enhanced turbulence and energy dissipation at ocean fronts the ocean surface boundary layer mediates air sea exchange in the classical paradigm and in current climate models its turbulence is driven by atmospheric forcing observations at a 1 kilometer wide front within the kuroshio current indicate that the rate of energy dissipation within the boundary layer is enhanced by one to two orders of magnitude suggesting that the front rather than the atmospheric forcing supplied the energy for the turbulence the data quantitatively support the hypothesis that winds aligned with the frontal velocity catalyzed a release of energy from the front to the turbulence the resulting boundary layer is stratified in contrast to the classically well mixed layer these effects will be strongest at the intense fronts found in the kuroshio current the gulf stream and the antarctic circumpolar current all of which are key players in the climate system

quantifying upper ocean turbulence driven by surface waves 1 nearly all operational ocean models use air sea fluxes and the ocean shear and stratification to estimate upper ocean boundary layer mixing rates this approach implicitly parameterizes surface wave effects in terms of these inputs here we test this assumption using parallel experiments in a lake with small waves and in the open ocean with much bigger waves under the same wind stress and adjusting for buoyancy flux we find the mixed layer average turbulent vertical kinetic energy in the open ocean typically twice that in the lake the increase is consistent with models of langmuir turbulence in which the wave stokes drift and not wave breaking is the dominant mechanism by which waves energize turbulence in the mixed layer applying these same theories globally we find enhanced mixing and deeper mixed layers resulting from the inclusion of langmuir turbulence in the boundary layer parameterization especially in the southern ocean

a comparison of shear and buoyancy driven planetary boundary layer flows abstract planetary boundary layer pbl flows are known to exhibit fundamental differences depending on the relative combination of wind shear and buoyancy forces these differences are not unexpected in that shear instabilities occur locally while buoyancy force sets up vigorous thermals which result in nonlocal transport of heat and momentum at the same time these two forces can act together to modify the flow field in this study four large eddy simulations less spanning the shear and buoyancy flow regimes were generated two correspond to the extreme cases of shear and buoyancy driven pbls while the other two represent intermediate pbls where both forces are important the extreme cases are used to highlight and quantify the basic differences between shear and convective pbls in 1 flow structures 2 overall statistics and 3 turbulent kinetic energy tke budget distributions results from the two intermediate les cases are used to develop and verify a velocity scaling and a tke budget mode

surface wave effects on high frequency currents over a shelf edge bank abstractseveral acoustic doppler current profilers and vertical strings of temperature conductivity and pressure sensors deployed on and around the east flower garden bank efgb were used to examine surface wave effects on high frequency flows over the bank and to quantify spatial and temporal characteristic of these high frequency flows the efgb about 5 km wide and 10 km long is located about 180 km southeast of galveston texas and consists of steep slopes on southern and eastern sides that rise from water depths over 100 m to within 20 m of the surface three dimensional flows with frequencies ranging from 0 2 to 2 cycles per hour cph were observed in the mixed layer when wind speed and stokes drift at the surface were large these motions were stronger over the bank than outside the perimeter the squared vertical velocity w2 was strongest near the surface and decayed exponentially with depth and the e folding length of w2 was 2 times larger than that of stokes drift the 2 h averaged w2 i

intensification of ocean fronts by down front winds abstract many ocean fronts experience strong local atmospheric forcing by down front winds that is winds blowing in the direction of the frontal jet an analytic theory and nonhydrostatic numerical simulations are used to demonstrate the mechanism by which down front winds lead to frontogenesis when a wind blows down a front cross front advection of density by ekman flow results in a destabilizing wind driven buoyancy flux wdbf equal to the product of the ekman transport with the surface lateral buoyancy gradient destabilization of the water column results in convection that is localized to the front and that has a buoyancy flux that is scaled by the wdbf mixing of buoyancy by convection and ekman pumping suction resulting from the cross front contrast in vertical vorticity of the frontal jet drive frontogenetic ageostrophic secondary circulations ascs for mixed layers with negative potential vorticity the most frontogenetic ascs select a preferred cross front width and do not translate with

