thrust fault growth and segment linkage in the active ostler fault zone new zealand abstract thrust faulting is a fundamental mode of crustal deformation yet many of the key geometrical attributes of thrust faults and the controls on fault rupture growth and linkage remain poorly resolved numerous surface rupturing thrust faults cut through upper quaternary glacial outwash terraces within the ostler fault zone an active thrust system in the southern alps new zealand we use these deformed marker surfaces to define the three dimensional deformation field associated with their surface expression and to map displacement and length on 40 fault segments displacement transfer across two fault segment arrays occurs in distinctly different styles in one displacement is transferred between en echelon fault segments to produce a smooth linear displacement gradient in the other large scale folding and a population of small faults transfer displacement between two non overlapping fault segments with a residual displacement minimum within the transfer zone size distribution of fault segment length and maximum displacement follow a power law scaling relationship maximum displacement d max scales linearly with and represents 1 of segment trace length l d max l data from the segments of the ostler fault zone display similar scaling to a global fault dataset this similarity is surprising given that the observed displacements along the ostler fault represent only 20 ky of slip on fault segments that are likely to be many times older

major pathways of atlantic water in the northern north atlantic and nordic seas toward arctic 1 the major pathways of near surface atlantic water in the northern north atlantic and nordic seas are identified as current speeds above 30 cm s using 1014 lagrangian drifters combined with previously published hydrography the inflow over the scotland greenland ridge and establishment of the two branch norwegian atlantic current nwac are described in light of the circulation in the northern north atlantic the western branch of the nwac appears as a jet in the polar front topographically guided from the iceland faroe front through the nordic seas toward fram strait the eastern branch starts as a shelf edge current above the irish scottish continental shelf and after passing through the faroe shetland channel it continues northward along the norwegian shelf edge toward the arctic with a branch bifurcating into the barents sea the nwac appears to maintain its two branch structure throughout the nordic seas with the atlantic water confined to a 200 600 km wide wedge

passive tracers and active dynamics a model study of hydrography and circulation in the northern north atlantic 1 a long standing problem in oceanography has been to understand the relationship between what can be measured in the ocean such as hydrography and what cannot such as the strength and structure of the complete meridional overturning circulation moc of the world oceans commonly considered the main oceanic long term modifier of earth s climate with the aid of a 50 year simulation from a numerical ice ocean model we have investigated this relationship in the area of the northernmost extension of the moc in the subpolar and nordic seas on interannual timescales we find that variability in the northward flux of salt and temperature in this region is controlled almost entirely by the volume flux confirming that a knowledge of the variability of the circulation strength proper is necessary the simulated hydrographic anomalies are within the range observed in the twentieth century thus fundamental changes to the circulation were not expected nor found it is seen that variability in either temperature or salinity does contain some information about the variability in current strength because hydrography and circulation generally respond to the same atmospheric forcing in the north atlantic sector whether it is temperature or salinity that contains the information is related to the parameter range of the equation of state at the location in question if density depends primarily on temperature then a salinity anomaly will tend to survive and vice versa the oceanic response involves hydrographic changes and propagation of these gyre strength changes and changes in the moc

relay zone geometry and displacement transfer between normal faults recorded in coal mine plans abstract overlap lengths separations and throw gradients were measured on 132 relay zones recorded on coal mine plans throws on the relay bounding fault traces are usually 2 m and individual structures are recorded on only one seam throw gradients associated with relay zones are not always higher than on single faults but asymmetry of throw profiles is diagnostic of relay zones bed geometries around larger faults in opencast mines are used to assess the displacement accommodated by shear in the vertical plane normal to the faults and displacement transfer accommodated by shear in the fault parallel plane three dimensional structure is defined for two relay zones each recorded on five seam plans these relay zones are effectively holes through the fault surfaces and overlap occurs between salients or lobes of the parent fault surfaces lobes initially terminated at tip lines but as the faults grew gradually rejoined the main fault surfaces along branch lines this type of relay zone originates by bifurcation of a single fault surface at a locally retarded tip line and is an almost inevitable result of a tip line irregularity

constraints on mantle evolution from 187os 188os isotopic compositions of archean ultramafic rocks from southern west greenland 3 8 ga and western australia 3 46 ga initial 187os 188os isotopic compositions for geochronologically and geologically well constrained 3 8 ga spinel peridotites from the itsaq gneiss complex of southern west greenland and chromite separates from 3 46 ga komatiites from the pilbara region of western australia have been determined to investigate the osmium isotopic evolution of the early terrestrial mantle the measured compositions of 187os 188os 0 0 10262 2 from an olivine separate and 0 10329 3 for a spinel separate from 3 8 ga peridotite g93 42 are the lowest yet reported from any terrestrial sample the corrections for in situ decay over 3 8 ga for these low re os phases are minimal and change the isotopic compositions by only 0 5 and 2 2 for the spinel and the olivine respectively resulting in 187os 188os 3 8 ga 0 1021 0 0002 and 0 1009 0 0002 respectively these data extend direct measurement of os isotopic compositions to much earlier periods of earth history than previously documented and provide the best constraints on the os isotopic composition of the early archean terrestrial mantle analyses of pilbara chromites yield 3 46 ga mantle compositions of 0 1042 0 0002 and 0 1051 0 0002 these new data combined with published initial os isotopic compositions from late archean and early proterozoic samples are compatible with the mantle or at least portions of it evolving from a solar system initially defined by meteorites to a modern composition of 187os 188os 0 0 1296 0 0008 as previously suggested from peridotite xenolith data meisel et al 2001 the associated 187re 188os 0 0 435 0 005 thus chondritic 187os 188os compositions were a feature of the upper mantle for at least 3 8 billion years requiring chondritic re os ratios to have been a characteristic of the very early terrestrial mantle in contrast nonchondritic initial compositions of some archean komatiites demonstrate that os isotopic heterogeneity is an ancient feature of plume materials reflecting the development of variable re os mantle sources early in earth history the lower average 187os 188os 0 1247 for abyssal peridotites snow and reisberg 1995 indicate that not all regions of the modern mantle have evolved with the same re os ratio the relative sizes of the various reservoirs are unknown although mass balance considerations can provide some general constraints for example if the unradiogenic 187os 188os modern abyssal peridotite compositions reflect the prevalent upper mantle composition then the complementary high re os basaltic reservoir must represent 20 to 40 by mass of the upper mantle taken here as 50 of the entire mantle depending on the mean storage age the difficulties associated with efficient long term storage of such large volumes of subducted basalt suggest that the majority of the upper mantle is not significantly re depleted rather abyssal peridotites sample anomalous mantle regions the existence of 3 8 ga mantle peridotites with chondritic 187os 188os compositions and with os concentrations similar to the mean abundances measured in modern peridotites places an upper limit on the timing of a late accretionary veneer these observations require that any highly siderophile element rich component must have been added to the earth and transported into and grossly homogenized within the mantle by 3 8 ga either large scale mixing of impact materials occurred on very short 0 100 myr timescales or the interpretation preferred here the late veneer of highly siderophile elements is unrelated to the lunar terminal cataclysm estimated to have occurred at 3 8 to 3 9 ga

