variability in southern hemisphere ocean circulation from the 1980s to the 2000s abstractinterannual to decadal variability of ocean circulation in the southern hemisphere was examined using data from the 1980s to the 2000s in a box inverse model to estimate transport across hydrographic sections and three ocean general circulation models ogcms the westerly wind stress over the ogcm southern ocean showed a steady increase of 5 8 decade 1 the meridional overturning circulation was quantified by the transport across 30 s the ogcms suggested a slight strengthening from 0 2 1 0 to 0 8 1 3 sv decade 1 1 sv 106 m3 s 1 of the upper meridional cell deacon cell and two ogcms showed a weakening 0 8 0 6 and 1 0 0 3 sv decade 1 of the lower meridional antarctic bottom water aabw cell partly explained by contraction of the aabw volume the box inverse estimates did not contradict these two findings for antarctic circumpolar current transport quantified by zonal transport across four key sections the box inverse model estimated a decrease of 5 21 sv decomposition

the low frequency variability of the southern ocean circulation abstractlong time series of sea surface height ssh sea surface temperature and wind stress curl are used to determine the main modes of low frequency variability of the southern ocean so circulation the dominant mode is a trend of increasing ssh at an average rate of 3 3 mm yr 1 similar trends have been reported in previous studies and the analysis indicates that the tendency of sea level increase over the so has become more spatially homogeneous during the last decade with changes in the increasing rate in 2000 and 2006 the other modes consist of stationary basin type modes and an eastward propagating wave the stationary modes are particularly dominant in the indian and atlantic ocean basins where their spatial structure appears to be shaped by the basin geometry and the bottom topography the wavelike patterns travel eastward with a period of approximately 10 years two waves were identified in the analysis a complete cycle between 1997 and 2007 and a second cycle starting in 2000 such w

a numerical study on convergence of alongshore flows over the texas louisiana shelf 1 a hydrodynamic model is used to investigate convergent alongshore flows over the texas louisiana shelf characterized by down coast flows over the northern shelf encountering up coast flows over the southern shelf the model s ability to reproduce realistic current salinity and surface elevation fields is demonstrated through positive model skill scores when comparing model simulations to observational data the convergent flows are explored on both weather band and seasonal time scales for weather band scales this study focuses on wintertime convergent events the model predicted locations of convergent flows are supported by current measurements we find that the formation of convergent flows is primarily caused by along coast variation in the alongshore component of wind forcing which in turn is due to the curvature of the texas louisiana coastline in general the alongshore currents are well correlated with alongshore winds however the convergence points of currents and winds are not colocated but rather convergence points in ocean currents typically occur down coast of convergence points in the wind this offset is demonstrated to be mainly caused by buoyancy forcing that can drive the convergence location in the currents farther down coast no specific temporal pattern is found for the weather band convergence locations whereas at seasonal time scales the monthly mean convergence exhibits a prominent seasonal pattern with up coast migration of convergence locations in spring and summer and down coast migration in fall and winter

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

fluid inclusion studies of the abawso gold prospect near the ashanti belt ghana the major ghanaian lode gold deposits are preferentially aligned along the western and eastern contacts of the kumasi basin with the ashanti and sefwi belts respectively the investigated area of the abawso small scale concession covering the workings of the old ettadom mine is situated 3 km west of the lithological contact of the birimian metavolcanic rocks of the akropong belt in the east with the birimian metasedimentary rocks of the kumasi basin in the west the rocks of the abawso concession represent a steeply nw dipping limb of a se verging anticline with an axis plunging to the sw quartz veining occurs predominantly in the form of en echelon dilatational veins along nne ssw striking shear zones of a few metres width and shows evidence of brittle and ductile deformation also stockwork style quartz veining occurs in the vicinity of the main shaft of the old ettadom mine hydrothermal alteration includes sericitisation sulphidation and locally carbonatisation the auriferous quartz veins mainly follow the trend of brittle to ductile deformed quartz veins however some occur in stockwork fluid inclusion studies reveal a large number of h2o inclusions along intragranular trails in auriferous quartz vein samples as well as an overall dominance of h2o and h2o co2 inclusions over co2 inclusions textural observations and physico chemical fluid inclusion properties indicate post entrapment modifications for all quartz vein samples due to grain boundary migration recrystallisation this process is interpreted to be responsible for the generation of the co2 inclusions from a h2o co2 parent fluid in comparison with mineralisation at the ashanti and prestea deposits which are characterised by co2 n2 inclusions the observed inclusion assemblage may be due to a shallower crustal level of mineralisation or different degrees and styles of recrystallisation or a less pronounced development of laminated quartz veins due to comparably restricted pressure fluctuations furthermore the microthermometric observations allow the reconstruction of a possible retrograde p t path depicting near isothermal decompression in the p t range of the brittle ductile transition

