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

a 6 year record of baroclinic transport variability of the antarctic circumpolar current at 140 e derived from expendable bathythermograph and altimeter measurements 1 repeat hydrographic sections across the antarctic circumpolar current are used to derive an empirical relationship between upper ocean temperature and the baroclinic transport stream function cross validation shows this relationship can be used to infer baroclinic transport above and relative to 2500 dbar from temperature measurements with an error of a few per cent the mean transport distribution derived from 31 austral summer expendable bathythermograph xbt sections over a 6 year period consists of westward flow immediately south of tasmania a broad band of strong eastward flow between 50 and 55 s and three cores of eastward flow south of 55 s by defining a second empirical relationship between surface dynamic height and cumulative transport a continuous time series of baroclinic transport is derived from altimeter measurements of sea surface height transports derived from altimetry in this way agree well with simultaneous in situ estimates root mean square error in net transport is 4 106 m3 s 1 suggesting sea level anomalies largely reflect baroclinic changes above 2500 dbar the 10 day sampling of the altimeter transport time series shows the irregular xbt sampling aliases variability at unresolved timescales the standard deviation of net transport above and relative to 2500 m is 4 3 106 m3 s 1 the variability in net transport is largest 2 7 106 m3 s 1 in the quasi annual band periods of 4 months to 1 5 years slightly smaller 2 3 106 m3 s 1 in the mesoscale band 1 5 years 1 5 106 m3 s 1 changes in transport are correlated with local changes in both wind stress and wind stress curl in the quasi annual and interannual bands but the transport time series is too short to draw significant conclusions

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

variability and forcing of the east australian current 1 the spatial and temporal variability of the east australian current eac is investigated using 6 years 1993 1998 of surface geostrophic stream function from an optimal interpolation of altimeter sea surface heights and velocities derived from tracking thermal features in satellite imagery variability appears as a series of cyclones and anticyclones propagating southwestward and westward with periods between 90 and 180 days the behavior of the variability changes over the 6 years energy in the mesoscale frequencies moves slowly south and diminishes with more westward propagation in the region where the current separates from the coast we find no evidence for a consistent forcing of the eac by mesoscale signals propagating westward from the south pacific basin we suggest that the observations are consistent with variability originating between 32 s and 35 s through intrinsic instabilities of the current

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

decadal variability of east australian current transport inferred from repeated high density xbt transects a ctd survey and satellite altimetry a time series of the net geostrophic transport through the tasman sea representing the flow of the east australian current eac extension is determined from a full depth ctd section 15 years of high density xbt transects and satellite altimetry data a section between sydney and wellington px34 has been occupied four times per year since 1991 with high resolution xbt sampling two methods to infer baroclinic transport from proxy data along the section are presented the first uses shallow xbt transects to derive geostrophic transport relative to a deep 2000 m reference level in the second approach synts the subsurface temperature and salinity structure are inferred from satellite surface height and temperature fields using a model developed from historical in situ observations the baroclinic transport is then computed in the usual manner the methods are validated using both a full depth ctd occupation of the px34 section and further transects crossing the eac in the northern tasman sea there is close agreement between the 49 xbt and synts px34 transport estimates obtained between 1992 and 2006 the time series of transport through the sydney wellington section shows a range of temporal signals from eddyscale seasonal interannnual to decadal in particular we note that the net eac flow ranges from 5 sv in 1995 to a maximum of 16 sv in 2000 2001 this decadal variation confirms the eac response to a spin up of the south pacific circulation forced by changes in the basin wide winds and matches the changes in oceanic properties observed in the tasman sea

east australian current volume transports at 30 s estimates from the world ocean circulation experiment hydrographic sections pr11 p6 and the pcm3 current meter array between september 1991 and march 1994 the oceanic region off the east coast of australia at 30 s was the subject of an intense observational program part of the world ocean circulation experiment the objective was to improve our understanding of the dynamics of the east australian current eac and to measure its volume and energy flux the two main components were the pacific current meter array 3 pcm3 with six moorings spanning a total distance of 120 km and repeat high resolution hydrographic surveys the long term average frompcm3 shows the eac as a narrow swift and highly variable current centered at 40 km from the coast with strong shear in the upper 1000 m and mean southward velocities of 0 6 m s 1 in the core the measurements also revealed a thick countercurrent underneath the poleward flow the mean volume transport for the entire section covered by the array between the coast and 154 4 e was 22 1 4 6 sv toward the south with an rms variability of 30 sv combining the data from the pcm3 array with the hydrographic sections generated nine detailed snapshots of the absolute geostrophic current field the snapshots were used to evaluate the reliability of the pcm3 data for determining volume transports the rms difference between transports derived from direct current observations and from hydrographie data was 3 8 sv indicating that the pcm3 array can be used to describe the current variability despite the sparse spatial distribution of velocity measurements transport variability was dominated by periods between 90 and 140 days which are attributed to eddy shedding in the region occasional intense northward flow events were observed where total transports reached up to 50 sv northward on those occasions the southward boundary current changed from being surface intensified and mainly baroclinic to northward and more barotropic related to the northward migration past the array of the eac coastal separation point

