comparison of near surface mean and eddy flows from two numerical models of the south atlantic ocean the near surface mean and eddy flows simulated by two eddy permitting models of the south atlantic s coordinate primitive equation model spem and ocean parallel opa model are compared these models are intrinsically different by virtue of their vertical discretizations versus geopotential coordinates respectively so that their solutions differ essentially through the representation of current topography interactions the path of the agulhas current the generation process the characteristics and the subsequent trajectory of the agulhas rings are differently affected by topography in the two models along the american western boundary spem traps a larger part of the antarctic circumpolar current acc around the falkland plateau and consequently produces a stronger malvinas current which overshoots far to the north inshore of a rather realistic brazil current and confluence regime in contrast opa allows a large part of the acc to flow across the scotia sea produces a weaker malvinas current traps the brazil and malvinas currents along the american coast and tends to distort the complex dynamics of the confluence region and the zapiola anticyclone some of these differences can be attributed to the particularities of each vertical coordinate system and to the representation of topographic slopes staircases in opa and facettes in spem more generally the topographic constraint trapping of boundary currents and interaction of mean and eddy flows with bathymetry is stronger in spem than in opa the topographic smoothing usually performed in sigma coordinate models removes mesoscale topographic roughness and reduces topographic slopes this treatment is probably responsible for several of the differences observed in the numerical solutions

three dimensional geometry of concentric intrusive sheet swarms in the geitafell and the dyrfjoll volcanoes eastern iceland sheet intrusions inclined sheets and dykes in the deeply eroded volcanoes of geitafell and dyrfjoll eastern iceland were studied at the surface to identify the location depth and size of their magmatic source s for this purpose the measured orientations of inclined sheets were projected in three dimensions to produce models of sheet swarm geometries for the geitafell volcano the majority of sheets converge toward a common focal area with a diameter of at least 4 to 7 km the location of which coincides with several gabbro bodies exposed at the surface assuming that these gabbros represent part of the magma chamber feeding the inclined sheets a source depth of 2 to 4 km below the paleoland surface is derived a second younger swarm of steeply dipping sheets crosscuts this gabbro and members of the first swarm the source of this second swarm is estimated to be located to the se of the source of swarm 1 below the present day level of exposure and deeper than the source of the first swarm for the dyrfjoll volcano we show that the sheets can be divided into seven different subsets three of which can be interpreted as swarms the most prominent swarm the njardvik sheet swarm converges toward a several kilometers wide area in the njardvik valley at a depth of 1 5 to 4 km below the paleoland surface two additional magmatic sources are postulated to be located to the northeast and southwest of the main source crosscutting relationships indicate contemporaneous as well as successive activity of different magma chambers but without a resolvable spatial trend the dyrfjoll volcano is thus part of a complex volcanic cluster that extends far beyond the study area and can serve as fossil analog for nested volcanoes such as askja whereas in geitafell the sheet swarms seem to have originated from a single focus at one time thus defining a single central volcanic complex such as krafla volcano

transtensional origin of multi order cross folds in a high grade gneiss complex southwestern grenville province formation during post peak gravitational collapse the well mapped western part of the ottawa river gneiss complex orgc new name a large metamorphic core complex hosts a system of gently plunging cross folds of outcrop to regional scale situated in the ductile detachment zone between the lower grade cover and high grade core of the complex the cross folds are buckle structures that deform the attenuated gneissic layering plunge parallel to the regional elongation lineation range from upright to recumbent and exhibit distinctive hinge parallel elongation lineations all features of extension dominated ductile transtension our l s fabric data are consistent both with kinematic modelling that predicts progressive constrictional strain in the hinge zones of transtensional folds and with dynamic modelling that predicts rotation of flattened fold limbs into moderately dipping attitudes on the basis of petrologic data we show that cross folding postdated the peak ottawan metamorphism and took place during retrogression and exhumation of the thrust sheet stack the cross folds form an inclined system that is principally developed in retrograde melt weakened amphibolite facies rocks with the transtensional origin implying that exhumation and retrogression of the high grade core of the complex took place in an oblique extensional setting a transtensional origin for the cross folds removes the need to appeal to orogen parallel regional shortening an implausible requirement of previous interpretations and is compatible with data indicating that much of the visible fabric and structure of amphibolite facies domains of the orgc developed during post peak exhumation retrogression and gravitational collapse of the thrust sheet stack

laccolithic as opposed to cauldron subsidence emplacement of the eastern mourne pluton n ireland evidence from anisotropy of magnetic susceptibility the structural evolution and emplacement of the eastern mourne pluton was investigated using anisotropy of magnetic susceptibility ams measurements carried out on 112 oriented block samples and structural data from the host rocks from these new data cauldron subsidence as the emplacement mechanism is disputed and evidence for an alternative laccolithic style model involving inflation is presented this includes deflection and uplift of host rock bedding close to contacts and the magnetic fabric pattern which has a gentle dome geometry even close to contacts the magnetic lineations usually plunge down dip near the external margins but otherwise have a general ssw nne trend that diverges northward this suggests a northward directed inflow direction the model for the emplacement of the eastern mourne pluton is a laterally fed laccolith emplaced south to north the eastern margin is interpreted as a faulted contact facilitating the inflation of an asymmetrical breached laccolith

error analysis for the determination of tectonic rotation from paleomagnetic data appendix b is available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document b83 001 2 50 payment must accompany order recent determinations of tectonic rotation and flattening from paleomagnetic data have exaggerated the size of the confidence limits or error bars by about 25 this has been caused by the misuse of conventional error propagation formulas to derive one degree of freedom error bars from a two dimensional cone of confidence 95 an analytical calculation which is valid when error bars are small shows that the correct error bars are 75 to 80 of the values derived in previous studies i have used numerical integration to check on the applicability of the analytical solution and to calculate error bars when the analytical approximation cannot be used the analytical approximation may be used whenever 95 is less than 10 and the mean inclination is not too close to vertical confidence limits given for tectonic rotation and flattening in recent literature are too large and should be reduced by 20 25 narrowing the error bars in this way permits a more accurate interpretation of paleomagnetic data

magnetic susceptibility of the rock matrix related to magnetic fabric studies non ferromagnetic minerals constitute what is called the rock matrix whose susceptibility k1 is directly accessible using only high magnetic fields measurements on minerals and a wide range of rock types show that k1 is mainly due to paramagnetism and hardly exceeds 10 3 si with an anisotropy degree p less than 1 35 different methods to estimate the role of the matrix component in low field susceptibility k and its anisotropy include petrological and chemical analysis evolution of p vs k low temperature studies and comparison of k with remanent magnetizations

caldera formation in the rum central igneous complex scotland the northern marginal zone of the rum central igneous complex in nw scotland represents part of the early felsic phase of the volcano the marginal zone is a relic of the early caldera floor and the infilling of sedimentary and igneous rocks its formation has been explored through field examination of the ring fracture system of the complex and its pyroclastic and epiclastic intracaldera facies a sequence of magmatic tumescence and chamber growth caused initial doming followed by the formation of a collapse structure without accompanying volcanism this collapse structure circular in plan is akin in origin to a salt basin formed by crustal stretching above a rising diapir we call this the proto caldera collapse breccias which represent the slumping and sliding of megablocks blocks and boulders of the torridonian sandstones which form the walls of the basin were the original infilling logs of these deposits reveal considerable variation in thickness of the breccias from 80 170 m in the complex indicating an uneven floor to the proto caldera consistent with piecemeal collapse following accumulation of up to 70 m thickness of breccia thin interbedded rhyodacitic crystal tuffs 10 30 cm record the earliest eruptions of felsic magma in the caldera caldera formation was then interrupted by a period of quiescence recorded by the presence of an epiclastic sandstone of locally several metres thickness formed by washout of fines from the breccias subsequent resurgence created a fracture pattern characteristic of doming along which rhyodacite magma rose in dykes and erupted up to perhaps 10 km3 of rhyodacitic intracaldera ignimbrites this major eruption caused further incremental subsidence of the caldera floor into a now partly emptied magma chamber mafic inclusions in the ignimbrites point to the eruption being triggered by multiple injections of basic magma into a chamber occupied by felsic magma

