profiles of trace elements and stable isotopes derived from giant long lived tridacna gigas bivalves potential applications in paleoclimate studies this study investigates the environmental and biological controls on trace element partitioning and stable isotope composition of modern giant long lived bivalves tridacna gigas with the aim to use these archives for paleoclimatic reconstructions firstly the intra shell variability is studied by measuring time equivalent profiles in the different shell layers characterised by different growth rates secondly the inter site variability is studied by comparing profiles derived from three modern specimens collected in sites across the indo pacific region characterised by different ranges of temperature and productivity these results show that 18o profiles are highly reproducible across the shell regardless of significantly different growth rates shell 18o is primarily controlled by water 18o and temperature comparison of intra shell mg ca profiles shows a clear and systematic partitioning where inner layer mg ca values are a least 2 3 times higher than outer layer and hinge areas inner layer mg ca shows seasonal oscillations but superimposed on an ontogenetic trend with increasing values and increasing amplitude mg ca oscillations with age the sr ca profiles do not show clear reproducible seasonal trends in the different shell zones it is concluded that mg ca and sr ca profiles appear to reflect a combination of biological and environmental controls that will need to be disentangled before using these proxies in paleoclimatic studies finally intra shell ba ca profiles are reproducible in great detail for all modern specimens studied inter site comparison shows that the amplitude and the timing of the ba ca peaks appear to reflect the timing and the amplitude of the chlorophyll peaks associated with phytoplankton blooms at each locality making this tracer a potential paleoproductivity indicator

strong biological controls on sr ca ratios in aragonitic marine bivalve shells 1 it is well known that skeletal remains of carbonate secreting organisms can provide a wealth of information about past environments sr ca ratios have been successfully used as a temperature proxy in corals and sclerosponges previous work on aragonitic bivalve shells has not been conclusive but suggests a major control of growth rate on sr ca ratios as many studies have used bivalve growth rates to determine temperature we tested if sr ca ratios could predict temperature through its relationship with growth rate shells from the two species of clams from the same family veneroidea studied here saxidomus giganteus and mercenaria mercenaria show vastly different seasonal sr ca profiles a strong relationship between average annual sr ca ratios and annual growth rate was found in s giganteus shells from both washington r2 0 87 and alaska r2 0 64 usa but not in m mercenaria shells from north carolina usa furthermore the sr ca growth rate relationship was also evident upon a more detailed inspection of subannual growth rates in s giganteus r2 0 73 although there were significant positive correlations between sr ca ratios and temperature in s giganteus shells the correlations were weak 0 09 r2 0 27 and thus sr ca ratios cannot be used as a reliable temperature proxy in these species of aragonitic bivalves it is clear from this study that sr ca ratios are not under thermodynamic control in either clam species since thermodynamics predict a negative correlation between sr ca ratios and temperature in aragonite this points toward dominance of biological processes in the regulation of sr2 this is also reflected by the largely differing sr ca partition coefficients dsr in these shells dsr 0 25 when compared to inorganic coral and sclerosponge studies dsr 1 all of which show a negative dependence of sr ca on temperature we suggest that caution be taken when using sr ca in any biogenic aragonite as a temperature proxy when the dsr greatly deviates from one as this indicates the dominance of biological controls on sr ca ratios

silicate versus carbonate weathering in the himalaya a comparison of the arun and seti river watersheds abstract we studied the water chemistry of two large and geologically differing himalayan watersheds in order to maximize the contrast between silicate versus carbonate weathering effects on river chemistry our previous research involved the seti river of westernmost nepal geologically typical of many rivers in nepal in draining mixed carbonate silicate lithologies including abundant carbonate rocks of the lesser himalayan sequence for comparison the arun river was chosen for study because south of the himalayan front it drains almost exclusively greater and lesser himalayan silicate rocks despite this dominance of silicate rocks carbonate weathering probably of metamorphic calcite in great himalayan paragneisses is clearly in evidence in many arun watersheds weathering of silicate rocks exposed all along the arun south of the range front has a small impact on mainstem river chemistry the mainstems of both the seti and arun systems are dominated by weathering of carbonate rocks although the contribution of silicate weathering is more visible in arun mainstem chemistry the carbonate weathering source to the arun mainstem is probably both limestone in the tethyan sequence widely exposed in northern headwaters of the system and metamorphic calcite within the greater himalayan sequence a number of small watersheds along the arun and seti appear to be carbonate free they probably provide the best constraints to date on the ca na and mg na ratios of waters draining himalayan silicate rocks two critical parameters for calculation of co 2 consumption by silicate weathering in the himalaya the observed ca na and mg na ratios would produce slightly higher estimates of silicate weathering fluxes than previous studies the geologic contrasts between the seti and the arun produce large differences in the 87 sr 86 sr ratio of each mainstem unlike the major element chemistry the seti mainstem displays much higher 87 sr 86 sr ratios than the arun mainstem the opposite of the expected relationship since radiogenic silicate rocks of the greater and lesser himalaya are so widely exposed along the arun 87 sr 86 sr ratios of the arun mainstem never exceed 0 734 and show little downstream change as the mainstem passes through silicate rocks of the greater and lesser himalaya 87 sr 86 sr ratios of the seti mainstem increase sharply from 0 725 to 0 785 when the river enters the belt of metacarbonate rocks of the northern lesser himalayan sequence a pattern also displayed by other himalayan rivers such as the kali gandaki and bhotse khola metacarbonate rocks including those of the lesser himalaya are a major source of radiogenic sr in modern himalayan rivers and probably have been key players in elevating marine 87 sr 86 sr ratios since the early miocene

