modeling mountain building and the seismic cycle in the himalaya of nepal a host of information is now available regarding the geological and thermal structure as well as deformation rate across the himalaya of central nepal these data are reconciled in a two dimensional mechanical model that incorporates the rheological layering of the crust which depends on the local temperature and surface processes over geological timescale 5 ma the 20 mm yr estimated shortening rate across the range is accommodated by localized thrust faulting along the main himalayan thrust fault mht the mht reaches the surface along the foothills where it is called the main frontal thrust fault mft the mht flattens beneath the lesser himalaya and forms a midcrustal ramp at the front of the higher himalaya consistent with the river incision and the anticlinal structure of the lesser himalaya farther northward the mht roots into a subhorizontal shear zone that coincides with a midcrustal seismic reflector aseismic slip along this shear zone is accommodated in the interseismic period by elastic straining of the upper crust increasing the coulomb stress beneath the front of the higher himalaya where most of the microseismic activity clusters negligible deformation of the hanging wall requires a low apparent friction coefficient less than 0 3 on the flat portion of the mht on the ramp might be as high as 0 6 sensitivity tests show that a rather compliant quartz rich rheology and a high radioactive heat production in the upper crust of 2 5 w m 3 is required erosion affects the thermal structure and interplays with crustal deformation a dynamic equilibrium is obtained in which erosion balances tectonic uplift maintaining steady state thermal structure topography and deformation field using a linear diffusion model of erosion we constrain the value of the mass diffusivity coefficient to 0 5 1 6 l0 4 m 2 yr this study demonstrates that the data are internally consistent and compatible with current understanding of the mechanics of crustal deformation and highlight the role of viscous flow in the lower crust and of surface erosion in orogeny processes on the long term as well as during interseismic period

malvinas current volume transport at 41 s a 24 yearlong time series consistent with mooring data from 3 decades and satellite altimetry fil artana camila indira instituto franco argentino sobre estudios del clima y sus impactos argentina centre national de la recherche scientifique francia universite pierre et marie curie francia

direct velocity measurements in the malvinas current we present a set of current meter measurements collected in the southwest atlantic from december 1993 to june 1995 four moorings were set out to monitor the malvinas falkland current at 40 41 s and one mooring was located within the brazil malvinas front area at 38 s the mean flow of the malvinas current has an equivalent barotropic structure whereas the vertical structure of the variable part of the flow is dominated by a barotropic like empirical mode for regions shallower than 2500 m surface intensified which appears as a linear combination of barotropic and baroclinic modes suggesting mode coupling due to the steep topography this mode appears to gradually become nearly exactly barotropic toward shallower depths higher empirical modes bottom intensified and associated with higher frequencies suggest waves trapped by the conjugated effects of topography and stratification the time variability is discussed in terms of along and cross isobath flows the along shelf flow features substantial energy in the 50 to 70 day band there is no evidence of an annual cycle nor of a distinct semiannual cycle but there is a suggestion of significant energy at periods a little shorter 135 days the cross shelf variability is important with a quite clear annual cycle associated with excursions of the subantarctic front its phase coincides with that of the brazil current transport suggesting that annual migrations of the front are predominately determined by the strength of the latter whereas the intensity of the malvinas current would only have marginal impact a conclusion that may not hold at other timescales

satellite altimetry and current meter velocities in the malvinas current at 41 s comparisons and modes of variations three year long current meter arrays were deployed in the malvinas current at 41 s below a satellite altimeter track at about 10 years intervals surface geostrophic velocities sgv derived from satellite altimetric data are compared with the in situ velocities at the upper current meter 300 m multisatellite gridded sgv compare better with in situ observations than along track sgv in spite of the proximity of the moorings to the complex brazil malvinas confluence bmc region satellite sgv are significantly correlated with the 20 day low passed in situ velocities 0 85 for along isobaths velocities 0 8 for cross isobaths velocities the recent in situ measurement period 2014 2015 stands out in the altimetry record with a long lasting 4 months high level of eddy kinetic energy at the mooring site and a southernmost location of the subantarctic front saf the first two modes of variations of sea level anomaly sla over the bmc remarkably match the first two modes of the low passed in situ velocities the first mode is associated with a latitudinal migration of the saf and the second with a longitudinal displacement of the brazil current overshoot the two modes dominate the 24 year long record of sla in the bmc with energy peaks at the annual and semiannual periods for the first mode and at 3 5 months for the second mode the sla over the southwest atlantic was regressed onto the two confluence modes of sla variations and showed remarkable standing wave train like structures in the argentine basin

interseismic strain accumulation on the himalayan crustal ramp nepal the departement of mines and geology has been monitoring the seismicity of the central himalayas of nepal since 1985 intense microseismicity and frequent medium size earthquakes ml 4 tend to cluster beneath the topographic front of the higher himalaya this 10 20km deep seismicity also correlates with a zone of localized uplift that has been evidenced from geodetic data both microseismic and geodetic data indicate strain accumulation on a mid crustal ramp that had been previously inferred from geological and geophysical evidence this ramp connects a flat decollement under the lesser and sub himalaya with a deeper decollement under the higher himalaya and probably acts as a geometric asperity where strain and stress build up during the interseismic period the large himalayan earthquakes could nucleate there and probably activate the whole flat and ramp system up to the blind thrusts of the sub himalaya

two repeat crossings of drake passage in austral summer 2006 short term variations and evidence for considerable ventilation of intermediate and deep waters abstract a high resolution full depth hydrographic section across drake passage with tracers and horizontal velocity measurements was repeated within three weeks in austral summer 2006 in situ data temperature salinity dissolved oxygen and horizontal current velocities are used to determine the location of the fronts and eddies of the antarctic circumpolar current acc inferred by barre et al 2011 from 7 day composite dynamic topography maps along the transect frontal displacements are about 40 km 2 stations along the section considerable differences in properties between the two sections are observed throughout the whole water column with values as high as 0 2 c in temperature 0 01 in salinity 0 03 kg m 3 in neutral density and 10 mol kg 1 in dissolved oxygen concentration found below a depth of 3000 m only part of the differences is attributable to frontal or eddy displacements along the section the other part results from the spatial heterogeneity of water properties upstream the section and the funnelling of the flow due to the topographic constraints of the shackleton fracture zone sfz the considerable short term differences in water properties in rather large scale structures that cannot be accounted for by frontal motions along the section call for caution when interpreting differences in hydrographical properties obtained by oceanographic cruises that are years apart in terms of climatic signals the two sections show efficient ventilation of antarctic intermediate water aaiw by winter water ww in the yaghan basin with an estimated eddy enhanced subduction rate of over 170 m year 1 the sfz constitutes a barrier causing the two southern acc fronts saccf branches to separate by about 400 km and creating sheltered conditions in partial isolation from the acc while promoting an active recirculation region in the ona basin this active recirculation marked by cyclonic eddies carrying cold fresh and oxygenated water from south of the southern boundary of the acc causes effective ventilation of the whole circumpolar deep water cdw density range the differences in small scale structures between the two sections deserve further analyses

