the potential of osl and tl for dating lateglacial and holocene dune sands tested with independent age control of the laacher see tephra 12 880 a at the section mainz gonsenheim abstract optically stimulated luminescence osl and thermoluminescence tl are applied in this study to date a lateglacial and holocene aeolian sediment sequence quartz and potassium rich feldspars extracted from dune sands from western germany were dated using both multiple aliquot ma and single aliquot sa protocols for luminescence dating this particular dune section was chosen for this test study because an independent age control is provided by a horizon of the laacher seetephra 12 880 a in contrast to the results for potassium feldspars which show underestimation of up to 25 the quartz fraction provides promising results with respect to the presumed geological ages

direct evidence for an ekman balance in the california current moored acoustic doppler current profiler velocity estimates and buoy wind observations made during a period of moderate southward winds were used to test the ekman balance at a site in the california current as in prior studies the wind driven flow was separated from the total flow by subtraction of a deep reference current the wind driven flow was shown to be in an ekman balance on daily timescales over a period of several months the mean observed transport was to the right of the wind and agreed to within 3 in magnitude and 4 in phase with the predicted ekman transport although the error bar was about 20 the mean velocity profile was a smooth spiral qualitatively similar although flatter than the theoretical ekman spiral prom the observed mean momentum balance profiles of the turbulent stress and eddy viscosity were inferred eddy viscosity estimates within the wind mixed layer were o 100 cm2 s 1

moored wind temperature and current observations made during coastal ocean dynamics experiments 1 and 2 over the northern california continental shelf and upper slope moored observations of winds currents and temperature made over the northern california shelf and upper slope during the 1981 and 1982 upwelling seasons as part of the coastal ocean dynamics experiment code are described in both field experiments code 1 and code 2 the onset of the upwelling season is triggered by the strengthening of the north pacific high off northern california and signalled by the presence of water colder than 9 c near the bottom over the shelf vertical temperature stratification over the shelf is reduced during active upwelling local winds and subtidal currents over the shelf are strongly polarized in the alongshelf direction and the mean wind stress is directed equatorward response of alongshelf currents to wind forcing is similar at all depths over the shelf the response of the cross shelf current is more complex in the surface layer offshelf flow is significantly and positively correlated with the upwelling favorable alongshelf wind stress beneath this layer a weak return flow exists the thickness of the upper mixed layer varies greatly reaching 60 m during upwelling events thus direct wind forcing affects a substantial fraction of the water over the shelf low frequency wind stress current and temperature fields are adequately described by a few energetic empirical orthogonal functions with simple spatial structure the most energetic mode typically accounts for 75 or more of the variance of wind stress and temperature over the middle and inner shelf the most energetic current mode accounts for 90 or more of the variance is dominated by he alongshelf component and veers to the left with depth the low frequency alongshelf flow fluctuations are quasi barotropic with some vertical shear but no reversal with depth vertical shear in alongshelf current and the cross shelf density gradient obey the thermal wind relation the simple structure of the subdiurnal currents allow estimation of the alongshelf volume transport between the 60 and 130 m isobaths through three cross shelf transects in code 2 volume transport over the shelf is often nearly two dimensional but occasional large differences indicate significant mass exchange between the shelf and the adjacent upper slope correlation of low frequency currents and alongshelf wind stress shows the response of alongshelf current to be maximum near the surface and near midshelf where a 15 cm 1 alongshelf flow lags a 1 dyn cm 2 alongshelf wind stress by the order of 10 hours currents over the upper slope are not significantly correlated with local wind alongshelf transport over the shelf is highly correlated with local wind stress explaining 80 of the variance in the low frequency transport during code 2 volume transport is best correlated with wind stress approximately 30 km to the south winds in the code area during spring and summer are characterized by strong and persistent upwelling favorable winds interrupted by shorter periods of weak winds regression analysis indicates that in the absence of wind a poleward barotropic current jet exists over the shelf with a maximum amplitude over the inner shelf in the code area an upwelling favorable wind counters this jet over the shelf so that the alongshore flow is everywhere equator ward during strong wind events since the maximum response to wind forcing is found at midshelf and near surface the mean current over the upwelling season is strongly sheared in both the vertical and cross shelf directions mean flow over the outer shelf is surface intensified and is directed offshelf and equatorward while the deeper flow at midshelf and through most of the water column over the inner shelf is directed poleward

lagrangian exploration of the california undercurrent 1992 95 abstract during the period 1992 95 nineteen isobaric rafos floats placed in the california undercurrent at intermediate depths 150 600 m off monterey and san francisco california reveal a region of varying width of subsurface poleward flow adjacent to the continental margin the float trajectories exhibit three patterns poleward flow in the undercurrent reversing but predominately alongshore flow adjacent to the continental margin and farther offshore anticyclonic motion accompanied by slow westward drift flow continuity of the undercurrent exists between pt reyes and at least cape mendocino with an average speed dependent on the float depth speeds were variable but common features were acceleration occurring to the south of pt arena and deceleration to the north of cape mendocino an important mechanism for floats and water to enter the ocean interior from the undercurrent is through the formation of submesoscale coherent vortices

diagenesis in okavango fan and adjacent dune deposits with implications for the record of palaeo environmental change in makgadikgadi okavango zambezi basin northern botswana abstract this work considers the spatial distribution and ages of western moz basin siliclastic sediments prior to providing insights into the diagenesis of degraded dune and alluvial fan sands previously published and new tl osl ages imply that extensive over washing of dune sands took place at least 100 ka ago while ages on okavango floodplains imply that the fan was formed ca 40 ka and has since undergone periods of higher and lower flood regimes sediment analyses indicate that both dune and fan sands contain a diagenetic matrix of clay enhanced amorphous silica ceas which bonds weakly formed aggregates the time of formation of diagenetic matrix products is inconclusive but may have been accelerated during or shortly after events dated using osl tl techniques hence earlier dune over washing may have led to greater porewater of an acidic to near neutral nature which in turn promoted smectite formation and silicic acid precipitation 100 000 years ago the relatively abundant ceas matrix in floodplain sands implies more recent semi continuous flood events again of an acidic near neutral nature leading to the formation of smectite in this case the floodplain sediments are dated as having been deposited around 40 and 11 ka when porewater content may have accelerated clay formation and silica dissolution the dual nature of the ceas in the islands reflects a changing environment from smectite dominated flooding events to sepiolite dominated desiccation events flooding may also correspond to tl osl ages over the past 40 000 years which contributed to accelerated ceas formation the sepiolite is associated with a ca rich matrix implying desiccation which may relate to drying events over the 40 000 year period or to riparian tree root pumping and selective salt accumulation this work shows that sedimentation in incipient rifts is complex and rarely explained totally in terms of primary depositional events the implications of different stages of sand diagenesis may be significant in enhancing palaeo environmental interpretations in semi arid fluvial environments

fine scale variability of isopycnal salinity in the california current system this paper examines the finescale structure and seasonal fluctuations of the isopycnal salinity of the california current system from 2007 to 2013 using temperature and salinity profiles obtained from a series of underwater glider surveys the seasonal mean distributions of the spectral power of the isopycnal salinity gradient averaged over submesoscale 12 30 km and mesoscale 30 60 km ranges along three survey lines off monterey bay point conception and dana point were obtained from 298 transects the mesoscale and submesoscale variance increased as coastal upwelling caused the isopycnal salinity gradient to steepen areas of elevated variance were clearly observed around the salinity front during the summer then spread offshore through the fall and winter the high finescale variances were observed typically above 25 8 kg m 3 and decreased with depth to a minimum at around 26 3 kg m 3 the mean spectral slope of the isopycnal salinity gradient with respect to wavenumber was 0 19 0 27 over the horizontal scale of 12 60 km and 31 to 35 of the spectra had significantly positive slopes in contrast the spectral slope over 12 30 km was mostly flat with mean values of 0 025 0 32 an increase in submesoscale variability accompanying the steepening of the spectral slope was often observed in inshore areas e g off monterey bay in winter where a sharp front developed between the california current and the california under current and the lower layers of the southern california bight where vigorous interaction between a synoptic current and bottom topography is to be expected

