a subtropical oceanic ring of magnitude storm in the eastern north atlantic physical chemical and biological properties a subtropical oceanic ring of magnitude storm that budded from the azores current was studied in the eastern north atlantic ocean in april 1999 the cyclonic eddy called leticia was centred at 32 4 n 28 7 w and extended across more than 200 km in an east west direction leticia had been previously detected by means of topex poseidon altimetry data and further intensively investigated using expendable bathythermograph and conductivity temperature depth stations the altimeter surface signature of the eddy revealed a 20 cm sea level depression an upward displacement of the 16 c isotherm of 125 m was linked to the eddy centre and geostrophic transport of the amount of water swirling cyclonically was 7 sv the temperature nitrate and oxygen anomalies on the 0 26 5 isopycnal surface inside leticia were 0 4 c 1 mol l 1 and 0 3 ml l 1 respectively with respect to surrounding waters shallowing 50 m of the deep chlorophyll maximum 0 3 mg m 3 was observed at the eddy centre associated with vertical displacements of the isotherms 100 m within the photic layer vertical excursions of the isopycnals and the deep chlorophyll maximum of more than 30 m were observed over temporal scales of a few 3 6 h integrated nitrate concentration over the photic layer was 4 fold higher inside leticia than outside however primary production rates were only slightly higher eddy diffusive fluxes across the nitracline located 30 m below the deep chlorophyll maximum ranged from 0 02 to 0 10 mmol no3 m 2 d 1 and explained 25 of the nitrate required to sustain the estimated new production 0 24 0 48 mmol no3 m 2 d 1

on the dynamics of β plumes abstract the dynamics of zonal recirculating flows plumes driven by a source of potential vorticity or a sink of mass located at the eastern boundary of an ocean basin are investigated using analytical solutions of the barotropic linear steady quasigeostrophic equation with bottom and lateral friction by scaling the ratio of the strength of the recirculation to that of the sink by that from the inviscid solution the regimes are identified in which friction becomes a dominant factor the primary new finding of this study is that the recirculating flow component disappears due to frictional effects when the meridional extent of the sink becomes small unlike for the zonal extent of the sink which affects the recirculating component only if it is on the order of the frictional boundary layer scale the deviation of the recirculating flow strength from that given by the inviscid solution is apparent for meridional sink scales which are much larger than the frictional boundary layer scale also lo

a coccolithophore based view on paleoenvironmental changes in the open ocean mid latitude north atlantic between 130 and 48 ka bp with special emphasis on mis 5e abstract as oceanographic changes in the north atlantic are known to modulate global climate they are key to the understanding of past and future climate changes especially the mid latitudes of the open ocean north atlantic may be of interest regarding the large area covered we therefore reconstructed past changes in productivity and hydrography from a new sediment core md08 3179cq taken in the open ocean mid latitude north atlantic in the vicinity of the azores current system concomitant to the reorganizations of environmental conditions in the north atlantic between 130 and 48 ka bp changes in coccolithophore assemblages and changes in the abundance of siliceous plankton diatoms indicate a southward shift of the azores front azf and hence a southward retreat of the north atlantic subtropical gyre as well as an increased productivity during glacial marine isotope stage mis 4 termination ii and during cold substages of mis 5 furthermore we hypothesize that the ecological changes led to distinct evolutionary patterns of coccolithophores resulting e g in a dominance of gephyrocapsa ornata between 76 and 105 ka bp additionally high resolution analysis of mis 5e indicate a short reversal towards cool conditions during mis 5e corresponding to a basin wide cooling event full interglacial conditions are reached only late in the azores region during mis 5e an increased advection of subantarctic mode water samw and or the possibility to occupy new habitats after glacial conditions result in a distinct coccolithophore productivity peak as global temperature during mis 5e are assumed to be similar to the expected future global climate change mis 5e serves as a possible scenario for future changes taking mis 5e as a possible analogue for expected future climate change our results indicate that an expected decrease in marine primary productivity due to the expansion of the oligotrophic gyres may be attenuated by increased coccolithophore productivity

some observations of the azores current and the north equatorial current the regions containing the two zonal currents of the subtropical gyre in the eastern north atlantic the azores current and the north equatorial current nec have quite different physical characteristics associated with the azores current are strong horizontal thermohaline gradients that can be located easily both at the surface and at depth with temperature data alone thus making satellite ir imagery and expendable bathythermograph profiles suitable for observing it during winter the surface expression of the azores current is often found to the north of the strongest subsurface gradients in contrast to the azores current and to the central water mass boundary just to the south the nec has relatively weak horizontal temperature and salinity gradients requiring density information in order to identify it there is no clear surface manifestation found with the nec common to both currents though is that each transports o 8 sv in the upper 800 m of the ocean near 27 w with the largest velocities being in the upper 400 m

strike slip motion in the minches nw scotland deduced from the trends of the scourie dyke swarm in areas of low laxfordian strain on the scottish mainland lewisian the strike of scourie dykes varies regionally trending almost westerly in the north at assynt and trending northwesterly in the south around loch torridon these divergent trends allow an imaginary point to be constructed on the map at the intersection of these directions in the outer hebrides a similarly variable arrangement of dyke trends is observed but the intersection point of the dyke trends does not coincide with that constructed for the scottish mainland the non coincidence of these intersection points is interpreted in terms of fault displacement and estimates are made of the combined slip on all faults in the minch region including the minch and outer isles faults although the data are insensitive to possible dip slip motions they indicate a sinistral strike slip component of between 34 145 km 90 confidence estimates with a best estimate of 84 km these results are in good agreement with those determined from the offset across the minch of correlated metamorphic zones and those measured by the displacement of palaeomagnetic zones

glacial to deglacial changes in north atlantic meltwater advection and deep water formation centennial to millennial scale 14c records from the azores plateau abstract the last deglacial was marked by tremendous changes in ocean temperature and circulation as well as atmospheric co2 and 14c we employed the 14c plateau tuning technique to a centennial scale planktic 14c record of core md08 3180 retrieved s w of the azores islands at 3060 m water depth to establish both a new standard of absolute age control and a record of past 14c reservoir ages of ocean surface waters both 18o minima of g bulloides and high planktic reservoir ages of 1600 to 2170 yr suggest two major melt water incursions that reached from the labrador sea up to the subtropics over heinrich stadial 1 hs 1 in parallel we established a record of apparent benthic ventilation ages that add the planktic 14c reservoir ages together with the benthic planktic 14c age difference at the site and time of deposition a sum finally adjusted to past changes in atmospheric 14c that occurred since the time of deep water formation near the azores apparent deep water ages of the last glacial maximum were as low as 340 740 yr which suggests a lateral advection of young north atlantic deep waters nadw from subpolar regions south of iceland in harmony with recent model simulation and in contrast to a widely assumed major shoaling of glacial deep water formation during hs 1 local benthic ventilation ages increased up to 2200 2550 yr thus suggest an incursion of old southern source deep waters an unstable regime that was interrupted by brief pulses of nadw incursion near 16 15 6 cal ka and most salient near 14 9 14 7 ka

sofar floats reveal midlatitude intermediate north atlantic general circulation part i a lagrangian descriptive view quasi lagrangian trajectories of 26 sound fixing and ranging sofar floats have been collected near a depth of 700 m in the central north atlantic between 1983 and 1989 aiming at studying the influence of the mid atlantic ridge on the large scale intermediate circulation launched as tight clusters 18 km near neighbor distance on either side of the mid atlantic ridge the floats dispersed quickly over a few months jumping from one mesoscale eddy to the next by and large cyclonic and anticyclonic eddy motions are equipartitioned apparently the mid atlantic ridge remains a barrier even at that shallow depth since only one float from either side drifted across the ridge after a few years floats have circulated through most of the western basin west of the mid atlantic ridge between 30 and 45 n while east of the ridge and south of the azores plateau floats advected east of the great meteor et al seamounts by the azores current wandered more sluggishly on this timescale float dispersion is much more efficient zonally than meridionally an anisotropy mainly seen west of the ridge where floats spread westward over 30 longitude while no float penetrated south of 30 n and only two crossed 45 n northward