pathways of eddies in the south atlantic ocean revealed from satellite altimeter observations 1 the majority of the kinetic energy of ocean currents is contained in the mesoscale eddies the pathways of ocean eddies which are the weather of ocean circulation are mapped from space using a decade long record of sea surface height measured by two simultaneously flying satellite radar altimeters the speed and direction of the propagation of eddies in the south atlantic ocean are presented in the paper the patterns of the eddy propagation velocity reveal the effects of the interaction between mean flow and eddies with strong influence of bottom topography the information describes a unique property of the ocean general circulation and serves as a basis for testing ocean models

wind modulation of upwelling at the shelf break front off patagonia observational evidence the south atlantic patagonian shelf is the largest chlorophyll a chl a hot spot in southern ocean color images while a persistent 1500 km long band of high chl a along the shelf break front sbf is indicative of upwelling the mechanisms that drive it are not entirely known along front wind oscillations can enhance upwelling and provide a nutrient pumping mechanism at shelf break fronts of western boundary currents here we assess wind induced upwelling at the sbf off patagonia from daily satellite chl a and winds historical hydrographic observations cross shelf chl a fluorescence transects from two cruises and in situ winds and water column structure from a mooring site satellite chl a composites segregated by along front wind direction indicate that surface chl a is enhanced at the sbf with southerly winds and suppressed with northerly winds northerly winds also result in enhanced chl a further offshore 25 50 km synoptic transects as well as mean hydrographic sections segregated by along front winds show isopycnals tilted upward for southerly winds spring observations from the mooring also suggest that southerly winds destratify the water column and northerly winds restratify in agreement with ekman transport interacting with the front moreover changes in water column temperature lag along front wind forcing by 2 4 days our results suggest that oscillations in along front winds on timescales typical of atmospheric storms 2 10 days can significantly modulate the upwelling and chl a concentrations at the sbf off patagonia revealing the importance of wind induced upwelling for shelf slope exchange at shelf break fronts of western boundary currents

brazil malvinas frontal system as seen from 9 years of advanced very high resolution radiometer data 1 surface thermal fronts in the southwestern atlantic swa ocean are examined using 9 years 1987 1995 of advanced very high resolution radiometer data fronts are detected considering a gradient based edge detector sea surface temperature gradients are calculated from 4 km resolution 5 day composite images covering the western argentine basin south of 30 s variability in the position and intensity of the fronts from seasonal to interannual timescales is characterized in six regions including different parts of the brazil current front bcf and the subantarctic front saf shelf break brazil sb b brazil malvinas collision bm c brazil current overshoot bc o shelf break malvinas sb m malvinas return flow mrf and falkland escarpment fe fronts in the sb b sb m mrf and fe regions are controlled by the bathymetry in the bm c region the bcf and saf appear to merge as a single front this front does not present large seasonal north south excursions as previously described though it pivots seasonally around a fixed point located approximately at 39 5 s 53 5 w changing its orientation from n s in winter to nw se in summer consequently on average the front intersects the 1000 m isobath at 38 30 s in summer and north of 37 s in winter in the bc o region the bcf has a u shape centered at 53 w the intensity of the fronts in each region except in the fe region presents large seasonal variability in the sb b bm c and bc o regions the frontal intensity is highest 0 35 c km during austral winter the annual components explain 83 67 and 71 of the total variance respectively in the sb m and mrf regions the saf is most intense 0 25 c km in summer and fall the annual component of the intensity fluctuations explains 29 and 38 of the total variance respectively in the fe region the annual component of frontal intensity explains only 17 of the variability in the six regions important interannual variability is found the zapiola rise centered at 45 s 43 w appears as a gradient free region closed planetary potential vorticity contours in this area suggest it is dynamically isolated

fronts of the malvinas current system surface and subsurface expressions revealed by satellite altimetry argo floats and mercator operational model outputs we examine the surface and subsurface signature of ocean fronts closely associated with themalvinas current dynamics we first evaluate the performances of the mercator ocean eddy permitting 1 128spatial resolution global operational system in the southwestern atlantic ocean over the last 10 years 2007 2016 using satellite argo float and in situ data collected near 418s observations versus model comparisons show that the model correctly reproduces the general circulation and the complex hydrographic features ofthe study area including the vicinity of the brazil malvinas confluence the model outputs accurately match the observations except in june 2015 the causes for the june 2015 mismatch are analyzed we then used themodel and satellite altimetry to identify isolines of absolute dynamic topography adt and potential densityat different depths associated with the mean front location and establish their correspondence with specificwater mass boundaries frontal displacements as depicted in satellite adt model adt and model potential density at 450 m are in general agreement the adt and potential density at 450 m provide nonidentical and complementary information on eddies shed by the polar front pf while adt depicts the surface circulation with pf eddies entrained into the energetic circulation over the deep argentine basin potential density at450 m is more effective at monitoring pf eddies feeding the malvinas current

remote and local forcing in the brazil malvinas region origins of the seasonal variability observed in current meter data from the malvinas falkland current are sought in the wind field on both a regional and circumpolar scale a singular value decomposition of the covariance of the fields makes it possible to distinguish between a local and a remote source of variability the local mode is the result of changes in the wind stress curl around 408s causing an annual modulation transverse to the mean path of the current and thus contributes little to the variability in transport it seems likely that the wind stress curl drives the annual excursions of the brazil malvinas front and forces the retroflection of the malvinas current the remote mode features increased transport trailing negative wind stress curl anomalies at drake passage with a lag of 20 30 days repeating this analysis with the winds on a circumpolar domain suggests that this might be the regional manifestation of a more global feature associating globally negative wind stress curl anomalies north of 608s with increased transport this analysis also shows that the malvinas current transport is anticorrelated with the zonal wind stress hence with the antarctic circumpolar current although initially counterintuitive this is confirmed through coherence analyses with bottom pressure measurements at the south of drake passage these results are further assessed using a 5 yr series of transport in the malvinas current derived from topex poseidon altimeter data which is compared with the circumpolar averages of both zonal wind stress and wind stress curl coherences are largest with the wind stress curl at latitudes north of drake passage up to the subtropics and also indicate that it is most influential in the pacific sector it is suggested that the antarctic circumpolar current and the malvinas current respond differently to the wind forcing and that these two modes cohabit at drake passage while the barotropic variations of the former have been shown to respond to the zonally averaged wind stress the fluctuations of the latter at timescales of 100 200 days are more sverdrupian that is sensitive to the wind stress curl lag 20 days explaining why they fluctuate with opposite phase superimposed on this intraseasonal variability at shorter periods 70 days results from baroclinic shelf waves trapped along the edge of the patagonian plateau these propagate from drake passage and may originate from equatorial kelvin waves in the pacific

