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 biogeochemical changes in the subtropical indian ocean associated with subantarctic mode water within the subantarctic mode water samw density level we study temporal changes in salinity nutrients oxygen and ttd transit time distribution ages in the western w and eastern e subtropical gyre of the indian ocean io from 1987 to 2002 additionally changes in total alkalinity ta and dissolved inorganic carbon dic are evaluated between 1995 and 2002 the mechanisms behind the detected changes are discussed along with the results from a hindcast model run community climate system model the increasing salinity and decreasing oxygen trends from 1960 to 1987 reversed from 1987 to 2002 along the gyre in the w io a decreasing trend in ttd ages points to a faster delivery of samw thus less biogenic matter remineralization explaining the oxygen increase and noisier nutrients decrease in the e io samw no change in ttd ages was detected therefore the trends in oxygen and inorganic nutrients relate to changes in the antarctic surface water transported into the e io samw formation area in the w io between 1995 and 2002 the dic increase is equal or even less than the anthropogenic input as the reduction in remineralization contributes to mask the increasing trend in the e io between 1995 and 2002 dic decreases slightly despite the increase in the anthropogenic input differences in the preformed e io samw conditions would explain this behavior trends in the w and e io samw are decoupled and related to different forcing mechanisms in the two main sites of samw formation in the io at 40 s 70 e and 45 s 90 e respectively

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

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

atlantic meridional overturning circulation and the southern hemisphere supergyre 1 the ocean s role in climate manifests itself through its high heat capacity its own rich internal dynamics and its ability to transport vast quantities of heat and freshwater of particular interest is the global ocean circulation associated with the atlantic meridional overturning amoc because observations are sparse the detailed global structure of the amoc remains poorly understood particularly the pathways along which water returns to the atlantic to compensate the export of north atlantic deep water nadw here we provide the first quantitative 3 dimensional global view of the amoc using a lagrangian reconstruction which integrates hundred of thousands water particle trajectories in an ocean model the resulting pattern elucidates the role of the wind in structuring the pathways of the amoc in particular the lagrangian analysis reveals a strong link with the three subtropical gyres of the southern hemisphere sh which merge into a supergyre spanning the three ocean basins the coupling between the upper ocean wind driven circulation and the overturning in the model suggests that changes in the sh winds can alter the pathways of the amoc and therefore the water properties and the associated heat and freshwater transports

low frequency variability of south pacific tropical water from argo based on the argo floats data the low frequency salinity variability of the south pacific tropical water sptw is investigated in this study subsurface salinity along the 24 5 surface in the south pacific subtropical gyre exhibits a trend with dipole like structure during 2004 2012 the northern flank of the sptw gets fresher by 0 3 practical salinity unit psu while the southern flank gets saltier by 0 2 psu suggesting a poleward shift of the water mass salinity along the sptw core shows a relatively weak interannual variability with a peak to peak amplitude of 0 05 psu such a subsurface salinity variability seems to be connected with the sea surface salinity variability in the sptw formation region and the dipole like structure of the salinity trend is further linked to the decadal variability of the evaporation minus precipitation in this region

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

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

delayed holocene reappearance of g menardii the planktonic foraminifera globorotalia menardii absent in the atlantic ocean during the last glacial period reappeared during the holocene as it was present in the indian ocean during glacial time its reappearance might be thought to have been connected to rejuvenation of conveyor circulation but as first shown by glenn jones and confirmed here it was a significant contributor to the atlantic s foraminifer population only after 7000 years ago

mongolian summits an uplifted flat old but still preserved erosion surface in gobi altay and altay mongolia several flat surfaces worn through basement rocks and uplifted during the ongoing tectonic episode to a similar altitude of 4000 m suggests disruption of a single large scale surface new thermochronology and field data show that the plateau surfaces represent uplifted parts of an ancient peneplain that formed during jurassic time the gobi altay and altay flattopped massifs are tectonically and geomorphologically unique their preservation for 150 m y implies that no further tectonic movements occurred before the onset of the last deformation episode 5 3 m y ago it also suggests that very low erosion rates were maintained by a dry climate over millions of years