california undercurrent variability and eddy transport estimated from rafos float observations 1 rafos float observations collected between 1992 and 2002 were analyzed to identify the seasonal variability of circulation in four geographical boxes which extended along the central and northern california coast and were successively located farther offshore the mean pressure of the floats was 375 dbar poleward flow associated with the california undercurrent dominated the two boxes closest to shore extending from the 400 m isobath to a distance of 190 km offshore for the box closest to shore the monthly mean alongshore velocity was maximum minimum 5 4 cm s 1 7 cm s in may june february while the eddy kinetic energy eke was minimum was 33 cm2 s2 21 cm2 s2 in september december february the mean eke in the coastal region was 28 cm2 s2 increasing to 50 cm2 s2 for the region farthest offshore a distance of about 400 km for that region farthest offshore eke had a broad maximum from june to november and a minimum in april lagrangian correlation and dispersion tensors were estimated for floats that left the coastal region three different dispersive regimes of float motion were identified as ballistic transport normal diffusion and anomalous sub diffusion westward sub diffusion was induced by rossby wave like structures with a periodicity of 100 120 days

testing optically stimulated luminescence dating of sand sized quartz and feldspar from fluvial deposits abstract we apply single aliquot optically stimulated luminescence osl dating to quartz and feldspar rich extracts from fluvial channel deposits of the rhine meuse system in the netherlands the time of deposition of these deposits is tightly constrained by radiocarbon dating or historical sources this allows us to compare osl ages obtained on quartz and infrared osl ir osl ages obtained on potassium rich feldspar with independent ages over the range of 0 3 13 ka we show that the quartz osl ages are in good agreement with the expected age using ir osl dating of feldspar we find a slight age overestimate for the youngest sample whereas for older samples the age is significantly underestimated we also apply osl dating to older fluvial and estuarine channel deposits with limited independent chronological constraints comparison of feldspar ir osl ages with the quartz osl ages up to 200 ka shows a clear trend where the former severely underestimates the latter this trend is similar to that found for the samples with independent age control indicating that the feldspar ir osl ages are erroneously young for the entire age range in the youngest samples incomplete resetting of the ir osl signal prior to deposition probably masks the age underestimation we show that the ir osl age underestimation is partly caused by changes in trapping probability due to preheating correction for this phenomenon improves the ir osl ages slightly but does not provide a complete solution to the discrepancy we suggest that in the light of the problems encountered in the ir osl dating of feldspar quartz is the mineral of choice for osl dating of these deposits however feldspar dating should continue to be investigated because it has potential application to longer time scales

altimeter derived variability of surface velocities in the california current system 2 seasonal circulation and eddy statistics abstract satellite surface height and temperature fields are used to examine the seasonal surface circulation in the california current system in spring and summer an equatorward jet develops next to the coast with an initial latitudinal structure that responds to the latitudinal distribution of equatorward alongshore winds this jet moves offshore from spring to fall and develops meanders and closed eddies that contribute eddy kinetic energy and water mass properties to the nearby deep ocean higher eke appears first in spring near the coast and moves offshore with the seasonal jet along altimeter tracks parallel to the coastline 200 and 400 km offshore the greatest eke is found in summer and fall respectively with wavelengths of approximately 300 km these are the wavelengths of the largest meanders and the distance between the largest eddies visible in altimeter snapshots of the jet at 600 800 km offshore the wavelengths are generally smaller 100 150 km similar to eddy sizes reported by others for the quiescent northeast pacific some energy with longer wavelengths arrives at the track 600 km offshore in winter and 800 km offshore in spring which we interpret as the most offshore extension of the eke generated by the jet and eddy system closer to the coast in the previous spring and summer a sequence of snapshots from october 1992 to october 1993 shows details of the evolution of the jet and eddy system over one complete annual cycle

hybrid modeling of p sv seismic motion at inhomogeneous viscoelastic topographic structures a new hybrid two step method for computation of p sv seismic motion at inhomogeneous viscoelastic topographic structure is presented the method is based on a combination of the discrete wavenumber dw finite difference fd and finite element fe methods in the first step the dw method is used to calculate the source radiation and wave propagation in the background 1d medium in the second step the fd fe algorithm is used to compute the wave propagation along the topographic structure the accuracy of the method has been separately tested for inclusion of the attenuation and for inclusion of the free surface topography through numerical comparisons with analytical and independent numerical methods the method is a generalization of the hybrid dw fd method of zahradnik and moczo 1996 for localized structures with a flat free surface numerical computations for a ridge sediment valley and the ridge neighboring the sediment valley show that a ridge can considerably influence the response of the neighboring sediment valley this means that the neighboring topographic feature should be taken into account even when we are only interested in the valley response

sedimentological and geochemical evidence for palaeo environmental change in the makgadikgadi subbasin in relation to the moz rift depression botswana abstract this work considers new evidence for palaeo environmental change taking place during the pleistocene in northern botswana duricrusted strandlines along the northeastern margin of sua pan provide palaeo environmental data pertaining to the makgadikgadi subbasin msb with inferences regarding the larger makgadikgadi okavango zambezi moz rift depression field xrd and geochemical data show that msb strandlines comprise calcretes lu1 type mgo rich calcretes with silica lu2 type sil calcrete lu3 type and silcrete lu4 type early freshwater episodes appear to have been followed by calcrete dominated drying phases interspersed with repeated silcretisation calcretisation through pan littoral sediments may have been both biogenically and environmentally induced calcite precipitation was in part controlled by the mg ca ratio of pore water in the pan littoral zone suggesting closed basin type evaporative conditions which were followed by a major desiccation interval phases of silcrete precipitation appear to be related to periods when the geochemistry of the lake littoral more closely resembled present day na co 3 so 4 cl type brines silica saturated acidic moderately saline groundwater preceded si precipitation which took place as the ph reduced si mobilisation occurred inter alia as a result of quartz grain dissolution enhanced by diatoms bacteria and algal growth in the moist pan littoral sio 2 rich pore waters migrated through cracked and desiccated calcrete into areas of lower salinity and lower ph resulting in preferential calcite removal and silcrete precipitation approximate tl dates imply that exposed littoral sand underwent calcretisation during the drying phases of extensive palaeo lakes which occurred prior to 110 ka 80 90 ka and 41 43 ka these wet periods compare fairly well with vostok core chronologies for southern africa

2d finite difference viscoelastic wave modelling including surface topography we have pursued two dimensional 2d finite difference fd modelling of seismic scattering from free surface topography exact free surface boundary conditions for the particle velocities have been derived for arbitrary 2d topographies the boundary conditions are combined with a velocity stress formulation of the full viscoelastic wave equations a curved grid represents the physical medium and its upper boundary represents the free surface topography the wave equations are numerically discretized by an eighth order fd method on a staggered grid in space and a leap frog technique and the crank nicholson method in time in order to demonstrate the capabilities of the surface topography modelling technique we simulate incident point sources with a sinusoidal topography in seismic media of increasing complexities we present results using parameters typical of exploration surveys with topography and heterogeneous media topography on homogeneous media is shown to generate significant scattering we show additional effects of layering in the medium with and without randomization using a von karman realization of apparent anisotropy synthetic snapshots and seismograms indicate that prominent surface topography can cause back scattering wave conversions and complex wave patterns which are usually discussed in terms of inter crust heterogeneities

a view of the 1993 1994 california current based on surface drifters floats and remotely sensed data near surface drifters were deployed in the california current system during the period 1993 1994 in order to study mean and eddy currents the deployment scheme allowed a 2 year period where data density was high enough to make meaningful estimates of eddy statistics and of seasonal mean currents and variances on a 5 grid eddy variability which tended to be isotropic was higher near the coast standard deviations around 0 2 m s 1 and decreased offshore down to 0 1 m s 1 seasonal mean surface flow west of california was southward during all seasons if a davidson current existed during 1993 1995 it was probably either short lived or only found closer to the coast than our study area i e within 100 150 km of shore in some cases drifter populations within a discrete feature were high enough to allow some detailed resolution of its behavior we note a tendency for individual eddies which can last for up to 3 5 months to drift westward at rates of o 5 km day 1 not all eddies in the region are surface intensified there is clear evidence for at least the occasional presence of a thin meandering southward jet in the region that can be 1000 km or more long this jet can be identified with that found in the coastal transition zone program in association with cool filaments the jet appears to become broader and slower south of point conception we hypothesize on the basis of others results as well as ours that the eddies that are strongest at the surface result primarily from instabilities on a southward alongshore mean current and that eddies that are maximal at depth are spawned by the northward undercurrent