orogeny and orography the effects of erosion on the structure of mountain belts a numerical model of the coupled processes of tectonic deformation and surface erosion in convergent orogens is developed to investigate the nature of the interaction between these processes crustal deformation is calculated by a two dimensional finite element model of deformation in response to subduction and accretion of continental crust erosion operates on the uplifted surface of this model through fluvial incision which is taken to be proportional to stream power the relative importance of the tectonic and erosion processes is given by a dimensionless erosion number relating convergence velocity rock erodibility and precipitation rate this number determines the time required for a system to reach steady state and the final topographic shape and size of a mountain belt fundamental characteristics of the model orogens include asymmetric topography with shallower slopes facing the subducting plate and an asymmetric pattern of exhumation with the deepest levels of exhumation opposite to subduction these characteristics are modified when the regional climate exhibits a dominant wind direction and orographically enhanced precipitation on one side of the mountain belt the two possible cases are dominant wind in the direction of motion of the subducting plate and dominant wind direction in the opposite direction of the subducting plate velocity models of the former case predict a broad zone of exhumation with maximum exhumation in the orogen interior models of the latter case predict a focused zone of exhumation at the margin of the orogen and at high erosion number a reversal in the topographic asymmetry natural examples of these two cases are presented the southern alps of new zealand exhibits the climate and exhumation asymmetry characteristic of wind in the direction opposite to motion of the subducting plate the asymmetry of topography suggests that erosion is not efficient enough to have reversed the topographic asymmetry the contrasting example of dominant wind in the direction of subduction motion is provided by the olympic mountains of washington state in this case exhumation of deep levels of the cascadia accretionary wedge shows a broad domal pattern consistent with the observed orographic precipitation

observations of the antarctic circumpolar current over the udintsev fracture zone the narrowest choke point in the southern ocean an up to date map of the antarctic circumpolar current acc fronts is constructed from the latest version of mean dynamic topography mdt from satellite altimetry and reveals the narrowest acc width in the udintsev fracture zone ufz with the strongest concentration of the three major acc fronts within a limited distance as short as 170 km about 40 narrower than that at drake passage at 144 w at the entrance of the ufz which lies between the pacific antarctic ridge par and its eastwardly offset segment offset par segment there is a triple confluence of the subantarctic front polar front and southern acc front downstream of this longitude the subantarctic front progressively meanders northward over the relatively shallow offset par segment before channeling through the eltanin fracture zone thus diverging from the polar front which proceeds through the ufz in situ observations from two recent cruises at 144 w confirm the satellite altimetry derived frontal circulation in the ufz region and yield a baroclinic transport relative to the bottom of 113 10 6 m 3 s comparable to that through drake passage the hydrographic sections show no antarctic bottom water colder than 0 2 c characteristics of major water masses are described and the implications for their potential downstream modifications at drake passage are discussed in terms of the meridional overturning circulation across the acc mesoscale eddy activity with periods shorter than 90 days is predominantly concentrated in the immediate downstream area of the offset par segment suggesting a substantial poleward eddy heat flux there

deep seismic reflection evidence for continental underthrusting beneath southern tibet the himalaya and adjacent tibetan plateau constituting earth s largest region of elevated topography and anomalously thick crust formed as a consequence of cenozoic collision between india and asia itself considered the archetypal continent continent collision1 3 here we report the first results from an attempt to image the structure of the crust beneath this region using deep seismic reflection profiling our 100 km long profile acquired in the tethyan himalaya shows a mid crustal reflection that prob ably marks the active thrust fault along which the indian plate is underthrusting southern tibet upper crustal reflections with geo metries suggestive of large scale structural imbrication of the upper crust and moho reflections from the base of the double normal thickness crust underlying the region these results lend substantial support to the view that crustal thickening beneath southernmost tibet was accomplished by wholesale underthrusting of indian continental crust beneath the structurally imbricated upper crust comprising the tethyan himalaya

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

understanding erosion rates in the himalayan orogen a case study from the arun valley understanding the rates and pattern of erosion is a key aspect of deciphering the impacts of climate and tectonics on landscape evolution denudation rates derived from terrestrial cosmogenic nuclides tcns are commonly used to quantify erosion and bridge tectonic myr and climatic up to several kiloyears time scales however how the processes of erosion in active orogens are ultimately reflected in 10be tcn samples remains a topic of discussion we investigate this problem in the arun valley of eastern nepal with 34 new 10be derived catchment mean denudation rates the arun valley is characterized by steep north south gradients in topography and climate locally denudation rates increase northward from 0 2 mm yr 1 to 1 5 mm yr 1 in tributary samples while main stem samples appear to increase downstream from 0 2 mm yr 1 at the border with tibet to 0 91 mm yr 1 in the foreland denudation rates most strongly correlate with normalized channel steepness r2 0 67 which has been commonly interpreted to indicate tectonic activity significant downstream decrease of 10be concentration in the main stem arun suggests that upstream sediment grains are fining to the point that they are operationally excluded from the processed sample this results in 10be concentrations and denudation rates that do not uniformly represent the upstream catchment area we observe strong impacts on 10be concentrations from local nonfluvial geomorphic processes such as glaciation and landsliding coinciding with areas of peak rainfall rates pointing toward climatic modulation of predominantly tectonically driven denudation rates

erosional control on the dynamics of low convergence rate continental plateau margins s u m m a r y over the last decade thermomechanical models have revealed the control of both tectonics and erosion on the morphology of continental plateaus margins however unravelling the specific effects of these two coupled processes has been difficult in practice here to assess the control of erosion we investigate the dynamics of the eastern and the northern borders of the tibetan plateau which are characterized by a low convergence rate and a steep topographic escarpment adjacent to the sichuan and tarim basins respectively thermomechanical modelling of continental lithosphere coupled with fluvial denudation reveals that important crustal deformation with large scale horizontal displacements can occur without any convergence as a response to mass transfer due to gravitational collapse and to erosional unloading these processes are sensitive to crustal structure geothermal gradient as well as surface erosion at a timescale of several million years our results suggest that this denudation triggered deformation exerts a primary control on the evolution of those plateau margins by counterbalancing the mass removal due to erosion and stabilizing the topographic escarpment this finding supports a possible explanation for the morphology of the longmen shan eastern tibet in which the paradoxical combination of persistent high topographic gradients close to the foreland and low convergence rates can be related to the influence of erosion on deformation patterns

three dimensional numerical simulations of crustal systems undergoing orogeny and subjected to surface processes as several modeling studies indicate the structural expression and dynamic behavior of orogenic mountain belts are dictated not only by their rheological properties or by far field tectonic motion but also by the efficiency of erosion and sedimentation acting on its surface until recently numerical investigations have been mainly limited to 2 d studies because of the high computational cost required by 3 d models here we have efficiently coupled the landscape evolution model cascade with the 3 d thermomechanically coupled tectonics code fantom details of the coupling algorithms between both codes are given we present results of numerical experiments designed to study the response of viscous plastic crustal materials subjected to convergence and to surface processes including both erosion and sedimentation in particular we focus on the equilibration of both the tectonic structures and on the surface morphology of the orogen we show that increasing the efficiency of fluvial erosion increases the frontal thrust angle which in turn decreases the width of the orogen in addition the maximum summit elevation of the orogen during transient evolution is significantly higher in those models showcasing surface processes than those that do not this illustrates the strong coupling between tectonics and surface processes we also demonstrate that an along strike gradient of erosion efficiency can have a major impact upon the landscape morphology and the tectonic structure and deformation of the orogen in both the across strike and along strike directions overall our results suggest that surface processes by enhancing localization of deformation can act as a positive forcing to topographic building