storm tracks in the southern hemisphere subtropical oceans ocean storm tracks have previously been associated with the midlatitude western boundary currents wbcs and the antarctic circumpolar current acc here we identify and examine large scale baroclinically unstable waves occurring within waveguides associated with potential density gradients in the subtropical regions of the southern hemisphere sh oceans where the trade winds and westerlies meet and at depths associated with mode water formation in contrast to the northern hemisphere subtropics the sh pathways are more extensive allowing large scale coherent disturbances to communicate information westward from the midlatitudes to the subtropics south pacific ocean and from the subtropics to the tropics indian ocean particular consideration is given to the subtropical south pacific ocean as this is a region where resonant interactions between large scale rossby waves and significant topographic features have been reported to occur using an ocean general circulation model and a simple potential energy transfer diagnostic we identify the relevant nonlinearly modified structures comparing their propagation characteristics to planetary rossby waves calculated using a shallow water model although at first appearance baroclinic disturbances resemble planetary rossby waves we show they are inherently nonlinear multiscale and are amplified where topography occurs the location of the disturbances coincides with regions of high variability in sea surface height observed in satellite altimetry and their speeds closely match the large scale coherent westward propagating structures described in the observational literature our study provides evidence that in addition to the midlatitude wbcs and the acc significant ocean storm tracks are also manifest in the sh subtropics

a numerical modeling study of the east australian current encircling and overwashing a warm core eddy 1 warm core eddies wces often form in the meanders of western boundary currents wbcs wces are frequently overwashed with less dense waters sourced from the wbc we use the regional ocean modelling system to investigate the ocean state during the overwashing of one such wce in october 2008 in the east australian current eac comparisons of model outputs with satellite sea surface temperature and vertical profiles show that the model provides a realistic simulation of the eddy during the period when the eac encircled and then overwashed the eddy during the encircling stage an eddy with closed circulation persisted at depth in the surface eac water entered from the north encircled the eddy and exited to the east the overwashing stage was initiated by the expulsion of cyclonic vorticity for the following 8 days after the expulsion waters from the eac washed over the top of the eddy transferring heat and anticyclonic vorticity radially inward after approximately one rotation period of overwashing the eddy separated the overwashing creates a two layer system that forms a subsurface maximum velocity at the interface of the two layers analysis of water mass properties eulerian tracer dynamics and lagrangian particle tracks show that the original eddy sinks 10 50 m during the overwashing period overwashing has been observed in many wbcs and occurs in most wces in the western tasman sea

the east australian current and property transport at 27 s from 2012 to 2013 abstractthe east australian current eac is the complex and highly energetic poleward western boundary current of the south pacific ocean a full depth current meter and property temperature and salinity mooring array was deployed from the continental shelf to the abyssal waters off brisbane australia 27 s for 18 months from april 2012 to august 2013 the eac mooring array is an essential component of the australian integrated marine observing system imos during this period the eac was coherent with an eddy kinetic to mean kinetic energy ratio of less than 1 the 18 month mean poleward only mass transport above 2000 m is 22 1 7 5 sverdrups sv 1 sv 106 m3 s 1 the mean poleward only heat transport and flow weighted temperature above 2000 m are 1 35 0 42 pw and 15 33 c respectively a difference in the poleward only and net poleward mass and heat transports above 2000 m of 6 3 sv and 0 24 pw reflects the presence of an equatorward eac retroflection at the eastern offshore end of the