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

a 3d discrete numerical elastic lattice method for seismic wave propagation in heterogeneous media with topography 1 a three dimensional elastic lattice method for the simulation of seismic waves is presented the model consists of particles arranged on a cubic lattice which interact through a central force term and a bond bending force particle disturbances are followed through space by numerically solving their equations of motion a vacuum free surface boundary condition is implicit in the method we demonstrate that a numerical implementation of the method is capable of modelling seismic wave propagation with complex topography this is achieved by comparing the scheme against a finite difference solution to the elastodynamic wave equation the results indicate that the scheme offers an alternative 3d method for modelling wave propagation in the presence of strong topography and subsurface heterogeneity we apply the method to seismic wave propagation on mount etna to illustrate its applicability in modelling a physical system

2d surface topography boundary conditions in seismic wave modelling new formulations of boundary conditions at an arbitrary two dimensional 2d free surface topography are derived the top of a curved grid represents the free surface topography while the grid s interior represents the physical medium the velocity stress version of the viscoelastic wave equations is assumed to be valid in this grid however the rectangular grid version attained by grid transformation is used to model wave propagation in this work in order to achieve the numerical discretization we show the detailed solution of the particle velocities at the free surface resulting from discretizing the boundary conditions by second order finite differences fds the resulting system of equations is spatially unconditionally stable the fd order is gradually increased with depth up to eighth order inside the medium staggered grids are used in both space and time and the second order leap frog and crank nicholson methods are used for time stepping we simulate point sources at the surface of a homogeneous medium with a plane free surface containing a hill and a trench applying parameters representing exploration surveys we present examples with a randomly realized surface topography generated by a 1d von karman function of order 1 viscoelastic simulations are presented using this surface with a homogeneous medium and with a layered randomized medium realization all generating significant scattering

new curvilinear scheme for elastic wave propagation in presence of curved topography we study a new curvilinear scheme for wave propagation modelling in presence of topography the discrete scheme takes advantage of recent developments in areoacoustics our new scheme relies on the conventional grid coupled with optimized filters to remove numerical noise in case of strong material heterogeneity we used non centred stencils for free surface implementation and optimized the explicit runge kutta scheme for the time differencing we performed a complete theoretical stability and dispersion analysis of the discrete scheme finally we illustrate the numerical accuracy of the new scheme by intensive experiments

methodology for a regional tidal model evaluation with application to central california abstract observations from disparate observational assets including tide gauges moorings and high frequency hf radars were used to depict the tidal variability and to evaluate model tidal simulations for a region off central california including the monterey bay for this study the hydrodynamic model was forced only with tides derived from a large scale model for the northeast pacific ocean homogeneous density and initially horizontally uniform density stratification cases were considered the model successfully reproduced tidal sea surface height variations within the model domain as determined by comparisons with sea level or bottom pressure measured at six locations to achieve tidal currents with realistic amplitudes as determined from hf radar and moored measurements it was found that barotropic velocity as well as sea level from the large scale regional tidal model must be included in specifying the open boundary condition however even with such forcing the model with homogeneous density field under predicted the semidiurnal and diurnal barotropic currents as estimated from depth averaged currents measured at 11 locations in the diurnal frequency band the observed surface and nearshore depth averaged currents are likely influenced by meteorological forcing which was not included in the model the hf radar measured surface tidal currents both semidiurnal and diurnal are consistent from year to year and between the winter season and the entire year semidiurnal surface tidal currents derived from year long hf radar measurements do not resemble either the modeled or measured barotropic current fields rather they exhibit amplitudes and small scale spatial variability indicative of the presence of internal tides thus indicating that model derived barotropic tidal currents cannot be validated over large spatial extents using long time series of hf radar derived surface currents with initially horizontally uniform vertical density stratification the model produced surface currents with spatial variability and amplitude range comparable to what was derived from hf radar surface current measurements but the point by point comparisons are not impressive for this region of complex topography likewise the subsurface current comparisons performed at four deepwater locations show considerable model data differences possible reasons for these disparities include the effects of atmospheric forcing spatially and temporally varying stratification remotely generated coastally trapped waves and remotely generated internal tides

a mesoscale eddy dipole in the offshore california current there is a transition zone in the california current system between inshore coastal and offshore oceanic flow this transition zone is associated with the main core of the california current and is populated with offshore mesoscale eddies the structure of isolated eddies and dipole eddy pairs found within the transition zone is examined using water mass analysis spiciness and dissolved oxygen the analyses show that these offshore mesoscale eddies have cores which contain california undercurrent water these observations and independent observations of the sitka eddy near sitka alaska support the conclusion that a bathymetrically induced instability of the california undercurrent is a likely generation mechanism for the offshore eddies this conclusion also is consistent with mathematical models of eddy generation in a subsurface poleward baroclinic current the similarity between long term mean conditions caicofi conditions observed during january 1981 and july 1985 and those of the sitka eddy coupled with the bathymetric effects provides a plausible explanation for the recurrence of offshore mesoscale eddies at preferred locations within the transition zone

poleward and equatorward currents in the pacific eastern boundary current in summer 1995 and 1998 and their relationship to the distribution of euphausiids abstract this paper examines the relationship between poleward and equatorward current patterns and the spatial distribution of euphausiids based on acoustic survey data collected in summer 1995 and 1998 in the california current ecosystem contiguous poleward usually an undercurrent and equatorward near surface current core areas were identified by applying current velocity and distance thresholds along each survey transect both currents were pervasive along the coast but poleward volume transport in both years was about an order of magnitude greater than the equatorward near surface current volume transports the poleward volume transport was higher in 1998 than in 1995 especially north of cape blanco the poleward transport centroid was generally further offshore than the surface transport centroid and was closer to the slope in 1998 than in 1995 the depth centroid of euphausiid patches was generally shallower than the depth centroid of the poleward volume transport centroids the onshore offshore location of euphausiid patches was significantly related to the location of the poleward transport centroids although not in all regions the patches were not related to the location of equatorward near surface transport centroids differences in the north south euphausiid distribution were observed between 1995 and 1998 in 1995 there was a much higher abundance of euphausiids in the region immediately north of cape blanco while in 1998 euphausiid abundance was high throughout the survey area we hypothesize this difference to be in part a result of differences in current patterns between the 2 years and the manner in which currents interact with euphausiid diel migration

