phosphorites co rich mn nodules and fe mn crusts from galicia bank ne atlantic reflections of cenozoic tectonics and paleoceanography a wide variety of marine mineral deposits were recovered from 750 to 1400 m water depths on galicia bank iberian margin mineral deposits include 1 carbonate fluorapatite phosphorite slabs and nodules that replaced limestone and preserved original protolith fabric 2 ferromanganese vernadite crusts with high mn and fe mn fe 1 contents and thick stratabound layers consisting mainly of mn up to 27 mno and fe 15 fe2o3 which impregnated and replaced the phosphorite 3 co rich mn nodules are composed of romanechite and todorokite laminae mn rich layers up to 58 mno contain up to 1 8 co 4 goethite nodules with fe up to 67 fe2o3 have low mn and trace metals we interpret this mineralization paragenesis to be related to major changes in oceanographic and tectonic regimes three phosphatization generations formed hardgrounds dated by 87sr 86sr isotopes as late oligocene early miocene and latest early miocene during the latest early miocene the hardground was fractured and breached due to regional intraplate tectonism which was coeval with a widespread regional erosional unconformity the stratabound layers and co rich manganese nodules were derived from low temperature geothermally driven hydrothermal fluids with fluid conduits along reactivated faults during middle and late miocene the introduction of vigorous deep water flow from the arctic generated growth of hydrogenetic ferromanganese crusts finally growth of diagenetic fe rich nodules late pliocene was promoted by the introduction of hypersaline mediterranean outflow water into the atlantic ocean

influence of the nazare canyon central portuguese margin on late winter coccolithophore assemblages abstract this paper presents a first attempt to characterize coccolithophore assemblages occurring in the context of an active submarine canyon coccolithophores from the upper middle sections of the nazare canyon central portuguese margin one of the largest canyons of the european continental margin were investigated during a late winter period 9 12 march 2010 species distributions were analyzed in a multiparameter environmental context temperature salinity turbidity chl a and nutrient concentrations monthly averaged surface water chl a concentrations between 2006 and 2011 assessed from satellite data are also presented as a framework for interpreting spatial and temporal distribution of phytoplankton in the nazare canyon the nazare canyon was observed to act as a conduit for advection of relatively nutrient poor oceanic waters of enacwst origin into nearshore areas of the continental shelf less than 10 km off the coast whilst at the surface a nutrient rich buoyant plume resulting from intensive coastal runoff prior and during the beginning of the cruise was spreading in oceanward direction two distinct coccolithophore assemblages appear representative for the coast to open ocean gradient 1 emiliania huxleyi together with gephyrocapsa ericsonii and coronosphaera mediterranea dominated the more productive assemblage present within coastal neritic surface waters and 2 syracosphaera spp and ophiaster spp displayed a higher affinity with open ocean conditions and also generally a broader vertical distribution local hotspots of coccolithophore and phytoplankton biomass potentially associated with perturbations of surface water circulation by the canyon are discussed

north atlantic potential vorticity and its relation to the general circulation abstract maps and sections of the large scale north atlantic potential vorticity q are presented here q is fd dz where f is the coriolis frequency the potential density and z the vertical coordinate they bear on the general circulation and on geostrophic waves instability and turbulence in many ways both eulerian and lagrangian mean circulations proceed along isostrophes q constant in a zero dissipation region in a resting fluid q varies simply as the sine of the latitude but we show here that the wind driven circulation reshapes the q field creating bowls and plateaus which allow the flow to cross latitude circles the implied nature of the western boundary current is very different than in classical frictional theory the maps show a region of uniform potential vorticity in the wind gyre 26 5 27 0 which fills the ocean between 15 37 n and 20 80 w such regions were prominent features of a circulation theory of rhines and young 1982a b at deeper levels and close to surface out

