petrology of the great abitibi dyke superior province canada the great abitibi dyke gad which can be traced northeast for 700 km across the abitibi belt in the southeastern superior province of the canadian shield is composed of olivine gabbro to monzodiorite weakly saturated to undersaturate d in silica all rocks of the gad can be derived by mainly plagioclase and olivine fractionation from a parental magma corresponding in composition to chilled margin samples two units can be distinguished a marginal unit unit 1 representing 0 50 crystallization and a central unit unit 2 found over about half of the dyke length representing 50 70 crystallization modelling using pearce elemental ratio analysis quantifies the fractionation history and allows mass balance calculations over the present exposure level of the dyke the approximate balance between the amounts of cumulate and fractionated rocks suggests that unit 1 differentiated essentially in situ as a closed system in contrast unit 2 rocks were formed by loss of substantial plagioclase and olivine from the parental magma this fractionate must have either been lost to depth or left behind in an external chamber unit 2 rocks show depletion in plagioclase and enrichment in mafic minerals along strike towards the southwest deeper exposure level a trend explained by density stratification regional variation in unit 1 chemistry is interpreted in terms of lateral magma injection towards the northeast from the locus of keweenawan rift volcanism feldspar olivine and augite compositions are linearly correlated with equilibrium temperature and extent of magma evolution the parent magma had a trace element chemistry corresponding to a within plate setting and was probably derived from an incompatible element enriched mantle similar to the source for ocean island basalts oibs

gravity driven and in situ fractional crystallization processes in the centre hill complex abitibi subprovince canada evidence from bilaterally paired cyclic units abstract the formation of layers in mafic intrusions has been explained by various processes making it the subject of much controversy the concept that layering originates from gravitational settling of crystals has been superseded in recent years by models involving in situ fractional crystallization here we present evidence from the centre hill complex that both processes may be operative simultaneously within the same intrusion the centre hill complex is part of the munro lake sill an archean layered mafic intrusion emplaced in volcanic rocks of the abitibi subprovince the centre hill complex comprises the following lithostratigraphic units six lower cyclic units of peridotite and clinopyroxenite a middle unit of leucogabbro six upper cyclic units of branching textured gabbro btg and clotted textured gabbro ctg the uppermost of these units being overlain by a marginal zone of fine grained gabbro the cyclic units of peridotite clinopyroxenite and btg ctg are interpreted to have formed concurrently through fractional crystallization associated with periodic replenishment of magma to the chamber the units of peridotite and clinopyroxenite formed by gravitational accumulation of crystals that grew under the roof the cyclic units of btg and ctg formed along the upper margin of the sill by two different mechanisms 1 layers of btg crystallized in situ along an inward growing roof and 2 layers of ctg formed by accumulation of buoyant plagioclase crystals the layers of btg are characterized by branching pseudomorphs after fayalite up to 50 cm in length that extend away from the upper margin the original branching crystals are interpreted to have grown from stagnant intercumulus melt in a high thermal gradient resulting from the injection of new magma to the chamber

vegetation history climate change and human activities over the last 6200 years on the liupan mountains in the southwestern loess plateau in central china abstract fossil pollen data from tianchi lake on the liupan mountains in the loess plateau in china were used to investigate the interplay of climate change vegetation history and human activities the chronology of an 11 m long sediment core was controlled by 19 accelerator mass spectrometry radiocarbon dates on terrestrial plant macrofossils the pollen record shows a long term change from a closed canopy forest to open landscape over the last 6200 years from mixed deciduous coniferous forest dominated by betula quercus picea and pinus at 6200 2900 cal yr bp to transitional steppe forest co dominated by trees betula picea and pinus and herbs mostly artemisia at 2900 1100 cal yr bp and to open landscape dominated by artemisia and poaceae after 1100 cal yr bp this general pattern of vegetation change indicates a drying climate trend consistent with other independent climate records mostly from the monsoon region that show a weakening summer monsoon since the mid holocene the gradual increase in both poaceae pollen and microscopic charcoal since about 2000 cal yr bp and a sharp increase in poaceae but a decrease in charcoal at 1000 cal yr bp indicate two phases of human impacts on vegetation the results from pollen and charcoal analysis together with archaeological and historical evidence suggest that human activities over the last 2000 years have significantly accelerated deforestation that was initiated by a drying climate since the mid holocene

on the development of internal chemical zonation in small mafic dykes three dolerite dykes small 3 2 cm middle 13 5 cm thick 50 cm from torsholma island sw finland reveal distinctly different internal zonation that becomes more complicated with increasing thickness of the dykes the small dyke shows a systematic inward increase in normative pl an ab or and a decrease in normative an 100 an an ab whole rock mgo mg number 100 mg mg fetotal tio2 k 2o and zr the middle dyke exhibits the same compositional pattern at the margins while the centre is distinguished by an abrupt increase in normative pl and an whole rock sr and mg number from the margins inwards the thick dyke displays first a compositional pattern identical to that observed in the small dyke and the margins of the middle dyke this is followed by a region where whole rock mgo mg number and normative an start increasing inwards while the transition to the centre of the dyke is characterized by a compositional pattern similar to that in the centre of middle dyke the origin of chemical zonation in these dykes is attributed to the operation of three independent physico chemical processes namely the small dyke formed exclusively by progressive changes in the composition of inflowing magma the middle dyke by changes in composition of inflowing magma margins and concentration of plagioclase and olivine phenocrysts by flow differentiation centre the thick dyke by changes in composition of inflowing magma margins in situ cumulate growth against dyke sidewalls middle and flow differentiation centre systematic changes in these processes and as a result in internal chemical zonation likely take place in response to crystallization of magma under less supercooled conditions with increasing dyke thickness a comprehensive geochemical study of the internal zonation of small mafic dykes worldwide is required to develop a complete understanding of the processes operating in mafic dykes

