absolute transports of mass and temperature for the north atlantic current subpolar front system the flow of subtropical waters carried into the northern north atlantic ocean by the north atlantic current subpolar front system nac spf is an important component of the meridional overturning circulation these waters become colder and denser as they flow through the subpolar region both by mixing with the colder subpolar waters and by atmospheric cooling the relative roles of these two processes remain to be quantified and the mechanisms driving lateral mixing need to be better understood to address those questions a new methodology is developed to estimate the mean absolute transports of mass and heat for the top 1000 dbar in the region of the nac spf for the time period 1993 2000 the transports are obtained by combining historical hydrography with isopycnal rafos float data from the area the mean absolute transport potential field shows an nac spf pipe defined by two bounding transport potential contours this pipe transports 10 0 6 3 5 sv sv 106 m3 s 21 top 1000 dbar from the subtropics into the eastern subpolar north atlantic in contrast to earlier studies the northward flowing nac follows a distinct meandering path with no evidence of permanent branches peeling off the current before reaching the northwest corner as the current enters the northwest corner it loses its tight structure and maybe splits into two or more branches which together constitute the eastward flow along the spf the eastward flow between the northwest corner and the mid atlantic ridge is not as tightly defined because of the meandering and or eddy shedding of the branches constituing the spf as the flow approaches the mid atlantic ridge it converges to cross above the charlie gibbs and faraday fracture zones the mean absolute temperature transport top 1000 dbar by the 10 sv pipe was estimated across 10 transects crossing the nac spf because the mean mass flux is constant in the pipe variations in the mean temperature transports result from lateral exchange and mixing across the pipe s side walls and from air sea fluxes across the surface of the pipe the nac spf current loses 0 18 6 0 05 pw on its transit through the region most of the loss occuring upstream of the northwest corner the heat loss is 10 times the corresponding heat lost to the atmosphere we conclude that cross frontal exchange induced by the steep meanders of the northward flowing nac is the main mechanism by which heat is lost along the current in the region between the tail of the grand banks and the mid atlantic ridge

break up of the atlantic deep western boundary current into eddies at 8 s the existence in the ocean of deep western boundary currents which connect the high latitude regions where deep water is formed with upwelling regions as part of the global ocean circulation was postulated more than 40 years ago1 these ocean currents have been found adjacent to the continental slopes of all ocean basins and have core depths between 1 500 and 4 000 m in the atlantic ocean the deep western boundary current is estimated to carry 10 40 times 106 m3 s 1 of water2 3 4 5 transporting north atlantic deep water from the overflow regions between greenland and scotland and from the labrador sea into the south atlantic and the antarctic circumpolar current here we present direct velocity and water mass observations obtained in the period 2000 to 2003 as well as results from a numerical ocean circulation model showing that the atlantic deep western boundary current breaks up at 8 s southward of this latitude the transport of north atlantic deep water into the south atlantic ocean is accomplished by migrating eddies rather than by a continuous flow our model simulation indicates that the deep western boundary current breaks up into eddies at the present intensity of meridional overturning circulation for weaker overturning continuation as a stable laminar boundary flow seems possible

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

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

the influence of high frequency atmospheric forcing on the circulation and deep convection of the labrador sea abstractthe influence of high frequency atmospheric forcing on the circulation of the north atlantic ocean with emphasis on the deep convection of the labrador sea was investigated by comparing simulations of a coupled ocean ice model with hourly atmospheric data to simulations in which the high frequency phenomena were filtered from the air temperature and wind fields in the absence of high frequency atmospheric forcing the strength of the atlantic meridional overturning circulation and subpolar gyres was found to decrease by 25 in the labrador sea the eddy kinetic energy decreased by 75 and the average maximum mixed layer depth decreased by between 20 and 110 depending on the climatology in particular high frequency forcing was found to have a greater impact on mixed layer deepening in moderate to warm years whereas in relatively cold years the temperatures alone were enough to facilitate deep convection additional simulations in which either the wind or temperature was filtered revealed that

passive seismic tomography using induced seismicity at a petroleum field in oman a borehole network consisting of five monitoring wells monitored the induced seismicity at a producing petroleum field for about 11 months nearly 5400 microseismic events were analyzed and used to image the reservoir based on a new double difference dd seismic tomography the dd tomography method simultaneously solved for event locations and vp vs and vp vs models using absolute and differential p s and s p arrival times microseismicity in the field was caused primarily by compaction of the reservoir in and above the gas bearing formation and was distributed along the two major northeast southwest faults in the field the model resolution analysis based on the checkerboard test and the resolution matrix showed that the central part of the model was resolved relatively well for the depth range of 0 7 to 1 1 km clear velocity contrasts were imaged across most parts of the two northeast southwest faults the vp vs ratio estimates from the tomographic inversion were low 1 75 in the shallow

