large scale pseudotachylytes and fluidized cataclasites from an ancient subduction thrust fault in the kodiak accretionary complex kodiak island alaska pseudotachylyte occurs in black locally vitreous ultrafine grained fault rock microscopic observations show that the pseudotachylytes are composed of glass with vesicles amygdules microlites and flow structures indicating a frictional melt the pseudotachylyte is gradational to cataclasite and shows outcrop scale injection and ductile deformation structures the cataclasite was ductily mobile i e fluidized simultaneous with the formation and emplacement of pseudotachylyte melt the pseudotachylytic rocks postdate the stratal disruption fabric of associated shear zone melanges and show similar direction of thrust transport and have undergone limited subsequent deformation we interpret the stratal disruption as resulting from underthrusting of the subducting plate and pseudotachylyte development as the final activity of this thrust surface the gradational contacts between pseudotachylyte and cataclasite demonstrate that the cataclasite also formed as a seismic product and may represent paleoseismic rupture zones possibly of very great earthquakes with or without accompanying pseudotachylytes the pseudotachylytes are voluminous and many are spatially disconnected from generation surfaces this style is distinct from pseudotachylytes described in other environments and this may explain the rarity of documented examples of subduction thrust pseudotachylyte

mechanisms of the 1997 1998 el nino la nina as inferred from space based observations 1 the intensity of the 1997 el nino and the 8 c sudden drop in sea surface temperature sst around 0 130 w during the turn into la nina in 1998 were a surprise to the scientific community this succession of warm and cold events was observed from start to finish with a comprehensive set of remotely sensed and in situ observations in this study we employ space based observations to demonstrate for the first time their maturity in capturing the preconditioning onset evolution and decay of the 1997 el nino and its transition into the 1998 la nina an accumulation of warm water in the west and equatorial wave reflection on the western ocean boundary appeared favorable for the development of el nino however the action of a series of westerly wind bursts from december 1996 to june 1997 notably in march 1997 was instrumental in setting up this huge el nino the westerly wind bursts excited equatorial downwelling kelvin waves and advected the eastern edge of the warm pool eastward which triggered a distinct warming over the central and eastern parts of the equatorial basin once these warmed regions joined the coupling between the sst and surface winds was fully effective and el nino reached its mature phase by that time much of the warm waters of the western equatorial pacific was transferred toward the east by surface eastward currents the demise of el nino and its turn into la nina in spring 1998 were due to the arrival in the east of various interrelated phenomena upwelling was brought from the west by favorable off equatorial wind stress curl and equatorial kelvin waves generated by easterly winds and wave reflection on the western ocean boundary additional upwelling was brought from the east by equatorial rossby waves generated by westerly winds these various upwelling signals were added to the general uplifting of the thermocline because of the slow discharge of the upper layer of the equatorial basin by diverging surface currents a series of equatorial kelvin and rossby waves characterized by upwelling and opposite surface currents led to the breakup of the warm waters the surfacing of the thermocline and the drastic drop in sst in may 1998 around 0 130 w with the arrival of cold water in the east the easterly winds expanded from the west and la nina turned into a growing mode this view of the 1997 1998 el nino la nina afforded from space enables the testing of various el nino theories