δ13c values of loess total carbonate a sensitive proxy for asian summer monsoon in arid northwestern margin of the chinese loess plateau abstract we measured carbon isotope ratio of loess total carbonates 13 cic from the jingyuan loess profile in the arid northwestern portion of the chinese loess plateau clp in order to examine the effectiveness and sensitivity of loess total carbonate 13 cic values as a potential paleoenvironmental indicator the 13 cic record in the loess profile shows large variations ranging from 1 to 7 during the past 70 ka the most negative 13 cic peaks coincide with paleosol formation s 0 l 1 ss 1 and l 1 ss 2 which occurred under relatively wetter climatic conditions during middle holocene and marine 18 o stages 3 on the other hand the least negative 13 cic values responded to loess accumulation during relative drier phases of lgm and marine 18 o stages 4 while 13 cic variations in the loess profile in arid area demonstrate a clear correlation with changes of total organic carbon isotope 13 coc of bulk sediments which has been widely used as a proxy for the past monsoon precipitation intensity the 13 cic values in the loess profile are more sensitive to the changes of paleohabitat controlled by the asian monsoon variation in the arid area we propose that carbon isotope compositions of total carbonates in loess profile can serve as a sensitive and reliable proxy for the asian summer monsoon in the arid northwestern chinese loess plateau

upper ocean temperature structure inertial currents and richardson numbers observed during strong meteorological forcing abstract upper ocean currents and temperature in the northeastern pacific were measured during a 14 day period in november 1980 as part of strex velocities in the upper ocean are dominated by near inertial frequency oscillations thew oscillations are modified by wind stress variations associated with the passage of a strong cold front the change in the inertial currents both in the mixed layer and below is qualitatively consistent with linear internal wave dynamics if turbulent stresses during the storm are assumed to extend 10 20 m below the mixed layer the ratio of mean squared buoyancy frequency n2 and mean squared shear s2 computed over a 10 m interval defines an average richardson number r0 n2 s2 r0 is approximately 2 5 except in regions of high inertial shear in particular values as low as 0 7 are obtained in a 20 m thick region immediately below the base of the mixed layer the data are consistent with a model of the oecanic shear field consisting of a background shear corresponding to a va

climate change and cultural response around 4000 cal yr b p in the western part of chinese loess plateau new data suggest that dramatic environmental change in the western loess plateau of china corresponded with substantial changes in human demography ca 4000 cal yr b p these data demonstrate that a rapid climatic transition from wet to dry led to an ecologically devastated period between 4090 and 3600 cal yr b p the sudden reduction in the number of archaeological sites during this period namely a reduction in the total number of sites and a contraction of the areal distribution of sites points to declining agricultural productivity associated with widespread aridification beginning at 4000 cal yr b p 2005 published by university of washington

on the bering sea ice edge front an oceanographic field program was carried out along the bering sea ice edge in winter 1982 83 to investigate the temperature salinity front associated with and paralleling the winter ice edge currents were measured using taut wire moorings that were in place over winter and an intensive ctd survey was carried out of the frontal structure in midwinter february march the midwinter front separated cold 0 c more saline 32 5 outer shelf water the front had northwestward baroclinic currents paralleling the front ice edge with near surface speeds of 5 6 cm s and an associated transport of about 0 3 106 m3 s these baroclinic currents were superimposed on a regional barotropic along isobath flow resulting in north westward midwinter upper layer flows with monthly mean speeds exceeding 10 cm s an upper layer flow component was directed beneath the ice and provided heat adequate to melt the ice and limit advance of the edge the resulting low salinity meltwater was mixed vertically to maintain the front by wind acting across a highly mobile hydrodynamically rough ice cover subtidal fluctuations were not significantly affected by the front or the ice cover and local winds accounted for less than one quarter of the observed current variability the remainder being probably due to regional variations in the barotropic flow

the energy flux from the wind to near inertial motions in the surface mixed layer abstract time series of wind stress computed from long term meteorological buoy data off north america are used to examine the forcing of surface inertial currents by the wind a simple damped slab model of the mixed layer is used to compute h the average flux of energy from the wind to mixed layer inertial currents in a mixed layer of fixed depth h the forcing of mixed layer inertial motions is highly intermittent most of the forcing occurs during the winter months with a few dozen events accounting for typically over half the total energy flux major forcing events are usually associated with translating cold fronts or small lows with scales of about 100 km the larger synoptic scale features have little energy at the inertial frequency and thus result in only weak forcing of inertial currents a strong seasonal signal exists in the inertial forcing at ows p 50 n 145 w 50 m is largest from october to february and is a factor of 12 above the june and july values if seasonally varying

