chemical and physical denudation in the amazon river basin we present major and trace element data on the suspended and dissolved phases of the amazon river and its main tributaries the sr isotopic composition of the dissolved load is also reported special attention is paid to the abundances of ree and to their fractionation between the dissolved and suspended phase the rivers of the amazon basin are among the richest in dissolved ree and are similar to the rivers of the congo system however a greater range of fractionation between lree and hree is reported here at a global scale the rivers have intermediate patterns between those of the congo system and those of high ph rivers such as the indus and mississippi rivers only few elements rb u ba k na sr and ca are mobilized by silicate weathering these elements are strongly depleted in the suspended phase with respect to upper continental crust in the dissolved load these elements are controlled by atmospheric inputs and the weathering of the main lithologies we propose a model based on mass budget equations that allow the proportions derived from the different sources to be calculated as a consequence silicate carbonate and evaporite weathering rates can be estimated as well as the consumption of co2 by weathering of each of these lithologies physical weathering rates can be estimated by two complementary approaches on the one hand the multi year average of suspended sediments yields can be used to estimate physical denudation on the other hand we have developed a steady state model of erosion that allows us to calculate physical erosion rates on the basis of the dissolved load of rivers a mean crustal composition is assumed in this model for the rock sources of the drainage basins comparison of the rates predicted by the model to the observed rates shows good agreement for the lowland rivers but a strong discrepancy for the rivers derived from the andes andean rivers solimoes madeira and amazon have observed sediment yields much greater than those predicted according to the steady state model of chemical and physical weathering two interpretations can account for this inconsistency the first is that these rivers are not in steady state and hence that the soils are being destroyed the second requires that the local continental crust is different from the average continental crust of taylor and mclennan and contains a large proportion of sedimentary rocks using the measured sediment yields and assuming a steady state we can estimate the amount of sediment recycling for each drainage basin for the amazon at santarem we find that at least 25 of the mass of the upper continental crust of the amazon drainage basin is constituted of recycled material

fate of particulate copper and zinc isotopes at the solimoes negro river confluence amazon basin brazil abstract the behaviour and fate of copper cu and zinc zn at river confluences is poorly understood although chemical and physical processes during mixing of compositionally different tributaries might condition metal availability and fluxes to the ocean to identify and quantify the effect of such processes in river mixing zones particulate cu and zn isotope signatures 65cuspm and 66znspm were measured along cross sections and vertical profiles at the largest river confluence in the world the encontro das aguas mixing zone of the amazon river where the organic rich negro river meets the sediment rich solimoes river the negro river suspended sediments with highly variable cu and zn concentrations as well as 65cuspm and 66znspm are mostly influenced by organic matter and by the lateritic cover of the watershed the solimoes river suspended sediments more homogeneous in cu and zn concentration and isotope composition across the river section reflect the signature of weathered silicate rich sediments derived from the andes the solimoes river supplies the majority of the suspended cu and zn to the amazon river and despite important flux losses across the confluence 35 for cu and 27 for zn 65cuspm and 66znspm show a conservative behaviour during the mixing in the dissolved load cu concentrations and 65cudiss mostly supplied by the solimoes river behave conservatively whereas zn derived mainly from the negro river suffers an important loss 58 that can be attributed to zn adsorption onto the suspended sediments from the solimoes river this transfer does not induce a significant 66znspm shift in the amazon river suspended sediments therefore cu and zn isotope ratios in the suspended sediments behave conservatively through this confluence which mixes two very chemically contrasted rivers our findings thus suggest that the riverine isotopic information on the sources of particulate cu and zn is preserved during tributary mixing

lagrangian exploration of the california undercurrent 1992 95 abstract during the period 1992 95 nineteen isobaric rafos floats placed in the california undercurrent at intermediate depths 150 600 m off monterey and san francisco california reveal a region of varying width of subsurface poleward flow adjacent to the continental margin the float trajectories exhibit three patterns poleward flow in the undercurrent reversing but predominately alongshore flow adjacent to the continental margin and farther offshore anticyclonic motion accompanied by slow westward drift flow continuity of the undercurrent exists between pt reyes and at least cape mendocino with an average speed dependent on the float depth speeds were variable but common features were acceleration occurring to the south of pt arena and deceleration to the north of cape mendocino an important mechanism for floats and water to enter the ocean interior from the undercurrent is through the formation of submesoscale coherent vortices

extreme water mass anomaly observed in the hawaii ocean time series extremely anomalous water mass properties with deviations as high as 35 were observed in the thermocline during january 2001 at the hawaii ocean time series site north of oahu the spatial distribution of the anomalous waters is consistent with a submesoscale vortex with radius 15 km possibly a remnant of a mesoscale eddy the most plausible source location of the anomalous waters is offshore of mexico near baja california given the southwestward subtropical gyre circulation it is unlikely that these waters were transported directly westward to hawaii unusual northward transport of equatorial waters along the north american coast during the 1997 98 el nino event and subsequent transport southwestward in the core of a california undercurrent eddy is more plausible el nino modulation of eddy transport and diffusion of water mass properties may substantially impact the mean distribution of properties in the north pacific subtropical gyre

iron isotope differences between earth moon mars and vesta as possible records of contrasted accretion mechanisms the iron isotope compositions of shergotty nakhla chassigny snc meteorites thought to come from mars eucrites and diogenites assumed to sample asteroid 4 vesta and rocks from the moon and earth have been measured using high precision plasma source mass spectrometry the means of eight samples from mars and nine samples from vesta are within error identical despite a range of rock types they are lighter by 0 1 in 57fe 54fe compared to the average of 13 terrestrial mantle derived rocks the latter value is identical within uncertainty with a previously published mean of 46 igneous rocks from the earth the average for 14 lunar basalts and highland plutonic rocks covering a broad spectrum of major element composition is heavier by 0 1 in 57fe 54fe relative to our estimate for the earth s mantle and therefore 0 2 heavier than the eucrites diogenites and snc meteorites however the data scatter somewhat and the apollo 15 green glass and apollo 17 orange glass are identical to samples from mars and vesta there is no clear relationship between petrological characteristics and fe isotope composition despite a wide spectrum of samples instead contrasted planetary isotopic signatures are clearly resolved statistically after evaluating alternative scenario it appears that the most plausible explanation for the heavier fe in the earth and moon is that both objects grew via processes that involved partial vaporisation leading to kinetic iron isotope fractionation followed by minor loss this is consistent with the theory in which the moon is thought to have originated from a giant impact between the proto earth and another planet combined with numerical simulations fe isotope data can offer the potential to provide constraints on the processes that occurred in planetary accretion

large iron isotope fractionation at the oxic anoxic boundary in lake nyos abstract the degassing of volcanic lake nyos cameroon provides the opportunity to study the strong isotopic variation of dissolved fe ii in a well constrained redox cycle and to identify the governing processes by reaction transport modeling two depth profiles sampled in the lake in march 2004 and 2005 reveal an increase in iron concentrations and 57 fe from around 1 mg l 1 and 1 88 at 55 m depth up to 344 mg l 1 and 0 83 at the bottom of the lake respectively a steep increase in 57 fe was observed across the oxic anoxic boundary as many biological and geochemical processes are known to fractionate fe isotopes we used a calibrated reaction transport model to disentangle the processes governing the fe cycle the model combines the isotopic signatures of dissolved fe ii and settling fe iii particles with the concentration profiles and settling fluxes of the fe particles in the lake we show that the strong shift in 57 fe is caused by isotopic fractionation via dissimilatory fe reduction across the oxic anoxic boundary of lake nyos the shift towards more positive values below the oxic anoxic interface could be attributed to vertical mixing of a heavier component from the bottom of the lake

the full glacial environment of the northern seward peninsula alaska reconstructed from the 21 500 year old kitluk paleosol abstract paleoenvironmental conditions are reconstructed from soils buried under volcanic ash ca 21 500 years ago on the seward peninsula soil development was minimal reflecting the continuous regional deposition of loess which originated from river floodplains and the exposed chukchi shelf cryoturbated soil horizons ice wedges and ice lens formation indicate a permafrost environment and mean annual temperatures below 6 to 8 c shallow active layers average 45 cm minimal evidence for chemical leaching of soils and the presence of earthen hummocks indicate a cold and seasonally dry climate neither steppe nor polar desert soils are appropriate analogues for these zonal soils of loess covered central beringia no exact analogues are known however soils underlying dry tundra near the arctic coast of northern yakutia russia and under moist nonacidic tundra of the alaskan north slope have properties in common with the buried soils

the cape ghir filament system in august 2009 nw africa in the framework of the canaries iberian marine ecosystem exchanges caibex experiment an interdisciplinary high resolution survey was conducted in the nw african region of cape ghir 30 38 n during august 2009 the anatomy of a major filament is investigated on scales down to the submesoscale using in situ and remotely sensed data the filament may be viewed as a system composed of three intimately connected structures a small shallow and cold filament embedded within a larger deeper and cool filament and an intrathermocline anticyclonic eddy ite the cold filament which stretches 110 km offshore is a shallow feature 60 m deep and 25 km wide identified by minimal surface temperatures and rich in chlorophyll a this structure comprises two asymmetrical submesoscale 18 km fronts with jets flowing in opposite directions the cold filament is embedded near the equatorward boundary of a much broader region of approximately 120 km width and 150 m depth that forms the cool filament and stretches at least 200 km offshore this cool region partly resulting from the influence of cold filament is limited by two asymmetrical mesoscale 50 km frontal boundaries at the ite located north of the cold filament we observe evidence of downwelling as indicated by a relatively high concentration of particles extending from the surface to more than 200 m depth we hypothesize that this ite may act as a sink of carbon and thus the filament system may serve dual roles of offshore carbon export and carbon sink

a numerical study of the upwelling circulation off central chile effects of remote oceanic forcing 1 a numerical ocean model is used to study the upwelling circulation off central chile in response to local winds and remote forcing in an idealized study of equatorial forced intraseasonal variability period of 50 days a first mode coastal trapped wave ctw paddle is applied to the northern boundary with coastal sea level amplitude of 12 cm without this ctw forcing the steady seasonal winds upwell undercurrent water from depths of 250 320 m to depths of 180 250 m the subsequent formation of mesoscale and headland eddies drive this water into the gulf of arauco and to depths of 50 120 m with the ctw paddle the circulation is strongly modified the mesoscale and headland eddies reform during the ctw upwelling phase during the ctw upwelling phase the upwelling over winds and eddies is enhanced by up to 40 m on the shelf model simulations are undertaken using realistic winds and a ctw paddle modulated by observed sea level without ctw forcing included in the model the agreement with data is poor in the gulf of arauco area the variability of alongshore currents below 130 m is dominated by ctw activity above 130 m wind driven current variability dominates in agreement with the idealized ctw analysis water is found to be upwelled from depths of 320 m to 100 m or less and 10 c undercurrent water is found at the surface and within the gulf

