surface eddy momentum flux and velocity variances in the southern ocean from geosat altimetry abstract satellite altimetry has previously been used to map the magnitude of the surface eddy variability of the global oceans but the direction of the time variable velocities have been more difficult to determine here a technique is presented for resolving both magnitude and direction of residual surface geostrophic velocities at geosat altimeter crossover points providing a two year time series with a temporal resolution of 17 days and horizontal resolution of around 100 km the time series of residual velocity components are then used to determine surface eddy statistics in the southern ocean and to investigate the role of transient eddies in the southern ocean momentum balance the surface eddy statistics from geosat crossover points show a complex spatial distribution in the surface reynolds stresses u 2 v 2 u v in contrast to the assumptions of isotropic variability in previous analyses of altimeter data velocity variance ellipses are found to be distinctly anisotropic in many regions

constraints on provenance of the central european triassic using detrital zircon fission track data the type of provenance information obtained from dating detrital grains will depend upon the thermal sensitivity of the isotopic dating method for detrital zircon the two methods fission track and u pb in routine use have widely different thermal sensitivities and therefore may provide quite different provenance information zircon fission track data are sensitive to thermal overprinting in the temperature range 200 300 c and therefore have the unique ability to provide source thermal history data the purpose of this study is to evaluate the suitability of zircon fission track data for provenance studies of the triassic siliciclastic sediments of central europe with an emphasis on testing proposed sediment pathways zircon fission track data obtained during this study are consistent with a sediment pathway linking fennoscandia with the central german basin in addition during carnian times there must also have been a pathway linking the schilfsandstein formation of the german basin with the lunzersandstein of the tethyan realm pointing to a european wide fluvial transport system detrital zircon fission track data are therefore a useful means for discerning sediment source and reconstructing sediment pathways

altimeter observations of the peru chile countercurrent data from geosat and topex altimeters are used to infer the structure of the peru chile countercurrent a jet that flows from at least as far north as 10 s historical data suggests 7 s to 35 40 s maintaining its position between approximately 100 300 km offshore although the annual mean current cannot be determined from altimeter observations the nearly antisymmetric patterns in spring and fall combined with historical observations suggest that the countercurrent is poleward at most times and is maximum in spring and minimum in fall previous studies have linked the offshore countercurrent at 7 s to the equatorial undercurrent west of the galapagos islands suggesting that the countercurrent is part of a continuous flow that extends from the western equatorial pacific to the region off chile between 35 40 s

dynamics of seasonal and interannual variability of the peru chile undercurrent 1 coastal sea level current satellite altimeter data and an equatorial kelvin wave model are used to study the dynamics of seasonal and interannual fluctuations of the peru chile undercurrent satellite altimetry shows that low frequency sea level anomalies near 30 s propagate offshore as expected from rossby wave theory those anomalies are related to disturbances of equatorial origin observed near the coast of south america with a wind forced equatorial kelvin wave model and simple rossby wave dynamics we show that much of the sea level anomalies and more than 50 of the observed undercurrent variability near 30 s at seasonal and interannual periods can be explained by long rossby waves forced by the equatorial kelvin waves the amplitude of the equatorial kelvin wave can be used to estimate the amplitude of the rossby wave near the south american coast and thus to monitor low frequency changes in the peru chile undercurrent

circulation and low frequency variability near the chilean coast remotely forced fluctuations during the 1991 92 el nino results are reported from the first long recording current meter observations over the slope off chile these observations at 308s during the 1991 92 el nino event are analyzed together with observations of currents at a local deep sea site local wind and sea level sea level from the peru and chile coasts and wind temperature and currents from the equatorial pacific mean poleward flow of 12 cm s21 was observed within the peru chile undercurrent over the slope mean flow in the depth range of antarctic intermediate water was not distinguishable from zero in the presence of strong low frequency lf variability which dominated slope currents at all depths the strongest lf fluctuations had periods of about 50 days but periods of 10 and about 5 days were also observed significant local wind forcing of slope currents was only found in the period band 6 10 days and may be related to coastal trapped waves in the atmosphere our analysis shows that free coastal trapped waves in the ocean arriving from the north dominated the lf variability over the shelf and slope off northern and central chile during the 1991 92 el nino event strong 50 day period fluctuations there started their journey about two months earlier and 15 000 km farther up the coastal equatorial waveguide near the date line in the equatorial pacific as equatorial kelvin waves forced by westerly wind events of similar period upon reaching the south american coast these waves forced coastal trapped waves which propagated along the peru coast into the study region likewise a scenario of equatorial trapped waves forcing coastal trapped waves may explain 10 day as well as 6 day and 4 5 day period coastal trapped waves off chile stemming from mixed rossby gravity and inertia gravity waves trapped at the equator since the large 50 day period coastal trapped waves may strongly modify coastal upwelling source water such remotely forced waves may have a significant influence on the pelagic ecosystem off chile at least during el nino events

vertical structure variability in a seasonal simulation of a medium resolution regional model of the eastern south pacific a seasonal simulation from a medium resolution ocean general circulation mode ogcm is used to investigate the vertical structure variability of the southeast pacific sep the focus is on the extra tropical rossby wave etrw variability and associated forcing mechanism some aspects of the model mean state are validated from available observations which justifies a vertical mode decomposition of the model variability the analysis of the baroclinic mode contributions to sea level indicates that the gravest mode is dominant over most of the domain at all frequencies annual variability is on average twice as large as the semi annual variability which is confined near the coast for all the modes the first baroclinic mode contribution to the annual cycle exhibits a clear westward propagation north of the critical latitude the higher order modes only contribute near the coast where they are associated with vertically propagating energy the residual variability which is the energy at all timescales other than annual and semi annual periods peaks offshore between similar to 20 degrees s and similar to 30 degrees s for all baroclinic modes the third baroclinic mode also exhibits a relative maximum variability off the coast of peru south of the critical latitude of the annual cycle similar to 13 degrees s where the peru chile undercurrent is the most intense sensitivity experiments to the atmospheric and boundary forcing suggest that the residual variability results from the non linear interaction between annual rossby waves and the mean flow while the annual etrws in the model result from the summed contribution from both the local wind stress and remote equatorial forcing overall the study extends the classical analysis of sea level variability in the sep based on linear theory and suggests that the peculiarities of the baroclinic modes need to be taken into account for interpreting the sea level variability and understanding its connection with the equatorial variability c 2008 published by elsevier ltd

cooling and uplift patterns in the lepontine alps south central switzerland and an age of vertical movement on the insubric fault line 96 new fission track ft apatite and zircon k ar and rb sr biotite and muscovite ages are presented for 19 samples mainly acid gneisses from a 40 km traverse through the lepontine alps in the maggia valley south central switzerland plotting measured mineral ages against assumed system closure temperatures yields cooling rates for each sample the entire profile shows a fairly uniform late neogene recent mean uplift rate of 0 5 mm a confirmed by a gradient of ft apatite age with elevation cooling from higher temperatures occurred earlier in the south where uplift rates of 2 2 mm a in the steep belt root zone indicate 9 km early miocene uplift of the northern pennine block this uplift started before 23 ma and is interpreted as resulting from a major phase of backthrusting along the insubric line and as dating the formation of the mylonite belt estimated cooling rates constrain the timing of lepontine mid tertiary metamorphism 3 schematic models are proposed which also consider published rb sr k ar mica and hornblende and u pb monazite ages slow cooling differential initial heating and subsequent cooling of different parts of the central alps and post 38 ma cooling with syntectonic metamorphism at 27 ma are postulated as alternative interpretations of isotopic data and geologic evidence from extrapolation between k ar and rb sr mica ages and apatite ft ages 240 50 c is proposed as the closure temperature for the retention of fission tracks in zircon

surface textures of heavy mineral grains a new contribution to provenance studies abstract the study zone is geologically very complex and corresponds to the western limits of the betic cordilleras sw spain materials from the triassic to holocene are found here this study demonstrates that most of the surface textures seen on quartz are present on the seven selected heavy minerals sem analysis of heavy mineral grains reveals that certain morphologies are in part associated with particular surface textures this textural analysis enables the source areas to be differentiated more clearly equally it contributes to a deeper knowledge of the various stages of the grains provenance a good example is the study of the heavy minerals of the guadalete river terraces

the role of fission track dating in discrimination of provenance determination of single crystal ages by fission track dating analysis of zircons and subordinately apatites within a detrital heavy mineral assemblage together with frequency distribution and radial plot analysis of the measured ages permits identification of different age modes synopses are presented of published fission track provenance studies in north central victoria northeastern tasmania barbados the rockall trough the english wealden mexico utah and the central alps from authors

can fission track annealing in apatite be described by first order kinetics abstract it is becoming commonplace to suggest that fission track annealing in apatite can be described by first order kinetics that is the decrease in track density and or length with time during isothermal annealing can be described by a single exponential equation a review of the literature reveals that there is no convincing evidence for such an assertion but more than ample evidence to the contrary simple graphical analysis of available annealing data from the literature clearly shows that the single exponential fails to adequately describe the data more rigorous statistical model fitting is not attempted due to the generally inadequate specification of annealing data in the literature most published annealing data suffer from flaws in experimental design that render them of limited value in defining viable kinetic models for the annealing process consideration of the processes taking place during annealing suggests that there is no good reason why first order kinetics would be expected to describe fission track annealing and more complex models should be considered in order to provide reliable data capable of yielding practically useful kinetic models laboratory annealing experiments should be designed to meet a number of strict criteria in identifying viable models the need is for those which adequately describe the data rather than for physically meaningful models although models should preferably be kept as simple as possible

fundamentals of fission track thermochronology fission track ft analysis has developed into one of the most useful techniques used throughout the geologic community to reconstruct the low temperature thermal history of rocks over geological time the ft method is based on the accumulation of narrow damage trails i e fission tracks in uranium rich mineral grains e g apatite zircon titanite and natural glasses which form as a result of spontaneous nuclear fission decay of 238u in nature price and walker 1963 fleischer et al 1975 the time elapsed since fission tracks began to accumulate is estimated by determining the density of accumulated tracks in a particular material in relation to the uranium content of that material chemical etching can be used to enlarge fission tracks that have formed within a mineral in order to make them readily observable under an ordinary optical microscope price and walker 1962 if a host rock is subjected to elevated temperatures fission tracks that have formed up to that point in time are shortened progressively and eventually erased by the thermal recovery i e annealing of the damage fleischer et al 1975 because thermal diffusion basically governs the annealing process the reduction in ft length is a function of heating time and temperature importantly fission tracks are partially annealed over different temperature intervals within different minerals this characteristic allows for the construction of time temperature paths of many different rock types by a plotting ft and other isotopic ages from different minerals versus their closure temperatures which is applicable in the case of a monotonous cooling history e g wagner et al 1977 zeilter et al 1982 and or by b the inverse modeling of observed ft age and confined track length data e g corrigan 1991 lutz and omar 1991 gallagher 1995 ketcham et al 2000 see also ketcham 2005