palaeomagnetism of the british tertiary igneous province rhum and canna summary palaeomagnetic measurements have been made on samples of lavas dykes and plutonic rocks from rhum and of lavas and dykes from canna all the samples are reversely magnetized except for three dykes cutting the rhum lavas and two dykes cutting the canna lavas the magnetizations are believed to be primary or to have been acquired only a short time after the units were formed the simplest interpretation of the polarities is that the majority of the rocks were formed in a single reversed interval with the normally magnetized dykes being intruded in the following normal interval however if the time during which the rhum centre was eroded prior to the extrusion of the lavas was long additional inversions of the earth s magnetic field could have escaped detection in this case the polarity sequence is extended from r n to r n r n with the final r n corresponding to the lavas and the normal dykes cutting them igneous activity began about 59 ma ago contemporary with activity elsewhere in the british tertiary igneous province

mapping climatological seasonal variations of surface currents in the tropical atlantic using ship drifts the seasonal variability of current velocities in the tropical atlantic was studied by grouping ship drift velocity observations into 2 5 boxes and calculating monthly mean velocity values these values were used to calculate and map the annual mean velocity the seasonal variation about the mean the annual and semiannual harmonics and the first two empirical orthogonal functions eofs the seasonal variation is primarily zonal in the equatorial band and in the north equatorial countercurrent necc and primarily alongshore near the coast of south america maxima of seasonal variation of 23 cm s are centered in the necc near 6 n 42 5 w and in the gulf of guinea near 2 n 7 5 w most 80 of the variance in the necc and along the western boundary of the area studied has an annual period most of the variance along the equator in the mid atlantic has a semiannual period over the whole region 49 of the seasonal variance is explained by the annual harmonic and 69 is explained by a combination of the annual and semiannual harmonics the second eof contains 29 of the variance of the data set and shows a simultaneous speeding slowing of the major equatorial currents the south equatorial current sec the north brazil current the necc and the guinea current along their principal axes of variation with a concurrent slowing speeding of the guyana current and the brazil current the pattern of variation resembles a large equatorial gyre centered along 4 n that flows clockwise from may to september and counterclockwise most of the rest of the year the first eof accounts for 35 of the variance and shows a simultaneous speeding slowing of eastward velocity from 5 s to 10 n except in the western sec the western end of the north brazil current and the guinea current the out of phase fluctuations apparent in the western sec near the equator are explained by the slowing and reversal of the south equatorial current near 2 n 40 w between april and june this slowing of the sec is associated with the start up of the necc which accelerates eastward in may june and july and flows eastward across the atlantic from july through december the sec divides seasonally near the eastern tip of brazil where residual alongshore velocities are northward for half the year peaking during may and june and southward for the other half of the year a second division can be seen north of the amazon where the north brazil current continues up the coast into the guyana current during the first half of the year but partially retroflects into the necc during the last half of the year a fast eastward flow in the necc coincides with below average velocities in the guyana current and above average velocities in the western sections of the north brazil current and the sec north of the equator

a wind driven isopycnic coordinate model of the north and equatorial atlantic ocean 1 model development and supporting experiments numerical approximations to the dynamic equations are given which allow basin size ocean circulation models formulated in isopycnic coordinates to accommodate variable bottom topography and irregular coastlines emphasis is placed on computational economy through the use of a split explicit time integration scheme on the proper formulation of the advection and coriolis terms in the momentum equation in case of strongly varying layer thickness and on the correct estimation of the horizontal pressure gradient force in grid boxes truncated by steep bottom slopes the algorithms are tested in a series of two and three layer double gyre experiments in cases of steady forcing leading to a steady circulation we are able to reproduce the expected motionless final state in coordinate layers that are below the direct influence of the wind forcing this includes layers intersecting topographic obstacles a long term 25 30 year vacillation tentatively associated with the outcropping of isopycnals along the edge of the cyclonic gyre in a steadily forced model is documented the paper forms the basis for a subsequent study in which circulation features obtained in a realistic north atlantic setting will be discussed

introduction from the british tertiary into the future modern perspectives on the british palaeogene and north atlantic igneous provinces the study of volcanic rocks and igneous centres has long been a classic part of geological research despite the lack of active volcanism the british isles have been a key centre for the study of igneous rocks ever since ancient lava flows and excavated igneous centres were recognized there in the 18th century hutton 1788 this led to some of the earliest detailed studies of petrology the starting point for many of these studies was the british palaeogene igneous province bpip formerly known as the british tertiary judd 1889 and still recognized by this name by many geologists around the globe this collection of lavas volcanic centres and sill dyke swarms covers much of the west of scotland and the antrim plateau of northern ireland and together with similar rocks in the faroe islands iceland and greenland forms a world class large igneous province this north atlantic igneous province naip began to form through continental rifting above a mantle plume at c 60 ma and subsequently evolved as north america separated from europe creating the north atlantic ocean

circulation characteristics in three eddy permitting models of the north atlantic a systematic intercomparison of three realistic eddy permitting models of the north atlantic circulation has been performed the models use different concepts for the discretization of the vertical coordinate namely geopotential levels isopycnal layers terrain following sigma coordinates respectively although these models were integrated under nearly identical conditions the resulting large scale model circulations show substantial differences the results demonstrate that the large scale thermohaline circulation is very sensitive to the model representation of certain localised processes in particular to the amount and water mass properties of the overflow across the greenland scotland region to the amount of mixing within a few hundred kilometers south of the sills and to several other processes at small or sub grid scales the different behaviour of the three models can to a large extent be explained as a consequence of the different model representation of these processes

petrology and geochemistry of the loch ba ring dyke mull n w scotland an example of the extreme differentiation of tholeiitic magmas the loch ba ring dyke in the tertiary igneous central complex of mull n w scotland is composed predominantly of a banded rhyolitic welded tuff the rhyolite contains numerous inclusions of dark aphanitic rock the textural relationships between the different rocks indicate rapid violent and intimate mixing during emplacement of the dyke the dark glassy component varies continuously from basaltic andesite to andesite dacite and rhyolite these glasses are enriched in feo and depleted in mgo at a given sio2 content in comparison to other tholeiitic highly differentiated volcanic rocks the rhyolite contains an average of 4 phenocrysts and is associated with the mineral assemblage plagioclase an32 to an21 sanidine or50 60 hedenbergite fayalite magnetite ilmenite apatite zircon mineral aggregates involving either plagioclase hedenbergite ilmenite or plagioclase fayalite magnetite are common but aggregates containing fayalite and hedenbergite together are scarce the dark glassy components are either phenocryst free or contain less than 0 2 phenocrysts the main phenocrysts associated with the dark glasses are plagioclase an65 an30 high calcium clinopyroxene ranging continuously from augite to pure hedenbergite pigeonite magnetite ilmenite and rare apatite zoning in minerals is generally weak or absent the plagioclase feldspar high calcium clinopyroxenes and pigeonites have similar compositional ranges to the minerals observed in the middle and upper zones of the skaergaard intrusion the mineral compositions are systematically related to sio2 content and mg number of the glasses the data demonstrate that mineral compositions and assemblages similar to the skaergaard form from silica rich andesitic to rhyolitic liquids the various mafic glasses are interpreted to have been derived from a zoned magma chamber underlying an upper layer of rhyolitic magma differentiation is attributed to fractional crystallization of the observed mineral assemblages causing sio2 enrichment and feo depletion however glasses with less than 57 sio2 have unusual compositions with very low mgo and p2o5 as well as variable al2o3 and tio2 their peculiarities could be explained by andesitic magmas assimilating cumulate mineral aggregates precipitated from more differentiated dacite and rhyolite magmas the bulk compositions of these cumulates have high feo low sio2 and negligible mgo and p2o5 it is suggested that the high density of the mineral aggregates containing fayalite hedenbergite magnetite and ilmenite caused them to settle through the zoned chamber to be assimilated by high temperature less differentiated magmas

