organized structures in subsurface bubble clouds langmuir circulation in the open ocean observations of the movement and distribution of subsurface bubbles reveal the structure of coherent motions near the ocean surface the measurements were obtained in the open ocean from a freely drifting self contained acoustical instrument equipped with side scan sonar dual frequency echo sounders and ambient sound recording systems the bubble clouds are organized into long narrow plumes aligned with the wind consistent with windrows caused by langmuir circulations they have widths of about 3 to 5 m and lengths up to 100 m with multiple scales coexisting their mean separation depends upon wind speed below 5 m s 1 mean spacings were about 5 m increasing to 10 m when winds exceeded 10 m s 1 the maximum depth to which the plumes were observed to penetrate depended to some extent on wind speed with the greatest penetrations of 12 m occurring at the highest wind speeds 13 m s 1 however the time averaged depth of observed bubble plume penetration bears only a weak dependence on wind speed whenever winds exceeded 5 m s 1 a mean penetration depth of 6 m was observed associated with these bubble plumes were maximum downward velocities of about 0 06 m s 1 these speeds were detected at 8 m depth in the center of the plumes magnitudes decreased to zero near the surface and horizontally toward the boundaries of the plumes

is the rotation real earth9s interior consists of a mantle liquid core and at the very center a solid inner core made of iron one of the inner core9s most peculiar properties is its anisotropy seismic waves travel slightly faster if they are parallel to earth9s rotation axis in her perspective souriau describes recent seismic studies that suggest the inner core rotates faster than earth9s mantle and comments on the current dilemma in interpreting the experimental findings

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

climatology of barrier jets along the alaskan coast part i spatial and temporal distributions abstract this paper investigates the temporal and spatial climatology of coastal barrier jets in the gulf of alaska the jets are divided into two categories based upon the origin of the air involved classic barrier jets fed primarily by onshore flow and hybrid jets fed primarily by gap flow from the continental interior the analyses are compiled from five years 1998 2003 of synthetic aperture radar images from the radarsat 1 satellite totaling 3000 images thermodynamic and kinematic data from the ncep reanalysis is used in the interpretation of the results the majority of coastal barrier jets occur during the cool season with the coastline near mount fairweather and the valdez cordova mountains experiencing the greatest number of barrier jets hybrid jets are even more strongly restricted to the cool season and are commonly found to the west of cross sound yakutat bay and icy bay some interannual variability in the total number of jets is observed coastal barrier jet formation is associate

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

responses of benthic foraminifera to environmental variability a case from the middle jurassic of the kachchh basin western india abstract at the western margin of the indian plate the jurassic sedimentary succession of the kachchh basin provides well developed exposures for fauna based studies based on a quantitative analyses of 67 samples spanning middle bathonian late callovian interval the paleoenvironment of the jumara section the depocenter of the kachchh basin is inferred four benthic foraminiferal assemblages are recognized by both clustering and nmds ordination methods these assemblages vary in biotic traits such as life habit and diversity as well as in abiotic traits such as sediment type nutrient availability and oxygen level the bathonian spirillina polygyrata assemblage that dominates an outer neritic oligotrophic setting has a preference for calcareous substrates in the earliest callovian the epistomina mosquensis assemblage replaced the latter as oxic conditions decreased and terrigenous influx increased two successive and less diverse assemblages had a preference for non calcareous substrates and dominated the mid early late callovian landscape these are the oxic lenticulina subalata assemblage inner to middle neritic oligotrophic setting in the mid early to mid middle callovian and the dysoxic reophax metensis assemblage mesotrophic to eutrophic middle neritic setting in the late middle to late callovian linear regression models suggested that sea level oxygenation and sediment type are the main abiotic factors controlling the distribution of the fauna moreover taxa with specific biotic traits such as shell composition calcareous vs agglutinated and selection strategy r vs k strategy occupied different environmental settings furthermore diversity and epifaunal infaunal ratio had a cyclic pattern comparable to those of third order sea level fluctuations

triassic to neogene geologic evolution of the queen charlotte region a wealth of new geological and geophysical data from recent studies of the queen charlotte region are integrated into a coherent model in this paper we summarize these new studies and discuss possible correlations with other areas four tectonostratigraphic divisions are distinguished by stratigraphic structural and magmatic character and each is separated by a major unconformity the oldest division comprises widely distributed upper paleozoic through middle jurassic strata of wrangellia that accumulated in volcanic arc and stable shelf and basinal settings no significant deformation occurred in the queen charlotte islands region during the accumulation of these rocks a middle and upper jurassic assemblage comprises two plutonic suites and volcanic and epiclastic rocks the unconformity below the middle and upper jurassic assemblage marks a regional southwest vergent contractional deformation that is the most significant mesozoic or cenozoic deformation in the region jurassic plutons in the que

organic petrology and geochemistry of organic rich rocks of the late triassic and early jurassic sandilands and ghost creek formations queen charlotte islands british columbia abstract latest triassic and early jurassic marine mudrocks on the queen charlotte islands comprise a composite interval up to 600 m thick of organic rich potential petroleum source rocks these strata assigned to the sandilands and ghost creek formations are the only known significant potential petroleum source rocks on canada s western continental margin regionally the strata range from immature 0 33 r o rand on northern graham island to overmature 5 r o rand on moresby island anomalously high levels of maturity exist in sediments adjacent to intrusive rocks and dyke swarms the weight per cent total organic carbon toc content of the strata ranges up to 6 1 and the organic matter as defined by rock eval is predominantly types i and ii with hydrogen indexes ranging up to 589 mg hc g c org petrographically the organic matter is predominantly algal in origin although minor to major amounts of vitrinite occur in many samples lateral variations in toc closely reflect lateral variations in maturity based on the n alkane distribution of the saturate fraction the strata of the sandilands formation are divisible into two groups 1 samples characterized by high concentrations of c 11 to c 31 with c 15 to c 17 dominant and 2 samples characterized by n alkanes of higher molecular weight with c 20 to c 23 dominant in most samples pristane is the dominant isoprenoid but in all samples the pristane to phytane ratio is less than 2 gas chromatography mass spectrometry gc ms of representative samples indicates the presence of both diasteranes and regular steranes with a predominance of c 29 regular homologues and a series of extended tricyclic terpanes from c 19 to at least c 35 there is a predominance of terpanes over steranes the rearranged to regular sterane ratio is less than 1 and the 18 h trisnorhopane 17 h trisnorhopane 18 h trisnorhopane ratio varies from 0 49 to 0 62 samples from the ghost creek formation have a similar n alkane distribution to group 1 from the sandilands formation and gc ms of two samples suggests less abundant terpanes and steranes than found in the sandilands formation the carbon isotope composition of the organic fraction of all the strata is relatively homogenous ranging from 13 c of 25 to 30 with a mean value of 28 8 there is no consistent stratigraphic trend in 13 c nor is there significant correlation between 13 c and any of the other geochemical indexes studied in general vitrinite rich terrestrially derived organic matter is isotopically heavier than strata dominated by marine organic matter the reverse from that found today but similar to that reported during some oceanic anoxic events both organic petrology and geochemistry indicate that the organic matter is comprised of a mixture of terrestrial and marine organic matter with marine organic matter of algal origin predominating in most samples the observed geochemical variation between samples is considered to reflect variations in maturity relative abundance of terrestrial and marine organic matter and to a lesser extent biodegradation