quantifying transient erosion of orogens with detrital thermochronology from syntectonic basin deposits abstract the evolution of an orogen is marked by phases of topographic growth equilibrium and decay during these phases erosion rates vary in response to temporal and spatial changes in climate topographic relief and slope and deformation detrital thermochronometer cooling age data collected from syntectonic basin deposits are a promising tool for quantifying erosion histories during orogenic evolution previous studies typically assume steady state erosion for interpreting detrital data although in many situations this assumption is not justified here we present a new numerical modeling approach that predicts thermochronometer cooling ages in a stratigraphic section where sediment is sourced from a region with a temporally variable erosion history multiple thermochronometer cooling ages are predicted at different stratigraphic horizons as a function of variable erosion histories rock cooling rates in the hinterland and thermophysical material properties and boundary conditions the modeling approach provides the context for the interpretation of natural data including geologically realistic situations with a temporally varying erosion rate the results of three end member hinterland erosion histories are explored 1 steady state erosion 2 increasing erosion rate with time and 3 decreasing erosion rate with time results indicate that for steady erosion rates between 0 2 and 1 0 mm yr up to 30 m y will pass following a change in erosion rate before the detrital ages have adjusted to reflect a new erosion regime in simulations with transient erosion the estimation of erosion rates from a detrital record using assumption of thermal steady state will generally be in error often by as much as 25 to 100 these results highlight that assumptions of steady erosion in mountain belts should be used with caution application of the model to thermochronometer cooling ages preserved in syntectonic sediments sourced from the nanga parbat region himalaya illustrates how the transient catchment averaged erosion history can be quantified with detrital thermochronology in this example we found that erosion rates increased over the past 20 ma from about 1 0 mm yr to modern rates in the range of 1 5 to 2 0 mm yr

changes in biological productivity and ocean climatic fluctuations during the last 1 5 kyr in the humboldt ecosystem off northern chile 27 s a multiproxy approach abstract a sedimentary box core biac072014 collected in a coastal environment in the humboldt current ecosystem hce inglesa bay 27 s northern chile was used to reconstruct the changes in biological productivity and ocean climate fluctuations during the last 1 5 kyr via geochemical mineralogical and micropaleontological analyses from 510 ce to 930 ce el nino like conditions prevailed while during the medieval climate anomaly mca 950 ce to 1450 ce la nina like conditions predominated this pattern might have resulted from weakening strengthening of the walker cell contraction expansion of the south pacific sub tropical high spsh and a predominance of warm cold phases of the pacific decadal oscillation pdo between 1820 ce and the present inglesa bay experienced a reduction in the oxygen minimum zone omz intensity and biological productivity an increase in the detritic input and a decrease in sea surface temperature sst despite the regional intensification and secular cooling 14 s and 27 s of coastal upwelling the similarity between the reduction in biological productivity and omz intensity in this region and that in the central zone of chile 36 s suggests that inglesa bay acts a transition zone in relation to the oceanographic behaviour of the hce the reduction in the omz intensity and biological productivity during the last 200 years could be explained by greater subsurface ventilation in intermediate depths due to more northward displacement of the subduction region of the eastern south pacific intermediate water espiw near 30 s in response to the strengthening of the circulation of the subtropical gyre the coastal cooling observed in the northern section of hce during the current warm period suggests that it is not possible to demonstrate that el nino like conditions promoted the reduction in biological productivity and omz intensity in inglesa bay

long term landscape evolution and post rift reactivation in the southeastern brazilian passive continental margin taubate basin zircon zft and apatite aft fission track low temperature thermochronology was applied at the brazilian passive continental margin in order to understand and reconstruct the post rift evolution since the breakup of southwestern gondwana the thermochronological data obtained from samples of both the precambrian basement and the paleogene to neogene sedimentary rocks from the continental rift of southeastern brazil provided zft ages between 148 15 and 64 6 ma and aft ages of 81 8 29 3 ma these data clearly indicate syn and post rift reactivations during the early cretaceous with great emphasis on paleogene to neogene times integrating the results of older thermochronological studies the reactivation of the southeastern brazilian margin can be described in three main phases related to the rift to post rift evolution of se brazil in general zft and aft data yield spread values that become younger as samples are closer to the reactivated neoproterozoic shear zones and might reflect source area exhumation the analysis of zft and aft data allowed interpretations regarding the main phases that occurred in the study area related to the thermotectonic and tectono stratigraphic evolution in southeastern brazil

statistical analysis of the surface circulation of the california current we use a set of mixed layer drifting buoy trajectories from the california current 20 n 40 n during 1985 1990 to obtain statistically reliable estimates of the mean currents the mean variance field and the geographically varying diffusivity integral timescales and integral space scales typical values for the diffusivity are 1 1 8 7 107 cm2 s 1 while the timescales and space scales are 2 1 7 1 days and 16 59 km respectively the variance field displays a strong westward gradient out to 125 w and diffusivity shows a tendency to decrease toward the southwest part of the domain significant anisotropy is found in the variance field near the coastal boundary and at 30 n 130 w which is the region where the subarctic and northern subtropical fronts approach the california current the antisymmetric component of the diffusivity tensor indicates that cyclonic eddies dominate the mesoscale signature of drifters in this region we seek simple parameterizations to relate the scales of motion of the random velocity field to the diffusivity by testing least squares fits to u02t and u0l where u02 is the velocity variance we found no cases for which these two hypotheses could be distinguished for the meridional component the linear regressions are not successful which suggests that the meridional departure velocities result from a flow regime that is significantly organized by for example waves or coherent structures a subset of the drifters measured temperature along their tracks and we use the resultant data to produce the first direct estimates of the horizontal eddy heat flux divergence based on lagrangian estimates in addition we separately compute the eddy diffusivity parameterization of the eddy heat flux divergence u using our diffusivity estimates and a sea surface temperature climatology the two independent terms agree well which provides a measure of reassurance about the diffusivity estimates the eddy heat flux divergence in the california current is very small 5 w m 2 and does not appear to be significant in the long term heat budget of the upper ocean in this region

satellite altimetry data reveal jet like dynamics of the humboldt current 1 satellite derived mean sea level anomalies were blended with mean dynamic topography to obtain seasonal climatologies of the eastern south pacific ocean s surface circulation with an emphasis on the humboldt current the humboldt current is confined to a narrow northward flowing jet like stream of about 350 km associated with maximum geostrophic velocities of more than 15 cm s 1 from 35 to 23 s the current streams closer to the coast in the south within 500 km but is found 500 km offshore in its northern section a bifurcation takes place at 23 s with a more coastal branch heading toward the coast of southern peru 15 s and an oceanic branch continuing in a north northwesterly direction the humboldt current intensifies by 3 cm s 1 in austral summer as compared to winter in contrast the humboldt current s coastal branch is stronger in austral winter by the same order of magnitude we attribute these distinct seasonal flow fields to the meridional movement of the south pacific anticyclone which includes a seasonal relocation of a strong wind stress curl nucleus from offshore central southern austral summer to central northern chile austral winter thus driving the humboldt current by means of seasonal sverdrup dynamics the geostrophic flow field in the eastern south pacific communicates colder and fresher sub antarctic surface water toward the tropics along the eastern rim of the subtropical gyre

vertical structure of mesoscale eddies in the eastern south pacific ocean a composite analysis from altimetry and argo profiling floats 1 the mean vertical structure of mesoscale eddies in the peru chile current system is investigated by combining the historical records of argo float profiles and satellite altimetry data a composite average of 420 526 profiles acquired by argo floats that surfaced into cyclonic anticyclonic mesoscale eddies allowed constructing the mean three dimensional eddy structure of the eastern south pacific ocean key differences in their thermohaline vertical structure were revealed the core of cyclonic eddies ces is centered at 150 m depth within the 25 2 26 0 kg m 3 potential density layer corresponding to the thermocline in contrast the core of the anticyclonic eddies aes is located below the thermocline at 400 m depth impacting the 26 0 26 8 kg m 3 density layer this difference was attributed to the mechanisms involved in the eddy formation while intrathermocline ces would be formed by instabilities of the surface equatorward coastal currents the subthermocline aes are likely to be shed by the subsurface poleward peru chile undercurrent in the eddy core maximum temperature and salinity anomalies are of 1 c and 0 1 with positive negative values for aes ces this study also provides new insight into the potential impact of mesoscale eddies for the cross shore transport of heat and salt in the eastern south pacific considering only the fraction of the water column associated with the fluid trapped within the eddies each ce and ae has a typical volume anomaly flux of 0 1 sv and yields to a heat and salt transport anomaly of 1 3 1011 w and 3 8 103 kg s 1 respectively

equatorial pacific 13 c water eddies in the eastern subtropical south pacific ocean abstract argo float profile data are used to analyze warm salty weakly stratified subthermocline eddies of tropical origin in the eastern subtropical south pacific ocean these eddies contain anomalous signatures of the equatorial pacific 13 c water that is carried poleward within the peru chile undercurrent pcu as it flows along the west coast of south america from their source along the chilean coast between 29 and 39 s the eddies spread westward and slightly northward likely at least partly advected by the subtropical gyre the eddy water properties contrast strongly with the colder fresher more strongly stratified waters of subantarctic origin being carried northward then westward by the gyre near the eddy source about 6 of argo profiles sample eddies that are above selected thresholds for both salinity and potential vorticity anomalies relative to maps of the mean distributions of these properties on and around the core isopycnal for the eddies the proportion of such profiles dimini

