lead precipitation fluxes at tropical oceanic sites determined from 210 pb measurements concentrations of lead 210 pb and 210 po were measured in rain selected for least influence by local sources of contamination at several tropical and subtropical islands enewetak pigeon key florida and american samoa and shipboard stations near bermuda and tahiti ratios expressed as ng pb dpm 210 pb in rain were 250 900 for pigeon key assuming 12 adsorption for 210 pb and no adsorption for lead depending on whether the air masses containing the analyzed rain came from the caribbean or from the continent respectively about 390 for the northern sargasso sea downwind from emissions of industrial lead in north america 65 for enewetak remote from continental emissions of industrial lead in the northern hemisphere and 14 near tahiti a remote location in the southern hemisphere where industrial lead emissions to the atmosphere are much less than in the northern hemisphere the american samoa sample yielded a higher ratio than tahiti the reason for this is not clear but may be due to local pb sources the corresponding fluxes of lead to the oceans based on measured or modeled 210 pb precipitation fluxes are about 4 ng pb cm 2y for tahiti 10 for enewetak and 270 for the sargasso sea site and between 110 to 390 at pigeon key

reach and geometry of dynamic gas driven fractures abstract dynamic gas fracturing is a well stimulation technique that is able to create multiple fractures emanating from a wellbore it operates by pressurizing at rise times and peak pressures intermediate between conventional hydraulic fracturing and explosive fracturing two consecutive processes operate during this fracturing process i generation and propagation of a dynamic stress wave that overpowers the static stress field and creates multiple radial fractures around borehole followed by ii quasi static pressurization and further extension of those starter fractures by the expanding gas dynamic analysis is first performed to follow the evolution of the stress wave propagating from the borehole the radial r distribution of peak tensile hoop stress diminishes as 1 r with the power exponent asymptoting to 2 as the loading rate decreases this rapid attenuation generally limits the length of the body wave generated radial fractures to several borehole radii the gas loading of the borehole wall is followed by permeation of the gas pressure into the newly created radial fractures linear elastic fracture mechanics lefm perturbation analysis shows that a regular distribution of multiple radial starter cracks will preferentially propagate the longer cracks at the expense of the shorter cracks that will arrest and snap shut this system naturally selects of the order of six dominant fractures that may grow in unison until the in situ stress field reasserts control as the fractures lengthen this restricts the maximum number of the dominant fractures to of the order of six at the conclusion of treatment a common observation in both in situ and laboratory experiments

new dates 415 ma for the etive dyke swarm and the end of the caledonian orogeny in the sw grampian highlands of scotland new laser stepwise heating 40 ar 39 ar dates 415 1 8 and 414 2 ma from the etive dyke swarm in the sw grampian highlands of scotland indicate that the dykes are 10 20 ma older than previously assumed the dykes constitute the final phase of the late caledonian granites in the region which themselves define the end of the caledonian orogeny therefore these dates can be taken as the end of the orogeny in this area the dates show a temporal link between the etive magmatism and early precious metal mineralization at tyndrum as well as emphasizing the nw to se diachronous nature of the end of caledonian magmatism across scotland

regression analysis of zonally narrow components of the mjo abstractrecent works have demonstrated that eastward propagating features smaller than zonal wavenumber 3 but with spatial structures similar to those of the madden julian oscillation mjo frequently develop over the indo pacific warm pool these signals are characterized by periods shorter than 4 weeks but since they occur as part of a spectral peak of the mjo they might be characterized by similar physics these zonally narrow features occur at any phase of traditionally defined 30 60 day mjo events but they occur most frequently in its active convective phase this work presents a linear regression analysis based on filtering in the wavenumber frequency domain to compare such signals with traditionally defined mjos and 15 30 m s 1 convectively coupled kelvin waves results show that the trough collocated with the easterly wind anomaly extends westward into the region of lower tropospheric westerly wind and deep convection in the zonally narrow slow signals and mjos the fast kelvin waves have a ri

mechanics of fluid driven fracture growth in naturally fractured reservoirs with simple network geometries 1 a numerical model has been developed for fluid driven opening mode fracture growth in a naturally fractured formation the rock formation contains discrete deformable fractures which are initially closed but conductive because of their preexisting apertures fluid flow that develops along fractures depends on fracture geometry defined by preexisting aperture distribution offsets along a fracture path and intersections of two or more fractures the model couples fluid flow elastic deformation and frictional sliding to obtain the solution which depends on the competition between fractures for permeability enhancement the fractures can be opened by fluid pressure that exceeds the normal stress acting on them and by interactions with intersecting closed fractures experiencing coulomb type frictional slip the newtonian fluid is assumed to flow through the conductive fractures according to a lubrication equation that relates the cube of an equivalent hydraulic aperture to fracture conductivity the rock material is assumed to be impermeable and elastic this paper provides the governing equations for the multiple fracture systems and the solution methods used flow distribution and fracture growth in conductive fracture sets are simulated for a range of geometric arrangements and hydraulic properties numerical results show that elastic interaction between fracture branches plays a controlling role in fluid migration although initial apertures can give rise to a preferential fluid flow direction during the early stage in the presence of offsets fracture segments subject to strong compression are difficult to open hydraulically and their resulting smaller permeability can increase overall upstream fracture pressure and opening the patterns of fluid flow become more complicated if fractures intersect each other a portion of injected fluid is lost into closed empty fractures that cut across the main hydraulic fracture and this delays the pressure increases required for fracture growth past the crosscutting fracture the nonlinear fluid loss rate depends on the geometric complexities of the fracture sets and on the fluid viscosity sometimes fracture growth can be accelerated by the fast fluid transport along an intersected relatively conductive natural fracture

the record of magnetic mineral and heavy metal deposition at regent street bog fredricton new brunswick canada measurements of isothermal remanence and of heavy metal concentrations are presented for two recent moss increment dated cores from hummocks of ombrotrophic peat from regent street bog fredricton new brunswick canada the magnetic record from both profiles appears to be closely related to the documented history of industrial and urban development in the region the heavy metal record displays greater variation between elements and profiles and mirrors less consistently the documentary record some vertical mobility within the peat column is inferred for all the metal elements measured

atmospheric input of heavy metals chronicled in lake sediments of the algonquin provincial park ontario canada the flux of pb zn cu ni and cd into ten remote lakes in the algonquin provincial park of ontario has been determined deviation from constant sedimentation rates in recent sediments depicted in the 210pb profiles can be related to human activities within the last 100 years sedimentation rates in these softwater lakes vary from 0 5 mm yr 1 62 g m 2 yr 1 to 2 9 mm yr 1 190 g mm 2 yr 1 the corresponding present day metal flux rates for ni cu pb zn and cd are 0 6 8 4 0 7 9 4 3 7 43 5 5 0 50 3 and 0 07 0 74 mg m 2 yr 1 respectively there is an overall 2 fold enrichment for ni cu zn and cd in surficial sediments together with a 25 fold increase for pb the gyttja contain 25 50 organic matter with organic c organic n ratios which strongly suggest high influx of allochthonous plant debris

recent estuarine sedimentation rates from shallow inter tidal environments in western scotland implications for future sea level trends and coastal wetland development during the mid late holocene large sections of the scottish coastline have been characterized by falling relative sea levels resulting from differential glacio isostatic uplift of this region of northern britain the complex interplay between crustal and sea level movements continues to influence the morphological development of the scottish coast a number of geophysical models predict ongoing uplift of the scottish landmass however a number of recent studies based upon the analysis of satellite altimetry data indicate a late 20th century acceleration in the rate of eustatic sea level rise detailed geochemistry radiometric dating and diatom analysis on selected sediment cores from four mature coastal marsh environments in argyll western scotland provides an opportunity to investigate the linkages between twentieth century crustal movements eustatic sea level rise and recent rates of sedimentation recorded within marsh sediments across the proposed scottish glacio isostatic uplift dome solid phase major and trace element geochemistry has been used to examine the extent to which post depositional physical disturbance and or chemical reactions may have influenced the reliability of the radiometric dating methods geochemical data indicate that the evolution of these marsh environments has not been significantly influenced by physical disturbance and overall the supply of minerogenic material to the marshes has been quite uniform vertical distributions of 210pbexcess and 137cs activity have been measured and used to develop models of recent marsh vertical accretion dating of the cores reveals subtle variations in the rates of sediment accumulation over the last c 70 years between sites for much of the last hundred years or so sedimentation rates have been in good overall agreement with various estimations for sea level rise although at the more easterly sites these estimates are generally exceeded however quasi equilibrium between marsh sedimentation and sea level rise for much of the twentieth century is indicated from the diatom analysis over the most recent period of marsh development 10 years a significant increase in the rate of surface sedimentation is recorded at all sites across the study area diatom analysis of these surface layers reveals an increase in the relative abundance of marine polyhalobous taxa in the near surface sediments this signifies a very recent increase in the rate of regional relative sea level rise indicating that a regional threshold in coastal forcing has now been exceeded these findings provide clear evidence that recent relative sea level rise is now outpacing estimated rates of glacio isostatic adjustment gia across the proposed scottish uplift dome

