dynamics of eddy motions in the eastern north atlantic abstract the behavior of the intense anticyclonic eddy observed during the tourbillon experiment september november 1979 is studied within the framework of quasi geostrophic dynamics the nondivergent part of the pressure held is estimated through objective analysis at the times of four quasi synoptic ctd arrays making use as well of velocity data from the current meter mooring array and subsurface acoustic floats maps of relative vorticity vortex stretching and potential vorticity allow identification of the signature of the eddy nearby companion anomalies caused by an intrusion of mediterranean water mw can be singled out and are comparable to those of the main eddy around 1200 m eulerian and lagrangian tests of the conservation of potential vorticity are presented and the close similarities of salinity and potential vorticity as tracers of mesoscale motions are vividly demonstrated computations of advection of vortex stretching and relative vorticity show that the anticyclonic path of the mai

stratigraphy and depositional environments of the late famennian late devonian of southern belgium and characterization of the strud locality the famennian upper devonian c 372 to 359 ma strata of belgium have recently received much attention after the discoveries of early tetrapod remains and outstandingly preserved continental arthropods the strud locality has yielded a diverse flora and fauna including seed plants tetrapods various placoderm actinopterygian acanthodian and sarcopterygian fishes crustaceans anostracans notostracans conchostracans and decapods and a putative complete insect this fossil assemblage is one of the oldest continental probably fresh water ecosystems with a considerable vertebrate and invertebrate diversity the study of the palaeoenvironment of the strud locality is crucial because it records one of the earliest and most important phases of tetrapod evolution that took place after their emergence but before their terrestrialization it raises the question of environmental and ecological conditions for the devonian aquatic ecosystem and the selection pressures occurring at the onset of tetrapod terrestrialization the present study characterized the fluvial facies of the upper famennian sedimentary rocks of strud and the surrounding areas the exceptional preservation of arthropods and plants in the main fossiliferous layers is explained by rapid burial in the fine grained sediment of the quiet and confined flood plain environment newly investigated fossiliferous sections in the meuse samson area led to the description and correlation of key sections strud wierde and jausse sections complemented by the less continuous haltinne huy and coutisse sections moreover the investigated sections allowed a review of the age of the fossiliferous horizon which is now definitely considered to be late famennian in age

magma supply path beneath mt asama volcano japan 1 obtaining a sharp image of magma supply path through dense geophysical observations is important for forecasting time and magnitude of hazardous future eruptions here we reveal a clear magma plumbing system using dense seismic and geodetic networks around mt asama central japan magma intrusions occurred several times beneath the western flank of mt asama forming a wnw ese directed zone with 1 km below sea level the eastern end of this zone connects a narrow vertical pathway extending right under the summit crater which erupted in 2004 monitoring magmatic activity with a well designed observational network is vital to mitigate future volcano hazards

zooplankton distribution and dynamics in a north pacific eddy of coastal origin ii mechanisms of eddy colonization by and retention of offshore species abstract mesoscale anticyclonic eddies form annually in late winter along the eastern margin of the subarctic north pacific eddies that originate off the southern tip of the queen charlotte islands near 52 n 132 w are called haida eddies during the subsequent 1 3 years they propagate westward into the alaska gyre enroute the eddies are colonized by zooplankton originating from the central british columbia continental shelf the continental slope and along slope boundary current and the oceanic alaska gyre eddies also gradually lose kinetic energy water properties and biota to the surrounding ocean in this paper we analyze zooplankton samples from haida eddies obtained in late winter early summer and autumn of 2000 and in early summer and autumn of 2001 and compare the within eddy zooplankton distributions abundances and community composition of the oceanic origin species to observations from the continental margin and alaska gyre source regions most between region comparisons were consistent with a hypothesis that the eddy zooplankton are a mixture intermediate in abundance and community composition between the bc continental margin and offshore alaska gyre source regions although usually closer to the alaska gyre however about 30 of the comparisons showed within eddy abundances higher than in either source region this outcome cannot arise from mixing alone aggregation and retention appear to be linked to vertical distribution behavior most of the successful taxa spend much of their time below the surface mixed layer this minimizes their exposure to wash out by three physical processes slow upwelling and surface divergence that accompanies weakening of the anticyclonic geostrophic currents rapid but intermittent flushing of the surface layer by ekman transport during strong wind events exchange across the eddy margin geostrophic streamlines caused by temporary displacement by wind driven inertial currents

frasnian conodonts at high palaeolatitude amazonas basin north brazil abstract a conodont fauna is studied from the subsurface of upper devonian black shales belonging to the abacaxis member of the barreirinha formation amazonas basin two samples of other members of this formation are barren the fauna consists of cryptotaxis sp a mehlina gradata ozarkodina aff sannemanni polygnathus sp and probably prioniodina sp this association suggests a late frasnian age agreeing with the age previously assigned to the latest frasnian to middle famennian palynomorphs the conodont fauna is added to another two late frasnian middle famennian conodont occurrences in bolivia and brazil the coincidence in age and facies black shales seems to indicate a unique time environment favourable to the immigration and development of conodonts in the devonian of northern south america the low diversity association suggests cold water dwelling taxa spreading to a high palaeolatitude during an episode of gentler latitudinal temperature gradient