iron isotopes in the amazon river system weathering and transport signatures abstract trace metal clean plankton tows river samples aerosol leachates and porewater samples from the amazon river system were measured for their iron isotopic composition the overall isotopic range observed was 1 5 with fe isotopic variability observed between different types of tributaries dissolved fe and suspended load fe from two main channel sites were isotopically similar 0 1 to 0 3 in contrast the dissolved fe and suspended load fe from an organic rich tributary the negro river were isotopically distinct with the dissolved slightly isotopically heavy 0 3 and the suspended load isotopically light 0 9 the isotopically lightest sample from the amazon region was shelf porewater 1 3 in river water seawater mixing experiments the fe isotopic signal of dissolved fe of river water was modified by flocculation of isotopically heavy fe the variability of the fe isotopic composition of natural samples including biological and aqueous samples demonstrates that significant fractionation is associated with fe biogeochemistry in the environment

on the mixing of rivers with a difference in density the case of the negro solimoes confluence brazil abstract confluences are common components of all riverine systems and characterized by converging streamlines and potential mixing of separate flows the fluid dynamics of confluences possess a highly complex structure with several common types of flow features observed an investigation was carried out in both low and relatively high flow conditions at the confluence of the negro and solimoes rivers brazil which ranks among the largest river junctions on earth during this field research acoustic doppler velocity profiling adcp and water quality sampling were applied to investigate hydrodynamics sediment transport and mixing characteristics at this confluence it was found that the location and the width of the mixing interface were closely related to changes of the discharge ratio between the tributaries due to both seasonal and annual variations second a timescales analysis was applied to comparatively identify the contribution to mixing at the negro solimoes confluence of four processes difference in 1 velocity and 2 density between the rivers 3 bed friction including form drag and 4 change in channel width the analysis demonstrated that adjustments of confluence hydrodynamics and morphodynamics can modify the relative importance of each contribution immediately downstream of the junction the effects of differences in velocity and density were comparable while farther downstream the latter was predominant and the role of bed friction was significant at the end this study suggests that mixing at the negro solimoes confluence can be explained as a combination of the four hydrologic and morphologic processes

rayleigh fractionation of iron isotopes during pedogenesis along a climate sequence of hawaiian basalt abstract we measured iron isotopic composition of surface 10 20 cm and subsurface 50 70 cm basaltic soil horizons from the island of maui along a climate gradient mcg ranging from 2 2 to 4 2 m mean annual precipitation map all soil forming factors except climate were conserved the mcg has a documented decrease in fe with increasing rainfall that is highly correlated with decreasing mean annual eh values we found that increasing map from 2 8 to 4 2 m resulted in a surface plus subsurface average increase of 0 56 0 09 56fe with the subsurface consistently 0 33 0 06 56fe greater than the surface horizons based on loss of fe relative to nb rayleigh fractionation was observed with 103ln lost retained values of 0 37 0 03 and 0 34 0 04 for the surface and subsurface respectively equivalent 103ln lost retained values for the surface and subsurface soils suggests fe loss is driven by similar mechanisms throughout the soil profile our calculated fractionation factor is about 1 3 the magnitude of laboratory determined fractionation factors for fe reduction suggesting other processes organic complexation fe re precipitation modulate the net fe loss along the mcg these results offer field scale confirmation of laboratory experiments on model systems that show anoxic weathering reactions produce materials enriched in heavy fe isotopes

a statistical study on the subthermocline submesoscale eddies in the northwestern pacific ocean based on argo data in this study statistical characteristics and spatiotemporal variability of the cold core subthermocline eddies stes discovered by zhang et al 2015 in the northwestern pacific are investigated with 14 years of argo temperature salinity t s data between 2002 and 2015 by applying an objective identification procedure to argo t s profiles a total of 337 lens like stes that trap cold and fresh homogeneous water are obtained the stes cores are primarily located between 26 5 and 26 9 0 300 800 m and their shapes share a uniform gaussian structure in vertical vertical and horizontal scale of the stes is generally between 100 and 200 m and 5 and 15 km respectively suggesting that they are in the category of submesoscale processes according to their different densities and seasonalities the stes are classified into upper and lower types with density interface of 26 7 0 the number of upper type stes is much larger in spring and summer than in autumn and winter while that of lower type ones show relatively uniform seasonal distributions spatially the stes are primarily distributed within the region between the kuroshio extension ke and subarctic front saf in meridional and 140 e 155 e in zonal direction based on stes spatial distributions and vertical locations we propose to name these stes as ke intermediate layer eddies kiddies water property analysis suggests that the kiddies most likely originated from the saf region for the upper type kiddies they are probably generated through subduction associated with mixed layer frontogenesis which at least contribute to 0 25 sv annual subduction rate for the layers 26 2 26 7 0

vertical structure of mesoscale eddies in the eastern south pacific ocean a composite analysis from altimetry and argo profiling floats 1 the mean vertical structure of mesoscale eddies in the peru chile current system is investigated by combining the historical records of argo float profiles and satellite altimetry data a composite average of 420 526 profiles acquired by argo floats that surfaced into cyclonic anticyclonic mesoscale eddies allowed constructing the mean three dimensional eddy structure of the eastern south pacific ocean key differences in their thermohaline vertical structure were revealed the core of cyclonic eddies ces is centered at 150 m depth within the 25 2 26 0 kg m 3 potential density layer corresponding to the thermocline in contrast the core of the anticyclonic eddies aes is located below the thermocline at 400 m depth impacting the 26 0 26 8 kg m 3 density layer this difference was attributed to the mechanisms involved in the eddy formation while intrathermocline ces would be formed by instabilities of the surface equatorward coastal currents the subthermocline aes are likely to be shed by the subsurface poleward peru chile undercurrent in the eddy core maximum temperature and salinity anomalies are of 1 c and 0 1 with positive negative values for aes ces this study also provides new insight into the potential impact of mesoscale eddies for the cross shore transport of heat and salt in the eastern south pacific considering only the fraction of the water column associated with the fluid trapped within the eddies each ce and ae has a typical volume anomaly flux of 0 1 sv and yields to a heat and salt transport anomaly of 1 3 1011 w and 3 8 103 kg s 1 respectively

an offshore study in the california current system preface l etude d un tourbillon de mesoechelle quasi permanent et quasi stationnaire dans le systeme du courant de californie comprend quatre parties dynamique au sein du systeme manifestations a la surface structure chimique et distribution du plancton

iron isotopic fractionation during continental weathering abstract the effect of continental weathering on the iron isotope compositions of natural materials is investigated unweathered igneous rocks pelagic clay and dust fall within the range 56 fe 0 0 3 rivers with large suspended loads also have 56 fe values near zero dilute streams have 56 fe values that trend towards lower 56 fe 1 suggesting that dissolved riverine iron is isotopically light relative to igneous rocks bulk soil and soil leaches display systematically different 56 fe profiles indicating that isotopically distinct fe pools are generated during pedogenesis nannofossil ooze which contains fe scavenged from the ocean water column has 56 fe 0 but is consistent with seawater dissolved fe having negative 56 fe it is inferred that continental weathering under modern oxidizing earth surface conditions preferentially releases dissolved fe with negative 56 fe which is transported in rivers to the ocean a preliminary analysis of the marine fe budget suggests that riverine fe has a substantial role in determining the 56 fe of both the modern and ancient oceans but other inputs particularly that from diagenesis of marine sediments may also be important since the chemical pathways of fe processing during weathering are dependent on oxidation state and biological activity fe isotopes may prove useful for detecting changes in these parameters in the geologic past

equatorial pacific 13 c water eddies in the eastern subtropical south pacific ocean abstract argo float profile data are used to analyze warm salty weakly stratified subthermocline eddies of tropical origin in the eastern subtropical south pacific ocean these eddies contain anomalous signatures of the equatorial pacific 13 c water that is carried poleward within the peru chile undercurrent pcu as it flows along the west coast of south america from their source along the chilean coast between 29 and 39 s the eddies spread westward and slightly northward likely at least partly advected by the subtropical gyre the eddy water properties contrast strongly with the colder fresher more strongly stratified waters of subantarctic origin being carried northward then westward by the gyre near the eddy source about 6 of argo profiles sample eddies that are above selected thresholds for both salinity and potential vorticity anomalies relative to maps of the mean distributions of these properties on and around the core isopycnal for the eddies the proportion of such profiles dimini

the origin of the pacific equatorial 13 c water abstract examination of the vertical distributions of temperature salinity oxygen and nutrient salts in the thermostad of the equatorial 13 c water in the eastern pacific ocean indicates that local vertical mixing is unimportant in creating the thermostad and the characteristics of the 13 c water maps are presented that show the oceanwide distributions of depth geostrophic flow salinity oxygen phosphate silica and nitrate on the 160 cl t 1 isanosteric surface which nearly coincides with the core of the 13 c water the maps suggest that the original characteristics of the 13 c water are acquired in the surface and thermocline layers to the northeast of new zealand and in the tasman sea by winter convection and vertical mixing the acquired characteristics are advected to the thermostad in the eastern pacific via a long route starting from the source region the flow is first eastward in high latitudes and then returns westward in low latitudes around the anticyclonic subtropical gyre of the sout

a mechanism for enhanced upwelling off central chile eddy advection 1 a regional numerical model is developed for the mid chile shelf and ocean circulation 30 s to 43 s the model is forced with mean summertime wind stress and transports from a global model over the first 10 days deep 250 300 m peru undercurrent puc water is upwelled to depths of 170 270 m after this time upwelling by the steady winds is largely shut down and a 55 km diameter cyclonic eddy is found to grow in deep water off punta lavapie the mechanism for eddy growth is identified to be baroclinic instability of an initial offshore meander of the equatorward chile coastal current ccc over a period of more than 100 days the onshore arm of the deep water eddy upwells puc water to depths of 150 m toward the shelf a shallow headland eddy then sweeps this puc water to depths of less than 50 m and into the gulf of arauco the net upwelling of 200 m is the largest found for the region observational evidence is cited for the existence of the deep water cyclonic eddy over a period of 4 months a spatially intermittent puc is also found to lie below the ccc in agreement with observational studies the model also predicts the existence of an offshore branch of the ccc that is directed to the northwest

global observations of submesoscale coherent vortices in the ocean abstract subsurface intensified anticyclones are ubiquitous in the ocean yet their impact on the large scale transport of heat salt and chemical tracers is poorly understood these submesoscale coherent vortices scvs can trap and advect waters thousands of kilometers away from the formation region providing a transport pathway that is unresolved by low resolution earth system models however knowledge of the importance of these eddies for the large scale circulation is hindered by the lack of systematic observations here we take advantage of the global network of argo floats to identify occurrences of these eddies which appear as weakly stratified anomalous water masses with gaussian shaped vertical structures we develop a general algorithm to detect subsurface eddies that have propagated away from their source region and apply it to the database of argo float profiles resulting in roughly 4000 detections from more than 20 years of observations we further group detections into regional populations to identify hot spots of generation and mechanisms of formation analysis of regional scv statistics reveals important sites of scv generation in eastern boundary upwelling systems marginal sea overflows and mode water formation regions along major open ocean fronts because of the heat and salt anomaly contained within their cores scv could leave a significant imprint on the hydrographic properties of water masses in regions of high scv density

