paleomagnetism of coastal california and baja california alternatives to large scale northward transport paleomagnetic data from the santa lucia orocopia sloa and baja borderland bba allochthons of coastal california and baja california have been interpreted to indicate up to 2500 km of post mid cretaceous northward transport of these regions with respect to interior north america however with neogene strike slip offsets taken into account geological interpretations correlate basement rocks of the coastal allochthons with continental basement rocks directly across the san andreas and related fault systems we have examined paleomagnetic data from sloa and bba and conclude that apparent discordances can be explained without large scale pre neogene tectonic transport three major observations are fundamental to this analysis 1 paleolatitudes derived from volcanic rocks of the jurassic eugenia formation of bba and coast range ophiolite of sloa are concordant when compared to revised jurassic reference paleomagnetic poles from interior north america 2 isotopic and paleobarometric data from the peninsula ranges batholith in southern california indicate that the batholith has been tilted northeast side up by an amount that can account for discordant paleomagnetic directions observed in plutonic rocks of the batholith without large scale northward transport 3 literal interpretation of the paleolatitudes determined from paleomagnetic directions in upper cretaceous and paleogene marine sedimentary rocks of sloa and bba requires north then south then north transport and a complex motion history between the two allochthons however concordant paleolatitudes are indicated by some sedimentary rocks while coeval or younger sedimentary rocks of the same allochthon have discordant paleolatitudes coupled with recent documentations of compaction shallowing of paleomagnetic inclination in other marine sedimentary rocks these inconsistencies suggest that paleolatitudes derived from most of the marine sedimentary rocks of sloa and bba are biased towards low paleolatitudes by compaction shallowing

features of coastal current instabilities in the north sea results of a numerical model coastal currents that are forced by buoyancy discharges from rivers often show a tendency to become unstable under certain conditions two such coastal current systems in the north sea the german bight and the skagerrak and their instabilities are investigated and compared here with the help of a fully nonlinear three dimensional baroclinic circulation model differences between the two regions were found with respect to three main aspects first in the skagerrak instabilities contribute to the kinetic energy on a scale that is comparable to the mean kinetic energy this does not hold for the german bight second of the two forms of instabilities fed by baroclinic and barotropic energy conversion in the skagerrak barotropic conversion is as important as baroclinic instability while in the german bight baroclinic conversion clearly dominates finally in the german bight instability tends to occur only if supported by wind in a direction that helps establishing a steep front against strong tidal mixing one explanation for the distinction in the features of the two regions is the water depth german bight is 40 m skagerrak is 300 m and consequently the amount of tidal mixing applied to the near surface coastal current front several deep and shallow water coastal currents outside the north sea are found to exhibit features similar to those presented for the skagerrak and german bight

resolving marine gravity with ers 1 satellite altimetry to estimate how well ers 1 data from the 35 day repeat mission can resolve fine structure in the marine geoid or gravity field we compare along track gravity and gridded gravity fields derived from ers 1 fast delivery altimeter data to those computed from geosat geodetic mission altimeter observations in the southern ocean we find that single passes of ers 1 data can resolve along track gravity anomalies with wavelengths as short as 28 30 km i e comparable to geosat however the ers 1 gridded gravity field can only resolve anomalies as short as 66 km versus 18 km for geosat this two dimensional resolution is limited by the larger ground track spacing 35 km at 60 s of ers 1 to resolve fine structure in the marine gravity field it is essential to have altimeter data along more closely spaced ground tracks such as those planned for the ers 1 176 day repeat mission in 1994

are mesoscale eddies in shelf seas formed by baroclinic instability of tidal fronts 1 the formation of eddies along tidal fronts in the shelf seas is investigated through both the analysis of high resolution conductivity temperature depth ctd data and drifters for the north sea as well as experiments with an eddy permitting model baroclinic eddies are difficult to observe in the shelf seas due to their small size and their surface signals are dampened by air sea interaction and eroded by wind and tidal mixing high resolution ctd profiles reveal possible eddy signals along the thermocline where there are intrusions of waters of reduced salinity on the eddy scale these freshwater intrusions carry low potential vorticity indicating their origin from the surface mixed layer an instability analysis of these frontal systems suggests that these eddy signals can be formed by baroclinic instability numerical model integrations reveal that mesoscale eddy variability along the thermocline increases in strength in late summer in accord with the increase in stratification the stability analysis of the modeled fronts and the scaling of the eddy kinetic energy to the available potential energy are also consistent with baroclinic instability theory while influencing the eddy variability through the passage of synoptic weather systems wind energy input is too small to explain the high values of eddy kinetic energy during late summer these eddy circulations provide localized regions of high vorticity and high stirring which are important for the transfer of tracers at middepth such as potential vorticity salinity and nutrients