moored observations of the current and temperature structure over the continental slope off central california 1 a basic description of the variability current meter data have been analyzed from seven moorings on the continental slope along the central california coast from point piedras blancas to point reyes the goal was to examine the subtidal variability in the 100 m to 1000 m depth range particularly with regard to alongshore propagating events and interactions with eddies and meanders of the california current offshore the 2 year time series available off point sur were first analyzed in conjunction with the local and remote surface wind stress and coastal synthetic subsurface pressure and then correlated with shorter coincident current records moored at similar depths to the north and south the poleward flowing california undercurrent was the most prominent feature at all the moorings except at one site located well into the monterey submarine canyon the strongest poleward flows over the slope occurred in 3 to 4 month bursts not phase locked with the seasons with vector speeds exceeding 40 cm s 1 south of the canyon an approximately monthly signal was identified which propagated poleward upward and offshore the behavior of this signal was consistent with that of an internal coastal kelvin wave generated at the surface by remote wind stress to the south and was likely not of equatorial origin the wave was apparently scattered by the abrupt topography of the canyon since its energy persisted to the north of the canyon but with unstable phase at least three eddy meander interaction events were observed these warm deep 1000 m anticyclonic features reversed the flow over the slope to equatorward when they moved onshore and interrupted the flow of the undercurrent one event forced anomalously strong 15 cm s 1 onshore flows off monterey bay and offshore flows off point sur while quantitative transport estimates could not be made with this sparse data set it seems apparent that such events play a significant role in the exchange of water properties between the shelf and the deep ocean

deep sea currents off northern california current meter records from 14 moorings in the deep sea basin 3000 4500 m deep south of the mendocino fracture zone are analyzed all moorings had current meters between 200 m and 500 m above the bottom and some extended to within 150 m of the surface there were high vertical correlations between measurements on the same mooring within 1500 m of the bottom and within 800 m of the surface but almost no significant correlation in the horizontal in the basin the presence of eddies appears strongest at depths below 1200 m several of the records exceed 3 years in length and one extended for 5 years spectral analysis of these shows that most of the kinetic energy below 3000 m is in the temporal mesoscale periods of 31 to 120 days while the spectral estimates in the upper 1000 m are dominated by longer time scales only in the deep records is there a significant southward mean flow neither a mean california current nor a poleward undercurrent is apparent in the shallower data above 1250 m the currents in the upper 500 m nearest the continental margin are influenced by the presence of cold filaments originating near point arena

dating volcanic and related sediments by luminescence methods a review abstract applications of luminescence dating of geological materials have undergone extensive development and refinement since 1974 when wintle first attempted to date volcanic lava using thermoluminescence tl today luminescence techniques are potentially highly useful methods for dating volcanic and related materials and events over timescales ranging from 10 2 to 10 6 years while luminescence approaches generally do not possess the precision afforded by techniques such as 40 ar 39 ar and 14 c methods they offer a useful alternative approach with advantages in terms of age range and scope of material although the application of luminescence methods has in some cases been successfully described a comprehensive study outlining and defining protocols for routine luminescence dating of volcanic materials has not been forthcoming this review surveys previous attempts to develop luminescence techniques to date volcanic products and discusses the state of knowledge of the luminescence behaviour of the four principal materials currently used for luminescence dating of volcanic events particular attention is paid to the red luminescence emissions primarily because of previous successes in using red thermoluminescence rtl of quartz and feldspar for dating volcanic products for which the upper age limit may extend beyond a million years proposals are made for future research directions these include technological developments in the measurement of optically stimulated red luminescence the systematic characterization of rtl and optically stimulated red luminescence as key luminescence parameters in volcanic quartz feldspar glass and polymineral sample fractions and optimization of luminescence dating methods to define a comprehensive protocol for routine dating of volcanic materials

subsurface jets in the northwestern gulf of mexico abstract subsurface jets defined as having velocity maxima 40 cm s 1 at depths between 100 and 350 m and being surrounded by much weaker near surface currents have been observed over the northwestern gulf of mexico continental slope the observations were from an array of 14 moorings equipped with upward looking 75 khz adcps deployed at 450 500 m a total of 10 jet events were observed in 18 adcp years of velocity profile data where these events were clearly not the result of downward propagating inertial internal waves the jets had durations from about 1 to 8 days and were usually associated with interactions between similarly sized cyclones and anticyclones over the slope or with the interaction of an eddy with upper slope topography the jets are associated with potential vorticity anomalies and their inferred length scales indicate that the dynamics depart from simple geostrophic balances observed anomalous density gradients present during the jets seem to involve the tilting of the vertical ax

the distribution of chlorophyll a and dominant planktonic components in the coastal transition zone off concepcion central chile during different oceanographic conditions abstract the oceanographic setting and the planktonic distribution in the coastal transition zone off concepcion 35 38 s 73 77 w an area characterized by its high biological production were assessed during two different seasons austral spring with equatorward upwelling favorable winds and austral winter with predominately northerly winds oceanographic and biological data total chlorophyll a particulate organic carbon microplankton large mesozooplankton 500 m as potential consumers of microplankton were obtained during two cruises october 1998 july 1999 together with satellite imagery for wind stress geostrophic flow surface temperature and chlorophyll a data the physical environment during the spring sampling was typical of the upwelling period in this region with a well defined density front in the shelf break area and high concentrations of surface chlorophyll a 5 mg m 3 on the shelf over the itata terrace during the winter sampling highly variable though weakly upwelling favorable winds were observed along with lower surface chlorophyll a values 100 km from the coast cyclonic and anti cyclonic eddies were evident in the flow field during both periods the former coinciding with higher chlorophyll a contents 1 mg m 3 than in the surrounding waters also a cold chlorophyll a rich filament was well defined during the spring sampling extending from the shelf out to 350 400 km offshore along a cross shelf transect the micro and meso planktonic assemblages displayed higher coastal abundances during the spring cruise but secondary peaks appeared in the oceanic area during the winter cruise coinciding with the distribution of the eddies these results suggest that the mesoscale features in this region in combination with upwelling play a role in potentially increasing the biological productivity of the coastal transition zone off concepcion

eddy properties in the california current system 1 eddy detection and tracking algorithms are applied to both satellite altimetry and a high resolution dx 5 km climatological model solution of the u s west coast to study the properties of surface and undercurrent eddies in the california current system eddy properties show remarkable similarity in space and time and even somewhat in polarity summer and fall are the most active seasons for undercurrent eddy generation while there is less seasonal variation at surface most of the eddies have radii in the range of 25 100 km sea level anomaly amplitudes of 1 4 cm and vorticity normalized by f amplitudes of 0 025 0 2 many of the eddies formed near the coast travel considerable distance westward with speeds about 2 km day consistent with the effect anticyclones and cyclones show equatorward and poleward displacements respectively long lived surface eddies show a cyclonic dominance the subsurface california undercurrent generates more long lived anticyclones than cyclones through instabilities and topographic coastline effects in contrast surface eddies and subsurface cyclones have much more widely distributed birth sites the majority of the identified eddies have lifetimes less than a season eddies extend to 800 1500 m depth and have distinctive vertical structures for cyclones and anticyclones eddies show high nonlinearity rotation speed higher than propagation speed and hence can be efficient in transporting materials offshore

upper ocean water mass characteristics of the california current summer 1993 abstract two large high resolution upper ocean surveys of the california current region were conducted in the summer of 1993 temperature and salinity were measured from a seasoar vehicle and velocity was measured by a ship borne acoustic doppler current profiler both surveys extended from the continental margin to 128 w and consisted of zonal sections 28 km apart the first survey 7 28 june extended from 39 5 n to 36 25 n and the second 16 august to 1 september extended from 39 0 n to 37 0 n the current field was fairly simple in june showing an equatorward surface jet with only one gentle meander a nearly continuous poleward california undercurrent near the continental margin and two anticyclonic subsurface eddies offshore of the jet by august meanders in the surface jet had strengthened and eddies dominated the flow field large scale trends in the water mass characteristics spiciness along three isopycnal surfaces 26 4 26 0 and 25 6 kg m 3 show that temperature and salinity tend to increase towards the equator and towards shore consistent with poleward advection along the continental margin local minima in spiciness tend to coincide with the equatorward surface jet local maxima in spiciness are associated with subsurface anticyclonic eddies which have a core depth of about 150 m and seem to originate in the california undercurrent over the continental slope at local latitudes we identified several different anticyclonic eddies each with different water mass characteristics all of the eddies we observed had diameters larger than the baroclinic radius of deformation water mass characteristics and migration rates are consistent with formation over the continental margin within the preceding 6 8 months