subthermocline eddies observed by rapid sampling argo floats in the subtropical northwestern pacific ocean in spring 2014 in spring 2014 two subthermocline eddies stes were observed by rapid sampling argo floats in the subtropical northwestern pacific stnwp the first one is a warm salty and oxygen poor lens with its temperature salinity dissolved oxygen t s do anomalies reaching 1 16 c 0 21 practical salinity unit psu 29 9 mol kg respectively near the 26 62 0 surface the other is a cold fresh and oxygen rich lens with its t s do anomalies reaching 1 95 c 0 34 psu 88 0 mol kg respectively near the 26 54 0 surface the vertical extent of the water mass anomalies in the warm cold ste is about 190 m 150 m and its horizontal length scale is 22 7 km 18 10 km according to their water mass properties we speculate that the warm and cold stes are generated in the north pacific subtropical and subarctic front region respectively the observed stes may play an important role in modifying the intermediate layer water properties in the stnwp and this needs to be confirmed by more focused observations in the future

iron isotope composition of the bulk waters and sediments from the amazon river basin abstract the present study provides iron concentrations and isotopic compositions determined by multi collector inductively coupled plasma mass spectrometry mc icp ms along with key chemical mineralogical and physical properties of 35 representative bulk unfiltered waters and bulk sediments from the amazon river basin these samples from the amazon river five of its main tributaries the solimoes negro madeira tapajos and trombetas rivers and four sub tributaries the purus jau ucayali and napo rivers were essentially collected during seven field missions conducted for over two years these encompassed the centennial flood of may 2009 and the exceptional low water stage of september october 2010 thereby providing the most extreme hydrological situations that have been recorded over the last hundred years while the data confirmed massive losses of iron up to 19 000 tons day ca 50 of the amazon river bulk water budget in the solimoes and negro rivers mixing zone the fe isotope signatures of these bulk waters behaved conservatively this property allows the use of bulk water fe isotope signature to track iron sources and explain such isotopic signature in terms of simple mixing unfiltered samples from the organic rich black water rivers present light 57 fe relative to the average continental crust composition this contrasts with the composition of the bulk white waters carrying a high mineral suspended load that have 57 fe values undistinguishable from the crustal isotopic signature 0 1 relative to irmm 14 this observation indicates that the fe isotopic composition represents a reliable direct tracer of the iron speciation and therefore of the host phases of iron in its sources specifically the white water 57 fe most likely trace the signatures of igneous and sedimentary sources as well as of their lateritic soil minerals while the bulk black water 57 fe track a preferential release of fe that has gone through a reduction step in the organic rich horizons of tropical podzols as a result of the biological activity this study shows that the total iron transferred by the amazon river represents between 5 and 30 of the world s ocean fe input by rivers and this amazon bulk water iron displays an isotopic composition indistinguishable from that of the average continental crust

interannual variability of the subsurface eddy field in the southeast pacific the southeast pacific which encompasses the coasts of peru and chile is one of the world s most productive regions resulting principally from the upwelling of subsurface nutrient rich waters over the satellite altimetry era there have been numerous evidence that surface mesoscale eddies play an important role in the offshore transport of rich coastal waters but it has been only recently that few observational numerical studies have highlighted the importance of the subsurface eddies the eddy field variability is explored using the results of a high resolution model experiment from 1979 to 2012 the model results indicate an asymmetry of the surface and subsurface eddy fields while surface intensified cyclones are slightly more frequent than anticyclones the subsurface field is dominated by anticyclones intrathermoclineeddies ites triggered by the instability of the subsurface peru chile undercurrent pcuc composite maps are consistent with in situ observations ites are associated with maximum vorticity around 150 200 m depth warmer and more saline core characteristic of the equatorial subsurface water from the pcuc we find that the variability of the ites is significantly correlated with the enso equatorial signal during strong el nino events e g 1982 1998 we find that while the pcuc transport increases the volume of coastal waters transported by ites however decreases during those periods we find that the relaxation of the isopycnals along the coast during el nino events leads to weakened baroclinic instability and to a decrease of the ites transport

eddies and an extreme water mass anomaly observed in the eastern south pacific at the stratus mooring in the tropical eastern south pacific the stratus ocean reference station ors 20 s 85 5 w is located in the transition zone between the oxygen minimum zone omz and the well oxygenated subtropical gyre in february march 2012 extremely anomalous water mass properties were observed in the thermocline at the stratus ors the available eddy oxygen anomaly was 10 5 1016 mol this anomalous water was contained in an anticyclonic mode water eddy crossing the mooring site this eddy was absorbed at that time by an anticyclonic feature located south of the stratus mooring this was the largest water property anomaly observed at the mooring during the 13 5 month deployment period the sea surface height anomaly ssha of the strong mode water eddy in february march 2012 was weak and while the lowest and highest ssha were related to weak eddies ssha is found not to be sufficient to specify the eddy strength for subsurface intensified eddies still the anticyclonic eddy and its related water mass characteristics could be tracked backward in time in ssha satellite data to a formation region in april 2011 off the chilean coast the resulting mean westward propagation velocity was 5 5 cm s 1 this extremely long lived eddy carried the water characteristics from the near coastal chilean water to the open ocean the water mass stayed isolated during the 11 month travel time due to high rotational speed of about 20 cm s 1 leading to almost zero oxygen in the subsurface layer of the anticyclonic mode water eddy with indications of high primary production just below the mixed layer

the formation of a subsurface anticyclonic eddy in the peru chile undercurrent and its impact on the near coastal salinity oxygen and nutrient distributions the formation of a subsurface anticyclonic eddy in the peru chile undercurrent pcuc in january and february 2013 is investigated using a multi platform four dimensional observational approach research vessel multiple glider and mooring based measurements were conducted in the peruvian upwelling regime near 12 30 s the dataset consists of 10000 glider profiles and repeated vessel based hydrography and velocity transects it allows a detailed description of the eddy formation and its impact on the near coastal salinity oxygen and nutrient distributions in early january a strong pcuc with maximum poleward velocities of 0 25 m s at 100 to 200 m depth was observed starting on january 20 a subsurface anticyclonic eddy developed in the pcuc downstream of a topographic bend suggesting flow separation as the eddy formation mechanism the eddy core waters exhibited oxygen concentrations 1 mol kg an elevated nitrogen deficit of 17 mol l and potential vorticity close to zero which seemed to originate from the bottom boundary layer of the continental slope the eddy induced across shelf velocities resulted in an elevated exchange of water masses between the upper continental slope and the open ocean small scale salinity and oxygen structures were formed by along isopycnal stirring and indications of eddy driven oxygen ventilation of the upper oxygen minimum zone were observed it is concluded that mesoscale stirring of solutes and the offshore transport of eddy core properties could provide an important coastal open ocean exchange mechanism with potentially large implications for nutrient budgets and biogeochemical cycling in the oxygen minimum zone off peru

hydrography of the eastern south pacific ocean results from the sonne 102 cruise may june 1995 abstract full depth conductivity temperature depth hydrographic measurements were taken in may june 1995 along 28 15 35 15 and 43 15 s from the chilean coast to 86 88 w from the r v sonne sections of potential temperature salinity neutral density and oxygen are presented to illustrate the water column structure in this sparsely sampled region a more comprehensive database on all available hydrographic data from the region was compiled these data and available meteorological data are used to help in the interpretation of the sonne results a number of important features found in the sections are discussed including a shallow salinity minimum apparently ventilated from south of 37 s salt fingering as a possible mechanism to transport high salinity subtropical water into the shallow salinity minimum equatorial subsurface water subantarctic mode water and antarctic intermediate water geostrophic calculations of alongshore flow show the poleward peru chile undercurrent at each of the three sections with a poleward descending core and peak velocities of 10 cm s 1 as in earlier works a deep pacific outflow is found near the chilean coast part of a clockwise deep circulation in the chile basin

a census of meddies tracked by floats recent subsurface float measurements in 27 mediterranean water eddies meddies in the atlantic are grouped together to reveal new information about the pathways of these energetic eddies and how they are often modified and possibly destroyed by collisions with seamounts twenty meddies were tracked in the iberian basin west of portugal seven in the canary basin during february 1994 14 meddies were simultaneously observed 11 of them in the iberian basin most 69 of the newly formed meddies in the iberian basin translated southwestward into the vicinity of the horseshoe seamounts and probably collided with them some meddies 31 passed around the northern side of the seamounts and translated southwestward at a typical velocity of 2 0 cm s into the canary basin some meddies observed there were estimated to be up to 5 yr old four meddies in the canary basin collided with the great meteor seamounts and three meddies were inferred to have been destroyed by the collision overall an estimated 90 of meddies collided with major seamounts the mean time from meddy formation to a collision with a major seamount was estimated to be around 1 7 yr combined with the estimated meddy formation rate of 17 meddies yr from previous work this suggests that around 29 meddies co exist in the north atlantic therefore during february 1994 we observed about half of the population of meddies

a mesoscale eddy dipole in the offshore california current there is a transition zone in the california current system between inshore coastal and offshore oceanic flow this transition zone is associated with the main core of the california current and is populated with offshore mesoscale eddies the structure of isolated eddies and dipole eddy pairs found within the transition zone is examined using water mass analysis spiciness and dissolved oxygen the analyses show that these offshore mesoscale eddies have cores which contain california undercurrent water these observations and independent observations of the sitka eddy near sitka alaska support the conclusion that a bathymetrically induced instability of the california undercurrent is a likely generation mechanism for the offshore eddies this conclusion also is consistent with mathematical models of eddy generation in a subsurface poleward baroclinic current the similarity between long term mean conditions caicofi conditions observed during january 1981 and july 1985 and those of the sitka eddy coupled with the bathymetric effects provides a plausible explanation for the recurrence of offshore mesoscale eddies at preferred locations within the transition zone

an offshore eddy in the california current system part i interior dynamics abstract from january 9 to 17 1981 detailed observations of the horizontal and vertical structure beneath one of the quasi permanent semi stationary mesoscale offshore eddy signatures in the california current system ccs discussed by bernstein breaker and whritner 1977 burkov and pavlova 1980 and simpson 1982 were made the vertical sections of temperature and density show the presence of three layer system a subsurface warm core eddy whose diameter is about 150 km at the 7 c isotherm is the dominant feature a warm surface layer which extends to a depth of 75 m lies over the eddy between the warm surface layer and the subsurface warm core eddy there is a cold core region which extends to a depth of about 200 m there is a high degree of symmetry about the vertical axis of rotation vertical sections of salinity and dissolved oxygen are entirely different from sections of temperature and density diagrams of water mass characteristics confirm that the core of the eddy found between 250 600 m consists of inshore water from the california undercurrent cu below about 700 m local waters from the deep poleward flow dpf have been incorporated into the eddy the observed distributions of properties t s o 2 are inconsistent with a single local generation process for the eddy system radial distributions of angular velocity normalized gradient velocity and relative vorticity support the use of a gaussian radial height field as an initial condition in eddy models possible reasons why ccs eddies may differ dynamically from gulf stream rings are given in the text at the time the observations were made the system as a whole was in near geostrophic balance local geostrophic balance however cannot explain the observed distribution of properties and structure the observed symmetry in the structure of the eddy system chemical evidence simpson 1984 biological distributions haury 1984 and satellite images of the cc koblinsky simpson and dickey 1984 suggest that lateral entrainment of warm oceanic and cold coastal water into the upper two layers of the three layer system by the subsurface eddy is a likely generation mechanism for the cold core region the coastal origin of the frontal structure along the northeastern quadrant and the oceanic origin of the frontal structure along the southwestern quadrant of the eddy system further support lateral entrainment as a generation mechanism for the cold core this entrainment makes the ccs eddy system different from cold core rings in the gulf stream and rather similar to some warm core eddies found in the east australian current the presence of cu water in the core of this eddy raises the question of how cu water was transported from the continental slope eddy generation mechanisms other than baroclinic instability of the cc may be required to explain the distribution persistence and core composition of offshore mesoscale eddies in the ccs there is evidence that barotropic in addition to baroclinic processes may be important