mechanism for low frequency variability and salt flux in the mediterranean salt tongue the role of baroclinic instability in the generation of low frequency variability in the interior of ocean subtropical gyres and its possible importance in the zonal flux of salt and heat within the mediterranean salt tongue are discussed the observed zonal enhancement of the low frequency variability is interpreted as the signature of baroclinic instability of the large scale wind driven flow the zonal orientation results from the relatively weak vertical shear of the large scale upper ocean flow and the stabilizing influence of the planetary vorticity gradient there is a reversal in the vertical shear of velocity at middepths in the eastern basin of the north atlantic that results in a local middepth maximum in the zonal eddy flux of density linear theory predicts a vertical structure of this density flux that is nearly coincident with the observed vertical distribution of the warm salty water of the mediterranean salt tongue a primitive equation model is used to investigate the nonlinear large amplitude regime the zonal eddy density or salt flux averaged over several wavelengths and several cycles of wave growth and breaking indicates that this mechanism may be an important component in the overall salt balance in this region

micro x ray fluorescence μxrf line scanning on cretaceous rudist bivalves a new method for reproducible trace element profiles in bivalve calcite the reconstruction of palaeoclimate on a sub annual scale requires the measurement of chemical proxies in fossil material at a high spatial resolution while various methods for trace element analysis on the micrometre scale are available they are usually destructive to the sample or not widely accessible this study evaluates the performance of a table top micro x ray fluorescence scanner in obtaining reproducible trace element profiles on bivalve calcite standard calibration and repeatability tests demonstrate the robustness of results obtained with this new generation micro x ray fluorescence device that uses a comparatively high excitation energy of 30 w results show that elemental abundances measured using this fast readily accessible and non destructive analytical setup are reproducible on the g g level and therefore suitable for the analysis of the abundance of commonly studied elements in bivalve calcite for example sr mn and fe spectra obtained in this study show considerable improvement in terms of signal to noise ratio compared to earlier table top xrf studies reliability of the measurements is tested using a conservative detection and quantification limit count rates of ca are used to check for point measurements disturbed by irregularities on the sample surface furthermore the method allows semi quantitative two dimensional element mapping which is a convenient tool for the detection of diagenetic alteration in fossil samples the method reveals records of sr ca fe ca and mn ca ratios in a late campanian vaccinites vesiculosus shell with sr ca ratios showing a trend opposite to mn ca and fe ca resulting trace element records are discussed in terms of seasonal cyclicity in the late cretaceous and diagenetic alteration of the fossil shell this article is protected by copyright all rights reserved

mesoscale variability transition from the western to the eastern atlantic along 48 n abstract the north atlantic low frequency variability along 48 n is described from 76 year long velocity temperature records obtained as part of the topogulf project whose main objective was to document the effects of the mid atlantic ridge upon the circulation the eddy energy is thermocline intensified and shows a fivefold decrease eastward from 35 to 10 w west of the ridge it penetrates more easily to the ocean floor between 1500 and 2500 m sudden energetic bursts are observed and we argue that they are associated with the passage of sub mesoscale concave cyclonic lenses depleted of labrador sea water at nearly all locations a negative zonal momentum flux u v is observed which may be linked to an energy transfer from the north atlantic current eddy heat fluxes are also obtained and are directed up down the mean gradient west east of the ridge crest

the subthermocline lens d1 part i description of water properties and velocity profiles abstract one remarkable result of the local dynamics experiment in polymode is the discovery of a large number of small energetic eddies using ctd data sofar float tracks and profiles of absolute velocity we describe one of these features the subthermocline eddy d1 the feature has an advective time scale of 1 day and its primary mode of movement is advection by the ambient flow field the eddy is resolved into a coordinate system moving with the velocity of the ambient flow which ranges from 11 16 cm s 1 its phase speed is less than 2 cm s 1 the eddy is a lens centered at 1500 db velocity profiles show the lens has no detectable signal in and above the main thermocline or below about 3000 db its subsurface velocity maximum is 28 6 cm s 1 at 1500 db 15 km from the center the radial variation of the azimuthal velocity is gaussian inside the velocity maximum but decays as e br beyond there is little evidence of the eddy beyond a radius of 25 km inside the velocity maximum the eddy is characte

plankton blooms ocean circulation and the european slope current response to weather and climate in the bay of biscay and w english channel ne atlantic abstract the flow of upper layer surface water and circulation for the bay of biscay continental slope and in the wider region of the ne atlantic is presented as well as the seasonality of flow and internal tides the marine plankton environments of biscay ocean biscay eddies biscay slope and biscay shelf are defined the shelf region armorican and celtic is further divided into stratified shelf frontal and tidally mixed seasonal distributions of chlorophyll a are given for all environment from in situ measurements and remote sensing data mixing and stabilisation of surface water in the euphotic layer for the start of the spring bloom using in situ profiling measurements is examined some regional responses for the slope current dinoflagellate blooms and interannual variations in spring diatom numbers with respect to weather and climate in the bay of biscay and around the british isles are suggested and discussed an example of the eastern european ocean margin continental slope response to winter weather sea level atmospheric pressure forcing resulting in warm winter water in the southern bay of biscay navidad with eddy production and off the shetland continental slopes the warm water supply route to the arctic is given from the slope climate observation series