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

pathways of the north atlantic current from surface drifters and subsurface floats the north atlantic east of the grand banks presents a thermal front from 40 to 50 n between the warm north atlantic current nac and the cold labrador current here we use the trajectories of 84 isopycnal rafos floats deployed on the 27 2 and 27 5 t surface in 1993 1995 and 218 surface drifters deployed by the international ice patrol and the institut fur meereskunde kiel germany between 1978 and 1993 to understand the pathways of the nac the mean flow pattern kinetic energy directional stability and most probable path through 1 by 1 boxes are derived for each of the three surfaces speed and kinetic energy decrease with depth although directional stability is comparable at all levels the axis of the nac which follows the 4000 m isobath along the western boundary is described by mean kinetic energy mke values surpassing 100 cm2 s 2 at the surface or 50 cm2 s 2 on the float surfaces and correspond to regions with directional stabilities in excess of 60 maximum values of eddy kinetic energy are found just offshore of the maximum mke associated with the nac main pathway and decrease rapidly to the east two cyclonic meanders are identified at 44 n 45 w near the newfoundland seamounts and at 46 n 42 w near flemish cap the main difference between the patterns derived for the surface drifters and floats was the greater eastward extent of the cyclonic trough at 44 n and intensity of the mann eddy 42 n 44 w during the float sampling period 1993 1995

export of labrador sea water from the subpolar north atlantic a lagrangian perspective abstract results from 59 acoustically tracked rafos floats obtained during 2003 2008 are analyzed here to study the spreading pathways of labrador sea water lsw from the subpolar to subtropical north atlantic an earlier paper based on a subset of these float data presented evidence of a potentially important interior pathway for the southward spreading of lsw here those results are reinforced with the full data set and new information on lsw pathways around the grand banks is presented about 70 of the rafos floats were expelled into the ocean interior east of the grand banks and meandered slowly eastward toward the mid atlantic ridge a pathway observed previously with profiling floats less than 10 was advected continuously around the grand banks by the deep western boundary current dwbc a larger fraction 17 drifted into the subtropical interior from the tail of the grand banks suggesting that this pathway is at least if not more important than the dwbc pathway for the export of lsw to the subtropics rafos floats released closest to the continental slope at 700 m depth were more likely to rapidly reach subtropical latitudes mainly because they drifted through flemish pass a 1100 m deep channel between the grand banks and the flemish cap which protects fluid parcels from being swept off the continental slope by meanders of the north atlantic current a statistical comparison of the rafos trajectories with more than 5000 simulated floats obtained from the family of linked atlantic models experiment flame high resolution ocean general circulation model reveals a similar pattern of lsw spreading the rafos and simulated floats are also used to show that contrary to a previous modeling study the isobaric rafos floats do not underestimate the amount of lsw that continuously follows the dwbc around the grand banks compared to isopycnal floats these results have implications for the connectivity of the deep limb of the atlantic meridional overturning circulation between the subpolar and the subtropical north atlantic

interannual variability in the pathways of the north atlantic current over the mid atlantic ridge and the impact of topography abstract recent studies have indicated that the north atlantic ocean subpolar gyre circulation undergoes significant interannual to decadal changes in response to variability in atmospheric forcing there are also observations however suggesting that the southern limb of the subpolar gyre namely the eastward flowing north atlantic current nac may be quasi locked to particular latitudes in the central north atlantic by fracture zones gaps in the mid atlantic ridge this could constrain the current s ability to respond to variability in forcing in the present study subsurface float trajectories at 100 1000 m collected during 1997 99 and satellite derived surface geostrophic velocities from 1992 to 2006 are used to provide an improved description of the detailed pathways of the nac over the ridge and their relationship to bathymetry both the float and satellite observations indicate that in 1997 99 the northern branch of the nac was split into two branches as it crossed the ridge one quasi lock

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

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

global observations of large oceanic eddies 1 ten years of sea surface height ssh fields constructed from the merged topex poseidon t p and ers 1 2 altimeter datasets are analyzed to investigate mesoscale variability in the global ocean the higher resolution of the merged dataset reveals that more than 50 of the variability over much of the world ocean is accounted for by eddies with amplitudes of 5 25 cm and diameters of 100 200 km these eddies propagate nearly due west at approximately the phase speed of nondispersive baroclinic rossby waves with preferences for slight poleward and equatorward deflection of cyclonic and anticyclonic eddies respectively the vast majority of the eddies are found to be nonlinear

historical position of the north atlantic current the path of the north atlantic current nac within the newfoundland basin is determined from the historical hydrographic database 1910 1988 horizontal probability distributions for dynamical and property front locations on specific volume anomaly surfaces are derived from an analysis of all available hydrographic stations in the basin these probability distributions indicate where the fronts were most likely to have been observed in the past they are observed to exhibit a pattern of stationary meanders with troughs located over the southcast newfoundland rise over the newfoundland seamounts and to the east of the flemish cap the width of the nac s envelope varies from 300 km over the southeast newfoundland rise temporal subsamples of the historical data indicate that the path and meander patterns are persistent features for all seasons and for the four decades between 1950 and 1990

