near inertial internal wave field in the canada basin from ice tethered profilers abstractsalinity and temperature profiles from drifting ice tethered profilers in the beaufort gyre region of the canada basin are used to characterize and quantify the regional near inertial internal wave field over one year vertical displacements of potential density surfaces from the surface to 750 m depth are tracked from fall 2006 to fall 2007 because of the time resolution and irregular sampling of the ice tethered profilers near inertial frequency signals are marginally resolved complex demodulation is used to determine variations with a time scale of several days in the amplitude and phase of waves at a specified near inertial frequency characteristics and variability of the wave field over the course of the year are investigated quantitatively and related to changes in surface wind forcing and sea ice cover

magmatic evolution of the eastern coast plutonic complex bella coola region west central british columbia the eastern coast plutonic complex in west central british columbia 51 54 n consists of a broad belt of jurassic to eocene granitic to dioritic intrusive rocks that collectively represent more than 140 m y of nearly continuous subduction related magmatism seven distinct intrusive suites have been identified in the bella coola region including from oldest to youngest the howe lake stick pass firvale desire fougner big snow and four mile suites pre late cretaceous rocks were produced by episodic subduction related magmatism characterized by partial melting of preexisting lower arc crust with minimal incorporation of evolved continental material the eastern coast plutonic complex experienced a magmatic lull between ca 110 and 95 ma coincident with sinistral transpression potentially linked to translational displacement of the wrangellia alexander composite terranes crustal thickening in late cretaceous time ca 100 90 ma possibly due to underplating of the wrangellia alexander terrane produced a deep crustal root 40 km that likely extended into the eclogite transition zone adakitic magmas ca 95 67 ma were produced by partial melting of an amphibolitic protolith in this thickened lower arc crust adakitic plutons are pre syn and postkinematic with respect to late cretaceous high angle shear zones and they are coeval and spatially associated with postkinematic two mica granites ca 70 75 ma having a hybrid a type geochemistry we suggest that delamination of this dense crustal root led to voluminous magmatism extension and crustal exhumation in paleocene eocene time the successive intrusive events in the eastern coast plutonic complex may reflect a predictable evolutionary progression common to all continental arc systems

fluid and sediment dynamics of upper stage plane beds to understand more fully the fluid and sediment dynamics of upper stage plane beds laboratory experiments were conducted using mobile and fixed beds where turbulent motions of fluid and sediment were measured using laser anemometry bed elevation fluctuations on mobile upper stage plane beds reveal millimeter high bed waves vertical profiles of flow velocity mixing length and eddy viscosity diffusivity are represented well by the law of the wall for the mobile bed von karman s 0 33 and equivalent sand roughness to mean bed grain size varies from 9 to 17 because of the presence of bed load and low relief bed waves for fixed beds with no sediment transport 0 41 and equivalent sand roughness is equal to the mean bedgrain size the decrease in for mobile beds is related to the relative motion of grains and fluid mobile bed turbulence intensities are greater than those for sediment free fixed beds because of enhanced wake formation from the lee side of near bed grains and low relief bed waves sediment diffusivities es calculated in a similar way to fluid diffusivities e indicate that es e sediment diffusivities calculated using the equilibrium balance between upward diffusion and downward settling of sediment are similar to e in near bed regions y d 0 3 suggesting that larger more energetic turbulent eddies are responsible for sediment suspension higher in the flow

thermal history of the ecstall pluton from 40ar 39ar geochronology and thermal modeling abstract new 40ar 39ar thermochronology results and thermal modeling support the hypothesis of hollister et al 2004 that reheating of the mid cretaceous ecstall pluton by intrusion of the coast mountains batholith cmb was responsible for spatially variable remagnetization of the ecstall pluton 40ar 39ar ages from hornblende and biotite from 12 locations along the skeena river across the northern part of the ecstall pluton decrease with proximity to the quottoon plutonic complex the nearest member of the cmb to the ecstall pluton the oldest 40ar 39ar ages are found farthest from the quottoon plutonic complex and are 90 3 ma for hornblende and 77 9 1 2 ma for biotite the youngest 40ar 39ar ages are found closest to the quottoon plutonic complex and are 51 6 1 2 ma for hornblende and 45 3 1 7 ma for biotite no obvious relationship between grain size and age is seen in the ecstall pluton biotites spatial trends in 40ar 39ar ages are consistent with model results for reheating by a thermal wall at the location of the quottoon plutonic complex although no unique solution is suggested our results indicate that the most appropriate thermal history for the ecstall pluton includes both reheating and northeast side up tilting of the ecstall pluton associated with intrusion of the quottoon plutonic complex estimates of northward translation from shallow paleomagnetic inclinations in the western part of the ecstall pluton are reduced to 3000 km consistent with the baja bc hypothesis when northeast side up tilting is accounted for

a new high resolution unstructured grid finite volume arctic ocean model ao fvcom an application for tidal studies 1 a spherical coordinate version of the unstructured grid 3 d fvcom finite volume coastal ocean model has been applied to the arctic ocean to simulate tides with a horizontal resolution ranging from 1 km in the near coastal areas to 15 km in the deep ocean by accurately resolving the irregular coastlines and bathymetry in the arctic ocean coastal regions this model reproduces the diurnal k1 and o1 and semidiurnal m2 and s2 tidal wave dynamics and captures the complex tidal structure along the coast particularly in the narrow straits of the canadian archipelago the simulated tidal parameters harmonic constituents of sea surface elevation and currents agree well with the available observational data high resolution meshes over the continental shelf and slope capture the detailed spatial structure of topographic trapped shelf waves which are quite energetic along the greenland siberia and spitsbergen continental slope and shelf break areas water stratification influences the vertical distribution of tidal currents but not the water transport and thus tidal elevation the comparison with previous finite difference models suggests that horizontal resolution and geometric fitting are two prerequisites to simulate realistically the tidal energy flux in the arctic ocean particularly in the canadian archipelago

flow separation and shear stress over angle of repose bed forms a numerical investigation large asymmetric bed forms commonly develop in rivers the turbulence associated with flow separation that develops over their steep lee side is responsible for the form shear stress which can represent a substantial part of total shear stress in rivers this paper uses the delft3d modeling system to investigate the effects of bed form geometry and forcing conditions on flow separation length and associated turbulence and bed form shear stress over angle of repose 30 lee side angle bed forms the model was validated with lab measurements that showed sufficient agreement to be used for a systematic analysis the influence of flow velocity bed roughness relative height bed form height water depth and aspect ratio bed form height length on the variations of the normalized length of the flow separation zone the extent of the wake region where the turbulent kinetic energy tke was more than 70 of the maximum tke the average tke within the wake region and the form shear stress were investigated form shear stress was found not to scale with the size of the flow separation zone but to be related to the product of the normalized extent of the wake region extent of the wake region extent of water body above the bed form and the average tke within the wake region the results add to understanding of the hydrodynamics of bed forms and may be used for the development of better parameterizations of small scale processes for application in large scale studies

the variability of critical shear stress friction angle and grain protrusion in water worked sediments the erodibility of a grain on a rough bed is controlled by among other factors its relative projection above the mean bed its exposure relative to upstream grains and its friction angle here we report direct measurements of friction angles grain projection and exposure and small scale topographic structure on a variety of water worked mixed grain sediment surfaces using a simple analytical model of the force balance on individual grains we calculate the distribution of critical shear stress for idealized spherical grains on the measured bed topography the friction angle projection and exposure of single grain sizes vary widely from point to point within a given bed surface the variability within a single surface often exceeds the difference between the mean values of disparate surfaces as a result the critical shear stress for a given grain size on a sediment surface is characterized by a probability distribution rather than a single value on a given bed the crtitical shear stress distributions of different grain sizes have similar lower bounds but above their lower tails they diverge rapidly with smaller grains having substantially higher median critical shear stresses large numbers of fines trapp ed within pockets on the bed or shielded by upstream grains are effectively lost to the flow our calculations suggest that critical shear stress as conventionally measured is defined by the most erodible grains entrained during transient shear stress excursions associated with the turbulent flow this implies a physical basis for the indeterminacy of initial motion these observations suggest that transport rate shear stress relationships may be controlled in part by the increasing numbers of grains that become available for entrainment as mean shear stress increases they also suggest that bed textures and grain size distributions may be controlled within the constraints of an imposed shear stress and sediment supply regime by the influence of each size fraction on the erodibility of other grain sizes present on the bed

a unified model for subaqueous bed form dynamics 1 bed form evolution remains dynamic even in the special case of steady uniform flow data from the sandy braided north loup river nebraska show that roughness features on the channel bottom display a statistical steady state and robust scaling that are maintained through the collective interactions of transient short lived bed forms motivated by such field data and laboratory observations of bed form growth we develop a nonlinear stochastic surface evolution model for the topography of bed load dominated sandy rivers in which instantaneous sediment flux explicitly depends on local elevation and slope this model quantitatively reproduces laboratory observations of initial growth and saturation of bed forms from a flat surface and also generates long term dynamical behavior characteristic of natural systems we argue that the variability in geometry and kinematics of bed forms in steady flow and the existence of roughness at all wavelengths up to the largest dunes are a consequence of the nonlinear relationship between sediment flux and topography subject to noise