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

radiocarbon evidence for mid late holocene changes in southwest pacific ocean circulation variability in the southwest sw pacific ocean circulation is influenced by the changes in the south pacific subtropical gyre and its western boundary current the east australian current eac the eac plays a significant role in transporting warm well ventilated nutrient poor waters to more temperate higher latitudes recent climate changes associated with eac intensification have led to anomalous warming in the south tasman with implications for marine ecosystems and environment a clear understanding of the significance of these changes requires knowledge of past natural variability here we have reconstructed a 4500 year record of regional sea surface radiocarbon reservoir ages r and local reservoir effects r our results reveal the centennial scale variability over the last 4500 years with r ranges as large as 390 14c yr older r 410 14c yr between 1610 to 1860 a d in our record corresponding to the little ice age suggests a weaker influence of the eac in the south tasman between 4000 and 1900 cal years b p r and r were significantly younger than the modern with values of 170 and 130 14c yr respectively indicating increased eac transport of tropical waters into the south tasman we propose that the large r variability was influenced by strong and abrupt el nino events which punctuated the muted el nino southern oscillation enso period in the mid late holocene and enabled increased westward flow of gyre waters into the sw pacific the strengthening of the eac extension appears to have been a response to the precession modulated enso southern annular mode interactions

the denudation history of the onshore continental margin of se brazil inferred from apatite fission track data a suite of 68 new apatite fission track analysis results from the onshore rift margin in southeast brazil are presented some of the results reflect resetting related to the eruption of the parana continental flood basalt 130 ma and four others are directly related to late cretaceous magmatism 80 ma the majority of the results were obtained from precambrian basement rocks and sediments from the parana basin the fission track ages broadly increase inland from 60 90 ma on the coastal plain to 300 ma in the continental hinterland the track length distributions show a characteristic trend being negatively skewed at the coast and showing increasing bimodality inland except for the oldest samples which are more unimodal these trends do not reflect rift related heating and resetting but are the result of protracted denudation since the opening of the south atlantic the results are consistent with more than 3 km of exhumation on the coastal plain but little more than 1 km in the hinterland the topographic morphology in the northern region of the study area is complex and is clearly influenced by structure and bedrock lithology for the region further south model calculations of the isostatic response to the denudation suggest that isostatic rebound makes a minor contribution to the long wavelength topography unless the flexural rigidity is more than 1025 n m in this case the initial elevation of the rift margin would need to be 2 5 km in order to accommodate the amount of denudation inferred from the fission track data however it is possible that the effective flexural rigidity varies across the margin becoming greater in the continental interior alternatively the broad scale wavelength topography may be the result of magmatic underplating related to the parana continental flood basalt event if so estimates of the volume of magma generated would need to be revised upward by as much as a factor of 5

u pb dating of granites in the neoproterozoic sergipano belt ne brazil implications for the timing and duration of continental collision and extrusion tectonics in the borborema province abstract the sergipano belt is the outcome of collision between the pernambuco alagoas massif and the sao francisco craton during neoproterozoic assembly of west gondwana field relationships and u pb geochronology of granites intruded in garnet micaschists of the macurure domain are used to constrain the main collisional event d 2 in the belt the granites are divided into two groups the pre collisional granites pre to early d 2 and the syn collisional granites syn to tardi d 2 the latter were emplaced as sheets along the s 2 axial plane foliation or they were collected at the hinge zones of f 2 folds a u pb shrimp zircon age of 628 12 ma was obtained for the pre collisional camara tonalite two u pb tims titanite ages were obtained for the syn collisional granites 584 10 ma for the angico granite and 571 9 ma for the pedra furada granite and these ages are close to the garnet whole rock sm nd isochron of 570 ma found for the peak of metamorphism in the sergipano belt the ages of the camara tonalite 628 ma and the pedra furada granite 571 ma mark respectively the maximum age for beginning of the d 2 event and minimum age for the end in the macurure domain using these ages the main neoproterozoic d 2 collisional event has been in operation in the sergipano belt for at least 57 million years correlation with coeval granitoids farther north in the borborema province indicate that while in the sergipano belt the syn d 2 granites ca 590 570 ma were emplaced under compression in the borborema province they emplaced under extensional conditions related to regional strike slip shear zones these contrasting emplacement settings for contemporaneous neoproterozoic granitoids are explained by a combination of continent continent collision and extrusion tectonics