turbulent large eddy momentum flux divergence during high wind events abstractmomentum transport by energy containing turbulent eddies in the oceanic mixed layer were investigated during high wind events in the northern gulf of alaska off kayak island sixteen high wind events with magnitudes ranging from 7 to 22 m s 1 were examined winds from the southeast prevailed from one to several days with significant wave heights of 5 9 m and turbulent langmuir numbers of about 0 2 0 4 surface buoyancy forcing was much weaker than the wind stress forcing the water column was well mixed to the bottom depth of about 73 m spectral analyses indicate that a major part of the turbulent momentum flux was concentrated on 10 30 min time scales the ratio of horizontal scale to mixed layer depth was from 2 to 8 turbulent shear stresses in the mixed layer were horizontally asymmetric the downwind turbulent stress at 10 20 m below the surface was approximately 40 of the averaged wind stress and was reduced to 5 10 of the wind stress near the bottom turbulent kinetic energy in the cros

a comprehensive model of the quiet time near earth magnetic field phase 3 summary the near earth magnetic field is caused by sources in the earth s core ionosphere magnetosphere lithosphere and from coupling currents between the ionosphere and the magnetosphere and between hemispheres traditionally the main field low degree internal field and magnetospheric field have been modelled simultaneously with fields from other sources being modelled separately such a scheme however can introduce spurious features especially when the spatial and temporal scales of the fields overlap a new model designated cm3 comprehensive model phase 3 is the third in a series of efforts to coestimate fields from all of these sources this model has been derived from quiet time magsat and pogo satellite and observatory hourly means measurements for the period 1960 1985 it represents a significant advance in the treatment of the aforementioned field sources over previous attempts and includes an accounting for main field influences on the magnetosphere main field and solar activity influences on the ionosphere seasonal influences on the coupling currents a priori characterization of the influence of the ionosphere and the magnetosphere on earth induced fields and an explicit parametrization and estimation of the lithospheric field the result is a model that describes well the 591 432 data with 16 594 parameters implying a data to parameter ratio of 36 which is larger than several popular field models

seafloor pressure measurements of nonlinear internal waves highly resolved pressure measurements on the seafloor over new jersey s continental shelf reveal the pressure signature of nonlinear internal waves of depression as negative pressure perturbations the sign of the perturbation is determined by the dominance of the internal hydrostatic pressure p 0 due to isopycnal displacement over the contributions of external hydrostatic pressure 0gh h is surface displacement and nonhydrostatic pressure p 0 each of opposite sign to p 0 this measurement represents experimental confirmation of the wave induced pressure signal inferred in a previous study by moum and smyth

measurements of the cretaceous paleolatitude of vancouver island consistent with the baja british columbia hypothesis a previously unsampled outcrop of gently dipping or flat lying upper cretaceous sedimentary strata in the vancouver island region which contains unaltered aragonitic mollusk fossils yielded a stable remanent magnetization that is biostratigraphically consistent with cretaceous magnetochrons 33r 33n and 32r these results characterized by shallow inclinations indicate an upper cretaceous paleolatitude of about 25 3 degrees north which is equivalent to that of modern day baja california these findings are consistent with the baja british columbia hypothesis which puts the insular superterrane well south of the oregon california border in the late cretaceous

geographical distribution of transitional vgps evidence for non zonal equatorial symmetry during the matuyama brunhes geomagnetic reversal abstract paleomagnetic records of the matuyama brunhes polarity reversal obtained recently from the northern equatorial and southern latitudes of the atlantic sector display a distinct symmetry with respect to the equator the virtual geomagnetic pole vgp paths from the mid latitude sites in the northern and southern hemispheres dsdp site 609 and core v16 58 are nearly coincident tracking northward through the americas the vgp path from the equatorial site odp site 664 tracks northward through eastern asia nearly antipodal to the other two paths modeling results indicate that superimposing an h 1 3 geometry onto a reversing axial dipole explains the sense of equatorial symmetry exhibited by these three records these results are consistent with the bulk of the data available from other records of this polarity transition suggesting that the transitional vgps during this reversal tend to fall along two distinct longitudinal bands the grouping of transitional vgps suggests that there is a strong geographical control over the reversal process an apparent correlation between the longitudinal bands of transitional vgps and the location of the major flux concentrations in the radial component of the historical geomagnetic field at the core mantle boundary 1 suggests that the processes which cause these flux concentrations may have influenced the geometry of the matuyama brunhes transitional field

velocity structure in the mixed layer during mildex abstract during october november 1983 a mixed layer dynamics experiment mildex took place off the coast of california as a part of mildex a number of sensors were deployed from the research platform flip in an effort to monitor the flow structure in the near surface mixed layer profiling current meters vmcms measured velocities down to 150 m on an hourly basis other vmvms were set at fixed depths depths of interest were examined using a package which measured three component velocities and displayed them in flip s laboratory in real time the current meters often observed sequences of downwind directed jets with maximum velocities exceeding 25 cm s 1 downwelling velocities of equal magnitude were also observed the strongest currents were found 10 to 35 m below the surface at mid depth in the mixed layer surface convergences associated with these jets were visualized by scattering tracers computer cards on the sea surface these features suggest langmuir circulation six doppler sonars wer

geomagnetic secular variation impulses the secular variation of the earth s internal magnetic field changes on time scales of the order of a year such impulses occurred in 1969 and probably in 1913 they provide constraints on deep mantle conductivity which appears to be rather low and on the motions of the top of the fluid core which are probably dominated by westward drift present data favour the existence of upwelling of core material at the core mantle boundary the impulses can be correlated with extrema in the earth s rotation rate and interpreted in terms of electromagnetic core mantle coupling

geology of the duncan canal shear zone evidence for early to middle jurassic deformation of the alexander terrane southeastern alaska the duncan canal shear zone central southeastern alaska disrupts and penetratively deforms devonian pennsylvanian and upper triassic strata of the lexander terrane the deformation is interpreted to have occurred within a regime of right lateral shear during early or middle jurassic time clastic and volcanic rocks correlated with the upper jurassic and lower cretaceous strata of the gravina belt lack the fabrics characteristic of the deformed alexander terrane strata and are inferred to unconformably overlie the shear zone deformational fabrics of mid cretaceous age observed in the gravina rocks locally truncate and deform the shear zone strata dextral strike slip faults of late cretaceous and or tertiary age that disrupt and modify fabrics of the shear zone are interpreted to accommodate some of the displacement observed on the clarence strait fault the duncan canal shear zone extends southward to the mosman inlet region on etolin island where it projects beneath jura cretaceous gravina strata in duncan canal and mosman inlet the shear zone evolved within the alexander terrane and does not coincide with any recognized terrane boundaries since the duncan canal shear zone is restricted to the currently exposed eastern margin of the alexander terrane the shear zone is interpreted to reflect deformation along the eastern margin of the alexander terrane

the matuyama brunhes transition recorded from lake tecopa sediments california abstract the paleomagnetic record of the matuyama brunhes reversal in the sediment of ancient lake tecopa provided the first evidence that the geomagnetic field during transition is not dipolar we resampled the section to increase the time resolution of the record our new data show that the characteristic direction could not be completely isolated by af demagnetization the transitional directions obtained from thermal demagnetization are thus quite different from those of the previous study but the primary conclusion that the field was non dipolar remains the vgp paths lying close to the site longitude is consistent with an axisymmetric transition field

global changes in intensity of the earth s magnetic field during the past 800kyr recent advances in palaeomagnetic and dating techniques have led to increasingly precise records of the relative intensity of the earth s past magnetic field at numerous field sites the compilation and analysis of these records can provide important constraints on changes in global magnetic field intensity and therefore on the earth s geodynamo itself a previous compilation for the past 200 kyr integrated 17 marine records into a composite curve1 with the geomagnetic origin of the signal supported by an independent analysis of 10be production made on different cores2 the persistence of long term features in the earth s magnetic intensity or the existence of long term periodic changes cannot however be resolved in this relatively short time span here we present the integration of 33 records of relative palaeointensity3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 into a composite curve spanning the past 800 kyr we find that the intensity of the earth s dipole field has experienced large amplitude variations over this time period with pronounced intensity minima coinciding with known excursions in field direction reflecting the emergence of non dipole components no stable periodicity was found in our composite record and therefore our data set does not support the hypothesis that the earth s orbital parameters have a direct and strong influence on the geodynamo

evidence suggesting extremely rapid field variation during a geomagnetic reversal abstract large systematic variations in direction of high temperature remanence as a function of vertical position occur in a basalt flow from the miocene volcanic sequence at steens mountain oregon that has provided a detailed record of a geomagnetic reversal these may have been caused by an impulsive change in the transitional field as the flow cooled during the reversal if this is true the short time required for the flow to cool by conduction and acquire its thermoremanent magnetization implies astonishingly high rates of change of the geomagnetic field at least 3 and 300 gammas per day

