuse a tracer in the antarctic circumpolar current beginning in the southeast pacific and progressing through drake passage we prescribe a diapycnal diffusivity which takes one value in the se pacific west of 67 w and another value in drake passage east of that longitude and optimize the diffusivities using a cost function to give a best fit to experimental data from the dimes diapycnal and isopycnal mixing experiment in the southern ocean tracer released near the boundary between the upper and lower circumpolar deep water we find that diapycnal diffusivity is enhanced 20 fold in drake passage compared with the se pacific consistent with previous estimates obtained using a simpler advection diffusion model with constant but different zonal velocities east and west of 67 w our result shows that diapycnal mixing in the acc plays a significant role in transferring buoyancy within the meridional overturning circulation

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

labrador sea water circulation in the northern north atlantic ocean abstract direct observation of velocities with drifting floats near 1500 m depth in the north atlantic ocean north of about 45 n are combined to derive a new basin wide mean circulation within the layer of labrador sea water lsw inverse methods are used to determine a basin scale circulation constrained by non divergence and conservation of climatological large scale potential vorticity pv with the aim of investigating large scale pv dynamics improving circulation estimates near the basin boundaries and determining the relative amount of recirculation in sub basin gyres with aliased direct velocity data eulerian averages are created from combined datasets and a streamfunction of the non divergent flow is computed from the velocity curl and the imposed boundary conditions unlike deep flow regimes at low latitudes where the mid depth interior circulation is dominated by zonal currents the mid depth subpolar flow is dominated by gyres as suggested by previous estimates of mid depth circulation the lsw layer is rapidly circulating around the periphery of the subpolar basin in northern and western boundary currents recirculation within basins and exchange between the labrador basin and irminger basin is modified by the large scale pv constraints eastward flow across the mid atlantic ridge is concentrated in the charlie gibbs fracture zone with return flow above the reykjanes ridge a weaker subtropical return flow around the azores plateau appears but data are insufficient to map adequately this region

the north atlantic current based on trajectories of satellite tracked buoys and hydrographic sections both dietrich s and worthington s schemes of the north atlantic current are reconsidered ninety satellite tracked buoys have been analyzed in order to distinguish between these schemes neither could be confirmed the north atlantic current appears as a superposition of a broad west wind drift and a frontal jet in the western part of the north atlantic north of 40 n which becomes independent from the subtropical gyre neither a permanent branching suggested by dietrich nor a confinement of the subpolar gyre to the east of newfoundland per worthington can be found the north atlantic current extends over the entire north atlantic carrying more than 20 sverdrups sv toward the north this northward transport is mainly due to the northward flow around flemish cap and a sudden turn of the north atlantic current east of the mid atlantic ridge the buoy tracks have been used to determine speed and direction in the upper layers 100 m we combine these results with hydrographic data in order to obtain an estimate of the mass transport transport across the mid atlantic ridge is based on recent sections fahrbach et al 1985 while transport in the northeastern north atlantic has been derived from the erika dan sections at 53 5 n and 59 5 n according to these two sections the return flow occurs mainly below 1000 m after water mass conversion in the northern areas the results imply that about 7 sv of atlantic water are transformed into deep water in the area between 53 5 n and 60 n

the climatology of the north atlantic abstract data from approximately 144 000 hydrographic stations in the north atlantic have been retrieved from the national oceanic data centre and analysed to produce maps of mean pressure temperature salinity and oxygen on selected potential density surfaces for the domain bounded by 0 85 w and 0 65 n the data span the period from 1904 to 1990 with the majority of the data from the last four decades the data set for this region is 60 larger than that used in the production of levitus climatological world atlas this increase in stations coupled with smoothing scales specific to the north atlantic rather than the global ocean considerably improves the resolution of the basin s features the mean property fields and their associated standard deviations are resolved on a one degree grid with little smoothing contrasting with the levitus atlas where properties although presented on a one degree grid have been smoothed on the order of 1000km another important feature of this database is the process by which irregularly spaced data are averaged onto a regular grid in a significant departure from the levitus analysis which averaged on depth surfaces these data were averaged on potential density surfaces thus eliminating an artificial mixing of water mass properties the database is used to describe the baroclinicity of well known features such as the gulf stream the north atlantic current and the deep western boundary current and to elucidate the recirculations associated with these currents it additionally resolves several new features in the intermediate and deep north atlantic these features include the signature of a large scale deep recirculation that extends southwestward from the eastward extension of the north atlantic current to the separation point of the gulf stream near cape hatteras this recirculation which spans approximately 2000m of the water column encompasses more local recirculations and potentially mixes subpolar and subtropical waters furthermore in the upper thermocline this database reveals a coherent azores current that stretches from the gulf stream system south of the tail of the grand banks to madeira this flow is marked by divergences to the south and convergences from the north such that its downstream transport is not much changed