40ar 39ar geochronological constraints on the evolution of lateritic iron deposits in the quadrilatero ferrifero minas gerais brazil weathering profiles overlying the sapecado pico and andaime iron ore deposits quadrilatero ferrifero qf minas gerais brazil reach depths of 150 400 m and host world class supergene iron orebodies in addition to hosting supergene ore bodies of global economic significance weathered banded iron formations at the quadrilatero ferrifero and elsewhere e g carajas hamersley are postulated to underlie some of the most ancient continuously exposed weathering profiles on earth laser incremental heating 40ar 39ar results for 69 grains of hollandite group manganese oxides extracted from 23 samples collected at depths ranging from 5 to 150 m at the sapecado pico and andaime deposits reveal ages ranging from ca 62 to 14 ma older mn oxides occur near the surface while younger mn oxides occur at depth however many samples collected at the weathering bedrock interface yield ages in the 51 41 ma range suggesting that the weathering profiles in the quadrilatero ferrifero had already reached their present depth in the paleogene the antiquity of the weathering profiles in the quadrilatero ferrifero is comparable to the antiquity of dated weathering profiles on banded iron formations in the carajas region brazil and the hamersley province western australia the age versus depth distributions obtained in this study but not available for other regions containing similar supergene iron deposits suggest that little further advance of the weathering front has occurred in the quadrilatero ferrifero lateritic profiles during the neogene the results suggest that weathering in some of these ancient landscapes is not controlled by the steady state advance of weathering fronts through time but may reflect climatic and geomorphological conditions prevailing in a remote past the geochronological results also confirm that the ancient landsurfaces in the quadrilatero ferrifero probably remained immune to erosion for tens of millions of years deep weathering mostly in the paleogene combined with low erosion rates account for the abundance and widespread distribution of supergene iron manganese and aluminum orebodies in this region

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 annual cycle of circulation of the southwest subtropical pacific analyzed in an ocean gcm abstract an ocean gcm interpreted in light of linear models and sparse observations is used to diagnose the dynamics of the annual cycle of circulation in the western boundary current system of the southwest pacific ocean the simple structure of annual wind stress curl over the south pacific produces a large region of uniformly phased stationary thermocline depth anomalies such that the western subtropical gyre spins up and down during the year directing flow anomalies alternately toward and away from the boundary at its northern end near 10 s the response of the western boundary currents is to redistribute these anomalies northward toward the equator and southward to the subtropical gyre a redistribution that is determined principally by linear rossby processes not boundary dynamics when the subtropical gyre and south equatorial current sec are strong in the second half of the year the result is both increased equatorward transport of the new guinea coastal current and poleward transport a

geochronological evidence for pervasive miocene weathering minas gerais brazil ar 40 ar 39 laser incremental heating analyses of 22 individual grains of supergene cryptomelane from three weathering profiles up to 400 km apart in the rio doce valley and barbacena regions at minas gerais brazil show that the formation of weathering profiles in these regions is contemporaneous suggesting a strong weathering event in the middle to late miocene 10 8 ma the preservation of these miocene samples at or near the present surface suggests that either erosion rates have been very low in the region since the miocene or that a much thicker weathering mantle was present in the region originally assuming a constant thickness of weathering profiles in the region throughout the tertiary we may calculate weathering front propagation rates of 4 8 m myr 1 during the past 10 ma copyright c 2004 john wiley sons ltd

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

drivers of decadal variability in the tasman sea in this study we compare optimally interpolated monthly time series tasman sea xbt data and a comprehensive set of ocean data assimilation models forced by atmospheric reanalysis to investigate the stability of the tasman sea thermocline and the transport variability of the east australian current eac the tasman front and eac extension we find that anomalously weaker eac transport at 25 s corresponds to an anomalously weaker tasman front and anomalously stronger eac extension we further show that post about 1980 and relative to the previous 30 years the anomalously weaker eac transport at 25 s is associated with large scale changes in the tasman sea specifically stronger stratification above the thermocline larger thermocline temperature gradients and enhanced energy conversion significant correlations are found between the maria island station sea surface temperature sst variability and stratification thermocline temperature gradient and baroclinic energy conversion suggesting that nonlinear dynamical responses to variability in the basin scale wind stress curl are important drivers of decadal variability in the tasman sea we further show that the stability of the eac is linked via the south caledonian jet to the stability of the pan basin subtropical south pacific ocean storm track