friction frontogenesis and the stratification of the surface mixed layer the generation and destruction of stratification in the surface mixed layer of the ocean is understood to result from vertical turbulent transport of buoyancy and momentum driven by air sea fluxes and stresses in this paper it is shown that the magnitude and penetration of vertical fluxes are strongly modified by horizontal gradients in buoyancy and momentum a classic example is the strong restratification resulting from frontogenesis in regions of confluent flow frictional forces acting on a baroclinic current either imposed externally by a wind stress or caused by the spindown of the current itself also modify the stratification by driving ekman flows that differentially advect density ekman flow induced during spindown always tends to restratify the fluid while wind driven ekman currents will restratify or destratify the mixed layer if the wind stress has a component up or down front i e directed against or with the geostrophic shear respectively scalings are constructed for the relative importance of friction versus frontogenesis in the restratification of the mixed layer and are tested using numerical experiments of mixed layer fronts forced by both winds and a strain field the scalings suggest and the numerical experiments confirm that for wind stress magnitudes mixed layer depths and cross front density gradients typical of the ocean wind induced friction often dominates frontogenesis in the modification of the stratification of the upper ocean the experiments reveal that wind induced destratification is weaker in magnitude than restratification because the stratification generated by up front winds confines the turbulent stress to a depth shallower than the ekman layer which enhances the frictional force ekman flow and differential advection of density frictional destratification is further reduced over restratification because the stress associated with the geostrophic shear at the surface tends to compensate a down front wind stress

modeling of the influence of sea ice cycle and langmuir circulation on the upper ocean mixed layer depth and freshwater distribution at the west antarctic peninsula

impacts of surface gravity waves on summer ocean dynamics in bohai sea abstract a one way coupled pomgcs swan model is applied to study the impacts of three wave processes i e langmuir turbulence coriolis stokes forcing csf and resolved scale craik leibovich vortex forcing clvf on ocean dynamics in bohai sea in summer both csf and clvf are included in the horizontal momentum equation the level 2 5 mellor yamada turbulence closure scheme is modified to contain the parameterization of langmuir turbulence numerical results show that this improved model reproduces the sea surface temperature sst better than the original one all of these wave effects considerably contribute to temperature variability at different vertical levels with the maximum temperature change of about 0 4 c based on the diagnostic experiments the impacts of the csf and clvf are much weaker than that of langmuir turbulence those wave processes reduce the current velocity and make the current more vertically uniform the horizontal distribution of langmuir number indicates that the langmuir turbulence is prevalent in bohai sea the large vertical kinematic viscosity coefficients containing the langmuir turbulence would lead to a strong vertical mixing

observations and simulations of upper ocean response to wind events during the ocean storms experiment abstract the ocean storms dataset is used to compile observations of the oceanic response to midlatitude storms of particular interest are episodic mixed layer temperature cooling events whose characteristics are reviewed the data include subsurface temperatures from drifting thermistor chains mixed layer temperature and velocity from mixed layer drifters conductivity temperature depth profiles and radiation measurements from ships and the surface meteorological parameters produced by the european centre for medium range weather forecasts a method for processing irregular drifting buoy position fixes to yield estimates of the geostrophic ageostrophic and inertial mixed layer currents is developed and shown to yield residuals that can mostly be attributed to errors in the positioning from these currents the ocean s dynamic responses namely the change in mixed layer inertial kinetic energy and the ageostrophic particle displacement are computed the process of removing horizontal and vertical a

surface mixed layer deepening through wind shear alignment in a seasonally stratified shallow sea inertial oscillations are a ubiquitous feature of the surface ocean here we combine new observations with a numerical model to investigate the role of inertial oscillations in driving deepening of the surface mixed layer in a seasonally stratified sea observations of temperature and current structure from a mooring in the western irish sea reveal episodes of strong currents 0 3 m s 1 lasting several days resulting in enhanced shear across the thermocline while the episodes of strong currents are coincident with windy periods the variance in the shear is not directly related to the wind stress the shear varies on a subinertial time scale with the formation of shear maxima lasting several hours occurring at the local inertial period of 14 85 h these shear maxima coincide with the orientation of the surface current being at an angle of approximately 90 to the right of the wind direction observations of the water column structure during windy periods reveal deepening of the surface mixed layer in a series of steps which coincide with a period of enhanced shear during the periods of enhanced shear gradient richardson number estimates indicate ri 1 4 at the base of the surface mixed layer implying the deepening as a result of shear instability a one dimensional vertical exchange model successfully reproduces the magnitude and phase of the shear spikes as well as the step like deepening the observations and model results therefore identify the role of wind shear alignment as a key entrainment mechanism driving surface mixed layer deepening in a shallow seasonally stratified sea