the polar front in drake passage a composite mean stream coordinate view the polar front pf is studied using 4 years of data collected by a line of current and pressure recording inverted echo sounders in drake passage complemented with satellite altimetry the location of the pf is bimodal in latitude a northern and southern pf exist at separate times separated geographically by a seafloor ridge the shackleton fracture zone and hydrographically by 17 cm of geopotential height expressed in stream coordinates vertical structures of buoyancy are determined with a gravest empirical mode analysis baroclinic velocity referenced to zero at 3500 dbar width and full transport about 70 sv of the jets are statistically indistinguishable the two jets alternate carrying the baroclinic transport rather than coexisting influences of local bathymetry and deep cyclogenesis manifest as differences in deep reference velocity structures downstream reference velocities of the pf n and pf s reach maximum speeds of 0 09 and 0 06 m s 1 respectively buoyancy fields are indicative of upwelling and poleward residual circulation at the pf based on potential vorticity and mixing lengths the northern and southern pf both act as a barrier to cross frontal exchange while remaining susceptible to baroclinic instability

upper circulation patterns in the ulleung basin abstract continuous acoustic travel time measurements from a two dimensional array of pressure gauge equipped inverted echo sounders spanning the entire ulleung basin of the southwestern japan east sea between june 1999 and july 2001 are used to examine the upper temperature and current patterns a new method referred to as the residual gem technique interprets the travel time data into a three dimensional x y p time series of daily synoptically mapped current and temperature fields during the two year measurement period at least five non repeating persistent flow patterns are found the patterns during the first year coincide with changes in the total volume transport through the korea tsushima strait while the patterns of the second year do not the mean temperature of the basin displays strong interannual variability and is correlated with the total korea tsushima strait transport with a higher mean temperature in the first year when total volume transport was higher in addition a new framework for describing the flow patterns is presented a newly described cold core eddy referred to as the dok cold eddy is about 60 km in diameter and typically forms southwest of dok island when the subpolar front loops southward between ulleung and dok takeshima islands and sheds an eddy the dok cold eddy is highly variable in space and time and it tends to propagate westward towards the coast of korea where it merges with cold waters from the north three such propagation events preceed the disappearance of the east korean warm current which then remains absent between june and november 2000 the offshore branch forms by branching in the korea tsushima strait and is present during much of our two year observation period

weak magnetic field changes over the pacific due to high conductance in lowermost mantle for the past few centuries the temporal variation in earth s magnetic field in the pacific region has been anomalously low the reason for this is tied to large scale flows in the liquid outer core near the core mantle boundary which are weaker under the pacific and feature a planetary scale gyre that is eccentric and broadly avoids this region however what regulates this type of flow morphology is unknown here we present results from a numerical model of the dynamics in earth s core that includes electromagnetic coupling with a non uniform conducting layer at the base of the mantle we show that when the conductance of this layer is higher under the pacific than elsewhere the larger electromagnetic drag force weakens the local core flows and deflects the flow of the planetary gyre away from the pacific the nature of the lowermost mantle conductance remains unclear but stratified core fluid trapped within topographic undulations of the core mantle boundary is a possible explanation high conductance in the lowermost mantle beneath the pacific deflects the planetary gyre which results in limited variation in the magnetic field in the region according to numerical modelling of earth s core dynamics

determining geostrophic velocity shear profiles with inverted echo sounders it is known that vertical acoustic travel time round trip from the seafloor to the sea surface as measured by inverted echo sounders iess can be interpreted in terms of dynamic height this relationship is generalized and quantified in this paper for dynamic height di j integrated between a variety of pressure limits pi pj which span different portions of the main thermocline the generalized form of the di j relationships is nonlinear the conventional linear relationship is valid when the limits of integration span the entire main thermocline velocity and temperature records are shown to be highly correlated vertically indicating that the variability of the gulf stream and adjacent eddy field is dominated by the lowest baroclinic mode which is called a gravest empirical mode gem a parallel isotherms model is used to approximate the gem and to develop analytic expressions for the observed di j relationships in the gulf stream the analytic expressions represent the observations well with noise to signal variance ratios that are typically 1 using these new di j relationships the baroclinic velocity structure can be determined geostrophically by measuring the horizontal gradients with laterally separated measurements from iess baroclinic velocities determined from a two dimensional array of iess in the gulf stream during 1988 1990 agree with velocity shears directly measured by current meters the rms velocity difference between these two measurements of velocity shear at 400 dbar relative to 1000 dbar was 12 cm s 1 in the presence of typical currents of 50 cm s 1 ageostrophic motions at both mesoscale and submesoscale measured by the current meters but not by the iess contribute most of the velocity differences