a case study of observed and modeled barrier flow in the denmark strait in may 2015 abstractmesoscale barrier jets in the denmark strait are common in winter months and have the capability to influence open ocean convection this paper presents the first detailed observational study of a summertime 21 may 2015 barrier wind event in the denmark strait using dropsondes and observations from an airborne doppler wind lidar dwl the dwl profiles agree well with dropsonde observations and show a vertically narrow 250 400 m barrier jet of 23 28 m s 1 near the greenland coast that broadens 300 1000 m and strengthens farther off coast in addition otherwise identical regional high resolution weather research and forecasting wrf model simulations of the event are analyzed at four horizontal grid spacings 5 10 25 and 50 km two vertical resolutions 40 and 60 levels and two planetary boundary layer pbl parameterizations mellor yamada nakanishi niino version 2 5 mynn2 5 and university of washington uw to determine what model configurations best simulate the observed jet

on the dynamics of sediment suspension by residual reynolds stresses confirmation of bagnold s theory bagnold s dynamic theory for sediment suspension requires that the immersed weight of suspended grains over unit bed area is supported by an upward directed residual reynolds stress yy arising from asymmetrical shear turbulence the present paper presents an analysis of previously published turbulence data which confirms the existence of this residual stress and indicates its generation in the lowermost part of the buffer layer of turbulent shear flows the magnitude of yy is estimated as about 0 3 yx calculations from experimental data on suspended fine sand transport over upper phase beds reveals that yy is in approximate equilibrium with the weight stress due to the suspended load

paleomagnetism and geochronology of the ecstall pluton in the coast mountains of british columbia evidence for local deformation rather than large scale transport 1 samples for geochronologic geobarometric and paleomagnetic analyses were collected across the northern portion of the ecstall pluton southeast of prince rupert british columbia al in hornblende geobarometry indicates pressures from 740 10 to 840 30 mpa corresponding to crystallization depths of 25 to 30 km u pb analyses of zircons from western central and eastern localities within the pluton yield crystallization ages of 91 5 1 0 ma 90 8 1 0 ma and 90 5 1 0 ma respectively rock magnetic experiments reflected light microscopy and thermal demagnetization behavior suggest that natural remanent magnetism is carried by low ti titanohematite unblocking temperatures of the characteristic remanent magnetization chrm are dominantly in the 560 c to 630 c range with age of magnetization approximated by the 40ar 39ar hornblende ages of 84 2 0 10 ma on the western margin and 76 4 0 6 ma in the center of the pluton site mean chrm directions were isolated for paleomagnetic samples from 23 sites and are distributed along a small circle with subhorizontal axis at 340 azimuth chrm directions from the central portion of the pluton are concordant with the expected cretaceous magnetic field direction while chrm directions from the western margin are discordant by 70 folding of the ecstall pluton either during late cretaceous west directed thrust transport above the convex upward prince rupert shear zone or during younger deformation of the pluton and underlying shear zone can account for the paleomagnetic data and is consistent with the geochronologic geobarometric and structural geologic observations

suspended sediment concentration and calibre in relation to surface flow structure in squamish river estuary southwestern british columbia surface grabs of suspended sediments from boils and the background flow in squamish estuary revealed strong differences between the two environments boils exhibit higher sediment concentrations and larger particle sizes than the background flow the higher sediment concentrations and larger grain sizes in boils are related to tidal phase with maximum concentrations and sediment sizes occurring in the early decelerating phase of the tidal flow sediment concentrations and grain sizes in the background flow are comparatively invariant with tidal phase boils appear to play an important if not dominant role in suspending and transporting sand sized sediments in squamish estuary

quadrant octant sequencing and the role of coherent structures in bed load sediment entrainment to permit the tracking of turbulent flow structures in an eulerian frame from single point measurements we make use of a generalization of conventional two dimensional quadrant analysis to three dimensional octants we characterize flow structures using the sequences of these octants and show how significance may be attached to particular sequences using statistical mull models we analyze an example experiment and show how a particular dominant flow structure can be identified from the conditional probability of octant sequences the frequency of this structure corresponds to the dominant peak in the velocity spectra and exerts a high proportion of the total shear stress we link this structure explicitly to the propensity for sediment entrainment and show that greater insight into sediment entrainment can be obtained by disaggregating those octants that occur within the identified macroturbulence structure from those that do not hence this work goes beyond critiques of reynolds stress approaches to bed load entrainment that highlight the importance of outward interactions to identifying and prioritizing the quadrants octants that define particular flow structures

remapping the thickness distribution in sea ice models in sea ice models with multiple thickness categories the ice thickness distribution evolves in time the evolution of the thickness distribution as ice grows and melts is analogous to one dimensional fluid transport and can be treated by similar numerical methods one such method remapping is applied here thickness categories are represented as lagrangian grid cells whose boundaries are projected forward in time the thickness distribution is approximated as a linear or quadratic polynomial in each displaced category and ice area and volume are transferred between categories so as to restore the original boundaries in simple test problems and in a single column model with forcing typical of the central arctic remapping performs significantly better than methods previously used in sea ice models it is less diffusive than a scheme that fixes the ice thickness in each category and behaves better numerically than a scheme that represents the thickness distribution as a set of delta functions also remapping converges faster i e with fewer thickness categories than the alternative schemes with five to seven categories the errors due to finite resolution of the thickness distribution are much smaller than the errors due to other sources linear remapping performs as well as the more complex quadratic version and is recommended for climate modeling its computational cost is minimal compared to other sea ice model components

on the spatial and temporal distribution of near inertial energy in the southern ocean 1 we use an eddying realistic primitive equation model of the southern ocean to examine the spatial and temporal distribution of near inertial wind power input wpi and near inertial energy nie in the southern ocean we find that the modeled near inertial wpi is almost proportional to inertial wind stress variance iwsv while the modeled nie is modulated by the inverse of the mixed layer depth we go on to assess recent decadal trends of near inertial wpi from trends of iwsv based on reanalysis wind stress averaged over the southern ocean annual mean iwsv is found to have increased by 16 over the years 1979 2011 part of the increase of iwsv is found to be related to the positive trend of the southern annular mode over the same period finally we show that there are horizontal local maxima of nie at depth that are almost exclusively associated with anticyclonic eddies

observation of cyclone induced inertial sea ice oscillation in fram strait 1 in march 2007 the field campaign framzy took place in the region between spitsbergen and greenland one goal of the experiment was the observation of cyclone impact on ice drift by means of autonomous meteorological buoys deployed on sea ice on 23 march an intense cyclone of about 500 km diameter passed with about 20 m s from south to north over the ice covered part of the fram strait and induced strong inertial oscillations of the sea ice ice drift velocity fluctuations abruptly increased by a factor of three to values of more than 1 m s this was caused by a resonant wind forcing for almost three quarters of the inertial oscillation depending on the local ice conditions the oscillations lasted over a two to five days period the inertial oscillations caused ice drift divergence fluctuations of 6 10 6s 1 and a reduction of ice concentration by up to 11

on the calculation of suspended load for noncohesive sediments calculation of suspended sediment transport rates requires integration of the product of sediment concentration times velocity over the depth of the flow hence accurate profiles of these quantities are required especially near the sediment bed although this would appear to be a straightforward task many effects can cause significant deviation of these quantities from those values expected from simple known relationships for example density stratification by suspended particulates can dampen turbulence fluctuations and significantly reduce the effective viscosity and diffusivity of the flow the momentum and suspended sediment equations are solved herein including the effects of stratification by suspended sediment and the effects due to size distribution and bedforms the results show that stratification and bedforms generally reduce the transport capacity of the flow whereas treating the sediment as an assemblage of different sizes rather than a single size d50 increases the expected transport

zircon and titanite recording 1 5 million years of magma accretion crystallization and initial cooling in a composite pluton southern adamello batholith northern italy abstract the southern part of the adamello batholith the so called re di castello unit is an example of a composite pluton ranging from gabbro to granodiorite in composition u pb dating of single zircon crystals from four tonalitic to granodioritic lithologies reveals that zircon crystallization is protracted in all studied lithologies showing apparent durations of growth between 90 and 700 ka the youngest zircons crystallized near the solidus and yield identical or slightly older ages than titanite the formation of these autocrystic zircons is considered to approximate the age of emplacement of the melt and its final crystallization in contrast to antecrystic zircons present in the same sample which had formed earlier in the magmatic column or were derived from re mobilized earlier magma the autocryst derived emplacement ages range from 42 43 0 09 ma to 40 90 0 05 ma recording 1 5 ma of intrusion and crystallization history we anticipate that extended periods of zircon crystallization may be common in silicic rocks whereas the zircons from residual melts from initially undersaturated mafic liquids should yield far more precise emplacement ages within our present analytical uncertainties of 0 1 0 2 in 206 pb 238 u age decreasing th u ratios of dated zircons within one melt batch document the depletion of the residual melt portion in th due to the contemporaneous crystallization of titanite preliminary hf isotopic compositions of the dated zircon grains suggest that the early stage melts of the southern re di castello unit represent hybrid melts with an important crustal component e hf between 2 8 and 3 0 subsequently emplaced melts are more juvenile at e hf values at 6 4 to 8 9 and may thus reflect the addition of large volumes of mafic melt to the magmatic system