surface circulation and fronts of the south pacific ocean east of 120 w the south pacific surface circulation east of 120 w is studied using satellite tracked drifters from 1979 2004 the major currents of this region are described such as the antarctic circumpolar the south pacific the chile peru and the cape horn currents we suggest the presence of a branch exiting from the acc between 100 120 w and transporting subantarctic surface water toward lower latitudes we also show the existence of an anticyclonic recirculation cell north of 35 s finally based on hydrographic sections we show that in the eastern south pacific the core of the subtropical front corresponds to the 14 c isotherm at 150 m depths and to the 2 7 m of dynamic height relative to 3000 m the subantarctic front is located by maximum temperature gradients in the range 3 8 c at 100 400 m depth

seasonal climatology of hydrographic conditions in the upwelling region off northern chile over 30 years of hydrographic data from the northern chile 18os 24os upwelling region are used to calculate the surface and subsurface seasonal climatology extending 400 km offshore the data are interpolated to a grid with sufficient spatial resolution to preserve cross shelf gradients and then presented as means within four seasons austral winter july september spring october december summer january march and fall april june climatological monthly wind forcing surface temperature and sea level from three coastal stations indicate equatorward upwelling favorable winds throughout the year weakest in the north seasonal maximum alongshore wind stress is in late spring and summer december march major water masses of the region are identified in climatological t s plots and their sources and implied circulation discussed surface fields and vertical transects of temperature and salinity confirm that upwelling occurs year round strongest in summer and weakest in winter bringing relatively fresh water to the surface nearshore surface geostrophic flow nearshore is equatorward throughout the year during summer an anticyclonic circulation feature in the north which extends to at least 200 rn depth is evident in geopotential anomaly and in both temperature and geopotential variance fields subsurface fields indicate generally poleward flow throughout the year strongest in an undercurrent near the coast this undercurrent is strongest in summer and most persistent and organized in the south south of 21os a subsurface oxygen minimum centered at 250 m is strongest at lower latitudes low salinity subsurface water intrudes into the study area near 100 m predominantly in offshore regions strongest during summer and fall and in the southernmost portion of the region the climatological fields are compared to features off baja within the somewhat analogous california current and to measurements from higher latitudes within the chile peru current system

subthermocline eddies in the western equatorial pacific as shown by an eddy resolving ogcm abstractsporadic in situ observations have shown evidence that subthermocline eddies exist off the mindanao coast these subthermocline eddies are believed to play an important role in the heat freshwater and other ocean property transports of the region but their characteristics and in particular their pathway and source of energy are poorly explored because of the lack of long term observations analysis of results from an eddy resolving general ocean circulation model has revealed that most subthermocline eddies off the mindanao coast originate from the equatorial south pacific ocean to the west of the ninigo group these eddies propagate northward along the new guinea coast cross the equator in the far western pacific and reach the mindanao coast at a typical propagation speed of 0 12 m s 1 the dominant time scales of these eddies range between 50 and 60 days

upper ocean water mass characteristics of the california current summer 1993 abstract two large high resolution upper ocean surveys of the california current region were conducted in the summer of 1993 temperature and salinity were measured from a seasoar vehicle and velocity was measured by a ship borne acoustic doppler current profiler both surveys extended from the continental margin to 128 w and consisted of zonal sections 28 km apart the first survey 7 28 june extended from 39 5 n to 36 25 n and the second 16 august to 1 september extended from 39 0 n to 37 0 n the current field was fairly simple in june showing an equatorward surface jet with only one gentle meander a nearly continuous poleward california undercurrent near the continental margin and two anticyclonic subsurface eddies offshore of the jet by august meanders in the surface jet had strengthened and eddies dominated the flow field large scale trends in the water mass characteristics spiciness along three isopycnal surfaces 26 4 26 0 and 25 6 kg m 3 show that temperature and salinity tend to increase towards the equator and towards shore consistent with poleward advection along the continental margin local minima in spiciness tend to coincide with the equatorward surface jet local maxima in spiciness are associated with subsurface anticyclonic eddies which have a core depth of about 150 m and seem to originate in the california undercurrent over the continental slope at local latitudes we identified several different anticyclonic eddies each with different water mass characteristics all of the eddies we observed had diameters larger than the baroclinic radius of deformation water mass characteristics and migration rates are consistent with formation over the continental margin within the preceding 6 8 months

mean surface circulation and mesoscale turbulent flow characteristics in the eastern south pacific from satellite tracked drifters 1 circulation of the eastern south pacific region 10 34 s 70 100 w was studied using drifting buoy trajectories from 1979 to 2003 three different current regimes were highlighted the south equatorial current flowing westward north of 26 s with surface velocities of 7 8 cm s 1 the south pacific current an eastward current of 2 cm s 1 south of 25 30 s and the chile peru current a northwestward flow of 6 cm s 1 found to the east of 82 w and south of 22 s the velocity variance distribution showed the regional flow to be anisotropic in nature maps of eddy kinetic energy obtained from drifter measurements and satellite altimetry data showed similar patterns with higher energy levels near the south american coast the lagrangian time and length scales of the turbulent flow revealed typical values of 5 9 0 6 days and 40 7 5 4 km in the zonal direction and of 3 5 0 4 days and 29 3 4 km in the meridional direction the estimated diffusivities were 4 9 0 5 107 cm2 s 1 and 2 6 0 3 107 cm2 s 1 in the eastward and northward directions respectively finally we estimated the respective role of horizontal advection and lateral diffusion on the mixed layer heat and salt budgets near the coast the lateral turbulent fluxes in the surface layer were two times larger than the horizontal transports associated with the large scale circulation mean horizontal heat and salt diffusive fluxes were around 25 w m 2 and 50 g m 2 d 1

the geochemical filter of large river confluences abstract this study reports the behaviour and fate of major and trace elements in solid and solution in the encontro das aguas mixing zone in the amazonian basin this area results from the confluence of acidic organic rich rio negro and andean sediment rich rio solimoes the differences existing between these two water masses are likely to modify the partitioning of elements between solid and solution or to induce losses by physical or chemical removal to account for lateral and vertical heterogeneities in the river sections the fluxes of elements in dissolved and solid loads were estimated as accurately as possible using an interpolation technique a general loss of suspended particulate matter spm of 23 is measured 80 km after the confluence but the various elements and their associated hosted minerals are not affected in a similar way sispm caspm naspm or srspm mostly associated with coarse phases quartz and ca na feldspars are preferentially lost refractory elements cospm crspm tispm alspm nispm other alkali a and alkali earth ae elements kspm mgspm baspm fespm or organic carbon oc are lost to a lesser extent due to their occurrence in finer fractions such as clays smectite illite or kaolinite oxides and particulate organic matter pom in solution a ae and cudiss mostly originating from the rio solimoes behave conservatively by contrast refractory elements coming mostly from the rio negro exhibit important losses from 10 for doc to 60 for codiss changes in ph and ionic strength during the mixing may induce a sorption of these elements to particles supplied by the rio solimoes a clustering and or a settling of nanokaolinites phases or a sorption of aldiss fediss codiss mndiss or zndiss by dissolved organic matter dom the differential elemental settling at a river confluence could thus induce a phase shift between element supply and export out of a watershed the physical and chemical processes reported here for a river confluence could be applied in other mixing zones such as estuaries or mining exhausts

nitrogen isotope ratios of nitrate and n anomalies in the subtropical south pacific nitrogen isotopic ratios of nitrate 15n no3 were analyzed above 1000 m water depth along 17 s in the subtropical south pacific during the revisit woce p21 cruise in 2009 the 15n no3 and n values were as high as 17 and as low as 18 mol n l 1 respectively at depths around 250 m east of 115 w but were as low as 5 and as high as 1 mol n l 1 respectively in subsurface waters west of 170 w the relationships among no3 concentrations n values 15n no3 values and oxygen and nitrite concentrations suggest that a few samples east of 90 w were from suboxic and nitrite accumulated conditions and were possibly affected by in situ water column denitrification most of the high 15n no3 and negative n waters were probably generated by mixing between subantarctic mode water from the southern ocean and oxygen deficit zone water from the eastern tropical south pacific with remineralization of organic matter occurring during transportation moreover the relationship between 15n no3 and n values as well as trichodesmium abundances and size specific nitrogen fixation rates at the surface suggest that the low 15n no3 and positive n subsurface waters between 160 e and 170 w were generated by the input of remineralized particles created by in situ nitrogen fixation mainly by trichodesmium spp therefore the 15n values of sediments in this region are expected to reveal past changes in nitrogen fixation or denitrification rates in the subtropical south pacific

main eddy vertical structures observed in the four major eastern boundary upwelling systems in the four major eastern boundary upwelling systems ebus mesoscale eddies are known to modulate the biological productivity and transport near coastal seawater properties toward the offshore ocean however little is known about their main characteristics and vertical structure this study combines 10 years of satellite altimetry data and argo float profiles of temperature and salinity and our main goals are i to describe the main surface characteristics of long lived eddies formed in each ebus and their evolution and ii to depict the main vertical structure of the eddy types that coexist in these regions a clustering analysis of the argo profiles surfacing within the long lived eddies of each ebus allows us to determine the proportion of surface and subsurface intensified eddies in each region and to describe their vertical structure in terms of temperature salinity and dynamic height anomalies in the peru chile upwelling system 55 of the sampled anticyclonic eddies aes have subsurface intensified maximum temperature and salinity anomalies below the seasonal pycnocline whereas 88 of the cyclonic eddies ces are surface intensified in the california upwelling system only 30 of the aes are subsurface intensified and all of the ces show maximum anomalies above the pycnocline in the canary upwelling system 40 of the aes and 60 of the ces are subsurface intensified with maximum anomalies extending down to 800 m depth finally the benguela upwelling system tends to generate 40 50 of weak surface intensified eddies and 50 60 of much stronger subsurface intensified eddies with a clear geographical distribution the mechanisms involved in the observed eddy vertical shapes are discussed

