discrete element modeling of progressive failure in a wide coal roadway from water rich roofs abstract progressive failure of roadway roofs is a common failure mechanism in underground coal mines especially when water rich roofs are in close proximity to the roadway in this case study at a chinese coal mine the udec voronoi method was used to investigate the process of progressive roof failure in a wide coal roadway from water rich roofs in the numerical scheme the studied domain was partitioned into polygonal blocks bonded through contacts with pre defined dimensions the parameters of polygons and contacts in the voronoi program were calibrated to rock mass properties obtained through laboratory tests based upon laboratory tests and previous research findings a time dependent strength degradation process from water absorption was assumed and implemented in the numerical modeling next the progressive failure of a roadway from water rich roofs was analyzed in detail the numerical results agreed well with field measurements and observations this method was demonstrated to reproduce the real phenomenon of roof failure in all of its complexity the numerical results revealed that the progressive failure mechanism was characterized by an initial fracturing of the roof due to strength degradation which was followed by significant dilation as fractures grew the large span of the roadway further contributed to the roof failure process the results also clearly showed that shear cracks were predominant in the roof and played a major role in the behavior of the roadway roof additionally support and excavation schemes that affect roof stability were observed

an investigation of the relationship between uniaxial compressive strength and degradation for selected rock types abstract the relationship between uniaxial compressive strength and degradation was investigated for selected rock types by using regression analyses to determine whether degradation was a useful predictor of compressive strength in addition the effects of aggregate particle size number of hammer blows during the degradation test engineering index properties petrographic characteristics and water saturation on the compressive strength degradation relationship were evaluated the results show that strong inverse relationships exist between compressive strength and degradation measured on a 9 5 4 75 mm size aggregate for sandstones and igneous metamorphic rocks but that no significant relationship exists for limestones dolomites the results also indicate a strong positive correlation between degradation and l a abrasion loss and can be used to establish a limit of allowable degradation for practical applications engineering index properties do not significantly affect the relationship between compressive strength and degradation but petrographic characteristics are important in explaining the strength and degradation behavior of the rocks studied water saturation decreases compressive strength and increases degradation to varying degrees

sulfate minerals control dissolved rare earth element flux and nd isotope signature of buoyant hydrothermal plume emso azores 37 n mid atlantic ridge abstract while hydrothermal vents are now thought to be a major source of dissolved iron to the oceans they have always been considered to be a sink for the dissolved rare earth elements drees however true dissolved ree observations in hydrothermal plumes are still lacking here we report for the first time the dree concentrations and neodymium isotopic compositions dend of buoyant hydrothermal fluids at lucky strike mid atlantic ridge we find that 27 to 62 of total hydrothermal drees are rapidly scavenged by anhydrite precipitation at the onset of buoyant plume formation after this initial loss all drees behave quasi conservatively within the buoyant plume dissolved phase end dend in the evolving plume are identical to black smoker dend of 9 0 and contrast radically with dend of the local deep water mass at 12 0 plume dend as low as 6 6 may be reconciled by dissolution of newly formed barite in the local environment and carrying seawater dend signature we find based on the first plume dree observations that hydrothermal plumes are in fact a source of dree to the north atlantic deep water precipitation dissolution processes of hydrothermally derived minerals i e sulfates in the buoyant plume and fe oxy hydroxide in the non buoyant plume will likely affect the fate of other trace metals and their isotopic composition

geology geochemistry and genesis of the zankan iron deposit in the west kunlun orogen xinjiang china the zankan iron deposit taxkorgan county xinjiang is a recently discovered large fe deposit in western china the deposit is hosted in the bulunkuole metamorphic complex in the taxkorgan terrane of the west kunlun orogen the ores are uniquely composed of magnetite pyrite and anhydrite with variable contents and show massive disseminated and banded styles the ores contain widely varying al2o3 tio2 0 28 5 48 wt zr 3 0 83 ppm and hf 0 2 2 ppm indicating a terrigenous clastic material input detrital contamination is minor as demonstrated by poor correlations of y ho ratio vs zr th hf and al2o3 contents as well as zr vs tio2 the ores contain seawater like lree depletion positive la and y anomalies and occasional eu enrichment which suggest hydrothermal contributions in addition three samples show relatively high rey 604 1254 ppm negative eu anomalies eu eu paas 0 36 0 96 and mree enrichment sm ybpaas 1 25 2 81 suggesting a probable fluvial input and shallow precipitation the 34s ratios range widely 3 2 32 8 and show an alternating and or mixing source of two end members the seawater sulfate may have been an indispensable end member and the other end member may have been the volcanic host rocks in the bulunkuole complex which has likely contributed the ore forming metals integrating evidence from regional geology ore geology and geochemistry we conclude that the zankan fe deposit was the result of an early cambrian seafloor hydrothermal system

rare earth element concentrations and nd isotopes in the southeast pacific ocean 1 three vertical profiles of rare earth element concentrations and nd isotopic compositions have been measured in the remote southeast pacific ocean the three stations represent contrasting environments the oligotrophic center of the gyre station gyr the transition zone east of the south tropical front station egy and the peru chile upwelling marked by a pronounced oxygen minimum station upx rare earth concentrations display nutrient like vertical profiles except at upx where surface waters are enriched at this station nd isotopic compositions are clearly more radiogenic than in the open ocean suggesting that boundary exchange process is releasing lithogenic rare earth element from the volcanic andes unexpected radiogenic values end reaching 3 7 are also observed at 2000 m at station gyr in the upper circumpolar deep water that commonly have end values around 6 exchange processes related to hydrothermal activity are suspected to produce this increase in end in the vicinity of the east pacific rise these results provide some guidance for higher resolution studies planned in this region by the international geotraces program

the hafnium and neodymium isotope composition of seawater in the atlantic sector of the southern ocean we present the first combined dissolved hafnium hf and neodymium nd concentrations and isotope compositions of deep water masses from the atlantic sector of the southern ocean eight full depth profiles were analyzed for hf and twelve for nd hafnium concentrations are generally depleted in the upper few hundred meters ranging between 0 2 pmol kg and 0 4 pmol kg and increase to relatively constant values of around 0 6 pmol kg in the deeper water column at the stations north of the polar front pf nd concentrations increase linearly from about 10 pmol kg at depths of 200 m to up to 31 pmol kg close to the bottom indicating particle scavenging and release within the weddell gyre wg however nd concentrations are essentially constant at 25 pmol kg at depths greater than 1000 m the distributions of both elements show a positive correlation with dissolved silicon implying a close linkage to diatom biogeochemistry hafnium essentially shows invariant isotope compositions with values averaging at ehf 4 6 whereas nd isotopes mark distinct differences between water masses such as modified north atlantic deep water nadw end 11 to 10 and antarctic bottom water aabw end 8 6 to 9 6 but also waters locally advected via the agulhas current can be identified by their unradiogenic nd isotope compositions mixing calculations suggest that a small fraction of nd is removed by particle scavenging during mixing of water masses north of the pf nevertheless the nd isotope composition has apparently not been significantly affected by uptake and release of nd from particles as indicated by mixing calculations a mixing envelope of an approximated north pacific and a north atlantic end member shows that nd isotope and concentration patterns in the lower circumpolar deep water lcdw can be fully explained by 30 70 percentage contributions of these respective end members

nd and sr isotope compositions of different phases of surface sediments in the south pacific extraction of seawater signatures boundary exchange and detrital dust provenance the radiogenic isotope composition of neodymium nd and strontium sr are useful tools to investigate present and past oceanic circulation or input of terrigenous material we present nd and sr isotope compositions extracted from different sedimentary phases including early diagenetic fe mn coatings unclean foraminiferal shells fossil fish teeth and detritus of marine surface sediments core tops covering the entire midlatitude south pacific comparison of detrital nd isotope compositions to deep water values from the same locations suggests that boundary exchange has little influence on the nd isotope composition of western south pacific seawater concentrations of rare earth elements ree and al ca ratios of unclean planktonic foraminifera suggest that this phase is a reliable recorder of seawater nd isotope composition the signatures obtained from fish teeth and nondecarbonated leachates of bulk sediment fe mn oxyhydroxide coatings also agree with unclean foraminifera direct comparison of nd isotope compositions extracted using these methods with seawater nd isotope compositions is complicated by the low accumulation rates yielding radiocarbon ages of up to 24 kyr thus mixing the signal of different ocean circulation modes this suggests that different past seawater nd isotope compositions have been integrated in authigenic sediments from regions with low sedimentation rates combined detrital nd and sr isotope signatures indicate a dominant role of the westerly winds transporting lithogenic material from south new zealand and southeastern australia to the open south pacific the proportion of this material decreases toward the east where supply from the andes increases and contributions from antarctica cannot be ruled out

the large scale evolution of neodymium isotopic composition in the global modern and holocene ocean revealed from seawater and archive data neodymium isotopic compositions 143nd 144nd or end have been used as a tracer of water masses and lithogenic inputs to the ocean to further evaluate the faithfulness of this tracer we have updated a global seawater end database and combined it with hydrography parameters temperature salinity nutrients and oxygen concentrations carbon isotopic ratio and radiocarbon of dissolved inorganic carbon archive end data are also compiled for leachates foraminiferal tests deep sea corals and fish teeth debris from the holocene period 10 000 years at water depths 1500 m property property plots show clear correlations between seawater end and the other variables suggesting that large scale water mass mixing is a primary control of deepwater end distribution at 200 m basin scale seawater t s end diagrams demonstrate the isotopic evolution of different water masses seawater and archive end values are compared using property property plots and t s end diagrams archive values generally agree with corresponding seawater values although they tend to be at the upper limit in the pacific both positive and negative offsets exist in the northern north atlantic applying multiple regression analysis to deep 1500 m seawater data we established empirical equations that predict the main large scale deepwater end trends from hydrography parameters large offsets from the predicted values are interpreted as a sign of significant local regional influence dominant continental influence on seawater and archive end is observed mainly within 1000 km from the continents generally seawater and archive end values form gradual latitudinal trend in the atlantic and pacific at depths 600 m consistent with the idea that nd isotopes help distinguish between northern southern sourced water contributions at intermediate and deep water depths