the open ocean side of the malvinas current in argo floats and 24 years of mercator ocean high resolution 1 12 physical reanalysis downstream of drake passage the northern branches of the antarctic circumpolar current the polar front and the subantarctic front veer northward and the latter forms the malvinas current mc the mc flows along the continental slope up to 38 s where it loops southward as the malvinas return flow using 24 years of mercator ocean physical reanalysis outputs and argo float data we explore the open ocean side of the mc we observe the occurrence of blocking events at 49 s a region where the mc is exposed to the warm and salty anticyclonic anomalies propagating westward along the steep slope of the malvinas escarpment during these events the mc is cut off from its source and the mc transport is considerably reduced at 49 s the open ocean side of the mc is regularly supplied with cold polar waters from the polar front the polar waters accumulate and recirculate between the mc and the malvinas return flow the water characteristics of the recirculation region change over time the recirculation region hosts significantly lighter and fresher waters during the period 1997 2003 compared with prior and later years the 1997 2003 salinity minimum in the recirculation region corresponds to a period with reduced feeding events at 49 s

quaternary extension in southern tibet field observations and tectonic implications we summarize evidence for quaternary and active faulting collected in the field during three sino french expeditions to southeastern tibet 1980 1982 detailed mapping of quaternary and active faults as well as microtectonic measurements indicate that normal faulting has been the dominant tectonic regime north of the himalayas in the last 2 0 5 m y the maximum horizontal principal stress in south tibet appears to be only the intermediate principal stress 2 1 being vertical south of the chord joining the eastern and western syntaxes of the himalayan arc extensional strains are principally localized within seven regularly spaced rift zones three of which have been studied in some detail the extension direction is determined to be n96 e 7 mainly from statistical averaging of strikes of newly formed normal faults throw rates on normal faults are evaluated for different time spans 2 0 5 m y 60 40 kyr and 10 2 kyr b p using structural and topographic reliefs as well as synglacial and postglacial vertical offsets the rate of quaternary extension is about 1 m y 1 along an 1100 km long ese traverse across south tibet this corresponds to a spreading rate of 1 0 6 cm yr this rate and the divergent horizontal projections of slip vectors of earthquakes along the himalayan front constrain the rate at which rigid india underthrusts southern tibet to be 2 1 cm yr although most of the normal faults appear to be independent of and nearly orthogonal to the e w mesozoic tertiary tectonic fabric the yadong gulu rift appears to be guided for over 130 km by the older oblique ne sw nyainqentanglha range and fault zones along it this reactivated zone is the most prominent left lateral strike slip fault system in se tibet excepting this zone and the vicinity of the se extremity of the karakorum fault quaternary strike slip faulting is rare in south tibet i e south of the chord between the syntaxes of the himalayan arc north of the chord the tectonic style is different there minor conjugate strike slip faulting is widespread and appears to control quaternary normal faulting which is more diffuse and subdued than in south tibet along the chord the presence of a major zone of active right lateral en echelon strike slip faults karakorum jiali fault zone probably reflects the greater facility of eastward extrusion in north central tibet in response to the northward push of india the eastern himalayan syntaxis may be an obstacle to such extrusion movements south of the chord

anatomy of the antarctic circumpolar current volume transports through drake passage the 20 year october 1992 to august 2013 observation based volume transport time series of the antarctic circumpolar current acc through drake passage dp across the jason altimeter track 104 is analyzed to better understand the acc transport variability and its potential causes the time series of three transport components total tt barotropic bt and baroclinic bc referenced to 3000 m present energetic intraseasonal fluctuations with a salient spectral peak at 50 and 36 days with the largest least variance being associated with the bt bc component low frequency variations are much less energetic with a significant variance limited to the annual and biannual timescales and show a nonstationary intermittent link with the southern annular mode and the nino 3 4 index for interannual timescales the region around 57 s in the yaghan basin appears to be a strategic point for a practical monitoring of the acc transport as the whole track tt is significantly correlated with the local tt r 5 0 53 and bt r 5 0 69 around 57 s these local bt and tt variations are associated with a well defined tripole pattern in altimetric sea level anomaly sla there is evidence that the tripole pattern associated with bt is locally generated when the bc associated mesoscale slas which have propagated eastward from an upstream area of dp cross the shackleton fracture zone to penetrate into the yaghan basin barotropic basin modes excited within the yaghan basin are discussed as a plausible mechanism for the observed energy containing intra seasonal spectral peaks found in the transport variability

bottom currents derived from a shipborne adcp on woce cruise a11 in the south atlantic abstract this paper is divided into two parts the first describing an enhancement of the shipborne adcp system and the second describing information about bottom currents that have been obtained therefrom on woce cruise a11 in the south atlantic punta arenas to cape town rrs discovery has been fitted with a gps3df receiver and an array of antennas about its bridge which determine the instantaneous attitude of the ship the heading record from this instrument has been compared with the ship s gyrocompass throughout the 40 day cruise differences have been calculated and examined according to heading speed and movements underway differences are found insensitive to heading except in a southerly sector but on station differences exhibit a sinusoidal dependence on heading with range 3 steaming from a station led to transient behavior with recognizable effects for 1 hour the results are generally consistent with earlier reports and are attributed to gyro error an improved heading measurement has a

the malvinas current at the confluence with the brazil current inferences from 25 years of mercator ocean reanalysis twenty five years of high resolution 1 12 ocean reanalysis are used to examine the confluence of the malvinas current mc with the brazil current bc from synoptic to interannual time scales the model transports of the mc 38 0 sv 7 4 sv 57 at 41 s and the bc 23 0 sv 11 sv at 36 s agree with observations the model shows the branching of the mc near the confluence with an offshore branch returning south and an inner branch sinking below the bc and managing to continue northward along the continental slope northward velocities associated with the subsurface inner branch peak at 40 cm s at 36 s at 700 m depth the model documents the migrations of the subantarctic saf and subtropical fronts stf at the confluence the saf and stf positions vary over a large range at synoptic 800 km and interannual scale 300 and 200 km respectively compared to the rather small seasonal migrations of the stf 150 km and saf 50 km while trends in the mc are small over the 25 years of the reanalysis the bc becomes more intense 12 5 cm s saltier 0 37 psu and warmer 2 5 c in the upper 1 000 m these trends are accompanied with a southward displacement of the stf and the saf of 150 and 50 km