oxygen and carbon isotope ratios of lampsilis cardium unionidae from two streams in agricultural watersheds of iowa usa abstract climate archives preserved as seasonal variation in oxygen and carbon isotope ratios 18o and 13c in unionid shells potentially provide records of pre instrumental environmental conditions in mid to high latitude continental regions this study measured 18o and 13c values of biogenic carbonate and 18owater to investigate the timing of growth line formation and to examine the utility of lampsilis cardium as an environmental archive we tested the hypotheses that 1 l cardium precipitates its shell in isotopic equilibrium with the environment during biomineralization and 2 growth lines form seasonally during winter months these questions were addressed by monitoring water chemistry by tagging l cardium to record growth and by combining sclerochronology and stable isotope geochemistry temperature and 18owater were measured fortnightly from september 2002 to july 2004 with a break in sampling from december 2003 to february 2004 in two iowa rivers boone river and buffalo creek these data were used to calculate expected 18o values to compare to measured shell values one hundred fifty four individuals were marked at the postero dorsal margin in september 2002 and june 2003 to monitor growth seven recaptured shells collected in july 2004 were analyzed for shell 18o and 13c across three growth lines including growth lines prior to the initial marking period from the growing edge toward the umbo comparison of shell 18o with expected values revealed precipitation of 18o in equilibrium with the ambient environment from early spring to early fall winter values were not recorded due to winter growth cessation change in temperature or reaching a threshold temperature appeared to control the onset and cessation of growth moreover the locations of seasonal growth lines corresponded to winter growth cessation allowing the assignment of calendar years to growth lines seasonal growth lines were distinguished from non seasonal disturbance lines by their seasonal location inferred from the 18o time series recorded in shell growth thus we can faithfully reconstruct ontogeny through time and environmental and climate conditions from mid to high latitudes using l cardium variation in 13cshell followed a more or less sinusoidal trend similar to the seasonal profiles of 18oshell suggesting that seasonal processes influenced the variation in carbon isotopes reduced amplitudes and more negative 13cshell values with increasing age suggest that kinetic and or metabolic isotope effects become important through ontogeny as observed in other bivalves the profiles of 13cshell potentially record local differences in landscape vegetation however specific factors influencing 13cshell are unknown and further study of water quality are required to fully assess the variation of 13cshell as an environmental proxy

labrador sea water in the eastern north atlantic part i a synoptic circulation inferred from a minimum in potential vorticity abstract a synoptic distribution of labrador sea water lsw in the eastern north atlantic is determined from a regularly sampled but sparse 3 resolution survey covering 39 to 54 n 11 to 34 w during spring 1991 the core of lsw can be defined by a minimum in potential vorticity pv using property values at this minimum the authors infer the circulation of lsw in addition using a known source function for salinities at the core of lsw estimates are able to be made of lsw vintages the authors then compared the synoptic circulation to historical data youngest 1986 vintage lsw crosses the mid atlantic ridge to the eastern basin between 48 and 51 n at 34 w this water then flows north to the iceland basin and eastward to the rockall trough where it was found to be of 1978 vintage tongues of low salinity low temperature and high oxygen extend southward on the eastern side of the mid atlantic ridge indicating that lsw also flows southward in the eastern basin at the southern edge of the s

a geochemical study on the specific distribution of barium in lake biwa japan the vertical distribution of alkaline earth elements aees was measured in a mesotrophic lake lake biwa of japan by comparing the distribution profiles of the elements it was noticed that the dissolved barium concentration markedly decreased in the bottom layer during the stagnation stage of the lake this characteristic distribution disappeared in the circulation stage but appeared repeatedly in the succeeding stagnation stage such periodic variation of the barium distribution profile contrasts with the result that other aees were uniformly distributed without regard to depth or stage of lake water circulation adsorption of aees onto synthetic hydrous manganese oxide hmo was examined in lake water the results suggest that the specific distribution of barium observed in lake biwa was caused by the selective adsorption of the element onto hmo which is naturally produced at the bottom of the lake

testing the effect of carbonate saturation on the sr ca of biogenic aragonite a case study from the river ehen cumbria uk it has been suggested that the incorporation of strontium into biogenic aragonite may be influenced by the degree of carbonate saturation in aquatic environments we measured the sr ca ratios of river water and the aragonitic shells of freshwater bivalves margaritifera margaritifera from two sites with different carbonate saturation states in the river ehen cumbria uk shell sr ca and river water sr ca are 0 1 mmol mol and 0 42 mmol mol lower respectively at the high carbonate saturation site however the distribution coefficients of strontium into aragonite kd are the same 0 28 at both sites these analyses show that sr uptake into aragonite bivalve shells is not affected by the degree of carbonate saturation of the water perhaps reflecting a strong biological control on trace element incorporation

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

reconstructing the history of fluid flow at cold seep sites from ba ca ratios in vesicomyid clam shells hydrogen sulfide discharge at cold seep sites is recorded as enrichment in the barium to calcium ba ca ratio in shells of vesicomyid clams collected live from cold seeps in monterey canyon and the cascadia margin a direct relationship between increased ba fluxes from cold seeps and ba incorporation into shells was established for the cascadia margin site for the monterey canyon site a 2 yr episode of high fluid flow centered on 1992 was inferred from coherent changes in the ba ca profiles of threecalyptogena kilmerishells comparison with precipitation and d 18 o data indicates that this high flow period may have been driven by an increase in rainfall after the 1988 1990 california drought high resolution records preserved in clam shells are shown to be useful in elucidating characteristics history and possible mechanisms driving fluid discharge at continental margin seeps thus establishing their potential use as paleotracers of fluid seepage events an extensive set of geophysical and geochemical measurements is currently available to document the flow and expulsion of fluids at transform and convergent margins it is now recognized that such fluid discharge has far reaching implications that include hydrocarbon prospecting benthic ecosystem structure and function and groundwater research moore 1999 at present we are unable to incorporate geochemical data from cold seeps to models quantifying their effects on marine geochemical budgets because we lack a clear understanding of the spatial and temporal variability of these systems and of the mechanisms responsible for the advective transport however vent macrofauna may afford such an opportunity by recording in their shells the immediate environment in which they grow and thereby allowing us to reconstruct the variability in fluid discharge rates vesicomyid clams live in association with sites of sulfide 1