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

imprint of the el nino modoki on decadal sea level changes 1 decadal variation in sea level is shown to manifest as higher than normal sea level in the central pacific flanked by lower than normal sea level on either side of the basin during the early 21st century this abnormal condition is evidently aided by frequent occurrences of el nino modoki events and associated wind convergence to the dateline during 2000 2004 the sea level rise in central pacific succeeded a phase of lower than normal sea level associated with la nina modoki events toward the end of 20th century a correlation analysis confirms the dominant influence of el nino la nina modoki on the sea level rise in the central pacific as compared to that of the el nino la nina this influence can even be seen in remote regions such as the coasts of california and mauritius through atmospheric teleconnections

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

interannual to decadal variability and trends of sea level in the south china sea interannual to decadal variability and trends of sea level in the south china sea scs are studied using altimetric data during 1993 2012 and reconstructed sea level data from 1950 2009 the interannual variability shows a strong seasonality surface wind anomalies associated with el nino southern oscillation explain the sea level anomaly pattern in the interior scs while rossby waves radiated from the eastern boundary dominate the sea level variability in the eastern scs decadal variability of sea level in the scs follows that in the western tropical pacific with large variance found west of luzon island local atmospheric forcing makes a negative contribution to decadal variability in the central scs and rossby waves radiated from the eastern boundary appear to be important during 1993 2012 decadal sea level averaged in the scs is significantly correlated with the pacific decadal oscillation pdo r 0 96 the decadal variability associated with the pdo accounts for most part of sea level trends in the scs in the last two decades

objectively mapped stream function fields on the texas louisiana shelf based on 32 months of moored current meter data on the basis of current measurements observed at 31 moorings during april 1992 through november 1994 as part of the texas louisiana shelf circulation and transport processes study we describe the horizontally nondivergent part of the near surface shelf wide scale low frequency circulation and its variability on the texas louisiana continental shelf by means of objectively fitted stream function fields the 32 month mean velocity stream function patterns generally support the cochrane and kelly 1986 circulation schema for the shelf circulation in which an elongated cyclonic gyre exists during the nonsummer period september through may but with flow in the summer june to august directed upcoast toward the mississippi delta over the entire shelf there exists significant interannual variability of the stream function fields especially in the transition period from spring to summer to fall and along the shelf break strong upcoast downcoast currents dominate at the western shelf break associated with the presence of energetic anticyclones cyclones the dominant pattern of stream function variability deduced by empirical orthogonal function eof analysis of 32 individual monthly mean patterns contains about 89 of the variance and shows a simple shelf wide along shelf pattern of circulation the monthly evolution in amplitude of this dominant eof pattern clearly mimics the monthly evolution of the along shelf component of the wind with squared correlation of 0 83 this provides strong evidence that the seasonal variation of the shelf circulation is wind forced in support of cochrane and kelly the second and residual eofs show more complex features near the shelf break that are associated with loop current eddies known to impact the continental slope and shelf break

