reduced north atlantic deep water flux to the glacial southern ocean inferred from neodymium isotope ratios the global circulation of the oceans and the atmosphere transports heat around the earth broecker and denton1 suggested that changes in the global ocean circulation might have triggered or enhanced the glacial interglacial cycles but proxy data for past circulation taken from sediment cores in the south atlantic ocean have yielded conflicting interpretations of ocean circulation in glacial times 13c variations in benthic foraminifera2 3 4 5 6 support the idea of a glacial weakening or shutdown of north atlantic deep water production whereas other proxies such as cd ca ba ca and 231pa 230th ratios show little change from the last glacial maximum to the holocene epoch7 8 9 here we report neodymium isotope ratios from the dispersed fe mn oxide component of two southeast atlantic sediment cores both cores show variations that tend towards north atlantic signatures during the warm marine isotope stages 1 and 3 whereas for the full glacial stages 2 and 4 they are closer to pacific ocean signatures we conclude that the export of north atlantic deep water to the southern ocean has resembled present day conditions during the warm climate intervals but was reduced during the cold stages an increase in biological productivity may explain the various proxy data during the times of reduced north atlantic deep water export

the estuarine chemistry of rare earth elements comparison of the amazon fly sepik and the gulf of papua systems abstract a comparison of the amazon fly gulf of papua and sepik river systems has shown that there are two distinct processes operating on dissolved rare earth elements ree in estuaries large scale salt induced coagulation in the low salinity region and small to extensive release in the mid to high salinity region fractionation of the ree occurs during both removal and release the order of removal follows lree mree hree and the order of release follows hree mree lree where l m and h refer to light middle and heavy ree respectively hence estuarine reactions can modify the relative abundance of dissolved ree reaching the oceans operating in tandem the removal and release lead to the preferential removal of the lree and the preferential release of hree during estuarine mixing this combination in turn results in an effective river water flux river flux after modifications by estuarine chemistry which is evolved toward the ree composition of seawater which has a heavy ree enriched composition when normalized against the ree composition of rivers or the earth s continental crust the increase of dissolved ree in the mid to high salinity waters of the amazon and fly estuaries suggests a sediment and or suspended sediment source the lack of ree increases in the sepik river estuary strengthens this explanation as the mixing zone of this estuary is located over a deep shelf where there is little physical contact between bottom sediment and estuarine waters in marked contrast the amazon and fly estuaries are dominated by the active resuspension and deposition of bottom sediments the resupply of ree accompanied by fractionation may result from ree carbonate complexation during the reaction of seawater with suspended particles and or bottom sediment estuarine and shelf sediments may be important sources of dissolved nd to the oceans thereby helping to maintain the inter ocean differences in the nd isotopic composition of seawater by reducing the residence time of nd in the oceans

behavior of rare earth elements in seawater at the ocean margin a study along the slopes of the sagami and nankai troughs near japan using a flow injection icp ms method yttrium and all the lanthanides in seawater were determined in the coastal offshore mixing regime near japan marked enrichments in the trivalent rare earth elements rees in the surface waters are ascribed to the influence of coastal waters from tokyo bay in march and perhaps somewhere else in september and october to this region at less than half of the stations where the detailed vertical profiles were obtained throughout the water column we found marked excess ree iii concentrations near the bottom these bottom concentration anomalies are probably caused by resuspension of underlying sediments excluding those surface and bottom anomalous concentrations the distribution of ree iii s in the midwater column are very similar to those of the open ocean and are highly correlated with each other r2 0 95 this suggests that the boundary effects on the chemical fractionation of ree iii s are small we find no effect of the boundary scavenging known for 210pb and 231pa on the ree distribution whereas there may be preferential release of light and middle ree iii s over heavy rees from slope sediments to the seawater much like 227ac from the shale normalized ree patterns we obtained up to 90 negative ce and 10 positive gd anomalies in the water column