tree ring eccentricity in the dendrogeomorphic analysis of landslides a comparative study abstract the chronological aspects of landslide research are of great interest regarding the hazard assessment of landslide triggers dendrogeomorphic methods provide a good ratio of chronology length and dating resolution an alternative to the standard dendrogeomorphic approaches used in landslide research based on reaction wood analysis a reaction to stem inclination is the analysis of tree ring eccentricity this study tests three frequently used dendrogeomorphic approaches based on tree ring eccentricity and verifies the results by comparing them with the results obtained by the standard dendrogeomorphic expert approach in total 125 individual fagus sylvatica l trees growing on the block type landslide of lipova stra in the foothills of the orlicke hory mts central europe were sampled and used for the analysis the first tested approach identifies landslide signals based on the analysis of mean eccentricity values from two moving windows the second tested approach determines landslide signals from a series of eccentricity values based on the use of an eccentricity threshold from reference trees the last tested approach organizes the eccentricity values into categories and identifies landslide signals based on the defined temporal patterns of the individual categories the limitations of each approach are revealed and recommendations for increasing the robustness of each approach are presented moreover the sensitivity of f sylvatica trees to landslide signals was tested using each approach the obtained results suggest the need for a specific sampling design regarding tree age for each tree ring eccentricity based approach

north atlantic nordic seas exchanges abstract the northeastern part of the north atlantic is unique in the sense that it is much warmer in the surface than other ocean areas at similar latitudes the main reason for this is the large northward transport of heat that extends to high latitudes and crosses the greenland scotland ridge to enter the nordic seas and the arctic there the warm atlantic water is converted to colder water masses that return southwards over the ridge partly as surface outflows and partly as overflows through the deep passages across the ridge in this paper the state of knowledge on the exchanges especially across the eastern part of the greenland scotland ridge is reviewed based on results from the ices nansen north atlantic norwegian sea exchanges project from the nordic woce project and from other sources the accumulated evidence allows us to describe the exchanges in fair detail the origins of the waters the patterns of their flow towards and over the ridge and their ultimate fate there is also increasing information on temporal variations of the exchanges although dynamical changes are still not well understood quantitative estimates for the volume transport of most of the overflow branches seem reasonably well established and transport measurements of the atlantic inflows to the nordic seas are approaching acceptable levels of confidence which allows preliminary budgets to be presented the deep overflows are driven by pressure gradients set up by the formation of deep and intermediate water the dominance of deep overflows over surface outflows in the water budget argues that this thermohaline forcing also dominates over direct wind stress and estuarine forcing in driving the atlantic water inflow across the greenland scotland ridge while wind stress seems to influence the characteristics and distribution of the atlantic water north of the ridge

changes in northeast atlantic hydrology during termination 1 insights from celtic margin s benthic foraminifera abstract using benthic foraminiferal based proxies in sediments from the celtic margin we provide a well dated record across the last deglaciation of the channel river dynamics and its potential impact on the hydrology of intermediate water masses along the european margin our results describe three main periods 1 during the last glacial maximum and before 21 ka bp the predominance of meso oligotrophic species suggests well oxygenated water masses after 21 ka bp increasing proportions of eutrophic species related to enhanced riverine supply occurs concomitantly with early warming in greenland air temperatures 2 a thick laminated deposit occurring during a 1500 years long period of seasonal melting of the european ice sheet eis is associated with early heinrich stadial 1 period 18 2 16 7 ka bp the benthic proxies describe low salinity episodes cold temperatures severe dysoxia and eutrophic conditions on the sea floor perhaps evidence for cascading of turbid meltwaters 3 during late hs1 16 7 14 7 ka bp conditions on the celtic margin s seafloor changed drastically and faunas indicate oligotrophic conditions as a result of the ceasing of eis meltwater discharges while surface waters were cold due to laurentide ice sheet lis icebergs releases increasing benthic mg ca ratios reveal a progressive warming of intermediate water masses whereas oxygen proxies indicate overall well oxygenated conditions in addition to the well known effect of eis meltwaters on surface waters in the celtic margin our benthic record documents a pronounced impact on intermediate water depths during hs1 which coincided with major amoc disruptions