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

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

processes controlling mid water column oxygen minima over the texas louisiana shelf we investigate distributions of dissolved oxygen over the texas louisiana shelf using spatially highly resolved observations in combination with a regional circulation model with simple oxygen dynamics the observations were collected using a towed undulating ctd during the mechanisms controlling hypoxia mch program mid water oxygen minimum layers dissolved oxygen lower than 3 2 ml l 1 were detected in many transects these oxygen minimum layers are connected with the bottom boundary layer and follow the pycnocline seaward as a tongue of low oxygen into the mid water column t s diagrams highlighting the low oxygen minima in both observations and simulations imply direct connections between low oxygen bottom water and the oxygen minimum layer the dynamics of these oxygen minimum layers in the mid water column are examined using a three dimensional hydrodynamic model based on the regional ocean modeling system roms convergence within the bottom boundary layer relative to density surfaces is calculated results show that there is a convergence in the bottom boundary layer at the location where the pycnocline intersects the bottom buoyancy advection forced by bottom ekman transport creates this convergent flow and the corresponding low oxygen intrusion similar intrusions of near bottom water into the pycnocline are observed in other regions the presence of hypoxia within the bottom boundary layer in the northern gulf of mexico creates a unique situation in which these intrusions are also associated with low dissolved oxygen

interannual to decadal variations of tropical subtropical exchange in the pacific ocean boundary versus interior pycnocline transports abstract interannual to decadal variations of tropical subtropical mass exchange in the pacific ocean are investigated using a near global ocean general circulation model along with satellite observations of sea level and wind and a data assimilation product the analysis focuses on the variability of pycnocline transports through the western boundary and interior near 10 n and 10 s in contrast to time mean exchange where boundary and interior pycnocline transports are both equatorward the variations of boundary and interior pycnocline transports are found to be generally anticorrelated to each other moreover the variation of the boundary pycnocline transport is smaller than that of the interior again different from time mean exchange where the boundary transport at 10 n is substantially larger than that through the interior interannual variations of the boundary and interior transports are consistent with near surface geostrophic flow inferred from sea level data interior pycnocline flow into th

tropical pacific sst drivers of recent antarctic sea ice trends abstracta strengthening of the amundsen sea low from 1979 to 2013 has been shown to largely explain the observed increase in antarctic sea ice concentration in the eastern ross sea and decrease in the bellingshausen sea here it is shown that while these changes are not generally seen in freely running coupled climate model simulations they are reproduced in simulations of two independent coupled climate models one constrained by observed sea surface temperature anomalies in the tropical pacific and the other by observed surface wind stress in the tropics this analysis confirms previous results and strengthens the conclusion that the phase change in the interdecadal pacific oscillation from positive to negative over 1979 2013 contributed to the observed strengthening of the amundsen sea low and the associated pattern of antarctic sea ice change during this period new support for this conclusion is provided by simulated trends in spatial patterns of sea ice concentrations that are similar to those obse

dynamics of the bottom boundary layer on the northern california shelf abstract time series measurements of velocity temperature and conductivity on the northern california shelf during two winter seasons permit an observational test in vertically integrated form of a simple set of subinertial momentum and heat balances for the bottom boundary layer which have resulted from recent theoretical work these are 1 an along isobath momentum equation that reduces to a classic ekman balance 2 a cross isobath momentum equation in which the ekman balance is modified by a buoyancy force caused by distortion of the isopycnal surfaces within the boundary layer and 3 a heat balance in which variability of temperature is produced by cross isobath advection the measurements confirm the importance of buoyancy in the cross isobath momentum equation and as has recently been predicted theoretically they indicate that buoyancy is a dominant effect when the boundary layer is thick which typically occurs during downwelling favorable flows an ekman balance describes subinertial flu

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

robustness of observation based decadal sea level variability in the indo pacific ocean we examine the consistency of indo pacific decadal sea level variability in 10 gridded observation based sea level products for the 1960 2010 period decadal sea level variations are robust in the pacific with more than 50 of variance explained by decadal modulation of two flavors of el nino southern oscillation classical enso and modoki amplitude of decadal sea level variability is weaker in the indian ocean than in the pacific all data sets indicate a transmission of decadal sea level signals from the western pacific to the northwest australian coast through the indonesian throughflow the southern tropical indian ocean sea level variability is associated with decadal modulations of enso in reconstructions but not in reanalyses or in situ data set the pacific independent indian ocean decadal sea level variability is not robust but tends to be maximum in the southwestern tropical indian ocean the inconsistency of indian ocean decadal variability across the sea level products calls for caution in making definitive conclusions on decadal sea level variability in this basin