lagrangian assessment of simulated surface current dispersion in the coastal ocean 1 a purely lagrangian assessment of dispersion from modeled surface current trajectories in the coastal ocean is presented modeled trajectories come from roms simulations for the southern california bight during the 1996 through 1999 period data are from surface current trajectories collected primarily in the santa barbara channel with code style drifters distributions of particle positions from trajectories emanating from launch locations within 10 kilometers of the coast throughout the santa barbara channel that advect for one through four days lagrangian pdfs are evaluated descriptively and quantitatively the two dimensional kolmogorov smirnov k s statistical test for comparing discrete sampled data with a known probability distribution is the quantitative basis in general dispersion distributions from observations are similar to lagrangian pdfs computed from modeled trajectories and the k s statistic quantifies this accordingly a few specific regions of poor model data agreement are indicated and discussed the purely lagrangian assessment elucidates an improved understanding of model performance and ocean circulation beyond that offered in a eulerian sense and is necessary when modeled trajectories are utilized for applied oceanographic and marine ecology problems

thrusting of the central california margin over the edge of the pacific plate during the transform regime wide angle seismic reflection and refraction data mapped geologic structures and marine magnetic anomalies provide evidence that oceanic crust underlies the coastal margin of california from morro bay northward beyond san francisco we interpret the presence of this oceanic slab to be at least partly the result of thrusting of north america over the pacific plate during pliocene to quaternary time well after the principal subduction regime ended likely causes of this thrusting are the change in plate motions at about 3 5 ma and extension in the basin and range province

simulations of nearshore particle pair dispersion in southern california knowledge of horizontal relative dispersion in nearshore oceans is important for many applications including the transport and fate of pollutants and the dynamics of nearshore ecosystems two particle dispersion statistics are calculated from millions of synthetic particle trajectories from high resolution numerical simulations of the southern california bight the model horizontal resolution of 250m allows the investigation of the two particle dispersion with an initial pair separation of 500m the relative dispersion is characterized with respect to the coastal geometry bathymetry eddy kinetic energy and the relative magnitudes of strain and vorticity dispersion is dominated by the submesoscale not by tides in general headlands are more energetic and dispersive than bays relative diffusivity estimates are smaller and more anisotropic close to shore farther from shore the relative diffusivity increases and becomes less anisotropic approaching isotropy 10km from the coast the degree of anisotropy of the relative diffusivity is qualitativelyconsistentwiththat foreddy kinetic energy thetotal relative diffusivity asa functionof pairseparation distance r is on average proportional to r 5 4 additional lagrangian experiments at higher horizontal numerical resolution confirmed the robustness of these results structures of large vorticity are preferably elongated and aligned with the coastline nearshore which may limit cross shelf dispersion the results provide useful information for the design of subgrid scale mixing parameterizations as well as quantifying the transport and dispersal of dissolved pollutants and biological propagules

relative dispersion of surface drifters in the benguela upwelling region abstractwe examine the relative dispersion of surface drifters deployed in groups of triplets at the boundaries of a filament in the upwelling region off namibia for both the entire ensemble and th

the kinematic paradox of the san andreas fault the pacific north america plate boundary along the san andreas fault system is notoriously a right lateral transpressive margin where both almost pure thrust and strike slip tectonics take place the pacific plate travels wnw forming an angle of about 25 with the boundary since the pacific is moving wnw faster than north america right lateral transtension should result along the san andreas system north america in turn travels westward obliquely to the boundary and a left lateral transpressive component would be expected along the same margin therefore the right lateral transpression of the san andreas system can be partitioned into i a sinistral transpression along the southwestern margin of the north america plate obliquely overriding ii a faster right lateral transtension occurring along the transfer margin of the pacific plate between the east pacific rise in the california gulf and the gorda ridge to the north west this is due to the oblique trend of the pacific and north america plate margins with respect to their motion in a absolute reference frame the geodynamics of california is marked by a unique setting in which there is a special subduction where in contrast with classic subduction zones the footwall of the subduction plane is obliquely diverging from the hanging wall in an e w section while it is converging at slower rates in a ne sw direction the extensional e w component is absorbed into the basin and range rifting whereas the compressive ne sw component is mainly expressed in the coast ranges and california offshore the compression perpendicular to the san andreas is then not intrinsic in the strike slip movement but it is rather an independent tectonic factor therefore the san andreas system cannot be considered as an archetype of a pure strike slip fault