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

atypical diagenetic effects on strontium isotope composition of early jurassic belemnites queen charlotte islands british columbia canada in this study strontium carbon and oxygen isotope data are reported from early jurassic belemnites from yakoun river queen charlotte islands qci british columbia assuming that the established ammonite correlations between canada and europe are accurate the seawater 87sr 86sr curve between europe and qci should be similar however the rarenodia planulata and phymatoceras crassicosta ammonite biozones from yakoun river record 87sr 86sr values that are lower than expected this shift is interpreted to be a result of diagenetic alteration by later hydrothermal fluid 87sr depleted in general the diagenetic samples have more negative 13cbel and 18obel values and higher mn concentrations but show no difference in fe concentration a 13cbel curve from diagenetically screened samples exhibits only slightly depleted values with respect to a similar curve generated from europe a similar curve for 18obel shows a striking similarity with that generated from europe this study illustrates that dia

the influence of crosswind tidal currents on langmuir circulation in a shallow ocean 1 langmuir circulation lc is a turbulent process driven by wind and surface waves that plays a key role in transferring momentum heat and mass in the oceanic surface layer on the coastal shelves the largest scale lc span the whole water column and thus couple the surface and bottom boundary layers and enhance turbulent mixing observations and large eddy simulations les of a shallow coastal ocean demonstrate that these relatively large scale langmuir cells are strongly influenced by crosswind tidal currents two mechanisms by which crosswind tidal shear may distort and disrupt langmuir cells are proposed the first mechanism involves cell shearing due to differential advection across the whole cell for the second mechanism middepth vertical lc currents advect sheared mean crosswind current leading to the attraction of upwelling and downwelling regions so that lc cells are unsustainable when both regions overlap scaling arguments indicate that lc cells are more susceptible to crosswind shear distortion for smaller lc surface velocity convergence and greater cell aspect ratio vertical to horizontal lc scale which is consistent with the results obtained from the observations and les these results imply that scaling of lc characteristics in a coastal ocean differs from that in the open ocean which has important practical implications for parameterizing enhanced mixing due to lc

high resolution record of the upper olduvai transition from po valley italy sediments support for dipolar transition geometry abstract a detailed record of the upper olduvai polarity transition composed of 100 transitional directions has been obtained from the crostolo section in northern italy a careful examination of the rock magnetic properties of the sediments using standard paleomagnetic techniques thermomagnetic scanning electron microscopy microprobe x ray diffraction and mossbauer analysis shows that greigite is the main magnetic carrier of the remanence the correlation of a shift in the magnetic record to a small scale sedimentary feature observed in the section indicates that the magnetization was acquired at deposition or very shortly after the virtual geomagnetic pole vgp path is largely confined along a great circle over north and south america 90 west of the site and consists of three stages first the vgp moves to southern mid latitudes then after a period of standstill it comes back to almost true north and finally the south pole is reached in a third step although different from a record from the southern indian ocean this path is virtually identical to those obtained for the same transition from north pacific deep sea cores and partly coincides with a north atlantic record which suggests that a dipolar component may be present in the transitional field during the upper olduvai reversal a review of the recently obtained records of various transitions shows that in more than two thirds of the cases the vgp paths are similarly confined along a meridian over the americas or antipodal to them irrespective of the sampling site and of the sense of the transition although not deterministic this tendency suggests that a similar dipolar component might be present in the transitional fields of other reversals of different ages

seismic evidence for ultralow velocity zones beneath africa and eastern atlantic sks waveforms recorded at distances of about 110 are extremely useful to constrain seismic velocity structure at the base of the mantle sks waves near this distance develop a complicated interference pattern with the phases sp dks and skp ds we report anomalous behavior of this interference in a number of recordings of deep earthquakes beneath south america from stations in europe and africa we model these data with two dimensional dome like structures at the base of the mantle which extend laterally by a few hundred kilometers and in which the shear velocity is up to 30 lower than in the preliminary reference earth model prem the spatial extent of these structures their position with respect to the sks core exit points and their seismic characteristics can not be uniquely determined however the presence of a dipping or a concaved upper interface is a key attribute of successful models models that invoke flat layers are insufficiently complex to explain the most erratic waveform behavior the most anomalous data correspond to sampling regions at the base of the mantle beneath the east african rift and beneath the iceland where possibly whole mantle upwellings form

tectonic history of the queen charlotte islands and adjacent areas a model the region including queen charlotte islands hecate strait and queen charlotte sound is underlain by two allochthonous terranes wrangellia and the alexander terrane the suture between them occurs in central graham island and central hecate strait and is coincident with the traces of the sandspit and rennell sound fault zones each of which developed in response to crustal rifting in queen charlotte sound during mid tertiary time the stratigraphic succession comprises four tectonic assemblages 1 the allochthonous assemblages comprise paleozoic rocks of the alexander terrane and upper triassic and jurassic rocks of wrangellia which on the basis of paleomagnetic and biogeographical data are clearly exotic the distribution of these terranes beneath queen charlotte sound and hecate strait is supported by geophysical information and subsurface data obtained from offshore wells 2 the suture assemblage is represented by extremely coarse conglomerates massive graywackes and turbidites of early cretac

a three dimensional representation of geomagnetic reversal records representations of the reversing geomagnetic field are generally based on paleomagnetic directions or virtual geomagnetic poles i e one coordinate related to field intensity is missing interpretations based on these representations have led to conflicting models of reversals we have assembled records of reversals for which an intensity determination is available either absolute volcanic sequences or relative sedimentary sequences and we have chosen to represent them in terms of directions in local cartesian coordinates this representation is identical to the zijderveld representation which is traditional in paleomagnetism the 38 selected records correspond to matuyama brunhes jaramillo olduvai and some older reversals up to 5 m y old a total of 22 are from volcanic sequences and the rest from sedimentary ones vector behavior falls into one of five categories a the reversing field follows the local trend of the geocentric axial dipole gad passing through the origin with noise added b same as a but offset by a constant component from the origin c the reversing field follows a linear trend going through the origin in cartesian coordinates but the direction is different from that of the gad d same as c but offset from the origin by a constant component e large noise no linear or other simple bahavior over half 55 of the records fall in either category a or b 18 in category e the c type data often consist of dipole parallel segments separated by jumps the significance of which is as yet unclear the number of cases with a linear behavior is remarkable 82 large directional swings in the traditional representations often correspond to far less conspicuous changes on the vector plots at points close to the origin behavior there is dominated by noise one source of which may simply be secular variation of the nondipole field the constant offsets sometimes observed 34 of the cases are as yet unexplained but may be due to rock magnetic problems and therefore may have no global significance we doubt whether the present data allow us to extract resolvable terms such as g20 or h31 which have been inferred from the directional representation

