rationalizing the spatial distribution of mesoscale eddy diffusivity in terms of mixing length theory observations and theory suggest that lateral mixing by mesoscale ocean eddies only reaches its maximum potential at steering levels surfaces at which the propagation speed of eddies approaches that of the mean flow away from steering levels mixing is strongly suppressed because the mixing length is smaller than the eddy scale thus reducing the mixing rates the suppression is particularly pronounced in strong currents where mesoscale eddies are most energetic here a framework for parameterizing eddy mixing is explored that attempts to capture this suppression an expression of the surface eddy diffusivity proposed by ferrari and nikurashin is evaluated using observations of eddy kinetic energy eddy scale and eddy propagation speed the resulting global maps of eddy diffusivity have a broad correspondence with recent estimates of diffusivity based on the rate at which tracer contours are stretched by altimetric derived surface currents finally the expression for the eddy diffusivity is extrapolated in the vertical to infer the eddy induced meridional heat transport and the overturning streamfunction

suppression of eddy diffusivity across jets in the southern ocean abstract geostrophic eddies control the meridional mixing of heat carbon and other climatically important tracers in the southern ocean the rate of eddy mixing is typically quantified through an eddy diffusivity there is an ongoing debate as to whether eddy mixing in enhanced in the core of the antarctic circumpolar current or on its flanks a simple expression is derived that predicts the rate of eddy mixing that is the eddy diffusivity as a function of eddy and mean current statistics this novel expression predicts suppression of the cross jet eddy diffusivity in the core of the antarctic circumpolar current despite enhanced values of eddy kinetic energy the expression is qualitatively and quantitatively validated by independent estimates of eddy mixing from altimetry observations this work suggests that the meridional eddy diffusivity across the antarctic circumpolar current is weaker than presently assumed because of the suppression of eddy mixing by the strong zonal current

the contribution of the precambrian continental lithosphere to global h 2 production the production of hydrogen gas from the precambrian continental lithosphere has been underestimated taking into account hydrogen from serpentinization and radiolysis may double estimates previously based on marine systems alone molecular hydrogen produced by interactions between water and rocks in the earth s subsurface and at deep ocean vents can sustain microbial ecosystems it was thought that global h2 production originates mainly from the marine lithosphere with a negligible contribution from precambrian rocks but here the authors present a global compilation of h2 concentration data that identifies the fracture waters in the precambrian continental subsurface as a domain of the terrestrial hydrosphere that produces h2 at a rate comparable to estimates from marine systems this finding revises our understanding of the production of reduced gases in the earth s subsurface and may aid in the exploration of life in deep habitat locations microbial ecosystems can be sustained by hydrogen gas h2 producing water rock interactions in the earth s subsurface and at deep ocean vents1 2 3 4 current estimates of global h2 production from the marine lithosphere by water rock reactions hydration are in the range of 1011 moles per year5 6 7 8 9 recent explorations of saline fracture waters in the precambrian continental subsurface have identified environments as rich in h2 as hydrothermal vents and seafloor spreading centres1 2 and have suggested a link between dissolved h2 and the radiolytic dissociation of water10 11 however extrapolation of a regional h2 flux based on the deep gold mines of the witwatersrand basin in south africa11 yields a contribution of the precambrian lithosphere to global h2 production that was thought to be negligible 0 009 1011 moles per year 6 here we present a global compilation of published and new h2 concentration data obtained from precambrian rocks and find that the h2 production potential of the precambrian continental lithosphere has been underestimated we suggest that this can be explained by a lack of consideration of additional h2 producing reactions such as serpentinization and the absence of appropriate scaling of h2 measurements from these environments to account for the fact that precambrian crust represents over 70 per cent of global continental crust surface area12 if h2 production via both radiolysis and hydration reactions is taken into account our estimate of h2 production rates from the precambrian continental lithosphere of 0 36 2 27 1011 moles per year is comparable to estimates from marine systems

subglacial processes from drumlins in clew bay western ireland interpretation of subglacial processes and environments can be usefully informed by the stratigraphy and structures of sediments preserved within drumlins and the down ice variability of these sediments drumlins in clew bay western ireland were formed by westward late pleistocene ice flow onto the atlantic shelf but the depositional processes and environments of these sediments remain uncertain this study describes and interprets the drumlin stratigraphy and sediment properties and structures from two drumlins on the south side of clew bay drumlin sediments are dominated by massive to stratified diamicton deposited subglacially by deformation of flows of varying rheology folds shears and clastic dikes within the sediments suggest active subglacial water flow related to variations in ice flow and ice bed coupling the distal ends of the drumlins are dominated by stratified diamicton and gravel units with sandy interbeds these sediments reflect deposition in a leeside subglacial cavity formed coevally with bedform development a model is proposed that can account for sediment stratigraphic patterns and drumlin formation copyright 2015 john wiley sons ltd

lateral eddy mixing in the subtropical salinity maxima of the global ocean abstracta suite of observationally driven model experiments is used to investigate the contribution of near surface lateral eddy mixing to the subtropical surface salinity maxima in the global ocean surface fields of salinity are treated as a passive tracer and stirred by surface velocities derived from altimetry leading to irreversible water mass transformation in the absence of surface forcing and vertical processes the transformation rate can be directly related to the integrated diffusion across tracer contours which is determined by the observed velocities the destruction rates of the salinity maxima by lateral mixing can be compared to the production rates by surface forcing which act to strengthen the maxima the ratio of destruction by eddy mixing in the surface layer versus the surface forcing exhibits regional differences in the mean from 10 in the south pacific to up to 25 in the south indian furthermore the regional basins show seasonal and interannual variability in eddy mixing th

circulation and stirring in the southeast pacific ocean and the scotia sea sectors of the antarctic circumpolar currenta abstractthe large scale middepth circulation and eddy diffusivities in the southeast pacific ocean and scotia sea sectors between 110 and 45 w of the antarctic circumpolar current acc are described based on a subsurface quasi isobaric rafos float based lagrangian dataset these rafos float data were collected during the diapycnal and isopycnal mixing experiment in the southern ocean dimes the mean flow adjusted to a common 1400 m depth shows the presence of jets in the time averaged sense with speeds of 6 cm s 1 in the southeast pacific ocean and upward of 13 cm s 1 in the scotia sea these jets appear to be locked to topography in the scotia sea but aside from negotiating a seamount chain are mostly free of local topographic constraints in the southeast pacific ocean the eddy kinetic energy eke is higher than the mean kinetic energy everywhere in the sampled domain by about 50 the magnitude of the eke increases drastically by a factor of 2 or more as the current crosses over the hero and

tectonic rotations within the bolivian altiplano implications for the geodynamic evolution of the central andes during the late tertiary paleomagnetic results from 61 sites in tertiary red beds and volcanic rocks from the bolivian andes allow quantification of tectonic rotations within the altiplano domain a total of 16 sites were also obtained in lower miocene ignimbrites that cover the forearc of the north chilean andes near arica in the southern altiplano lipez region a local clockwise rotation of up to 38 is recorded in lower miocene volcanic rocks farther north near the salar de uyuni there is no evidence of significant rotations counterclockwise rotations are observed in the northern altiplano the largest counterclockwise rotation 28 is found in eocene oligocene red beds tiwanaku formation along the eastern border of the corque syncline middle miocene sediments located within the center of the corque basin record a counterclockwise rotation of only 10 about 200 km north of the corque basin eocene oligocene sedimentary rocks near the locality of viacha record only 10 counterclockwise rotation paleomagnetic results in lower miocene ignimbrites from the forearc near the arica bend do not show evidence for late cenozoic rotation of the forearc these new results suggest that the 20 to 25 counterclockwise rotation of the southern peruvian forearc occurred prior to the miocene anisotropy of magnetic susceptibility ams data show a magnetic fabric mostly controlled by bedding but slight ams lineations are found almost parallel to the major regional structural trends such as fold axes the apparent relationship between tectonic rotations ams lineations and structural trends suggests that rotations occured after or during the final stage of folding paleomagnetic data obtained in paleozoic rocks show evidence of clockwise rotation of the southern sub andean ranges tectonic rotations during the neogene are mostly localized on the eastern side of the central andes the curvature of the occidental margin near arica was likely acquired prior to the last stage of andean deformation although the magnitude of the rotations may vary from one locality to the other there is a consistent pattern showing counterclockwise rotations to the north and clockwise to the south a large scale regional mechanism is needed to explain this pattern of tectonic rotations within the central andes we propose a model in which along strike segmentation of the andean foreland and indentation of the altiplano by a curved forearc are the major factors controlling tectonic rotations within the altiplano eastern cordillera and sub andean ranges