age of the ballachulish and glencoe igneous complexes scottish highlands and paragenesis of zircon monazite and baddeleyite in the ballachulish aureole u pb zircon ages are presented for the ballachulish igneous complex 207 pb 206 pb age 427 1 ma 206 pb 238 u age 423 0 3 ma and glencoe volcanic complex 207 pb 206 pb age 406 6 ma of the scottish highlands these ages are significantly more precise than pre existing age constraints and discriminate a previously unresolved age difference of c 20 ma between the two complexes this difference in age provides an explanation for the c 10 km difference in crustal level between the two magmatic events and constrains exhumation rates for the argyll region to be on average c 0 4 km ma 1 over the period c 425 405 ma with improved age constraints on the ballachulish igneous complex in place the associated metamorphic aureole is used as a type locality to investigate the metamorphic behaviour of the u bearing accessory minerals baddeleyite zircon and monazite baddeleyite formed in impure dolomites by the reaction of detrital zircon with dolomite and gives the same u pb age as the intrusive complex consistent with its contact metamorphic origin detrital zircon appears to be inert throughout much of the metamorphic aureole with contact metamorphic zircon growth being restricted to migmatite grade rocks a possible exception is the development of enigmatic very narrow overgrowths at temperatures between c 500 and 600 c monazite exhibits a variety of textures in lower grade parts of the aureole

elemental evidence for crustal contamination of mantle derived caledonian syenite by metasediment anatexis and magma mixing abstract this paper presents elemental evidence that the mafic unit of the caledonian glen dessarry syenite northern scotland u k has been variably contaminated with material derived from the surrounding moine metasediments uncontaminated portions are shown to have trace element abundances and ratios similar to those of the central leucosyenite and island arc high k or shoshonitic magmas from present day oceanic settings by comparison contaminated samples display grossly disturbed trace element patterns including higher u th zr hf nb ta and heavy rare earths lower ba and sr and negative eu anomalies these features are matched in the elemental systematics of the moinian envelope but bulk incorporation of excessive amounts of metasediment would be required to reproduce the observed perturbations in especially the high field strength elements xenoliths within the contaminated mela syenites and parts of the adjacent country rock show petrographic evidence of melting since the source composition moine metasediment and residual mineralogy xenoliths are known simple geochemical models of melting and subsequent mixing with uncontaminated melasyenite melt have been computed the results provide close approximations to the observed geochemistry of the contaminated melasyenites particularly for the ree s moreover the residues of this hypothetical process have similar ree patterns to several samples of metasediment from immediately adjacent to the syenite contact nevertheless contemporaneous crystal liquid separation is required to explain the full range of elemental data contamination by this mechanism of melting followed by magma mixing is not immediately apparent in the major element relationships of the two melasyenite groups this seems to be the result of the approximate colinearity of the established melasyenite crystal fractionation path and the proposed granitic contaminant and may be a more general problem in the recognition of in situ contamination with metasedimentary melts in plutons whose fractionation itself proceeds towards a broadly granitic terminus

land use change and erosional history in a lake catchment system on the canadian prairies abstract the introduction of agriculture in the late 1800s and early 1900s brought about many changes in the natural prairie landscape of western canada the objective of this research project is to evaluate landscape response to land use change by relating observed changes in the sedimentary record of a lake drainage basin to documented land use change that has occurred since the onset of settlement a 52 cm lake sediment core was sectioned into 1 cm layers the sediment was separated into allogenic and authigenic fractions using a wet chemical extraction technique close interval 210pb dating enabled the calculation of sediment and elemental influx rates prior to european settlement erosion rates were low

on the interpretation of eof analysis of enso atmospheric kelvin waves and the mjo abstractempirical orthogonal function eof analysis is frequently applied to derive patterns and indexes used to identify and track weather and climate modes as expressed in state variables or proxies of convection individual eofs or pairs of eofs are often taken to be a complete description of the phenomenon they are intended to index at the same time in the absence of projection of the phenomenon onto multiple eofs yielding multiple similar eigenvalues each eof is often assumed to represent a physically independent phenomenon this project analyzed the leading eofs of the earth s skin temperature on the equator and outgoing longwave radiation olr anomalies filtered for atmospheric equatorial kelvin waves results show that the leading two eofs of the skin temperature data including east pacific el nino and el nino modoki frequently evolve as a quadrature pair during el nino events even though the first eof explains roughly 6 times as much variance as the second they together diagnose the longit

copper and manganese in hemipelagic sediments at 21 n east pacific rise diagenetic contrasts abstract relatively rapidly accumulating 7 cm kyr and organic rich 1 5 corg epr sediments near 21 n are characterized by pronounced nitrate reduction in the upper decimetre and by an enrichment of mn and increased fe al ratio in surficial sediments joint consideration of solid phase and pore water data indicates that the distributions of both mn and fe in the sediments are in disequilibrium with their respective pore water profiles precipitation of upward diffusing mn and fe is occurring at present below the enriched horizons producing perched enrichments indicative of non steady state diagenesis consideration of a high resolution 14c age vs depth curve and a decrease toward the interface from 1 51 to 1 37 wt over the top 7 cm of the corg profile suggests that the diagenetic disequilibrium evident for mn and fe may be due to a geologically recent decrease in productivity such a decrease would be manifest in the sediments by a downwardly migrating oxidation front which would progressively erode the mn and fe pore water profiles producing the existing decoupled surface enrichments in contrast to mn the distribution of cu has apparently not been perturbed by non steady state phenomena a first order decrease with depth of the dissolved copper concentration is accompanied by a first order increase in solid phase cu application of a diffusion reaction model to these data predicts a sedimentation rate of 8 cm kyr 1 which agrees well with the 14c determined rate of 7 3 cm kyr 1 implying that the pore water and solid phase distributions are in diagenetic equilibrium available evidence suggests that the major host for non detrital cu in hemipelagic sediments is authigenic nontronite because this phase appears to form slowly there may be a kinetic constraint on the amount of copper which can be incorporated authigenically in rapidly accumulating hemipelagic deposits support for this hypothesis is given by the observed inverse proportionality between the sedimentation rate and the concentration of non detrital cu in surface sediments from at least seven widespread locations in the eastern pacific it is suggested that the variation observed in the salt and caco3 free cu concentration in hemipelagic sediments is a consequence largely of the residence time of sediments at the surface where high dissolved cu concentrations prevail

terrane and basement discrimination in northern britain using sulphur isotopes and mineralogy of ore deposits this study of four well characterized and adjacent terranes in northern britain outlines the sulphur isotope variations assesses the overall importance of crustal and mantle sulphur and presents a model that can be applied to terrane distinction throughout the north atlantic caledonides the characteristics of metal components within the mineralization provide additional information that can be related to the nature of underlying basement and events from the onset of sedimentation to the cessation of mineralization within stratigraphically linked packages of rock the delta 34s data show that the dominant crustal units in each terrane whether upper crustal sediments or cratonic basement provide the main alternative sulphur source to the mantle and act also as the main contaminant of subcrustal melts the delta 34s values of granitoid related mineralization are either within the subcrustal melt range of 3 per thousand to 3 per thousand or deviate toward the values of major crustal units in the terrane i e toward 34s depletion in the southern uplands and toward 34s enrichment in the lakesman and grampian terranes more complex mineralization in the northern highland terrane is linked to the presence of thick north atlantic craton beneath upper crustal metasediments across the region the vein systems beyond the influence of magmatic components represent homogenized sulphur metals and fluids from local upper crustal units the sulphur isotope data and style of mineralization for the british terranes are compared with terranes of similar age along strike in eastern canada revealing notable correlations

do s type granites commonly sample infracrustal sources new results from an integrated o u pb and hf isotope study of zircon in contrast to i type granites which commonly comprise infracrustal and supracrustal sources s type granites typically incorporate predominantly supracrustal sources the initial aim of this study was to identify the sources of three scottish caledonian 460 ma s type granites kemnay cove and nigg bay by conducting oxygen u pb and hf isotope analyses in zircon in order to characterise one potential end member magma involved in the genesis of the voluminous late caledonian 430 400 ma i type granites field whole rock geochemical and isotopic data are consistent with the generation of the s type granites by melting their dalradian supergroup country rocks while hf isotope compositions of magmatic zircon u pb data of inherited zircons and high mean zircon 18o values of 9 0 2 7 2sd and 9 8 2 0 for the kemnay and cove granites support this model the nigg bay granite contains zircons with much lower 18o values 6 8 2 1 similar to those found in scottish i type granites this suggests that the nigg bay granite contains low 18o material representing either altered supracrustal material or more likely an infracrustal source component with mantle like 18o mixing trends in plots of 18o vs ehf for s type granite zircons indicate involvement of at least two sources in all three granites this pilot study of scottish caledonian s type granites demonstrates that while field and whole rock geochemical data are consistent with local melting of only supracrustal sources the oxygen isotopic record stored in zircon reveals a much more complex petrogenetic evolution involving two or more magma sources