zinc and copper behaviour at the soil river interface new insights by zn and cu isotopes in the organic rich rio negro basin abstract the complex behaviour of zn and cu at the soil river interface was investigated in soil and riverine water samples from the rio negro basin a secondary tributary of the rio amazonas using their stable isotope compositions this acidic and organic river drains two types of intensely weathered terrains podzols in its upstream part and lateritic soils downstream bulk soil particles suspended particulate matter spm as well as colloidal fractions were sampled across the whole basin during low and high water stages in the basin zn and cu are mostly exported from lateritic soils and transported by organic colloids where significant losses are observed in the downstream part of the river the use of 66zn and 65cu measurements reveals distinct stories for these two metals in suspended sediments and colloids in the colloids the constant 66zncoll across the basin is induced by the same weak association mode between zn and organic ligands regardless of the origin of the water by contrast in spm the speciation of zn and thus 66znspm differ according to the type of drained soils zn is associated with organic complexes in particles exported with water draining podzol whereas zn2 is incorporated in the structure of the remaining kaolinite clays in lateritic output the stronger reactivity of cu than zn with organic ligands induces its complete complexation copper is controlled by refractory particulate organic matter pom and by reactive colloidal organic matter the latter being enriched in 65cu due to stronger binding interactions than in pom while the cu content remains constant in the upstream part of the rio negro downstream the decrease of spm and colloidal cu fluxes is associated with a constant 65cuspm and with an increase of 65cucoll at the rio negro outlet geochemical mass balance modelling based on spm cu and zn fluxes in spm and their associated isotopic signatures confirms distinct host phases for zn and cu and identifies the most probable places where losses of these two metals occur in colloids the observed cu isotope fractionation from 0 24 to 0 45 superimposed on the significant cucoll loss is assumed to result from a new isotopic equilibrium in a low velocity and high productivity zone cu rich colloids enriched in 63cu aggregate and settle down whereas the remaining heavy cu is partially complexed on strong organic ligands secreted by phytoplankton forming new cu colloids

organic complexation and translocation of ferric iron in podzols of the negro river watershed separation of secondary fe species from al species abstract the development of podzols in lateritic landscapes of the upper amazon basin contributes to the exportation of organic carbon and associated metals in the black waters of the negro river watershed we have investigated the distribution of feiii in the clay size fraction of eight organic rich horizons of waterlogged plateau podzols to unravel the weathering conditions and mechanisms that control its transfer to the rivers the speciation and amount of feiii stored in residual mineral phases of laterites or bound to organic compounds of weakly and well expressed podzols were determined by electron paramagnetic resonance spectroscopy combined with chemical analyses reducing conditions restrict the production of organo fe complexes in the subsoil b horizons of waterlogged podzols and most of the fe2 released from the dissolution of fe oxides is exported to the rivers via the perched groundwater however significant amounts of diluted feiii bound to organic ligands feiiiom and nano fe oxides are produced at the margin of the depression in the topsoil a horizons of weakly expressed podzols due to shorter periods of anoxia the downward translocation of organically bound metals from topsoil a to subsoil b horizons of podzols occurs in shorter distances for fe than it does for al this separation of secondary fe species from al species is attributed to the physical fractionation of their organic carriers in texture contrasted b horizons of podzols as well as to the effect of ph on metal speciation in soil solutions and metal binding onto soil organic ligands mostly for al this leads us to consider the topsoil a horizons of weakly expressed podzols as well as the subsoil bh horizon of better expressed ones as the main sources for the transfer of feiiiom to the rivers the concentration of feiiiom rises from soil sources to river colloids suggesting drastic biogeochemical changes in more oxygenated black waters of the negro river watershed the contribution of soil organic matter to the transfer of fe to rivers is likely at the origin of the peculiar fe isotope pattern recently recognized in podzolic environments

front eddy influence on water column properties phytoplankton community structure and cross shelf exchange of diatom taxa in the shelf slope area off concepcion 36 37 s in eastern boundary current systems ebcss submesoscale to mesocale variability contributes to cross shore exchanges of water properties nutrients and plankton data from a short term summer survey and satellite time series january february 2014 were used to characterize submesoscale variability in oceanographic conditions and phytoplankton distribution across the coastal upwelling and coastal transition zones north of punta lavapie and to explore cross shelf exchanges of diatom taxa a thermo haline front frn 1 flanked by a mesoscale anticyclonic intrathermocline eddy ite 1 or mode water eddy persisted during the study period and the survey was undertaken during a wind relaxation event at the survey time ite 1 contributed to an onshore intrusion of warm oceanic waters southern section and an offshore advection of cold coastal waters northern section with the latter forming a cold high chlorophyll a filament in situ phytoplankton and diatom biomasses were highest at the surface in frn 1 and at the subsurface in ite 1 whereas values in the coastal zone were lower and dominated by smaller cells diatom species typical of the coastal zone and species dominant in oceanic waters were both found in the frn 1 and ite 1 interaction area suggesting that this mixture was the result of both offshore and onshore advection overall front eddy interactions in ebcss could enhance cross shelf exchanges of coastal and oceanic plankton as well as sustain phytoplankton growth in the slope area through localized upward injections of nutrients in the frontal zone combined with ite induced advection and vertical nutrient inputs to the surface layer

extreme iron isotope fractionation between colloids and particles of boreal and temperate organic rich waters abstract significant and systematic variations of iron isotopic composition in surface water sample fractions obtained by frontal cascade filtration and ultrafiltration have been recorded in 1 subarctic organic rich boreal river and stream mire lake and soil solutions in northern taiga zone karelia nw russia and 2 temperate river and lake waters of the southern boreal zone central russia water samples were filtered in the field employing progressively decreasing pore size from 100 m to 1 kda followed by iron isotope analysis in all river samples there was a gradual increase of 57fe relative to irmm 14 with decreasing pore size from 0 4 0 1 at 100 m up to 4 2 0 1 at 10 kda fraction in the subarctic zone and from 0 024 0 2 at 100 m up to 1 2 0 2 at 10 kda in the temperate zone in the series of filtrates ultrafiltrates of subarctic and temperate streams and rivers the 57fe value decreases with increasing molar fe corg ratio therefore small size fe poor c rich colloids 1 10 kda and low molecular weight lmw fractions of oxygenated water exhibit strong enrichment in heavy isotope whereas high molecular weight fe rich colloids 100 kda 0 22 m and particles 1 100 m are isotopically lighter and closer to the continental crust fe isotope composition the relative enrichment of 1 10 kda ultrafiltrates in heavy isotopes suggests that low molecular weight ligands bind fe more strongly fe o c bonds than fe iii oxy hydr oxides fe o fe bonds in accord with quantum mechanics principles highly positive 57fe of the lmw fraction of labile and potentially bioavailable fe in small subarctic rivers may turn out to be a very important source of isotopically heavy fe in the arctic ocean the mechanisms involved in the production of this isotopically heavy fe may lead this tracer to become a new indicator of environmental changes occurring in the boreal zone

spreading of levantine intermediate waters by submesoscale coherent vortices in the northwestern mediterranean sea as observed with gliders since 2007 gliders have been regularly deployed in the northwestern mediterranean sea a crucial region regarding the thermohaline circulation of the mediterranean sea it revealed for the first time very warm 10 48c and saline 10 1 submesoscale anticyclones at intermediate depth characterized by a small radius 5 km high rossby 0 3 and burger 0 7 numbers they are likely order of 10 to be formed each year have a life time order a year and certainly contribute significantly to the spreading of the levantine intermediate waters liw toward the whole subbasin thus potentially impacting wintertime vertical mixing through hydrographical and dynamical preconditioning they could be mainly formed by the combined action of turbulent mixing and flow detachment of the northward flow of liw at the northwestern headland of sardinia upwelling conditions along the western coast of sardinia associated with a southward geostrophic flow within the upper layers seem to play a key role in their formation process

structure and surface properties of eddies in the southeast pacific ocean 1 a number of studies have posited that coastally generated eddies could cool the southeast pacific ocean sep by advecting cool upwelled waters offshore we examine this mechanism by characterizing the upper ocean properties of mesoscale eddies in the sep with a variety of observations and by estimating the surface layer eddy heat flux divergence with satellite data cyclonic and anticyclonic eddies observed during two cruises featured deep positive salinity anomalies along the 26 5 kg m 3isopycnal indicating that the eddies had likely trapped and transported coastal waters offshore the cyclonic eddies observed during the cruises were characterized by shoaling isopycnals in the upper 200 m and cool near surface temperature anomalies whereas the upper ocean structure of anticyclonic eddies was more variable using a variety of large scale observations including argo float profiles drifter records and satellite sea surface temperature fields we show that relative to mean conditions cyclonic eddies are associated with cooler surface temperatures and that anticyclonic eddies are associated with warmer surface temperatures within each data set the mean eddy surface temperature anomalies are small and of approximately equal magnitude but opposite sign eddy statistics drawn from satellite altimetry data reveal that cyclonic and anticyclonic eddies occur with similar frequency and have similar average radii in the sep a satellite based estimate of the surface layer eddy heat flux divergence while large in coastal regions is small when averaged over the sep suggesting that eddies do not substantially contribute to cooling the surface layer of the sep

iron and silicon isotope behaviour accompanying weathering in icelandic soils and the implications for iron export from peatlands abstract incipient warming of peatlands at high latitudes is expected to modify soil drainage and hence the redox conditions which has implications for fe export from soils this study uses fe isotopes to assess the processes controlling fe export in a range of icelandic soils including peat soils derived from the same parent basalt where fe isotope variations principally reflect differences in weathering and drainage in poorly weathered well drained soils non peat soils the limited fe isotope fractionation in soil solutions relative to the bulk soil 57fesolution soil 0 11 0 12 is attributed to proton promoted mineral dissolution in the more weathered poorly drained soils peat soils the soil solutions are usually lighter than the bulk soil 57fesolution soil 0 41 0 32 which indicates that fe has been mobilised by reductive mineral dissolution and or ligand controlled dissolution the results highlight the presence of fe organic complexes in solution in anoxic conditions an additional constraint on soil weathering is provided by si isotopes the si isotope composition of the soil solutions relative to the soil 30sisolution soil 0 92 0 26 generally reflects the incorporation of light si isotopes in secondary aluminosilicates under anoxic conditions in peat soils the largest si isotope fractionation in soil solutions relative to the bulk soil is observed 30sisolution soil 1 63 0 40 and attributed to the cumulative contribution of secondary clay minerals and amorphous silica precipitation si supersaturation in solution with respect to amorphous silica is reached upon freezing when al availability to form aluminosilicates is limited by the affinity of al for metal organic complexes therefore the precipitation of amorphous silica in peat soils indirectly supports the formation of metal organic complexes in poorly drained soils these observations highlight that in a scenario of decreasing soil drainage with warming high latitude peatlands fe export from soils as fe organic complexes will increase which in turn has implications for fe transport in rivers and ultimately the delivery of fe to the oceans

