response of southern ocean ventilation to changes in midlatitude westerly winds abstractchanges in ventilation of the southern hemisphere oceans in response to changes in midlatitude westerly winds are examined by analyzing the ideal age tracer from global eddy permitting ocea

decadal changes in the south pacific western boundary current system revealed in observations and ocean state estimates observations and ocean state estimates are used to investigate the nature and mechanism of decadal variability in the east australian current eac system and south pacific subtropical gyre a 62 year record on the tasmanian continental shelf shows decadal variations of temperature and salinity as well as a long term trend which has been related to wind driven variations in the poleward extension of the eac repeat expendable bathythermograph lines spanning the last 15 years suggest that low frequency variations in the transport of the eac extension and tasman front are anticorrelated but the time series are too short to draw firm conclusions here we use two ocean state estimates spanning the past 50 years to diagnose the physical mechanisms and spatial structure of the decadal variability of the south pacific subtropical gyre the observations and state estimates paint a consistent picture of the decadal variability of the gyre and eac system strengthening of the basin wide wind stress curl drives a southward expansion of the subtropical gyre as the gyre shifts south the eac extension pathway is favored at the expense of the tasman front resulting in the observed anticorrelation of the these two major currents the results suggest that the subtropical gyre and western boundary current respond to decadal variability in basin scale wind stress curl consistent with island rule dynamics that strong decadal variability of the south pacific gyre complicates efforts to infer trends from short term records and that wind stress curl changes over the south pacific basin drive changes in the eac system that are likely to have implications for marine ecosystems and regional climate

decadal changes of wind stress over the southern ocean associated with antarctic ozone depletion using 40 yr ecmwf re analysis era 40 data and in situ observations the positive trend of southern ocean surface wind stress during two recent decades is detected and its close linkage with spring antarctic ozone depletion is established the spring antarctic ozone depletion affects the southern hemisphere lower stratospheric circulation in late spring early summer the positive feedback involves the strengthening and cooling of the polar vortex the enhancement of meridional temperature gradients and the meridional and vertical potential vorticity gradients the acceleration of the circumpolar westerlies and the reduction of the upward wave flux this feedback loop together with the ozone related photochemical interaction leads to the upward tendency of lower stratospheric zonal wind in austral summer in addition the stratosphere troposphere coupling facilitated by ozone related dynamics and the southern annular mode cooperates to relay the zonal wind anomalies to the upper troposphere the wave mean flow interaction and the meridional circulation work together in the form of the southern annular mode which transfers anomalous wind signals downward to the surface triggering a striking strengthening of surface wind stress over the southern ocean

antarctic ozone depletion causes an intensification of the southern ocean super gyre circulation 1 recent climate trends over the southern hemisphere sh summer feature a strengthening of the circumpolar westerly and a weakening of the midlatitude westerly extending from the stratosphere to earth s surface much of the change is attributable to antarctic ozone depletion however the consequential ocean circulation changes are unknown here i demonstrate that the observed surface wind changes have forced a southward shift and spin up of the super gyre which links the subtropical south pacific indian and atlantic ocean circulation advecting more warm water southward the circulation change includes a strengthening of the east australian current eac flow passing through the tasman sea the southward shift may be responsible for the observed unusually large warming in the sh midlatitude ocean and may contribute to the reported range extension to the south of many marine species in the south west pacific

temporal variability of transformation formation and subduction rates of upper southern ocean waters 1 kinematic and thermodynamic approaches are employed to diagnose the time dependent transformation formation and subduction rates of upper southern ocean waters in a multidecadal simulation within an eddy permitting coupled climate model in the subantarctic mode water samw density class a convergence of diapycnal volume fluxes leads to the formation and inflation of mixed layer waters during winter a portion of this water is detrained into the pycnocline during early spring when surface heating restratifies the deep winter mixed layer the annually averaged subduction rate of samw shows pronounced interannual variability partly controlled by the temporal tendency of the winter mixed layer depth from one year to the next no significant correlation between the southern annular mode sam and the isopycnally integrated samw subduction rate is apparent however ekman downwelling upwelling intensities modulated by the sam influence interannual variations in the subduction rates of water masses lighter and heavier than samw with an opposing sign during positive phases of the sam more pycnocline waters are entrained into the mixed layer and transformed into lighter densities within the antarctic intermediate water density class whereas more mixed layer waters are subducted into the pycnocline within the subtropical mode water density class such distinct responses of upper southern ocean water masses to the sam are qualitatively consistent with observational constraints based on a comparison between offline kinematic and thermodynamic diagnostics we infer that diapycnal mixing within the mixed layer may contribute up to 50 of the formation rate of samw on interannual timescales