observing the fluctuations of gyre scale ocean circulation a study of the subtropical south pacific abstract seasonal and interannual variability of the subtropical gyre in the south pacific ocean are investigated by means of a time series of expendable bathythermograph xbt sections between new zealand 36 s 175 e and fiji 18 s 178 e the experiment spans much of the subtropical gyre and is a prototype for future basin scale observations eddy resolving transects along the precisely repeating ship track spanning four years are used to estimate the mean field and fluctuations of temperature and geostrophic velocity the mean field dominates on very large spatial scales while the fluctuations dominate on small scales mean and fluctuations have equal energy at a horizontal wavelength of about 2000 km the study region contains three recurring small scale features these are the east auckland current flowing eastward along the new zealand continental slope a front at about 29 s which is likely an extension of the tasman front and a weaker feature the tropical convergence at about 22 s at lowe

do east australian current anticyclonic eddies leave the tasman sea using satellite altimetry and high resolution model output we analyze the pathway of large long lived anticyclonic eddies that originate near the east australian current eac separation point we show that 25 30 of these eddies propagate southward around tasmania leave the tasman sea and decay in the great australian bight this pathway has not been previously documented owing to poor satellite sampling off eastern tasmania as eddies propagate southward they often stall for several months at near constant latitude along the pathway eddies become increasingly barotropic eddy intensity is primarily influenced by merging with other eddies and a gradual decay otherwise surface temperature anomaly associated with anticyclonic eddies changes as they propagate while surface salinity anomaly tends to remain relatively unchanged as they propagate

flows in the tasman front south of norfolk island the tasman front is a narrow band of eastward flowing subtropical water crossing the tasman sea from australia to north cape new zealand it is the link between the two subtropical western boundary currents of the south pacific the east australian current eac off eastern australia and the east auckland current eauc off northeastern new zealand here we report the first direct measurements of flow in the tasman front from a moored array deployed across gaps in the submarine ridges south of norfolk island and hydrographic and adcp measurements during the deployment and recovery voyages the mean flow through the array over july 2003 to august 2004 was found to be eastward only in the upper 800 m with a transport of 6 sv below 800 m a weak westward mean flow 1 5 sv was measured associated with antarctic intermediate water aaiw using sea surface height to account for additional transport south of the moored array results in a total mean eastward transport between norfolk island and north cape new zealand of 8 sv varying between 4 and 18 sv the measurements show that the tasman front is much shallower than either the eac or eauc both of which extend below 2000 m depth has less transport than either the eac or eauc and has instances of flow reversal thus the tasman front is a weaker connection between the eac and eauc than the paradigm of a contiguous south pacific western boundary current system would suggest

calibrating altimetry to geopotential anomaly and isotherm depths in the western north atlantic sixty two temperature sections were taken to depths of 800 m by aircraft along geosat ground tracks within 1 2 days of the satellite orbit the sections are 500 700 km long and cross the gulf stream and its rings from pairs of sections that repeat on the same ground track collinear differences of geopotential anomaly 0 25 mpa and the depth of the 16 c isotherm were collected as along track signals of the change of baroclinic conditions the corresponding collinear differences of sea elevation were collected from the geosat orbits these difference signals from aircraft and altimeter were fit to one another along common ground track segments by removing residual orbit error as a tilt and bias and proportionally scaling the magnitudes of the signals the ratio of geopotential anomaly to sea elevation by this method is 0 84 0 10 dyn m m 1 that is fluctuations of geopotential anomaly which correlate to sea elevation across the gulf stream are smaller by this proportional value the difference of this ratio from unity is consistent with a barotropic signal of about 0 10 m as estimated from reported measurements of abyssal velocity under the stream because the uncertainties in the aircraft data are of the same order as the scatter in the calibration it is unclear whether greater precision is impeded primarily by these uncertainties or by random barotropic signals the ratio of the displacement of 16 c to sea elevation is 480 75

coral record of variability in the upstream kuroshio current during 1953 2004 the kuroshio current kc one of the most important western boundary currents in the north pacific ocean strongly affects regional hydroclimate in east asia and upper ocean thermal structure limited by few on site observations the responses of the kc to regional and remote climate forcings are still poorly understood here we use monthly coral 18o data to reconstruct a kc transport record with annual to interannual resolution for the interval 1953 2004 the field site is located in southern taiwan on the western flank of the upstream kc increased reduced kc transport would generate strong weak upwelling resulting in relatively high low local coral 18o the upstream kc transport and downstream transport off tatsukushi bay japan covary on interannual and decadal timescales this suggests common forcings such as meridional drift of the north equatorial current bifurcation or zonal climatic oscillations in the pacific the intensities of kc transport off southeastern and northeastern taiwan are in phase before 1990 and anti phase after 1990 this difference may be due to a poleward shift of the subtropical western boundary current as a response to global warming