recognising the taghanic crisis in the devonian terrestrial environment and its implications for understanding land sea interactions the late mid devonian eday marl formation from the orcadian basin scotland is a terrestrial equivalent of the marine devonian taghanic crisis the eday marl from orkney contains a high resolution archive of climatic change controlled by the relative strength of the seasonal insolation this includes several distinct and discrete episodes of basin flooding as demonstrated by the deposition of lacustrine laminites bedded evaporites marginal sheet flood sands and marine influenced bioturbated sheet sands these flooding events are intercalated with intense and sustained episodes of aridity indicating that insolation was relatively weak and the monsoon climate was ineffective at drawing in seasonal rainfall recognition of these basin flooding events has enabled the definition of three new units the wha taing roeberry and berstane members the eday marl formation can be correlated offshore and also recognised within marginal facies as an aeolian intercalation an environmental hydrological and climatic interpretation is given for the different events recognised in the eday marl this sequence of events when combined with the palynological age dates enables a detailed correlation to be made with the marine tully formation of new york state this suggests that regressions forced by climatic aridity are significant for understanding the deposition of the shallow water carbonates of the tully formation in what is otherwise a clastic depositional system comparison with the pelagic marine record shows that the latter as yet gives only limited resolution of the taghanic crisis recognising the taghanic as a rapid alternation of cool arid and relatively hotter pluvial events provides a unifying explanation for the associated collapse in the terrestrial vegetation and the parallel faunal changes in the marine realm

a census of tehuantepec and papagayo eddies in the northeastern tropical pacific 1 we use a 12 year 1992 2004 time series of satellite altimetry to characterize long lived wind generated anticyclonic eddies originating in the gulfs of tehuantepec and papagayo in the northeastern tropical pacific a total of 42 tehuantepec and 26 papagayo eddies were observed eddy merging usually of a tehuantepec papagayo pair was observed on 16 occasions on average the eddy season began in late october and lasted approximately 250 days until early july with 3 5 tehuantepec and 2 2 papagayo eddies formed each year minimum average eddy lifespan was 143 days and 84 days for tehuantepec and papagayo eddies respectively there was considerable interannual variability in eddy activity with greater fewer number of eddies more intense weaker eddies and a longer shorter eddy season during el nino la nina years eddy intensification was consistently observed at the east pacific rise

characteristics of two counter rotating eddies in the leeuwin current system off the western australian coast abstract a multi disciplinary r v southern surveyor cruise was conducted in october 2003 to quantify upper ocean productivity within two adjacent counter rotating mesoscale eddies an eddy pair off the coast of western australia wa in the southeast indian ocean in this study a combination of satellite data altimeter sea surface temperature and chlorophyll a and shipboard measurements acoustic doppler current profiler adcp and conductivity temperature depth ctd were used to characterize the temporal evolution and spatial structures of the eddy pair satellite data show that the eddy pair evolved from meander structures of the poleward flowing leeuwin current lc in may 2003 and fully detached from the current in late august early september gaussian fits to the adcp velocities show that the anticyclonic eddy had a maximum azimuthal velocity of 65 cm s 1 at 63 km from the eddy centre the apparent radius and the cyclonic eddy had a maximum azimuthal velocity of 60 cm s 1 at the apparent radius of 49 km the mixed layer temperature and salinity properties in the cores of the eddy pair were quite stable over the period of the cruise temperature salinity diagrams indicate that the mixed layer water in the core of the anticyclonic eddy was composed mainly of lc water while in the core of the cyclonic eddy the mixed layer water was similar to surrounding open ocean water the total volume of the lc water retained in the anticyclonic eddy was 5 6 1012 m3 equivalent to 19 days annual mean transport of the lc the chlorophyll a concentration in the surface layer of the anticyclonic eddy lc water was higher than in the cyclonic eddy open ocean water which was likely a result of the entrainment of the productive water from the continental shelf during the eddy formation stage the offshore transport of the chlorophyll a biomass may be important for the pelagic ecosystem off the coast of wa

calibrating the devonian time scale a synthesis of u pb id tims ages and conodont stratigraphy the recalibrated devonian time scale represents an important improvement of devonian chronology regarding two aspects firstly a data set of 13 biostratigraphically well bracketed u pb id tims zircon and monazite ages constitutes the framework of the scale secondly approximately time linear biostratigraphic scales have been used for the interpolation between the isotopic ages the new construction thus represents a biochronometric time scale which allows the assignment of numeric ages not only to stage boundaries but also to each biozone boundary the method of interpolation applied also enables the projection of the geochronological error onto the time scale according to the newly calibrated scale the devonian lasted 57 4 5 7 ma from 418 1 3 0 to 360 7 2 7 ma this is compared to previously published time scales the longest time span ever calculated for this period the age interpolations for the eight stage boundaries are famennian tournaisian devonian carboniferous 360 7 2 7 ma frasnian famennian 376 1 3 6 ma givetian frasnian 383 7 3 1 ma eifelian givetian 388 1 2 6 ma emsian eifelian 391 9 3 4 ma pragian emsian 409 1 3 8 ma lochkovian pragian 412 3 3 5 ma pridolian lochkovian silurian devonian 418 1 3 0 ma full size table table options view in workspace download as csv the duration of the middle devonian is calibrated here as quite short with 8 2 ma and the emsian and the famennian are the longest stages with interpolated durations of 17 2 and 15 4 ma respectively together all devonian stages contain 57 conodont zones including subzones according to the standard conodont zonation giving a mean duration of about 1 ma in the highly resolved part of the time scale mid eifelian to the devonian carboniferous boundary zonal resolution averages 0 6 ma in contrast the lowest resolution is shown in the early emsian to mid eifelian interval with zonal durations of up to 5 5 ma serotinus zone