climate and marine carbon cycle response to changes in the strength of the southern hemispheric westerlies 1 it has been previously suggested that changes in the strength and position of the southern hemisphere westerlies could be a key contributor to glacial interglacial atmospheric co2 variations to test this hypothesis we perform a series of sensitivity experiments using an earth system model of intermediate complexity a strengthening of the climatological mean surface winds over the southern ocean induces stronger upwelling and increases the formation of antarctic bottom water enhanced ekman pumping brings more dissolved inorganic carbon dic rich waters to the surface however the stronger upwelling also supplies more nutrients to the surface thereby enhancing marine export production in the southern hemisphere and decreasing the dic content in the euphotic zone the net response is a small atmospheric co2 increase 5 ppmv compared to the full glacial interglacial co2 amplitude of 90 ppmv roughly the opposite results are obtained for a weakening of the southern hemisphere westerly winds

the southwest pacific ocean circulation and climate experiment spice the southwest pacific ocean circulation and climate experiment spice is an international research program under the auspices of clivar the key objectives are to understand the southwest pacific ocean circulation and the south pacific convergence zone spcz dynamics as well as their influence on regional and basin scale climate patterns south pacific thermocline waters are transported in the westward flowing south equatorial current sec toward australia and papua new guinea on its way the sec encounters the numerous islands and straits of the southwest pacific and forms boundary currents and jets that eventually redistribute water to the equator and high latitudes the transit in the coral solomon and tasman seas is of great importance to the climate system because changes in either the temperature or the amount of water arriving at the equator have the capability to modulate the el nino southern oscillation while the southward transports influence the climate and biodiversity in the tasman sea after 7 years of substantial in situ oceanic observational and modeling efforts our understanding of the region has much improved we have a refined description of the spcz behavior boundary currents pathways and water mass transformation including the previously undocumented solomon sea the transports are large and vary substantially in a counter intuitive way with asymmetries and gating effects that depend on time scales this paper provides a review of recent advancements and discusses our current knowledge gaps and important emerging research directions

meridional volume transport in the south pacific mean and sam related variability the large increase in upper ocean sampling during the past decade enables improved estimation of the mean meridional volume transport in the midlatitude south pacific and hence of the climatically important meridional overturning circulation transport is computed using argo float profile data for geostrophic shear and trajectory data for reference velocities at 1000 m for the period 2004 2012 the mean geostrophic transport across 32s is 20 6 6 0 sv in the top 2000 m of the ocean from west to east this includes the southward east australian current 23 3 2 9 sv its northward recirculation 16 3 3 6 sv the broad interior northward flow 18 4 4 1 sv and the net northward flow 9 2 2 2 sv in opposing currents in the eastern pacific the basin integrated geostrophic transport includes 7 3 0 9 sv of surface and thermocline waters 4 9 1 0 sv of subantarctic mode water and 4 9 1 4 sv of antarctic intermediate water interannual variability in volume transport across 32s in the south pacific shows a southern annual mode signature characterized by an increase during the positive phase of the southern annular mode and a decrease during the negative phase maximum amplitudes in geostrophic transport anomalies seen in the east australian current and east australian current recirculation are consistent with wind stress curl anomalies near the western boundary key points improved meridional volume transport in the south pacific using argo eac transport variability tied to the sam published 2014 this article is a u s government work and is in the public domain in the usa

wave driven zonal flow vacillation in the southern hemisphere the variability of the zonal mean flow in the southern hemisphere during the period 1985 94 is studied using european centre for medium range forecasts analyses the dominant mode of variability has approximately equivalent barotropic variations of opposite signs centered at 40 8 and 608s this structure is dominant in all seasons and has similar variance in all seasons the temporal variance of the amplitude of this mode is well modeled as gaussian red noise with a correlation e folding time of about 10 days zonal wind anomalies are maintained against frictional drag by variations in the zonal flow accelerations driven by transient eddies and associated mean meridional circulations the eddy structures suggest that equatorward propagation is favored when the jet is displaced poleward and zonal propagation is favored when the jet is displaced equatorward