factors affecting the spatial pattern of the deep chlorophyll maximum in the region of the azores front abstract results are given of two surveys of the deep chlorophyll maximum dcm in the vicinity of an oceanic front south west of the azores the surveys made in late april and may 1981 used mainly a towed undulating fish seasoar fitted with ctd and in situ fluorometer in the latter survey observations of underwater irradiance nitrate concentration and primary production were also made the front was baroclinic and is considered to be an arm of the gulf stream return flow in the north east atlantic the current associated with the front made a large meander through the area and during the observation period shed an eddy which later drifted westwards the front separated two distinct water types which were termed east atlantic water eaw and west atlantic water waw the dcm in waw was on average 20 m deeper and between 50 and 60 of the magnitude of that in eaw however the 1 light level coincided with the depth of the dcm in both water types and this fact together with observations on the different nitrate concentrations in the two water types led to the theory that the differences in the dcm could be explained by assuming an overall lower level of primary productivity in waw although differences in vertical mixing may have been a contributory factor the measurements of primary production imply that the specific growth rate of phytoplankton in the dcm was less than 0 1 day 1 in the front itself there was some evidence for small scale 20 km eddy like features which produced patchiness of the same scale in the dcm there was also evidence for advective intrusions along isopycnals of eaw across the front into waw in two cases this process produced deep subsidiary maxima below the dcm with chlorphyll a concentrations of 0 1 mg m 3 as deep as 170 m in the late april survey two of the seasoar sections showed higher phytoplankton chlorophyll concentrations on the eaw side of the front but in general on both surveys there was little evidence for increased phytoplankton biomass associated with the front

the near surface flow in the subtropical gyre south of the azores this study presents evidence that the azores current azc is a permanent feature of the north atlantic subtropical gyre and that it feeds the north equatorial current nec the azc path is located south of the azores its velocity is mostly geostrophic and the energy level in the mesoscale range is higher than in the nec the nec velocity appears to be mostly ageostrophic and the wind driven surface velocity is at about 15 to the right of the mean wind field

swirling in the ocean immature loggerhead turtles seasonally target old anticyclonic eddies at the fringe of the north atlantic gyre abstract in a highly heterogeneous open ocean swirling oceanographic structures such as eddies drive ocean productivity and aggregate many predators including oceanic sea turtles during early life juvenile loggerhead turtles can spend more than a decade feeding on gelatinous zooplankton in the open ocean but the way they use mesoscale eddies is still poorly understood here we investigated the relationships between 1 the distribution and 2 the diving behaviour of immature loggerhead turtles of the north east atlantic and mesoscale eddies for this purpose 28 turtles were satellite tracked from the azores archipelago using the residence time rt analysis as a proxy to identify high use areas the tracks and dive data of the turtles as well as drifter trajectories were analysed in relation to eddy characteristics which include eddy radius amplitude type cyclonic vs anticyclonic lifetime and region inner core outer core periphery the turtles dispersed widely using many distinct high use areas although there were always more cyclones than anticyclones over the study region the individuals seasonally associated more with the inner cores of old anticyclonic eddies likely due to the higher productivity of decaying anticyclones the comparison between passive drifters and turtles movements showed an active swimming behaviour from the turtles rather than a passive advection through currents three dive types were identified and the one associated with the highest rt was characterized by dives of medium duration and depths in the inner cores of eddies this study is the first to highlight strong affinities of oceanic loggerhead turtles for old anticyclonic eddies around the azores suggesting a greater complexity of these warm core eddies that appear to be much more productive than cyclones

interaction of mediterranean water eddies with sedlo and seine seamounts subtropical northeast atlantic abstract during years 2003 and 2004 both sedlo and seine seamounts lying in the area of influence of the mediterranean water outflow in the northeast atlantic were investigated in the framework of the eu funded project oasis analysis of ctd data shows that the levels of major variability in temperature and salinity were confined to the upper ocean layer which is subject to seasonal air sea heat exchange and to the mediterranean water mw level in this paper we concentrate on the latter case and show that the variability observed resulted from mediterranean water eddies meddies colliding with the seamounts combined data from ctd surveys current meter moorings ship mounted adcp and satellite altimetry suggest that during the period of observations there was only one meddy interacting with each of the seamounts on sedlo seamount intensive interaction resulted in the loss by the meddy of about 25 of the salt around the seamount whereas on seine the meddy or portion of it escaped the seamount after performing several rotations around the summit without any significant interaction

canary current and north equatorial current from an inverse box model 1 the large scale canary basin circulation is estimated from a box inverse model applied to hydrographic data from a quasi synoptic survey carried out in september 2003 the cruise consisted of 76 full depth ctd and oxygen stations circulation is required to nearly conserve mass and anomalies of salinity and heat within layers bounded by neutral surfaces it permits advective and diffusive exchange between layers and an adjustment of the ekman transport and the freshwater flux divergences the canary current at the thermocline layer transports a net mass of 4 7 0 8 sv southward north of the canary islands from the african coast to 19 w it is divided into a northward circulation at a rate of 1 1 0 5 sv between the african coast and lanzarote island and a southward transport of 5 8 0 6 sv it transports north atlantic central water and organic matters advected offshore by the filaments protruding from the upwelling system off northwest africa at 24 n the canary current feeds the north equatorial current that transports a mixture of north and south atlantic central waters westward in the intermediate layer a southwestward flow of 1 2 1 1 sv transports mediterranean water to the subtropical gyre though the highest salt flux is transported by a meddy oxygen distribution and mass transport suggest a northeastward deep flow of a water mass colder than 2 2 c consisting of diluted antarctic bottom water the heat and freshwater divergences and the average dianeutral velocity and diffusion between the sections and the african coast are negligible

the azores front since the last glacial maximum the spatial distribution of warm surface water in the atlantic ocean reflects the state of the thermohaline circulation the azores current front which is a recirculation of the gulf stream marks the northeastern boundary of the north atlantic subtropical gyre its position is therefore diagnostic of the width of the atlantic warm water sphere here we report high resolution stable isotope and faunal abundance records of planktonic foraminifera in a sediment core from the gulf of cadiz southwest spain which reflects shifting of the azores front since the last glacial maximum lgm today the azores front does not penetrate into the gulf of cadiz even though the front resides at the same latitude as the gulf of cadiz in the atlantic our results indicate that the azores front is a robust feature of the atlantic surface circulation and that is present both in interglacial times and during the lgm at roughly the same latitude however during the lgm prior to 16 ka bp and during the younger dryas the azores front did penetrate eastward into the gulf of cadiz

circulation patterns and transport of the azores front current system in this paper different types of new data sets hydrography lagrangian and eulerian current measurements and quasi geostrophic model results obtained after altimetric data assimilation are used to study the structure and variability of the azores current and frontal system the azores current was observed to transport between 11 0 and 18 0 sv eastwards and the associated counter current some 2 0 10 0 sv to the west resulting in a net value of about 8 9 sv furthermore both data and model results revealed a meandering azores current where some freely rotating eddies were also identified these hydrographic and lagrangian results exhibit space and time scales that agree fairly well with the dynamics shaped by baroclinic instability current meters moored across the azores current system delineated a mean counter current flowing westwards with a maximum subsurface core of about 2 0 cm s at a mean depth of 800 dbar this is in excellent agreement with previous studies which explains this azores counter current as the rectification process of the geostrophic turbulence occurring north of the main azores current stream a new scheme is proposed for the formation mechanism of the freely rotating cyclonic eddies observed south of the azores it is shown that the north south contrast thickness of the 17 19 c water layer across the azores front decreases downstream this will create in turn a downstream increase of the most unstable wavelength in a non linear baroclinic instability context as a consequence both large cyclonic and anticyclonic features are able to form at the eastern side of the azores current around 19 w while at the western side around 35 w only large anticyclones will survive western generated cyclones will be small enough to be quickly dissipated this means that the eastern cyclones of the azores current may live longer than the shorter western ones however because longer lived cyclonic eddies propagate westwards with a mean speed of 2 5 km day they may be observed south of azores and of the main stream several months later although they were not formed there