fronts meanders and eddies in drake passage during the ant xxiii 3 cruise in january february 2006 a satellite perspective abstract we used satellite altimetric data to provide a context for the results of the ant xxiii 3 cruise in january february 2006 both in time 16 years and space the whole of drake passage the repeat of the hydrographical section within 3 weeks permitted different comparisons between the in situ datasets and the satellite data products comparisons suggested that the multi satellite product improved the temporal resolution on a jason 1 track a detailed analysis of the four absolute dynamic topography maps contemporaneous with the ant xxiii 3 cruise permitted identification of the location of the frontal branches of the antarctic circumpolar current of the major meanders and eddies this spatial context proved particularly valuable for the interpretation of the in situ data see companion papers of provost et al 2011 renault et al 2011 sudre et al 2011 the altimetric time series documented the long term trends in sea surface height the recurrence of major frontal meanders and eddies and the statistical links between them negative trends in the yaghan basin indicated that both the subantarctic front and the polar front have shifted to the north of their climatological location this northward shift in the yaghan basin contrasts with the large scale southward shift in the polar front current core described in the literature and is probably related to the local bottom topography in drake passage sea level anomaly patterns observed during the cruise were related to statistical modes of the corresponding variations in drake passage for example the southward meander of the subantarctic front at the entrance to drake passage was part of a dipole comprising an adjacent polar front meander and occurred with a close to annual periodicity a census of eddies in the ona basin revealed that the spatial distribution of anticyclonic eddies was consistent with generation from a meander of the polar and southern acc fronts over the ona seafloor depression while cyclonic eddies mostly originated from meanders of southern fronts associated with two rises on the continental slope the ona rise and the terror rise

study of plate deformation and stress in subduction processes using two dimensional numerical models two dimensional finite element modeling is used to model subduction of an oceanic lithospheric plate beneath continental lithosphere the subduction process is initiated along a preexisting inclined fault and continues until reaching 400 km of total convergence the lithosphere is assumed to be underlain by an in viscid asthenosphere different rheological laws have been considered for the lithosphere including elasticity and elastoplasticity the modeling shows that both the stress system in the plates and the surface topography are strongly dependent on two main parameters the density contrast between lithosphere and asthenosphere l a and the coefficient of friction along the subduction plane varying these two parameters allows explanation of the main characteristics of real subduction zones and results in two major regimes manifested by extension or compression in the arc back arc system extension and back arc rifting corresponds to a positive density contrast and a low coefficient of friction while negative values and or high friction leads to a compressional regime the coexistence of trench arc compression and back arc tension is only possible for a coefficient of friction lower than 0 1 the results of the numerical experiments agree with those of experimental modeling conducted under similar physical assumptions

decoupling of erosion and precipitation in the himalayas the hypothesis that abrupt spatial gradients in erosion can cause high strain rates in active orogens has been supported by numerical models that couple erosional processes with lithospheric deformation via gravitational feedbacks1 2 3 most such models invoke a stream power rule in which either increased discharge or steeper channel slopes cause higher erosion rates spatial variations in precipitation and slopes are therefore predicted to correlate with gradients in both erosion rates and crustal strain here we combine observations from a meteorological network across the greater himalaya nepal along with estimates of erosion rates at geologic timescales greater than 100 000 yr from low temperature thermochronometry across a zone of about 20 km length spanning the himalayan crest and encompassing a more than fivefold difference in monsoon precipitation significant spatial variations in geologic erosion rates are not detectable decreased rainfall is not balanced by steeper channels instead additional factors that influence river incision rates such as channel width and sediment concentrations must compensate for decreasing precipitation overall spatially constant erosion is a response to uniform upward tectonic transport of greater himalayan rock above a crustal ramp

bathymetric prediction from dense satellite altimetry and sparse shipboard bathymetry the southern oceans south of 30 s are densely covered with satellite derived gravity data track spacing 2 4 km and sparsely covered with shipboard depth soundings hundreds of kilometers between tracks in some areas flexural isostatic compensation theory suggests that bathymetry and downward continued gravity data may show linear correlation in a band of wave lengths 15 160 km if sediment cover is thin and seafloor relief is moderate at shorter wave lengths the gravity field is insensitive to seafloor topography because of upward continuation from the seafloor to the sea surface at longer wavelengths isostatic compensation cancels out most of the gravity field due to the seafloor topography we combine this theory with wiener optimization theory and empirical evidence for gravity noise to signal ratios to design low pass and band pass filters to use in predicting bathymetry from gravity the prediction combines long wavelengths 160 km from low pass filtered soundings with an intermediate wavelength solution obtained from multiplying downward continued band pass filtered 15 160 km gravity data by a scaling factor s s is empirically determined from the correlation between gravity data and existing soundings in the 15 160 km band by robust regression and varies at long wave lengths we find that areas with less than 200 m of sediment cover show correlation between gravity and bathymetry significant at the 99 level and s may be related to the density of seafloor materials in these areas the prediction has a horizontal resolution limit of 5 10 km in position and is within 100 m of actual soundings at 50 of grid points and within 240 m at 80 of these in areas of very rugged topography the prediction underestimates the peak amplitudes of seafloor features images of the prediction reveal many tectonic features not seen on any existing bathymetrie charts because the prediction relies on the gravity field at wavelengths 160 km it is insensitive to errors in the navigation of sounding lines but also cannot completely reproduce them therefore it may be used to locate tectonic features but should not be used to assess hazards to navigation the prediction is available from the national geophysical data center in both digital and printed form

the role of vorticity fluxes in the dynamics of the zapiola anticyclone 1 the argentine basin in the south atlantic ocean is one of the most energetic regions in the ocean with complicated dynamics which plays an important role in the global climate a number of observations have discovered an intense anticyclonic gyre of barotropic circulation around the zapiola rise in the center of the basin theoretical studies have shown that the zapiola anticyclone represents an eddy driven flow controlled by bottom friction recent advances in high resolution global ocean data syntheses performed using nasa supercomputing facilities provide realistic simulations of the circulation and the variability in the argentine basin using these simulations and satellite altimeter observations we analyzed the vorticity balance of the zapiola anticyclone our results suggest the dominance of vorticity fluxes and the advection of the potential vorticity over a nonuniform bottom topography in determining the variability of the gyre while the impact of the local wind stress is small the divergence of the relative vorticity anomaly advection by eddies is found to be the most important contributor to the relative vorticity flux divergence influencing the variability of the zapiola anticyclone our results demonstrate that the relative vorticity influencing the variability of the anticyclone is mainly advected from the south where the northern branch of the antarctic circumpolar current at the subpolar front is located

malvinas current variability from argo floats and satellite altimetry the malvinas current mc is an offshoot of the antarctic circumpolar current acc downstream of drake passage the northern fronts of the acc veer northward cross over the north scotia ridge nsr and the malvinas plateau and enter the argentine basin we investigate the variations of the mc circulation between the nsr and 41 s and their possible relations with the acc circulation using data from argo floats and satellite altimetry the data depict meandering and eddy shedding of the northern acc jets as they cross the nsr the altimetry fields show that these eddies are trapped break down and dissipate over the malvinas plateau suggesting that this region is a hot spot for dissipation of mesoscale variability variations of sea level anomalies sla across the nsr do not impact the mc further north except for intra seasonal variability associated with coastal trapped waves altimetry and float trajectories show events during which a large fraction of the mc is cut off from the acc blocking events at around 48 5 s are a recurrent feature of the mc circulation over the 23 year altimetry record we detected 26 events during which the mc surface transport at 48 5 s was reduced to less than half its long term mean blocking events last from 10 to 35 days and do not present any significant trend these events were tracked back to positive sla that built up over the argentine abyssal plain future work is needed to understand the processes responsible for these blocking events