a numerical simulation of underwater slope failures generated by salt diapirism combined with active sedimentation this paper describes advanced finite element simulations of a geologically active and periodically unstable 700 m high underwater escarpment located in the gulf of mexico that has been created by uplifting salt diapirs combined with sediment deposition the site s geological history soil permeability and clay shear strength characteristics govern current slope stability and determine the timing of any future failure the geological and geotechnical conditions are reported before presenting fully coupled large displacement numerical simulations employing critical state formulations of the slope s evolution over the last 600 000 years the latter form the basis for strain softening analyses of the pore pressure equalisation and progressive failure processes that control current slope stability the analyses also address the ground movement patterns that precede instability giving useful information for geohazard risk assessment and early warning monitoring system design

barotropic and deep referenced baroclinic ssh variability derived from pressure inverted echo sounders pies south of africa 1 the objective of this paper is to evaluate the baroclinic and barotropic components of sea surface height ssh anomalies in the southern ocean and investigates the causes for the weak correlation between hydrographically derived and satellite measured ssh anomalies to this end data obtained by six pressure inverted echo sounders pies deployed south of africa were used to derive baroclinic and barotropic ssh anomalies our results show that the barotropic component accounts for 30 60 of the variability between the jets of the antarctic circumpolar current acc in contrast the jets associated with the major acc fronts are predominantly baroclinic the deep baroclinic component is important in the acc and accounts for the major part of the baroclinic variability the comparison with along track satellite altimetry jason 1 2 shows correlations coefficients of 0 24 0 92 with low values in regions of high barotropic variability the comparison with gridded aviso satellite altimetry generally shows higher correlation coefficients 0 33 0 92 and lower root mean square rms errors compared to the along track product in conclusion the barotropic ssh anomaly plays a major role in this region and has to be accounted for when assimilating ssh into ocean models due to their high baroclinic component the correct representation of the time and space varying acc fronts seems to be crucial for the right ssh anomaly partitioning used for assimilation purposes gridded products namely aviso seems to be more suitable compared to along track products jason 1 2 in representing the variability of ssh anomalies

subsurface geostrophic velocities inference from altimeter data application to the sicily channel mediterranean sea 1 coupled pattern reconstruction cpr and multivariate empirical orthogonal function reconstruction meof r techniques have been applied to infer the vertical structure of the sea from surface integrated measurements in the sicily channel mediterranean sea the data used to train the methods are the ctd casts present in the medar medatlas climatology the independent test and validation data set consisted of topex poseidon sea level measurements and ctd profiles collected during the synoptic mesoscale plankton experiment symplex 1996 and 1998 cruises meof r was found to give the more accurate and promising results being able to discriminate and reconstruct the main processes that drive the variability inside the channel in particular the analysis of the covariance of steric heights temperature and salinity profiles confirmed that mesoscale processes are predominant in fact the first meof steric height pattern closely resembles the first baroclinic normal mode estimated from the mean stratification profile a critical discussion on the signals contributing to the sea level variability has been done before applying the meof r to altimetric data the steric contribution of the upper 300 dbar has then been estimated from topex poseidon measurements the effects of the adjustment of altimeter data with a synthetic mean dynamic topography have also been quantified

a two dimensional gravest empirical mode determined from hydrographic observations in the subantarctic front abstract south of australia where the baroclinicity in the subantarctic front extends almost to the seafloor the geopotential height of the sea surface and the vertical acoustic travel time exhibit a tight empirical relationship to each other and to the entire vertical structure of temperature t p salinity s p and specific volume anomaly p measurements of provide proxy estimates of the profiles tg p sg p and g p based on a two dimensional gravest empirical mode gem representation of the vertical structure fitted to 212 hydrographic stations a seasonal model was fitted in the near surface layers using additional historical data at each depth in the range 150 3000 dbar more than 96 of the variance in both the t and fields is captured by the gem representation during the subantarctic flux and dynamics experiment mar 1995 mar 1997 inverted echo sounders ies and current meters were moored in a 2d array along the woce sr3 transect south of australia at each i