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

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

apatite fission track thermochronology of the precambrian aksu blueschist nw china implications for thermo tectonic evolution of the north tarim basement the precambrian aksu blueschist is located in the northwestern margin of the tarim block nw china in recent decades many studies were carried out with focus on the metamorphic age however a complete understanding of the evolution of the tarim block requires the cooling history of the precambrian metamorphic rocks and the time temperature paths as determined by low temperature thermochronometry therefore apatite fission track aft technique was applied on the precambrian aksu blueschist to reveal the thermo tectonic evolution of the north tarim basement all of the six blueschist samples analysed in this study yielded aft ages spanning 107 5 62 5 ma much younger than the blueschist facies metamorphic age of neoproterozoic and confined track lengths are between 10 46 and 12 12 m based on regional stratigraphic sequences the aft thermal history modeling as well as previous chronological results the thermo tectonic evolution of the aksu blueschist can be roughly reconstructed with four stages 1 the precambrain aksu blueschist exhumed to the surface soon after its formation erosion during the early sinian is indicated by the lack of sedimentation until the late sinian 2 the late sinian strata are continuous while the middle upper silurian and the lower middle carboniferous strata are absent the total thickness of the late sinian and paleozoic strata probably reached 10 000 m and resulted in the total annealing and thermal resetting of aft ages 3 the aft ages in the cretaceous are related with the widespread uplift in tian shan and its adjacent regions that restarted the aft clock during the late mesozoic these reflect a distant effect of the collision of the lhasa terrane with eurasia in the late jurassic early cretaceous and 4 sediments of cenozoic are documented in the aksu area the aksu blueschist was heated to partial annealing zone with the overlying cenozoic sediments during miocene time the aksu blueschist was re exhumed which was probably a distant response to the ongoing india eurasia convergence

the importance of apatite composition and single grain ages when interpreting fission track data from plutonic rocks a case study from the coast ranges british columbia abstract fission track results determined from granitic rocks exposed within the coast ranges of british columbia indicate that significant variations in apatite chemistry may occur in small plutonic rock samples to test ages determined earlier by parrish using the population method of fission track dating new apparent apatite ages were completed using the external detector method so that single grain ages could be generated in most cases the new apatite ages were similar to the earlier ones within 2 however in many cases it was found that individual samples contained significant variations in single grain apatite ages microprobe analyses showed the spread in ages were directly related to variations in apatite chemistry such that chlorine rich apatites retained older ages than fluorine rich grains examination of the single grain age data suggested that the spread in single grain ages provided information which constrained the thermal history of the sample and that distributions of single grain ages reflected the temperatures at which they resided during cooling these results suggest that it is important to generate more than a few single grain fission track ages when dating apatite from granitic rocks since variations in the chlorine concentration in apatite grains may exist in kg sized granitic rock samples therefore it is no longer a valid assumption that each apatite grain separated from a small granite sample will have a similar chlorine concentration and in future apatite fission track studies of granitic terrains it is important to recognize that the apatite composition might be heterogeneous when interpreting results

the role of eddies in the southern ocean temperature response to the southern annular mode the role of eddies in modulating the southern ocean response to the southern annular mode sam is examined usinganoceanmodelrunatmultipleresolutionsfromcoarsetoeddyresolving thehigh resolution versionsof the model showan increase in eddy kinetic energy that peaks 2 3 yr after a positive anomalyin the sam index previous work has shown that the instantaneous temperature response to the sam is characterized by predominant cooling south of 458s and warming to the north at all resolutions the model captures this temperatureresponse this responseis also evidentin the coarse resolution implementation of the model with no eddy mixing parameterization showing that eddiesdo not play an important role in the instantaneous response on the longer time scales an intensification of the mesoscale eddy field occurs which causes enhanced poleward heat flux and drives warming south of the oceanic polar front this warming is of greater magnitude and occurs for a longer period than the initial cooling response the results demonstrate that this warming is surface intensified and strongest in the mixed layer non eddy resolving models are unable to capturethedelayededdy driventemperatureresponsetothesam theauthorsthereforequestiontheability