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

circulation along the mexican caribbean coast 1 data from an array of seven subsurface upward looking moored acoustic doppler current profilers adcps and four subsurface pressure sensors deployed from august 2002 to august 2003 along the caribbean coast of mexico showed that the currents in the area have a predominant northeastward direction along the coast are coherent within the upper 130 m of the water column and have a general tendency to increase northward reaching magnitudes of 2 4 m s north of cozumel in addition important weeklong reversal periods southward flows are observed around chinchorro bank a vertical current profile eof analysis at each station indicates high coherence within the study area with the first vertical mode at each station explaining at least 69 of variance and current vectors aligned with the coast a second eof analysis carried out for any uniform depth level using current data from all stations shows high coherence in the horizontal as well the first mode explains at least 59 of the variance and has a dominant 3 month long variability comparison between the current patterns along the mexican caribbean coast and in the yucatan channel suggests that dynamics of the entire area might be strongly influenced by the passage of eddies through the region comparison of a singular spectral analysis ssa of the principal components of currents with the pressure difference across the channels supports the idea of eddies modulating current variability numerical model results indicate that high values of the current intensity indexes are associated with eddies the flow along chinchorro and cozumel channels is in geostrophic balance most of the observation time but with week long ageostrophic periods which are predominant off cozumel these events appear to occur when eddies are traversing the region

the retroflection paradox abstract the classical question of what happens when a warm western boundary current such as the north brazil current nbc retroflects is addressed analytically using a reduced gravity nonlinear model the traditional view is that the northwestward flowing current separates from the wall turns to the right looking offshore and forms a zonal boundary current that flows eastward integration of the steady inviscid momentum equation along the boundary gives the longshore momentum flux or flow force and shows that such a scenario leads to a paradox to resolve the paradox the separated current must constantly shed anticyclones which propagate to the northwest due to and an interaction with the boundary this new eddy shedding mechanism which is not related to the traditional instability of a zonal jet may explain why the nbc must produce rings a nonlinear analytical solution to the problem is constructed with the aid of a powerful theoretical approach based on the idea that nonlinear periodic

the great eucrite intrusion of ardnamurchan scotland reevaluating the ring dike concept ring dikes are cylindrical sheet intrusions that develop at a subvolcanic level due to ascent of magma along steep outward dipping ring fractures magma ascent is triggered by central block subsidence and fully formed ring dikes are composed of a flat lying sill like roof as well as steeply outward dipping walls on all sides the great eucrite of the ardnamurchan paleocene igneous complex nw scotland is a spectacular gabbro intrusion that has been cited as one of the classic examples of a ring dike for the past 70 yr we combine field observations detailed structural measurements of primary magmatic features and anisotropy of magnetic susceptibility data in a reinvestigation of this intrusive body magmatic layering and macroscopic planar crystal arrangements dip inward and magnetic lineations plunge consistently toward the center of the intrusion in contrast to what would be expected for a ring dike we propose that the great eucrite ring dike is in fact a lopolithic intrusion with an overall funnel shape geometry this conclusion brings into question the presence of three individual foci of activity in ardnamurchan purported to have shifted throughout the development of the complex it also has significant implications for the status and structural evolution of other igneous complexes of the british paleocene igneous province which contain layered mafic intrusions currently regarded as ring dikes

mesoscopic and magnetic fabrics in arcuate igneous bodies an example from the mandi karsog pluton himachal lesser himalaya field microstructural and anisotropy of magnetic susceptibility ams data from the palaeozoic mandi karsog pluton in the lesser himalayan region reveal a concordant relationship between fabric of the proterozoic host rock and the granite the pluton displays a prominent arcuate shape on the geological map the margin parallel mesoscopic and magnetic fabrics of the granite and warping of the host rock fabric around the pluton indicate that this regional curvature is either synchronous or pre dates the emplacement of the granite body mesoscopic fabric magnetic fabric and microstructures indicate that the northern part of the pluton preserves its pre himalayan magmatic fabric while the central and southern part shows tectonic fabric related to the tertiary himalayan orogeny the presence of nw se trending aplitic veins within the granite indicates a post emplacement stretching in the ne sw direction shear sense indicators in the mylonites along the margin of the pluton suggest top to the sw shearing related to the himalayan orogeny based on these observations it is envisaged that the extension that gave rise to this rift related magmatism had a ne sw trend that is normal to the trend of the aplite veins subsequently during the himalayan orogeny compression occurred along this same ne sw orientation these findings imply that the regional curvature present in the himachal lesser himalaya is in fact a pre himalayan feature and the pluton has formed by filling a major pre himalayan arcuate extension fracture

new insights in the french guiana continental shelf circulation and its relation to the north brazil current retroflection 1 moored current measurements carried out from 6 october 2003 to 18 february 2004 over the french guiana continental shelf are presented two contrasted situations have been evidenced in which the currents were either weak and oscillating during the first period from october to early december or strong and northwestward during the rest of the survey further analysis of these measurements in light of moderate resolution imaging spectroradiometer satellite images have revealed that these situations are mainly due to the motion of an outer shelf mesoscale feature the north brazil current nbc retroflection two other main results have also been evidenced in this survey 1 when the nbc retroflection occurs northwestward of the french guiana continental shelf part of the nbc climbs over the shelf slope and propagates to the inner shelf and 2 the guyana current does not persist throughout the year at a 22 m depth and below finally the location of the nbc retroflection has also a strong impact on the spread of the amazon plume over the french guiana continental shelf and is felt to have an influence on the nutrient supply in this region

carbon cycle in st lawrence aquatic ecosystems at cornwall ontario canada seasonal and spatial variations abstract seasonal studies of a cross section through the upper st lawrence river in 1995 and 1996 revealed strong biogeochemical gradients between a wetland a creek embayments and the main river near the city of cornwall ontario canada these local differences are much more pronounced than over the entire length of the main river indicating the importance of near shore ecosystems in the riverine carbon cycle the aqueous pco2 ranged from atmospheric equilibrium to values as high as 5450 ppmv reflecting a gradient from the great lakes dominated main river to the peripheral ecosystems with active biological recycling the isotopic composition of dissolved inorganic carbon fits this observation with 13 c dic values ranging from 2 2 to 13 7 from the main river to near shore ecosystems warm season samples of embayments revealed active photosynthesis with po2 values up to 50 higher than those of the atmosphere and pco2 below atmospheric equilibrium while photosynthetic activity was mostly caused by phytoplankton as indicated by chlorophyll a up to 63 0 mg l an active periphyton and macrophyte community also contributed to oxygen oversaturations in the littoral zone in situ respiration dominated in the wetland particularly during winter and spring when dissolved organic carbon up to 17 3 mg l was transformed into co2 leading to 13 c dic values as low as 12 3 the creek was the only ecosystem with a respiratory signal inherited from near shore baseflow as indicated by its 18 o h 2 o composition that was similar to local groundwater during peak runoff periods its peak doc concentrations of 38 3 mg l the highest amongst the studied ecosystem may have resulted in further enhanced respiratory activity

isotopic composition of dissolved inorganic carbon in a large polluted river the vistula poland abstract the vistula is a large lowland temperate river receiving high loads of pollutants from a densely populated catchment on the other hand the river is to a relatively small extent affected by channelisation and damming this study is the first attempt to characterise stable isotope aspects of dissolved inorganic carbon in the vistula which is a major source of pollution to the baltic sea isotopic composition of dic and other chemical properties were measured biweekly at the upper reach and monthly at the mouth of the river two longitudinal samplings were performed in hydrological summer and winter conditions short term and short range observations were carried out in an anthropogenically influenced urban reach at cracow most water samples from the vistula and its tributaries analysed in this study had 13 c dic values around the range 12 to 11 typical for european lowland rivers fed by groundwaters on carbonate areas variablity of 13 c dic in this river system is limited except for the impoundments and the specific hydrological conditions the few impoundments that exist on the vistula intensify the photosynthesis respiration cycle as well as the exchange of co 2 with the atmosphere enhanced contribution of biogenic carbon during floods is reflected by lowering of 13 c dic low flows facilitate photosynthetic assimilation and evasion of co 2 into the atmosphere resulting in positive shifts of 13 c dic principal component analysis confirmed that 13 c dic variability at the fixed cross section in cracow reflected releases and withdrawals of co 2 from the riverine dic pool the apparent 13 c dic variability depends to some extent on the spatio temporal context of observations diurnality can be very pronounced in the impounded anthropogenically influenced reaches in warm periods interpretation of the observed riverine 13 c dic patterns can be difficult as the spatial and temporal variabilities combine resulting in convoluted isotopic signals isotopic investigations into the nature of riverine carbon cycling should be supplemented by discharge records and by observations of the parameters influenced by the photosynthesis respiration cycle dissolved oxygen ph p co 2 and of those conservative with respect to biological processes electrical conductivity stable isotope composition of water