tracing past ocean circulation to understand how ocean circulation and climate may change in the future we must first understand how the system operated in the past without man9s influence new inorganic isotopic tracers are now helping to elucidate past ocean circulation patterns but controversies remain regarding the relative influence of ocean circulation and weathering on the isotopic signals

characteristics and formation of eastern south pacific intermediate water 1 newly gathered hydrographic data from the eastern south pacific is combined with other high quality data mainly woce to reassess the properties and boundaries of the eastern south pacific intermediate water espiw to date the espiw has been only poorly described the espiw core is found off central and northern chile between the coast and 90 w and 20 38 s located at 50 400 m of depth its temperature varies between 11 13 c salinity ranges from 34 1 34 3 and its sigma t lies between 25 75 26 25 kgm 3 espiw spreads with the subtropical gyre circulation and can be traced to at least 150 w formed through the process of subduction southeastward of the wind driven gyre circulation the espiw communicates surface properties of the waters off central chile to tropical latitudes

investigation of the excavation damaged zone around deep tbm tunnel using a voronoi element based explicit numerical manifold method abstract a voronoi element based explicit numerical manifold method is adopted to investigate the evolution process and failure characteristics of the excavation damaged zone around a deeply buried tbm tunnel an explicit time integration scheme of numerical manifold method is adopted as the numerical platform based on which a voronoi polygon assemblage is generated to approximate the blocky structure of the surrounding rock mass resulting from discrete fracture networks a new mathematical mesh generation method is developed to better adapt to the voronoi polygons and an excavation algorithm including both in situ stress equilibrium and tbm excavation modelling techniques is proposed to capture the mechanical response of the tbm tunnelling process with the newly developed ve enmm approach the progressive failure process of the surrounding rock mass in a headrace tunnel of yindajihuang project is simulated and the formation mechanism of the excavation damaged zone is explored simulation results show that a large extent of excavation damaged zone is easily formed in the highly fractured rock mass due to the high in situ stress in deep grounds besides relatively large convergence displacements are predicted around the tunnel surface leading to a high risk of tbm shield jamming as in the practical situation however the development of damaged zone is effectively restrained and the convergence displacements are well controlled by an early installation of the tunnel lining segments thus preventing the occurance of tbm shield jamming additional simulations are conducted to study the effects of the lateral in situ stress ratio on the excavation damaged zone it is inferred that the increase of lateral stress ratio facilitates the fracturing of the surrounding rock mass which results in a larger extent of the damaged zone and more severe squeezing deformation compared with those under lower lateral stresses

hydrothermal contribution to the oceanic dissolved iron inventory mineral dust and marine sediment resuspension are generally considered the primary sources of the nutrient iron to the oceans numerical model results suggest that iron released by hydrothermal activity is also an important source of dissolved iron particularly in the southern ocean iron limits phytoplankton growth and hence the biological carbon pump in the southern ocean1 models assessing the impacts of iron on the global carbon cycle generally rely on dust input and sediment resuspension as the predominant sources2 3 although it was previously thought that most iron from deep ocean hydrothermal activity was inaccessible to phytoplankton because of the formation of particulates4 it has been suggested that iron from hydrothermal activity5 6 7 may be an important source of oceanic dissolved iron8 9 10 11 12 13 here we use a global ocean model to assess the impacts of an annual dissolved iron flux of approximately 9 108 mol as estimated from regional observations of hydrothermal activity11 12 on the dissolved iron inventory of the world s oceans we find the response to the input of hydrothermal dissolved iron is greatest in the southern hemisphere oceans in particular observations of the distribution of dissolved iron in the southern ocean3 chever et al manuscript in preparation bowie et al manuscript in preparation can be replicated in our simulations only when our estimated iron flux from hydrothermal sources is included as the hydrothermal flux of iron is relatively constant over millennial timescales14 we propose that hydrothermal activity can buffer the oceanic dissolved iron inventory against shorter term fluctuations in dust deposition

effect of heterogeneity of brittle rock on micromechanical extensile behavior during compression loading a grain based universal distinct element code model was developed to generate a deformable polygonal grain like structure to simulate the microstructure of brittle rock it takes into account grain scale heterogeneity including microgeometric heterogeneity grain scale elastic heterogeneity and microcontact heterogeneity the microgeometric heterogeneity can be used to match the grain size distribution of the rock the discrete element approach is able to simulate the microheterogeneity caused by elastic variation and contact stiffness anisotropy the modeling approach was evaluated using lac du bonnet granite and a aspo diorite the microheterogeneity played an important role in controlling both the micromechanical behavior and the macroscopic response when subjected to uniaxial compression loading the crack initiation stress was found to be controlled primarily by the microscale geometric heterogeneity while the microcontact heterogeneity controlled the strength characteristics the effect of heterogeneity on the distribution and evolution of tensile stresses and associated extension cracks was also examined

south pacific dissolved nd isotope compositions and rare earth element distributions water mass mixing versus biogeochemical cycling despite its enormous extent and importance for global climate the south pacific has been poorly investigated in comparison to other regions with respect to chemical oceanography here we present the first detailed analysis of dissolved radiogenic nd isotopes end and rare earth elements rees in intermediate and deep waters of the mid latitude 40 s south pacific along a meridional transect between south america and new zealand the goal of our study is to gain better insight into the distribution and mixing of water masses in the south pacific and to evaluate the validity of nd isotopes as a water mass tracer in this remote region of the ocean the results demonstrate that biogeochemical cycling scavenging processes in the eastern equatorial pacific and release of lrees from the sediment clearly influence the distribution of the dissolved ree concentrations at certain locations nevertheless the nd isotope signatures clearly trace water masses including aaiw antarctic intermediate water average end 8 2 0 3 lcdw lower circumpolar deep water average end 8 3 0 3 npdw north pacific deep water average end 5 9 0 3 and the remnants of nadw north atlantic deep water average end 9 7 0 3 filtered water samples taken from the sediment water interface under the deep western boundary current off new zealand suggest that boundary exchange processes are limited at this location and highlight the spatial and temporal variability of this process these data will serve as a basis for the paleoceanographic application of nd isotopes in the south pacific

nd isotopic structure of the pacific ocean 40 10 ma and evidence for the reorganization of deep north pacific ocean circulation between 36 and 25 ma abstract early paleogene neodymium nd isotopic reconstructions of ocean circulation in the pacific suggest a bipolar mode of overturning circulation characterized by convection of deep water masses from 70 to at least 40 ma this mode is fundamentally different from the sluggish diffusive mode that characterizes the modern north pacific therefore major reorganization of pacific circulation must have occurred between 40 ma and the modern to investigate the potential timing of such a reorganization we present new nd isotope data from drill sites spanning 40 to 10 ma here we use nd isotopic analyses to identify the sources of dissolved nd to the pacific in order to evaluate the application of the nd proxy for ancient water mass composition we combine analyses of fossil fish debris sequentially leached oxide coatings and leach residues to further refine our understanding of nd marine geochemical cycling and to contribute new constraints on the paleoceanographic history of the pacific overall these data support previous interpretations of the convection of deep water in the pacific sector of the southern ocean and surface ventilated north pacific deep water formation from 70 to 40 ma the new nd isotope data suggest a gradual transition between 36 and 25 ma a time period characterized by global cooling this transition consists of a change from north pacific nd isotopic signatures controlled by convection and water mass mixing to values heavily influenced by overprinting from other sources of nd to the deep pacific such a transition is consistent with a change in overturning circulation from a paleogene mode to a mode dominated by sluggish diffusive mixing after 25 ma the data indicate a significant contribution of radiogenic dissolved nd to the deep waters of the north pacific the most likely source of radiogenic dissolved nd would have been labile volcanic ash that altered the composition of the water mass as it slowly advected through the north pacific a slowing of overturning circulation in the north pacific could have resulted in diminished poleward heat transport increasing equator to pole thermal gradients and contributing to a cooling global climate

fish from the upper devonian of the shan thai terrane indicate proximity to east gondwana and south china terranes we report the first discovery of abundant devonian vertebrates from thailand an unusual form of coronodontid shark tooth with six equal sized cusps occurs only in the upper devonian of thailand shan thai terrane and south china and a new species of phoebodus is reported that occurs elsewhere only in south china and australia east gondwana terrane the occurrence of the chondrichthyan harpagodens thrinacodus ferox turner 1982 in the late devonian of thailand australia and south china predates the appearance of this species in euramerica early carboniferous these data suggest late devonian proximity of the shan thai south china and east gondwana terranes and is in accord with recent paleomagnetic data

the contrasting biogeochemistry of iron and manganese in the pacific ocean abstract vertical and horizontal distributions of dissolved and suspended particulate fe and mn and vertical fluxes of these metals obtained with sediment traps were determined throughout the pacific ocean in general dissolved fe is low in surface and deep waters 0 1 to 0 7 nmol kg with maxima associated with the intermediate depth oxygen minimum zone 2 0 to 6 6 nmol kg vertical distributions of dissolved mn are similar to previous reports exhibiting a surface maximum a subsurface minimum a mn maximum layer coincident with the oxygen minimum zone and lowest values in deep waters near shore removal processes are more intense for dissolved fe than for dissolved mn dissolved mn in the surface mixed layer remains elevated much farther offshore than dissolved fe elevated near surface dissolved mn concentrations occur in the north pacific equatorial current suggesting transport from the eastern boundary near surface mixed layer dissolved mn concentrations are higher in the north pacific gyre reflecting enhanced northern hemisphere aeolian sources residence time estimates for the settling of refractory paniculate fe and mn from the upper water column are 62 220 days fe and 105 235 days mn in contrast residence times for the scavenging of dissolved fe and mn are 2 13 years fe and 3 74 years mn scavenging residence times for dissolved mn based on horizontal mixing in the surface mixed layer of the northeast pacific are 0 4 years nearshore to 19 years 1000 km offshore there is no evidence for in situ fe redox dissolution within sub oxic waters in the eastern tropical north pacific dissolved fe appeared to be controlled by dissolution from sub oxic sediments with oxidative scavenging in the water column or upper sediment layers however in situ mn dissolution within the oxygen minimum zone was evident