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

cenozoic uplift of nuussuaq and disko west greenland elevated erosion surfaces as uplift markers of a passive margin remnants of a high plateau have been identified on nuussuaq and disko central west greenland we interpret the plateau as an erosion surface the summit erosion surface formed mainly by a fluvial

denudation history of the bocaina plateau serra do mar southeastern brazil relationships to gondwana breakup and passive margin development abstract the bocaina plateau which is situated on the eastern flank of the continental rift of southeastern brazil is the highest part of the serra do mar topographic relief in this area is suggested to be closely related to its complex tectono magmatic evolution since the breakup of western gondwana and opening of the south atlantic ocean apatite fission track ages and track length distributions from 27 basement outcrops were determined to assess these hypotheses and reconstruct the denudation history of the bocaina plateau the ages range between 303 32 and 46 5 ma and are significantly younger than the stratigraphic ages mean track lengths vary from 13 44 1 51 to 11 1 1 48 m with standard deviations between 1 16 and 1 83 m contrasting ages within a single plateau and similar ages at different altitudes indicate a complex regional tectonothermal evolution the thermal histories inferred from these data imply three periods of accelerated cooling related to the early cretaceous continental breakup early cretaceous alkaline magmatism and the paleogene evolution of the continental rift of southeastern brazil the oldest fission track ages 200 ma were obtained in the serra do mar region suggesting that these areas were a long lived source of sediments for the parana bauru and santos basins

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

frontal movements and property fluxes contributions to heat and freshwater trends in the southern ocean we examine the synoptic variability of temperature and salinity in the southern ocean using a static gravest empirical mode gem mapping based on historical hydrography and a time evolving projection of the gem created using satellite altimetry satgem the gem and satgem projections allow the separation of observed trends into a component due to a shift of the circumpolar fronts adiabatic using the satgem and a component due to changes in water masses diabatic expressed as a temporal trend in residual between historical hydrography and the static gem the mean southward movement of the antarctic circumpolar current acc fronts drives an adiabatic warming of 1 196 0 090 w m 2 distributed over most of the acc and at all depths this is strongest where the meridional temperature gradient is largest such as in the upper 1000 dbar of the subantarctic front saf there is a weak adiabatic freshening of 6 57 0 18 mm yr 1 m 2 concentrated mainly below the antarctic intermediate water and south of the saf residuals between historical hydrography and the static gem field driven by diabatic changes in the water mass structure have temporal trends in temperature and salinity when these trends are integrated over the whole acc there is a net cooling of 0 628 0 129 w m 2 and strong freshening of 30 27 0 70 mm yr 1 m 2 by combining the diabatic and adiabatic components and integrating over the acc the net increase in heat and freshwater in the region is 0 570 0 099 w m 2 and 36 91 0 72 mm yr 1 m 2 respectively the sum of the adiabatic and diabatic changes are consistent with previous trends inferred from observations

late cretaceous reactivation of major crustal shear zones in northern namibia constraints from apatite fission track analysis abstract namibia s passive continental margin records a long history of tectonic activity since the proterozoic the orogenic belt produced during the collision of the congo and kalahari cratons in the early proterozoic led to a zone of crustal weakness which became the preferred location for tectonism during the phanerozoic the pan african damara mobile belt forms this intraplate boundary in namibia and its tectonostratigraphic zones are defined by ductile shear zones where the most prominent is described as the omaruru lineament waterberg thrust oml wt the prominance of the continental margin escarpment is diminished in the area of the central and northern zone of the damara belt where the shear zones are located this area has been targeted with a set of 66 outcrop samples over a 550 km long 60 km broad coast parallel transect from the top of the escarpment in the south across the damara sector to the kamanjab inlier in the north apatite fission track age and length data from all samples reveal a regionally consistent cooling event thermal histories derived by forward modelling bracket this phase of accelerated cooling in the late cretaceous maximum palaeotemperatures immediately prior to the onset of cooling range from ca 120 to ca 60 c with the maximum occurring directly south of the omaruru lineament because different palaeotemperatures indicate different burial depth at a given time the amount of denudation can be estimated and used to constrain vertical displacements of the continental crust we interpret this cooling pattern as the geomorphic response to reactivation of basement structures caused by a change in spreading geometry in the south atlantic and south west indian oceans

wind forced variability in eddy formation eddy shedding and the separation of the east australian current the east australian current eac like many other subtropical western boundary currents is believed to be penetrating further poleward in recent decades previous observational and model studies have used steady state dynamics to relate changes in the westerly winds to changes in the separation behavior of the eac as yet little work has been undertaken on the impact of forcing variability on the eac and tasman sea circulation here using an eddy permitting regional ocean model we present a suite of simulations forced by the same time mean fields but with different atmospheric and remote ocean variability these eddy permitting results demonstrate the nonlinear response of the eac to variable nonstationary inhomogeneous forcing these simulations show an eac with high intrinsic variability and stochastic eddy shedding we show that wind stress variability on time scales shorter than 56 days leads to increases in eddy shedding rates and southward eddy propagation producing an increased transport and southward reach of the mean eac extension we adopt an energetics framework that shows the eac extension changes to be coincident with an increase in offshore upstream eddy variance via increased barotropic instability and increase in subsurface mean kinetic energy along the length of the eac the response of eac separation to regional variable wind stress has important implications for both past and future climate change studies