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

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

mineralogical siting and distribution of gold in quartz veins and sulfide ores of the ashanti mine and other deposits in the ashanti belt of ghana genetic implications the ashanti belt of ghana constitutes a gold province which has produced a total of about 1500 t of gold historically gold mineralization is found in steep nne ssw to ne sw trending shear zones predominantly transecting metasediments of the palaeoproterozoic birimian supergroup 2 2 2 1 ga disseminated in ca 2 1 ga granitoids in paleo conglomerates of the tarkwaian group 2135 ma and in recent placers the distribution of gold its chemistry paragenesis and mineralogical siting in the mesothermal ores of the major mines in the ashanti belt namely konongo ashanti bogosu and prestea mine are the subject of this study at the localities studied gold is present in two main types of ores 1 quartz veins with free milling gold the gold is relatively silver rich true fineness values from 730 to 954 and is accompanied by a distinct suite of cu pb sb sulfides 2 sulfide ores consisting of arsenopyrite pyrite and rarer pyrrhotite and marcasite with refractory gold the ores have apparent fineness values larger than 910 arsenopyrite and locally at bogosu pyrite were identified as the hosts of submicroscopic gold mean concentrations of gold in arsenopyrite in various samples from the different mines obtained by secondary ion mass spectrometry sims range from 67 to 314 ppm au gold concentration mapping in individual arsenopyrite crystals from the different deposits revealed similar patterns of gold distribution the grains possess a gold poor core and elevated gold contents are present along distinct crystal growth zones towards their rims the outermost crystal layer is usually gold poor the well preserved distribution patterns also indicate that remobilization of gold from the sulfides played an insignificant role in the ores of the ashanti belt multiple quartz veining and growth zoning of the sulfides are interpreted as manifestations of multiple episodes of fluid infiltration fluid flow and mineral deposition the bimodal occurrence of gold in spatially closely associated quartz vein and sulfide ores indicates a genetic link between these ore types a model implying a grossly coeval formation of the ores from mesothermal fluids is proposed

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

large scale variability in the midlatitude subtropical and subpolar north pacific ocean observations and causes abstract altimetric data from the 8 yr topex poseidon t p mission oct 1992 jul 2000 are used to investigate large scale circulation changes in the three current systems of the midlatitude north pacific ocean the north pacific current npc the alaska gyre and the western subarctic gyre wsg to facilitate the understanding of the observed changes a two layer ocean model was adopted that includes first mode baroclinic rossby wave dynamics and barotropic sverdrup dynamics the npc intensified steadily over the t p period from 1992 to 1998 much of this intensification is due to the persistent sea surface height ssh drop on the northern side of the npc a similar ssh trend is also found in the interior of the alaska gyre both of these ssh changes are shown to be the result of surface wind stress curl forcing accumulated along the baroclinic rossby wave characteristics initiated from the eastern boundary in addition to the interior ssh signals the intensity of the alaska gyre is shown to depend

low frequency circulation on the texas louisiana continental shelf for the texas louisiana coast west of 92 5 w long series of data from near freeport texas together with shorter series from other locations show strong response of coastal current to wind stress in agreement with coastal jet concepts we infer from coastal winds scattered current measurements and distributions of sea surface salinity and geopotential that a cyclonic gyre elongated along the shelf is the dominant feature of the prevailing shelf circulation the inshore limb of the gyre is the coastal jet driven by wind with a west or southward downcoast component which prevails along much of the coast except in july august because the coast is concave the shoreward prevailing wind results in a convergence of coastal currents which marks the downcoast extent of the gyre corresponding to the convergence is a seaward flow which forms the southwest limb of the gyre a prevailing countercurrent north or eastward flow along the shelf break includes the outer limb of the gyre the eastern shoreward flowing limb of the gyre corresponds to divergence along the coast centered near 92 5 w the convergence at the western or southern end of the gyre migrates seasonally with the direction of the prevailing wind reaching south of the rio grande mouth in fall and the cameron offing in july the gyre is normally absent in july but reappears in august september when a downcoast wind component develops