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

tectonic motion and deformation from satellite laser ranging to lageos satellite laser ranging slr to lageos acquired during the period 1978 1988 has been analyzed to yield estimates of tectonic motion for 22 laser tracking stations situated on seven major plates the analysis is based on the precise modeling of the orbit dynamics of lageos and includes the determination of other geodynamic and nonconservative force model parameters involved in the orbit determination problem at the centimeter level site velocities were recovered from station positions determined each calendar quarter using a network adjustment procedure which maintains the reference frame within the stable interior of tectonic plates the recovered motions indicate good agreement with existing estimates of stress fields particularly across northern europe the eastern pacific and in the basin and range province of north america a comparison of the intersite motions for stations centrally located on separate plates between slr and those implied by the nuvel 1 geologic motion model yield a strong positive correlation of 0 989 and a 3 7 scale difference which may be attributable to recent changes in relative velocities or geologic time scale uncertainties sites located at or within 250 km of convergent plate boundaries have additional components of motion indicating a need for further tectonic modeling beyond that provided by simple rigid plate motions for lines crossing the north atlantic the san andreas fault and within the basin and range province the geodesic rates determined by slr are in good agreement with those determined by very long baseline interferometry an alternative space geodetic technique

tectonic implications of post 30 ma pacific and north american relative plate motions the pacific plate moved northwest relative to north america since 42 ma the rapid half rate of pacific farallon spreading allowed the ridge to approach the continent at about 29 ma extinct spreading ridges that occur offshore along 65 of the margin lonsdale 1991 document that fragments of the subducted farallon slab became captured by the pacific plate and assumed its motion prior to the actual subduction of the spreading ridge this plate capture process can be used to explain much of the post 29 ma cordilleran north america extension strike slip and the inland jump of oceanic spreading in the gulf of california the pacific and north american contact zone lengthened with each successive plate capture event underpinning the parts of western north america directly inland with a strong plate undergoing pacific relative motion we suggest that much of the post 29 ma continental tectonism is the result of the strong traction imposed on the deep part of the continental crust by the gently inclined slab of subducted oceanic lithosphere as it moved to the northwest relative to the overlying continent the plate capture hypothesis is distinctly different from theories involving shallow slab gaps kinematic problems associated with shallow slab gap models cause us to question them this conclusion is consistent with seismic refraction interpretations that suggest there is an inclined layer with high velocities like that of basalt or gabbro at the base of the continental crust beneath much of the californian margin and the documented reduction of slab pull forces and density associated with young subducting slabs thermal and rheologic modeling suggests that coastal california was a strong zone at all depths allowing it to be firmly linked to pacific motion our model shows that deformed regions such as the basin and range and borderland provinces developed in predicted weak parts of the crustal section but they have been incompletely linked to the deep plate across the ductile middle and lower crustal layer

current plate velocities relative to the hotspots incorporating the nuvel 1 global plate motion model nuvel 1 is a new global model of current relative plate velocities demets et al 1990 which differ significantly from those of prior models here we incorporate nuvel 1 into hs2 nuvel1 a new global model of plate velocities relative to the hotspots hs2 nuvel1 was determined from the hotspot data and errors used by minster and jordan 1978 to determine am1 2 which is their model of plate velocities relative to the hotspots am1 2 is consistent with minster and jordan s relative plate velocity model rm2 here we compare hs2 nuvel1 with am1 2 and examine how their differences relate to differences between nuvel 1 and rm2 hs2 nuvel1 plate velocities relative to the hotspots are mainly similar to those of am1 2 minor differences between the two models include the following 1 in hs2 nuvel1 the speed of the partly continental apparently non subducting indian plate is greater than that of the purely oceanic subducting nazca plate 2 in places the direction of motion of the african antarctic arabian australian caribbean cocos eurasian north american and south american plates differs between models by more than 10 3 in places the speed of the australian caribbean cocos indian and nazca plates differs between models by more than 8 mm yr although 27 of the 30 rm2 euler vectors differ with 95 confidence from those of nuvel 1 only the am1 2 arabia hotspot and india hotspot euler vectors differ with 95 confidence from those of hs2 nuvel1 thus substituting nuvel 1 for rm2 in the inversion for plate velocities relative to the hotspots changes few euler vectors significantly presumably because the uncertainty in the velocity of a plate relative to the hotspots is much greater than the uncertainty in its velocity relative to other plates