crustal deformation at the southernmost part of the ryukyu subduction east taiwan as revealed by new marine seismic experiments abstract the southernmost part of the ryukyu subduction where the philippine sea plate is subducting under the eurasian plate is known to be a very seismically active region of transition from a north dipping subduction along the ryukyu subduction to an se nw collision along the taiwanese orogenic wedge in this paper we will focus on the ryukyu forearc area close to taiwan where the deformation is paroxysmal in order to decipher the nature of the seismic deformation in this region a three month passive experiment combining 22 ocean bottom seismometers and 51 onland stations has been led starting from an a priori heterogeneous model we have obtained 801 well located earthquake hypocenters a precise p wave tomography model and 14 focal mechanisms the seismicity along the ryukyu forearc is mainly located not only in the vicinity of the interplate seismogenic zone isz but also within both the subducting psp and the overriding plate seismicity within the upper plate is essentially localized east of nanao basin where nw se extension occurs and northwest of the hoping basin where strike slip dominates as revealed by both the p wave velocity structure and the newly derived seismicity we argue that a sub vertical step offsetting the subducting psp around 10 km may support the presence of a trench parallel tear the psp also undergoes extension in its upper part that is probably caused by buckling and slab pull the p wave velocity structure reveals three other major features 1 a continuity between the central range and the ryukyu arc with a shallower moho 30 km depth between 122 3 n and 122 5 n along the ryukyu arc 2 high p wave velocities along the eastern side of the central range and 3 two bodies with similar high crustal velocities 6 5 7 0 km s at 12 18 km depths embedded within the ryukyu arc basement just north of hoping basin and north of the nanao basin

dynamics and thermodynamics of a warming event in a coupled tropical atmosphere ocean model abstract a simple coupled ocean atmosphere model similar to that of zebiak and cane is used to examine the dynamic and thermodynamic processes associated with el nino southern oscillation enso the model is run for 300 years the interannual variability which results is regular with a period of either 3 or 4 years quantized by the annual cycle the amplitude 1 5 m s 1 wind and 2 c sst anomalies period and structure of the interannual variability compare well with observations the model warm event is initiated in the spring prior to the event peak and is well described as an instability of the coupled system during instability growth the sea surface temperature sst anomaly is primarily generated by vertical upwelling processes the sst anomaly can be approximately described by the expression t t kth t where t is the sst anomaly t time h the upper layer thickness pycnocline perturbation and an effective damping time which includes heat loss to the atmosphere kt parameterizes

heat flow of norway and its continental shelf abstract terrestrial heat flow influences a large collection of geological phenomena its determination and understanding is of prime interest for oil industry because geothermal processes impact directly maturation histories and economic potential of oil fields and reservoirs published systematic heat flow determinations from major oil provinces are however seldom robust heat flow determinations in drillholes require logging of undisturbed temperatures and intensive sampling of core material for petrophysical measurements temperature logging in exploration drillholes is traditionally conducted during drilling breaks or shortly after drilling resulting in temperatures severely disturbed by mud circulation and coring is restricted to selected intervals alternatively test temperatures information from electric logs and lithological descriptions of drill cuttings can be used to overcome these limitations the present contribution introduces new heat flow determinations based on 63 exploration drillholes from the norwegian north sea the mid norway margin and the barents shelf our analyses are based on released dst temperatures precise lithological descriptions of drill cuttings previously measured rock matrix thermal conductivities and established porosity laws for the sake of comparison we carefully review previous heat flow studies carried out both onshore and offshore norway our results suggest median heat flow values of 64 mw m 2 65 mw m 2 and 72 mw m 2 for the north sea the mid norway margin mainly the trondelag platform and the sw barents shelf respectively in detail heat flow increases by 10 mw m 2 from the southern norwegian north sea towards the mid norway margin this result appears to be in very good agreement with seismic tomographic studies suggesting northward thinning of the underlying mantle lithosphere our results together with published marine heat flow data from the mid norway margin suggest a gradual decrease in heat flow levels from both the north sea and the trondelag platform towards the centres of the deep more and voring basins this latter effect is attributed to reduced heat input from crustal sources caused by the extreme attenuation of the crystalline basement below these two basins heat flow in the sw barents shelf increases westwards this is interpreted as lateral heat transfer from the adjacent young ocean tentative corrections for quaternary sedimentation erosion effects suggest similar heat flow levels for the three studied areas but the above mentioned regional trends remain unchanged