trace metal deposition and mobility in the sediments of two lakes near sudbury ontario the accumulation and mobility of fe mn al cu ni and pb in the sediments of two lakes clearwater ph 4 5 and mcfarlane ph 7 5 near sudbury ontario have been investigated the al cu and ni concentrations are expectedly relatively high in the overlying waters of clearwater lake and much lower for al and cu in mcfarlane lake the low trace metal concentrations found in the anoxic porewaters of clearwater lake could be explained by a sharp increase in porewater ph concomitant with so42 reduction and h2s production within the first 1 2 cm of the sediments which has conceivably led to the precipitation of mineral phases such as al oh 3 nis and cus in both lakes fe concentrations in anoxic porewaters appear to be controlled by fes and or feco3 formation solubility calculations also indicate mnco3 precipitation in mcfarlane lake in clearwater lake however both porewater and total mn were relatively low a possible result of the continuous loss of mn ii through the acidic interface it is suggested that upwardly decreasing total mn profiles resulting from the removal of mn from the top sediment layers under acidic conditions may constitute a reliable symptom of recent lake acidification the downward diffusion of ai cu and ni from the overlying water to the sediments has been estimated from their concentration gradients at the interface and compared to their total accumulation rates in the sediments in both lakes the diffusion of al is negligible compared to its accumulation rate however diffusion accounts for 24 52 of the accumulation of cu in the sediments of clearwater lake but appears negligible in mcfarlane lake the downward diffusive flux of ni is important and may explain 76 161 of the estimated ni accumulation rate in clearwater lake and 59 in mcfarlane lake the porewater cu and ni profiles suggest that the subsurface sedimentary trace metal peaks observed in clearwater lake as in other acid lakes may not be caused by sediment leaching or by a recent reduction in sedimentation but may have a diagenetic origin instead diffusion to the sediments thus appears to be an important and previously overlooked trace metal deposition mechanism particularly in acid lakes

sr o and pb isotope evidence for origin and evolution of etive igneous complex scotland a multi isotope approach has been applied to the origin of one of the largest and latest newer granite complexes of the scottish caledonides contributions from both mantle and unexposed late proterozoic lower continental crust are recognized indicating that granite magmatism is a mechanism for both primary crustal growth and reworking of older crustal rocks

classification seasonality and persistence of low frequency atmospheric circulation patterns abstract orthogonally rotated principle component analysis rpca of northern hemisphere 1 month mean 700 mb heights is used to identify and describe the seasonality and persistence of the major modes of interannual variability the analysis is detailed and comprehensive in that 1 a high resolution approximately equal area 358 point grid is used for the virtually maximum possible 35 year period of record 2 a positive bias in the nmc data base in the early 1950s in the subtropics is largely eliminated for the first time and 3 homogeneous separate analyses of each month of the year are carried out detailing the mouth to month changes in the dominant circulation patterns winter results are similar to those of other recent rpca and teleconnection studies except that some less obvious patterns are identified and further detail of the better known patterns is provided two north south dipole patterns are found over the pacific ocean west pacific oscillation and east pacific pattern and over the atla

systematic variation in chemistry and nd sr isotopes across a caledonian calc alkaline volcanic arc implications for source materials abstract sr and nd isotope compositions and major and trace element chemistry are reported for 42 primitive calc alkaline lavas from the siluro devonian scottish old red sandstone northwestward increases in concentrations of sr ba k p and lree associated with northwest subduction of iapetus ocean crust 1 are not accompanied by change in rb th or ti group elements these relationships show that the spatial variation cannot be simply the result of change in the degree of partial melting with depth initial 143 nd 144 nd expressed as e nd at 410 ma shows a wide range from 6 4 to 3 7 and in contrast to e sr decreases markedly to the northwest samples from the midland valley show a strong anticorrelation between e nd and e sr with the correlation band offset to more radiogenic compositions than that defined by modern oceanic volcanic rocks the mantle array such an offset is common in modern volcanic arc magmas but cannot be explained by addition to the overlying mantle of a single component enriched in radiogenic sr derived from subducted lithosphere southwest highland lavas lie in a completely separate field on an e sr e nd diagram most fall within the mantle array but samples with highest concentrations of sr etc are offset to less radiogenic compositions consideration of the chemical and isotopic relationships with respect to several models of crustal contamination shows that the additional lree in the northwest cannot be derived from a crustal source the data imply the existence beneath scotland of a large region of mantle with time integrated lree enrichment parts of which may have anomalous nd sr isotopic compositions less radiogenic than the mantle array midland valley lavas are probably derived from a long term lree depleted mantle source modified by interaction with subducted oceanic lithosphere the coexistence of two mantle sources with differing histories is best explained by vertical stratification with deeper more lree enriched layers accessible only to magmas formed at great depth in a subduction zone the spatial variation probably in part reflects this mantle layering and in part the operation of some mantle zone refining process that permits efficient concentration of incompatible elements from large regions of mantle

contrasting eastern pacific and central pacific types of enso abstract surface observations and subsurface ocean assimilation datasets are examined to contrast two distinct types of el nino southern oscillation enso in the tropical pacific an eastern pacific ep type and a central pacific cp type an analysis method combining empirical orthogonal function eof analysis and linear regression is used to separate these two types correlation and composite analyses based on the principal components of the eof were performed to examine the structure evolution and teleconnection of these two enso types the ep type of enso is found to have its sst anomaly center located in the eastern equatorial pacific attached to the coast of south america this type of enso is associated with basinwide thermocline and surface wind variations and shows a strong teleconnection with the tropical indian ocean in contrast the cp type of enso has most of its surface wind sst and subsurface anomalies confined in the central pacific and tends to onset develop and decay in situ

hydromechanical bond based peridynamic model for pressurized and fluid driven fracturing processes in fissured porous rocks abstract in this paper a new fully coupled hydromechanical model in terms of bond based peridynamics is proposed to simulate the pressured and fluid driven fracturing process in fissured porous rocks a fissured porous rock model is established based on the classic biot poroelasticity theory the coupled hydromechanical bond based peridynamic model consists of two parts fluid flow and mechanical deformation a governing equation of fluid flow in terms of peridynamics is established along with an integral differential equation of motion in the fissured porous medium moreover a fracture criterion in the hydromechanical bond based peridynamic model is introduced to simulate the failure caused by high fluid pressure finally four numerical simulations are conducted to verify the accuracy and correctness of the proposed model

the proterozoic hustad igneous complex a low strain enclave with a key to the history of the western gneiss region of norway the hustad igneous complex hic is a concentrically zoned high k calc alkaline intrusive complex with a core of quartz monzonite and granite surrounded successively by monzodiorite and pyroxenite preserved in a 10 km2 lens within the strongly caledonised western gneiss region wgr of norway upper intercept u pb zircon ages of 1654 1 and 1653 2 ma obtained from the granite and the monzodiorite respectively overlap with a rb sr whole rock age of 1656 49 ma i r 0 70193 0 0009 mswd 6 6 obtained from the felsic members of the complex and a sm nd whole rock age of 1555 180 ma i r 0 51067 13 mswd 3 3 the u pb age of 1654 1 ma is interpreted to date the time of intrusion a 50 m thick dolerite dyke that can be followed for almost 4 km across the hic yields a u pb zircon and baddeleyite age of 1251 3 ma the dyke also contains a secondary polycrystalline zircon generation which together with baddeleyite defines a lower intercept age of 384 9 ma the caledonian events were also marked by the emplacement of a swarm of pegmatites which crosscut all the other units and provide a u pb zircon age of 401 1 ma a rb sr whole rock age for the pegmatites is older at 452 26 ma i r 0 7105 mswd 4 3 indicating some initial isotopic heterogenity and formation of the pegmatites from material with a long crustal residence time a concordant u pb monazite age of 390 2 ma from the pegmatite and the above 384 9 ma lower intercept age date metamorphism caused by percolating fluids post pegmatite deformation transformed the complex along shear zones into gneisses indiscernible from the surrounding gneisses the hic is characterised by high mg numbers 0 39 0 80 high ni and cr values and depletion of nb and ta relative to lil elements phenocrysts of ortho and clinopyroxene have high concentrations of cr supporting the cr rich nature of the complex the suite is lree enriched has a fractionated and u shaped ree pattern cen 90 143 ybn 12 40 end values ranging from 0 0 to 2 7 and the felsic members display weak positive eu anomalies while the pyroxenite has a negative eu anomaly the complex bears a geochemical resemblance to the late tectonic high ba sr granite complexes of west scotland and particularly to their volcanic counterparts the mg rich old red sandstone andesites overall the data suggest generation of the suite in a subduction environment from material derived by melting of a recently enriched but previously long term lree depleted mantle the hic is one of the few well preserved remnants of the igneous protoliths of the 1686 1640 ma gneisses that make up the wgr in fact the pyroxenite is compositionally identical to orthopyroxene eclogite found as lenses in the surrounding gneisses and forms a likely protolith to this enigmatic rock the metamorphism had little influence on the rb sr and sm nd systems of the felsic rocks but it appears to have affected more strongly those in the mafic rocks probably as a result of the more intense mineralogical transformations and metasomatic loss of rb and lree during high grade metamorphism

the crustal evolution of central scotland and the nature of the lower crust pb nd and sr isotope evidence from caledonian granites abstract the identification of the wide range of isotope characteristics and chemical heterogeneities within the sub continental mantle has demanded a re appraisal of the crustal evolution of many terrains a recent publication has suggested that such heterogeneities may also exist beneath scotland 1 this together with inadequate knowledge of the age and geochemical nature of the lower crust has fuelled the controversy of the relative involvement of mantle and crust in the formation of the caledonian granites 2 8 this paper reports 31 pb isotope analyses on feldspars from six granite complexes and four new nd and four new sr whole rock analyses these data demonstrate that a major source of the granites is the lower crust which is characterised by relatively unradiogenic sr pb and nd it is by inference old depleted in u and th and has a low th u ratio isotopic constraints suggest the sub grampian central scottish lower crust is dominated by grenville ca 1200 1000 ma age rocks in addition to an older scourian ca 2700 ma component the major episodes of crustal growth in central scotland occurred during the scourian and grenville orogenies the caledonian orogeny produced only limited crustal addition