impact of haida eddies on chlorophyll distribution in the eastern gulf of alaska mesoscale haida eddies influence the distribution of surface phytoplankton in the eastern gulf of alaska through two processes enhanced productivity in central eddy water and seaward advection of highly productive coastal waters in the outer rings of eddies these two processes were observed in a sequence of monthly images over five years for which images of seawifs derived chlorophyll distributions were overlaid by contours of mesoscale sea surface height anomaly derived from topex and ers 2 satellite observations satellite measurements were supplemented with ship based chlorophyll observations through one of the eddies haida eddies are deep anticyclonic mesoscale vortices that normally form in winter and early spring near the southwest coast of the queen charlotte islands high levels of chlorophyll observed in eddy centres indicated that they supported phytoplankton blooms in spring of their natal years with timing of these blooms varying from year to year and exceeding in magnitude the chlorophyll concentrations of surrounding water elevated chlorophyll levels also were observed in eddy centres in late summer and early autumn of their natal year enhanced chlorophyll biomass is attributed to higher levels of macro nutrients and higher levels of iron enclosed within eddies than in surface deep ocean water by late spring and summer when coastal water supported higher chlorophyll biomass than did oceanic offshore regions eddies that straddled the continental margin entrained high chlorophyll coastal water into their outer rings and carried it several hundred kilometres into the gulf of alaska along their southern sides on some occasions a deep ocean eddy would entrain chlorophyll from an adjacent eddy located closer to the coast forming a conveyor belt transport process to inject coastal biota into the deep sea region of the gulf this process extended the coastal region of high chlorophyll surface water and therefore phytoplankton rich water several hundred kilometres seaward and dominated the shelf to deep ocean exchange of chlorophyll from late winter to the following autumn

age and correlation of the transgressive gonioclymenia limestone famennian tafilalt eastern anti atlas morocco the widely quarried and commercially exploited gonioclymenia limestone of the western and southern tafilalt platform anti atlas se morocco represents a transgressive but strongly condensed and shallowing upwards unit that overlies conformably or unconformably famennian to lower devonian deposits it is characterized by abundant giant sized gonioclymenia speciosa which characterizes the famennian v b and rare leviclymenia ramula sp nov associated conodont faunas fall in the bispathodus costatus subzone of the b aculeatus aculeatus middle expansa zone a rare outcrop at jebel ihrs west proved that kalloclymenia and conodont faunas of the b ultimus ultimus upper expansa zone occur in a separate overlying unit of the lower part of famennian vi consequently joint occurrences of gonioclymenia and kalloclymenia on large limestone slabs that are on offer in rock shops are artificial assemblages there is no evidence for a regional co occurrence of both genera this is supported by correlation into thicker sections of the adjacent maider and tafilalt basins the tafilalt gonioclymenia transgression may represent the regional expression of a eustatic pulse in the b costatus subzone that is known on the ardennes shelf as the transgressive epinette event the conodont faunas yielded neopolygnathus fibula sp nov pseudopolygnathus primus tafilensis ssp nov new morphotypes of b spinulicostatus and pseudopolygnathus primus primus the oldest siphonodella eosiphonodella and variable siphonodelloids that are currently left in open nomenclature

interaction of dipole eddies with the western continental slope of the mozambique channel abstract sea level anomaly sla data were used to track a southward propagating eddy dipole along the western slope of the mozambique channel over some 6 months in april 2005 this dipole with the cyclone to the south was close to the continental slope off southern mozambique the contact zone between the contra rotating vortices and the slope was surveyed by ship using onboard s adcp and ctd lines the data showed strong 1 4 m s 1 southward geostrophic currents over the slope adjacent to the anticyclone with horizontal divergence over the shelf edge significant slope upwelling between the dipole and the shelf was evident concomitant with enhanced nutrient and chlorophyll levels enriching shelf near surface waters satellite observations depicted a 300 km long surface chlorophyll filament extending offshore in the frontal zone between the contra rotating vortices a satellite tracked drifter deployed at the coastal base of this filament confirmed the offshore advection of chlorophyll enriched shelf water which ultimately wrapped around the cyclone and filling its centre the slope upwelling was also clearly evident in hourly temperature data collected by a recorder deployed on a nearby reef zambia reef in a depth of 18 m according to the sla data the dipole took several weeks to pass zambia reef causing prolonged bouts of upwelling that finally ceased when it left the continental slope and moved southwards into the open ocean further analysis showed that lone anticyclones and cyclones against the mozambique continental shelf also induce slope upwelling as a result of horizontal divergence created by the radial circulation of the vortex in the case of cyclones the divergence occurs north of the contact zone overall this case study confirms that eddies moving southwards along the western side of the mozambique channel are the main mechanism for pumping nutrients into the otherwise oligotrophic surface waters and moreover provide a vigorous mechanism for shelf open ocean exchange