when mixed layers are not mixed storm driven mixing and bio optical vertical gradients in mixed layers of the southern ocean author s carranza mm gille st franks pjs johnson ks pinkel r girton jb abstract 2018 american geophysical union all rights reserved mixed layers are defined to have homogeneous density temperature and salinity however bio optical profiles may not always be fully homogenized within the mixed layer the relative timescales of mixing and biological processes determine whether bio optical gradients can form within a uniform density mixed layer vertical profiles of bio optical measurements from biogeochemical argo floats and elephant seal tags in the southern ocean are used to assess biological structure in the upper ocean within the hydrographically defined mixed layer the profiles show significant vertical variance in chlorophyll a chl a fluorescence and particle optical backscatter biological structure is assessed by fitting chl a fluorescence and particle backscatter profiles to functional forms i e gaussian sigmoid exponential and their combinations in the southern ocean which characteristically has deep mixed layers only 40 of nighttime bio optical profiles were characterized by a sigmoid indicating a well mixed surface layer of the remaining 60 that showed structure 40 had a deep fluorescence maximum below 20 m depth that correlated with particle backscatter furthermore a significant fraction of these deep fluorescence maxima were found within the mixed layer 20 80 depending on mixed layer depth definition and season results suggest that the timescale between mixing events that homogenize the surface layer is often longer than biological timescales of restratification we hypothesize that periods of quiescence between synoptic storms which we estimate to be 3 5 days depending on season allow bio optical gradients to develop within mixed layers that remain homogeneous in density

lagrangian investigation of wave driven turbulence in the ocean surface boundary layer abstractturbulent processes in the ocean surface boundary layer osbl play a key role in weather and climate systems this study explores a lagrangian analysis of wave driven osbl turbulence base

seasonality of submesoscale flows in the ocean surface boundary layer a signature of submesoscale flows in the upper ocean is skewness in the distribution of relative vorticity expected to result for high rossby number flows such skewness has implications for mixing dissipation and stratification within the upper ocean an array of moorings deployed in the northeast atlantic for one year as part of the osmosis experiment reveals that relative vorticity is positively skewed during winter even though the scale of the rossby number is less than 0 5 furthermore this skewness is reduced to zero during spring and autumn there is also evidence of modest seasonal variations in the gradient rossby number the proposed mechanism by which relative vorticity is skewed is that the ratio of lateral to vertical buoyancy gradients as summarized by the inverse gradient richardson number restricts its range during winter but less so at other times of the year these results support recent observations and model simulations suggesting the upper ocean is host to a seasonal cycle in submesoscale turbulence

cataclastic deformation mechanism for the development of core mantle structures in amphibole core mantle structures in mineral grains have typically been interpreted as having formed during crystal plastic deformation optical scanning electron and transmission electron microscope investigations of what appear to be core mantle structures in amphibole from the cheyenne belt southeastern wyoming indicate that subgrainlike structures herein subgrains formed as a result of cataclastic rather than crystal plastic deformation optical and scanning electron microscope evidence to support a cataclastic origin include 1 the angular shape of subgrains with boundaries commonly parallel to 110 cleavage 2 the wide variety of subgrain sizes 3 the compositional zonation of the amphibole subgrains with actinolitic hornblende interiors overgrown by magnesio hornblende and 4 the observation that some of the undulatory extinction in porphyroclast cores is due to slip along cleavage planes whether dislocations observed in the amphibole grains were formed prior to cataclastic deformation work hardening or formed in response to crack propagation is unknown the implication of these observations is that core mantle structures in other minerals may at least in some cases have also formed during cataclastic deformation rather than during recovery and or recrystallization therefore optical identification of core mantle structures is not a priori evidence for a crystal plastic deformation mechanism

large eddy simulations and observations of atmospheric marine boundary layers above nonequilibrium surface waves abstract winds and waves in marine boundary layers are often in an unsettled state when fast running swell generated by distant storms propagates into local regions and modifies the overlying turbulent fields a large eddy simulation les model with the capability to resolve a moving sinusoidal wave at its lower boundary is developed to investigate this low wind fast wave regime it is used to simulate idealized situations with wind following and opposing fast propagating waves swell and stationary bumps les predicts momentum transfer from the ocean to the atmosphere for wind following swell and this can greatly modify the turbulence production mechanism in the marine surface layer in certain circumstances the generation of a low level jet reduces the mean shear between the surface layer and the pbl top resulting in a near collapse of turbulence in the pbl when light winds oppose the propagating swell turbulence levels increase over the depth of the boundary layer and the surface drag increases