structure and circulation of the upper atlantic ocean northeast of the azores historical data primarily from the igy but spanning the years 1914 1983 have been re examined in an attempt to define the structure and circulation of the upper ocean 0 800 m in the eastern north atlantic 30 50 n 10 40 w the saline greater than 35 7 anticyclonic surface gyre shallows to the north like a wedge being 300 500 m deep at 36 n east of 30 w and outcropping at about 45 n it lies above the mediterranean water separated from it by a salinity minimum and by a pycnostad of subpolar mode water mccartney and talley 1982 eastward flow between 36 n and 46 n is primarily confined to the saline wedge with speeds of 2 4 cm s 1 the flow converges gradually towards the east resulting in fronts and strong meridional property gradients e g mixed layer depth robinson bauer and schroeder 1979 east of 15 w the majority of the supolar mode water is formed by deep winter convection north of the saline wedge and subducts to the south under it southward advection and ventilation rates in the northeast atlantic the main ventilation region for the north atlantic sarmiento rooth and roether 1982 are similar estimated to be 0 2 cm s 1 the freshening of the surface layer between 1967 and 1976 that has been found in widely separated regions of the north atlantic rockall trough sargasso sea labrador sea is also present northeast of the azores salinities down to 500 m have decreased by 0 1 equivalent to an addition of a 1 4 m column of fresh water at the surface the freshening on t 27 1 decreases to negligible values southwards of 40 n it is suggested that changes in the balance of evaporation and precipitation must have occured

the source of the canary current in fall 2009 1 the source of the canary current has been inferred from an inverse box model applied to the hydrographic data of a survey carried out in 2009 in the northeast subtropical gyre 29 37 n 9 24 w the portugal current is observed between 13 5 and 14 8 w at 37 n carrying 1 8 0 4 sv southward this current presumably merges with the eastward transport of the azores current system and partly contributes to the mediterranean inflow and partly to the northward recirculation of the azores current through the gulf of cadiz the azores current system is located in the meridional range 33 50 36 25 n at 24 50 w this system transports eastward 7 2 0 5 sv in the thermocline layers and 1 1 0 8 sv at intermediate layers the azores current intermediate water mass has the highest portion of sub arctic intermediate water saiw in the region while the azores countercurrent intermediate waters mass is mainly mediterranean water the canary current extends from 22 25 to 18 50 w at 29 n the westernmost position ever observed this current transports southward 6 2 0 6 sv in the thermocline layers and 2 0 0 8 sv in the intermediate layers this intermediate flow shows a relative maximum of oxygen and a relative minimum in nutrient concentration indicating the presence of saiw the study concludes that at least in fall 2009 the canary current extends to the intermediate waters n 27 9220 approximately 1600 dbar and that azores current feeds the canary current at surface and intermediate layers

distribution of large emiliania huxleyi in the central and northeast atlantic as a tracer of surface ocean dynamics during the last 25 000 years the coccolithophore species emiliania huxleyi is characterized by a wide range of sizes which can be easily distinguished in the light microscope in this study we have quantified the abundance of

currents fronts and eddy fluxes in the canary basin hydrographic data from two cruises in the canary basin meteor 57 july 1981 poseidon 86 april 1982 are analysed with respect to current distribution and lateral heat flux in the azores madeira region the first part of the data base consists of long transects of xbt and g e k measurements between cape finisterre north west spain and the northern canary basin where several year long current meter records exist further information is obtained by thermosalinograph surface data and by expendable current profilers xcp geostrophic currents are derived from xbt profiles using the tight temperature salinity relationship in the depth range of the warmwassersphare the results compare well with the g e k and xcp current observations the second part consists of ctd data from an eddy resolving box shaped ctd survey 500 500 km2 centered at the mooring location 33 n 22 w the observations are supplemented by satellite buoy trajectories horizontal parameter distribution is shown in terms of objectively contoured maps bands of spatially enhanced energetic structures seen in the long transects are further resolved by the box survey as a deep jet like current system cross the canary basin in a west east direction associated with this azores current is a frontal zone with near surface temperature and salinity steps of order 2 k and 0 3 practical salinity units the dynamic topography field can be decomposed into a linear background field a rossby wave and a mesoscale eddy field we find that major contributions to the meridional eddy heat flux are confined to the vicinity of the azores current frontal zone it is shown that the principal balance in the temperature equation is between heating by the mean horizontal advection terms and cooling by the eddy flux divergence

adjoint assimilation of altimetric surface drifter and hydrographic data in a quasi geostrophic model of the azores current the flow characteristics in the region of the azores current are investigated by assimilating topex poseidon and ers 1 altimeter data into the multilevel harvard quasigeostrophic qg model with open boundaries miller et al 1983 using an adjoint variational scheme moore 1991 the study site lies in the path of the azores current where a branch retroflects to the south in the vicinity of the madeira rise the region was the site of an intensive field program in 1993 semaphore we had two main aims in this adjoint assimilation project the first was to see whether the adjoint method could be applied locally to optimize an initial guess field derived from the continous assimilation of altimetry data using optimal interpolation oi the second aim was to assimilate a variety of different data sets and evaluate their importance in constraining our qg model the adjoint assimilation of surface data was effective in optimizing the initial conditions from oi after 20 iterations the cost function was generally reduced by 50 80 depending on the chosen data constraints the primary adjustment process was via the barotropic mode altimetry proved to be a good constraint on the variable flow field in particular for constraining the barotropic field the excellent data quality of the topex poseidon t p altimeter data provided smooth and reliable forcing but for our mesoscale study in a region of long decorrelation times o 30 days the spatial coverage from the combined t p and ers 1 data sets was more important for constraining the solution and providing stable flow at all levels surface drifters provided an excellent constraint on both the barotropic and baroclinic model fields more importantly the drifters provided a reliable measure of the mean field hydrographic data were also applied as a constraint in general hydrography provided a weak but effective constraint on the vertical rossby modes in the model finally forecasts run over a 2 month period indicate that the initial conditions optimized by the 20 day adjoint assimilation provide more stable longer term forecasts

a quasi synoptic survey of the thermocline circulation and water mass distribution within the canary basin shipboard hydrographic measurements and moored current meters are used to infer both the large scale and mesoscale water mass distribution and features of the general circulation in the canary basin we found a convoluted current system dominated by the time dependent meandering of the eastward flowing azores current and the formation of mesoscale eddies at middepths several distinctly different water masses are identified subpolar mode and labrador sea water are centered in the northwest subantarctic intermediate water is centered in the southeast and the saltier warmer mediterranean tongue lies between them mesoscale structures of these water masses suggest the presence of middepth meanders and detached eddies which may be caused by fluctuations of the azores current

a view of the canary basin thermocline circulation in winter during january and february 1989 the recirculation of the subtropical gyre in the eastern north atlantic was surveyed with a three ship experiment the analysis of hydrographic measurements and velocity data from a shipboard acoustic doppler current profiler reveals the synoptic scale circulation patterns and water mass distributions in the canary basin the geostrophic transport stream function estimated with a horizontally varying reference level of no motion highlights the major currents in three layers representing the vertical structure of the horizontal circulation the classical circulation scheme is shown by the stream function in the upper 200 m the azores canary and north equatorial currents unlike the deep penetrating azores current the canary current and the north equatorial current are restricted to the upper 200 m both carry north atlantic central water along the water mass boundary with south atlantic central water south atlantic central water flows through the passage between the cape verde archipelago and africa via narrow currents into the area north of 14 5 n at the southern edge of the subtropical gyre we identify an eastward flow of antarctic intermediate water between 700 and 1200 m

