transport of pb and sr in leaky aquifers of the bufa del diente contact metamorphic aureole north east mexico the sr and pb isotopes from the 31 6 0 3 ma 2 old diente del bufa alkali syenite northeastern mexico and marbles of its contact aureole were used to trace the sources and the mobility of these metals during hydrothermal activity chert layers form aquifers within the marbles the marbles represent aquitards during fluid wallrock reaction the chert layers developed wollastonite rims early wollastonite rims have sr and pb isotopic compositions similar to those of their immediate host marbles which indicates that the isotopic composition of sr and pb is initially buffered by the marble later wollastonite and other replacement minerals rimming the aquifer have sr and pb isotopic compositions that carry with time increasingly larger contributions from the high salinity magmatic brine the sr and pb contributions from the alkali syenite can be traced isotopically for more than 90 m away from the contact of the intrusion in contrast sr and pb originating from the alkali syenite are traceable within the marbles only for 3 to 5 cm from the aquifer marble boundary this distance is comparable to the spatial distribution of isotopic alterations of c and o implying that sr and pb were transported into the marbles through a fluid phase the isotopic variation of sr pb c and o across the aquifer marble profiles reflects infiltration as a transport mechanism rather than diffusion because sr and pb are minor components in both the infiltrating fluid and the rock and because their concentrations are strongly affected by the distribution coefficients among the solid phases present there is little correlation between the isotopic compositions of the trace elements sr and pb and those of c and o which are major components in fluid and rock very thin meta argillite rinds at the outer margin of the aquifer represent residual material after the dissolution of calcite they are distinctly enriched in rb sr and u the rb and sr are to some extent residual from the original limestone mineralogy whereas u is dominantly derived from the magmatic fluid and leaked from the aquifer with the escaping immiscible co2 rich h2o co2 fluid that was produced by decarbonation the 238u 204pb values ranging from 100 to 250 and distinctly lowered th u in the meta argillite rims 1 demonstrate that u was transported with the magmatic fluid along the aquifer and 2 imply that during unmixing of the highly saline magmatic fluid u fractionated into the co2 rich h2o co2 fluid from which it precipitated selectively in the meta argillite band across the aquifer radioautographs demonstrate that the upper meta argillite rim has 20 to 40 times more u than the lower rim which implies that 20 to 40 times more co2 rich h2o co2 fluid has left through the upper aquifer contact

circulation mixing and production of antarctic bottom water abstract the antarctic source of bottom water to the abyssal layer of the world ocean is examined as well as its large scale flow pattern and ultimate entrainment rate into the deep water above we make use of the available high quality station data in the southern ocean to construct bottom maps of neutral density and mean property maps including chlorofluorocarbon cfc for the abyssal layer underneath a selected neutral density surface the maximum density at the sill depth of drake passage is used to distinguish between the voluminous deep water mass that is a continuous component of the antarctic circumpolar current from the relatively denser bottom water originated along the antarctic continental margins based on water density antarctic bottom water aabw is defined here generically to include all volumes of non circumpolar water of antarctic origin over the shelf regime multiple localized sources of specific aabw types contribute to the abyssal layer of the adjacent antarctic basins characteristics of these dense bottom waters reflect closely those observed on the parent shelf water mass spreading paths of newly formed deep and bottom waters over the slope regime and their subsequent oceanic circulation patterns are analyzed on the basis of global property maps for the aabw layer interior mixing and interbasin exchanges of aabw are deduced from mean characteristic curves following the southern streamline of the antarctic circumpolar current outflow and mixing of aabw from the weddell sea to the argentine basin is depicted using density and cfc distributions of two zonal hydrographic lines recirculation and mixing of deep and bottom waters within the weddell gyre are also detailed using a meridional section along the greenwich meridian the strength of all localized sources of aabw combined is estimated by two independent approaches an estimate of the total production rate of aabw is calculated based on the oceanic cfc budget for the aabw layer offshore of the 2500 m isobath the sum of all downslope inputs of well ventilated bottom water types underneath the top isopycnal must account for the measured cfc content in the bottom layer the resulting total aabw production rate is about 8 sv which is a conservative figure that neglects the loss of cfc bearing waters across the top isopycnal in recent years whereas about 9 5 sv is calculated assuming a well mixed bottom layer making use of their transient nature cfc distributions at the top of the aabw layer indicate that more direct and rapid entrainment of cfc rich bottom waters below occurs over localized areas with relatively strong upwelling rates and enhanced vertical mixing a second more ad hoc but independent oceanic mass budget of the bottom layer is also constructed a typical basin wide rate of deep upwelling of 3 10 7 m s 1 requires 10 sv 1 sv 106 m3 s 1 of newly formed aabw to sink down the slope around antarctica we have also formulated a spatial distribution of deep upwelling on the isopycnal at the top of the aabw it is expressed as a combination of wind topographic and turbulent components which in turn are functions of the isopycnal depth bottom depth and bottom layer thickness this non uniform upwelling field yields about 12 sv of aabw exported across the top isopycnal fortuitously the overall average of upward speed at the top isopycnal 3 7 10 7 m s 1 compares well with previous estimates of deep upwelling in the northern basins a series of likely sites for strong vertical entrainment of aabw are clearly identified in the modeled distribution of deep upwelling consonant with the observed cfc distributions on the top isopycnal altogether regions with relatively high upwelling rates 5 10 7 m s 1 occupy only a quarter of the total areal extent of the top isopycnal but they account for as much as 45 of the total vertical transport

flow hydrography turbulent mixing and dissipation at fieberling guyot examined with a primitive equation model 1 the extensive set of measurements previously taken at fieberling guyot provides a backdrop for model results on flow hydrography turbulent mixing and derivative variables a z level primitive equation model driven at subinertial and superinertial tidal frequencies allows the nonlinear interaction of free and topographically trapped motions to jointly determine model outcomes model residual flows mean hydrographic features topographic amplification of oscillatory currents turbulent dissipation and vertical diffusivity kv profiles are all examined in the light of the observations azimuthal residual flows are toroidal above the summit with maximum speed 20 cm s 1 diurnal flow over the summit is intensified by a factor 20 downward vertical flow as a time mean w t occurs from 150 m above the summit apex to summit rim depth with radially inward flow above the apex and radial outward flow below upward w t rings the summit at larger r the existence of the observed cold dome is shown to depend on w t in the summit circulation cell vertical current shear is concentrated in a 150 m thick cap above the summit accounting for a domed distribution of and kv with maxima of 10 7 w kg 1 and 30 cm2 s 1 respectively profiles most like the observations of kv are obtained with a subgrid scale parameterization in which the turbulent prandtl number pr depends on the shear richardson number ri

oxygen isotope trends and anomalies in granitoids of the tibetan plateau abstract extreme transhimalayan oceanic mantle i type and high himalayan anatectic collision s type granitoids in the himalaya kashmir and tibet range in their original oxygen isotope composition from 6 to 7 5 and from 10 to 12 5 18osmow respectively in the sutured paleozoic and mesozoic orogen of the eastern tibetan plateau purely oceanic batholiths seem absent shalouli shan 8 10 but high himalayan values are matched in dongda shan and at luxi towards the east oceanic values are found again only on the margin of the yangtse platform the regional pattern of normal oxygen isotope data provides a background for anomalous feldspars to 1 in lhasa granite and in the active geothermal system at yangbachen recharged by 6000 m a s l meteoric water for lhasa granite oxygen isotope exchange paths and preliminary k ar dating of feldspars suggest exchange with meteoric water from over 3000 m altitude before 20 ma ago

landscape and drainage evolution during the cenozoic in the salinas grandes basin andean plateau of nw argentina abstract endorheic basins are distinctive features of the modern andean plateau these basins record thick neogene to modern evaporite successions that are considered as the onset of internal drainage and aridity some isolated older paleogene evaporites and intermontane depocenters have been also described across the argentine puna suggesting that some degree of hydrological isolation would have pre dated the main miocene pliocene plateau uplift evaporites beds however are not conclusive evidence for endorheism given that their formation depends not only on the tectonically driven paleo drainage but also on other sensitive variables as climate and salinity of the sources here we discuss the paleo drainage evolution across the eastern puna plateau at 23 24 s combining landscape numerical modeling with seismic stratigraphy seismic observations suggest an intermontane configuration as early as the late paleogene and relief formation to the east and west basin margins using different combinations of precipitation rates our landscape models allowed us to reproduce the modern elevations observed in the study region as well as published thermochronological data our results suggest that endorheism would have started in the paleogene and would have dominated most 70 of the cenozoic basin history models show the recurrence of endorheism interrupted by intermittent phases of drainage connectivity exorheism to the east foreland in the upper half eocene and the early miocene according to these results the formation of closed basins in the puna region would have pre dated the main miocene pliocene uplift stage of the andean plateau

temporal variability of transformation formation and subduction rates of upper southern ocean waters 1 kinematic and thermodynamic approaches are employed to diagnose the time dependent transformation formation and subduction rates of upper southern ocean waters in a multidecadal simulation within an eddy permitting coupled climate model in the subantarctic mode water samw density class a convergence of diapycnal volume fluxes leads to the formation and inflation of mixed layer waters during winter a portion of this water is detrained into the pycnocline during early spring when surface heating restratifies the deep winter mixed layer the annually averaged subduction rate of samw shows pronounced interannual variability partly controlled by the temporal tendency of the winter mixed layer depth from one year to the next no significant correlation between the southern annular mode sam and the isopycnally integrated samw subduction rate is apparent however ekman downwelling upwelling intensities modulated by the sam influence interannual variations in the subduction rates of water masses lighter and heavier than samw with an opposing sign during positive phases of the sam more pycnocline waters are entrained into the mixed layer and transformed into lighter densities within the antarctic intermediate water density class whereas more mixed layer waters are subducted into the pycnocline within the subtropical mode water density class such distinct responses of upper southern ocean water masses to the sam are qualitatively consistent with observational constraints based on a comparison between offline kinematic and thermodynamic diagnostics we infer that diapycnal mixing within the mixed layer may contribute up to 50 of the formation rate of samw on interannual timescales