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

sr mg ratios of modern marine calcite empirical indicators of ocean chemistry and precipitation rate holocene biotic and abiotic marine calcite have a similar range of mg contents 0 to 22 and 4 to 21 mol mgco3 respectively yet biotic calcite has sr2 concentrations that are consistently 1250 ppm higher than those of abiotic calcite as in laboratory experiments a positive linear relation is observed between dsr and calcite mg content this produces two distinct linear trends on a plot of sr2 vs mg2 concentrations principal axes of variation for both trends have similar slopes yet distinctly different sr2 concentration intercepts biotic y 0 024x 1298 r2 0 70 abiotic y 0 027x 47 r2 0 77 the similar slopes of these trends reflect the constancy of mgca and srca ratios of modern seawater equations describing the dependence of dsr on calcite mg content are derived from both trends biotic dsr 3 16 x 10t 6 ppm mg 0 169 abiotic dsr 3 52 x 10 6 ppm mg 0 0062 characterization of sr mg trends for holocene materials allows comparison with analogous trends from ancient samples to estimate relative changes in seawater mgca and srca ratios the relatively high sr contents of biotic calcite result from rapid precipitation rates associated with shell accretion in marine organisms calcites precipitated from seawater in laboratory experiments have dsr values that are similar to those of biotic marine calcite suggesting that both precipitate at approximately the same rate our estimates of surface area normalized precipitation rates in planktonic and benthonic foraminifera are comparable to those of seeded ph stat experiments we conclude that the dsr values for biotic and experimental marine calcite are kinetically controlled whereas the lower precipitation rates of abiotic marine calcite yield dsr values that approximate equilibrium conditions experimentally derived equations describing the relation between dsr and calcite precipitation rate indicate that the offset in sr content between biotic and abiotic calcite is the result of abiotic precipitation rates that are two to five orders of magnitude lower than those of biotic precipitates however observations of naturally occurring marine cements suggest that the five order of magnitude offset best represents natural system processes

biological and water chemistry controls on sr ca ba ca mg ca and δ18o profiles in freshwater pearl mussel hyriopsis sp abstract we investigated oxygen isotope and sr ca ba ca and mg ca ratios in shells of a commercially cultured freshwater pearl mussel hyriopsis sp unionidae and ambient water the first order fluctuations of oxygen isotope ratios of the outer shell layer along the maximum growth axis recorded the mussels annual growth from 2002 to 2007 clear annual sr ca cycles suggest that sr was incorporated into the shells at a high rate during warm seasons all three examined shells showed a clear decrease in annual average sr ca with age inter and intra annual trends suggest that sr incorporation was higher during periods of faster growth the ba concentration and the ba ca ratio of ambient water showed neither an annual periodicity nor a seasonal trend in contrast to the findings of an inorganic aragonite precipitation experiment ba ca was positively correlated with ambient temperature in addition ba ca and sr ca ratios were positively correlated with each other these results suggest that not thermodynamic equilibrium partitioning but the shell growth rate controls ba incorporation into hyriopsis shells the mg ca profiles of the three shells suggest that complex factors control the incorporation of mg into shell aragonite water temperature and annual growth rates did not significantly influence mg incorporation and substantial interspecimen differences suggested that physicochemical factors do not exert any systematic control on mg ca ratios in hyriopsis instead the mg content of shell aragonite might reflect biological contamination with organic material or adsorption phenomena during crystal precipitation rather than regulated substitution into the aragonite crystal lattice our results suggest that trace element profiles in aragonitic bivalve shells could be interpreted as the result of strong biological controls over riding environmental influences on trace element incorporation

and ratios in skeletal calcite of mytilus trossulus covariation with metabolic rate salinity and carbon isotopic composition of seawater minor element and isotopic compositions of marine bivalve calcite are frequently used as proxy records of seawater temperature and salinity although molluscan calcite is secreted at or near oxygen isotope equilibrium the influence of metabolic activity i e vital effects on skeletal srca ratios and 13c values is not well known we present measurements of skeletal chemistry from a consecutive samples milled in chronological order from the organism s final year of growth and b adjacent samples within three separate growth bands of the marine mussel mytilus trossulus to investigate chemical disequilibrium effects among different parts of the shell seawater temperature and salinity were monitored for one year at squirrel cove british columbia at the end of the year a young rapidly growing mussel mussel a and an old slowly growing mussel mussel b were harvested from this site growth bands within the shells were sampled to provide a chronological record of shell carbonate chemistry results from consecutive samples show 1 a significantly higher average srca ratio in mussel a than that in mussel b and 2 13c values that correlate well with salinity in mussel a but not in mussel b results from time equivalent adjacent samples show 1 higher srca and 13c values near the ventral margin than at time equivalent regions on lateral margins of the shell and 2 little or no variation in 18o values these observations suggest that skeletal chemistry srca and 13c is primarily controlled by rate of mantle metabolic activity and secondarily modified by variation in seawater salinity because metabolic activity in the mantle at the site of carbonate precipitation varies with shell curvature the composition of calcite secreted along lateral margins is influenced to a greater extent by metabolic activity than calcite secreted coevally at the central margin of the shell hence the chemistry of calcite secreted at the ventral margin is precipitated in near equilibrium with seawater and allows accurate estimation of seawater srca ratios and carbon isotopic composition in contrast shell precipitation along lateral margins is dominantly controlled by metabolic activity and calcite chemistry is not in equilibrium with ambient seawater in this context we present a biomineralization model where variations in skeletal srca and 13c values are explained in the context of mantle metabolic activity and seawater salinity

minor and trace elements in sclerosponge ceratoporella nicholsoni biogenic aragonite near the inorganic endmember abstract the trace and minor element composition have been investigated in the accretionary skeletons of two specimens of the caribbean sclerosponge species ceratoporella nicholsoni one from tongue of the ocean bahamas toto and the other from pear tree bottom jamaica ptb both sclerosponges were analyzed at high resolution using laser ablation icp ms la icp ms and verified using wet chemical methods icp oes the shallow ptb sclerosponge 25 m was analyzed for a short temperature calibrated record of trace and minor elements while the toto sclerosponge 146 m was analyzed for a century long record from subsurface waters the resulting ba ca mg ca pb ca and u ca ratios were compared with sr ca ratios which have been shown to reliably record seasonal scale temperature change in sclerosponges close to equilibrium precipitation of inorganic aragonite sclerosponge aragonite incorporates minor and trace elements according to general mineralogic constraints with less vital effects than other calcium carbonate secreting organisms this is perhaps most obvious in the behavior of mg ca ratios which show an inverse correlation to temperature unlike any other calcite or aragonite organism despite having mg concentrations 1 mmol mol within published estimates of equilibrium aragonite ratios of mg ca and ba ca show a strong positive correlation despite large differences in ionic radii and u ca values 3 15 mol mol are 2 5 higher in sclerosponge aragonite than in aragonite from corals supporting earlier work ratios of u ca show an insignificant correlation with temperature dependent sr ca ratios r 2 0 05 supporting existing theories that temperature signals recorded by u ca ratios can be convolved with ph co 3 2 and phosphate signals differences between sclerosponge aragonite and other calcium carbonate arising from siliceous spicule contamination are unlikely because of the small mole percent of silicon in the aragonite small differences between the two sclerosponges were noticed in pb ca and sr ca because of the average ages of the sampled material and average temperatures of the ambient environment respectively anomalies between la icp ms and icp oes were noticed in measurements of ba ca and pb ca due to standardization differences for la icp ms ba ca and measurements close to the instrument detection limits of pb icp oes

