geochemistry of the granitic rocks from the kwandonkaya complex northern nigeria abstract the kwandonkaya complex forms one of the most prominent and typical ring structures in the centre of jos plateau state nigeria lithologically it is composed of amphibole and biotite granites emplaced within archean basement gneisses and migmatites the chemical and mineralogical characteristics of this complex suggest that it was derived from crustal source materials trace elements are high in rb li f sn nb w and low in sr and ba compared to the world average for rocks of similar composition indicating a high degree of fractionation however the k rb ratios and petrographic evidence indicate that recrystallization may have redistributed the elements after the initial solidification of the rocks particularly in the biotite granites and that the distribution of tin may have been initially controlled by crystal silicate melt equilibra tin probably preferentially entered the aqueous phase during the late stages of solidification it was the interaction between this phase and early formed minerals that led to greisenization and tin tungsten mineralization although total rock chemical composition show no marked trends the composition of the biotites and hornblende define a trend in the compositional triangle fe3 fe2 mg when the biotites are related to the experimentally studied ternary system kfe33 alsi3o12 h 1 kfe32 alsi3o10 oh 2 kmg3alsi3o10 oh 2 and coupled with the estimated position of biotite solid solutions for different oxygen buffers the trend suggests that oxygen fugacities in the magmas during biotite formation were slightly higher than those defined by the fe2sio4 sio2 fe3o4 buffer the ratio of ferric to ferrous iron in pairs of the minerals from the kwandonkaya complex is the same for both hornblende and biotite and suggests crystallization in a closed but buffered environment

a numerical study on convergence of alongshore flows over the texas louisiana shelf 1 a hydrodynamic model is used to investigate convergent alongshore flows over the texas louisiana shelf characterized by down coast flows over the northern shelf encountering up coast flows over the southern shelf the model s ability to reproduce realistic current salinity and surface elevation fields is demonstrated through positive model skill scores when comparing model simulations to observational data the convergent flows are explored on both weather band and seasonal time scales for weather band scales this study focuses on wintertime convergent events the model predicted locations of convergent flows are supported by current measurements we find that the formation of convergent flows is primarily caused by along coast variation in the alongshore component of wind forcing which in turn is due to the curvature of the texas louisiana coastline in general the alongshore currents are well correlated with alongshore winds however the convergence points of currents and winds are not colocated but rather convergence points in ocean currents typically occur down coast of convergence points in the wind this offset is demonstrated to be mainly caused by buoyancy forcing that can drive the convergence location in the currents farther down coast no specific temporal pattern is found for the weather band convergence locations whereas at seasonal time scales the monthly mean convergence exhibits a prominent seasonal pattern with up coast migration of convergence locations in spring and summer and down coast migration in fall and winter

hydrothermal alteration of tertiary igneous rocks from the isle of skye northwest scotland hydrothermal alteration of tertiary granites from skye involed the reaction of igneous amphibole biotite ferroaugite fayalite alkali feldspar plagioclase feldspar magnetite and ilmenite with aqueous fluid primarily to combinations of secondary alkali feldspar chlorite and montmorillonite lesser amounts of muscovite calcite epidote prehnite zeolite and pyrite also developed during mineralogical alteration of the granites there was a net addition to rock of h and a net loss of ca fe and probably na there is no positive evidence for a significant change in their al si mg or k contents hydrothermal alteration of skye granite involved not only large scale migration of 18o 16o d and h but also of ca fe and probably na mineral thermometry combined with textural observations suggests that chemical isotopic and most mineralogical alteration were synchronous and occurred at 350 450 c textural observations further suggest that the mechanism of isotopic exchange between granite and hydrothermal fluid primarily was solution reprecipitation

biennial quasi biennial and decadal oscillations of potential vorticity in the northern stratosphere seasonal and interannual variations of the northern hemisphere stratosphere on the 600 k isentropic surface 20 35 hpa are investigated by using observations for 1964 1996 an area diagnostic is defined in terms of ertel s potential vorticity pv which measures the area enclosed by pv contours as a function of equivalent latitude and is not tied to the spherical coordinate system data from all seasons are examined for oscillations with periods of 6 months to more than a decade spectral analysis of pv at equivalent latitudes from 20 n to the pole reveals several possible signals 1 in addition to the well known annual cycle of the polar vortex there is a striking semiannual oscillation of pv in middle equivalent latitudes at 34 53 n the semiannual oscillation is larger than the annual cycle this oscillation arises from the formation of a surf zone in winter due to planetary wave breaking superposed on the annual cycle 2 a signal associated with the quasi biennial oscillation qbo of the equatorial stratosphere with average period slightly less than 30 months is strongest at low equivalent latitudes and is apparent in middle equivalent latitudes up to 67 n through interaction with the annual cycle oscillations with periods of 20 2 and 8 5 months are generated these three spectral peaks at approximately 30 20 and 8 5 months have been observed in ozone and wind data and are seen here for the first time in pv 3 at middle to high equivalent latitudes on the other hand we observe biennial and associated 8 month oscillations related to the occurrence of stratospheric warmings and strong undisturbed vortices in midwinter to late winter the data record is remarkable in that at high equivalent latitudes strong and weak polar vortices alternated from year to year producing the biennial signal and a significant negative lag 1 year autocorrelation the addition of an 8 month harmonic generates a much better fit to the sharp late winter anomalies 4 south of 60 n a spectral peak at 10 6 years is observed with the clearest signal near 20 n this spectral peak may be caused by the solar cycle or it may arise through interaction of biennial and quasi biennial oscillations