tropical pacific baroclinic mode contribution and associated long waves for the 1994 1999 period from an assimilation experiment with altimetric data an ocean general circulation model ogcm of the tropical pacific in which combined topex poseidon and ers sea level anomalies are assimilated over january 1994 through july 1999 is used to investigate equatorial wave characteristics during the intense 1997 1999 el nino la nina event near the equator the linear vertical modes are estimated at each grid point of the ogcm simulation with and without assimilation consistently with an increase of the vertical gradient within the thermocline and a rise of the thermocline depth in the eastern basin the assimilation results in an increased contribution of the higher order baroclinic modes in the eastern basin and a decreased contribution of the first baroclinic mode in the western pacific for the zonal current variability for pressure the first baroclinic mode contribution is reduced whereas the higher order modes contribution is weakly impacted kelvin and first meridional rossby waves are then derived for the first two more energetic baroclinic modes in the simulation with assimilation kelvin waves of both modes constructively contribute to the strong warming observed in 1997 with the first second baroclinic mode being more energetic than the second first baroclinic mode in the early mature stage of the warming kelvin waves of both modes reflect as first meridional rossby waves at the eastern boundary reflection efficiency of 95 and contribute to push back the warm pool westward the reversal of the warming is apparently initiated by the second baroclinic mode contribution which controls the position of the 28 c isotherm in the surface layer in the far eastern pacific from january 1998 at the western boundary reflections of rossby waves take place for both modes with an estimated total efficiency of 50 at 165 e this suggests that in our model the delayed oscillator theory is not applicable for explaining the reversal from warm to cold conditions in 1998 while the zonal advective feedback was at work more generally the study suggests that it is necessary to take into account the vertical structure of the ocean when interpreting altimetric data which can be done through an assimilation experiment

on the importance of subsurface variability for enso simulation and prediction with intermediate coupled models of the tropical pacific a case study for the 1997 1998 el nino 1 two intermediate ocean atmosphere coupled models of the tropical pacific are used to investigate the sensitivity of the forecasts of the 1997 1998 el nino to the configuration of the oceanic vertical structure the models consist in a three baroclinic mode tropical pacific ocean and differ from their atmospheric part which is either a gill 1980 s tropical atmosphere or a statistical atmosphere forced with observed winds the ocean model simulates dynamical fields in better agreement with observations compared to a single baroclinic mode model in forecasting sea surface temperature anomalies in the eastern pacific the models are comparable to prediction systems of similar complexity results of sensitivity tests to the oceanic vertical structure indicate that the second and third baroclinic mode contributions are necessary to better capture the rise in sst anomalies from april 1997 along with the amplitude of the event at its mature phase

the characteristic oscillation induced by coupled processes between oceanic vertical modes and atmospheric modes in the tropical pacific an intermediate coupled model icm based on an ocean model with three vertical modes and a statistical atmosphere model was used to investigate the relationship between the dominant modes of variability in the ocean and the atmosphere in the tropical pacific tests on sensitivity to the oceanic vertical structure of the ocean show that the time scale of variability in the sea surface temperature anomaly ssta mainly depends on the relative contribution of the baroclinic modes the first two atmospheric modes i e the central and off equatorial modes play different roles in modulating the impact of oceanic baroclinic modes on sst changes through coupled processes in the model the central mode excites the second oceanic mode which drives the observations like interannual variability in the model the atmospheric off equatorial mode on the other hand favors the gravest baroclinic mode through the forcing of rossby waves and consequently shortens the frequency of ssta variability in the tropical pacific this suggests a possible mechanism governing time modulation of the el nino events characteristics in the tropical pacific

