instability waves in the equatorial atlantic ocean abstract evidence is presented for the generation of planetary waves by barotropic instability within the cyclonic shear region of the atlantic ocean s south equatorial current sec immediately following the springtime intensification of the southeast trade wind which accelerates the sec westward a packet of waves with central periodicity of around 25 days is observed lasting for about three cycles independent wavenumber analyses on 1983 and 1984 data give newly identical zonal wavelengths and phase speed estimates of around 1100 km and 50 cm s 1 the waves are anisotropic and spatially inhomogeneous with generation confined primarily to the mixed layer an energetics analysis using 1983 data centered upon the equator at 28 w shows a rapid increase in total perturbation energy tpe reaching values of 2000 erg cm 3 within two weeks the subsequent decrease in tpe at this location is due primarily to meridional pressure work divergence baroclinic instability is negligible because both the meridional

from swallow floats to argo the development of neutrally buoyant floats neutrally buoyant floats have been a vital tool in the exploration of the global ocean circulation and now provide a central element of the in situ ocean observing system through the argo project the paper traces the development of neutrally buoyant floats from their origins in the mid 1950s to the present day and highlights areas of ocean science to which floats made significant contributions

on the average absolute transport of the deep western boundary currents east of abaco island the bahamas abstract data obtained from a line of absolute current profiler pegasus and ctd stations at 26 5 n east of abaco island in the northern bahamas are used to estimate the average transport and overall level of variability of the deep below 800 m southward flow associated with the so called deep western boundary current dwbc at this latitude from april 1985 to september 1987 a total of 11 sections were made along a line extending from near the island boundary to 85 km offshore as part of the subtropical atlantic climate studies stacs program in all but two cases when pegasus data were obtained over the total depth absolute velocities were determined from 0 to about 3000 db while ctd derived relative velocities were determined over the total depth using the combined datasets it is possible to reference the relative geostrophic velocity with pegasus data thereby obtaining an estimate of the absolute southward transport of the deep flow the average value of transport determined in this man

lagrangian circulation of antarctic intermediate water in the subtropical south atlantic this study combines float data from different projects collected between 1991 and 2003 in the south atlantic to describe the flow of antarctic intermediate water aaiw velocity space time averages are calculated for various grid resolutions and with cells deformed to match the bathymetry f h or f h with h being the water depth and h being the thickness of the aaiw layer when judged by the degree of alignment between respective isolines and the resulting average velocity fields the best grid is based on a nominal cell size of 3o latitude by 4o longitude with cell shapes deformed according to f h using this grid objectively estimated mean currents and their associated errors as well as meridional and zonal volume transports are estimated results show an anticyclonic subtropical gyre centred near 36os and spanning from 23o 1 s to 46 1os the south atlantic current meanders from 33os to 46os and shows a mean speed of 9 6 7 8 cm s 1 8 5 sv 3 5 sv 1 sv 1 106 m3 s 1 the northern branch of the subtropical gyre is located between 22os and 32os and flows westward with a mean speed of 4 7 3 3 cm s 1 9 3 sv 3 4 sv evidence of a cyclonic tropical gyre divided in two sub cells is visible on the stream function

dynamic impact of oscillating sources on the north atlantic deep circulation a process study in this process study the dynamic effects of fluctuating deep water sources on the deep circulation of the north atlantic are examined by means of a 1 layer model the model is used with a realistic topography of the atlantic ocean between 65 n and 25 s and has an open southern boundary according to observations the northern inflow of deep water is subject to variability on timescales between days and decades the same holds for the deep western boundary current dwbc which acts as a link between the deep water inflow and the interior circulation the timescales of the observed variability motivate the forcing functions used in the model they determine the nature of the models response the flow response relative to the local mean flow can be considerably larger than the original perturbation at the source normalizing the perturbed flow with the local steady state flow leads to the identification of sensitive areas their location and shape are determined by the difference between the characteristic travel paths of the perturbation and the streamlines of the steady state circulation in the eastern equatorial atlantic a forcing with periods between 1 and 3 months gives rise to larger flow perturbations than a forcing with periods between half a year and 1 year forcing with the latter periods leads to a stronger response in the western equatorial atlantic and in the interior ocean changes in the direction of the deep equatorial flow are driven by low frequency oscillations of the dwbc in the model this is consistent with observations in the area perturbations radiate into the interior away from the eastern boundary as long rossby waves as this propagation is along geostrophic contours consequently large parts of the abyssal interior are inaccessible the results support the notion that the area where the dwbc encounters the equator is not only a key region for the slow interhemispheric exchange of heat and tracers but also for the transport of information by fast internal waves along the equator

hemispheric asymmetry of deep water transport modes in the western atlantic subtropical studies of the atlantic meridional cold water flow show a hemispheric contrast in the dominant southward transport mode below 2000 m in the north atlantic lower deep water ldw 1 8 2 4 c dominates with small transport of middle deep water mdw 2 4 3 2 c while in the south atlantic the opposite is observed we use numerous observations in the western basins of the tropics to show that the transition occurs rapidly near the equator in the western atlantic a meridional section in the central brazil basin suggests zonal flows are responsible for the transition ldw transport from the guiana basin north of the equator flows eastward in the northern brazil basin and is inferred to continue on through the romanche fracture zone into the eastern atlantic an opposing flow of mdw from the eastern tropical atlantic flows toward the western boundary where it bifurcates to supply mdw to the deep western boundary current dwbc of the brazil basin as well as to feed the northward flow of mdw in the guiana basin offshore of the dwbc the magnitude of each of these oppositely directed flows is roughly 7 sv we furthermore speculate that they are connected predominantly by upwelling from ldw to mdw within the low latitude eastern basin the overall deep water transport system below 2000 m in the western basins of the mid and low latitude atlantic is thus found to comprise the following three distinct components 1 a strong dwbc transport of ldw with associated recirculation dominates the guiana basin north of the equator 2 in the northern brazil basin just south of the equator a narrow eastward flow absorbs the ldw and carries it eastward while a somewhat broader westward flow imports mdw into the western basin 3 this mdw flow then bifurcates with the southward branch causing the mdw dominance in the brazil basin where the mdw dominated dwbc and associated recirculations are the third component of the deepwater transport system

circulation of water masses in the baltic proper revealed through iodine isotopes abstract tracer technology has been used to understand water circulation in marine systems where the tracer dose is commonly injected into the marine waters through controlled experiments accidental releases or waste discharges anthropogenic discharges of 129i have been used to trace water circulation in the arctic and north atlantic ocean here 129i together with 127i is utilized as a tracer of water pathways and circulation in the baltic sea through collection of seawater depth profiles the results indicate the presence of 129i signatures which are distinct for each water mass and provide evidence for 1 inflow water masses through the drogden sill that may reach as far as the sw of the arkona sea 2 a portion of north atlantic water in the bottom of arkona basin 3 cyclonic upwelling which breaks through the halocline in a pattern similar to the baltic haline conveyor belt and 4 more influx of fresher water from the gulf of finland and bothnian sea in august relative to april these findings provide advances in labeling and understanding water pathways in the baltic sea

a statistical description of the mean circulation and eddy variability in the northwestern atlantic using sofar floats abstract velocity data obtained from trajectories of sofar floats launched as part of several experiments carried out in the northwest atlantic during the last two decades are used to give a statistical description of the mean gulf stream and its recirculation the distribution of eddy variability in the region is also presented a mean gulf stream which bifurcates between 55 and 45 w to feed the north atlantic current and a southern recirculation can be clearly identified a weak interior sverdrup flow is also suggested the spatial distribution of eddy variability is consistent with previous descriptions showing a maximum near the gulf stream