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

shallow overturning circulation of the western indian ocean the indian ocean differs from the other two oceans in not possessing an eastern equatorial upwelling regime instead the upwelling occurs dominantly in the northwestern arabian sea and to a lesser degree around the indian subcontinent subduction on the other hand occurs dominantly in the southern hemisphere the result is a shallow cross equatorial cell connecting both regimes the northward flow at thermocline levels occurs as part of the somali current and the southward upper layer return flow is carried by the ekman transports that are directed southward in both hemispheres the main forcing is by the southwest monsoon that overwhelms the effects of the northeast monsoon and is the cause for the annual mean northern hemisphere upwelling and southward ekman transports in the southern hemisphere the annual mean upwelling at the northern rim of the southeast trades causes a zonally extended open ocean upwelling regime that is apparent in isopycnal doming in the 3 12 s band it drives a shallow subtropical cell

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

shear related gold mineralization in northwest ghana the julie deposit abstract the julie deposit is currently the largest gold prospect in nw ghana it is hosted in sheared granitoids of ttg composition of the paleoproterozoic julie greenstone belt the main mineralization consists of a corridor of gold bearing quartz veins forming a network of a few tens of metres in thickness trending e w and dipping 30 60 n contained within the main shear zone that affects these rocks the core of this vein corridor is altered by sericite quartz ankerite calcite tourmaline and pyrite and is surrounded by an outer halo consisting of albite sericite calcite chlorite pyrite and rutile a second set of veins conjugate to the first set occurs in the area these veins have alteration halos with a similar mineralogy as the main corridor however their extent as well as the size of the mineralization is less important in the main corridor gold forms micron sized grains that occur in pyrite as inclusions on its edges and in fractures crosscutting it silver tellurium bismuth copper and lead commonly accompany the gold pyrite occurs disseminated in the veins and in the surrounding rocks up to several ppm au occurs in the structure of pyrite from the main mineralization

upwelling and convergence in the middle atlantic bight shelfbreak front convergent and upwelling circulation within the shelfbreak front in the middle atlantic eight are detected using a dye tracer injected into the bottom boundary layer at the foot of the front from the three day displacement and dispersion of two dye injections within the front we infer lagrangian isopycnal diapycnal velocities and diffusivities of 2 x 10 2 m s 4 x 10 6 m s and 9 m 2 s 6 x 10 6 m 2 s these results substantiate model predictions of chapman and lentz 1994 and previous dye tracer observations by houghton 1997

new findings on the route of heat transport between the indo pacific and southern ocean since the end of the twentieth century the global mean surface temperature gmst exhibited a shift from a rapid warming to an unexpected deceleration an anomalous heat was transported from the pacific ocean into the indian ocean through a strengthened indonesian throughflow during the same period within this background it is essential to continue tracking the fate of the anomalous heat arriving in the indian ocean to form a comprehensive picture of the global ocean energy redistribution the anomalous heat may continue flowing westward into the atlantic ocean along the main pathway of the regional ocean currents via the south equatorial current sec and agulhas current however here we examine an alternate pathway a southward heat transport in conjunction with a weakened sec diverting the canonical westward transport this additional transport pathway causes an increase in heat content in the south indian ocean mid latitudes 15 30 s 95 110 e may contribute to the southern ocean warming and intensifies hemispheric asymmetry of oceanic heat content the heat increase has important climate impacts such as changes to rainfall and increased coral bleaching over the western coast of australia the new path discovered here may be an essential route of heat transport linking the tropical indo pacific ocean and the southern ocean in 2003 2012

a simple theory for the fate of buoyant coastal discharges abstract a simple theory that predicts the vertical structure and offshore spreading of a localized buoyant inflow onto a continental shelf is formulated the theory is based on two competing mechanisms that move the buoyant fluid offshore 1 the radial spread of the lighter water over the ambient water being deflected by the coriolis force and producing an anticyclonic cyclostrophic plume and 2 offshore transport of buoyant water in the frictional bottom boundary layer that moves the entire plume offshore while maintaining contact with the bottom the surface expression of the cyclostrophic plume moves offshore a distance ys 2 3g h0 2i 2g h0 2i 1 2f where g is reduced gravity based on the inflow density anomaly h0 is the inflow depth i is the inflow velocity and f is the coriolis parameter the plume remains attached to the bottom to a depth given by hb 2l ih0f g 1 2 where l is the inflow width both scales are based solely on parameters of the buoyant inflow at its source there