kinematics and tectonic significance of transpressive structures within the coast plutonic complex british columbia abstract structural data from the coast plutonic complex near prince rupert british columbia are consistent with a deformational history dominated by dextral transpression from campanian to paleocene time penetrative east side up southwest directed ductile shearing produced moderately northeast plunging overturned kilometer scale isoclinal folds these folds are dextrally sheared and refolded into kilometer scale upright northwest plunging folds and steeply dipping transposed foliations with moderate to shallow northwest plunging lineations along their western side an east side up component to the transcurrent shearing is kinematically compatible with east side up shearing found within the great tonalite sill kinematic and geometric gradients and the spatial distribution of the finite stretching direction are interpreted to result from partitioning of transpression the location of these structures and overprinting relationships suggest the great tonalite sill intruded late kinematically into a crustal scale dextral transpressive shear zone these results indicate this shear zone could form part of the baja b c fault system that would have accommodated large northward displacements of the terranes making up western british columbia and southeast alaska this conclusion is based on 1 it is favorably located to accommodate the proposed displacements 2 deformation occurred during the time period of proposed large displacement 83 59 ma 3 the 15 km thickness of the shear zone indicates it records large displacements

timing of the permian triassic biotic crisis implications from new zircon u pb age data and their limitations abstract the most profound biotic crisis in the earth s history causing the near extinction of both terrestrial and marine life occurred at the end of the permian period about 253 myr ago and marks the paleozoic mesozoic era boundary the cause of this event is still a matter of vigorous debate with both brief and catastrophic as well as gradual mechanisms having been proposed similar to a recent landmark study this study uses the u pb method on zircons from the uppermost permian lowermost triassic ash fall deposits at meishan zhejiang province se china in order to examine time and rate constraints for these events the results of both this study and previous work show that for these ash layers the effects of pb loss are combined with varying amounts and sources of inheritance resulting in an age scatter which prohibits the extraction of a statistically robust age in many cases though the effects of pb loss on the zircons analyzed in this study were reduced by leaching the grains in hydrofluoric acid as opposed to commonly applied air abrasion prior to analysis the presence within a single ash layer of multiple generations of older xenocrysts in many cases only slightly older than the depositional age has made quantitative interpretation even more difficult when these combined phenomena bias individual zircon ages by less than a percent they are extremely difficult to deconvolute and if multi grain analyses are used can become impossible to recognize because of the resulting age averaging monte carlo simulations using actual measurements of individual zircon crystals show that age excursions due to pb loss and xenocrystic contamination for the meishan bentonites are easily homogenized to the point of undetectability when replicate analyses of multi grain zircon samples are compared thus this study uses only high precision analyses of single crystals whether from our work or that of previous studies three main conclusions have emerged first our data require a significant increase in the age of the permian triassic boundary by more than 2 myr compared to the previous study which shifts the age to a value older than 253 ma second neither our data nor those from previous work can confirm or negate the possibility of a very abrupt biotic crisis third even large suites of very high quality single zircon u pb analyses for these tuffs cannot in most cases yield objective reliable and robust dates with accuracies at the sub myr level though the temptation to perform arbitrary selection of subsets of the analyses for that purpose is almost irresistible the last conclusion is not an indictment of zircon u pb dating in general other rocks and other zircon populations can and do behave very differently and further technical advances will likely improve our ability to prepare grains or sub grains of adequately enhanced quality for analysis consequently the results of the present study strongly suggest that for problems requiring time scale accuracy inferences from zircon u pb dating must be based on sufficiently large suites of single crystal or crystal domain high precision analyses

large eddy simulation of sediment transport currents over ripples a large eddy simulation has been performed to study the detailed sediment dynamics that occur in channel flow over ripples the code solves the navier stokes equations and an advection diffusion equation for the sediment and has been verified to produce quantitatively accurate hydrodynamic results for the flow domains used in this study the main features of interest in this flow are seen because of the high resolution of the grid especially near the ripple boundary this yields a detailed bottom shear stress distribution properly identified coherent structures and resolved sharp gradients in the sediment concentration globally the sediment is carried up into the flow from locations where the shear stress is high on the upslopes of ripple crests and is advected downstream by the current and upward by the vertical velocity component regions of positive vertical velocity are associated with gortler vortices which represent a significant sediment transport mechanism in this flow

pluton emplacement by sheeting and vertical ballooning in part of the southeast coast plutonic complex british columbia batholiths of the coast plutonic complex in the area of harrison lake british columbia are interpreted to have formed by horizontal sheeting and vertical inflation zoned ovoid batholiths exhibit sheeted margins as thick as 3 km shallow floors are indicated by moderately to gently inward dipping magmatic foliations the observed trace of floor contacts across topography and a published deep seismic reflection transect mineralogic aureoles under the floors preserve a paragenetic record of increasing pressure during aureole crystallization initial pressures of

winter atmospheric buoyancy forcing and oceanic response during strong wind events around southeastern greenland in the regional arctic system model rasm for 1990 2010 abstractstrong mesoscale tip jets and barrier winds that occur along the southeastern greenland coast have the potential to impact deep convection in the irminger sea the self organizing map som training algorithm was used to identify 12 wind patterns that represent the range of winter november march ndjfm wind regimes identified in the fully coupled regional arctic system model rasm during 1990 2010 for all wind patterns the ocean loses buoyancy primarily through the turbulent sensible and latent heat fluxes haline contributions to buoyancy change were found to be insignificant compared to the thermal contributions patterns with westerly winds at the cape farewell area had the largest buoyancy loss over the irminger and labrador seas due to large turbulent fluxes from strong winds and the advection of anomalously cold dry air over the warmer ocean similar to observations rasm simulated typical ocean mixed layer depths mld of approximately 400 m throughout the irminger basin with indi

numerical simulation of turbulence and sediment transport of medium sand a model of sand transport in water is produced by combining a turbulence resolving large eddy simulation les with a discrete element model dem prescribing the motion of individual grains of medium sand the momentum effect of each particle on the fluid is calculated at the les cell containing the particle and the fluid velocity and pressure interpolated to each particle center is used to derive fluid force on each particle in the dem eleven numerical experiments are conducted of an initially flat bed of particles the experiments span a range of motion from essentially no motion to vigorous suspension hydraulic roughness is found to increase abruptly at the transition from bed load to suspended load transport suspended sediment extracts momentum from the flow and decreases the rate of shear whereas slightly higher in the flow vertical drag by suspended grains damps turbulence and increases the rate of shear vertical sediment diffusivity and effective particle settling velocity are much smaller than is commonly assumed in suspended sediment models the bed load experiments suggest that saltation by itself is a poor model of bed load sand transport in contrast to expectations from saltation models the peak bed load flux occurs at essentially the same level as the bed and grains move slowly in frequent contact with other grains higher and faster moving bed load grains that can be considered to be in saltation represent a smaller portion of the total flux entrainment of bed load grains occurs in response to fluid penetration of the bed by high vorticity turbulence structures embedded within broader high speed fluid regions referred to as a sweeps or high speed wedges

the influence of high frequency atmospheric forcing on the circulation and deep convection of the labrador sea abstractthe influence of high frequency atmospheric forcing on the circulation of the north atlantic ocean with emphasis on the deep convection of the labrador sea was investigated by comparing simulations of a coupled ocean ice model with hourly atmospheric data to simulations in which the high frequency phenomena were filtered from the air temperature and wind fields in the absence of high frequency atmospheric forcing the strength of the atlantic meridional overturning circulation and subpolar gyres was found to decrease by 25 in the labrador sea the eddy kinetic energy decreased by 75 and the average maximum mixed layer depth decreased by between 20 and 110 depending on the climatology in particular high frequency forcing was found to have a greater impact on mixed layer deepening in moderate to warm years whereas in relatively cold years the temperatures alone were enough to facilitate deep convection additional simulations in which either the wind or temperature was filtered revealed that

high precision u pb geochronology of the butedale pluton british columbia the butedale pluton a ca 100 km long compositionally zoned batholith is part of the coast plutonic complex that extends the length of the canadian pacific coast its age and thermal history are relevant to the butedale pluton s role as a test case of the baja bc hypothesis as paleomagnetic evidence suggests that it may have formed thousands of kilometres to the south and moved northward along what is now the coast shear zone high resolution u pb chemical abrasion thermal ionization mass spectrometry ca tims zircon analysis of rocks across the width of the butedale pluton indicates that it is actually made up of at least two distinct magmatic events that formed the west butedale pluton ca 95 ma and the east butedale pluton ca 85 ma the east butedale pluton was reheated by the emplacement of a younger adjacent pluton which may have caused partial pb loss and resulting excess scatter of 206pb 238u zircon ages within individual samples the west butedale pluton may be the same age as and