velocity probability density functions for oceanic floats probability density functions pdfs of daily velocities from subsurface floats deployed in the north atlantic and equatorial atlantic oceans are examined in general the pdfs are approximately gaussian for small velocities but with significant exponential tails for large velocities correspondingly the kurtoses of the distributions are greater than three similar pdfs are found in both western and eastern regions above and below 1000 m depth with more significant non gaussianity in the north atlantic than at the equator analogously lagrangian statistics in decaying two dimensional turbulence also display non gaussian velocity pdfs with approximately exponential tails in the limit of large reynolds number

the mean flow field of the tropical atlantic ocean the mean horizontal sow eld of the tropical atlantic ocean is described between 20in and 20is from observations and literature results for three layers of the upper ocean tropical surface water central water and antarctic intermediate water compared to the subtropical gyres the tropical circulation shows several zonal current and countercurrent bands of smaller meridional and vertical extent the wind driven ekman layer in the upper tens of meters of the ocean masks at some places the sow structure of the tropical surface water layer as is the case for the angola gyre in the eastern tropical south atlantic although there are regions with a strong seasonal cycle of the tropical surface water circulation such as the north equatorial countercurrent large regions of the tropics do not show a signi cant seasonal cycle in the central water layer below the eastward north and south equatorial undercurrents appear imbedded in the westward sowing south equatorial current the antarcic intermediate water layer contains several zonal current bands south of 3in but only weak sow exists north of 3in the sparse available data suggest that the equatorial intermediate current as well as the southern and northern intermediate countercurrents extend zonally across the entire equatorial basin due to the convergence of northern and southern water masses the western tropical atlantic north of the equator is an important site for the mixture of water masses but more work is needed to better understand the role of the various zonal under and countercurrents in cross equatorial water mass transfer 1999 elsevier science ltd all rights reserved

structure of the atlantic ocean equatorial deep jets the equatorial deep jets in the atlantic ocean are described using vertical strain jz estimated from all available deep ctd stations in the region wavelet analysis reveals a distinct energy peak around 661 sdbar vertical wavelength 1232 dbar pressure and 61 58 latitude from the equator this high vertical wavenumber and off equatorial maximum coupled with previously published velocity data that show nodes in zonal velocity near 61 58 is grossly consistent with the structure of first meridional mode equatorial rossby waves however the meridional scale obtained from the observations exceeds by about 1 5 the theoretical meridional scale for these waves the jets are strong with zonal velocities similar in magnitude to the kelvin wave phase speed for their vertical wavelength harmonics of jz at vertical wavelengths of 1 2 1 4 and perhaps 1 8 that of the primary peak provide evidence of a large amplitude structure although sparse available phase data at the 661 sdbar vertical wavelength suggest downward and westward phase propagation assuming sinusoidal character in time and longitude gives estimates of a 5 61 yr period and a 708 6608 zonal wavelength these vertical temporal and zonal scales are roughly consistent with first meridional mode equatorial rossby wave dynamics however although vertical and zonal phase propagation are discernible there is no obvious signature of upward energy propagation in the variance vertical maxima which is problematic for a simple linear rossby wave interpretation

modeling the pathways and ages of inflowing salt and freshwater in the baltic sea abstract a three dimensional eddy permitting ocean circulation model with implemented bottom boundary layer model and flux corrected transport scheme is used to calculate the pathways and ages of various water masses in the baltic sea the agreement between simulated and observed temperature and salinity profiles of the period 1980 2004 is satisfactory especially the renewal of the deep water in the baltic proper by gravity driven dense bottom flows is better simulated than in previous versions of the model based upon these model results details of the mean circulation are analyzed for instance it is found that after the major baltic inflow in january 2003 saline water passing the slupsk furrow flows directly towards northeast along the eastern slope of the hoburg channel however after the baroclinic summer inflow in august september 2002 the deep water flow spreads along the southwestern slope of the gdansk basin further the model results show that the patterns of mean vertical advective fluxes across the halocline that close the large scale vertical circulation are rather patchy mainly within distinct areas are particles of the saline inflow water advected vertically from the deep water into the surface layer to analyze the time scales of the circulation mean ages of various water masses are calculated it is found that at the sea surface of the bornholm basin gotland basin bothnian sea and bothnian bay the mean ages associated to inflowing water from kattegat amount to 26 30 28 34 34 38 and 38 42 years respectively largest mean sea surface ages of more than 30 years associated to the freshwater of the rivers are found in the central gotland basin and belt sea at the bottom the mean ages are largest in the western gotland basin and amount to more than 36 years in the baltic proper vertical gradients of ages associated to the freshwater inflow are smaller than in the case of inflowing saltwater from kattegat indicating an efficient recirculation of freshwater in the baltic sea

fluorine geochemistry of basaltic rocks from continental and oceanic regions and petrogenetic application fluorine contents in about 300 samples of various types of basalts and related rocks from continental southwestern u s a zaire deccan and south africa and oceanic regions hawaii and mid atlantic ridge between 23 n and 40 n were determined by a selective ion electrode method

on deep western boundary currents the stommel and arons 1960a b theory of the deep circulation of the world ocean does not directly address the physics of deep boundary currents in the present paper a maximally simple steady state physics for deep western boundary currents is developed and integrated into the stommel arons model this is accomplished by modifying the assumptions of the latter to include effective horizontal eddy viscous terms everywhere in the deep water including in the interior the resulting solution for the meridional velocity in a rectangular ocean on a beta plane is mathematically analogous to that of munk 1950 for the wind driven circulation in the interior the meridional velocity reduces identically to that of stommel and arons among other benefits the solution eliminates the theoretical difficulties associated with the crossing of the equator by the deep western boundary current as an initial test of the theory s consistency with observation theoretical plots of pressure and meridional velocity as a function of longitude are qualitatively compared with hydrographic sections and inferred meridional velocity fields in the eastern and western basins of the abyssal north atlantic also the theoretical profile for the meridional velocity as a function of longitude is qualitatively compared with observations of longshore velocity as a function of offshore distance in the deep western boundary current of the north atlantic deep water

observations of the deepwater flow into the baltic sea it has earlier been hypothesized that the deep water flowing into the baltic sea forms a bottom pool in the arkona sea just inside the entrance sills the flow from the pool farther into the baltic sea was assumed to be baroclinic geostrophic and controlled by the pool stratification this was supported by a realistic statistical description of the deepwater flow into the baltic sea computed using historical vertical density profiles from a hydrographical station in the arkona sea however basin wide synoptic measurements of density and currents were not available for a direct verification of the pool model a hydrographic survey was undertaken in the arkona sea shortly after a major inflow event in the beginning of 1993 the conductivity temperature depth sections reveal a thick bottom pool of deep water separated by a halocline from the surface water of baltic origin approaching the northern coastal boundary from the central parts of the pool the halocline sank by about 20 m before hitting the bottom the ship mounted acoustic doppler current profiler recorded a complicated current field however subtraction of the assumed barotropic part gives a current field quite similar to the baroclinic geostrophic current field computed from the density distribution thus a dense bottom pool including a baroclinic geostrophic boundary current along the northern flank of the pool is quite evident from our measurements

