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

wind generated eddy characteristics in the lee of the island of hawaii 1 weekly satellite sea surface height ssh anomaly data are used to clarify the mesoscale eddy characteristics in the lee of the island of hawaii the largest island in the hawaiian island chain the lee eddy variability can be separated into two geographical regions in the immediate lee southwest of hawaii region e eddy signals have a predominant 60 day period and a short life span whereas in the region along 19 n west of 160 w region w the eddy variability is dominated by 100 day signals and extends over a broad region by applying a linear ekman pumping model forced by the weekly quikscat wind data we find that the observed 60 day eddy signals originate in the southwest corner of hawaii and are induced by the local 60 day wind stress curl variability associated with the blocking of the trade wind by the island of hawaii the relationship between the wind forcing and the observed ssh signals demonstrates the role of the ocean as an integrator that responds more effectively to the low frequency synoptic atmospheric forcing 60 days than to the higher frequency forcing 30 days since the large amplitude 60 day ssh anomalies take 1 2 weeks to fully develop it is possible that real time observed wind stress data can be used for the prediction of these anomalies in contrast to the wind induced 60 day eddy signals in the lee of the island of hawaii the 100 day eddy signals in region w are likely generated by the instability of the sheared north equatorial current and hawaii lee countercurrent

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

low frequency variability of southern ocean jets both observations and high resolution numerical models show that the southern ocean circumpolar flow is concentrated in a large number approximately 8 to 12 of narrow filamentary jets it is shown here that coherent jets exhibit a range of low frequency variability on timescales of months to years that can lead to displacement and to intermittent formation and dissipation of jets using output from an eddy resolving ocean general circulation model in local regions near topographic features the impact of energy exchange between eddy and mean flow components on jet persistence and variability is examined a novel approach that uses a time dependent definition of the mean flow provides a clearer picture of eddy mean flow interactions in regions with spatially and temporally varying flow structure the dynamics are largely consistent with those in idealized quasi geostrophic models including topographically organized and surface enhanced reynolds stress forcing of the mean flow jets form during periods of enhanced eddy activity but may persist long after the eddy activity has decayed similarly jets may evolve in a downstream sense with jet formation localized near topography and undergoing modification in response to changing bathymetry the evolution of both temperature and potential vorticity is used to show that the low frequency variability of the jets impacts water mass structure and tracer transport this study highlights various examples of southern ocean dynamics that will prove difficult to capture through parameterizations in coarser climate models

a case of man induced ground subsidence and building settlement related to karstified gypsum oviedo nw spain this paper presents the research carried out to shed light on a sudden settlement and its consequences that occurred in the city of oviedo ground subsidence in the ventanielles area led to severe damage and the subsequent demolition of two buildings with 362 flats resulting in losses of 18 million euros the investigation allowed the identification of a buried sinkhole filled with up to 13 m of fluvial sediments linked to the dissolution of a paleogene gypsum unit with a maximum thickness of 18 m and containing metre sized cavities the triggering process that reactivated the paleosinkhole was found to be the pumping of water from a confined aquifer related to excavation work during the construction of a nearby underground parking lot this extraction modified the natural hydrological regime the compaction and migration of alluvial sand towards the karstic cavities were the main subsidence mechanisms responsible for the structural damage aggravated by the poor quality of the buildings and the geotechnical behaviour of the supporting ground

field investigation and analysis of ground sinking development in a metropolitan city seoul korea either geological features or some artificial factors like sewer pipe leakage or incomplete construction work cause ground sinking in urban areas this study reports on a recent ground sinking which occurred on account of complex factors related to geology and artificial excavation work a cylindrical displacement of 14 m long in the ground with a sinking of 3 m deep on the surface was studied this occurrence was situated adjacent to the excavation site which was 38 m deep during the construction of the high rise building fine grained soils were spilled out with groundwater leaking through the bottom of the cutoff wall and before the ground sinking occurred completely a scrutinized field survey was conducted through several means such as observation through pit excavation standard penetration test spt and ground penetrating radar gpr exploration numerical groundwater flow analysis was also performed to evaluate the influence of the flow behavior from the surrounding area toward the excavated site using visual modflow the study revealed that the geology of the site was comprised of multiple alluvial layers formed by many floods from the han river in seoul and it was very vulnerable to the piping near the excavation wall the results of spt displayed some void spaces of 20 30 cm thick under the sinking area and the changes of soil properties are recognized before the excavation and after the ground sinking the sequential displacement mechanism for ground sinking in this site is suggested from the analyses of the numerical groundwater flow model and the data obtained from field investigation