transient diapycnal mixing and the meridional overturning circulation abstract an idealized three dimensional model of buoyancy forced flow in a single hemisphere is used to investigate whether transient diapycnal mixing can sustain the meridional overturning circulation in the annual mean mixing transience had little effect on the meridional overturning when mixing occurred on basin boundaries the overturning strength was found to be insensitive to mixing transience for mixing that was highly localized in space away from basin boundaries oceanic meridional mass and heat transport decreased as mixing became more transient the increased sensitivity in the highly localized case is likely due to the inhibition of surface heat flux into the thermocline the dynamic response to transient mixing featured large scale internal oscillations that increased in amplitude with the transience of mixing but were confined to the tropics and had little effect on the overturning cell through midlatitudes these results indicate that transient diapycnal mixing with a distribution sug

modern and long term evaporation of central andes surface waters suggests paleo archives underestimate neogene elevations abstract central andean paleoelevations reconstructed from stable isotope and paleofloral data imply a large magnitude 2 km miocene to modern surface uplift however the isotopic relationships between precipitation surface waters and soil waters upon which these reconstructions are based remain poorly constrained for both past and in many cases modern conditions we quantify the relationships between central andean precipitation and surface waters by measuring the isotopic composition of 249 stream water samples 18o and d collected between april 2009 and october 2012 the isotopic compositions of stream waters match precipitation along the eastern flank in contrast altiplano surface waters possess a lower d 18o slope 4 59 vs 8 for meteoric waters not observed in precipitation which signals heavy isotope evaporative enrichment in surface waters paleoclimate models indicate that highly evaporative conditions have persisted on the plateau throughout andean uplift and that conditions may have been more evaporative when the andes were lower thus more ancient proxy materials may have a greater evaporative bias than previously recognized and paleoelevation reconstructions from stable isotope based central andean plateau proxy materials likely overstate miocene to present surface uplift we propose altiplano paleoelevations of 1 2 km at 24 5 ma 1 5 2 9 km by 11 45 ma and modern elevations by 6 ma based on the lightest isotopic compositions observed in altiplano proxy materials which are least likely to be influenced by evaporation these constraints limit total late miocene to modern uplift to

once again once again tidal friction topex poseidon t p altimetry has reopened the problem of how tidal dissipation is to be allocated there is now general agreement of a m2 dissipation by 2 5 terawatts 1 tw 1012 w based on four quite separate astronomic observational programs allowing for the bodily tide dissipation of 0 1 tw leaves 2 4 tw for ocean dissipation the traditional disposal sites since jeffreys 1920 have been in the turbulent bottom boundary layer bbl of marginal seas and the modern estimate of about 2 1 tw is in this tradition but the distribution among the shallow seas has changed radically from time to time independent estimates of energy flux into the marginal seas are not in good agreement with the bbl estimates t p altimetry has contributed to the tidal problem in two important ways the assimilation of global altimetry into laplace tidal solutions has led to accurate representations of the global tides as evidenced by the very close agreement between the astronomic measurements and the computed 2 4 tw working of the moon on the global ocean second the detection by ray and mitchum 1996 of small surface manifestation of internal tides radiating away from the hawaiian chain has led to global estimates of 0 2 to 0 4 tw of conversion of surface tides to internal tides measurements of ocean microstructure yields 0 2 tw of global dissipation by pelagic turbulence away from topography we propose that pelagic turbulence is maintained by topographic scattering of barotropic into baroclinic tidal energy via internal tides and internal waves previous estimates by baines 1974 baines 1982 of this conversion along 150 000 km of continental coastlines gave a negligible 0 02 tw evidently the important conversion takes place along mid ocean ridges the maintenance of the abyssal global stratification requires a much larger expenditure of power 2 tw versus 0 2 tw this is usually attributed to wind forcing if tidal power is to play a significant role here then the bbl estimates need to be reduced the challenge is to estimate dissipation from the energy flux divergence in the t p adjusted tidal models without prior assumptions concerning the dissipation processes

the growth of the central andes 22 s 26 s we synthesize geologic observations with new isotopic evidence for the timing and magnitude of uplift for the central andes between 22 s and 26 s since the paleocene to estimate paleoelevations we used the stable isotopic composition of carbonates and volcanic glass combined with another paleoelevation indicator for the central andes the distribution of evaporites paleoelevation reconstruction using clumped isotope paleothermometry failed due to resetting during burial the andes at this latitude rose and broadened eastward in three stages during the cenozoic the fi rst in what is broadly termed the incaic orogeny ended by the late eocene when magmatism and deformation had elevated to 4 km the bulk 50 of what is now the western and central andes the second stage witnessed the gradual building of the easternmost puna and eastern cordillera starting with deformation as early as 38 ma to 3 km by no later than 15 ma the proximal portions quadej email arizona edu quade j dettinger m p carrapa b decelles p murray k e huntington k w cartwright a canavan r r gehrels g and clementz m 2015 the growth of the central andes 22 s 26 s in decelles p g ducea m n carrapa b and kapp p a eds geodynamics of a cordilleran orogenic system the central andes of argentina and northern chile geological society of america memoir 212 p 277 308 doi 10 1130 2015 1212 15 for permission to copy contact editing geosociety org 2014 the geological society of america all rights reserved on january 15 2015 memoirs gsapubs org downloaded from

phytoplankton and nutrient dynamics of six south west indian ocean seamounts abstract a survey of six seamounts and two transects through the subtropical convergence zone scz in the south indian ocean in november and december 2009 showed a strong latitudinal gradient from the subtropics to the sub antarctic front concentrations of oxygen nitrate nitrite soluble reactive phosphorous as well as phytoplankton biomass measured as chlorophyll a increased while salinity and temperature decreased with an increase in latitude these differences resulted in significant differences between seamounts the chlorophyll a maximum became shallower at higher latitudes changing from a depth of 85 m in the subtropics to 35 m over the seamounts and in the scz the mixed layer depth also increased from 50 m in the subtropics to 100 m at higher latitude stations the n p and n si ratio indicated that no 3 was limiting at all the seamounts except one at which sio 4 was the limiting nutrient the phytoplankton community also showed a latitudinal gradient with decreasing diversity and a change in dominance from dinoflagellates in the tropics to diatoms towards the scz the dominant diatom genus of the survey 50 of the cell counts was pseudo nitzschia nutrients exhibited an inverse linear relationship with temperature and salinity the oligotrophic subtropical areas differed from the mesotrophic seamounts in temperature while waters over seamounts north and south of the agulhas return current arc differed in salinity the phytoplankton 148 taxa responded to these differences showing three communities subtropical seamount phytoplankton atlantis seamount walters seamount and off mount samples phytoplankton of the waters north of the arc melville bank sapmer bank middle of what seamount and phytoplankton south of the arc coral seamount scz1 characterised by a bloom of phaeocystis antarctica the environmental drivers most strongly linked to these observed differences were nitrate temperature and oxygen these environmental drivers displayed a clear latitudinal gradient unaffected by mesoscale variability of the arc eddy field and allowing the three phytoplankton communities to persist phytoplankton biomass was enhanced in the shallow

diapycnal diffusivity at the upper boundary of the tropical north atlantic oxygen minimum zone a deliberate tracer release experiment in 2008 2010 was used to study diapycnal mixing in the tropical northeastern atlantic the tracer cf3sf5 was injected on the isopycnal surface 26 88 kg m 3 which corresponds to about 330 m depth three surveys performed 7 20 and 30 months after the release sampled the vertically and laterally expanding tracer patch the mean diapycnal mixing estimate over the entire region occupied by the tracer and the period of 30 months was found to be 1 19 0 18 10 5 m2 s 1 or alternatively 3 07 0 58 10 11 kg m 3 2 s 1 as computed from the advection diffusion equation in isopycnal coordinates with the thickness weighted averaging the latter method is preferable in the regions of different stratification for it yields local diapycnal mixing estimates varying less with stratification than their cartesian coordinate counterparts results of this study are comparable to the results of the north atlantic tracer release experiment natre however the internal wave wave interaction models predict reduced mixing from the breaking of internal waves at low latitudes thus the diapycnal diffusivity found in this study is higher than parameterized by the low latitude of the site 4 n 12 n

large scale cenozoic wind erosion in the puna plateau the salina del fraile depression wind erosion is integral to the evolution of arid landscapes on earth and mars but the nature of long term wind erosion of bedrock is poorly understood here we describe the salina del fraile sdf

aspects of the antarctic circumpolar current dynamics investigated with drifter data interactions between eddies and mean flow are essential to close the momentum budget of the southern ocean as well as to determine the structure of the global meridional overturning circulation both the structure of the antarctic circumpolar current and the eddy dynamics arising at its heart are importantfor water mass circulation and global ocean ventilation and therefore for the global climate however the characterization of the eddy fields of heat and momentum are still poorly sampled by direct observations and are difficult to accurately resolve or parameterize in numerical models here we present observation based eddy statistics and eddy heat flux ehf from a consistent dataset and estimate southern ocean surface ehf from direct measurements without any parameterization assumption observations obtained from near surface drifters represent a very useful dataset to analyze the eddy field because of their ability to catch a large number of scales of motion while providing a quasi synoptic coverage of the investigated area differences between winter and summer distributions of mean velocities mean kinetic energy and eddy kinetic energy are shown to be strongly constrained by bottom topography and suggest a winter shift of the polar front in specific areas around the circumpolar belt overall the flow follows the contours of constant planetary vorticity set by the depth of the ocean and creates anisotropy in eddy dispersion with maximum dispersion along these contours furthermore eddy mean flow interactions are strongly influenced by topography with eddies having a tendency to accelerate jets upstream of ridges and decelerate them further downstream these strong regional variabilities introduced by topography affect the flux of heat induced by eddies and therefore affect formation and subduction of the main surface and intermediate southern ocean water masses integrated over the southern ocean subduction of water masses induced by ehf appears as an order on component for the southern ocean thermocline ventilation our results based on direct observations emphasizes once more the importance of continuing sustained effort to better represent the effect of mesoscale eddies in a coarse climate model if we are to represent and predict future climate