a new approach to the nd residence time in the ocean the role of atmospheric inputs concentrations of rare earth elements ree and nd isotopic ratios were analyzed for seawater filtered suspension and sediment trap samples collected in the tropical atlantic ocean eumeli program eutrophic mesotrophic and oligotrophic sites 20 n 18 21 w this is the first ree nd dataset on solution and different sized particles collected at the same site we present direct evidence of the nd isotopic exchange between particulate lithogenic fraction and seawater without significant mass transfer this exchange is probably one of the main factors that simultaneously constrains the nd concentration and isotopic ratio budget we propose a new approach to estimate the residence time of nd in the ocean nd based on isotopic exchange 200 yr nd 1000 yr the exchange requires a partial dissolution of lithogenic nd we estimate that the fraction of soluble nd proportion in atmospheric dust is of the order of 20 based on the isotopic ratios we suggest that the partial dissolution of atmospheric fallout is probably one of the main ree sources of the ocean

rare earth element distributions in the west pacific trace element sources and conservative vs non conservative behavior abstract recent studies suggest that transport and water mass mixing may play a dominant role in controlling the distribution of dissolved rare earth element concentrations ree at least in parts of the north and south atlantic and the pacific southern ocean here we report vertically and spatially high resolution profiles of dissolved ree concentrations ree along a nw se transect in the west pacific and examine the processes affecting the ree distributions in this area surface water ree patterns reveal sources of trace element te input near south korea and in the tropical equatorial west pacific positive europium anomalies and middle ree enrichments in surface and subsurface waters are indicative of te input from volcanic islands and fingerprint in detail small scale equatorial zonal eastward transport of tes to the iron limited tropical east pacific the low ree of north and south pacific tropical waters and antarctic intermediate water are a long range i e preformed laterally advected signal whereas increasing ree with depth within north pacific intermediate water result from release from particles optimum multiparameter analysis of deep to bottom waters indicates a dominant control of lateral transport and mixing on ree at the depth of lower circumpolar deep water 3000 m water depth 75 100 explained by water mass mixing allowing the northward tracing of lcdw to 28 n in the northwest pacific in contrast scavenging in the hydrothermal plumes of the lau basin and tonga fiji area at 1500 2000 m water depth leads to ree deficits 40 60 removal and marked ree fractionation in the tropical west pacific overall our data provide evidence for active trace element input both near south korea and papua new guinea and for a strong lateral transport component in the distribution of dissolved rees in large parts of the west pacific

neodymium isotopic composition in foraminifera and authigenic phases of the south china sea sediments implications for the hydrology of the north pacific ocean over the past 25 kyr end and normalized rare earth elements ree patterns of benthic and planktonic foraminifera and fe mn coatings precipitated on sediments have been investigated for the south china sea scs to 1 assess the reliability of the extraction of past seawater end in the scs and to 2 reconstruct past hydrological changes during the last 25 kyr reductively cleaned mono specific planktonic foraminifera globigerinoides ruber and mixed benthic foraminifera in core top sediments from 1500 to 2400 m display similar end values to those of the modern pacific deep water pdw end of 3 9 to 4 4 furthermore the end of the reductive cleaning solutions shows similar end values to ones obtained on cleaned foraminifera combined with paas normalized ree patterns these results confirm that the oxidative and reductive cleaning procedure applied to foraminifera does not totally remove all of the fe mn coatings and that end values yielded by cleaned planktonic foraminifera retain the end imprint of the bottom and or pore water end values obtained from a leaching procedure carried out on the bulk non decarbonated sediments are comparable to the end values of the modern pdw whereas a similar leaching procedure applied to decarbonated sediments reveals a bias due to contamination with nd deriving from lithogenic particles in core md05 2904 seawater end reconstructed from planktonic foraminifera indicates that the last glacial period is characterized by lower end 5 2 0 2 to 6 4 0 3 than the late holocene 4 1 0 2 assuming that nd input from river does not change strongly the end of the pdw of the northern scs these end variations suggest a higher relative proportions of southern sourced water in the deep water of the western subtropical pacific ocean during the last glacial period

numerical observations of the failure of a laminated and jointed roof and the effective of different support schemes a case study roof failure related to laminated and jointed rock masses has been recognized as a major cause of fatalities in underground coal mines this paper presents numerical simulations of the failure of a laminated and jointed roof using the discrete element method while focusing on the initiation and propagation of and the interactions between microcracks and macroscopic fractures and the development of the associated damage stress and deformation in the laminated and jointed roof numerical modeling shows that the behaviors of bedding planes and vertical joints governed the progressive failure of the laminated and jointed roof microseismic activity corresponding to the development of microcracks in the roof intensified before major roof displacements and subsided in the later stages such activity could serve as a precursor of roof fall events the effectiveness of various support elements rock bolts metal meshes and anchor cables on the roof stability was numerically evaluated rock bolts and or anchor cables produced a banded compressive stress in the laminated roof restricting the separation of bedding planes rock bridges in the bolted roof suppressed the formation of macroscopic fractures and significantly reduced the interactions between fractures the roof skin support with a metal mesh provided confinement to the fractured roof thereby preventing fragmented rocks from falling and restricting progressive spalling between bolts the numerical simulations presented in this paper can be helpful for understanding the likely failure mechanisms of laminated and jointed roofs and for finding potential solutions

multi approach back analysis of a roof bed collapse in a mining room excavated in stratified rock roof bed deformation mechanics is a complex topic in mining practice there are a number of empirical analytical and numerical techniques that can be used to analyze and design underground excavations in stratified rock masses each has particular drawbacks however so the use of just one approach in order to obtain consistent and economic designs is not practical to deepen understanding of this topic it is useful to study real failure in mines in this paper we describe how a roof bed failure in an underground mine excavated in a stratified rock mass was back analyzed using different approaches namely the empirical stability graph method the analytical voussoir techniques and the numerical discrete element method the study enabled us to better understand the conditions of failure and to define the most significant parameters affecting the failure it has also been shown how relaxation or loss of confinement stress can play an important role in roof bed deformation

strontium and neodymium isotopes in hot springs on the east pacific rise and guaymas basin we have determined the concentrations and isotopic compositions of sr and nd in hydrothermal fluids from 21 n east pacific rise and guaymas basin gulf of california the purest solutions analyzed from 21 n exhibit a small range in sr concentration between individual vents from 5 8 to 8 7 ppm close to normal seawater sr concentrations they exhibit a small range in 87 sr 86 sr from e sr 0 13 4 to 17 7 corresponding to e sr 0 18 2 in the pure hydrothermal end member these results indicate extensive but not complete isotopic exchange with sr in the depleted oceanic crust e sr 0 31 8 and suggest that sr concentrations in these solutions are buffered in contrast the concentration and isotopic composition of nd in solutions show large variations between vents the concentration of nd ranges from 20 to 336 pg g 6 100 times seawater nd concentrations the isotopic composition ranges from e nd 0 3 6 similar to pacific seawater to 7 9 many samples show substantial contributions from morb but all have e nd 0 well below morb at this locality e nd 0 9 7 in spite of very large enrichments in nd concentrations while complete isotopic exchange with water rock 2 or exchange with anomalous oceanic crust can explain the sr data the nd data require exchange with a reservoir having e nd 0 pacific seawater low temperature reactions with metalliferous sediments on the ridge flanks may provide such a source both sr and nd in the guaymas basin solution are very different from21 n e sr 0 11 0 and e nd 0 11 4 and are consistent with the fluid exchanging sr and nd with heated sediments having a substantial component of old continental detritus some irregularities in the nd isotopic data reported here indicate that there must be a problem of contamination for some ultra low level trace elements during sample collection and processing which requires further attention using a simple box model the estimates for hydrothermal nd fluxes are compared with fluxes which would be required to maintain the relatively radiogenic value of e nd 0 3 in the pacific against the influx of more negative antarctic waters e nd 0 9 it is shown that the hydrothermal flux of nd from mid ocean ridges falls far short of that necessary to maintain the isotopic balance this indicates that weathered material from volcanic terranes e nd 0 7 is the most reasonable major source of radiogenic nd in the pacific

the distribution of neodymium isotopes and concentrations in the eastern equatorial pacific water mass advection versus particle exchange the radiogenic isotope composition of the rare earth element ree neodymium nd is a powerful water mass proxy for present and past ocean circulation the processes controlling the nd budget of the global ocean are not quantitatively understood and in particular source and sink mechanisms are still under debate in this study we present the first full water column data set of dissolved nd isotope compositions and nd concentrations for the eastern equatorial pacific eep where one of the globally largest oxygen minimum zones omz is located this region is of particular interest for understanding the biogeochemical cycling of rees because anoxic conditions may lead to release of rees from the shelf whereas high particle densities and fluxes potentially remove the rees from the water column data were obtained between 1 40 n and 16 s along a nearshore and an offshore transect near surface zonal current bands such as the equatorial undercurrent euc and the subsurface countercurrent sscc which are supplying oxygen rich water to the omz are characterized by radiogenic nd isotope signatures end 2 surface waters in the northernmost part of the study area are even more radiogenic end 3 most likely due to release of nd from volcanogenic material deep and bottom waters at the southernmost offshore station 14 s are clearly controlled by advection of water masses with less radiogenic signatures end 7 originating from the southern ocean towards the equator however the deep waters show a clear trend towards more radiogenic values of up to end 2 the northernmost station located in the panama basin shows highly radiogenic nd isotope signatures in the entire water column which indicates that particle scavenging downward transport and release processes play an important role this is supported by relatively low nd concentrations in deep waters 3000 6000 m in the eep 20 pmol kg compared to locations in the northern and central pacific 40 60 pmol kg which suggests enhanced removal of nd in the eep