direct velocity measurements in the subantarctic front and over campbell plateau southeast of new zealand 1 flow variability in the subantarctic front saf and over the campbell plateau southeast of new zealand is examined using data from a current meter mooring array along with conductivity temperature depth ctd and satellite altimetry data these data are part of an ongoing study of ocean climate variability in the region contrasting flow regimes were found with very energetic and highly variable flows in the saf flowing along the subantarctic slope and much weaker flows over the campbell plateau currents up to 75 cm s 1 were observed in the core of the saf while flows over the plateau were typically less than 10 cm s 1 estimates of the total bottom referenced transport from three ctd sections across the saf varied between 48 and 68 sv transports were also estimated using topex poseidon altimetry sea truthed with the ctd data the resulting 8 year time series exhibited high variability resulting from current meanders and eddy activity one event in the record appeared to be the result of a cyclonic eddy passing through the mooring array this event was modeled using an idealized geostrophic eddy the simulation reproduces the main features observed in the current meter records and the surface topography from the topex poseidon altimeter inspection of the topex poseidon data suggests that large cyclonic and anticyclonic eddies occur in the frontal region with a frequency of around 9 yr 1

circumpolar structure and distribution of the antarctic circumpolar current fronts 2 variability and relationship to sea surface height 1 in part 1 of this study we showed that the antarctic circumpolar current acc consisted of multiple fronts each of which was consistently associated with a particular contour of sea surface height ssh or approximate streamline in part 2 we have used maps of ssh to examine the variability of the acc fronts between 1992 and 2007 the ssh label associated with each frontal branch is nearly constant around the circumpolar belt the front labels are also nearly constant in time the bands of enhanced ssh gradient i e fronts occur along the same streamlines throughout the 15 year period of observations both short and long period changes of the ssh frontal labels of the acc are small based on a tight relationship between dynamic height and cumulative baroclinic transport of the acc the baroclinic transport variability of the individual branches of the acc is also expected to be small the major change in the total acc baroclinic transport occurs in the drake passage the streamline associated with the northern branch of the saf saf n does not pass through drake passage and the waters carried by this branch are not observed there instead the transport of the saf n turns north in the pacific to supply the export of water to the indian ocean north and south of australia strong eddy activity in the southeast pacific acts to dissipate the hydrographic signature of the saf n there in the atlantic the saf n reappears as the same streamline is again associated with enhanced ssh gradients to the east of the brazil malvinas confluence zone while the large changes in ssh have occurred in the southern ocean between 1992 and 2007 there are strong regional differences because the acc fronts are robustly associated with particular ssh contours the changes in ssh reflect shifts in the position of the acc fronts in the circumpolar average each of the acc fronts has shifted to the south by about 60 km the changes in ssh in the southern ocean are largely due to changes in ocean circulation rather than warming and freshening by atmospheric fluxes much larger changes in ssh are observed in some locations of the southern ocean particularly where the fronts interact with large scale topography the northern branch of the pf pf n near the kerguelen plateau is an extreme example where the pf n followed a path around the northern end of kerguelen plateau between 1992 and 1997 passed through the fawn trough after 2003 and oscillated between the two paths between 1997 and 2003

eddy heat diffusion and subantarctic mode water formation subantarctic mode waters samw form in the deep winter mixed layers occuring north of the subantarctic front saf the recent increase of hydrographic and surface drifter data in the southern ocean allows a better spatial representation of the distinct regions of samw formation this study focuses on the thermodynamical processes acting on the winter mixed layer heat budget eddy heat diffusion play a substantial role in the local heat balance whereas its action vanishes with large scale averaging south of the western boundary currents and north of the saf the eddy heating plays an important role in specific regions counterbalancing the cooling of the mixed layer by ekman advection and air sea fluxes specifically the eddy diffusion term reduces the tendency for mixed layer destabilisation north of the saf in the western indian ocean downstream of the agulhas retroflection and in the western pacific downstream of campbell plateau this role for mixed layer eddy fluxes emphasizes a large scale control of mixed layer properties by topography and mesoscale processes in the southern ocean