derivation of s and pb in phanerozoic intrusion related metal deposits from neoproterozoic sedimentary pyrite great basin united states the thick 8 km regionally extensive section of neoproterozoic siliciclastic strata terrigenous detrital succession tds in the central and eastern great basin contains sedimentary pyrite characterized by mostly high 34 s values 11 6 to 40 8 70 exceed 10 51 analyses derived from reduction of seawater sulfate and by markedly radiogenic pb isotopes 207 pb 204 pb 19 2 15 analyses acquired from clastic detritus eroded from precambrian cratonal rocks to the east southeast in the overlying paleozoic section pb zn cu ag au deposits associated with jurassic cretaceous and tertiary granitic intrusions intrusion related metal deposits contain galena and other sulfide minerals with s and pb isotope compositions similar to those of tds sedimentary pyrite consistent with derivation of deposit s and pb from tds pyrite minor element abundances in tds pyrite e g pb zn cu ag and au compared to sedimentary and hydrothermal pyrite elsewhere are not noticeably elevated implying that enrichment in source minerals is not a precondition for intrusion related metal deposits three mechanisms for transferring components of tds sedimentary pyrite to intrusion related metal deposits are qualitatively evaluated one mechanism involves 1 decomposition of tds pyrite in thermal aureoles of intruding magmas and 2 aqueous transport and precipitation in thermal or fluid mixing gradients of isotopically heavy s radiogenic pb and possibly other sedimentary pyrite and detrital mineral components as sulfide minerals in intrusion related metal deposits a second mechanism invokes mixing and s isotope exchange in thermal aureoles of pb and s exsolved from magma and derived from decomposition of sedimentary pyrite a third mechanism entails melting of tds strata or assimilation of tds strata by crustal or mantle magmas tds derived or assimilated magmas ascend decompress and exsolve a mixture of tds volatiles including isotopically heavy s and radiogenic pb from sedimentary pyrite and volatiles acquired from deeper crustal or mantle sources in the central and eastern great basin the wide distribution and high density of small to mid sized vein replacement and skarn intrusion related metal deposits in lower paleozoic rocks that contain tds sedimentary pyrite s and pb reflect 1 prolific jurassic cretaceous and tertiary magmatism 2 a regional substrate reservoir of s and pb in permeable and homogeneous siliciclastic strata and 3 relatively small scale concentration of substrate and magmatic components large intrusion related metal deposits in the central and eastern great basin acquired s and most pb from thicker lithospheric sections

a bottom driven mechanism for distributed faulting in the gulf of california rift abstract observations of active faulting in the continent ocean transition of the northern gulf of california show multiple oblique slip faults distributed in a 200 70 km 2 area developed some time after a westward relocation of the plate boundary at 2 ma in contrast north and south of this broad pull apart structure major transform faults accommodate pacific north america plate motion here we propose that the mechanism for distributed brittle deformation results from the boundary conditions present in the northern gulf where basal shear is distributed between the cerro prieto strike slip fault southernmost fault of the san andreas fault system and the ballenas transform fault we hypothesize that in oblique extensional settings whether deformation is partitioned in a few dip slip and strike slip faults or in numerous oblique slip faults may depend on 1 bottom driven distributed extension and shear deformation of the lower crust or upper mantle and 2 the rift obliquity to test this idea we explore the effects of bottom driven shear on the deformation of a brittle elastic plastic layer with the help of pseudo three dimensional numerical models that include side forces strain localization results when the basal shear abruptly increases in a step function manner while oblique slip on numerous faults dominates when basal shear is distributed we further explore how the style of faulting varies with obliquity and demonstrate that the style of delocalized faulting observed in the northern gulf of california is reproduced in models with an obliquity of 0 7 and distributed basal shear boundary conditions consistent with the interpreted obliquity and boundary conditions of the study area

signature of coseismic decarbonation in dolomitic fault rocks of the naukluft thrust namibia unequivocal geological signatures of seismic slip are rare exceptionally so in carbonate hosted faults where carbonate minerals dissociate at temperatures lower than those required for producing a friction melt this thermal dissociation leads to significant fault weakening by increased fluid pressure and or nanoparticle lubrication preventing further heating of the fault surface pseudotachylyte is therefore unlikely to form in carbonate hosted faults and other evidence for seismic slip must be identified we studied the lower cambrian naukluft thrust which crops out in central namibia it contains a cataclastic dolomite fault rock referred to as gritty dolomite which we interpret as a signature of coseismic carbonate dissociation and subsequent fluid rock interactions the fault was active at ambient temperatures below 2001c gritty dolomite contains rounded low aspect ratio dolomite clasts with a uniform fe rich dolomite coating euhedral to subhedral magnetite quartz and k feldspar in a fine grained massive to laminated carbonate matrix of particulate dolomite and crystalline calcite cement the fault rock texture combined with evidence of injectites of gritty dolomite into the wallrock indicates the cataclasite deformed as a fluidized granular flow at seismic slip velocities frictional heating caused dissociation of dolomite to co 2 and ca fe and mg oxides this release of co2 decreased the ph of the pore fluid in the fault causing dissolution and rounding of dolomite clasts within an inertial grain flow and precipitation of carbonate coatings and euhedral silicates and oxides during subsequent cooling and co2 escape examples of similar rocks having some if not all of these characteristics have been described from other carbonate hosted faults the geological setting of the naukluft thrust is unique in spatial extent and quality of exposure allowing us to eliminate alternative hypotheses for sources of co2 to drive fluidization