gravity anomalies flexure of the indian plate and the structure support and evolution of the himalaya and ganga basin bouguer gravity anomalies along four profiles across the western himalaya and ganga basin show large deviations from local isostatic equilibrium a deficit of mass characterizes the ganga basin and an excess underlies the lesser himalaya both can be understood if the indian plate is flexed down by the distributed load of part of the mountains the cross sectional shape of the ganga basin seems to be controlled by the deflection of the indian plate which we compute assuming the indian plate to overlie an inviscid fluid from the shapes of both bouguer anomaly profiles and the basement topography we place bounds on the flexural rigidity of such a plate if the ganga basin is a steady state feature then the age of the basal sediments in a given locality should be proportional to the distance of that locality from the southern edge of the basin if the rate of convergence of india and the himalaya were constant that rate should equal the distance divided by the corresponding age we find a rate of 10 to 15 mm a for the last 15 to 20 ma which is consistent with a large part of the 50 mm a rate of convergence between india and eurasia being absorbed by the eastward extrusion of parts of tibet profiles of bouguer gravity anomalies show only a small peak or plateau over the southern edge of the lesser himalaya implying that the boundary between the light sediments of the ganga basin and the heavier crustal rocks of the lesser himalaya is not sharp and that there exists some light material beneath the range we infer that some sediment deposited in the ganga basin has been underthrust beneath the lesser himalaya but the quantity is small most of this sediment probably is scraped off the indian plate to make the foothills of the range we find that the load of the high himalaya is too large to be supported solely by elastic stress in the indian plate if the flexural rigidity of the plate is constant and if no other external forces act on the plate the observed gradient in bouguer gravity anomalies increases from an average of about 1 mgal km over the ganga basin and lesser himalaya to about 2 mgal km over the high himalaya this increase in the gravity gradient implies that the moho dips more steeply 10 15 beneath the high himalaya than beneath the lesser himalaya 2 3 we interpret this steepening of the moho to be due to a weakening of the plate which allows it to bend more sharply beneath the high himalaya than farther south with the inclusion of a weak segment of indian plate beneath the high himalaya calculated anomalies show a somewhat increased gradient beneath the high himalaya but when the weight of the entire himalaya is used as a load on the plate calculated anomalies are more negative than observed therefore an external force system is needed to support much of the weight of the high himalaya as well as to bend the plate sufficiently beneath the high himalaya the magnitudes of the bending moment and the force per unit length that must be applied to the end of the plate are compatible with their sources being gravity acting on a part of india s mantle lithosphere stripped of its crust and underthrust beneath southern tibet

on the origins of the variability of the malvinas current in a global eddy permitting numerical simulation 1 this article investigates the origins of the variability of the malvinas current mc transport using the results of an eddy permitting ocean general circulation model first the dynamical links between the variabilities of the mc and the antarctic circumpolar current acc transports at the drake passage are established time series analyses indicate that the connection between the transport variations of the acc and the mc is masked by high frequency oscillations although a substantial portion of this highfrequency variability is produced and dissipated locally there are also anomalies that propagate between those regions the most conspicuous of these signals has an average speed of 6 7 cm s 1 and a period of 150 days second the contribution of the wind forcing to the variability of the acc and the mc is determined from principal estimator patterns analysis the analysis indicates that the variance of the transport of both currents is more directly related to the variability of the wind stress than to the wind stress curl the transport variability is particularly sensitive to zonal wind stress anomalies in the latitudinal range of the drake passage that extends farther north over the south indian ocean a rather counterintuitive result of our analysis is that the wind stress forcing over the south atlantic ocean is unimportant to the variability of the mc transport

sediment flux from a mountain belt derived by landslide mapping in humid uplands landsliding is the dominant mass wasting process in the western southern alps of new zealand landslides are scale invariant and have a power law magnitude frequency distribution independent studies from other regions suggest that this is a general property of landsliding this observation is of critical importance to the evaluation of the impact of events of different length scales over different time intervals on landscape evolution it is particularly useful when estimating regional geomorphic rates because it constrains the frequency and overall significance of extreme events which cannot otherwise be evaluated by integrating the complete response of the system we estimate the regional denudation rate due to landsliding to be 9 4 mm yr 1 sediment discharge from the western southern alps is dominated by landslide derived material

quantifying sand provenance and erosion marsyandi river nepal himalaya we use petrographic and mineralogical data on modern sediments to investigate erosion patterns in the marsyandi basin of the central himalaya a privileged natural laboratory in which a series of multidisciplinary geomorphological sedimentological geochemical and geochronological studies have been recently carried out to unravel the interrelationships between tectonic climatic and sedimentary processes in high relief orogenic belts although relative erosion patterns are effectively constrained by analyses of replicate samples along six successive tracts of the marsyandi river uncertainties are caused by potential compositional variation between the monsoon and post monsoon season estimates of erosion rates are significantly affected by poor knowledge of total sediment flux through the basin ourresults support focusederosion of the southern tectonically lower part of the greater himalayain the hangingwall of the mct zone where thesummer monsoon reachesitspeak intensity up to 5 m a andsediment yieldsanderosion ratesreach14 100 3400t km 2 and 5 1 1 2 mm a erosion rates sharply decrease southward in low relief lesser himalayan units 1 6 0 6 mm a and also progressivelydecreasenorthwardsinthehigh altitude tectonically upperpartofthegreaterhimalaya whererainfalldecreasesrapidly to b2 m a even areas of extreme topography such as the manaslu granite are characterized by relatively low erosion rates 2 4 0 9 mm a because precipitations become too scarce to feed significant ice flux and glacial activity monsoonal rainfall decreases further tob0 5 m a in the tethys himalayan zone farther north where erosion rates are 1 mm a coupling between erosion and peak monsoonal rainfall along the southern front of the greater himalaya is consistent with both channel flow models of tectonic extrusion

erosion as a driving mechanism of intracontinental mountain growth in nature mountains can grow and remain as localized tectonic features over long periods of time 10 m y by contrast according to current knowledge of lithospheric rheology and neglecting surface processes any intracontinental range with a width that exceeds that which can be supported by the strength of the lithosphere should collapse within a few tens of millions of years for example assuming a quartz dominated crustal rheology the relief of a range initially 3 km high and 300 400 km wide is reduced by half in about 15 m y as a result of lateral spreading of its crustal root we suggest that surface processes might actually prevent such a subsurface collapse removal of material from topographic heights and deposition in the foreland oppose spreading of the crustal root and could eventually drive a net influx of material toward the orogeny we performed a set of numerical experiments in order to validate this hypothesis a section of a lithosphere with a brittle elasto ductile rheology initially loaded by a mountain range is submitted to horizontal shortening and to surface processes if erosion is intense material is removed more rapidly than it can be supplied by crustal thickening below the range and the topography is rapidly smoothed for example a feature 3 km high and 300 400 km wide is halved in height in about 15 m y for an erosion coefficient k 10 3 m 2 yr the erosion rate is of the order of a few 0 1 mm yr this regime might be called erosional collapse if erosion is not active enough the crustal root spreads out laterally and subsurface collapse occurs in the third intermediate regime removal of the material by erosion is dynamically compensated by isostatic rebound and inward flow in the lower crust so that the range can grow in this mountain growth regime the range evolves toward a characteristic graded shape that primarily depends on the erosion law the erosion rate may be high e g 0 5 0 9 mm yr close to the rate of tectonic uplift e g 0 7 1 1 mm yr and few times higher than the rate of topographic uplift 0 15 0 2 mm yr these experiments show that surface processes can favor localized crustal shortening and participate in the development of an intracontinental mountain surface processes must therefore be taken into account in the interpretation and modeling of long term deformation of continental lithosphere conversely the mechanical response of the lithosphere must be accounted for when large scale topographic features are interpreted and modeled in terms of geomorphologic processes