foraminiferal end in the deep north western subtropical pacific ocean tracing changes in weathering input over the last 30 000 years abstract this study focuses on the neodymium isotopic composition end of mixed planktonic foraminifera species in sediment cores collected on the north western margin of the south china sea scs and in the western equatorial pacific the aim was to identify temporal changes in the end of the upper circumpolar deep water ucdw during its northward penetration in the western subtropical pacific and to re evaluate the significance of deep water end changes at the northern margin of the scs over the past 25 kyr the past seawater end record derived from sediments of the subtropical western pacific displays a narrow range from 2 9 0 3 to 1 6 0 4 this suggests that the end of the ucdw is greatly modified during its northward penetration through the process of boundary exchange along the western volcanic margin of the south pacific and that the unradiogenic end signature of the ucdw observed in the south pacific about 6 has not been propagated beyond the equatorial pacific at least not over the last 25 kyr seawater end values obtained from the northern scs display large variations with values that are lower 6 8 0 3 to 5 6 0 2 for the last glacial period than for the late holocene 5 7 0 3 to 4 1 0 2 such glacial end cannot be attributed to a higher proportion of southern sourced water ssw as end values of the ucdw in the equatorial western pacific are more radiogenic than those observed in the scs the evolution of the seawater end values of the northern scs during the last glacial period and the last climatic transition is coeval with variations in the contribution of sediments from the pearl river the low sea level stand of the last glacial period resulted in a more proximal position of the pearl river mouth relative to core md05 2904 which a higher input of freshwater and in particular detrital sedimentary particles originating from the pearl river that partially dissolved during sinking led to a decrease in the seawater end along the north western margin of the scs enhanced rainfalls associated with intensified monsoon and more frequent typhoon activities during the early holocene climatic optimum from 9 to 7 cal kyr bp are linked to a decrease in sea surface salinity lower 18o values of planktonic foraminifera and a decrease in end values 6 2 0 3 induced by lithogenic nd input from pronounced freshwater and sediment discharge from distal rivers

the sedimentary flux of dissolved rare earth elements to the ocean abstract we determined pore fluid rare earth element ree concentrations in near surface sediments retrieved from the continental margin off oregon and california usa these sites represent shelf to slope settings which lie above within and below the oxygen minimum zone of the northeast pacific the sediments are characterized by varying degrees of net iron reduction with pore fluids from the shelf sites being generally ferruginous and the slope sediments having less pronounced iron reduction zones that originate deeper in the sediment package ree concentrations show maxima in shallow upper 2 10 cm subsurface pore fluids across all sites with concentrations that rise more than two orders of magnitude higher than seawater these pore fluid enrichments highlight the importance of a sedimentary source of rees to the ocean s water column here we use our measurements to estimate the diffusive flux of nd out of ocean sediments resulting in a global flux between 18 and 110 10 6 mol nd yr 1 while we do assume that our pore fluid profiles as well as the very limited data previously published are representative of a wide array of ocean environments this calculated flux can account for the modeled missing nd source flux 76 10 6 mol nd yr 1 in global budgets arsouze et al 2009 pore fluid normalized ree patterns show distinct variation in the middle ree and heavy ree enrichments with sediment depth and amongst sites these patterns show that the heavy ree enrichment of pore fluids at our deep slope site 3000 m water depth is closest to the heavy ree enrichment of seawater this observation supports the view that ree cycling within the upper ten centimeters of deep sea marine sediments as opposed to shallower continental shelf and slope sediments plays a significant role in controlling the integrated global ree flux from the pore fluids and consequently the broad scale ree pattern in seawater

the origin of carbonate veins within the sedimentary cover and igneous rocks of the cocos ridge results from iodp hole u1414a carbonate veins in the igneous basement and in the lithified sedimentary cover of the cocos ridge at international ocean discovery program iodp hole 344 u1414a reveal the hydrologic system and fluid rock interactions iodp hole 344 u1414a was drilled on the northern flank of the cocos ridge and is situated 1 km seaward from the middle america trench offshore costa rica isotopic and elemental compositions were analyzed to constrain the fluid source of the carbonate veins and to reveal the thermal history of hole 344 u1414a the formation temperatures oxygen isotope thermometer of the carbonate veins in the lithified sedimentary rocks range from 70 to 92 c and in the basalt from 32 to 82 c 87sr 86sr ratios of the veins in the altered cocos ridge basalt range between 0 707307 and 0 708729 the higher ratios are similar to seawater strontium ratios in the neogene 87sr 86sr ratios lower 0 7084 indicate exchange of sr with the igneous host rock the calcite veins hosted by the sedimentary rocks are showing more primitive 87sr 86sr ratios 0 706396 the isotopic compositions indicate seawater modified into a hydrothermal fluid by subsequent heating as the main fluid source low temperature alteration and the presence of a high temperature fluid resulted in different carbonate precipitates forming up to several cm thick veins the geochemical data combined with age data of the sedimentary rocks suggest intraplate seamount volcanism in the area between the galapagos hot spot and the cocos island as an additional heating source after the formation of the cocos ridge at the galapagos hot spot

composition and timing of carbonate vein precipitation within the igneous basement of the early cretaceous shatsky rise nw pacific numerous calcium carbonate veins were recovered from the igneous basement of the early cretaceous shatsky rise during integrated ocean drilling program iodp expedition 324 the chemical sr ca mg ca and isotopic 87sr 86sr 143nd 144nd 18o 13c compositions of these veins were determined to constrain the timing of vein formation a dominant control by seawater chemistry on calcite composition is evident for most vein samples with variable contributions fromthe basaltic basement slightly elevated precipitation temperatures as inferred from oxygen isotope ratios indicative of hydrothermal vein formation are only observed at site u1350 in the central part of shatsky rise the highest 87sr 86sr ratios least basement influence of vein samples at each drill site range from 0 70726 to 0 70755 and are believed to reflect the contemporaneous seawater composition during the time of calcite precipitation in principle age information can be deduced by correlating these ratios with the global seawater sr isotope evolution since the sr isotopic composition of seawater has fluctuated three times between the early and mid cretaceous no unambiguous precipitation ages can be constrained by this method and vein precipitation could have occurred at any time between 80 and 140 ma however based on combined chemical and isotopic data and correlations of vein compositionwith formation depth and inferred temperature we argue for a rather early precipitation of the veins shortly after basement formation at each respective drill site

water masses in the humboldt current system properties distribution and the nitrate deficit as a chemical water mass tracer for equatorial subsurface water off chile abstract three sections are used to analyze the physical and chemical characteristics of the water masses in the eastern south pacific and their distributions oceanographic data were taken from the scorpio may june 1967 piquero may june 1969 and krill june 1974 cruises vertical sections of temperature salinity dissolved oxygen nitrate nitrite phosphate and silicate were used to analyze the water column structure five water masses were identified in the zone through t s diagrams subantarctic water subtropical water equatorial subsurface water antarctic intermediate water and pacific deep water their proportions in the sea water mixture are calculated using the mixing triangle method vertical sections were used to describe the geographical distributions of the water mass cores in the upper 1500 m several characteristic oceanographic features in the study area were analyzed the shallow salinity minimum displacement towards the equator the equatorial subsurface salinity maximum associated with a dissolved oxygen minimum zone and a high nutrient content displacement towards the south and the equatorward intermediate antarctic salinity minimum associated with a dissolved oxygen maximum the nitrate deficit generated in the denitrification area off peru and northern chile is proposed as a conservative chemical tracer for the equatorial subsurface waters off the coast of chile south of 25 s

composition of rare earth elements in settling particles collected in the highly productive north pacific ocean and bering sea implications for siliceous matter dissolution kinetics and formation of two ree enriched phases abstract settling particles were sampled monthly for 1 year using an automated time series sediment trap positioned at similar depths at two sites of high diatomaceous productivity in the north pacific ocean and bering sea the particles were analyzed for rare earth elements rees by inductively coupled plasma mass spectrometry icp ms with and without chemical treatment of the bulk samples to isolate siliceous fractions the ree composition of the bulk samples is explained largely by the contribution of two distinct components i carbonate with a higher ree concentration a negative ce anomaly and lighter ree lree enrichment ii opal with a lower ree concentration a weaker negative ce anomaly and heavier ree hree enrichment the siliceous fractions of settling particles are characterized by high si al ratios 30 190 reflecting high diatom productivity at the studied sites the la al ratio of the siliceous fraction is close to that of the upper crust but the lu al and lu la ratios are significantly higher than those of the upper crust or airborne particles indicating the presence of excess hrees in the siliceous fraction diatoms are believed to be important carriers of hrees the ce anomaly eu anomaly slope of the ree pattern and ree of the siliceous fraction vary exponentially with decreasing total mass flux they can be well reproduced according to the differential dissolution kinetics of elements in the order of ce

mechanical degradation of emplacement drifts at yucca mountain a modeling case study part i nonlithophysal rock abstract this paper outlines rock mechanics investigations associated with mechanical degradation of planned emplacement drifts at yucca mountain which is the designated site for the proposed us high level nuclear waste repository the welded tuff emplacement horizon consists of two groups of rock with distinct engineering properties nonlithophysal and lithophysal units based on the relative proportion of lithophysal cavities the term lithophysal refers to hollow bubble like cavities in volcanic rock that are surrounded by a porous rim formed by fine grained alkali feldspar quartz and other minerals lithophysae are typically a few centimeters to a few decimeters in diameter part i of the paper concentrated on the degradation behavior of the generally hard strong and fractured nonlithophysal rock part ii concentrates on the host rock in the lithophysal units lithophysal rock is characterized by lithophysal cavities interconnected by fracturing fracture sets are not as clearly defined as in the nonlithophysal rock the rock mass porosity in the lithophysal units has been shown to be the primary physical factor that governs elastic and strength properties the degradation behavior of the tunnels in the lithophysal rock is controlled by the spalling of the surrounding rock mass a discontinuum material model has been developed to represent the drift scale rock mass properties in which slip and separation of contacting rock blocks can be estimated two dimensional discontinuum analyses were developed with the consideration of in situ thermal and seismic loads time dependent degradation was also considered in this study field and laboratory data and numerical analyses are well integrated to provide a solution for the unique problem of modeling drift degradation