the norwegian atlantic current in the lofoten basin inferred from hydrological and tracer data 129i and its interaction with the norwegian coastal current 1 from three hydrological sections taken across the lofoten basin in may 2000 we estimated geostrophic transports of 7 2 sv sverdrup 106 m3 s 1 for the norwegian atlantic current nac and its division between northern 4 8 sv and eastern 2 4 sv branches from 129i 127i concentration ratio measurements and transport estimations we calculated 129i mass flux across the three sections it appears that in the lofoten basin a 129i tracer laden norwegian coastal current ncc is transporting northward 55 kg y of 129i assuming a volume flux of 0 7 sv b the estimated mass fluxes of 129i by the nac and the ncc are comparable c the total mass flux of 129i by the nac and ncc accounts only for about 1 3 of the 129i annual discharge 350 kg y from two reprocessing plants based in france and uk if these measurements are representative of annual mean it suggests an important transfer of 129i outside the nac ncc system

passive probing of the sound fixing and ranging channel with hydro acoustic observations from ridge earthquakes the international monitoring system includes a hydro acoustic part to verify the comprehensive nuclear test ban treaty besides explosive signals monitoring stations also detect acoustic waves from earthquakes that travel through the sound fixing and ranging sofar channel the travel times of such detections are listed in the reviewed event bulletin which is statistically evaluated for the stations located in the pacific indian and atlantic oceans the celerities of ridge earthquakes are calculated to build up a homogeneous data set based on similar source mechanisms the celerity is defined as the epicentral distance divided by the travel time the global characteristics of these celerities can be well understood in terms of temperature variations in the sofar channel a detailed velocity profile has been retrieved for the atlantic ocean where large differences 14 m s are found between the southern and northern parts of the basin propagation modeling with normal modes supports these findings which shows that the celerity gives an estimate of the sound speed in the sofar channel these results compare remarkably well with those from active experiments showing the ability of passively probing the sofar channel with hydro acoustic waves from earthquake sources

impact of the equatorial deep jets on estimates of zonal transports in the atlantic the structure and variability of the zonal equatorial flow in the atlantic is studied on the basis of velocity profiles obtained with lowered acoustic doppler current profilers during multiple surveys the vertical extent of the zonal currents is found to vary considerably it can be as small as 100 m or as large as 1000 m in the atlantic vertical scales of 400 600 m have been associated with the equatorial deep jets they are also frequently called deep jets or stacked jets typical amplitudes of the zonal velocity are about 20 cm s 1 an analysis of quasi synoptic surveys indicates that the zonal extent of most jets is likely to be at least 27d they can rise or deepen from west to east although the deepening was observed more often and is often more pronounced the west to east deepening can be as large as 320 m 10d basin wide mean depth changes of the jets are mostly on the order of 50 m 10d and the largest depth changes are typically observed between 35d and 23d w the existence of these changes indicates that vertically propagating equatorially trapped waves might be one cause for the jet structure however the dependence of the slope on the longitude indicates that other processes must be involved as well the typical vertical extent of the jets is small enough to result in several direction changes of the zonal flow in the antarctic intermediate water aaiw and the north atlantic deep water nadw layer from transport estimates for 14 meridional sections it is found that the transport for the westward component of the flow within the aaiw layer 500 1000 m can be as large as 24 sv 1 sv 10 6 m s 1 within 1d of the equator for the eastward component of the flow in the aaiw layer the transport can be as large as 8 sv adding the transport components for each section results in a range of total aaiw transports from 24 to 7 sv this suggest that the annual mean transport of aaiw is westward the only months with eastward total transports are june and july this is consistent with earlier lagrangian and some other observations that indicated that the aaiw flow along the equator is governed by an annual cycle in the nadw layer 1200 3900 m the transport for the westward eastward flow can be as large as 25 sv 23 sv within 1d of the equator this results in a range of total nadw transports from 10 to 18 sv the variations of the total transports of aaiw and nadw are anti correlated with a correlation coefficient of 0 86 since only eight sections reached deep enough to allow transport estimates in the nadw layer it is more difficult to come to a conclusion about the mean transport in this layer than for the transport in the aaiw layer for the latter layer 14 sections were available nevertheless the obtained estimates suggest that the total nadw transport may be eastward

encounter of a deep western boundary current with the equator a numerical spin up experiment the encounter of a deep western boundary current with the equator is studied using an ultra high resolution numerical model of the equatorial ocean in a study of the origin of the deep equatorial current system the integration was carried out from a state of rest to 3500 days the spin up experiment shows that the deep western boundary current upon encountering the equator first turns along the equator the time scale of spin up is fast along the equator and the boundaries about 250 days but is considerably slower off the equator after this initial response the western boundary current slowly begins to penetrate into the opposite hemisphere as expected from the linear theory the eastward equatorial current gradually slows down the total water mass transport in the equatorial branch decreases steadily until by day 3000 it has dwindled to zero and all the mass transport in the western boundary current crosses into the other hemisphere however a vestige of the equatorial branch remains until the end of the integration with the speed of less than 3 cm s and with intermittent meandering an analysis of the momentum balance indicates that this meander may be a free equatorial inertial oscillation we postulate that a permanent steady bifurcation of the mid depth western boundary current that carries substantial mass does not occur and eventually all of the mass transport will continue into the opposite hemisphere the asymptotic flow field seems incompatible with the tracer field observed in the atlantic which clearly shows a splitting at the equator of the tracer signal associated with the upper north atlantic deep water we speculate that an inherently time dependent explanation of the tracer tongue is called for

dynamics of nonlinear cross equatorial flow part ii the tropically enhanced instability of the western boundary current abstract a linear stability analysis of the shallow water system in the tropical ocean examines the stability of the western boundary current and its latitudinal dependence despite a highly idealized formulation that assumes a purely meridional basic state and makes a local f plane approximation the stability analysis successfully predicts a length scale of the disturbance a latitude for its origin and a critical reynolds number that agree well with accompanying numerical results realistic western boundary current profiles undergo a horizontal shear instability that is partially stabilized by viscosity calculations of the growth rate at several latitudes indicate that the instability is enhanced in the tropics where the internal deformation radius is a maximum

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

the atlantic deep western boundary current water masses and transports near the equator the distributions and transports of deepwater masses at the western boundary in the tropical atlantic off brazil have been studied on three surveys along 35 degrees w and 5 degrees s and one at 10 degrees s transports are obtained from direct measurements of the velocity fields pegasus profiling system and lowered acoustic doppler current profiler and from geostrophic computations using chlorofluoromethane cfm and hydrographic distributions four water masses could be identified forming the north atlantic deep water nadw system two of these have a high cfm content the shallow upper nadw sunadw and the overflow lower nadw olnadw these exhibit the highest velocity signals at 35 degrees w where distinct flow cores seem to exist most of the southeastward flow of the sunadw centered around 1600 m occurs 320 km offshore between 3 degrees 09 s and 1 degrees 50 s 9 7 3 3 sv farther north in that section a highly variable reversing flow is found in a second velocity maximum the transport of olnadw centered around 3800 m of 4 6 2 6 sv is guided by the parnaiba ridge at 1 degrees 45 s 35 degrees w the water masses located between the two cfm maxima the labrador sea water lsw and the lnadw old water mass lnadw old did not show any persistent flow features however a rather constant transport of 11 1 2 6 sv was observed for these two layers the total southeastward flow of the nadw at 35 degrees w showed a transport of 26 8 7 0 sv if one neglects the reversing sunadw north of 1 degrees 50 s at 5 degrees s the flow of all deepwater masses shows vertically aligned cores the main southward transport occurred near the coast 19 5 5 3 sv the boundary current is limited offshore by a flow reversal present in all three surveys but located at different longitudes at 10 degrees s a southward transport of 4 7 sv was observed in november 1992 however the section extended only to 32 degrees 30 w so that probably a significant part of the flow has been missed an important result is the large transport variability between single cruises as well as variability of the spatial distribution of the flow at 35 degrees w which could lead to large uncertainties in the interpretation of single cruise observations despite these uncertainties we suggest a circulation pattern of the various deepwater masses near the equator by combining our mean transport estimates with other observations