observed and modeled drifters at a tidal inlet material transport and dispersion near the mouth of a tidal inlet new river inlet nc are investigated using gps tracked drifters and numerical models for ebb tide releases velocities are largest 1 m s 1 in two approximately 30 m wide channels that bisect the 1 3 m deep ebb shoal in the channels drifter and subsurface current meter velocities are similar consistent with strong vertical mixing and 2 d hydrodynamics drifters were preferentially entrained in the channelized jets where drifter cluster lateral spreading rates in were small in 0 5 m2 s 1 at the seaward edge of the ebb shoal jet velocities decrease linearly with distance to 0 2 m s 1 about 1 km from shore and cluster spreading rates are larger with out 3 m2 s 1 although the models coawst and nearcom generally reproduce the observed trajectory directions certain observed drifter properties are poorly modeled for example modeled mean drifter velocities are smaller than observed and upon exiting the inlet observed drifters turn north more than modeled drifters the model simulations do reproduce qualitatively the spreading rates observed in the inner inlet the flow deceleration and the increase in out observed in the outer inlet however model spreading rates increase only to out 1 m2 s 1 smaller modeled than observed out may result from using unstratified models noncoincident in space observations show evidence of a buoyant plume 1 kg m 3 in the outer inlet likely affecting drifter lateral spreading generally drifter based model performance is good within the inlet channels where tidal currents are strongest whereas model data differences are significant farther offshore

relative dispersion of surface drifters in a barrier reef region 1 the spreading of two clusters of satellite tracked surface drifters was quantified by relative dispersion and relative diffusivity the time derivative of relative dispersion in two regions of the southern great barrier reef gbr a low density reef matrix of complex topography and a shelf lagoon over flat bathymetry although based on a small data set averaged values of these parameters over a 12 day period with concurrent measurements for the two regions indicated that relative dispersion and diffusivity of drifter pairs were 182 and 52 times greater respectively along the reef matrix than found in the lagoon relative diffusivities in the southern gbr were anisotropic and varied largely in space and time within the spatial scales of 1 100 km and temporal scales of hours to 16 20 days they were considerably enhanced by high frequency tidal processes submesoscale processes 20 km were important in the southern gbr particularly in areas with complex topography where secondary circulations around the reefs and regions of steep bathymetry caused abrupt increase in dispersion although the dispersion was much higher along the reef matrix the presence of ring circulations around the islands and wake eddies in the lee of islands can act as trapping mechanisms to keep particles within the reef matrix retarding the loss to open water areas this provides an efficient physical mechanism for both enhancing larval connectivity between reefs and at the same time trapping larvae when in the vicinity of reefs

ocean convergence and the dispersion of flotsam floating oil plastics and marine organisms are continually redistributed by ocean surface currents prediction of their resulting distribution on the surface is a fundamental long standing and practically important problem the dominant paradigm is dispersion within the dynamical context of a nondivergent flow objects initially close together will on average spread apart but the area of surface patches of material does not change although this paradigm is likely valid at mesoscales larger than 100 km in horizontal scale recent theoretical studies of submesoscales less than 10 km predict strong surface convergences and downwelling associated with horizontal density fronts and cyclonic vortices here we show that such structures can dramatically concentrate floating material more than half of an array of 200 surface drifters covering 20 20 km2 converged into a 60 60 m region within a week a factor of more than 105 decrease in area before slowly dispersing as predicted the convergence occurred at density fronts and with cyclonic vorticity a zipperlike structure may play an important role cyclonic vorticity and vertical velocity reached 0 001 s 1 and 0 01 ms 1 respectively which is much larger than usually inferred this suggests a paradigm in which nearby objects form submesoscale clusters and these clusters then spread apart together these effects set both the overall extent and the finescale texture of a patch of floating material material concentrated at submesoscale convergences can create unique communities of organisms amplify impacts of toxic material and create opportunities to more efficiently recover such material

state of stress and crustal deformation along weak transform faults the state of stress and style of crustal deformation along weak transform plate boundaries is discussed in the context of available data and simple analytical models appreciable evidence indicates that while the frictional strength of the upper crust is high in general accordance with simple faulting theory and laboratory derived coefficients of friction the frictional resistance to motion along transform plate boundaries is extremely low these conditions require that horizontal principal stresses must be oriented approximately parallel and perpendicular to the transform fault zone to minimize the shear stresses acting parallel to the transform along plate margins that must accommodate relative convergence transpressive margins a pattern of near fault normal compression and fault normal crustal shortening is expected along divergent plate margins transtensional margins extension is expected to occur perpendicular to the transform as the direction of minimum horizontal principal stress is expected to be nearly perpendicular to it these patterns of stress and deformation can be observed along a number of transform faults around the world