p wave velocity structure beneath asama volcano japan inferred from active source seismic experiment an active seismic survey with unprecedented density of seismometers found a high velocity zone to the west of the summit of asama volcano japan the high velocity zone coincides with an area of magma filled crack dike intrusion associated with the 2004 eruptions inferred from precise earthquake relocations and ground deformation modeling it also coincides with an area of high resistivity surrounded by low resistivity indicating that the solidification of magma due to repeating intrusions is responsible for the high velocity this thus endorses the magma pathway previously speculated by seismic and geodetic observations these findings demonstrate that dense seismic exploration combined with geophysical monitoring is an effective way to understand the dynamics of volcanic eruptions

formation of the haida 1998 oceanic eddy 1 two large mesoscale anticyclonic eddies formed along the west coast of the queen charlotte islands of western canada in early 1998 altimetry measurements from topex poseidon and ers 2 satellites suggest that these eddies first appeared near cape st james at the southern tip of the islands the eddies merged in june to form haida 1998 the highest eddy ever observed in the region currents near cape st james in winter follow complicated patterns attributed to tidal rectification and pressure driven outflow from hecate strait the adjustment of these flows to the bathymetric features likely contributes to the formation of haida eddies eddies that first appear farther north along the west coast of the queen charlotte islands are set up by other processes such as baroclinic instability

magnetostratigraphy susceptibility of the frasnian famennian boundary magnetosusceptibility event and cyclostratigraphy msec is used to establish a non polarity based magnetostratigraphy susceptibility mss between the stratotype region for the frasnian famennian f f boundary sequence in the montagne noire of southern france the eastern rheinisches schiefergebirge of germany belgium the eastern anti atlas of morocco and the arbuckle mountains of southern oklahoma usa despite differences of depositional environment the mss is remarkably consistent and can be described in the context of a hierarchy of magnetozones that allow the extension of correlation away from the montagne noire reference section the nature of the controls on the influx of iron into the marine system produces a natural hierarchy of at least seven orders or magnetozones designated msz1 msz2 msz3 msz4 msz5 msz6 and msz7 these are characterized in terms of the magnitude of their duration the mss reference section of choice for the f f boundary is the well known trench c at la serre lsc in the northeastern montagne noire of southern france the f f boundary is located at the lower boundary of magnetozone la serre i 3b at la serre as well as in all other sections studied msz4 and msz5 magnetozones are used to establish intra and inter regional correlation between the reference sequence and the other regions the base of the upper kellwasser event is as variable within the mss zonation as it is within the biostratigraphic zonation as is the position of the lower kellwasser event

three dimensional seismic refraction tomography a comparison of two methods applied to data from the faeroe basin this paper presents a comparison of two tomographic methods for determining three dimensional 3 d velocity structure from first arrival travel time data the first method is backprojection in which travel time residuals are distributed along their ray paths independently of all other rays the second method is regularized inversion in which a combination of data misfit and model roughness is minimized to provide the smoothest model appropriate for the data errors both methods are nonlinear in that a starting model is required and new ray paths are calculated at each iteration travel times are calculated using an efficient implementation of an existing method for solving the eikonal equation by finite differencing both inverse methods are applied to 3 d ocean bottom seismometer obs data collected in 1993 over the faeroe basin consisting of 53 479 travel times recorded at 29 obss this is one of the most densely spaced large scale 3 d seismic refraction experiments to date different starting models and values for the free parameters of each tomographic method are tested a new form of backprojection that converges more rapidly than similar methods compares favorably with regularized inversion but the latter method provides a simpler model for little additional computational expense when applied to the faeroe basin data bounds on two model features are assessed using regularized inversion with combined smoothness and flatness constraints an inversion of synthetic data corresponding to 100 data recovery from the real experiment shows a marked improvement in lateral resolution at deeper depths and demonstrates the potential of currently feasible 3 d refraction experiments to provide well resolved long wavelength velocity models the similarity of the final models derived from the two tomographic methods suggests that the results from the new form of backprojection can be relied on when limited computational resources rule out regularized inversion

the expression of the hangenberg event latest devonian in a relatively shallow marine succession pomeranian basin poland the results of a multi proxy investigation the uppermost famennian lowermost tournaisian interval has been analysed in detail using biostratigraphy sedimentology magnetic susceptibility and geochemistry in a reference section of the relatively shallow carbonate ramp environment within the pomeranian basin high resolution biostratigraphic study based on miospores allows recognition of the standard western european lepidophyta nitidus ln and verrucosus incohatus vi zones as well as the convolutispora major zone a local pomeranian equivalent of the european standard hibernicus distinctus hd zone the sedimentary succession and specific phenomena recognized close to the devonian carboniferous boundary such as fluctuations in water column euxinia wildfire evidence relative sea level changes and perturbations of the carbon cycle reflected by positive carbon excursions display a pattern partly similar to that observed in many areas in europe during the hangenberg event although the hangenberg black shale horizon is not developed here these important microscale environmental perturbations were observed not only within the famennian ln miospore zone but in a wide interval between the ln and the lowermost local convolutispora major miospore zones lower part of hd standard miospore zone it is still uncertain whether the recognized event s were connected solely with the hangenberg event which was possibly complex and multi phased as is sometimes suggested or whether they represent a succession of regionally limited post hangenberg events this question needs to be further investigated on broader stratigraphic and geographical scales