toward a k profile parameterization of langmuir turbulence in shallow coastal shelves abstractinteraction between the wind driven shear current and the stokes drift velocity induced by surface gravity waves gives rise to langmuir turbulence in the upper ocean langmuir turbulence consists of langmuir circulation lc characterized by a wide range of scales in unstratified shallow water the largest scales of langmuir turbulence engulf the entire water column and thus are referred to as full depth lc large eddy simulations less of langmuir turbulence with full depth lc in a wind driven shear current have revealed that vertical mixing due to lc erodes the bottom log law velocity profile inducing a profile resembling a wake law furthermore in the interior of the water column two sources of reynolds shear stress turbulent nonlocal transport and local stokes drift shear production can combine to lead to negative mean velocity shear meanwhile near the surface stokes drift shear serves to intensify small scale eddies leading to enhanced vertical mixing and disruption of the surface

effect of planetary rotation on oceanic surface boundary layer turbulence abstracta large eddy simulation les model is configured to investigate the effect of the horizontal northward component of earth s rotation on upper ocean turbulence the focus is on the variab

abrupt transitions in submesoscale structure in southern drake passage glider observations and model results abstractenhanced vertical velocities associated with submesoscale motions may rapidly modify mixed layer depths and increase exchange between the mixed layer and the ocean interior these dynamics are of particular importance in the southern ocean where the ventilation of many density classes occurs here we present results from an observational field program in southern drake passage a region preconditioned for submesoscale instability due to its strong mesoscale eddy field persistent fronts strong down front winds and weak vertical stratification two gliders sampled from december 2014 through march 2015 upstream and downstream of shackleton fracture zone sfz the acquired time series of mixed layer depths and buoyancy gradients enabled calculations of potential vorticity and classifications of submesoscale instabilities the regions flanking the sfz displayed remarkably different characteristics despite similar surface forcing mixed layer depths were nearly twice as deep and horizontal buoyancy

evolution of oceanic near surface stratification in response to an autumn storm abstractunderstanding the processes that control the evolution of the ocean surface boundary layer osbl is a prerequisite for obtaining accurate simulations of air sea fluxes of heat and trace ga

parameterization of mixed layer eddies part i theory and diagnosis ageostrophic baroclinic instabilities develop within the surface mixed layer of the ocean at horizontal fronts and efficiently restratify the upper ocean in this paper a parameterization for the restratification driven by finite amplitude baroclinic instabilities of the mixed layer is proposed in terms of an overturning streamfunction that tilts isopycnals from the vertical to the horizontal the streamfunction is proportional to the product of the horizontal density gradient the mixed layer depth squared and the inertial period hence restratification proceeds faster at strong fronts in deep mixed layers with a weak latitude dependence in this paper the parameterization is theoretically motivated confirmed to perform well for a wide range of mixed layer depths rotation rates and vertical and horizontal stratifications it is shown to be superior to alternative extant parameterizations of baroclinic instability for the problem of mixed layer restratification two companion papers discuss the numerical implementation and the climate impacts of this parameterization

interaction of langmuir turbulence and inertial currents in the ocean surface boundary layer under tropical cyclones abstractbased on a large eddy simulation approach this study investigates the response of the ocean surface boundary layer osbl and langmuir turbulence lt to extreme wind and complex wave forc

a case study of air sea interaction during swell conditions air sea interaction data from a situation with pronounced unidirectional swell have been analyzed measurements of turbulence at three levels 10 18 and 26 m above mean sea level together with directional wave buoy data from the site ostergarnsholm in the baltic sea were used the situation which lasted for 48 hours appeared in the aftermath of a gale the wind direction during the swell situation turned slowly within a 90 sector both during the gale phase and the swell phase the over water fetch was 150 km the wind speed during the swell phase was typically 4 m s 1 during the swell phase a wind maximum near or below the lowest wind speed measuring level 10 m was observed the net momentum flux was very small resulting in cd values 0 7 10 3 throughout the lowest 26 m covered by the tower measurements turbulence intensities in all three components remained high despite the low value of the kinematic momentum flux u w resulting in a reduction of the correlation coefficient for the longitudinal and vertical velocity from its typical value around 0 35 to between 0 2 and 0 and with some positive values at the higher measuring levels appearing abruptly at wave age c0 u10 equal to 1 2 turbulence spectra of the horizontal components were shown not to scale with height above the water surface in contrast to vertical velocity spectra for which such a variation was observed in the low frequency range in addition spectral peaks in the horizontal wind spectra were found at a frequency as low as 10 3 hz from a comparison with results from a previous study it was concluded that this turbulence is of the inactive kind being brought down from the upper parts of the boundary layer by pressure transport