observing surf zone dispersion with drifters abstract surf zone dispersion is studied using drifter observations collected within about 200 m of the shoreline at depths of less than about 5 m on a beach with approximately alongshore uniform bathymetry and waves there were about 70 individual drifter releases each 10 20 min in duration on two consecutive days on the first day the sea swell significant wave height hs was equal to 0 5 m and mean alongshore currents were moderate 0 1 m s 1 on the second day the obliquely incident waves were larger with hs equal to 1 4 m and at some surf zone locations was greater than 0 5 m s 1 the one particle diffusivity was larger with larger waves and stronger currents on both days the one particle diffusivity tensor is nonisotropic and time dependent the major axis is initially parallel to the cross shore direction but after a few wave periods it is aligned with the alongshore direction in both the along and cross shore directions the asymptotic diffusivity is reached sooner within r

pairwise surface drifter separation in the western pacific sector of the southern ocean the southern ocean plays a critical role in global climate yet the mixing properties of the circulation in this part of the ocean remain poorly understood here dispersion in the vicinity of the southern antarctic circumpolar current front one of the branches of the antarctic circumpolar current is studied using 10 pairs of surface drifters deployed systematically across the frontal jet and its flanks drifter pairs were deployed with an initial separation of 13 m and report their position every hour the separation of the pairs over 7 months in terms of their finite scale lyapunov exponents fsle dispersion and diffusivity is characterized and related to expected behavior from quasi geostrophic qg and surface quasi geostrophic sqg theories the fsle analysis reveals two submesoscale regimes with sqg like behavior at scales below 3 2 km and mixed qg sqg behavior at scales between 3 2 and 73 km the dispersion analysis however suggests qg like behavior for the smallest scales both dispersion and diffusivity appear isotropic for scales up to 500 km finally there is no clear indication of a cross jet variation of drifter dispersion

deep crustal reflection profiling offshore southern central california deep crustal reflection profiling offshore southern central california shows that the offshore santa maria basin and adjacent shelf and slope are underlain by oceanic crust which underthrusts the margin on common midpoint cmp sections the top of the oceanic crust appears as a strong coherent reflection occurring at 6 s two way time twt the reflection can be traced continuously more than 50 km from the deep ocean basin eastward beneath the continental shelf depth conversion places the top of oceanic crust at 6 16 km depth with a dip of 8 toward the coast beneath the santa lucia high the crustal reflection breaks up into several east dipping segments above the oceanic crust an accretionary wedge increases in thickness from 3 km at the base of the slope to over 12 km beneath the santa lucia high the neogene sedimentary section above the accretionary prism exhibits relatively little deformation implying that most of the accretion occurred during pre neogene convergence between the north american plate and oceanic plates located to the west the offshore santa maria basin exhibits at least two periods of neogene deformation an early extensional phase accompanied by strike slip faulting occurred in the lower to middle miocene followed by compression and basin inversion in the upper miocene lower pliocene the development of structures in the basin began in the northwest and is progressively younger to the southeast faults identified in the offshore sedimentary column offset acoustic basement but are not imaged in the franciscan basement material below 2 3 s twt and do not extend to or offset the deep reflections we suggest that the oceanic crust served as a detachment surface above which the shallow deformation occurred neogene sediments in the offshore basins show only 1 3 km of shortening this implies that shortening due to neogene oblique plate motion between the pacific and north american plates extends east of the offshore santa maria basin and is distributed across the entire transform margin

space geodetic measurement of crustal deformation in central and southern california 1984 1992 we estimate the velocity field in central and southern california using global positioning system gps observations from 1986 to 1992 and very long baseline interferometry vlbi observations from 1984 to 1991 our core network includes 12 gps sites spaced approximately 50 km apart mostly in the western transverse ranges and the coastal borderlands the precision and accuracy of the relative horizontal velocities estimated for these core stations are adequately described by a 95 confidence ellipse with a semiminor axis of approximately 2 mm yr oriented roughly north south and a semimajor axis of approximately 3 mm yr oriented east west