abyssal mixing where it is not abstract a parameterization based on internal wave wave interaction theory which infers turbulence production from finescale internal wave shear is applied to 114 full water depth velocity profiles in the sargasso sea an average eddy diffusivity of 0 1 10 4 m2 s 1 independent of depth is inferred this value is consistent with full water depth microstructure measurements from abyssal basins in the eastern north atlantic and eastern north pacific it is an order of magnitude smaller than the values inferred from a simple vertical advection diffusion balance or bulk budgets thus the mixing needed to close deep global water mass budgets does not appear to occur over midlatitude abyssal plains this suggests that ocean mixing is either i confined to boundary layers as in ideal thermocline theory or ii localized to hotspots such as over rough topography or restrictive passages abyssal diffusivities do not display any dependence on bottom slope for slopes less than 7 10 2 based on 5 10 km bathy

internal tides and turbulence along the 3000 m isobath of the hawaiian ridge full depth velocity and density profiles taken along the 3000 m isobath characterize the semidiurnal internal tide and bottom intensified turbulence along the hawaiian ridge observations reveal baroclinic energy fluxes of 21 5k w m 1 radiating from french frigate shoals 17 2 5 kw m 1 from kauai channel west of oahu and 13 3 5 kw m 1 from west of nihoa island weaker fluxes of 1 4 2k w m 1 radiate from the region near necker island and east of nihoa island observed off ridge energy fluxes generally agree to within a factor of 2 with those produced by a tidally forced numerical model average turbulent diapycnal diffusivity k is 0 5 1 10 4 m 2 s 1 above 2000 m increasing exponentially to 20 10 4 m 2 s 1 near the bottom microstructure values agree well with those inferred from a finescale internal wave based parameterization a linear relationship between the vertically integrated energy flux and vertically integrated turbulent dissipation rate implies that dissipative length scales for the radiating internal tide exceed 1000 km

intensive surveys of the azores front 2 inferring the geostrophic and vertical velocity fields the geostrophic and vertical velocity fields are inferred using density and horizontal velocity data from three seasoar acoustic doppler current profiler surveys of the azores front the analysis is a two step procedure consisting of 1 objective analyses to reflect the observed length scales and 2 dynamical adjustments so that the density field is statically stable and the velocity field is in geostrophic balance the vertical velocity is inferred using a version of the quasi geostrophic omega equation in which the stratification is allowed to vary in the horizontal the resulting vertical velocity peaks at 2 10 4 m s 1 at 200 300 m there is a tendency for the denser water to the north of the front to be downwelled while the warmer water to the south is upwelled the implied heat flux exceeds 10 w m 2 near 100 m depth so the upper 100 m is warmed while the lower water column is cooled tending to stratify the upper ocean ageostrophic horizontal flow is toward the dense side of the front at the surface the dominant terms in the density balance are time rate of change and horizontal advection the inferred circulation cells may be an important mechanism of subduction in the upper ocean

permeability generation and resetting of tracers during metamorphic fluid flow implications for advection dispersion models advection dispersion fluid flow models implicitly assume that the infiltrating fluid flows through an already fluid saturated medium however whether rocks contain a fluid depends on their reaction history and whether any initial fluid escapes the behaviour of different rocks may be illustrated using hypothetical marble compositions marbles with diverse chemistries e g calcite dolomite quartz are relatively reactive and will generally produce a fluid during heating by contrast marbles with more restricted chemistries e g calcite quartz or calcite only may not if the rock is not fluid bearing when fluid infiltration commences mineralogical reactions may produce a reaction enhanced permeability in calcite dolomite quartz or calcite quartz but not in calcite only marbles the permeability production controls the pattern of mineralogical isotopic and geochemical resetting during fluid flow tracers retarded behind the mineralogical fronts will probably be reset as predicted by the advection dispersion models however tracers that are expected to be reset ahead of the mineralogical fronts cannot progress beyond the permeability generating reaction in the case of very unreactive lithologies e g pure calcite marbles cherts and quartzites the first reaction to affect the rocks may be a metasomatic one ahead of which there is little pervasive resetting of any tracer centimetre scale layering may lead to the formation of self perpetuating fluid channels in rocks that are not fluid saturated due to the juxtaposition of reactants such layered rocks may show patterns of mineralogical resetting that are not predicted by advection dispersion models patterns of mineralogical and isotopic resetting in marbles from a number of terrains for example chillagoe marulan south reynolds range australia adirondack mountains old woman mountains notch peak usa and stephen cross quarry canada vary as predicted by these models

late cenozoic topographic evolution of the eastern cordillera and puna plateau margin in the southern central andes nw argentina abstract the andes constitute an important orographic barrier in the southern hemisphere impacting atmospheric circulation the amount and distribution of rainfall and earth surface processes in a highly asymmetric manner in the central andes of nw argentina the andean plateau puna and the intermontane basins of the adjacent eastern cordillera constitute geological archives that furnish spatiotemporal information on surface uplift and associated paleo environmental change today rainfall in nw argentina is focused along the windward flanks of the eastern cordillera while its intermontane basins and the puna constitute high elevation regions with strongly reduced rainfall the present day influence of these topographic characteristics on precipitation patterns is reflected by systematic changes in the hydrogen stable isotope ratios of meteoric water proxy archives from basin strata record past environmental conditions and provide insight into the nature of topographic growth through time we present 34 new hydrogen isotopic compositions of volcanic glass dg extracted from tuffs interbedded with the sedimentary deposits of three different regions across the eastern andean margin between ca 24 s and 25 s latitude combined with new zircon u pb geochronology our data show clear spatiotemporal variations in dg correlating with topographic growth and ensuing orographic effects during the miocene and pleistocene in particular variations in dg indicate that the pastos grandes puna and the toro eastern cordillera basins had attained modern elevations by ca 8 and 6 ma respectively a strong positive shift in the dg record of the toro basin after 840 ka coincides with deposition of thick fluvial alluvial conglomerates suggesting orographically induced aridification due to progressive range uplift to the east other dg records from the eastern cordillera show similar but diachronous events emphasizing the importance of regional tectonics for environmental change with implications for the formation of orogenic plateaus

spatially heterogeneous diapycnal mixing in the abyssal ocean a comparison of two parameterizations to observations 1 the spatial distributions of the diapycnal diffusivity predicted by two abyssal mixing schemes are compared to each other and to observational estimates based on microstructure surveys and large scale hydrographic inversions the parameterizations considered are the tidal mixing scheme by jayne st laurent and co authors jsl01 and the roughness diffusivity model rdm by decloedt and luther comparison to microstructure surveys shows that both parameterizations are conservative in estimating the vertical extent to which bottom intensified mixing penetrates into the stratified water column in particular the jsl01 exponential vertical structure function with fixed scale height decays to background values much nearer topography than observed jsl01 and rdm yield dramatically different horizontal spatial distributions of diapycnal diffusivity which would lead to quite different circulations in ogcms yet they produce similar basin averaged diffusivity profiles both parameterizations are shown to yield smaller basin mean diffusivity profiles than hydrographic inverse estimates for the major ocean basins by factors ranging from 3 up to over an order of magnitude the canonical 10 4 m2 s 1abyssal diffusivity is reached by the parameterizations only at depths below 3 km power consumption by diapycnal mixing below 1 km of depth between roughly 32 s and 48 n for the rdm and jsl01 parameterizations is 0 40 tw 0 28 tw respectively the results presented here suggest that present day mixing parameterizations significantly underestimate abyssal mixing in conjunction with other recently published studies a plausible interpretation is that parameterizing the dissipation of bottom generated internal waves is not sufficient to approximate the global spatial distribution of diapycnal mixing in the abyssal ocean

on a simple empirical parameterization of topography catalyzed diapycnal mixing in the abyssal ocean abstract the global spatial distribution of the turbulent diapycnal diffusivity in the abyssal ocean is reexamined in light of the growing body of microstructure data revealing bottom intensified turbulent mixing in regions of rough topography a direct and nontrivial implication of the observed intensification is that the diapycnal diffusivity k is depth dependent and patchily distributed horizontally across the world s oceans theoretical and observational studies show that bottom intensified mixing is dependent upon a variety of energy sources and processes whose contributions to mixing are sufficiently complex that their physical parameterization is premature only rudimentary parameterizations of tidally induced mixing have been attempted although the tides likely provide no more than half of the mechanical energy available for diapycnal mixing in the abyssal ocean here an empirical and still rudimentary parameterization of the spatially variable mean diffusivity k based on a large collection

comparison of deep ocean finescale shear at two sites along the mid atlantic ridge abstract four drifting floats were used to measure the magnitude of the vertical derivative of horizontal velocity in waters above the rough bathymetry of the mid atlantic ridge this derivative is typically the dominant component of the velocity gradient the shear two floats were at the site of the brazil basin tracer release experiment bbtre in the south atlantic and two were near the site of the guiana abyssal gyre experiment gage in the north atlantic floats operated for 1 year except for one bbtre float which operated for 100 days shear was measured over a vertical span of 9 5 m using drag elements that caused the floats to rotate slowly in response to shear for each float the first second and fourth moments of shear were elevated above levels associated with the garrett munk model internal wave spectrum three of the four floats were tracked as they moved over mountainous terrain allowing shear intensity to be measured as a function of height above the bottom a deep bbtre float showed enhancement of rms shear near the bottom floats at both areas provided measurements at 2000 m above the bottom with differing results the gage site had a lower fourth moment of shear diapycnal diffusivity proxy than the bbtre site however application of normalization factors accounting for differences between the sites in bottom roughness latitude dependent internal wave dynamics and tidal current speeds brings the results into agreement