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

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

winter atmospheric circulation in the arctic basin and possible relationships to the great salinity anomaly in the northern north atlantic variations in synoptic activity are assessed in terms of potential influences on ice transport and indicators of shifts in the arctic atmospheric circulation related to the great salinity anomaly of the northern north atlantic winter pressure anomalies suggest an increased contribution to the fram strait sea ice flux by multiyear ice from along the northern coasts of greenland and ellesmere island this may be related to a teleconnection involving changes in anticyclonicity over the central arctic ocean and canadian arctic archipelago

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 north atlantic tritium distribution in 1972 the distribution of tritium in the north atlantic in 1972 is compared with the distribution of salinity and the first order potential voracity as mapped on six constant potential density surfaces in the north atlantic the picture presented suggests an advective transport regime which is consistent with currently developing notions of the large scale gyre structure lateral mixing along isopycnals appears to be important in the northwestern region of the subtropical gyre and vertical cross isopycnal mixing needs to be invoked only in near surface layers

the changing morphology of an open lava channel on mt etna an open channel lava flow on mt etna sicily was observed during may 30 31 2001 data collected using a forward looking infrared flir thermal camera and a minolta land cyclops 300 thermal infrared thermometer showed that the bulk volume flux of lava flowing in the channel varied greatly over time cyclic changes in the channel s volumetric flow rate occurred over several hours with cycle durations of 113 190 min and discharges peaking at 0 7 m3 s 1 and waning to 0 1 m3 s 1 each cycle was characterized by a relatively short high volume flux phase during which a pulse of lava with a well defined flow front would propagate down channel followed by a period of waning flow during which volume flux lowered pulses involved lava moving at relatively high velocities up to 0 29 m s 1 and were related to some change in the flow conditions occurring up channel possibly at the vent they implied either a change in the dense rock effusion rate at the source vent and or cyclic variation in the vesicle content of the lava changing its bulk volume flux pulses would generally overspill the channel to emplace p hoehoe overflows during periods of waning flow velocities fell to 0 05 m s 1 blockages forming during such phases caused lava to back up occasionally backup resulted in overflows of slow moving a that would advance a few tens of meters down the levee flank compound levees were thus a symptom of unsteady flow where overflow levees were emplaced as relatively fast moving p hoehoe sheets during pulses and as slow moving a units during backup small localized fluctuations in channel volume flux also occurred on timescales of minutes volumes of lava backed up behind blockages that formed at constrictions in the channel blockage collapse and or enhanced flow under around the blockage would then feed short lived wave like down channel surges real fluctuations in channel volume flux due to pulses and surges can lead to significant errors in effusion rate calculations

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

vivaldi 1991 a study of the formation circulation and ventilation of eastern north atlantic central water abstract a synoptic hydrographic data set comprising 32 full depth ctd casts and 2500 ctd seasoar profiles to 500 m is used to describe the s properties and circulation of central water east of the mid atlantic ridge and between 39 n and 54 n eastward transport of 20 10 6 m 3 s 1 in the north atlantic current turns entirely northwards to the west of 54 n 20 w this transport consists in the upper layers of western north atlantic water freshened at temperatures below 10 c by mixing with subarctic intermediate water northern and southern branches of the north atlantic current are well defined and both turn northwards west of 20 w a further 10 10 6 m 3 s 1 of eastern north atlantic water forms and recirculates anticyclonically to the west of spain south of the north atlantic current and north of 40 n eastern north atlantic water is most weakly stratified east of 20 w and there is clear correlation between weakly stratified pycnostads and positive salinity anomalies relative to western north atlantic water thus eastern north atlantic water is a winter mode water in which strong winter cooling has increased the density and hence also the salinity anomaly at a given temperature near the southern entrance to the rockall trough there is evidence that salinities are also increased by mediterranean water influence circulation south of the north atlantic current is complex there is no evidence for direct ventilation southwards across 40 n where water properties s potential vorticity and cfc 113 and historical data all indicate westward ventilation east of 24 w with weak southward ventilation occurring further west in the vicinity of the azores the circulation pattern suggested is remarkably similar to that proposed by helland hansen and nansen in 1926 the eastern north atlantic geophysiske publicajoner 4 1 76 with anticyclonic circulation of colder eastern north atlantic water north of 40 n meeting warmer water from south of 40 n circulating cyclonically north of the azores current the distribution of pycnostads and s properties between 20 w and 35 w north of the azores indicates alternate bands of western and eastern north atlantic water moving eastward and westward respectively including evidence for westward motion immediately south of the southern branch of the north atlantic current possibly by westward propagation of anticyclonic eddies containing deep pycnostads