neodymium isotopic composition and concentration in the western north atlantic ocean results from the geotraces ga02 section the neodymium nd isotopic composition of seawater is commonly used as a proxy to study past changes in the thermohaline circulation the modern database for such reconstructions is however poor and the understanding of the underlying processes is incomplete here we present new observational data for nd isotopes and concentrations from twelve seawater depth profiles which follow the flow path of north atlantic deep water nadw from its formation region in the north atlantic to the northern equatorial atlantic samples were collected during two cruises constituting the northern part of the dutch geotraces transect ga02 in 2010 the results show that the different water masses in the subpolar north atlantic ocean which ultimately constitute nadw have the following nd isotope characteristics upper labrador sea water ulsw end 14 2 0 3 labrador sea water lsw end 13 7 0 9 northeast atlantic deep water neadw end 12 5 0 6 northwest atlantic bottom water nwabw end 11 8 1 4 in the subtropics where these source water masses have mixed to form nadw which is exported to the global ocean upper nadw is characterised by end values of 13 2 1 0 2sd and lower nadw exhibits values of end 12 4 0 4 2sd while both signatures overlap within error the signature for lower nadw is significantly more radiogenic than the traditionally used value for nadw end 13 5 due to the dominance of source waters from the nordic seas nwabw and neadw comparison between the concentration profiles and the corresponding nd isotope profiles with other water mass properties such as salinity silicate concentrations neutral densities and chlorofluorocarbon cfc concentration provides novel insights into the geochemical cycle of nd and reveals that different processes are necessary to account for the observed nd characteristics in the subpolar and subtropical gyres and throughout the vertical water column while our data set provides additional insights into the contribution of boundary exchange in areas of sediment resuspension the results for open ocean seawater demonstrate at an unprecedented level the suitability of nd isotopes to trace modern water masses in the strongly advecting western atlantic ocean

towards explaining the nd paradox using reversible scavenging in an ocean general circulation model abstract the isotopic composition of the rare earth element neodymium nd has the potential to serve as water mass tracer because it is naturally tagged by continental sources with distinct ages and lithologies however in order to understand the limitations of this approach we need to know more about the physical and biogeochemical processes controlling the distribution of nd in the modern ocean for example nd isotope ratios behave quasi conservatively while concentrations in the water column generally increase with depth showing a broadly nutrient like behaviour we define this decoupling of nd concentrations and isotopic compositions as the nd paradox for the first time we model nd concentrations and isotopic compositions simultaneously and address the hypothesis that the nd paradox can be explained by a combination of lateral advection and reversible scavenging we impose a reversible scavenging model of nd removal from the ocean on the ocean circulation fields from the mit general circulation model using the transport matrix method we conclude that reversible scavenging is an active and important component in the cycling of nd in the ocean in the absence of an adequate alternative explanation reversible scavenging should be considered a necessary component in explaining the nd paradox

strength reduction on saturation of coal and coal measures rocks with implications for coal pillar strength coal and associated coal measures rocks including shales mudstones and sandstones may lose significant strength on water saturation due to the absorption of water stress corrosion or mineralogical changes to the clays within the rock matrix as most coal seams are natural aquifers water ingress into underground mine workings is common and is typically controlled during mining by dewatering pumps after a mine has closed unless ongoing pumping is maintained workings will flood and coal pillars and the pillar roof and floor foundations will revert to fully saturated conditions this paper reports on a study of how flooding effects pillar strength in an abandoned coal mine in queensland australia the reduction in strength of coal and coal measures rocks between unsaturated and saturated water moisture contents has been quantified through physical testing these strength data along with the distribution of lithologies in a coal pillar from the mine were used as inputs for numerical modelling of the strength reduction of a coal pillar on water saturation it was found that the modelled pillar strength reduction could be estimated by the average strength reduction of all the lithological components of the pillar weighted by the thickness of each lithology

from the subtropics to the central equatorial pacific ocean neodymium isotopic composition and rare earth element concentration variations 1 neodymium isotopic compositions end and rare earth element ree concentrations were measured for filtered surface to deep waters 112 samples in the southern tropical pacific the relatively detailed picture of these tracer distributions allowed us to refine the areas where oceanic end variations occur end values increase for most of the water masses flowing from samoa to the solomon sea and in the papua new guinea png area as already observed furthermore water masses arriving from the eastern equatorial pacific 200 550 m depth also revealed radiogenic values possibly acquired in the vicinity of the south american coasts and galapagos islands these end variations affect the whole water column the most likely process causing such variations is boundary exchange between the numerous radiogenic slopes margins located in this area and seawater flowing past dissolution of atmospheric deposition and or diffuse streaming of volcanic ash are also suggested to explain the radiogenic end observed at the surface in the png area interestingly a positive europium eu anomaly characterizes the normalized ree patterns of most of the studied water masses this anomaly is consistent with the ree patterns of sediment and rock samples that are potential sources for the local waters such consistency reinforces the hypothesis that lithogenic sources play a major role in the oceanic ree budget thanks to boundary exchange the data set presented here is a good basis for further sampling that will be realized in the framework of the ongoing geotraces program www geotraces org

seasonal variations in the siliciclastic fluxes to the western philippine sea and their impacts on seawater end values inferred from 1 year of in situ observations above benham rise

a preliminary analysis of failure mechanisms in karst and man made underground caves in southern italy abstract natural and anthropogenic caves may represent a potential hazard for the built environment due to the occurrence of instability within caves that may propagate upward and eventually reach the ground surface inducing the occurrence of sinkholes in particular when caves are at shallow depth the effects at the ground surface may be extremely severe apulia region southern italy hosts many sites where hazard associated with sinkholes is very serious due to presence of both natural karst caves and anthropogenic cavities the latter being mostly represented by underground quarries the pliocene pleistocene calcarenite a typical soft rock was extensively quarried underground by digging long and complex networks of tunnels with time these underground activities have progressively been abandoned and their memory lost so that many apulian towns are nowadays located just above the caves due to urban expansion in the last decades therefore a remarkable risk exists for society which should not be left uninvestigated the present contribution deals with the analysis of the most representative failure mechanisms observed in the field for such underground instability processes and the factors that seem to influence the processes as for example those causing weathering of the rock and the consequent degradation of its physical and mechanical properties aimed at exploring the progression of instability of the cavities numerical analyses have been developed by using both the finite element method for geological settings represented by continuous soft rock mass and the distinct element method for jointed rock mass conditions both the effects of local instability processes occurring underground and the effects of the progressive enlargement of the caves on the overall stability of the rock mass have been investigated along with the consequent failure mechanisms in particular degradation processes of the rock mass as a consequence of wetting and weathering phenomena in the areas surrounding the caves have been simulated the results obtained from the numerical simulations have then been compared with what has been observed during field surveys and a satisfactory agreement between the numerical simulations and the instability processes as detected in situ has been noticed

rare earth elements and nd isotopes as tracers of modern ocean circulation in the central mediterranean sea abstract seawater rare earth element ree concentrations and nd isotopic composition end are increasingly applied as valuable tracers of oceanographic processes such as water mass mixing and lithogenic inputs to seawater however their measurements are basically lacking in the mediterranean sea water column this study analyzes 9 seawater stations around the central mediterranean sea to clarify the relative importance of external sources vertical biogeochemical processes and lateral water mass transport in controlling ree and end distributions concentrations of ree do not show nutrient like profiles with depth likely indicative of relatively young waters with limited accumulation of remineralized ree light ree lree present a non conservative behavior which largely peak at surface waters and rapidly decrease with depth the negative correlation of surface lree enrichment with offshore distance highlights the influence of continental input from the western italian coast to the tyrrhenian surface waters in contrast to other regions with reported boundary exchange this process does not modify the end values here on the other side distributions of dissolved heavy ree hree and end display a conservative behavior that can be explained by mixing of western maw and wmdw and eastern liw and emdw originated waters we test this hypothesis with an optimum multi parameter analysis ompa including hree and end parameters even though the limited data set consistent results of water mass fractions are obtained for the four main water masses although with some particularities while liw takes on major importance when considering hree in the model emdw fractions are preferentially detected with end this latter finding implies a noticeable deep water flux across the sicily strait into the western mediterranean that was not clearly evidenced before

tracing papua new guinea imprint on the central equatorial pacific ocean using neodymium isotopic compositions and rare earth element patterns abstract the nd isotopic composition ic and rare earth patterns of hydrodynamic structures of the equatorial pacific ocean were characterized along 140 w the nd ic of antarctic intermediate water aaiw and of the lower layer of the equatorial undercurrent euc at 140 w 13 c water are much more radiogenic at the equator than at their origin in the south equatorial current 12 s revealing that these water masses have been in contact with the highly radiogenic papua new guinea png slope in both cases only a small fraction less than 9 of the sediment deposited on the png slope is required to be exchanged or dissolved to explain these nd ic variations whereas the hydrographic properties of the same water masses remain unchanged this confirms the usefulness of this tracer to identify pathways of water masses these results emphasize the importance of jets in transporting lithogenic material into the subsurface layers of remote areas where aeolian inputs are particularly weak and corroborate the previous results on fe and al maximum in this area m l wells g k vallis e a silver nature 398 1999 601 604 the nd ic of the upper layer of the euc contrasts strongly to that of the subpycnocline layer indicating that the equatorial upwelling only affects the surface waters and is not effective between 120 and 150 m we calculate that the nd imprint of the png input is likely to vanish from this surface layer as it traverses the basin due to the replacement of upwelled waters by non radiogenic ones

dissolved rare earth elements distribution in the solomon sea abstract trace elements and isotopes teis were measured as part of the geotraces pandora cruise july august 2012 r v l atalante among them rare earth elements rees as pertinent tracers of land ocean inputs and water mass transformations this work discusses results of 19 dissolved ree dree profiles measured using a trispike method in the coral sea and inside and at the exits of the solomon sea a semi enclosed sea with complex topography and straits overall drees except the insoluble ce show nutrient like profiles i e depleted at the surface and enriched at depth illustrative nd concentrations range from 5 pmol kg at the surface to 25 pmol kg at 5000 m depth however local dree enrichments are observed mostly in the straits indispensable solomon and vitiaz straits and along the island coasts a box model allows calculating and discussing the fate of the drees in the different water layers flowing through the solomon sea finally subtle variations revealed by la ce eu anomalies and the normalized light versus heavy ree ratio expressed as ndn ybn allows the identification of specific mechanisms affecting the distribution of the different drees the positive eu anomaly observed in the surface layers reflects the basaltic origin of external inputs consistent with the intensive weathering and or volcanic activity affecting the surrounding islands these data also confirm that the distributions of heavy drees like yb are better correlated to the dsi concentrations than that of the other rees this article is part of a special issue entitled cycles of trace elements and isotopes in the ocean geotraces and beyond edited by tim m conway tristan horner yves plancherel and aridane g gonzalez