statistical analysis of the surface circulation in the california current system using satellite tracked drifters abstract a kinematic description of the surface circulation in the southern california current system is presented using the statistics of the 7 11 month long trajectories of 29 satellite tracked mixed layer drifters the drifters were released north of 30 n and traveled southward at an average speed of 3 4 cm s 1 along baja california through an inhomogeneous field of mesoscale eddies of 15 cm s 1 rms variability lagrangian and eulerian statistics of the variations about this mean southward drift are computed the drifter ensemble mean lagrangian decorrelation time scale is 4 5 days and the lagrangian decorrelation space scale is 40 50 km the computation of dispersion of single particles about the mean drift shows that the theory of diffusion by homogeneous random motion taylor s theory describes these dispersive motions well ensemble mean diffusivities of about 4 107 cm2 s 1 are found on a 200 200 km2 spatial average single partial diffusivities are found to be proportional to the kinetic ene

seasonal dynamics of the near surface alongshore flow off central chile 1 the seasonal cycle of the near surface circulation off central chile was analyzed using satellite altimetry and an oceanic model to evaluate the role of the wind stress curl on the circulation we performed two identical simulations except for the wind forcing the control run used long term monthly mean wind stress and the no curl run used a similar wind stress field but without curl the observed and modeled control run surface currents showed a strong seasonal cycle and a well defined equatorward flow with a jet like structure this jet develops during spring and summer consistent with the presence of a low level wind jet south of punta lavapie cape 37 s the equatorward surface current remains close to the coast after the flow passes this cape however it separates to become an offshore jet in contrast in the no curl simulation the separation at punta lavapie is not observed and the offshore jet farther north is not present demonstrating the importance of the wind stress curl on the dynamics of this flow although the offshore integrated sverdrup transport was similar to the model transport the offshore jet was not located where the wind stress curl was maximum instead the position of the jet followed approximately the zero wind stress curl which corresponds to the climatological location of the low level wind jet axis these results illustrate the importance of the offshore upwelling downwelling associated with curl driven ekman pumping which tilts isopycnals upward downward toward the east west of the wind jet forcing a northward flow through thermal wind balance

assessing effective provenance methods for fluvial sediment in the south china sea sediment is delivered by the rivers of se asia to the south china sea where it provides an archive of continental environmental conditions since the eocene interpreting this archive is complicated because sediment may be derived from a number of unique sources and the rivers themselves have experienced headwater capture that also affects their composition a number of methods exist to constrain provenance but not all work well in this area anthropogenic impacts most notably agriculture mean that the modern rivers contain more weathered materials than they did up until about 3000 years ago the rivers have also changed their bulk chemistry and clay mineralogy in response to climate change so that these proxies as well as sr isotopes are generally unreliable provenance indicators nd isotopes resolve influx from luzon but many other sources in se asia have similar values and clear resolution of end members can be difficult instead thermochronology methods are best suited especially apatite fission track which shows more diversity in the sources than either u pb zircon or ar ar muscovite dating nonetheless even fission track is best used as part of a multiproxy approach if a robust quantitative budget is desired

detrital thermochronology of rhine elbe and meuse river sediment central europe implications for provenance erosion and mineral fertility here we present detrital apatite fission track aft zircon fission track zft and a few apatite u th he ahe data of middle pleistocene to modern rhine meuse and elbe river sediments in order to resolve processes that control detrital age distributions provenance erosion and mineral fertility we used a modelling approach to compare observed with theoretically predicted age distributions from an interpolated in situ aft and zft age map in situ cooling ages do show large differences in the rhine drainage basin facilitating the differentiation between different source regions inconsistencies between observed and theoretical age distributions of the meuse and elbe samples can be explained by mixing and reworking of sediments with different provenances meuse middle pleistocene terrace sediment and a yet unexplored source region with old aft ages elbe samples overall the results show that detrital thermochronology is capable of identifying the provenance of middle pleistocene to modern sediments the aft age distributions of rhine sediments are dominated 70 by aft ages representing the alps a possible explanation is higher erosion rates in the alps as compared to areas outside the alps a late pleistocene sample from the upper rhine graben contains apatite grains from the molasse and hegau volcanics which we explain with a shift of the headwaters of the rhine to the north as a result of intense middle pleistocene riss glaciation contrary to the observed dominance of alpine derived aft ages in rhine sediments the relative contribution of zircon ages with sources in the alps is lower and significantly decreases downstream suggesting a major source of zircons outside the alps this can be explained by increased zircon fertility of sediments derived from the rhenish massif therefore we conclude that erosion and mineral fertility are the main processes controlling detrital aft and zft age distributions of the sampled river sediment in case of the rhine samples aft age distributions are mainly controlled by differences in erosion rates whereas this impact is completely balanced by differences in mineral fertility for the zft data

new information on the thermal history of the southwestern lower saxony basin northern germany based on fission track analysis the southwestern part of the lower saxony basin lsb is characterized by gravity and magnetic anomalies and by an extremely high thermal maturity of organic matter this was for many years attributed to a late cretaceous intrusion but actually deep burial is being debated the complex thermal history of the area has been studied by fission track analysis zircon data provide evidence for widespread hydro thermal activity during the permian and upper jurassic lower cretaceous apatite ages indicate a major cooling event in the mid cretaceous 89 72 ma reflecting the time of inversion of the lsb during the cretaceous the cooling of the basin centre was rapid compared to the basin margins apatite fission track ages from borehole samples which are recently within the upper part of the apaz indicate a young heating of the sedimentary sequences until present

air sea carbon dioxide fluxes in the coastal southeastern tropical pacific comprehensive sea surface surveys of the partial pressure of carbon dioxide pco2 have been made in the upwelling system of the coastal 0 200 km from shore southeastern tropical pacific since 2004 the shipboard data have been supplemented by mooring and drifter based observations air sea flux estimates were made by combining satellite derived wind fields with the direct sea surface pco2 measurements while there was considerable spatial heterogeneity there was a significant flux of co2 from the ocean to the atmosphere during all survey periods in the region between 4 and 20 south latitude during periods of strong upwelling the average flux out of the ocean exceeded 10 moles of co2 per square meter per year during periods of weaker upwelling and high productivity the co2 evasion rate was near 2 5 mol m2 yr the average annual fluxes exceed 5 mol m2 yr these findings are in sharp contrast to results obtained in mid latitude upwelling systems along the west coast of north america where the average air sea co2 flux is low and can often be from the atmosphere into the ocean in the peruvian upwelling system there are several likely factors that contribute to sea surface pco2 levels that are well above those of the atmosphere in spite of elevated primary productivity 1 the upwelling source waters contain little pre formed nitrate and are affected by denitrification 2 iron limitation of primary production enhanced by offshore upwelling driven by the curl of the wind stress and 3 rapid sea surface warming the combined carbon nutrient and oxygen dynamics of this region make it a candidate site for studies of global change

fission track dating of volcanically derived sedimentary rocks depositional ages of sedimentary rocks can be determined using fission track single grain ages on zircons from layers of volcanic ash or bentonite even when the layers have been contaminated by older grains this is done by compiling an age probability distribution or age spectrum for a sample from individual grain ages an age spectrum is a simple and unambiguous way of testing for contamination and extracting useful age information the youngest peak in the age spectrum approximates the time of deposition in most contaminated samples 30 or more grains should be counted to produce a reliable spectrum however useful reproducible ages can be obtained by counting less than 10 grains in samples where most of the older contaminating grains can be removed the few older grains that remain after removing the obviously abraded ones may then be eliminated by examining the age spectrum although ages determined in this way are probably not precise enough for use in defining stratigraphic boundaries they still provide a means of obtaining an isotopic age in sediments that cannot be dated by other radiometric methods 18 references 3 figures 3 tables

eulerian and lagrangian eddy statistics of the tasman sea and southwest pacific ocean 1 ocean eddy variability dominates many important processes in the ocean at a range of length and timescales we describe the eddy statistics in the tasman sea new zealand region using drifter data from the global drifter program gdp to derive lagrangian statistics and topex poseidon t p satellite data to derive eulerian statistics the ratio of the lagrangian to eulerian timescales is also a measure of length scales in the ocean when is high lagrangian length scales are short compared with eulerian length scales and vice versa we compute both in the time domain from temporal autocorrelations of drifter and satellite data and in the frequency domain from drifter and satellite velocity spectra the zonal component of this ratio appears to be constant in the tasman sea whereas the meridional component shows a latitudinal dependence we argue that if is known all eulerian and lagrangian timescales can be determined from relatively easy measurements of the eulerian timescale and eddy kinetic velocity

fission track dating of phosphate minerals and the thermochronology of apatite several phosphate minerals have been investigated for their usefulness in geochronology and thermochronology by the fission track method of these apatite ca5 po4 3 f cl oh has proved pre eminently suitable for this purpose for reasons discussed below apatite was one of the first minerals amongst many others to be investigated for fission track dating by fleischer and price 1964 and has subsequently become by far the most important of all the minerals used for dating by this method the usefulness of apatites for fission track dating arises from their near universal tendency to concentrate uranium within their structure at the time of crystallization and their widespread occurrence in all of the major rock groups price and walker 1963 first recognized the possibility that the accumulation of radiation damage tracks in natural minerals from the spontaneous nuclear fission of 238u within their lattices could be used for geological dating they also demonstrated that a simple chemical etching procedure served to enlarge these fission tracks to optical dimensions so that they could be observed and measured under an ordinary optical microscope price and walker 1962b 1963 this simple procedure quickly opened the way for a wide range of nuclear particle track studies in natural minerals and glasses e g fleischer et al 1975 the most important of which was fission track dating fleischer et al 1964 also showed that spontaneous or fossil fission tracks provided an explanation for various anomalous etch pits in apatite which had puzzled crystallographers over many years the essence of a fission track age determination involves measuring the number of tracks that have accumulated over the lifetime of the mineral along with an estimate of the amount of uranium that is present knowing the rate of spontaneous fission decay a geological age can be calculated detailed