the upper oceanic response to overflows a mechanism for the azores current abstract the oceanic response to overflows is explored using a two layer isopycnal model overflows enter the open ocean as dense gravity currents that flow along and down the continental slope while descending the slope overflows typically double their volume transport by entraining upper oceanic water the upper oceanic layer must balance this loss of mass and the resulting convergent flow produces significant vortex stretching overflows thus represent an intense and localized mass and vorticity forcing for the upper ocean in this study simulations show that the upper ocean responds to the overflow induced forcing by establishing topographic plumes that are aligned more or less along isobaths and that have a transport that is typically a few times larger than that of the overflows for the topographic plume driven by the mediterranean overflow the occurrence of eddies near cape st vincent portugal allows the topographic plume to flow across isobaths the modeled topographic plume circu

large and mesoscale variability of the water masses and the deep chlorophyll maximum in the azores front 1 coupling between the physical and biological fields in the upper ocean around the azores front af was studied in summer 1998 during an oceanographic cruise to the southern azores islands 30 n 38 n and 20 w 33 w on the basis of conductivity temperature depth ctd acoustic doppler current profiler adcp and fluorescence data several large scale mesoscale and submesoscale physical features are described the adcp data and geostrophic field revealed an eastward transport associated with the azores current ac and weak countercurrents to the south and north of the ac the water mass field shows a strong latitudinal variation in the af with an eastward modification from the surface to 300 dbar the saline distribution strongly defined the af as a very sharp vertical front the horizontal thermohaline gradient increased to the east and reached a maximum at approximately 150 dbar the 16 2 c isotherm and 36 2 isohaline at 150 dbar precisely located the af along the whole area in agreement with the dynamic field to the west of 26 w the azores current was 140 km wide while the af was only 15 25 km wide to the east of 26 w the ac underwent a strong meandering the water mass characteristics in the southern part of the af show an eastward evolution between 18 c seawater and madeira mode water data from a ctd fluorometer mounted on an undulator system allowed the small scale structure of af to be mapped describing several eddies and meanders the deep chlorophyll maximum dcm showed highest values 0 9 to 1 2 mg chl m 3 toward the west 32 w on the southern side of the af chlorophyll concentrations at the dcm 0 4 0 6 mg chl m 3 on the northern side of the study area were moderate and fairly constant whereas low values 0 3 mg chl m 3 were measured at the very deep dcm 120 140 m in the southeast associated with high saline waters examination of a cold eddy showed similar chlorophyll concentrations to those found on the northern side of the af the thermohaline structure of the eddy was similar to the af with northern water enclosed within saline and warm southern water

glacial cold water coral growth in the gulf of cadiz implications of increased palaeo productivity a set of 40 uranium series datings obtained on the reef forming scleractinian cold water corals lophelia pertusa and madrepora oculata revealed that during the past 400 kyr their occurrence in the gulf of cadiz goc was almost exclusively restricted to glacial periods this result strengthens the outcomes of former studies that coral growth in the temperate ne atlantic encompassing the french iberian and moroccan margins dominated during glacial periods whereas in the higher latitudes irish and norwegian margins extended coral growth prevailed during interglacial periods thus it appears that the biogeographical limits for sustained cold water coral growth along the ne atlantic margin are strongly related to climate change by focussing on the last glacial interglacial cycle this study shows that palaeo productivity was increased during the last glacial this was likely driven by the fertilisation effect of an increased input of aeolian dust and locally intensified upwelling after the younger dryas cold event the input of aeolian dust and productivity significantly decreased concurrent with an increase in water temperatures in the goc this primarily resulted in reduced food availability and caused a widespread demise of the formerly thriving coral ecosystems moreover these climate induced changes most likely caused a latitudinal shift of areas with optimum coral growth conditions towards the northern ne atlantic where more suitable environmental conditions established with the onset of the holocene

drifting buoy trajectories in the north atlantic current despite intensive research there are still large gaps in our knowledge of the north atlantic current which is considered to be the link between the gulf stream off the east coast of north america and the anomalously warm surface waters off northwestern europe in the classical scheme given in fig 1 which was constructed by dietrich1 on the basis of data obtained during 1957 58 the current is seen to comprise several branches two important difficulties arise from this interpretation first the data for the area east of newfoundland are not sufficient to define the causes of why the branching of the north atlantic current is stationary in its source area over the slope off grand banks2 second rapid surveys of the oceanic temperature structure by means of expendable sondes and increasingly of long term moored instrumentation and satellite tracked drifting buoys3 have revealed that the oceanic current field is dominated by mesoscale eddies and meanders rather than by large scale steady flows we report here two experiments using satellite tracked buoys which address these difficulties our results clarify the pathway of the north atlantic current and confirm that the current indeed consists of mesoscale eddies and meanders

coccolithophore species as indicators of surface oceanographic conditions in the vicinity of azores islands abstract during summer 2008 and spring 2009 surface oceanographic surveys were carried out around three islands of the azores archipelago terceira sao miguel and santa maria to assess the phytoplankton distribution and associated physico chemical processes the azores archipelago is a major feature in the biogeochemical north atlantic subtropical gyre nast province although its influence on the productivity of the surrounding ocean is poorly known surface phytoplankton was studied by microscopy and hplc high precision liquid chromatography the mean values for biomass proxy chlorophyll a chl a ranged from 0 04 to 0 55 g l 1 chl a maximum 0 86 g l 1 and coccolithophores were the most abundant group followed by small flagellates cyanobacteria diatoms and dinoflagellates being the least abundant group the distribution of phytoplankton and coccolithophore species in particular presented seasonal differences and was consistent with the nearshore influence of warm subtropical waters from the south azores current and colder subpolar waters from the north the satellite derived circulation patterns showed southward cold water intrusions off terceira and northward warm water intrusions off santa maria the warmer waters signal was confirmed by the subtropical coccolithophore assemblage being discosphaera tubifera a constant presence under these conditions the regions of enhanced biomass either resulting from northern cooler waters or from island induced processes were characterized by the presence of emiliania huxleyi diatoms and dinoflagellates indicated coastal and regional processes of nutrient enrichment and areas of physical stability respectively

lagrangian transport pathways in the northeast atlantic and their environmental impact this study focused on mapping the general transport pathways of the northeast atlantic ocean by using the regional oceanic modeling system to calculate ocean current velocity components u v w and ariane an off line fortran code dedicated to the computation of three dimensional streamlines from velocity fields to calculate the transport of particles around the numerical model domain the study was undertaken using a 10 year climatic simulation statistical comparisons with satellite and in situ data showed that the ocean circulation model captured known regional oceanographic features four depth ranges showed different lagrangian transport pathways 0 10 m 20 200 m 300 500 m and 600 2000 m confirming that these routes are consistent with the known ocean circulation patterns our results were supported by multiple sources i connectivity between the african coast and the canary islands for sardine sardina pilchardus anchovy engraulis encrasicolus ii panmixia of lobsters scyllarides latus and palinurus elephas and european conger eel conger conger iii connectivity between azores and canary archipelagos for sponge phorbas fictitius and iv observed drifting of crude oil from the prestige oil tanker spill these results should help guide future observational campaigns as well as the interpretation of open ocean transport patterns and the distribution of marine organisms and chemical tracers in the northeast atlantic region

neocene and quaternary extent and geometry of the subducted pacific plate beneath north island new zealand implications for kaikoura tectonics abstract the extent and geometry of the obliquely subduced oceanic pacific plate beneath north island new zealand for five million year intervals through the mid miocene to quaternary are presented in a series of maps and cross sections these show that the subducted plate progressively increased its extent from ne to sw beneath the north island and in the more northern regions where it was first emplaced concomitantly increased its dip from 10 to 50 the changing extent and geometry of the subducted slab has been established from the age pattern of orogenic andesites and from the geochemical k 2 o h parameter of depth of magma generation the radiometric dates show a migration of the volcanic front back towards the trench at an average rate of 20 km my the trenchward migration is explained by a model of increasing slab dip which is corroborated by the k 2 o data calibrated against the presently active arc taupo volcanic zone with the exception of northern coromandel peninsula the andesitic magmas were generated at 85 100 km depth the interpretation of the dates adopted here indicates that the subducted slab originated at the ne sw trending kermadec hikurangi trench and implies a different and much simpler evolution of the australia pacific plate boundary in the vicinity of north island than other recent models subduction geometry has been found elsewhere to be a principal influence upon the state of stress and deformational style in an over riding plate the possibility is explored that the timing nature and pattern of the neogene to quaternary kaikoura orogeny in north island is due to this influence apart from the effect of oblique subduction in eastern north island there is an accord between the onset of deformation and the emplacement sequence of the shallow slab beneath north island and between the change in subduction geometry and a progressive north to south change in northern north island from compression to extension