simulating the ice thickness distribution in a coupled climate model climate simulations in a global coupled model are investigated using a dynamic thermodynamic sea ice and snow model with sophisticated thermodynamics and a subgrid scale parameterization for multiple ice thicknesses in addition to the sea ice component the model includes a full primitive equation ocean and a simple energy moisture balance atmosphere we introduce a formulation of the ice thickness distribution that is lagrangian in thickness space the method is designed to use fewer thickness categories because it adjusts to place resolution where it is needed most and it is free of diffusive effects that tend to smooth eulerian distributions experiments demonstrate that the model does reasonably well in simulating the mean arctic climate we find the climate of the arctic and northern north atlantic is sensitive to resolving the ice thickness distribution when comparing the model results to a simulation with a two level sea ice model the ice thickness distribution causes ice export through fram strait to be more variable and more strongly linked to meridional overturning in the north atlantic ocean the lagrangian formulation of the ice thickness distribution allows for the inclusion of a vertical temperature profile with relative ease compared to an eulerian method we find ice growth rates and ocean surface salinity differ in our model with a well resolved vertical temperature profile in the ice and snow and an explicit brine pocket parameterization compared to a simulation with semtner zero layer thermodynamics although these differences are important for the climate of the arctic the effects of an ice thickness distribution are more dramatic and extend into the northern north atlantic sensitivity experiments indicate that five ice thickness categories with 50 cm vertical temperature resolution capture the effects of the ice thickness distribution on the heat and freshwater exchange across the surface in the presence of sea ice in these simulations

near inertial internal waves and sea ice in the beaufort sea the evolution of the near inertial internal wavefield from ice free summertime conditions to ice covered wintertime conditions is examined using data from a yearlong deployment of six moorings on the beaufort continental slope from august 2008 to august 2009 when ice is absent from july to october energy is efficiently transferred from the atmosphere to the ocean generating near inertial internal waves when ice is present from november to june storms also cause near inertial oscillations in the ice and mixed layer but kinetic energy is weaker and oscillations are quickly damped damping is dependent on ice pack strength and morphology decay scales are longer in early winter november january when the new ice pack is weaker and more mobile decreasing in late winter february june when the ice pack is stronger and more rigid efficiency is also reduced as comparisons of atmospheric energy available for internal wave generation to mixed layer kinetic energies indicate that a smaller percentage of atmospheric energy is transferred to nearinertial motions when ice concentrations are 90 however large kinetic energies and shears are observed during an event on 16 december and spectral energy is elevated above garrett munk levels coinciding with the largest energy flux predicted during the deployment a significant amount of near inertial energy is episodically transferred to the internal wave band from the atmosphere even when the ocean is ice covered however damping by ice and less efficient energy transfer still leads to low arctic internal wave energy in the near inertial band increased kinetic energy below 300m when ice is forming suggests some events may generate internal waves that radiate into the arctic ocean interior

on the relationship between flow and suspended sediment transport over the crest of a sand dune rio parana argentina the links between large scale turbulence and the suspension of sediment over alluvial bedforms have generated considerable interest in the last few decades with past studies illustrating the origin of such turbulence and its influence on flow resistance sediment transport and bedform morphology in this study of turbulence and sediment suspension over large sand dunes in the rio parana argentina time series of three dimensional velocity and at a point suspended sediment concentration and particle size were measured with an acoustic doppler current profiler and laser in situ scattering transmissometer respectively these time series were decomposed using wavelet analysis to investigate the scales of covariation of flow velocity and suspended sediment the analysis reveals an inverse relationship between streamwise and vertical velocities over the dune crest where streamwise flow deceleration is linked to the vertical flux of fluid towards the water surface in the form of large turbulent fluid ejections regions of high suspended sediment concentration are found to correlate well with such events the frequencies of these turbulent events have been assessed from wavelet analysis and found to concentrate in two zones that closely match predictions from empirical equations such a finding suggests that a combination and interaction of vortex shedding and wake flapping changing length of the lee side separation zone are the principal contributors to the turbulent flow field associated with such large alluvial sand dunes wavelet analysis provides insight upon the temporal and spatial evolution of these coherent flow structures including information on the topology of dune related turbulent flow structures at the flow stage investigated the turbulent flow events and their associated high suspended sediment concentrations are seen to grow with height above the bed until a threshold height ca 0 45 flow depth is reached above which they begin to decay and dissipate

pb u and th diffusion in natural zircon zircon zrsio4 is one of the most widely used minerals for determining the age origin and thermal history of rocks by u th pb geochronology but the parameters describing the solid state volume diffusion rates of these elements in natural zircon which are themselves important for establishing the limits on the applicability of zircon for geochronological studies have remained poorly quantified1 this is because of the measurement difficulties associated with the low p p m concentrations and low diffusion rates of these elements in natural zircon and the chemical and physical heterogeneity present in most crystals here we present direct measurements of the uranium thorium and lead loss from a thermally treated gem quality natural zircon and show that lead diffuses much faster than uranium or thorium we find that the u th pb isotopic system in natural zircon will typically have a closure temperature greater than 900 c which explains why zircon is apparently such a robust geochrometer and is capable of remaining isotopically closed through extended periods of high grade metamorphism and partial melting of the host rock

revisiting internal waves and mixing in the arctic ocean 1 to determine whether deep background mixing has increased with the diminishment of the arctic sea ice we compare recent internal wave energy and mixing observations with historical measurements since 2007 the north pole environmental observatory has launched expendable current probes xcps as a part of annual airborne hydrographic surveys in the central arctic ocean mixing in the upper 500 m is estimated from xcp shear variance and conductivity temperature depth ctd derived brunt vaisala frequency internal wave energy levels vary by an order of magnitude between surveys although all surveys are less energetic and show more vertical modes than typical midlatitude garrett munk gm model spectra survey averaged mixing estimates also vary by an order of magnitude among recent surveys comparisons between modern and historical data reanalyzed in identical fashion reveal no trend evident over the 30 year period in spite of drastic diminution of the sea ice turbulent heat fluxes are consistent with recent double diffusive estimates both mixing and internal wave energy in the beaufort sea are lower when compared to both the central and eastern arctic ocean and expanding the analysis to mooring data from the beaufort sea reveals little change in that area compared to historical results from arctic internal wave experiment we hypothesize that internal wave energy remains lowest in the beaufort sea in spite of dramatic declines in sea ice there because increased stratification amplifies the negative effect of boundary layer dissipation on internal wave energy

annual regime of bedforms roughness and flow resistance lillooet river british columbia bc a field study to examine the statistical character of dune morphology and the correlation among dune morphology discharge and flow resistance was conducted in a meandering reach of lillooet river near pemberton british columbia canada the field season spanned the 1995 1996 hydrologic year with sample day discharge events ranging between 33 and 425 m3 s 1 surveys of the bed morphology along the thalweg in two dune fields a and b were completed using an echo sounder with chart recorder that enabled the measurement of more than 4000 dunes dune height ranged between 0 08 and 0 96 m length between 2 01 and 20 99 m and steepness between 0 02 and 0 10 histograms of each dune shape height length steepness sample most often displayed positive skewness and non gaussian distributions gamma beta and weibull median sample height and length histograms displayed positive skewness and steepness was nearly gaussian histograms of all dimensionless dunes i e measurement divided by average measurement of sample were gaussian and slightly leptokurtic neither the height nor length of dunes measured in this investigation were successfully predicted by the empirical models of allen allen j r l 1984 developments in sedimentology sedimentary structures their character and physical basis 2nd edn elsevier new york vol 30 a and b 1256 pp fredsoe j hydraul div am soc civ eng 108 hy8 1982 932 or yalin j hydraul div am soc civ eng 90 hy5 1964 105 least squares regression models for dune height relations produced here are similar to models published by other field researchers regression models for dune length only conform to those developed elsewhere if the discharge of the study rivers was similar the energy gradient in dune field a varied within a smaller range than in field b enabling dune size to become more fully equilibrated with respect to flow environment although the average froude numbers were much less than critical dunes appeared to wash out towards a plane bed as discharge increased due to a change from a bedload to suspended load dominated sediment transport regime flow resistance increased most rapidly during changes in base flow and at the beginning and end of the seasonal flood resistance tended to be smaller in field a than b reflecting local differences in energy gradient flow resistance increased until a dune steepness of 0 070 was attained and then decreased the steepness value was considered to be coincident with kolk generation dyer k r 1986 coastal and estuarine sediment dynamics wiley ny 342 pp suggesting that macroturbulent flow structures play an important role in defining the roughness of dunes on a channel bed