seismological evidence for differential rotation of the earth s inner core the travel times of seismic waves that traverse the earth s inner core show a small but systematic variation over the past three decades this variation is best explained by a rotation of the inner core that moves the symmetry axis of its known seismic anisotropy the inferred rotation rate is on the order of 1 per year faster than the daily rotation of the mantle and crust

northward translation of baja british columbia along the late cretaceous to paleocene margin of western north america paleomagnetic data suggest that a large part of british columbia and southern alaska was at the latitude of baja california mexico in early late cretaceous time this allochthonous block baja bc includes the insular talkeetna in alaska and intermontane composite terranes the miniterranes between them and possibly part of the omineca metamorphic belt assuming that baja bc was adjacent to north america by middle cretaceous an analysis using plate kinematics of the pacific basin produces a model of northward movement of baja bc which is compatible with the known geology of the reconstructed margin of western north america baja bc moved north 2400 km as part of the kuia plate along a transform margin with north america from 85 to 66 ma this time interval is marked by the cessation of igneous activity in the sierra nevada development of wrench faults and basins along coastal california and initiation of laramide style tectonics to the east within baja bc diminished igneous activity to the west was coeval with possible wrench tectonic basins along its eastern margin by the end of the cretaceous baja bc was positioned from oregon to northern british columbia between 66 and 56 ma baja bc became attached to north america in a dextral transpressive stage during which the kula north america plate boundary expanded to encompass the whole block with a series of northwest trending strike slip faults a fold and thrust belt in the east and large scale uplifts and the formation of an incipient volcanic arc on the west southern alaska was the site of convergence during the whole of the period of northward translation of baja bc a late cretaceous subduction zone in alaska evolved into a major compressional belt as the basin and miniterranes on the northern margin of baja bc collided with interior alaska the collision culminated in the paleocene with formation of the mckinley granites and coeval dextral slip on the denali fault system

the last two geomagnetic polarity reversals recorded in high deposition rate sediment drifts high resolution records of geomagnetic polarity transitions are rare owing to the difficulty of preserving in the geological record details of a process with a duration of only a few thousand years lavas can record the instantaneous field on cooling but lava records are themselves discontinuous and therefore polarity transition fields are seldom captured sedimentary records are more continuous but typical deep sea sedimentation rates of a few cm kyr 1are too low to record transition fields adequately here we report transition records from north atlantic drift deposits with high sedimentation rates 12 cm kyr 1 at the ocean drilling program sites 983 and 984 virtual geomagnetic polar vgp paths are similar within and between sites for the last two geomagnetic reversals attesting to a memory effect spanning back to back reversals the complex vgp paths feature two vgp clusters one located in northeastern asia and the other in the south atlantic ocean off south america and provide a link between the longitudinally constrained transitional vgps often recorded in sediments1 2 which represent highly smoothed renditions of transition fields and the scattered transitional vgps3 and vgp clusters4 observed in lava records

the paleomagnetic field from equatorial deep sea sediments axial symmetry and polarity asymmetry paleomagnetic data from 89 equatorial deep sea sediment cores indicate that the configuration of the time averaged geomagnetic field depends strongly on polarity state but that it remains within 1 degree of axial symmery throughout the pliocene and pleistocene last 5 million years the relative magnitude of the nondipole field was greater by almost a factor of 2 during reverse than during normal polarity intervals these results thus support earlier suggestions that there may be a standing nonreversing component of the geomagnetic dynamo

numerical models of the geodynamo and observational constraints 1 the past few years have seen the emergence of a large number of numerical simulations of the geodynamo in parallel both new and old geomagnetic archeomagnetic and paleomagnetic observations have been interpreted as actual geomagnetic features and used as constraints for dynamo models naturally model predictions should be tested against actual characteristics of the geomagnetic field despite huge differences sometimes in excess of a billion between the values of parameters used in the simulations and those estimated for the earth it is intriguing that many available simulations succeed in producing largely axial dipolar magnetic fields with weaker nondipolar structures in agreement with the first order characteristics of the geomagnetic field yet when considering finer characteristics there are significant differences and failures to actually produce a number of fundamental characteristic features in this presentation we first review numerical results obtained to date then we attempt to summarize which field characteristics derived from observational data sets can be considered robust on the basis of simple criteria used to evaluate the degree of confidence that can be placed in each datum we sort presumably characteristic geomagnetic features into three categories robust controversial and unlikely we conclude that numerical models should be illustrated with a number of key predictions averaged over at least 10 dipole diffusion times these predictions should be tested against the subset of robust observations only controversial observations should await additional confirmation

paleosecular variation during sequential geomagnetic reversals from hawaii abstract paleomagnetic directions measured from 175 flows in four volcanic sequences on the island of o ahu hawaii cover about 0 3 m y of geomagnetic field changes and include detailed records of the successive gilbert gauss 3 57 ma and lower mammoth reversals 3 33 ma the dominant pattern of the directional changes is the presence of large inclination variations with increasing amplitude and steep values during the transitional periods the morphology of these recurring features during different transitions is reminiscent of the characteristics of the non dipole field inferred from studies of paleosecular variation in the pacific these observations are consistent with transitional mechanisms yielding the emergence of non dipole components with characteristics similar to those during periods of stable polarity the three different records of the lower mammoth reversal show that clusters of transitional pole positions are not reproducible between parallel sections and are thus linked to local eruptions and not to long lived states of the transitional field

jurassic foraminifera from the queen charlotte islands british columbia canada biostratigraphy paleoenvironments and paleogeographic implications abstract lower and middle jurassic sinemurian to callovian foraminifera were examined from 66 localities of the queen charlotte islands british columbia canada over 200 species of well preserved benthic calcareous and agglutinated taxa belonging to 50 genera were identified foraminifera from the lower jurassic are represented by an abundant and diverse tethyan derived calcareous assemblage with boreally derived agglutinated taxa becoming gradually more dominant in the upper lower jurassic to lower middle jurassic sedimentary strata and their faunal components and position of hiatuses correlate approximately with the jurassic eustatic sea level curve sea level changes have resulted in a variety of depositional environments ranging from deep water euxinic shales with abundant tuff beds characterized by small pyritized foraminifera to a well oxygenated outer shelf setting characterized by a major faunal increase to shoreface sandstones and conglomerates with absent to rare benthic foraminifera a gradual shallowing from a slope to a shelf dominated deposition with a magmatic arc provenance is suggested for the lower jurassic changing in the middle jurassic to an inner shelf to upper shoreface setting dominated by sedimentary strata of volcaniclastic origin a marked faunal turnover is observed in the lower jurassic whiteaves formation middle toarcian with the extinction of several earlier species and the appearance of a new diverse assemblage of 225 taxa this turnover is also observed in the ammonite and radiolarian assemblages of the queen charlotte islands in comparison to the dominantly tethyan derived taxa of pre middle toarcian age many of the species from the middle toarcian are found in northern latitudes such as on the northern slope of alaska arctic islands and the northwest territories hence foraminifera in conjunction with existing radiolarian and ammonite data suggest a northward displacement of the queen charlotte islands from low to mid paleolatitudes by late early jurassic toarcian to early middle jurassic bajocian time

a middle jurassic to early tertiary andean sierran arc model for the coast belt of british columbia regional tectonic features of the western canadian cordillera can be interpreted in terms of middle jurassic accretion of a single composite superterrane stikinia wrangellia alexander to ancestral north america closure of the intervening cache creek bridge river ocean moved the continental edge to a new position west of the accreted superterrane the coast belt is primarily a succession of superimposed middle jurassic to early tertiary magmatic arcs related to prolonged subduction of pacific ocean lithosphere beneath the new north american margin discrete magmatic pulses separated by lulls or periods of relative quiescence successively overprinted the new margin the insular and intermontane superterranes previously viewed as widely separate entities prior to mid cretaceous time were already amalgamated before an initial middle jurassic overprint produced an ancestral coast belt late jurassic to early cretaceous rift related marine basins mid to late cretaceous compressional structures and early tertiary extensional features coincident with the coast belt are subsidiary intraplate attributes that reflect external adjustments in plate motions within a primary subduction related andean magmatic arc