the south pacific current the southern hemisphere subtropical front stf is a narrow zone of transition between upper level subtropical waters to the north and subantarctic waters to the south it is found near 40 degrees s across the south atlantic and south indian oceans and is associated with an eastward geostrophic current band the current band in each basin is found at or just north of the surface front except near the eastern boundaries where most of the subtropical waters turn north into the eastern limbs of the subtropical gyres the bands associated with the stf are thus distinct features separated from the strong zonal flows of the antarctic circumpolar current farther south the authors have referred to the current bands in the two respective oceans as the south atlantic current and the south indian ocean current in this paper the authors use the historical database from the south pacific ocean to investigate the geostrophic flow associated with the stf there the stf extends across the southern tasman sea from south of tasmania to southern new zealand and a weak eastward flow appears to be associated with it the transport amounts to only about 3 sv 1sv 10 6 m 3 s 1 little of which passes south of new zealand mixing within the eddy rich tasman sea may account for this weakness while also setting up another more significant front in the northern tasman sea the tasman front it branches off from the east australian current toward the north of new zealand along which moves a flow of about 14 sv after passing north of new zealand a portion of this current flows east to contribute to a current band near 30 degrees s while another portion turns south as the east auckland current and meets with subantarctic waters near chatham rise 44 degrees s thus reestablishing the stf an enhanced eastward current band is associated with the front there one that extends across the remainder of the south pacific and is referred to as the south pacific current in comparison with its counterparts in the other basins which typically begin by carrying 30 sv atlantic to 60 sv indian in the upper 1000 m in their western portions before weakening to 10 15 sv in the east the south pacific current is weak near chatham rise it starts with a transport of approximately 5 sv and it remains near this strength as it shifts gradually north across the basin toward south america the current appears to split into two smaller bands in the region of 115 degrees 85 degrees w while near 28 degrees 5 83 degrees w it begins to turn more strongly north and becomes shallower and weaker potential vorticity distributions indicate that this current acts as an impediment toward the northward spreading of antarctic intermediate water but why the south pacific current east of new zealand should be so much weaker than its counterparts in the other basins is not particularly clear it may be due to the presence of new zealand and other topographic barriers to deep now east of australia to the axis of the subtropical gyre in the south pacific shifting more rapidly southward with depth than those elsewhere thus causing greater reductions in the underlying zonal velocities and to strong poleward eddy heat and salt fluxes in the other two basins leading to smaller cross stf gradients in the pacific

interannual to decadal changes in the western south atlantic s surface circulation 1 a combination of surface drifters and altimetry is used to analyze the seasonal to interannual variability of the surface velocity field in the brazil malvinas confluence of the western south atlantic ocean longer term changes are inferred from wind and sea surface temperature fields during the period october 1992 to december 2007 a southward shift of 0 6 to 0 9 decade 1 is found in the confluence latitude of the brazil and malvinas currents a comparable trend is found in the latitude of the maximum wind stress curl averaged across the south atlantic basin allowing a proxy for the confluence latitude to be calculated for the prealtimeter time period this longer time series suggests that the recent trend may be part of a longer term oscillation which has returned to values last sustained in the early 1980s this variation does not appear to be related to the multidecadal trend in the southern annular mode but instead is inversely related to long term variations in the sea surface temperature anomaly in the agulhas benguela pathway of the eastern south atlantic subtropical basin