surface circulation in the eastern north atlantic from drifters and altimetry a description of the near surface circulation and its properties is the result of the analysis of a drifting buoy data set in the eastern north atlantic between the iberian peninsula the azores and the canary islands world ocean circulation experiment tropical ocean global atmosphere experiment drifters equipped with holey sock drogues centered at 15 m depth collected a total of 14 4 years of data the drifters sampled a rather inhomogeneous velocity field with a weak mean flow regime and eddies of different scales they meandered southward everywhere in the study region except in the iberian coastal transition zone north of 41degreesn where they headed northward the near surface mean velocity field obtained from the drifter data set shows all important mean currents including the poleward portugal coastal countercurrent during the fall winter and early spring off western and northern iberia the southward portugal coastal current the slow offshore southward flow of the portugal current during the whole year the southwestward canary current and the eastward azores current which extends to the vicinity of the african coast near the gulf of cadiz maps of the eddy kinetic energy field were obtained from the drifters and from satellite altimetry it provides the largest part of the total kinetic energy the rate of dispersion is estimated from the lagrangian statistics of the drifting buoys the dispersion of the drifters in the study region is well modeled by a simple description of eddy diffusion assuming homogeneous turbulence ensemble mean diffusivities k and the langrangian integral length scales and timescales l and t were obtained for the zonal and meridional directions the sea surface temperature measured along the drifter trajectories is used to produce estimates of the eddy diffusivity which is compared with the diffusivity estimates obtained from the theory of taylor the eddy diffusivity is found to be approximately proportional to the eddy kinetic energy discrete eddies and meanders were observed using drifters and altimetry in order to map and describe their geographical distribution and characteristics in the eastern north atlantic

mass transport in the bay of biscay from an inverse box model 1 mass transports in the bay of biscay for thermocline intermediate and deep water masses are estimated from a box inverse model applied to hydrographic data from a quasi synoptic survey carried out in august 2005 the model obeys conservation statements for mass in a volume of ocean bounded by 43 full depth ctd stations in the horizontal and neutral density layers in the vertical it permits advective exchange between layers and an adjustment of the ekman transport and the freshwater flux divergences bay of biscay has a thermocline transport of 8 0 0 7 sv with an anticyclonic recirculation of 6 9 0 6 sv an equatorward flow of 0 5 0 4 sv is attributed to the slope current close to the northwestern spanish coast the mean wind stress curl for the region corresponds with a clockwise upper layer flow which produces a downwelling of 0 6 0 4 sv the surface circulation pattern agrees with the obtained with the jason 1 altimeter intermediate waters follow the same surface pattern of the thermocline waters as a subsurface eastern boundary current with an eastward flow of 7 9 1 0 sv and a southwestward flow of 8 0 1 0 sv finally our results show that deep waters also flow into the box with a net transport of 3 6 2 0 sv and flow out of the box with a net transport of 2 3 2 0 sv

observed mean and mesoscale upper ocean circulation in the midlatitude northeast atlantic 1 lagrangian instruments and altimetry data are used to investigate the upper 0 to 500 m mean and mesoscale circulations in a region of the midlatitude northeast atlantic 36 47 n 13 23 w a formation and subduction area of subpolar mode water lagrangian data were collected between september 2000 and september 2001 with isobaric subsurface floats totaling 34 0 float years and surface drifting buoys totaling 27 9 buoy years the near surface 0 100 m mean circulation is dominated by two weak 5 cm s eastward currents which veer southward in the domain in the 100 to 500 m deep layer these eastward mean currents retroflect westward and form two anticyclonic circulation cells opened to the west and separated by a cyclonic cell eddy kinetic energy is decreasing from the northwest to the southeast of the area from 100 200 cm s 2 to 20 30 cm s 2 long lived anticyclones and cyclones display mean coherent displacements both to the southwest westward eddy propagation speeds close to that of long rossby waves increase southward and are consistent with a superposition of beta effect and advection by mean currents southward eddy displacements are coherent with the observed mean currents in the north anticyclones are seen to consist of central and subpolar mode water eddies most of them likely originating from the eastern boundary whereas in the south most anticyclonic features result from the influence of mediterranean water eddies meddies on the upper layers cyclonic activity is concentrated in cyclonic zones which are seen to exchange floats and water properties