convectively driven turbulent mixing in the upper ocean abstract two experiments were performed to study the characteristics of turbulence in convective mixed layers in the upper ocean in the first a diurnal convective mixed layer developed in the bahamas under the influence of the cycle of daytime solar heating and nighttime evaporative cooling the mixed layer reached as deep as 100 m each night and restratified each day in the second the mixed layer of a warm core gulf stream ring deepened from less than 50 m to more than 150 m in a little more than a day when subjected to rapid cooling during a cold air outbreak although individual profiles of the rate of viscous dissipation of turbulent kinetic energy had considerable spatial and temporal variability the mean dissipation profiles were similar to those in convecting atmospheric boundary layers the is established by the surface buoyancy flux jb0 jb0 0 61 and 0 72 in the bahamas and ring data respectively compared with 0 64 in convecting atmospheric mixed layers the mean profiles decre

a geomagnetic jerk for the early 1990 s abstract records from geomagnetic observatories in europe are showing indications of another impulse in the third time derivative of the east component around 1991 these impulses otherwise known as jerks have occurred in the past at about 1925 1969 and 1978 and possibly also 1900 and 1913 they are believed to be internal in origin and have implications for the understanding of the fluid motions in the core which create them or for lower mantle conductivity or both

vertical circulation revealed by diurnal heating of the upper ocean in late winter part i observations abstract during a 5 day period in late winter 1984 temperature were measured at 9 depths beneath a drifting spar buoy to a relative accuracy of 2 mk the depths ranged from 15 to 145 m in a mixing layer that was nearly homogeneous to over 250 m a diurnal temperature signal was observed whose maximum amplitude decreased from 40 mk at 15 m to 20 mk at 145 m surface heat fluxes in particular the diurnal variation in solar radiation are too small to account for the diurnal variations in mixed layer heat content instrumental errors are ruled out the lagrangian experiment minimized horizontal advection which had in any case been quantified using a towed ctd seasoar the seasoar was used to survey the upper 380 m on horizontal scales from 1 40 km around the drifting spar but revealed no advection that could account for the diurnal signal it is concluded that the spar was trapped in a convergence zone where vertical velocities possibly as large as 0 04 m s 1 carried diurnally heated surface water down

small scale structure of the geodynamo inferred from oersted and magsat satellite data the geodynamo in the earth s liquid outer core produces a magnetic field that dominates the large and medium length scales of the magnetic field observed at the earth s surface1 2 here we use data from the currently operating danish oersted3 satellite and from the us magsat2 satellite that operated in 1979 80 to identify and interpret variations in the magnetic field over the past 20 years down to length scales previously inaccessible projected down to the surface of the earth s core we found these variations to be small below the pacific ocean and large at polar latitudes and in a region centred below southern africa the flow pattern at the surface of the core that we calculate to account for these changes is characterized by a westward flow concentrated in retrograde polar vortices and an asymmetric ring where prograde vortices are correlated with highs and retrograde vortices with lows in the historical 400 year average magnetic field4 5 this pattern is analogous to those seen in a large class of numerical dynamo simulations6 except for its longitudinal asymmetry if this asymmetric state was reached often in the past it might account for several persistent patterns observed in the palaeomagnetic field7 8 9 10 we postulate that it might also be a state in which the geodynamo operates before reversing

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

structure and variability of langmuir circulation during the surface waves processes program a cooperative multiplatform field experiment was conducted in the eastern north pacific during february and march of 1990 as part of the surface waves processes program swapp one of the experimental objectives was to investigate langmuir circulation so that its role in the evolution of the oceanic surface boundary layer could be better understood the concurrent use of different observational techniques ranging from simple surface drifters to complex doppler sonar systems resulted in new information about langmuir circulation structure and variability estimates of langmuir cell spacing indicated that a broad range of scales from about 2 to 200 m was excited during periods of strong surface forcing and that the energy containing scales evolved with time estimates of cell spacing based on doppler velocities from a surface scanning sonar directed crosswind showed this scale evolution but estimates based on backscattered intensity did not this was attributed to the fact that the intensity based estimates were only indirectly related to circulation strength the near surface convergent velocities from the sonar were used to form an objective quantitative measure of the temporal variations in langmuir circulation strength as expected the circulation strength increased dramatically during strong wind events however circulation strength and wind stress did not decrease simultaneously and langmuir circulation was detectable for up to a day after abrupt reductions in wind stress energy from the surface wave field which decayed more slowly than the wind was apparently responsible for maintaining the circulation the variation of circulation strength was found to be better related to u us than to u where u is the friction velocity is the wind stress and us is the surface wave stokes drift this scaling is consistent with wave current interaction theories of langmuir cell generation

tracking geomagnetic impulses at the core mantle boundary abstract the main magnetic field of the earth is generated and maintained by convective motions in the fluid outer core temporal field variations occur on an impressive variety of scales ranging from months to millions of years among these the most intriguing features are geomagnetic impulses or jerks v courtillot j ducruix and j l le mouel sur une acceleration recente de la variation seculaire du champ magnetique terrestre acad sci paris c r d287 1978 1095 1098 j l le mouel j ducruix and c ha duyen geophys res lett 5 1983 369 1 2 here we investigate these very rapid events at the surface of the earth s core using a global model designed for use at this depth we identify two regions of very active variations where wave like structures propagate the geometrical characteristics of these wave like motions provide new constraints on the intricate dynamics of the core

evidence for a new geomagnetic reversal from lava flows in idaho discussion of short polarity reversals in the brunhes and late matuyama polarity chrons k ar ages and paleomagnetic data for basalt samples from a new core hole site e at the idaho national engineering laboratory inel indicate that the age of the reversed polarity event recorded in snake river plain lavas is older than 465 50 ka 1000 years before present reported previously by champion et al 1981 nine basalt flows eight with normal polarity and one with reversed polarity were recognized in the site e core hole the flows above and below the reversed flow have ages of 491 80 ka and 580 93 ka respectively the inclination of the paleomagnetic field direction of the reversed flow at site e agrees with the inclination of reversed flows elsewhere at inel which have an age of 565 14 ka these reversed flows were previously thought to be correlative with the emperor event we suggest that this polarity event is an older event which we name the big lost reversed polarity subchronozone and subchron a review of data documenting short reversal records from volcanic and sedimentary rocks shows that there is evidence for eight polarity subchrons in the brunhes and two besides the jaramillo in the late matuyama these 10 short subchrons begin to indicate the many short events that cox 1968 hypothesized must exist if polarity interval lengths have a poisson distribution these events are true subchrons not excursions and may or may not have low associated paleointensities although low field strengths might explain why the reversal process aborts the mean sustained polarity interval length since late matuyama chron time is 90 000 years the similarity of this number with the 105 year period of the earth s orbital eccentricity suggests anew that linkage between geomagnetic paleoclimatic and possible underlying earth orbital parameters should be evaluated

on the recent variations of the apparent westward drift rate quantitative study of the westward drift w d was initiated by bullard et al 1950 and then followed by many others using more or less similar methods e g yukutake 1962 harwood and malin 1976 more recently magsat results have enhanced the interest in the subject see for example fig 1 of peddie 1982 in the present paper we compute the w d rate in the 1950 1980 time interval using different methods and we establish that the 1969 1970 secular acceleration impulse the so called jerk clearly shows up in the results