two independent processes responsible for compositional zonation in mafic dykes of the aland aboland dyke swarm kestio island sw finland abstract detailed sampling across three dolerite dykes of different size small 7 cm middle 75 cm and thick 675 cm of the aland aboland dyke swarm has revealed an internal zonation of an anomalous nature the small almost glassy dyke exhibits a systematic inward decrease in whole rock mgo and mg indicating a normal fractionation trend together with a simultaneous increase in normative an and cpx and decrease in whole rock zr y cao tio 2 indicating a reverse fractionation trend the middle dyke shows similar compositional trends across its narrow margins but in the more crystalline interior whole rock mgo and mg gradually but steadily increase inwards as a result normal and reverse fractionation trends of the margins grade to exclusively reverse fractionation trends of the interior the thick almost totally crystalline dyke exhibits an internal zonation similar to that of the middle dyke with fractionation trends becoming only much more pronounced in the centre of the dyke the almost glassy nature of small dyke suggests that its anomalous compositional zonation most likely resulted from temporal changes in the composition of magma as it formed the dyke the mechanism s responsible for such systematic changes in composition of inflowing magma remains however unknown the margins of middle and thick dyke form in a similar way whereas their interiors formed by in situ cumulate growth against dyke sidewalls this process resulted in a gradual inward increase in the proportion of cumulus phases owing to magma crystallization in progressively less supercooled conditions with increasing distance from cold country rocks the compositional zonation of these dolerite dykes is thus produced by two independently operating mechanisms successive changes in composition of inflowing magma an external liquid state process and an in situ cumulate growth on dyke sidewalls an internal crystal liquid process based on the relatively minor development of internal zonation in interiors of middle and thick dykes the former mechanism appears to be several times more effective in causing magma differentiation than the latter it remains to be determined whether these two processes are a general reason for the formation of marginal reversals in mafic ultramafic dykes sills and large layered intrusions

a heat balance for the bering sea ice edge abstract detailed oceanographic meteorological and sea ice observations were obtained from the bering sea marginal ice zone miz during the february march 1983 marginal ice zone experiment mizex west these data have been used in estimating a mean midwinter upper layer heat balance for the miz during a period when the ice edge was stationary the dominant source term in the heat budget was the advective input from northward flow of relatively warm water beneath the ice edge the associated mean heat flux per unit length of ice edge was about 22 mw m 1 approximately equal to the heat required to melt the southward moving ice heat was also input by upward diffusion from the warm deeper water layer that underlay the miz this upward flux was driven primarily by double diffusive convection and was about 8 mw m 1 heat loss resulted from sea air flux primarily through open leads of about 13 mw m 1 estimated errors in the individually computed flux terms varied from 10 to 70 percent within these limit

petrology of the grenville swarm of gabbro dikes canadian precambrian shield the grenville tholeiitic dikes of late proterozoic or early paleozoic age cut marbles and gneisses of the grenville province within and adjacent to the ottawa rift structure where traversed the swarm consists of about 40 large dikes up to 100 m wide representing a crustal extension of 1 km the principal minerals are olivine augite pigeonite plagioclase magnetite ilmenite k feldspar and quartz crystals of pigeonite around olivine and complex augite pigeonite composite grains suggest that the reactions olivine melt pigeonite and pigeonite melt augite have taken place conspicuous zoning and grain to grain variation in the composition of augite are consistent with fractional crystallization but crystal melt equilibrium during crystal growth is indicated by a restricted range in pyroxene paleotemperatures of 1180 1060 c rock textures subophitic combined ophitic subophitic and equigranular in dike centres are related to dike width and are determined principally by the influence of

detailed description of deformation induced semi geostrophic frontogenesis examen dans la limite de la semi geostrophie d une variante du probleme classique de la frontogenese de surface induite par la deformation le systeme particulier d ecoulement considere constitue la reponse a un champ de deformation donne d une atmosphere barocline semi infinie stratifiee et a vorticite potentielle uniforme resultats obtention d une classe de solutions analytiques simples dans l espace geostrophique obtention d une solution explicite de l equation de sawyer eliassen relative a la circulation ageostrophique obtention d une equation autonome non lineaire dans l espace reel relative au developpement a la surface de la composante du vent alignee le long du front application aux divers aspects frontogenes a savoir l echelle temporelle du developpement du front la co occurrence des differents types frontaux la pente et le mouvement des figures frontales la structure et la force de la circulation ageostrophique et le degre de validite de l approximation semi geostrophique

thermal and mechanical aspects of magma emplacement in giant dike swarms we consider the thermal history and dynamics of magma emplacement in giant feeder dikes associated with continental flood basalts for driving pressure gradients inferred for giant dike swarms thicknesses of 10 m would enable dikes to transport magma laterally over the distances observed in the field up to thousands of kilometers without suffering thermal lock up using time dependent numerical solutions for the thermal evolution of a dike channel under laminar and turbulent flow conditions in the presence of phase transitions we investigate the possibility that the observed dike thicknesses of the order of 100 m result from thermal erosion of the country rocks during dike emplacement this implies that the observed range of dike widths in giant dike swarms may reflect variations in the source volume and not the excess magma pressure it is found that the total volume of intruded magma required to produce an order of magnitude increase in dike width via wall rock melting broadly agrees with the estimated volumes of individual flows in continental flood basalts the presence of chilled margins and apparently low crustal contamination characteristics of some giant dikes may be consistent with turbulent magma flow and extensive melt back during dike emplacement in this case measurements of the anisotropy of magnetic susceptibility most likely indicate magma flow directions during the final stages of dike intrusion shear stresses generated at the dike wall when the dike starts to freeze strongly decrease with increasing dike width which implies that thicker dikes may have less tendency to produce consistent fabric alignment our results suggest that if the dike was propagating downslope off a plume related topographic swell the mechanism responsible for flow termination could possibly have been related to underpressurization and collapse implosion of the shallow magma plumbing system feeding the intrusion radial dikes that erupted at the periphery of the topographic uplift might have increased rather than decreased extensional stresses in the crust within the topographic uplift upon their solidification