observational evidence of winter spice injection abstract temperature and salinity t s profiles from the global array of argo floats support the existence of spice formation regions in the subtropics of each ocean basin where large destabilizing vertical salinity gradients coincide with weak stratification in winter in these characteristic regions convective boundary layer mixing generates a strongly density compensated sdc layer at the base of the well mixed layer the degree of density compensation of the t s gradients of an upper ocean water column is quantified using a bulk vertical turner angle tub between the surface and upper pycnocline the winter generation of the sdc layer in spice formation zones is clearly seen in argo data as a large amplitude seasonal cycle of tub in regions of the subtropical oceans characterized by high mean tub in formation regions argo floats provide ample evidence of large abrupt spice injection t s increase on subducted isopycnals due to vertical mixing associated with the winter increase in tub a simp

on the mediterranean water composition abstractthe mediterranean outflow water mow spills from the mediterranean sea east north atlantic basin west off the strait of gibraltar as mow outflows it entrains eastern north atlantic central waters enacw and intermediate waters to form the neutrally buoyant mediterranean water mw that can be traced over the entire north atlantic basin its high salinity content influences the thermohaline properties of the intermediate deep water column in the north atlantic and its dynamics here the composition of mw in its source region the gulf of cadiz west off strait of gibraltar is investigated on the basis of an optimum multiparameter analysis the results obtained indicate that mixing of mow 34 1 0 3 occurs mainly with overlying enacw 57 1 0 8 in a process broadly known as central water entrainment a diluted form 80 of dilution of the antarctic intermediate water aaiw reaches the region and also takes part in mw formation 8 3 0 5 finally the underlying labrador sea wat

the great salinity anomaly in the northern north atlantic 1968 1982 the widespread freshening of the upper 500 800m layer of the northern north atlantic which this paper describes represents one of the most persistent and extreme variations in global ocean climate yet observed in this century though a range of explanations have been advanced to explain this event including in situ changes in the surface moisture flux this paper describes the great salinity anomaly as largely though not entirely an advective event traceable around the atlantic subpolar gyre for over 14 years from its origins north of iceland in the mid to late 1960s until its return to the greenland sea in 1981 1982 the overall propagation speed around this subpolar gyre is estimated at about 3cm s 1 of the total salt deficit associated with the anomaly as it passed south along the labrador coast in 1971 1973 about 72 109 tonnes a deficit equivalent to about two thirds of this figure 47 109 tonnes ultimately passed through the faroe shetland channel to the barents sea arctic ocean and greenland sea during the mid 1970s possible effects on deep water formation and on the representativeness of historical section data are discussed

the vertical structure of upper ocean variability at the porcupine abyssal plain during 2012 2013 this study presents the characterization of variability in temperature salinity and oxygen concentration including the vertical structure of the variability in the upper 1000 m of the ocean over a full year in the northeast atlantic continuously profiling ocean gliders with vertical resolution between 0 5 and 1 m provide more information on temporal variability throughout the water column than time series from moorings with sensors at a limited number of fixed depths the heat salt and dissolved oxygen content are quantified at each depth while the near surface heat content is consistent with the net surface heat flux heat content of the deeper layers is driven by gyre scale water mass changes below 150m heat and salt content display intraseasonal variability which has not been resolved by previous studies a mode 1 baroclinic internal tide is detected as a peak in the power spectra of water mass properties the depth of minimum variability is at 415m for both temperature and salinity but this is a depth of high variability for oxygen concentration the deep variability is dominated by the intermittent appearance of mediterranean water which shows evidence of filamentation susceptibility to salt fingering occurs throughout much of the water column for much of the year between about 700 900 m the water column is susceptible to diffusive layering particularly when mediterranean water is present this unique ability to resolve both high vertical and temporal variability highlights the importance of intraseasonal variability in upper ocean heat and salt content variations that may be aliased by traditional observing techniques