horizontal dispersion within an anticyclonic mesoscale eddy abstract ship mounted adcp and buoy data are used to fit an azimuthal velocity profile to a n e atlantic mesoscale eddy chosen as a site for a lagrangian biogeochemical survey the cruise forming part of the uk plankton reactivity in the marine environment prime initiative together with the buoy derived locus of the eddy centre the adcp derived velocity field allows observations of a sulphur hexafluoride sf6 tracer release within the eddy to be put into a non translating non rotating frame analysis of the transformed data suggests that the patch of tracer though spreading remained coherent throughout the nine day survey a linear regression on the square of the radial patch width versus time gives an estimate for the effective horizontal diffusion coefficient of 22 10 m 2 s 1 this is consistent with previous estimates of diffusion rates at the o 10 km lengthscale of the patch theory predicts a corresponding along streamline spreading time of 14 days this implies that the tracer patch mixed little with the surrounding waters during the first five days of the survey suggesting that biogeochemical processes were little affected by lateral mixing during this period the theory is inapplicable at later times because the area was struck by a storm at the start of the sixth day which resulted in the halving of sf6 concentrations using a model of a circular eddy with the calculated velocity profile the dispersion of the initial patch of tracer is simulated for different diffusivities the results confirming the estimate of along streamline mixing time and demonstrating the enhancement of azimuthal diffusion by the radial shear of the flow

mesoscale eddies dominate surface phytoplankton in northern gulf of alaska abstract the hnlc waters of the gulf of alaska normally receive too little iron for primary productivity to draw down silicate and nitrate in surface waters even in spring and summer our observations of chlorophyll sensed by seawifs north of 54 n in pelagic waters 500 m depth of the gulf found that on average more than half of all surface chlorophyll was inside the 4 cm contours of anticyclonic mesoscale eddies the ratio approaches 80 in spring months yet these contours enclosed only 10 of the total surface area of pelagic waters in the gulf therefore eddies dominate the chlorophyll and phytoplankton distribution in surface pelagic waters we outline several eddy processes that enhance primary productivity eddies near the continental margin entrain nutrient and fe rich and chlorophyll rich coastal waters into their outer rings advecting these waters into the basin interior to directly increase phytoplankton populations there in addition eddies carry excess nutrients and iron in their core waters into pelagic regions as they propagate away from the continental margin as these anticyclonic eddies decay their depressed isopycnals relax upward injecting nutrients up toward the surface layer we propose that this transport brings iron and macro nutrients toward the surface mixed layer where they are available for wind forced mixing to bring them to surface these mesoscale eddies decay slowly but steadily perhaps providing a relatively regular upward supply of macro nutrients and iron toward euphotic layers they might behave as isolated oases of enhanced marine productivity in an otherwise iron poor basin we note that much of this productivity might be near or just below the base of the surface mixed layer and therefore poorly sampled by colour sensing satellites it is possible then that eddies enrich phytoplankton populations to a greater extent than noted from satellite surface observations only

ichthyoplankton assemblage structure in two meso scale leeuwin current eddies eastern indian ocean larval fish assemblages within two meso scale eddies located off the coast of south western australia were investigated as part of an interdisciplinary study examining the biophysical nature of the eddies larval fish were sampled using oblique and depth stratified plankton tows taken within the centre body and perimeter of both a cold core cyclonic eddy and a warm core anti cyclonic eddy larvae from the oceanic families myctophidae phosichthyidae and gonostomatidae were the most abundant within the larval fish assemblage with larvae from the families sternoptychidae paralepididae and stomiidae also common larval fish assemblages from the warm core eddy were significantly different to those from the cold core eddy significant differences were found between assemblages from the centre and body and the centre and perimeter of the warm core eddy but there were no significant differences across zones in the cold core eddy assemblages were more strongly structured with depth in the cold core eddy than in the warm core eddy the correlation of environmental data to larval fish assemblages showed that sea surface temperature was the variable best correlated with larval fish assemblage structure between eddies depth of the mixed layer was best correlated with assemblages in the warm core eddy only but no significant environmental correlations existed in the cold core eddy assemblages we hypothesise that this was a result of the differing oceanographic structure between the two eddies

the anticyclonic baroclinic eddy off sitka alaska in the northeast pacific ocean abstract among the many mesoscale eddies found in the northeast pacific ocean is a well developed anticyclonic baroclinic eddy situated within a few hundred kilometers of sitka alaska 57 n 138 w it has definitely been observed during spring and summer 1958 summer 1960 and summer 1961 observations made at other times show some evidence of its occurrence also the trajectories of three norpax drifting buoys for april may 1977 also indicated the probable presence of an eddy there the eddy whose diameter ranges from 200 to 300 km and whose depth extends to 100 m and probably to as much as 2000 m recurs at the same location the center of the eddy is characterized by the following features the surface water is less saline and only somewhat warmer than at its periphery at depths within and below the halocline it is warmer less saline and contains more dissolved oxygen than at the periphery and a warm core is situated within the halocline the halocline is usually depressed by less than 100 m but