the vertical partition of oceanic horizontal kinetic energy to produce an interpretation of the surface kinetic energy as measured by altimeters a survey is made of the vertical structure of kinetic energy profiles in a large number of globally distributed long current meter records although the data are geographically confined primarily to a latitude band in the north pacific to the north atlantic and to a few moorings in the south atlantic the results show generally speaking that most regions are dominated by the barotropic and first baroclinic modes because of the near surface intensification of baroclinic modes altimeters primarily reflect the first baroclinic mode and thus the motion of the main thermocline there is good quantitative agreement with a few exceptions with estimates of the surface kinetic energy obtained from the topex poseidon altimeter and from vertical extrapolations to the surface of the mooring profiles these results are consistent with previous suggestions that barotropic models have little skill in depicting variability as seen in the altimeter data an eof analysis is shown to produce fictitious mode coupling unless the dynamical modes have very different energy levels

mineral magnetic analyses as a means of lithostratigraphic correlation and provenance indication of glacial diamicts intra and interunit variation mineral magnetic analyses are applied to a series of diamict samples taken from the quaternary sequence in the isle of man in order to assess the relative magnitude of the intra and inter unit variation of the magnetic properties the results are analysed both qualitatively and quantitatively and show that the level of intra unit variation is significantly less than the level of inter unit variation the intra unit variation detected appears to show some relationship to the basic stratigraphy previous correlations based upon field evidence of diamict units exposed upon the east and west coasts of the isle of man are supported by their mineral magnetic properties the statistically significant differences in the magnetic mineralogy of the stratigraphically lower wyllin and shellag tills and the upper orrisdale ballavarkish and ballaquark tills suggests distinct provenances for these two suites of sediments allowing potential source areas to be suggested these source areas are consistent with published data on ice flow directions in the irish sea basin during the devensian

understanding the regional variability of eddy diffusivity in the pacific sector of the southern ocean a diagnostic framework is presented based on the nakamura effective diffusivity to investigate the regional variation in eddy diffusivity comparison of three different diffusivity calculations enables the effects of locally enhanced tracer diffusion to be distinguished from the streamwise average it also enables the distinction to be made between locally generated complexity in the tracer structure and that advected into a particular domain the technique is applied to the pacific sector of the southern ocean the results highlight the important role that the mean flow plays in determining eddy diffusivity the effective diffusivity is not simply related to the eddy kinetic energy in regions of a strong mean flow the eddy diffusivity can be suppressed even in the presence of moderately strong eddy activity conversely in a region of weak mean flow the eddy diffusivity can be enhanced even in the presence of only weak eddy activity this casts doubt on the ability of parameterizations based solely on the eddy kinetic energy to adequately characterize the eddy diffusivity in regions of strongly varying mean flow such as the southern ocean the results are however consistent with the eddy transport and mixing variability predicted by potential vorticity based arguments

estimating suppression of eddy mixing by mean flows particle and tracer based estimates of lateral diffusivities are used to estimate the suppression of eddy mixingacrossstrongcurrents particlesandtracersare advectedusingavelocityfieldderivedfromseasurface height measurements from the south pacific in a region west of drake passage this velocity field has been used in a companion paper to show that both particle and tracer based estimates of eddy diffusivities are equivalent despite recent claims to the contrary these estimates of eddy diffusivities are here analyzed to show 1 that the degree of suppression of mixing across the strong antarctic circumpolar current is correctly predicted by mixing length theory modified to include eddy propagation along the mean flow and 2 that the suppressioncan beinferredfromparticletrajectoriesby studyingthestructureofthe autocorrelationfunction of the particle velocities beyond the first zero crossing these results are then used to discuss how to compute lateral and vertical variations in eddy diffusivities using floats and drifters in the real ocean

enhancement of mesoscale eddy stirring at steering levels in the southern ocean abstract meridional cross sections of effective diffusivity in the southern ocean are presented and discussed the effective diffusivity keff characterizes the rate at which mesoscale eddies stir properties on interior isopycnal surfaces and laterally at the sea surface the distributions are obtained by monitoring the rate at which eddies stir an idealized tracer whose initial distribution varies monotonically across the antarctic circumpolar current acc in the absence of observed maps of eddying currents in the interior ocean the advecting velocity field is taken from an eddy permitting state estimate of the southern ocean sose a three dimensional advection diffusion equation is solved and the diffusivity diagnosed by applying the nakamura technique on both horizontal and isopycnal surfaces the resulting meridional sections of keff reveal intensified isopycnal eddy stirring reaching values of 2000 m2 s 1 in a layer deep beneath the acc but rising toward the surface on the equatorward flank

open ocean regimes of relative dispersion as two fluid particles separate in time the entire spectrum of eddy motions is being sampled from the smallest to the largest scales in large scale geophysical systems for which the earth rotation is important it has been conjectured that the relative diffusivity should vary respectively as d2 and d4 3 for distances respectively smaller and larger than a well defined forcing scale of the order of the internal rossby radius with d the r m s separation distance particle paths data from a mid latitude float experiment in the central part of the north atlantic appear to support these statements partly two particles initially separated by a few km within two distinct clusters west and east of the mid atlantic ridge statistically dispersed following a richardson regime d2 t3 asymptotically for r m s separation distances between 40 and 300 km in agreement with a d4 3 law at early times and for smaller separation distances an exponential growth in agreement with a d2 law was briefly observed but only for the eastern cluster with an e folding time around 6 days after a few months or separation distances greater than 300 km the relative dispersion slowed down naturally to the taylor absolute dispersion regime

weak mixing in the eastern north atlantic an application of the tracer contour inverse method abstract the tracer contour inverse method is used to infer mixing and circulation in the eastern north atlantic solutions for the vertical mixing coefficient d the along isopycnal mixing coefficient k and a geostrophic streamfunction are all direct outputs of the method the method predicts a vertical mixing coefficient o 10 5 m2 s 1 in the upper 1000 m of the water column consistent with in situ observations the method predicts a depth dependent along isopycnal mixing coefficient that decreases from o 1000 m2 s 1 close to the mixed layer to o 100 m2 s 1 in the interior which is also consistent with observations and previous hypotheses the robustness of the result is tested with a rigorous sensitivity analysis including the use of two independently constructed datasets this study confirms the utility of the tracer contour inverse method the results presented support the hypothesis that vertical mixing is small in the thermocline of the subtropical atlantic ocean a strong depth dependence o