clay mineral composition of river sediments in the amazon basin abstract clay minerals are important in evaluating the maturity of suspended sediments weathering intensity and source area however there are processes that can change the mineral assemblage such as river transportation deposition remobilization and tributary inputs in terms of water discharge and sediment yield the amazon is one of the largest rivers in the world most of the suspended sediments come from the andes crossing the lowlands before reaching the ocean this study measures the spatial distribution of clay mineral assemblages over the entire amazon basin the results obtained show the main features of the amazon river main stem and larger tributaries from their sources to their confluence clay mineral composition highlights the evolution of the madeira and maranon solimoes river which start in the andes with high illite chlorite content downstream smectite contents increase moreover all shield tributaries show high kaolinite content the lower amazon river is characterized by relative high smectite content different from the andean sources the clay mineral results show that suspended sediments of the amazon river have three main sources 1 the andes mountains 2 the amazon shields and 3 the piedmont basins especially the pastaza alluvial megafan and the fitzcarrald arch basin lateral bank erosion plays also a significant role by the introduction of more mature sediments into the river enriched in smectite

limited iron isotope variations in recent lateritic soils from nsimi cameroon implications for the global fe geochemical cycle laterites are oxidized fe rich soils covering one third of the continents and are drained by half of the continental waters they therefore represent a key component of the iron geochemical cycle at the earth s surface yet no iron isotope study has been conducted on recent laterites so far building on previous integrated morpho pedological studies of soils located in an equatorial rainforest southern cameroon we have undertaken a mineralogical elemental and isotopic study of iron in two lateritic profiles one is a borehole 3620 cm deep going to the parent granodioritic rock located at the top of a hill whereas the other is 675 cm deep and is located downhill mossbauer spectroscopy reveals that typically geq 96 of the soil s iron is held in nanocrystalline hematite and goethite iron isotope measurements performed by plasma source mass spectrometry show that fe isotopic equilibrium was rarely reached between these iron oxide and hydroxide despite their small size overall it is found that most samples display iron isotope signatures very close to the mean crustal value with a maximum range of 0 2 in delta 57 fe given that lateritic soils evolve over millions of years show large variations in fe concentrations and mineralogical abundances this range is surprisingly small when compared to other fe isotope studies of soils from different climatological contexts that can easily show delta 57 f e ranges in excess of 1 at the bulk sample scale the most likely explanation of this finding is that despite notable vertical and lateral fe mobility in the studied laterites from cameroon as computed using the open system mass fraction transport function tau fe w iron remained mostly in the oxidized form as shown by mossbauer pectroscopy this probably results from the strong bioturbation and pedoturbation of these lateritic soils that lead them to remain porous over a large thickness and facilitated the flow of oxygenated waters from the surface down to the saprolite horizon this study therefore reveals that soils that remained as an open system for iron do not necessarily show large fe isotopic variations it is suggested that the fe drained from such lateritic soils should have delta 57 fe values within sim 0 1 of that of the continental crust this is in contrast with previous soil studies notably from sites located at higher latitudes that imply that these soils should release isotopically more variable fe to surface waters such possible contrasted isotopic signatures from different surface waters will likely lead to an isotopically heterogeneous ocean given the short residence time of fe in seawater

the fox permafrost tunnel a late quaternary geologic record in central alaska the fox permafrost tunnel which penetrates 110 m into frozen sediments of gold stream valley provides a continuous exposure of fossiliferous silt and alluvium above schistose bedrock deposition of fluvial gravel was followed by a long interval of loess accretion and permafrost aggradation that was punctuated by episodes of thaw and of gullying and redeposition of silt imbricated sandy gravel above the bedrock contains lenses of finer alluvium that contain wood fragments and some rooted stumps radiocarbon dates indicate that the gravel is older than 40 ka but absence of mature soil and weathering profiles at its upper contact indicates that fluvial activity must have continued until shortly before loess accretion began at the tunnel site silt is the most widespread depositional unit in the tunnel this deposit is of eolian origin loess but some has been redeposited by slope processes the silt units contain abundant ground ice as pore filings lenses wedges and buried pond ice loess accretion was interrupted by a period when little loess accumulated and when large ice wedges formed in the lower loess unit and subsequently were truncated by thaw loess began forming sometime before 40 ka and was rapidly accreting by 39 ka under xeric conditions with open vegetation a sharply decreased rate of loess accretion associated with local erosion and thaw between about 36 and 30 ka is marked by anomalous cation concentration values lenses of buried sod fossils indicative of moist to wet substrates and truncated ice wedges beneath small frozen ponds or streamlets that occupied ice wedge troughs a later episode of rapid loess influx under drier conditions began after 30 ka and coincided with glacial advances of late wisconsin age in the adjoining alaska range large ice wedges also formed in the upper loess unit but only their bases are exposed in the tunnel and their history of development is uncertain fanlike deposits of poorly sorted debris near the tunnel portal formed between about 12 5 and 11 ka during deep erosion of loess slopes under moister conditions the deposits locally form two subunits the younger over whelmed a stand of tall willows on the floor of goldstream valley between about 11 3 and 11 1 ka the older may have formed about 1 000 yr earlier stratigraphic records elsewhere in central alaska indicate variable middle wisconsin environments followed by colder and drier conditions that began between 30 and 25 ka and persisted until perhaps 12 5 ka widespread loess erosion and redeposition subsequently occurred under moister and probably warmer conditions renewed early holocene loess deposition may have been widespread but its exact environmental controls are uncertain our data challenge three generally accepted concepts of late quaternary periglacial processes in central alaska we contend that 1 many ice wedge systems may have formed under interstadial conditions rather than full glacial conditions 2 episodes of rapid loess influx may have been partly out of phase with episodes of glacier expansion and 3 redeposition of loess by solifluction sheetwash and gully formation may have been episodic and required conditions moister than those under which the loess initially accreted

mesoscale variability and nutrient phytoplankton distributions off central southern chile during the upwelling season the influence of mesoscale eddies abstract mesoscale features are recurrently found in the coastal transition zone ctz off central southern chile 35 40 s a region characterized by seasonal wind driven coastal upwelling in this study oceanographic data from two consecutive cruises carried out during the upwelling season january 2009 were combined with satellite time series data in order to characterize the structure and evolution of mesoscale eddies and to explore their influence on phytoplankton structure and nutrient distribution in the context of organic carbon exchanges between the coastal upwelling zone and the ctz two coastally generated contiguous mesoscale eddies 2 months old were characterized a surface cyclonic eddy cc1 and a subsurface anticyclonic eddy aa1 the distributions of salinity and dissolved oxygen together with nutrients suggested that both eddies were sites of vertical injection of high nutrient concentrations from the equatorial subsurface water mass essw into the upper layer in the ctz in addition eddy aa1 in combination with an upwelling plume was involved in the offshore advection of nutrients from the core of the essw located in the coastal zone at shallow depths

a pacific hydrographic section at 88 w water property distribution full depth conductivity temperature depth ctd hydrographic measurements with high horizontal and vertical resolution were made in february april 1993 along a line lying at a nominal longitude of 88 w and extending from southern chile 54 s to guatemala 14 n it crossed five major deep basins southeast pacific chile peru panama and guatemala basins east of the east pacific rise vertical sections of potential temperature salinity potential density oxygen silica phosphate nitrate and nitrite are presented to illustrate the structure of the entire water column some features of interest found in the sections are described and an attempt is made to interpret them in terms of the isopycnal property distributions associated with the large scale ocean circulation these features include various near surface waters observed in the tropical and subtropical regions and the fronts that mark the boundaries of these waters the possible importance of salt fingering to the downward salt transfer from the high salinity subtropical water a shallow thermostad pycnostad developed at 16 18 5 c in the subtropical water low salinity surface water in the subantarctic zone west of southern chile large domains of extremely low oxygen in the subpycnocline layer on both sides of the equator and a secondary nitrite maximum associated with a nitrate minimum in these low oxygen domains high salinity low oxygen high nutrient subpycnocline water that is carried poleward along the eastern boundary by the peru chile undercurrent the subantarctic mode and antarctic intermediate waters middepth isopycnal property extrema observed at the crest of the sala y gomez ridge influences of the north pacific and the north atlantic upon deep waters along the section and the characteristics and sources of the bottom waters in the five deep basins along the section

iron isotope systematics in estuaries the case of north river massachusetts usa abstract recent studies have suggested that rivers may present an isotopically light fe source to the oceans since the input of dissolved iron from river water is generally controlled by flocculation processes that occur during estuarine mixing it is important to investigate potential fractionation of fe isotopes during this process in this study we investigate the influence of the flocculation of fe rich colloids on the iron isotope composition of pristine estuarine waters and suspended particles the samples were collected along a salinity gradient from the fresh water to the ocean in the north river estuary ma usa estuarine samples were filtered at 0 22 m and the iron isotope composition of the two fractions dissolved and particles were analyzed using high resolution mc icp ms after chemical purification dissolved iron results show positive 56 fe values with an average of 0 43 0 04 relative to the irmm 14 standard and do not display any relationships with salinity or with percentage of colloid flocculation the iron isotopic composition of the particles suspended in fresh water is characterized by more negative 56 fe values than for dissolved fe and correlate with the percentage of fe flocculation particulate 56 fe values vary from 0 09 at no flocculation to 0 1 at the flocculation maximum which reflect mixing effects between river borne particles lithogenic particles derived from coastal seawaters and newly precipitated colloids since the process of flocculation produces minimal fe isotope fractionation in the dissolved fe pool we suggest that the pristine iron isotope composition of fresh water is preserved during estuarine mixing and that the value of the global riverine source into the ocean can be identified from the fresh water values however this study also suggests that 56 fe composition of rivers can also be characterized by more positive 56 fe values up to 0 3 relative to the crust than previously reported in order to improve our current understanding of the oceanic iron isotope cycling further work is now required to determine the processes controlling the fractionation of fe isotopes during continental run off

subthermocline eddies over the washington continental slope as observed by seagliders 2003 09 abstractin the california current system subthermocline lenslike anticyclonic eddies generated within the california undercurrent cu are one mechanism for lateral transport of the warm saline waters of the cu garfield et al established the name cuddies for eddies of this type and hypothesized that they account for a significant fraction of the offshore transport of cu water this study presents observations of subthermocline eddies collected from a time series of seaglider surveys in the northern california current system gliders made 46 crossings of subthermocline anticyclones and 17 crossings of subthermocline cyclones over 5 5 yr close inspection grouped these into 20 distinct anticyclones and 10 distinct cyclones water properties at the core of anticyclonic eddies were similar to those in the core of the cu over the continental slope these anticyclones are examples of cuddies anticyclonic cyclonic eddies had average radii of 20 4 20 6 km peak azimuthal current speeds of 0 25 0 23

iron isotope fractionation during microbial reduction of iron the importance of adsorption in experiments investigating the causes of fe isotope fractionation the d 56 54 fe value of fe ii remaining in solution fe ii aq after reduction of fe iii goethite by shewanella putrefaciens is 21 2 relative to the goethite in agreement with previous research the addition of an electron shuttle did not affect fractionation suggesting that fe isotope fractionation may not be related to the kinetics of the electron transfer furthermore in abiotic anaerobic fecl2 aq experiments in which approximately one third of fe ii aq is lost from solution due to adsorption of fe ii onto goethite the d 56 54 fe value of fe ii aq remaining in solution is shifted by 20 8 relative to fecl 2 this finding demonstrates that anaerobic nonbiological interaction between fe ii and goethite can generate signif icant fe isotope fractionation acid extraction of sorbed fe ii from goethite in experi ments reveals that heavy fe preferentially sorbs to goethite simple mass balance modeling indicates that the isotopic composition of the sorbed fe ii pool is 11 5 to 12 5 heavier than fe in the goethite 2 7 3 7 heavier than aqueous fe ii mass balance is also consistent with a pool of heavy fe that is not released to solution during acid extraction