soret separation of mid ocean ridge basalt magma chemical differentiation of an initially homogeneous mid ocean ridge basalt morb liquid has been experimentally observed in a temperature gradient above the liquidus the magnitude of this effect in producing differences in composition is comparable to that of crystal liquid fractionation for a given temperature difference however the chemical changes produced by the two processes soret and crystal liquid fractionation are different soret separations resemble those observed in a third process silicate liquid immiscibility this similarity is a reflection of the fact that the soret separable components are the same network former network modifier structural components which segregate during silicate liquid immiscibility

evidence of inertial oscillations of the surface wind at marcus island near inertial oscillations of the surface wind were observed at marcus island 24 n 154 e in the subtropical pacific area kinetic energy spectra of the surface wind show a peak at a period of 1 1 days in the clockwise component spectrum this period is slightly 6 shorter than the local inertial period 1 2 days the peak period varies slightly during the record analyzed but tends to remain below the local inertial period complex demodulation with a filter shows that the large inertial amplitudes occur intermittently and decay rapidly most of the occurrences of large inertial events seem to be related to passing cold frontal systems or migrating low pressure systems

age of the grenville dyke swarm ontario quebec implications for the timing of lapetan rifting u pb baddeleyite and zircon ages for three diabase dykes from widely spaced localities within the grenville dyke swarm indicate a single age of emplacement at ma the 700 km long grenville dyke swarm located in the southeastern part of the canadian shield was emplaced syntectonically with the development of the ottawa graben this graben may represent a plume generated lapetan failed arm that developed at the onset of the breakup of laurentia other precisely dated lapetan rift related units such as the callander alkaline complex and the tibbit hill formation volcanic rocks indicate a protracted 36 ma period of rifting and magmatism prior to volcanism along this segment of the lapetan margin the age of the grenville dykes is the youngest in a progression of precisely dated mafic magmatic events from the 723 ma franklin dykes and sills to the 615 ma long range dykes along the northern and northeastern margins of laurentia respectively thus the age for these dykes represents a key time marker for

modulation of near inertial oscillations by low frequency current variations on the inner scotian shelf abstractnear inertial oscillations nios on the inner scotian shelf are studied using observations a simple slab model and two operational shelf circulation models high frequency radar and adcp

a paleomagnetic and u pb geochronology study of the western end of the grenville dyke swarm rapid changes in paleomagnetic field direction at ca 585 ma related to polarity reversals a paleomagnetic study of the western end of the similar to 585 ma grenville dyke swarm shows that individual dykes are characterized by high coercivity and unblocking temperature magnetizations that can differ in direction by as much as 90 degrees field tests including baked contact studies and the continuity of paleomagnetic direction along dyke strike suggest that the magnetizations are primary precise u pb baddeleyite dating on these dykes indicates that changes in magnetization direction of similar to 90 degrees occur in less than 4 million years and their close temporal association with reversals of the axial dipole field suggest that certain dykes are recording an equatorial dipole field as a transitional field between opposite polarity states the documented instability in the earth s field occurs less than 10 myr before the first recorded appearance of macroscopic multi cellular organisms on earth inviting speculation that an extended period of frequent magnetic reversals may play a part in faunal evolution c 2014 elsevier b v all rights reserved less

palaeoclimatic changes in the qinghai lake area during the last 18 000 years abstract multi proxy analysis of a sediment core from qinghai lake including pollen carbonate toc tn and 13 c of organic matter was used to document regional climatic changes during the last 18 000 years climate was very cold and dry before 16 9 cal kyr bp the warm and wet period which began at about 14 1 cal kyr bp culminated at 6 5 cal kyr bp and came to its end at about 4 5 cal kyr bp after that the climate gradually became colder and drier during the transitional period from the late glacial to the holocene the climate fluctuated frequently the short term climatic oscillations including the bolling allerod younger dryas and the cooling event at ca 8 2 cal kyr bp appear to be recorded in the qinghai lake sedimentary record the climatic evolution in the qinghai lake area during the past 18 000 years indicates that solar insolation changes on the ten thousand year scale are the likely driving force of the east asia monsoon

on the behavior of internal waves in the wakes of storms abstract the rossby adjustment process in the wake of a storm is studied with a view to finding within the context of linear theory how wave dispersion in both the vertical and meridional directions spreads energy which is initially confined entirely to the mixed layer comparisons are made between three cases 1 a periodic storm on the f plane where dispersion is purely vertical 2 a bounded storm on the f plane and 3 a bounded storm centered 2700 km from the equator on an equatorial beta plane particular attention is paid to the initial rate of loss of energy from the mixed layer and some simple formulas which work very well in the cases studied are derived these show that the rate of loss goes up when the mixed layer depth is increased and also that the rate scales as the square of the wavenumber values of the rates are sufficient to provide a major source of energy for internal waves below the mixed layer the often observed tendency for phase lines to propagate upward is found in all case