wind and buoyancy induced transport of the norwegian coastal current in the barents sea 1 the focus of this study is on the fluxes and forcing of the norwegian coastal current ncc at the entrance to the barents sea the structure and dynamics of the ncc which consists of a slope branch and an offshore branch are investigated using 1 a recent 1 year full depth current meter record in the core of the slope region 2 repeated hydrographic data at an inshore monitoring station 3 broader regional hydrographic surveys and 4 atmospheric reanalysis data the total fluxes are estimated to 1 8 sv for volume and 26 msv for freshwater relative to a reference salinity of 34 8 with the largest contributions from baroclinic offshore branch the heat flux calculated for the slope branch only is 34 tw these estimates are higher compared to earlier estimates but are based on more comprehensive data the major mode of variability in the slope branch is consistent with a continental shelf wave on time scales in the range of 3 16 days forced by the along coast component of the wind stress maximum along slope currents during fall winter corresponding to the stronger wind forcing during these seasons suggest that the observed seasonality in the ncc can be attributed to a similar mechanism

early stage evolution of growth faults 3d seismic insights from the levant basin eastern mediterranean the geometry and kinematic evolution of small growth faults were analysed from a high resolution 3d seismic dataset located at the margins of the levant basin in the eastern mediterranean the 3d geometry segmentation history and throw distribution of one particular fault was reconstructed to evaluate and illustrate the changes in dimension and displacement distribution that occurred during the transition from purely blind propagation to propagation at the free surface the fault is considered to have grown by blind radial propagation of three main segments that hard linked prior to surface interaction the fault subsequently reached the seabed and continued to accrue displacement as a syn sedimentary fault most of the fault surface area formed during the blind propagation phase but most of the displacement was added during the syn sedimentary phase of the growth history with little increase in surface area the interaction of the fault with the free surface led to a change in the position of the point of maximum displacement as well as modifying the vertical throw distribution the amount of displacement added after this transition from blind fault to growth fault is discussed with respect to existing fault growth models

a 20 year coupled ocean sea ice atmosphere variability mode in the north atlantic in an aogcm in order to understand potential predictability of the ocean and climate at the decadal time scales it is crucial to improve our understanding of internal variability at this time scale here we describe a 20 year mode of variability found in the north atlantic in a 1 000 year pre industrial simulation of the ipsl cm5a lr climate model this mode involves the propagation of near surface temperature and salinity anomalies along the southern branch of the subpolar gyre leading to anomalous sea ice melting in the nordic seas which then forces sea level pressure anomalies through anomalous surface atmospheric temperatures the wind stress associated to this atmospheric structure influences the strength of the east greenland current across the denmark strait which in turn induces near surface temperature and salinity anomalies of opposite sign at the entrance of the labrador sea this starts the second half of the cycle after approximatively 10 years the time scale of the cycle is thus essentially set by advection of tracers along the southern branch of the subpolar gyre and by the time needed for anomalous east greenland current to accumulate heat and freshwater anomalies at the entrance of the labrador sea the atlantic meridional overturning circulation amoc does not play a dominant role in the mode that is confined in the subpolar north atlantic but it also has a 20 year preferred timescale this is due to the influence of the propagating salinity anomalies on the oceanic deep convection the existence of this preferred timescale has important implications in terms of potential predictability of the north atlantic climate in the model although its realism remains questionable and is discussed

variability along the atlantic water pathway in the forced norwegian earth system model the growing attention on mechanisms that can provide predictability on interannual to decadal time scales makes it necessary to identify how well climate models represent such mechanisms in this study we use a high 0 25 horizontal grid and a medium 1 resolution version of a forced global ocean sea ice model utilising the norwegian earth system model to assess the impact of increased ocean resolution our target is the simulation of temperature and salinity anomalies along the pathway of warm atlantic water in the subpolar north atlantic and the nordic seas although the high resolution version has larger biases in general at the ocean surface the poleward propagation of thermohaline anomalies is better resolved in this version i e the time for an anomaly to travel northward is more similar to observation based estimates the extent of these anomalies can be rather large in both model versions as also seen in observations e g stretching from scotland to northern norway the easternmost branch into the nordic and barents seas carrying warm atlantic water is also improved by higher resolution both in terms of mean heat transport and variability in thermohaline properties a more detailed assessment of the link between the north atlantic ocean circulation and the thermohaline anomalies at the entrance of the nordic seas reveals that the high resolution is more consistent with mechanisms that are previously published this suggests better dynamics and variability in the subpolar region and the nordic seas in the high resolution compared to the medium resolution this is most likely due a better representation of the mean circulation in the studied region when using higher resolution as the poleward propagation of ocean heat anomalies is considered to be a key source of climate predictability we recommend that similar methodology presented herein should be performed on coupled climate models that are used for climate prediction

reversal of the 1960s to 1990s freshening trend in the northeast north atlantic and nordic seas hydrographic time series in the northeast north atlantic and nordic seas show that the freshening trend of the 1960s 1990s has completely reversed in the upper ocean since the 1990s temperature and salinity have rapidly increased in the atlantic inflow from the eastern subpolar gyre to the fram strait in 2003 2006 salinity values reached the previous maximum last observed around 1960 and temperature values exceeded records the mean properties of the atlantic inflow decrease northwards but variations seen in the eastern subpolar gyre at 57 n persist with the same amplitude and pattern along the pathways to fram strait time series correlations and extreme events suggest a time lag of 3 4 years over that distance this estimate allows predictions to be made the temperature of atlantic water in the fram strait may start to decline in 2007 or 2008 salinity a year later but both will remain high at least until 2010

kinematic analysis of faults in a physical model of growth faulting above a viscous salt analogue abstract syn sedimentary faults overlying an extended ductile layer within a sand model provide an analogue for studying some aspects of the geometry and kinematics of basin scale extensional listric faults associated with salt rollers the displacement analysis techniques used to examine displacement variations over fault surfaces within the sand model show that displacement varies in a regular and predictable manner deviations from simple fault displacement patterns are due to transfers of displacement onto adjacent synthetic faults aggregation of the displacements on adjacent synthetic faults produces more regular patterns of displacement distribution and demonstrates the geometric coherence of the aggregated faults rapid upward decreases in displacement on the model faults are due to fault growth during sedimentation elsewhere in the model post sedimentary faulting is associated with very low upward displacement gradients and pre and syn faulting sedimentation are readily distinguished on cross sectional fault traces in three dimensions a non horizontal line separating the pre faulting and syn faulting sequences tracks the lateral extent of a fault through time backstripping of fault displacements by subtracting the fault displacement of a sedimentary horizon from the displacements of underlying horizons gives the displacement distribution on a fault surface at the time of deposition of the backstripped horizon backstripped fault displacement distributions also allow examination of the general fault structure through time backstripping of fault displacements on one of the larger faults within the model and on an associated hanging wall synthetic splay shows that the two structures originated as a relay zone which was breached by lateral propagation of one of the overlapping faults which form the relay zone the backstripping technique allows determination of the geometrical changes during growth of a fault system

simulation of the atlantic circulation with a coupled sea ice mixed layer isopycnal general circulation model part i model description abstract a diabatic ocean general circulation model based on primitive equations is described it uses isopycnals as lagrangian coordinates in the vertical and predicts a free surface prognostic fields of temperature and salinity enter the dynamics as active tracers through a realistic equation of state the surface boundary layer is parameterized by a detailed mixed layer model a sea ice model with a viscous plastic rheology is coupled to the mixed layer thermal forcing wind stress and surface input of turbulent kinetic energy are determined from monthly mean values of atmospheric quantities while the freshwater flux still is parameterized by a newtonian relaxation towards the observed surface salinity the model equations are written in layer formulation each interface represents an isopycnal as the equations are written in flux form the mass flux and the content of mass heat and salt are conserved in the model domain a potential vorticity conserving scheme is included except for the mixed