observed growth of langmuir circulation surface velocity patterns and upper ocean density profiles are presented from a period following a sudden increase in wind a prior wind speed of 8 m s failed to produce visible signs of langmuir circulation after the wind speed increased to 13 m s langmuir circulation developed within 15 min the initial scale observed was about 16 m streak to streak and may have been restricted by the depth scale of the measurements this spacing is about two thirds of the dominant wavelength 4 s period waves the streak spacing two cell widths increased at roughly 40 m h for the next hour the density measurements indicate a depth of mixing which increased over the same period at a rate of 20 m h thus the vertical to horizontal aspect ratio was about 1 1 prior stratification was weak buoyancy frequency of about 1 5 cph and probably did not affect the circulation initially mixing at the surface of the oceans is important to a wide variety of concerns including global climate and the health of marine life two main causes of this mixing can be identified 1 when surface water is cooled it becomes denser and sinks mixing downward either to the bottom or until limited by the preexisting stratification and 2 the wind can mechanically stir the surface layer to some depth usually limited by stratification the former can result in mixing to considerable depths but the latter occurs more often over the majority of the world oceans frequently the two driving forces occur together what are the details of this mixing for example are bubbles dragged deep into the mixed layer injecting gases at depth are there repeatable features which could lead to improved models of surface mixing and its effects when wind blows over water lines are often visible on the surface running roughly parallel to the wind in an exemplary series of experiments langmuir 1938 found these to be lines of convergence along the surface with downwelling below each line he found also that maxima in the downwind surface currents occur along these lines thus the mixing layer is organized into rolls of alternating sign aligned with the wind and water parcels follow helical paths downwind this form of circulation in surface layers of water has come to be called langmuir circulation historically this term has not implied any particular mechanism of formation and it generally has not been used in reference to other similar structures e g roll vortices in the atmosphere or in wall bounded convection langmuir 1938 p 123 expressed his belief that the helical vortices set up by wind apparently constitute the essential mechanism by which the epilimnion is produced clearly this form of helical vortices is efficient in transporting momentum energy and matter throughout the surface layer of water three mechanisms are currently considered to drive langmuir circulation 1 an interaction between surface waves and winddriven shear gives rise to this form of circulation as a linear instability a review of this theory and of observations before 1983 is given by leibovich 1983 2 even without surface waves turbulent mixing will occur due to the breakdown of the

the pliensbachian toarcian early jurassic extinction a global multi phased event abstract during the pliensbachian toarcian interval of the early jurassic there is a well known second order marine extinction that is observable at the species and genus levels ammonite diversity data from successions throughout europe and parts of the arctic suggest that this extinction may have been multi phased with diversity declining over six separate intervals the main phase of decline begins at the pliensbachian toarcian boundary and extends into the lower toarcian to a level that is correlative with the tenuicostatum serpentinum zone boundary to date only the main phase of extinction has been demonstrated as being global in extent and affecting multiple taxonomic groups this multi phased extinction has been attributed to regional and global controlling mechanisms that are associated with the volcanic greenhouse scenario which links the eruption of the karoo ferrar large igneous province lip to global warming and mass extinction we compare stratigraphic ranges of ammonite and foraminiferal species in pliensbachian toarcian successions of western north america to the record in europe and parts of the arctic in order to test the geographic extent of the multiple phases of extinction our results show six intervals of species level decline that correlate with those recognized in europe 1 middle of the lower pliensbachian middle whiteavesi middle freboldi zones 2 middle of the upper pliensbachian upper kunae lower carlottense zone 3 pliensbachian toarcian boundary into the lower toarcian upper carlottense middle kanense zones 4 middle toarcian upper planulata lower crassicosta zones 5 upper middle lower upper toarcian middle crassicosta hillebrandti zones and 6 upper toarcian lower yakounensis zone recognition of this multi phased event in three separate ocean basins paleo pacific paleo arctic and tethys oceans in at least two taxonomic groups greatly expands the known geographic extent of this multi phased event and argues for a controlling mechanism that is global in its reach in relation to the volcanic greenhouse scenario our study shows that four of the six pulses of extinction occur within the main phase of karoo magmatism the decline in the early pliensbachian previously thought to be separate from this event occurs within error range of the onset of karoo magmatism and the decline in the late toarcian coincides with the later stages of magmatism these observations extend the known duration of this multi phased extinction event to the early pliensbachian and support the volcanic greenhouse scenario specifically the eruption of the karoo ferrar lip as a preeminent factor driving the multi phased extinction of the pliensbachian toarcian

three dimensional idealized simulations of barrier jets along the southeast coast of alaska abstract three dimensional idealized simulations using the fifth generation pennsylvania state university ncar mesoscale model mm5 down to 6 km grid spacing were performed in order to understand how different ambient conditions wind speed and direction stability and inland cold pool and terrain characteristics impact barrier jets along the southeastern alaskan coast the broad inland terrain of western north america is important in alaskan jet development since it rotates the impinging flow cyclonically more coast parallel well upstream of the coast thus favoring more low level flow blocking while also adding momentum and width to the barrier jet near the steep coastal terrain the largest wind speed enhancement factor 1 9 2 0 in the terrain parallel direction relative to the ambient onshore directed wind speed occurs at relatively low froude numbers fr 0 3 0 4 these low froude numbers are associated with 10 15 m s 1 ambient wind speeds and wind directions orientated 30 45 from terra

the skewness of temperature derivatives in oceanic boundary layers abstract the skewness of the derivative of temperature measured by sensors in the upper ocean boundary layer in convective conditions has been measured and is observed to have a sign opposite to that found in conditions of stable heating this is consistent with observations in the atmospheric boundary layer high resolution measurements in the benthic boundary layer on a continental rise show a variation of skewness during the m2 tidal cycle which dominates the motion with negative skewness consistent with conditions favoring convection occurring during the upslope phase of the motion the observations are compared with laboratory studies of the reflection of internal waves from a slope we suggest that information about the gross features of a turbulent oceanic boundary layer flow may be derived from relatively simple measurements

langmuir turbulence in shallow water part 1 observations during extended deployment at an ocean observatory off the coast of new jersey a bottom mounted five beam acoustic doppler current profiler measured large scale velocity structures that we interpret as langmuir circulations filling the entire water column these circulations are the large eddy structures of wind wave driven turbulent flows that occur episodically when a shallow water column experiences prolonged strong wind forcing many observational characteristics agree with former descriptions of langmuir circulations in deep water the three dimensional velocity field reveals quasi organized structures consisting of pairs of surface intensified counter rotating vortices aligned approximately downwind maximum downward velocities are stronger than upward velocities and the downwelling region of each cell defined as a pair of vortices is narrower than the upwelling region maximum downward vertical velocity occurs at or above mid depth and scales approximately with wind speed the estimated crosswind scale of cells is roughly 3 6 times their vertical scale set under these conditions by water depth the long axis of the cells appears to lie at an angle 10 20 to the right of the wind a major difference from deep water observations is strong near bottom intensification of the downwind jets found typically centred over downwelling regions accessible observational features such as cell morphology and profiles of mean velocities turbulent velocity variances and shear stress components are compared with the results of associated large eddy simulations reported in part 2 of shallow water flows driven by surface stress and the craik leibovich vortex forcing generally used to represent generation of langmuir cells a particularly sensitive diagnostic for identification of langmuir circulations as the energy containing eddies of the turbulent flow is the depth trajectory of invariants of the turbulent stress tensor plotted in the lumley triangle corresponding to realizable turbulent flows when langmuir structures are present in the observations the lumley map is distinctly different from that of surface stress driven couette flow again in agreement with the large eddy simulations les unlike the les observed velocity fields contain two distinct and significant scales of variability documented by wavelet analysis of observational records of vertical velocity variability with periods of many minutes is that expected from langmuir cells drifting past the instrument at the slowly time varying crosswind velocity shorter period variability of the order of 1 2 min has roughly the observed periodicity of surface wave groups suggesting a connection with the wave groups themselves and or the wave breaking associated with them in high wind conditions