springtime ice motion in the western antarctic peninsula region abstract oscillatory motion of sea ice is examined using two ice drifting buoys separated by 1 latitude near 66 s during the winter to spring transition in the marguerite bay region west of the antarctic peninsula the buoys motions exhibit spectrally distinct periods 12 87 0 04 and 13 03 0 04 h respectively despite highly correlated motion between them r2 is 0 62 and 0 81 for u and v respectively the periods shift with latitude and nearly match the local inertial periods 13 00 and 13 10 h respectively the oscillations are further examined with respect to the kinematics involved in the breakup process of sea ice these include hourly resolved manifestations of circular trajectories semi circular oscillations with compressed trajectory cusps and accordion like compressions along straight line trajectories oscillations are found in all trajectory types over the lifetime of both buoys several months traditional circular and semi circular oscillations are particularly prominent during two episodes one of which is preceded by strong wind events and a substantial decrease in ice thickness and concentration these episodes combine with seasonally warming temperatures to break up and melt the sea ice cover we discuss potential relationships between the degradation of the ice pack during spring breakup and the increase in energy at near inertial frequencies including the appearance of a non linear cascade of energy within the ice from the low frequencies commensurate with storms and fortnightly tides to semi diurnal frequencies we further comment on the implications this type of high frequency motion has on local biological ecosystems specifically we find that sea ice semi diurnal oscillations are at their peak during the final decay of sea ice just before springtime primary productivity begins hence the oscillatory motion of sea ice not only serves as an effective mixing agent within the ice ocean mixed layer but also serves as an effective seeding platform for distributing phyto and zooplankton overwintering within and around the ice floes

suspended sediment transport and deposition over a dune rio parana argentina field data from the rio parana argentina are used to examine patterns of suspended sediment transport over a sand dune measurements of three dimensional velocity are made with an acoustic doppler current profiler whilst suspended sediment concentration and particle size have been quantified using a laser in situ sediment scattering transmissometer suspended sediment concentration and streamwise and vertical sediment flux are highest close to the bed with an upward vertical flux over the stoss side of the dune and downward flux over the lee side suspended sediment concentrations are higher over the crest compared with the trough and suspended sediment is coarsest near the bed about 17 of the suspended load transported over the crest is deposited in the lee side before it reaches the trough most of this deposited sand is coarser sediment that originates close to the bed over the crest a result consistent with simulations based on the model of mohrig and smith water resources research 1996 32 3207 3217 for the excursion lengths of sediment dispersed in the lee side of a dune copyright 2009 john wiley sons ltd

the paleomagnetic effects of reheating the ecstall pluton british columbia abstract paleomagnetic data of plutons from the western canadian cordillera are currently interpreted to indicate thousands of kilometers of latitudinal transport in situ tilting or post intrusion folding for the ecstall pluton of british columbia the inclination of magnetic remanence directions steepens to the east from 16 to 81 butler et al j geophys res 107 2002 between 24 and 12 km west of a thermal boundary with the coast mountains batholith cmb the cmb was at 700 800 c between 60 and 52 ma the stable remanent magnetization is in ilmenohematite grains with exsolved lamellae of ferrian ilmenite it has the characteristic properties of lamellar magnetism robinson et al nature 418 2002 517 520 which is acquired with exsolution in ilmenohematite below 390 c ghiorso phys chem minerals 25 1997 28 38 thus it is thermal chemical remanent magnetization tcrm our heat flow calculations show that the thermal effects of eocene cmb on the adjacent 91 ma ecstall pluton were enough to reset the remanent magnetization directions reheating to the temperatures necessary for tcrm is supported by k ar and ar ar cooling dates on hornblende and biotite which young from west to east towards the cmb in concert with the change in inclinations thus the progressive steepening of magnetization inclinations is attributed to reheating during the eocene of the 91 ma ecstall pluton by the cmb this reheating followed post solidification northward latitudinal displacement of the pluton the amount of translational displacement of the coastal terranes of british columbia prior to 60 ma hinges on the interpretation of discordant magnetizations from plutons that may have cooled slowly after emplacement in the mid to lower crust as was the case for the ecstall pluton many of these plutons contain ilmenohematite as an accessory magnetic phase our interpretation for the low temperature acquisition of tcrm in the ecstall pluton may have far reaching implications for understanding enigmatic discordant paleomagnetic directions reported from plutons of the western canadian cordillera

formation of new continental crust in western british columbia during transpression and transtension crustal growth in the coast mountains along the leading edge of the canadian cordillera was the result of processes associated with horizontal flow of material during transpression and subsequent transtension and the vertical accretion of mantle derived melts from 85 to 58 ma as exotic terranes were translated northward during transpression the crust was thickened to about 55 km and melt that originated from a mix of mantle derived basalt with partial melt of the thickened crust intruded into crustal scale transpressive shear zones when the orogen extended between 58 and 50 ma there was large scale decompression melting in the mantle and dehydration melting in the lower crust voluminous emplacement of sub horizontal sills facilitated by ductile flow of the gneissic country rocks partially filled space created as the crust was pulled apart and as 15 to 20 km of tectonic exhumation occurred across low angle normal ductile shear zones by 50 ma the final crustal thickness of the new continental crust was about 34 km comparison of seismic data with other crustal sections suggests that the crust forming processes identified in western british columbia have general applicability to models for the formation of continental crust

strain partitioning and batholith emplacement at the root of a transpressive magmatic arc abstract an integrative study of the high pressure ecstall batholith and its country rocks prince rupert area british columbia reveals the interplay of deformation and plutonism produced in the largest cordilleran magmatic arc i e the coast plutonic complex during mid cretaceous convergence between the farallon oceanic plate and north america the results emphasize the interference between three strain fields 1 an early 92 ma crustal wedge produced by orogen perpendicular sw vergent thrusting 2 an orogen parallel sinistral strike slip shear zone active until 87 ma and 3 the lateral expansion of the batholith 93 91 ma against the shear zone the batholith expanded in a direction oblique with respect to the shear zone trend 20 by extruding country rocks against its head in a direction normal to its expansion direction during sinistral strike slip partitioned transpression the batholith s emplacement combined far field batholith boundary normal translation extrusion related rotation and radial and concentric elongation in its structural aureole this case study may typify the process by which a modern magmatic arc grows longitudinally at depth during transpression the direction and sense of growth being determined by the direction of plate motion relative to the magmatic arc and the degree of strike slip partitioning of transpression

significance of stress transfer in time dependent earthquake probability calculations 1 a sudden change in stress is seen to modify earthquake rates but should it also revise earthquake probability data used to derive input parameters permit an array of forecasts so how large a static stress change is required to cause a statistically significant earthquake probability change to answer that question effects of parameter and philosophical choices are examined through all phases of sample calculations drawing at random from distributions of recurrence aperiodicity pairs identifies many that recreate long paleoseismic and historic earthquake catalogs probability density functions built from the recurrence aperiodicity pairs give the range of possible earthquake forecasts under a point process renewal model consequences of choices made in stress transfer calculations such as different slip models fault rake dip and friction are tracked for interactions among large faults calculated peak stress changes may be localized with most of the receiving fault area changed less than the mean thus to avoid overstating probability change on segments stress change values should be drawn from a distribution reflecting the spatial pattern rather than using the segment mean disparity resulting from interaction probability methodology is also examined for a fault with a well understood earthquake history a minimum stress change to stressing rate ratio of 10 1 to 20 1 is required to significantly skew probabilities with 80 85 confidence that ratio must be closer to 50 1 to exceed 90 95 confidence levels thus revision to earthquake probability is achievable when a perturbing event is very close to the fault in question or the tectonic stressing rate is low

the application of computational fluid dynamics to natural river channels eddy resolving versus mean flow approaches in the last decade as computing power has increased there has been an explosion in the use of eddy resolving numerical methods in the engineering earth and environmental sciences for complex geomorphic flows where accurate field investigations are difficult to perform and where experiments may be difficult to scale these numerical approaches are beginning to give key insights into the nature of these flows eddy resolving methods such as large and detached eddy simulation les des may be contrasted with the time averaged three dimensional simulations that only really began to be applied seriously in geomorphology fifteen years ago while the potential of les for geomorphology has been examined previously des is a relatively recent method that deserves further consideration in this paper we explain the method and then utilise examples from meander and confluence flows as well as flow near the bed of a gravel bed river to highlight the improvements to both the representation of the mean flow and to the representation of time varying processes that result from the use of les des some suggestions are provided for the future use of such techniques in geomorphology

observations of tidally induced currents over the continental slope of the laptev sea arctic ocean abstracttwo year long 2004 05 and 2005 06 records of currents from two moorings deployed at the continental slope of the laptev sea 78 26 n 125 40 e are used in order to define the properties of tidal currents in the upper 200 m ocean layer harmonic and spectral analyses of currents showed that the semidiurnal tidal constituent s2 dominates over the semidiurnal m2 and diurnal constituents this dominance of the s2 constituent in the tidal currents is due to resonant interaction of the superinertial wave with sloping bottom topography in contrast to the tidal currents sea level changes are dominated by the m2 constituent as seen from a tidal model by l padman and s erofeeva using assimilation of observational data strong anticorrelation 0 73 0 05 was found between the upper 50 m s2 current amplitudes and local sea ice concentration with fourfold from 2 0 to 8 5 cm s 1 amplification of tidal currents under ice free conditions this is probably due to a change of local resonance condit