crossing of the equator by the deep western boundary current in the western atlantic ocean abstract property distributions and geostrophic shear from a hydrographic section near 37 w in the atlantic ocean show the deep western boundary current dwbc in the north atlantic deep water nadw established against the western boundary of the brazil basin immediately south of the equator between 2 and 5 s the dwbc thus has directly crossed the equator to the south atlantic following the east southeast trend of the continental slope isobaths the estimated dwbc transport of nadw is 35 106 m3 s 1 similar to other estimates from the tropics discussed here these large dwbc transports are opposed by flow of deep water to the north atlantic immediately offshore of the dwbc with as much as two thirds of the dwbc transport being returned as these recirculations one recirculation center is the guiana basin north of the equator but extends at least a few hundred kilometers south of the equator another is visible at 11 s in the brazil basin the degree of connection of these two observed recirculatio

low frequency variability in the equatorial atlantic abstract low frequency v and u component oscillations in the eastern equatorial atlantic are addressed using lime series of up to 1 5 years duration from the lower portion of the main thermocline a distinct frequency separation is observed with characteristic time scales of 1 month for v and 4 8 months for u the principal v component oscillations correspond to seasonally modulated linear equatorially trapped rossby gravity waves apparently generated at the surface in the central equatorial atlantic by shear instability between the south equatorial current and the north equatorial countercurrent their length and time scales are well defined and they agree with theoretical predictions the principal u component oscillations correspond to the deep zonal jets observed by recent profiling experiments in the indian and pacific oceans the vertical scales found here agree with the results from the other oceans however insufficient data are available anywhere to ascertain zonal scales linear theory would

antarctic intermediate water circulation in the tropical and subtropical south atlantic recent hydrographic data from the south atlantic ventilation experiment cruises and others are combined with historical data and used to map the isopycnal properties corresponding to the antarctic intermediate water aaiw in the atlantic ocean the low salinity of the aaiw extends eastward across the south atlantic just south of the equator 3 4 s evidence of a weak eastward flow just north of the equator 1 2 n is also shown lateral and vertical homogenization of properties in the aaiw is found at the equator between 2 s and 2 n there is no clear zonal gradient in salinity just along the equator these observations suggest enhanced mixing within the equatorial baroclinic deformation radius the south atlantic tropical gyre is shown to consist of the following three cells one cyclonic cell centered at about 7 s another centered at about 19 s in the west and 23 s in the east and one anticyclonic cell centered at about 13 s these cells are associated with a westward extension at 10 s of high salinity and low oxygen which originates in the eastern tropical south atlantic and a front in these properties at about 15 s in the west and about 20 s in the east

atlantic equatorial deep jets space time structure and cross equatorial fluxes the so called equatorial stacked jets are analyzed with ship board observations and moored time series from the atlantic ocean the features are identified and isolated by comparing vertical wavenumber spectra at the equator with those a few degrees from the equator mode filtering gives clear views of the jets in meridional sections the typical extent being 618 in latitude the vertical structure can be well described explaining 82 of the variance by n21 stretched cosines with a gaussian amplitude tapering in the vertical the stretched wavelengths are somewhat variable fitting jets of a fixed stretched wavelength to four moored sensors in the depth range 1300 1900 m allows one to track the vertical phase of the jets with an rms error of 308 458 the resulting fit from a 20 month moored time series shows long periods of unchanging jet conditions and intermittent times of high variability there is no significant vertical propagation on these timescales nor a seasonal reversal using a composite from many different experiments interannual variability is visible however a possible mechanism for the stacked jets is inertial instability resulting from background meridional shears at the equator a condition is that the ertel potential vorticity becomes zero somewhere due to meridional asymmetries in the zonal flows the ship board observations show that this may be approximately fulfilled by the instantaneous zonal low mode flows at various depths resulting from an excess of zonal momentum south of the equator most of the time inertial instability should act to redistribute this zonal momentum and our mooring data show indeed persistent northward momentum flux but not at the depth levels expected the momentum transport might suggest that the jets can also flux or mix other properties across the equator

nonlinear and dissipative dynamics in the connection region between western boundary currents and equatorial currents the roles of nonlinearity and dissipation in connecting a western boundary current to an equatorial current are explored with a 1 layer numerical model a permanent western boundary current equatorial current system is maintained between a mass source located near the western boundary several deformation radii from the equator and a sponge layer located along the eastern boundary when a no slip boundary condition is used the western boundary current separates within two deformation radii after crossing the equator to feed the eastward equatorial current because of equatorial scalings flow within the connection region between these two currents is nearly nondivergent and similarities with barotropic models of western boundary current extensions are emphasized by potential vorticity analysis a series of experiments explores the relative importance of inertia to dissipation measured by the reynolds number by varying the forcing strength for small reynolds numbers advection of relative vorticity out of the western boundary layer eastward results in a meandering equatorial current which is interpreted as a damped stationary rossby wave at higher reynolds numbers the boundary current is susceptible to horizontal shear instability resulting in eddies which translate along the western boundary at yet higher reynolds numbers eddy variability is not confined to the western boundary disturbances are advected out of the boundary layer producing large 300 km diameter eddies in the connection region variability also radiates eastward along the equator as free yanai wave packets with periods between 30 and 70 days even in the presence of energetic eddies net flow across the equator is due mostly to vorticity dissipation in the western boundary current the effect of different boundary conditions is also examined when a free slip rather than no slip boundary condition is used the boundary current overshoots well outside the equatorial waveguide but all flow returns to the equatorial region in an offshore countercurrent and the solution is otherwise similar to solutions with a no slip boundary condition

eddies in the north brazil current retroflection region observed by geosat altimetry mesoscale fluctuations in the western tropical atlantic are analyzed in geosat altimetry sea surface height ssh and geostrophic velocity anomalies to investigate the role of eddies in the north brazil current nbc retroflection zone the detachment of anticyclonic eddies from the nbc retroflection is observed during november through january when the nbc retroflection into the north equatorial countercurrent necc weakens and finally breaks down these eddies are traced over more than 2 months between 50 and 60 w on their way toward the caribbean at average speeds of 15 cm s 1 in one case an apparent merger of two anticyclonic eddies occurs one detached from the retroflection zone and one detached from the necc cyclonic eddies are also observed but are generally less persistent mesoscale ssh variance just west of the retroflection increases by a factor of 2 from early summer to winter mainly because of the anticyclonic eddies interhemispheric water mass transfer associated with the eddy flux out of the nbc retroflection may amount to an average transport of 3 sv

large scale mass transports water mass formation and diffusivities estimated from world ocean circulation experiment woce hydrographic data 1 a global inversion is used to estimate the oceanic mass transports and vertical diffusivities based on a subset of hydrographic data from the world ocean circulation experiment woce and java australia dynamic experiment the analysis is based on the linear inverse box model of ganachaud and wunsch 2000 that consistently combines the transoceanic sections a globally consistent solution is obtained for a depth independent adjustment to the thermal wind field the freshwater flux divergences the ekman transport and the advective and diffusive dianeutral fluxes between layers a detailed error budget permits calculation of statistical uncertainties taking into account both the nonresolved part of the solution and the systematic errors due to the temporal oceanic variability the horizontal structure of the transports for different density classes is analyzed regionally during the woce period 1985 1996 net meridional transports are estimated with 16 2 sv 106 m3 s of north atlantic deep water nadw being produced in the northern north atlantic moving southward entraining antarctic bottom water aabw and antarctic intermediate water increasing in volume transport to 23 3 sv at 30 s in the southern ocean 21 6 sv of bottom water was formed from lower circumpolar deep water which corresponds approximately to the lower nadw density range bottom water inflows nadw aabw mixture to the atlantic indian and pacific oceans are estimated at 6 1 3 11 4 and 7 2 sv respectively in the indian and pacific oceans this water returns southward at deep and intermediate levels property anomaly conservation constraints permit estimation of dianeutral diffusivities in deep layers with a global average of 3 7 0 7 cm2s 1 north of 30 s