quantitative mapping of the east australian current encroachment using time series himawari 8 sea surface temperature data the east australian current eac is a highly dynamic western boundary current that exerts significant influences on the marine ecosystem off south east margin of australia for the first time a quantitative mapping of the eac system was conducted using himawari 8 sea surface temperature data and a topographic position index tpi based image processing technique the validation using bluelink reanalysis data suggested good reliability of our mapping results subsequent quantitative examination provides new insights into the eac s cross shelf movement which is a driving force of adjacent slope shelf circulations along the coast of new south wales nsw large scale and high frequency eac encroachment was observed being every 60 80 days upstream 30 32 s and every 90 100 days downstream 33 35 s which is associated with the eac s intrinsic oscillation and eddy shedding downstream the eac encroachment exhibits a 20 day longer period and a double amplitude such dephasing is most likely due to the abrupt change of regime at the eac separation point 32 33 s upstream the eac encroachment also exhibits seasonality being 10 15 km closer to the coast in austral summer which is due to the seasonal eac broadening higher frequency 16 32 days and smaller magnitude eac intrusion was observed along the entire nsw coast 28 37 s which is possibly associated with eac s meanders and frontal eddies in the extension zone 37 30 44 s we observed maximum eac encroachment in summer which is an expression of the seasonal boundary flow off eastern tasmania a dataset of eac encroachment 2015 2017 is available see data availability

the unusual cyclicity of the triassic carnian bleiberg facies of the wetterstein formation drau range austria the carbonate platform of the upper wetterstein formation cordevol of the drau range austria shows a distinct facies differentiation which depends on the palaeotopography although most areas of the platform were permanently flooded a periodically emergent palaeotopographic high bleiberg facies occurred near to the centre of the platform the resulting cyclic sequences are composed of subtidal and intertidal to supratidal carbonates and emersion horizons typical shallowing upward cycles occur as well as deepening upward symmetrical and incomplete cycles these types of cycles with long term emersion phases can be explained by eustatic sea level oscillations it can be shown due to an excellent lithostratigraphy based on distinct emersion horizons that the cycle type varies along a marker bed while the vertical distance between the emersion horizons is retained therefore the cycles cannot be explained by eustatic sea level oscillations alone local events which produce a local relief are necessary

eddy shedding and energy conversions in the east australian current 1 mesoscale variability and eddy shedding in the tasman sea particularly of the east australian current eac is studied through the analysis of remotely sensed observations and outputs from a global ocean model previous observations of the western boundary current separation from the coast showed strong variability at periods ranging between 90 and 140 days we show from satellite altimetric observations that rapid northward migration of the separation point of the eac follows the formation of large eddies at periods of 100 days after an eddy separation event the normally southward flowing current swiftly assumes a more zonal configuration near the separation latitude with a cyclonic circulation developing inshore the formation of large separation eddies is preceded by the southward propagation of sea level anomalies along the east australian continental slope from 25 s sea level anomalies grow as they travel south eventually being pinched off in the form of large anticyclones at 32 s in the current retroflection area energy conversion terms in a global ocean model and in altimetric data suggest both barotropic and baroclinic instability may account for the growth of these anomalies as they propagate south east of the main eac jet there is evidence that eddies may be feeding potential energy back to the mean flow

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

the mean and variability of ocean circulation past northern new zealand determining the representativeness of hydrographic climatologies eastward flow in the tasman sea from the separated east australia current reattaches to the shelf break near north cape new zealand and then continues alongshore to the southeast as the east auckland current a series of three permanent warm core eddies occurs along the offshore side the mean transport of the east auckland current is about 9 sv with an additional 10 sv or more of circulation in the eddies an extensive hydrographic data set archived broad scale expendable bathythermograph xbt data two repeating high resolution xbt transects neutrally buoyant float trajectories and topex altimetric data are used to estimate the temperature and absolute flow fields and to characterize variability the aim is to examine the usefulness of time series information and absolute velocity measurements in the interpretation of hydrographic snapshots and climatologies as well as to describe a region having intrinsic oceanographic interest and complexity issues of representativeness of the hydrographic data of the magnitude and scales of the underlying variability of the existence of permanent fine scale features and of the appropriateness of deep reference levels are addressed directly the relatively well sampled hydrographic climatology is shown to contain the equivalent of as many as 10 independent realizations temperature errors relative to the true mean are typically a few tenths of a degree significant seasonal bias is identified in the surface layer and interannual bias is seen in the position of an eddy near north cape the dynamic height field at 1000 dbar relative to 2000 dbar is similar to estimates based on float trajectories and the assumption of geostrophic dynamics this study underlines the value of time series data in the interpretation of a hydrographic climatology in quantifying the errors in the estimated mean field as well as determining the magnitude and nature of variability it also highlights the fact that the mean circulation of the oceans contains significant mesoscale structure unnoticed in coarsely smoothed climatologies