suppression of baroclinic instabilities in buoyancy driven flow over sloping bathymetry abstractbaroclinic instabilities are ubiquitous in many types of geostrophic flow however they are seldom observed in river plumes despite strong lateral density gradients within the plume front supported by results from a realistic numerical simulation of the mississippi atchafalaya river plume idealized numerical simulations of buoyancy driven flow are used to investigate baroclinic instabilities in buoyancy driven flow over a sloping bottom the parameter space is defined by the slope burger number s nf 1 where n is the buoyancy frequency f is the coriolis parameter and is the bottom slope and the richardson number ri n2f2m 4 where m2 hb is the magnitude of the lateral buoyancy gradients instabilities only form in a subset of the simulations with the criterion that sh sri 1 2 uf 1w 1 m2f 2 0 2 where u is a horizontal velocity scale and sh is a new parameter named the horizontal slope burger number suppression of instability formation for certain flow conditions contrasts

rutile as a pathfinder for metals exploration abstract the use of detrital rutile as an indicator of mineralisation is contingent on the identification of trace element signatures that uniquely distinguish rutile grains derived from mineralisation from those sourced from barren rocks in order to discriminate rutile sources principal component analysis was applied to a total of 3149 la icp ms analyses of rutile from ore environments au au cu pegmatites carbonatites lamprophyres vhms and barren igneous and metamorphic rocks hierarchical clustering of the results of principal component analysis pca determined sb and cr exhibit the most chemical variation in ore derived rutile rutile sourced from au deposits and enriched in sb can be distinguished from rutile from pegmatites which are enriched in nb ta and sn discriminating rutile from barren rocks can be done primarily using w and fe contents which can also provide insight on source rocks based on metamorphic grade and degree of crustal input clustering all rutile chemistries based on pca of 12 elements identified nine chemically distinct groups from ore mineralisation and barren igneous and metamorphic rocks primarily using variation in w and cr contents two groups are solely derived of rutile from au ores high versus low sb rutile of the remaining seven groups one group is comprised mainly of rutile from pegmatites high nb ta sn four groups are comprised solely of rutile from barren rocks and two groups are a mix of ore and non ore rutile rutile from au ore similar to the giant kalgoorlie and big bell au deposits is distinctive compared to rutile from all other rocks and can be distinguished from other ores and barren environments using multi element clustering of pca analysis thus rutile chemistry of detrital rutile grains is a valuable tool in au exploration

cross equatorially radiating stratospheric rossby waves upper atmosphere research satellite observations of constituent distributions in the middle stratosphere show that extratropical rossby waves from the winter hemisphere can at certain times radiate across the equator and reach the summer subtropics before they break and are absorbed conditions are most favorable for rossby waves to radiate into the tropics when the westerlies of the winter hemisphere extend to low latitudes as usually occurs during november and december in the northern hemisphere cross equatorial radiation of quasi stationary rossby waves requires westerly equatorial winds as occurred in the middle stratosphere in late 1992 constituent distribution maps show numerous episodes of rossby wave radiation across the equator during this early winter period but not after early january 1993 wave breaking in both the winter and summer subtropics above 22 mb causes constituent exchange between the tropics and extratropics including deep tropical in mixing

interhemispheric differences in stratospheric water vapour during late winter in version 4 mls measurements observations of stratospheric water vapour made by the microwave limb sounder mls during the 1992 and 1993 arctic and 1992 antarctic late winters have now been produced using version 4 of the retrieval software these improved measurements are analysed as equivalent latitude zonal means major interhemispheric differences are revealed in the water vapour content of the vortex in the lower stratosphere this technique emphasises mixing ratio gradients at the edges of both polar vortices and a local maximum at the edge of the antarctic vortex there are some small interhemispheric differences in mixing ratios in mid latitudes but they are not strongly related to the dehydration of the antarctic vortex a mixing ratio gradient across the interior of the antarctic vortex at 530k indicates it is not isentropically mixed a strong local maximum in mixing ratio at the centre of the antarctic vortex in the mid stratosphere indicates it is not well mixed in the mid stratosphere also there is little evidence of significant structure inside the arctic vortex

changes in the heterogeneity of mesoscale distribution patterns of larval fish associated with a shallow coastal haline front abstract in june 1983 there was a large outflow of inland fresh waters from the rhone river that covered a broad area off the northern coast of catalonia northwestern mediterranean giving rise to a surface plume of fresh water with a distinct haline front at its southern edge this hydrodynamic event brought about substantial changes in the structure of the larval fish community in the area which was in turn reflected in an increase in spatial heterogeneity large numbers of species and individuals were found along the southern edge of the plume in association with the haline front whereas with the exception of certain species larval fish concentrations in the area covered by the plume tended to be considerably lower than in the rest of the area species predominantly located in the surface water layers were probably transported by the plume out to the plume s edge other species which apparently enjoy a broader vertical distribution range were less affected by the surface advection processes

origins of karenia brevis harmful algal blooms along the texas coast the dinoflagellate karenia brevis is the major harmful algal bloom hab species in the gulf of mexico given that the rapid appearance of k brevis cannot be explained by plankton growth alone advection is likely important in bloom initiation forward and backward moving numerical surface drifters were employed in a numerical model of the texas louisiana shelf to help determine the basic physical mechanisms explaining sporadic interannual occurrences of k brevis along the texas coastline results from data analysis from the area show that hab events occur in years in which there are weaker mean downcoast along shore wind speeds the drifter experiments suggest that southern waters play a role in hab event initiation providing an offshore source of cells at the end of summer as winds switch from upcoast to downcoast in early fall offshore populations of k brevis are swept southward by wind driven currents in years with strong downcoast winds however when the downshore wind is weak shoreward ekman transport creates a convergent flow near the coast that allows cells to concentrate and initiate a bloom