temporal evolution of the tracer signal in the deep western boundary current tropical atlantic four world ocean circulation experiment woce repeat cruises october 1990 to march 1994 in the tropical atlantic off brazil are used to study the spatial and temporal evolution of the chlorofluorocarbon cfc components cfc 11 and cfc 12 and tritium signal in the upper north atlantic deep water nadw its shallowest part located in the tropical atlantic around 1600 m depth is the shallow upper north atlantic deep water sunadw it is characterized by a distinct tracer maximum which is presumably received through winter time convection in the subpolar north atlantic here we discuss the tracer fields and the temporal evolution of the tracer signal of the sunadw in the tropical atlantic along two meridional sections at 44 degrees and 35 degrees w and two zonal sections at 5 degrees and 10 degrees s off brazil the spatial and temporal development of the tracer field in the tropical atlantic as well as the correlation with hydrographic parameters show that the temporal tracer change being due to the arrival of younger water is disturbed by other processes in particular the impact of variable mixing and spreading pathways on the observed tracer variability in the sunadw is evident in the observations

vertical mixing in the baltic sea and consequences for eutrophication a review abstract in the transition area between the north sea and the baltic sea entrainment processes dominate the vertical mixing in the inflowing saline bottom water the hot spots of these processes are located at the darss sill and the bornholm channel in the western baltic sea in the central baltic sea the horizontal advection of saline water in deep layers below the permanent halocline dominate the temporal changes and associated transports this is accompanied by the turbulent vertical transport through the halocline into the surface layers the related vertical salt transport into the entire surface mixed layer estimated by various methods is slightly above 30 kg m 2 a during stagnation periods the residence time of the deep water in the eastern gotland basin increases roughly by a factor of five vertical mixing through the halocline is drastically reduced when inflows are lacking the potential processes of diapycnal mixing are discussed to the present knowledge the turbulent motion resulting from breaking internal waves is capable of turbulent transports through the halocline corresponding to the estimates of the salt transport into the surface mixed layer the actual knowledge about boundary mixing due to internal waves in the baltic sea is poor mesoscale eddies may contribute to the vertical mixing but it is not known whether they really do and which of the possible direct and indirect mixing mechanisms is most effective near bottom currents induced by inflow events likely enhance vertical mixing coastal upwelling certainly contributes to the vertical transport but the depth of its origin and the volume transport are hard to determine for large scale quantifications the short spatiotemporal scale of turbulent transports through the halocline resulting in a weakening of the halocline during summer together with the mixing of the entire surface layer down to the halocline in winter form a consistent description of the vertical salt transport it is hypothesised that the longer residence time of the deep water during stagnation periods results from the lack of energy imported by the inflows and directly or indirectly feeding the diapycnal mixing processes the vertical transport of nutrients such as the phosphate is quantitatively not sufficiently understood and needs further interdisciplinary research activities

enhanced h and f incorporation in borian olivine b containing olivine from the tayozhnoye fe deposit siberia russia has unusually high h and f contents of 0 012 h and 0 026 0 043 f per formula unit of four o atoms there are a minimum of eight infrared o h absorption bands none of which correlates with the known o h band frequencies of hydrous magnesium silicates the o h band at 3672 cm 1 has not been observed in previously published olivine spectra transmission electron microscopy indicates substantial replacement of olivine by clinohumite and disordered mixtures of olivine and humite group minerals near the rims of the olivine grains whereas the interiors of the olivine grains contain regions of unaltered olivine structure h 2o contents calculated from the defect stoichiometry and defect density are approximately one tenth of the total h 2o content estimated from the infrared data the o h bands therefore are believed to reflect the presence of oh within the olivine crystal structure infrared active stretching vibrations at 758 1164 and 1257 cm 1 are consistent with the presence of 4 bo 4 groups within the olivine structure our data represent the first direct evidence of the coupled substitution b f oh si 1 o 1 in orthosilicate minerals as a potential carrier of b f and h in the subducted oceanic lithosphere olivine may play a key role in recycling these elements into the mantle

an experimental study of partitioning of fluorine between k richterite apatite phlogopite and melt at 20 kbar phase relations have been determined at 20 kbar and primarily under suprasolidus conditions in the fe ti free f bearing k richterite phlogopite and k richterite apatite systems in order to assess the partitioning of f among phlogopite k richterite apatite and melt under upper mantle conditions both systems are pseudoternary because they contain forsterite enstatite and a diopside rich clinopyroxene from the breakdown of the mica and k richterite the f bearing k richterite systems have lower minimum melting temperatures than the f bearing phlogopite apatite system at the same pressure however in the systems studied f in phlogopite appears the most effective component in altering minimum liquid compositions whereas comparison between the present study and previous systems suggests that the presence of p2o5 during melting may result in more k enriched melts variations in the compositions of the f bearing phases are primarily controlled by the bulk compositions of the end member minerals and by temperature although buffering by non f bearing minerals e g clinopyroxene may be effective distribution coefficients as wt ratios between f bearing minerals and coexisting liquids have been determined as functions of bulk composition and temperature for products of experiments distribution coefficients between k richterite liquid apatite liquid and phlogopite liquid are 1 to slightly 1 for most bulk compositions indicating thatf is generally a compatible element this conclusion is in agreement with the sequence off distribution for similar phases in ultrapotassic rocks these results preclude f bearing mineral reservoirs in the mantle at depths corresponding to 20 kbar being capable of producing f enrichment in ultrapotassic magmas or being effective in redox melting processes

deep cross equatorial flow in the atlantic measured with sofar floats neutrally buoyant sofar floats at nominal depths of 800 1800 and 3300 m were tracked for 21 months in the vicinity of tropical boundary currents in the atlantic near 6 n and at several sites near 11 n as well as along the equator trajectories at 1800 m show a swift 50 cm s narrow 100 km wide southward flowing deep western boundary current dwbc extending from 7 n to the equator the average transport per unit depth in the dwbc was estimated to be 13 8 103 m2 s coupling this value with mean velocities measured in the dwbc by current meters gave a volume transport of 15 106 m3 s between depths of 900 m and 2800 m approximately 6 106 m3 s recirculated northward between the dwbc and the mid atlantic ridge leaving 9 106 m3 s as cross equatorial transport no obvious dwbc nor swift equatorial current was observed by the 3300 m floats a low mean velocity at this depth lay between f 11 and higher velocity cores above and below the 1800 m trajectories also suggest that at times february march 1989 the north atlantic deep water in the dwbc turned eastward and flowed along the equator and at other times august september 1990 the dwbc crossed the equator and continued southward the velocity near the equator calculated by grouping floats in a box along the equator was eastward at 4 1 cm s from february 1989 to february 1990 and westward at 4 6 cm s from march 1990 to november 1990 thus the amount of cross equatorial flow in the dwbc appeared to be linked to low frequency variability of the structure of the equatorial current system floats in antarctic intermediate water at 800 m revealed a northwestward western boundary current although flow patterns were complicated three floats that significantly contributed to the northwestward flow looped in anticyclonic eddies that translated up the coast at 8 cm s six 800 m floats drifted eastward along the equator between 5 s and 6 n at a mean velocity of 11 cm s one reached 5 w in the gulf of guinea suggesting that the equatorial currents at this depth extended at least 35 40 along the equator three of these floats reversed direction near the end of the tracking period