similarity structure in the convective boundary layer of a lake natural convection influences a variety of geophysical phenomena including daily mixing cycles in the atmosphere and in surface waters the seasonal overturn of lakes and global climate variability conceptual models of convection in water are primitive and based on very limited data particularly at small dissipative scales here i present an analysis of microscale data from the convective boundary layer of a lake indicating a complex depth dependence in the rate at which temperature fluctuations are dissipated suitably scaled this vertical structure is remarkably similar to that found in the atmospheric convective boundary layer1 2 stirred by rising thermals of buoyant air heated at the earth s surface this comparison consistent with recent documentation of similarity in the more uniform vertical structure of energy dissipation3 5 suggests another unifying link in the structure and dynamics of convection in boundary layers of lakes oceans and the atmosphere6

time variations of the earth s magnetic field from daily to secular variations in time of the earth s natural magnetic field have a frightfully wide spectrum ranging over more than 20 orders of magnitude they extend from well over 103 hz where they merge into the radioelectric noise spectrum to probably more than 100 m y in rough summary the higher frequencies stem from external sources in the ionosphere and above into the magnetosphere whereas the longer periods arise from internal sources primarily fluid motions in the core at depths in excess of 2900 km methods for separating external and internal signals have been available since the time of gauss 1 838 but the accuracy the space distribution and the time duration of available data are often not sufficient to unambiguously solve the problem for all types of variations although periods shorter than 1 yr should clearly be assigned to external sources the extent to which the spectra of the external and internal parts overlap is the subject of recent debate and progress currie 1966 1 968 proposed that there was little overlap and a cutoff of 3 7 yr a long debated l l yr contribution due to the solar cycle was clearly demonstrated by currie 1973a courtillot le mouei 1976a b and alldredge 1976 and the cutoff period was thus rejected to at least 20 yr the situation seemed to be confused again when courtillot et al 1978a provided evidence for sharp impulses of 1 yr duration i n the internal so called secular variation the debate that followed over the reality of brief internal events is one of the topics addressed in this review we first provide a short historical account of successive discoveries

geomagnetic jerks and rapid hydromagnetic waves focusing at earth s core surface geomagnetic jerks are abrupt changes in the second time derivative the secular acceleration of earth s magnetic field that punctuate ground observatory records as their dynamical origin has not yet been established they represent a major obstacle to the prediction of geomagnetic field behaviour for years to decades ahead recent jerks have been linked to short lived temporally alternating and equatorially localized pulses of secular acceleration observed in satellite data associated with rapidly alternating flows at earth s core surface here we show that these signatures can be reproduced in numerical simulations of the geodynamo that realistically account for the interaction between slow core convection and rapid hydromagnetic waves in these simulations jerks are caused by the arrival of localized alfven wave packets radiated from sudden buoyancy releases inside the core as they reach the core surface the waves focus their energy towards the equatorial plane and along lines of strong magnetic flux creating sharp interannual changes in core flow and producing geomagnetic jerks through the induced variations in magnetic field acceleration the ability to numerically reproduce jerks offers a new way to probe the physical properties of earth s deep interior geomagnetic jerks in the earth s magnetic field are caused by the arrival of hydromagnetic waves and could be generated by sudden releases of buoyancy in the earth s core suggest geodynamic numerical model simulations

equatorially dominated magnetic field change at the surface of earth s core slow temporal variations in earth s magnetic field originate in the liquid outer core we analyzed the evolution of nonaxisymmetric magnetic flux at the core surface over the past 400 years we found that the most robust feature is westward motion at 17 kilometers per year in a belt concentrated around the equator beneath the atlantic hemisphere surprisingly this motion is dominated by a single wavenumber and persists throughout the observation period this phenomenon could be produced by an equatorial jet of core fluid by hydromagnetic wave propagation or by a combination of both discrimination between these mechanisms would provide useful constraints on the dynamics of earth s core

a new approach to directly determine the secular variation from magnetic satellite observations 1 observatory monthly means provide an excellent opportunity to study the temporal changes of the geomagnetic field at a given location unfortunately determination of the global pattern of changes using observatory data is hampered by their uneven distribution satellite data provide excellent global coverage but the spacecraft movement makes direct comparisons of satellite and observatory data difficult to investigate short period secular variation in observatory and satellite data we developed an approach to extract satellite monthly means for virtual observatories at 400 km altitude using champ magnetic measurements comparison of these virtual observatory monthly means with the corresponding ground values shows a remarkably well correlated signal at time scales of months to years which is beyond the temporal resolution limit of recent global models here we describe this newly developed approach its validation and discuss how it can be used to understand short period changes of the recent geomagnetic field

marine triassic faunas of north america their significance for assessing plate and terrane movements the distribution of marine triassic invertebrate faunas in north america is reviewed to recognize forms that may have paleolatitudinal significance

time dependent mapping of the magnetic field at the core mantle boundary we consider the problem of constructing a time dependent map of the magnetic field at the core mantle boundary we use almost all the available data from the last 300 years to produce two maps one for the period 1690 1840 and the other for 1840 1990 we represent the spatial dependency of the field using spherical harmonics the time dependency using a cubic b spline basis and seek the smoothest solutions compatible with the observations particular attention must be paid to the effects of the crustal field in the data we argue that for observations from permanent magnetic observatories the most efficient strategy is to use first differences of annual means for satellite data the most efficient strategy is simply to limit the number of data used so as to minimize any tendency to map the crustal field into the core field the resulting model fits the observatory data better than any previous model yet has less power in the secular variation than previous models demonstrating that very simple models fit the data the resulting time dependent field map exhibits much of the same structure in the field and its secular variation identified in earlier studies

coherent structures at the ocean surface in convectively unstable conditions the turbulent boundary layer at the ocean surface has some dynamical similarities to the atmospheric boundary layer1 4 the atmospheric turbulent boundary layer may exhibit not only random fluctuations but also spatially coherent organized motion5 6 thorpe1 conjectured that such organized motion should also be found in the upper ocean boundary layer in convectively unstable conditions here i report on observations made in the tropical atlantic ocean which confirm this view horizontal temperature profiles obtained at a depth of 2 m at night revealed ramp like structures vertical velocity profiles in the upper few metres of the ocean was determined using a free rising profiler and exhibited abrupt changes corresponding to sudden changes in temperature these features are known5 6 to be characteristic of spatially coherent organized motions in turbulent boundary layers

evolution of langmuir circulation during a storm wind stress waves stratification velocity profiles and surface fields of radial velocity and acoustic backscatter intensity were measured along a drift track 50 to 150 km off point arguello california on march 8 1995 the wind increased from calm to 12 m s from the se opposing swell from the nw it increased to 15 m s at noon utc on march 9 remained steady over the next 12 hours briefly dropped and veered by 60 then returned a mixed layer deepened quickly to 25 m then held roughly steady through the next 2 days in spite of gusty winds continuing at 15 25 m s a phased array doppler sonar system took measurements covering 250 m by 150 m of the surface with 5 m by 10 m spatial resolution averages over 6 min removed surface waves permitting continuous assessment of strength orientation spacing and degree of organization of features associated with surface motion e g langmuir circulation even when conditions were too rough for visual assessment several results stand out 1 as found previously most wind mixing arises from inertial shear across the thermocline 2 consistent with wind wave forcing of langmuir circulation plueddemann et al 1996 suggest that surface velocity variance scales like u us where u is friction velocity and us is the surface stokes drift however the measurements here scale with us 1 alone once langmuir circulation is established 3 the velocity variance is weaker here than expected given the magnitudes of wind and waves leading to a smaller estimated mixing effect 4 large vacillations in lc strength are seen just before the brief veering of the wind it is suggested that bubble buoyancy could play a dynamic role 5 mean orientation and spacing can differ for intensity versus radial velocity features