the forced annual reversal of the atlantic north equatorial countercurrent abstract we analyze the variability of the thermal structure associated with the atlantic north equatorial countercurrent necc and its relation to the seasonally varying winds the analysis performed allows us to establish the period of time and the region where the necc reverses direction west of 25 w the depth of the thermocline in the southern side of the necc 4 to 7 n annually oscillates 180 out of phase to the oscillations on the northern side 7 to 10 n east of 25 w the thermocline rises and falls nearly in phase across the countercurrent if the flow can be uniquely presumed from the thermal structure the necc disappears during the boreal spring in the western basin the reversal of phase from north to south over one part of the ocean but no the other is shown to be mirrored in the annual variation of the curl of the stress induced at the surface by the winds in order to quantify this result the different terms of the vorticity equation are calculated from the data we conclude that t

caribbean current and eddies as observed by surface drifters abstract recent satellite tracked surface drifter trajectories were analyzed to describe the mean currents and eddies in the caribbean sea the structure of the caribbean current and its variability were determined from high resolution 1 2 degree maps of the mean velocity and eddy kinetic energy looping drifter trajectories were used to identify discrete cyclones and anticyclones and their characteristics were described and related to the structure of the mean flow the translation rate of eddies in different areas was found to be similar to the mean velocity of the local background flow fields suggesting that the eddies were largely advected by the background flow ten energetic anticyclones translated westward at 13 cm s in the venezuela and colombia basins these anticyclones tended to lie in two bands centered near 15 n and 17 n coinciding with two jets of the caribbean current the northern weaker jet contains water primarily from the north atlantic the southern stronger jet contains water from the tropical and south atlantic the anticyclones are thought to have formed in the eastern caribbean from the anticyclonic vorticity derived from north brazil current rings the ring vorticity enters the eastern caribbean through island passages and is probably amplified by the anticyclonic shear on the northern side of the jets southwest of cuba a cyclone anticyclone pair was observed to translate slowly 2 cm s westward into the yucatan current the cyclone was tracked for 10 5 months with four drifters making it the longest tracked of the caribbean eddies

on the seasonal variability and eddies in the north brazil current insights from model intercomparison experiments the time dependent circulation of the north brazil current is studied with three numerical ocean circulation models which differ by the vertical coordinate used to formulate the primitive equations the models are driven with the same surface boundary conditions and their horizontal grid resolution isotropic 1 3 at the equator is in principle fine enough to permit the generation of mesoscale eddies our analysis of the mean seasonal currents concludes that the volume transport of the north brazil current nbc at the equator is principally determined by the strength of the meridional overturning and suggests that the return path of the global thermohaline circulation is concentrated in the nbc models which simulate a realistic overturning at 24 n of the order of 16 18 sv also simulate a realistic nbc transport of nearly 35 sv comparable to estimates deduced from the most recent observations in all models the major part of this inflow of warm waters from the south atlantic recirculates in the zonal equatorial current system but the models also agree on the existence of a permanent coastal mean flow to the north west from the equator into the carribean sea in the form of a continuous current or a succession of eddies important differences are found between models in their representation of the eddy field the reasons invoked are the use of different subgrid scale parameterisations and differences in stability of the nbc retroflection loop because of differences in the representation of the effect of bottom friction according to the vertical coordinate that is used finally even if differences noticed between models in the details of the seasonal mean circulation and water mass properties could be explained by differences in the eddy field nonetheless the major characteristics mean seasonal currents volume and heat transports appears to be at first order driven by the strength of the thermohaline circulation

correction to apparent and true polar wander and the geometry of the geomagnetic field over the last 200 myr 1 in the paper apparent and true polar wander and the geometry of the geomagnetic field over the last 200 myr by jean besse and vincent courtillot journal of geophysical research 107 b11 2300 doi 10 1029 2000jb000050 2002 the data in the top part of table 4 were incorrect the correct table 4 is given here journal of geophysical research vol 108 no b10 2469 doi 10 1029 2003jb002684 2003

the british tertiary igneous province palaeomagnetism of the dyke swarm along the sleat coast of skye summary a palaeomagnetic investigation has been made of a swarm of more than 400 dykes along the south coast of skye scotland by the sound of sleat seven red lamprophyre dykes have palaeomagnetic directions inconsistent with tertiary age and not inconsistent with their previously held caledonian age the remaining 409 dykes have palaeomagnetic directions that are consistent with a lower tertiary age we present evidence suggesting that the tertiary dykes might have been emplaced during a short time over which the geomagnetic polarity occupied as few as three polarity intervals nrn or rnr certain intermediate directions of magnetization have also been found and are presented here

the palaeomagnetism of the tertiary igneous complex of ardnamurchan summary samples have been taken systematically through the intrusive sequence for the three centres which form the tertiary central intrusive ring complex palaeomagnetic measurements show that all the units are reversely magnetized as are the earlier lavas an extension of those of mull and morvern which they intrude this is in contrast to mull skye and arran where the igneous sequences have been shown to span at least three polarity intervals but is similar to rhum where the only normal units are a few late dykes since rhum and ardnamuchan both lie on the dyke swarm which passes through muck the two complexes are considered to be closely related if the ardnamurchan central complex was formed in a single reversed interval the total duration of igneous activity was less than 3 myr

weathering processes in the ganges brahmaputra basin and the riverine alkalinity budget abstract we present river chemistry data for a network of rivers draining the western and central nepal himalaya our sampling locations cover the system from the sources of rivers in tibet to the gangetic plain water samples were collected throughout the year including the monsoon season for rivers in nepal and for the ganges and brahmaputra in bangladesh rivers draining the north himalaya are characterized by low discharge under a cold and arid climate main stream waters have 13 c dic near 0 and high so42 so42 hco3 ratios xso4 with values around 40 eq and high cl ca is the dominant cation ca2 cations 55 to 75 eq after correction of sodium by chloride dissolved sulfate is produced in waters from the tethian sedimentary series whereas chlorine is related to thermal waters dissolved sulfate is primarily derived from sulfide oxidation rather than evaporite dissolution 13 c dic values of up to 3 9 show that metamorphic co2 is an important weathering agent rivers of the north himalayan basins have about 50 of their alkalinity derived from carbonate dissolution 20 from biogenic activity and 30 from metamorphic co2 on the south flank of the himalaya rivers are more depleted in 13 c and have on average lower xso4 most rivers have 13 c dic and xso4 values compatible with a simple mixing between soil co2 and sulfate derived from sulfide oxidation during the monsoon discharge increases by a factor 20 but the total dissolved concentration is only slightly reduced xso4 and 13 c decrease while ca cations increases implying enhanced dissolution of pedogenic calcite as a whole the g b riverine flux of alkalinity derived from silicate weathering is around 2 7 1011 mol year modest at the global scale sulphuric acid controls 20 30 of the weathering reaction in the brahmaputra and 6 to 9 in the ganges na and k balance 60 to 65 of the silicate derived alkalinity flux and the long term co2 consumption by ganges and brahmaputra is near 6 4 1010 mol year the flux of metamorphic co2 converted to alkalinity via weathering reactions is ca 1 1010 mol year