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 record of continental dust from australia in tasman sea sediments abstract the flux of aeolian dust from australia to sediments of the tasman sea has increased during glacial stages of the last four glacial cycles low fluxes of dust from australia before 350 ka were followed by an increase in stage 10 and high fluxes in peak glacial periods thereafter the initiation of higher dust fluxes in stage 10 is consisten with previous estimates of the age of onset of aridity in the source area dust flux to the tasman sea is thought to record the intensity of deflation from the source area in interior southeastern australia which was marked by arid conditions and possibly greater windiness during the last glacial a transect of five cores from the central tasman sea revealed consistently low dust fluxes north of 33 s increasing southward to approximately 40 s glacial to interglacial movement of the northern boundary of the dust plume governed by the position of the subtropical ridge was less than 6 latitude probably closer to 3 350 km the position of the dust plume determined in this study and its response to climate change are significantly different from a previous reconstruction based on the measurement of quartz content of the non biogenic sediment fraction

sea level changes forced by southern ocean winds 1 on regional scales changes in sea level are significantly affected by local dynamical changes westerly winds over the southern ocean have been strengthening and shifting southward in recent decades and this change is projected to continue in the future this study applies wind forcing anomalies to an eddy permitting ocean model to study the dynamical response to a southern hemisphere westerly wind increase and or southward shift it is shown that the applied wind anomalies result in a change in sea surface slope across the antarctic circumpolar current such that a fall in sea level occurs around the antarctic continental margin the antarctic circumpolar current transport and regional sea level are particularly sensitive to latitudinal shifts in the wind with a much more muted response found when only wind strengthening is applied in addition to the local sea level changes southern ocean winds also have a global effect through changing ocean heat content and the global overturning circulation

the origin typology spatial distribution and detrimental effects of the sinkholes developed in the alluvial evaporite karst of the ebro river valley downstream of zaragoza city ne spain three types of sinkhole have been mapped in a 50 km2 stretch of the ebro river valley downstream of zaragoza large collapse sinkholes large shallow subsidence depressions and small cover collapse sinkholes the sinkholes relate to the karstification of evaporitic bedrock that wedges out abruptly downstream giving way to a shale substratum twenty three collapse sinkholes up to 50 m in diameter by 6 m deep and commonly hosting saline ponds have been identified in the floodplain they have been attributed to the upward stoping of dissolutional cavities formed within the evaporitic bedrock by rising groundwater flows twenty four large shallow subsidence depressions were mapped in the floodplain these may reach 850 m in length and were formed by structurally controlled interstratal karstification of soluble beds halite or glauberite and gypsum by rising groundwater flow and the progressive settlement of the overlying bedrock and overburden sediments a total of 447 small cover collapse or dropout sinkholes have been recognized in a perched alluvial level along the southern margin of the valley these sinkholes result from the upward propagation of voids through the alluvial mantle caused by the downward migration of detrital sediments into dissolutional voids the majority of these sinkholes commonly 1 5 2 m in diameter are induced by human activities over the karstic bedrock there is a significant increase in sinkhole density downstream this is interpreted as being a result of the evaporitic bedrock wedging out and the convergence of the groundwater flow lines in the karstic aquifer the collapse sinkholes in this area locally with a probability of occurrence higher than 140 sinkholes km2 year cause substantial damage to the linear infrastructures buildings and agriculture and they might eventually cause the loss of human lives copyright 2006 john wiley sons ltd

multiple jets of the antarctic circumpolar current south of australia abstract maps of the gradient of sea surface height ssh and sea surface temperature sst reveal that the antarctic circumpolar current acc consists of multiple jets or frontal filaments the braided and patchy nature of the gradient fields seems at odds with the traditional view derived from hydrographic sections that the acc is made up of three continuous circumpolar fronts by applying a nonlinear fitting procedure to 638 weekly maps of ssh gradient ssh it is shown that the distribution of maxima in ssh i e fronts is strongly peaked at particular values of absolute ssh i e streamlines the association between the jets and particular streamlines persists despite strong topographic and eddy mean flow interactions which cause the jets to merge diverge and fluctuate in intensity along their path the ssh values corresponding to each frontal branch are nearly constant over the sector of the southern ocean between 100 e and 180 the front positions inferred from ssh agree closely with