a standard analytic curve of potential temperature versus salinity for the western north atlantic abstract an algorithm is described for computing salinity as a continuous function of potential temperature for the western north atlantic the algorithm uses historical data compiled by worthington and melcalf 1961 for the deep western north atlantic and iselin 1936 for shallow and intermediate waters of the same region

pervasive sources of isotopically light zinc in the north atlantic ocean abstract in this study we report seawater dissolved zinc zn concentration and isotope composition 66 zn from the geotraces ga01 geovide section in the north atlantic across the transect three subsets of samples stand out due to their isotopically light signature those close to the reykjanes ridge those close to the sediments and those pervasively in the upper ocean similar to observations at other locations the hydrothermal vent of the reykjanes ridge is responsible for the isotopically light zn composition of the surrounding waters with an estimated source 66 zn of 0 42 this isotopically light zn is then transported over a distance greater than 1000 km from the vent sedimentary inputs are also evident all across the trans atlantic section highlighting a much more pervasive process than previously thought these inputs of isotopically light zn ranging from 0 51 to 0 01 may be caused by diffusion out of zn rich pore waters or by dissolution of sedimentary particles the upper north atlantic is dominated by low 66 zn a feature that has been observed in all zn isotope datasets north of the southern ocean using macronutrient to zn ratios to better understand modifications of preformed signatures exported from the southern ocean we suggest that low upper ocean 66 zn results from addition of isotopically light zn to the upper ocean and not necessarily from removal of heavy zn through scavenging though the precise source of this isotopically light upper ocean zn is not fully resolved it seems possible that it is anthropogenic in origin this view of the controls on upper ocean zn is fundamentally different from those put forward previously

seasonal stable isotope variations of the modern amazonian freshwater bivalve anodontites trapesialis in a floodplain lake of the amazon river near the city of iquitos northeastern peru a one year monitoring experiment was conducted during which water samples and living bivalves anodontites trapesialis were collected with the aim to investigate seasonal 18o variation in and fractionation between bivalve aragonite and host water both host water and molluscan growth increments show more than 8 seasonal variation in 18o in the floodplain lake under study the 18o variation of the water is controlled by contrasting dry and wet season evaporation precipitation regimes molluscan 18o appears to be in equilibrium with the host water although an approximately 4 0 offset occurs 13c records of water and bivalves are in good agreement suggesting that both 18o and 13c of the shells of freshwater bivalve a trapesialis are good recorders of palaeo environmental conditions the 13c of dissolved inorganic carbon dic is governed by plant growth and or by changes in aquatic chemistry affecting the dic pool

lagrangian observations of the middepth and deep velocity fields of the northeastern atlantic ocean the circulation of the northeastern atlantic ocean at intermediate depths is characterized by watermass transformation processes that involve iceland scotland overflow water isow from the northeast labrador sea water lsw from the west and mediterranean water from the south field observations were carried out with 89 eddy resolving floats rafos and marvor types the data coverage achieved is remarkably high and enables a comprehensive study of the eastern basins between iceland and the azores the trajectories show typical pathways of the water masses involved and the role that the complex bottom topography plays in defining them the isow paths tend to lean against the slopes of the reykjanes ridge and rockall plateau westward escapes through multiple gaps in the ridge are possible superimposed on a sustained southward flow in the eastern basin along the mid atlantic ridge lsw pathways leading to the eastern basins are subject to high variability in flow direction and eddy activity in addition to a selection of characteristic trajectories maps of the horizontal distributions of lagrangian eddy kinetic energy and integral time scales are presented these reveal distinct areas of intensified mixing in the iceland basin as well as the sharp contrast between the subpolar and subtropical dynamics a self contained eddy detection scheme is applied to obtain statistics on individual eddy properties and their abundance it is suggested that much of the intensified mixing can be related to cyclonic activity particularly in the subpolar region

an inverse model of the north atlantic general circulation using lagrangian float data abstract a nonlinear finite difference inverse model is used for estimating the north atlantic general circulation between 20 and 50 n the inverse model with grid spacing 2 latitude and 2 5 longitude is based on hydrography and is in geostrophic and hydrostatic balances the constraints of the inverse model are surface and subsurface float mean velocities ekman pumping derived from wind data conservations of mass heat and salt and the planetary vorticity equation at the reference level the mass heat and salt conservations are applied in a vertically integrated form the model does not have explicit mixing or air sea flux terms vertical velocities result from the nondivergence of the 3d velocity field after inversion float velocities hydrographic data and dynamical constraints are generally compatible within error bounds a few float velocities are however rejected by the model mainly due to inadequate time or space sampling of the 2 latitude by 5 longitude boxes for which mean float v

deep dissolved iron profiles in the eastern north atlantic in relation to water masses concentrations of dissolved iron dfe 0 2 m were determined at two stations in the biscay abyssal plain north east atlantic in march 2002 dfe concentrations in the surface layer 0 23 0 34 nm were typical of winter conditions in this area at 1000 m dfe concentrations increased to 0 62 0 86 nm this feature is consistent with the production of dfe by remineralization of the biogenic material however at this depth mediterranean outflow water mow could be an additional source of dfe below 2500 m dfe concentrations were constant 0 75 0 04 nm an interesting feature of the profiles was the intermediate maximum of dfe 1 19 1 12 nm around 2000 m associated with the labrador sea water lsw we suggest that the iron enrichment of lsw occurred when this water mass reached the continental margin likely in the vicinity of the goban plateau vertical distributions were highly dependent on water masses encountered