open ocean submesoscale motions a full seasonal cycle of mixed layer instabilities from gliders abstractthe importance of submesoscale instabilities particularly mixed layer baroclinic instability and symmetric instability on upper ocean mixing and energetics is well documented in regions of strong persistent fronts such as the kuroshio and the gulf stream less attention has been devoted to studying submesoscale flows in the open ocean far from long term mean geostrophic fronts characteristic of a large proportion of the global ocean this study presents a year long submesoscale resolving time series of near surface buoyancy gradients potential vorticity and instability characteristics collected by ocean gliders that provides insight into open ocean submesoscale dynamics over a full annual cycle the gliders continuously sampled a 225 km2 region in the subtropical northeast atlantic measuring temperature salinity and pressure along 292 short 20 km hydrographic sections glider observations show a seasonal cycle in near surface stratification throughout the fall september november

effect of maturity and petroleum expulsion on pyrrolic nitrogen compound yields and distributions in duvernay formation petroleum source rocks in central alberta canada abstract a quantitative study of pyrrolic nitrogen compounds was conducted on a series of marine carbonate petroleum source rock extracts taken from the upper devonian duvernay formation in the central alberta portion of the western canada sedimentary basin with increasing thermal maturity concentrations of various pyrrolic nitrogen compounds in the rock extracts increase drastically together with significant compositional variations related to alkyl substitution position the study provides circumstantial evidence for adsorptive interactions operating between organic nitrogen compounds and solid organic mineral phases in subsurface sedimentary rocks during petroleum generation and expulsion the absolute concentrations and relative distributions of pyrrolic nitrogen compounds in the extracts of different maturity ranges provide background information for the calibration of such data in migrated petroleums as an independent measurement of secondary oil migration range of duvernaysourced oils in the basin

diapycnal mixing in the antarctic circumpolar current the vertical dispersion of a tracer released on a density surface near 1500 m depth in the antarctic circumpolar current west of drake passage indicates that the diapycnal diffusivity averaged over 1 yr and over tens of thousands of square kilometers is 1 3 6 0 2 3 10 25 m 2 s 21 diapycnal diffusivity estimated from turbulent kinetic energy dissipation measurements about the area occupied by the tracer in austral summer 2010 was somewhat less but still within a factor of 2 at 0 75 6 0 07 3 10 25 m 2 s 21 turbulent diapycnal mixing of this intensity is characteristic of the midlatitude ocean interior where the energy for mixing is believed to derive from internal wave breaking indeed despite the frequent and intense atmospheric forcing experienced by the southern ocean the amplitude of finescale velocity shear sampled about the tracer was similar to background amplitudes in the midlatitude ocean with levels elevated to only 20 50 above the garrett munk reference spectrum these results add to a long line of evidence that diapycnal mixing in the interior middepth ocean is weak and is likely too small to dictate the middepth meridional overturning circulation of the ocean

mixed layer instabilities and restratification abstract the restratification of the oceanic surface mixed layer that results from lateral gradients in the surface density field is studied the lateral gradients are shown to be unstable to ageostrophic baroclinic instabilities and slump from the horizontal to the vertical these instabilities which are referred to as mixed layer instabilities mlis differ from instabilities in the ocean interior because of the weak surface stratification spatial scales are o 1 10 km and growth time scales are on the order of a day linear stability analysis and fully nonlinear simulations are used to study mlis and their impact on mixed layer restratification the main result is that mlis are a leading order process in the ml heat budget acting to constantly restratify the surface ocean climate and regional ocean models do not resolve the scales associated with mlis and are likely to underestimate the rate of ml restratification and consequently suffer from a bias in sea surface temperatures and ml depths in a

a global perspective on langmuir turbulence in the ocean surface boundary layer the turbulent mixing in thin ocean surface boundary layers osbl which occupy the upper 100 m or so of the ocean control the exchange of heat and trace gases between the atmosphere and ocean here we show that current parameterizations of this turbulent mixing lead to systematic and substantial errors in the depth of the osbl in global climate models which then leads to biases in sea surface temperature one reason we argue is that current parameterizations are missing key surface wave processes that force langmuir turbulence that deepens the osbl more rapidly than steady wind forcing scaling arguments are presented to identify two dimensionless parameters that measure the importance of wave forcing against wind forcing and against buoyancy forcing a global perspective on the occurrence of wave forced turbulence is developed using re analysis data to compute these parameters globally the diagnostic study developed here suggests that turbulent energy available for mixing the osbl is under estimated without forcing by surface waves wave forcing and hence langmuir turbulence could be important over wide areas of the ocean and in all seasons in the southern ocean we conclude that surface wave forced langmuir turbulence is an important process in the osbl that requires parameterization citation belcher s e et al 2012 a global perspective on langmuir turbulence in the ocean surface boundary layer geophys res lett 39 l18605 doi 10 1029 2012gl052932