architecture of normal faults in the rift zone of central north iceland this work examines the architecture and propagation of normal faults that accommodate extension in the rift zone of central north iceland it is based on a structural study of portions of three grabens their normal faults and dilational fractures in basaltic lavas of the fremri namur and dyngjufjol volcanic systems we analyzed the shape throw and dilation along faults in order to infer their possible evolution the shape of throw profiles departs from elliptical varying along each fault with throw being lower at the fault and segment tips propagation of fault segments is accommodated by dilational fractures nucleating at their respective tips segments link by lateral propagation of one or both tips or by the development of intervening linking segments two orders of fault segmentation indicate that the present throw accumulated by many increments as the fault scarps changed their geometries faults have large dilational components weakly correlated with fault throw and length

estimation of average to maximum displacement ratio by using fault displacement distance profiles abstract fault displacement is an important factor in the study of discontinuous deformation considering that the values of average displacement dav and maximum displacement dmx are linearly related by dav dmx we calculate the values of estimated from 205 published displacement distance profiles the following results are obtained a the value of is largest for the mesa type or flat topped m type profiles b the value of increases when ductile continuous deformation is added to the displacement profile c generally the value of for a linked fault array is smaller than that for segmented faults in the array i e the value of changes with fault evolution and at the stage where linkage occurs the value of becomes smaller d the simulation results indicate that for an ellipse function the value of varies from 0 667 to 0 785 for trapezoid m type profiles the value of is from 0 5 to 1 depending on the ratio of the upper base to the lower base for best fit polynomial curves the value of can be less than 0 5 e the values of more frequently observed in the published profiles are between 0 6 and 0 7 the average value is 0 6023 and the standard deviation 0 1123 these data indicate that the displacement distance profiles are hybrids from the triangular profile to the elliptical or mesa profile the average value 0 6023 would be useful to determine the average displacement in cases where not enough displacement data can be obtained finally the value change of with fault evolution can be used to quantitatively evaluate the level of interaction between segmented faults

slip accumulation and lateral propagation of active normal faults in afar we investigate fault growth in afar where normal fault systems are known to be currently growing fast and most are propagating to the northwest using digital elevation models we have examined the cumulative slip distribution along 255 faults with lengths ranging from 0 3 to 60 km faults exhibiting the elliptical or bell shaped slip profiles predicted by simple linear elastic fracture mechanics or elastic plastic theories are rare most slip profiles are roughly linear for more than half of their length with overall slopes always 0 035 for the dominant population of nw striking faults and fault systems longer than 2 km the slip profiles are asymmetric with slip being maximum near the eastern ends of the profiles where it drops abruptly to zero whereas slip decreases roughly linearly and tapers in the direction of overall aden rift propagation at a more detailed level most faults appear to be composed of distinct shorter subfaults or segments whose slip profiles while different from one to the next combine to produce the roughly linear overall slip decrease along the entire fault on a larger scale faults cluster into kinematically coupled systems along which the slip on any scale individual fault or fault system complements that of its neighbors so that the total slip of the whole system is roughly linearly related to its length with an average slope again 0 035 we discuss the origin of these quasilinear asymmetric profiles in terms of initiation points where slip starts and barriers where fault propagation is arrested in the absence of a barrier slip apparently extends with a roughly linear profile tapered in the direction of fault propagation

reduced mixing from the breaking of internal waves in equatorial waters in the oceans heat salt and nutrients are redistributed much more easily within water masses of uniform density than across surfaces separating waters of different densities but the magnitude and distribution of mixing across density surfaces are also important for the earth s climate as well as the concentrations of organisms most of this mixing occurs where internal waves break overturning the density stratification of the ocean and creating patches of turbulence predictions of the rate at which internal waves dissipate were confirmed earlier at mid latitudes here we present observations of temperature and velocity fluctuations in the pacific and atlantic oceans between 42 degrees n and 2 degrees s to extend that result to equatorial regions we find a strong latitude dependence of dissipation in accordance with the predictions in our observations dissipation rates and accompanying mixing across density surfaces near the equator are less than 10 of those at mid latitudes for a similar background of internal waves reduced mixing close to the equator will have to be taken into account in numerical simulations of ocean dynamics for example in climate change experiments

progressive mixing of meteoritic veneer into the early earth s deep mantle komatiites are ancient volcanic rocks mostly over 2 7 billion years old from the archaean era that formed through high degrees of partial melting of the mantle and therefore provide reliable information on bulk mantle compositions1 in particular the platinum group element pge contents of komatiites provide a unique source of information on core formation mantle differentiation and possibly core mantle interaction2 3 4 5 6 7 8 most of the available pge data on komatiites are from late archaean 2 7 2 9 gyr old or early proterozoic 2 0 2 5 gyr old samples here we show that most early archaean 3 5 3 2 gyr old komatiites from the barberton greenstone belt of south africa and the pilbara craton of western australia are depleted in pge relative to late archaean and younger komatiites early archaean komatiites record a signal of pge depletion in the lower mantle resulting from core formation this signal diminishes with time owing to progressive mixing in to the deep mantle of pge enriched cosmic material that the earth accreted as the late veneer during the early archaean 4 5 3 8 gyr ago meteorite bombardment

warm and saline events embedded in the meridional circulation of the northern north atlantic 1 ocean state estimates from 1958 to 2005 from the simple ocean assimilation system soda system are analyzed to understand circulation between subtropical and subpolar atlantic and their connection with atmospheric forcing this analysis shows three periods 1960s around 1980 and 2000s with enhanced warm saline waters reaching high latitudes alternating with freshwater events originating at high latitudes it complements surface drifter and altimetry data showing the subtropical subpolar exchange leading to a significant temperature and salinity increase in the northeast atlantic after 2001 the warm water limb of the atlantic meridional overturning cell represented by soda expanded in density salinity space during these warm events tracer simulations using soda velocities also show decadal variation of the gulf stream waters reaching the subpolar gyre and nordic seas the negative phase of the north atlantic oscillation index usually invoked in such variability fails to predict the warming and salinization in the early 2000s with salinities not seen since the 1960s wind stress curl variability provided a linkage to this subtropical subpolar gyre exchange as illustrated using an idealized two layer circulation model the ocean response to the modulation of the climatological wind stress curl pattern was found to be such that the northward penetration of subtropical tracers is enhanced when amplitude of the wind stress curl is weaker than normal in this case both the subtropical and subpolar gyres weaken and the subpolar density surfaces relax hence the polar front moves westward opening an enhanced northward access of the subtropical waters in the eastern boundary current

quantifying the influence of atlantic heat on barents sea ice variability and retreat abstractthe recent arctic winter sea ice retreat is most pronounced in the barents sea using available observations of the atlantic inflow to the barents sea and results from a regional ice ocean model the authors assess and quantify the role of inflowing heat anomalies on sea ice variability the interannual variability and longer term decrease in sea ice area reflect the variability of the atlantic inflow both in observations and model simulations during the last decade 1998 2008 the reduction in annual july june sea ice area was 218 103 km2 or close to 50 this reduction has occurred concurrent with an increase in observed atlantic heat transport due to both strengthening and warming of the inflow modeled interannual variations in sea ice area between 1948 and 2007 are associated with anomalous heat transport r 0 63 with a 70 103 km2 decrease per 10 tw input of heat based on the simulated ocean heat budget it is found that the heat transport into the western barents sea sets the bou