currents and mixing in the irminger sea and in the iceland basin on the basis of a hydrographic section from the faeroe islands toward greenland along 62m 0n and the deployment of about 20 satellite tracked buoys it is shown that the irminger current branches at the reykjanes ridge its total transport amounts to 17 18 sv the eastern branch of the irminger current 8 sv turns east and enters the norwegian sea both through the faeroe shetland channel 3 sv and by passing northeast of the faeroe islands maximum speeds of 70 cm s 1 are reached at the outer edge of the east and west greenland current very intensive mixing is observed between the four water masses that flow into the irminger basin stirring by eddies plays a dominant role for strong interleaving subsequent salt fingering and double diffusive layering conditions for these processes are optimal nearly everywhere in the irminger sea

drifting buoy in the field of flow of two eddies on east thulean rise northeast atlantic the track of an argos buoy drogued at a depth of 70 m over a year s deployment from april 18 1989 to april 18 1990 in the ne atlantic is described the mean speed of the buoy over a year s period was 1 4 cm s 1 to the ne for 320 days there was little net movement and during this time the buoy spent 66 days in a cyclonic eddy and 130 days in an anticyclonic eddy the anticyclonic eddy diameter was about 200 km and the buoy completed 21 complete revolutions around the eddy center at a radius of 55 km the rotation rate was 10 days in the eye of the anticyclonic eddy the rotation rate was 36 hours the inertial period for the latitude 51 5 n was 15 3 hours and inertial motions were occasionally marked in the anticyclonic eddy the observed inertial period was about half an hour longer than the inertial period corresponding to the latitude both eddies appeared to be partially trapped to east thulean rise water depth 3000 m and moved at a mean speed of about 1 cm s 1 to the nw along the rise following water depth contours though the anticyclonic eddy was stationary for about 50 days over the more central region of the rise the track of an imperfectly drogued buoy in a circular eddy field is then examined analytically a simple balance of stress forces on the drogued assembly is assumed and commonly adopted assumptions for the stress forces are made with assumptions the idealized study shows that under conditions of a steady surface stress a surface wind or current for example a buoy can remain trapped within an eddy field and show no tendency for steady translation in the direction of the surface stress for a clockwise eddy the displacement of the buoy s track is to the right of the surface stress direction for larger surface stresses or time varying winds the buoy may be blown out of an eddy of limited extent

persistent westward flow in the azores current as seen from altimetry and hydrography temporal and spatial variability of the eastward flowing jet like azores current is investigated by applying a new method for combining altimetry with hydrography in order to produce absolute surface geostrophic currents challenor et al 1996 the altimeter surface measurements contain information about both the geoid and the geostrophic ocean circulation the geoid signal dominates and is generally not sufficiently well known at the small length scales required to identify the mesoscale ocean signal in this study hydrography is used to distinguish the mean ocean signal from the geoid along an ers 1 satellite track south of the azores during both 3 day repeat phases and thereby determine cross stream absolute dynamic topography of the azores current at high temporal resolution hydrographic data collected near 28 w in march 1992 is combined with ers 1 altimeter data from january march 1992 and january to early april 1994 time series of 3 day repeat profiles of absolute surface geostrophic velocity perpendicular to the altimeter cruise track are examined the azores current absolute velocity profile along this track is rather coherent the current variability is less than the mean surprisingly a persistent westward flow of 25 cm s 1 is observed near 35 n 28 w this flow appears to be a retroflection from the main eastward flowing current an isopycnal analysis reveals the westward flow to be cooler by 0 5 c and fresher by 0 15 practical salinity units than the main body of the azores current the flow appears to persist throughout each of the above 3 month periods in late winter early spring but the question of whether this is a seasonal feature or more permanent remains open it is suggested that the westward flow is topographically controlled

general circulation of the western subtropical north atlantic observed using profiling floats 1 the general circulation of the subtropical western north atlantic is described using hydrography and subsurface velocity measured simultaneously by 71 profiling floats during the period july 1997 to december 2002 subsurface trajectories of the floats revealed a strong topographic influence and depth dependence of the gulf stream its recirculation gyres and the north atlantic current we discuss eddy like and nonsteady flows in several subregions especially near the major topographic features the seasonal cycle of volume transport estimated using the absolute geostrophic velocity in the upper 900 m was shown to be a maximum in winter and minimum in summer the eddy kinetic energy and eddy diffusivity derived from the float data and mapped over the subtopical gyre show seasonal variability in the vicinity of the gulf stream with a maximum in spring and minimum in winter for both quantities

the branching of the gulf stream southeast of the grand banks during march april 1987 101 hydrographic stations were occupied on three sections spanning a triangle between the azores faial the southern tip of the grand banks of newfoundland and bermuda information on the near surface processes in the interior of the triangle were obtained from 32 satellite tracked buoys deployed during the cruise and a composite infrared image based on cloud free noaa 9 data during april 1987 the data were combined to analyze the eddy field and the branching of the gulf stream into the north atlantic current and the azores current calculations of mass transports through the legs of the triangle gave a total of 46 sv supplied by the gulf stream 31 sv of which left the area as the north atlantic current and westwind drift north of the azores the remaining 14 sv continued towards east southeast as the azores current and southern recirculation additional conductivity temperature depth stations from a cruise in april 1986 into the same area allowed also study of the large scale circulation within that triangle in deeper layers the azores current appears as a baroclinic stream which reaches down to approximately 1000 m intensive mixing was observed at the continental slope of newfoundland between water of the labrador current and the gulf stream mixed water owing to cabbeling and consecutive convective mixing this water penetrates down to 2000 m depth and creates horizontal density gradients to the surrounding gulf stream water which intensifies the north atlantic current this process is considered to be an important energy source for this current

coccolithus pelagicus subsp pelagicus versus coccolithus pelagicus subsp braarudii coccolithophore haptophyta a proxy for surface subarctic atlantic waters off iberia during the last 200 kyr abstract a multivariate morphon analysis mma of coccolithus pelagicus s l coccoliths was performed on 178 samples from an oceanic core recovered off the portuguese margin md95 2040 in order to define the morphometric boundaries of its morphotypes and their behaviour during the last two glacial cycles the recurrent occurrence of the smaller morphotype of this taxon c pelagicus subsp pelagicus was recognized for the first time off the portuguese coast three sections around heinrich layers 1 and 6 and termination ii eemian were selected to establish high resolution comparisons between c pelagicus subsp pelagicus and c pelagicus subsp braarudii and two independent proxies for cold water masses the records of the planktonic foraminifera neogloboquadrina pachyderma sinistral and ice rafted detritus ird there is an overall negative correlation between c pelagicus subsp pelagicus and c pelagicus subsp braarudii as expressed by mma factor 1 the scores of which respond similarly to those of two non cocolithophore proxies and consequently is proposed as a calcareous nannoplankton proxy for the influence of subpolar waters in the region detailed analysis however showed occasional decoupling amongst these three proxies which are used to highlight significant changes between the cooling warming sequences of distinct events off iberia