210pb and 137cs in air and soils measure the rate and vertical profile of aerosol scavenging we have determined the deposition rates of sup 210 pb and sup 137 cs from the atmosphere to the landscape of the eastern and mid western united states by measuring their inventories in core samples of undisturbed soils the mean inventories in lowland sites are 27 7 dpm cm sup 2 for sup 210 pb and 21 8 dpm cm sup 2 for sup 137 cs as of january 1984 the mean annual concentration of sup 210 pb in surface air at the 9 sites of the sure network decreases smoothly from about 0 060 dpm m sup 3 near the mississippi river to about 0 030 near the atlantic coast the ratio of deposition rate to surface air concentration is 0 62 0 03 cm s sup 1 for sup 210 pb and 1 36 0 08 cm s sup 1 for sup 137 cs using the activity vs altitude profiles of moore et al 1973 for sup 210 pb and the fission product nuclide sup 90 sr we calculate tropospheric aerosol mean residence times for sup 210 pb and sup 137 cs of 4 8 and 5 5 days respectively this near equality precludes a rapid decrease of the aerosol scavenging rate constant in the mid troposphere the sup 137 cs sup 210 pb ratios in soils from elevations above 1000 m in the appalachian mountains aremore lower than those in adjacent lowland soils indicating the preferential removal of aerosols from the lower layer of the troposphere presumably by cloud droplet impaction or by seeder feeder clouds less

the protocontinental nature and regional variability of the central metasedimentary belt of the grenville province lead isotope evidence the lead isotopic compositions of sulphide samples mainly galenas from a representative set of mineral deposits within the central metasedimentary belt of the grenville province have been determi

particulate metal speciation in surficial sediments from loch dee southwest scotland u k the geochemical partitioning of ten elements in stratified holocene sediments from loch dee southwest scotland has been established by use of a five stage sequential extraction procedure samples from below 15 cm sediment depth show minimal evidence of modification by anthropogenic contamination or active diagenesis and hold fe mg cu cd co pb and ni primarily in detrital silicates or organic complexes while mn ca and zn reside largely in adsorbed and reducible oxide phases in the uppermost ca 15 cm of sediment enhanced total concentrations of zn cu and pb reflect increased atmospheric deposition during the postindustrial period of these metals only pb displays any notable adjustment of partitioning in the enriched zone showing disproportionate accumulation in labile oxides and organic pb phases the lack of pb and zn carbonates in the contaminated horizon may reflect inherent thermodynamic instability under the acid surface and pore water conditions of loch dee increments to total mn and co in the surficial ca 5 cm of sediment are attributable to the accumulation of secondary oxides and adsorbed species consistent with precipitation from the interstitial pore waters across a sedimentary redox front the presence of metals such as zn and cd in soluble or acid volatile phases in the interfacial sediment has implications for the future management of the loch dee basin with leaching into the overlying waters likely given the continuation of current trends of lake acidification

subduction related shoshonitic and ultrapotassic magmatism a study of siluro ordovician syenites from the scottish caledonides syenites are important or predominant components of several plutonic complexes emplaced between 456 and 415 ma along the nw margin of the caledonian orogenic belt adjacent to the lewisian foreland in w and nw scotland although there are in detail chemical differences between the syenites from each centre they form a well defined compositional group overall ratios amongst their trace elements especially very high values of la nb are quite different from those trachytes and syenites formed by fractional crystallisation of ocean island basalts and their continental equivalents emplaced in regions of anorogenic crustal tension instead the scottish caledonian syenites closely resemble chemically the fractional crystallisation residua of potassic subduction related magmas such as the shoshonitic series a comendite minor intrusion from a swarm associated with the loch borralan and loch ailsh syenitic complexes is remarkably similar in composition to recent obsidian from the shoshonitic volcano of lipari in the aeolian arc published sr and pb isotopic ratios preclude a significant component of either upper proterozoic moine schists or lower crust granulite facies archaean lewisian or proterozoic grenvillian gneisses in all these syenites except in local syenitic facies of the glenelg ratagain complex fractional crystallisation appears to be the mechanism by which the liquids which formed these syenites evolved from basic parental magmas the phases involved in this process may have included plagioclase alkali feldspar pyroxene amphibole biotite garnet fe ti oxide sphene allanite apatite zircon and zirconolite and therefore all the ratios amongst even the so called incompatible elements may have changed during the evolution of the leucocratic magmas nevertheless a detailed study of the glen dessarry complex shows that the changes are insufficient to disguise the geochemical nature of the parental magmas these appear to be picritic shoshonite mgo 15 ni 400ppm la yb 20 la nb 5 for the glen dessarry loch borralan and loch ailsh syenites and picritic ultrapotassic magmas mgo 15 ni 400 ppm la yb 60 la nb 7 such as would crystallise to minettes for the loch loyal and glenelg ratagain syenites mafic shoshonites were erupted amongst the 410 ma lome lavas of this region and also occur as widespread approximately contemporaneous volcanic feeder plugs minettes of similar age are also common as dykes in nw scotland numerous large tonalite granite complexes with minor diorites and gabbros were emplaced in w and nw scotland between 435 and 400 ma these are generally acknowledged to be mixtures of magmas from crustal and mantle sources their more mafic members show compositional features such as very high ba and sr which group them with the rare syenites and the lorne lavas of the same region into a distinctive geochemical province within which shoshonitic and allied magmas were the mantle derived component two models are presented to account for the generation of strongly potassic subduction related magmas several hundred km behind a nw directed subduction zone or during the period immediately following continental collision

natural fractures in the barnett shale and their importance for hydraulic fracture treatments gas production from the barnett shale relies on hydraulic fracture stimulation natural opening mode fractures reactivate during stimulation and enhance efficiency by widening the treatment zone knowledge of both the present day maximum horizontal stress which controls the direction of hydraulic fracture propagation and the geometry of the natural fracture system which we discuss here is therefore necessary for effective hydraulic fracture treatment design we characterized natural fractures in four barnett shale cores in terms of orientation size and sealing properties we measured a mechanical rock property the subcritical crack index which governs fracture pattern development natural fractures are common narrow 0 05 mm 0 002 in sealed with calcite and present in en echelon arrays individual fractures have high length width aspect ratios 1000 1 they are steep 75 and the dominant trend is west northwest other sets trend north south the narrow fractures are sealed and cannot contribute to reservoir storage or enhance permeability but the population may follow a power law size distribution where the largest fractures are open the subcritical crack index for the barnett shale is high indicating fracture clustering and we suggest that large open fractures exist in clusters spaced several hundred feet apart these fracture clusters may enhance permeability locally but they may be problematic for hydraulic fracture treatments the smaller sealed fractures act as planes of weakness and reactivate during hydraulic fracture treatments because the maximum horizontal stress trends northeast southwest and is nearly normal to the dominant natural fractures reactivation widens the treatment zone along multiple strands

modes of climate variability synthesis and review of proxy based reconstructions through the holocene abstract modes of climate variability affect global and regional climates on different spatio temporal scales and they have important impacts on human activities and ecosystems as these modes are a useful tool for simplifying the understanding of the climate system it is crucial that we gain improved knowledge of their long term past evolution and interactions over time to contextualise their present and future behaviour we review the literature focused on proxy based reconstructions of modes of climate variability during the holocene i e the last 11 7 thousand years with a special emphasis on i proxy based reconstruction methods ii available proxy based reconstructions of the main modes of variability i e el nino southern oscillation pacific decadal variability atlantic multidecadal variability the north atlantic oscillation the southern annular mode and the indian ocean dipole iii major interactions between these modes and iv external forcing mechanisms related to the evolution of these modes this review shows that modes of variability can be reconstructed using proxy based records from a wide range of natural archives but these reconstructions are scarce beyond the last millennium partly due to the lack of robust chronologies with reduced dating uncertainties technical issues related to proxy calibration and difficulty elucidating their stationary impact or not on regional climates over time while for each mode the available reconstructions tend to agree at mutidecadal timescales they show notable disagreement on shorter timescales beyond the instrumental period the reviewed evidence suggests that the intrinsic variability of modes can be modulated by external forcing such as orbital solar volcanic and anthropogenic forcing the review also highlights some modes experience higher variability over the instrumental period which is partly ascribed to anthropogenic forcing these features stress the paramount importance of further studying their past variations using long climate proxy records for the progress of climate science