the tropical stratopause in the ukmo stratospheric analyses evidence for a 2 day wave and inertial circulations summary large scale atmospheric motions near the low latitude stratopause in the uk meteorological office stratospheric analyses during the northern hemisphere winter are investigated focusing in particular on the 2 day wave and inertial eddies the 2 day wave is a westward propagating planetary wave which appears recurrently in the summer subtropical upper stratosphere and mesosphere space time spectral analysis of the assimilated fields of temperature and winds and high resolution transport of water vapour reveal large amplitude breaking planetary waves in the summer subtropics principally a 2 day wave 3 and a wave 1 of a period near 7 days a region of anomalous zonal mean meridional gradient of potential vorticity also exists pointing to a barotropic instability mechanism for the origin of the 2 day wave by contrast the winter subtropics are characterized by mixing on less than planetary scales during the period considered occurring during the easterly phase of the stratospheric semi annual oscillation water vapour is mixed turbulently into gyres and drawn in narrow filaments out of the southern hemisphere the potential vorticity field displays vertically layered zonally asymmetric variations the behaviour of the model assimilated fields is supported by along track water vapour distribution observed by the microwave limb sounder aboard the upper atmosphere research satellite shows evidences for intermittent filamentary mixing in the northern subtropics and a 2 day wave signature in the summer subtropics based on these results a possible mechanism connecting the initiation of the austral 2 day wave events to strong planetary wave activity in the winter is proposed the winter planetary waves provide the background conditions for development of inertial instabilities at low latitudes of the winter hemisphere which in turn create conditions favourable for barotropic instability of the summer subtropical easterly jet

cryogenic infrared spectrometers and telescopes for the atmosphere crista experiment and middle atmosphere variability the cryogenic infrared spectrometers and telescopes for the atmosphere crista instrument was built to determine whether and to what extent small scale structures in global trace gas distributions and in dynamics are present in the middle atmosphere to achieve this trace gases were measured in the middle infrared by the limb scan technique at the highest possible horizontal and vertical resolution crista uses three telescopes i e three view directions simultaneously and has three grating spectrometers for the middle ir 4 14 m and one spectrometer for the far ir 15 71 m the optics and detectors are cooled to cryogenic temperatures by supercritical helium or subcooled helium respectively in a double cryostat an instrument overview is given and the design guidelines are sketched the crista experiment was flown on the space shuttle sts 66 as part of nasa mission atlas 3 on november 3 14 1994 orbit altitude was 300 km and inclination was 57 a campaign of ground based balloon and rocket validation and complementary measurements was performed simultaneously the crista instrument performed flawlessly a horizontal resolution of 200 km 650 km was achieved at the equator with higher horizontal resolution at higher latitudes a vertical resolution of 2 5 km or better was obtained the middle atmosphere was found to be highly variable at scales of 1000 km in the stratosphere three streamers of tropic subtropic air extending to higher latitudes are described their meridional scale is 1000 km while the zonal scale is of the order of 10 000 km and more the streamers appear to be typical of specific winter conditions and to play a role in meridional transport at mesospheric heights a strong tidal temperature oscillation was observed which extended well into the lower thermosphere

a tale of two plutons petrographic and mineralogic constraints on the petrogenesis of the red lake and eagle peak plutons central sierra nevada california the red lake and eagle peak plutons are similar in age k ar 87 89 m y and range in composition from granodiorite to granite the red lake pluton is equigranular has a locally greisened marginal zone and shows only minor mineralogical and chemical zoning whereas the eagle peak pluton is mineralogically compositionally and texturally zoned with an equigranular margin and a porphyritic core modal and normative trends within each pluton are consistent with separation of plagioclase and mafic minerals leading to a residual liquid enriched in quartz and alkali feldspar the formation of the prominent alkali feldspar megacrysts in the eagle peak core was promoted by plagioclase separation h 2 o undersaturation and a slower cooling rate relative to the red lake magma early loss of volatiles and a resulting increase in magma melt crystals viscosity inhibited crystal segregation within the red lake pluton and prevented the development of zoning late stage aplites associated with both plutons f

phyllosilicate and rutile compositions as indicators of sn specialization in some southeastern australian granites biotites from unaltered sn granites in southeastern australia are highly ferroan fe fe mg mn 0 75 whereas biotites from barren granites are less ferich fe fe mg mn 0 65 similar distinctions between sn specialized and barren granites can be observed in the other phyllosilicates especially chlorite biotites and muscovites from sn granites have greater be cs f li mo rb sc sn tl y and zn and lesser ba abundances than corresponding micas from barren granites in the same district alteration of barren granites also results in similar enrichments in micas of these elements sn and zn because of their abundance and retention during degradation of biotite to chlorite are the best trace element discriminants between barren granites and sn granites altered granites with the sn content of phyllosilicates being a better indicator than zn rutile inclusions within phyllosilicates from unaltered sn granites have nb2o5 contents up to 26 the ta content tends to increase with nb content but especially high ta contents occur in the rutile inclusions of granites that give rise to pegmatitic deposits the rutile inclusions in sn granites may also have substantial sn and w contents the rutiles of barren granites have low nb ta sn and w contents but sn and w increase with alteration together the ratio fe fe mg mn and sn contents in phyllosilicates and rutile compositions can be used to identify the sn mineralization potential of a granite