regional climate variability and ocean heat transport in the southwest pacific ocean the winter of 1992 was the coldest on record in new zealand since the 1940s temperatures in new zealand were as much as 3 c below average with heavy rain and unusual snow the oceanic surface layer in the southwest pacific was also anomalously cold over the same period a world ocean circulation experiment woce hydrographic section p14c between auckland and fiji during september 1992 found cold sea surface temperatures and deep mixed layers near new zealand when compared to 8 years of high resolution expendable bathy thermograph xbt temperature measurements collected along the same transect high nutrient and low dissolved oxygen concentrations in the surface layer indicated recent entrainment of thermocline waters the auckland to fiji xbt section is one of three woce high resolution xbt survey lines in the tasman box region whose boundaries are auckland fiji fiji brisbane and wellington sydney transects plus the australian coast geostrophic shear and transport were estimated from 10 realizations of the tasman box during the period 1991 1993 the time series of geostrophic transport shows that following a convergence in late 1991 early in 1992 there was a substantial divergence of mass in the upper waters equivalent to a thinning of the warm water layer the phase of this anomalous divergence is matched to an observed amplification of the seasonal oceanic heat storage cycle in 1991 1992 the top 200 m average temperature was warmer in the 1992 summer than in 1991 or 1993 but the winter of 1992 was the coldest of the 8 year record along the auckland fiji line the divergence thinning of the warm water layer appears to have preconditioned the region for the exceptionally cold 1992 winter the alternative cool conditions from anomalous air sea heat exchange caused by variability in the wind field is considered unlikely as large fluctuations in heat loss are not observed in the air sea flux data during this period the severe weather conditions and anomalous ocean heat transport are most likely related to the prolonged el nino southern oscillation episode that began in early 1991

high precision u th dating of storm transported coral blocks on frankland islands northern great barrier reef australia abstract high energy storm transported coral blocks are widespread on the reef flats of the great barrier reef gbr australia and have the potential to be used as proxies for reconstructing past storm cyclone events prior to historical or instrumental records in this study samples from 42 individual transported coral blocks were collected from the inshore frankland islands northern gbr for high precision mc icpms u th dating with their surface mortality ages recording the timing of individual storms or cyclones responsible for their uplift from their original growth position the dated mortality ages were found to match well with known historical storm cyclone events in the last century with 80 of them falling within episodes of increased storm activity 1910 1915 1945 1950 1955 1960 1975 1990 1995 2000 ad captured by instrumental historic records confirming that transported coral blocks on inshore reefs can be used as proxies for past storm cyclone occurrences using this approach this study also identified 17 additional storm cyclone events that occurred before european settlement in the 1850s including three oldest events at 758 4 3 7 777 9 4 9 and 985 2 4 8 ad respectively our results despite still preliminary suggest that the storm cyclone activity in this region tends to broadly correlate with the positive modes of the pacific decadal oscillation pdo during the last millennium in addition there appears to be a decreasing age trend from the shore to the reef edge from 758 4 3 7 ad to 1988 3 1 6 ad which can be attributed to sea level fall and or reef island progradation over the last 2000 years

interannual variations of volume transport in the western labrador sea based on topex poseidon and woce data abstract the interannual variations of volume transport in the western labrador sea are estimated using six years of topex poseidon altimeter data and hydrographic data from a woce repeat section and a method based on the linear momentum equation in which the sea surface is the level of known motion the interannual variation of the total transport in spring summer has a range of 6 2 sv sv 106 m3 s 1 and is positively correlated with the fall winter north atlantic oscillation nao index and wind patterns in the northwest north atlantic the total transport anomaly is decomposed into a barotropic and a baroclinic component the interannual change of the barotropic transport is similar to that of the total transport and is positively correlated with the fall winter nao index the baroclinic transport anomaly in comparison has a smaller magnitude and the opposite sign the authors conjecture that the deepened icelandic low in high index years generates a strong cyclonic wind stress curl which in tur