saw toothed variations of relative paleointensity and cumulative viscous remanence testing the records and the model a recent model kok and tauxe 1996a that attempts to explain asymmetrical sawtooth patterns of relative paleointensity from sediments valet and meynadier 1993 as the consequence of cumulative long term viscosity effects has been tested theoretically and experimentally a mathematical description of the model demonstrates that only a sharp distribution of relaxation times would be able to match the paleomagnetic record which implies that all the magnetic grains would be identical this has direct consequences for the distribution of the blocking temperatures tb which would not exceed 260 c and for the coercivities of the natural remanent magnetization nrm this tb spectrum derived from the model is inconsistent with the unblocking temperatures of the nrm and with the tb spectrum of the experimental thermoremanent magnetization trm of the sediment that recorded the sawtooth new results including thermal demagnetization and thellier thellier experiments across brunhes matuyama confirm the overall stability of the original records the stability of the older part of the record 2 to 4 ma has also been strengthed the sawtooth is unchanged between 20 mt and 65 mt and thermal demagnetization in a neutral atmosphere at 300 c and 450 c duplicates the results obtained by alternation field a f demagnetization thus viscous processes at least within the framework of a cumulative viscous model and for the existing data sets are not responsible for saw toothed paleointensity records

paleointensity across the reunion event in ethiopia abstract paleointensity experiments have been conducted on a volcanic series of 33 flows which recorded the geomagnetic reunion event successive determinations of absolute paleointensity from 20 flows indicate that the reunion event would actually be characterized by two successive periods of low field intensity with a total duration not in excess of 30 kyr the first period has a mean paleointensity of 12 t and shows significant deviations from initial reverse polarity but no signs of fully normal polarity it is followed by field recovery then a decrease prior to the second directional episode the second period has a mean paleointensity of 17 t and is associated with full normal directions and thus likely a dominantly dipolar configuration these results are compatible with a simple earthlike magnetic field model with a large decrease in dipole field strength which yields local emergence of relatively stronger non dipole components field characteristics from this configuration would be different at different locations and could explain the variability of the paleomagnetic records collected around the world we propose that the absence of field recovery following the event is responsible for not leading to a durable polarity interval

high resolution sedimentary record of a geomagnetic reversal a detailed study of a geomagnetic reversal shows that during the transition the geomagnetic field undergoes both short and long term fluctuations the first are thought to be linked to the reversal process the second are present with the same time constants both before and during the reversal this suggests that the secular variation at least in its longer period terms is not affected by the reversal of the main field this feature has important consequences for the validity of the frozen flux approximation

paleointensity variations across the last geomagnetic reversal at la palma canary islands spain a detailed volcanic record of absolute paleointensity has been obtained for the period encompassing the last geomagnetic reversal from a succession of 69 distinct lava flows in two adjacent sections on the island of la palma the correlation between the two sections relies on the positions of the brunhes matuyama boundary and on the flow chronology obtained by a refined potassium argon k ar dating technique several pretransitional flows exhibit very shallow paleomagetic inclinations but they cannot be considered as really transitional paleointensity experiments conducted on 288 specimens provided 168 successful determinations 14 were obtained after correction for 50 lava flows that were considered to represent 45 distinct units the evolution of the paleofield intensity can be constructed by assuming uniform extrusion rates between three dated lava flows the period preceding the transition is characterized by large fluctuations with typical peak to peak amplitudes between 20 and 40 t which decrease down to 7 t prior to the transition the 100 kyr long interval following the reversal is associated with field intensities as high as 60 t and depict a strong and rapid restoration of the dipole field the virtual dipole moments vdms have been compared with sedimentary vdms generated from the record of relative paleointensity from ocean drilling program site 851 to which have been added non dipole components similar to the present geomagnetic field a reasonable fit can be made between the two curves which implies variations in the eruption rates but not incompatible with the uncertainties in the k ar age determinations thus these results can support but do not fully demonstrate the existence of asymmerical saw toothed variations in field intensity

large eddy simulation of a coastal ocean under the combined effects of surface heat fluxes and full depth langmuir circulation abstractresults are presented from the large eddy simulations les of a wind driven flow representative of the shallow coastal ocean under the influences of langmuir forcing and surface heating and cooling fluxes langmuir wind and surface gravity wave forcing leads to the generation of langmuir turbulence consisting of a wide range of langmuir circulations lcs or parallel counterrotating vortices that are aligned roughly in the direction of the wind in unstratified shallow coastal regions the largest of the lcs reach the bottom of the water column full depth lcs are investigated under surface waves with a significant wave height of 1 2 m and a dominant wavelength of 90 m and wave period of 8 s for a wind speed of 7 8 m s 1 in a 15 m deep coastal shelf region both unstable and stable stratification are imposed by constant surface heat fluxes and an adiabatic bottom wall simulations are characterized by rayleigh and richardson numbers representative of surface buoyancy forcing relative to wind

relative geomagnetic field intensity and reversals for the last 1 8 my from a central equatorial pacific core we have made a new analysis of core kk78o30 from the central equatorial pacific this core has recorded the last 4 reversals mineral magnetic analysis establishes that these sediments meet the current criteria for reliable relative paleointensity determinations normalisation with arm irm and yields very similar results there is no evidence for a saw tooth pattern such as the one obtained by valet and meynadier 1993 and meynadier et al 1994 for the last 4 million years rather the average field intensity record appears to display more or less symmetric peaks and troughs superposed to a broad high between reversals

the role of the earth s mantle in controlling the frequency of geomagnetic reversals a series of computer simulations of the earth s dynamo illustrates how the thermal structure of the lowermost mantle might affect convection and magnetic field generation in the fluid core eight different patterns of heat flux from the core to the mantle are imposed over the core mantle boundary spontaneous magnetic dipole reversals and excursions occur in seven of these cases although sometimes the field only reverses in the outer part of the core and then quickly reverses back the results suggest correlations among the frequency of reversals the duration over which the reversals occur the magnetic field intensity and the secular variation the case with uniform heat flux at the core mantle boundary appears most earth like this result suggests that variations in heat flux at the core mantle boundary of the earth are smaller than previously thought possibly because seismic velocity anomalies in the lowermost mantle might have more of a compositional rather than thermal origin or because of enhanced heat flux in the mantle s zones of ultra low seismic velocity

rheology of the earth and a thermoconvective mechanism for sedimentary basin formation summary a power law non newtonian fluid is usually assumed to model slow flows in the mantle and in particular convective flows however the power law fluid has no memory in contrast to a real material a new non linear integral having a memory model is proposed to describe the rheology of rocks the model is consistent with the theory of simple fluids with fading memory and with laboratory studies of rock creep the proposed model reduces to the power law fluid model for stationary flows and to the andrade model for flows associated with small strains stationary convection beneath continents has been studied by fleitout yuen 1984 who used the power law fluid model and obtained the cold immobile boundary layer continental lithosphere in a stability analysis of this layer the andrade model must be used the analysis shows that the lithosphere is overstable the period of oscillation is about 200 ma in the present study it is suggested that these thermoconvective oscillations of the lithosphere are a mechanism for sedimentary basin formation the vertical crustal movement in sedimentary basins can be considered as a slow subsidence on which small amplitude oscillations are superimposed the longest period of oscillatory crustal movement is of the same order of magnitude as the period of convective oscillation of the lithosphere found in the stability analysis taking into account the diverence between depositional and erosional transport rates we can explain the permanent subsidence as well as the oscillations