paleomagnetic evidence for displacement from the south of the coast plutonic complex british columbia the mid cretaceous spuzzum and porteau plutons of the coast plutonic complex of british columbia have two magnetizations a and b the a magnetization eight sites 83 specimens d 30 3 i 56 7 95 4 9 paleolatitude 37 5 n paleopole 65 0 n 14 9 w a95 6 2 is considered to have been acquired in the age range 105 90 ma this result differs from the field established for cratonic north america in this time range the difference could be caused either by previously undetected tilting about a horizontal axis of the plutons or by their rotation about a vertical axis and lateral displacement relative to the craton previously observed mid cretaceous magnetizations from other rock units from the western canadian cordillera and the cascades of washington united states are similarly discordant with respect to the craton this similarity over such a large area indicates that although local undetected tilting could be partly responsible it is unlikely to be the prime cause and we argue ther

modeling the high frequency component of arctic sea ice drift and deformation abstract buoy observations of sea ice drift show that sea ice motion and deformation contain substantial high frequency variability at subdaily timescales however numerical simulations of the sea ice dynamics normally do not include processes on such short timescales instead by applying traditional water drag formulations for the ocean sea ice boundary layer the inertial frequencies tend to be omitted in the spectra of modeled sea ice motion and deformation due to fictitious ocean damping here a dynamic thermodynamic sea ice model is presented that includes inertial embedding of the sea ice into the oceanic boundary layer to reproduce sea ice motion and deformation not only at daily and lower frequencies but also at subdaily frequencies up to 2 cycles per day and higher comparison with buoy data shows that the embedded model much more successfully simulates the observed sea ice motion in regard to the high frequency component the results demonstrate that both inertial embedding of the sea ice oc

the fluid dynamics of river dunes a review and some future research directions 1 dunes are present in nearly all fluvial channels and are vital in predicting flow resistance sediment transport and deposition within many rivers progress in understanding the fluid dynamics associated with alluvial dunes has been significant in the last 15 years and has witnessed huge advances in field laboratory and numerical investigations progress has been made in detailing the principal features of mean and turbulent flow over asymmetric dunes that possess flow separation in their leesides and how these forms affect both downstream boundary layer structure and stress partitioning over the dune additionally the links between sediment transport over dunes and instantaneous coherent flow structures are being increasingly understood with the feedback of dune three dimensionality upon flow and sediment dynamics over these bed forms beginning to be recognized as vital such research now provides an outstanding background for beginning to address areas of greater complexity that will enable a fuller understanding of these important natural features this review paper summarizes the principal features of mean and turbulent flow over alluvial sand dunes five areas are then highlighted and discussed as a possible focus for future research 1 the influence of dune leeside angle upon flow processes in the dune wake and downstream flow field 2 the influence of three dimensionality in dune shape upon the generation of turbulence and distribution of bed shear stress 3 flow field modification resulting from bed form superimposition and amalgamation 4 the scale and topology of dune related turbulence and its interactions with sediment transport and the flow surface and 5 the influence of suspended sediment on the dune flow field and dune morphology

pb diffusion in zircon abstract chemical diffusion of ti under anhydrous conditions at 1 atm and under fluid present elevated pressure 1 1 1 2 gpa conditions has been measured in natural zircon the source of diffusant for 1 atm experiments was a zro2 tio2 zircon mixture with experiments run in crimped pt capsules diffusion experiments done in the presence of h2o co2 fluid were run in a piston cylinder apparatus using a source of ground tio2 zrsio4 and sio2 with oxalic acid added to produce h2o co2 vapor and partially melt the solid source material yielding an assemblage of rutile zircon melt vapor nuclear reaction analysis nra with the resonant nuclear reaction 48ti p 49v was used to measure diffusion profiles for both sets of experiments the following arrhenius parameters were obtained for ti diffusion normal to cover the temperature range 1350 1550 c at 1 atm d ti 3 33 10 2 exp 754 56 kj mol 1 r t m 2 s 1 ti diffusivities were found to be similar for experiments run under fluid present conditions a fit to all of the data yields the arrhenius relation d 1 34 102 exp 741 46 kj mol 1 rt m2 s 1 these data suggest that zircon should be extremely retentive of ti chemical signatures indicating that the recently developed ti in zircon crystallization geothermometer watson e b harrison t m 2005 zircon thermometer reveals minimum melting conditions on earliest earth science 308 841 844 will be quite robust in preserving temperatures of zircon crystallization titanium diffuses somewhat faster in zircon than larger tetravalent cations u th and hf but considerably more slowly than pb the ree and oxygen hence ti crystallization temperatures may be retained under circumstances when radiometric ages or other types of geochemical information are lost

modeling sea ice transport using incremental remapping sea ice models contain transport equations for the area volume and energy of ice and snow in various thickness categories these equations typically are solved with first order accurate upwind schemes which are very diffusive with second order accurate centered schemes which are highly oscillatory or with more sophisticated second order schemes that are computationally costly if many quantities must be transported e g multidimensional positive definite advection transport algorithm mpdata here an incremental remapping scheme originally designed for horizontal transport in ocean models is adapted for sea ice transport this scheme has several desirable features it preserves the monotonicity of both conserved quantities and tracers it is second order accurate except where the accuracy is reduced locally to preserve monotonicity and it efficiently solves the large number of equations in sea ice models with multiple thickness categories and tracers remapping outperforms the first order upwind scheme and basic mpdata scheme in several simple test problems in realistic model runs remapping is less diffusive than the upwind scheme and about twice as fast as mpdata

a field study of turbulence and sediment dynamics over subaqueous dunes with flow separation this study examines flow turbulence and sand suspension over large dunes in canoe pass a distributary channel of the fraser river delta canada dune morphology is characterized by a symmetrical shape and steep leeside slopes over 30 velocity was measured with an electromagnetic current meter and suspended sand concentration with four optical backscatter obs probes the general patterns of time averaged velocity and sand suspension are consistent with previous studies including an increase in mean velocity and decrease in turbulence intensity and sand concentration with height above the bed reversed flow with high turbulence intensity and high sand concentrations in the leeside flow separation zone and an increase in near bed velocity and sand concentration along the stoss side of the dune frequency spectra of near bed velocity and obs records from leeside separation zones are composed of two distinct frequencies providing field confirmation of scale relations based on flume experiments the low frequency spectral signal probably results from wake flapping and the high frequency signal from vortex shedding the wake flapping frequency predominates outside the separation zone and is linked to turbulent structures that suspend sand predictions from a depth scale strouhal law show good agreement with measured wake flapping frequencies cross correlations of obs records reveal that turbulent sand suspension structures advect downstream at 23 25 above the horizontal these advection angles are similar to coherent flow structures measured in flumes and to sand suspension structures visualized over large dunes in the field

suspension of bed material over sand bars in the lower mississippi river and its implications for mississippi delta environmental restoration 1 understanding specific pathways for sand transport in the lower reaches of large rivers including the mississippi is a key for addressing multiple significant geologic problems such as delta building and discharge to the oceans and for environmental restoration efforts in deltaic environments threatened by rising sea levels field studies were performed in the mississippi river 75 100 km upstream of the gulf of mexico outlet in 2010 2011 to examine sand transport phenomena in the tidally affected river channel over a range of discharges methods included mapping bottom morphology multibeam sonar cross sectional and longitudinal measurements of water column velocity and acoustic backscatter suspended sediment sampling and channel bed sampling substantial interaction was observed between the flow conditions in the river boundary shear stress channel bed morphology size and extent of sandy bedforms and bed material sand transport quantity transport mode and spatial distribution a lateral shift was observed in the region of maximum bed material transport from deep to shallow areas of subaqueous sand bars with increasing water discharge bed material was transported both in traction and in suspension at these water discharges and we posit that the downriver flux of sand grains is composed of both locally and drainage basin sourced material with distinct transport pathways and relations to flow conditions we provide suggestions for the optimal design and operation of planned river diversion projects

global distribution of the decay timescale of mixed layer inertial motions observed by satellite tracked drifters 1 the decay timescale of mixed layer inertial amplitudes has been estimated from satellite tracked drifter trajectories from 1990 to 2004 as the e folding timescale of the temporal correlation functions the decay timescales increase with latitude in all basins except the north atlantic a beta dispersion model shows that dephasing leads to meridional variations of the decay timescale in the north pacific and the southern ocean but meridional variations of the buoyancy structure in the north atlantic act to compensate the beta effect leading to a lack of meridional variation of the decay timescale in that ocean

burst like sediment suspension events in a sand bed river in a much quoted paper jackson 1976 hypothesized that turbulent bursting motions such as those documented in laboratory boundary layers play a major role in alluvial sediment suspension to date the hypothesis remained largely untested due to difficulties in monitoring turbulent suspension in rivers this study provides field data documenting burst like turbulent motions over a sandy bed channel and quantifying the role of these motions in sand suspension the data were collected in a 10 m deep channel of the fraser river near mission british columbia canada turbulent fluctuations of both flow components downstream and normal to the bed along with the output of an optical suspended sediment sensor were monitored 1 m above the river bed typical flow velocities averaged 0 9 ms 1 at the sensors where mean suspended sediment concentrations were 500 mgl 1 decimetre height small dunes on the backs of larger half metre amplitude dunes covered the channel bed in the area brief but intense burst like ejection and inrush events were identified in the flow records where they are responsible for a high degree of intermittency in shear stress over the dunes 80 per cent of the turbulent momentum exchange across the 1 m level can be ascribed to such brief 3 8 s duration events active under 12 per cent of the time in addition the record of fluctuating sediment concentrations reveals these burst like motions to be highly effective in vertically mixing suspended sediment and thus ultimately in maintaining suspended sediment transport above the dune bed the bulk 60 and 90 per cent in two deployments of the vertical sediment mixing was accomplished by intense events active some 10 per cent of the time no discrete recurrence timescale for these burst like mixing events is evident however rather a continuous variation of return periods was observed as a function of the magnitude of vertical mixing event considered to that extent conceptual models of sediment transport in terms of burst events with a predictable recurrence such as proposed by jackson 1976 may be misleading