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

trickle or treat the dynamics of nutrient export from polar glaciers cold based polar glacier watersheds contain well defined supraglacial ice marginal and proglacial elements that differ in their degree of hydrologic connectivity sources of water e g snow ice and or sediment pore water meltwater residence times allochthonous and autochthonous nutrient and sediment loads we investigated 11 distinct hydrological units along the supraglacial ice marginal and proglacial flow paths that drain joyce glacier in the mcmurdo dry valleys of antarctica we found that these units play unique and important roles as sources and or sinks for dissolved inorganic nitrogen and dissolved inorganic phosphorus and for specific fractions of dissolved organic matter dom as waters are routed from the glacier into nutrient poor downstream ecosystems changes in nutrient export from the glacial system as a whole were observed as the routing and residence times of meltwater changed throughout the melt season the concentrations of major ions in the proglacial stream were inversely proportional to discharge such that there was a relatively constant trickle of these solutes into downstream ecosystems in contrast no3 concentrations generally increased with discharge resulting in delivery of episodic pulses of dissolved inorganic nitrogen rich water treats into those same ecosystems during high discharge events dom concentrations or fluorescence did not correlate with discharge rate but high variability in dom concentrations or fluorescence suggests that dom may be exported downstream as episodic treats but with spatial and or temporal patterns that remain poorly understood the strong nutrient specific responses to changes in hydrology suggest that polar glacier drainage systems may export meltwater with nutrient compositions that vary within and between melt seasons and watersheds because nutrient dynamics identified in this study differ between glacier watersheds with broadly similar hydrology climate and geology we emphasize the need to develop conceptual models of nutrient export that thoroughly integrate the biogeochemical and

southwest pacific ocean response to a warmer world insights from marine isotope stage 5e paleoceanographic archives derived from 17 marine sediment cores reconstruct the response of the southwest pacific ocean to the peak interglacial marine isotope stage mis 5e ca 125 ka paleo sea surface temperature sst estimates were obtained from the random forest model an ensemble decision tree tool applied to core top planktonic foraminiferal faunas calibrated to modern ssts the reconstructed geographic pattern of the sst anomaly maximum sst between 120 and 132 ka minus mean modern sst seems to indicate how mis 5e conditions were generally warmer in the southwest pacific especially in the western tasman sea where a strengthened east australian current eac likely extended subtropical influence to ca 45 s off tasmania in contrast the eastern tasman sea may have had a modest cooling except around 45 s the observed pattern resembles that developing under the present warming trend in the region an increase in wind stress curl over the modern south pacific is hypothesized to have spun up the south pacific subtropical gyre with concurrent increase in subtropical flow in the western boundary currents that include the eac however warmer temperatures along the subtropical front and campbell plateau to the south suggest that the relative influence of the boundary inflows to eastern new zealand may have differed in mis 5e and these currents may have followed different paths compared to today

upper ocean temperature and the baroclinic transport stream function relationship in drake passage repeat hydrographic sections across the antarctic circumpolar current acc in drake passage are used to derive an empirical relationship between upper ocean temperature and the baroclinic transport stream function cross validation shows this relationship can be used to infer baroclinic transport above and relative to 2500 m from expendable bathythermograph xbt temperature measurements with an error of a few per cent transport errors of less than 2 sv are obtained if temperature at depths between 600 and 1600 m is used to define the relationship temperature at depths above 300 m provides an unreliable index of transport because of variability in temperature salinity t s properties produced by air sea interaction the scatter in the relationship between temperature and stream function from repeat observations along a single line is similar in magnitude to the scatter observed when data from the broader drake passage area are considered in both cases variability about the mean temperature stream function relationship reflects advection of water with anomalous t s properties the tight relationship between temperature and stream function in drake passage and south of australia suggests baroclinic transports can be inferred from xbt temperatures with high accuracy in the southern ocean providing a cost effective means of monitoring acc variability however care must be taken at the end points particularly in the drake passage where the strong flow of the subantarctic front sometimes lies over the continental slope