the effect of localized mixing on the ocean circulation and time dependent climate change observations indicate that intense mixing in the ocean is localized above complex topography and near the boundaries model experiments presented here illustrate that accounting for this fact can be important in particular it is found that in the case of localized mixing the rate of overturning circulation is proportional to the net rate of generation of potential energy by the vertical mixing linked to the net downward heat diffusion rather than to the value of the mean vertical diffusivity coefficient furthermore it is shown that two climate models having the same vertical profile of diffusivity but differing in their distribution horizontally uniform versus topography boundary intensified can simulate significantly different meridional oceanic circulations vertical heat transfers and responses of simulated climate to atmospheric co2 increase this is found for relatively large o 1 0 cm 2 s 1 horizontal mean values of vertical diffusivity in the pycnocline however in cases of relatively small o 0 1 cm 2 s 1 mean diffusivity in the pycnocline the simulated integral quantities such as meridional mass and heat transports do not depend much on the details of the mixing distribution even so it is found that the deep western boundary currents are more localized near the boundaries in the case of topography boundary intensified mixing also the stratification in the deep ocean is set through the localized regions of intense vertical mixing in addition it is shown that reconciling the observed basin mean values of diffusivity in the abyssal ocean of o 10 cm 2 s 1 with realistic stratification can be problematic unless the regions of enhanced vertical mixing are localized

multiple regimes and low frequency variability in the quasi adiabatic overturning circulation 2015 american meteorological society when interior mixing is weak the ocean can support an interhemispheric overturning circulation on isopycnals that outcrop in both the northern hemisphere and a high latitude southern circumpolar channel this overturning cell participates in a salt advection feedback that counteracts the precipitation induced surface freshening of the northern high latitudes the net result is an increase in the range of isopycnals shared between the two hemispheres which strengthens the overturning circulation however if precipitation in the northern hemisphere sufficiently exceeds that in the southern hemisphere the overturning cell collapses and is replaced by a cell circulating in the opposite direction whose southern end point is equatorward of the channel this reversed cell is shallower and weaker than its forward counterpart and is maintained diffusively for a limited range of parameters freshwater hysteresis occurs and multiple overturning regimes are found for the same forcing these multiple regimes are by definition unstable with regard to finite amplitude disturbances since a sufficiently large perturbation can affect a transition from one regime to the other both overturning regimes show pronounced nearly periodic thermohaline variability on multidecadal and multicentennial time scales the multidecadal oscillation is expressed in the north hemisphere gyre and driven by a surface thermohaline instability the multicentennial oscillation has the character of an interhemispheric loop oscillation these oscillations mediate transitions between overturning regimes by providing an internal source of finite amplitude disturbances as the diffusivity is reduced the reverse cell becomes weaker and thus less stable to a given perturbation amplitude this causes the width of the hysteresis to decrease with decreasing diffusivity

dynamics of an abyssal circulation driven by bottom intensified mixing on slopes the large scale circulation of the abyssal ocean is enabled by small scale diapycnal mixing which observations suggest is strongly enhanced toward the ocean bottom where the breaking of internal tides and lee waves is most vigorous as discussed recently bottom intensified mixing induces a pattern of near bottom up and downwelling that is quite different from the traditionally assumed widespread upwelling here the consequences of bottom intensified mixing for the horizontal circulation of the abyssal ocean are explored by considering planetary geostrophic dynamics in an idealized bathtub geometry up and downwelling layers develop on bottom slopes as expected and these layers are well described by boundary layer theory the basin scale circulation is driven by flows in and out of these boundary layers at the base of the sloping topography which creates primarily zonal currents in the interior and a net meridional exchange along western boundaries the rate of the net overturning is controlled by the up and downslope transports in boundary layers on slopes and can be predicted with boundary layer theory

intense mixing of lower thermocline water on the crest of the mid atlantic ridge the mixing of warm upper ocean water with the colder water beneath is an essential component of global ocean circulation because it increases the buoyancy of deep water but it is not clear where this mixing takes place louis st laurent and andreas thurnherr have measured the mixing that occurs as water flows through a narrow passage on the crest of the mid atlantic ridge the rates they observe are unusually high if similar mixing rates occur in the other narrow passages on the mid atlantic ridge in the north atlantic basin these sites could account for as much buoyancy flux at the depth of the passages as the rest of the basin combined so mixing in narrow passages on mid ocean ridges sites that have previously been overlooked may make a significant contribution to buoyancy flux at the global scale observations from the crest of the mid atlantic ridge suggest that passages in rift valleys and ridge flank canyons provide the most energetic sites for oceanic turbulence measurements show that large diffusivities characterize the mixing downstream of a sill in a well stratified boundary layer with mixing levels remaining of the order of 10 4m2 s 1 at the base of the main thermocline buoyancy exchange between the deep and the upper ocean which is essential for maintaining global ocean circulation mainly occurs through turbulent mixing1 2 this mixing is thought to result primarily from instability of the oceanic internal wave field3 but internal waves tend to radiate energy away from the regions in which they are generated rather than dissipate it locally as turbulence4 and the resulting distribution of turbulent mixing remains unknown another more direct mixing mechanism involves the generation of turbulence as strong flows pass through narrow passages in topography but the amount of turbulence generated at such locations remains poorly quantified owing to a lack of direct measurements here we present observations from the crest of the mid atlantic ridge in the subtropical north atlantic ocean that suggest that passages in rift valleys and ridge flank canyons provide the most energetic sites for oceanic turbulence our measurements show that diffusivities as large as 0 03 m2 s 1 characterize the mixing downstream of a sill in a well stratified boundary layer with mixing levels remaining of the order of 10 4 m2 s 1 at the base of the main thermocline these mixing rates are significantly higher than the diffusivities of the order of 10 5 m2 s 1 that characterize much of the global thermocline and the abyssal ocean5 our estimates suggest that overflows associated with narrow passages on the mid atlantic ridge in the north atlantic ocean produce as much buoyancy flux as has previously been estimated for the entire romanche fracture zone6 7 a large strait in the mid atlantic ridge that connects the north and south atlantic basins this flux is equivalent to the interior mixing that occurs in the entire north atlantic basin at the depth of the passages suggesting that turbulence generated in narrow passages on mid ocean ridges may be important for buoyancy flux at the global scale

tidally induced turbulent mixing at irving seamount modeling and measurements 1 the relationship of tidal currents and turbulence over irving seamount is examined by model and measurement surface tides are partially scattered into internal tides and particularly over the seamount summit current strength and shear greatly increase current shear causes the model s turbulent mixing at irving modeled turbulent mixing as represented by vertical diffusivity is largest o 10 3 m2 s 1 in the bottom boundary layer and in a turbulent column rising to the sea surface directly above the seamount pockets of less intense mixing occur within the turbulent column but their locations are highly variable field measurements confirm a turbulent mixing column atop irving of comparable intensity increased model diffusivity average of 7 10 5 m2 s 1 also occurs to a distance of several hundred kilometers from the seamount flanks in a band vertically centered at 800 m depth

equatorial deep jets and abyssal mixing in the indian ocean abstract vertical profiles of horizontal currents and hydrographic measurements from three cruises along 80 5 e from the coast of sri lanka to 6 s between december 1990 and september 1994 are used to investigate the scales of the indian ocean deep jets as well as internal wave parameters and dissipation at the equator the deep jets at 80 5 e have a vertical wavelength of 660 sm stretched meters and amplitudes exceeding 10 cm s 1 in zonal velocity they are observed throughout the water column and their flow direction reverses at 2 off the equator the vertical positions of the jets differ among the cruises and are consistent with a flow reversal between the data collected in winter and summer during september 1994 the jets were less pronounced due to the meridional distribution of their zonal velocity and the phase relationship between zonal velocity and vertical displacement the jets are best described as nondispersive first mode equatorial rossby waves the hydrographic data revealed thick layer

finescale shear at 1660 and 2850 dbar over the mid atlantic ridge in the eastern brazil basin abstract two drifting shearmeter instruments have provided records of the magnitude of shear the magnitude of the vertical derivative of horizontal velocity measured over a 10 m aperture in the vicinity of the brazil basin tracer release experiment the floats drifted at roughly 1660 and 2850 dbar where the buoyancy frequencies were n 1 1 and 0 5 cph respectively two additional floats provided deep trajectories but no shear data the records of hourly mean values of shear magnitude with mean values denoted sh exhibit strong temporal variability with time scales comparable to those of fortnightly tidal modulation the deep record exhibits stronger mean sh near the seafloor than above with the exception of the bin closest to the seafloor sh from neither float correlates strictly with tidal forcing shallow sh varies in apparent response to atmospheric forcing the mean squared shear of the shallow record is 4 times the n dependent value associated with the garrett munk spectral model and that

inferences and observations of turbulent dissipation and mixing in the upper ocean at the hawaiian ridge abstract the hawaiian ridge is one of the most energetic generators of internal tides in the pelagic ocean the density and current structure of the upper ocean at the hawaiian ridge were observed using seasoar and doppler sonar during a survey extending from oahu to brooks banks and up to 200 km from the ridge peak survey observations are used to quantify spatial changes in internal wave induced turbulent dissipation and mixing the turbulent dissipation rate of kinetic energy e and diapycnal eddy diffusivity k are inferred from an established parameterization using internal wave shear as input at the kauai channel kc and french frigate shoals brooks banks sites e and k decay away from the ridge with maxima exceeding minima by 5 times at both sites average k is everywhere greater than the canonical open ocean value of 10 5 m2 s 1 along the ridge e and k vary by up to 100 times and are largest at sites of largest numerical model internal tide energy density in the eastern kc k 10 3 m2 s

north pacific subtropical mode water volume decrease in 2006 09 estimated from argo observations influence of surface formation and basin scale oceanic variability abstractanalysis of argo temperature and salinity profiles gridded at 0 5 0 5 resolution for 2005 12 shows a strong north pacific subtropical mode water npstmw volume and density decrease during 2006 09 in this time period upper ocean temperature stratification and potential vorticity pv all increased within the region in and around the npstmw low pv pool contributing to the npstmw volume decrease in two ways i the volume of water satisfying the low pv constraint that is part of the mode water definition decreased and ii some water that was initially in the npstmw density range 25 0 25 5 kg m 3 was transformed into lighter water both changes in density and in pv in the npstmw region were a manifestation of basinwide changes a positive pv anomaly started to propagate westward from the central pacific in 2005 followed by a negative density anomaly in 2007 which caused a dramatic npstmw volume and density decrease a walin estimate of surface formation in the npstmw density ran