stirring in the global surface ocean 1 global variations of stirring in the surface ocean are quantified using finite time lyapunov exponents ftles calculated from currents derived from satellite altimetry it is shown that the stirring is highly non uniform and the probability distribution functions pdfs of the ftles are broad asymmetric and have long high stretch tails the characteristics of the pdfs vary with mesoscale activity and integration time there are larger values and broader pdfs in regions of high strain rates and eddy kinetic energy eke e g western boundary currents and the antarctic circumpolar current and for shorter integration times the pdfs have a near universal relationship with the mean strain of a region and are reasonably well fit by weibull distributions the above variations in the stirring may help our understanding of the distribution and spatial heterogeneities of biogeochemical tracers and raise the possibility of developing a parameterization of the stirring based on the easily calculated eke

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

circulation and transports in the newfoundland basin western subpolar north atlantic the southwestern part of the subpolar north atlantic east of the grand banks of newfoundland and flemish cap is a crucial area for the atlantic meridional overturning circulation here the exchange between subpolar and subtropical gyre takes place southward flowing cold and fresh water is replaced by northward flowing warm and salty water within the north atlantic current nac as part of a long term experiment the circulation east of flemish cap has been studied by seven repeat hydrographic sections along 47 degrees n 2003 2011 a 2 year time series of current velocities at the continental slope 2009 2011 19 years of sea surface height and 47 years of output from an eddy resolving ocean circulation model the structure of the flow field in the measurements and the model shows a deep reaching nac with adjacent recirculation and two distinct cores of southward flow in the deep western boundary current dwbc one core above the continental slope with maximum velocities at mid depth and the second farther east with bottom intensified velocities the western core of the dwbc is rather stable while the offshore core shows high temporal variability that in the model is correlated with the nac strength about 30 sv of deep water flow southward below a density of sigma 27 68 kg m 3 in the dwbc the nac transports about 110 sv northward approximately 15 sv originating from the dwbc and 75 sv recirculating locally east of the nac leaving 20 sv to be supplied by the nac from the south

mesoscale eddies off peru in altimeter records identification algorithms and eddy spatio temporal patterns relatively little is known about coherent vortices in the eastern south pacific along the peruvian coast even with regard to basic facts about their frequency of occurrence longevity and structure this study addresses these issues with nearly 15 years of relatively high resolution satellite altimetry measurements we first compare two distinct automated methods for eddy identification the objective validation protocol shows that the rarely used geometrical or winding angle method based on the curvature of the streamline functions is more accurate than the commonly used okubo weiss algorithm which defines a vortex as a simple connected region with values of okubo weiss parameter weaker than a given threshold we then investigate vortices off peru using more than 20 000 mesoscale eddies identified by the winding angle method coherent eddies characterized by a high ratio of vorticity to deformation rate are typically formed along the coast and propagate westward at 3 6 cm s 1 the vortices have a mean radius of 80 km increasing northward and are most frequently observed off of chimbote 9s and south of san juan 15s the mean eddy lifetime is about 1 month but if eddies survive at least 2 months the probability for surviving an additional week or month is constant at 90 or 67 anticyclonic eddies tend to propagate northwestward whereas cyclonic vortices migrate southwestward in general cyclones and anticyclones are similar except for eddies surviving at least 6 months in this case after a similar 3 4 months of radius and amplitude growth amplitudes or sizes decay particularly rapidly for anticyclonic or cyclonic eddies in terms of intensity cyclonic eddies show a rapid decay during the first 3 months before arriving at a quasi constant value whereas anticyclones exhibit steady decline finally eddy temporal variations were examined at seasonal and interannual scales in the coastal region favorable to the formation of energetic mesoscale structures on seasonal scales eddy activity is maximal in fall and minimum in spring at interannual scales the eddy activity index was maximal during the strong el nino of 1997 1998 but another strong maximum of eddy activity also occurred late in 2004 these temporal variations are probably associated with the intensification of the upwelling thermal front and with the passage of coastal trapped waves which generate baroclinic instabilities further investigation of the mechanisms involved on the eddy genesis is needed

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

weddell sea anomalies excitation propagation and possible consequences 1 antarctic marginal seas are susceptible to significant decadal variability as revealed by the analysis of a 200 year integration of a regional ice ocean model forced with the atmospheric output of the ipcc climate model echam5 mpiom the strongest signal occurs on the southern and western weddell sea continental shelf where changes in bottom salinity are initiated by a variable sea ice cover and modification of surface waters near the greenwich meridian related zonal shifts of the western rim current guide deep waters with different temperature out of the weddell sea with a deep boundary current the temperature signal propagates westward through southern drake passage and along the upper continental rise in the southeast pacific thereby influencing the hydrographic conditions on the continental shelf of bellingshausen amundsen and ross seas