slurry flow gravitational settling and a proppant transport model for hydraulic fractures the goal of this study is to analyse the steady flow of a newtonian fluid mixed with spherical particles in a channel for the purpose of modelling proppant transport with gravitational settling in hydraulic fractures the developments are based on a continuum constitutive model for a slurry which is approximated by an empirical formula it is shown that the problem under consideration features a two dimensional flow and a boundary layer which effectively introduces slip at the boundary and allows us to describe a transition from poiseuille flow to darcy s law for high proppant concentrations the expressions for both the outer i e outside the boundary layer and inner i e within the boundary layer solutions are obtained in terms of the particle concentration particle velocity and fluid velocity unfortunately these solutions require the numerical solution of an integral equation and as a result the development of a proppant transport model for hydraulic fracturing based on these results is not practicable to reduce the complexity of the problem an approximate solution is introduced to validate the use of this approximation the error is estimated for different regimes of flow the approximate solution is then used to calculate the expressions for the slurry flux and the proppant flux which are the basis for a model that can be used to account for proppant transport with gravitational settling in a fully coupled hydraulic fracturing simulator

a sedimentary record of the deposition of heavy metals and magnetic oxides in the loch dee basin galloway scotland since c ad 1500 geochemical analyses of a 210pb dated piston core from loch dee have highlighted trends of increased pb and cu deposition within the catchment as early as ad 1500 probably as a consequence of local mining and smelting activity more marked atmospheric pollutant deposition appears to have occurred in association with european industrialization after c 1840 causing a conspicuous enhancement of pb zn cu and magnetically detectable fe oxide concentrations in the uppermost 8 cm of sediment the co variability of these contaminants through the surficial sediment suggests that they emanate from a common industrial process and the presence of magnetic oxides in cenospheric particulates implicates thermal power generation plant as a principal pollutant source this interpretation is further supported by the temporal comparability of trace metal magnetic oxide influxes at loch dee and documented records regarding european fossil fuel combustion levels over the past 150 years the reduced heavy metal concentrat

natural enrichment of arsenic in loch lomond sediments abstract concentrations of arsenic in surface or near surface sediment in 12 of 13 cores from the three major basins of loch lomond are substantially enhanced up to 675 mg kg compared with background values of 15 50 mg kg sedimentary as profiles are attributed to post depositional enrichment processes since there are no recent significant sources of environmental as contamination anthropogenic or natural in the loch lomond area the enrichments can be interpreted in terms of post depositional diagenetic remobilization processes in sediment reducing zones followed by upward migration of as through interstitial waters and oxidation adsorption precipitation reactions in near surface oxidizing layers confirmation of the diagenetic adsorption hypothesis is provided directly by the analysis of as species 1 5 81 g l in pore water and indirectly via comparison with sedimentary phosphorus

paleolimnological evidence for the long range atmospheric transport of acidic pollutants and heavy metals into the province of quebec eastern canada the present study deals with the geochemical stratigraphic evolution of the recent sediments of 26 lakes located throughout the province of quebec canada although there is no major anthropogenic activity within the watersheds of many of these lakes it is shown that pb zn hg and cu levels in the most recent sediments of all lakes increased significantly from 1940 onwards it is suggested that these increases are due to the increased burning of fossil fuels particularly coal the heavy metal increases tend to be relatively high especially for pb hg and zn in the sediments of lakes from areas close to the u s a quebec boundary while lakes in more remote areas show smaller increases in the strata laid down in the same time periods pb contents in the sediments show a sustained increase in all of the upper strata however the subsequent reduction in the stratigraphic concentration of zn and hg since 1960 in both an acidified system lake tantare and a non acidified lake lake laflamme might be

convectively coupled kelvin waves in cmip5 coupled climate models this study provided a quantitative evaluation of convectively coupled kelvin waves cckws over the indian ocean and the pacific ocean simulated by 20 coupled climate models that participated in coupled model intercomparison project phase 5 the two leading empirical orthogonal function eof modes of filtered daily precipitation anomalies are used to represent the eastward propagating cckws in both observations and simulations the eigenvectors and eigenvalues of the eof modes represent the spatial patterns and intensity of cckws respectively and the lead lag relationship between the two eof principle components describe the phase propagation of cckws a non dimensional metric was designed in consideration of all the three factors i e pattern amplitude and phase propagation for evaluation the relative rankings of the models based on the skill scores calculated by the metric are conducted for the indian ocean and the pacific ocean respectively two models noresm1 m and mpi esm lr are ranked among the best 20 for both the regions three models inmcm4 mri cgcm3 and hadgem2 es are ranked among the worst 20 for both the regions while the observed cckw amplitude is greater north of the equator in the pacific some models overestimate the cckw ampliutde in the southern hemisphere this bias is related to the mean state precipitation bias along the south pacific convergence zone

geochronology of late caledonian magmatism in northern britain rb sr k ar ar ar and sm nd isotopic data are presented for mineral separates and whole rock samples from old red sandstone ors lavas associated minor intrusions and 9newer granite9 intrusive complexes from the cheviot hills north to shetland these data yield 16 internally consistent rb sr mineral ages and one each of ar ar sm nd and k ar ages when considered with precise and reliable published data it is clear that there are systematic differences in the age of late caledonian magmatism through the geological regions of scotland in the grampian highlands and the scottish midland valley magmatism was concentrated during the period 423 to 410 ma ors volcanism in the highlands occurred around 420 ma with plutonism continuing to about 408 ma volcanism and plutonism in the midland valley took place between 415 and 410 ma in the southern uplands magmatism occurred earlier in the north with all magmatism close to the southern uplands fault dated around 408 ma and that close to the iapetus suture dated at around 394 ma as no evidence exists for ocean closure prior to c 400 ma the age of igneous activity north of the southern uplands fault is consistent with chemical evidence for a relationship to active nw directed subduction the younger magmatism of the s part of the southern uplands cannot be subduction related and the c 408 ma plutons nearer the southern uplands fault can only be subduction related if tectonic construction of the southern uplands was a two stage process

analysis of convectively coupled kelvin waves in the indian ocean mjo abstract the active convective phase of the madden julian oscillation hereafter active mjo comprises enhanced moist deep convection on its own temporal and spatial scales as well as increased variance in convection associated with higher frequency modes synoptic scale cloud superclusters apparently associated with convectively coupled kelvin waves occur within the active convective envelopes of most mjo events these convectively coupled kelvin waves also occur during the suppressed convective phase of the mjo hereafter suppressed mjo this observational study presents an analysis of outgoing longwave radiation and reanalysis data to determine how these waves behave differently as they propagate through the active and suppressed mjo time indices of the mjo and kelvin waves are derived for over the equatorial indian ocean dates of local extrema in these indices are used to composite data to discern how the waves and associated circulations behave on average then further composites are made based o

diagenetic metal profiles in recent sediments of a scottish freshwater loch integrated total elemental phase specific and pore water analyses of sediment cores from loch ba scotland show that early diagenetic processes have promoted extensive metal enrichment immediately beneath the sediment water interface the accumulation of mn pb zn cu and co in sedimentary solids upward of 3 cm depth is accompanied by an increasing residence of these elements in adsorbed and hydrous oxide phases such phases are formed through oxidative precipitation from the interstitial pore fluids following the upward migration of metals from more deeply buried anaerobic sectors of the sediment pile there is good evidence that fe and ni are subject to similar influences although their total abundances near the sediment surface are less conspicuously modified in the loch ba sediments the oxic conditions promoting metal precipitation are entirely confined to strata of postindustrial age in the absence of fully diagnostic pore water and sequential chemical data similar diagenetic profiles could plausibly be misinterpreted as the product of anthropogenic contamination

sedimentation and sediment accretion in michigan coastal wetlands u s a abstract sediment transport and accretion rates were studied for three different types of coastal wetlands of lake michigan u s a a forested intradunal wetland cranberry bog no 1 near stevensville michigan displayed sediments in the form of detritus and exported them very little sedimentary material entered by streamflow these features of bottom land wetlands were confirmed by radioisotope studies on cores which showed low accretion rates of 210 pb the mass fluxes were found to range from 0 01 to 0 2 g cm 2 yr 1 the equivalent linear growths are 0 5 9 0 mm yr 1 the suspended material from this wetland entered a filling shrub bog lake complex known as cranberry bog no 2 a considerable fraction of the incoming sediments were retained in this intradunal basin wetland this was confirmed via radioisotope studies with cores showing higher accretion rates than in the bottom land wetland the river delta wetland at pentwater michigan had little sediment trapping ability large amounts of water and suspended materials entered this riverine wetland but no annual average removal was found radioisotope studies of cores at selected locations within this system showed little or no accretion in stream channels and normal accumulation of organic material in non channel areas no net annual effect on water quality of the streams as they discharged to lake michigan was found storm events caused no notable import or export of suspended material presumably the sand substrate in the vicinity of all three wetlands caused runoff events to be mediated by subsurface flow through this porous soil these three sand based coastal wetlands appear to have little net effect on suspended solids the 210 pb method proved more valuable than 137 cs because of the small depth of occurrence of the latter isotope interpretation of isotope profiles required information on acid fraction soluble profiles results are expressed in terms of mass units since compaction of cores distorts the linear accretion rate delayed transfers of radionuclides appear to have occurred perhaps as a result of integration of atmospheric inputs by the watersheds the total activities of 210 pb and 137 cs are well correlated which indicates particle trapping efficiency as the primary factor for affecting accumulation of both isotopes