morphotectonics of a high plateau on the northwestern flank of the continental rift of southeastern brazil abstract integration of landform and structural analysis allowed the identification of late pleistocene holocene pulses of tectonic activity in the campos do jordao plateau with ages and regimes similar to the ones from the continental rift fault reactivation along precambrian shear zones give rise to a series of conspicuous morphotectonic features determine the formation of stream piracy phenomena and divide the plateau into smaller blocks recognition of these tectonic pulses as well as of their effects in landform development particularly clear on the campos de sao francisco at the highest area of the se edge of the plateau show that besides the climate related quaternary environmental changes significant neotectonic instability should be considered in the geomorphic evolution of the campos do jordao plateau

quantifying passive margin denudation and landscape development using a combined fission track thermochronology and cosmogenic isotope analysis approach abstract a new approach to empirically constraining numerical models of denudation and landscape development across passive continental margins is presented involving a combination of apatite fission track thermochronology and cosmogenic isotope analysis this integrated strategy is applied to the namibian sector of the south west african margin where the conventional landscape evolution model of inland retreat of an escarpment initiated at the coast at break up implies a mean rate of retreat of 1 km ma 1 the thermochronological and cosmogenic isotope data are incompatible with a simple escarpment retreat model since they show that denudation rates oceanward of the present escarpment position have been low 1 since the end of the eocene and the estimated rate of escarpment retreat has been only 10 m ma 1 this low rate of retreat is however consistent with numerical landscape evolution models where the escarpment is pinned at an inland drainage divide

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

simulated effects of southern hemispheric wind changes on the pacific oxygen minimum zone a coupled ocean biogeochemistry circulation model is used to investigate the impact of observed past and anticipated future wind changes in the southern hemisphere on the oxygen minimum zone in the tropical pacific we consider the industrial period until the end of the 21st century and distinguish effects due to a strengthening of the westerlies from effects of a southward shift of the westerlies that is accompanied by a poleward expansion of the tropical trade winds our model results show that a strengthening of the westerlies counteracts part of the warming induced decline in the global marine oxygen inventory a poleward shift of the trade westerlies boundary however triggers a significant decrease of oxygen in the tropical oxygen minimum zone in a business as usual co2 emission scenario the poleward shift of the trade westerlies boundary and warming induced increase in stratification contribute equally to the expansion of suboxic waters in the tropical pacific

the position of the amazonian craton in supercontinents abstract this paper examines the extensive regions of proterozoic accretionary belts that either formed most of the amazonian craton or are marginal to its southeastern border their overall geodynamic significance is considered taking into account the paleogeographic reconstruction of columbia rodinia and gondwana amazonia would be part of columbia together with laurentia north china and baltica forming a continuous continental landmass linked by the paleo to mesoproterozoic mobile belts that constitute large portions of it the rodinia supercontinent was formed in the mesoproterozoic by the agglutination of the existing cratonic fragments such as laurentia and amazonia during contemporary continental collisions worldwide the available paleomagnetic data suggest that laurentia and amazonia remained attached until at least 600 ma since all other cratonic units surrounding laurentia have already rifted away by that time the separation between amazonia and laurentia marks the final break up of rodinia with the opening of the lapetus ocean

observed characteristics and vertical structure of mesoscale eddies in the southwest tropical pacific in the southwest pacific ocean waters transit from the subtropical gyre before being redistributed equatorward and poleward while the mean pathways are known the contribution to the mixing and transport of the water from mesoscale eddies has not been comprehensively investigated in this research satellite altimetry data combined with an eddy detection and tracking algorithm is used to investigate the distribution and surface characteristics of mesoscale eddies in this region of complex bathymetry 10 s 30 s 140 e 190 e detected eddies are then colocalized with in situ data from argo floats to determine their vertical structure and the effect of eddies on the water masses the numerous islands affect the eddy behavior as most eddies are formed in the lee of islands propagate westward and decay when encountering shallow bathymetry eddies are sparse and short lived in the tropical area north of fiji impacting only the top 200 meters of water they do not appear to be able to trap and transport waters in this region in the coral sea a region of lateral shear between currents transporting waters of different origins eddies are more numerous and energetic they affect the water properties down to at least 500 m depth and anticyclonic eddies trap water to 200 m contributing to the upper thermocline waters mixing and transport south of new caledonia mesoscale eddies are ubiquitous with typical lifetimes longer than 5 months they affect the temperature salinity and velocities down to 1 000 m depth and weakly contribute to the mixing of lower thermocline waters