influence of diel biogeochemical cycles on carbonate equilibrium in a karst river abstract variations in temperature photosynthesis and respiration force diel variations in ph and dissolved co 2 concentrations of surface streams possibly controlling carbonate equilibrium between river water and carbonate stream beds diel cycles of water chemistry and 13 c of dissolved inorganic carbon dic were measured to assess how biogeochemical processes affect dissolution and precipitation of calcite and thus channel development in ichetucknee river a large spring fed river discharge 6 m 3 s flowing over carbonate karst terrain in north central florida usa samples were collected at a 4 h sampling interval during two one week periods and at a 1 h interval during a single 24 h period simultaneously temperature ph dissolved oxygen do and no 3 concentrations were measured using in situ sensors at 15 min or 1 h intervals ca 2 dic and no 3 concentrations decreased during the day and increased at night causing diel changes of in stream specific conductivity these changes were inversely related to diel changes in ph pco 2 and do concentrations this work shows that photosynthesis and respiration of subaquatic vegetation are the dominant processes influencing in stream diel variation during the day a simultaneous increase of 13 c dic and decrease in dic indicates that photosynthesis was the primary control on dic concentrations calcite saturation indices ranged from 0 to 0 5 with the highest value in daylight as a result of co 2 consumption causing carbonate precipitation the water remained saturated with respect to calcite at night and 13 c dic values decreased indicating that co 2 production from ecosystem respiration was the dominant process affecting dic concentrations but was insufficient to induce significant carbonate dissolution at night outgassing maintained in stream dic concentrations lower than the supersaturated dic springs source but a drop in 13 c dic indicates that ecosystem respiration had a dominant influence over outgassing although co 2 outgassing occurs it is shown to be a minor component of the dic mass balance while carbonate precipitation represents 88 of dic loss these results indicate that in stream biological processes influence carbonate mineral diagenesis in large clear water rivers

the genesis ascent and emplacement of the northern arran granite scotland implications for granitic diapirism integrated structural and petrological data are used to trace the evolution of the northern arran coarse granite during the latter stages of its ascent and its emplacement structural analysis of the aureole of the granite suggests that it rose as a single body of magma which is confirmed by petrological data during its ascent the pluton intersected the downward dipping limb of an existing synform refolding and displacing it upward to form a concentric or rim synform this direct evidence of vertical displacement of the country rocks confirms that the pluton is a diapir diapiric ascent was permitted by a reduction in wall rock viscosity and hence viscous drag forces on the pluton aided by heat loss due to crystallization during ascent most of the deformation within the aureole can be attributed to ascent of the pluton the early rim synform is overprinted by flattening strains and faulting caused by in situ radial expansion which represents the ultimate evolution of a diapiric body the final shape of the pluton is determined by inhomogeneous deformation of the aureole which is partly controlled by pre existing faults

eddies in the north brazil current retroflection region observed by geosat altimetry mesoscale fluctuations in the western tropical atlantic are analyzed in geosat altimetry sea surface height ssh and geostrophic velocity anomalies to investigate the role of eddies in the north brazil current nbc retroflection zone the detachment of anticyclonic eddies from the nbc retroflection is observed during november through january when the nbc retroflection into the north equatorial countercurrent necc weakens and finally breaks down these eddies are traced over more than 2 months between 50 and 60 w on their way toward the caribbean at average speeds of 15 cm s 1 in one case an apparent merger of two anticyclonic eddies occurs one detached from the retroflection zone and one detached from the necc cyclonic eddies are also observed but are generally less persistent mesoscale ssh variance just west of the retroflection increases by a factor of 2 from early summer to winter mainly because of the anticyclonic eddies interhemispheric water mass transfer associated with the eddy flux out of the nbc retroflection may amount to an average transport of 3 sv

palaeomagnetic and anisotropy of magnetic susceptibility data bearing on the emplacement of the western granite isle of rum nw scotland the western granite is the largest of several granitic bodies around the margin of the rum central igneous complex we report palaeomagnetic and anisotropy of magnetic susceptibility ams data that bear on the emplacement and deformation of the western granite the collection includes samples from 27 sites throughout the western granite five sites in adjacent feldspathic peridotite and two sites in intermediate to mafic hybrid contact aureole rocks palaeomagnetic data from 22 of the 27 sites in the granite provide an in situ group mean d 213 2 i 69 5 95 5 5 that is discordant to an early paleocene reverse polarity expected field about 184 66 95 4 3 the discrepancy is eliminated by removing an inferred 15 of northwest side down tilting about a best fit horizontal tilt axis trending 040 data from the younger peridotite and hybrid rocks of the rum layered suite provide an in situ group mean of d 182 6 i 64 8 95 4 0 which is statistically indistinguishable from an early paleocene expected field and imply no post emplacement tilting of these rocks since remanence acquisition the inferred tilt recorded in the western granite which did not affect the younger layered suite suggests that emplacement of the ultrabasic rocks resulted in roof uplift and associated tilt of the western granite to make space for mafic magma emplacement magnetic fabric magnitude and susceptibility parameters yield two subtle groupings in the western granite ams data set group 1 data defined by rocks from exposures to the east and south have comparatively high bulk susceptibilities kmean 29 51 10 3 in si system stronger anisotropies pj 1 031 and oblate susceptibility ellipsoids group 2 data from rocks in the west part of the pluton have lower values of kmean 15 89 10 3 si and pj 1 014 and triaxial susceptibility ellipsoids magnetic lineations argue for emplacement of the granite as a tabular sheet from the south southeast toward the north and west moderate to steeply outward dipping magnetic foliations together with deflection of the country rock bedding in the north are consistent with doming accompanying magma emplacement

carbon fluxes pco2 and substrate weathering in a large northern river basin canada carbon isotope perspectives abstract isotopic composition of dissolved inorganic carbon 13 c dic in the ottawa river basin is about 8 and 16 for lowland carbonate and upland silicate tributaries respectively this suggests that 1 the source of dic to the ottawa river is soil respiration and carbonate weathering 2 exchange with the atmosphere is unidirectional or volumetrically unimportant and 3 in river respiration and photosynthesis are not significant influences on the river carbon budget accepting these constraints chemical and isotopic data are used to reconstitute soil pco2 for tributary catchments averages for upland silicate mixed and lowland carbonate basins are calculated to be roughly 2000 5000 and 30 000 ppm respectively these values are used as input to model the pathway of carbon through the watershed rain water to soil water to river water the flux of carbon from the ottawa river as dic is calculated to be 4 3 1010 mol c a utilizing carbon isotopes 75 and 25 of the ca2 mg2 flux is calculated to originate from carbonate and silicate weathering respectively and 61 of the dic is calculated to originate from organic respiration the latter represents some 6 of respired carbon in the basin assuming an average respiration rate of 0 5 mmol c m 2 h 1 based on a diffusion model co2 evasion to the atmosphere from the ottawa river and its tributaries is estimated to be 1 3 1010 mol c a or 30 of the dic flux

flow lobes in granite the determination of magma flow direction in the trawenagh bay granite northwestern ireland using anisotropy of magnetic susceptibility anisotropy of magnetic susceptibility ams has been determined from 152 sites over the 64 km2 trawenagh bay granite part of the 400 ma caledonian donegal batholith microscopic observations thermomagnetic analyses high field torque magnetometry and heating experiments demonstrate that the ams fabric is carried by biotite with varying amounts of mimetic magnetite in the biotite cleavage planes the ams fabric is interpreted as a flow fabric because microstructures indicate magmatic state deformation it defines large scale macroscopic flow features flow lobes in this weakly deformed granite at pluton scale the data set shows a gentle westward plunging lineation at a smaller scale many lobate magnetic foliation patterns can be discerned in which the magnetic lineation is usually symmetrically disposed about the long axes of the lobes in three dimensions the lobes are tongue like 1500 m wide subunit scale and elongated east west parallel with the general lineation they close consistently westward and younger lobes in the east appear to deflect older lobes in the west the trawenagh bay granite is west of a major synplutonic shear zone that hosts the main donegal granite pluton these structures are interpreted as frozen flow lobes and indicate that the magma flowed in a westward direction from within the active shear zone of the main donegal granite into the weakly deformed wall rock trawenagh bay granite intra unit pulses or surges have long been suspected in granite plutons however this study reports the most detailed description of such structures to date