on the dispersion and diffusion near estuaries and around islands abstract a series of diffusion experiments using surface drifters were performed in the coastal waters of south western taiwan near a small estuary and around an island two stages or regimes of drifter dispersion can be identified for all experiments a coherent regime in the beginning stage when the drifters remained clustered with little dispersion occurred and a rapid disperse regime in the latter stage when the separation of drifters grew to the order of a few kilometres our results show that near estuaries the extent of the dispersive influence is limited to the tidal excursion distance and the dispersion coefficient is about 12 15 m 2 s 1 on the other hand the dispersion coefficient downstream of an island in a strong flow 1 5 m s 1 can reach a much larger value 45 m 2 s 1 which can be attributed to the enhanced mixing and transport processes due to island wakes theoretical scaling parameters for coastal water flows are also presented to predict the formation of island wakes after applying three different methods to exclude the effects of shear flow the turbulent diffusivities for our experiments amount to 0 2 5 m 2 s 1 analysis of the differential kinematic properties indicates that a close relationship exists among the dispersion diffusion and the effect of shear flow

observations of near surface current shear help describe oceanic oil and plastic transport plastics and spilled oil pose a critical threat to marine life and human health as a result of wind forcing and wave motions theoretical and laboratory studies predict very strong velocity variation with depth over the upper few centimeters of the water column an observational blind spot in the real ocean here we present the first ever ocean measurements of the current vector profile defined to within 1 cm of the free surface in our illustrative example the current magnitude averaged over the upper 1 cm of the ocean is shown to be nearly four times the average over the upper 10 m even for mild forcing our findings indicate that this shear will rapidly separate pieces of marine debris which vary in size or buoyancy making consideration of these dynamics essential to an improved understanding of the pathways along which marine plastics and oil are transported

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

model based directed drifter launches in the adriatic sea results from the dart experiment abstract a high resolution numerical model of the adriatic sea is used to predict lagrangian coherent structure boundaries quantified by finite size lyapunov exponents fsle for flow features in the region of the gargano peninsula during the course of the dynamics of the adriatic in real time dart observational program fsle fields computed from two day model forecasts of the surface velocity indicate distinct regions of high relative drifter dispersion model predictions of such regions located on available ship tracks were used to direct the launching of pairs of surface drifters on three days during march 2006 with the goal of maximizing coverage of the sampling area for two of the three launches the observed trajectories separated at locations and along directions closely approximated by those predicted from the model fsle fields the third case acted as an inadvertent control experiment model predictions at release time showed minimal fsle structure at the launch locations and the observed drifter pair advected in a coherent fashion for two days while there are considerable differences between individual drifter observations and trajectory envelopes computed from ensembles of synthetic drifters the experiment confirms the model s ability to approximate the location and shape of energetic flow features controlling the near time fate of quasi lagrangian particles overall the combined use of fsles with realistic coastal circulation models appears to be a promising avenue to aid real time directed drifter launches in observational programs

north america pacific plate boundary an elastic plastic megashear evidence from very long baseline interferometry i investigate a number of lithospheric deformation models based upon the concept that the motions of points near the north america pacific plate boundary are a linear combination of north america and pacific velocities this concept entails a shear strain transition zone in the vicinity of the boundary the best of these models fit 95 of the variance in 139 very long baseline interferometry vlbi length and transverse velocity observations taken over 5 5 years and require only 90 of the relative plate motion predicted by rm2 residual misfits in the megashear models are largely explained by a 6 1 mm yr component of basin and range spreading perpendicular to the plate boundary instantaneous shear deformation associated with plate tectonics is apparently developing in a zone 450 km wide paralleling the san andreas fault some of this deformation will be recovered through elastic rebound the rest will be permanently set through plastic processes thus depending on the elastic plastic composition of the borderlands the width and pattern of strain accumulation in the megashear over geological time may or may not be significantly different than what is currently observed because vlbi data have been assembled for only a small fraction of the earthquake cycle plastic and elastic strains are indistinguishable other information will have to be brought to bear to discriminate elastic and plastic behaviors and reconcile instantaneous and geologic deformation near the north america pacific margin

lagrangian drifter dispersion in the southwestern atlantic ocean abstractin the framework of monitoring by ocean drifters mondo project a set of lagrangian drifters were released in proximity of the brazil current the western branch of the subtropical gyre in the south atlantic ocean the experimental strategy of deploying part of the buoys in clusters offers the opportunity to examine relative dispersion on a wide range of scales adopting a dynamical systems approach the authors focus their attention on scale dependent indicators like the finite scale lyapunov exponent fsle and the finite scale mean square relative velocity fsrv between two drifters as a function of their separation and compare them with classic time dependent statistical quantities like the mean square relative displacement between two drifters and the effective diffusivity as functions of the time lag from the release the authors find that dependently on the given observable the quasigeostrophic turbulence scenario is overall compatible with their data analysis with discrepancies fr