how biophysical interactions associated with sub and mesoscale structures and migration behavior affect planktonic larvae of the spiny lobster in the juan fernandez ridge a modeling approach abstract the juan fernandez ridge jfr is a chain of topographical elevations in the eastern south pacific 33 35 s 76 81 5 w rich in endemic marine species this ridge is frequently affected by the arrival of mesoscale eddies originating in the coastal upwelling zone off central southern chile the impacts of these interactions on the structure and dynamics of the jfr pelagic system have however not been addressed yet the present model based study is focused on the coupled influence of mesoscale submesoscale processes and biological behavior i e diel vertical migration on the horizontal distribution of planktonic larvae of the spiny lobster jasus frontalis around the jfr waters two case studies were selected from a hydrodynamic regional ocean modeling system to characterize mesoscale and submesoscale structures and an individual based model ibm to simulate diel vertical migration dvm and its impact on the horizontal distribution and the patchiness level dvm behavior of these larvae has not been clearly characterized therefore three types of vertical mechanisms were assessed on the ibm 1 no migration lg 2 a short migration 0 50 m depth dvm1 and 3 a long migration 10 200 m depth dvm2 the influence of physical properties eddy kinetic energy stretching deformation and divergence on larval aggregation within meso and submesoscale features was quantified the patchiness index assessed for mesoscale and submesoscale structures showed higher values in the mesoscale than in the submesoscale however submesoscale structures revealed a higher accumulation of particles by unit of area both vertical migration mechanisms produced larger patchiness indices compared to the no migration experiment dvm2 was the one that showed by far the largest aggregation of almost all the aggregation zones larval concentrations were highest in the submesoscale structures these zones were characterized by low eddy kinetic energy negative stretching deformation and slight convergence stretching deformation flow appeared to be triggered by the eddy eddy interactions and the robinson island barrier effect and it likely promotes the aggregation of the spiny lobster larvae in the juan fernandez system these results highlighted the importance of the coupled effect of physical mesoscale and submesoscale oceanographic features and biological processes dvm in the generation of larval patchiness and concentration of spiny lobster larvae around the jfr which could be key for their survival and retention in those waters

eddy mean flow decomposition and eddy diffusivity estimates in the tropical pacific ocean 1 methodology 1 eddy diffusivity of the surface velocity field in the tropical pacific ocean was estimated using satellite tracked drifting buoys 1979 through mid 1996 the tropical pacific surface current system is characterized by nonstationarity strong meridional shear and an energetic mesoscale velocity field eddy diffusivity may be defined as the integral of the autocovariance of lagrangian eddy velocities requiring both stationary and homogeneous statistics of the eddy field eddy velocities were obtained by removing a splined mean field to eliminate mean shear from observations binned 1 spatially to group data that have similar dispersion characteristics and 2 temporally to create stationary eddy statistics zonal diffusivity estimates are up to 7 times larger than meridional diffusivity estimates in the high eddy energy regions this anisotropy is associated with the meridional mesoscale wave motion i e by equatorial and tropical instability waves that increases eddy variance but does not lead to a proportional increase in water parcel diffusion because of the coherent character of the trajectory motion at least for initial time lags simple autoregressive models of first and second order are used to describe and classify the resulting eddy statistics an independent confirmation of the diffusivity estimate in the central eastern pacific was obtained by comparing tracer flux divergence computed from a parameterization using diffusivity estimates of our analysis with that from direct eddy reynolds stress flux divergence our results show that diffusivity can be estimated for regions not considered previously either because of sparse data or the complexities of the velocity field

proterozoic plate tectonics in canada with emphasis on evidence for a late proterozoic rifting event abstract several early proterozoic fold belts in the canadian shield have been interpreted in terms of plate tectonic processes the most impressive evidence comes from those preserved on the margins of archaean cratons such as the wopmay orogen and the penokean fold belt there are striking similarities in the stratigraphic successions of many widely separated early proterozoic fold belts within the canadian shield most of these are currently best interpreted in terms of some modified version of plate tectonics post grenville rocks contain several independent lines of evidence that support a major episode of continental fragmentation stratigraphic and sedimentological evidence from the cordilleran region records a dramatic change from widespread development of essentially platformal marine sediments l mackenzie mountains supergroup through rift related evaporites and clastics u mackenzie mountains supergroup to a largely resedimented sequence ekwi or windermere supergroup that has been interpreted as a continental margin facies a closely comparable succession of facies can be documented in other parts of the world but perhaps the closest analogue is found in s e australia it has been suggested that these two regions may formerly have been juxtaposed and represent the sundered fragments of a late proterozoic supercontinent relevant to these interpretations are geochemical data such as 34s values from late proterozoic evaporites and 87sr 86sr measurements from carbonates and processes involved in precipitation of glacially related iron formations such as those of the rapitan group in the n cordillera preservation of late proterozoic ophiolites in north africa provides additional evidence of plate tectonic processes at that time these several lines of evidence all suggest a significant period of late proterozoic continental breakup which produced many of the continental margins that were and are the loci of subsequent phanerozoic orogenic activity

hydrography of the eastern south pacific ocean results from the sonne 102 cruise may june 1995 abstract full depth conductivity temperature depth hydrographic measurements were taken in may june 1995 along 28 15 35 15 and 43 15 s from the chilean coast to 86 88 w from the r v sonne sections of potential temperature salinity neutral density and oxygen are presented to illustrate the water column structure in this sparsely sampled region a more comprehensive database on all available hydrographic data from the region was compiled these data and available meteorological data are used to help in the interpretation of the sonne results a number of important features found in the sections are discussed including a shallow salinity minimum apparently ventilated from south of 37 s salt fingering as a possible mechanism to transport high salinity subtropical water into the shallow salinity minimum equatorial subsurface water subantarctic mode water and antarctic intermediate water geostrophic calculations of alongshore flow show the poleward peru chile undercurrent at each of the three sections with a poleward descending core and peak velocities of 10 cm s 1 as in earlier works a deep pacific outflow is found near the chilean coast part of a clockwise deep circulation in the chile basin

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

lagrangian study of the panama bight and surrounding regions near surface circulation of the panama bight and surrounding regions 0 9 n 73 w 90 w was studied using satellite tracked drifter trajectories from 1979 2004 this region encompasses three major currents showing typical velocities of 30 cm s 1 1 the eastward north equatorial counter current necc 2 the near circular panama bight cyclonic gyre pbcg and 3 the westward south equatorial current sec we do not observe significant modification of the mean surface circulation during el nino southern oscillation events even if the sec is slightly reinforced during relatively warm el nino periods at seasonal scales the circulation is strongly controlled by the activity of the panama wind jet in boreal winter the currents are stronger and an anticyclonic cell is present west of the pbcg this dipole leads to a strong 200 km wide southward current which then disappears during the rest of the year in summer the three major currents have reduced intensity by 30 40 large scale current vorticity shows that the upwelling associated with the pbcg is also 3 4 times stronger in winter than during summer months the kinetic energy is largely dominated by eddy activity and its intensity is double in winter than during summer ageostrophic motions and eddy activity appear to have a substantial impact on the energy spatial distribution in the necc and sec regions lagrangian scales are anisotropic and zonally enhanced in the direction of the mean currents the typical integral time and length scales of these regions are 2 5 days and 50 60 km in the zonal direction and 1 5 days and 25 30 km in the meridional direction lateral eddy diffusivity coefficients are on the order of 11 14 107 cm2 s 1 zonally and 5 6 107 cm2 s 1 meridionally in contrast in the pbcg region the lagrangian characteristics are isotropic with typical timescales of 1 7 days space scales of 30 km and eddy diffusivity coefficients of 6 107 cm2 s 1 in both directions

wind driven motions in the northeast pacific as measured by lagrangian drifters abstract analysis is presented of the time dependent motion of 47 surface drifters in the northeast pacific during fall 1987 and 16 drifters in fall and winter 1989 90 the drifters were designed at 15 m depth and were designed to have wind produced slips less than 2 cm s 1 for wind speeds up to 20 m s 1 the coherence of velocity and local wind is presented for motions with periods between 1 day and 40 days for periods between 5 and 20 days drogue motion at 15 m depth is found to be highly coherent with local wind with an average phase of 70 to the right of the rotating wind vector these results differ from analyses of fgge type drifters as reported by mcnally et al and niiler in the same area a model of wind produced slip as a function of drifter design is used to provide a possible explanation of the differences a linear regression which accounts for 20 40 of the current variance gives water motion al 0 5 of wind speed and 68 to the right of the wind vector assuming an ekman type balance

active rifting in southwestern mexico manifestations of an incipient eastward spreading ridge jump a major ongoing episode of continental rifting has formed a system of three intersecting grabens in the western mexican volcanic belt these structures may mark the initial stage of an eastward spreading ridge jump beneath continental crust eastward ridge segment jumps have been propagating northward along this part of the east pacific rise for the past 12 m y but this is the first plate boundary reorganization event to involve continental crust since the separation of baja california in the miocene since pliocene time small volumes of unusual alkaline magmas have erupted in the graben areas in close association with the more abundant subduction related calc alkaline magmas erupted from andesitic stratovolcanoes the alkaline magmas are varieties found in zones of active rifting elsewhere in the world

zonal structure of the mean flow and eddies in the azores current system 1 the surface circulation and eddy field from the azores current system are studied here by analyzing surface drifters records and altimetry maps collected over more than 16 years clear differences in mean flow and eddy characteristics allow for a classification of the azores current in three zonal sectors west of 30 w between the mid atlantic ridge and the hyeres atlantis seamount system between 30 w and the longitude of madeira and east of madeira a detailed and quantitative characterization of each sector is given the transition between the western and central parts is controlled by the hyeres atlantis ridge in the transition to the eastern sector there is a change in the dynamics and the flow is forced by the cyclonic recirculation driven by the mediterranean outflow there is no clear expression of a continuous surface northern counterflow but three distinct westward flows are seen one along the southeastern border of the azores plateau another one southwest of madeira and a third one along 31 n west of the hyeres seamount no clear tilt in the axis of the azores current is found in the calculated mean surface flow from surface drifters observations from both drifters and altimetry data show that anticyclonic features dominate in the northern region whereas cyclonic ones dominate in the southern region overall cyclones are more numerous constituting 60 of large eddies the eddy features detected in the west tend to be larger than those in the east both in size and sea level anomaly there is indication of different mean propagation speeds east and west of 25 w 30 w with the mean speeds consistently increasing by 25 45 in the west estimates for the rate of formation of strong eddies range from 1 4 to 2 4 year 1 for cyclones and 1 2 to 1 7 year 1 for anticyclones