eddy response to southern ocean climate modes 1 interannual variations in southern ocean eddy kinetic energy eke are investigated using 16 years of altimetric data circumpolar averages show a peak in eke from 2000 to 2002 2 3 years after the peak in the southern annular mode sam index although the sam forcing is in phase around the circumpolar band we find the eke response varies regionally the strongest eke is in the pacific with energy peaks occurring progressively later toward the east we suggest that this is due to the presence of two climate modes sam and enso when strong positive sam events coincide with la nina periods as in 1999 anomalous meridional wind forcing is enhanced in the south pacific ocean contributing to the observed increase in eke 2 3 years later when positive sam events coincide with el nino periods as in 1993 the climate modes are in opposition in the south pacific leading to a weak eke response during the mid 1990s numerical modeling supports these observations by applying different combinations of sam and enso we can reproduce both the elevated pacific eke response to sam as well as an additional amplification suppression of eke during la nina el nino in general we find that the eke response depends on the interplay between wind forcing topography and mean flow and produces a strongly heterogeneous distribution in the southern ocean

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

eddy mean flow interaction in the decadally modulating kuroshio extension system abstract satellite altimeter sea surface height ssh data of the past 16 years are used to investigate the decadal changes of the kuroshio extension ke system that oscillated between a stable and an unstable dynamic state during the stable state of 10 1992 06 1995 and 01 2002 12 2004 the ke jet was intense and had a northerly zonal mean path and a well defined southern recirculation gyre during the unstable state of 07 1995 12 2001 and 01 2005 present the ke jet had a reduced eastward transport and a more southerly flow path transitions between the two dynamic states are caused by the basin scale wind stress curl forcing in the eastern north pacific related to the pacific decadal oscillations pdos or the north pacific gyre oscillations npgos during the positive pdo or negative npgo phase the intensified aleutian low generates negative ssh anomalies in the eastern north pacific through ekman divergence as these wind induced negative ssh anomalies propagate to the west as baroclinic rossby waves they weaken the zonal ke jet and shift its path southward as its path is pushed southward 32 n the deep reaching ke jet has to ride over the shallow shatsky rise generating localized disturbances that lead to their subsequent development along the ke jet west of the shatsky rise the sequence opposite to that listed above occurs when the pdo npgo changes to its negative positive phase after the ke system transitions from a stable to unstable state the enhanced eddy interaction is found to strengthen both the southern recirculation gyre and quasi stationary meanders along the ke s upstream path this nonlinear eddy interaction is important in determining the amplitude of the observed decadal ke variability

formation of regolith collapse sinkholes in southern illinois interpretation and identification of associated buried cavities three regolith collapse sinkholes formed near the dongola unit school and the pentecostal church in the southern illinois village of dongola union county during the spring of 1993 the sinkholes appeared over a three month period that coincided with development of a new municipal well the new well was drilled through clay rich valley fill sediment into karstified limestone bedrock the piezometric surface of the limestone aquifer is above land surface indicating the presence of an upward hydraulic gradient in the valley and that the valley fill is acting as a confining unit pumping during development of the well lowered the piezometric surface of the limestone aquifer to an elevation below the base of the valley fill it is hypothesized that drainage of water from the sediments the resulting loss of hydrostatic pressure and buoyant force in overlying sediments increased intergranular pressure and the initiation of groundwater flow toward the well resulted in rapid sediment transport subsurface erosion and collapse of the valley fill sediment the sinkholes follow an approximately east west alignment which is consistent with one of the two dominant alignments of passages of nearby joint controlled caves a constant electrode separation resistivity survey of the school playground was conducted to locate areas that might contain incipient sinkholes the survey revealed a positive resistivity anomaly trending n75e in the southern part of the study area the anomaly is linear between 5 and 10 m wide and its trend either intersects or is immediately adjacent to the three sinkholes the anomaly is interpreted to be a series of pumping induced cavities in the valley fill sediments that formed over a preexisting crevice in the karstified bedrock limestone