a shallow subtropical subducting westward propagating eddy swesty swesty is a shallow subtropical subducting westward propagating eddy that was observed to move across the eastern basin of the north atlantic at a latitude near 25 n the eddy was first detected by the movement and temperature of a drogued argos buoy near 23 w 26 n in february 1993 by december 1993 the drogued buoy had moved 1000 km westward to 33 w and a winter eddy survey was made from rrs charles darwin the eddy was about 100 km in diameter and had a centre water mass core at a depth of 190 m with characteristic temperature 19 9 c and salinity 37 06 psu but was best resolved by properties related to vertical gradient structure e g brunt vaisala frequency temperature perturbation structure the eddy was particularly flat with a height to width aspect ratio of only ca 0 14 and a vertical decay scale of ca 250 m for temperature displacements maximum azimuthal currents were ca 16 cm s 1 at a depth of 175 m and the eddy azimuthal transport was only 3 sv however the potential vorticity in the eddy core was 1 5 x 10 11 rad ms 1 comparable with other deep anticyclonic lenses and lower than background values by a factor of ten the eddy appeared slightly elliptical with a detectable sea surface cooling ca 0 2 c over its centre three argos buoys with drogues set at a depth of 200 m were deployed near the centre of the eddy and one buoy continued looping westward for a further ca 800 km the drogued argos buoy results showed that the eddy moved westward at ca 100 km month 1 and about half this westward rate was attributed to self propagation during this ca 1650 km continuously drogued journey the eddy only slipped southward by about one degree of latitude and so was perhaps resisting the southward component of flow of the subtropical gyre the buoy results suggested that the central rotation rate increased with time but the eddy became smaller the initial rotation period of the central core was ca 8 d giving a corresponding normalized relative vorticity of 0 3 about 400 d later the period of core rotation was ca 5 d with normalized relative vorticity of 0 5 some of the increase in central rotation rate was attributed to subduction effects variance spectra and filtered components of velocity were derived from the buoy positions kinetic energy levels in the eddy ca 73 cm 2 s 2 were markedly elevated with respect to background levels ca 29 cm 2 s 2 the core properties of the eddy indicated a winter formation near 27 n 22 w and hydrographic sections showed that the eddy would be sinking at a rate of about 40 m a 1 by the second year the subducted water parcel the eddy core was sufficiently deep below the surface of the ocean to escape further effects of winter mixing

organic matter deposition in the ghadames basin libya during the late devonian a multidisciplinary approach the organic rich deposits of late devonian age are the second most important petroleum source rocks in the ghadames basin libya from available stratigraphy the peak of organic matter deposition corresponding to a level of radioactive shales easily recognized in gamma ray logs occurred at the frasnian famennian transition the present study was focused on samples from borehole d1 26 located in the central part of the ghadames basin belonging to the aouinet ouenine iii and iv formations frasnian to famennian the mineral and organic content of the rocks were analyzed in order to determine the origin of organic matter accumulation and estimate if the organic matter enrichment could be related to the well known upper kellwasser event the results indicate that during the frasnian the planktonic primary productivity was moderate but anoxic conditions reaching the euphotic zone were frequent and allowed efficient preservation of the organic matter at the frasnian famennian transition the deposition of the radioactive shales level can be related to a eustatic rise which allowed incursion of nutrient rich water in the basin leading to increase in primary productivity and photic zone anoxia during the famennian the conditions changed associated with a relative sea level fall and or a progradation of detrital sediments originating from the south photic zone anoxia was only episodic and plankton derived organic matter was poorly preserved nevertheless the important influx of organic matter of terrestrial origin allowed significant enrichment of the sediment in organic matter several indications suggest the radioactive shales interval could be coeval with the upper kellwasser level nevertheless further stratigraphic work is needed to confirm this hypothesis

structure of velocity and temperature in the northeast pacific as measured with lagrangian drifters in fall 1987 abstract in october 1987 49 lagrangian surface drifters tristar ii were released in a 200 km 200 km square area southeast of ocean station papa as part of the ocean storms experiment the drifters measured temperature at the drogue level and reported their position through argos approximately 11 times per day thirty one of the drifters retained drogues for longer than three months and data from those instruments are used to describe the evolving fall 1987 pattern of current and temperature structures at 15 m in the area between 46 and 49 n 142 w and 132 w time variable currents were dominated by mesoscale eddies of anticyclonic rotation with horizontal radii of 53 86 km and rotational speeds of 10 20 cm s 1 these eddies persisted for at least 90 days as evidenced by successive drifter trajectories through the eddies currents with periods longer than 1 day had a mean to the east of 4 4 cm s 1 and a mean to the north of 0 7 cm s 1 background eddy kinetic energy levels were 40 cm s 2 thus eddy