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

closing the time varying mass and heat budgets for large ocean areas the tasman box abstract the role of oceanic advection in seasonal to interannual balances of mass and heat is studied using a 12 yr time series of quarterly eddy resolving expendable bathythermograph xbt surveys around the perimeter of a region the authors call the tasman box in the southwestern pacific the region contains the south pacific s subtropical western boundary current system and associated strong mesoscale variability mean geostrophic transport in the warm upper ocean temperature greater than 12 c is about 3 8 sv 1 sv 106 m3 s 1 southward into the box across the brisbane australia fiji northern edge net outflows are 3 3 sv eastward across the auckland new zealand fiji edge and 2 7 sv southward across sydney australia wellington new zealand mean ekman convergence of 2 2 sv closes the mass budget net water mass conversions in the upper ocean consist of inflow of waters averaging about 26 c and 35 4 psu balanced by outflow at about 18 c and 35 7 psu and reflect the net evaporation and heat los

on the variability of the east australian current jet structure meandering and influence on shelf circulation given the importance of western boundary currents over a wide range of scales in the ocean it is crucial that we understand their dynamics to accurately predict future changes for this we need detailed knowledge of their structure and variability here we investigate the jet structure of the east australian current eac using observations from hf radars and moorings deployed at 30 s 31 s meandering core velocity width and eddy kinetic energy eke are quantified from 4 years of hourly 1 5 km resolution surface current maps 2012 2016 to obtain the most detailed representation of the surface eac jet to date the eac flows predominantly over the 1 500 m isobath 50 km offshore but makes large amplitude displacements eastward every 65 100 days the time scale associated with mesoscale eddy shedding at the eac separation smaller amplitude higher frequency meanders occur every 20 45 days using a coordinate frame that follows the jet we show core velocity and eke exhibit seasonality in both magnitude and variance being maximum in summer 1 55 m s 1 mean core velocity minimum in winter 0 8 m s 1 however it is the eddy shedding time scale that dominates jet variability as the eac moves shoreward shelf temperature and along stream velocity vary linearly with jet movement within 35 km of the core the eac is within this range 75 of the time demonstrating its importance to the shelf circulation temperature and velocity fluctuations at the 70 m 100 m isobath are more influenced by wind eac encroachment with the strongest response occurring when wind and eac act constructively

optimal estimation of hydrographic station data and derived fields abstract optimal estimation is applied to contouring and analysis of hydrographic sections measured fields such as temperature and salinity and derived fields such as geostrophic velocity are decomposed into large scale and small scale components first a heavily sampled basin scale field is estimated and subtracted from the data a small scale field barely resolved by the hydrography is then found from the residuals the power and utility of the technique are illustrated by means of examples using a short section from the straits of florida and a transatlantic section along 24 n

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

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

a tale of two eddies the biophysical characteristics of two contrasting cyclonic eddies in the east australian current system mesoscale cyclonic eddies are known to be highly productive less well known are the dynamics and productivity of smaller cyclonic eddies known as frontal eddies that form on the landward side of western boundary currents in this study we investigate the physical and biogeochemical properties of two contrasting cyclonic eddies in the east australian current eac the first murphy a mesoscale cyclonic eddy that formed at 28 s with a diameter of 160 km and high surface chlorophyll a concentrations which lived 47 days the second freddy a smaller frontal eddy 35 km diameter that formed from a shelf water billow 7 days prior to sampling at 31 5 s and was advected off the shelf along the eac front from 200m to 4000m of water both eddies were at least 1000m deep with a similar steric height anomaly we introduce and employ the method of closest approach using shipboard adcp velocities to estimate the eddy centers which reveals significant tilting through the water column we estimate rotation rates of 4 10 days and 1 9 days and rossby numbers 0 25 0 1 and 0 6 0 1 from the surface to 600m for murphy and freddy respectively high resolution altimetry measurements from the saral altika satellite provide estimates of the ageostrophic component of rotation our results show that the frontal eddy is significantly more ageostrophic energetic and productive than the mesoscale cyclone despite its small size and short life 4 weeks we suggest that frontal eddies have potential to contribute significantly to the net productivity of the tasman sea region this article is protected by copyright all rights reserved

variability of the atlantic off equatorial eastward currents during 1993 2010 using a synthetic method 1 we have developed validated and applied a synthetic method to monitor the off equatorial eastward currents in the central tropical atlantic this method combines high density expendable bathythermograph xbt temperature data along the ax08 transect with altimetric sea level anomalies slas to estimate dynamic height fields from which the mean properties of the north equatorial countercurrent necc the north equatorial undercurrent neuc and the south equatorial undercurrent seuc and their variability can be estimated on seasonal to interannual timescales on seasonal to interannual timescales the synthetic method is well suited for reconstructions of the necc variability reproduces the variability of the neuc with considerable skill and less efficiently describes variations of the seuc which is located in a region of low sla variability a positive correlation is found between interannual variations of the necc transport and two indices based on an interhemispheric sea surface temperature sst gradient and southeasterly wind stress in the central tropical atlantic the neuc is correlated on interannual timescales with ssts and meridional wind stress in the gulf of guinea and zonal equatorial wind stress this study shows that both altimetry and xbt data can be effectively combined for near real time inference of the dynamic and thermodynamic properties of the tropical atlantic current system