on the reasons for the formation and variability of the azores current abstract recent studies have shown that the formation of the well defined zonally oriented azores current may be the result of water mass transformation associated with the mediterranean outflow in the gulf of cadiz as the denser mediterranean water descends down the continental slope it entrains overlying north atlantic central water it is believed that the azores current then forms as part of the horizontal recirculating gyre generated through the plume mechanism in this study the authors further explore this hypothesis by performing a series of numerical experiments these experiments are based on a high resolution general circulation model that includes the mediterranean sea and that realistically simulates the water mass exchange through the strait of gibraltar and the transport and variability of the azores current the authors show that the divergence of the relative vorticity flux and the planetary vorticity flux associated with planetary waves are the main factors determining the variab

on the connection between the mediterranean outflow and the azores current as the salty and dense mediteranean overflow exits the strait of gibraltar and descends rapidly in the gulf of cadiz it entrains the fresher overlying subtropical atlantic water a minimal model is put forth in this study to show that the entrainment process associated with the mediterranean outflow in the gulf of cadiz can impact the upper ocean circulation in the subtropical north atlantic ocean and can be a fundamental factor in the establishment of the azores current two key simplifications are applied in the interest of producing an economical model that captures the dominant effects the first is to recognize that in a vertically asymmetric twolayer system a relatively shallow upper layer can be dynamically approximated as a single layer reduced gravity controlled barotropic system and the second is to apply quasigeostrophic dynamics such that the volume flux divergence effect associated with the entrainment is represented as a source of potential vorticity two sets of computations are presented within the 1 layer framework a primitive equation based computation which includes the divergent flow effects is first compared with the equivalent quasigeostrophic formulation the upper ocean cyclonic eddy generated by the loss of mass over a localized area elongates westward under the influence of the b effect until the flow encounters the western boundary in the steady state the circulation pattern consists of bidirectional zonal flows with a limited meridional extent eastward to the south of the sink and westward to the north of the sink the localized sink drives a horizontal circulation in the interior ocean whose strength is approximately an order of magnitude greater than the sink s strength it is demonstrated that the induced circulation in the far field from a localized sink is insensitive to the neglect of the divergent flow component a set of parameter sensitivity experiments is then undertaken with the quasigeostrophic model for an idealized midlatitude circulation driven both by wind forcing and thermohaline flow through the open southern and northern boundaries when a sink near the eastern boundary is superimposed on the idealized midlatitude circulation it is shown to alter significantly the upper ocean flow and induce an eastward zonal current which resembles the azores current in location and transport this mechanism also generates a westward current to the north of the sink location which could be associated with the azores countercurrent an extensive series of sensitivity experiments is conducted to determine the response of this current system to changes in the boundary layer processes sink strength sink distribution model resolution and wind forcing the magnitude of the current transports is found to be sensitive to the sink intensity and to its distance from the coastline

hydrography and high temperature heat flux of the rainbow hydrothermal site 36 14 n mid atlantic ridge on the basis of an extensive set of conductivity temperature depth lowered acoustic doppler current profiler ladcp and nephelometry profiles and tow yos the hydrography flow field and particle plume of the rainbow hydrothermal site on the mid atlantic ridge are analyzed in the rift valley the water column is less dense and stratified than both eastern and western off ridge water with t s characteristics consistent with inflow across a sill from the east the buoyant hydrothermal plumes rise into a strong boundary current flowing along the slope of a topographic high which partially blocks the rift valley below 1950 m the bulk of the neutrally buoyant plume is advected across a sill which forms both the narrowest and the shallowest part of the valley and acts as a hydraulic control point for the flow below 2000 m large amplitude internal waves consistent with tidal forcing are observed near the sill but ladcp measurements suggest that the tidal signal is not strong enough to lead to flow reversal at plume depth above 2000 m the mean current across the topography generates lee waves which radiate energy upward and downstream density averaged light scattering profiles show the hydrothermal particle plume to be gaussian in depth even in the near field where many of the individual profiles are characterized by multiple peaks and the horizontal variability is highest the temperature anomalies associated with the mean near source particle plume are of order 5 10 3 c that is the plume is cold fresh as expected from the background hydrography of the deep atlantic using the flow field light scattering and hydrographic anomaly observations the heat flux associated with the hydrothermal particle plume at rainbow is estimated to lie between 1 and 5 gw

surface currents in the canary basin from drifter observations satellite tracked drifting buoys deployed in the canary basin as part of the subduction experiment between july 1991 and october 1993 and the french semaphore experiment during october 1993 were used to obtain a description of surface currents and temperature in the canary basin the study focuses on surface water convergence eddy energy production and heat transport the azores current associated with the subtropical convergence zone is clearly visible at 34 n and bifurcates around 22 w with the major branch of the current circling the madeira plateau and joining the canary current along the continental slope eddy kinetic energy maxima are found along the azores current the mean current revealed a region of maximum convergence north of the azores current around longitude 29 w occurring with a negative heating anomaly and positive work done by the reynolds stress the southward meridional temperature fluxes in the ekman layer 0 50 m between 37 w and the african and european coast are estimated between 0 076 0 022 l015 w produced by mean southward volume transport in our study area the residual between local surface heat fluxes and horizontal convergence of heat implies a vertical heat convergence process associated with mesoscale temperature and flow fields

on the origin of the azores current the azores current south of the azores archipelago is part of the subtropical north atlantic gyre using an international hydrographic data set we analyze mean and seasonal geostrophic transport fields in the upper 800 m of the ocean in order to determine the origin of the azores current in the western basin and seasonal changes in the related flow geostrophic currents are obtained by using the method applied by stramma 1984 in the eastern basin the azores current is found to originate in the area of the southwest newfoundland rise figure 10 in winter an almost uniform current connects this region of origin with the azores current while a branching into two current bands is observed in summer with the southern band forming a marked cyclonic loop within the upper 800 m all of the transport in the northern band and about 70 of the transport in the southern band recirculates in the eastern basin additionally expendable bathythermograph data from the azores current region indicate an increase of eddy potential energy from winter to summer

physical oceanography of the azores front abstract there is a considerable body of evidence for the existence of a permanent front sw of the azores surveys in the summer of 1981 show the structure to penetrate to a depth of 2 000 m and suggest that its meandering is related to the alignment of the atlantis gt meteor seamount chain the total volume transport above 2 000 m is between 10 and 12 106 m3 s 1 towards the east the main water mass contrasts across the front are confined to the upper 400 m of the water column only a small change in mediterranean water strength was seen across the front satellite tracked drogued buoys seeded into the front showed surface speeds of up to 40 cm sec 1 and revealed the formation of a closed cold core eddy some 100 115 km in diameter which propagated westward at 2 2 km day 1 over a 200 day period sea surface temperature contrasts across the frontal boundary are small and together with frequent cloud cover prevent the detection of the front and associated eddies by satellite infra red imagery the front apparently marks the eastward extension of the southern branch of the gulf stream recirculation and the northern limit of the 18 c water mass eddies formed at the front could propagate westward into the interior of the sargasso sea but have not yet been observed to cross the mid atlantic ridge

global assessment of semidiurnal internal tide aliasing in argo profiles abstractthough unresolved by argo floats internal waves still impart an aliased signal onto their profile measurements recent studies have yielded nearly global characterization of several consti

paleoceanography of the atlantic mediterranean exchange overview and first quantitative assessment of climatic forcing 1 the mediterranean sea provides a major route for heat and freshwater loss from the north atlantic and thus is an important cause of the high density of atlantic waters in addition to the traditional view that loss of fresh water via the mediterranean enhances the general salinity of the north atlantic and the interior of the eastern north atlantic in particular it should be noted that mediterranean water outflowing at gibraltar is in fact cooler than compensating inflowing water the consequence is that the mediterranean is also a region of heat loss from the atlantic and contributes to its large scale cooling uniquely this system can be understood physically via the constraints placed on it by a single hydraulic structure the gibraltar exchange here we review the existing knowledge about the physical structure of the gibraltar exchange today and the evidential basis for arguments that it has been different in the past using a series of quantitative experiments we then test prevailing concepts regarding the potential causes of these past changes we find that 1 changes in the vertical position of the plume of mediterranean water in the atlantic are controlled by the vertical density structure of the atlantic 2 a prominent early holocene contourite gap within the gulf of cadiz is a response to reduced buoyancy loss in the eastern mediterranean during the time of sapropel 1 deposition 3 changes in buoyancy loss from the mediterranean during mis3 caused changes in the bottom velocity field in the gulf of cadiz but we note that the likely cause is reduced freshwater loss and not enhanced heat loss and 4 strong exchange at gibraltar during atlantic freshening phases implies that the gibraltar exchange provides a strong negative feedback to reduced atlantic meridional overturning given the very counterintuitive way in which the strait of gibraltar system behaves we recommend that without quantitative supporting work qualitative interpretations of how the system has responded to past external forcing are unlikely to be robust