a poleward jet and an equatorward undercurrent observed off oregon and northern california during the 1997 98 el nino abstract the timing and intensity of the effects of the 1997 98 el nino on sea surface temperature sst and coastal sea level along the us west coast are examined using in situ time series measurements and the effects on upper ocean currents on the continental shelf and slope off oregon and northern california are examined using repeated shipborne adcp transects a mid shelf mooring off newport oregon and an hf surface current radar an initial transient positive anomaly was observed in both adjusted sea level and sst during may june 1997 followed by anomalously high coastal sea levels generally strongest during september 1997 through february 1998 and abruptly returned to normal in late february 1998 and by positive temperatures anomalies over the mid shelf that persisted longer into april 1998 low frequency coastal sea level anomalies propagated poleward at 2 1 m s poleward flow over the shelf and slope was enhanced at most depths during the el nino compared with following years northward currents in the upper 12 m over the continental shelf off newport oregon averaged 13 7 cm s stronger during august 1997 through february 1998 than during the same period the following year enhanced poleward flow was present at all latitudes sampled during november 1997 and february 1998 particularly over the continental slope these transects also provided clear views of a fall winter equatorward undercurrent which was both strongest and had the most alongshore similarity of form during the enso finally subsurface intensified anticyclonic eddies originating in the poleward undercurrent appear to be a recurrent feature of the circulation off newport late in the upwelling season

use of the geochemical and biological sedimentary record in establishing palaeo environments and climate change in the lake ngami basin nw botswana sediment samples from a continuous 4 6 m profile in the dry bed of lake ngami in nw botswana were analysed for geochemistry and dated using both 14c and tl methods certain units in the profile were found to be diatom rich and these with the geochemical results were used as indicators of high and low lake levels within the basin the lake ngami sediments contain a high proportion of sio2 51 92 5 wt avg 72 4 wt and variable levels of al2o3 2 04 17 2 wt avg 8 88 wt based on elevated al2o3 and organic matter loiorgc results lacustrine conditions occurred at ca 42 ka until 40 ka and diatom results suggest that relatively deep but brackish conditions prevailed at 40 ka the lacustrine sedimentary record was terminated abruptly possibly by tectonic activity at ca 19 ka shallow aerobic turbulent conditions were prevalent but lake levels were at this time increasing to deeper water conditions up until ca 17 ka this period coincides with the late glacial maximum a period of increased aridity in the central southern africa region generally increasing sr ca ratios and decreasing loiorgc and al2o3 from ca 16 to 5 ka suggest decreasing inflow into the basin and declining lake levels based on the enrichment of lree results slightly alkaline conditions prevailed at ca 12 ka diatom results also support shallow alkaline conditions around this time these lake conditions were maintained primarily by local rainfall input as the region experienced a warmer wetter phase between 16 and 11 ka lake levels rose rapidly by 4 ka probably in response to enhanced rainfall in the angolan catchment these results indicate that lake levels in the lake ngami basin are responding to rainfall changes in the angolan catchment area and local rainfall the results confirm that the present day anti phase rainfall relationship between southern africa and regions of equatorial africa was extant during the late quaternary over the angolan highlands and nw botswana

elastic wave propagation simulation in the presence of surface topography summary we present a 2 d numerical modelling algorithm based on a pseudo spectral method which accounts for surface topography the modelling scheme uses fourier derivative operators for spatial differencing in the horizontal direction whereas a chebyshev operator is used for vertical derivatives the incorporation of surface topography is achieved by mapping a rectangular grid onto a curved grid modelling of surface topography is important to study near surface effects of wave propagation in field seismic situations since diffraction and scattering at rough surfaces are non ray effects and can only be understood as wave phenomena static corrections cannot always account for these effects and some care has to be taken in their interpretation the presented modelling algorithm can serve as a powerful tool for the study of wave propagation phenomena in the vicinity of non planar surfaces or interfaces

equilibrium structure and dynamics of the california current system this paper addresses the structure and dynamical mechanisms of regional and mesoscale physical variability in the subtropical northeast pacific ocean using the regional oceanic modeling system roms the model is configured with a u s west coast domain that spans the california current system ccs with a mesoscale horizontal resolution up to as fine as 3 5 km its mean seasonal forcing is by momentum heat and water fluxes at the surface and adaptive nudging to gyre scale fields at the open water boundaries its equilibrium solutions show realistic mean and seasonal states and vigorous mesoscale eddies fronts and filaments the level of eddy kinetic energy eke in the model is comparable to drifter and altimeter estimates in the solutions with sufficiently fine resolution because the model lacks nonseasonal transient forcing the authors conclude that the dominant mesoscale variability in the ccs is intrinsic rather than transiently forced the primary eddy generation mechanism is the baroclinic instability of upwelling alongshore currents there is progressive movement of meanseasonal currents and eddy energy offshore and downward into the oceanic interior in an annually recurrent cycle the associated offshore eddy heat fluxes provide the principal balance against nearshore cooling by mean ekman transport and upwelling the currents are highly nonuniform along the coast with important influences by capes and ridges in both maintaining mean standing eddies and launching transient filaments and fronts

3d free boundary conditions for coordinate transform finite difference seismic modelling new alternative formulations of exact boundary conditions for arbitrary three dimensional 3d free surface topographies on seismic media have been derived they are shown to be equivalent to previously published formulations thereby verifying the validity of each set of formulations the top of a curved grid represents the free surface topography while the interior of the grid represents the physical medium we assume the velocity stress version of the viscoelastic wave equations to be valid in this grid before transforming the equations to a rectangular grid in order to perform the numerical discretization we apply the latter version of the equations for seismic wave propagation simulation in the medium the numerical discretization of the free surface topography boundary conditions by second order finite differences fds is shown as well as the spatially unconditional stability of the resulting system of equations the fd order is increased by two for each point away from the free surface up to eight which is the order used in the interior we use staggered grids in both space and time and the second order leap frog and crank nicholson methods for wavefield time propagation an application using parameters typical of teleseismic earthquakes and explosions is presented using a 200 x 100 km 2 area of real topography from southwestern norway over a homogeneous medium a dipping plane wave simulates a teleseismic p wave incident on the surface topography results show conversion from p to rg short period fundamental mode rayleigh waves in the steepest and or roughest topography as well as attenuated waves in valleys and fjords the codes are parallelized for simulation on fast supercomputers and pc clusters to model high frequencies and or large areas

looping rafos floats in the california current system abstract looping motions of rafos floats deployed off the central california coast between 1992 and 2010 are described most floats were deployed in the california undercurrent floats at 300 m were observed to loop 26 of the time with anticyclonic rotation observed about twice as often as cyclonic rotation characteristics of anticyclonic rotation at 300 m included median swirl speeds of 14 cm s for diameters of 59 km and 14 day periods long lived 70 days and at least 8 consecutive loops anticyclonic loopers are identified as california undercurrent eddies or cuddies one cuddy was observed to move southwestward 1650 km over a period of 520 days before observations ended kinematically cuddies are similar to mediterranean water eddies meddies in the iberian basin except that meddies are somewhat stronger larger and deeper over the slope most cuddies were formed between either pt sur and pt reyes or cape mendocino and cape blanco the region north of cape mendocino is estimated to generate six cuddies each year these eddies form from waters on the inshore side of the california undercurrent as they move past cape mendocino topographic drag is the most likely formation mechanism two of eight deep floats were observed to loop one anticyclonically 1545 m for 279 days and the other cyclonically 1167 m for 192 days looping for these floats ended near taney seamounts