satellite and hydrographic observations of eddy induced shelf slope exchange in the northwestern gulf of alaska 1 satellite and hydrographic observations of oceanographic conditions in the northwestern gulf of alaska indicate that anticyclonic eddies propagating adjacent to the continental shelf alter the structure of the shelf break front and in doing so influence the shelf slope exchange of biota and water mass properties eddies typically form in the northern gulf of alaska during fall and winter and propagate southwestward within an 200 km wide corridor along and above the continental slope eddy activity within this corridor diminishes in the downstream direction the trajectories of faster propagating 4 km day eddies tend to lie closer to the shelf break than do the trajectories of slower propagating 1 5 km day eddies the interaction between azimuthal eddy currents and the shelf break frontal jet 1 establishes an upwelling zone associated with the leading flank of the eddy that strengthens cross slope gradients 2 weakens cross slope gradients and promotes shelf slope exchange where the eddy is adjacent to the shelf and 3 reestablishes a weak upwelling zone associated with the trailing flank of the eddy

lower sappington formation palynofacies in montana confirm upper famennian black shale paleoenvironments and sequences across western north america abstract for the first time late devonian palynofacies analyses of the lower sappington shale units u1a d was carried out at peak 9559 sacajawea and ainger lake in the bridger range of montana diagnostic spore species apiculiretusispora verrucosa diducites mucronatus and d versabilis allowed the correlation of our u1a d with the european late famennian a verrucosa v hystricosus palynozone the first appearance of gorgonisphaeridium winslowiae in u1 is the oldest record before the inception of retispora lepidophyta four palynofacies correlative with u1a d and new findings of invertebrates and microfossils allow the interpretation of paleoenvironmental changes amorphous organic matter marine phytoplankton and pyrite in black shales of u1a b indicate anoxic bottom conditions occurred in offshore marine environments an erosional fossiliferous phosphatic lag above these units confirms a regional sb u1c black shales composed by aom marine and terrestrial phytoplankton land derived remains and pyrite reveal shallower dysoxic anoxic brackish water environments a thin layer at the base of unit 1d yielded aom and marine phytoplankton and low terrestrial input indicating dysoxic anoxic conditions were maintained the lack of organic matter and the presence of invertebrates and microfossils in a thin green fossiliferous mudstone supports the establishment of normal oxygenated marine conditions maintained in the basal middle sappington member u2 these two thin units are not part of the underlying anoxic black shale u1a b sequence as commonly was over simplified instead they are part of a transgressive interval with the basal middle sappington a correlation of the u1 shale interval is established with the global multiphase dasberg event

mechanisms for vertical nutrient transport within a north atlantic mesoscale eddy abstract prompted by observational evidence for an enhanced source of surface nutrients within an anticyclonic eddy in the ne atlantic we investigate vertical transport processes that may produce such a phenomenon for the eddy investigated the dominant mechanism is found to be ageostrophic circulation resulting from a perturbation of the circular flow of the eddy this can produce upwelling velocities of order 10 m d 1 ekman pumping due to wind stress on the eddy also produces upwelling within but on a smaller scale of 0 5 m d 1 there is no evidence that self propagation of the eddy leads to an enhanced nutrient flux by displacement upwards of nutrient laden deeper isopycnals over the core of the eddy deeper winter mixing within the eddy relative to the surroundings however may contribute to the elevated nutrient levels

a quantitative approach to the dike intrusion process inferred from a joint analysis of geodetic and seismological data for the 1998 earthquake swarm off the east coast of izu peninsula central japan 1 a series of earthquake swarms off the east coast of izu peninsula central japan is typically associated with dike intrusion around active volcanoes numerous studies in this region have documented the seismic activity and ground deformations without fully resolving the process of dike intrusion this study involves a joint analysis of geodetic and seismic data from the most recent major activity in this region occurring in 1998 to reveal the process of dike intrusion quantitatively we combine data from a dense gps array including 10 temporary stations with seismic analysis published previously we estimate the location of the dikes from seismic data and the volume of intruded magma from geodetic data combined analysis of both data sets enables us to reveal the kinematic process of dike intrusion associated with the 1998 earthquake swarm the process of dike intrusion is quantitatively modeled using the time evolution of recorded dike volume and the use of seismic hypocenters as an indicator of the site of instantaneous dike intrusion on the basis of these observations we propose the following process of the dike intrusion the magma rose upward through a pathway aligned vertically and created a dike when it lost buoyancy we also evaluate the dike intrusion process quantitatively using a model of a circular dike that grows under a continuous magma supply from a deep magma reservoir from the observational data we infer the time evolution in the dike shape pressure distribution and magma viscosity in the dike the acquired viscosity increases over time and it may be reasonable because magma cools gradually however its value is too large compared to typical basaltic magma expected in this region it may represent magma within the dike that is nearly solidified otherwise the magma is supplied intermittently and the dike growth is mainly controlled by the magma supply rate from a deep reservoir the quantitative description of the dike intrusion process in nature described in this study is very rare and our results provide constraints on several parameters that have not been solved in many previous theoretical studies on the dike intrusion process