verification of geosat sea surface topography in the gulf stream extension with surface drifting buoys and hydrographic measurements altimeter data from geosat have been analyzed in the gulf stream extension area horizontal maps of the sea surface height anomaly relative to an annual mean for various 17 day intervals were constructed using an objective mapping procedure the mean sea level was approximated by the dynamic topography from climatological hydrographic data geostrophic surface velocities derived from the composite maps mean plus anomaly are significantly correlated with surface drifter velocities observed during an oceanographie experiment in the spring of 1987 the drifter velocities contain much energy on scales less than 100 km which are not resolved in the altimetric maps it is shown that the composite sea surface height also agrees well with ground verification from hydrographic data along sections in a triangle between the azores newfoundland and bermuda except in regions of high mean gradients

eddy kinetic energy in the north atlantic from surface drifters one hundred ten satellite tracked freely drifting buoys measured velocities and trajectories of the near surface currents in the north atlantic mean velocity values and the velocity variance about the mean were calculated for different regions a horizontal map of eddy kinetic energy was prepared on a 2 2 grid between latitudes 20 and 55 n maximum eddy energy 3000 cm2 s 2 coincides with the high speed gulf stream jet where it begins large amplitude meanders near 37 n 67 w a tongue of high eddy energy coincides with the stream s path eastward and around the grand banks into the newfoundland basin where values of 1000 cm2 s 2 are found a weaker tongue extends eastward across the mid atlantic ridge near 45 n a second weak extension reaches southeastward from the stream and crosses the mid atlantic ridge between 30 and 35 n north and south of the stream eddy energy diminishes rapidly reaching an e folding at 300 km from the axis values of 200 cm2 s 2 were observed in the mid gyre region and 100 cm2 s 2 in the eastern north atlantic and north equatorial current although the gross distribution of eddy energy is similar to that determined from ship drift measurements there are significant differences eddy energy from drifters amounts to about twice the value measured by ship drift in the gulf stream and one half the ship drift values in the mid gyre it is suggested that these differences are due to the horizontal averaging of mesoscale motion and the errors in navigation both of which are problems with the ship drift technique

long term changes in the thermocline of the subtropical northeast atlantic 33 n 22 w highlights unique data set of daily temperature and current measurements over almost 30 years cooling of the thermocline in the 1980s and extensive warming in the 2000s currents indicate northward displacement of n atlantic subtropical gyre in 1990s influence of nao and enso on current regime even in 500 m water depth data from almost thirty years of time series observations from a deep sea mooring kiel276 33 n 22 w which was operated in the northeast atlantic ocean between 1980 and 2009 are studied to reveal information on the long term changes in the upper thermocline this includes daily records of temperature and currents at two depths 240 m and 500 m until 1988 our analysis shows decreasing temperature in the entire thermocline followed by a slight increase at both depths from 2000 on extensive warming began at the shallower depth 240 m and eight years later at the deeper 500 m level a northward displacement of the north atlantic subtropical gyre is indicated by both current measurements and calculated kinetic energy between 1991 and 1998 resulting in an altered current regime in terms of absolute velocity and current directions in the last ten years compared to the first twenty years coherences of the currents with large scale climatic patterns such as north atlantic oscillation and el nino southern oscillation evidence the atmospheric impact even at 500 m water depth

meddies and decadal changes at the azores front from 1980 to 2000 twenty years of time series observations from the deep sea mooring kiel276 are used to obtain information on the frequency and propagation of meddies mediterranean water eddies on long term changes in flow properties and on a possible relation to the north atlantic oscillation the mooring was set at the nominal position 33 n 22 w at a water depth of more than 5200 m in the northern canary basin it is located near the southern boundary of the azores current ac which is part of the north atlantic subtropical gyre and also in the large scale mediterranean water mw tongue originating from the strait of gibraltar the amplitudes of time varying vertical quasi geostrophic modes and the correlation of current and temperature changes at levels in the mw and the north atlantic central water above are used to identify meddies a total of 10 meddies passed the mooring during the period 1980 2000 half of the events can be related to earlier observations directional changes in meddy related velocities are used to estimate speeds and directions of meddy propagation directions of propagation are very homogeneous with all the 10 meddies observed propagating with a southward velocity component within a sector of 90 and typical speeds are 2 3 cm s meddy occurrence was uneven in time with six meddies found during the first four years and only four meddies during the remaining 16 years decadal changes show the annual mean and the fluctuating kinetic energy levels at the site changing from lower values in the 1980s to high values in the 1990s this change appears to be correlated with variations in the north atlantic oscillation nao index with a delay in oceanic response of about 3 years a conceptual model of ac meanders is used to identify meander signals in the upper layer time series the ac axis appears to be closer to the site during the 1990s than during the preceding decade and indicates a southward or southwestward displacement of the ac with increasingly positive values of the nao index meddy frequency is lower when the ac gets closer from the north a reduction in meddy occurrence in the region just south of the ac is possibly caused by the shear induced blocking of some meddies crossing the front from the north

optimum multiparameter analysis of the water mass structure in the western north atlantic ocean hydrographic data of temperature salinity oxygen nitrate phosphate and silicate at 81 stations with 435 samples on 3 sections between the azores the grand banks of newfoundland and the bermuda islands are used to determine the mixing of water masses by optimum multiparameter analysis over the depth range 100 1500 m the method optimally utilizes all information from our hydrographic data set by solving an overdetermined set of linear mixing equations for all parameters using the method of least squares residuals it is shown that the method gives quantitative information on the influence of the various water masses of the western north atlantic the gulf stream and the north atlantic current appear as broad bands transporting large amounts of western north atlantic central water at their warm flank western subarctic intermediate water and shelf water supplied by the labrador current and containing significant amounts of labrador current water are found on their inshore side the area of the azores front is found in the vicinity of the comer seamounts where the uniform water mass distribution of the sargasso sea changes into a more complex structure that reflects the influence of water masses originating in the labrador sea small scale structures like eddies or gulf stream rings are also detectable by this analysis method comparison with dynamic height analysis supports the circulation pattern of the north atlantic current as a continuation of the gulf stream and of the southeastward flowing azores current originating in the area of the southeast newfoundland rise