high resolution holocene record in the southeastern bay of biscay global versus regional climate signals abstract core ks10b north east atlantic 43 50 n 2 03 w water depth 550 m was recovered at a location of high sediment deposition and hence includes a high resolution palaeoclimatic record for the southeastern bay of biscay over the last 9000 cal yr bp the effect of global and regional climatic forcing factors e g orbital forcing north atlantic oscillation nao and their subsequent control on water temperature sea level hydrology and continental influence were investigated by studying planktic and benthic foraminiferal faunas 150 m sedimentology and stable isotopes results indicate probable episodic long term incursions of the warm and salty iberian poleward current ipc into the bay of biscay during the holocene by the intermittent presence of subtropical globigerinoides ruber in the otherwise temperate fauna these incursions seem to be triggered by negative nao like conditions our data show five main climatic periods which are in general agreement with the literature data on the climatic variability in the north atlantic and the iberian peninsula the early holocene 9000 7400 cal yr bp is characterized by low sea level significant downslope transport eutrophic benthic settings and high surface water productivity these environmental characteristics are probably due to the general wet and warm climate under a prevailing negative nao increasing precipitation and river runoff and favouring the incursion of the ipc into the bay of biscay the climatic optimum appears between 7400 and 6000 cal yr bp under a generally positive nao index in the following 6000 3500 cal yr bp surface water cooling is matching a steep decline of the northern hemisphere summer insolation meanwhile benthic settings are changing progressively towards present day trophic conditions the time interval from 3500 to 1800 cal yr bp encompasses the iberian roman humid period characterized by warm and humid conditions and increasing primary production under a prevailing negative nao index the last 1800 years were characterized by stable cool conditions reflecting a change towards a positive nao state

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

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

meridional overturning transports at 7 5n and 24 5n in the atlantic ocean during 1992 93 and 2010 11 abstract transatlantic hydrographic sections along latitudes 7 5n and 24 5n have been repeated with about 20 years difference at the beginning of the 1990s and 2010s for each period an inverse model is applied to the closed box bound by both sections the model imposes mass conservation for individual layers defined by isoneutral surfaces and the whole water column using surface ekman transport and several transport constraints for specific ranges of longitudes and depths as a result the velocities at the reference layer for each station pair and the dianeutral velocities between layers are estimated and the horizontal velocity fields and the water heat and freshwater transports are calculated in particular we find that mass transport per stratum at 24 5n in 2011 is in good agreement with the transport estimates from the rapid watch array during both realizations the dianeutral velocities downwell from the upper north atlantic deep water unadw to the lower north atlantic deep water lnadw strata resulting in the merging of the two southward flowing strata at 24 5n into one deep southward moving stratum at 7 5n at 24 5n there is an increase in southward unadw transport between 1992 and 2011 compensated by a decrease of southward lnadw transport a descent in the upper limit of the antarctic bottom water aabw from 1992 to 2011 is also inferred the atlantic meridional overturning circulation amoc is larger in 1992 93 than in 2010 11 decreasing from 24 7 1 7 to 20 1 1 4 sv at 24 5n and from 29 2 1 7 to 16 9 1 5 sv at 7 5n much of this decrease arises because of the northward flow of antarctic intermediate water aaiw which was much more intense in 1992 93 than in 2010 11 as a consequence heat transport at 24 5n is not significantly different in 1992 1 4 0 1 pw and 2011 1 2 0 1 pw the estimation of heat transport at 7 5n strongly depends on the magnitude of the north brazil current over the american continental platform the freshwater flux into the box bounded by the two transoceanic sections decreases significantly from 1992 93 0 45 0 05 sv to 2010 11 0 36 0 3 sv meaning a decrease in net evaporation over this same area

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