hawaiian imprint on dissolved nd and ra isotopes and rare earth elements in the central north pacific local survey and seasonal variability abstract dissolved neodymium isotopes 143nd 144nd expressed as end and rare earth elements rees have the potential to trace the provenance of lithogenic material as well as water masses the central north pacific is poorly investigated with respect to its nd isotope signature and ree cycling and little is known about the contributions of volcanic islands such as hawaii relative to dust input from asian deserts to the surface water ree budgets here we present dissolved nd isotope and ree data along with long lived radium isotope activities from hawaii ocean time series station aloha and coastal waters from oahu sampled for a geotraces process study in february 2011 the data are supplemented with seasonal samples from aloha our results show a clear influence of the hawaiian islands on the coastal ocean and surface waters at aloha during february expressed by higher surface water ra activities radiogenic surface end end 1 4 to 1 0 and elevated eu anomalies eu eu 1 3 seasonal cycles of asian dust deposition most likely contribute to the seasonal end variability of surface waters at aloha as suggested by more negative end and the lack of eu anomalies in summer neodymium isotopes in the intermediate and deep water column at aloha trace typical north pacific water masses such as north pacific intermediate water and north pacific deep water we suggest that a radiogenic end excursion in 1000 2000 m water depth observed in various north pacific profiles is controlled by advection of a modified upper circumpolar deep water or north equatorial pacific intermediate water we further present an updated average end signature of 3 5 0 5 for north pacific deep water and show that ree patterns of deep waters at aloha are dominantly controlled by vertical processes

variability of neodymium isotopes associated with planktonic foraminifera in the pacific ocean during the holocene and last glacial maximum abstract the deep pacific ocean holds the largest oceanic reservoir of carbon which may interchange with the atmosphere on climatologically important timescales the circulation of the deep pacific during the last glacial maximum lgm however is not well understood neodymium nd isotopes of ferromanganese oxide coatings precipitated on planktonic foraminifera are a valuable proxy for deep ocean water mass reconstruction in paleoceanography in this study we present nd isotope compositions e nd of planktonic foraminifera for the holocene and the lgm obtained from 55 new sites widely distributed in the pacific ocean the holocene planktonic foraminiferal e nd results agree with the proximal seawater data indicating that they provide a reliable record of modern bottom water nd isotopes in the deep pacific there is a good correlation between foraminiferal e nd and seawater phosphate concentrations r 2 0 80 but poorer correlation with silicate r 2 0 37 our interpretation is that the radiogenic nd isotope is added to the deep open pacific through particle release from the upper ocean during deep water mass advection and aging the data thus also imply the nd isotopes in the pacific are not likely to be controlled by silicate cycling in the north pacific the glacial nd isotopic compositions are similar to the holocene values indicating that the nd isotope composition of north pacific deep water npdw remained constant 3 5 to 4 during the lgm the southwest pacific cores throughout the water column show higher e nd corroborating previous studies which suggested a reduced inflow of north atlantic deep water to the pacific however the western equatorial pacific deep water does not record a corresponding radiogenic excursion implying reduced radiogenic boundary inputs during the lgm probably due to a shorter duration of seawater particle interaction in a stronger glacial deep boundary current a significant negative glacial e nd excursion is evident in mid depth 1 2 km cores of the eastern equatorial pacific eep which may suggest a stronger influence of npdw return flow to the core sites and decreased local input in the eep taken together our nd records do not support a dynamically slower glacial pacific overturning circulation and imply that the increased carbon inventory of pacific deep water might be due to poor high latitude air sea exchange and increased biological pump efficiency in glacial times

dispersal patterns for hydrothermal plumes in the south pacific using manganese as a tracer abstract manganese profiles over the spreading axis of the east pacific rise epr between 22 15 s and 19 25 s disclose a series of plumes which are formed by buoyant emanations of hot hydrothermal vent fluids the plume ceilings or anomaly maxima can occur several hundred meters above the sea floor these plumes are dispersed laterally and are detectable as mid depth manganese anomalies 2000 km from the spreading axis along this section the plumes are dispersed mainly westward but at 30 s the plumes are advected eastward the asymmetrical dispersal pattern inferred from these data is coincident with the asymmetrical distribution of metalliferous sediments about the epr which suggests that plumes generated by high temperature venting play a dominant role in the formation of these sediments

water weakening behavior of hawkesbury sandstone in brittle regime abstract this paper investigates the effect of water on the mechanical behavior of intact hawkesbury sandstone a massive rock formation in sydney australia two sets of cylindrical samples air dried and water saturated were tested under the confining pressures of 4 10 18 and 25 mpa water saturated samples were tested under undrained conditions with initial pore water pressures of 1 4 7 2 and 10 mpa respectively initial pore water pressure was observed to increase with increasing deviatoric stress during undrained tests and the maximum induced pore water pressure was observed to increase with increasing effective confining pressure peak effective strength showed an increasing trend with increasing confining pressure for both sample sets and the strengths of dry samples were always greater peak strength drops of 13 36 25 27 34 70 and 38 12 were observed due to water at the confining pressures of 4 10 18 and 25 mpa respectively results for the residual strength of tested samples displayed that it increased with increasing confining pressure for both sample sets the volumetric strain response revealed that the volume reduction due to compaction increases with increasing confining pressure and dilatancy related volume increase close to sample failure was not significant at higher confining pressures for both sample sets the samples tested under dry conditions showed a considerably higher volume reduction by compaction than that for the samples tested under undrained conditions analysis of failure mechanisms indicated that all samples failed mainly by shear localization where the angle of the failure plane measured from the minor principal stress direction was varied from c 55 to c 45 for dry samples and from c 50 to c 40 for the samples tested under undrained conditions at 4 and 25 mpa confining pressures respectively fracture propagation behavior was studied using an acoustic emission detection system and the results demonstrated that the micro crack initiation occurred very close to the failure stress under low confining pressures leading to a more brittle sudden failure w hereas under higher confining pressures it occurred relatively earlier compared to the failure stress showing more quasi brittle characteristics

the geochemical balance of the rare earth elements and neodymium isotopes in the oceans profiles of ree concentrations and neodymium isotope measurements in the western indian ocean are consistent with published data from the other major oceans ree concentrations show a strong hydrographic control the influence of intermediate water masses is particularly significant surface water concentrations vary with salinity paniculate rees are less than 5 of dissolved concentration except for ce where up to 20 of total rees are present as 0 4 m particles in contrast to dissolved profiles concentration profiles of paniculate rees including ce all increase with depth ree concentrations correlate with silica over all but the deepest waters although in detail correlations are complex the neodymium isotopic composition of indian ocean seawater avg nd 0 8 3 is intermediate between that for the atlantic and pacific oceans comparison of ree data from the major oceans shows that the hrees behave more like si than do the lrees sm nd ratios are near constant for all oceans whereas ernd ratios vary between the atlantic indian and pacific oceans the fractionation of the rees in surface seawaters can be explained by fractionation factors relative to silica from 0 12 for la to 0 05 for er use of a seven box model shows that the interoceanic variations in neodymium isotopic compositions and nd concentrations cannot be reconciled unless particle water exchange is invoked the degree of exchange required is consistent with particle residence times of 1 10 yr

vertical and horizontal extension of the oxygen minimum zone in the eastern south pacific ocean recent hydrographic measurements within the eastern south pacific 1999 2001 were combined with vertically high resolution data from the world ocean circulation experiment high resolution profiles and bottle casts from the world ocean database 2001 and the world ocean atlas 2001 in order to evaluate the vertical and horizontal extension of the oxygen minimum zone 600 m off peru between 5 and 13 s and to about 1000 km offshore its upper boundary is shallowest 150 m off peru shoaling towards the coast and extending well into the euphotic zone in some places offshore the thickness and meridional extent of the oxygen minimum zone decrease until it finally vanishes at 140 w between 2 and 8 s moving southward along the coast of south america the zonal extension of the oxygen minimum zone gradually diminishes from 3000 km 15 s to 1200 km 20 s and then to 25 km 30 s only a thin band is detected at 37 s off concepcion chile simultaneously the oxygen minimum zone s maximum thickness decreases from 300 m 20 s to less than 50 m south of 30 s the spatial distribution of ekman suction velocity and oxygen minimum zone thickness correlate well especially in the core off chile the eastern south pacific intermediate water mass introduces increased vertical stability into the upper water column complicating ventilation of the oxygen minimum zone from above in addition oxygen enriched antarctic intermediate water clashes with the oxygen minimum zone at around 30 s causing a pronounced sub surface oxygen front the new estimates of vertical and horizontal oxygen minimum zone distribution in the eastern south pacific complement the global quantification of naturally hypoxic continental margins by helly and levin 2004 global distribution of naturally occurring marine hypoxia on continental margins deep sea research i 51 1159 1168 and provide new baseline data useful for studies on the role of oxygen in the degradation of organic matter in the water column and the related implications for biogeochemical cycles coastal upwelling zones along the eastern pacific combine with general circulation to provide a mechanism that allows renewal of upper pacific deep water the most oxygen poor and oldest water mass of the world oceans

the mechanism for antarctic intermediate water renewal in a world ocean model abstract realistic representation of the low salinity tongue of antarctic intermediate water aaiw has been achieved in a coarse resolution ocean general circulation model the authors find that this water mass is not generated by direct subduction of surface water near the polar front instead the renewal process is concentrated in the southeast pacific ocean off southern chile the outflow of the east australian current progressively cools by heat loss to the atmosphere and freshens by assimilation of polar water carried north by the surface ekman drift during its slow movement across the south pacific toward the aaiw formation zone further deep warm advection near chile enables more convective overturn resulting in very deep mixed layers from which aaiw is fed into the south pacific and also into the malvinas current along with this isolated region of aaiw renewal the model relies on alongisopycnal mixing of fresh surface water from the polar front to capture a realistic circumpolar tongue