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

nitrate isotope anomalies reflect n2 fixation in the azores front region subtropical ne atlantic 1 the subtropical northeast atlantic has previously been identified as a marine environment with an apparent imbalance between low nitrate supply to the surface and concurrent high export production to better constrain the sources and fluxes of mixed layer nitrate and to assess the potential role of n2 fixation in providing new nitrogen n we investigated the depth distribution of nitrate 15n and 18o at six stations across the azores front in the ne atlantic in addition we measured the 15n of dissolved organic n don in surface waters and of sinking particulate n collected in sediment traps at 2000 m depth between 2003 and 2005 at station kiel276 the nitrate isotope profiles at the majority of the hydrographic stations displayed a decrease in the 15n from depth toward low nitrate surface waters concomitant with an increase in 18o given that nitrate uptake by phytoplankton leads to a proportional increase in nitrate 15n and 18o the observed surface water nitrate isotope anomalies 15 18 up to 6 indicate that nitrate assimilation is not the sole process controlling the isotopic composition of nitrate in the photic zone and implicate a significant addition of newly fixed n that is remineralized in surface and subsurface waters both the concentration of don and its 15n in surface water were spatially invariant showing mean values of 4 7 0 5 mol l 1 and 2 6 0 4 n 35 respectively supporting the conjecture of a mostly recalcitrant don pool the weighted biannual mean 15n of sinking particulate n 1 8 0 8 n 33 was low with respect to thermocline nitrate the anomalous dual nitrate isotope signatures together with the low 15n of export production and elevated nitrate to phosphate ratios in surface and subsurface waters strongly suggest that n2 fixation represents a substantive source of n in this part of the subtropical northeast atlantic simple isotope mass balance suggests that locally n2 fixation supplies between 56 and 259 mmol n m 2 a 1 for phytoplankton growth in the photic zone accounting for up to 40 of the estimated export production

sofar floats reveal midlatitude intermediate north atlantic general circulation part ii an eulerian statistical view abstract part i of this paper has given a descriptive view of the trajectories of 26 sofar floats drifting near 700 m depth in the central north atlantic during the mid 1980s as part of the topogulf experiment here an eulerian analysis of the 53 4 collected float years is performed by grouping data in 2 latitude 4 longitude boxes the mean circulation lacks a significant southward sverdrupian flow and shows instead zonal bands of alternating westward and eastward currents except in the canary basin west of the ridge and north of 38 n the general northeastward flow of the gulf stream system is recovered while south of 38 n the westward recirculation observed from historical float data between 70 and 55 w is shown to extend as far as 40 w a mean azores current is observed both west of the ridge near 33 n and east of 30 w near 34 n in between east of the ridge a tongue of high eddy energy indicates stronger eddy activity and local instabilities of the azores current eddy kinetic energy and e

on the role of the azores current in the ventilation of the north atlantic ocean three high resolution ocean circulation models of the north atlantic differing chiefly in their description of the vertical coordinate are used to examine the ventilation of the north atlantic subtropical gyre all the models produce mode waters of realistic densities in the sargasso sea and the european basin but have azores currents of differing strengths which are categorised as strong of realistic transport intermediate and weak these differences have a critical impact upon the ventilation of the gyre most importantly the strong azores current forms an effective barrier to the southward ventilation of eastern north atlantic water from the northern european basin initially driving it southwestwards into the central gyre before turning it back eastwards again in a general cyclonic circulation north of the current the intermediate and weak azores currents instead allow the southward ventilation of this water mass near the european and african coasts the situation in nature appears to be intermediate between these two cases with the azores current acting as a partial block the study also raises the possibility of the azores current forming an advective connection between the sargasso sea mode waters in the western basin and modes of similar densities found in the eastern basin on the southern side of the current although there are high levels of variability in the extent of these lighter modes in the eastern basin in nature this postulate is supported by a number of observational studies in addition the present study also provides some support for the local production of madeira mode water in the eastern basin associated with retroflecting current branches on the southern side of the azores current overall the azores current is therefore likely to have a critical impact upon the ventilation of the subtropical gyre over a large area rather than just locally affecting the potential vorticity and density structure of the upper ocean between subtropical latitudes and the northern european basin the study also contributes to an ongoing community effort to assess the realism of our current generation of ocean models

observations in the canary basin and the azores frontal region using geosat data this paper discusses observations of the sea level in the azores frontal region and the canary basin as seen by the geosat altimeter frorn 5 to 45 w and 25 to 45 n two years of geosat exact repeat data were processed by colocating the data on a 0 06 grid then removing the mean by the along track difference method and removing the orbit error by a crossover analysis technique the data set was then interpolated by the successive correction method onto 15 day 0 5 maps to produce 47 residual height fields which were analyzed using complex empirical orthogonal functions eof and spectral analysis the results show that there is a region of high variability in the northwest corner reflecting the gulf stream extension and a region of medium variability at approximately 35 n reflecting the azores current the variability changes only slightly throughout the year with the winter season being the highest the data set also shows first mode baroclinic rossby waves between 30 and 35 n there is evidence that these rossby waves have different wavenumbers to the east and west of the mid atlantic ridge it is postulated that these waves have different generation mechanisms the mid atlantic ridge topography in the west and some other generation mechanism in the canary basin rossby waves are not apparent at 40 n

impact of the azores front on the distribution of planktic foraminifers shelled gastropods and coccolithophorids abstract the azores front current system south of the azores islands has been studied in order to reveal the direct impact of an open oceanic thermohaline front on the distribution of the calcareous plankton planktic foraminifers pteropods heteropods and coccolithophorids were sampled from the upper 2500 m of the water column during august 1997 and january 1999 in addition the hydrography was recorded across the frontal jet on combined ctd and xbt transects in august 1997 a strong seasonal thermocline capped the azores front af at about 60 90 m water depth below the thermocline a distinct hydrographic front was indicated by temperature and salinity gradients the central af was an area of low planktic foraminiferal gastropod and coccolithophorid production and was a faunal barrier for shallow and deep dwelling species highest numbers of planktic foraminifers gastropods and coccolithophores were recorded from above the thermocline north of the af the most frequent planktic foraminiferal and pteropod species were globigerinoides ruber white and limacina inflata respectively below 100 m planktic foraminifers were most frequent north of the af and gastropod shells were rare in particular the deep dwelling planktic foraminifer globorotalia scitula was frequent only at sampling sites north of the af in january 1999 the surface water temperature of the azores front current system was lower and the thermocline was deeper than in august 1997 the planktic foraminiferal standing stock was three times higher than in august 1997 and no water depth related faunal changes occurred the fauna was dominated by globorotalia truncatulinoides and turborotalita humilis was frequent during both january and august the fauna from south of the azores was different from that to the southeast recording the occurrence of two different water masses in this study we present a micropaleontological definition of the af in order to provide a paleoceanographic tool that may be used to decipher the late quaternary current system of the north atlantic ocean

meandering of the subtropical front south east of the azores a subtropical front was observed in the area south and southeast of the azores during cruises of fs meteor and fs poseidon in early 1982 the front has a basically west east extension with considerable meandering observed meso scale eddies are found on both sides the overall flow pattern corresponds to earlier results on geopotential differences in the upper northeast atlantic but the baroclinic transport of the order of 107 m3 s 1 is found to be concentrated in a 60 km wide jet we suggest here that the current band is part of the gyre circulation resulting from a branching of the north atlantic current

large structures and temporal change in the azores front during the semaphore experiment the structure des echanges mer atmosphere proprietes des heterogeneites oceaniques recherche experimentale semaphore mesoscale experiment took place from july to november 1993 in the northern canary basin where the circulation is dominated by the eastward flowing azores current ac a large data set was acquired from three hydrographic arrays phases 1 2 3 current meter moorings surface drifters drogued at 150 m and 2000 m deep rafos floats the analysis confirmed the large scale observations previously made in this region but also provided new insights into fine scale dynamics of the ac the front was observed over the 6 month period it was narrow 100 km and mostly surface intensified velocities reaching 40 50 cm s 1 whereas at the beginning of the experiment phase 1 the ac was mainly zonal with weak oscillations large meridional meanders were observed from phase 2 until the end of the experiment they seem to be related to the arrival of two mediterranean eddies meddies which interacted with the ac kase and zenk 1996 tychensky and carton this issue the front had a deep dynamical signature down to 2000 m with a 16 18 sverdrup sv volume transport 0 2000 m depth integrated the southward recirculation branch of the ac near 22 degrees 23 degrees w klein and siedler 1989 corresponds to meridional transport of 5 6 sv then 4 5 sv of these waters are recirculating westward along 31 degrees 32 degrees n some interesting new oceanographic results were obtained by examining the rafos float trajectories over the abyssal plain the circulation is similar to that observed at the surface with mean velocities of about 1 3 cm s 1 and eddy kinetic energy 4 cm 2 s 2 in agreement with the analysis of current meter data this reveals a significant barotropic component in the azores madeira flow field of roughly 3 3 5 cm s 1