the potential of optically stimulated luminescence for dating periglacial slope deposits a case study from the taunus area germany periglacial deposits overlying bedrock are widespread in the german low mountain ranges the age of these deposits is still a matter of debate and therefore three sections in the taunus area were investigated with luminescence dating techniques in general the heterogeneity of the sediment which is characterized by a mixture of grain sizes from clay to cobbles is the main problem for dating as dose rate determination is complicated this is demonstrated based on comparisons of high resolution ray spectrometry neutron activation analysis counting and in situ measurements of the dose rate insufficient bleaching due to the transport mode and consequently age overestimation was expected to be a major problem for luminescence dating of periglacial slope deposits in order to get a detailed insight into equivalent dose variations due to partial bleaching single aliquot regenerative dose sar protocols have been applied to the polymineralic fine grain fraction sand sized k feldspar and quartz extracts our results do not confirm partial bleaching as a problem except for the basal layer the luminescence properties vary substantially depending on the site the layer and the mineral fraction that is measured for equivalent dose determination however hardly any systematic tendencies can be observed micromorphology analysis indicates post depositional mixing which complicates the equivalent dose estimation even further due to the lack of accuracy the relevance of the presented data for palaeolandscape reconstruction is limited based on these observations suggestions are made to improve future attempts of dating periglacial cover beds with optically stimulated luminescence osl

a synthesis and review of the geological evidence for palaeotsunamis along the coast of southeast australia the evidence issues and potential ways forward abstract in recent years the role of extreme events such as tsunamis and storms in shaping coastal evolution and change has been increasingly appreciated around the world tsunami geologists are increasingly recognising the signatures of palaeotsunamis almost everywhere they look and in many cases base their interpretations on similar evidence for quaternary tsunamis first identified in australia geological research suggests that the coast of south east australia and others worldwide may have been impacted by palaeotsunamis many times larger than the catastrophic 2004 indian ocean and 2011 t hoku events in australia the debate centres on the hypothesis that the coast of south east australia preserves evidence for repeated large magnitude quaternary tsunamis if independently validated this hypothesis has profound implications for risk despite the potential importance of this hypothesis no synthesis or comprehensive review of the proposed geological evidence and chronology exists as a result it is difficult to assess the evidence and to draw conclusions about the nature of the hazard and risk along the coast this synthesis details the spatial distribution of reported palaeotsunami deposits along the coast of new south wales south east australia and summarises the distribution of different types of sedimentary and erosional evidence the age range of reported palaeotsunami deposits is identified and mapped before discussing same age chronologically correlated deposits these data are then used to draw broad conclusions about the evidence and identify future research questions to aid in the testing of the hypothesis for repeated tsunami inundation we show that 60 sites are purported to contain evidence of tsunami inundation over 650 km of the south east australian coast with a spatial concentration south of sydney geomorphic evidence distinctly different to that used elsewhere in global palaeotsunami studies is reported at 54 sites with erosional features described as the most frequent indication of inundation proposed tsunami deposits are evident at 44 sites with the dominant deposit type being imbricated boulder stacks radiocarbon dating at 39 of the sites led to a proposition of nine events during the quaternary eight of which occurred during the holocene interestingly 18 sites have no chronological data associated with them alternative interpretations are offered at six type field sites purported to contain palaeotsunami evidence attention is drawn to the disjunct between historical and geological scales of tsunami inundation in the region in addition to the contrast between the scale of reported palaeotsunamis and the robust evidence of smaller events a synthesis of research into the nature of the evidence is offered including critiques of evidence type and mechanisms a critical review of the chronological data is also presented in addition to the recalibration and analysis of published radiocarbon data the paper concludes with an outline of research questions for further work on proposed palaeotsunami sites in australia as well as a statement about likely risk in south east australia it also advocates the need for caution when interpreting evidence for palaeotsunamis elsewhere around the world when those interpretations are based on signatures originally reported in south east australia

subthermocline eddies over the washington continental slope as observed by seagliders 2003 09 abstractin the california current system subthermocline lenslike anticyclonic eddies generated within the california undercurrent cu are one mechanism for lateral transport of the warm saline waters of the cu garfield et al established the name cuddies for eddies of this type and hypothesized that they account for a significant fraction of the offshore transport of cu water this study presents observations of subthermocline eddies collected from a time series of seaglider surveys in the northern california current system gliders made 46 crossings of subthermocline anticyclones and 17 crossings of subthermocline cyclones over 5 5 yr close inspection grouped these into 20 distinct anticyclones and 10 distinct cyclones water properties at the core of anticyclonic eddies were similar to those in the core of the cu over the continental slope these anticyclones are examples of cuddies anticyclonic cyclonic eddies had average radii of 20 4 20 6 km peak azimuthal current speeds of 0 25 0 23

spatial and temporal characteristics of the mesoscale circulation of the california current from eddy resolving moored and shipboard measurements moored observations of currents and temperatures made in the upper 600 rn on eddy resolving scales over a 2 year period are used to examine the spatial and temporal characteristics of the california current mesoscale circulation the observations were made at three principal longitudes 124ow 126ow and 128ow in the vicinity of point arena they bracket the 600 km wide band of high mesoscale variability found along the eastern boundary of the north pacific at all locations the mesoscale variability was larger than the mean flow and the spatial modes of variability as determined from empirical orthogonal function analysis consisted of an alongshore mode a cross shore mode and a rotational mode observations made near the continental slope 124ow were dominated by the poleward flowing california undercurrent with mesoscale eddies and meanders superposed the nearshore eddy kinetic energy peaked in a band centered around 60 days observations made at 128ow near the offshore boundary between the energetic mesoscale band and the eddy desert of the northeast pacific were characterized by small means fewer eddy events and a peak in eddy kinetic energy at 120 180 days the good horizontal resolution of the current meter arrays allowed us to estimate the relative vorticity horizontal divergence and rossby number and therefore to evaluate the relative strength and occurrence of anticyclones and cyclones we found the mesoscale eddy field to be strongly nonlinear with rossby numbers ranging from 0 1 to 0 5 all of the eddies observed at the offshore site were nonlinear deep warm anticyclones shipboard hydrography revealed the origin of one of these anticyclones to be the california undercurrent and this eddy retained its strong anomalies after several months and several hundred kilometers of propagation despite the lower incidence of eddies as one moves west from the coast the eddies that we observed offshore provide evidence for propagation and transport of properties from the coast to the central north pacific across the california current system

3 d finite difference elastic wave modeling including surface topography three dimensional finite difference fd modeling of seismic scattering from free surface topography has been pursued we have developed exact 3 d free surface topography boundary conditions for the particle velocities a velocity stress formulation of the full elastic wave equations together with the boundary conditions has been numerically modeled by an eighth order fd method on a staggered grid we give a numerical stability criterion for combining the boundary conditions with curved grid wave equations where a curved grid represents the physical medium with topography implementation of this stability criterion stops instabilities from arising in areas of steep and rough topographies we have simulated scattering from teleseismic p waves using a plane vertically incident wavefront and real topography from a 40 40 km area centered at the noress array of seismic receiver stations in southeastern norway synthetic snapshots and seismograms of the wavefield show clear conversion from p waves to rg sh

lagrangian measurement of subsurface poleward flow between 38 n and 43 n along the west coast of the united states during summer 1993 subsurface lagrangian measurements at about 140 m showed that the path of the california undercurrent lay next to the continental slope between san francisco 37 8 n and st george reef 41 8 n during mid summer 1993 the mean speed along this 500 km path was 8 cms 1 the flow at this depth was not disturbed by upwelling centers at point reyes or cape mendocino results also demonstrate the ability to acoustically track floats located well above the sound channel axis along the california coast