objectively mapped stream function fields on the texas louisiana shelf based on 32 months of moored current meter data on the basis of current measurements observed at 31 moorings during april 1992 through november 1994 as part of the texas louisiana shelf circulation and transport processes study we describe the horizontally nondivergent part of the near surface shelf wide scale low frequency circulation and its variability on the texas louisiana continental shelf by means of objectively fitted stream function fields the 32 month mean velocity stream function patterns generally support the cochrane and kelly 1986 circulation schema for the shelf circulation in which an elongated cyclonic gyre exists during the nonsummer period september through may but with flow in the summer june to august directed upcoast toward the mississippi delta over the entire shelf there exists significant interannual variability of the stream function fields especially in the transition period from spring to summer to fall and along the shelf break strong upcoast downcoast currents dominate at the western shelf break associated with the presence of energetic anticyclones cyclones the dominant pattern of stream function variability deduced by empirical orthogonal function eof analysis of 32 individual monthly mean patterns contains about 89 of the variance and shows a simple shelf wide along shelf pattern of circulation the monthly evolution in amplitude of this dominant eof pattern clearly mimics the monthly evolution of the along shelf component of the wind with squared correlation of 0 83 this provides strong evidence that the seasonal variation of the shelf circulation is wind forced in support of cochrane and kelly the second and residual eofs show more complex features near the shelf break that are associated with loop current eddies known to impact the continental slope and shelf break

the north pacific a global scale estuary abstract the atmospheric net flow of water from the atlantic to the pacific ocean is supposed to maintain the salinity difference between the two oceans assuming the existence of a subsurface level of no horizontal pressure gradient in the ocean the mean sea level in the northern pacific must be higher than in the arctic ocean this mean sea level difference is supposed to drive the observed mean flow through the bering strait the estimated flow of freshwater through the bering strait is approximately equal to the estimated atmospheric net flow of water from the north atlantic to the north pacific this justifies the formulation of a simple estuary model for the north pacific in which the brackish water exits through the bering strait the salinity difference between the two oceans is shown to be controlled by the topography of the bering strait the estuary model gives residence times for water in the upper layer 1000 m thick of approximately 1000 years and in the lower layer of approximately 400

coastal fresh water discharge in the northeast pacific very high annual rates of precipitation in the coastal mountains that border the northeast pacific ocean produce large fresh water discharges 23000 m3 s 1 this discharge has been ignored previously since it does not enter the ocean in the form of large rivers but instead the water enters by way of numerous small rivers and streams thus it acts as a line source instead of a point source this coastal discharge contributes at least 40 of the fresh water that enters the northeast pacific from the atmosphere the discharge is comparable to the mean annual discharge of the mississippi river system the fresh water creates a cross shelf density gradient that drives an alongshore baroclinic jet the width of this jet is less than 25 km with speeds in excess of 100 cm s 1 it extends along the coast from southeast alaska to at least kodiak island apparently the flow is maintained as a narrow current adjacent to the coast by wind stress that causes downwelling conditions here throughout most of the year

tin content of biotites from the afu younger granite complex central nigeria the sn content determined by electron microprobe of 36 biotites from granitic rocks of the afu complex ranges from 50 to 1 000 ppm and averages 500 and 150 ppm for biotites from mineralized and barren granites respectively these results show that the sn content of biotites associated with mineralization is three times greater than the sn content of biotites from barren granites thus the possibility of differentiating between mineralized and unmineralized granite on the basis of the sn content of biotite is suggested the relationship of the tin content of the biotites to that of the rock is nearly constant at approximately 10 1 the biotites have less than 40 percent of the amount of tin than the granites have the concentration of tin in the biotites appears to be a function of the chemical evolution of the granites sn may increase in the biotites with decreasing oxygen fugacity and temperature of crystallization the low oxygen fugacity and low temperature of crystallization seem due largely to the high concentration of f rb and other volatile elements in the magma

the fate of river discharge on the continental shelf 2 transport of coastal low salinity waters under realistic wind and tidal forcing a three dimensional numerical simulation of shelf circulation is presented we employ realistic forcing for the southeast u s continental shelf during the spring season we show that the strongest offshore transport of river induced coastal low salinity waters and associated materials occurs near the surface the preferred mean pathway is in the northeastward direction and it takes about 2 months to cross the entire shelf owing to the mean direction of surface transport and the topography of the south atlantic bight shelf the preferred location for springtime removal is off charleston south carolina and presumably in the vicinity of the charleston bump the transport and fate of the river induced coastal low salinity waters during the spring season are determined by 1 the stratification of nearshore waters which is due to the high river runoff and causes the decoupling between near surface and near bottom layers 2 the prevailing northeastward winds which cause significant offshore transport within the shallow near surface ekman layer and 3 the tidally induced bottom stirring m2 tides comparison of model and data time series of currents shows very good agreement standard deviations of the model and data computed empirical orthogonal functions are almost identical while the respective variance conserving spectra agree both in amplitude and phase