the tungsten isotopic composition of the earth s mantle before the terminal bombardment it has long been speculated that a late heavy bombardment of earth by meteoritic material replenished the mantle s budget of siderophile iron loving elements such as tungsten that were largely lost to the core during its segregation however evidence for this late veneer remains indirect and its influence has been much debated matthias willbold and colleagues present high precision tungsten isotope analyses of ancient greenland rocks and show that they have significantly higher 182w 184w ratios than modern terrestrial samples this finding is in good agreement with the expected influence of a meteoritic late heavy bombardment they speculate that both the tungsten isotope data and the observed decrease in 142nd 144nd neodymium ratios can be explained if late meteorite bombardment triggered the onset of the current style of mantle convection many precious iron loving metals such as gold are surprisingly abundant in the accessible parts of the earth given the efficiency with which core formation should have removed them to the planet s deep interior1 one explanation of their over abundance is a late veneer a flux of meteorites added to the earth after core formation as a terminal bombardment that culminated in the cratering of the moon2 some 3 8 billion year old rocks from isua greenland are derived from sources that retain an isotopic memory of events pre dating this cataclysmic meteorite shower3 4 these isua samples thus provide a window on the composition of the earth before such a late veneer and allow a direct test of its importance in modifying the composition of the planet using high precision less than 6 parts per million 2 standard deviations tungsten isotope analyses of these rocks here we show that they have a isotopic tungsten ratio 182w 184w that is significantly higher about 13 parts per million than modern terrestrial samples this finding is in good agreement with the expected influence of a late veneer we also show that alternative interpretations such as partial remixing of a deep mantle reservoir formed in the hadean eon5 6 more than four billion years ago or core mantle interaction7 do not explain the w isotope data well the decrease in mantle 182w 184w occurs during the archean eon about four to three billion years ago potentially on the same timescale as a notable decrease in 142nd 144nd refs 3 and 6 we speculate that both observations can be explained if late meteorite bombardment triggered the onset of the current style of mantle convection

a mechanism to explain rift basin subsidence and stratigraphic patterns through fault array evolution rift basin stratigraphy commonly records an early stage of slow subsidence followed by an abrupt increase in subsidence rate the physical basis for this transition is not well understood although an increase in extension rate is commonly implied here a numerical fault growth model is used to investigate the influence of segment linkage on fault displacement rate patterns along an evolving normal fault array the linkage process we describe is controlled by a stress feedback mechanism which leads to enhanced growth of optimally positioned faults model results indicate that even with constant extension rates slow displacement rates prevail during an initial phase of distributed extension followed by an increase in displacement rates as strain becomes localized on linked fault arrays this is due to the dynamics of fault interactions rather than mechanical weakening comparison of model simulations with rift basin subsidence and stratigraphic patterns in the gulf of suez and north sea suggests that the occurrence and timing of rapid basin deepening can be explained by the mechanics of fault zone evolution without invoking a change in regional extension rates

subpolar mode water in the northeastern atlantic 1 averaged properties and mean circulation 1 subpolar mode waters spmw in the eastern north atlantic subpolar gyre are investigated with hydrographic and lagrangian data surface drifters and isopycnal floats historical hydrographic data show that spmws are surface water masses with nearly uniform properties confined between the ocean surface and the permanent pycnocline spmws represented by densities 27 3 27 4 and 27 5 are present in the eastern subpolar gyre and are influenced by the topography and the regional circulation construction of an absolute surface stream function from surface drifters shows that spmws are found along the mean path of each of the several branches of the north atlantic current nac and their density increases gradually downstream the rockall trough branch of the nac carries 27 3 27 4 and 27 5 spmw toward the iceland faroe front in the iceland basin the subarctic front along the western flank of the rockall plateau carries a similar sequence of spmw the western side of the central iceland basin branch of the nac on the other hand veers westward and joins the east reykjanes ridge current feeding the 27 5 spmw on the reykjanes ridge the separation among the various nac branches most likely explains the different properties that characterize the 27 5 spmw found on the reykjanes ridge and on the iceland faroe ridge since the branches of the nac have a dominant northeastward direction the newly observed distribution of spmw combined with the new stream function calculation modify the original hypothesis of mccartney and talley 1982 of a smooth cyclonic pathway for spmw advection and density increase around the subpolar gyre

parameterization of mixed layer eddies part i theory and diagnosis ageostrophic baroclinic instabilities develop within the surface mixed layer of the ocean at horizontal fronts and efficiently restratify the upper ocean in this paper a parameterization for the restratification driven by finite amplitude baroclinic instabilities of the mixed layer is proposed in terms of an overturning streamfunction that tilts isopycnals from the vertical to the horizontal the streamfunction is proportional to the product of the horizontal density gradient the mixed layer depth squared and the inertial period hence restratification proceeds faster at strong fronts in deep mixed layers with a weak latitude dependence in this paper the parameterization is theoretically motivated confirmed to perform well for a wide range of mixed layer depths rotation rates and vertical and horizontal stratifications it is shown to be superior to alternative extant parameterizations of baroclinic instability for the problem of mixed layer restratification two companion papers discuss the numerical implementation and the climate impacts of this parameterization

on the flow of atlantic water and temperature anomalies in the nordic seas toward the arctic ocean the climatic conditions over the arctic ocean are strongly influenced by the inflow of warm atlantic water conveyed by the norwegian atlantic slope current nwasc based on sea surface height ssh data from altimetry we develop a simple dynamical measure of the nwasc transport to diagnose its spatio temporal variability this supports a dynamical division of the nwasc into two flow regimes the svinoy branch svb in the southern norwegian sea and the fram strait branch fsb west of spitsbergen the svb transport is well correlated with the ssh and atmospheric variability within the nordic seas factors that also affect the inflow to the barents sea in contrast the fsb is influenced by regional atmospheric conditions around svalbard and northern barents sea using a composite analysis we further relate anomalous strong svb flow events to temperature fluctuations along the core of atlantic water a warm composite anomaly is found to propagate northward with a tendency to amplify enroute after these events a roughly 12 months delayed temperature signal is identified in the fsb however also in the lofoten basin interior a delayed temperature signal is found which appears to originate from the nwasc this study suggests that hydrographic anomalies both upstream from the north atlantic and locally generated in the norwegian sea are important for the oceanic heat and salt transport that eventually enters into the arctic

the role of off fault damage in the evolution of normal faults abstract recent measurements of slip profiles on normal faults have found that they are usually triangular in shape this has been explained to be a consequence of on fault processes such as slip dependent friction however the recent observation that cumulative slip profiles on normal faults and fault systems in afar are both triangular and self similar excludes this explanation and requires some form of off fault deformation here we use elastic modelling to show that large triangular zones of off fault damage can explain the observed triangular slip profiles provided damage is anisotropic in the form of cracks sub parallel to the fault our modelling suggests that these triangular damage zones result from the enlargement of the crack tip damage area as the fault or system lengthens our modelling also demonstrates that different types of barriers can cause the slip profiles to terminate abruptly at one or both fault ends as observed in afar and elsewhere

growth of the volcano flank koa e fault system hawaii structural mapping of the koa e fault system located on the south flank of kilauea volcano hawaii has been carried out to study the relationship between fault propagation and re surfacing by lava flows the 1 9 km long white rabbit fault faces uphill towards the summit of the kilauea and has produced c 8 m vertical offset of a young lava flow 500 750 years the fault exhibits multiple peaks in its throw distance profile suggesting recent linkage between at least 2 separate faults at the surface however the width of a monocline associated with the fault shows a single maximum of c 40 m located near the centre of the overall fault trace we suggest monocline width is related to heave across the fault at depth a minimum of c 40 m beneath the most recent lava that re surfaced the fault the surface monocline records re emergence of a fault that had previously propagated to the surface prior to recent lava deposition rather than upward propagation of a new fault overall the fault displays a growth geometry with displacements increasing with depth the above implies that the koa e faults pre date the lavas exposed at the surface on the volcano flank and are a long lived feature of the volcano dynamics despite the small offsets across the faults at the surface