river plume dynamics in the kara sea from altimetry based lagrangian model satellite salinity and chlorophyll data abstract two largest siberian rivers ob and yenisei inflow in the arctic ocean in the kara sea basin mixing of fresh river waters and saline sea waters leads to the formation of the large river plume with typical thickness about 10 m which can cover a considerable part of the basin the paper is devoted to the study of interannual variability of the river plume dynamics in the kara sea using multi satellite observations first satellite salinity aquarius and chlorophyll a modis data for 2011 2014 along with hydrological observations are used in order to identify areas covered by the plume and to validate the satellite measurements it is shown that both types of satellite data are consistent with in situ observations and provide realistic information about propagation of fresh and turbid plume waters second we introduce particle tracking model for pathways calculation of the plume propagation that is based on satellite altimetry and wind data reanalysis the model is successfully validated using aquarius and modis data model calculations are used to describe the significant interannual variability of the river plume pathways over twenty year period 1993 2013 and identify the driving mechanisms of its propagation it is shown that the plume self organizing geostrophic circulation which is induced by the differences in the buoyancy of light plume water and dense ocean water and changes of prevailing wind direction are the main factors controlling the plume dynamics and its interannual variability

seasonal and interannual variability of atmospheric convergence zones in the tropical pacific observed with ers 1 scatterometer monthly images of atmospheric convergence zones in the tropical pacific were produced with 1992 1994 ers 1 scatterometer wind vectors from the images the position width and intensity of the convergence zones can be determined latitude time sections of ocean surface wind divergence show that the summer position of the itcz in the eastern pacific during the observed period exceeded the normal position northward by 3 6 latitude and the annual cycle in the western pacific for 1994 was quite weak implying a persistently unusual case

water mass transformation by cabbeling and thermobaricity water mass transformation is an important process for the global ocean circulation nonlinearities in the equation of state of seawater lead to water mass transformation due to cabbeling and thermobaricity here the contribution of cabbeling and thermobaricity to water mass transformation is calculated in a neutral density framework using temperature gradients derived from observationally based gridded climatologies and observationally based estimates of the spatially varying eddy diffusivities it is shown that cabbeling and thermobaricity play a significant role in the water mass transformation budget with cabbeling having a particularly important role in the formation of antarctic intermediate water and antarctic bottom water a physical hypothesis is presented which explains why cabbeling is important for antarctic intermediate water formation it is shown that spatially varying estimates of eddy diffusivities are essential to correctly quantify the role of cabbeling to the formation of antarctic intermediate water

critical role for mesoscale eddy diffusion in supplying oxygen to hypoxic ocean waters 1 estimates of the oceanic lateral eddy diffusion coefficient aredi vary by more than an order of magnitude ranging from less than a few hundred m2 s to thousands of m2 s this uncertainty has first order implications for the intensity of oceanic hypoxia which is poorly simulated by the current generation of earth system models using satellite based estimate of oxygen consumption in hypoxic waters to estimate the required diffusion coefficient for these waters gives a value of order 1000 m2 s varying aredi across a suite of earth system models yields a broadly consistent result given a thermocline diapycnal diffusion coefficient of 1 10 5 m2 s

global surface eddy diffusivities derived from satellite altimetry 1 velocities derived from aviso sea surface height observations adjusted to be nondivergent are used to simulate the evolution of passive tracers at the ocean surface eddy mixing rates are derived from the tracer fields in two ways first the method of nakamura is applied to a sector in the east pacific second the osborn cox diffusivity is calculated globally to yield estimates of diffusivity in two dimensions the results from the east pacific show weak meridional mixing at the surface in the southern ocean 1000 m2 s 1 consistent with previous results but higher mixing rates 3000 5000 m2 s 1 in the tropical ocean the osborn cox diagnostic provides a global picture of mixing rates and agrees reasonably well with the results from the east pacific it also shows extremely high mixing rates 104 m2 s 1 in western boundary current regions the osborn cox diffusivity is sensitive to the tracer initialization which we attribute to the presence of anisotropic mixing processes the mixing rates are strongly influenced by the presence of a mean flow nearly everywhere as shown by comparison with an eddy only calculation with the mean flow absent finally results are compared with other recent estimates of mixing rates using lagrangian and inverse methods

the origin history and role of water in the evolution of the inner solar system water as the oxide of the most abundant element in the universe is widespread in the galaxy on the earth it plays a fundamentally important role in both the earth and life sciences water controls the rheology of the deep earth and its ability to convect affects igneous processes by increasing

extensive noachian fluvial systems in arabia terra implications for early martian climate valley networks are some of the strongest lines of evidence for extensive fluvial activity on early noachian 3 7 ga mars however their purported absence on certain ancient terrains such as arabia terra is at variance with patterns of precipitation as predicted by warm and wet climate models this disagreement has contributed to the development of an alternative icy highlands scenario whereby valley networks were formed by the melting of highland ice sheets here we show through regional mapping that arabia terra shows evidence for extensive networks of sinuous ridges we interpret these ridge features as inverted fluvial channels that formed in the noachian before being subject to burial and exhumation the inverted channels developed on extensive aggrading flood plains as the inverted channels are both sourced in and traverse across arabia terra their formation is inconsistent with discrete localized sources of water such as meltwater from highland ice sheets our results are instead more consistent with an early mars that supported widespread precipitation and runoff

float derived isopycnal diffusivities in the dimes experiment as part of the diapycnal and isopycnal mixing experiment in the southern ocean dimes 210 subsurface floats were deployed west of the drake passage on two targeted density surfaces absolute single particle diffusivities are calculated for the floats the focus is on the meridional component which is less affectedby the meanshear the diffusivitiesare estimatedin severalways including a novelmethodbased on the probability density function of the meridional displacements this allows the determination of the range of possible lateral diffusivities as well as the period over which the spreading can be said to be diffusive the method is applied to the float data and to synthetic trajectories generated with the massachusetts institute of technologygeneral circulationmodel mitgcm becauseof ballastingproblems manyofthefloatsdid not remain on their targeted density surface however the float temperature records suggest that most occupied asmallrangeofdensities sothefloatsweregroupedtogetherfortheanalysis thelatterfocuseson asubsetof 109 of the floats launched near 1058w the different methods yield a consistent estimate for the diffusivity of 800 6 200m 2 s 21 the same calculations were made with model particles deployed on 20 different density surfaces and the result for the particles deployed on the neutral density surface g 5 27 7 surface was the same within the errors the model was then used to map the variation of the diffusivity in the vertical near the core of the antarctic circumpolar current acc the results suggest mixing is intensified at middepths between 1500 and 2000m consistent with several previous studies

till stratigraphy and sedimentology at the margins of terrestrially terminating ice streams case study of the western canadian prairies and high plains complex glacigenic sediment sequences arranged in large arcuate assemblages and demarcating the lobate termini of fast ice flow corridors in western canada represent the terrestrial equivalents of the trough mouth fans of the marine palaeo ice stream record intensive sedimentological and stratigraphic investigations at a regional scale are employed in the interpretation of thick units or sequences of diamicton and two depositional scenarios are proposed first glacier marginal till thickening and the stacking of till wedges takes place in areas where an ice stream margin was stationary for short periods of time stacks of subglacial traction tills potentially record annual sub marginal incremental thickening at ice stream margins especially in areas where densely spaced recessional push moraines appear to record seasonal climatic forcing second proglacial lake and valley infilling with glacilacustrine rhythmites and mass flow diamictons is associated with the advection of sub marginal till into preglacial bedrock depressions and records ice stream marginal oscillations and debris influx into discontinuous proglacial lakes which act as subaqueous sediment sinks for materials that would otherwise have been used to construct sub marginal till wedges and moraines glacial overriding modifies the deposits produced in both scenarios through deformation and the dislocation and entrainment of bedrock and sediment rafts at the margins of bedrock valley walls resulting in the widespread development of glacitectonites and megablocks the occurrence of the thickest deposits as preglacial valley fills may be significant in groundwater siphoning away from subglacial deforming layers and the promotion of sticky spots