enso to multi decadal time scale changes in east australian current transports and fort denison sea level oceanic rossby waves as the connecting mechanism the connection between east australian current eac transport variability and australia s east coast sea level has received little treatment in the literature this is due in part to the complex interacting physical processes operating in the coastal zone combined with the sparsity of observations available to improve our understanding of these possible connections this study demonstrates a statistically significant at the 490 level relationship between interannual to decadal time scale variations in observed estimates of the eac transport changes and east coast sea level measured at the high quality long record fort denison tide gauge in sydney harbour australia 3315101800s 15111303200e we further demonstrate using a linear reduced gravity ocean model that enso to decadal time scale variations and the ocean adjusted multi decadal trend approx 1 cm decade in observed sea level at fort denison are strongly connected to modulations of eac transports by incoming westward propagating oceanic rossby waves we show that eac transport and fort denison sea level vary in a manner expected from both tasman sea generated rossby waves which account for the interannual and multi annual variability and remotely forced from east of new zealand rossby wave connections through the mid latitudes accounting for the ocean adjusted multi decadal trend observed at the new south wales coast with the regional tasman sea forcing explaining the greatest overall proportion of eac transport and sea level variances

decadal variability in the large scale sea surface height field of the south pacific ocean observations and causes large scale sea surface height ssh changes in the extraequatorial south pacific ocean are investigated using satellite altimetry data of the past 12 yr the decadal ssh signals in the 1990s were dominated by an increasing trend in the 30 50 s band and a decreasing trend in the central south pacific ocean poleward of 50 s in recent years since 2002 there has been a reversal in both of these trends spatially varying low frequency ssh signals are also found in the tropical region of 10 25 s where the decadal ssh trend is negative in the eastern basin but positive in the western basin to clarify the causes for these observed spatially varying ssh signals a 11u2 layer reduced gravity model that includes the wind driven baroclinic rossby wave dynamics and the responses forced by ssh changes along the south american coast was adopted the model hindcasts the spatially varying decadal trends in the midlatitude and the eastern tropical regions well accumulation of the wind forced ssh anomalies along rossby wave characteristics is found to be important for both previously reported long term trends and their reversals in recent years the boundary forcing associated with the time varying ssh signals along the south american coast is crucial for understanding the observed ssh signals of all time scales in the eastern tropical south pacific basin but it has little impact upon the midlatitude interior ssh signals

the response of the southern annular mode the east australian current and the southern mid latitude ocean circulation to global warming 1 climate models predict an upward trend of the southern annular mode sam in response to increasing atmospheric co2 concentration however the consequential impact of this change on oceanic circulation has not been explored here we analyse the outputs of a series of global warming experiments from the csiro mark 3 climate model we show that although for the zonal wind stress change the maximum is located at approximately 60 s in terms of the change in surface wind stress curl the maximum is situated at approximately 48 s this change in the wind stress curl causes a spin up of the entire southern midlatitude ocean circulation including a southward strengthening of the subtropical gyres particularly the east australia current eac the intensified eac generates a warming rate in the tasman sea that is the greatest in the southern hemisphere sh with significant implications for sea level rise the pan southern ocean scale suggests a broad impact on the marine ecosystem of the entire southern midlatitude ocean

low frequency variability of the south pacific subtropical gyre as seen from satellite altimetry and argo abstractlow frequency variability of the south pacific subtropical gyre is investigated using satellite altimeter and argo data in most of the region studied both sea surface height and steric height exhibit a linearly increasing trend with its largest amplitude in the western part of the basin analysis of the argo data reveals that the steric height increase north of 30 s is primarily caused by variations in the upper 500 m while the steric height increase south of 30 s is determined by variations in the whole depths from the sea surface to 1800 m with contributions from below 1000 m accounting for about 50 of the total variance most of the steric height increase is due to thermal expansion except below 1000 m where haline contraction is of comparable magnitude with thermal expansion correspondingly the south pacific subtropical gyre has strengthened in the past decade within the latitude range between 10 and 35 s transport of the gyre circulation increased by 20 30 in the upper 1000 m an