pre eruptive magma mixing in ash flow deposits of the tertiary rum igneous centre scotland the northern marginal zone of the rum igneous centre is a remnant of an early caldera and its infill it is composed of intra caldera breccias and various small volume pyroclastic deposits overlain by prominent rhyodacite ash flow sheets of up to 100 m thickness the ash flows were fed from a feeder system near the caldera ring fault and intrusive rhyodacite can locally be seen grading into extrusive deposits a variety of features suggest that the ash flows were erupted from a magma chamber that contemporaneously hosted felsic and mafic magmas i chilled basaltic inclusions in rhyodacite ii formerly glassy basaltic to andesitic enclaves with fluid fluid relationships iii feldspars with thick reaction rims enclosed in the basaltic to andesitic inclusions yet with cores chemically resembling those of the rhyodacite iv trace element compositions of the rhyodacite and the mafic enclaves form a mixing line between the end member rhyodacite and basalt compositions additionally textural and chemical features in the rhyodacite feldspar phenocrysts are consistent with magma mixing v feldspars with resorption embayments cutting through internal zonation of the crystals vi complexly zoned crystals with sieve textured zones that are overgrown with euhedral zones vii oscillatory zonation of feldspar phenocrysts in the rhyodacite showing sharp increases in anorthite an 10 followed by gradual decrease in an content an 4 this evidence points to eruption of ash flows from a felsic magma chamber that was periodically replenished by injection of mafic magma diffusional mixing between the two magmas was permitted by temperature and compositional differences but was slow due to the contrast in viscosities and densities the fe ti p enriched basic magma that replenished the chamber was degassing on entering the lower temperature environment and soon equilibrated thermally followed by chemical exchange between the two end member magmas this process formed hybrid andesite enclaves enriched in trace elements beyond that caused by simple mixing implying trace element diffusion in addition to bulk mixing eruption was caused by replenishment with and degassing of the basic magma and the chamber partially evacuated while the process of hybridisation was underway the erupted products record magma mixing by chamber replenishment blending of two magmas and elemental exchange in the magma chamber and also physical mingling in the eruptive conduit

rapid formation of the small isles tertiary centre constrained by precise 40ar 39ar and u pb ages the relative chronology of magmatic and tectonic events is key to an understanding of the influence of the iceland plume on the north atlantic in particular the location and duration of magmatism is of fundamental importance initial widespread flood basalt formation occurred in baffin island greenland and britain before complete plate break up at 56 ma after which time magmatism became concentrated in the active rift zone historically the british tertiary igneous province btip has been instrumental in advancing many concepts of igneous petrology however the absolute age and duration of the province remains unresolved here we present new internally consistent 40ar 39ar ages that help to constrain the volcanic activity in the small isles centre to within 2 my this short duration has implications for the onset of magmatism in the larger north atlantic province the rapid unroofing of the rum volcano and more significantly some of the evidence used to propose pulsing of the iceland plume

mechanisms of decadal variability in the shallow subtropical tropical circulation of the atlantic ocean a model study a suite of basin scale models of the thermohaline and wind driven circulation in the atlantic ocean is used to study the mechanisms of decadal variability in the shallow subtropical tropical cells stcs the emphasis is on the spatial patterns of the transport anomalies in the tropical thermocline particularly their manifestation in the equatorial current system and on the relative role of changes in the deep meridional overturning cell moc associated with variations in the formation of labrador sea water lsw in the subpolar north atlantic using wind stress and heat flux variations based on ncep ncar reanalysis products the variability of the zonally integrated stc transports is similar to that obtained in a recent regional model study corroborating the role of both the southern and northern stc in supporting wind driven transport anomalies of o 2 sv near the equator sensitivity experiments indicate that changes in subarctic moc transports associated with the strong variability in lsw formation during the last decades contributed a signal of o 0 3 sv to the upper layer equatorial transports whereas the local wind driven variability clearly dominates on interannual decadal timescales and is confined to depths down to 150 m the weak moc related signal is primarily reflected in an interdecadal modulation of the stc transports while a strong part in the stc s transport anomalies is associated with the western boundary current nbc there is an important contribution also by weaker interior ocean flow anomalies which tend to counteract the variability of the nbc

seasonal and interannual modulation of the eddy kinetic energy in the caribbean sea abstractvariability of the mesoscale eddy field in the caribbean sea is analyzed over the period 1993 2009 using geostrophic anomalies derived from altimeter data and a high resolution regional model the colombia basin presents the largest values of eddy kinetic energy eke and its semiannual cycle with a main peak in august october and a secondary peak in february march is the dominant feature in the whole caribbean eke cycle the analysis of energy conversion terms between low frequency currents and eddies explains these peaks by enhanced baroclinic and barotropic instabilities in response to seasonally varying currents in the region of the guajira peninsula the semiannual acceleration of the atmospheric caribbean low level jet intensifies the southern caribbean current scc twice a year in this region together with its vertical and horizontal velocity shears the asymmetry of the eke seasonal cycle in the colombia basin is explained by a summer peak in the annual cycle of the whole scc numeric

on the dynamics of the zapiola anticyclone recent observations obtained in the south atlantic suggest the existence of a strong anticyclonic flow positioned over a major bottom topographic feature known as the zapiola drift here a numerical simulation of the south atlantic is described in which this anticyclone is reproduced and the model is used to diagnose the dynamics maintaining this flow with a mean barotropic transport of 140 sv and bottom velocities of 10 cm s 1 the simulated zapiola anticyclone compares well with in situ observations furthermore the model surface eddy kinetic energy shows a local minimum over the drift in agreement with observations from topex poseidon numerical experiments show that the circulation feature is sensitive to the intensity of the eddy field and to the particular value of the bottom friction both of these tendencies are in agreement with a theoretical explanation of the zapiola anticyclone that has recently appeared elsewhere thus we argue that the anticyclone is maintained by eddy driven potential vorticity fluxes accelerating flow within topographically closed ambient potential vorticity contours as far as we know this is the first south atlantic simulation to reproduce the zapiola anticyclone in a realistic fashion the quantitative success of this experiment is attributed to the use of a topography following sigma coordinate in a spatially well resolved model

how topographic smoothing contributes to differences between the eddy flows simulated by sigma and geopotential coordinate models abstract the characteristics of the mesoscale turbulence simulated at a resolution of by a sigma coordinate model spem and a geopotential coordinate model opa of the south atlantic differ significantly these two types of models differ with respect to not only their numerical formulation but also their topography smoothed in spem as in every sigma coordinate application in this paper the authors examine how these topographic differences result in eddy flows that are different in the two models when the topography of the agulhas region is smoothed locally in opa as is done routinely in spem the production mechanism of the agulhas rings their characteristics and their subsequent drift in the subtropical gyre are found to converge toward those in spem furthermore the vertical distribution of eddy kinetic energy eke everywhere in the basin interior becomes similar in spem and opa and according to some current meter data becomes more realistic when mesoscale topographic roughness is re

magmatic lineations inferred from anisotropy of magnetic susceptibility fabrics in units 8 9 and 10 of the rum eastern layered series nw scotland the eastern layered series of the rum layered suite nw scotland comprises a sequence of sixteen 30 150 m thick cyclic units the upper troctolite olivine gabbro parts of each of these units exhibit small scale modal layering and a pervasive layerparallel mineral lamination that is often associated with soft sediment deformation structures a sporadic macroscopic magmatic lineation measurable on mineral lamination surfaces is also observed in places anisotropy of magnetic susceptibility ams fabrics were studied in three of these cyclic units 8 9 and 10 in the northern part of the eastern layered series magnetic fabrics measured in the troctolites and gabbros yield one dominant trend in which magnetic foliations parallel magmatic layering and magnetic lineations trend nw se and plunge gently magnetic fabrics measured for two detailed traverses through unit 10 on the northern side of hallival also yield one dominant trend similar to that measured elsewhere in the eastern layered series however toward the centre of unit 10 in each traverse magnetic lineations sometimes plunge approximately downdip sw on the magnetic foliation planes the implications of these results are discussed with reference to previous textural and fabric observations on rum a model is suggested in which weak linear arrangements of cumulus olivine and plagioclase crystals are developed due to slumping and soft sediment deformation of unconsolidated crystal mushes during central sagging of the rum layered suite 2007 elsevier b v all rights reserved