pacific modulation of accelerated south indian ocean sea level rise during the early 21st century the south indian ocean has shown an unprecedented sea level rise during the early 21st century sea level rise in the south indian ocean is found to be 37 quicker than the global mean sea level during 2000 2015 observational datasets and long term proxy records identify pacific origin of the south indian ocean sea level rise our results indicate that co evolution of the cold phase of pacific decadal oscillation pdo and prolonged la nina like condition enhances the equatorial pacific easterlies stronger in phase association of these major pacific climate modes and equatorial pacific easterlies enhances the indonesian throughflow itf transporting fresh and warm water anomalies from western tropical pacific into the south indian ocean as a result south indian ocean sea level rise has accelerated more than the global with 40 contribution from the halosteric sea level primarily through the itf transport and a secondary from the local processes during 2000 2015 the co evolution of pdo and the south indian ocean sea level is also evident from the long term proxy records indicating that the association is part of an internal mode of variability modulated on decadal time scales the finding from the study cautions that accelerated heat and freshwater intrusion from the western pacific with the co evolution of pdo and la nina like condition may lead to the accelerated sea level rise and marine heat waves in the south indian ocean imposing threats to the life of coral reefs and marine ecosystems

multidecadal sea level and gyre circulation variability in the northwestern tropical pacific ocean abstractsea level rise with the trend 10 mm yr 1 has been observed in the tropical western pacific ocean over the 1993 2009 period this rate is 3 times faster than the global mean value of the sea level rise analyses of the satellite altimeter data and repeat hydrographic data along 137 e reveal that this regionally enhanced sea level rise is thermosteric in nature and vertically confined to a patch in the upper ocean above the 12 c isotherm dynamically this regional sea level trend is accompanied by southward migration and strengthening of the north equatorial current nec and north equatorial countercurrent necc using a 1 layer reduced gravity model forced by the ecmwf reanalysis wind stress data the authors find that both the observed sea level rise and the nec necc s southward migrating and strengthening trends are largely attributable to the upper ocean water mass redistribution caused by the surface wind stresses of the recently strengthened atmospheric walker circulation based on the lo

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

numerical treatment of cross shelf open boundaries in a barotropic coastal ocean model abstract using a barotropic coastal ocean model with a straight coastline and uniform cross shelf bottom slope seven different cross shelf open boundary conditions four of which are applied in either implicit or explicit form are compared in three numerical experiments 1 a mound of water is allowed to collapse and radiate waves toward the open boundaries 2 a uniform alongshelf wind stress is applied at zero time over the entire shelf and held constant for the duration of the experiment 3 a uniform cross shelf wind stress is applied at zero time over the entire shelf and held constant for the duration of the experiment the boundary condition which is most transparent to waves consists of a sponge at the outer edge of the model domain with an orlanski radiation condition at the outer edge of the sponge several open boundary conditions perform adequately in the wind stress experiments but the orlanski radiation condition alone without a sponge appears to give the best total performance of thes

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

the tropical indian ocean decadal sea level response to the pacific decadal oscillation forcing the tropical indian ocean sea level displayed decadal variations in response to pacific decadal oscillation pdo contrasting patterns of decadal oscillation in sea level is found during the opposite phases of pdo especially in the thermocline ridge region of the indian ocean trio 50 e 80 e 15 s 5 s epochal mean sea level rise is observed over the trio region during the cold phase of pdo 1958 1977 whereas epochal mean sea level fall is observed during the warm phase of pdo 1978 2002 analysis reveals that the decadal variability in the sea level pattern in the trio region is in accordance with the pdo phase shifts and is primarily caused by changes in the surface forcing over the indian ocean as a response to pdo the changes in the large scale walker circulation over the tropical indian ocean region during the different phases of pdo support our hypothesis the winds and wind stress curl variations associated with these large scale circulation changes are primarily inducing the observed regional decadal sea level variability over trio the decadal forcing through indonesian through flow itf oceanic channel however did not show any significant impact on the trio sea level variability further ocean general circulation model ogcm sensitivity experiments are carried out to understand the mechanisms and the possible contribution of the pacific ocean through oceanic pathways in the decadal variability of the trio sea level it is noted that wave propagation from the pacific ocean to the indian ocean through itf region has contributed to the sea level variations in the eastern indian ocean but on the decadal time scale tropical indian ocean trio sea level is unaffected by decadal variability in the itf moreover the itf contribution to the decadal sea level variability in the indian ocean is found to be significant only in the region south of 20 s