geometry segmentation pattern and displacement variations along a major apennine thrust zone central italy abstract hundreds of kilometres long arc shaped continuous thrust faults commonly imply very large displacements by detachment dominated thrusting therefore their occurrence has a large impact on fold thrust belt structure one of the major thrust faults of the central northern apennines the umbria marche sabina thrust zone is traditionally believed to represent one such feature characterised by displacements of several tens of kilometres however detailed studies of this structure revealed that it is actually composed of a series of partially overlapping fault segments rather than consisting of a single continuous thrust cross section balancing and restoration carried out by the integration of surface geological data with available sub surface information points out relatively limited amounts of thrust displacement

patterns of displacement along large normal faults implications for basin evolution and fault propagation based on examples from east africa seismic reflection data across six boundary faults from east africa have revealed information about the way boundary faults develop with respect to the synkinematic basin fill previous models of basin fill assume that lateral fault propagation and deposition occur simultaneously which gives rise to along axis onlap of the basin fill onto the prerift basement propagating basin model seismic reflection data from boundary faults in east africa show only rare evidence for along axis broadening of the basins instead the basin margins appear to be fixed from a very early stage in the basin history nonpropagating basin model depocenters shift not by gradual lateral propagation but by abrupt changes in location such observations indicate that boundary fault propagation to near maximum length occurs rapidly during the very early stages of rifting probably by linkage of numerous small faults displacement then builds following the b value earthquake model along the fault during basin development out of phase with the main propagation phase mature fault systems may have experienced several phases of jumps in fault length or the location of fault activity major boundary faults exhibit three basic patterns of evolution these patterns of evolution can have many variants and include 1 simple displacement where maximum displacement is approximately at the center of the fault and decreases gradually toward the fault tips 2 variable along strike displacement that incorporates linkage of in line or en echelon relatively large displacement faults of similar age leaving transverse anticlines and synclines and 3 asymmetric propagation where one tip of a fault remains more or less fixed while the other tip propagates a relatively long distance asymmetric propagation can occur smoothly and gradually or alternatively there can be a jump in the location of the fault and a new fault of different age can form along strike from the older fault eventually the new fault propagates and links with the older fault segment reactivating the older fault to some extent addition ally long lived faults may be composites of fault types 1 3

segmentation and growth of an obliquely reactivated normal fault abstract detailed kinematic analysis of a large 1800 m maximum displacement reactivated normal fault in the taranaki basin new zealand has been conducted using high quality 3d seismic data the parihaka fault is approximately north south striking in basement where it accrued late cretaceous to early eocene displacements in response to east west extension and was obliquely reactivated by nw se extension in the pliocene reactivation resulted in upward propagation newly formed segmentation and up dip clockwise rotation of the fault surface by up to 20 from the strike of the basement fault fault segmentation and map view soft linkage by relay zones in post miocene strata was synchronous with the formation of antithetic faults in late miocene strata at bends in the fault surface fault segment lengths antithetic faults and relay zone dimensions were formed geologically instantaneously during initial reactivation of the main fault at 3 7 3 4 ma i e within the first 10 of faulting rapid formation of pliocene fault segments is followed by displacement accumulation without an increase in fault segment length until eventual relay breaching when continued ramp rotation is unsustainable this evolutionary history is consistent with a model in which arrays of fault segments are from inception components of a single coherent structure

the 3d geometry of small scale relay zones between normal faults in soft sediments serial cross sections of faults within soft sediments of miocene age on the east coast of denmark were collated to provide 3d data sets with which to study the geometry of minor faults displacements 10 cm from the wide variety of geometrical complexities displayed by these faults many due to mutually cross cutting relationships between opposed dipping faults we present relatively simple structures considered to demonstrate stages in the evolution of relay zones between overlapping fault segments the structures described are 1 initial embayments in fault tip lines 2 established relay zones displaying transfer of displacement between overlapping fault segments 3 breached relay zones and 4 fault bound lenses an individual relay zone may display more than one of these structures along its length and relay zones that are intact on one cross section may be breached along strike on another examples of relay zones that are isolated from the fault tip line and are effectively holes within a continuous fault are also observed the observed relay zones breach by propagation of the initial parent fault through the relay zone rather than by the formation of a new breaching fault

on model differences and skill in predicting sea surface temperature in the nordic and barents seas the nordic seas and the barents sea is the atlantic ocean s gateway to the arctic ocean and the gulf stream s northern extension brings large amounts of heat into this region and modulates climate in northwestern europe we have investigated the predictive skill of initialized hindcast simulations performed with three state of the art climate prediction models within the cmip5 framework focusing on sea surface temperature sst in the nordic seas and barents sea but also on sea ice extent and the subpolar north atlantic upstream the hindcasts are compared with observation based sst for the period 1961 2010 all models have significant predictive skill in specific regions at certain lead times however among the three models there is little consistency concerning which regions that display predictive skill and at what lead times for instance in the eastern nordic seas only one model has significant skill in predicting observed sst variability at longer lead times 7 10 years this region is of particular promise in terms of predictability as observed thermohaline anomalies progress from the subpolar north atlantic to the fram strait within the time frame of a couple of years in the same model predictive skill appears to move northward along a similar route as forecast time progresses we attribute this to the northward advection of sst anomalies contributing to skill at longer lead times in the eastern nordic seas the skill at these lead times in particular beats that of persistence forecast again indicating the potential role of ocean circulation as a source for skill furthermore we discuss possible explanations for the difference in skill among models such as different model resolutions initialization techniques and model climatologies and variance

average regional strain due to slip on numerous faults of different orientations if a region is cut by faults with different orientations and if the faults intersect the boundaries of the region of interest then the average finite rotational strain eij ui xj is given by eij mij v where is the shear modulus v is the volume of the region and mij represents the sum of asymmetric moment tensors mij for each fault mij m0 u n where m0 is the scalar seismic moment and u and n are the unit vectors parallel to the slip vector and perpendicular to the fault plane this result is applicable when the average regional strain occurs primarily by displacements of essentially rigid blocks that together compose the region of interest and hence when both elastic strains and inelastic strains due to folding and bending are small

recirculation of atlantic water in the western barents sea 1 in this article the atlantic inflow with the north cape current to the barents sea and potential recirculation of this water in the bear island trough is investigated this is resolved by combining continuous current meter and repeated hydrographic section data in the barents sea opening the estimated annual mean net fluxes when excluding the contribution from the norwegian coastal current are 1 1 sv and 39 tw estimated relative to a reference temperature of 0 c the estimated heat flux associated with the outflow in the bear island trough is relatively large 12 tw long term current meter records do not show a close relationship between variations in the inflow and the outflow one year low pass filtered variations in temperature and salinity of the outflowing waters in the bear island trough are positively correlated with variations of the inflowing atlantic water with a lag of about seven months on the basis of a simple mixing model the outflow water consists of about 80 atlantic water that is additionally cooled by 2 0 2 5 c by heat loss to the atmosphere by considering the relative weak mean currents in this region it can be inferred that the fraction of the atlantic water that recirculates follows a relatively short pathway in the bear island trough before returning to the norwegian sea