sensitivity of the overturning circulation in the southern ocean to decadal changes in wind forcing abstractthe sensitivity of the overturning circulation in the southern ocean to the recent decadal strengthening of the overlying winds is being discussed intensely with some works attributing an inferred saturation of the southern ocean co2 sink to an intensification of the overturning circulation while others have argued that this circulation is insensitive to changes in winds fundamental to reconciling these diverse views is to understand properly the role of eddies in counteracting the directly wind forced changes in overturning here the authors use novel theoretical considerations and fine resolution ocean models to develop a new scaling for the sensitivity of eddy induced mixing to changes in winds and they demonstrate that changes in southern ocean overturning in response to recent and future changes in wind stress forcing are likely to be substantial even in the presence of a decadally varying eddy field this result has significant implications for the ocean s role in the carbon cycle and

diagnosing the southern ocean overturning from tracer fields abstract the strength and structure of the southern hemisphere meridional overturning circulation smoc is related to the along isopycnal and vertical mixing coefficients by analyzing tracer and density fields from a hydrographic climatology the meridional transport of upper circumpolar deep water ucdw across the antarctic circumpolar current acc is expressed in terms of the along isopycnal k and diapycnal d tracer diffusivities and in terms of the along isopycnal potential vorticity mixing coefficient kpv uniform along isopycnal 600 m2 s 1 and low vertical mixing 10 5 m2 s 1 can maintain a southward transport of less than 60 sv sv 106 m2 s 1 of ucdw across the acc which is distributed largely across the south pacific and east indian ocean basins for vertical mixing rates of o 10 4 m2 s 1 or greater the inferred transport is significantly enhanced the transports inferred from both tracer and density distributions suggest a ratio k to d of o 2 106 particularly on deeper layers

styles of till deposition at the margin of the last glacial maximum north sea lobe of the british irish ice sheet an assessment based on geochemical properties of glacigenic deposits in eastern england the geochemical composition of last glacial maximum lgm tills and glacitectonites in east yorkshire and lincolnshire was analysed to assess vertical changes in their geochemical signature with respect to the current regional stratigraphic division and generic models of till deposition results fail to precisely differentiate the traditional basement skipsea and withernsea till types instead there is often more variability within these till types than between them the geochemical signatures are also laterally discontinuous and are often repeated vertically at a number of sites suggesting that the till sequences are composed of a number of lithologically distinct rafts which have been tectonically stacked or elevated to higher levels in the sediment pile at dimlington the production of a glacitectonically folded and stacked moraine is proposed as a mechanism to explain the remarkably thick sequence of withernsea till and the repetitions in geochemical composition we argue that the changes in till matrix geochemistry are related to changes in the dominance of ice lobes of different provenance which reworked pre existing quaternary sediments excavated local bedrock and progressively mixed these sediments with more far travelled material from further north the most significant implication of these findings is that the current lgm till stratigraphy of east yorkshire and lincolnshire is too simplified and therefore does not recognise the sedimentary and structural complexity produced by repeated onshore possibly surging flow by a dynamic north sea lobe at the eastern margin of the british irish ice sheet

net primary production in the gulf stream sustained by quasi geostrophic vertical exchanges we analyze 12 years of mesoscale vertical motion derived from an observation based product in the top 1000 m of the north west atlantic ocean vertical velocities o 10 m d 1 associated with gulf stream instabilities consist of alternating cells of upwelling and downwelling here we show that the magnitude of the vertical motions decays exponentially southward with an e folding length scale that is informative on the dynamics of the system we further investigate the impact of the vertical supply of nutrients about phytoplankton growth with a conceptual model incorporating the mean effect of nutrient distribution quasi geostrophic dynamics and ekman suction pumping results confirm that the mean effect of mesoscale vertical velocity variability alone can sustain observed levels of net primary production in the immediate vicinity of the gulf stream while other mechanisms including horizontal advection and submesoscale dynamics need to be considered when moving toward the subtropical gyre

oceanic isopycnal mixing by coordinate rotation abstract current numerical models of oceanic circulation differentiate between the eddy diffusion and viscosity transport along the geopotential horizontal and vertical directions only in order to model the effect of anisotropic turbulence as diffusive transport along and across density surfaces the isopycnal mixing tensor has been transformed from a diagonal second rank tensor in the isopycnal coordinate system to a tensor containing off diagonal elements in the geopotential coordinate system

the diabatic deacon cell abstract southern ocean air sea fluxes from the coads dataset are examined for compatibility between buoyancy gain and northward ekman transport an analysis in density classes points to an upwelling of upper circumpolar deep water and subsequent buoyancy gain from air sea exchange as water flows northward in the ekman layer the upper circumpolar deep water layer is too shallow to admit southward geostrophic flow along topography and an eddy mass flux mechanism for southward transport in this layer to replenish the upwelling is advanced based on observed large scale potential vorticity gradients estimates of the strength and vertical structure of the meridional flow are given using repeated hydrographic sections and a new climatology

a multi technique study of the glacial stratigraphy of co clare and co kerry southwest ireland a multi technique approach has been adopted in a study of the lithostratigraphy of glacial deposits in southwestern ireland including clast lithological analysis fine sand geochemistry low frequency mass specific susceptibility and fine sand calcium carbonate equivalent content a revised lithostratigraphical scheme is suggested for the quaternary glacial deposits of the region together with a simple strategy that may be adopted for stratigraphical studies in other regions of southern ireland it appears that geochemical determinations via inductively coupled plasma atomic absorption spectrometry are particularly useful in characterising and discriminating between till units within local stratigraphical studies and may be used to inform the applicability of other utilitarian techniques for use on a regional scale copyright 2002 john wiley sons ltd

four views of a portion of the north atlantic subtropical gyre abstract data from four cruises to the triangle centered at 27 n 32 30 w were smoothed by fitting second degree polynomials at each of about 30 different density surfaces the density intervals were p 0 3 corresponding to about 50 db intervals in pressure from the polynomials determination was made of central values horizontal derivatives and laplacians of the fields of pressure salt oxygen and dynamic height in addition maps of the fits and deviations of each nation from the smoothed fits were produced from the steady advective diffusive equation and the smoothed fits to the age oxygen and dynamic height fields the lateral isopycnal diffusivity as estimated to be kh 0 5 103 m2 s 1 although the salt field was reasonably stable from cruise to cruise the variability of the baroclinic velocity shear was found to be as large as the baroclinic shear itself the maps suggest a wobble of the gyre the standard deviation of the fluctuations at each nation from the smoothed fits when norma

phase speed cross spectra of eddy heat fluxes in the eastern pacific this study investigates the observed spectral character of eddy heat fluxes near the ocean surface focusing on the distribution in wavenumber and phase speed space eddy heat fluxes in the eastern pacific are calculated from concurrent satellite sea surface height and sea surface temperature data a high resolution coupledclimatemodelis alsoanalyzedin ordertoverifythephysicalmechanismsinvolvedandtovalidatethe model against observations wavenumber frequency and phase speed power spectra and cross spectra are constructed and presented as a function of latitude these spectra reveal the dominance of coherent mesoscale eddies in both the length scale and phase speed of eddy heat fluxes the breadths of the spectra are characterized via spectral moments these moments show that the eddy fluxes are relatively concentrated around the dominant wavenumber and phase speed good agreement is found between the model and the observed spectra the integrated heat transport and corresponding eddy diffusivity are shown to compare well with previous studies but the results give a deeper insight into what determines the heat flux implications for eddy parameterization are discussed