late neogene and quaternary tectonics associated with northward growth of the san andreas transform fault northern california strain patterns within the forearc at a convergent margin adjacent to a passing fault fault trench triple junction show a systematic evolution we describe late neogene and quaternary deformation in northern coastal california in the last 3 m y associated with the migration of the mendocino triple junction deformation in the north american forearc near humbolt bay consists of a 30 km wide zone of on land contraction with a narrower zone of translation to the east the zone of subaerial contraction is part of the relatively wide southernmost extent of forearc contraction within the cascadia subduction zone net quaternary northeast southwest contraction across forearc thrust faults is at least 7 9 km and minimum fault slip rates on the six major thrust faults are 0 8 2 3 mm yr net right slip within the zone of translation is a minimum of 3 km south of the forearc translation is predominant in the north american plate and is accommodated along two major right lateral fault zones of the san andreas transform boundary the lake mountain and garberville fault zones discontinuous exposures of late neogene sediments along these faults near covelo and garberville respectively indicate that crustal contraction expressed by thrust faults and associated folding predated translational deformation at each site inception of contraction near covelo was related to inception of internal deformation of the gorda plate at 3 ma this contraction due to coupling of the convergent plates migrated northward in the forearc in advance of and at the rate of migration of the triple junction present day deformation near humboldt bay thus reflects contraction associated with subduction of the gorda plate and translation farther east associated with oblique convergence at the plate boundary as the triple junction migrates the strike slip faults of the san andreas transform boundary will extend to the north northwest into the present forearc and forearc strike slip faults will become faults of the san andreas system contractional structures near humboldt bay will then cease to be active and will be preserved in the geologic record in the same way as contractional structures are preserved farther south

a compaction correction for the paleomagnetism of the cretaceous pigeon point formation of california the paleomagnetism of the cretaceous pigeon point formation turbidites was reexamined to determine whether the 25 of southerly paleolatitudinal offset originally observed champion et al 1984 for these rocks was all or in part due to compaction shallowing of their paleomagnetic inclination the study consisted of two parts 1 a standard paleomagnetic study including detailed thermal and alternating field demagnetization was conducted on oriented cores collected at pigeon point approximately 50 km south of san francisco california the results of this study were combined with the alternating field demagnetized results for samples provided by d champion from the initial pigeon point paleomagnetic study the combined data set has a mean direction for pigeon point i 41 6 d 346 9 similar to that originally obtained by champion et al 1984 2 material from the pigeon point formation was disaggregated given a laboratory analog of a postdepositional remanence and compacted to pressures as high as 0 13 mpa which caused volume losses up to 53 the laboratory compacted samples were alternating field demagnetized and their magnetic inclination and anisotropy of anhysteretic remanence were both measured these data were used to derive correction curves following jackson et al 1991 which describe the specific relationship between remanence anisotropy and inclination shallowing for the pigeon point formation two correction curves were determined one assuming that the magnetic particle orientation distribution experienced a prolate deformation after remanence acquisition and one assuming an oblate deformation these two different corrections were necessary because the anisotropy of anhysteretic remanence indicates a composite fabric due to both a prelithification technically caused lineation and a burial compaction foliation the anisotropy of anhysteretic remanence measured for each paleomagnetic sample and the correction curves determined from the laboratory compaction experiments indicate that the inclination of the pigeon point formation has been shallowed by burial compaction the compaction corrected pigeon point mean directions assuming either a prolate i 53 1 d 347 2 or an oblate i 49 8 d 346 8 deformation suggest only 13 to 16 of southerly paleolatitudinal offset for the pigeon point formation in the cretaceous not the 25 originally observed champion et al 1984 the resulting paleolatitude for the pigeon point formation could indicate that salinia served as a link between the cratonic sierra nevada arc to the north and the peninsula ranges baja borderlands allochthon to the south alternatively our results suggesting a 10 compaction inclination shallowing for the pigeon point turbidites may indicate that many of the paleomagnetic studies placing the peninsula ranges baja borderlands 15 to the south of north america in the cretaceous and tertiary may have suffered from a similar effect and that the allochthon has been nearly in place since the cretaceous