estimates of eddy heat flux crossing the antarctic circumpolar current from observations in drake passage abstractthe 4 yr measurements by current and pressure recording inverted echo sounders in drake passage produced statistically stable eddy heat flux estimates horizontal currents in the antarctic circumpolar current acc turn with depth when a depth independent geostrophic current crosses the upper baroclinic zone the dynamically important divergent component of eddy heat flux is calculated whereas full eddy heat fluxes differ greatly in magnitude and direction at neighboring locations within the local dynamics array lda the divergent eddy heat fluxes are poleward almost everywhere case studies illustrate baroclinic instability events that cause meanders to grow rapidly in the southern passage where eddy variability is weak heat fluxes are weak and not statistically significant vertical profiles of heat flux are surface intensified with 50 above 1000 m and uniformly distributed with depth below summing poleward transient eddy heat transport across the lda of 0 010 0 005 pw with the stat

temperature flux carried by individual eddies across 47 n in the atlantic ocean surface geostrophic velocity fields derived from satellite altimetry between january 1993 and april 2014 are used to detect and investigate eddies in the north atlantic between 40 55 n and 60 10 w focus is on a zonal section along 47 n roughly at the boundary between the subpolar and the subtropical gyres sea surface temperature data are used to quantify the temperature anomalies associated with eddies and the respective surface temperature fluxes related to these eddies identified eddy pathways across 47 n are related to the mean background velocity from full depth ship observations carried out on 11 cruises between 2003 and 2014 the analysis is repeated in two model simulations with 1 4 and 1 12 horizontal resolution respectively for the period 2002 2013 the analysis reveals almost 37000 altimeter derived eddies with a lifetime longer than one week in the area the highest number of eddies is found along the pathway of the north atlantic current roughly following the 4000 m isobath and on the grand banks of newfoundland time series of temperature fluxes by eddies crossing 47 n reveal that single isolated eddies with large sst signatures contribute 25 to the surface temperature flux relating the observed eddies to the observed top to bottom velocity distribution at 47 n points to the existence of eddy pathways across 47 the highest temperature fluxes are linked to the fastest and most pronounced current branches in the western newfoundland basin while there are fewer eddies in both model simulations the key findings are consistent between the observations and the two model simulations this article is protected by copyright all rights reserved

transformation of the warm waters of the north atlantic from a geostrophic streamfunction perspective to obtain a description of the hydrographic state of the north atlantic current subpolar front nac spf system historical hydrographic data from the subpolar north atlantic are projected into a baroclinic streamfunction space resulting in three dimensional gravest empirical mode gem fields for temperature and specific volume anomaly parameterized by pressure dynamic height and day of the year from the specific volume anomaly gem the corresponding potential vorticity field is calculated these fields are constructed for 12 subregions chosen to follow the mean path of the nac spf system analysis of the seasonal potential vorticity cycle of the gem fields shows that the main mechanism for the formation of subpolar mode water is winter convection the gem fields are also used to obtain the approximate location of formation sites for the different subpolar mode water classes the evolution of the mean fields for the waters is studied along baroclinic streamlines of the nac spf system this shows that cross frontal mixing between the cold and fresh subpolar waters and the salty and warm waters coming north from the subtropics via the gulf stream is the dominant mechanism for the light to dense transformation process of the nac spf waters that enter the western subpolar region on the other hand a combination of atmospheric cooling vertical mixing during wintertime convection and entrainment of the saltier waters found on the northeastern subtropical gyre is the main factor transforming the nac spf waters that enter the eastern subpolar gyre this suggests that an influx along the eastern margin of salty water from the european basin plays a significant role in the transformation of the nac spf waters that continue their way toward the nordic seas

the subpolar mode water of the north atlantic ocean abstract the warm waters of the subtropical and subpolar basins of the north atlantic have tight regional temperature salinity relationships and are conventionally called the regional central waters a volumetric census of the temperature salinity characteristics of the north atlantic by wright and worthington 1970 shows that waters characterized by certain segments of the t s relationships have large volumes compared to those of other segments volumetric mode waters such mode waters appear as layers with increased vertical separation between isopycnals pycnostads the present study reports on the existence of pycnostads in the central and eastern north atlantic these subpolar mode waters are formed by deep winter convection in the subpolar north atlantic and participate in the upper water circulation of the northern north atlantic the seasonal outcropping of the pycnostads occurs within and adjacent to the north atlantic current the irminger current the east and west greenland currents and