isopycnal lagrangian statistics from the north atlantic current rafos float observations one hundred isopycnal floats were tracked on the 27 2 and 27 5 surfaces in the newfoundland basin nfb from july 1993 to july 1995 to study the current structure and exchanges of waters between the subtropical and subpolar gyres the float mapped mean flow consists of weak flows in the nfb and a strong boundary current the north atlantic current nac which separates from the boundary at the northwest corner becoming a diffusive zonal drift the nac meanders are linked to topography and have similar patterns on the two isopycnals despite the fact that the upper layer velocities are twice as fast as the lower layer ones perturbation velocity from the mean is used to compute isopycnal turbulent dispersion and diffusivity this large data set allows us to resolve a narrow mean nac and results in a gaussian turbulence the turbulence approximately follows the classic taylor dispersion theory integral timescales and length scales and turbulent isopycnal diffusivity are of 1 5 2 5 days 20 30 km and 1 7 103 m2 s 1 respectively the timescale increases with depth and decreases with latitude the length scale decreases with depth and longitude and the diffusivity decreases with depth and from nac to nfb compared to previous results from surface drifters and isobaric floats our isopycnal statistics are more isotropic and agree better with the taylor dispersion theory because 1 the mean velocity has a better resolution and 2 the isopycnal floats are better lagrangian followers the diffusivity scales better with the rms velocity and length scale than with the velocity variance and timescale

tectonic relationships between forearc basin strata and the accretionary complex at bath barbados the island of barbados exposes the crestal zone of the accretionary prism of the lesser antilles forearc tertiary rocks at bath barbados include four lithic suites 1 inter bedded volcanogenic and mainly calcareous pelagic rocks the oceanic beds 2 radiolarite 3 siliceous hemipelagic rocks and 4 melange suites 1 3 are in structurally discrete groups of fault packets melange occurs in apparently diapiric crosscutting bodies the oceanic beds occupy a pre pleistocene nappe complex that underlies much of barbados radiolarite and hemipelagic rocks belong to a thick accretionary basal complex and constitute the relative autochthon to the oceanic nappes fault rocks of the sub oceanic fault zone developed during emplacement of the oceanic nappes the lower portion of the tectonic stack is deformed in a major south verging fold couple with wavelength of 250 m lower early emplaced oceanic nappes are restricted to the core of the major synform and are increasingly deformed with depth structures suggest easterly transport of oceanic nappes and upward younging of nappe emplacement indicating that the deformation of oceanic beds propagated westward the oceanic nappes provided a seal to rising fluids transport of nappes may have been facilitated by elevated fluid pressure beneath their sole thrust pre and post nappe folds record north south shortening about shallow west plunging axes consistent with folded accretionary strata elsewhere on barbados deformation occurred under shallow nonmetamorphic conditions the oceanic beds are interpreted as being trapped outer forearc basin strata that have been tectonically shouldered by the arcward migrating prism flank or crest the hemipelagic and radiolarite suites may be offscraped abyssal plain and trench wedge accumulations paleogene lower miocene oceanic strata were deposited at depths between 2 0 and 4 8 km middle miocene oceanic beds accumulated at shallower depths 1 1 5 km thus early miocene was the probable time of inception of major uplift and arcward shouldering in the crestal zone of the accretionary prism accretion of the basal complex of barbados probably occurred in late eocene time

surface circulation and fronts of the south pacific ocean east of 120 w the south pacific surface circulation east of 120 w is studied using satellite tracked drifters from 1979 2004 the major currents of this region are described such as the antarctic circumpolar the south pacific the chile peru and the cape horn currents we suggest the presence of a branch exiting from the acc between 100 120 w and transporting subantarctic surface water toward lower latitudes we also show the existence of an anticyclonic recirculation cell north of 35 s finally based on hydrographic sections we show that in the eastern south pacific the core of the subtropical front corresponds to the 14 c isotherm at 150 m depths and to the 2 7 m of dynamic height relative to 3000 m the subantarctic front is located by maximum temperature gradients in the range 3 8 c at 100 400 m depth

eddy momentum flux and its contribution to the southern ocean momentum balance a large amount of momentum is transferred to the southern ocean by strong westerly winds analytical and numerical models have suggested that transient eddies may be important in transporting this momentum away from the region of wind forcing either horizontally1or vertically downwards where it is balanced by bottom topographic drag2 5 there are however few long term in situ observations of horizontal eddy momentum flux6 8 and no large scale measurements of vertical eddy fluxes to test these models as a result the momentum balance of the antarctic circumpolar current acc remains uncertain and the role of eddies controversial here we use geosat satellite altimeter data to resolve directional eddy kinetic energy and horizontal eddy momentum flux in the acc on fine spatial and temporal scales the complex spatial distribution of surface eddy momentum flux is strongly influenced by bottom topography the horizontal eddy momentum flux tends generally to concentrate the mean flow although some regions of divergence are observed our results show that the zonally averaged horizontal eddy momentum flux from transient eddies is an order of magnitude too small and in the wrong direction to directly balance the eastward momentum input from wind1

impacts of andean uplift on the humboldt current system a climate model sensitivity study 1 using both an atmospheric global circulation model and a regional oceanic model we assess the impact of the andes uplift on the humboldt current system hcs with three topographic scenarios for the andes we show that the uplift played a crucial role in shaping the lower troposphere dynamics over the pacific ocean and in turn affected the physical characteristics of the system our results show that the uplift has triggered a marked southward shift of the hcs changing the latitudinal position of coastal upwelling areas as well as the strength of the south pacific gyre our oceanic modeling experiments show that the latitudinal pattern of sea surface temperatures is dramatically modified with reduced andes with anomalies reaching up to 3 c we discuss the feedbacks of these changes on south american climate as well as the potential onset of an altitudinal threshold that would have had triggered these changes

seasonal climatology of hydrographic conditions in the upwelling region off northern chile over 30 years of hydrographic data from the northern chile 18os 24os upwelling region are used to calculate the surface and subsurface seasonal climatology extending 400 km offshore the data are interpolated to a grid with sufficient spatial resolution to preserve cross shelf gradients and then presented as means within four seasons austral winter july september spring october december summer january march and fall april june climatological monthly wind forcing surface temperature and sea level from three coastal stations indicate equatorward upwelling favorable winds throughout the year weakest in the north seasonal maximum alongshore wind stress is in late spring and summer december march major water masses of the region are identified in climatological t s plots and their sources and implied circulation discussed surface fields and vertical transects of temperature and salinity confirm that upwelling occurs year round strongest in summer and weakest in winter bringing relatively fresh water to the surface nearshore surface geostrophic flow nearshore is equatorward throughout the year during summer an anticyclonic circulation feature in the north which extends to at least 200 rn depth is evident in geopotential anomaly and in both temperature and geopotential variance fields subsurface fields indicate generally poleward flow throughout the year strongest in an undercurrent near the coast this undercurrent is strongest in summer and most persistent and organized in the south south of 21os a subsurface oxygen minimum centered at 250 m is strongest at lower latitudes low salinity subsurface water intrudes into the study area near 100 m predominantly in offshore regions strongest during summer and fall and in the southernmost portion of the region the climatological fields are compared to features off baja within the somewhat analogous california current and to measurements from higher latitudes within the chile peru current system

mean surface circulation and mesoscale turbulent flow characteristics in the eastern south pacific from satellite tracked drifters 1 circulation of the eastern south pacific region 10 34 s 70 100 w was studied using drifting buoy trajectories from 1979 to 2003 three different current regimes were highlighted the south equatorial current flowing westward north of 26 s with surface velocities of 7 8 cm s 1 the south pacific current an eastward current of 2 cm s 1 south of 25 30 s and the chile peru current a northwestward flow of 6 cm s 1 found to the east of 82 w and south of 22 s the velocity variance distribution showed the regional flow to be anisotropic in nature maps of eddy kinetic energy obtained from drifter measurements and satellite altimetry data showed similar patterns with higher energy levels near the south american coast the lagrangian time and length scales of the turbulent flow revealed typical values of 5 9 0 6 days and 40 7 5 4 km in the zonal direction and of 3 5 0 4 days and 29 3 4 km in the meridional direction the estimated diffusivities were 4 9 0 5 107 cm2 s 1 and 2 6 0 3 107 cm2 s 1 in the eastward and northward directions respectively finally we estimated the respective role of horizontal advection and lateral diffusion on the mixed layer heat and salt budgets near the coast the lateral turbulent fluxes in the surface layer were two times larger than the horizontal transports associated with the large scale circulation mean horizontal heat and salt diffusive fluxes were around 25 w m 2 and 50 g m 2 d 1

lateral diffusivity and lagrangian scales in the pacific ocean as derived from drifter data 1 the global drifter program surface velocity program data set is used to derive maps of the lateral diffusivity and lagrangian scales of velocity length and time across the whole pacific for the lateral diffusivity the minor principal component of both the davis diffusivity tensor and the half growth rate of the single particle dispersion tensor were calculated in 5 5 bins from drifters for the period 1979 1999 estimates of the lateral diffusivity k obtained by means of the minor principal component approach are shown to correspond well with other authors estimates for the pacific the highest values of k 2 3 104 m2 s are found in the eastern equatorial pacific while the lowest ones 2 3 103 m2 s are typical for forty odd degrees in latitude northward of the subpolar fronts in both hemispheres and for the subtropics in the eastern part of the south pacific high values of k about 1 104 m2 s are also observed in the kusoshio kuroshio extension area and in the equatorial pacific along the whole length of the equator there are two approximately symmetrical tongues of high k value in the western pacific centered around 21 n and 24 s respectively in general k has a tendency to increase westward eastward in the midlatitudes equatorial region and toward the equator in both hemispheres in the midlatitudes the lagrangian length scale l is found to be approximately equal to the first mode baroclinic radius of deformation ri while the rossby number defined as ro tearth t sin where t is the lagrangian timescale tearth is the period of the earth s rotation and is the latitude is less than unity implying that the quasigeostrophic mesoscale eddies are the main mechanism for lateral mixing the lateral diffusivity in the midlatitudes is suggested to be parameterized as k v2ri where v2 is the lagrangian velocity scale inherent to a mesoscale eddy field in the low latitudes l becomes less than ri and the condition ro 1 is no longer valid which implies the change of the eddy controlled mechanism of lateral mixing by another mechanism