a review of numerical ocean modeling 1983 1986 midlatitude mesoscale and gyre scale for the years 1983 to the present numerical modeling of midlatitude ocean circulation on the mesoscale and gyre scale is reviewed numerical results have shown great similarity to recent thermocline theories but also some important differences in particular ventilation of the pool zone caused by convective processes is substantial also solutions employing explicitly resolved eddies differ significantly from their equilibrium counterparts inverse methods have provided improved estimates of meridional heat transport and tropical upwelling of tracers the crucial influence of the western boundary on the circulation of the gyre interior is beginning to be understood research has focused on the conditions for radiation by jets the relationship between a jet s structure and its stability and the generation of deep mean flows by eddy activity near the surface constraints on the structure of isolated vortices imposed by instability mechanisms have been explored with new balanced models which provide an inexpensive but accurate alternative to primitive equation models for many oceanic processes transport of salinity by gulf stream rings has been found to be comparable to the effects of evaporation and precipitation in the slope water it has also been shown that radial circulation in warm core rings cannot be disregarded as a possible cause of ring spin down in anticipation of a dramatic increase in the oceanic observational data base from altimetry scatterometry tomography and in situ measurement new modeling techniques for data assimilation and prediction are beginning to be developed

atmosphere ocean momentum exchange in general circulation models a series of two layer quasigeostrophic solutions for the ocean circulation driven by a steady wind in a channel with topography and in a flat bottom rectangular basin are presented in which the atmosphere and ocean are inertially coupled through the surface stress relation the only other frictional processes are biharmonic lateral friction under free slip boundary conditions and topographic form stress there is no bottom friction involved the results indicate that realistic momentum balances can be obtained on this physical basis two types of solutions are obtained which are called i the i series in which the inertial coupling relation is applied directly in the earth reference frame with no current averaging and almost steady stream fields occur and ii the s series in which the inertial coupling relation is applied for long current averaging periods of the order 100 days rather than instantaneously the solutions for the longer current averaging periods produce vigorous eddy fields but their time mean is very similar to the corresponding solution with no current averaging surface stokes drift streamfields are also generated by the inertial coupling mechanism some implications of the results for general circulation modeling are discussed

isotopic composition of neodymium in waters from the drake passage the isotopic composition of neodymium has been determined in seawaters from the drake passage the antarctic circumpolar current which controls interocean mixing flows through this passage the parameter e nd 0 which is a function of the ratio of neodymium 143 to neodymium 144 is found to be uniform with depth at two stations with a value which is intermediate between the values for the atlantic and the pacific and indicates that the antarctic circumpolar current consists of about 70 percent atlantic water cold bottom water from a site in the south central pacific has the neodymium isotopic signature of the waters in the drake passage by using a box model to describe the exchange of water between the southern ocean and the ocean basins to the north together with the isotopic results an upper limit of approximately 33 million cubic meters per second is calculated for the rate of exchange between the pacific and the southern ocean concentrations of samarium and neodymium were also determined and found to increase approximately linearly with depth these results suggest that neodymium may be a valuable tracer in oceanography and may be useful in paleo oceanographic studies

a comparison of observed and modeled sea surface topographic time series near the new england seamounts yearlong data records from four arrays of inverted echo sounders ies equipped with pressure sensors from the northwest atlantic and 2 year records from a two layer primitive equation numerical model of this region including a prescribed deep western boundary current are compared standard deviations of barotropic and total sea surface topographic variability and the correlations between them are examined as a function of horizontal position variances contained in three spectral bands secular longer than 150 days mesoscale 20 150 days and high frequency 2 20 days are also examined the eastward penetration scale of modeled gulf stream variability shows a significant improvement over a previous comparison hallock et al 1989 standard deviations of observed sea surface height components compare favorably with those derived from model output with maxima of about 30 cm 10 cm for the barotropic contribution high correlations 0 6 0 8 between surface height and the barotropic component are found for both model and observations spectral shape is dominated by the temporal mesoscale east of the new england seamounts for both observed and modeled variability west of the seamounts the secular low frequency band becomes more important particularly for the surface height variability this result is more pronounced for model output gulf stream geostrophic current direction statistics from ies dynamic heights compare favorably with those derived from model dynamic heights upstream and downstream of the seamounts