deep water formation the subpolar gyre and the meridional overturning circulation in the subpolar north atlantic on interannual to decadal times scales model simulations suggest a strong relationship between anomalies in the deep water formation rate the strength of the subpolar gyre and the meridional overturning circulation in the north atlantic whether this is valid can only be confirmed by continuous long observational time series several measurement components are already in place but crucial arrays to obtain time series of the meridional volume and heat transport in the subpolar north atlantic are still missing here we summarize the recent developments of the deep water formation rates and the subpolar gyre transports we discuss how existing observational components in the subpolar north atlantic could be supplemented to provide long term monitoring of the meridional heat and volume transport through a combined analysis of observations and model results the temporal and spatial scales that had to be covered with instruments are discussed together with the key regions with the highest variability in the velocity and temperature fields

variability in deep western boundary current transports preliminary results from 26 5 n in the atlantic 1 transport fluctuations of the deep limb of the meridional overturning circulation moc near the western boundary are presented from a line of inverted echo sounders bottom pressure sensors and a deep current meter east of abaco island bahamas at 26 5 n from september 2004 through september 2005 the mean southward flow between 800 dbar and 4800 dbar was 39 106 m3 s 1 with a northward recirculation of 28 106 m3 s 1 leaving a net southward flow of 11 106 m3 s 1 as the through flow of the deep western boundary current dwbc the mean southward dwbc flow essentially equals previous values that were measured at the same location by arrays of current meters deployed from 1986 to 1992 dwbc transport spectra indicate that barotropic and baroclinic changes have very similar energy levels at most periods less than 10 days and that barotropic changes dominate at periods of 10 80 days

vertical structure and transport on a transect across the north atlantic current near 42 n time series and mean a new method is presented for combining historical hydrography with the acoustic travel time measurements from an inverted echo sounder ies to obtain time series of full water column profiles of temperature t and specific volume anomaly hydrography is used to demonstrate that profiles constructed from the ies measurement account for more than 90 of the t and variance through the main thermocline range horizontal gradients between neighboring pairs of instruments when combined with measurements from bottom pressure sensors and deep current meters provide accurate estimates of absolute geostrophic velocity profiles a section of iess and current meters across the north atlantic current nac along world ocean circulation experiment line acm6 near 42 5 n is analyzed using these methods and the eulerian mean temperature and absolute velocity sections are calculated the mean transport for the combined nac and northward flow within the inshore portion of the mann eddy is 146 13 106 m3 s 1 the temporal standard deviation of the northward transport is 41 106 m3 s 1 arising not only from changes in the transport of the nac but also from lateral shifts of the currents and eddies captured by the fixed span of moorings assumption of a level of no motion at the bottom and at 2000 dbar underestimates the true absolute transport by 33 or 60 respectively historical measurements indicate that 50 60 106 m3 s 1 circulates within the mann eddy adjacent to the north atlantic current thus 86 96 106 m3 s 1 appears to be throughput at the acm6 line because the throughput observed on the acm6 line considerably exceeds the combined historical estimates of northward and eastward outflow from the newfoundland basin of 30 106 m3 s 1 these measurements suggest a substantial 50 106 m3 s 1 recirculation or southward flow within the newfoundland basin in addition to the historical recirculation within the mann eddy

calibrated seismic imaging of eddy dominated warm water transport across the bellingshausen sea southern ocean seismic reflection images of thermohaline circulation from the bellingshausen sea adjacent to the west antarctica peninsula were acquired during february 2015 this survey shows that bright reflectivity occurs throughout the upper 300 m by calibrating these seismic images with coeval hydrographic measurements intrusion of warm water features onto the continental shelf at marguerite and belgica troughs is identified and characterized these features have distinctive lens shaped patterns of reflectivity with lengths of 0 75 11 00 km and thicknesses of 100 150 m suggesting that they are small mesoscale to submesoscale eddies abundant eddies are observed along a transect that crosses belgica trough near alexander island drift a large of order urn x wiley 21699275 media jgrc22803 jgrc22803 math 0001 km3 bowl like feature that may represent an anticyclonic taylor column is imaged on a pair of orthogonal images a modified iterative procedure is used to convert seismic imagery into maps of temperature that enable the number and size of eddies being transported onto the shelf to be quantified finally analysis of prestack shot records suggests that these eddies are advecting southward at speeds of urn x wiley 21699275 media jgrc22803 jgrc22803 math 0002 m s 1 consistent with limited legacy hydrographic measurements concentration of observed eddies south of the southern antarctic circumpolar current front implies they represent both a dominant and a long lived mechanism of warm water transport especially across belgica trough our observations suggest that previous estimates of eddy frequency may have been underestimated by up to 1 order of magnitude which has significant implications for calculations of ice mass loss on the shelf of the west antarctic peninsula