the neodymium isotopic composition of waters masses in the eastern pacific sector of the southern ocean the antarctic circumpolar current is one of the key components of ocean circulation and a knowledge of its isotopic composition is essential to the use of neodymium nd isotopes to trace circulation now and in the past here we present 57 new analyses of the nd isotopic composition of the water column in the eastern pacific sector of the southern ocean documenting both the variation in three dimensions as well as the controls on that variability nd isotopic data for the middle of the water column demonstrate the homogeneity of circumpolar deep water cdw at an end value of 8 7 0 1 this homogeneity reflects the large nd inventory in the acc flow and the degree to which this large inventory buffers the nd characteristics of the acc against extra oceanic inputs from the continents either via dust from the atmosphere or through dissolved and particulate material from the adjacent continents cdw upwells onto the amundsen sea shelf and even here its nd isotopic properties are close to conserved in the middle of the water column end 8 0 0 2 at 600 m at the top and bottom of the shelf water column however the nd isotopic and concentration characteristics are strongly modified to end as high as 4 5 all the shelf water column data obtained here are consistent with net addition of nd to bottom and surface waters with a contrasting isotopic composition that is matched by local sediment end 1 to 2 followed by conservative mixing of that water into intermediate levels mixing with this shelf composition also leads to significant modification of open ocean surface water nd isotopic shift around 1 epsilon unit in the acc as it flows eastwards modification of open ocean bottom waters by interaction with sediment is more subtle but there is marked non conservative removal of nd accompanied by significant changes in isotopic composition in waters within 10 m of the seabed the new data demonstrate the conservativity of nd in the middle water column especially for such large volume flows as the acc though boundary exchange type processes are clearly important in this region and their imprint on both the shelf and open ocean surface water is significant there is no observable impact on the main core of cdw this finding augurs well for the use of nd isotopes as a conservative water mass tracer now and in the past for example these data suggest that the only likely control on the temporal variability of southern component deep water exported northwards into the atlantic through the last glacial cycle is variations in the input of north atlantic deep water in the atlantic sector on the other hand the data also suggest caution in the use of sedimentary archives of bottom water nd as records of deep water nd isotopic characteristics given the dramatic modification of bottom waters on the shelf and the more subtly non conservative behaviour in the open ocean bottom water that are both suggestive of modification of the nd characteristics of bottom waters by sediment

rare earth element behavior during groundwater seawater mixing along the kona coast of hawaii abstract groundwater and seawater samples were collected from nearshore wells and offshore along the kona coast of the big island of hawaii to investigate rare earth element ree behavior in local subterranean estuaries previous investigations showed that submarine groundwater discharge sgd is the predominant flux of terrestrial waters to the coastal ocean along the arid kona coast of hawaii groundwater and seawater samples were filtered through 0 45 m and 0 02 m pore size filters to evaluate the importance of colloidal and soluble i e truly dissolved ionic species and or low molecular weight lmw colloids fractions of the rees in the local subterranean estuaries mixing experiments using groundwater collected immediately down gradient from a wastewater treatment facility wwtf proximal to the kaloko hanokohau national historic park and more pristine groundwater from a well constructed in a lava tube at kiholo bay were conducted with local seawater to study the effect of solution composition i e ph salinity on the concentrations and fractionation behavior of the rees as groundwater mixes with seawater in kona coast subterranean estuaries the mixed waters were also filtered through 0 45 or 0 02 m filters to ascertain the behavior of colloidal and soluble fractions of the rees across the salinity gradient in each mixing experiment concentrations of the rees were statistically identical two tailed student t test 95 confidence between the sequentially filtered sample aliquots indicating that the rees occur as dissolved ionic species and or lmw colloids in kona coast groundwaters the mixing experiments revealed that the rees are released to solution from suspended particles or colloids when kona coast groundwater waters mix with local seawater the order of release that accompanies increasing ph and salinity follows light ree lree middle ree mree heavy ree hree release of rees in the mixing experiments is driven by decreases in the free metal ion activity in solution and the concomitant increase in the amount of each ree that occurs in solution as dicarbonato complexes i e ln co3 2 as ph increases across the salinity gradient input normalized ree patterns of kona coast groundwater and coastal seawater are nearly identical and relatively flat compared to north pacific seawater indicating that sgd is the chief source of these trace elements to the ocean along the kona coast additionally ree concentrations of the coastal seawater are between 10 and 50 times higher than previously reported open ocean seawater values from the north pacific further demonstrating the importance of sgd fluxes of rees to these coastal waters taken together these observations indicate that large scale removal of rees which characterizes the behavior of rees in the low salinity reaches of many surface estuaries is not a feature of the subterranean estuary along the kona coast a large positive gadolinium gd anomaly characterizes groundwater from the vicinity of the wwtf the positive gd anomaly can be traced to the coastal ocean providing further evidence of the impact of sgd on the coastal waters estimates of the sgd fluxes of the rees to the coastal ocean along the kona coast i e 1 3 2 6 mmol nd day 1 are similar to recent estimates of sgd fluxes of rees along florida s east coast and to rhode island sound all of which points to the importance of sgd as significant flux of rees to the coastal ocean

modeling the distribution of nd isotopes in the oceans using an ocean general circulation model nd isotopic compositions of authigenic phases in marine archives are increasingly used as a tracer of past changes in ocean circulation such applications assume that water masses are tagged with distinct nd isotope compositions in source regions and that away from these regions the nd isotope ratios observed in deep waters mainly reflect water mass mixing however the degree to which the simple assumption of quasi conservative mixing reflects the complicated reality of general circulation in the oceans is not well understood here we present numerical simulations of the nd isotope distribution in seawater using an offline ocean general circulation model ogcm treating the nd isotopic composition of seawater as a conservative tracer nd isotope data from modern surface waters are used to generate an interpolated map of nd isotope compositions for the entire surface ocean this map is treated as a fixed surface boundary condition that is propagated into the interior ocean by the advective diffusive transport of the ocean model until a steady state is reached this treatment of nd isotopes was chosen because it mimics the behavior of well known and well understood conservative tracers such as potential temperature and salinity the model results for all non surface grid points are then compared to published data this simple approach produces nd isotope estimates for north atlantic deep water that are consistent with observations but produces values lower than observed in the deep pacific and southern oceans indicating the need for a source of radiogenic nd directly to the deep pacific ocean sensitivity tests show this to be a robust result by fixing the return flow of the pacific ocean to the southern ocean with nd isotope ratios that are consistent with modern observations the model results are brought into close agreement with a majority of the available data with the addition of a deep pacific source of radiogenic nd more than half of the simulated values from the interior ocean fall within one e unit of the corresponding observations our results thus indicate that the deep pacific ocean requires a source of radiogenic nd in addition to inputs to the surface ocean and that when the deep waters of the north atlantic and north pacific are set with realistic values a majority of intermediate areas are consistent with quasi conservative mixing of these two end members

neodymium isotopic composition of the oceans a compilation of seawater data a global compilation of the neodymium isotopic composition of seawater is presented with 880 data points it confirms the gradual end increase for intermediate deep water masses from the northwest north atlantic via the austral and indian oceans to the pacific this confirms the usefulness of this tracer for studying large scale oceanic circulation the compilation stresses the need for documenting the oceans south of 30 s from which less than 4 of the data are derived the associated neodymium concentrations display heterogeneous vertical gradients among major oceanic basins in addition to particle remineralization along the global thermohaline circulation the database suggests that basin size differences also contribute to that heterogeneity

new insights into hydrological exchange between the south china sea and the western pacific ocean based on the nd isotopic composition of seawater abstract rare earth element ree concentrations and nd isotopic compositions end of 16 seawater profiles collected in the northern south china sea scs and the philippine sea were investigated 1 to establish the distribution of the nd isotopic composition of water masses along the tropical western pacific and the scs until now underexplored 2 to constrain hydrological exchanges between the scs and the philippine sea through the luzon strait and 3 to test in the context of the semi closed marginal sea scs the possible impact of the process of exchange of nd between scs water masses and unradiogenic sediments from its north western margin end values for mid and deep water masses of the philippine sea and the scs range from 2 3 to 4 4 and generally increase slightly as water depth increases in the philippine sea end values for the north pacific intermediate water npiw reach 2 7 0 4 at mid depths 500 to 1400 m below 1800 m the pacific deep water pdw is characterised by less radiogenic nd 4 1 0 5 indicating the intrusion of southern sourced water for most of the stations in the northern scs water masses below 1500 m pdw display homogenous end values 4 1 identical to those of the pdw in the philippine sea end values for the south china sea intermediate water scsiw 500 1500 m vary from 3 0 to 3 9 as a result of the vertical mixing of the npiw with the pdw in the scs seawater end values for the scs display local modification 5 3 to 7 0 in areas where water passes above sediment drift deposit systems this implies locally confined boundary exchange with unradiogenic sediments around 11 insufficient to alter the nd isotopic composition of the pdw in the northern scs in addition end values analysed for the first time in nepheloid layers collected along the north western margin of the scs do not exhibit any significant modification of the seawater end which remains into a narrow range between 3 7 and 4 3 similar to that of the pdw a compilation of end from the sea surface water of the scs indicates lower end values in the western and the central scs 3 3 to 9 5 induced by sediments riverine input which are characterised by unradiogenic end around 11 finally as significant variations are observed in seawater end at mid depth between the scs and the philippine sea end values could be used in the future to track intermediate water mass exchange in the luzon strait a process which at present remains poorly understood

the concentration and isotopic composition of diffusible nd in fresh and marine waters abstract variations in the nd isotopic composition of ocean water through time recorded in marine deposits are suggested to document changes in erosional input and ocean circulation thus characterization of the dissolved nd component in seawater is important but few attempts have been made to directly measure truly dissolved nd here we report nd data obtained using the technique of diffusive gradients in thin films dgt designed to measure in situ diffusible labile trace metals in aqueous solutions the method samples free ions and possibly very small complexes the concentration and isotopic composition of nd in fresh brackish and seawater have been determined with dgt analyzed with thermal ionization mass spectrometry and compared with filtered and bulk water samples concentrations measured in water samples and with dgt show that the relative amount of diffusible nd increases with salinity from being about 10 in the fresh water to 42 in seawater at each sampled site the isotopic composition of nd in the water shows a similar isotopic composition within errors with nd sampled using the dgt method these results indicate that there is a complete exchange between the particulate colloidal fraction and the truly dissolved phase therefore our findings suggest that solute nd reflects both the isotopic composition of the marine sediments and the bulk water