decadal phase change in large scale sea level and winds in the indo pacific region at the end of the 20th century 1 satellite observations of sea surface height ssh and wind stress for the period of 1993 2006 reveal a near coherent large scale decadal variability in much of the indo pacific region with a phase change at the turn of the 20th century trade wind variations in the tropical pacific and south indian ocean are anti correlated with each other as are ssh differences across these two basins implying anti correlated variation of the subtropical cells in the two oceans decadal changes in large scale ssh in the extra tropics are mostly associated with well defined patterns of wind stress curl indicating a near coherent decadal variation in the strength of subtropical and subpolar gyres together these variations reflect a linkage in the circulation of the pacific and indian oceans via atmospheric and oceanic bridges the phase change in the tropical pacific tends to occur earlier than elsewhere suggesting a potential role of the tropical pacific in regulating decadal variability of the entire region

interpretation of recent southern hemisphere climate change climate variability in the high latitude southern hemisphere sh is dominated by the sh annular mode a large scale pattern of variability characterized by fluctuations in the strength of the circumpolar vortex we present evidence that recent trends in the sh tropospheric circulation can be interpreted as a bias toward the high index polarity of this pattern with stronger westerly flow encircling the polar cap it is argued that the largest and most significant tropospheric trends can be traced to recent trends in the lower stratospheric polar vortex which are due largely to photochemical ozone losses during the summer fall season the trend toward stronger circumpolar flow has contributed substantially to the observed warming over the antarctic peninsula and patagonia and to the cooling over eastern antarctica and the antarctic plateau

recent freshening of the east australian current and its eddies the east australian current eac has a relatively weak mean flow and an energetic eddy field that dominates the circulation the properties of the mean flow have been studied in detail but the changes in the eddy field have received little attention we analyze argo temperature and salinity profiles for 2005 2012 to construct a picture of the time mean and time varying properties of eac eddies we find that eddies and the surrounding waters of the western tasman sea are freshening at a rate of 0 017 0 025 practical salinity unit yr over the top 100 m with no significant temperature change consistent with the observations fields from an eddy resolving ocean model show freshening with no temperature trend moreover the model results indicate that observed changes are significant in the context of the variability over the last 20 years and may be part of a multiyear perhaps decadal cycle we attribute the freshening of the region to increased precipitation off eastern australia

intensification and variability of the confluence of subtropical and subantarctic boundary currents east of new zealand the confluence of subtropical and subantarctic boundary currents east of new zealand creates strong fronts the fronts have clear signatures in sea surface height ssh and sea surface temperature sst which make the confluence a good region to investigate the variability of the boundary currents of the south pacific analysis of the 20 year time series of the ssh is used to investigate the location and strength of fronts measured as the gradient in ssh ssh and the eddy kinetic energy eke and their relationship to local and large scale wind forcing the intensity of the ssh and the eke have increased at a rate of 0 02 cm km 1 and 32 cm2 s 2 decade 1 respectively there is a significant correlation r 0 7 p 0 01 between the ssh and eke signals reflecting baroclinic instabilities inherent in the fronts differences between northward and southward wind driven transports across the confluence from the island rule are also increasing at 7 5 sv decade 1 along with an upward trend in the sst differences across the region time series of the southern annular mode sam and southern oscillation index soi and local winds were compared to the frontal strength although the positive trend in the soi coincides with increasing subtropical inflows there is little correspondence of the indices and local winds with short term variability while these results indicate a connection between the intensification of the confluence and south pacific winds there is little change in frontal location north of bollons seamount which suggests bathymetry influences the location of the confluence