stable isotopic investigations of modern and charred foxtail millet and the implications for environmental archaeological reconstruction in the western chinese loess plateau stable isotopic analysis of carbon and nitrogen in human and faunal remains has been widely used to reconstruct prehistoric diets and environmental changes isotopic analysis of plant remains allows for a more extensive consideration of paleodiets and can potentially provide information about the environment in which the crops were grown this paper reports the results of delta c 13 and delta n 15 analyses performed on modem and charred archaeological foxtail millet samples collected from the western part of the chinese loess plateau the delta c 13 mean value of modem samples is lower than that of ancient samples there is a significant difference between grain and leaf delta n 15 values these results challenge the standard assumption in isotope studies that the nitrogen isotope signals of the different part of plants consumed by humans and animals are the same the 3 5 parts per thousand difference between human and animal delta n 15 values is always regarded as an indicator of whether human diets contained considerable animal protein the difference between grain and leaf delta n 15 values makes this assumption problematic in a foxtail millet dominated society c 2015 university of washington published by elsevier inc all rights reserved

magma differentiation and crystallization in basaltic conduits by two competing petrogenetic processes abstract magma differentiation processes that take place in conduits delivering basaltic magmas to the earth s surface are still poorly understood to get new insights into this problem we have studied in detail the whole rock geochemistry of a section across a dolerite dyke 21 m thick and three sections across its narrow apophysis 69 cm 29 cm and 17 cm thick from the russian fennoscandian shield the dyke is fresh aphyric and shows no evidence of in situ contamination by crustal rocks chemical zonation in the dyke changes systematically with the thickness of the sections in particular rocks become more primitive inwards mgo mg number and normative an increase and p 2 o 5 decreases in the main dyke while rocks become more evolved inwards in the apophysis in addition the chemical zonation of the apophysis is anomalous since compatible and incompatible elements behave in a manner inconsistent with fractional crystallization of basaltic magma to explain the chemical zonation we introduce a novel concept that attributes compositional trends in mafic dykes to competition between two processes a the filling of dykes with magmas that become increasingly more evolved with time as a result of fractionation in the deeper parts of conduits and b in situ crystal growth on dyke walls accompanied by effective removal of evolved melt by through flowing magma the processes have opposite effects on rock geochemistry with the first making dykes more evolved and the second more primitive inwards the key idea is that dykes become more evolved inwards when quenching of inflowing magmas controls the distribution of all components and become more primitive inwards when in situ crystal growth governs the distribution of all components anomalous compositional trends develop when these two processes control the distribution of different groups of chemical components the chemical zonation in the studied dyke can be attributed to a change from rocks mainly produced by quenching of progressively more evolved magmas in the apophysis to those predominantly formed by in situ crystal growth in the main dyke this happens in response to a decreasing degree of undercooling as sections of the magma conduit become thicker we believe that the competitive operation of these two petrogenetic processes is likely a general feature of magma differentiation and crystallization in basaltic conduits

on the nature of near inertial oscillations in the uppermost part of the ocean and a possible route toward hf radar probing of stratification abstractinertial band response of the upper ocean to changing wind is studied both theoretically and by analysis of observations in the northwestern mediterranean on the nontraditional f plane because of the horizontal component of the earth s rotation for waves of inertial band with frequencies slightly below the local inertial frequency f there is a waveguide in the mixed layer confined from below by the pycnocline it is argued that when the stratification is shallow these waves are most easily and strongly excited by varying winds as near inertial oscillations nios these motions have been overlooked in previous studies because they are absent under the traditional approximation the observations that employed buoys with thermistors adcps and two 16 3 mhz wellen radar wera hf radars were carried out in the gulf of lion in april june 2006 the observations support the theoretical picture a pronounced inertial band response occurs only in the presence of shallow stratification and is confined

near inertial and tidal currents detected with a vessel mounted acoustic doppler current profiler in the western mediterranean sea 1 the objective of this study is to separate the subinertial inertial and tidal fields from vessel mounted acoustic doppler current profiler vm adcp observations acquired during six cruises in the catalan and alboran seas western mediterranean sea to fulfill this objective we use a method that successfully detects and filters out the main high frequencies that are present in the vm adcp data the resulting near inertial component has frequencies below the coriolis frequency f in the catalan sea and above f in the alboran sea the tidal component is consistent with observed and modeled tides in the catalan and alboran seas the steady component is highly correlated with the geostrophic field there is also a nonfitted or residual component which represents the misfit between the vm adcp data and the model proposed

a near inertial internal wave spectrum for the sargasso sea in late summer abstract independent estimates of the frequency wavenumber spectrum of near inertial waves for the sargasso sea in late summer were made using 8 time series of horizontal velocity from a single moored vertical array and 58 vertical profiles of horizontal velocity from a horizontal array of expendable velocity profilers the profiler data were analyzed to produce an internal wave frequency wavenumber spectrum with sufficient resolution to resolve the details of the inertial peak and compute the vertical energy flux comparison with the lower resolution spectrum from the moored array shows qualitative agreement the differences are most likely due to biases in both techniques and to intermittency of the internal wave field these data reveal a marked asymmetry of the near inertial internal wave field with a net downward enemy flux of 0 12 0 12 ergs cm 2 s 1 the downward propagating waves have more energy a larger horizontal scale and a lower frequency than the upward propagating waves the magnitude of t