a model study of the influence of the quasi biennial oscillation on trace gas distributions in the middle and upper stratosphere the dominant tracer transport processes in the equatorial and subtropical latitudes of the middle and upper stratosphere are investigated distributions of water vapor in northern hemisphere winter from the microwave limb sounder onboard the upper atmosphere research satellite are employed together with a three dimensional stratosphere mesosphere model that incorporates a representation of the quasi biennial oscillation qbo the model reproduces the observed tracer distributions in particular a staircase feature that is present in northern winter of 1992 easterly qbo phase but not in 1993 westerly qbo phase this feature is highly asymmetric about the equator the model circulation is diagnosed to show that while the induced qbo circulation in the lower stratosphere of the model is relatively symmetric about the equator in the middle and upper stratosphere it is highly asymmetric and in the correct sense to give rise to the staircase feature model experiments are compared in which trajectories are advected by 1 the full three dimensional circulation and 2 the residual mean circulation only thereby removing the local effects of isentropic mixing by planetary waves on the trajectory distributions these confirm the importance of advection by the qbo circulation at equatorial and subtropical latitudes however sharpening of the tracer gradients at the subtropical edge of the surf zone by the action of planetary waves is shown to be important in the formation of a subtropical cliff between 10 and 20 mbar at 20 30 n the model results also suggest that the prominence of the summer subtropical peak in easterly phase years compared with westerly phase years is not entirely due to increased summer upwelling of the large scale global circulation caused by the stronger planetary wave driving the depression of the winter half of the equatorial peak by the local asymmetric qbo circulation is also shown to be important

quasi biennial and subbiennial variations of stratospheric trace constituents derived from haloe observations interannual variability of trace constituents in the stratosphere is examined using methane water vapor and ozone data from the halogen occultation experiment aboard the upper atmosphere research satellitein 1992 99 application of rotated principal component analysis to the dataset reveals dominant modes of variability consisting of annual semiannual and quasi biennial oscillations qbos together with subbiennial variations evidently due to nonlinear interaction between the annual cycle and qbo the structure of quasi biennial variability is approximately symmetric about the equator while subbiennial variability with certain exceptions is approximately antisymmetric and confined mostly to the subtropics the vertical structure and downward propagation of the ozone qbo at the equator is described by a pair of symmetric eofs having separate amplitude maxima in the lower and upper stratosphere a second pair of eofs explains the seasonal dependence of subtropical ozone anomalies for each tracer the subtropical anomaly is larger in the northern hemisphere a novel phase diagram illustrates the joint seasonal and qbo dependence of tracer anomalies a pair of principal components are used to define the phase of the dynamical qbo when plotted against the phase of the annual cycle the qbo follows a diagonal trajectory with regular phase progression except for an occasional slowing of easterly shear zone descent near 50 hpa tracer principal components of symmetric and antisymmetric eofs plotted along this trajectory display the distinct signatures of quasi biennial and subbiennial variation tracer anomalies reconstructed using an idealized representation of qbo and subbiennial harmonics display the seasonal synchronization and decadal modulation characteristic of qbo annual cycle interaction

rossby wave propagation into the tropical stratosphere observed by the high resolution doppler imager stratospheric wind observations by the high resolution doppler imager on the upper atmosphere research satellite show that quasi stationary rossby waves propagate into the tropics rossby wave breaking and dissipation causes meridional transport and direct deposition of momentum and has a significant influence on the evolution of the mean tropical winds in the upper stratosphere deeper penetration into the tropics occurs when the quasi biennial oscillation is in its westerly phase above 30 km during northern winter subtropical momentum deposition by rossby waves occurs only in late november through december while during southern winter this occurs primarily in august and september

persistent lagrangian transport patterns in the northwestern gulf of mexico abstractpersistent lagrangian transport patterns at the ocean surface are revealed from climatological lagrangian coherent structures clcss computed from daily climatological surface current velo

effects of coastal transport on larval patches models and observations abstract we used a combination of field observations and numerical modeling to examine the physical mechanisms responsible for the evolution and transport of patches of blue crab larvae in the mouth of delaware bay the observations consisted of larval collections and surface salinity measurements taken along a moving spatial grid whose origin was determined by a satellite tracked drifter examination of field observations revealed a slender larval patch that was aligned with salinity contours measurement of the salting rate of the larval patch indicated that the patch moved through the offshore edge of a buoyant plume due to wind driven upwelling circulation a numerical model that provided realistic simulations of the flow field at the mouth of delaware bay and the adjoining coastal ocean was used to examine the physical mechanisms responsible for the movement and evolution of the patch we conducted a series of simulations in which we separately examined the effects of tides buoyancy driven flow and wind driven transport results showed that both tides and buoyancy driven flow tend to elongate an initially square fluid element although winds alone have little effect on the shape of a patch wind driven flow can effectively move a patch through a complex flow field in which the deformation by tides and buoyancy driven circulation can have significant effects this study represents the first observation and analysis of a larval patch that remains intact while moving through the edge of a buoyant plume it provides new insight into the shape of larval patches in delaware bay and any region with strong buoyancy and tidally driven flow suggesting that typical larval patches may not be characterized by equal across and alongshelf dimensions but instead tend to be slender shapes that are aligned with the flow field

seasonal asymmetry of the low and middle latitude qbo circulation anomaly abstract it is usually assumed that the circulation anomaly induced directly by the quasi biennial oscillation qbo in the equatorial zonal wind is approximately a seasonally independent two cell structure symmetric about the equator and confined to the tropics it is shown here using a simple two dimensional model that although the two cell structure exists at equinox at solstice the summer cell disappears and the winter cell is greatly strengthened about three times stronger than at equinox and expanded strong cross equatorial flow is induced near the shear zone where the qbo winds are easterly this result may explain why the observed anomalies in trace gases are small in the summer hemisphere and it also reduces the need for a modulation of the planetary wave fluxes at low and middle latitudes in order to explain the modulation of the circulation there at low latitudes the shape of the isopleths of a modeled tracer closely resemble those observed in both easterly and westerly phases of the q