subarctic and arctic sea surface temperature and its relation to ocean heat content 1982 2010 1 this is an examination of sst variability in the subarctic and arctic during the 29 year period 1982 2010 based primarily on data from the pathfinder avhrr data set as well as operational sst products from noaa and the uk meteorological office a goal is to explore the connection between sst variations in the subpolar gyres and sst variations further north with emphasis on the nordic seas because of their atmospheric exposure and connection to the overturning circulation after identifying and correcting for biases in pathfinder avhrr also present in the operational products the seasonal cycle and 29 year warming trend is described the analysis shows that much of the warming of the north atlantic subpolar gyre during the period occurred in 1990s and compensated for cooling during the decades of the early 1960s to mid 1990s in this same region superimposed on this warming trend the analysis reveals a succession of residual sst anomalies with 0 5 c amplitudes that seem to move out of the north atlantic subpolar gyre into the nordic seas following the north atlantic and norwegian currents within the nordic seas these sst anomalies slowly advect in a counterclockwise direction after approximately six years part of the anomalies exits the nordic seas through the east greenland current the connection between these sst anomalies and underlying anomalies of 0 300 m heat content is discussed the existence of these sst anomaliesand their origin at lower latitudes highlights the importance of ocean exchanges in influencing arctic climate

water masses and circulation pathways through the iceland basin during vivaldi 1996 quasi synoptic data from late 1996 spanning the subpolar north atlantic have been used to determine the major pathways of the north atlantic current nac at that time high spatial resolution allows fronts to be accurately positioned on each seasoar section a clearly defined front of the nac the southern branch turns north at around 25 w and continues through the middle of the iceland basin as far as 60 n 20 w a second branch the northern branch or subarctic front turns north around 30 w and retroflects westward north of 54 n to re enter the irminger basin and become part of the irminger current up the western side of the reykjanes ridge a third eastward branch turns sharply northwest at the mouth of the rockall trough to skirt the southwestern margin of hatton bank this branch carries a tongue of saline eastern north atlantic water enaw over hatton bank and in consequence enaw covers the whole of the hatton and rockall banks as well as the rockall trough bounded in the west by the southern branch the most saline water found in rockall trough spills out into the northern iceland basin between rockall and lousy banks this saline weakly stratified tongue can be traced westward to the south of iceland continuing southwestward along the eastern flank of the reykjanes ridge subarctic intermediate water is carried into the iceland basin creating a fresh tongue bounded east and west by the more saline enaw over hatton bank and the eastern flank of the reykjanes ridge respectively

great salinity anomalies in the north atlantic abstract we revisited the great salinity anomaly of the 1970s gsa 70s dickson et al 1988 and documented the newly identified great salinity anomaly of the 1980s hence termed gsa 80s both propagated around the north atlantic in a similar fashion the advective mechanism initially proposed to explain the observed sequence of low salinity low temperature events during the gsa 70s apparently holds also for the gsa 80s the latter was successively observed in the west greenland current 1982 the labrador current 1983 the flemish pass 1984 near the charlie gibbs fracture zone 1984 1985 in the rockall channel 1985 south of iceland 1985 1988 in the north sea 1986 1987 norwegian sea 1987 1988 barents sea 1988 1989 and iceland sea 1989 1990 the advection speed of the gsa 80s seems to be greater than the one of the gsa 70s the 1980s anomaly reached the barents sea 6 to 7 years after peaking in the west greenland current while the 1970s anomaly traveled the same route in 8 to 10 years these anomalies however seem to be of different origin the gsa 70s was apparently boosted remotely by a freshwater sea ice pulse from the arctic via fram strait consequently the gsa 70s was accompanied by a large sea ice extent anomaly in the greenland and iceland seas which propagated into the labrador sea in contrast the gsa 80s was likely formed locally in the labrador sea baffin bay mainly because of the extremely severe winters of the early 1980s but supplemented with a possible contribution of the arctic freshwater outflow via the canadian archipelago facilitated by strong northerly winds which would have enhanced stability and ice formation this anomaly was also associated with a positive sea ice extent anomaly in the labrador sea baffin bay which however had no upstream precursor in the greenland sea thus the gsas are not necessarily caused solely by an increased export of freshwater and sea ice from the arctic via fram strait these results are corroborated by the early 1990s data when a new fresh cold anomaly was formed in the labrador sea and accompanied by a large positive sea ice extent anomaly the harsh winters of the early 1990s were however confined to the labrador sea baffin bay area while the atmospheric and oceanic conditions in the greenland iceland and irminger seas were normal the labrador sea baffin bay area appears therefore to play a key role in formation of gsas as well as in propagation of the gsas formed upstream a likely contribution of the enhanced canadian archipelago freshwater outflow to the gsa formation also seems to be significant two major modes of the gsa origin are thus identified remote generated by an enhanced arctic ocean freshwater export via either fram strait or the canadian archipelago and local resulting from severe winters in the labrador sea baffin bay both modes should be taken into account to model decadal variability of the coupled ocean ice atmosphere system in the north atlantic arctic basin

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

structural features of an active strike slip fault on the sliding flank of mt etna italy abstract the strike slip pernicana fault system pfs was activated along the eastern flank of mt etna during an earthquake in september 2002 and one month later during the eruption of the ne rift structural and volcanological data suggest that the pfs was activated as a result of the slide of the ne flank of etna this activation produced surface fracturing on walls and on paved and unpaved roads the segments of the pfs arranged in a right stepping en echelon configuration show a an inverse proportion between length and frequency b fractal behavior over scales of 10 2 10 1 m between their length overstep and overlap c consistent strike with regard to their fault array and d a progressive eastward decrease in the displacement along the smallest faults the consistent geometric and kinematic features of the pfs related to the sector collapse of etna are similar to those of faults in strike slip settings

fault growth by linkage observations and implications from analogue models abstract using time sequence analyses of extensional fault models we demonstrate the pivotal role played by fault segmentation in the accumulation of displacement and length during the growth of faults experiments are described in which incremental steps during the development of individual faults have been reconstructed from time lapse photographs taken during model deformation these records confirm the composite segment hierarchy of fault structure a pattern that is frequently recognised in many natural arrays they reveal the progressive enlargement of individual faults to be the product of a repetitive cycle of tip line propagation overlap and linkage between nearest neighbours by contrasting the displacement patterns of successive increments during growth convincing evidence is also presented to suggest that individual segments of faults may remain kinematically independent once they are physically linked this behaviour is shown to be responsible for the characteristic saw tooth patterns often recognised in strike parallel fault displacement profiles such patterns are believed to arise where relict segment boundaries remain preserved as asperities to slip so that displacement is confined to discrete parts of a fault plane surface growth in this way also causes the maximum displacement d and surface length l of faults to continually change by different proportions incremental displacement records presented here corroborate field evidence which shows that linkage between fault segments during growth is responsible for a significant component of the spread of values often recorded in d versus l compilations finally we speculate that linkage between fault segments also accounts for transient irregularities recorded in the frequency distribution of the fault length populations of each model

size distributions for large and small earthquakes small and large earthquakes obey different scaling laws and inhabit distinct populations both characterized by power laws with different exponents when considering earthquakes on a single fault or fault segment the one large earthquake that occurs during a seismic cycle is discontinuous with the population of small earthquakes here it is shown that these two observations together with the scaling laws are self consistent when proper account is taken of the size distribution of faults

influence of the atlantic subpolar gyre on the thermohaline circulation during the past decade record high salinities have been observed in the atlantic inflow to the nordic seas and the arctic ocean which feeds the north atlantic thermohaline circulation thc this may counteract the observed long term increase in freshwater supply to the area and tend to stabilize the north atlantic thc here we show that the salinity of the atlantic inflow is tightly linked to the dynamics of the north atlantic subpolar gyre circulation therefore when assessing the future of the north atlantic thc it is essential that the dynamics of the subpolar gyre and its influence on the salinity are taken into account