near inertial motions over a mid ocean ridge effects of topography and hydrothermal plumes we investigate the spatial structure of near inertial motions in the vicinity of the endeavour segment of juan de fuca ridge approximately 48 n 129 w in the northeast pacific ocean on the basis of time series current and water property data collected from september 1984 to september 1987 near inertial motions are ubiquitous features of the 2200 m water column with root mean square rms current speeds comparable to those of the dominant m2 tidal currents within the lower 1000 m of the water column where most of the observations were obtained near inertial oscillations have rms current speeds of o 1 cm s and vertical isotherm displacements of o 10 m the fluctuations are confined to the frequency band 0 966 1 079 f f is the local coriolis parameter and have characteristic event durations of 1 week although the spectra of subsurface motions are dominated by the blue shifted superinertial band significant spectral peaks are found also in the subinertial and inertial frequency bands marked alteration of the near inertial current amplitudes occurs over two well defined depth zones within the study region within the 200 m zone immediately above the 2100 m ridge crest current amplitudes are amplified by a factor of 1 2 1 7 because of bottom reflection and or scattering of the downward propagating energy evidence that the amplification may be linked to bottom reflection rather than to scattering is provided by flattening and cross slope rotation of the near inertial current ellipses with increased proximity to the top of the ridge reflection would occur at grazing angles of less than 1 and would be associated with surface generated waves originating at distances of over 100 km from the observational site in contrast to the enhanced amplitudes immediately above the top of the ridge near inertial currents within the 1600 to 1800 m depth range undergo pronounced attenuation and frequency alteration amplitude attenuation is especially pronounced for motions in the superinertial band and may arise through critical layer absorption of downward propagating waves as they encounter increased vertical shear in the background flow the increased shear is most likely associated with buoyancy induced flow formed by the extensive hydrothermal plume emanating from vent sites in the axial valley along the ridge crest but it could also be related to bottom trapped oscillations over the steep ridge topography near inertial motions are estimated to have vertical coherence scales of the order of 10 100 m while horizontal coherence scales exceed the 50 km separation between the mooring locations minimum vertical and horizontal coherences are found for the depth zone 1600 1800 m while maximum correlation occurs for near bottom motions immediately above the crest of the ridge weak near inertial motions are observed within the 100 m deep axial valley

geochemistry of the grenville dyke swarm role of plume source mantle in magma genesis major and trace element data of samples from the approximately 590 ma grenville dyke swarm in the southeastern parts of the canadian shield were used to evaluate the extent of crustal contamination of the dyke magma and to model its probable mantle source the dyke rocks are mostly saturated quartz tholeiites a few samples represent transitional basalts their overall chemistries are similar to those of continental flood basalts their compositions resemble those of liquids initially produced in the garnet peridotite mantle zone and then subjected to polybaric fractionation however fractionation models fail to mass balance ti fe k and p geochemical and isotopic criteria indicate that crustal contamination was minimal the incompatible elements zr y k rb nb v ta hf and th show hyperbolic elemental ratio ratio distributions indicative of mixing between two end members one end member has elemental ratios similar to those of a depleted n morb source and the second of a p morb i e ertile or plume morb source the more enriched dyke compositions can be successfully reproduced by mixing models in the ratio of 6 1 between the most depleted morb like dyke magma and a liquid composition similar to metasomatic glass veinlets coexisting with mica peridotite mantle xenoliths and subsequent crystal fractionation the grenville dykes are probably a synrift swarm that was emplaced along a rift arm related to an iapetan rrr triple junction that is thought to have formed over a mantle plume the chemistry of the dyke swarm is consistent with its derivation from a plume head in that the minor enriched source can be identified with plume source mantle and the major depleted source with entrained mantle the magma probably originated in the upper cooler parts of the plume head

the early evening boundary layer transition various mechanisms which lead to nocturnal accelerations and formation of the low level jet are examined by analysing wangara data the stress field is inferred from the wind field and equations of motion the evolution of the stress divergence during the evening transition from daytime mixed layer flow to nocturnal boundary layer flow is found to increase the ageostrophic flow and subsequent nocturnal accelerations by roughly a factor of two during this transition the stress divergence in the lowest few hundred metres increases due to the fact that the influence of decreasing boundary layer depth exceeds the effect of decreasing surface stress this leads to temporary deceleration and rotation of the low level wind vector towards low pressure and thus increases the ageostrophic flow diurnal variation of the geostrophic wind is also found to significantly strengthen the nocturnal flow this diurnal variation is apparently due to heating and cooling over terrain which slopes gently upward east of the location of the wangara experiment

shallow ocean response to tropical cyclones observed on the continental shelf of the northwestern south china sea based on observed temperature and velocity in 2005 in northwestern south china sea the shallow ocean responses to three tropical cyclones were examined the oceanic response to washi was similar to common observations with 2 degrees c cooling of the ocean surface and slight warming of the thermocline resulted from vertical entrainment moreover the wavefield was dominated by first mode near inertial oscillations which were red shifted and trapped by negative background vorticity leading to an e folding timescale of 12 days the repeated reflections by the surface and bottom boundaries were thought to yield the successive emergence of higher modes the oceanic responses to vicente appeared to be insignificant with cooling of the ocean surface by only 0 5 degrees c and near inertial currents no larger than 0 10 m s as a result of a deepened surface mixed layer however the oceanic responses to typhoon damrey were drastic with cooling of 4 5 degrees c near the surface and successive barotropic like near inertial oscillations during the forced stage the upper ocean heat content decreased conspicuously by 11 65 and the stratification was thoroughly destroyed by vertical mixing in the relaxation stage the water particle had vertical displacement of 20 30 m generated by inertial pumping the current response to damrey was weaker than washi due to the deepened mixed layer and the destroyed stratification our results suggested that the shallow water oceanic responses to tropical cyclones varied significantly with the intensity of tropical cyclones and was affected by local stratification and background vorticity