detrital thermochronology and sediment petrology of the middle siwaliks along the muksar khola section in eastern nepal abstract sediment derived from erosion of the himalaya during the miocene pliocene was deposited in the himalayan foreland basin and is now exposed in the siwalik formation between the main boundary thrust and main frontal thrust these sediments hold important information on orogenic exhumation during this time in this preliminary study we sampled the middle siwalik formation in eastern nepal along the muksar khola section for thermochronologic and sediment petrologic analysis detrital zircon fission track thermochronology shows that the age signal of the middle siwalik formation of eastern nepal has some similarities but also differences with published data for western central nepal the muksar khola section samples show two static peaks at about 14 and 140 ma which is similar to the siwalik formation of western central nepal in contrast a signal of consistently fast exhumation was not observed in the upper middle siwaliks in eastern nepal this could be related to a position of the main central thrust further south to overall less erosional exhumation of higher himalayan rocks or to a reduced exposure of the underlying lesser himalayan units in comparison with western central nepal based on our apatite fission track data we propose that above the section dated by ojha et al 2009 with magnetostratigraphy about 1000 m of overlying upper siwalik formation exist

structure and surface properties of eddies in the southeast pacific ocean 1 a number of studies have posited that coastally generated eddies could cool the southeast pacific ocean sep by advecting cool upwelled waters offshore we examine this mechanism by characterizing the upper ocean properties of mesoscale eddies in the sep with a variety of observations and by estimating the surface layer eddy heat flux divergence with satellite data cyclonic and anticyclonic eddies observed during two cruises featured deep positive salinity anomalies along the 26 5 kg m 3isopycnal indicating that the eddies had likely trapped and transported coastal waters offshore the cyclonic eddies observed during the cruises were characterized by shoaling isopycnals in the upper 200 m and cool near surface temperature anomalies whereas the upper ocean structure of anticyclonic eddies was more variable using a variety of large scale observations including argo float profiles drifter records and satellite sea surface temperature fields we show that relative to mean conditions cyclonic eddies are associated with cooler surface temperatures and that anticyclonic eddies are associated with warmer surface temperatures within each data set the mean eddy surface temperature anomalies are small and of approximately equal magnitude but opposite sign eddy statistics drawn from satellite altimetry data reveal that cyclonic and anticyclonic eddies occur with similar frequency and have similar average radii in the sep a satellite based estimate of the surface layer eddy heat flux divergence while large in coastal regions is small when averaged over the sep suggesting that eddies do not substantially contribute to cooling the surface layer of the sep

near coastal circulation in the northern humboldt current system from shipboard adcp data the near coastal circulation of the northern humboldt current system is described analyzing 8700 velocity profiles acquired by a shipboard acoustic doppler current profiler sadcp during 21 surveys realized between 2008 and 2012 along the peruvian coast this data set permits observation of i part of the peru coastal current and the peru oceanic current that flow equatorward in near surface layers close to the coast and farther than 150 km from the coast respectively ii the peru chile undercurrent pcuc flowing poleward in subsurface layers along the outer continental shelf and inner slope iii the near surfacing equatorial undercurrent renamed as ecuador peru coastal current that feeds the pcuc and iv a deep equatorward current referred to as the chile peru deep coastal current flowing below the pcuc a focus in the pcuc core layer shows that this current exhibits typical velocities of 5 10 cm s 1 the pcuc deepens with an increasing thickness poleward consistent with the alongshore conservation of potential vorticity the pcuc mass transport increases from 1 8 sv at 5 s to a maximum value of 5 2 sv at 15 s partly explained by the sverdrup balance the pcuc experiences relatively weak seasonal variability and the confluence of eddy like structures and coastal currents strongly complicates the circulation the pcuc intensity is also affected by the southward propagation of coastally trapped waves as revealed by a strong pcuc intensification in march 2010 coincident with the passage of a downwelling coastal wave associated with a weak el nino event

surface circulation in the eastern north atlantic from drifters and altimetry a description of the near surface circulation and its properties is the result of the analysis of a drifting buoy data set in the eastern north atlantic between the iberian peninsula the azores and the canary islands world ocean circulation experiment tropical ocean global atmosphere experiment drifters equipped with holey sock drogues centered at 15 m depth collected a total of 14 4 years of data the drifters sampled a rather inhomogeneous velocity field with a weak mean flow regime and eddies of different scales they meandered southward everywhere in the study region except in the iberian coastal transition zone north of 41degreesn where they headed northward the near surface mean velocity field obtained from the drifter data set shows all important mean currents including the poleward portugal coastal countercurrent during the fall winter and early spring off western and northern iberia the southward portugal coastal current the slow offshore southward flow of the portugal current during the whole year the southwestward canary current and the eastward azores current which extends to the vicinity of the african coast near the gulf of cadiz maps of the eddy kinetic energy field were obtained from the drifters and from satellite altimetry it provides the largest part of the total kinetic energy the rate of dispersion is estimated from the lagrangian statistics of the drifting buoys the dispersion of the drifters in the study region is well modeled by a simple description of eddy diffusion assuming homogeneous turbulence ensemble mean diffusivities k and the langrangian integral length scales and timescales l and t were obtained for the zonal and meridional directions the sea surface temperature measured along the drifter trajectories is used to produce estimates of the eddy diffusivity which is compared with the diffusivity estimates obtained from the theory of taylor the eddy diffusivity is found to be approximately proportional to the eddy kinetic energy discrete eddies and meanders were observed using drifters and altimetry in order to map and describe their geographical distribution and characteristics in the eastern north atlantic

age of mineralization by basinal fluids at the el soldado manto type copper deposit chile 40ar 39ar geochronology of k feldspar abstract manto type copper deposits of the southern central andes are strata bound epigenetic mineral concentrations hosted by bimodal volcanic and volcaniclastic rock suites they are economically important but since they are not obviously related to intrusions their genesis has been controversial to some extent because it has proven difficult to date the ore forming event and distinguish it from the age of low grade regional metamorphism el soldado the largest manto type copper deposit in central chile is hosted by marine volcanic and subvolcanic intrusive rocks of the lower cretaceous extensional arc to discriminate between regional metamorphism and mineralization we dated 11 samples of k feldspar by the stepwise heating 40 ar 39 ar method hydrothermally precipitated k feldspar associated with copper sulfides precipitated at temperatures of 300 c and range in age from 100 5 1 5 to 106 1 1 1 ma mean 103 1 6 ma n 8 syn mineralization k feldspar gave an age of 102 5 2 0 which is interpreted to be the age of mineralization k feldspar unrelated to ore yields older ages between 109 4 1 1 and 112 2 ma mean 110 3 1 4 ma n 3 is variably reset by the younger ca 103 ma mineralization episode the above ages are interpreted to represent the age of alkali redistribution and crystallization due to burial metamorphism of the host sequence fission track dating of apatite in the host rocks yields an age of ca 90 ma indicating fast cooling of the system to less than ca 100 c after mineralization time temperature modeling of fission track length data are compatible with initial fast exhumation followed by slow exhumation and cooling to surface temperatures high levels of atmospheric ar were detected in all k feldspar samples and are tentatively attributed to connate meteoric fluids incorporated into the basinal metamorphic mineralizing fluids

a pacific hydrographic section at 88 w water property distribution full depth conductivity temperature depth ctd hydrographic measurements with high horizontal and vertical resolution were made in february april 1993 along a line lying at a nominal longitude of 88 w and extending from southern chile 54 s to guatemala 14 n it crossed five major deep basins southeast pacific chile peru panama and guatemala basins east of the east pacific rise vertical sections of potential temperature salinity potential density oxygen silica phosphate nitrate and nitrite are presented to illustrate the structure of the entire water column some features of interest found in the sections are described and an attempt is made to interpret them in terms of the isopycnal property distributions associated with the large scale ocean circulation these features include various near surface waters observed in the tropical and subtropical regions and the fronts that mark the boundaries of these waters the possible importance of salt fingering to the downward salt transfer from the high salinity subtropical water a shallow thermostad pycnostad developed at 16 18 5 c in the subtropical water low salinity surface water in the subantarctic zone west of southern chile large domains of extremely low oxygen in the subpycnocline layer on both sides of the equator and a secondary nitrite maximum associated with a nitrate minimum in these low oxygen domains high salinity low oxygen high nutrient subpycnocline water that is carried poleward along the eastern boundary by the peru chile undercurrent the subantarctic mode and antarctic intermediate waters middepth isopycnal property extrema observed at the crest of the sala y gomez ridge influences of the north pacific and the north atlantic upon deep waters along the section and the characteristics and sources of the bottom waters in the five deep basins along the section

wildfire thermochronology and the fate and transport of apatite in hillslope and fluvial environments 1 wildfire heating of the outer few centimeters of exposed rock or soil generates shortduration high temperature thermal events that produce characteristic thermochronologic signatures in minerals contrasting activation energies of fission track annealing and he diffusion in apatite lead to a kinetic crossover whereby wildfire heating resets fission track ft ages much faster than u th he ages resulting in inverted ft he ages in single grains this can be used to trace wildfire affected detritus at the earth s surface we show that in exposed bedrock inverted apatite ft he ages vary systematically with depth to 3 cm and detrital clasts on hillslopes also show strong but heterogeneous wildfire resetting signatures in soils colluvium and low order channel sediments strongly wildfire reset apatite grains are abundant and in some cases dominate the population of detrital apatite to depths at least as great as 10 cm wildfire reset apatite is rare however in fluvial sediments sampled from larger basins indicating a strong fractionation of apatite populations from hillslopes to rivers characteristic dissolution features in hillslope apatite and slower relative dissolution rates of other common minerals suggest that wildfire reset apatite grains are rare or absent in rivers because they dissolve relatively rapidly in soil profiles apatite that does contribute to fluvial sediments is likely to be dominantly derived from bedrock landslides in steep regions or from large clasts containing grains protected from both wildfire heating and dissolution this means that apatite in fluvial sediment is spatially fractionated with respect to its sources in the catchment even if catchment erosion rates are spatially uniform

an index to distinguish surface and subsurface intensified vortices from surface observations in this study the authors first show that it is difficult to reconstruct the vertical structure of vortices using only surface observations in particular they show that the recent surface quasigeostrophy sqg and interior and surface quasigeostrophy isqg methods systematically lead to surface intensified vortices and those subsurface intensified vortices are thus not correctly modeled the authors then investigate the possibility of distinguishing between surface and subsurface intensified eddies from surface data only using the sea surface height and the sea surface temperature available from satellite observations a simple index based on the ratio of the sea surface temperature anomaly and the sea level anomaly is proposed while the index is expected to give perfect results for isolated vortices the authors show that in a complex environment errors can be expected in particular when strong currents exist in the vicinity of the vortex the validity of the index is then analyzed using results from a realistic regional circulation model of the peru chile upwelling system where both surface and subsurface eddies coexist the authors find that errors are mostly associated with double core eddies aligned surface and subsurface cores and that the index can be useful to determine the nature of mesoscale eddies surface or subsurface intensified from surface satellite observations however the errors reach 24 and some possible improvements of the index calculations are discussed