vertical diffusivity of the western arctic ocean halocline a nearly year long series of upper ocean temperature conductivity and temperature microstructure profiles were collected from an ice camp drifting in the beaufort gyre as part of the 1997 1998 surface heat budget of the arctic experiment sheba geographically the record includes portions over the deep canada basin and the steep bathymetry of the chukchi borderlands region hydrographically the record includes cool pacific origin haloclines which contain a variety of subsurface temperature maxima and cold haloclines typical of the eurasian basins we present estimates of the vertical turbulent diffusivity derived from the dissipation rate of thermal variance and calculations of the associated vertical heat fluxes we find that vertical diffusion proceeds at molecular rates in the deep basins and away from topographic features while still relatively small diffusivity is enhanced by 1 order of magnitude near and above the chukchi borderlands the enhanced diffusivity is correlated to an increase in water column strain variance above the borderlands providing a linkage between bathymetry internal wave activity and turbulence the chukchi borderlands play a significant role in heat transport in the western arctic they are a pathway for horizontal heat transport and a hot spot for vertical heat transport vertical fluxes make a substantial contribution to the energy balance of the sea ice cover in this region heat fluxes between the halocline and underlying atlantic water are shown to be small and lacking vertical connection near surface waters

isotopic characterization of late neogene travertine deposits at barrancas blancas in the eastern atacama desert chile abstract here we explore the potential of spring related surface and subsurface carbonates as an archive of paleoenvironmental change at barrancas blancas located in the broadest and driest sector of the atacama desert at 24 5 s from these deposits we present a new stable isotopic record of paleoenvironmental conditions over portions of the past 11 5 ma u pb dates from the carbonates both surface and subsurface demonstrate that springs have discharged at this location over much of the last 11 5 ma attesting to the exceptional geomorphic stability of the central atacama many of the sampled vein systems line vertical fissures and formed within the aquifer before groundwater discharged at the surface carbonates in such circumstances should not undergo off gassing and kinetic fractionation prior to formation simplifying the interpretation of their isotopic composition oxygen isotopic compositions of carbonates are generally high 5 vpdb and using paleospring water temperatures of 3 13 c reconstructed from clumped isotopes point to strongly up to 50 evaporated water isotope values like those associated with the hyperarid core of the atacama desert today carbon isotopic compositions are also high 3 pdb reflecting a recharge area essentially devoid of plants and dominated by volcanic co 2 as is the case today our isotopic results are very similar to those from the calama basin to the north suggesting that the western face of the andes between 21 and 25 s has been highly evaporative and nearly plantless when these springs discharged over the last 11 5 ma the spring carbonates at barrancas blancas strongly resemble those found at devils hole and furnace creek in death valley usa and as such warrant further exploration as potential archives of climate change

a turbulent convection model with an observational context for a deep sea hydrothermal plume in a time variable cross flow 1 a turbulent convection model for a hydrothermal fluid discharging into a tidally modulated stratified cross flow is used to investigate time variable conditions in plumes such as the one rising from dante a sulfide mound at 2175 m depth on the endeavour segment of the juan de fuca ridge that plume is the consequence of the coalescence of 10 or more small individual plumes from chimneys discharging hot salt diminished fluid into the near bottom ocean at dante the discharge encounters ambient horizontal currents with speeds oscillating from near zero to a maximum of 7 cm s 1 speeds which can bend a plume more than 45 from the vertical model results are compatible with field measurements of the plume footprint size and vertical velocity both 20 m above the source when earlier estimates for dante s heat flux of 50 mw drive the convection the small scale short period variability of velocities and properties distributions observed in the field is mimicked in model results plumes pool above a source during periods of weak cross flows but stream away from the source with more diluted concentrations and lower rise heights at other times plume distributions at identical cross flow speeds differ whether the flow is accelerating or decelerating small changes in background hydrographic profiles create differences in rise heights comparable to those caused by large changes in source buoyancy flux if put into an entrainment context results suggest an entrainment coefficient eff that varies from 0 11 to 0 025 with increasing height 2 76 m above the source

the relationship between water mass formation and the surface buoyancy flux with application to phillips red sea model abstract a buoyancy flux across the sea surface between the outcropping of isopycnals must be balanced by a subsurface diapycnal buoyancy flux if this flux were only advective its derivative with respect to buoyancy would provide a direct estimate of the buildup of volume between isopycnals or rate of water mass formation a diapycnal velocity however requires diapycnal mixing which also causes a diapycnal buoyancy flux and it is shown that there is no reason to expect a simple relationship between the advective and diffusive fluxes for a surface layer with vigorous vertical mixing and weak horizontal mixing however the diapycnal diffusive flux of buoyancy is small and the flow through the base of the mixed layer can be derived from the derivative of the surface buoyancy flux with respect to buoyancy these points are illustrated by examination of the phillips similarity solution for the convective circulation driven in a channel by a uniform surface buoyancy loss

the internal wave driven meridional overturning circulation abstractthe upwelling diapycnal limb of the ocean s meridional overturning circulation is driven by divergence of diabatic turbulent buoyancy fluxes w b across density surfaces a global assessment of zonally averaged internal wave driven turbulent diapycnal buoyancy fluxes from a strain based finescale parameterization is used to infer mean diapycnal transports in the interior and near the bottom boundary bulk interior diabatic transports dominate above 2500 m depth buoyancies b g n 0 0 267 m s 2 neutral densities n 27 9 kg m 3 upwelling at 10 11 sv 1 sv 106 m3 s 1 2 5 and 3 4 sv in the indian pacific and atlantic respectively but are weak in the abyss boundary water mass transformations peak at 18 25 sv 4 6 10 14 and 4 5 sv in the indian pacific and atlantic near buoyancy b 0 268 m s 2 n 28 1 kg m 3 4500 m depth between bottom and lower deep waters consistent with published 20 30 sv global antarctic bottom water aabw transport estimates interior transpor

global abyssal mixing inferred from lowered adcp shear and ctd strain profiles abstract internal wave wave interaction theories and observations support a parameterization for the turbulent dissipation rate e and eddy diffusivity k that depends on internal wave shear vz2 and strain z2 variances its latest incarnation is applied to about 3500 lowered adcp ctd profiles from the indian pacific north atlantic and southern oceans inferred diffusivities k are functions of latitude and depth ranging from 0 03 10 4 m2 s 1 within 2 of the equator to 0 4 0 5 10 4 m2 s 1 at 50 70 diffusivities k also increase with depth in tropical and subtropical waters diffusivities below 4500 m depth exhibit a peak of 0 7 10 4 m2 s 1 between 20 and 30 latitudes where semidiurnal parametric subharmonic instability is expected to be active turbulence is highly heterogeneous though the bulk of the vertically integrated dissipation e is contributed from the main pycnocline hotspots in e show some correlation with small scale bottom roughness and near bottom flow at sites where st

spatial and temporal patterns of small scale mixing in drake passage temperature and salinity profiles obtained with expendable ctd probes throughout drake passage between february 2002 and july 2005 are analyzed to estimate turbulent diapycnal eddy diffusivities to a depth of 1000 m diffusivity values are inferred from density temperature inversions and internal wave vertical strain both methods reveal the same pattern of spatial variability across drake passage diffusivity estimates from inversions exceed those from vertical strain by a factor of 3 over most of drake passage the polar front pf separates two dynamically different regions strong thermohaline intrusions characterize profiles obtained north of the pf south of the pf stratification is determined largely by salinity and temperature is typically unstably stratified between 100 and 600 m depth in the upper 400 m turbulent diapycnal diffusivities are o 10 3 m2 s 1 north of the pf but decrease to o 10 4 m2 s 1 or smaller south of the pf below 400 m diffusivities typically exceed 10 4 m 2 s 1 diffusivities decay weakly with depth north of the pf whereas diffusivities increase with depth and peak near the local temperature maximum south of the pf the meridional pattern in near surface mixing corresponds to local maxima and minima of both wind stress and wind stress variance near surface diffusivities are also found to be larger during winter months north of the pf wind driven near inertial waves strong mesoscale eddy activity and double diffusive convection are suggested as possible factors contributing to observed mixing patterns

mixing estimates from a large scale hydrographic survey in the north atlantic 1 a large scale hydrographic survey from 2003 rv meteor cruise m59 2 is used to map turbulent mixing by means of eddy diffusivities from finescale shear and strain in the subpolar north atlantic covering various hydrographic and bathymetric conditions results from the analysis indicate small o 10 5 m2s 1 diffusivities below the labrador sea water layer at mid depth in the open ocean higher values exceeding 10 4 m2s 1 are found in the abyss close to rough topography and over the flanks of the mid atlantic ridge the strongest mixing with diffusivities of 10 3 m2s 1 occurs in the deep western boundary current off flemish cap the results of this study convey the need to map mixing globally from existing sets of ctd ladcp data as well as its feasibility the similarities and differences in mixing patterns as compared to other studies indicate that large scale patterns of small scale processes are still not well known and understood

a dissipation integral with application to ocean diffusivities and structure an integral balance is developed for steady fluid flows relating dissipation in volumes bounded by isosurfaces of a tracer quasi conserved quantity and solid boundaries to the covariance of the tracer value and surface fluxes across the boundaries the balance is used to estimate upper bounds for vertical eddy diffusion coefficients for temperature and salinity in various volumes of the ocean the vertical temperature diffusivity is calculated to be small o 0 1 3 1024 m2 s21 except for the warmest and coldest volumes of the ocean the vertical salinity diffusivity for the volume that makes up most of the deep ocean is estimated to be o 1 3 1024 m2 s21 sources of error in these calculations are discussed and the sensitivity to errors in the surface flux data is evaluated the dissipation integral is also applied to demonstrate some related results concerning extrema and homogenization the prandtl batchelor theorem is a special case of one of these results as a consequence of these results if turbulent transfer is downgradient and there are no internal sources or sinks a necessary but not sufficient condition for a climatological tracer distribution to be in a steady state is the absence of internal extrema the climatological salinity distribution does not appear to violate this condition