deglacial upslope shift of ne atlantic intermediate waters controlled slope erosion and cold water coral mound formation porcupine seabight irish margin abstract turbulent bottom currents significantly influence the formation of cold water coral mounds and sedimentation processes on continental slopes combining records from coral mounds and adjacent slope sediments therefore provide an unprecedented palaeo archive to understand past variations of intermediate water mass dynamics here we present coral ages from coral mounds of the belgica province porcupine seabight ne atlantic which indicate a non synchronous holocene re activation in mound formation suggested by a temporal offset of 2 7 kyr between the deep start 11 3 ka bp at 950 m depth and shallow start 8 6 ka bp at 700 m depth mounds a similar depth dependent pattern is revealed in the slope sediments close to these mounds that become progressively younger from 22 1 ka bp at 990 m to 12 2 ka bp at 740 m depth based on core top ages we suggest that the observed changes are the consequence of enhanced bottom water hydrodynamics caused by internal waves associated to the re invigoration of the mediterranean outflow water mow and the development of a transition zone tz between the mow and the overlying eastern north atlantic water enaw which established during the last deglacial these highly energetic conditions induced erosion adjacent to the belgica mounds and supported the re initiation of mound formation by increasing food and sediment fluxes the striking depth dependent patterns are likely linked to a shift of the enaw mow tz moving the level of maximum energy 250 m upslope since the onset of the last deglaciation

controls on magnesium manganese strontium and barium concentrations recorded in freshwater mussel shells from ohio abstract freshwater bivalve shells may record inter annual fluctuations in water chemistry which in turn may archive variations in solute load due to pollution or discharge events here using weekly surface water chemistry collected at two locations and shells of lampsilis cardium grown in the surface water we investigate if the mg ca mn ca sr ca and ba ca ratios measured at high resolution in the shells on an intra annual time scale consistently reflect the chemistry of the surface water two relationships appear highly correlated sr cacarb and sr cawater and mn cacarb and temperature ba cacarb correlated strongly with ba cawater in one shell but temperature in another shell yielding inconclusive results mn cacarb and mg cacarb were not strongly correlated with elemental ratios in the water but mn cacarb did show variable weak to moderate correlation with ph we found consistent partition coefficient dme values between individual shell samples grown in the same water with mean dmg 0 0006 dmn 17 dba 0 13 and dsr 0 176 sr cacarb and sr cawater exhibited the strongest most consistent correlation with partitioning coefficients that were consistent with published values suggesting sr cacarb can be used as a proxy for sr cawater in freshwater mussels

the long lived mollusc arctica islandica a new paleoceanographic tool for the reconstruction of bottom temperatures for the continental shelves of the northern north atlantic ocean the carbonate shell of the bivalve arctica islandica has been recognized for more than a decade as a potentially important marine geochemical biorecorder owing to this species great longevity 200 years and wide geographic distribution throughout the northern north atlantic ocean a region vital to global climate and ocean circulation however until now this potential has not been realized owing to the difficulty of precisely sampling the shell of this slow growing species using newly available automated microsampling techniques combined with micromass stable isotope mass spectrometry a stable oxygen isotope record 1956 1957 and 1961 1970 has been obtained from a live captured 38 year old a islandica specimen collected near the former position of the nantucket shoals lightship 41 n 69 w the shell s 18o signal is compared with an expected signal derived from ambient bottom temperature and salinity data recorded at the lightship for the same period the results show that a islandica s 18o record 1 is in phase with its growth banding confirming the annual periodicity of this species growth bands 2 is in oxygen isotopic equilibrium with the ambient seawater 3 shows a consistent shell growth shutdown temperature of 6 c which translates into an 8 month may december shell growth period at this location and 4 records the ambient bottom temperature with a precision of 1 2 c these results add important information on the life history of this commercially important shellfish species and demonstrate that a islandica shells can be used to reconstruct inter and intra annual records of the continental shelf bottom temperature

labrador sea water in the eastern north atlantic part ii mixing dynamics and the advective diffusive balance abstract deep wintertime convection in the labrador basin produces labrador sea water lsw which spreads throughout the north atlantic the lsw is not formed with constant characteristics but varies on decadal timescale these changes in the source of lsw propagate throughout the north atlantic having a dramatic impact on middepth properties in regions far removed from the labrador basin here by means of a property variance correlation analysis on isopycnal surfaces through the core of lsw the authors show that the boundary anomalies of lsw survive the effects of mixing over the length and timescales taken for lsw to reach the eastern north atlantic typically the anomaly amplitude is reduced by a factor of 5 during transit and from a simple estimate the integrated timescale for this reduction is seven years uncertainties in the oxygen anomaly analysis exclude specific interpretation but constrain the boundary condition variability to about 5 the lateral effect of unresolved processes resembl

the use of oxygen isotope variation in shells of estuarine mollusks as a quantitative record of seasonal and annual colorado river discharge abstract we describe a new method for the calculation of river flow that uses the oxygen isotope composition of bivalve mollusk shells that grew in the river water seawater mixing zone of the colorado river estuary sclerochronological techniques are used to identify tidally induced fortnight scale bundles of daily growth increments within shell cross sections these fortnightly markers are used to establish a chronology for samples taken for 18 o analysis a composite seasonal 18 o profile derived from five shells that grew in the absence of river water flow is used as a baseline against which profiles of river influenced shells are compared because this comparison is between matched fortnights within a year the temperature of shell growth is likely to be very similar the difference in 18 o between the river influenced shell and the no flow composite shell therefore represents the change in the 18 o of the water due to the presence of river water in the mixing zone the river water end member is also determined within a fortnightly context so that the change in the 18 o of mixing zone water can be used to calculate the relative proportions of seawater and fresh water the fresh water end member is calculated from the 18 o of bivalves alive prior to the emplacement of dams and water diversions on the colorado river the marine end member is based on direct measurements of the 18 o of northern gulf of california water during times of no colorado river flow the system has been calibrated to absolute flow amounts using recent releases of known volume and rate