intrathermocline eddies in the coastal transition zone off central chile 31 41 s 1 the three dimensional structure and the origin of mesoscale anticyclonic intrathermocline eddies ites in the coastal transition zone ctz off central chile 31 41 s were analyzed through the combination of data from oceanographic cruises and satellite altimetry and the application of an eddy resolving primitive equation ocean model coupled with a numerical experiment using a passive tracer in this region ites are represented by subsurface lenses 100 km diameter 500 m thickness or vertical extension of nearly homogeneous salinity 34 5 and oxygen deficient 1 0 ml l 1 waters properties which are linked to the equatorial subsurface water mass essw transported poleward by the peru chile undercurrent pcuc in the coastal band at least five to seven ites were observed simultaneously in the area between 31 and 38 s during winter cruises in 1997 and 2009 satellite data indicated that the ites identified from in situ data moved westward each at a mean speed of 2 km d 1 and transported a total volume of 1 106 m3 s 1 1 sv the lifespan of each ite ranged from a few months to 1 year model results indicate that ites become detached from the pcuc under summer upwelling conditions in the coastal zone

an index to distinguish surface and subsurface intensified vortices from surface observations in this study the authors first show that it is difficult to reconstruct the vertical structure of vortices using only surface observations in particular they show that the recent surface quasigeostrophy sqg and interior and surface quasigeostrophy isqg methods systematically lead to surface intensified vortices and those subsurface intensified vortices are thus not correctly modeled the authors then investigate the possibility of distinguishing between surface and subsurface intensified eddies from surface data only using the sea surface height and the sea surface temperature available from satellite observations a simple index based on the ratio of the sea surface temperature anomaly and the sea level anomaly is proposed while the index is expected to give perfect results for isolated vortices the authors show that in a complex environment errors can be expected in particular when strong currents exist in the vicinity of the vortex the validity of the index is then analyzed using results from a realistic regional circulation model of the peru chile upwelling system where both surface and subsurface eddies coexist the authors find that errors are mostly associated with double core eddies aligned surface and subsurface cores and that the index can be useful to determine the nature of mesoscale eddies surface or subsurface intensified from surface satellite observations however the errors reach 24 and some possible improvements of the index calculations are discussed

iron isotope fractionation between aqueous ferrous iron and goethite abstract the equilibrium fe isotope fractionation factor between aqueous fe ii and goethite has been experimentally measured to be 1 05 0 08 in 56 fe 54 fe 2 at 22 c using the three isotope method experiments were done using two sizes of goethite 81 11 nm and 590 42 nm and the experimental products were subjected to serial extraction using acid partial dissolution techniques to determine if surface fe iii atoms have different isotopic properties than the bulk goethite these experiments indicate that the interaction of fe ii aq and goethite is dynamic and results in complete or near complete fe isotope exchange over 30 days involving at least four components fe ii aq goethite sorbed fe ii and fe iii surface the equilibrium fractionation factor between fe ii aq and fe ii sorb is the same for both sizes of goethite at 56 fe fe ii aq fe ii sorb 1 24 0 14 this fractionation factor is significantly different than the results of previous studies on fe ii sorption to goethite the proportion of the fe iii surface component is greatest in the experiments that used the smallest goethite and the fe iii surface fe ii aq fractionation is estimated to be at least 2 1 the high fe iii surface fe ii aq fractionation may exert a significant influence on the fe isotope compositions of aqueous fe ii in natural systems that contain nanoparticulate goethite including those involving bacterial iron reduction these results demonstrate that the isotopic properties of nano scale minerals may be distinct from micron scale or larger minerals as is the case for other thermodynamic properties of nanoparticles

chemical weathering in the drainage basin of a tropical watershed nsimi zoetele site cameroon comparison between organic poor and organic rich waters abstract this study deals with the weathering processes operating at the scale of a small catchment nsimi zoetele cameroon and is focused on the role of organic colloids on mineral weathering and transport of elements in natural waters samples of river spring and groundwaters from nsimi zoetele were filtered through membranes of decreasing pore size 0 22 m 0 025 m or 300 000 da 5000 da to separate colloidal fractions from the truly dissolved one major and trace elements and dissolved organic carbon doc were analysed in each fraction two kinds of waters can be distinguished in the catchment clear and coloured waters clear waters exhibit low concentrations of major and trace elements and doc elements are carried in these solutions in a true dissolved form except al and rare earth elements rees by contrast the higher abundances of al fe and trace elements in coloured waters are controlled by the colloidal fraction thermodynamic equilibrium calculations show that clear waters are in equilibrium with kaolinite and iron oxi hydroxide which are major minerals in the weathered soil for coloured waters the aqueous speciation of ca mg cu fe al la and th was calculated taking into account the complexes with humic acids speciation calculations for cu fe al la th show a strong complexation with humic acids in good agreement with the results of the filtration experiments by contrast although filtration experiments show a strong control of major cations by organic matter for example 75 for ca speciation calculations reveal that their complexes with humic ligands do not exceed a few percent of total dissolved elements this discrepancy is explained as an artefact induced by the organic colloids and occurring during the filtration procedure finally both filtration experiments and speciation calculations show that organic matter plays an important role in natural doc rich waters organic acids increase significantly the dissolution rates of silicates and oxi hydroxides and thus the amounts of solutes and of complexed elements leaving the catchment

coastal transition zone off chile 1 seven years of subsurface current observations at deep sea and continental slope moorings off chile 30 s satellite sea surface anomaly and satellite wind stress are used to examine space time and propagation characteristics of the mesoscale eddy activity in the coastal transition zone off chile this zone off chile extends from the coast to 600 800 km offshore and can be separated into two latitudinal regions the first region between 29 and 39 s off central chile is characterized by high eddy kinetic energy and strong but variable equatorward wind stress the second region between 19 and 29 s off northern chile is characterized by low eddy kinetic energy and weak but persistent equatorward wind stress low frequency mesoscale variability off central chile is mainly associated with baroclinic instability of coastal currents and westward propagation of rossby waves from the eastern boundary and is strongly modulated over el nino la nina cycles application of a new rotary wavelet spectrum method to the recording current meter data and the use of current estimates from satellite altimeter data show that mesoscale eddies and meanders in the coastal transition zone fluctuate with periods centered on 120 days and with length scales centered on 200 km cross rotary wavelet analyses of currents and wind stress indicate that fluctuations of coastal currents with periods longer than 220 days propagated westward as free rossby waves during 1995 1996 and as forced rossby waves during 1999 2001

the flow of the undercurrent over the continental borderland off southern california 1 iniroduction 2 background the bottom topography off southern california has been the cc a slow had equatornard flow is the eastern limb of termed a continental borderland to distinguish it from the ordinary the large scale anticyclonic gyre of the temperate north pacific shelf slope morphology found along most continental margins ocean the cc carries relatively cool low salinity waters of shepard and emuy 19411 islands shallow banks basins and subarctic origin to lower latitudes on average the core of the cc troughs form a complex bathymetric region extending from the has velocities of 0 10 to 0 15 m s and traces a path roughly coast to 200 lon offshore the southern california coastline has a parallel to the california baja california coastline localized concave curvature between the headland at point conception to measurements of flow can exceed 0 5 m s davis 19851 an the u s mexican border as a whole this region is referred to as instantaneous realization of the cc includes a tangle of meanders the california bight the geographic bathymetric dguration eddies and narrow jetlike flows and counterllows the cc lies at of the bight exm a pronounced influence upon the local circula varying distances off the coast and at the latitude of the tion patterns and heme upon the distributions of physical e u s mexican border there is a strong shoreward component to sverdrup and fleming 19411 and biological quantities e g the flow in most seasons especially summa the flow splits one allen 1945 owen 19801 during 1985 we conducted an oceano branch turns and flows northward into the california bight graphic survey off southern california the sampling grid was becoming the eastern limb of a cyclonic eddy centered about the designed to reveal the mumce of the geographic bathymetric offshore banks seasonally fall and winter a weak inshore features upon the circulation of the california current system countercurrent ic develops at the surface along various portion6 ccs especially the flow of the california undercurrent cu of the coastline reid et d 19581 at depth the cu cdes the survey grid also includes station lines mss the core of the waters of subtropical origin poleward along the continental slope california current cc and transects an offshore dipole eddy these waters are relatively warm and saline and have low mm simpson and lym this issue the station grid of this study trations of dissolved oxygen the cu also demonstrates a welldiffers considerably from that used by the california cooperative defined seasonality and at times opposes the overlying dace oceanic fisheries investigations calcofi surveys in both its flow maps and sections of the long term seasonal means of relaspatial resolution and depth of sampling the objectives of thic tive geostrophic velocity and distributions of ocean characteristics report are 1 to examine the spatial continuity of the cu through for the ccs are available in calcofi atlas 30 lym et d 19821 the complex bathymeny of the bight 2 to trace the poleward for a comprehensive review of the long term seasonal large scale paths and offshore spread of waters of southern origin transported description of the ccs the readex is referred to recent papas by by the cu 3 to contrast this subsurface flow with the surface hickey 1979 chelton 19841 and lynn andslnpsm 19871 and flow and 4 to compare these results with the long term calcofi to important references of pioneering work given therein mean conditions

global observations of large oceanic eddies 1 ten years of sea surface height ssh fields constructed from the merged topex poseidon t p and ers 1 2 altimeter datasets are analyzed to investigate mesoscale variability in the global ocean the higher resolution of the merged dataset reveals that more than 50 of the variability over much of the world ocean is accounted for by eddies with amplitudes of 5 25 cm and diameters of 100 200 km these eddies propagate nearly due west at approximately the phase speed of nondispersive baroclinic rossby waves with preferences for slight poleward and equatorward deflection of cyclonic and anticyclonic eddies respectively the vast majority of the eddies are found to be nonlinear

intermediate depth circulation of the indian and south pacific oceans measured by autonomous floats as part of the world ocean circulation experiment 306 autonomous floats were deployed in the tropical and south pacific ocean and 228 were deployed in the indian ocean to observe the basinwide circulation near 900 m depth mean velocities seasonal variability and lateral eddy diffusivity from the resultant 2583 float years of data are presented area averages local function fits and a novel application of objective mapping are used to estimate the mean circulation patterns of mean circulation resemble those at the surface in both basins well developed subtropical gyres twice as strong in the indian ocean as in the pacific feed western boundary currents tropical gyres are separated by eastward flow along the equator in both hemispheres of both basins although the indian subcontinent splits the north indian tropical gyre the antarctic circumpolar current acc and west wind drifts are prominent in both basins generally tending slightly southward but deviating to the north behind the del cano kerguelen and campbell plateaus and of course south america remarkably the eastern boundaries of the southern subtropical gyres in all three basins apparently occur in the ocean interior away from land the indian ocean s subtropical gyre and perhaps part of the south atlantic s reaches east to a retroflection just upstream of the campbell plateau south of new zealand seasonal variability at 900 m is focused around the equator with weaker variability found near certain bathymetric features there is a remarkable agreement between the observed seasonable variability and that predicted by the jet propulsion laboratory jpl estimating the circulation and climate of the ocean ecco data assimilating numerical model aside from seasonal effects eddy variability is greatest along the equator in tropical and subtropical western basins and along the acc integrals of velocity across regional passages tasman sea mozambique channel provide useful reference for hydrographic analyses of transport across whole ocean basins however the uncertainty associated with the appropriate continuity relation for horizontal flow e g geostrophy vs nondivergence is comparable to the mean flow