on the sensitivity of the drake passage transport to air sea momentum flux an eddy permitting state estimate and its adjoint are used to analyze the influence of wind stress perturbations on the transport of the antarctic circumpolar current acc system through drake passage the transport is found to be sensitive to wind stress perturbations both along the acc path and also in remote regions the time scale of influence of wind stress perturbations is on the order of 100 days regarding spatial scales the sensitivity of transport to wind stress is relatively smooth in regions offlat topography in boundary regions and regions with complex topography however the sensitivity is enhanced and characterized by shorterlengthscalesoforder100 km positiveperturbationstothezonalwindstressusuallyincreasetheacc transport though the wind stress curl is of primary influence where the currents are steered by topography highlighting locations where the acc is especially responsive to air sea momentum fluxes reveals where an accurate determination of atmospheric winds may best enhance ocean modeling efforts

decadal spinup of the south pacific subtropical gyre abstract an increase in the circulation of the south pacific ocean subtropical gyre extending from the sea surface to middepth is observed over 12 years datasets used to quantify the decadal gyre spinup include satellite altimetric height the world ocean circulation experiment woce hydrographic and float survey of the south pacific a repeated hydrographic transect along 170 w and profiling float data from the global argo array the signal in sea surface height is a 12 cm increase between 1993 and 2004 on large spatial scale centered at about 40 s 170 w the subsurface datasets show that this signal is predominantly due to density variations in the water column that is to deepening of isopycnal surfaces extending to depths of at least 1800 m the maximum increase in dynamic height is collocated with the deep center of the subtropical gyre and the signal represents an increase in the total counterclockwise geostrophic circulation of the gyre by at least 20 at 1000 m a comparison of woce and

mesoscale structure of the mean east australian current system and its relationship with topography abstract we document the mean circulation of the east australian current eac system which is the major western boundary current in the southwest pacific ocean a new high resolution climatology of the region csiro atlas of regional seas cars is used to produce regional fields of steric height and sections of geostrophic velocity the realism of these fields has been enhanced by the high spatial resolution allowance for bathymetric control and the influence of land barriers the increased detail in the maps and sections reveal the major influence that the complex regional topography has on the circulation the results also provide the appropriate resolution for comparison with recent model studies of the region we have been able to both resolve well known features with greater detail and identify previously unrecognized aspects of the circulation important results include 1 the zonal inflow north of 30 s breaks into a series of individual jets after flowing through the island chains as suggested by recent model results 2 the interaction of the zonal inflow with the local topography as it undergoes bifurcation is documented 3 a detailed picture of the evolution of the eac at the western boundary is presented including surface currents and transports 4 separation and recirculation of the eac within the tasman abyssal basin are shown to occur as a double cell structure constrained by bathymetry 5 the eac outflow is resolved as a series of eastward and northeastward currents 6 the path of the tasman front is defined as it interacts with the tasman ridge systems 7 a quasi permanent eddy is identified for the first time adjacent to the norfolk ridge northwest of new zealand

meridional displacement of the antarctic circumpolar current observed long term warming trends in the southern ocean have been interpreted as a sign of increased poleward eddy heat transport or of a poleward displacement of the entire antarctic circumpolar current acc frontal system the two decade long record from satellite altimetry is an important source of information for evaluating the mechanisms governing these trends while several recent studies have used sea surface height contours to index acc frontal displacements here altimeter data are instead used to track the latitude of mean acc transport altimetric height contours indicate a poleward trend regardless of whether they are associated with acc fronts the zonally averaged transport latitude index shows no long term trend implying that acc meridional shifts determined from sea surface height might be associated with large scale changes in sea surface height more than with localized shifts in frontal positions the transport latitude index is weakly sensitive to the southern annular mode but is uncorrelated with el nino southern oscillation

long term trends in the east australian current separation latitude and eddy driven transport an observed warming of the tasman sea in recent decades has been linked to a poleward shift of the maximum wind stress curl and a strengthening of the poleward flow along the coast of southeastern australia however changes in the east australian current eac separation latitude as well as in the contribution of the eac the eac extension and its eddy field to the total southward transport due to such a strengthening remain unknown this study uses 30 years 1980 2010 of the ocean forecast for the earth simulator ofes sea surface height and velocity outputs to obtain a three decade long time series of i the eac separation latitude ii the southward transport along the coast of southeastern australia 28 s 39 s and iii the southward transport across the eac separation latitude a lagrangian approach is implemented and the spin parameter is used to provide a quantitative distinction between the transports occurring outside and inside cyclonic and anticyclonic eddies significant positive trends of the low pass southward transports indicate that the intensification of the poleward flow has occurred both within the eac and in the eac extension in addition a significant increase in southward transport inside and outside eddies is found importantly the contribution of eddy driven transport has a large temporal variability and shows a sharp increase from 2005 onward finally our results show that the eac has not penetrated further south but it has separated more frequently at the southernmost latitudes within the region where it typically turns eastward