cyclone climatology of the bering sea and its relation to sea ice extent abstract a monthly storm track climatology is derived from monthly maps of cyclone tracks for the winter season october through march averaged over 23 years 1957 58 1979 80 for a 2 latitude 4 longitude grid bounded by 51 n 65 n 157 w and 171 e there is a decrease in the number of cyclones with latitude in all months and division into two storm tracks one propagating north northeast along the siberian peninsula and one entering the southern bering sea on a northeasterly course and either curving northward into the central bering sea or continuing parallel to the aleutian island chain monthly average ice extents are established for february and march 1958 80 along a line from norton sound southwest toward the ice edge perpendicular to the average maximum extent comparison of composite cyclone charts summed over the winter season and over the five heaviest and five lightest ice years shows a shift in cyclone centers toward the west in light ice years the correlation between maximum seasonal ice

the origin of basic ultrabasic sills with s d and i shaped compositional profiles by in situ crystallization of a single input of phenocryst poor parental magma an attempt is made to develop an in situ crystallization model based on the concept of soret fractionation to explain the origin of commonly observed s d and i shaped compositional profiles in sills formed from a single pulse of phenocryst poor parental magma the model envisages that the various compositional profiles observed in sills can be interpreted in terms of different combinations of four principal units basal zone and layered series forming the floor sequence and top zone and upper border series constituting the roof sequence the basal and top zones represent mirror images of the layered and upper border series respectively and therefore are referred to as basal and top reversals it is proposed that the formation of basal and top reversals takes place through the non equilibrium soret differentiation of liquid boundary layers which form as a consequence of the temperature gradient imposed by the cold country rock in contrast the layered and upper border series originate predominantly through the crystal liquid boundary layers developing in equilibrium conditions the model permits the production of s d and i shaped compositional profiles from the same magma composition all that is necessary to produce a specific shape of compositional profile is an appropriate temperature gradient imposed by the cold country rock on the liquid boundary layers of a parental magma of a given composition

alteration of 15n14n and 13c12c ratios of plant matter during the initial stages of diagenesis studies utilizing archaeological specimens from peru abstract the stable carbon and nitrogen isotope ratios of plants extracted from peruvian archaeological sites ranging in age from 400 to 4000 years b p have been measured the 13 c and 15 n values of prehistoric plants that were carbonized prior to deposition are similar to those of modern plants which have the same carbon dioxide fixation or nitrogen assimilation mechanisms in contrast the 15 n values of prehistoric plants that were not carbonized are generally 10 20 and as much as 35 more positive than those of their modern counterparts the 13 c and 15 n values of different parts of prehistoric uncarbonized plants differ by as much as 8 and 21 respectively whereas the same parts of modern plants have 13 c or 15 n values that lie within 2 of one another sem analysis etiminated the possibility that diagenetic alteration of the isotope ratios of the prehistoric uncarbonized plants was caused by the adsorption of particulate soil matter isotopic analysis of the organic residues that remained after the prehistoric uncarbonized plants were treated to remove fractions that might have been added in the depositional environment indicated that the alteration of the 13 c values resulted from the adsorption of humic and fulvic acids whereas the diagenetic shifts of the nitrogen isotope ratios were not caused by adsorption of 15 n enriched organic or inorganic forms of nitrogen from the soil our observations do not permit us to speculate on a mechanism that accounts for the 13 n enrichment of the prehistoric uncarbonized plant remains although the excellent state of preservation of these samples suggests that isotopic fractionation during microbial decomposition was not the cause the observation that the isotope ratios of the prehistoric carbonized plants are similar to those of their modern counterparts indicates that it will be possible to separate carbonized plants residues into three groups legumes non leguminous c 3 plants or c 4 and cam plants based on their 13 c and 15 n values this method should provide useful information to archaeologists working in environments in which carbonized plant remains often burned beyond morphological recognition are the only archaeobotanical remains which are recovered

observations of near inertial waves in acoustic doppler current profiler measurements made during the mixed layer dynamics experiment measurements of upper ocean shear made during the mixed layer dynamics experiment mildex provide evidence of large horizontal scale motion at near inertial frequency the measurements consist of shipboard acoustic doppler current profiles four large scale spatial surveys of 2 4 days duration were made by the r v wecoma as a set of boxes approximately 60 km per side around a drifting current meter buoy velocity time series from the drifting buoy and from sonar measurements made from flip also indicated the presence of motions at near inertial frequency horizontal length and time scales of the motion are estimated from the phase of the shear vector measured during the spatial surveys estimates of the length scale of the waves range from 500 to 1000 km and the frequency is approximately 1 1f the behavior of the phase is found to be consistent with a model of narrow band inertial waves with vertical structure such that there is a zero crossing in velocity at the base of the mixed layer 40 60 m

grenville metagabbro complexes of the otter lake area quebec metagabbro complexes in a portion of the grenville province lying northwest of ottawa occur as sheets cylinders and irregular bodies within a medium to high grade marble gneiss amphibolite terrane the largest bodies 0 5 10 km in greatest dimension consist principally of felsic metagabbro mafic metagabbro and minor metapyroxenite major element and select trace element analyses show that different complexes contain distinctly different amounts of k and other elements resulting in different interelement trends microstructure and microprobe mineral analyses provide evidence that the following metamorphic changes have occurred i recrystallization of ca pyroxene orthopyroxene and plagioclase ii reaction of mg rich olivine with plagioclase to produce reaction zones consisting of orthopyroxene and a hornblende spinel intergrowth iii reaction of mg fe olivine with plagioclase to produce garnet and hornblende iv production of anthophyllite and hornblende from orthopyroxene and plagioclase v