hydraulic fracturing with leakoff in a pressure sensitive dual porosity medium abstract hydraulic fracturing is a key method in the stimulation of shale gas reservoirs shale gas formations often contain natural fractures which are fluid pressure sensitive and dilate in response to the inflation of the fracture increasing fluid loss and slowing down and potentially prematurely arresting fracture propagation models typically assume 1 d single porosity permeability carter leakoff perpendicular to the hydraulic fracture however the leakoff process in naturally fractured formations is considerably more complex in this study we present an hydraulic fracturing model based on the pkn formalism which accommodates leakoff into a pressure sensitive dual porosity medium proppant transport is accommodated by introducing empirical constitutive equations to determine the proppant distribution during the hydraulic fracturing treatment the model is solved numerically and is validated against known small and large time asymptotic solutions the model is capable of providing a rapid estimation of the morphology of hydraulic fractures in naturally fractured formations and the corresponding proppant distribution the simulation results illustrate that the leakoff into a dual porosity medium where fracture permeability is a strong function of applied fluid pressure results in a reduced length of the propagating fracture due to the fugitive fluid leakoff from the fracture into the surrounding formation and that this in turn results in a reduced maximum width during the treatment the ability to infuse proppants in fluid driven fractures penetrating large distances from the injection wellbore is further limited by premature screen out this may compromise the ultimate efficiency of the final hydraulic fracture regarding gas recovery reduced propagation and premature screen out are limited by low permeability and large spacing of the natural fractures the presence of an existing network of natural fractures including those adjacent to the hydraulic fracture that may become propped aids in the recovery of the resource by reducing diffusion lengths of the hydrocarbon to the main fracture

stable isotope geochemistry of caledonian granitoids from the british isles and east greenland abstract the british caledonian granites bcg comprise a compositionally diverse group of intrusive rocks ranging from diorite to leucogranite which were emplaced across the british isles in and adjacent to the caledonian metamorphic belt during the early paleozoic although the largest volume of caledonian magmatic activity in britain postdates the polyphase deformation and metamorphism of the grampian orogeny a small number of plutons were emplaced prior to the main orogenic event and another group are essentially contemporaneous with it o isotope ratios for the bcg are extremely variable and essentially overlap the full range of o isotope variations documented for orogenic granitoids the margins of two plutonic complexes have been affected by subsolidus hydrothermal exchange with meteoric fluids for the older 440 ma bcg plutons 18 o 6 6 12 1 and d 83 to 45 whereas for the younger c 400 ma plutons 18 o 7 1 12 4 and d 97 to 44 there is a general positive correlation between o and sr isotope variations in the post tectonic granitoids which is absent in their pre tectonic counterparts caledonian plutonic rocks occur in east greenland in the southern half of the fold belt between 70 75 n the earliest intrusions are sheets of monzonite and granodiorite emplaced slightly before the climax of caledonian orogenic activity subsequently a suite of post tectonic granites was emplaced c 450 370 ma two of the east greenland plutons have been affected by post emplacement meteoric hydrothermal alteration the 18 o range for the unaltered east greenland plutons is 8 5 13 9

ferrimagnetic sulfide formation in recent sediments of loch ba scotland and implications for magnetostratigraphic interpretation magnetic and chemical analyses of 1 m piston cores from loch ba scotland illuminated the presence of a ferrimagnetic mineral which is sensitive to atmospheric oxidation and is soluble in h2o2 this phase plausibly only an authigenic sulfide is probably spinel fe3s4 greigite authigenesis of fe3s4 requires reactive fes and elemental s the latter likely being derived from in situ oxidation of bisulfide near the sediment redoxycline this is consistent with the observation of maximum oxidation sensitive magnetic fractions around the oxic anoxic sediment boundary at ca 4 16 cm depth progressive pyritization of fe3s4 during burial provides the most viable explanation for the loss of oxidation sensitive phases at greater depth the results extend the range of environments known to be subject to postdepositional magnetic enhancement to include oligotrophic lakes with relatively low productivity this may have ramifications for magnetically based sediment source linkage core correlation and pollution studies which fail to demonstrate that magnetostratigraphic profiles are solely reflectively of allogenic mineral presence

mercury contamination chronologies from connecticut wetlands and long island sound sediments sediment cores were used to investigate the mercury deposition histories of connecticut and long island sound most cores show background pre 1800s concentrations 50 100 ppb hg below 30 50 cm depth strong enrichments up to 500 ppb hg in the core tops with lower hg concentrations in the surface sediments 200 300 ppb hg a sediment core from the housatonic river has peak levels of 1 500 ppb hg indicating the presence of a hg point source in this watershed the hg records were translated into hg contamination chronologies through 210pb dating the onset of hg contamination occurred in 1840 1850 in eastern connecticut whereas in the housatonic river the onset is dated at around 1820 the mercury accumulation profiles show periods of peak contamination at around 1900 and at 1950 1970 peak hg hg hg measured minus hg background accumulation rates in the salt marshes vary dependent on the sediment character between 8 and 44 ng hg cm2 per year whereas modern hg accumulation rates range from 4 17 ng hg cm2 per year time averaged hg accumulation rates are 15 ng hg cm2 per year these hg accumulation rates in sediments are higher than the observed hg atmospheric deposition rates about 1 2 ng hg cm2 per year indicating that contaminant hg from the watershed is focused into the coastal zone the long island sound cores show similar hg profiles as the marsh cores but time averaged hg accumulation rates are higher than in the marshes 26 ng hg cm2 a year because of the different sediment characteristics in situ atmospheric deposition of hg in the marshes and in long island sound is only a minor component of the total hg budget the 1900 peak of hg contamination is most likely related to climatic factors the wet period of the early 1900s and the 1950 1970 peak was caused by strong anthropogenic hg emissions at that time spatial trends in total hg burdens in cores are largely related to sedimentary parameters amount of clay except for the high inventories of the housatonic river which are related to hg releases from hat making in the town of danbury much of the contaminated sediment transport in the housatonic river basin occurs during floods creating distinct layers of hg contaminated sediment in western long island sound the drop of about 40 in hg accumulation rates between the 1960s and 1990s seems largely the result of reduced hg emissions and to a much lesser extent of climatic factors

reconstructing historical trends in metal input in heavily disturbed contaminated estuaries studies from bilbao southampton water and sicily estuaries may be important reservoirs for contaminants as they tend to act as sinks for fine contaminant reactive sediments and historically they have acted as centres for industrial and urban development analysis of dated sediment cores from these areas may allow historical trends in heavy metal input to be reconstructed and recent and historical inputs of metal contaminants to be compared undisturbed saltmarsh settings have been used widely in the reconstruction of historical trends in metal input as saltmarshes provide a stable vegetated substrate of dominantly fine sediments and are less prone to erosion and reworking than adjacent mudflat areas in comparison much less research on historical pollution trends has been undertaken at estuarine sites which are prone to severe local disturbance such as intertidal areas which are routinely dredged or where sedimentary processes have been modified by human activities such as shipping salt working port activities land claim etc this paper assesses the usefulness of 210pb and 137cs dating combined with geochemical studies in reconstructing historical trends in heavy metal input and sediment accretion in 3 heavily modified industrialised estuarine areas in europe the bilbao estuary spain southampton water uk and the mulinello estuary sicily of these sites only a salt marsh core from the mulinello estuary provides a high resolution record of recent heavy metal inputs in southampton water only a partial record of changing metal inputs over time is retained due to land claim and possible early diagenetic remobilisation while at bilbao the vertical distribution of heavy metals in intertidal flats is mainly controlled by input on reworked sediment particles and variations in sediment composition where 137cs and 210pb distributions with depth allow a chronology of sediment deposition to be established and early diagenetic remobilisation has been minimal mudflat and saltmarsh cores from even the most heavily disturbed estuarine sites can provide useful information on variations in historical contaminant input when the sediments have been vigorously mixed or reworked large scale compositional variations are present or significant early diagenetic remobilisation has occurred however only general information on the scale of contamination can be obtained

convectively coupled equatorial waves 1 convectively coupled equatorial waves ccews control a substantial fraction of tropical rainfall variability their horizontal structures and dispersion characteristics correspond to matsuno s 1966 solutions of the shallow water equations on an equatorial beta plane namely kelvin equatorial rossby mixed rossby gravity and inertio gravity waves because of moist processes the tilted vertical structures of ccews are complex and their scales do not correspond to that expected from the linear theory of dry waves the dynamical structures and cloud morphology of ccews display a large degree of self similarity over a surprisingly wide range of scales with shallow convection at their leading edge followed by deep convection and then stratiform precipitation mirroring that of individual mesoscale convective complexes ccews have broad impacts within the tropics and their simulation in general circulation models is still problematic although progress has been made using simpler models a complete understanding of ccews remains a challenge in tropical meteorology