lagrangian eddy scales in the northern atlantic ocean eddy time and length scales are calculated from surface drifter and subsurface float observations in the northern atlantic ocean outside the energetic gulf stream subsurface timescales are relatively constant at depths from 700 m to 2000 m length scale and the characteristic eddy speed decrease with increasing depth below 700 m but length scale stays relatively constant in the upper several hundred meters of the gulf stream it is suggested that this behavior is due to the lagrangian sampling of the mesoscale field in limits set by the eulerian eddy scales and the eddy kinetic energy in high energy regions of the surface and near surface north atlantic the eddy field is in the frozen field lagrangian sampling regime for which the lagrangian and eulerian length scales are proportional however throughout much of the deep ocean interior the eddy field may be in the fixed float regime for which the lagrangian and eulerian timescales are nearly equal this does not necessarily imply that the deep interior is nearly linear as fixed float sampling is possible in a flow field of o 1 nonlinearity

the glacial mid depth radiocarbon bulge and its implications for the overturning circulation published reconstructions of radiocarbon in the atlantic sector of the southern ocean indicate that there is a mid depth maximum in radiocarbon age during the last glacial maximum lgm this is in contrast to the modern ocean where intense mixing between water masses results in a relatively homogenous radiocarbon profile ferrari et al 2014 suggested that the extended antarctic sea ice cover during the lgm necessitated a shallower boundary between the upper and lower branches of the meridional overturning circulation this shoaled boundary lay above major topographic features associated with strong diapycnal mixing isolating dense southern sourced water in the lower branch of the overturning circulation this isolation would have allowed radiocarbon to decay and thus provides a possible explanation for the mid depth radiocarbon age bulge we test this hypothesis using an idealized 2 d residual mean dynamical model of the global overturning circulation concentration distributions of a decaying tracer that is advected by the simulated overturning are compared to published radiocarbon data we find that a 600 km 5 of latitude increase in sea ice extent shoals the boundary between the upper and lower branches of the overturning circulation at 45 s by 600 m and shoals the depth of north atlantic deep water convection at 50 n by 2500 m this change in circulation configuration alone decreases the radiocarbon content in the mid depth south atlantic at 45 s by 40 even without an increase in surface radiocarbon age in the source region of deep waters during the lgm

estimates and implications of surface eddy diffusivity in the southern ocean derived from tracer transport abstract near surface effective diffusivities associated with geostrophic eddies in the southern ocean are estimated by numerically monitoring the lengthening of idealized tracer contours as they are strained by surface geostrophic flow observed by satellite altimetry the resulting surface diffusivities show considerable spatial variability and are large 2000 m2 s 1 on the equatorward flank of the antarctic circumpolar current and are small 500 m2 s 1 at the jet axis regions of high and low effective diffusivity are shown to be collocated with regions of respectively weak and strong isentropic potential vorticity gradients the maps of diffusivity are used along with climatological estimates of surface wind stress and air sea buoyancy flux to estimate surface meridional residual flows and the relative importance of eulerian and eddy induced circulation in the streamwise averaged dynamics of the antarctic circumpolar current

an idealized model of weddell gyre export variability recent observations suggest that the export of antarctic bottom water aabw from the weddell sea has a seasonal cycle in its temperature and salinity that is correlated with annual wind stress variations this variability has been attributed to annual vertical excursions of the isopycnals in the weddell gyre modifying the water properties at the depth of the orkney passage recent studies attribute these variations to locally wind driven barotropic dynamics in the northern weddell sea boundary current this paper explores an alternative mechanism in which the isopycnals respond directly to surface ekman pumping which is coupled to rapidly responding mesoscale eddy buoyancy fluxes near the gyre boundary a conceptual model of the interface that separates weddell sea deep water from circumpolar deep water is described in which the bounding isopycnal responds to a seasonal oscillation in the surface wind stress different parameterizations of the mesoscale eddy diffusivity are tested the model accurately predicts the observed phases of the temperature and salinity variability in relationship to the surface wind stress the model despite its heavy idealization also accounts for more than 50 of the observed oscillation amplitude which depends on the strength of the seasonal wind variability and the parameterized eddy diffusivity these results highlight theimportanceofmesoscaleeddiesinmodulatingtheexportofaabwinnarrowboundarylayersaroundthe antarctic margins

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

large scale alignment of oceanic nitrate and density 1 by analyzing global data we find that over large scales surfaces of constant nitrate are often better aligned with isopycnals than with isobars particularly below the euphotic zone this is unexplained by the movement of isopycnal surfaces in response to eddies and internal waves and is perhaps surprising given that the biological processes that alter nitrate distributions are largely depth dependent we provide a theoretical framework for understanding the orientation of isonitrate surfaces in relation to isopycnals in our model the nitrate distribution results from the balance between depth dependent biological processes nitrate uptake and remineralization and the along isopycnal homogenization of properties by eddy fluxes parameterized by eddy diffusivity where the along isopycnal eddy diffusivity is relatively large nitrate surfaces are better aligned with isopycnals than isobars we test our theory by estimating the strength of the eddy diffusivity and biological export production from global satellite data sets and comparing their contributions indeed we find that below the euphotic zone the mean isonitrate surfaces are oriented along isopycnals where the isopycnal eddy diffusivity is large and deviate where the biological export of organic matter is relatively strong comparison of nitrate data from profiling floats in different regions corroborates the hypothesis by showing variations in the nitrate density relationship from one part of the ocean to another

lagrangian time scales and eddy diffusivity at 1000 m compared to the surface in the south pacific and indian oceans abstractargo floats cannot be regarded as true lagrangian drifters because they periodically rise to the surface hence previous estimates of eddy diffusivity at depth using single particle statistics have been limited to one submerged cycle however unless the lagrangian time scale is significantly shorter than the argo cycle time this single particle calculation can have a large bias here eddy diffusivity computed from single particle statistics using argo data is compared to that computed by assuming that eulerian scales at depth are the same as at the surface and that the relationship between lagrangian and eulerian time scales derived by middleton is valid if the methods provide the same answer one can have confidence in both methods eddy diffusivity calculated from the single particle statistics shows the same spatial structure as that computed from inferred time scale but is smaller by a factor of about 2 it is suggested that this is because the deep lagrangian time scale over much of th

direct estimate of lateral eddy diffusivity upstream of drake passage abstractthe first direct estimate of the rate at which geostrophic turbulence mixes tracers across the antarctic circumpolar current is presented the estimate is computed from the spreading of a tracer released upstream of drake passage as part of the diapycnal and isopycnal mixing experiment in the southern ocean dimes the meridional eddy diffusivity a measure of the rate at which the area of the tracer spreads along an isopycnal across the antarctic circumpolar current is 710 260 m2 s 1 at 1500 m depth the estimate is based on an extrapolation of the tracer based diffusivity using output from numerical tracers released in a one twentieth of a degree model simulation of the circulation and turbulence in the drake passage region the model is shown to reproduce the observed spreading rate of the dimes tracer and suggests that the meridional eddy diffusivity is weak in the upper kilometer of the water column with values below 500 m2 s 1 and peaks at the steering level near 2 km where the eddy ph

three dimensional space dependent mesoscale diffusivity derivation and implications abstractrecently we presented a parameterization of an arbitrary tracer 3d mesoscale flux that describes both diabatic and adiabatic regimes without using arbitrary tapering functions however we