seasonality of sporadic physical processes driving temperature and nutrient high frequency variability in the coastal ocean off southeast australia physical processes forced by alongshore winds and currents are known to strongly influence the biogeochemistry of coastal waters combining in situ observations moored platforms hydrographic surveys and satellite data sea surface wind and sea surface height we investigate the transient occurrence of wind driven upwelling downwelling and current driven upwelling events off southeast australia remote sensed indices are developed and calibrated with multiannual time series of in situ temperature and current measurements at two shelf locations based on archives up to 10 years long climatological analyses of these indices reveal various latitudinal regimes with respect to seasonality magnitude duration of events and their driving mechanisms wind or current generally downwelling favorable winds prevail in this region however we demonstrate that up to 10 wind driven upwelling days per month occur during spring summer at 28 33 5 degrees s and up to 5 days in summer further south current driven upwelling upstream of the east australian current separation zone approximate to 32 degrees s occurs twice as often as downstream using independent in situ data sets we show that the response of the coastal ocean is consistent with our climatology of shelf processes upwelling leads to a large range of temperatures and elevated nutrient concentrations on the shelf maximized in the wind driven case while downwelling results in destratified nutrient poor waters the combination of these sporadic wind and current driven processes may drive an important part of the high frequency variability of coastal temperature and nutrient content our results suggest that localized nutrient enrichment events of variable magnitude are favored at specific latitudes and seasons potentially impacting coastal ecosystems key points multisensor analysis of shelf processes combining in situ and satellite data spatio temporal variability of transient wind and current driven up downwelling cold nutrient rich water intrusions favoured at specific locations seasons

seasonal circulation around tasmania an interface between eastern and western boundary dynamics 1 the seasonal circulation connecting the pacific and indian oceans around tasmania is documented using seasonal maps from satellite altimetry and sea surface temperature sst and in situ mean fields from a high resolution climatology of the region commonwealth scientific and industrial research organisation csiro atlas of regional seas cars in general the surface variability displays a very different character off the east and west coasts off the east coast the variability is generated externally being dominated by the western boundary dynamics of the east australian current eac in the west it is weaker and arises from the seasonal rise and fall of the coastal sea level which is due to the seasonal reversing wind patterns a high variability tongue associated with the eac stretches poleward off the east coast tracing out a waveguide between the major topographic structures it has a broad peak in power between 180 and 365 days 0 08 m which is a surface height expression of the energetic mesoscale eddy activity associated with the eac distinctive summer and winter patterns of the surface circulation are described which are influenced by the eac and the zeehan current zc respectively on the east coast in summer january march there is a poleward advection of warm saline water forced by an episodic coastal boundary flow the cross shelf pressure gradient driving this flow is formed from the difference between the seasonal changes in coastal sea level and the offshore eddies there is a seasonal reversal of this flow in winter with cool fresh modified subantarctic surface waters drawn up from the south off the west coast the zeehan current operates 180 out of phase with the eac it is strongest in winter when it projects warm relatively saline waters down the western tasmania coast and around the southern tip of tasmania there is a sharp division between the eac and zc influence adjacent to the tasman peninsula off southeast tasmania

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

observations of variability in the south pacific subtropical gyre abstract variability of the subtropical gyre in the south pacific ocean was investigated using high resolution expendable bathythermograph sections along a repeated track between new zealand and hawaii the southern part of the section sampled most of the zonal flow in the subtropical gyre with the eastward flowing branch between new zealand and fiji and the westward branch extending north of fiji to approximately 10 s the time series began in september 1987 and extended through 1994 averaging four cruises every year the geostrophic shear field was calculated relative to 800 m with the aid of a mean t s relationship variability was present at a broad range of spatial and temporal scales but annual fluctuations were particularly prominent the authors conclude that 30 snapshots of temperature measured over a period of seven years are sufficient to resolve the annual cycle of the gyre scale circulation along the transect the shape and intensity of the gyre varied seasonally throughout the water c