geological evidence for a global tectonic polarity inferences about plate motions over the past 40 ma based on structural and geodetic data suggest that there is a coherent movement direction on a global scale moreover a westward drift of the lithosphere relative to the asthenosphere is indicated by plate motions in the hot spot reference frame independent geological observations such as the different styles of deformation in thrust belts associated with subduction following or opposing the relative eastward or northeastward mantle flow also support this global tectonic polarity unfortunately most hot spot reference frames are based on assumptions which strongly limit their validity for example many combine magmatic sources originating from different depths in the mantle including hot spots located along oceanic ridges which are not fixed relative to one another using a hot spot reference frame filtered to exclude shallow hot spots and anomalous wet spots we would predict a much higher relative westward drift of the lithosphere plate motions are not random rather that they are controlled by the relative motion between lithosphere and asthenosphere and by gradients in lithospheric thickness and composition triangular shaped plates may experience rotations resulting from differential drag at the base of the lithosphere with respect to the asthenosphere e g the clockwise rotation of south america plates appear to follow an undulatory pattern of motion on a global scale and their poles of rotation fall into a main cone located near the earth s rotation poles plate rotations induced by triangular shape differential basal drag or lithospheric anisotropies along subduction zones may generate the scattered distribution of euler poles this might have inhibited the recognition of a coherent global tectonic pattern

near surface horizontal convergence and dispersion near the tidal mixing front on northeastern georges bank abstract horizontal dispersion and convergence are evaluated from near surface drifter data collected during the summer and autumn of 1988 and summer of 1989 in the vicinity of the tidal mixing front on northeastern georges bank the effective horizontal diffusivity coefficient k e estimated from the relative motion of the drifters over the duration of the cluster tracking increases as the cluster length scale with a range from approximately 100 to 450 m 2 s 1 for length scales of approximately 5 to 58 km at length scales k e is near zero with many negative estimates indicative of convergence at length scales 20 km k e increases in magnitude and scatter above 30 km length scales k e is typically between 200 400 m 2 s 1 the dispersion as a function of length scale is compared to published estimates using apparent diffusivities which are adjusted for the finite size of the drifter cluster at release georges bank shows lower apparent diffusivities at length scales 20 km the latter are believed to be principally due to the large horizontal gradients in the seasonal flow field although other processes perhaps associated with the large tidal currents may also contribute at the shorter length scales the low dispersion is due to convergent processes examples of convergence at different locations and under different wind and stratification conditions are presented convergence near the tidal mixing front tends to occur under light wind conditions and was observed in both seasons and in both years during two intense southwestward windstorms drifters also converged in the bank s vertically well mixed zone apparently due to a combination of spatially varying ekman depth and topographic effects

can we detect submesoscale motions in drifter pair dispersion abstracta cluster of 45 drifters deployed in the bay of bengal is tracked for a period of four months pair dispersion statistics from observed drifter trajectories and simulated trajectories base

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

targeted lagrangian sampling of submesoscale dispersion at a coastal frontal zone 1 the potential impact of rapidly evolving submesoscale motions on relative dispersion is at the forefront of physical oceanography posing challenges for both observations and modeling a persistent coastal front driven by river outflows in the north western mediterranean sea is targeted by two observational cruises conducted in the summer of 2010 the frontal zone is sampled using drifters launched with a multi scale strategy consisting of modules of triplets released on either side of the front by small boats this experiment is original in that the submesoscale range of 100 m to 1000 m is directly targeted and the results are expected to provide guidance for practical applications such as prediction of the initial spreading of pollutants and biogeochemical tracers the influence of submesoscale motions on relative dispersion is quantified using both particle mean square separation as a function of time and scale dependent finite size lyapunov exponents fsle our main finding is the identification of a local dispersion regime with values reaching as high as 20 days 1 at drifter pair separation distances of 100 m this value is more than an order of magnitude greater than that obtained by drifters in the offshore ligurian current the ligurian sea circulation is modeled using a fully realistic regional ocean modeling system roms with 1 60 horizontal resolution it is found that the numerical model significantly underestimates the relative dispersion at submesoscales indicating the need for particle dispersion parameterizations for unresolved processes

surface relative dispersion in the southwestern gulf of mexico abstractsurface dispersion properties in the southwestern gulf of mexico are studied by using a set of 441 drifters released during a 7 yr period and tracked for 2 months on average the drifters have a drogue below the surface ekman layer so they approximately follow oceanic currents this study follows two different approaches first two particle or pair statistics are calculated relative dispersion and finite scale lyapunov exponents fsles relative dispersion estimates are consistent with theoretical dispersion regimes of two dimensional turbulence an exponential growth during the first 3 days a richardson like regime between 3 and 20 days in which relative dispersion grows as a power law in time and standard dispersion linear growth for longer times the fsles yield a power law regime for scales between 10 and 150 km but do not detect an exponential regime for short separations less than 10 km robust estimates of diffusivities based on both relative dispersion and fsles are provided