an analysis of sst gradients off the peruvian coast the impact of going to higher resolution abstract the peruvian coastal upwelling system pcus is one of the most productive fisheries in the world upwelling events are associated with changes in the magnitude and location of frontal structures sst gradients from four different data sets ncdc remss ostia and mur are compared in two test areas off the pcus paita 5 s and pisco 14 s in both areas gradients derived from the mur data set show greater magnitudes as well as larger seasonal cycles off pisco the magnitude of the seasonal cycle of 2 2 c 100 km in mur is larger than the one derived from the lower resolution data sets all data sets at pisco exhibit a seasonal cycle that peaks in late austral summer and early fall hovmoller diagrams calculated at 5 5 s 10 5 s and 14 5 s show clearly defined offshore maxima in the cross shore gradients for all the data sets upwelling scales determined by the distance to the first maxima vary depending on the data set used at 5 5 s upwelling scales vary from 10 km for mur to 50 km for ncdc at 14 5 s the scales vary from 20 km for mur to 40 km for ostia all four data sets show similar large scale structures associated with the peruvian upwelling however mur shows finer scale structures that are most likely due to submesoscale to mesoscale eddies sub sampled mur 1 km data at the 25 km 9 km and 4 km resolutions compare well in magnitude and phase with the lower resolution products agreement in gradient magnitude between the lower resolution data sets and the mur sub sampled at their respective resolutions implies that the pixel to pixel analysis noise in mur is at a similar level as the other data sets

coastal transition zone off chile 1 seven years of subsurface current observations at deep sea and continental slope moorings off chile 30 s satellite sea surface anomaly and satellite wind stress are used to examine space time and propagation characteristics of the mesoscale eddy activity in the coastal transition zone off chile this zone off chile extends from the coast to 600 800 km offshore and can be separated into two latitudinal regions the first region between 29 and 39 s off central chile is characterized by high eddy kinetic energy and strong but variable equatorward wind stress the second region between 19 and 29 s off northern chile is characterized by low eddy kinetic energy and weak but persistent equatorward wind stress low frequency mesoscale variability off central chile is mainly associated with baroclinic instability of coastal currents and westward propagation of rossby waves from the eastern boundary and is strongly modulated over el nino la nina cycles application of a new rotary wavelet spectrum method to the recording current meter data and the use of current estimates from satellite altimeter data show that mesoscale eddies and meanders in the coastal transition zone fluctuate with periods centered on 120 days and with length scales centered on 200 km cross rotary wavelet analyses of currents and wind stress indicate that fluctuations of coastal currents with periods longer than 220 days propagated westward as free rossby waves during 1995 1996 and as forced rossby waves during 1999 2001

characteristics of the near surface currents in the indian ocean as deduced from satellite tracked surface drifters part i pseudo eulerian statistics using the 1985 2013 record of near surface currents from satellite tracked drifters the pseudo eulerian statistics of the near surface circulation in the indian ocean io are analyzed it is found that the distributions of the current velocities and mean kinetic energy mke in the io are extremely inhomogeneous in space and nonstationary in time the most energetic regions with climatologic mean velocity over 50cms 21 and mke over 500cm 2 s 22 are found off the eastern coast of somalia with maxima of over 100cms 21 and 1500cm 2 s 22 and the equatorial io associated with the strong annually reversing somalia current and the twice a year eastward equatorial jets high eddy kinetic energy eke is found in regions of the equatorial io western boundary currents and agulhas return current with a maximum of over 3000cm 2 s 22 off the eastern coast of somalia the lowest eke 500cm 2 s 22 occurs in the south subtropical gyre between 308 and 408s and the central eastern arabian sea annual and semiannual variability is a significant fraction of the total eke off the eastern coast of somalia and in the central eastern equatorial io in general both the mke and eke estimated in the present study are qualitatively in agreement with but quantitatively larger than estimates from previous studies these pseudo eulerian mke and eke fields based on the most extensivedrifterdatasettodate arethemostpreciseinsituestimatestodateandcanbeusedtovalidatesatellite and numerical results

resolution of the age structure of the detrital zircon populations of two lower cretaceous sandstones from the weald of england by fission track dating modes in the frequency of distribution of fission track ages obtained from detrital zircon grains may prove characteristic of individual sandstone bodies supporting the identification of the sources from which a particular flow of sedimentary detritus was derived and thus allowing new inferences to be made concerning palaeogeography a computer program has been written and used to identify modes in the zircon fission track age distribution within two lower cretaceous sandstone samples from the weald of southern england pronounced modes appear in one rock around 119 ma 160 ma 243 ma and 309 ma and in the other around 141 ma 175 ma 257 to 277 ma and 394 to 453 ma the geological implications of these quite dissimilar zircon age spectra are discussed it is concluded that they support the palaeogeographical models of allen 1981 and indicate that the provenance of the first sample from the top ashdown sandstone member at dallington in east sussex was almost entirely southerly while that of the second from the netherside sand member at northchapel in west sussex was more varied but predominantly westerly and northerly

seasonal and interannual variability of currents and temperature off central chile results are reported for continuous 6 year records of current and temperature from a continental slope station at 308s off chile these observations for november 1991 to november 1997 span the moderate weak and strong el nino events of 1991 1992 1994 and 1997 and the la nina event of 1995 1996 results for current and temperature are analyzed together with observations of wind along the south american coast from the ers 1 and 2 satellite scatterometers wind from a local coastal site sea level from northern and central chile sea surface temperature anomalies from the south pacific region and traditional el nino indices mean poleward flow of 12 8 cm s 21 was observed for the 6 year period in the core of the peru chile undercurrent 220 m mean flow in the depth range of antarctic intermediate water 750 m was equatorward at 1 1 cm s 21 intraseasonal scale variability associated with coastal trapped waves was weaker during the austral winter greatest during el nino events and weakest during the la nina event winds adjacent to the coast showed a strong annual cycle with a southward progression of maximum equatorward upwelling favorable winds alongshore flow over the slope exhibited strong semiannual and weaker annual variations poleward flow in the undercurrent was strongest in the austral spring and fall and weakest in the winter near the bottom 750 m seasonal scale variability was less intense but led that higher up in the water column 220 m by 1 month strong interannual variability of alongshore current and temperature was found at all depths over the slope whereby changes at depth led changes higher up a rapid warming event was observed at the end of 1996 beginning of 1997 over the slope this event also seen in sea level and sea surface temperature off chile led el nino indices by several months and may be best explained by local wind anomalies coupled to atmospheric teleconnections from the western tropical pacific at the onset of el nino some aspects of our current and temperature observations are consistent with results from eastern boundary current models our results indicate that both ocean and atmosphere pathways from the equatorial pacific contribute significantly to interannual scale variability of alongshore flow and thermocline depth off chile

mesoscale eddy buoyancy flux and eddy induced circulation in eastern boundary currents abstracta dynamical interpretation is made of the mesoscale eddy buoyancy fluxes in the eastern boundary currents off california and peru chile based on regional equilibrium simulations the eddy fluxes are primarily shoreward and upward across a swath several hundred kilometers wide in the upper ocean as such they serve to balance mean offshore air sea heating and coastal upwelling in the stratified interior the eddy fluxes are consistent with the adiabatic hypothesis associated with a mean eddy induced velocity advecting mean buoyancy and tracers furthermore with a suitable gauge choice the horizontal fluxes are almost entirely aligned with the mean horizontal buoyancy gradient consistent with the advective parameterization scheme of gent and mcwilliams the associated diffusivity is surface intensified matching the vertical stratification profile the fluxes span the across shore band of high eddy energy but their alongshore structure is unresolved because of sampling limitations in the sur

fission track dating of alluvial zircons and heavy mineral provenance in northeast tasmania three alluvial zircon concentrates from the blue tier region have been fission track dated in a heavy mineral provenance study of cenozoic sediments in ne tasmania zircons in one concentrate are euhedral and are fine grained mostly 0 1 to 0 3 mm dating gave a combined age of 367 15 ma confirming their derivation from upper devonian granites zircons from the other concentrates are rounded and coarser grained mostly 2 5mm they gave a combined age of 46 7 0 6 ma this agrees with the k ar radiometric dates obtained from three blue tier basalts sutherland wellman pers comm some of the geological implications of this study are outlined in this paper

a numerical study of the seasonal variability in the circulation off central chile the princeton ocean model is used to study the coastal ocean circulation off central chile between 30 and 45 s and its seasonal transitions in response to monthly mean climatological wind stress and surface heat flux the model reproduces many of the dominant circulation features including an equatorward coastal current coastal upwelling and a poleward undercurrent to get the correct seasonal variability in the undercurrent it was necessary to prescribe the inflow of the undercurrent on the northern model boundary meanders and eddies form throughout the simulation period seaward of the coastal current in response to baroclinic instability of the flow the flow associated with the meanders shows upwelling in the shoreward flow and downwelling in the seaward flow this upwelling downwelling pattern is explained by conservation of relative vorticity in the flow the upwelling velocity associated with the meanders corresponds to a vertical migration of 15 30 m over a typical timescale of the meanders of 1 2 months it is argued that this upwelling may be important for maintaining observed high phytoplankton biomass and primary production seaward of the coastal zone directly affected by wind driven upwelling