ecological and hydroclimate responses to strengthening of the hadley circulation in south america during the late miocene cooling near modern ecosystems were established as a result of rapid ecological adaptation and climate change in the late miocene on land late miocene aridification spread in tandem with expansion of open habitats including c4 grassland ecosystems proxy records for the central andes spanning the late miocene cooling lmc show the reorganization of subtropical ecosystems and hydroclimate in south america between 15 and 35 s continental pedogenic carbonates preserved in neogene basins record a general increase of 18o and 13c values from pre lmc to post lmc most robustly occurring in the subtropics 25 to 30 s suggesting aridification and a shift toward a more c4 plant dominated ecosystem these changes are closely tied to the enhancement of the hadley circulation and moisture divergence away from the subtropics toward the intertropical convergence zone as revealed by climate model simulations with prescribed sea surface temperatures ssts reflecting different magnitudes of lmc steepening of equator to pole temperature gradient and co2 decline

two dimensional patterns of metamorphic fluid flow and isotopic resetting in layered and fractured rocks pa one dimensional advection dispersion models predict that characteristic 18o vs distance and 18o vs 13c profiles should be produced during isothermal metamorphic fluid flow under equilibrium conditions however the patterns of isotopic resetting in rocks that have experienced fluid flow are often different from the predictions two dimensional advection dispersion simulations in systems with simple geometries suggest that such differences may be as a result of fluid channelling and need not indicate disequilibrium high dispersivities or polythermal flow the patterns of isotopic resetting are a function of 1 the permeability contrast between more permeable layers channels and less permeable layers matrix 2 the width and spacing of the channels 3 the width and spacing of discrete fractures and 4 the orientation of the pressure gradient with respect to layering in fractured systems the efficiency of isotopic transport depends on the fracture aperture and the permeability of the surrounding rock resetting initially occurs along and immediately adjacent to the fractures but with time isotopic resetting because of flow through the rock as a whole increases in importance application of the one dimensional advection dispersion equations to metamorphic fluid flow systems may yield incorrect estimates of fluid fluxes intrinsic permeabilities dispersivities and permeability contrasts unless fluid flow occurred through zones of high permeability that were separated by relatively impermeable layers

cretaceous to middle cenozoic exhumation history of the cordillera de domeyko and salar de atacama basin northern chile

impacts of localized mixing and topography on the stationary abyssal circulation abstract stommel and coworkers calculated the stationary geostrophic circulation in the abyssal ocean driven by prescribed sources representing convective downwelling sites and sinks slow widespread upwelling through the thermocline the applied basin geometries were highly idealized with nearly uniform upwelling and gradual bottom slopes in this paper the classical stommel arons theory for the abyssal circulation is extended by introducing pronounced bathymetry in the form of a midocean ridge and strongly enhanced upwelling in the vicinity of this ridge modeled after direct observations of diapycnal mixing rates in the deep ocean locally enhanced upwelling over a midocean ridge drives a plume circulation that is modified by topographic stretching the dynamics of this abyssal circulation pattern are explained by analyzing the combined impacts of the upwelling pattern and the bathymetry on the stationary circulation building on their well known separate impacts on the western flank of the ri

determination of diapycnal diffusion rates in the upper thermocline in the north atlantic ocean using sulfur hexafluoride 1 the apparent diapycnal diffusivity below the wind driven surface mixed layer of the ocean was determined in an anticyclonic eddy in the eastern north atlantic using sulfur hexafluoride sf6 tracer data collected in june 1998 in this tracer experiment the downward penetration of sf6 was measured for 3 weeks following the deliberate injection of sf6 in the surface mixed layer the resulting data were used to constrain the one dimensional fickian diffusion model to estimate the diapycnal diffusivity the model also includes the lateral diffusion component so that it can more accurately represent the time evolution of the sf6 concentrations along the isopycnal surface this affects the estimation of the diapycnal diffusivity for the upper thermocline immediately below the surface mixed layer we estimated the diapycnal diffusivity for the 3 week period as 0 3 0 2 cm2 s 1 at a buoyancy frequency of 8 2 cph

satellite observations of phytoplankton enrichments around seamounts in the south west indian ocean with a special focus on the walters shoal abstract spatial anomalies associated with seamounts and islands have been detected in the south west indian ocean using a new surface chlorophyll a based enrichment index ei calculated from daily l3 4 km modis chl a data from 2003 to 2018 the ei was used to quantify recurrent seasonal surface enrichment associated with these features most notable were the shallow walters shoal 18 m and nearby deeper ws 2 seamount 480 m both located on the southern madagascar ridge which showed high ei values of 40 and 15 local enhancement tromelin island east of madagascar exhibited more moderate values of 15 local increase other shallower seamounts including la perouse 60 m and mad ridge 240 m exhibited sporadic or no measurable surface maxima regions of strong mesoscale activity such as south of madagascar where the south east madagascar current detaches from the continent also revealed high ei values a marked seasonality of the ei was observed over the walters shoal with higher values during the oligotrophic season than in the austral winter the seasonal variability of the mld in combination with the seamount bathymetry appears to induce the thermal and biological anomalies observed there possibly favoured by the presence of a taylor cap at the summit ship collected in situ measurements showed the satellite observed enrichment to be associated with shallowing of the deep chlorophyll maximum as well as a shift of phytoplankton groups towards diatoms and small flagellates no net increase of integrated chl a was measured but a potential doubling in primary productivity is expected the ei developed in this study designed to reveal sporadic small localised chl a maxima is likely applicable to other areas in the ocean where there is local enrichments

a middle miocene 13 5 12 ma deformational event constrained by volcanism along the puna eastern cordillera border nw argentina abstract the features of middle miocene deposits in the puna eastern cordillera transition valles calchaquies indicate that cenozoic deformation sedimentation and volcanism follow a complex spatiotemporal relationship the intense volcanic activity recorded in the eastern puna border between 14 and 11 5 ma coincides with the occurrence of one of the most important deformation events of the neogene tectonic evolution in the region studies performed across the puna eastern cordillera transition show different relationships between volcanic deposits of ca 13 5 12 1 ma and the oligocene miocene angastaco formation in this paper we describe the ash flow tuff deposits which are the first of this type found concordant in the sedimentary fill of valles calchaquies several analyses performed on these pyroclastic deposits allow a correlation to be made with the alto de las lagunas ignimbrite ca 13 5 ma of the pucarilla cerro tipillas volcanic complex located in the puna outcrops of the ca 13 5 ma pyroclastic deposits are recognised within the puna and the valle calchaqui however in the southern prolongation of the valle de hualfin tiopampa pucarilla depression that separates the puna from the valle calchaqui at these latitudes these deposits are partially eroded and buried and thus their occurrence is recorded only by abundant volcanic clasts included in conglomerates of the angastaco formation the sedimentation of the angastaco formation was aborted at ca 12 ma in the tiopampa pucarilla depression by the pucarilla ignimbrite which unconformably covers the synorogenic units on the contrary in the valle calchaqui the sedimentation of the angastaco formation continued until the late miocene the different relationships between the miocene angastaco formation and the ignimbrites with ages of ca 13 5 and ca 12 ma reveal that in this short period 1 5 m y a significant deformation event took place and resulted in marked palaeogeographic changes as evidenced by stratigraphic sedimentological and chronological records in the angastaco formation

buoyancy forcing by turbulence above rough topography in the abyssal brazil basin abstract observations of turbulent dissipation above rough bathymetry in the abyssal brazil basin are presented relative to regions with smooth bathymetry dissipation is markedly enhanced above rough topography of the mid atlantic ridge with levels above bathymetric slopes exceeding levels observed over crests and canyon floors furthermore mixing levels in rough areas are modulated by the spring neap tidal cycle internal waves generated by barotropic tidal flow over topography are the likely mechanism for supplying the energy needed to support the observed turbulent dissipation a model of the spatial and temporal patterns in the turbulent dissipation rate is used to constrain the diapycnal advection in an inverse calculation for the circulation in an area of rough bathymetry this inverse model uses both beta spiral and integrated forms of the advective budgets for heat mass and vorticity and contains sufficient information to resolve the full three dimensional flow the inverse model solution re

is the deep indian ocean moc sustained by breaking internal waves the indian ocean hosts a vigorous basin scale overturning that constitutes one of the major deep upwelling branches of the global meridional overturning circulation moc the extent to which the deep indian ocean moc is sustained by breaking internal waves is assessed by quantifying and comparing the energetics of the overturning and those of the regional internal wave field a range of published inverse estimates of the circulation across 32 s is used to assess the basin average buoyancy fluxes the turbulent dissipation needed to sustain the moc ranges between 0 17 0 04 and 1 19 0 17 tw which is consistent with the estimated 0 35 0 26 1 04 tw dissipated by breaking internal waves as inferred from observed fine structure both estimates of turbulent dissipation are consistent with the total energy input into the regional internal wave field 0 21 0 05 0 08 tw based on published estimates of energy conversion from winds tides and geostrophic bottom flows however a discrepancy arises when comparing the energetics at different density levels at mid ocean density levels 1000 3000 m the dissipation of internal wave energy is found to be significantly smaller factor 5 10 than the dissipation needed to sustain inverse estimates of the moc the uncertainty related to undersampling of internal wave breaking hot spots was analyzed and found to be small which suggests that mixing processes other than wave breaking due to weak wave wave interactions may be significant in the deep indian ocean