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

energetic eddies at the northern edge of the antarctic circumpolar current in the southwest pacific abstract two year time series measurements of current and temperature were made at the northern edge of the antarctic circumpolar current in the southwestern pacific from 1978 to 1980 to investigate eddy heat and momentum fluxes in the circumpolar region the measurement site near 49 30 s 170 w is at a transition zone or front between subantarctic and subtropical waters in which meridional temperature and salinity gradients and hence vertical shear in eastward velocity extend down to 2 000 m depth energetic eddies are found to have typical amplitudes of 20 cm s 1 at 1 000 m depth to be vertically coherent over the depth range from 1 000 to 5 000 m to vary over temporal scales of 20 days and horizontal scales of 60 km and to propagate southeastward at about 12 cm s 1 observed eddy kinetic energy of 169 cm2 s at 1 000 m depth is larger than that at comparable depths in the gulf stream and kuroshio extension regions and in central drake passage like drake passage eddies these eddies transport a significant amount of heat poleward in the band of periods between 20 and 50 days but this band does not dominate the spectrum the way it does in drake passage energetic fluctuations with periods longer than 50 days effect an eddy heat flux whose sign is ambiguous so that the net meridional heat flux is not statistically significant eddy momentum fluxes transport eastward momentum northward away from the circumpolar current these fluxes are statistically significant but are only about one fourth of the size required to balance the eastward momentum put into the water column by the wind an estimate of the standing eddy momentum flux due to large spatial scale variations in the circumpolar current is also too small so that pressure forces against bottom topography is likely to be the mechanism by which the wind input is balanced

definition of antarctic oscillation index following walker s work about his thmous three oscillations published during the 1920 30s many papers were written about atmospheric oscillations a iburth atmospheric oscillation in the middle and high southern latitudes was lbund and nanted the grotarctic oscillation ao a refiers to a large scale alternation of atmospheric mass between the mid latitudes and high latitudes surthce pressure in order to understand the spatial structure of sea level pressure variation in detail empirical orthogonal fitnction analysis is applied an objective index of the antarctic oscillation index aoi is defined as the diffierence of zonal mean sea level pressure between 40os and 65os the aoi has the potential tbr clarifying climate regimes in the southern hemisphere similar to how the na and the npo has been used in the northern hemisphere were there other oscillation s besides nao npo and s especially in the southern hemisphere it had been supposed that there might be other atmospheric oscillation s in the high southern latitudes although as early as in the first quarter of this century walker 1928 had stated that just as in the north atlantic there is a pressure opposition between the azores and iceland there is an opposition between the high pressure belt across chile and the argentine on the one hand and the low pressure area of weddell sea and the bellingshausen sea on the other the scarcity of data in the southern hemisphere hindered the search tbr new oscillation s during the last two decades more comprehensive data over the southern hemisphere became available and more analyses were carried out see kidson 1975 rogers and van loon 1982 mo and l 7 ite 1985 2 4o 1986 connolley 1997 gong and wang 1998 a tburth atmospheric oscillation in the middle and high southern latitudes was tbund and nanted as the antarctic oscillation a wang 1992 gong and wang 1998 the term ao relrs to a large scale alternation of atmospheric mass between the mid latitude sur hce pressure

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

inverting the source mechanism of strombolian explosions at mt yasur vanuatu using a multi parameter dataset abstract the source mechanism of strombolian explosions at mt yasur vanuatu is analyzed using a unique data set which enables us to combine different methodologies the novelty of the approach presented here lies in the combination of seismic acoustic and doppler radar data thus using infrasound and doppler radar observations we are able to provide independent estimates of the volume of the eruptive source in the following we show that a correlation exists between source volume and the maximum particle velocity of the expelled volcanic products in order to determine the source location and the associated mechanism and to compare those two methods we use time reversal imaging and moment tensor inversion while the first method also applies to extended sources the latter might be biased by its intrinsic point source approximation we show that time reversal imaging can deliver an estimate of the source depth without any a priori assumptions even in an unfavorable scenario in terms of topography and receiver setup the inverted source mechanism retrieved from moment tensor inversion is found to be largely isotropic with minor deviatoric components the inverted source location points towards an area to the north west of the active craters indicative of a common feeder system of the activity at mt yasur however it is also evident that to fully locate the source of strombolian activity at yasur location precision must be enhanced

response of the antarctic circumpolar current to atmospheric variability abstract historical hydrographic profiles combined with recent argo profiles are used to obtain an estimate of the mean geostrophic circulation in the southern ocean thirteen years of altimetric sea level anomaly data are then added to reconstruct the time variable sea level and this new dataset is analyzed to identify and monitor the position of the two main fronts of the antarctic circumpolar current acc during the period 1993 2005 the authors relate their movements to the two main atmospheric climate modes of the southern hemisphere the southern annular mode sam and the el nino southern oscillation enso the study finds that although the fronts are steered by the bathymetry which sets their mean pathway on first order in flat bottom areas the fronts are subject to large meandering because of mesoscale activity and atmospheric forcing while the dominant mode of atmospheric variability in the southern hemisphere sam is relatively symmetric the oceanic response of the fronts is not show