organic matter characterization in mixed hydrocarbon producing areas within the duvernay formation western canada sedimentary basin alberta this paper characterizes organic matter in the mixed hydrocarbon oil dry gas oil condensate producing areas of the late devonian duvernay formation in alberta canada by high resolution rockeval data n 246 and petrography n 35 at three drillhole locations locations a and c distal location b proximal to leduc reef respectively total organic carbon toc ranges from 0 15 622 wt at location a 0 43 820 wt at location b and 1 84 5 23 wt at location c with an overall median value of 3 42 wt s2 values range from 0 20 7 42 mg hc g of rock at location a 022 4 23 mg hc g of rock at location b and 1 68 5 04 mg hc g of rock at location c these results for samples from locations a b and c indicate that kerogen is type i to type ii the hydrogen index hi of these rocks is significantly lower 160 mg hc g toc than that of traditional oil producing source rocks of this age similar to 400 700 mg hc g toc at locations a and c t max lies within the oil window with a mean value of 459 degrees c at location b t max varies greatly between 434 and 488 degrees c between the oil and gas window with no observable association with sample depth vitrinite reflectance of samples ranges from 0 99 1 32 t max values do not correlate with vitrinite reflectance of the samples r 2 0 04 nor with depth r 2 0 4 suggesting that t max is not a reliable indicator of thermal maturity in this system low toc s2 high mineral carbon is associated with intervals of intergrown sparry calcite and pyrite in petrographic samples at location b organic matter within the duvernay formation was characterized as almost entirely solid bitumens with very minor inertinite 1 by volume the rockeval and petrographic observations suggest that secondary diagenetic effects are the cause for the mixed hydrocarbon signature rather than any spatial variation in depositional environment or thermal maturation regimes c 2016 elsevier b v all rights reserved

lagrangian transport by nonbreaking and breaking deep water waves at the ocean surface abstractusing direct numerical simulations dns deike et al found that the wave breaking induced mass transport or drift at the surface for a single breaking wave scales linearly with the slop

rapid changes in mixed layer stratification driven by submesoscale instabilities and winds 1 submesoscale eddies generated by baroclinic instability of upper ocean fronts lead to rapid restratification of the mixed layer on a time scale of days this restratification can be opposed by a down front wind stress acting in the direction of the geostrophic velocity that drives a surface ekman flow from the dense side to the light side of the front to arrest the slumping of isopycnals a scaling diagnostic is suggested to determine whether the effect of eddies or wind dominates under different conditions using a numerical model we investigate the juxtaposition of submesoscale eddies and down front winds acting on the mixed layer by estimating the eddy induced overturning stream function in the mixed layer we separate the along and cross isopycnal fluxes of buoyancy associated with submesoscale mixed layer eddies and demonstrate the need for parameterization of the advective along isopycnal flux though the cross front transport of buoyancy induced by the down front component of the wind opposes restratification by mixed layer eddies it becomes diminished as the eddies and growth of the frontal instability disrupt alignment between the wind and frontal axis

an argo mixed layer climatology and database a global climatology and database of mixed layer properties are computed from nearly 1 250 000 argo profiles the climatology is calculated with both a hybrid algorithm for detecting the mixed layer depth mld and a standard threshold method the climatology provides accurate information about the depth properties extent and seasonal patterns of global mixed layers the individual profile results in the database can be used to construct time series of mixed layer properties in specific regions of interest the climatology and database are available online at http mixedlayer ucsd edu the mlds calculated by the hybrid algorithm are shallower and generally more accurate than those of the threshold method particularly in regions of deep winter mixed layers the new climatology differs the most from existing mixed layer climatologies in these regions examples are presented from the labrador and irminger seas the southern ocean and the north atlantic ocean near the gulf stream in these regions the threshold method tends to overestimate winter mlds by approximately 10 compared to the algorithm