seasonal stable isotope evidence for a strong asian monsoon throughout the past 10 7 m y o of wet season rainfall was signi cantly morenegative 29 5 smow prior to 7 5 ma than after 26 5 smow if this change is attributable to a lessening of the amounteffect in rainfall this agrees with oral and soil geochemical datathat indicate increasing aridity beginning at 7 5 ma keywords tibetan plateau monsoon stable isotopes paleohydrology seasonality introductionthe tibetan plateau is the engine that drives the modern asianmonsoon by generating a high altitude region of low pressure in thesummer as the plateau heats and a region of high pressure in the winteras the plateau cools hastenrath 1991 during the summer warm airrises from the plateau pulling moist air off the ocean across the indiansubcontinent and into the highlands this results in heavy summer rain fall on the subcontinent the opposite occurs in the winter resultingin cold dry air spilling off the plateau and effectively excluding rainfrom the subcontinent thus the presence of a strong wet season dry season alternation implies the presence of a plateau broad and highenough to drive the monsoon the timing of the uplift of the plateau remains a matter of con siderable debate because there are few direct indicators of paleotopog raphy in the geologic record consequently past workers in tibet re lying on indirect indicators of uplift have proposed dates ranging from40 to 3 4 ma on the basis of initiation of potassic volcanism chunget al 1998 turner et al 1993 or extension on the plateau harrisonet al 1995 coleman and hodges 1995 changes in marine sedimen tation rates burbank et al 1993 sediment types rea et al 1998 or biota nigrini and caulet 1992 kroon et al 1991 and changesin stable carbon isotope and palynological patterns on the indian sub continent quade et al 1989 chen 1981 although different areasof the plateau may have risen at different times many workers haveinferred rapid simultaneous uplift of large areas of the plateau at 7 8ma by a process such as lithospheric delamination molnar et al 1993 this inference was based on the following approximately coevalphenomena a major change in plant communities of the indian sub continent quade et al 1989 and shifts in marine upwelling patternsthat are linked to an intense monsoon kroon et al 1991 althoughthere is strong evidence for signi cant climate change at 7 8 ma it isunclear whether this is the onset of the monsoon the oral transitionseems to have been a global rather than local phenomenon cerling etal 1997 and monsoonally driven upwelling may have already beenpresent by 10 12 ma nigrini and caulet 1992 kroon et al 1991 because there is an intimate association between the intense sea sonality of the modern monsoon and a high tibetan plateau and be cause evaporation can be unambiguously recognized in the d

spreading of labrador sea water in the eastern north atlantic the spreading of labrador sea water lsw in the eastern north atlantic south of 55 n is described on the basis of recent high resolution hydrographic lines and using an inverse model of that basin general circulation the isopycnic salinity anomaly relative to a standard s curve is used to detect the main branches and limits of dominant influence of the intermediate water masses the lsw crosses the mid atlantic ridge at latitudes around 50 n with parts spreading farther eastward and southward one southward pathway along the eastern side of the mid atlantic ridge stands out as an eastern basin counterpart of the western atlantic deep western boundary current an entry into the bay of biscay in its northern part is also evidenced with striking similitudes between two data sets from 1974 and 1989 1990 at the southern limit of the lsw extension in the vicinity of the azores biscay rise a marked front exists basinwide around 1800 m with the more saline deep mediterranean water dmw the inverse model velocity field is consistent with most features of the tracer distributions and allows estimation of lsw transports 6 3 1 2 sv of lsw with salinities lower than 34 94 cross the 35 w meridian eastward between 44 n and 54 n one fourth of which recirculates southwestward in the western basin while another fourth turns northward across 54 n and the remaining half proceeds southward in the eastern basin the model circulation suggests that dmw results from mixing between eastern basin lsw and the overlying mediterranean outflow water most probably through double diffusion we finally describe several mesoscale structures of anomalously high lsw influence south of the lsw dmw front notably one sampled by a rafos float the velocity and potential vorticity fields suggest that these lsw eddies are formed through baroclinic instability at the lsw dmw front

paleomagnetism of the lac st jean anorthosite and related rocks grenville province quebec alternating field and thermal demagnetization study of the lac st jean anorthosite and related rock units in the central portion of the exposed grenville province reveals two components of magnetization one of reversed and the other of normal polarity both components are thought to have been acquired during the last regional metamorphism which was sufficiently intense in this area mostly amphibolite grade to reset any earlier magnetization corresponding paleopoles at 193 w 8 s dm 7 3 dp 4 6 and 213 w 19 s dm 10 5 dp 8 5 lie along the 950 900 ma segment of the recently calibrated grenville track of the north american apparent polar wander path a track that has thus far been defined largely by results from rock units of the western grenville