variations of the argentine gyre observed in the grace time variable gravity and ocean altimetry measurements this work is supported by taiwan ministry of science and technology grants 105 2811 m 001 031 and 106 2116 m 001 013 and by national nature science foundation of china grants 41474019 41504014 and 41704012

fluvial incision and tectonic uplift across the himalayas of central nepal the pattern of fluvial incision across the himalayas of central nepal is estimated from the distribution of holocene and pleistocene terraces and from the geometry of modern channels along major rivers draining across the range the terraces provide good constraints on incision rates across the himalayan frontal folds sub himalaya or siwaliks hills where rivers are forced to cut down into rising anticlines and have abandoned numerous strath terraces farther north and upstream in the lesser himalaya prominent fill terraces were deposited probably during the late pleistocene and were subsequently incised the amount of bedrock incision beneath the fill deposits is generally small suggesting a slow rate of fluvial incision in the lesser himalaya the terrace record is lost in the high range where the rivers are cutting steep gorges to complement the terrace study fluvial incision was also estimated from the modern channel geometries using an estimate of the shear stress exerted by the flowing water at the bottom of the channel as a proxy for river incision rate this approach allows quantification of the effect of variations in channel slope width and discharge on the incision rate of a river the determination of incision rates requires an additional lithological calibration the two approaches are shown to yield consistent results when applied to the same reach or if incision profiles along nearby parallel reaches are compared in the sub himalaya river incision is rapid with values up to 10 15 mm yr it does not exceed a few millimeters per year in the lesser himalaya and rises abruptly at the front of the high range to reach values of 4 8 mm yr within a 50 km wide zone that coincides with the position of the highest himalayan peaks sediment yield derived from the measurement of suspended load in himalayan rivers suggests that fluvial incision drives hillslope denudation of the landscape at the scale of the whole range the observed pattern of erosion is found to closely mimic uplift as predicted by a mechanical model taking into account erosion and slip along the flat ramp flat geometry of the main himalayan thrust fault the morphology of the range reflects a dynamic equilibrium between present day tectonics and surface processes the sharp relief together with the high uplift rates in the higher himalaya reflects thrusting over the midcrustal ramp rather than the isostatic response to reincision of the tibetan plateau driven by late cenozoic climate change or late miocene reactivation of the main central thrust

circumpolar structure and distribution of the antarctic circumpolar current fronts 1 mean circumpolar paths 1 high resolution hydrographic sections and maps of the gradient of sea surface height ssh reveal that the antarctic circumpolar current acc consists of multiple jets or frontal filaments here we use a 15 year time series of ssh observations to determine the circumpolar structure and distribution of the acc fronts the jets are consistently aligned with particular streamlines along the entire circumpolar path confirming and extending the results of an earlier study restricted to the region south of australia the intensity of the fronts as measured by the cross front gradient of ssh varies along the fronts and the individual branches merge and diverge often in response to interactions with bathymetry maps of absolute velocity at 1000 m depth derived from argo trajectories confirm the existence of multiple current cores throughout the southern ocean high resolution hydrographic sections and profiles of temperature and salinity from argo floats are used to show that the front locations derived from fitting ssh contours to maps of ssh gradient are consistent with locations inferred from the traditional criteria based on water mass properties suitably modified to account for multiple frontal branches three regions are examined in detail the crozet plateau the kerguelen plateau and the scotia sea these examples show how recognition of the multiple jets of the acc can help resolve discrepancies between previous studies of acc fronts

thrust tectonics crustal shortening and the structure of the far eastern nepal himalaya balanced and restored structural sections across the far eastern nepal himalaya have been constructed in order to determine the structure and evolution of the himalayan orogenic wedge and the amount of tectonic shortening the region has undergone since the initiation of thrusting along the main central thrust mct the far eastern nepal himalaya is comprised of three distinct thrust bound tectonic packages the higher himalayan crystalline thrust sheet the lesser himalayan metasediment thrust package and the sub himalayan imbricate fan the higher himalayan crystallines consisting of kyanite and sillimanite bearing gneisses intruded by the miocene jannu leucogranites have been thrust over the lesser himalayan metasediments along the mct for a distance of 140 km to 175 km the lesser himalayan metasediments are a 12 km thick unit consisting primarily of phyllites metaquartzites and mylonitic augen gneisses in which garnet biotite and chlorite metamorphic zones are exposed in progressively deeper structural levels the lesser himalayan metasediment thrust package is underlain by a decollement the main detachment fault mdf which lies at a calculated depth of between 6 and 10 km underneath the mahabharat lekh and at a calculated depth of 20 to 25 km north of the tamar khola dome the tamar khola dome overlies a footwall ramp along the mdf where the mdf cuts upsection through the lesser himalayan metasediments the lesser himalayan thrust package probably has an internal structure aproximating a hinterland dipping duplex with the mct and the mdf corresponding to the roof and floor thrusts respectively both the tamar khola thrust an out of sequence breach thrust and the main boundary thrust mbt are splay thrusts off of the mdf the sub himalaya consisting of nonmetamorphosed sedimentary rocks displays an emergent imbricate fan geometry and is underlain by the southern continuation of the mdf which lies at a depth of 5 5 km to 6 km beneath the siwalik hills folding and thrusting within the lesser himalayan thrust package and the sub himalayan imbricate fan have accomodated 45 to 70 km of tectonic shortening total north south shortening across the higher lesser and sub himalaya of far eastern nepal south of the tibetan plateau has been of the order of 185 km to 245 km and has occurred at an average rate of 7 4 mm to 15 3 mm per year since the initiation of the mct between 16 and 25 ma

himalayan tectonics explained by extrusion of a low viscosity crustal channel coupled to focused surface denudation recent interpretations of himalayan tibetan tectonics have proposed that channel flow in the middle to lower crust can explain outward growth of the tibetan plateau1 2 3 and that ductile extrusion of high grade metamorphic rocks between coeval normal and thrust sense shear zones can explain exhumation of the greater himalayan sequence4 5 6 7 here we use coupled thermal mechanical numerical models to show that these two processes channel flow and ductile extrusion may be dynamically linked through the effects of surface denudation focused at the edge of a plateau that is underlain by low viscosity material our models provide an internally self consistent explanation for many observed features of the himalayan tibetan system8 9 10