an advective reflective conceptual model for the oscillatory nature of the enso recent findings about zonal displacements of the pacific warm pool required a notable modification of the delayed action oscillator theory the current leading theory for the el nino southern oscillation enso simulations with a linearized coupled ocean atmosphere model resulted in 3 to 6 year enso like oscillations with many of the variable model parameters found to be very close to their observed values this simple model suggests that ocean processes that are ignored or underestimated in the delayed action oscillator theory such as zonal current convergence zonal advection of sea surface temperature and equatorial wave reflection from the eastern ocean boundary are fundamental to the development of the enso in particular to its manifestations in the central equatorial pacific

modes of covariability between sea surface temperature and wind stress intraseasonal anomalies along the coast of peru from satellite observations 2000 2008 1 the tropical rainfall measuring mission microwave imager sea surface temperature sst and quikscat wind stress satellite data are used to investigate the intraseasonal upwelling variability along the coat of peru over the period 2000 2008 two regions of peak variance correspond to the central peru region pisco region 15 s and the northern peru region piura region 5 s a covariance analysis reveals a significant coherency between winds and sst anomalies off pisco consistent with ekman pumping and transport dynamics the upwelling cell consists in a meridionally extended fringe of colder warmer water extending as far as 250 km from the coast at 15 s in the piura region the intraseasonal covariability pattern is represented by two modes one relevant to the direct ekman dynamics and the other one associated with the remote forcing of intraseasonal oceanic kelvin wave two regimes of variability are evidenced a low period regime 10 25 days is the signature of ekman transport pumping dynamics and is remotely forced by the migratory atmospheric disturbances across the southeastern pacific anticyclone a high period regime 35 60 day band is associated with the combined forcing of oceanic equatorial kelvin waves and migratory atmospheric disturbances in the midlatitudes in particular the modes of covariability exhibit a prominent 50 day period energy peak it is shown that this period arises from the impact of the first two baroclinic modes kelvin wave with the second baroclinic mode kelvin wave being more influential on the piura region

strong and moderate nonlinear el nino regimes it has been previously proposed that two el nino en regimes strong and moderate exist but the historical observational record is too short to establish this conclusively here 1200 years of simulations with the gfdl cm2 1 model allowed us to demonstrate their existence in this model and by showing that the relevant dynamics are also evident in observations we present a stronger case for their existence in nature in cm2 1 the robust bimodal probability distribution of equatorial pacific sea surface temperature sst indices during en peaks provides evidence for the existence of the regimes which is also supported by a cluster analysis of these same indices the observations agree with this distribution with the en of 1982 1983 and 1997 1998 corresponding to the strong en regime and all the other observed en to the moderate regime the temporal evolution of various indices during the observed strong en agrees very well with the events in cm2 1 providing further validation of this model as a proxy for nature the two regimes differ strongly in the magnitude of the eastern pacific warming but not much in the central pacific observations and model agree in the existence of a finite positive threshold in the sst anomaly above which the zonal wind response to warming is strongly enhanced such nonlinearity in the bjerknes feedback which increases the growth rate of en events if they reach sufficiently large amplitude is very likely the essential mechanism that gives rise to the existence of the two en regimes oceanic nonlinear advection does not appear essential for the onset of strong en the threshold nonlinearity could make the en regimes very sensitive to stochastic forcing observations and model agree that the westerly wind stress anomaly in the central equatorial pacific in late boreal summer has a substantial role determining the en regime in the following winter and it is suggested that a stochastic component at this time was key for the development of the strong en towards the end of 1982