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

recirculating components to the deep boundary current of the northern north atlantic abstract the meridional overturning system of the north atlantic is conventionally thought of as transporting warm water 4 c to high latitudes and covd water to low latitudes the northern cold water sources for this system are dense overflow from the nordic seas and less dense water from the labrador sea lsw the overflow components are carried westward by a deep northern boundary current dnbc that is shown here actually to begin southeast of the overflow regions the dnbc lies along the southern side of a system of islands and submarine ridges that divides the nordic seas from the subpolar basins the overflows act to increase the transport of the dnbc and this transport is further increased through the entrainment of warm waters once inside the labrador sea the dnbc is joined by lsw before continuing south to low latitudes as a cold deep western boundary current dwbc however published transport estimates are larger than can be explained by warm water entrainment alone thus indicating entrainment also of recirculating cold components the subject of this paper their sources are shown to be the lsw and cold abyssal waters originating from the southern hemisphere the lsw is entrained downward into the denser part of the dnbc and laterally into the upper part of the dwbc whereas the cold abyssal waters are supplied by an eastern intensified northward flow in the eastern atlantic that serves as the initial source of the dnbc and by a similar northward flow in the western atlantic the meridional overturning system described includes recirculations and poleward transport of cold water in addition tothe components described by the conventional system the cold abyssal waters in both the eastern and western basins have relatively low levels of oxygen and high concentrations of silicate reflecting their southern origin but their influence in the northwestern atlantic is somewhat obscurred by strong recirculating cyclonic gyres in the newfoundland and labrador basins this influence is detected by a deep silicate maximum extending poleward from the mid latitude western atlantic through the two gyres with eastern concentration and recirculating back diluted toward the south in the dwbc within the respective basins such a maximum also extends northward through the irminger basin into the dnbc but there is an ambiguity as to whether this is a direct extension of the signal from the south in the western basin or if it comes from the mid latitude eastern basin by way of westward flow through the charlie gibbs fracture zone it is perhaps consequence of both estimates of the volume transports of the various recirculating cold components indicate that they supply about as much water to the deep boundary currents as do the combined cold water sources in the north

mg ca sr ca and stable isotopes in modern and holocene protothaca staminea shells from a northern california coastal upwelling region this study explores the potential of intertidal protothaca staminea shells as high resolution geochemical archives of environmental change in a coastal upwelling region mg ca and sr ca ratios were analyzed by excimer laser ablation inductively coupled plasma mass spectrometry la icp ms at sub weekly temporal resolution in shells growing 1 mm per month growth patterns of a modern p staminea shell from humboldt bay california collected in december 1999 made it possible to infer a lifespan from 1993 to 1998 growth hiatuses in the shell may have excluded records of extreme events mg ca ratios appeared to be partly controlled by water temperature the correlation coefficient between temperature and mg ca was r 0 71 in one of four growth increments significant year to year differences in the sensitivity of mg ca to temperature in p staminea could not be explained however sr ca ratios appeared to be more closely related to shell growth rate oxygen isotopes measured at 2 week temporal resolution in the same shell did not show a clear relation to local temperature in summer possibly because temperatures were higher and less variable at the king salmon mudflat where the shell was collected than in the main channel of humboldt bay where water properties were monitored negative shell 13c values 0 5 marked spring and summer coastal upwelling events the mg contents of p staminea midden shells dated to 3 ka and 9 ka were significantly lower than in the modern shell this may have resulted from degradation of a mg rich shell organic matrix and precluded quantitative interpretation of the older high resolution records elevated 13c values in the 3 ka shell suggested that the individual grew in highly productive or stratified environment such as a shallow coastal embayment or lagoon

the flux of overflow water through the charlie gibbs fracture zone we report the results of a set of measurements made within the charlie gibbs fracture zone in 1988 1989 the principal data sources are year long current meter records 16 in number and 23 conductivity temperature depth stations the aim was to determine the flux of overflow water passing westward out of the iceland basin in the eastern north atlantic within the fracture zone overflow water is defined either as having salinity greater than 34 94 at the present time or more generally as having a potential density 0 27 8 kg m3 in 1988 1989 the core salinity had a value equal to that reported in 1981 and 1983 but was fresher by about 0 02 than was found in 1964 the flux was estimated twice per day and was found to fluctuate strongly with energy spread in a broad band of periods ranging from 10 to 400 days no annual signal could be detected the mean value was 2 4 0 5 sv less than all previous estimates based on hydrography alone it is suggested that hydrography may systematically overestimate transport because diffusion is neglected flux estimates from current meter arrays are rarely used in initializing numerical ocean models consequently measurements like those reported here are an independent and important means for assessing the performance of such models at the deepest levels water enters the two transform valleys of the fracture zone from the west in the northern valley the flow is periodically flushed out by energetic bursts of overflow water a critical value of an inverse froude number is shown to define the flushing threshold

the water masses of the central north atlantic in 1983 84 abstract hydrographic surveys carried out in 1983 84 along both sides of the mid atlantic ridge between 24 and 53 n provide a detailed description of the well known north atlantic water masses with particular emphasis on their meridional distribution and zonal dissymetry in the upper layers the dense horizontal sampling resolves the several narrow gulf stream extensions into the ocean interior giving the image in the central water density range of a mosaic of mode waters separated by fronts at intermediate depths a vertical shear in the distributions of the mediterranean water and labrador sea water stands out both water masses having their lower part displaced southwards relative to their upper parts bottom waters containing nearly 20 percent of pure antarctic bottom water are observed at 50 n in the eastern basin in contrast with the western basin where proportions greater than 10 percent were found only south of 36 n along our section this water mass analysis also gives indications that stron

new constraints on the pb and nd isotopic evolution of ne atlantic water masses 1 time series of lead pb and neodymium nd isotope compositions were measured on three ferromanganese crusts recording the evolution of ne atlantic water masses over the past 15 ma the crusts are distributed along a depth profile 700 4600 m comprising the present day depths of mediterranean outflow water and north east atlantic deep water a pronounced increase of the 206pb 204pb in the two deeper crusts starting at 4 ma and a decrease in 143nd 144nd in all three crusts took place between 6 4 ma and the present these patterns are similar to isotope time series in the western north atlantic basin and are consistent with efficient mixing between the two basins however the changes occurred 1 3 ma earlier in the eastern basin indicating that the northeastern atlantic led the major change in pb and nd isotope composition probably due to a direct supply of labrador seawater via a northern route the pb isotope evolution during the pliocene pleistocene can generally be explained by mixing between two end members corresponding to mediterranean outflow water and north east atlantic deep water but external sources such as saharan dust are likely to have played a role as well the pb isotope composition of the shallowest crust that grew within the present day mediterranean outflow water does not show significant pb isotope changes indicating that it was controlled by the same pb sources throughout the past 15 ma

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