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

global statistics of inertial motions statistics of inertial currents in the north pacific north atlantic and southern ocean are derived for the period 1997 2003 from surface trajectories of argo profiling floats by employing a method developed recently by park et al 2004 the distribution of inertial amplitudes is non gaussian in the range 0 80 cm sec with an average value of 13 7 cm sec the inertial amplitude in the mid latitude 30 45 n band exceeds those in both the low 15 30 n and high 45 60 n latitude bands in three basins the amplitude in summer is greater than that in winter by 15 25 the inertial energy in the mixed layer reaches approximately 1100 j m2 1165 j m2 globally the spatiotemporal patterns of inertial amplitudes in the north atlantic mostly depend on the mld which exhibits strong meridional gradients however the small meridional gradient of the mld in the north pacific does not contribute significantly to the spatial distribution of inertial amplitudes the total inertial energy estimated from the floats is consistent with the theory that inertial energy could contribute significantly to sustaining the meridional overturning circulation

spectral analysis of turbulent flow and suspended sediment transport over fixed dunes laboratory measurements of turbulent fluctuations in velocity and suspended sediment concentration were obtained synchronously over fixed two dimensional dunes in a sediment starved flow contour maps of turbulent flow parameters demonstrate that the flow separation cell and a perturbed shear layer are the main sources of turbulence production and that the distribution of suspended sediment is controlled by spatially dependent macro turbulent flow structures spectral analysis reveals that peak spectral energies generally occur at 1 2 hz for the stream wise velocity component and 2 4 hz for the cross stream and vertical velocity components spectra show larger and better defined energy peaks near the shear layer peak spectral energies for suspended sediment concentration occur near 1 hz throughout the flow squared coherency values for cospectral analysis of velocity and sediment concentration are insignificant integral timescales for velocity range from 0 20 s for the streamwise component to 0 06 s for the cross stream and vertical components integral length scales for velocity range from 0 065 to 0 135 m for the streamwise component which is comparable to flow depth and from 0 020 to 0 030 m for the crossstream and vertical components which is comparable to dune height for suspended sediment concentration integral timescales and length scales are similar to the streamwise velocity component

three dimensional versus two dimensional bed form induced hyporheic exchange the hyporheic zone is often a critical component of river systems hyporheic exchange is generally forced by variation in riverbed topography such as due to bed forms most previous research on bed form driven hyporheic flow has focused on two dimensional 2 d dunes and ripples while little has been done on their three dimensional 3 d counterparts here we compared hyporheic exchange and associated metrics for a previously studied pair of corresponding 2 d and 3 d bed forms to accomplish this a series of multiphysics computational fluid dynamics models were conducted both in 2 d and 3 d with similar open channel reynolds numbers re results show that the pressure gradient along the sediment water interface is highly sensitive to the spatial structure of bed forms which consequently determines hyporheic flow dynamics hyporheic flux is a function of re for both 2 d and 3 d dunes via a power law however the equivalent 3 d dunes have a higher flux since the 3 d form induces more drag the hyporheic zone depths and volumes are only slightly different with the 3 d case having a larger volume the mean fluid residence times for both cases are related to re by an inverse power law relationship with the 3 d dune having smaller residence times at moderate to high re the effects of increasing flux on residence time in 3 d dunes are partly modulated by a slightly increasing hyporheic volume our results suggest that a 2 d idealization is a reasonable approximation for the more complex 3 d situation if local details are unimportant but that development of predictive models for mean fluxes and residence times which are critical for biogeochemical processes based on 2 d models may be insufficient

modeling m2 tidal variability in arctic sea ice drift and deformation semi diurnal oscillations are a ubiquitous feature of polar sea ice motion over much of the arctic basin inertial and semi diurnal tidal variability have similar frequencies so that periodicity alone is inadequate to determine the source of oscillations we investigate the relative roles of tidal and inertial variability in arctic sea ice using a barotropic ice ocean model with sea ice embedded in an upper boundary layer results from this model are compared with levitated ice ocean coupling used in many models in levitated models the mechanical buoyancy effect of sea ice is neglected so that convergence of ice for example does not affect the oceanic ekman flux we use rotary spectral analysis to compare simulated and observed results this helps to interpret the rotation sense of sea ice drift and deformation at the semi diurnal period and is a useful discriminator between tidal and inertial effects results indicate that the levitated model generates an artificial inertial resonance in the presence of tidal and wind forcing contrary to the embedded sea ice model we conclude that sea ice mechanics can cause the rotational response of ice motion to change sign even in the presence of strong and opposing local tidal forcing when a physically consistent dynamic ice ocean coupling is employed

mean and turbulent velocity fields near rigid and flexible plants and the implications for deposition 1 the transport of fine sediment and organic matter plays an important role in the nutrient dynamics of shallow aquatic systems and the fate of these particles is closely linked to vegetation we describe the mean and turbulent flow near circular patches of synthetic vegetation and examine how the spatial distribution of flow is connected to the spatial distribution of suspended sediment deposition patches of rigid emergent and flexible submerged vegetation were considered with two different stem densities for the rigid emergent vegetation flow adjustment was primarily two dimensional with flow deflected in the horizontal plane horizontal shear layers produced a von karman vortex street flow through the patch shifted the vortex street downstream resulting in a region directly downstream of the patch in which both the mean and turbulent velocities were diminished net deposition was enhanced within this region in contrast for the flexible submerged vegetation flow adjustment was three dimensional with shear layers formed in the vertical and horizontal planes because of strong vertical circulation turbulent kinetic energy was elevated directly downstream of the patch consistent with this deposition was not enhanced at any point in the wake this comparison suggests that morphological feedbacks differ between submerged and emergent vegetation further enhanced deposition occurred only in regions where both turbulent and mean velocities were reduced relative to the open channel reduced deposition indicating enhanced resuspension occurred in regions of high turbulence kinetic energy regardless of local mean velocity these observations highlight the importance of turbulence in controlling deposition

predicting the migration rates of subaqueous dunes in this paper we develop a simple physically based method for predicting what fraction of sediment moving over the crests of dunes will bypass their lee faces the bypass fraction is found by calculating a characteristic excursion length for every grain size making up a particular train of dunes all particles with excursion lengths greater than the downstream span of the lee face of the average dune are assumed not to contribute to dune propagation bypass fractions based on distributions of excursion lengths account for the discrepancies between total sediment discharge and dune migration rate measured by stein 1965 and guy et al 1966 in laboratory flumes as well as by us in the north loup river of nebraska calculations and these data agree over sediment transporting conditions associated with the entire stability field for dunes composed of medium sand the two laboratory studies show that commonly 30 60 of all sand moving over fully developed dunes is not deposited on slip faces measurements from the north loup river reveal that of all sediment moving over the dune crests there roughly 45 is not being captured on lee faces even though 99 of sediment is transported within 2 cm of the bed the method developed herein successfully estimates measured values for the bypass fraction from 0 to 80 our analysis indicates that the division between grains that are deposited versus those that are bypassing falls within the range of sand sizes making up the suspended load at dune crests