fluorine partitioning between hydrous minerals and aqueous fluid at 1 gpa and 770 947 c a new constraint on slab flux abstract mechanisms of volatile element transfer from subducting slab to the melting region beneath arc volcanoes are probably the least understood process in arc magma genesis fluorine which suffers minimal degassing in arc primitive melt inclusions is highly enriched in arc lavas and retains information about the role of volatiles during magma genesis at depth experimentally determined solubility of f in aqueous fluids and partition coefficients of f between fluid and minerals provide first order geochemical constraints about the character of the volatile transporting agent we present experimentally determined f solubility in fluid in equilibrium with hornblende and a humite group mineral at 1 gpa from 770 to 947 c and partition coefficients between these phases the composition of the fluid is determined by mass balance calculations and consistency is verified by high pressure liquid chromatography measurements of the quenched fluids the partition coefficient d f flu hb can be represented by a single value of 0 13 0 03 the average f concentration in the fluid is 2700 ppm for f rich experiments constraining the maximum amount of f carried by fluid in the presence of amphibole where the initial natural f concentrations in the slab are much lower than in our experiments the increase of f concentration in the sub arc mantle by a fluid in equilibrium with hornblende is expected to be no more than a few ppm thus significant arc lava f enrichments cannot result from aqueous fluids deriving from an amphibole bearing subducting slab

variability of the horizontal velocity structure in the upper 1600 m of the water column on the equator at 10 w this paper presents initial results from new velocity observations in the eastern part of the equatorial atlantic ocean from a moored current meter array during the equalant program 1999 2000 a mooring array was deployed around the equator near 10 w that recorded one year of measurements at various depths horizontal velocities were obtained in the upper 60 m from an upward looking acoustic doppler current profiler adcp and at 13 deeper levels from current meters between 745 and 1525 m to analyze the quasiperiodic variability observed in these records a wavelet based technique was used quasiperiodic oscillations having periods between 5 and 100 days were separated into four bands 5 10 10 20 20 40 and 40 100 days the variability shows i a strong seasonality the first half of the series is dominated by larger periods than the second one and ii a strong dependence with depth some oscillations are present in the entire water column while others are only present at certain depths for the oscillations that are present in the entire water column the origin of the forcing can be traced to the surface while for the others the question of their origin remains open phase shifts at different depths generate vertical shears in the horizontal velocity component with relatively short vertical scales this is especially visible in long duration events 100 days of the zonal velocity component comparison with a simultaneous lowered acoustic doppler current profiler ladcp section suggests that some of these flows may be identified with equatorial deep jets a striking feature is a strong vertical shear lasting about 7 months between 745 and 1000 m these deep current meter observations would then imply a few months of duration for the jets in this region

kinematic elements of antarctic intermediate water in the western south atlantic the northward flowing antarctic intermediate water aaiw is a major contributor to the large scale meridional circulation of water masses in the atlantic together with bottom and thermocline water aaiw replaces north atlantic deep water that penetrates into the south atlantic from the north on the northbound propagation of aaiw from its formation area in the south western region of the argentine basin the aaiw progresses through a complex spreading pattern at the base of the main thermocline this paper presents trajectories of 75 subsurface floats seeded at aaiw depth the floats were acoustically tracked covering a period from december 1992 to october 1996 discussions of selected trajectories focus on mesoscale kinematic elements that contribute to the spreading of aaiw in the equatorial region intermittent westward and eastward currents were observed suggesting a seasonal cycle of the aaiw flow direction at tropical latitudes just offshore the intermediate western boundary current the southward advection of an anticyclonic eddy was observed between 5 degrees s and 11 degrees s farther offshore the flow lacks an advective pattern and is governed by eddy diffusion the westward subtropical gyre return current at about 28 degrees s shows considerable stability with the mean kinetic energy to eddy kinetic energy ratio being around one farther south the eastward deeper south atlantic current is dominated by large scale meanders with particle velocities in excess of 60 cm s 1 at the brazil falkland current confluence zone a cyclonic eddy near 40 degrees s 50 degrees w seems to act as injector of freshly mixed aaiw into the subtropical gyre in general much of the mixing of the various blends of aaiw is due to the activity of mesoscale eddies which frequently reoccupy similar positions c 1999 elsevier science ltd all rights reserved

deep jets in the equatorial atlantic ocean deep velocity profiles taken in the equatorial atlantic ocean show equatorially trapped deep jets with similar features to those of the indian and pacific oceans a zonal velocity of the order of 10 to 20 cm s 1 and a meridional scale of 1 in the pacific and indian oceans the zonal extent of the jets is at least 15 of longitude owing to the lack of synoptic measurements we have no information on the zonal scale in the atlantic ocean but we present here zonal velocity profiles made at a 16 month interval that have identical baroclinic structure in the western 35 w and central basin 13 w the atlantic jets have a vertical scale larger 400 600 m than those observed in the pacific ocean 250 400 m our measurements confirm the opposite directions of the jets for different seasons in the atlantic ocean furthermore for a given season the vertical profiles of zonal velocity at 35 w 0 are astonishingly similar at a 5 year interval as in the pacific and indian oceans the jets are embedded in a large vertical scale current that changes direction with time the few profiles available in the equatorial atlantic ocean suggest a seasonal reversal of the jets but neither this nor the temporal variability of the large scale current has been adequately resolved

equatorial currents at 1000 m in the atlantic ocean twenty seven profiling alace palace floats were deployed in the equatorial atlantic during july august 1997 the floats were ballasted to drift at 1000 m for 10 to 14 days return to the surface while obtaining a temperature profile transmit data via satellite and then after one day return to 1000 m one year float paths are now available floats deployed on the equator were launched into a deep westward jet the jet extends some 1 o 2 o north of the equator with eastward motion observed in floats to the north of 2 on the equatorial current reverses in the central basin to the east in mid october and then back to the west in mid february flow to the north also reverses the short space and time scales contrast with earlier work based on fewer floats that inferred space scales of some 5 o 10 o in latitude and time scales greater than one year the new results are consistent with models that indicate that equatorial rossby waves are the cause of the reversing currents

eddies of newly formed upper labrador sea water a new type of submesoscale eddy has been observed south of the labrador sea during late winter embedded in equatorward flow along the western boundary the eddy radius is 20 km with a weak dynamic signature swirl speed of 0 5 cm s the center of the eddy is characterized by weak stratification elevated concentrations of oxygen and anthropogenic tracers and low tracer ages all indicative of newly ventilated water strong lateral intrusions distort the shape of the feature the water mass contained in the eddy is not classical labrador sea water from the central labrador sea but is significantly fresher and hence lighter it is of the correct density to be the source of the high chlorofluorocarbon layer of the shallow deep western boundary current observed further south and hence is termed upper labrador sea water using a combination of hydrographic data sets along the western boundary to implement a simple lateral diffusion model it is shown that such eddies decay of the order of several months and are difficult to observe equatorward of the grand banks of newfoundland this is in contrast to deeper lenses of classical labrador sea water which persist further equatorward tracer derived ages of the upper labrador sea water eddy range from 3 to 5 years much older than the lifetime deduced from their lateral diffusion a simple convection model of tracer age shows that this age discrepancy is caused by gas exchange being unable to maintain equilibrium between the deep convecting mixed layer and the atmosphere during formation