circumpolar response of southern ocean eddy activity to a change in the southern annular mode 1 analysis of satellite altimeter data reveals anomalously high eddy kinetic energy eke in the antarctic circumpolar current acc during the period 2000 2002 around 2 3 years earlier 1998 the circumpolar eastward wind stress as quantified by the southern annular mode sam showed a significant positive peak and we have shown previously that the acc peaked around 1998 in response an eddy resolving ocean model is used to investigate the delay between wind forcing and the eddy response and demonstrates that the lag is due to the time taken to influence the deep circulation of the acc winds over the southern ocean have shown a strong climatic increase over the past few decades if this increase in winds is also reflected as an increase in eddy activity as our analysis suggests it might then the increased poleward heat flux may have played a significant role in the observed warming of the southern ocean citation meredith m p and a m hogg 2006 circumpolar response of southern ocean eddy activity to a change in the southern annular mode geophys res lett 33 l16608 doi 10 1029 2006gl026499

new cnes cls09 global mean dynamic topography computed from the combination of grace data altimetry and in situ measurements 1 an accurate knowledge of the ocean mean dynamic topography mdt is mandatory for the optimal use of altimetric data including their assimilation into operational ocean forecasting systems a new global 1 4 resolution mdt was computed for the 1993 1999 time period with improved data and methodology compared to the previous rio05 mdt field first a large scale mdt is obtained from the cls01 altimetric mean sea surface and a recent geoid model computed from 4 5 years of grace gravity recovery and climate experiment data altimetric sea level anomalies and in situ measurements are then combined to compute synthetic estimates of the mdt and the corresponding mean currents while the rio05 mdt was based on 10 years of in situ dynamic heights and drifting buoy velocities the new field benefits from an enlarged data set of in situ measurements ranging from 1993 to 2008 and includes all hydrological profiles from the argo array moreover the processing of the in situ data has been updated a new ekman model was developed to extract the geostrophic velocity component from the drifting buoy measurements the handling of hydrologic measurements has also been revisited compared to the previous rio05 solution the new global mdt resolves much stronger gradients in western boundary currents with mean velocities being doubled in some places moreover in comparison to several other recent mdt estimates we find that the new cnes cls09 mdt is in better agreement with independent in situ observations

natural and human induced sinkholes in gypsum terrain and associated environmental problems in ne spain the central ebro basin comprises thick evaporite materials whose high solubility produces typically karstic landforms the sinkhole morphology developed in the overlying alluvium has been studied using gravimetry and ground penetrating radar gpr on stream terraces as well as analyzing the evolution of sinkhole morphologies observed in aerial photographs taken in 1928 1957 and 1985 the sinkhole morphologies give some idea of possible subsurface processes as well as an indication of the final mechanisms involve in sinkhole development on stream terraces and cover pediments the most commonly encountered dolines are bowl shaped in their morphology with both diffuse and scarped edges in contrast dolines developed in the gypsiferous silt infilled valleys have a funnel and well shaped morphology the diffuse edged bowl shaped dolines are developed through the progressive subsidence of the alluvial cover due to washing down of alluvial particles through small voids and cracks into deeper subsurface caves resulting in a decrease alluvial density future compaction of the alluvial cover will produce surface subsidences this type of dolines are associated with negative gravity anomalies in contrast the scarped edge dolines are formed by the sudden collapse of a cavity roof the cavities and cracks formed in the gypsum karst may migrate to the surface through the alluvial deposits by piping and they may subsequently collapse in this instance the cavities can be detected by both gravity and gpr anomalies where the voids are not deeper than 4 5 m from the surface these processes forming sinkholes can be enhanced by man induced changes in the groundwater hydrologic regime by both inflows due to irrigation ditch losses or pipe leakages and by outflows from pumping activities