time scales of pluton construction at differing crustal levels examples from the mount stuart and tenpeak intrusions north cascades washington deciphering the magmatic history of continental magmatic arcs in general and the growth history of individual intrusions in particular is key to understanding the complex history of magma generation segregation and transport that define the dynamics of crustal growth we utilize high precision u pb geochronology to resolve a detailed magmatic history from two composite intrusions the 2 4 kbar mount stuart batholith and the 7 10 kbar tenpeak pluton emplaced in the cretaceous north cascades arc this temporal framework provides a way to evaluate models of pluton growth that explain common features of intrusions such as concentric compositional zoning and internal magmatic contacts u pb zircon crystallization ages were obtained from 12 samples of the mount stuart batholith and 8 samples of the tenpeak intrusion representing the range of compositional diversity and geographical extent these dates indicate that the mount stuart batholith was constructed over a 5 5 m y time period that was punctuated by four intervals of high magma flux the durations of the high flux periods are short a few hundred thousand years relative to the duration of the batholith the consistent pattern of magmatic fabrics and the lack of distinct contacts in the batholith may be explained by the juxtaposition of melt rich and mush zones with subtle contacts between mineralogically and texturally similar tonalite and time transgressive magma fabrics in contrast the tenpeak intrusion was constructed over a 2 6 m y time period with magma influx distributed throughout the intrusive history and texturally distinct magma bodies the tenpeak intrusion lacks distinct age domains which suggests that any magma reservoir was smaller in size and potentially more ephemeral although the distinct age domains and discrete compositional and textural phases indicate that pluton growth occurred incrementally neither pluton bears resemblance to a purely end member incremental growth model whereby a pluton is constructed from hundreds to thousands of discrete magma pulses that have little if any interaction in particular ages from the youngest domain of the mount stuart batholith indicate that a melt rich magma reservoir of 520 km 3 existed over a 170 90 k y time span

batholith emplacement at mid crustal levels and its exhumation within an obliquely convergent margin abstract emplacement of the central part of the coast mountains batholith of northern coastal british columbia occurred within a regime characterized by oblique convergence between the farallon kula and north american plates we use new structural kinematic and u pb isotopic data to show that the locations geometry and mechanisms of pluton emplacement within this batholith were controlled by displacements within a network of normal faults and transtensional shear zones these data also show that the most active period of pluton emplacement from 67 to 51 ma coincided with a change in style of deformation within the batholith prior to 67 ma plutons were emplaced within an arc dominated by regional scale contractional shear zones in contrast emplacement of 67 51 ma plutons occurred in an arc increasingly dominated by normal faults with arc parallel to oblique displacement and by sinistral transtensional shear zones we have identified and mapped the structure of three plutonic complexes composed of 67 to 51 ma plutons the khyex sill complex arden lake plutonic complex and quottoon plutonic complex shear zone controlled emplacement of plutons within the batholith accounts for the widely different orientations and structural features that characterize plutons within these three complexes during and after this latest cretaceous paleogene period of intense plutonic activity and accompanying deformation the deep roots of the batholith were rapidly unroofed by ductile normal faulting prior to 50 ma

the morphodynamics of fluvial sand dunes in the river rhine near mainz germany ii hydrodynamics and sediment transport the dynamics of large isolated sand dunes moving across a gravel lag layer were studied in a supply limited reach of the river rhine during daylong surveys suspended sediment concentration bedload transport rate water depth flow velocity turbulence intensity near bed shear stress and water temperature were recorded over individual isolated dunes this paper considers the hydrodynamic environment and sediment transport over the dunes a companion paper details the sedimentology and morphology of the dunes flow over the flat gravel lag upstream of large dunes is more uniform than that over dunes and gravels are rarely entrained by in bank discharges unsteady and non logarithmic velocity profiles are common within the boundary layer above the stoss side of large dunes and the near bed flow demonstrates evidence of large scale coherent low frequency flow structures these may reflect stacked sequences of separated boundary layers generated by secondary dunes however the low amplitude morphology of large dunes does not affect the statistical properties of turbulence production over the stoss sides bed roughness and near bed shear stress commonly increase steadily over the stoss of dunes but may decrease near the crest especially where a crestal platform exists that is devoid of secondary bedforms bed roughness scales with the physical size of bed roughness elements however variability in roughness lengths is large owing to the composite nature of bed roughness bedload transport over stoss slopes is spatially variable but often shows an increase with increasing bed shear stress over the stoss well formed wakes only develop downstream of lee slopes which are close to the angle of repose otherwise separation is weak and suspension and settling of fine sediments is of little consequence to dune evolution wake flow is characterized by turbulence production one order of magnitude greater than over the stoss side which may be related to vortex shedding from the dune however wake current speeds are extremely low and variable in direction reverse flow is not sustained and no retrogressive bedforms occur in the lee of large dunes near bed shear stress and bed roughness are usually low within the wake reflecting low current speeds weak wake flow reattachment occurs at a variable distance downstream up to several times the duneform height a two dimensional numerical model for flow over dune topography calibrated using average parameter values provided a reasonable description of the flow upstream and over the backs of large dunes as far as the crestal region wake flow could not be modelled however the temporal and spatial complexity of natural three dimensional flow over the dunes resulted in variance in parameter estimates this variance precluded modelling of flow and bedload transport consequently it was not possible to model dune evolution in a deterministic sense

simulating transient ice ocean ekman transport in the regional arctic system model and community earth system model this work evaluates the fidelity of the polar marine ekman layer in the regional arctic system model rasm and community earth system model cesm using sea ice inertial oscillations as a proxy for ice ocean ekman transport a case study is presented that demonstrates that rasm replicates inertial oscillations in close agreement with motion derived using the gps this result is obtained from a year long case study pre dating the recent decline in perennial arctic sea ice using rasm with sub hourly coupling between the atmosphere sea ice and ocean components to place this work in context the rasm coupling method is applied to cesm increasing the frequency of oceanic flux exchange from once per day in the standard cesm configuration to every 30 min for a single year simulation this change causes a considerable increase in the median inertial ice speed across large areas of the southern ocean and parts of the arctic sea ice zone the result suggests that processes associated with the passage of storms over sea ice e g oceanic mixing sea ice deformation and surface energy exchange are underestimated in earth system models that do not resolve inertial frequencies in their marine coupling cycle

large scale transpressive shear zone patterns and displacements within magmatic arcs the coast plutonic complex british columbia the coast plutonic complex is the largest magmatic arc of the north american cordillera extending from northwestern washington state to eastern alaska it forms the transition between two tectonic domains that are suspected to have undergone several phases of large several thousands of kilometers orogen parallel displacement during the mesozoic and early cenozoic a compilation of fabric data published isotopic ages and new structural observations shows that the western coast plutonic complex was affected by subvertical orogen parallel crustal scale shear zones these shear zones mainly reflect sinistral transpression and were sequentially active from 110 to 87 ma during the intrusion of voluminous batholiths sinistral shearing was roughly coeval with the development of the thrust belts flanking the coast plutonic complex between 101 and 85 ma suggesting plate scale transpression was a first order process in the construction of the coast mountains orogen these shear zones separate panels with distinct plutonic and cooling histories suggesting the sinistral displacements between crustal blocks were large greater than tens to hundreds of kilometers this transpressive shear system likely reflects the jurassic to early late cretaceous migration of outboard cordilleran terranes to the south suggested by paleomagnetic evidence and plate reconstruction models this example from the coast orogen shows how transpression is partitioned between a thermally weakened magmatic arc and outwardly vergent fold and thrust belts our analysis further shows that the 2000 km long late cretaceous to early tertiary coast shear zone has a minimum extent toward the south to at least 51 30 n

rethinking the emplacement and evolution of zoned plutons geochronologic evidence for incremental assembly of the tuolumne intrusive suite california new u pb geochronologic data indicate that the tuolumne intrusive suite california was assembled over a period of at least 10 m y between 95 and 85 ma and that the half dome granodiorite intruded over a period approaching 4 m y simple thermal considerations preclude the possibility that a magma chamber the size of the half dome pluton could have existed as a liquid at shallow crustal depths for that long rather field evidence for sheeting along the margins of the suite the range of ages and the regular decrease of ages toward the center of the suite and within individual plutons suggest incremental assembly geochronologic evidence for incremental assembly is consistent with the failure of geophysical methods to detect large magma chambers with more than 20 melt even in active volcanic areas because it is unlikely that the individual plutons composing the tuolumne ever coexisted as liquid rich magmas the chemical evolution of the suite cannot be the result of simple fractionation and or mixing between exposed units but instead must reflect processes occurring during magma generation

response of low angle dunes to variable flow current understanding of bedform dynamics is largely based on field and laboratory observations of bedforms in steady flow environments there are relatively few investigations of bedforms in flows dominated by unsteadiness associated with rapidly changing flows or tides as a consequence the ability to predict bedform response to variable flow is rudimentary using high resolution multibeam bathymetric data this study explores the dynamics of a dune field developed by tidally modulated fluvially dominated flow in the fraser river estuary british columbia canada the dunes were dominantly low lee angle features characteristic of large deep river channels data were collected over a field ca 1 0 km long and 0 5 km wide through a complete diurnal tidal cycle during the rising limb of the hydrograph immediately prior to peak freshet yielding the most comprehensive characterization of low angle dunes ever reported the data show that bedform height and lee angle slope respond to variable flow by declining as the tide ebbs then increasing as the tide rises and the flow velocities decrease bedform lengths do not appear to respond to the changes in velocity caused by the tides changes in the bedform height and lee angle have a counterclockwise hysteresis with mean flow velocity indicating that changes in the bedform geometry lag changes in the flow the data reveal that lee angle slope responds directly to suspended sediment concentration supporting previous speculation that low angle dune morphology is maintained by erosion of the dune stoss and crest at high flow and deposition of that material in the dune trough