water mass and coastal current variability near barbados west indies moored current meter observations complimented by conductivity temperature depth ctd profiles and shipboard acoustic doppler current profiler measurements have revealed two distinctly different coastal circulation patterns south of the island of barbados west indies in the springs of 1990 and 1991 in the first year an abrupt increase in speed and change in direction of the currents south of the island was found to be associated with a large anticyclonic horizontally sheared circulation and a marked variation in temperature salinity characteristics the shift in currents was also accompanied by the incursion of a shallow pool of low salinity water a strong internal semidiurnal tidal signal and a change in the location of larval fish assemblages west of the island rapid variations in current speed and direction were also observed in 1991 though less persistent than in the previous year in this year the island was at one time completely surrounded by a large shallow pool of low salinity water a comparison was made of the 1990 hydrographic observations with ctd data from the national oceanographic data center archive for the region 0 20 n 40 60 w this suggests that the variation in hydrographic characteristics was due to the intrusion of a water mass of north brazil current origin which displaced the ambient north atlantic subtropical underwater around the island several recent studies have demonstrated that mesoscale anticyclonic eddies formed near the retroflection region of the north brazil current can be advected toward the eastern caribbean before being dissipated it is concluded that the most likely cause of the observed high energy event in 1990 was the passage of such an eddy past barbados

labrador sea water tracked by profiling floats from the boundary current into the open north atlantic fifteen profiling floats were injected into the deep boundary current off labrador they were ballasted to drift in the core depth of labrador sea water lsw at 1500 m depth and were deployed in two groups during march and july august 1997 initially for about three months the floats were drifting within the boundary current and the flow vectors were used to determine the mean horizontal structure of the deep labrador current which was found to be about 100 km wide with an average core speed of 18 cm s 1 north of flemish cap the boundary current encounters complicated topography around orphan knoll and there the lsw outflow splits up into different routes one obvious lsw path is eastward through the charlie gibbs fracture zone and another route is a narrow recirculation toward the central labrador sea a surprising result was that none of the floats were able to follow the boundary current southward to the grand banks area and exit into the subtropics trajectories and temperature profiles of the eastward drifting floats indicate the importance of the north atlantic current for dispersing the floats even at the level of lsw

float trajectories in the deep western boundary current and deep equatorial jets of the tropical atlantic abstract fourteen neutrally buoyant sofar floats at a nominal depth of 1800 m were tracked acoustically for 3 7 yr in the vicinity of the western boundary and the equator of the atlantic ocean the trajectories revealed a swift narrow southward flowing deep western boundary current dwbc extending from 7n across the equator two floats crossed the equator in the dwbc and went to 10s two other floats left the dwbc and drifted eastward in the equatorial band 3s 3n three floats entered the dwbc from the equatorial current system and drifted southward these results suggest that at times the dwbc flows directly southward across the equator with a mean velocity of 8 9 cm s averaged over long distances 2800 km at other times dwbc water is diverted eastward near the equator for long periods 2 3 yr which can reduce the mean along boundary velocity to 1 2 cm s this is much less than the instantaneous along boundary velocities in the dwbc which are often above 25 cm s and occasionally exceed 50 cm s mean eastward flowing jets were observed near 2n and 2s bounding a mean westward jet centered on the equator 1s 1n the southern jet at 2s coincides with a cfc rich plume centered south of the equator the cfc plume is inferred to have been advected by the southern jet across the atlantic and into the gulf of guinea

the intermediate depth circulation of the western south atlantic the subsurface oceanic circulation is an important part of the earth climate system subsurface currents traditionally are inferred indirectly from distributions of temperature and dissolved substances occasionally supplemented by current meter measurements neutrally buoyant floats however now enable us to obtain for the first time directly measured intermediate depth velocity fields over large areas such as the western south atlantic here our combined data set provides unprecedented observations and quantification of key flow patterns such as the subtropical gyre return flow 12 sv 1 sverdrup 10 6 m 3 s 1 its bifurcation near the santos plateau and the resulting continuous narrow and swift northward intermediate western boundary current 4 sv this northward flowing water passes through complex equatorial flows and finally enters into the north atlantic

sofar float observations of an intermediate depth eastern boundary current and mesoscale variability in the eastern tropical atlantic ocean two neutrally buoyant sofar floats vigorously looped and meandered at depths of 950 1150 m in the eastern tropical atlantic ocean the float trajectories illustrate a poleward flow along the tropical eastern boundary and significant intermediate depth mesoscale variability in the low latitude eastern basin one float caught within an energetic cyclonic eddy near the eastern boundary looped cyclonically 14 times while translating 600 km northward parallel to the african coastline a second float launched near the mid atlantic ridge meandered eastward with a lagrangian zonal wavelength of 400 km and meridional amplitude exceeding 200 km satellite infrared imagery indicates that horizontal shear associated with the system of near surface zonal equatorial currents may contribute to the observed intermediate depth variability

phase relations in the phlogopite apatite system at 20 kbar implications for the role of fluorine in mantle melting phase relations have been determined at 20 kb in the simple fe ti free systems hydroxyphlogopite hydroxyapatite and hydroxyfluorphlogopite hydroxyfluorapatite in order to determine distribution of fluorine between phlogopite apatite and melt under mantle conditions no excess h2o was present in the hydroxyphlogopite hydroxyapatite system and the f oh ratio was unity in the f bearing system both systems are pseudobinary and contain forsterite at phlogopite rich compositions in the f absent system the minimum melting occurs at 1225 c and phl85ap15 whereas in the f bearing system this temperature is 1260 c and phl66ap34 phlogopite in the f absent system has lower al than in the f bearing system with both showing si mg iv al vi al as the principal substitution increase in cao in forsterite increases with increasing apatite in the bulk composition and is more pronounced in the f absent system distribution of fluorine between phlogopite and liquid and apatite and liquid shows that d f phl glass ranges from 2 1 25 depending on temperature and bulk composition whereas the d f apat glass is about unity these results suggest that fluorine will tend to remain in the solid phases rather than the melt during partial melting in the mantle hence the enrichment of fluorine in ultrapotassic magmas and its role in their evolution are constrained

western boundary current structure and variability east of abaco bahamas at 26 5 n abstract during april 1987 to june 1988 a four mooring transport resolving current meter array was deployed in a section extending 70 km eastward from abaco bahamas at 26 5 n mean currents in the upper layer 800 m showed a clockwise rotation that appears to be associated with a small scale quasi permanent anticyclonic gyre centered just northeast or the bahamas deep mean currents were persistenly southward and indicated a strong deep jet the deep western boundary current dwbc reaching core speeds of 20 cm s 1at 2500 m depth about 25 km seaward of the western boundary vertically integrated meridional volume transport over the section showed a surprisingly large variability ranging from approximately 20 sv northward to 70 sv southward 1 sv 106m3s 1 the mean meridional volume transport was 30 sv to the south with about 3 sv flowing northward above 800 m which could be produced by a weak antilles current and 33 sv flowing southward below 800 m the deep southward transport of 33 sv i

deep circulation in the equatorial atlantic ocean in the atlantic ocean the northward export of warm surface water is compensated by a southward flow of cold north atlantic deep water nadw the nadvv is transported southward along the american continental margin within the deep western boundary current dwbc some tracer and float observations have shown that part of the dwbc water flows eastward along the equator here we present three meridional velocity sections which give an instantaneous image of the lop to bottom zonal circulation along the equatorial atlantic they reveal the presence of equatorial deep jets edjs between 1 30 n and 1 30 s alternating eastward westward currents with short vertical scale surrounded by columns of eastward currents the extra equatorial jets or eejs at 2 n and 2 s in addition to direct velocity measurements tracer distributions give indications of water mass feeding of the edjs and eejs by the dwbc