effects of swell on transport and dispersion of oil plumes within the ocean mixed layer the transport in the ocean mixed layer oml of oil plumes originated from deepwater blowouts is studied using large eddy simulations in particular we focus on the effects of swell on the modulation of turbulence in the oml and its impact on oil transport results show that when the misalignment between the wind and the swell propagation is small langmuir cells develop and significantly enhance the vertical dilution of the oil plume conversely when the misalignment is large vertical dilution is suppressed when compared to the no swell case due to the strong directional shear of the mean flow within the oml plume depth significantly impacts mean transport direction the size of oil droplets in the plume also plays an important role in vertical dilution and mean transport direction

a mechanism of mixed layer formation in the indo western pacific southern ocean preconditioning by an eddy driven jet scale overturning circulation abstractthe formation of a narrow band of the deep winter mixed layer hereinafter mixed layer wedge in the indo western pacific southern ocean is examined using an eddy resolving parallel ocean program pop model simulation the mixed layer wedge starts to deepen in june centered at 47 5 s with a meridional scale of only 2 latitude its center is located 1 north of the model s subantarctic front saf the argo based observed mixed layer is similarly narrow and occurs adjacent to the observed saf in the small sector of 130 142 e where the saf is persistent and the mixed layer is deepest the formation of the narrow mixed layer wedge coincides with destratification underneath the mixed layer this destratification can be attributed primarily to the downwelling branch of a jet scale overturning circulation jsoc the jsoc which was reported in an earlier study by the authors is driven by eddy momentum flux convergence and is therefore thermally indirect its descending branch occurs on the

similarity theory in the surface layer of large eddy simulations of the wind wave and buoyancy forced southern ocean abstractmonin obukhov similarity theory is applied to the surface layer of large eddy simulations les of deep southern ocean boundary layers observations from the southern ocean flux station pro

global estimates of lateral springtime restratification abstractsubmesoscale frontal dynamics are thought to be of leading order importance for stratifying the upper ocean by slumping horizontal density gradients to produce vertical stratification presented here is an investigation of submesoscale instabilities in the mixed layer mixed layer eddies mles as a potential mechanism of frontal slumping that stratifies the upper ocean during the transition from winter to spring when wintertime forcings weaken but prior to the onset of net solar warming observations from the global argo float program are compared to predictions from a one dimensional mixed layer model to assess where in the world s oceans lateral processes influence mixed layer evolution the model underestimates spring stratification for 75 25 of the world s oceans relationships between vertical and horizontal temperature and salinity gradients are used to suggest that in 30 20 of the oceans this excess stratification can be attributed to the slumping of horizontal density fronts fin

southern ocean mixed layer depth from argo float profiles 1 argo float profiles of temperature salinity and pressure are used to derive the mixed layer depth mld in the southern ocean mld is determined from individual profiles using both potential density and potential temperature criteria and a monthly climatology is derived from individual mlds using an objective mapping method quantitative data are available in the auxiliary material the spatial structures of mlds are similar in each month with deep mixed layers within and just north of the antarctic circumpolar current acc in the pacific and indian oceans the deepest mixed layers are found from june to october and are located just north of the acc where antarctic intermediate water aaiw and subantarctic mode water samw are formed examination of individual mlds indicates that deep mixed layers mld 400 m from both the density and temperature criteria are concentrated in a narrow surface density band which is within the density range of samw the surface salinity for these deep mixed layers associated with the samw formation are slightly fresher compared to historical estimates differences in air sea heat exchanges wind stress and wind stress curl in the pacific and indian oceans suggest that the mode water formation in each ocean basin may be preconditioned by different processes wind mixing and ekman transport of cold water from the south may assist the samw formation in the indian ocean in the eastern pacific the formation of mode water is potentially preconditioned by the relative strong cooling and weak stratification from upwelling