use of the geostrophic approximation to estimate time varying zonal currents at the equator moored thermistor chains at 2 n and 2 s and current temperature moorings at 0 are used to examine the accuracy of geostrophically estimated zonal velocity on the equator in the eastern 110 w and western 165 e pacific the meridionally differentiated form of the geostrophic balance is used to eliminate large errors due to wind balanced cross equatorial pressure gradients statistical analyses indicate that for time scales longer than 30 50 days the observed and geostrophically estimated zonal velocities are similar correlation coefficients of 0 6 0 9 and comparable amplitudes thus low frequency equatorial current oscillations are reasonably well represented by the geostrophic approximation however the mean currents are poorly resolved with the available array in the eastern pacific the mean zonal speed difference over the 10 month comparison period is 25 cm s 1 at 25 m and increases to 60 cm s 1 at 125 m at 165 e mean differences in the upper 250 m are typically 50 cm s 1 over a 4 month record the principal reason for these large mean differences is that the meridional scale of the mean currents is smaller than the spacing of the moorings comparison of observed and geostrophic velocity profiles obtained from shipboard sampling indicates that meridional spacing of about 1 latitude would be optimum for estimating the zonal velocity

anisotropic material transport by eddies and eddy driven currents in a model of the north atlantic this study analyzes anisotropic properties of the material transport by eddies and eddy driven zonal jets in a general circulation model of the north atlantic through the analysis of lagrangian particle trajectories spreading rates defined here as half the rate of change in the particle dispersion in the zonal direction systematically exceed the meridional rates by an order of magnitude area averaged values for the upperocean zonal and meridional spreading rates are approximately 8100 and 1400 m 2 s 21 respectively and in the deep ocean they are 2400 and 200 m 2 s 21 the results demonstrate that this anisotropy is mainly due to the actionofthetransienteddiesandnotto thesheardispersionassociated withthetime meanjets thisproperty is consistent with the fact that eddies in this study have zonally elongated shapes with the exception of the upper ocean subpolar gyre eddies also cause the superdiffusive zonal spreading significant variations in the spreading rate in the vertical and meridional directions and the difference between the westward and eastward spreading

surface drifter pair spreading in the north atlantic 1 this study examines spreading of surface drifter pairs deployed as part of the clivar mode water dynamic experiment climode project in the gulf stream region the spreading is resolved at hourly resolution and quantified by relative dispersion and finite scale lyapunov exponents at scales from 1 3 km to 300 500 km the dispersion follows richardson s law indicating stirring by eddies comparable in scale to the pair separation distance at larger scales the spreading becomes a random walk described by a constant diffusivity the behavior from 1 3 km to the local deformation radius is inconsistent with the enstrophy cascade of 2 d quasigeostrophic turbulence to test various hypotheses for this result drifter pair spreading is examined for pairs that were not launched together pairs deployed in the eastern subtropical north atlantic and climode pairs subsampled to daily temporal resolution our results indicate the presence of significant energy at the submesoscale in the gulf stream region which flattens the wave number spectrum and dominates surface stirring at this scale range results in the less energetic subtropical eastern atlantic are more equivocal

shear flow dispersion internal waves and horizontal mixing in the ocean abstract two models of advection diffusion in the oscillatory sheared velocity field of an internal wave are discussed our goal is to develop intuition about the role of such currents in horizontal ocean mixing through the mechanism of shear dispersion the analysis suggests simple parameterizations of this process i e those in eqs 7 36 and 42 the enhanced horizontal diffusion due to the interaction of the vertical diffusion and vertical shear of the wave field can be described by an effective horizontal diffusivity which is equal to the actual horizontal diffusivity plus a term equal to the mean square vertical shear of horizontal displacement times the vertical diffusivity provided the vertical length scale of the horizontal velocity field is not too small in the limit of small vertical length scale the expression reduces to taylor s 1953 result in which the effective horizontal diffusivity is inversely proportional to the actual vertical diffusivity the solutions also incidentally

a global analysis of sverdrup balance using absolute geostrophic velocities from argo using observations from the argo array of profiling floats the large scale circulation of the upper 2000 decibars db of the global ocean is computed for the period from december 2004 to november 2010 the geostrophic velocity relative to a reference level of 900db is estimated from temperature and salinity profiles and the absolute geostrophic velocity at the reference level is estimated from the trajectory data provided by the floats combining the two gives the absolute geostrophic velocity on 29 pressure surfaces spanning the upper 2000db of the global ocean these velocities together with satellite observations of wind stress are thenusedtoevaluatesverdrupbalance thesimplecanonicaltheoryrelatingmeridionalgeostrophictransport to wind forcing observed transports agree well with predictions based on the wind field over large areas primarily in the tropics and subtropics elsewhere especially at higher latitudes and in boundary regions sverdrup balance does not accurately describe meridional geostrophic transports possibly due to the increased importance of the barotropic flow nonlinear dynamics and topographic influence thus while it provides an effective framework for understanding the zero order wind driven circulation in much of the global ocean sverdrup balance should not be regarded as axiomatic

robustness of an effective diffusivity diagnostic in oceanic flows the robustness of nakamura s effective diffusivity diagnostic for quantifying eddy diffusivities of tracers within a streamwise average framework is carefully examined in an oceanographic context and the limits of its applicability are detailed the near surface southern ocean geostrophic flow obtained from altimetric observations is chosen for particular examination since it exhibits strong eddy activity careful analysis indicates that the effective diffusivity calculation is not strongly sensitive to the resolution of the velocity field or to the tracer initial conditions after a spinup time of 3 months and that a numerical diffusivity of 50 m 2 s 21 is appropriate to resolve the batchelor scale at a computational resolution of 1 208 the spatial variability of the effective diffusivity is examined and shown to be related to the eddy kinetic energy eke mean zonal current u and phase speed of the eddies c following the streamwise averge of eke u 2 c 2 in agreement with linear baroclinic instability theory the temporal variability of the effective diffusivity over the period 1996 2001 indicates significant variability on seasonal time scales with a magnitude of 610 215 interannual variations are investigated and discussed in the context of changes in the wind stress associated with the southern annular mode

interpretation of the propagation of surface altimetric observations in terms of planetary waves and geostrophic turbulence 1 the interpretation of surface altimetric signals in terms of rossby waves is revisited rather than make the long wave approximation the horizontal scale of the waves is adjusted to optimally fit the phase speed predicted by linear theory to that observed by altimetry assuming a first baroclinic mode vertical structure it is found that in the tropical band the observations can be fit if the wavelength of the waves is assumed to be large of order 600 km or so however poleward of 30 it is more difficult to fit linear theory to the observations and the fit is less good than at lower latitudes the required scale of the waves must be reduced to about 100 km somewhat larger than the local deformation wavelength it is argued that these results can be interpreted in terms of rossby wave baroclinic instability and turbulence theory at low latitudes there is an overlap between geostrophic turbulence and rossby wave timescales and so an upscale energy transfer from baroclinic instability at the deformation scale produces waves at high latitudes there is no such overlap and waves are not produced by upscale energy transfer these ideas are tested by using surface drifter data to infer turbulent velocities and timescales that are compared to those of linear rossby waves a transition from a field dominated by waves to one dominated by turbulence occurs at about 30 broadly consistent with the transition that is required to fit linear theory to altimetric observations

isopycnal diffusivities in the antarctic circumpolar current inferred from lagrangian floats in an eddying model average 750 250 m 2 s 1 around the polar frontal zone the results imply that parameterizations that only use eddy kinetic energy to parameterize the diffusivities are incomplete we suggest that dominant correlations of lagrangian eddy diffusivities with eddy kinetic energy found in previous studies may have been due to the use of too short time lags in the integration of the velocity autocovariance used to infer the diffusivities we find evidence that strong mean flow inhibits cross stream mixing within the acc but there are also areas where cross stream diffusivities are large in spite of strong mean flows for example in regions close to topographic obstacles such as the kerguelen plateau