hafnium and neodymium isotopes in surface waters of the eastern atlantic ocean implications for sources and inputs of trace metals to the ocean we present hafnium hf and neodymium nd isotopic compositions and concentrations in surface waters of the eastern atlantic ocean between the coast of spain and south africa these data are complemented by hf and nd isotopic and concentration data as well as rare earth element ree concentrations in saharan dust hafnium concentrations range between a maximum of 0 52 pmol kg in the area of the canary islands and a minimum value of 0 08 pmol kg in the southern angola basin neodymium concentrations also show a local maximum in the area of the canary islands 26 pmol kg but are even higher between 20n and 4n reaching maximum concentrations of 35 pmol kg these elevated concentrations provide evidence of inputs from weathering of the canary islands and from the partial dissolution of dust from the sahara sahel region the inputs from ocean island weathering are also reflected in radiogenic hf and nd isotopes the hf isotopic compositions of dust samples themselves are highly variable ranging between ehf 20 and 0 6 the combined hf and nd isotopic compositions of dust plot close to the terrestrial array during periods of appreciable dust load in the atmosphere during low atmospheric dust loading combined hf and nd isotopic compositions similar to seawater are observed most of the variability can be explained in terms of variable degrees of zircon loss from the dust samples which in turn is linked to sorting during atmospheric transport to the eastern atlantic ocean and possibly presorting by sedimentary redistribution on the continent in addition increasing relative proportions of radiogenic clay minerals with decreasing grain size may contribute to the radiogenic hf isotopic compositions observed while the nd isotopic composition in the surface ocean reflects the nd isotopic composition of the saharan dust adjacent to the sahara sahel region the release of hf from that dust appears to be incongruent and results in surface ocean hf isotopic compositions which are 10 ehf more radiogenic than the bulk dust radiogenic hf appears to be released from clays and possibly from trace apatite rare earth element patterns of dust samples indicate the presence of apatite but provide no evidence for ferromanganese grain coatings suggesting that such coatings are insignificant in the release of hf and nd from saharan dust to the surface ocean the nd isotopic composition of the surface waters becomes less radiogenic south of the equator most likely reflecting the release of nd from congo river sediments the release of hf from saharan dust and the congo river sediments however does not produce distinct hf isotopic signatures in the surface ocean implying that the mobile fraction of hf integrated over large continental areas is isotopically uniform the hf isotopic uniformity in the surface ocean means that the limited variability in deep water isotopic compositions is consistent with a short deep water residence time and reflects homogenous continental inputs rather than efficient deep water homogenization

modeling the neodymium isotopic composition with a global ocean circulation model abstract for the first time modeling of the neodymium nd isotopic composition expressed as end is performed in an ocean global circulation model opa orca2 0 model in the interest of simplicity nd concentration is not explicitly included and end is modeled as a passive tracer recent studies suggest that dissolved particulate exchanges between continental margin sediments and seawater termed boundary exchange be could be the dominant source sink terms that determine the distribution of neodymium isotopes in the global ocean to test this hypothesis we only included this be source sink term in the model be was parameterized as a relaxing term that forces end of seawater to the isotopic composition of the continental margin over a characteristic exchange time sensitivity tests were made using different exchange times and parameterizations the model reproduces most of the general trends of end composition in seawater at global scale inter basin gradient composition of some of the main water masses these results suggest that be process may account for the major sources and sinks of oceanic nd while indicating that the characteristic time of interaction between seawater and margins varies from about half a year in surface waters to several years at depth the disparities between the model and observations might reflect the typical shortcomings of utilizing a coarse resolution ocean model circulation fields or neglected sources of neodymium such as dissolution of aeolian inputs or dissolved river loads

neodymium isotopic composition of intermediate and deep waters in the glacial southwest pacific abstract neodymium nd isotopes tracers of deep water mass source and mixing were measured on sedimentary planktic foraminifera with authigenic coatings from a depth transect of cores 1400 4800 m from chatham rise in the southwest pacific over the past 30 ka we observe deglacial variations in the nd isotopic composition which showed an average glacial composition of e nd 5 0 1 0 3 n 4 for cores sites below 3200 mbsl no significant deglacial variation was observed in the nd isotopic composition of intermediate depth waters 1400 mbsl in contrast with benthic foraminifera c 13 data the deglacial e nd shift of cdw in the southwest pacific is consistent with changes observed in the deep south atlantic and equatorial indian ocean but e nd values are offset by 1 e nd unit to more radiogenic values throughout the deglacial records likely due to admixture of a nd isotope signal which was modified in the southern ocean or pacific perhaps by boundary exchange however this modification did not overprint the deglacial nd isotope change the consistent deglacial evolution of e nd in the south atlantic equatorial indian and southwest pacific cdw is evidence for the connection of cdw during the glacial and propagation of diminished north atlantic deep water export to the glacial southern ocean in contrast spatial heterogeneities in the benthic foraminifera c 13 of cdw have been observed in the atlantic indian and pacific basins of the deep glacial southern ocean the nd isotope data implies a well connected deep southern ocean which transported waters from the atlantic to the indian and pacific oceans during the glacial this suggests that basin scale variability in the glacial c 13 composition of cdw was unrelated to circulation changes

modelling nd isotopes with a coarse resolution ocean circulation model sensitivities to model parameters and source sink distributions the neodymium nd isotopic composition nd of seawater is a quasi conservative tracer of water mass mixing and is assumed to hold great potential for paleoceanographic studies here we present a comprehensive approach for the simulation of the two neodymium isotopes 143nd and 144nd using the bern3d model a low resolution ocean model the high computational efficiency of the bern3d model in conjunction with our comprehensive approach allows us to systematically and extensively explore the sensitivity of nd concentrations and nd to the parametrisation of sources and sinks previous studies have been restricted in doing so either by the chosen approach or by computational costs our study thus presents the most comprehensive survey of the marine nd cycle to date our model simulates both nd concentrations as well as nd in good agreement with observations nd covaries with salinity thus underlining its potential as a water mass proxy results confirm that the continental margins are required as a nd source to simulate nd concentrations and nd consistent with observations we estimate this source to be slightly smaller than reported in previous studies and find that above a certain magnitude its magnitude affects nd only to a small extent on the other hand the parametrisation of the reversible scavenging considerably affects the ability of the model to simulate both nd concentrations and nd furthermore despite their small contribution we find dust and rivers to be important components of the nd cycle in additional experiments we systematically varied the diapycnal diffusivity as well as the atlantic to pacific freshwater flux to explore the sensitivity of nd concentrations and its isotopic signature to the strength and geometry of the overturning circulation these experiments reveal that nd concentrations and nd are comparatively little affected by variations in diapycnal diffusivity and the atlantic to pacific freshwater flux in contrast an adequate representation of nd sources and sinks is crucial to simulate nd concentrations and nd consistent with observations the good agreement of our results with observations paves the way for the evaluation of the paleoceanographic potential of nd in further model studies

rare earth element transport in the western north atlantic inferred from nd isotopic observations the isotopic composition of nd in the water column from several western north atlantic sites and formational areas for north atlantic deep water shows extensive vertical structure at all locations in regions where a thermocline is well developed large isotopic shifts 2 to 3 units are observed across the base of the thermocline regions without a thermocline are characterized by much more gradual shifts in isotopic composition with depth in general the data reveal an excellent correlation between the nd isotopic distribution in the western north atlantic water column and the distribution of water masses identified from temperature and salinity characteristics nadw as identified from t s properties is also characterized by a well defined isotopic composition having nd 0 13 5 0 5 this signature is associated with waters identified as nadw from high latitudes near formational areas in the labrador sea down to the equatorial region the isotopic signature of nadw would appear to be formed by a blend of more negative waters originating in the labrador sea nd 0 18 and more positive waters originating in the overflows from the norwegian and greenland seas nd 0 8 to 10 and is consistent with classical theories on the formation of nadw the isotopic signature of nadw is propagated southward to the equator where it is gradually being thinned out by mixing from above and below with more radiogenic nd associated with northward spreading antarctic intermediate and bottom waters the preservation of the isotopic signature of nadw over these large distances indicate that the ree undergo extensive lateral transport the isotopic composition of nd is largely conservative over the time scales of mixing within the atlantic in spite of the intrinsic nonconservative behavior of neodymium nd concentration gradients generally show surface waters to be depleted in nd relative to deep waters which must require vertical transport processes however isotopic differences in the water column preclude the local downward transport of ree from the surface into underlying deep waters as a simple explanation of the concentration gradient the apparent decoupling of ree in nadw from overlying local surface waters and the increasing concentration with depth provide a conflict with simple vertical transport mechanisms that is not yet resolved

numerical simulation of progressive rock failure and associated seismicity in this paper a numerical approach to modeling progressive failure leading to collapse in rock and associated seismicity is reported in the first part a newly developed numerical code rfpaz rock failure process analysis is introduced the program allows modeling of the observed evolution of damage and associated seismic events due to progressive failure leading to collapse in brittle rock there are three features distinguishing the approach from conventional numerical methods such as fem 1 by introducing heterogeneity of rock parameters into the model rfpaz can simulate non linear behavior in rock using a linear method 2 by introducing elastic modulus reduction for failed elements rfpa2d can process discontinuum mechanics problems by a continuum mechanics method and 3 by recording the event rate of failed elements the seismicities associated with the progressive failure in rock can be simulated in the second part of the paper the applications of rfpa2d in simulating geological process and in solving mining design problems are illustrated numerical simulation of a fault initiation process indicates that some of the important phenomena such as coalescence of microfracture the nucleation and growth of crack clusters fault initiation and development elastic rebound dilatation uplift and seismic behavior etc can be simulated with this numerical code the simulation of progressive failure leading to collapse in underground openings demonstrates the capacity of this code in solving mining design problems