british columbian continental shelf as a source of dissolved iron to the subarctic northeast pacific ocean 1 the distribution of dissolved 0 4 m iron fe across the continental shelf and slope of queen charlotte sound on the west coast of canada was examined to estimate the potential of these waters as a source of fe to the fe limited waters of the subarctic northeast pacific iron profiles obtained in shelf slope and offshore waters demonstrate decreasing concentrations of fe with distance from the continent within 50 m of the shelf sediments dissolved fe concentrations were 5 3 0 3 nm this signal was detected although attenuated by 80 along the isopycnal surface at offshore stations 40 50 km seaward of the shelf break strongly suggesting cross shelf transport of an fe rich plume originating in low dissolved oxygen 3 ml l 1 130 mol kg 1 waters in subsurface water over the continental shelf several physical mechanisms that may cause these fe enriched waters to advect offshore in this region i e tidal currents and ekman transport in the bottom boundary layer coastal downwelling relaxation from upwelling and the formation of anticyclonic westward propagating coastal eddies are discussed we suggest that strong tidal currents over broad continental shelves may play a key role in fe supply to ocean basins

wave properties and focal mechanisms of n type earthquakes at asama volcano abstract n type earthquakes sometimes occur before the eruption of andesitic volcanoes but their source mechanism has not been understood well their waveforms have stationary periods and decay slowly resembling to damped oscillation they have common characteristics of spectra among the different stations these spectral peaks appear at almost equal intervals of 1 0 hz with common sharpness we made detailed analysis on the n type earthquakes observed at asama volcano in july 1995 during 10 days activity the duration of each earthquake increased gradually from 40 s to 3 min while the peak frequency decreased from 2 7 to 0 8 hz hypocenters are distributed slightly west under the summit crater with 0 4 1 7 km above sea level source mechanism of the n type earthquake is determined using a waveform inversion technique synthetic waveforms are calculated using 2d finite difference method surface topography is included in the calculation to incorporate the case that the source region is higher than the stations since the optimum solution has a large volumetric component we approximated the volumetric part as a volume change of fluid filled sphere or cylinder or plane crack and decomposed the solution into volumetric and non volumetric part consequently it is revealed that the optimum solution can be expressed as crack expansion contraction small fault slip because the spectral peak distribution advocates the crack expansion model among these three candidates the frequency change during this activity may be explained by the time variation of the sound speed of inner fluid from 300 to 100 m s the change of the void fraction of water steam phase might have caused the decrease of the sound speed

a basin scale oceanic instability event in the gulf of alaska a composite noaa 14 satellite advanced very high resolution radiometer image of the gulf of alaska for early march 1995 reveals a sequence of six anticyclonic oceanic eddies spanning more than 1500 km of the continental margin of north america from central british columbia to central alaska although isolated mesoscale eddies have previously been documented for this eastern boundary region the composite image provides the first evidence that trains of such eddies can develop simultaneously along the entire coast the 80 km radius and 250 km spacing of these warm core eddies are consistent with a baroclinic instability event in the poleward coastal current that prevails along the northwest continental margin of north america in winter roughly october through march wind data from offshore meteorological buoys combined with partial cloud free thermal images for january and february suggest that the event was triggered in mid january by an abrupt coast wide reversal in the prevailing poleward wind the instability event disrupted the alongshore transport of relatively warm high salinity water and presumably resulted in a greatly enhanced cross shore flux of brackish nutrient rich coastal water into the open ocean on the basis of its basin scale extent and more than 2 month duration it is feasible that the event had a major impact on the early spring recruitment and survival of zooplankton and pelagic fish within the highly productive fishery zones of coastal british columbia and alaska less extensive eddy sequences found in several earlier satellite images for the region suggest that these instability events are fairly common if so this indicates that the poleward current that forms over the eastern pacific continental slope in late fall herein the northeast pacific coastal current is marginally stable and likely to deform into a series of mesoscale eddies following abrupt basin scale reversals in the seasonally dominant wind provided these wind events occur early enough in the season the coastal current could reform with the onset of poleward winter winds

shallow resistivity structure of asama volcano and its implications for magma ascent process in the 2004 eruption asama volcano is an active volcano with many historical records of vulcanian eruptions its most recent eruptions occurred in 2004 at the summit crater in this paper we argue the resistivity structure shallower than 3 km obtained by a dense magnetotelluric survey the magnetotelluric data were obtained at 74 measurement sites mainly along the four survey lines across the volcano the resistivity profiles obtained by two dimensional inversions are characterized by a resistive surface layer and an underlying conductive layer the dominant feature of the profiles is the existence of resistive bodies at a depth range of a few hundred meters to a few kilometers surrounded by a highly conductive region considering that the location of resistive bodies correspond to the old eruption centers one corresponds to the 24 ka collapse caldera and the other to the 21 ka lava dome the resistive bodies imply zones of old and solidified intrusive magma with low porosity because geothermal activities exist near the resistive bodies the enclosing highly conductive regions are interpreted as a hydrothermal system driven by the heat from the old solidified magma beneath the resistive body under the collapsed caldera intrusion of magma is inferred from the studies of volcano tectonic earthquakes and continuous global positioning system gps observation implying the structural control of magma activity within the volcano in this study we propose that the magma ascent was impeded by the old and solidified remnant magma and partly migrated horizontally to the east and finally ascended to the summit resulting in the 2004 eruptions