neodymium isotopic variations in northwest pacific waters abstract four vertical profiles of the concentration and isotopic composition of nd in seawater were obtained in the western north pacific two profiles from the kuroshio current regime showed congruently that although the nd concentration increases gradually with depth its isotopic composition varies significantly with depth depending upon the water mass occupying the water column the high salinity kuroshio waters originating from the north pacific tropical water nptw carry the least radiogenic nd nd 7 4 to 8 7 to this region at 250 m from the western margin continental shelves most likely from the east china sea the nd isotopic compositions in the north pacific intermediate water npiw that occurs at 600 to 1000 m in the subtropical region are fairly uniform at nd 3 7 the profile data from the 38 to 40 n kuroshio oyashio mixed water region off sanriku of honshu japan also suggest that the newest npiw with nd 3 2 is formed there by the mixing of various source waters and the radiogenic component of nd is derived mainly from the oyashio waters in the pacific deep water pdw below 1000 m the nd isotopic composition is neither vertically nor horizontally homogeneous suggesting that it serves as a useful tracer for sluggish deep water circulation as well two profiles from the izu ogasawara trench showed a minimum nd value at 2000 m suggesting that there exists a horizontal advective flow in the vicinity of honshu japan there is some evidence from other chemical properties to support this observation the waters below 4000 m including those within the trench in the subtropical region have nd values of around 5 suggesting that the deep waters are fed from the south along the western boundary ultimately from the antarctic bottom water aabw in the south pacific this extends up to 40 n along the japanese islands in the subarctic region 42 n the waters have more radiogenic nd with nd 4 0 throughout the water column presumably due to the supply of nd by weathering in such igneous provinces as the kuril kamchatska aleutian island chain the lateral inhomogeneity of the nd isotopic composition in pdw suggests that there may be different circulation and mixing regimes in the north pacific basin

possible source of advected water mass and residence times in the multi structured sea of japan using rare earth elements 1 the sea of japan is a small fast acting model of global oceanic circulation observations from 1998 and 2001 are analyzed to clarify its circulation new bottom water formed in early 2001 off vladivostok was observed later that year near the southeastern edge of the japan basin implying a velocity of 2 3 3 9 cm s 1 tb yb patterns of rare earth elements distinguish two classes of water volume inactive old well mixed water and active relatively young water frequently affected by the subduction of the surface water originating from tsushima warm current twc the proportion of twc to old water and each residence time are 50 75 and 15 years 200 400 m and 35 80 and 38 years 600 1500 m using six strata an improved estimate of the average residence time of japan sea proper water is 86 years this includes the contributions from active and inactive strata

reevaluating the roles of eddies in multiple barotropic wind driven gyres multiple gyre ocean models have a weaker mean subtropical circulation than single gyre calculations with the same viscosity and subtropical forcing traditionally this reduction in circulation is attributed to an intergyre eddy vorticity flux that cancels some of the wind input part of which does not require a lagrangian mass exchange theory of dissipative meandering herein the intergyre eddy vorticity flux is shown to be a controlling factor in barotropic models at high reynolds number only with exactly antisymmetric gyres and slip boundary conditions almost no intergyre flux occurs when no slip boundary conditions are used yet the subtropical gyre is still significantly weaker in multiple gyre calculations sinuous modes of instability present only in multiple gyres are shown here to vastly increase the eddy vorticity transport efficiency this increase in efficiency reduces the mean circulation necessary for equilibrium with slip boundary conditions the intergyre eddy transport is possibly much larger however with wind forcing relevant for the ocean two unequal gyres a mean flow flux of vorticity rather than an eddy flux between the regions of opposing wind forcing is increasingly important with increasing reynolds number a physical rationalization of the differing results is provided by diagnosis of the equilibrium vorticity budget and eddy transport efficiency calculations varying 1 boundary conditions 2 sources and sinks of vorticity 3 eddy transport efficiency and 4 the degree of symmetry of the gyres are discussed

observed and modeled mesoscale variability near the gulf stream and kuroshio extension our earliest intercomparisons between western north atlantic data and eddy resolving two layer quasi geostrophic symmetric double gyre steady wind forced numerical model results focused on the amplitudes and largest horizontal scales in patterns of eddy kinetic energy primarily abyssal here intercomparisons are extended to recent eight layer model runs and new data which allow expansion of the investigation to the kuroshio extension and throughout much of the water column two numerical experiments are shown to have realistic zonal vertical and temporal eddy scales in the vicinity of the kuroshio extension in one case and the gulf stream in the other model zonal mean speeds are larger than observed but vertical shears are in general agreement with the data a longitudinal displacement between the maximum intensity in surface and abyssal eddy fields as observed for the north atlantic is not found in the model results the numerical simulations examined are highly idealized notably with respect to basin shape topography wind forcing and of course dissipation therefore the zero order agreement between modeled and observed basic characteristics of mid latitude jets and their associated eddy fields suggests that such properties are predominantly determined by the physical mechanisms which dominate the models where the fluctuations are the result of instability processes the comparatively high vertical resolution of the model is needed to compare with new higher resolution data as well as for dynamical reasons although the precise number of layers required either kinematically or dynamically or numerically has not been determined we estimate four to six when no attempt is made to account for bottom or near surface intensified phenomena