satellite tracked drifter measurement of inertial and semidiurnal currents in the northeast pacific we examine current variability in the open northeast pacific using 3 hourly sampled trajectories from satellite tracked drifters drogued at depths of 15 and 120 m within the wind mixed layer and permanent pycnocline respectively findings show the following 1 motions were dominated by inertial currents which accounted for 58 35 of the total variance measured by the shallow deep drifters semidiurnal motions accounted for roughly 10 of the variance at both depths there were detectable currents at twice the inertial frequency 2f 3 cpd and negligible diurnal currents 2 inertial currents attained root mean square rms speeds of around 50 cm s in the mixed layer and 10 cm s in the pycnocline speeds in the semidiurnal band were similar 10 cm s at both depths 3 inertial and semidiurnal currents were strongly clockwise rotary while low frequency currents 0 95 occurred for drifter separations r 500 km semidiurnal currents were uncorrelated beyond several tens of kilometers 6 inertial currents appear to be linked to the passage of atmospheric lows and semidiurnal currents to the passage of remotely generated baroclinic tides the spectral peak near 2f is indicative of nonlinear inertial wave interactions

a plume generated segment of the rifted margin of laurentia southern canadian appalachians seen through a completed wilson cycle the southern part of the canadian appalachians and the adjacent parts of the craton show a range of distinctive features pertaining to the evolution of the rift and rift drift transition stages of a segment of the continental margin of laurentia despite the effects of a completed wilson cycle several lines of evidence point to an initial lithospheric rupture in the form of a three pronged rift possibly induced by a rising mantle plume the earliest synrift igneous products to penetrate the crust in the area are represented by a swarm of tholeiitic diabase dykes intruded at ca 590 ma the swarm is more than 700 km long and radiates from the inferred location of the rrr triple junction dyke emplacement and the initiation of rifting were probably synchronous approximately 35 m y later a rapid outburst of volcanism occurred at the triple junction probably as a harbinger of sea floor spreading the volcanic products are predominantly basalts of mildly alkaline to transitional character but with a minor comenditic component the voluminous nature of the volcanic outburst and the compositional characteristics of its products indicate higher than normal asthenospheric temperatures coupled with thinning of the lithosphere suggesting continued mantle plume activity the volcanic sequence is overlain by rift facies elastics that are locally interrupted and augmented by a deltaic deposit representing the delta of a river that drained the failed arm into the nascent lapetus ocean the rift facies elastics and the associated deltaic deposits are overlain by rocks of marine origin signalling the beginning of the drifting stage possibly at ca 550 ma

near inertial current oscillations in the vicinity of the bering sea marginal ice zone near inertial current oscillations with 10 20 cm s amplitudes were prevalent over the bering sea shelf during november 1982 and again in march and april 1983 and also evident at reduced amplitudes during the intervening winter spectral peak frequencies were consistently within 1 of the local inertial frequency in contrast to the more superinertial 5 above frequencies commonly reported elsewhere a superinertial secondary energy peak at 1 038 was evident corresponding to the first mode wave amplitudes decreased with distance shoreward from the shelf break consistent with the effects of decreasing bottom depth and increasing mixed layer depth the oscillations were highly coherent over 100 km distances similar to observations reported by thomson and huggett 1981 for the british columbia coast whereas near inertial oscillations have been commonly reported to be uncoupled over much shorter 10 km distances in other regions vigorous near inertial ringing was associated with rapidly passing weather systems the decline in near inertial oscillation amplitudes during winter was partially due to a significant reduction in both cyclone frequency and occurrence of wind events causing clockwise wind shifts the decline was enhanced by reduction in the vertical stratification needed to support inertio gravity internal waves as the shelf waters apparently became mixed from top to bottom the loose mobile sea ice in the winter marginal ice zone miz did not appear to inhibit wind generation of the inertial oscillations the presence of sea ice appears in fact to have contributed to the spring increase of near inertial current amplitudes through restratification of the water column caused by melting ice our observations particularly the spatial coherency and spectral properties were generally consistent with kundu and thomson s 1985 model for inertio gravity waves generated in the wake of a translating weather front the half wavelength typical of these waves forced by transiting weather fronts on the bering shelf appears to be 150 km or approximately the width of the winter miz the associated near inertial currents are 180 out of phase with those a half wavelength away in the direction of phase propagation thus a storm passing perpendicular to the ice edge can excite waves at near inertial frequencies which compress deform and dilate the ice pack by up to a few percent of the miz width we suggest that this mechanism in conjunction with near inertial interfacial shear which can increase upward heat flux influences the width scale of the miz

intermittent and elliptical inertial oscillations in the atmospheric boundary layer abstract as a convective boundary layer over land decays in the late afternoon the atmosphere responds to the release of turbulent stresses for many years this response has been presumed to take the form of an inertial oscillation a horizontal circulation with a frequency equal to the local coriolis frequency though published documentation of inertial oscillations in the atmosphere has been rare in fact documentation of inertial oscillations has been more associated with frontal passages than with the evening transition of the atmospheric boundary layer a month of boundary layer wind profiler data from the cooperative atmosphere surface exchange study 1999 field program is analyzed here with the hilbert huang transform hht which allows analysis of intermittent nonstationary and amplitude varying wave events inertial motions are found in this dataset but neither the onset times of these inertial motions nor the preferred levels of occurrence are consistent with the evening transition hypothe