evidence of meridional motion in the summer lower stratosphere adjacent to monsoon regions twenty one years of rawinsonde data were used together with 8 years of uninitialized european centre for medium range weather forecasts ecmwf analyses to describe the climatological structure of large scale circulations adjacent to monsoon regions in northern and southern hemisphere summers in the upper troposphere and lower stratosphere equatorward and poleward motions occur on the eastern and western sides of monsoon regions respectively it is shown that significant meridional velocities 1 ms 1 penetrate the lower stratosphere up to a maximum height of 50 30 mbar largest meridional velocities are observed in connection with the asian monsoon in northern summer although evanescent in height these motions are relatively important for horizontal transport of constituents in the summer lower stratosphere when planetary waves are otherwise small asian and mexican monsoons in this season are displaced sufficiently far from the equator in close proximity to the tropopause break to have a significant role in stratosphere troposphere s t exchange the companion paper by chen 1995 provides evidence of irreversible s t exchange in the upper middle world during northern summer

flow induced aggregation of plankton at a front a 2 d eulerian model study abstract we use a simple 2 d eulerian numerical model to illustrate a mechanism whereby depth keeping swimming behavior on the part of an organism combined with a convergent flow field at a surface front can create dense populations in this model a steady flow field and vertical diffusivity are prescribed along with an initial plankton distribution the plankton swim vertically with speeds that depend only on depth where the form of that dependence may reflect such factors as the vertical variation in light level or the concentration of some prey organism the eulerian nature of the model enables diffusion to be treated explicitly the numerical model describes the evolution of an initial plankton patch in time a parameter study illustrates the roles played by diffusion water velocity and details of the animals swimming behavior on patch evolution output from the model is compared with data taken at a dense plankton patch observed near a small scale front in the northern great south channel in early june 1989

low frequency circulation on the texas louisiana continental shelf for the texas louisiana coast west of 92 5 w long series of data from near freeport texas together with shorter series from other locations show strong response of coastal current to wind stress in agreement with coastal jet concepts we infer from coastal winds scattered current measurements and distributions of sea surface salinity and geopotential that a cyclonic gyre elongated along the shelf is the dominant feature of the prevailing shelf circulation the inshore limb of the gyre is the coastal jet driven by wind with a west or southward downcoast component which prevails along much of the coast except in july august because the coast is concave the shoreward prevailing wind results in a convergence of coastal currents which marks the downcoast extent of the gyre corresponding to the convergence is a seaward flow which forms the southwest limb of the gyre a prevailing countercurrent north or eastward flow along the shelf break includes the outer limb of the gyre the eastern shoreward flowing limb of the gyre corresponds to divergence along the coast centered near 92 5 w the convergence at the western or southern end of the gyre migrates seasonally with the direction of the prevailing wind reaching south of the rio grande mouth in fall and the cameron offing in july the gyre is normally absent in july but reappears in august september when a downcoast wind component develops

pathways of pacific water across the chukchi sea a numerical model study 1 pathways of pacific water flowing from the north pacific ocean through bering strait and across the chukchi sea are investigated using a two dimensional barotropic model in the no wind case the flow is driven only by a prescribed steady northward flow of 0 8 sv through bering strait the resulting steady state circulation consists of a broad northeasterly flow basically following the topography with a few areas of intensified currents about half of the inflow travels northwest through hope valley while the other half turns somewhat toward the northeast along the alaskan coast the flow through hope valley is intensified as it passes through herald canyon but much of this flow escapes the canyon to move eastward joining the flow in the broad valley between herald and hanna shoals another area of slightly intensified currents there is a confluence of nearly all of the flow along the alaskan coast west of pt barrow to create a very strong and narrow coastal jet that follows the shelf topography eastward onto the beaufort shelf thus in this no wind case nearly all of the pacific water entering the chukchi sea eventually ends up flowing eastward along the narrow beaufort shelf with no discernable flow across the shelf edge toward the interior canada basin travel times for water parcels to move from bering strait to pt barrow vary tremendously according to the path taken e g less than 6 months along the alaskan coast but about 30 months along the westernmost path through herald canyon this flow field is relatively insensitive to idealized wind forcing when the winds are from the south west or north in which cases the shelf transports tend to be intensified however strong northeasterly to easterly winds are able to completely reverse the flows along the beaufort shelf and the alaskan coast and force most of the throughflow in a more northerly direction across the chukchi sea shelf edge potentially supplying the surface waters of the interior canada basin with pacific water the entire shelf circulation reacts promptly to changing wind conditions with a response time of 2 3 days the intense coastal jet between icy cape and pt barrow implies that dense water formed here from winter coastal polynyas may be quickly swept away along the coast in contrast there is a relatively quiet nearshore region to the west between cape lisburne and icy cape where dense water may accumulate much longer and continue to become denser before it is carried across the shelf

the interior shelves of the arctic ocean physical oceanographic setting climatology and effects of sea ice retreat on cross shelf exchange abstract the interior shelves of the arctic mediterranean are the shelves of the kara sea laptev sea east siberian sea and beaufort sea they comprise approximately 40 of the total arctic shelf area 2 5 10 6 km 2 and are distinguished from inflow and outflow shelves by their principal forcing dynamics along their southern continental boundary the interior shelves are dominated by the major arctic rivers receiving over 80 of the total freshwater input to the arctic ocean in the mid shelf region wind and ice motion surface stresses dominate mixing and circulation resulting in high variability along their northern seaward boundary they are forced by upwelling and downwelling favourable surface stresses which drive shelf basin exchanges with atlantic and pacific origin cyclonic boundary currents over the upper slope shelf basin exchange is further modified by shelf break morphometry e g canyons valleys headlands and bottom slope here we review the physical oceanographic settings and forcing of the interior shelves and then focus on shelfbreak exchange and supply of nutrients for new primary production due to upwelling across the shelfbreak as a proxy for this nutrient supply we show seasonal and annual time series of along shelfbreak surface stress due to wind and ice motion from 1979 to 2011 we apply this analysis to the shallow shelves from the kara sea to the beaufort sea and comment on recent increases due to atmospheric changes and sea ice retreat