variations in the malvinas current volume transport since october 1992 1 we present a set of new current meter measurements collected to monitor the malvinas current mc near its merger with the brazil current at 40 41 s from december 2001 to february 2003 below a jason 1 altimeter track these measurements are compared to former measurements obtained 8 years earlier at the same location they also provide new information on the core of the mc on the continental slope above the 1000 m isobath where a mooring had been previously lost there most of the velocity variation is along isobath 80 of the variance and shows a significant annual cycle the two data sets provide coherent means and statistical parameters on the vertical structure of the flow a 14 year long time series of mc volume transport is derived using satellite altimetry the good correlation between the altimetry derived transport and the transport estimated from the current meter data persists in time over 0 7 for each measurement period a spectacular shift in the spectral composition of transport variations was observed from 1992 until the end of 1997 transport variations occurred at rather short periods 50 90 days and to some degree around 180 days whereas after year 2000 longer periods including a seasonal cycle predominated altimetry derived anomalies of surface geostrophic velocities along the core of the mc show a similar shift in spectral composition suggesting a remote forcing origin

gravity anomalies crustal structure and thermo mechanical support of the himalaya of central nepal summary we use two gravity profiles that we measured across central nepal in conjunction with existing data to constrain the mechanical behaviour and the petrological structure of the lithosphere in the himalayan collision zone the data show 1 overcompensation of the foreland and undercompensation of the higher himalaya as expected from the flexural support of the range 2 a steep gravity gradient of the order of 1 3 mgal km x1 beneath the higher himalaya suggesting a locally steeper moho and 3 a 10 km wide hinge in southern tibet we compare these data with a 2 d mechanical model in which the indian lithosphere is flexed down by the advancing front of the range and sedimentation in the foreland the model assumes brittle coulomb failure and nonlinear ductile flow that depends on local temperature which is computed from a steadystate thermal model the computed moho fits seismological constraints and is consistent with the main trends in the observed bouguer anomaly it predicts an equivalent elastic thickness of 40 50 km in the foreland the flexural rigidity decreases northwards due to thermal and flexural weakening resulting in a steeper moho dip beneath the high range residuals at short wavelengths over distances of 20 30 km are interpreted in terms of 1 sediment compaction in the foreland dr 150 kg m x3 between the lower and middle siwaliks 2 the contact between the tertiary molasse and the meta sediments of the lesser himalaya at the mbt dr 220 kg m x3 and 3 the palung granite intrusion in the lesser himalaya dr 80 kg m x3 finally if petrological transformations expected from the local p t are assumed a gravity signature of the order of 250 mgal is predicted north of the lesser himalaya essentially due to eclogitization of the lower crust which is inconsistent with the gravity data we conclude that eclogitization of the indian crust does not take place as expected from a steady state local equilibrium assumption we show however that eclogitization might actually occur beneath southern tibet where it could explain the hinge observed in the gravity data we suspect that these eclogites are subducted with the indian lithosphere

numerical modeling of mountain building interplay between erosion law and crustal rheology 1 coupling between erosion and tectonics is thought to play a determinant role in orogenic evolution here we investigate the interplay in this coupling between the assumed erosion law and the crustal rheology at the margin of a collisional plateau like the himalaya of central nepal lithospheric deformation is calculated over a time scale of 100 kyr by a 2d finite element model that incorporates the rheological layering of the crust and the main features of the convergence across the range for the upper boundary condition two surface processes were tested a linear diffusion model and a 1d1 2 integrative model including fluvial incision along the fluvial network and hillslope erosion by landsliding model results and their sensitivity to the chosen combinations of erosion law and crustal properties are discussed in light of the constraining geologic and geomorphologic observations in contrast with the conclusions of cattin and avouac 2000 where a compliant quartz rich crustal rheology and diffusion law were required we combine a composite quartz diabase rheology for the crust with fluvial incision erosion law to account for erosion and elevation profiles across the himalaya of central nepal more generally it is proposed that because of the interplay between the dominant denudation conditions and the rheology of the crust both well documented erosion rates and processes can provide significant constraints on crustal properties within an active orogen

subregional characterization of mesoscale eddies across the brazil malvinas confluence horizontal and vertical motions associated with coherent mesoscale structures including eddies and meanders are responsible for significant global transports of many properties including heat and mass mesoscale vertical fluxes also influence upper ocean biological productivity by mediating the supply of nutrients into the euphotic layer with potential impacts on the global carbon cycle the brazil malvinas confluence bmc is a western boundary current region in the south atlantic with intense mesoscale activity this region has an active role in the genesis and transformation of water masses and thus is a critical component of the atlantic meridional overturning circulation the collision between the malvinas and brazil currents over the patagonian shelf slope creates an energetic front that translates offshore to form a vigorous eddy field recent improvements in gridded altimetric sea level anomaly fields allow us to track bmc mesoscale eddies with high spatial and temporal resolutions using an automated eddy tracker we characterize the eddies across fourteen 5 5 subregions eddy centric composites of tracers and geostrophic currents diagnosed from a global reanalysis of surface and in situ data reveal substantial subregional heterogeneity the in situ data are also used to compute the evolving quasi geostrophic vertical velocity qg associated with each instantaneous eddy instance the qg eddy composites have the expected dipole patterns of alternating upwelling downwelling however the magnitude and sign of azimuthally averaged vertical velocity varies among subregions maximum eddy values are found near fronts and sharp topographic gradients in comparison with regional eddy composites subregional composites provide refined information about mesoscale eddy heterogeneity this article is protected by copyright all rights reserved

fuzzy clustering of oceanographic sound speed profiles for acoustic characterization historic oceanographic sound speed profiles have traditionally been grouped by area and time period usually one degree square area and monthly time after grading the profiles mean profiles and standard deviations are calculated from the accepted profiles and in the acoustics community they are then used to predict the expected acoustic response of the region here the historic profiles in noaa s world ocean database 2005 wod2005 will be divided into the same area and time periods but in subsets with a sufficient number of profiles fuzzy clustering will be employed on acoustically relevant oceanographic parameters mixed layer depth surface temperature sound speed gradient etc to divide the population into multiple clusters a parabolic equation acoustic transmission model is then applied on the wod2005 statistical profiles and on the fuzzy cluster populations conclusions will be drawn about the suitability of this clustering to capture the variability of acoustic response at a given time and p

anatomy of subinertial waves along the patagonian shelf break in a 1 12 global operational model the patagonian slope hosts a variety of waves we used a state of the art ocean reanalysis to examine waves at the shelf break and in the core of the malvinas current mc at periods larger than 10 days statistics over 25 years indicated three types of signals in phase signals at specific locations of the shelf break to the south of 47 s fast propagating signals all along the shelf break phase speed from 140 cm s to 300 cm s at periods between 5 and 110 days and slower signals in the core of the mc phase speeds from 10 cm s to 30 cm s at 20 day 60 day and 100 day periods the large zonal wind stress variations south of 47 s forced in phase along slope velocity variations and triggered fast propagating waves at distinct sites corresponding to abrupt changes in the shelf break orientation the shelf break waves modulated the intensity of the inshore jet which varied from 0 to 30 cm s at 100 m depth and had spatial and temporal structures and scales consistent with those of observed upwelling events slow propagating waves in the core of the mc had along slope wavelengths between 450 and 1200 km and were not forced by the local winds they were tracked back to the drake passage and the malvinas escarpment