oscillating relationship between the east asian winter monsoon and enso abstractthis work investigates the interdecadal variations of the relationship between the el nino southern oscillation enso and the east asian winter monsoon eawm further explores possible mechanisms and finally considers a recent switch in the enso eawm relationship the 23 yr sliding correlation between the nino 3 4 index and the eawm index reveals an obvious low frequency oscillation with a period of about 50 yr in the enso eawm relationship warm enso events during high correlation periods are associated with an unusually weak east asian trough a positive phase of the north pacific oscillation npo significant southerly wind anomalies along coastal east asia and warmer east asian continent and adjacent oceans however there are no robust and significant anomalies in the eawm related circulation during low correlation periods because of the southeastward shift of the walker circulation the area of anomalously high pressure in the western pacific retreats south of 25 n confining it to the

near resonant ocean response to sea breeze on a stratified continental shelf abstract the spatial structure and temporal characteristics of sea breeze and the associated coastal ocean response in the northwest gulf of mexico are investigated using moored instruments hydrographic stations and wind measurements near the study area of 30 n motions in the diurnal inertial band dib may be significantly enhanced by a near resonant condition between local inertial and diurnal forcing frequencies wavelet analysis is used to quantify the results results indicate that diurnal sea breeze variability peaks in summer and extends at least 300 km offshore with continuous seaward phase propagation the maximum dib oceanic response occurs in june when there is a shallow mixed layer strong stratification and an approximately 10 day period of continuous sea breeze forcing dib current variance decreases in july and august as the consequence of the deepening of the mixed layer and a more variable phase relationship between the wind and current river discharge varies interannually and can s

pacific ocean circulation rebounds 1 recent observations indicate that the shallow meridional overturning circulation in the tropical pacific ocean has rebounded since 1998 following 25 years of significantly weaker flow convergence of cold interior ocean pycnocline water towards the equator increased to 24 1 1 8 106 m3 s 1 during 1998 2003 from a low of 13 4 1 6 106 m3 s 1 during 1992 98 intensified circulation led to the development of anomalously cool tropical pacific sea surface temperatures which may have affected pacific marine ecosystems and global climate the abruptness of the rebound also obscures presumed anthropogenic warming trends in the instrumental temperature record of the tropical pacific

multi decadal oscillations of the ocean active upper layer heat content spatial patterns in multi decadal variability in upper ocean heat content for the last 60 years are examined using a numerical model developed at the institute of numerical mathematics of russia inm model and sea water temperature salinity data from the world ocean database in levitus noaa atlas nesdis 66 u s wash gov printing office 2009 both the model and the observational data show that the heat content of the active upper layer aul in particular regions of the atlantic pacific and southern oceans have experienced prominent simultaneous variations on multi decadal 25 35 years time scales these variations are compared earlier revealed climatic alternations in the northern atlantic region during the last century byshev et al in doklady earth sci 438 2 887 892 2011 we found that from the middle of 1970s to the end of 1990s the aul heat content decreased in several oceanic regions while the mean surface temperature increased on northern hemisphere continents according to ipcc in stocker et al contribution of working group i to the fifth assessment report of the intergovernmental panel on climate change cambridge university press cambridge 2013 this means that the climate forcing effect of the ocean atmosphere interaction in certain energy active areas determines not only local climatic processes but also have an influence on global scale climate phenomena here we show that specific regional features of the aul thermal structure are in a good agreement with climatic conditions on the adjacent continents further the ocean aul in the five distinctive regions identified in our study have resumed warming in the first decade of this century by analogy inference from previous climate scenarios this may signal the onset of more continental climate over mainlands

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