interaction of extratropical rossby waves with westerly quasi biennial oscillation winds the role of laterally radiating stratospheric rossby waves from the winter hemisphere in the momentum balance of the quasi biennial oscillation qbo remains an unresolved issue observations of extratropical rossby waves penetrating close to the equator suggest that rossby wave absorption in the tropics must occur at least occasionally this paper presents numerical simulations using a global shallow water model to examine the pattern of wave absorption at low latitude during the westerly wind phase of the qbo earlier results indicating that extratropical rossby waves radiating to the equator do not break there when the qbo phase is westerly are reproduced it is shown that the westerly qbo jet can persist undiminished at its core over seasonal length integrations because the laterally radiating rossby waves are absorbed along the qbo jet s flanks where easterly acceleration occurs the net effect of the rossby waves on the westerly qbo jet is a reduction in the width of its meridional profile but not its core strength this behavior is interpreted by considering the filtering of equatorward radiating rossby waves by critical layer absorption a process that depends on the background zonal mean wind and the waves phase speed and amplitude the simulations also show that adequate horizontal resolution is needed to capture the suppression of wave breaking at the qbo jet core and persistence of the jet core strength over seasonal timescales the implications of this result for simulations of the qbo in general circulation models are considered

characteristics of the great whale river plume observations of the motion field and dilution effects associated with the plume of great whale river in hudson bay are presented for both open water and ice covered conditions in the summer months a distinct plume of about 100 km2 in area is formed offshore which is characterized by a 1 2 m thickness and large velocities directed away from the river mouth in contrast to slower currents parallel to the shore in the ambient waters underneath surface drifter results suggest that the outer boundary of plume may be a zone of frontal convergence under ice covered conditions the plume was significantly thicker and extended much farther offshore in spite of a marked reduction in river runoff at this time

seasonal circulation on the western shelf of the gulf of mexico using a high resolution numerical model 1 the seasonal circulation on the western shelf of the gulf of mexico is studied using a high resolution numerical simulation historical hydrographic data sea level data and satellite images three regions are distinguished the tamaulipas veracruz tave shelf the louisiana texas latex shelf and the western campeche bank on the tave shelf there is a swift reversal of the along shelf current downcoast from september to march and upcoast from may to august when there is upwelling due to offshore ekman transport circulation on the western campeche bank is upcoast throughout the year the latex shelf has a cyclonic circulation except during summer months when the flow is eastward during spring summer the upcoast current on the tave shelf reaches the southern texas shelf where it encounters a downcoast coastal current favoring offshore transports in the fall winter the downcoast current reaches the southern bay of campeche where it meets an opposing along shelf current generating seasonal offshore transports during fall and winter cool low salinity water from the mississippi and atchafalaya rivers is advected westward along the latex shelf onto the tave shelf developing along shelf fronts and temperature inversions commonly observed over the outer shelf and shelf break the main forcing over the western shelf of the gulf is the along coast wind stress component the existence of the cross shelf transports in the confluence regions is supported by chlorophyll a data up to 80 of the seasonal sea level variability is explained by the along shelf currents and the low frequency variability of the atmospheric sea level pressure

the siberian coastal current a wind and buoyancy forced arctic coastal current we describe circulation and mixing in the siberian coastal current scc using fall shipboard measurements collected between 1992 and 1995 in the western chukchi sea the scc forced by winds siberian river outflows and ice melt flows eastward from the east siberian sea it is bounded offshore by a broad 60 km front separating cold dilute siberian coastal water from warmer saltier bering sea water the alongshore flow is incoherent because the current contains energetic eddies and squirts probably generated by frontal baroclinic instabilities these enhance horizontal mixing and weaken the cross shore density gradient along the scc path eventually the scc converges with the northward flow from bering strait whereupon it deflects offshore and mixes with that inflow deflection occurs where the alongshore pressure gradient vanishes that location varies on synoptic and seasonal timescales because this gradient depends on the winds buoyancy fluxes and the sea level difference between the pacific and arctic oceans deflection usually occurs on the chukchi shelf but the scc occasionally flows southward through bering strait such events are short lived 1 10 days and occur mainly in fall and winter under northerly winds scc transport is likely small 0 1 sv but its dilute waters could substantially freshen the bering strait inflow and affect the disposition of pacific waters in the arctic ocean arctic river outflows should preferentially form surface advected fronts rather than bottom advected fronts because vertical mixing energy is low on arctic shelves surface advected fronts are more susceptible to upwelling winds and for the scc the pressure gradient between the pacific and arctic oceans than bottom advected fronts the scc never developed in fall 1995 because of anomalously steady upwelling winds the western chukchi shelf could have formed upper halocline source water in the winter of 1995 1996

the contiguous panarctic riverine coastal domain a unifying concept the riverine coastal domain rcd is a narrow 15 km shallow 10 m contiguous feature that is primarily forced driven by an aggregate of continental runoff sources and which extends clockwise 10 103 km around northern north america we hypothesize that a similar feature extends around northern eurasia the rcd carries a terrestrial signal that affects light nutrient and carbon regimes and provides a coastal pathway for the dispersal and migration of marine biota the physical and biogeochemical variables within the rcd yield a contiguous gradient of environmental conditions along and across the panarctic coastal zone the rcd acts as the initial connector between terrestrial and marine ecosystems and may become even more prominent as terrestrial runoff permafrost thawing and local ice melt are assumed to increase in the near future climate