mixing of a tracer in the pycnocline a patch of sulfur hexafluoride was released in may 1992 in the eastern north atlantic on an isopycnal surface near 300 m depth and was surveyed over a period of 30 months as it dispersed across and along isopycnal surfaces the diapycnal eddy diffusivity k estimated for the first 6 months was 0 12 0 02 cm2 s while for the subsequent 24 months it was 0 17 0 02 cm2 s the vertical tracer distribution remained very close to gaussian for the full 30 months as the root mean square rms dispersion grew from 5 to 50 m lateral dispersion was measured on several scales the growth of the rms width of the tracer streaks from less than 100 m to approximately 300 m within 2 weeks implies an isopycnal diffusivity of 0 07 m2 s at scales of 0 1 to 1 km larger than expected from the interaction between vertical shear of the internal waves and diapycnal mixing teasing of the overall patch initially about 25 km across into streaks with an overall length of 1800 km within 6 months supports predictions of exponential growth by the mesoscale strain field at a rate of 3 0 5 10 7 s 1 the rms width of these streaks estimated as 3 km and maintained in the face of the streak growth indicates an isopycnal diffusivity of 2 m2 s at scales of 1 to 10 km much greater than expected from internal wave shear dispersion the patch was painted in albeit streakily by 12 months confirming expectations from analytical and numerical models homogenization of the patch continued during the subsequent 18 months while the patch continued to spread with an effective isopycnal eddy diffusivity on the order of 1000 m2 s acting at scales of 30 to 300 km

high temperature retrogression of granulite facies marbles form the reynolds range group central australia phase equilibria isotopic resetting and fluid fluxes reynolds range group rocks underwent granulite facies metaintroduction morphism m2 at 1 6 ga 5 kbar 750 800 c and were the uplift history of high grade metamorphic belts comsubsequently retrogressed in narrow strike parallel zones at 1 59 monly involves partial re equilibration of mineral as1 57 ga within these zones metacarbonates that initially equisemblages to lower temperature and pressure conditions librated at x 2 0 8 during m2 were mineralogically reset this re equilibration is facilitated by fluid rock interby the infiltration of water rich fluids x 2 0 02 0 3 at action and new mineral assemblages are often best 650 700 c and 3 4 kbar do carb values of the retrogressed developed in discrete zones of extensive retrogression metacarbonates were variably reset during fluid infiltration with the e g van reenen 1986 cartwright 1988 peters lowest values 10 13 suggesting that the fluids that caused wickham 1994 cartwright buick 1995 petrological retrogression were exsolved from segregated partial melts themselves studies of retrograde mineral assemblages may provide derived from the underlying granulite facies metapelites minimportant information about the tectonics and hydroeralogical and isotopic resetting were locally accompanied by silica geology of the lower and middle crust metasomatism the mineralogically reset marbles record time inhowever although there have been many recent quantegrated fluid fluxes of typically 10 10 m m and metasomatic titative studies of metamorphic fluid rock interaction in rocks record time integrated fluid fluxes as high as 10 10 m contact aureoles cartwright valley 1991 ferry m for upward flow of high temperature fluids through the marbles dipple 1991 young morrison 1992 jamveit et al over a distance of 200 m in 18 ma the observed mineralogical 1992 davis ferry 1994 and during prograde regional and isotopic resetting and metasomatism require intrinsic permetamorphism bickle baker 1990a 1990b ferry meabilities between 10 and 10 m that vary across strike 1992 stern et al 1992 leger ferry 1993 cartwright on a centimetre to metre scale indicating that fluid flow was strongly et al 1995 buick cartwright 1996 there have been channelled relatively few studies of high temperature retrogression vennemann stuart smith 1992 peters wickham 1994 cartwright buick 1995 therefore the origins of the retrograde fluids and the absolute timing of

observations of boundary mixing over the continental slope observations of mixing over the continental slope using a towed body reveal a great lateral extent several kilometers of continuously turbulent fluid within a few hundred meters of the boundary at depth 1600 m the largest turbulent dissipation rates were observed ove ra5k mhorizontal region near a slope critical to the m2 internal tide over a submarine landslide perpendicular to the continental slope enhanced mixing extended at least 600 m above the boundary increasing toward the bottom the resulting vertical divergence of the heat flux near the bottom implies that fluid there must be replenished intermediate nepheloid layers detected optically contained fluid with u s properties distinct from their surroundings it is suggested that intermediate nepheloid layers are interior signitures of the boundary layer detachment required by the near bottom flux divergance

deformation history of the puna plateau central andes of northwestern argentina abstract two tectonic shortening events created the first order structural characteristics of the puna plateau one in the paleozoic and a second during the andean orogeny in the cenozoic to constrain the structural characteristics and timing of andean deformation in the puna plateau we focus on differentiating these two shortening events and provide cooling ages apatite fission track and apatite u th he to determine the amount of andean exhumation on the hanging wall of major cenozoic faults two contrasting expressions of shortening are documented in ordovician strata strain requires four stages folding flattening through cleavage formation low angle faulting and local distributed shear in the mesozoic and cenozoic strata shortening is expressed as reverse faults fault propagation folds and dipping panels dissimilarities reflect different p t conditions and amount of strain as structures in the ordovician rocks require higher temperatures and strain than andean structures in the mesozoic and cenozoic strata furthermore local cretaceous aft cooling ages in pervasively cleaved ordovician rocks reveal these rocks did not reach temperatures compatible with cleavage formation during the andean event lastly our data show a middle eocene to oligocene exhumation history that supports an overall continuous development of the andean thrust belt in the puna plateau since the early cenozoic

internal tides in monterey submarine canyon abstract the m2 internal tide in monterey submarine canyon is simulated using a modified version of the princeton ocean model most of the internal tide energy entering the canyon is generated to the south on sur slope and at the head of carmel canyon the internal tide is topographically steered around the large canyon meanders depth integrated baroclinic energy fluxes are up canyon and largest near the canyon axis up to 1 5 kw m 1 at the mouth of the upper canyon and increasing to over 4 kw m 1 around monterey and san gregorio meanders the up canyon energy flux is bottom intensified suggesting that topographic focusing occurs net along canyon energy flux decreases almost monotonically from 9 mw at the canyon mouth to 1 mw at gooseneck meander implying that high levels of internal tide dissipation occur the depth integrated energy flux across the 200 m isobath is order 10 w m 1 along the majority of the canyon rim but increases by over an order of magnitude near the canyon head where internal ti

widening of the andes an interplay between subduction dynamics and crustal wedge tectonics shortening of the continental lithosphere is generally accommodated by the growth of crustal wedges building above megathrusts in the mantle lithosphere we show that the locus of shortening in the western margin of south america has largely been controlled by the geometry of the slab numerical models confirm that horizontal subduction favors compression far from the trench above the asthenospheric wedge and steeply dipping segment of the subducting slab as a result a second crustal wedge grows in the hinterland of the continent and widens the andes in the bolivian orocline this wedge corresponds to the eastern cordillera whose growth was triggered by a major episode of horizontal subduction when the slab returned to a steeper dip angle shortening and uplift pursued facilitated by the structural and thermo chemical alteration of the continental lithosphere we review the successive episodes of horizontal subduction that have occurred beneath south america at different latitudes and show that they explain the diachronic widening of the andes we infer that the present day segmented physiography of the andes results from the latitudinally variable transient interplay between slab dynamics and upper plate tectonics over the cenozoic we emphasize that slab flattening or absence thereof is a major driving mechanism that sets the width of the andes at any latitude

retroarc basin reorganization and aridification during paleogene uplift of the southern central andes u s national science foundation ear 1049605 robert r shrock foundation at indiana university nsf ear award 1338583 project pdts unsj e985

decadal variability of north pacific eastern subtropical mode water a significant decadal variability of the north pacific eastern subtropical mode water npestmw related to the pacific decadal oscillation is identified from the gridded argo and en4 observational data sets to investigate the decadal variability of the npestmw volume the high resolution estimating the circulation and climate of the ocean phase ii simulation is used to diagnose the volume budget of the npestmw density layer in the npestmw formation region 20 degrees 36 degrees n 160 degrees 120 degrees w between 1992 and 2016 results show that npestmw is formed through subduction of low potential vorticity pv water this low pv water subduction is mainly determined by mixed layer depth change and lateral induction which account for approximately 58 and 32 respectively the decadal npestmw volume anomaly is originated from the pacific decadal oscillation induced decadal anomaly of air sea buoyancy flux this decadal buoyancy flux anomaly drives the decadal anomaly of mixed layer depth change then causes anomalous subduction and leads to anomalous low pv water subduction the decadal npestmw volume anomaly is finally generated by this anomalous low pv water subduction

surface uplift and convective rainfall along the southern central andes angastaco basin nw argentina stable isotopic and sedimentary records from the orogenic puna plateau of nw argentina and adjacent intermontane basins to the east furnish a unique late cenozoic record of range uplift and ensuing paleoenvironmental change in the south central andes today focused precipitation in this region occurs along the eastern windward flanks of the eastern cordillera and sierras pampeanas ranges while the orogen interior constitutes high elevation regions with increasingly arid conditions in a westward direction as in many mountain belts such hydrologic and topographic gradients are commonly mirrored by a systematic relationship between the oxygen and hydrogen stable isotope ratios of meteoric water and elevation the glass fraction of isotopically datable volcanic ash intercalated in sedimentary sequences constitutes an environmental proxy that retains a signal of the hydrogen isotopic composition of ancient precipitation this isotopic composition thus helps to elucidate the combined climatic and tectonic processes associated with topographic growth which ultimately controls the spatial patterns of precipitation in mountain belts however between 25 5 and 27 s present day river based hydrogen isotope lapse rates are very low possibly due to deep convective seasonal storms that dominate runoff if not accounted for the effects of such conditions on moisture availability in the past may lead to misinterpretations of proxy records of rainfall here we present hydrogen isotope data of volcanic glass dg extracted from 34 volcanic ash layers in different sedimentary basins of the eastern cordillera and the sierras pampeanas combined with previously published dg records and our refined u pb and u th he zircon geochronology on 17 tuff samples we demonstrate hydrogen isotope variations associated with paleoenvironmental change in the angastaco basin which evolved from a contiguous foreland to a fault bounded intermontane basin during the late mio pliocene we unravel the environmental impact of mio pliocene topographic growth and associated orographic effects on long term hydrogen isotope records of rainfall in the south central andes and potentially identify temporal variations in regional isotopic lapse rates that may also apply to other regions with similar topographic boundary conditions