status report on stability of k rich phases at mantle conditions abstract experimental research on k rich phases and observations from diamond inclusions uhp metamorphic rocks and xenoliths provide insights about the hosts for potassium at mantle conditions k rich clinopyroxene kcpx km3 si2o6 can be an important component in clinopyroxenes at p 4 gpa dependent upon coexisting k bearing phases solid or liquid but not apparently upon temperature maximum kcpx content can reach 25 mol with 17 mol the highest reported in nature partitioning k d cpx liquid above 7 gpa 0 1 0 2 require ultrapotassic liquids to form highly potassic cpx or critical solid reactions e g between kspar and di phlogopite can be stable to about 8 gpa at 1250 c where either amphibole or liquid forms when fluorine is present it generally increases in phl upon increasing p and probably t to about 6 gpa but reactions forming amphibole and or kmgf3 limit f content between 6 and 8 gpa the perovskite kmgf3 is stable up to 10 gpa and 1400 c as subsolidus breakdown products of phlogopite upon increasing p m4 k substituted potassic richterite ideally k kca mg5si8o22 oh f 2 is produced in k rich peridotites above 6 gpa and in di phl from 6 to 13 gpa k content of amphibole is positively correlated with p al and f content decrease with p in the system 1kspar 1h2o k cymrite hydrous hexasanidine kalsi3o8 nh2o kcym is stable from 2 5 gpa at 400 to 1200 c and 9 gpa kcym can be a supersolidus phase formation of kcym is sensitive to water content not forming within experiments with h2o kspar phase x a potassium di magnesium acid disilicate k1 x n 2 mg1 nmn3 2si2o7h2x forms in mafic compositions at t 1150 1400 c and p 9 17 gpa and is a potential host for k and h2o at mantle conditions with a low t geotherm or in subducting slabs the composition of phase x is not fixed but actually represents a solid solution in the stoichiometries 2mg2si2o7h2 k mg2si2o7h k2mg2si2o7 vacancy apparently stable only near the central composition k hollandite kalsi3o8 is possibly the most important k rich phase at very high pressure as it appears to be stable to conditions near the core mantle boundary 95 gpa and 2300 c other k rich phases are considered

tracer distributions and deep circulation in the western tropical atlantic during cither 1 and etambot cruises 1993 1996 this paper presents cfc and nontransient tracer observations in the western equatorial atlantic ocean on repeated sections along 7 30 n the 35 w meridian and a transect crossing the ceara rise three world ocean circulation experiment cruises have been carried out in this area in february march 1993 cither 1 and september october 1995 and april may 1996 etambot 1 and 2 together with the tracer data the direct current measurements are used to deduce the circulation pathways the data confirm the principal circulation features of the upper north atlantic deep water within the area the deep western boundary current flows southward along the continental slope while adjacent to the dwbc there is a northward flow corresponding to the dwbc recirculation whose origin appears variable the largest variability is observed along the 35 w meridional section where the dwbc bifurcates eastward north of 3 s but the eastward equatorial flow does not appear to be permanent at the middle north atlantic deep water level cfc distributions exhibit the most important contrast between waters of northern and southern origin the circulation at the lower north atlantic deep water level mainly controlled by the topography looks more permanent because the dwbc is regularly observed during the three cruises and there is no evidence for a northwestward recirculation along the mid atlantic ridge the transient behavior of cfc distributions which is superimposed on local circulation effects can be seen clearly through their temporal evolution within the dwbc the variability of the deep circulation observed during the 1993 1996 interval rules out a dominant variability in response to semi annual forcing

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

tracing water masses with 129i in the western nordic seas in early spring 2002 two long lived halogen radionuclides 36cl t1 2 301 kyr and 129i t1 2 15 7 myr have been studied by means of accelerator mass spectrometry ams at the uppsala tandem laboratory the 36cl measurements in natural samples using a medium sized tandem accelerator 1 mev amu have been considered a gas filled magnetic spectrometer gfm was proposed for the separation of 36cl from its isobar 36s semi empirical monte carlo ion optical calculations were conducted to define optimal conditions for separating 36cl and 36s a 180 gfm was constructed and installed at the dedicated ams beam line 129i has been measured in waters from the arctic and north atlantic oceans most of the 129i currently present in the earth s surface environment can be traced back to liquid and gaseous releases from the nuclear reprocessing facilities at sellafield uk and la hague france the anthropogenic 129i inventory in the central arctic ocean was found to increase proportionally to the integrated 129i releases from these reprocessing facilities the interaction and origin of water masses in the region have been clearly distinguished with the help of 129i labeling predictions based on a compartment model calculation showed that the atlantic ocean and deep arctic ocean are the major sinks for the reprocessed 129i the variability in 129i concentration measured in seawater along a transect from the baltic sea to the north atlantic suggests strong enrichment in the skagerrak kattegat basin the 129i inventory in the baltic and bothnian seas is equal to 0 3 of the total liquid releases from the reprocessing facilities a lake sediment core sampled in northeastern ireland was analyzed for 129i to study the history of the sellafield releases in particular the nuclear accident of 1957 high 129i concentration was observed corresponding to 1990 and later while no indication of the accident was found the results of this thesis research clearly demonstrate the uniqueness and future potential of 129i as a tracer of processes in both marine and continental archives

the mechanics of eddy transport from one hemisphere to the other summary the trajectory of a dense eddy propagating along the bottom of a meridional channel of parabolic crosssection from the southern to the northern hemisphere is described by a hamiltonian system with two degrees of freedom two simplie ed types of motion exist in which the meridional acceleration vanishes in midlatitudes the motion is geostrophic poleward equatorward directed along the western eastern e ank of the channel while on the equator the motion consists of zonal oscillations along the potential well generated by the bottom parabolic cross section of the channel the eddy s propagation along the equator is much faster than that in midlatitudes which enhances its dissipation via mixing with the overlying ocean water for motions that occur slightly off the equator the eastward segment isstable while the westward segment isunstable so an expulsion from the equatorial regime takes place during the latter a dense eddy that arrives near the equator along the west eank of the channel has to cross the channel to its east eank where it can either oscillate back westward to the other side or move poleward from the equator along the channel s east e ank the eddy s dissipation during the equatorial part of its trajectory is very large and the probability of the dissipated eddy leaving the equator to either hemisphere is identical the non integrability of the system is manifested in the sensitive combination of the equatorial and the midlatitude regimes that renders the dynamics of the transport of dense eddies across the equator chaotic this description explains both the sharp decrease in the amount of antarctic bottom water mass in the immediate vicinity of the equator in the western atlantic ocean and the splitter effect of the equator this effect encountered in earlier e uid dynamical numerical simulations causes a current and a cloud of particles to chaotically split into two parts eowing in different hemispheres

tracing lower north atlantic deep water across the equator water whose ultimate source is the overflow at the denmark strait can be traced using maps of salinity dissolved oxygen and silica concentration on deep density surfaces south along the american continent to at least 5 s several property extrema whose resolution is at the limit of accuracy of the measurements occur on these density surfaces which nevertheless may indicate areas of stronger mixing along the crest of the mid atlantic ridge transport estimates for that part of the southward flow within 600 km of the western boundary near 10 n suggest that 10 3 106 m3 s 1 of lower north atlantic deep water moves south there the total southward deep water transport near 10 n is estimated to be closed to 25 106 m3 s 1