mobility and diagenesis of pb and 210pb in peat peatlands long have been considered to preserve the record of atmospheric deposition of anthropogenic contaminants such as pb in the past two decades sup 210 pb has been widely used to data recent strata of peat and to calculate accumulation rates the assumption that pb and sup 210 pb are immobile and not subject to diagenesis in peat has been questioned but not rigorously tested the authors attempted to determine if pb is mobile in peatlands and if pb profiles are altered by diagenic processes by constructing a mass balance for pb about a small peatland by comparing inventories concentrations and accumulation rates of pb and sup 210 pb in peatlands across northeastern north america and by examining the relationship between concentrations of pb in bog waters and peat in numerous sites the results clearly demonstrate that pb and sup 210 pb are mobilized by the organic rich waters of peatlands profiles of pb and sup 210 pb at depths below the water table do not preserve the record of atmospheric deposition and inventories of pb and sup 210 pb are depleted in peatland hollows concentrations of pb in bog waters are regulated by the concentration of pb in the peat and the concentration of dissolved organicmore carbon the mass balance for one bog indicated that over the specific three year period of study more than 30 of inputs of pb were not retained within the peat as a result of this mobility dates based on sup 210 pb can be biased and inaccurate by as much as 30 years dates based on sup 210 pb should be verified by other techniques especially when the inventory of sup 210 pb is less than that expected from local rates of deposition less

permeability anisotropy induced by the shear displacement of rough fracture walls 1 the permeability anisotropy that results from a shear displacement between the complementary self affine walls of a rough fracture is investigated experiments in which a dyed fluid radially injected into a transparent fracture displaces a transparent one are presented a clear anisotropy is observed in the presence of shear displacements and allows us to estimate the ratio of the permeabilities for flows parallel and perpendicular to a simple model which accounts for the development of channels perpendicular to qualitatively explains these results and predicts a permeability decreasing increasing linearly with the variance of the aperture field for flow parallel perpendicular to the shear displacement these predictions are then compared to the results of numerical simulations performed using a lattice boltzmann technique and to the anisotropies measured in displacement experiments

boron beryllium and sulfur in holocene sediments and peats of the nile delta egypt their use as indicators of salinity and climate abstract the concentrations of 14 major and trace elements b ba be co cr cu fe mn ni p s v zn and organic c in bulk sediment samples of holocene age from bore holes in the nile delta egypt are considered in terms of sediment grain size and depositional setting using this background information an attempt is made to evaluate paleosalinity and paleoclimatic change by geochemical analyses of peats in every sediment facies examined we find that grain size is a major controlling factor of geochemical composition but the b be ratio is helpful in paleoenvironmental interpretations organic matter content is the major factor affecting element concentrations in peats zn cr fe be cu mn concentrations on an organic matter free basis are lower in these organic rich layers than in other nile delta sediment facies the sulfur content of the peats indicates a decreased importance of freshwater input to holocene lagoons from about 8000 to 3400 years bp high boron beryllium ratios and the presence of gypsum in peats deposited between 6300 and 4900 years bp record the most evaporitic phase affecting this region this geochemical finding is in close agreement with results of other independent paleoclimatic studies which indicate the onset of arid conditions in northeast africa at about 5000 years bp

estimation and uncertainty of recent carbon accumulation and vertical accretion in drained and undrained forested peatlands of the southeastern usa the purpose of this study was to determine how drainage impacts carbon densities and recent rates past 50 years of vertical accretion and carbon accumulation in southeastern forested peatlands we compared these parameters in drained maple gum mapl atlantic white cedar cdr and pocosin poc communities in the great dismal swamp national wildlife refuge gds of virginia north carolina and in an intact undrained cdr swamp in the alligator river national wildlife refuge ar of north carolina peat cores were analyzed for bulk density percent organic carbon and 137cs and 210pb an uncertainty analysis of both 137cs and 210pb approaches was used to constrain error at least partially related to mobility of both radioisotopes gds peats had lower porosities 89 6 sd 1 71 versus 95 3 0 18 and higher carbon densities 0 082 0 021 versus 0 037 0 009 g c cm 3 than ar vertical accretion rates 0 10 0 56 cm yr 1 were used to estimate a time period of 84 362 years for reestablishment of peat lost during the 2011 lateral west fire at the gds carbon accumulation rates ranged from 51 to 389 g c m 2 yr 1 for all sites in the drained gds versus intact ar cdr sites carbon accumulation rates were similar with 137cs 87gds versus 92ar g c m 2 yr 1 and somewhat less at the gds than ar as determined with 210pb 111gds versus 159ar g c m 2 yr 1 heightened productivity and high polyphenol content of peat may be responsible for similar rates of carbon accumulation in both drained and intact cdr peatlands

el nino modoki and its possible teleconnection 1 using observed data sets mainly for the period 1979 2005 we find that anomalous warming events different from conventional el nino events occur in the central equatorial pacific this unique warming in the central equatorial pacific associated with a horseshoe pattern is flanked by a colder sea surface temperature anomaly ssta on both sides along the equator empirical orthogonal function eof analysis of monthly tropical pacific ssta shows that these events are represented by the second mode that explains 12 of the variance since a majority of such events are not part of el nino evolution the phenomenon is named as el nino modoki pseudo el nino modoki is a classical japanese word which means a similar but different thing the el nino modoki involves ocean atmosphere coupled processes which include a unique tripolar sea level pressure pattern during the evolution analogous to the southern oscillation in the case of el nino hence the total entity is named as el nino southern oscillation enso modoki the enso modoki events significantly influence the temperature and precipitation over many parts of the globe depending on the season the impacts over regions such as the far east including japan new zealand western coast of united states etc are opposite to those of the conventional enso the difference maps between the two periods of 1979 2004 and 1958 1978 for various oceanic atmospheric variables suggest that the recent weakening of equatorial easterlies related to weakened zonal sea surface temperature gradient led to more flattening of the thermocline this appears to be a cause of more frequent and persistent occurrence of the enso modoki event during recent decades

coupled sm nd and u pb systematics in late caledonian granites and the basement under northern britain the british late caledonian granites display a close correspondence between inherited u pb systematics in zircons and initial end indicating that both were controlled by the age of a major component of continental crust the data confirm and refine previous models of a basement comprising young crust in the south which includes arc and oceanic crust scrapings and progressively older continental crust northwestwards across scotland

changes of lead and barium with time in california off shore basin sediments during ancient times the natural deposition fluxes of lead which can be leached with dilute acid from sediments in santa barbara santa monica and san pedro basins offshore from the los angeles urban complex were about 0 7 0 1 and 0 2 g pb cm 2 yr respectively since there was little difference in biological productivity in surface waters of these basins it is proposed that clay is a major transport vehicle for sequestered soluble lead which then explains why the lead deposition flux within the santa barbara basin was so much larger compared to the other basins the fluxes of silicate mud in the basins in ancient times were about 92 19 and 30 mg cm 2 yr in santa barbara santa monica and san pedro basins respectively today deposition fluxes of acid soluble lead within these three basins are 3 to 9 fold greater being about 2 1 1 1 and 1 8 g pb cm 2 yr respectively partly in the form of directly deposited large sewage particles which account for none 2 3 and 3 4 of the total industrial lead deposition fluxes in the respective basins concentrations of leachable lead in varve dated sediment layers increase with time and isotopic compositions of these leads change in accordance with corresponding known changes of isotopic compositions of industrial lead in the los angeles atmosphere lead remaining in acid leached sediment residues originates from igneous and clay minerals exhibiting no change in concentration or isotopic composition since pre industrial times deposition fluxes of total barium in sediments among the three basins were proportional to mass deposition fluxes before 1950 in the same manner as for lead afterwards there are barium concentration maxima with time in both santa monica and san pedro basin sediments which are attributable to industrial sewage rather than to episodic erosion from barium rich sedimentary evaporite strata exposed locally along the shore an increase of barium concentrations in present day santa barbara basin sediments may reflect dispersal of barium rich drilling mud from local drilling operations

dispersion of solids in fracturing flows of yield stress fluids solids dispersion is an important part of hydraulic fracturing both in helping to understand phenomena such as tip screen out and spreading of the pad and in new process variations such as cyclic pumping of proppant whereas many frac fluids have low viscosity e g slickwater others transport proppant through increased viscosity in this context one method for influencing both dispersion and solids carrying capacity is to use a yield stress fluid as the frac fluid we propose a model framework for this scenario and analyse one of the simplifications a key effect of including a yield stress is to focus high shear rates near the fracture walls in typical fracturing flows this results in a large variation in shear rates across the fracture in using shear thinning viscous frac fluids flows may vary significantly on the particle scale from stokesian behaviour to inertial behaviour across the width of the fracture equally according to the flow rates hele shaw style models give way at higher reynolds number to those in which inertia must be considered we develop a model framework able to include this range of flows while still representing a significant simplification over fully three dimensional computations in relatively straight fractures and for fluids of moderate rheology this simplifies into a one dimensional model that predicts the solids concentration along a streamline within the fracture we use this model to make estimates of the streamwise dispersion in various relevant scenarios this model framework also predicts the transverse distributions of the solid volume fraction and velocity profiles as well as their evolutions along the flow part