turbulent mixing and exchange with interior waters on sloping boundaries abstractmicrostructure measurements along the axes of monterey and soquel submarine canyons reveal 200 300 m thick well stratified turbulent near bottom layers with average turbulent kinetic energy dissipation rates e 4 10 8 w kg 1 and eddy diffusivities k 16 10 4 m2 s 1 assuming mixing efficiency 0 2 to at least thalweg depths of 1200 m turbulent dissipation rates are an order of magnitude lower in overlying waters whereas buoyancy frequencies are only 25 higher well mixed bottom boundary layer thicknesses hn are an order of magnitude thinner than the stratified turbulent layer hn he because well stratified turbulent layers are commonly observed above slopes arguments that mixing efficiency should be reduced on sloping boundaries do not hold in cases of energetic internal wave generation or interaction with topography an advective diffusive balance is used to infer velocities and transports predicting horizontal upslope flows of 10 50 m day 1 extrapolating this estimate globa

geometry and late mesozoic cenozoic evolution of the salar de atacama basin 22 30 24 30 s in the northern central andes new constraints from geophysical geochronological and field data abstract the late mesozoic cenozoic evolution of the central andes of northern chile consists of a series of events related to changing conditions along the plate margin leading to different episodes of compression and extension a long lasting basin which records these changes corresponds to the salar de atacama basin its tectonic history has been blurred by several interpretations of seismic reflection lines and multiple chronostratigraphic correlations between subsurface surface units as such many aspects of its tectonic evolution are still unclear in this study we performed an e w gravimetric profile across the barros arana syncline and the basin we analyzed interval velocities obtained from seismic reflection studies and reviewed the profiles closest to the gravity survey four u pb samples for detrital zircon analysis were obtained from late cretaceous paleogene units geophysical data show a segmentation of physical properties within the basin with denser units and faster interval velocities around the late mesozoic early cenozoic units and lighter slower units in the actual salt pan the main contrast in physical properties is observed in the evaporitic and fine grained continental deposits of the san pedro formation geophysical and geological constraints show that its thickness varies between 800 and 1200 m and that it was deformed during later events the u pb data show that the rocks within the barros arana syncline reach well into the paleogene and that they were mainly deformed during the late eocene incaic event where an east verging thrust system also involving permo triassic units was developed establishing the actual structural configuration the late oligocene early miocene units were then deposited in a post orogenic setting with minor compression a stronger phase around the late miocene reactivated previous structures and folded these deposits this continuous compressive history of the basin which is mostly a result of the incaic event is in agreement with the regional evolution of the central andes

the spatiotemporal structure of diabatic processes governing the evolution of subantarctic mode water in the southern ocean abstracta coupled ice ocean eddy permitting southern ocean state estimate sose for 2008 10 is used to describe and quantify the processes forming and destroying water in the subantarctic mode water samw density range 26 7 27 2 kg m 3 all the terms in the temperature and salinity equations have been diagnosed to obtain a three dimensional and time varying volume budget for individual isopycnal layers this study finds that air sea buoyancy fluxes diapycnal mixing advection and storage are all important to the samw volume budget the formation and destruction of water in the samw density range occurs over a large latitude range because of the seasonal migration of the outcrop window the strongest formation is by wintertime surface ocean heat loss occurring equatorward of the subantarctic front spring and summertime formation occur in the polar gyres through the freshening of water with 27 2 kg m 3 with an important contribution from sea ice melt further buoyancy gain by heating is ac

formation of wollastonite by chemically reactive fluid flow during contact metamorphism mt morrison pendant sierra nevada california usa quartz calcite sandstones experienced the reaction calcite introduction quartz wollastonite co2 during prograde contact metaflow of chemically reactive fluid may control the minmorphism at p 1500 bars and t 560 c rocks were in eralogy stable isotope composition and trace element equilibrium during reaction with a co2 h2o fluid with xco2 chemistry of rocks during contact metamorphism e g 0 14 the transition from calcite bearing wollastonite free to labotka et al 1988 jamtveit et al 1992a 1992b nabelek wollastonite bearing calcite free rocks across the wollastonite isograd labotka 1993 bowman et al 1994 roselle et al is only several millimeters wide the wollastonite forming reaction 1999 a number of aspects of metamorphic fluid flow was driven by infiltration of quartz calcite sandstone by chemically however remain the subject of debate including the reactive h2o rich fluids and the distribution of wollastonite directly direction of flow labotka et al 1988 ferry dipple images the flow paths of reactive fluids during metamorphism the 1992 ferry 1995a hanson 1995a whether numerical mapped distribution of wollastonite and modeling of an o isotope models that assume uniform rock properties adequately profile across a lithologic contact indicate that the principal direction predict the geometry of fluid flow in aureoles that contain of flow was layer parallel directed upward with any cross layer a variety of anisotropic structural features hanson 1992 component of flow 0 1 of the layer parallel component fluid 1995b cook et al 1997 and the degree to which local flow was channeled at a scale of 1 100 m by pre metamorphic mineral fluid equilibrium is attained lasaga rye dikes thrust and strike slip faults fold hinges bedding and 1993 bolton et al 1999 lasaga et al 2000 these and stratigraphic contacts limits on the amount of fluid based on related questions were addressed in an investigation of minimum and maximum estimates for the displacement of the contact metamorphism in the mt morrison pendant wollastonite reaction front from the fluid source are 0 7 1 9 eastern sierra nevada california the location is an 10 cm fluid cm rock the sharpness of the wollastonite isograd exceptional site for the study of metamorphic fluid flow the consistency of mineral thermobarometry the uniform measured for several reasons first the mt morrison sandstone o o fractionations between quartz and calcite and model the focus of this study is ideal for application of concalculations all argue for a close approach to local mineral fluid tinuum models of coupled fluid flow and reaction because equilibrium during the wollastonite forming reaction it is unusually homogeneous in mineralogy and texture

large along strike variations in the onset of subandean exhumation implications for central andean orogenic growth abstract plate tectonics drives mountain building in general but the space time pattern and style of deformation is influenced by how climate geodynamics and basement structure modify the orogenic wedge growth of the subandean thrust belt which lies at the boundary between the arid high elevation central andean plateau and its humid low elevation eastern foreland figures prominently into debates of orogenic wedge evolution we integrate new apatite and zircon u th he thermochronometer data with previously published apatite fission track data from samples collected along four subandean structural cross sections in bolivia between 15 and 20 s we interpret cooling ages vs structural depth to indicate the onset of subandean exhumation and signify the forward propagation of deformation we find that subandean growth is diachronous south 11 3 ma vs north 6 2 ma of the bolivian orocline and that subandean exhumation magnitudes vary by more than a factor of two similar north south contrasts are present in foreland deposition hinterland erosion and paleoclimate these observations both corroborate diachronous orogenic growth and illuminate potential propagation mechanisms of particular interest is an abrupt shift to cooler more arid conditions in the altiplano hinterland that is diachronous in southern bolivia 16 13 ma vs northern bolivia 10 7 ma and precedes the timing of subandean propagation in each region others have interpreted the paleoclimate shift to reflect either rapid surface uplift due to lithosphere removal or an abrupt change in climate dynamics once orographic threshold elevations were exceeded these mechanisms are not mutually exclusive and both would drive forward propagation of the orogenic wedge by augmenting the hinterland backstop either through surface uplift or spatially variable erosion in summary we suggest that diachronous subandean exhumation was driven by piecemeal hinterland uplift orography and the outward propagation of deformation

oligocene to present shallow subduction beneath the southern puna plateau abstract the southern puna plateau is a conspicuous example of a high elevation orogenic plateau in a non collisional setting this orogenic sector is currently located above an anomalously shallow subduction segment in which timing and relation to upper plate tectonics have been widely overlooked this subduction segment here referred to as the southern puna shallow subduction spss is characterized by a 200 km wide shallow area located at 300 km from the trench at a depth of 100 120 km and dipping 10 12 to the east to determine the onset of the spss and its link to the tectonic and magmatic activity in this region we analyzed the tectonomagmatic record of the southern puna plateau from preexisting datasets also we present a new approach based on global subduction data that provides a straightforward methodology to extract potential paleo slab angles from the bedrock arc record this analysis reveals that a pronounced eastward arc front migration and magmatic broadening took place at 26 ma and was preceded by 4 ma of reduced magmatic activity which we link to the inception of the spss as expected in shallow subduction settings a change to basement cored distributed deformation south of 25 s in the southern puna plateau coincides with the beginning of shallow subduction also the spss is coincident with the enigmatic post eocene intraplate deformation of the otumpa hills located at 950 km from the trench we suggest that this succession of events is not fortuitous and that the development of the spss impacted directly the overriding plate since the oligocene contributing to the building of one of the largest topographies 3 km and thickest orogenic crusts 70 60 km on earth the shallow subduction would have acted jointly with cenozoic changes in plate kinematics and climate enhancing andean orogenesis at studied latitudes

a basinwide estimate of vertical mixing in the upper pycnocline spreading of bomb tritium in the north pacific ocean abstract the vertical diffusivity kv in the upper half kilometer of the north pacific subtropical pycnocline is estimated from observations of the spreading rate of anthropogenic tritium the calculation is based on approximately 300 ocean tritium profiles made since tritium was introduced to the atmosphere via bomb testing in the 1960s the data coverage does not permit detailed mapping of tritium penetration especially in the sparsely sampled western pacific for this reason and to minimize advective effects the spreading rate is averaged within the closed streamlines of the subtropical gyre spanning 5 n to 40 n the result kv 1 5 0 7 10 5 m2 s 1 is consistent with inferences from microstructure and purposefully released tracer measurements in the north atlantic confirming that the spatially averaged rate of mixing in the upper pycnocline is substantially lower than the canonical munk estimate for the lower pycnocline