zonal penetration scale of model midlatitude jets abstract all available observations indicate that the most energetic time dependent currents are located in the vicinity of intense large scale oceanic current systems this characteristic is also a basic property of eddy resolving gyre scale numerical models an initial detailed intercomparison of two layer eddy resolving numerical experiments with observation focused on the largest scales of horizontal structure in patterns of abyssal eddy kinetic energy and on time scales the numerical experiments examined generally had relevant temporal and meridional scales but not necessarily realistic zonal scales the model eddy field did not penetrate as far from the western boundary as observed distributions by a factor of 2 to 3 the present study examines the physical processes that govern the model zonal penetration scale and suggests reasons for the previous discrepancy it is demonstrated that a subtle balance exists between the complex instability processes that tend to tear the jet apart restricting

tracing the flow rate and mixing ratio of the changjiang diluted water in the northwestern pacific marginal seas using radium isotopes we measured ra isotopes 223ra and 228ra in surface seawater of the northwestern pacific marginal seas to trace the flow rate and mixing of the changjiang diluted water cdw in the summer of 2012 based on the horizontal distribution of 223ra activities the arrival time of cdw from the river mouth to 450 km offshore northeast was estimated to be 20 35 days which is similar to that determined in previous studies moreover we successfully calculated the relative contribution of cdw at each sampling station using a salinity and 228ra diagram using this unique method we found that the relative contribution of cdw was more than 30 in most surface seawaters of the northern east china sea the yellow sea and the southern sea off korea our results suggest that cdw is of high significance in the biogeochemistry of surface seawater of these northwestern pacific marginal seas during the summer monsoon period

western boundary current separation sensitivity studies using a quasigeostrophic ocean model abstract the sensitivity of the separation of the western boundary current of an idealized single gyre circulation to the specification of various model parameters is investigated through a series of quasigeostrophic simulations the model parameters considered are the value of bottom topography lateral boundary conditions deformation radius of the first baroclinic mode horizontal friction and model resolution changes in these model parameters affect western boundary current separation characteristics but those parameter changes also produced changes in several measures of the global flow field such as level of mean and eddy kinetic energies a number of flow field statistics are correlated with the average separation point and it was found that total average baroclinic kinetic energy is the most highly correlated variable to the average separation point with higher levels of kinetic energy being correlated with more poleward penetration in the immediate vicinity of the separation point the a

three dimensional kinematic and microphysical evolution of florida cumulonimbus part iii vertical mass transport mass divergence and synthesis abstract a statistical technique is employed to examine the evolving properties of the ensemble small scale variability of high resolution radar data collected in a multicellular florida thunderstorm this paper examines vertical mass transport and mass divergence and synthesizes these observations with results from the first two parts of the study into a self consistent conceptual model that describes the convective to stratiform transition of the storm vertical mass transport distributions indicate that the more numerous weak and moderate strength upward and downward velocities not the few strongest accomplished most of the vertical mass transport in the storm hence most of the mass of precipitation is condensed outside the areas of intense upward motion these data thus suggest a change in the way we think about convection although the few regions of strongest vertical motion play a part in the overall storm evolution by dispersing particles throughout the depth of the storm it is the more preva

tracing papua new guinea imprint on the central equatorial pacific ocean using neodymium isotopic compositions and rare earth element patterns abstract the nd isotopic composition ic and rare earth patterns of hydrodynamic structures of the equatorial pacific ocean were characterized along 140 w the nd ic of antarctic intermediate water aaiw and of the lower layer of the equatorial undercurrent euc at 140 w 13 c water are much more radiogenic at the equator than at their origin in the south equatorial current 12 s revealing that these water masses have been in contact with the highly radiogenic papua new guinea png slope in both cases only a small fraction less than 9 of the sediment deposited on the png slope is required to be exchanged or dissolved to explain these nd ic variations whereas the hydrographic properties of the same water masses remain unchanged this confirms the usefulness of this tracer to identify pathways of water masses these results emphasize the importance of jets in transporting lithogenic material into the subsurface layers of remote areas where aeolian inputs are particularly weak and corroborate the previous results on fe and al maximum in this area m l wells g k vallis e a silver nature 398 1999 601 604 the nd ic of the upper layer of the euc contrasts strongly to that of the subpycnocline layer indicating that the equatorial upwelling only affects the surface waters and is not effective between 120 and 150 m we calculate that the nd imprint of the png input is likely to vanish from this surface layer as it traverses the basin due to the replacement of upwelled waters by non radiogenic ones