mangrove development and its response to environmental change in yingluo bay sw china during the last 150years stable carbon isotopes and mangrove pollen abstract located at the interface of terrestrial and marine ecosystems mangroves are particularly sensitive to environmental change they provide a sedimentary sink for organic carbon whereby cores can provide detailed records of mangrove species we aimed to trace the history of mangrove development over the past 150 years in yingluo bay sw china sedimentation rates avg 0 32 and 0 37 cm year were calculated on the basis of ln 210 pb ex vs mass depth and offset the rate of relative sea level rise 0 22 0 24 cm year leading to a seaward expansion of new mangrove habitats chemical tracers 13 c org and c n and an isotope mixing model were utilized to trace the contribution of mangrove derived organic matter mom changes in the relative abundance of pollen from mangrove plants was used to compensate for diagenetic alteration of the stable isotope values and potential overlaps in isotope values for different sources of organic matter the result of pearson correlation analysis showed that the mom was moderately positive correlated with total mangrove pollen indicating that stable carbon isotopes and mangrove pollen provide similar information for tracing mangrove ecosystems based on results from this study compositional changes in mangrove communities could be divided into two main stages a degradation period 1870 1930 ad and a flourishing period 1930 2011 ad corresponding to colder temperature and warmer temperature respectively owing to the location being far away from any industrial area and human activity temperature may be a key factor for mangrove development

field measurements of normal and shear fracture compliance abstract field estimates of the normal and shear compliance of water saturated fractures were obtained from a seismic experiment carried out on a wave cut platform of upper caithness flagstone on the north coast of scotland the rocks are cut by two orthogonal sets of vertical fractures vertical geophones were glued to the rock surface and seismic waves were generated by striking the surface with a sledge hammer first arrival traveltimes were obtained for source receiver distances up to 30 m differences of compressional velocity with direction across the platform were interpreted as resulting from the compliance of the fractures intersected by the transmitted waves the average normal compliance for fractures at this site is 4 0 10 12 1 0 10 12 m pa there is much less certainty about the precise value of shear compliance however the normal shear compliance ratio is determined to be 0 1

the origin and evolution of the menderes massif w turkey a rubidium strontium and oxygen isotope study the menderes massif located in the alpine orogen of western turkey has three litho structural units a basal gneiss core a schist mantle covering the gneiss core and an overlying marble mantle this study reports isotopic data from samples of metasediments and migmatites from the southern type a and of tonalitic to granitic metaigneous rocks from the northern menderes massif type b type a rocks define a rb sr whole rock isochron age of 502 10 ma and an initial87sr 86sr ratio of 0 71174 73 this is interpreted as the age of migmatization type b rocks give a rb sr whole rock isochron age of 471 9 ma with an initial87sr 86sr ratio of 0 70684 25 which we interpret as the intrusion age k white micas from rock type a give an average rb sr mineral age of 56 1 ma which can be interpreted as the formation age of the alpine mineral paragenesis k white micas from rock type b give rb sr mixed ages of 120 230 ma between alpine and pan african orogenies biotites from both rock types yield an average rb sr age of 37 1 ma which is interpreted as an alpine cooling age the oxygen isotope ratios of type a rocks range from 10 4 to 14 6 and of type b from 8 9 to 11 8 the oxygen and strontium isotopic compositions together clearly distinguish rocks of types a and b compositions of type a rocks suggest a crustal origin type b rocks have compositions transitional between those of crustal and mantle derived materials

experimental evidence of the anisotropy of tracer dispersion in rough fractures with sheared walls 1 dispersion experiments are compared for two model fractures with identical complementary rough walls but with a relative shear displacement parallel u or perpendicular u to the flow velocity u the flowing fluid is a shear thinning polymer solution with a newtonian behavior at low shear rates for u the mixing fronts display large structures well reproduced by assuming parallel channels of conductance deduced from the aperture field this model also explains the amplification of the structures in the shear thinning regime and the distribution of the local transit times x y for u the front is much flatter the local thickness of the front is characterized by a dispersivity x y its distribution is narrow enough to define an effective value pe only for u and in this case pe has a taylor aris like variation with pe

lead isotope evidence for the nature of the mantle beneath caledonian scotland abstract recent nd sr pb isotope studies of caledonian granitoids 1 4 have reopened the question of the existence of an unusual or enriched mantle source beneath caledonian scotland this was postulated 5 following a nd sr isotope geochemical study of lavas associated with the scottish old red sandstone pb isotope data for the same lavas reported here restrict any major crustal involvement in southwest highland primitive lavas to ca 1750 ma old rb depleted granulites the lack of such crustal material within scotland together with pb sr isotopic relationships strongly suggests that a large volume mantle source with low rb sr and sm nd has been present at depth under western scotland since the early proterozoic it is unlikely that this is the same enriched mantle source observed from xenoliths in younger magmas 25 and is probably located deep in the lithosphere or within the asthenosphere this source has contributed extensively to the incompatible element budget of caledonian granitoids implying that the caledonian orogeny did result in significant growth of the british crust

the spectrum of convectively coupled kelvin waves and the madden julian oscillation in regions of low level easterly and westerly background flow abstractthe zonal wavenumber frequency power spectrum of outgoing longwave radiation in the global tropics suggests that power in convectively coupled kelvin waves and the madden julian oscillation mjo is organized into two distinct spectral peaks with a minimum in power in between this work demonstrates that integration of wavelet power in the wavenumber frequency domain over geographical regions of moderate trade winds yields a similar pronounced spectral gap between these peaks in contrast integration over regions of background low level westerly wind yields a continuum of power with no gap between the mjo and kelvin bands results further show that signals in tropical convection are redder in frequency in these low level westerly wind zones confirming that kelvin waves tend to propagate more slowly eastward over the warm pool than other parts of the world results are consistent with the perspective that portions of disturbances labeled as kelvin waves and the mjo that are proximate to kelvin wa

hemispheric asymmetry of the structure of dayside auroral oval a comprehensive analysis of long term and multispectral auroral observations made in the arctic and antarctica demonstrates that the dayside auroral ovals in two hemispheres are both presented in a two peak structure namely the prenoon 09 00 magnetic local time mlt and postnoon 15 00 mlt peaks the two peak structures of dayside ovals however are asymmetric in the two hemispheres i e the postnoon average auroral intensity is more than the prenoon one in the northern hemisphere but less in the southern hemisphere the hemispheric asymmetry cannot be accounted for by the effect of the interplanetary magnetic field by component and the seasonal difference of ionospheric conductivities in the two hemispheres which were used to interpret satellite observed real time auroral intensity asymmetries in the two hemispheres in previous studies we suggest that the hemispheric asymmetry is the combined effect of the prenoon postnoon variations of the magnetosheath density and local ionospheric conductivity

enso regimes reinterpreting the canonical and modoki el nino 1 we propose that the first two empirical orthogonal function eof modes of tropical pacific sea surface temperature sst anomalies do not describe different phenomena i e el nino southern oscillation enso and el nino modoki but rather the nonlinear evolution of enso we introduce two new uncorrelated indices e and c based on the leading eofs that respectively account for extreme warm events in the eastern and cold moderate warm events in the central equatorial pacific corresponding to regimes with different evolution recent trends in enso can be described as an increase in the central pacific c variability that is associated with stronger cold events as well as a reduction in the eastern pacific e variability within the cold moderate warm regime consistent with model projections however little can be said observationally with respect to the extreme warm regime

weathering fluxes and sediment provenance on the sw scottish shelf during the last deglaciation the reconstruction of past ice sheet dynamics can shed a light on long term ice stream activity and in turn provide constraints on the response of modern ice sheets to climate change the hebrides ice stream his flowed across part of the western scottish shelf to the shelf break during the last glacial cycle and drained a large portion of the northern sector of the british irish ice sheet to investigate the deglacial dynamics of the his following the last glacial maximum lead pb isotope records were extracted from the femn oxyhydroxide and detrital fractions of recovered laminated glacimarine mud sequences to monitor the changing activity of his during its retreat these provide timing and some source information of glacially weathered inputs to the marine environment the femn oxyhydroxide fraction in the samples is dominated by allochthonous particles pre formed and shows a marked decrease from radiogenic 20 05 206pb 204pb at 21 cal ka bp to less radiogenic pb isotope compositions 19 48 towards the windermere interstadial 15 4 13 ka this decrease represents a reduction in the flux of subglacially derived radiogenic pb to the continental shelf is interpreted as being associated with the break up of the ice stream in western scotland around that time the pb sr and nd isotopic signatures of the detrital fraction indicate a preponderance of moine sourced fine sediments originated from the nw highlands in the core locations from 21 to 15 cal ka bp dimlington stadial windermere interstadial most likely dictated by the orientation of ice flow tidal and oceanic current directions and sediment delivery in contrast ice rafted debris in a 21 cal ka bp old basal diamicton contains volcanic derived material suggesting different provenance for different grain sizes the femn oxyhydroxide 208pb 204pb ratio shows an unusual inversion relative to the other pb isotope ratios and is attributed to the introduction of secondary weathering phases from a source with contrasting 208pb 204pb but similar 206pb 204pb and 207pb 204pb in the detrital fraction the inversions are constrained to periodic spikes which may indicate an increased contribution from a high th u source potentially the neighbouring archaean amphibolitic lewisian basement in the outer hebrides this study demonstrates how geochemical investigation on continental shelves can be used to constrain the timing activity and flow sources of palaeo ice streams