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

observed evolution of a california undercurrent eddy abstracta california undercurrent eddy cuddy was repeatedly surveyed using multiple seagliders for over three months found and tracked off of the washington vancouver island coasts this cuddy t

mesoscale variability in current meter measurements in the california current system off northern california current meter data from a triad of moorings located on the continental rise offshore of point reyes point arena and from a mooring site located about 250 km offshore and to the northwest of the array are analyzed the continental rise moorings were deployed from october 1984 to july 1985 and each had five meters at depths from about 150 to about 3560 m the offshore mooring was deployed from september 1982 to august 1983 with six meters positioned from about 150 to 3800 m velocity components were highly vertically coherent in the upper 600 m and were in phase for periods longer than about 10 days temperature tended to be less coherent there was some horizontal coherence in the continental rise array coherence at 9 13 days between the deep temperature t at about 3200 m measurements at m1 and m2 located about 120 km offshore and separated by about 100 km coincided with very high in phase coherence in the northward velocity component v although there was no coherence between the first baroclinic modal components at m1 and m2 the eastward barotropic velocity component was coherent at periods of 9 11 days and the northward barotropic velocity component was coherent at 8 15 days and 4 5 6 days the triad provided a complete data set only at 350 m the highest coherence was between out of phase v components and also t at m2 and m3 about 100 km seaward of m2 at periods of 45 90 days with the dominant time domain empirical orthogonal function eof representing strong horizontal shear between m2 and m3 at periods of 9 13 days there was bottom and surface intensification in the nearshore kinetic energy spectra suggestive of a superposition of a barotropic mode with the first two baroclinic modes and partially consistent with the presence of topographic rossby waves the vertical structure at m2 differed from that at w10 the offshore mooring where the deep about 3000 m flow tended to be stronger than that near the continental slope and rotary behavior was apparent at 3000 m the barotropic modal energy was higher at w10 than at m2 but the first baroclinic modal energy was comparable at the two sites at m2 when they were coherent the barotropic and first baroclinic modes enhanced each other in the upper water column and led to reduced flow at deeper levels at w10 these modes were mainly out of phase and so enhanced the flow at deeper levels these differences which may be spatial rather than temporal increase the complications of initialization of predictive models from mass field data alone there are some indications of current and temperature variability due to fluctuating winds for example the northward components of wind stress and barotropic current were coherent at all locations at periods of 8 9 days at w10 there was also coherence between the eastward components of barotropic current and wind stress at 16 19 days on the basis of frequency domain eofs some of the current variability was forced by large scale i e about 1000 km wind stress at periods of between 5 and 10 days however less than half the current variability was demonstrably related to the wind stress at m2 and m3 at 150 m large amplitude about 1 c temperature variations which are sustained for several weeks are influenced by alongshore flow convergence and offshore jets coherence between t at 350 m and wind stress curl is suggestive of ekman pumping at m3 but the temperature was also related to alongshore convergence and offshore flow

last glacial aeolian landforms and deposits in the rhone valley se france spatial distribution and grain size characterization abstract in the rhone valley a north south oriented cenozoic rift in southeast france thick pleistocene loess deposits have been recognized since the beginning of the last century these loess records which are disconnected from the north european loess belt nelb are of significant interest to document the evolution of perimediterranean landscapes and environments during the last glacial to overcome the poor precision of available aeolian distribution maps aeolian deposits were mapped using the topsoil textural database provided by the land use and cover area frame statistical survey project lucas the grain size distribution of aeolian sand and loess was first determined using 116 samples taken from surveyed outcrops then the areas showing a similar grain size composition were extracted from the lucas rasters the resulting map reproduces the conventional maps correctly but suggests a more significant extension of loess in better agreement with the known distribution of outcrops the map shows that the distinctive morphology of the valley dominantly controls the distribution of aeolian deposits the deflation related landforms i e yardangs closed depressions pans and desert pavements are widespread south of narrowings of the rhone valley between latitudes 44 n and 45 n they indicate palaeowinds blowing from the north northwest aeolian sand loessic sand sandy loess and loess deposits successively spread on both sides of the rhone river the loess is characterized by a coarse texture main mode around 60 m strong local thickness 5 m limited extension and abundant bioturbation this preservation results from the persistence of a shrub vegetal cover during the coldest and driest phases of the last glacial that allowed for trapping the saltating and suspended particles close to the alluvial sources

2d finite difference elastic wave modelling including surface topography1 a 2d numerical finite difference algorithm accounting for surface topography is presented higher order dispersion bounded cost optimized finite difference operators are used in the interior of the numerical grid while non reflecting absorbing boundary conditions are used along the edges transformation from a curved to a rectangular grid achieves the modelling of the surface topography we use free surface boundary conditions along the surface in order to obtain complete modelling of the effects of wave propagation it is important to account for the surface topography otherwise near surface effects such as scattering are not modelled adequately even if other properties of the medium for instance randomization can improve numerical simulations inclusion of the surface topography makes them more realistic

elastic modelling on a grid with vertically varying spacing1 we present a discrete modelling scheme which solves the elastic wave equation on a grid with vertically varying grid spacings spatial derivatives are computed by finite difference operators on a staggered grid the time integration is performed by the rapid expansion method the use of variable grid spacings adds flexibility and improves the efficiency since different spatial sampling intervals can be used in regions with different material properties in the case of large velocity contrasts the use of a non uniform grid avoids spatial oversampling in regions with high velocities the modelling scheme allows accurate modelling up to a spatial sampling rate of approximately 2 5 gridpoints per shortest wavelength however due to the staggering of the material parameters a smoothing of the material parameters has to be applied at internal interfaces aligned with the numerical grid to avoid amplitude errors and timing inaccuracies the best results are obtained by smoothing based on slowness averaging to reduce errors in the implementation of the free surface boundary condition introduced by the staggering of the stress components we reduce the grid spacing in the vertical direction in the vicinity of the free surface to approximately 10 gridpoints per shortest wavelength using this technique we obtain accurate results for surface waves in transversely isotropic media

3 d elastic modeling with surface topography by a chebychev spectral method the 3 d numerical chebychev modeling scheme accounts for surface topography the method is based on spectral derivative operators spatial differencing in horizontal directions is performed by the fourier method whereas vertical derivatives are carried out by a chebychev method that allows for the incorporation of boundary conditions into the numerical scheme the method is based on the velocity stress formulation the implementation of surface topography is done by mapping a rectangular grid onto a curved grid boundary conditions are applied by means of characteristic variables the study of surface effects of seismic wave propagation in the presence of surface topography is important since nonray effects such as diffractions and scattering at rough surfaces must be considered several examples show this the 3 d modeling alogrithm can serve as a tool for understanding these phenomena since it computes the full wavefield

diagnosis of the three dimensional circulation associated with mesoscale motion in the california current a high resolution upper ocean survey of a cyclonic jet meander and an adjacent cyclonic eddy in the california current region near 388n 1268w was conducted as part of the summer of 1993 eastern boundary currents program temperature and salinity were measured from a seasoar vehicle and velocity was measured by shipboard acoustic doppler current profiler adcp seasoar data show a density front at a depth of 70 100 m with strong cyclonic curvature the geostrophic velocity fields referenced to the adcp data at 200 m show a strong surface intensified jet maximum speed of 0 9 m s 21 that follows the density front along a cyclonic meander relative vorticities within the jet are large ranging from 20 8 f to 11 2 f where f is the local coriolis parameter the seasoar density and adcp velocity data are used to diagnose the vertical velocity via the q vector form of the quasigeostrophic omega equation the diagnosed vertical velocity field shows a maximum speed of 40 45 m d21 the lateral distribution of vertical velocity is characterized by two length scales a large 75 km pattern where there is downwelling upstream and upwelling downstream of the cyclonic bend and smaller patches arrayed along the jet core with diameters of 20 30 km geostrophic streamline analysis of vertical velocity indicates that water parcels make net vertical excursions of 20 30 m over 2 3 days resulting in net vertical velocities of 7 15 m d21 water parcels moving along geostrophic streamlines experience maximum vertical velocities in the regions of maximum alongstream change in relative vorticity an indication of potential vorticity conservation