yucatan channel flow observations versus clipper atl6 and mercator pam models 1 the statistical properties of the flow structure in the yucatan channel s main section based on 2 years of continuous observations august 1999 to june 2001 are compared with those simulated by the ocean parallelise opa primitive equation model in two different configurations the atl6 configuration from the clipper project the whole atlantic domain with a 1 6 resolution and the prototype atlantique mediterranee pam configuration from the mercator project the north atlantic domain with 1 12 resolution while the observed 2 year mean transport into the gulf of mexico is 23 06 sv atl6 has a 5 year mean of 27 49 sv and pam has a 3 year mean of 29 06 sv apart from this discrepancy in the mean transport both simulations are able to reproduce well in structure and magnitude details of the mean current and its variability features like the yucatan current core and the deep countercurrents in the yucatan and cuban sides are both well reproduced as is the presence of a minimum surface current variability at the center of the channel the two principal empirical modes of current variability which are related to the passage of eddies through the channel are also reproduced by the simulations the observed and simulated transports above and below the 6 c isotherm show no coherency at any frequency except for a significant coherent peak at a period around 20 days which we interpret as a first baroclinic kelvin mode between the two layers as in the observations the shedding of eddies by the loop current in the simulations is preceded by periods of diminished negative horizontal vorticity flux into the gulf of mexico

origin ascent and oblique emplacement of magmas in a thickened crust an example from the cretaceous fangshan adakitic pluton beijing abstract the fangshan pluton in the western hills of beijing records a history of emplacement from primarily vertical ascent to oblique injection along a detachment fault thus the pluton provides a classic example answering the room problem this pluton and the nanjiao apophyse were produced by cretaceous magmatism that formed the regionally extrusive east china mesozoic igneous province the fangshan pluton includes two intrusive phases a 136 ma monzodiorite phase intruded by a 131 ma quartz monzodiorite phase rocks from both phases have chondrite normalized ree patterns enriched in lree and depleted in hree they have primitive mantle normalized trace element patterns with distinct negative nb and ti anomalies and high sr 1067 1348 ppm and low y 8 17 ppm with high sr y ratios 71 137 these features are characteristic of adakites and suggest that the magmas were derived by partial melting of the lower part of a thickened continental crust the pluton has magmatic foliations and lineation indicative of the intrusion of the earlier magmas slightly obliquely from se to nw the magmatic fabrics have enclave ratios rfmag rp of 3 0 3 5 asymmetric solid state deformational fabrics and strains rs for the northwestern 3 5 4 0 and southeastern parts 1 5 2 0 again suggest a later oblique injection of magmas from se to nw both the fangshan pluton and nanjiao apophyse suggest that magmas migrated most probably along the pre existing detachment fault such an emplacement is also supported by the aeromagnetic polarization data and strong deformation of the beiling syncline thus magma emplacement in the fangshan pluton probably involved creation of space by both faulting and wallrock strain

structure of a hypovolcanic acid complex inferred from magnetic susceptibility anisotropy measurements the western red hills granites skye scotland thulean igneous province the geochemistry and the injection mechanism of hypovolcanic ring dykes have been extensively studied but such is not the case for their internal fabric the tertiary western red hills epigranites of the isle of skye are a classic example of such intrusions using anisotropy of magnetic susceptibility measurements we present the first structural data of their internal magmatic fabric the magnetic foliations equated with the magmatic flow planes have strikes which roughly follow the walls of the different intrusions they dip steeply toward the convex wall of each intrusion the lineations or maximal magnetic susceptibility axes generally have shallow plunges except in the latest granite intrusion these structures appear to be related to the compressional deformation of each intrusion toward the end of its crystallization this shortening would be a consequence of a radial and compressive stress field acting after each injection of magma this radial stress field is interpreted as the effect of high magma pressures originating from the acid magma chamber underlying the ring dyke complex at a shallow depth

the contact zone of the rhum ultrabasic intrusion evidence of peridotite formation from magnesian magmas the eastern layered series of the rhum ultrabasic complex formed in situ and was not tectonically emplaced as previously suggested field relations along the contact show no evidence for the existence of a late marginal gabbro instead peridotite and allivalite layers can be traced to within 2 m of the surrounding partially melted country rocks local preservation of a chilled margin to one peridotite layer indicates that the parental magma consisted of an olivine tholeiite liquid carrying approximately 19 vol olivine crystals in suspension

magnetic properties of natural goethite iii magnetic behaviour and properties of minerals originating from goethite dehydration during thermal demagnetization summary the magnetic behaviour during stepwise demagnetization of a set of artificial samples containing well defined natural goethite from five localities chemical composition crystallite size and grain size are known is reported differential scanning calorimetry measurements indicated that the goethites converted to haematite between 260 and 360 c in this temperature range a small decrease in initial susceptibility and an additional remanence decay leading toward an extra bending point in the thermal decay curve are observed because titanomagnetite or pyrrhotite are absent in the samples this extra bending point is tentatively interpreted as being due to recrystallization of the minor haematite already present in the original goethite concentrates facilitated by water made available through the goethite haematite conversion at much higher temperatures at some 600 c a self reversal of the remanence is observed in most specimens the haematite derived from the goethites between 260 and 360 c appeared to be prone to further alteration at successive higher demagnetization temperatures chemical alterations in the magnetic mineral suite starting at temperatures from 380 c upward depending on the grain size of the original goethite were inferred from an increase in initial susceptibility the susceptibility behaviour showed an appreciable variation due to the creation of varying trace amounts of magnetite which appeared to be already present after the 400 c step after the final 685 c demagnetization step the magnetic mineralogy was usually dominated by magnetite the observed variation is thought to be the result of local within specimen differences in availability of the amount and possibly also the composition of the vapour phase the vapour phase is due to chemical reactions between the matrix constituents waterglass and calcite leading to a c02 h20 vapour phase reducing capacity necessary for the magnetite formation is envisaged to be created by decomposition of trace amounts of organic matter at relatively low temperatures up to some 400 c at higher temperatures over 550 c decomposition of traces of ferrous iron bearing clayminerals presumably donates the ferrous iron differences in the magnetite haematite ratio as well as in the properties of both minerals were assessed in some detail with more or less routine rockmagnetic methods acquisition of the isothermal remanent magnetization at room temperature in fields up to 11 2mam or 14t af demagnetization and low temperature cycling of the saturation remanence this was done after the 400 c step to study the magnetic properties of the newly formed haematite and after the 685 c step to evaluate the properties of the magnetite and more evolved haematite after the 400 c step the haematite appeared to be very fine crystalline and magnetically extremely hard its saturation remanence is considerably lower than that of well crystalline haematite after the 685 c step its hardness has decreased and its saturation remanence slightly increased chemical differences between the

on the north brazilian eddy field abstract the region of large eddies occurring off the coast of brazil between approximately 3 n 10 n is revealed in some detail by repeated temperature observations on the along shore sea lane by ships of opportunity augmented by one airborne xbt expendable bathythermograph survey the general pattern of the circulation implied by the temperature structure is similar to that indicated by past hydrographic measurements and drifter tracks in general a large anticyclonic eddy to the north 7 n 10 n as well as a southern eddy like feature 3 n 6 n appear to be permanent patterns of the western north equatorial circulation this pattern somewhat resembles that found in the somali basin during the southwest monsoon

late stage oxide growth associated with hydrothermal alteration of the western granite isle of rum nw scotland 1 the paleogene western granite isle of rum nw scotland represents a westward tilted shallow level felsic intrusion associated with the early growth stages of the classic early paleogene rum igneous centre rock magnetic data reveal an east to west variability in magnetic properties across the intrusion that is also reflected in petrographic and geochemical observations it is argued that the subtle intraplutonic variations in oxide grain size and composition observed in the western granite might be a common feature of shallow epizonal igneous intrusions as these mineralogical differences are not easily detectable without detailed rock magnetic study this research underscores the need for comprehensive rock magnetic studies when interpreting the postemplacement history of shallow level plutons paleomagnetic data indicate that the eastern part of the intrusion represents the shallower part of the exposed intrusion as further evidenced by roof pendants of lewisian gneiss and abundant drusy miarolitic cavities indicative of shallow emplacement in contrast the western part represents a deeper 900 m part of the intrusion as evidenced by the lack of roof pendants and existence of only minor drusy cavities rock magnetic data indicate that the dominant magnetic phase is low ti titanomagnetite with some titanomaghemite magnetic grain sizes range from pseudosingle domain in the west and multidomain in the east with a slight increase in ti content of the titanomagnetite phases in the east as revealed by curie point estimates we interpret these data to indicate that late stage subsolidus hydrothermal deuteric fluids associated with emplacement of the stage 2 rum layered suite produced secondary growth of fe ti oxide mineral phases along silicate grain boundaries in the eastern part of the intrusion the secondary oxide growth resulted in a slightly coarser magnetic grain size fraction and an increase in ti content of the titanomagnetite grains the deeper structural levels of the western part of the intrusion and its distance from the contact of the rum layered suite inhibited secondary oxide growth and thus this part of the intrusion preserves a primary magmatic oxide phase of a smaller magnetic grain size and near pure magnetite chemistry