petrographic and isotope constraints on the origin of authigenic carbonate minerals and the associated fluid evolution in late permian coal measures bowen basin queensland australia authigenic carbonate minerals are ubiquitous throughout the late permian coal measures of the bowen basin queensland australia in the northern bowen basin carbonates include the following assemblages siderite i delta o 18 smow 11 4 to 17 delta c 13 pdb 5 3 to 120 fe mg calcite ankerite siderite ii mineral association delta o 18 smow 7 2 to 10 20 delta c 13 pdb 10 9 to 1 80 for ankerite and a later calcite delta o 18 smow 5 9 to 14 60 delta c 13 pdb 11 4 to 4 40 in the southern bowen basin the carbonate phase consists only of calcite delta o 18 smow 12 5 to 14 80 delta c 13 pdb 19 4 to 0 80 where it occurs extensively throughout all stratigraphic levels siderite i occurs in mudrocks and sandstones and predates all other carbonate minerals this carbonate phase is interpreted to have formed as an early diagenetic mineral from meteoric waters under cold climate and reducing conditions fe mg calcite ankerite siderite il occur in sandstones as replacement of volcanic rock fragments clay minerals illite smectite chlorite and kaolinite postdate ca fe mg carbonates and precipitation of the later calcite is associated with clay mineral formation the ca fe mg carbonates and later calcite of the northern bowen basin are regarded as having formed as a result of hydrothermal activity during the latest triassic extensional tectonic event which affected this part of the basin rather than deep burial diagenesis during the middle to late triassic as previously reported this hypothesis is based on the timing relationships of the authigenic mineral phases and the low delta o 18 values of ankerite and calcite together with radiometric dating of illitic clays and recently published regional geological evidence following the precipitation of the ca fe mg carbonates from strongly o 18 depleted meteoric hydrothermal fluids continuing fluid circulation and water rock interaction resulted in dissolution of these carbonate phases as well as labile fragments of volcaniclastic rocks subsequently the later calcite and day minerals precipitated from relatively evolved o 18 enriched fluids the nearly uniform delta o 18 values of the southern bowen basin calcite have been attributed to very low water rock ratio in the system where the fluid isotropic composition was buffered by the delta o 18 values of rocks c 2000 elsevier science b v all rights reserved

nonlocal transport and implied viscosity and diffusivity throughout the boundary layer in les of the southern ocean with surface waves abstractobservations from the southern ocean flux station provide a wide range of wind buoyancy and wave stokes forcing for large eddy simulation les of deep southern ocean boundary layers a

wave induced transport and vertical mixing of pelagic eggs and larvae the transport of pelagic plankton by wind driven ocean currents and surface gravity waves is investigated for the example of northeast arctic cod eggs and larvae on the coast of northern norway previous studies indicate that the wave induced drift i e stokes drift is relevant for the transport of particles in the upper ocean we use an ocean general circulation model together with a numerical wave prediction model and a lagrangian particle tracking model to calculate trajectories of fish eggs and larvae waves are considered not only for particle drift but also for the air sea momentum flux its contribution to the coriolis force and vertical mixing the sample species provides the advantage that many of its physical and behavioral properties are well known e g egg buoyancy allowing investigation of vertical particle displacement by turbulent mixing in response to wind forcing and wave breaking the approach accounting for particle mixing by breaking waves enhances agreement between observed and modeled egg profiles results also show a general shoreward transport of particles by the stokes drift this wave drift exhibits a more constant direction than the eulerian current and hence stabilizes particle diffusion to favor a dominant direction for the case of northeast arctic cod waves concentrated model eggs and larvae on average 1 5 km closer to shore which is 20 of their total distance to the coast this increases the residence time of first feeding larvae close to the spawning areas compared to earlier models

the gulf of mexico ecosystem six years after the macondo oil well blowout abstract the gulf of mexico ecosystem is a hotspot for biological diversity and supports a number of industries from tourism to fishery production to oil and gas exploration that serve as the economic backbone of gulf coast states the gulf is a natural hydrocarbon basin rich with stores of oil and gas that lie in reservoirs deep beneath the seafloor the natural seepage of hydrocarbons across the gulf system is extensive and thus the system s biological components experience ephemeral if not frequent hydrocarbon exposure in contrast to natural seepage which is diffuse and variable over space and time the 2010 macondo oil well blowout represented an intense focused hydrocarbon infusion to the gulf s deepwaters the macondo blowout drove rapid shifts in microbial populations and activity revealed unexpected phenomena such as deepwater hydrocarbon plumes and marine oil snow sedimentation and impacted the gulf s pelagic and benthic ecosystems understanding the distribution and fate of macondo oil was limited to some degree by an insufficient ability to predict the physical movement of water in the gulf in other words the available physical oceanographic models lacked critical components in the past six years much has been learned about the physical oceanography of the gulf providing transformative knowledge that will improve the ability to predict the movement of water and the hydrocarbons they carry in future blowout scenarios similarly much has been learned about the processing and fate of macondo hydrocarbons here we provide an overview of the distribution fate and impacts of macondo hydrocarbons and offer suggestions for future research to push the field of oil spill response research forward