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

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

the gortian temperate stage abstract interglacial sediments assigned to the gortian temperate stage are recorded at eleven sites throughout ireland but they remain undated by absolute means however the unique vegetational assemblages found within the gortian appear to belong to the middle pleistocene on biostratigraphic grounds the gortian vegetational records are reviewed and a summary of the possible age of the interglacial is presented along with recent work that has been carried out on stratigraphically important sites within ireland

subtropical surface layer salinity budget and the role of mesoscale turbulence the subtropical north atlantic exhibits the saltiest surface waters of the open ocean eventually that water subducted from the surface and exported toward the equator as a subsurface salinity maximum s max forming the lower limb of the subtropical cell climatologically the winter subtropical surface water coinciding with the deepest mixed layer of 100 m is saltier and colder than the s max towed ctd measurements in march april 2013 a component of the field program spurs within the north atlantic subtropical surface salinity maximum reveal several relatively fresh warm anomalies which deviate strongly from climatological conditions these features introduce a large amount of freshwater into the subtropical region exceeding the amount introduced by local rain events observed scales and evolution of the features strongly suggest a connection to mesoscale dynamics this is supported by high resolution regional model output which produces an abundance of features that are similar in scale and structure to those observed it is hypothesized that turbulent transport in the surface ocean is a crucial process for setting mixed layer characteristics which spread into s max stratum high variability in the eke implies a high potential for interannual variability in the resulting s max water properties by ocean dynamics in addition to the variability caused by air sea fluxes this has likely consequences to the meridional transport of heat and freshwater of the subtropical cell in the north atlantic and to the larger scale ocean and climate system

eddy stirring and horizontal diffusivity from argo float observations geographic and depth variability stirring along isopycnals is a significant factor in determining the distribution of tracers within the ocean salinity anomalies on density surfaces from argo float profiles are used to investigate horizontal stirring and estimate eddy mixing lengths eddy mixing length and velocity fluctuations from the ecco2 global state estimate are used to estimate horizontal diffusivity at a 300 km scale in the upper 2000 m with near global coverage diffusivity varies by over two orders of magnitude with latitude longitude and depth in all basins diffusivity is elevated in zonal bands corresponding to strong current regions including western boundary current extension regions the antarctic circumpolar current and equatorial current systems the estimated mixing lengths and diffusivities provide an observationally based data set that can be used to test and constrain predictions and parameterizations of eddy stirring

re evaluation of the middle pleistocene stratigraphy of herefordshire england lithostratigraphical analysis of remnants of high level poorly sorted gravel remnants in northeast herefordshire has allowed the revision and expansion of the existing regional middle pleistocene stratigraphical sequence to incorporate two new formations the oldest pleistocene sediments in the region the humber formation represents part of a major northerly derived cold stage fluvial system which incorporated the ancestors of the rivers lugg and wye and tributaries of the severn the risbury formation consists of glacigenic sediments which were deposited by a large ice lobe emanating from a welsh ice cap the risbury formation is correlated with glacigenic deposits in the cradley brook valley on the west side of the malvern hills which were formerly ascribed to a pre hoxnian severn valley ice sheet 1998 john wiley sons ltd

a synoptic and statistical description of the gulf stream and subtropical gyre using sofar floats abstract trajectories of 17 sofar floats ballasted to nominal depth of 700 and 2000 m and tracked for 15 months have been analyzed to produce synoptic and statistical descriptions of the gulf stream and subtropical gyre sofar floats launched in and near the gulf stream along with positions of the surface gulf stream and satellite tracked buoys demonstrate strong baroclinic shear nevertheless the horizontal patterns of the gulf stream meanders and gulf stream rings are the same at the surface and at 700 and 2000 m depth above the thermocline particle speeds greater than the propagation speed of the meanders cause parcels of water to move with the flow pattern at greater depths the velocities are at most equal to the propagation speed and the deep trajectories are free to pass through the gulf stream or ring strong temporal variability is found near the tail of the grand banks instances of flow both southward into a narrow gulf stream recirculation and northward into the north atlantic current can

stirring in the global surface ocean 1 global variations of stirring in the surface ocean are quantified using finite time lyapunov exponents ftles calculated from currents derived from satellite altimetry it is shown that the stirring is highly non uniform and the probability distribution functions pdfs of the ftles are broad asymmetric and have long high stretch tails the characteristics of the pdfs vary with mesoscale activity and integration time there are larger values and broader pdfs in regions of high strain rates and eddy kinetic energy eke e g western boundary currents and the antarctic circumpolar current and for shorter integration times the pdfs have a near universal relationship with the mean strain of a region and are reasonably well fit by weibull distributions the above variations in the stirring may help our understanding of the distribution and spatial heterogeneities of biogeochemical tracers and raise the possibility of developing a parameterization of the stirring based on the easily calculated eke

the fate of water within earth and super earths and implications for plate tectonics the earth is likely to have acquired most of its water during accretion internal heat of planetesimals by short lived radioisotopes would have caused some water loss but impacts into planetesimals were insufficiently energetic to produce further drying water is thought to be critical for the development of plate tectonics because it lowers viscosities in the asthenosphere enabling subduction the following issue persists if water is necessary for plate tectonics but subduction itself hydrates the upper mantle how is the upper mantle initially hydrated the giant impacts of late accretion created magma lakes and oceans which degassed during solidification to produce a heavy atmosphere however some water would have remained in the mantle trapped within crystallographic defects in nominally anhydrous minerals in this paper we present models demonstrating that processes associated with magma ocean solidification and overturn may segregate sufficient quantities of water within the upper mantle to induce partial melting and produce a damp asthenosphere thereby facilitating plate tectonics and in turn the habitability of earth like extrasolar planets this article is part of the themed issue the origin history and role of water in the evolution of the inner solar system

robust and nonrobust aspects of atlantic meridional overturning circulation variability and mechanisms in the community earth system model abstractrobust and nonrobust aspects of atlantic meridional overturning circulation amoc variability and mechanisms are analyzed in several 600 yr simulations with the community earth system mode

some expectations for submesoscale sea surface height variance spectra abstractin anticipation of the surface water and ocean topography swot wide swath altimetry mission this study reviews expectations for sea surface height ssh variance spectra at wavelengths o

understanding the origin and evolution of water in the moon through lunar sample studies a paradigm shift has recently occurred in our knowledge and understanding of water in the lunar interior this has transpired principally through continued analysis of returned lunar samples using modern analytical instrumentation while these recent studies have undoubtedly measured indigenous water in lunar samples they have also highlighted our current limitations and some future challenges that need to be overcome in order to fully understand the origin distribution and evolution of water in the lunar interior another exciting recent development in the field of lunar science has been the unambiguous detection of water or water ice on the surface of the moon through instruments flown on a number of orbiting spacecraft missions considered together sample based studies and those from orbit strongly suggest that the moon is not an anhydrous planetary body as previously believed new observations and measurements support the possibility of a wet lunar interior and the presence of distinct reservoirs of water on the lunar surface furthermore an approach combining measurements of water abundance in lunar samples and its hydrogen isotopic composition has proved to be of vital importance to fingerprint and elucidate processes and source s involved in giving rise to the lunar water inventory a number of sources are likely to have contributed to the water inventory of the moon ranging from primordial water to meteorite derived water ice through to the water formed during the reaction of solar wind hydrogen with the lunar soil perhaps two of the most striking findings from these recent studies are the revelation that at least some portions of the lunar interior are as water rich as some mid ocean ridge basalt source regions on earth and that the water in the earth and the moon probably share a common origin

evidence for enhanced eddy mixing at middepth in the southern ocean abstract satellite altimetric observations of the ocean reveal surface pressure patterns in the core of the antarctic circumpolar current acc that propagate downstream eastward but slower than the mean surface current by about 25 the authors argue that these observations are suggestive of baroclinically unstable waves that have a steering level at a depth of about 1 km detailed linear stability calculations using a hydrographic atlas indeed reveal a steering level in the acc near the depth implied by the altimetric observations calculations using a nonlinear model forced by the mean shear and stratification observed close to the core of the acc coinciding with a position where mooring data and direct eddy flux measurements are available reveal a similar picture albeit with added details when eddy fluxes are allowed to adjust the mean state computed eddy kinetic energy and eddy stress are close to observed magnitudes with steering levels between 1 and 1 5 km broadly consistent with observatio