re os isotopic systematics of the voisey s bay ni cu co magmatic ore system labrador canada abstract re and os concentrations and os isotopic compositions have been obtained for massive matrix and disseminated sulphide ores from three environments within the voisey s bay intrusion the ovoid eastern deeps and discovery hill zone in order to assess the role of crustal contamination in the genesis of this large cu ni co deposit these samples have high re concentrations 148 to 288 ppb in 100 sulphide for their common os concentrations 4 8 to 24 ppb in 100 sulphide yielding high re os ratios 12 to 33 these data confirm that the magma parental to the voisey s bay ore system was broadly basaltic in major element chemistry rather than picritic consistent with the low ni cu ratio of the ores 1 5 re os isotopic data exhibit a limited spread in 187 re 188 os 57 to 157 and define an imprecise 1323 135 ma model 3 isochron likely the result of small r factor variations within the ore system the re os isochron age is within error of 1334 ma u pb ages obtained for baddeleyite from the ore bearing troctolites demonstrating that whole rock re os isotopic systematics have remained closed since crystallisation the initial os isotopic composition of the isochron os 1040 200 implies significant magma interactions with radiogenic os that most likely resides in the nain churchill province crust these data are therefore consistent with the parental magma achieving sulphide saturation as a result of contamination by radiogenic crustal components with further addition of base and precious metals as a function of r factor analyses of sulphide separates from the proterozoic tasiuyak churchill and archaean nain gneisses confirm that both units contained significant os 8 6 ppb and 0 38 ppb respectively that was very radiogenic at 1334 ma os 1908 and 5202 respectively yielding crustal residence tchur model ages of 2200 to 2400 ma however these model ages may have been affected by re and or os mobility during the 1 85 ga torngat and 1 1 ga grenville orogeny re os isotopic modelling suggests that a reasonable fit to the ore data may be obtained via bulk crustal contamination of magmas parental to the nain plutonic suite nps with either tasiuyak 2 contamination or nain 16 contamination gneiss followed by an r factor process 200 to 1000 which improved the tenor of the sulphide liquid during transport in active magma conduits or after deposition in an active replenished voisey s bay intrusion magma chamber however the dominance of plagioclase rich high al2o3 magmas in the mafic members of the nps troctolites and anorthosites may indicate that other deeper forms of lithospheric interaction potentially involving mafic lower crust may be crucial to understanding this style of magmatic sulphide ore system

revisiting the circulation of the east australian current its path separation and eddy field abstract the traditional view of the east australian current eac as depicted in many schematics is of a continuous boundary current that flows along the shelf off eastern australia between approximately 18 s and about 32 5 s where it separates from the coast and continues either towards new zealand along the tasman front or towards tasmania as the eac extension additionally it is widely recognised that eddies are prevalent in the eac region particularly south of the eac separation we revisit this long standing paradigm and suggest that the eac is perhaps better viewed as a continuous meandering stream flowing adjacent to the coast that feeds a field of mesoscale eddies observations show that eac eddies are prevalent over a broad region of the western tasman sea as far north as 25 s typically with maximum intensity between 30 and 35 s at any instant in time the eac jet is usually evident as a poleward stream adjacent to the continental shelf edge other commonly accepted components of the eac system including the tasman front and eac extension are rarely seen as distinct identifiable features rather these features are evident only in time mean fields when the eddy variability is filtered out it is also common for the eac to be spatially discontinuous due to the presence of eddies often with multiple short streams that sometimes separate and re attach to the coast recognition of the eac as an eddy dominated current system has seen many recent studies focus on various aspects of eddies in the eac system providing new insights into mesoscale ocean dynamics recent studies of individual eddies have shown that the circulation within eddies including tilting and vertical motion is more complex than previously understood a summary of these studies along with a review of the eac system particularly its path separation and eddy field is presented here