weathering and morphogenesis in a tropical plateau summary weathering phenomena on the campos do jordao plateau have been analysed in order to show their relationship to geomorphic compartition and morphogenetic dynamics correlations between weathering characteristics of surficial materials and geomorphic compartments are more conspicuous in saprolite than in soils on the plateau highest areas gibbsite is the most important secondary mineral at lower altitudes kaolinite prevails thus the spatial distribution of secondary minerals seems to outline two weathering processes alitization and monosialitization defined and interpreted as two different stages within a general alitic weathering trend on hillslopes bedrock weathering degree reflects the intensity of morphogenetic actions hillslope deposit profiles frequently show degrees and sequences of weathering related to downslope mouvement processes rather than to incipient post depositional pedogenetic activity red ferralitic materials overlaid by superficial podzolized ones point to the superposition of two pedogenetic trends linked to variations in environmental conditions ferralitic materials would be remnants of weathering processes active during the tertiary at lower altitudes prior to the plateau uplift

decadal variability in the south pacific subtropical countercurrent and regional mesoscale eddy activity abstractdecadal variability of eddy activity in the western subtropical south pacific is examined using the past two decades of satellite altimetry data between 21 and 29 s there is a band of heightened eddy activity in this region the eastward south pacific subtropical countercurrent stcc overlays the westward south equatorial current sec this vertically sheared stcc sec system is subject to baroclinic instabilities by using the european centre for medium range weather forecasts ecmwf ocean reanalysis system version 4 oras4 data and verifying with the gridded argo float data low frequency variations in the state of the ocean in this region are investigated it is found that the low frequency changes in the shearing and stratification of the stcc sec region simultaneously work to modulate the strength of baroclinic instabilities as measured through the baroclinic growth rate these changes in the strength of the instabilities consequently affect the observed eddy activity using a line

consolidation and break up of the south american platform in southeastern brazil tectonothermal and denudation histories the different tectonic stages that occurred at the end of the proterozoic and during the phanerozoic have an important bearing on the tectonothermal history of the south american platform and its consolidation geochronological data u pb monazite 40ar 39ar whole rock and apatite fission track analysis from precambrian rocks of the southeastern brazilian coastline permit the modeling of a long term thermal history of the crust and constrain variable denudation rates using these data a temperature time diagram reflects a period of accelerated exhumation during the end of the brasiliano orogeny followed by long stability and reactivation of the platform during the rifting phase of the south atlantic ocean u pb zircon and monazite blocking temperature of ca 650 c data from a series of igneous bodies suggest that a tangential and transpressional tectonic regime occurred between 625 and 610 ma during the following escape tectonics between 610 and 590 ma the exhumation process indicates cooling rates of ca 12 c ma 40ar 39ar biotite ages between 540 and 510 ma ca 300 c and a corrected fission track age on apatites 100 c of 480 ma indicate an exhumation event related to block tectonics with huge vertical displacement along shear zones a long stabilization phase with low exhumation and cooling rate around 0 25 c ma was recorded from the cambro ordovician to the mesozoic at 65 ma an acceleration of the exhumation through denudation and reworking of the south american surface with cooling rate of 1 5 c ma is observed the uplift of the mantiqueira and serra do mar mountain ranges along the southeast brazilian coastline works as a climatic barrier provoking lateral erosional processes causing long term scarp retreat combined with intense but progressive denudation towards the continent a denudation of 2 5 to 4 km was calculated for such processes this lateral retreat of escarpments and flexural response can provide important insights regarding marginal isostatic uplift and the evolution of offshore sedimentary basins of southeast brazil

paleomagnetic and geochronological results from the zhela and weimei formations lava flows of the eastern tethyan himalaya new insights into the breakup of eastern gondwana