pattern and velocity of propagation of the global ocean eddy variability 1 satellite altimeter data are used to study the characteristics of the horizontal propagation of eddy variability of the global oceans decade long time series of sea surface height is analyzed for finding the maximum cross correlation with neighboring time series within a window of space and time lags the space and time lags corresponding to the maximum correlation allow an estimate of the propagation velocity of the eddy variability that dominates the variance of sea surface height anomalies the method cannot distinguish the various forms of eddy variability isolated eddies and fronts the meandering of ocean currents or planetary waves however the results provide at a given location of the global oceans a uniquely determined propagation velocity that represents a time averaged description of the tendency of the movement of the local eddy variability the propagation velocity is highly inhomogeneous in space outside the equatorial zone the zonal propagation is intrinsically westward modified by ocean currents which could reverse the zonal propagation to eastward in regions like the gulf stream and the antarctic circumpolar current at midlatitudes and high latitudes the propagation pattern is highly affected by the path of ocean currents and the shape of bottom topography at tropical latitudes the meridional propagation is convergent toward the equator in the western basins and divergent away from the equator in the eastern basins comparison with the simulations of an eddy permitting ocean general circulation model shows overall agreement especially in the latitudinal variation of the zonal propagation velocity the result suggests that the model has captured the essence of the dynamics governing the propagation of ocean eddy variability

seasonality of surface stirring by geostrophic flows in the bay of bengal abstract stirring of passive tracers in the bay of bengal driven by altimetry derived daily geostrophic surface currents is studied on subseasonal timescales to begin with hovmoller plots wavenumber frequency diagrams and power spectra confirm the multiscale nature of the flow advection of latitudinal and longitudinal bands highlights the chaotic nature of stirring in the bay via repeated straining and filamentation of the tracer field an immediate finding is that stirring is local i e of the scale of the eddies and does not span the entire basin further stirring rates are enhanced along the coast of the bay and are relatively higher in the pre and post monsoonal seasons indeed finite time lyapunov exponent ftle and finite size lyapunov exponent fsle maps in all the seasons are patchy with minima scattered through the interior of the bay further these maps bring out a seasonal cycle wherein rapid stirring progressively moves from the northern to southern bay during pre and post monsoonal periods respectively the non uniform stirring of the bay is reflected in long tailed probability density functions of ftles that become more stretched for longer time intervals quantitatively advection for a week shows the mean ftle lies between 0 13 0 07 day 1 while extremes reach almost 0 6 day 1 averaged over the bay relative dispersion initially grows exponentially followed by a power law at scales between approximately 100 and 250 km which finally transitions to an eddy diffusive regime quantitatively below 250 km a scale dependent diffusion coefficient is extracted that behaves as a power law with cluster size while above 250 km eddy diffusivities range from 6 10 3 1 6 10 4 m2s 1 in different regions of the bay these estimates provide a useful guide for resolution dependent diffusivities in numerical models that hope to properly represent surface stirring in the bay

eddy induced particle dispersion in the near surface north atlantic abstractthis study investigates the anisotropic properties of the eddy induced material transport in the near surface north atlantic from two independent datasets one simulated from the sea surface height altimetry and one derived from real ocean surface drifters and systematically examines the interactions between the mean and eddy induced material transport in the region the lagrangian particle dispersion which is widely used to characterize the eddy induced tracer fluxes is quantified by constructing the spreading ellipses the analysis consistently demonstrates that this dispersion is spatially inhomogeneous and strongly anisotropic the spreading is larger and more anisotropic in the subtropical than in the subpolar gyre and the largest ellipses occur in the gulf stream vicinity even at times longer than half a year the spreading exhibits significant nondiffusive behavior in some parts of the domain the eddies in this study are defined as deviations from the long term time mean the contr

horizontal mixing in the southern ocean from argo float trajectories we provide the first observational estimate of the circumpolar distribution of cross stream eddy diffusivity at 1000 m in the southern ocean using argo float trajectories we show that argo float trajectories from the float surfacing positions can be used to estimate lateral eddy diffusivities in the ocean and that these estimates are comparable to those obtained from rafos floats where they overlap using the southern ocean state estimate sose velocity fields to advect synthetic particles with imposed behavior that is argo like and rafos like diffusivity estimates from both sets of synthetic particles agreed closely at the three dynamically very different test sites the kerguelen island region the southeast pacific ocean and the scotia sea and support our approach observed cross stream diffusivities at 1000 m calculated from argo float trajectories ranged between 300 and 2500 m2 s 1 with peaks corresponding to topographic features associated with the scotia sea the kerguelen plateau the campbell plateau and the southeast pacific ridge these observational estimates agree with previous regional estimates from the diapycnal and isopycnal mixing experiment in the southern ocean dimes near the drake passage and other estimates from natural tracers helium inverse modeling studies and current meter measurements these estimates are also compared to the suppressed eddy diffusivity in the presence of mean flows the comparison suggests that away from regions of strong topographic steering suppression explains both the structure and magnitude of eddy diffusivity but that eddy diffusivities in the regions of topographic steering are greater than what would be theoretically expected and the acc experiences localized enhanced cross stream mixing in these regions

the search for and analysis of direct samples of early solar system aqueous fluids we describe the current state of the search for direct surviving samples of early inner solar system fluids fluid inclusions in meteorites meteoritic aqueous fluid inclusions are not rare but they are very tiny and their characterization is at the state of the art for most analytical techniques meteoritic fluid inclusions offer us a unique opportunity to study early solar system brines in the laboratory inclusion by inclusion analyses of the trapped fluids in carefully selected samples will in the immediate future provide us detailed information on the evolution of fluids as they interacted with anhydrous solid materials thus real data can replace calculated fluid compositions in thermochemical calculations of the evolution of water and aqueous reactions in comets asteroids moons and the terrestrial planets this article is part of the themed issue the origin history and role of water in the evolution of the inner solar system

water mass and biogeochemical variability in the kerguelen sector of the southern ocean a machine learning approach for a mixing hot spot author s rosso isabella mazloff matthew r talley lynne d purkey sarah g freeman natalie m maze guillaume

global observations of horizontal mixing from argo float and surface drifter trajectories mixing by mesoscale eddies in the ocean plays a major role in setting the distribution of oceanic tracers with important implications for physical and biochemical systems at local to global scales roach et al 2016 https doi org 10 1002 2015jc011440 demonstrated that a two particle analysis of argo trajectories produces robust estimates of horizontal mixing in the southern ocean here we extend this analysis to produce global 1 1 maps of eddy diffusivity at the nominal argo parking depth of 1 000 m we also applied this methodology to estimate surface eddy diffusivities from global drifter program gdp surface drifters the global mean eddy diffusivity was 543 155 m2 s at 1 000 m and 2637 311 m2 s at the surface with elevated diffusivities in regions of enhanced eddy kinetic energy such as western boundary currents and along the antarctic circumpolar current the eddy kinetic energy at the equator is high at both the surface and depth but the eddy diffusivity is only enhanced near the surface at depth the eddy diffusivity is strongly suppressed due to the presence of mean flow we used our observational estimates to test the validity of an eddy diffusivity parameterization that accounts for mixing suppression in the presence of zonal mean flows our results indicated that this parameterization generally agrees with the directly observed eddy diffusivities in the midlatitude and high latitude oceans