the gubbio normal fault central italy geometry displacement distribution and tectonic evolution abstract normal faults within orogenic belts can be pre syn or post orogenic features we studied the gubbio normal fault central italy which is an example of a pre orogenic fault reactivated in a post orogenic stage the gubbio fault is a 22 km long fault bordering a quaternary basin and part of an active faults system in the umbria marche region central italy the interpretation of a set of seismic profiles enables us to reconstruct the fault geometry in detail and to measure displacement and throw distributions along the fault strike seismic data indicate that the gubbio fault represents an example of multiple reactivation at least a portion of the fault was active in the miocene and only a part of the total displacement was achieved in the quaternary the reconstruction of the fault geometry at depth shows that the fault is characterised by listric geometry the fault is also characterised by a bend along strike and structure contours show that this geometry is maintained at depth as the fault is commonly addressed as presently active the maximum fault dimensions are correlated to the maximum expected earthquake and the presence of the fault bend is discussed as a possible barrier to seismic ruptures propagation

sandbox models of relay ramp structure and evolution relay ramps are a common feature formed during the growth of normal fault systems we performed analogue experiments to investigate the structure and evolution of relay ramps an extending rubber sheet induces extension at the base of a sand pack brittle crust analogue silicone bars between the rubber and the sand control the location of fault nucleation we tested the role of fault spacing fault length overlap length and fault strike in the evolution of relay ramps the modelled relay ramps evolved in three stages characterized by the growth of the normal faults their interaction and linkage interaction and linkage occurred only when the combined length of the two interacting faults was larger than eight times their spacing the length to width ratio of the relay ramps during the interaction stage showed preferred geometries clustering around three the propagation of the fault tips was observed both before and after the linkage stage overlap length and spacing relations of the modelled relay ramps are similar to those in nature at different scales and can be explained using existing mechanical models nevertheless the further propagation of the fault tips after linkage has not been described previously

3d seismic characterisation of an array of blind normal faults in the levant basin eastern mediterranean the geometry throw distribution and kinematics of an array of blind normal faults were investigated using a high resolution 3d seismic dataset located in the levant basin offshore israel to establish criteria allowing true blind faults to be distinguished from minor synsedimentary faults a detailed analysis of throw distribution on the fault planes shows that the displacement exhibits a crudely concentric pattern about a maximum region located centrally on a fault plane as expected for ideal blind faults however vertical displacement profiles do not exhibit classical linear or triangular profiles but are mostly flat topped or hybrid in type comparison of unrestricted blind faults to those that interacted with a mechanical boundary or another structure suggests that such interactions significantly modify the throw spatial distribution on a fault plane to distinguish small synsedimentary faults from blind faults we use a combination of three criteria to assess whether a fault grew by blind propagation 1 plunging upper tip region and complementary pattern in the throw contours 2 presence of upper tip propagation fold and 3 absence of stratigraphic evidence that the fault interacted with the free surface

deformation within a strike slip fault network at westward ho devon u k domino vs conjugate faulting abstract a system of ne trending left lateral faults and nw trending right lateral faults at westward ho north devon u k cut steeply dipping 60 strata faults were accurately mapped in the field and from aerial photography and lateral separations of marker beds measured along the fault traces these data are used to examine the displacements within the network of interacting faults and to calculate variations in the density and relative proportions of the fault sets the displacements are also used in a tensor analysis of the strain and together with block rotations used to restore the deformation the results show a range of heterogeneity within the fault network both in terms of the fault patterns and strain some sub areas show a dominance of one fault set with regularly spaced larger displacements separating relatively weakly deformed blocks with smaller antithetic faults within these areas up to 20 rotation of the faults and bedding produces a domino style deformation that accommodates up to 15 extension the domino regions are separated by areas of conjugate faulting in which both sets of faults are equally developed and have similar displacement ranges conjugate areas have little or no rotation of the bedding and generally lower strains than domino regions

assessing variability in the size and strength of the north atlantic subpolar gyre recent studies on the size and strength of the north atlantic subpolar gyre spg offer contrasting assessments of the gyre s temporal variability studies that use empirical orthogonal function eof analyses of satellite sea surface height ssh report a rapid decline in spg size and strength since 1992 20 per decade while concurrent in situ observations report either no trend or a slight decline here we investigate this discrepancy by analyzing the size and strength of the spg with satellite ssh from 1993 to 2015 with two separate methods indirectly via eof analysis and more directly through measurements of the gyre center and boundary we define the boundary of the gyre as the largest closed contour of ssh the center as the minimum ssh and the strength as the difference between the ssh at the boundary and the center we identify a linear decline over the study period in the spg strength 5 1 per decade but find no statistically significant trend in the spg area the trend in the gyre strength is weaker than the eof based trend and is most likely below the level of detection of the in situ measurements we conclude that the variability previously identified as a sharp decline in spg circulation can be more appropriately attributed to basin wide sea level rise during the satellite altimetry period in addition we find that the properties of the eastern spg do not co vary with the spg size suggesting that spg dynamics do not control the strength of the inter gyre throughput

grain size variations in the earth s mantle and the evolution of primordial chemical heterogeneities 1 chemical heterogeneities with relatively high viscosity are known to be poorly mixed by mantle convection one of the factors which can cause viscosity variations is the grain size analysis of various physical processes in the earth s mantle suggests that variation in the grain size can be extremely large even outside of subducting slabs the largest grains are formed in the early molten earth where ostwald ripening is controlled by liquid state diffusion the smallest grains are formed due to recrystallization by the spinel perovskite phase transformation in downwelling flow and subsequent ostwald ripening the viscosity contrast between primordial large grain size material and recrystallized material is likely to be many orders of magnitude preliminary numerical simulations show that strongly time dependent mantle convection can process primordial large grain size heterogeneities through the spinel perovskite phase boundary only after a few overturns this reduces the viscosity contrasts and leads to rapid mixing by mantle convection a more steady flow in the lower mantle may lead to the formation of stagnant poorly mixed regions which may never have had a chance to cross the 660 km discontinuity and be recrystallized by the spinel perovskite phase transformation heterogeneities can also avoid grain size reduction and mixing if their density is slightly larger than the surrounding mantle in this case they accumulate at the core mantle boundary

growth of normal faults in multilayer sequences a 3d seismic case study from the egersund basin norwegian north sea abstract we investigate the structural style and evolution of a salt influenced extensional fault array in the egersund basin norwegian north sea through analysis of 3d reflection seismic and well data analysis of fault geometry morphology throw distribution and syn kinematic strata reveal an intricate but systematic style of displacement and growth suggesting an evolution of 1 initial syn sedimentary fault growth contemporaneous with salt mobilization initiated during the late triassic 2 cessation of fault activity and burial of the stagnant fault tips and 3 subsequent nucleation of new faults in the cover above contemporaneous salt re mobilization initiated during the late cretaceous with downward propagation and linkage with faults stage 3 was apparently largely controlled by salt mobilization in response to basin inversion as reactivated faults are located where the underlying salt is thick while the non reactivated faults are found where salt is depleted based on the 3d throw analyses we conclude that a combination of basement faulting and salt re mobilization is the driving mechanisms behind fault activation and reactivation even though the sub and supra salt faults are mainly geometrically decoupled through the salt a kinematic coupling must have existed as sub salt faults still affected nucleation and localization of the cover faults