mesoscale eddies off peru in altimeter records identification algorithms and eddy spatio temporal patterns relatively little is known about coherent vortices in the eastern south pacific along the peruvian coast even with regard to basic facts about their frequency of occurrence longevity and structure this study addresses these issues with nearly 15 years of relatively high resolution satellite altimetry measurements we first compare two distinct automated methods for eddy identification the objective validation protocol shows that the rarely used geometrical or winding angle method based on the curvature of the streamline functions is more accurate than the commonly used okubo weiss algorithm which defines a vortex as a simple connected region with values of okubo weiss parameter weaker than a given threshold we then investigate vortices off peru using more than 20 000 mesoscale eddies identified by the winding angle method coherent eddies characterized by a high ratio of vorticity to deformation rate are typically formed along the coast and propagate westward at 3 6 cm s 1 the vortices have a mean radius of 80 km increasing northward and are most frequently observed off of chimbote 9s and south of san juan 15s the mean eddy lifetime is about 1 month but if eddies survive at least 2 months the probability for surviving an additional week or month is constant at 90 or 67 anticyclonic eddies tend to propagate northwestward whereas cyclonic vortices migrate southwestward in general cyclones and anticyclones are similar except for eddies surviving at least 6 months in this case after a similar 3 4 months of radius and amplitude growth amplitudes or sizes decay particularly rapidly for anticyclonic or cyclonic eddies in terms of intensity cyclonic eddies show a rapid decay during the first 3 months before arriving at a quasi constant value whereas anticyclones exhibit steady decline finally eddy temporal variations were examined at seasonal and interannual scales in the coastal region favorable to the formation of energetic mesoscale structures on seasonal scales eddy activity is maximal in fall and minimum in spring at interannual scales the eddy activity index was maximal during the strong el nino of 1997 1998 but another strong maximum of eddy activity also occurred late in 2004 these temporal variations are probably associated with the intensification of the upwelling thermal front and with the passage of coastal trapped waves which generate baroclinic instabilities further investigation of the mechanisms involved on the eddy genesis is needed

an exchange window for the injection of antarctic intermediate water into the south pacific antarctic intermediate water aaiw occupies the intermediate horizon of most of the world oceans formed in the southern ocean it is characterized by a relative salinity minimum with a new denser in situ national oceanographic data center dataset the authors have reanalyzed the export characteristics of aaiw from the southern ocean into the south pacific ocean these new data show that part of the aaiw is exported from the subpolar frontal region by the large scale circulation through an exchange window of 10 width situated east of 90 w in the southeast corner of the pacific basin this suggests the origin of this water to be in the antarctic circumpolar current a set of numerical modeling experiments has been used to reproduce these observed features and to demonstrate that the dynamics of the exchange window is controlled by the basin scale meridional pressure gradient the exchange of aaiw between the southern and pacific oceans must therefore be understood in the context of the large basin scale dynamical balance rather than simply local effects

eddy characteristics in the eastern south pacific 1 the main eddy characteristics length scales rotation period swirl and translation velocities are determined in the eastern south pacific region 10 35 s and 70 100 w based on surface drifter measurements satellite altimetry and hydrographic data from the woce p19 section the chile peru current eddies have a typical diameter of order of 30 km smaller than the typical rossby radii observed in the region they are principally formed near the south american coast and propagate seaward with a translation velocity varying from 3 cm s 1 in the southern part of the study domain to 6 cm s 1 north of 15 s long lived anticyclonic eddies propagate northwestward with a mean angle of around 333 t whereas cyclonic vortices propagate westward consistent with the vortices propagation theory on a plane the radial distribution of the swirl velocity shows that the chile peru current eddies have a maximum diameter of order 200 km with a swirl velocity of around 14 cm s 1 and a rotation period of 50 days hydrographic data reveal a vertical extent down to around 2000 m for energetic eddies no significant difference is observed between the tangential velocities of cyclonic and anticyclonic eddies geostrophic balance can be considered for large radii whereas ageostrophic dynamics may play an important role near the eddy centers

unroofing history of a suture zone in the himalaya of pakistan by means of fission track annealing ages abstract the uplift history of the swat valley and hazara region of northwestern pakistan has been established using 22 fission track dates on apatite zircon and sphene a major fault the main mantle thrust mmt strikes east west across the swat valley separates regions of markedly differing fission track age regimesm and may be a suture zone separating an extinct island arc terrane on the north from the indian plate to the south fission track ages ranging from about 55 to 58 m y for sphene 18 to 53 m y for zircon and 9 to 17 m y for apatite were obtained from the region north of the mmt to the south the fission track age ranges are 20 to 25 m y for sphene 17 to 26 m y for zircon and 16 to 23 m y for apatite disparate zircon and sphene ages on each side of the mmt imply different cooling histories for each side of the fault prior to 15 m y similar apatite ages on both sides of the fault imply similar cooling histories during the past 15 m y this may indicate that faulting ceased by 15 m y mean uplift rates have been derived from the fission track data using mainly the mineral pair method uplift rates in the region north of the mmt increased from 0 07 to 0 20 mm yr during the period 55 to 15 m y south of the fault uplift rates averaged in excess of 0 70 mm yr for the period 25 to 15 m y during the past 15 m y uplift across the mmt in the swat valley showsno discontinuities ranging from 0 16 mm yr in the south to 0 39 mm yr in the north a plausible interpretation for the fission track uplift data has the mmt verging to the south with overthrusting taking place at a depth between 3 5 and 6 0 km juxtaposing two terranes that were originally separated by a substantial but unknown distance in this model regional uplift followed cessation of faulting just prior to 15 m y

estimating horizontal diffusivity in the east sea sea of japan and the northwest pacific from satellite tracked drifter data we use data of satellite tracked mixed layer drifters collected for the world ocean circulation experiment tropical ocean global atmosphere woce toga surface velocity program in the east sea sea of japan and the northwest pacific ocean during 1991 1997 to obtain reliable estimates of geographically varying horizontal diffusivity integral timescale and space scale for the diffusivity we suggest calculation of both the minor principal component of the diffusivity tensor in a definition by davis 1991 and the half growth rate of the minor principal component of the displacement variance tensor numerical simulation of particle motion is used to prove that the minor principal component estimates of diffusivity in contrast to regular estimates are insensitive to ensemble averaging over particles taken from a finite area in a shear mean flow in the east sea typical values of the diffusivity timescale and space scale are 1 7 5 2 10 7 cm 2 s 1 0 7 1 7 days and 10 25 km respectively in the northwest pacific ocean typical estimates of the diffusivity timescale and space scale in mean are a factor 2 3 larger namely 2 3 15 1 x 10 7 cm 2 s 1 1 7 3 7 days and 18 62 km respectively it was found that the space scale l and the first mode internal rosshy radius ri are related as l ri which suggests a parameterization of lateral diffusivity k of the form k u ri where u is the rms current velocity fluctuation

a users guide to fission track dating calibration abstract misconceptions regarding the fission track dating method prompt the description of five handling procedures and the derivation of commonly used system calibrations problems of registration geometry inhomogeneous uranium distribution accumulated radiation damage and anisotropic etching largely invalidate all but the population and external detector methods and impose strict limitations upon even their routine application complexities of unique absolute thermal neutron dosimetry are illustrated by the calibration and use of the nbs pre irradiated glass srm 962 the 20 disparity in measured f decay constant values cannot be isolated from neutron fluence measurement and calibration frequently a calibration ratio f is evaluated against an age standard and then split into its component parts to illustrate this interdependence of f and zircon fission track ages in agreement with independent k ar ages are obtained by calculating the same track count data with each of the preferred values of f f 7 03 10 17 yr 1 and8 46 10 17 yr 1 together with appropriate selected neutron dosimetry schemes an alternative approach is presented formally relating unknown ages of samples to known ages of standards either by direct comparison of standard and sample track densities or by the repeated calibration of a glass against age standards practical recommendations are given for the reporting and critical assessment of fission track data

fission track evidence for the source of accreted sandstones barbados a part of the accretionary wedge associated with the lesser antilles arc system is exposed in an area of approximately 50 km in northeastern barbados zircon separates from sandstones collected from the scotland district barbados w i were analyzed using the fission track technique in order to assess the spectrum of source areas from which these terrigenous sediments were derived and to better constrain the timing of deposition results yielded a mixture of ages with strong groupings from 25 80 ma 200 350 ma and greater than 500 ma the youngest population indicates that some of the scotland beds previously dated by paleontologic methods as eocene may actually be as young as late oligocene possible source areas include the lesser antilles arc the netherlands venezuelan antilles arc and the caribbean mountains of venezuela the 200 350 ma population may reflect partially annealed cratonic material an andean component and or material associated with a triassic rifting event the oldest zircons 500 ma and metamict zircons were likely derived from the south american craton detrital feldspars separated from sandstone at the base of chalky mount were analyzed by the 40ar 39ar age spectrum technique results yield what is interpreted to be a slow cooling gradient from 1350 ma to 925 ma and provides additional evidence of a cratonic source for the accreted sediments based on results from this study and paleogeographical constraints it is proposed that source areas for the scotland sandstones of barbados may have included the guayana shield central cordillera uplifted areas of coastal south america and the lesser antilles volcanic arc we speculate that in late oligocene time an immense proto orinoco river system flowed in a northeasterly direction from the shield through the northern venezuelan mountain system cordillera de la costa and araya paria finally emerging into the caribbean sea in the area now occupied by unare depression sediments comprising this deltaic complex and deep sea fan were either deposited directly into the trench or onto the sea floor where they were soon after caught up in the accretionary wedge of the lesser antilles arc system this article contains supplementary material

isoprenoid and branched gdgt based proxies for surface sediments from marine fjord and lake environments in chile abstract proxies based on glycerol dialkyl glycerol tetraether gdgt lipids from archaea isoprenoid gdgts and bacteria branched br gdgts in 33 surface sediments from marine fjord and lake systems between 25 s and 50 s in chile were analyzed the regional texh86 calibration obtained from the marine and fjord sediments and mean annual surface temperature t 59 6 texh86 33 0 r2 0 9 n 23 is statistically identical to the global ocean calibration based on suspended particulate material in terms of slope but not in terms of intercept the regional surface and subsurface texh86 calibrations were statistically different from the existing global ocean core top calibrations the tex86 calibration model based on most of the relatively large lakes studied here t 50 7 tex86 11 8 r2 0 9 n 5 is statistically identical to the global lake calibration the relatively high tex86 values from smaller lakes suggested an additional source for isoprenoid gdgts likely terrestrial or aquatic methanogenic archaea application of the soil calibrated mbt cbt methylation and cyclization of br gdgts respectively temperature proxy to the marine and fjord sediments resulted in an overestimation of continental mean annual air temperature maat suggesting in situ production of certain br gdgts in the water column or surface sediment for the lakes mbt cbt based surface air temperature estimates were 3 6 c below maat however temperature estimates from the lake specific mbt cbt global calibration were in good agreement with mean annual surface temperature for all the lakes the results highlight the need for testing local vs global calibrations of gdgt based proxies before their application for palaeoenvironmental reconstruction