the influence of the quasi biennial oscillation on global constituent distributions long lived stratospheric constituents observed by the upper atmosphere research satellite are compared between late northern winters 1991 1992 and 1992 1993 the phase of the quasi biennial oscillation qbo was such that the equatorial zonal wind was easterly westerly in the lower stratosphere during the first second winter in the tropics winter to winter differences in the latitude height distribution of zonally averaged n 2 o and h 2 o are associated with differences in large scale upwelling the qbo s mean meridional circulations and lateral mixing by incident extratropical rossby waves in the extratropics significant differences in zonally averaged n 2 o and h 2 o are also found which are believed to represent the extratropical constituent qbo the transport processes creating the extratropical constituent qbo are tentatively identified in the winter extratropics qbo modulation of the residual circulation appears to dominate in the upper stratosphere while qbo modulated rossby wave isentropic mixing dominates below about 10 mbar analysis of rossby waves at low latitudes as deduced from isobaric constituent distribution maps suggests that the meridional distribution of rossby wave breaking depends on the tropical zonal winds easterly qbo winds prevent rossby wave radiation into the tropics so that a strong constituent concentration gradient is generated in the winter subtropics westerly qbo winds allow some wave radiation into the tropics accompanied by isentropic mixing in the winter subtropics cross equatorial propagation and occasional mixing in the summer subtropics these effects depend on altitude and appear to vary in accord with the descending phases of the qbo

idealized three dimensional modeling of seasonal variation in the alaska coastal current 1 seasonal variation of the buoyancy and downwelling wind forced alaska coastal current acc and the fate of freshwater contained in it is considered using idealized analytical and numerical models of the acc formed from a half line source of buoyant inflow the coastal current initially develops two dimensionally but becomes three dimensional from a balance between coastal influx of buoyancy and its downstream transport which leads to a coastal current depth limit hmax 1 2 where x is along shelf distance q is the line source strength for unit length f is the coriolis frequency and g is the reduced gravity of the buoyant inflow this limit is unchanged under downwelling wind stress and is reached on timescales of less than 1 month for the acc the coastal current width is roughly constant in x and increases in time at the same rate as the two dimensional solution imposition of a downwelling wind stress results in an approximate balance among wind stress and along and cross shelf momentum advection so that the current width is reduced to ywind ld 1 2 where ld is the rossby radius of deformation is the wind stress and 0 is a reference density waves eddying motions eventually grow in the half line source coastal current with wavelengths proportional to the coastal current width and with a downstream phase speed slower than the maximum current speed these features cause an offshore flux of buoyant water a broader coastal current and further accumulation of buoyancy on the shelf increasing downwelling wind stress reduces the effects of the instabilities continual accumulation of buoyancy on the shelf occurs during all model runs but is nearly absent under maximum winter downwelling wind stress it is suggested that freshwater accumulation on the shelf during spring summer and fall may be largely lost downstream during winter

retention of crab larvae in a coastal null zone alongshelf transport in the southern middle atlantic bight is forced by buoyancy driven currents originating in three large estuaries along the bight these currents are strongest in the coastal ocean near the southern terminus of each estuary while the analogous region on the northern side is characterized by weak subtidal flow we used a combination of field observations and numerical modeling to test the hypothesis that these regions of weak subtidal flow are coastal null zones that serve as retention areas for larvae the field study consisted of a four day shipboard investigation of the distribution of blue crab larvae callinectes sapidus near the mouth of delaware bay 39 n 75 w in late summer 2004 hydrographic surveys of the study site were conducted with a hull mounted surface measuring system results showed a sharp boundary between the null zone and the buoyancy driven current to the south blue crab larvae were collected in surface plankton tows along a 30 km transect that encompassed these two areas stations with higher densities of larvae were clustered in the null zone during both ebb and flood tides a numerical model was used to examine the physical mechanisms responsible for the observed distribution model results agreed with the field survey and showed that simulated larvae are aggregated in the null zone the simulations also demonstrated that larvae spawned within the null zone have a much greater probability of settling in juvenile nursery habitat within the bay the close agreement between field and model results provides consistent support for the hypothesis that coastal null zones associated with the buoyancy driven circulation of large estuaries may allow retention of larvae in the vicinity of the natal spawning population

estuary plumes and fronts in shelf waters a layer model abstract a layer model that treats fronts as discontinuities is developed to study the steady state behavior of shallow estuary plumes on the continental shelf the complete range of earth rotation effect is evaluated from small scale or nonrotating plumes kelvin number equal zero to large scale rotating plumes kelvin number equal order one supercritical flow is assumed in the outlet channel and the method of characteristics is used to compute the flow downstream nonrotating plumes have strong boundary fronts and concentrate their greatest layer depth and mass transport offshore near the front but form no coastal current rotating plumes have boundary fronts that weaken soon after discharge form a turning region where coriolis action deflects the flow toward shore and subsequently set up a coastal current soon after its formation this coastal current is bounded offshore by a strong front called the coastal front across which the momentum balance changes from nearly inertial in the turning regi

mixing zone in the tropical stratosphere above 10 mb observations of trace constituents obtained from the upper atmosphere research satellite in late winter 1991 92 reveal a zone of quasi horizontal stirring in the tropical stratosphere above 10 mb equatorward of the subtropical jet this mixing region was separated from the midlatitude surf zone by a strong gradient of potential vorticity and tracer along the jet axis the jet and accompanying gradients are climatological features mixing equatorward of the jet evidently depends on the phase of the quasi biennial oscillation