gulf stream excursions and sectional detachments generate the decadal pulses in the atlantic multidecadal oscillation abstractdecadal pulses within the lower frequency atlantic multidecadal oscillation amo are a prominent but underappreciated amo feature representing decadal variability of the subpolar gyre e g the great salinity anomaly of the 1970s and wielding notable influence on the hydroclimate of the african and american continents here clues are sought into their origin in the spatiotemporal development of the gulf stream s gs meridional excursions and sectional detachments apparent in the 1954 2012 record of ocean surface and subsurface salinity and temperature observations the gs excursions are tracked via meridional displacement of the 15 c isotherm at 200 m depth the gs index whereas the amo s decadal pulses are targeted through the amo tendency which implicitly highlights the shorter time scales of the amo index the gs s northward shift is shown to be preceded by the positive phase of the low frequency north atlantic oscillation lf nao and followed by a positive amo tendency by 1 25 and 2 5 yea

relay zones between mesoscopic thrust faults in layered sedimentary sequences abstract we examine the geometry formation and destruction of relay zones in well bedded sedimentary sequences containing thrust fault segments with maximum observed displacements of 0 64 8 m contractional extensional and neutral relay zones are distinguished based on the stepping sense of the interacting fault segments and the orientation of the associated fault slip vectors large displacement gradients 0 17 1 0 in relay zones are mainly accommodated by folding with aggregate displacements maintained across segment boundaries and a significant component of the fault slip converted to fold related shortening folds in contractional relay zones verge in the direction of hanging wall motion with the steeper limb defining a parallelogram shaped zone between thrusts fault segment lengths are established after minimal displacement and folds in relay zones grow between segments as displacement accrues on the thrusts with increasing displacement upper and lower thrust tip lines in contractional and extensional relay zones are fixed at stratigraphic boundaries while the lateral thrust tip lines may propagate in a strike parallel direction upper and lower tip lines may eventually propagate to bypass relay zones that formed early in the fault growth history contractional relay zones remain intact at higher displacements than extensional relay zones

overlapping faults intrabasin highs and the growth of normal faults normal fault systems bounding extensional basins are typically adjoined by a series of subbasins separated by intrabasin highs the strata within these basins form syndepositional anticlines and synclines whose axes are transverse to the strike of the main bounding fault one possible explanation for these intrabasin highs is that they result from persistent along strike deficits in fault displacement such deficits are incompatible with scaling relationships observed between fault displacement and length based on large populations of faults we present data from active normal faults within the basin and range province and from inactive normal faults of the newark basin of eastern north america demonstrating a clear correlation between the along strike position of overlapping splay faults and the location of intrabasin highs as well as syndepositional transverse folds summed displacements for all faults within an intrabasin high are comparable to the displacements on faults bounding flanking subbasins o

mechanisms for variable north atlantic nordic seas exchanges 1 the variable oceanic exchanges between the nordic seas and the atlantic proper have been investigated using an isopycnic coordinate ocean model for the period 1948 2007 observed and simulated time series of volume transports in the denmark strait ds between iceland and the faroe islands and in the faroe shetland channel fsc are used to evaluate the model and the model captures much of the variability the inflow of atlantic water in the fsc and the outflow of light polar water in the ds and of dense overflow water in both fsc and ds are all found to covary with an atmospheric pattern resembling the north atlantic oscillation an increase in the fsc inflow is associated with a decrease in the fsc overflow and an increase in the ds overflow the exchanges response to the atmospheric forcing is mainly of a barotropic nature but they are also influenced by baroclinic processes the modeled antiphase between fsc inflow and overflow is connected to a vertical displacement of the isopycnal separating the two water masses in the channel and along the path of the norwegian atlantic slope current consistent with hydraulic control of the fsc exchanges

discontinuous fault zones abstract many tectonic faults and tension fractures are at least initially composed of separate segments this note deals with a little explored reason for this phenomenon which in faulting has obvious implications both for the migration of hydrocarbons and for the sealing capacity of faults theoretical arguments based on coulombmohr s theory of shear failure and on a theorem for the integrability of vector fields lead to the expectation that in general non uniform and truly three dimensional stress fields will impede the formation of smooth coherent fault surfaces this is in contrast to the stress fields that are associated with plane deformation examples are given and special attention is drawn to the role of tectonic stress fields with horizontal principal stresses that change with depth in magnitude and direction

formation of segmented normal faults a 3 d perspective the interpretation of fault kinematics from geometric data is an essential step in developing an understanding of the growth of fault systems constraints on fault geometry are however often restricted to 2 d maps or cross sections in this article we consider the extent to which kinematic interpretations of faulting benefit from a 3 d rather than 2 d geometrical perspective concentrating on relay zones and segmented normal fault arrays we suggest that very different interpretations of their evolution arise from the recognition that the propagation directions of faults and fault segments will rarely be contained within the inspection plane of 2 d data a 3 d perspective favours an interpretation in which the segments of a fault array are kinematically interrelated from their initiation individual segments in such systems may link into a single fault surface out of the plane of inspection or may be unconnected in 3 d we argue that this interpretation which conflicts with the often suggested model of incidental overlap of originally isolated faults should be the preferred model for the generation and growth of segmented normal fault arrays

probing the mantle past until recently geologists generally believed that all evidence of the first few hundred million years of earth s 4 56 billion year history had been erased by mantle convection and plate tectonics although planetary analogs with mars and the moon suggest that earth likely experienced large scale melting soon after accretion vigorous convection in the early mantle due to higher heat production from radioactive decay core formation and large impacts followed by 4 billion years of crustal recycling at plate boundaries was thought to have efficiently mixed and homogenized the mantle obliterating all signs of earth s youthful exuberance that all changed with the discovery of zircon grains more than 4 0 billion years old from the jack hills in western australia in 1983 1 followed by the demonstration in 2003 that geochemical signals linked to decay of short lived radioactive isotopes are preserved in some ancient crustal terrains the recognition of 142nd isotopic variations produced by decay of 146sm with a half life of 103 million years in 3 8 billion year old terrestrial rocks 2 proved that traces of earth s earliest history are still legible in the rock record on page 1065 of this issue touboul et al 3 report highly precise measurements of the isotopic composition of tungsten w in 2 8 billion year old komatiites a type of basaltic rock known to be derived from source regions deep within the mantle the results help to produce a clearer picture of the dynamic processes involved in the formation of earth s early mantle

water mass transformation and the north atlantic current in three multicentury climate model simulations 1 the warm and saline subtropical water carried by the north atlantic current undergoes substantial transformation on its way to higher latitudes predominantly from oceanic heat loss to the atmosphere the geographical distribution of the surface forced water mass transformation is assessed in multicentury climate simulations from three different climate models bcm ipslcm4 and mpi m esm with a particular focus on the eastern subpolar north atlantic ocean a diagnosis originally introduced by walin 1982 estimates the surface water mass transformation from buoyancy forcing while the depth structure of the atlantic meridional overturning circulation amoc is similar in all models their climatological heat and freshwater fluxes are very different consistently the models differ in their mean pathways of the north atlantic current location of upper ocean low salinity waters as well as in sea ice cover in the two models with an excessive sea ice extent in the labrador sea most of the water mass transformation in the subpolar region occurs in the eastern part east of 35 w the variability of the eastern water mass transformation on decadal time scales is related to the variable warm northward flow into the subpolar region the upper branch of amoc where a strengthened flow leads an intensified transformation this relationship seems to disappear with a weak connection between the subtropical and subpolar gyres