worldwide distribution of continental rock lithology implications for the atmospheric soil co2 uptake by continental weathering and alkalinity river transport to the oceans 1 the silicate rock weathering followed by the formation of carbonate rocks in the ocean transfers co2 from the atmosphere to the lithosphere this co2 uptake plays a major role in the regulation of atmospheric co2 concentrations at the geologic timescale and is mainly controlled by the chemical properties of rocks this leads us to develop the first world lithological map with a grid resolution of 1 1 this paper analyzes the spatial distribution of the six main rock types by latitude continents and ocean drainage basins and for 49 large river basins coupling our digital map with the gem co2 model we have also calculated the amount of atmospheric soil co2 consumed by rock weathering and alkalinity river transport to the ocean among all silicate rocks shales and basalts appear to have a significant influence on the amount of co2 uptake by chemical weathering

origin of particulate organic carbon in the upper st lawrence isotopic constraints abstract seven sampling locations in the upper st lawrence river near the city of cornwall ontario canada including the main river and six near shore ecosystems a creek embayments and a wetland were studied in order to determine the origin of particulate organic carbon parameters studied included chlorophyll a chl a particulate organic carbon poc and dissolved inorganic carbon dic as well as the isotopic compositions of the latter two 13cpoc 13cdic the results show that in situ photosynthesis and detrital inputs are both significant contributors to the poc pool in the isolated embayments the former dominates during warm seasons with poc concentrations up to 2663 g l and chl a concentrations up to 26 1 g l near shore ecosystems have a wide range of 13cpoc values 31 5 to 16 3 but this variability is not reflected in the main channel there the 13cpoc signal is uniformly close to 27 in accord with estimates from earlier studies on the river s estuary this suggests that the poc contribution from near shore ecosystems is minor although the main channel has low chl a concentrations model calculations suggest that most of its poc originates from photosynthetic activity probably within the great lakes

δ13c pattern of dissolved inorganic carbon in a small granitic catchment the strengbach case study vosges mountains france abstract the transfers and origins of dissolved inorganic carbon dic were studied for a year in a soil spring stream system in the strengbach catchment vosges mountains france this 80 ha experimental research basin is located on the eastern side of the mountains at an altitude ranging from 883 to 1146 m a s l and is mainly covered by spruce 80 brown acid and podzolic soils developed on a granitic basement and as a result the dic originates solely from co2 generated by oxidation of soil organic matter the 13 c dic in catchment waters is highly variable from about 22 in the springs and piezometers to about 12 in the stream at the outlet of the catchment in the springs pronounced seasonal variations of 13 c dic exist with the dic in isotopic equilibrium with the soil co2 that has estimated 13 c of about 24 in winter and 20 in summer these seasonal variations reflect an isotopic fractionation that seems only induced by molecular diffusion of soil co2 in summer in stream water seasonal variations are small and the relatively heavy dic 12 on average is a result of isotopic equilibration of the aqueous co2 with atmospheric co2

controls on emplacement of the caledonian ross of mull granite nw scotland anisotropy of magnetic susceptibility and magmatic and regional structures abstract anisotropy of magnetic susceptibility ams was measured from 139 sites across the exposed portion of the caledonian ross of mull granite argyllshire nw scotland to investigate the internal architecture of the pluton field and petrographic observations support the results of the ams study and a complementary suite of rock magnetic experiments was used to quantify the magnetic mineralogy of the granite ams data reveal a fabric that records a partial tectonic overprint of an emplacement related magma inflow fabric the partially preserved inflow pattern indicates a south to north emplacement of subhorizontal sheets that coalesced to form a tabular pluton the ams data are remarkably consistent across the intrusion with clear north south strikes and trends dominating the magnetic foliation and lineation patterns respectively these ams fabrics are discordant to internal zonation in the granite in the southernmost part of the granite ams data are parallel to bedding cleavage orientations preserved in many large 100 m proterozoic moine blocks the scarcity of moine blocks in the northern part of the intrusion and the prevalence of randomly oriented stoped blocks suggest that this part of the intrusion is nearer to the ceiling of the pluton the partial tectonic overprint consistent with east west compression occurred during the latter stages of emplacement and mainly affected the younger granite facies rm2 while the oldest granite facies rm1 and certain magmatic structures diorite enclaves preserve the original emplacement fabric an alternative explanation interprets the magnetic lineations as an intersection fabric between a shallowly dipping emplacement fabric and a steep tectonic fabric we argue that emplacement was not associated with eastward orogenic collapse of the scandian moine nappes as proposed by previous workers but occurred either before orogenic collapse or during a period of compressional reactivation

lateral versus vertical emplacement in shallow level intrusions the slieve gullion ring complex revisited recent studies on shallow level arcuate intrusions have identified numerous examples of horizontal mineral fabrics these are commonly interpreted as reflecting considerable lateral flow during magma emplacement thus querying established semi vertical ring dyke models we question the recent lateral emplacement model proposed for the palaeocene slieve gullion ring complex ne ireland where the absence of steep fabrics in parts of the ring complex has been used to support a shallow semi horizontal sheet intrusion mechanism we argue that such simple flow models cannot be applied to explosive ring fissure eruptions and that fabric data alone do not warrant rejection of the ring dyke model moreover the apparent absence of steep intrusive contacts along the intrusion s perimeter is readdressed and we present numerous examples of outcrops 27 with steep sided geometries the camlough breccias are reinterpreted as the product of gas driven tuffisites injected along the active ring fault rather than of purely tectonic origin crucially the porphyritic microgranite and porphyritic rhyolite ring dyke rocks exhibit geochemical and petrographic signatures of contamination by the geographically restricted palaeozoic newry granodiorite and are best explained through crustal interaction vertically beneath the ring complex subsequently these silicic magmas rose into ignimbrite feeders along a caldera ring fault system that was emplaced into near surface vent filling breccias

response of circulation and heat transport in the north atlantic to changes in thermohaline forcing in northern latitudes a model study to avoid an explicit simulation of the overflows across the greenland scotland ridge many models of the large scale ocean circulation seek to include the net effect of the inflowing dense water masses by restoring temperature and salinity near the ridge to observed conditions in this paper the authors examine the effect of different datasets for the northern restoring condition in two versions eddy resolving and non eddy resolving of the model of the north and equatorial atlantic that has been developed in recent years as a community modeling effort for woce it is shown that the use of smoothed climatological fields of temperature and salinity south of the denmark strait leads to strong deficiencies in the simulation of the deep flow field in the basin a switch to actual hydrographic data from the denmark strait ignites a rapid dynamic response throughout the north atlantic affecting the transport and vertical structure of the deep western boundary current and by virtue of the jebar efffect the transport of the horizontal gyres meridional overturning and northward heat transport too weak in the cases with climatological boundary conditions increase to more realistic levels in the subtropical north atlantic the initial response to switches in the high latitude thermohaline forcing is mediated by fast waves along the westurn boundary leading to changes in the deep western boundary current in low latitudes after about two years in the non eddy resolving cast the initial timescale depends on the horizontal grid spacing of the model in the high resolution case the first signal reaches the equator in a few months the adjustment to a new dynamic quasi equilibrium involves kelvin waves along the equator and rossby wave in the interior and is attained in less than two decades throughout the north atlantic it is suggested that these fast dynamic adjustment processes could play an important role in possible fluctuations of the thermohaline circulation or transitions between different equilibrium states of the coupled ocean atmosphere system and may have determined the timescale of the observed climatic transitions before and during the last deglaciation