late quaternary environmental changes in the taklamakan desert western china inferred from osl dated lacustrine and aeolian deposits sediment records from the tarim basin of western china are of great importance for understanding late quaternary climatic variability in central asia a chronology of aeolian and lacustrine deposits from the centre and southern margin of the taklamakan desert central tarim basin has been established using optical dating methods distinct variations in humidity during the last 40 000 a in this extremely arid inland basin have been identified lacustrine sediments were deposited in the centre of the taklamakan during two periods of wetter than present day conditions at around 2000 and 30 000 a ago another humid period is recorded between 40 000 and 30 000 a ago aeolian processes the development of large migrating dune fields dominated during periods of more arid conditions sand wedges at the southern margin of the taklamakan are dated at ca 40 000 a and ca 18 000 a and imply a significant temperature decrease in that area sedimentological evidence for a late holocene humid period are consistent with records in ancient chinese literature wetter environmental conditions in the past within the taklamakan as indicated by the presence of lacustrine deposits are also supported by data from adjacent regions it is assumed that changes of global westerlies and of the mobile polar high triggered the fluctuations of precipitation in the study area however variations in temperature in the taklamakan desert are presumed to be mainly controlled by the intensity of the winter monsoon

wind forced variability of the deep eastern north pacific observations of seafloor pressure and abyssal currents data from an array of bottom pressure gauges and a string of current meters in the vicinity of 47on 139ow are used to examine the deep ocean variability forced by ocean surface wind stress curl from august 1987 to june 1988 bottom geostrophic currents are computed from the pressure gauge array and these correspond well to the long period directly measured currents at 3000 m the supratidalperiod bottom pressure variations are coherent at 95 confidence with the wind stress curl in period bands of 3 4 days and 15 60 days but removed in distances of 400 and 700 km to the northwest and the southeast respectively a linear two layer hydrodynamic model is used to examine the theoretical forcing produced by random phased surface wind fields for the conditions of the eastern north pacific and the 15 to 60 day period observed response is reproduced credibly to model 3 to 15 day variations more realistic models are required currents are related to surface winds were derived from yearlong current meter records in a cluster of moorings north and east of barbados koblinsky and niiler 1982 showed that significant coherences existed between the 4 to 40 dayperiod east west pulsations of the trade winds r x above barbados and the north south currents v at all depths in the ocean at 15on 54ow the response amplitude of v to r x was depth and period dependent it decreased by a factor of 3 from 150 to 4000 m depths and increased by a factor of 5 from 8 to 40 day periods the interpretation of these data was that the deep ocean forcing was produced by large horizontal scale wind stress curl hereinafter referred to simply as curl due to westward propagating pulses in the trade winds with larger east west than north south scale the amplitude of the deep wind related currents was 1 3 cm s thus deep ocean forcing should be observable in many places where the mesoscale eddy energy is low theoretically wind forced deep ocean motions should depend upon wind stress curl mt iller and frankignoul 1981 using a model of randomly forced linear motions in a stratified infinite flat bottom beta plane ocean computed local coherences and showed that motions across the planetary vorticity gradient should exhibit the strongest coherence with the local wind stress curl niiler and koblinsky 1985 using current meter data demonstrated that such a dynamical link does in fact exist locally at 42on 152ow although at a shorter period than was predicted by milller and frankignoul both the amplitude and the phase of the currents that were forced across the planetary potential vorticity field orf h contours on a 150 km horizontal scale were predicted from the local surface wind stress computed from a similar 150 km scale wind field the 4000 m oscilla

altimeter derived variability of surface velocities in the california current system 1 evaluation of topex altimeter velocity resolution in this paper we evaluate the temporal and horizontal resolution of geostrophic surface velocities calculated from topex satellite altimeter heights moored velocities from vector averaging current meters and an acoustic doppler current profiler at depths below the ekman layer are used to estimate the temporal evolution and accuracy of altimeter geostrophic surface velocities at a point surface temperature gradients from satellite fields are used to determine the altimeter s horizontal resolution of features in the velocity field the results indicate that the altimeter resolves horizontal scales of 50 80 km in the along track direction the rms differences between the altimeter and current meters are 7 8 cm s 1 much of which comes from small scale variability in the oceanic currents we estimate the error in the altimeter velocities to have an rms magnitude of 3 5 cm s 1 or less uncertainties in the eddy momentum fluxes at crossovers are more difficult to evaluate and may be affected by aliasing of fluctuations with frequencies higher than the altimeter s nyquist frequency of 0 05 cycles d 1 as indicated by spectra from subsampled current meter data the eddy statistics that are in best agreement are the velocity variances eddy kinetic energy and the major axis of the variance ellipses spatial averaging of the current meter velocities produces greater agreement with all altimeter statistics and increases our confidence that the altimeter s momentum fluxes and the orientation of its variance ellipses the statistics differing the most with single moorings represent well the statistics of spatially averaged currents scales of 50 100 km in the ocean besides evaluating altimeter performance the study reveals several properties of the circulation in the california current system 1 velocity components are not isotropic but are polarized strongly so at some locations 2 there are instances of strong and persistent small scale variability in the velocity and 3 the energetic region of the california current is isolated and surrounded by a region of lower energy starting 500 700 km offshore this suggests that the source of the high eddy energy within 500 km of the coast is the seasonal jet that develops each spring and moves offshore to the central region of the california current rather than a deep ocean eddy field approaching the coast from farther offshore

variability of the near surface eddy kinetic energy in the california current based on altimetric drifter and moored current data low pass filtered velocities obtained from world ocean circulation experiment woce surface drifters deployed in the california current off northern california during 1993 1995 have been compared with surface geostrophic velocity estimates made along subtracks of the topex poseidon altimeter and with moored acoustic doppler current profiler adcp data to obtain absolute geostrophic velocities a mean sea surface height ssh field was estimated using the mean drifter velocities and historical hydrographic data and was added to the altimetric ssh anomalies the correlation between collocated drifter and altimetric velocities is 0 73 significant at the 95 level the component of the drifter velocity which was uncorrelated with the altimetric velocity was correlated with the wind in the ekman transport sense monthly averages of eddy kinetic energy eke estimated using all drifter and altimeter data within the domain 124 132 w 33 40 5 n show energy levels for the drifters that are about 13 greater than those for the altimeter drifter altimeter and adcp measurements all exhibit similar seasonal cycles in eke with the altimeter data reaching maximum values of about 0 03 m 2 s 2 in late summer fall wavenumber spectra of the altimeter velocity indicate that the velocity fluctuations were dominated by features with wavelengths of 240 370 km while the adcp data suggest that the temporal scales of these fluctuations are at least several months between 36 and 40 5 n the region of monthly maximum eke migrates westward to about 128 w on a seasonal timescale this region of maximum eke coincides with the maximum zonal ssh gradient with increased eke associated with increased southward flow a simple model shows that much of the seasonal cycle of the ssh anomalies can be produced by linear processes forced by the curl of the wind stress although the model cannot explain the offshore movement of the front

poleward flow off central california during the spring and summer of 1981 and 1984 currents and winds measured over the continental shelf and upper continental slope during the first half of 1984 are analyzed to determine the character of the flow off central california point conception to san francisco the mean flow was poleward from point conception to point sur in opposition to the equatorward wind stress the mean flow was equatorward north of point sur fluctuations in alongshore currents over the shelf were highly correlated with local winds everywhere except off point conception where currents were not only uncorrelated with wind but also poorly correlated with currents farther north north of point buchon there is evidence for poleward propagation of shelf current variability at 175 200 cm s the correlation between currents and local wind forcing dropped considerably beyond the shelf break only 10 15 km offshore from the shelf moorings during extended periods of weak equatorward winds the poleward shelf flow south of point sur spreads farther offshore over the continental slope a three week period of calm winds in july 1984 resulted in a 100 km wide tongue of poleward flow extending 300 km along the california coast similar but somewhat weaker poleward surface flow occurred during the same period in 1981 a 2 to 3 week period of calm winds in late june and early july 1981 resulted in a 100 km wide tongue of poleward flow extending at least 150 km along the california coast in contrast to the poleward flow on the shelf which appears to be normal during spring and summer the poleward surface flow observed over the slope in july 1981 and 1984 is unusual based on historical hydrographic surveys off the central california coast poleward surface flow over the continental slope occurs seasonally in the winter but is not generally observed after february