on the time averaged flow of quasi geostrophic wind driven gyres the time averaged flow of a three layer eddy resolving quasi geostrophic ocean model is considered in the light of two analytical models of wind driven gyres in which the vertical structure of the gyre is set by assuming that potential vorticity is uniform beneath layers exposed to forcing the first due to young and rhines 1982 supposes that the depth integrated meridional transport is set by the imposed wind stress curl in contrast in the baroclinic fofonoff gyres of marshall and nurser 1986 1988 inertial aspects of the flow are emphasized without imposing a sverdrup constraint the mean fields from the model are seen to lie between the two extremes represented by these analytical solutions in the interior of the gyre away from inertial boundary currents and jets the sverdrup constraint is obeyed and the mean flows resemble the young and rhines solution however the essential character of the overspun recirculation including the weakly depth dependent nature of the currents in its return flow seem to be well captured in the inertial limit considered by marshall and nurser

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

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

neodymium isotopic composition of the mediterranean outflow and the eastern north atlantic the neodymium concentration and isotopic composition of the mediterranean outflow in the strait of gibraltar has been directly determined the outflow has a dissolved nd concentration of 23 pmoles kg with nd 0 9 4 these results are in clear disagreement with previous values inferred for the mediterranean this concentration and nd 0 do not sharply contrast with north atlantic deep water nadw values and can produce isotopic anomalies no larger than 1 unit in the north atlantic a new profile in the eastern north atlantic does not exhibit an nd 0 anomaly at the depth of the mediterranean water core in accordance with the above inferences while concentrations and nd 0 at this site indicate that nd is conservative in the deep eastern north atlantic a previously reported nd 0 anomaly in the eastern north atlantic originally associated with the mediterranean outflow has a different source the direct contribution of the mediterranean outflow to the nadw nd budget is small 10 of the high latitude sources however the outflow plus entrained water supply 30 of the total nd associated with northern latitude deep water sources concentrations of dissolved nd in the outflow are enriched compared to the atlantic inflow which has 16 pmoles kg with nd 0 11 8 the principal source of the excess dissolved nd is inferred to be partial dissolution of detrital particles simple mass balance calculations suggest that 0 6 of the nd associated with detrital river transported sediments and or 3 5 of the nd associated with eolian particles delivered to the mediterranean is mobilized during passage into the marine environment if general these mobilization efficiencies imply that the dissolution of detrital particles is a significant source of dissolved nd and other rare earth elements in seawater

rare earth element transport in the western north atlantic inferred from nd isotopic observations the isotopic composition of nd in the water column from several western north atlantic sites and formational areas for north atlantic deep water shows extensive vertical structure at all locations in regions where a thermocline is well developed large isotopic shifts 2 to 3 units are observed across the base of the thermocline regions without a thermocline are characterized by much more gradual shifts in isotopic composition with depth in general the data reveal an excellent correlation between the nd isotopic distribution in the western north atlantic water column and the distribution of water masses identified from temperature and salinity characteristics nadw as identified from t s properties is also characterized by a well defined isotopic composition having nd 0 13 5 0 5 this signature is associated with waters identified as nadw from high latitudes near formational areas in the labrador sea down to the equatorial region the isotopic signature of nadw would appear to be formed by a blend of more negative waters originating in the labrador sea nd 0 18 and more positive waters originating in the overflows from the norwegian and greenland seas nd 0 8 to 10 and is consistent with classical theories on the formation of nadw the isotopic signature of nadw is propagated southward to the equator where it is gradually being thinned out by mixing from above and below with more radiogenic nd associated with northward spreading antarctic intermediate and bottom waters the preservation of the isotopic signature of nadw over these large distances indicate that the ree undergo extensive lateral transport the isotopic composition of nd is largely conservative over the time scales of mixing within the atlantic in spite of the intrinsic nonconservative behavior of neodymium nd concentration gradients generally show surface waters to be depleted in nd relative to deep waters which must require vertical transport processes however isotopic differences in the water column preclude the local downward transport of ree from the surface into underlying deep waters as a simple explanation of the concentration gradient the apparent decoupling of ree in nadw from overlying local surface waters and the increasing concentration with depth provide a conflict with simple vertical transport mechanisms that is not yet resolved