seasonal and interannual variability of currents and temperature off central chile results are reported for continuous 6 year records of current and temperature from a continental slope station at 308s off chile these observations for november 1991 to november 1997 span the moderate weak and strong el nino events of 1991 1992 1994 and 1997 and the la nina event of 1995 1996 results for current and temperature are analyzed together with observations of wind along the south american coast from the ers 1 and 2 satellite scatterometers wind from a local coastal site sea level from northern and central chile sea surface temperature anomalies from the south pacific region and traditional el nino indices mean poleward flow of 12 8 cm s 21 was observed for the 6 year period in the core of the peru chile undercurrent 220 m mean flow in the depth range of antarctic intermediate water 750 m was equatorward at 1 1 cm s 21 intraseasonal scale variability associated with coastal trapped waves was weaker during the austral winter greatest during el nino events and weakest during the la nina event winds adjacent to the coast showed a strong annual cycle with a southward progression of maximum equatorward upwelling favorable winds alongshore flow over the slope exhibited strong semiannual and weaker annual variations poleward flow in the undercurrent was strongest in the austral spring and fall and weakest in the winter near the bottom 750 m seasonal scale variability was less intense but led that higher up in the water column 220 m by 1 month strong interannual variability of alongshore current and temperature was found at all depths over the slope whereby changes at depth led changes higher up a rapid warming event was observed at the end of 1996 beginning of 1997 over the slope this event also seen in sea level and sea surface temperature off chile led el nino indices by several months and may be best explained by local wind anomalies coupled to atmospheric teleconnections from the western tropical pacific at the onset of el nino some aspects of our current and temperature observations are consistent with results from eastern boundary current models our results indicate that both ocean and atmosphere pathways from the equatorial pacific contribute significantly to interannual scale variability of alongshore flow and thermocline depth off chile

a subsurface warm eddy off northern baja california in july 2004 1 upper ocean eddies are commonly observed from remote sensing but submerged eddies are more difficult to detect during july 2004 a 21 day hydrographic survey in the southern region of the california current was carried out to investigate the mesoscale variability we observed for the first time a subsurface anticyclonic eddy off northern baja california with the same water mass characteristics as the california undercurrent the core of the eddy was quasi circular with radii of 35 km and thickness of 250 m the maximum swirl velocity was 3 cms 1 the water mass of the core of the eddy was characterized by potential temperature of 11 c salinity of 34 5 and dissolved oxygen of 1 4 mll 1 the eddy propagated westward the subsurface warm eddy could transport relatively saline water into the north pacific subtropical gyre

southern ocean contributions to the eastern equatorial pacific heat content during the holocene abstract temperature reconstructions from a shallow core 375 m from the peru margin are used to test the influence of subantarctic mode water samw on the eastern equatorial pacific eep thermostad and thus the effect of southern high latitude climate on interior ocean heat content ohc temperature estimates based on mg ca measurements of planktonic and benthic foraminifera neogloboquadrina dutertrei and uvigerina spp respectively show higher temperatures in the early holocene a cooling of 2 by 8 kyr b p and after relatively stable temperatures to the present the temperature signal is similar in direction and timing to a rather robust holocene climate signal from the southern high latitudes suggesting it originated there and was advected to the core site in the eep based on the n dutertrei and uvigerina mg ca temperature and 13c records we conclude that samw acted as a conduit transporting the southern high latitude climate to the interior of the equatorial pacific we propose that the early holocene warmth is related to a southward migration of the subtropical front which enhanced the influence of warm subtropical water in the region of samw formation and was then transported to the eep thermostad the early holocene warmth recorded in the eep thermostad has a muted sea surface temperature expression indicating this mechanism is important for sequestering heat in the ocean interior

eddy characteristics in the eastern south pacific 1 the main eddy characteristics length scales rotation period swirl and translation velocities are determined in the eastern south pacific region 10 35 s and 70 100 w based on surface drifter measurements satellite altimetry and hydrographic data from the woce p19 section the chile peru current eddies have a typical diameter of order of 30 km smaller than the typical rossby radii observed in the region they are principally formed near the south american coast and propagate seaward with a translation velocity varying from 3 cm s 1 in the southern part of the study domain to 6 cm s 1 north of 15 s long lived anticyclonic eddies propagate northwestward with a mean angle of around 333 t whereas cyclonic vortices propagate westward consistent with the vortices propagation theory on a plane the radial distribution of the swirl velocity shows that the chile peru current eddies have a maximum diameter of order 200 km with a swirl velocity of around 14 cm s 1 and a rotation period of 50 days hydrographic data reveal a vertical extent down to around 2000 m for energetic eddies no significant difference is observed between the tangential velocities of cyclonic and anticyclonic eddies geostrophic balance can be considered for large radii whereas ageostrophic dynamics may play an important role near the eddy centers

insights into iron sources and pathways in the amazon river provided by isotopic and spectroscopic studies abstract the present study investigated the weathering and transport mechanisms of fe in the amazon river a particular emphasis was placed on fe partitioning speciation and isotopic fractionation in the contrasting waters of the solimoes and negro rivers and their mixing zone at the beginning of the amazon river samples collected in the end member rivers and thirteen sites distributed throughout the mixing zone were processed through frontal vacuum filtration and tangential flow ultrafiltration to separate the different suspended solid fractions i e particulate p 0 45 m and p 0 22 m colloidal 0 22 m c 5 kda and truly dissolved elements td 57 fe values relative to irmm 14 while the particulate fractions yielded light isotopic compositions of 0 344 for p 0 22 m and 0 104 for p 0 45 m fractions the mineral particulate rich waters of the solimoes river had dissolved and colloidal fractions with light isotopic composition 0 532 and 0 176 respectively whereas the particulate fractions yielded 57 fe values close to those of the continental crust i e 0 029 for p 0 22 m and 0 028 for p 0 45 m ten kilometers downstream from the negro and solimoes junction the concentrations of colloidal and dissolved fe species deviate markedly from conservative mixing a maximum fe loss of 43 g l i e 50 of the dissolved and colloidal fe is observed 110 km downstream from the rivers junction the contrasting negro and solimoes rivers isotopic compositions along the pore sized water fractions is attributable to the biogeochemical processes involving different types of upland soils and parental materials for instance the isotopic composition of colloidal and dissolved fe from the negro river are consistent with fe oxidation and complexation mechanisms at the interface between waterlogged podzols and river networks as supported by strong organo fe complexes signals observed by epr conversely the particulate and colloidal fractions from the solimoes river have 57 fe consistent with strong mechanical erosion in the andean cordillera and upland soils as evidenced by high concentrations of fe 3 oxides sensu lato measured by epr the massive dissolved and colloidal fe removal is associated with the evolution of the physical and chemical composition of the waters i e ionic strength during mixing which influences organo fe 3 and fe 3 oxyhydroxides stability several models are discussed to explain fe non conservative behavior including dissociation of organo fe complexes and the subsequent formation of solid fe 3 oxyhydroxides and semiquinone free radicals as evidenced by epr spectra demonstrating that organo fe signals decrease as fe 3 oxyhydroxides and free radicals signals increase as in estuarine regions the mechanisms involving fe transfer and loss in the mixing zone has a negligible effect on the bulk water fe isotopic composition this result suggests that a tropical basin similar to the amazon river basin delivers to the ocean waters with an fe isotopic composition similar to that of the earth s continental crust

the isotopic fingerprint of fe cycling in an equatorial soil plant water system the nsimi watershed south cameroon abstract following an initial study of a tropical lateritic hillside system showing little iron isotope fractionation despite a strong accumulation within the soil profile the present work investigates iron isotope signatures within the organic matter rich swamp system that represents 20 of the studied watershed surface from nsimi south cameroon this study considers the soil plant water continuum in order to better understand the fe elemental and isotopic transfer out of the ecosystem within the swamp system the iron isotope compositions of gleysol samples 57 fe irmm 14 0 6 are significantly heavier than both the continental crust baseline and the reference lateritic soils from the hillslope 57 fe irmm 14 0 1 this enrichment towards heavy isotopes is attributed to a preferential removal of light iron isotopes during soil forming processes pedogenic transformations i e gleyzation organic complexation of metal and leaching are responsible for the reductimorphic features observed in ferralitic horizons i e incomplete degradation of organic matter in surface and soil whitening favored by good draining conditions the organic carbon rich waters of the swamp system are prone to redox processes and strong metal chelation the dissolved iron i e fraction 57 fe signatures with a downstream enrichment in heavy isotopes from 0 511 0 266 to 1 076 0 240 the binding of iron fe iii with organic matter can explain the observed enrichment in heavy isotopes in the dissolved fraction on the contrary plant leaves are significantly enriched in light fe 57 fe of 0 665 0 035 and 1 119 0 080 relative to i the litter compartment 0 166 0 078 to 0 262 0 013 for 57 fe and ii the most superficial soils iron isotopic compositions in plants and litter vary as a function of both plant species and season hence the differences in fe isotopic compositions between the various studied compartments suggest that fe isotopes can be used i to study elemental transfers during soil pedogenesis in tropical environment and ii to better appraise and constrain iron biogeochemical cycle between surface horizon of soils surface waters and the vegetation

on the iron isotope homogeneity level of the continental crust abstract assessing the level of homogeneity of different planetary reservoirs is an essential step to establish a new isotopic tracer in recent studies we concluded that most igneous rocks from the continental crust were homogeneous to 71 wt sio2 that we concluded were significantly heavier than less silicic rocks from the crust on the basis of fe isotopic analyses of seven bulk rock samples from different geological settings beard and johnson beard b l johnson c m 2006 comment on heavy iron isotope composition of granites determined by high resolution mc icp ms by f poitrasson and r freydier chemical geology volume 222 pages 132 147 chem geol this issue challenge this finding on the basis of previously published data it is shown here that this controversy stems from the confusion between whole rock and mineral iron isotope analyses since this isotopic tracer like many others is more heterogeneous at the mineral scale than the bulk rock scale thus minerals cannot be used in place of bulk rock fe isotope compositions the controversy also arises from different levels of analytical uncertainties if only the best fe isotope probes of planetary reservoirs bulk rocks are considered then the conclusion that igneous rocks with sio2 71 wt are significantly heavier than the mean 57fe of the continental crust poitrasson f freydier r 2005 heavy iron isotope composition of granites determined by high resolution mc icp ms chem geol 222 132 147 remains valid nonetheless given that granites represent only a minor fraction of the continental crust this finding does not change the bulk igneous fe isotope composition estimate previously defined for the earth