the long term topographic response of a continent adjacent to a hyperextended margin a case study from scandinavia we present data that link scandinavia s passive margin domains under a unified system invoking isostatically driven postextension phase vertical adjustments to severe crustal thinning topographic and geological data indicate that the relative location of the first landward occurrence of total crustal embrittlement or deformation coupling the taper break controlled and continues to control scandinavia s post thinning geomorphic evolution formed during late jurassic or early cretaceous thinning yet marked today by seismicity the taper break closely approximates the boundary between 1 less stretched lithosphere that increases in rigidity both toward land and through postrift time and 2 the highly attenuated pervasively faulted permanently weakened lithosphere of the distal margin following the stretching thinning and exhumation phases proposed by other workers an accommodation phase is warranted commencing during sag basin time and continuing today it is probably driven by thermal cooling and mass transfer from the escarpment to the basins offshore the accommodation phase does not entirely coincide with the traditional postrift phase as the former may contain the latter during accommodation the original synrift escarpments can be eroded to very low base levels sharply tapered margin segments can undergo subsequent rejuvenation by out of sequence normal faulting and footwall uplift probably in response to tensile bending stresses engendered by lithospheric scale flexure accommodation phase uplift at passive margins is the inexorable and penultimate phase of hyperextension and may perhaps be followed by the onset of subduction localized by the weakened lithosphere of the distal margin and the ocean continent transition

extreme frictional processes in the volcanic conduit of mount st helens usa during the 2004 2008 eruption abstract the 2004 2008 eruption of mount st helens saw the extrusion of seven high viscosity spines and formation of discrete shear zones along the conduit margin at spine 7 this shear zone consists of four structurally distinct layers the outer surface gouge l1 crosscuts a dark banded layer l2 which grades into a moderately sheared layer l3 and undeformed rock l4 inside the spine field observations porosity measurements geochemistry mineralogy microstructure crystal size and shape distribution kinetic properties and magnetic analyses chart the evolution of deformation processes and products throughout the eruption gouge formation was concomitant with characteristic microseismic drumbeats at depths 0 5 1 km in addition the seismic record shows two larger earthquakes with similar seismic signatures in august 2006 which we conclude represent larger slip amounts along the conduit margin of spine 7 extensive slip resulted in frictional heating on the order of several hundreds of degrees melting the highly viscous crystalline ascending magma plug and forming a pseudotachylyte high ambient temperatures in the conduit resulted in near equilibrium melting and slow recrystallisation thus impeding the development of signature pseudotachylyte characteristics and hindering identification thus frictional melting and recrystallisation in ascending magma plugs may be a common but unidentified phenomena at composite volcanoes worldwide

an extended kalman filter to assimilate satellite altimeter data into a nonlinear numerical model of the tropical pacific ocean method and validation a new implementation of the extended kalman filter scheme is developed for the purpose of assimilating observations into a high resolution nonlinear numerical model of the tropical pacific ocean it is characterized by two successive stages 1 approximation of the error covariance matrix by a singular low rank matrix which leads to making corrections only in those directions for which the error is not naturally attenuated by the system in this respect it is quite similar to the approach adopted by cane et al 1996 and 2 modification of these directions over time according to the model dynamics thus reflecting the evolutive nature of the filter the filter is initialized by a method based on the empirical orthogonal functions obtained from free runs of the model the reduction of the error covariance matrix avoids the overwhelming burden of computing the temporal evolution of the prediction error with all the degrees of freedom of the full state vector this assimilation scheme is implemented in the gent and cane 1989 primitive equation reduced gravity model this model has the advantage of using a coordinate in the vertical which allows a geographical refinement of the vertical resolution for thermocline gradients it is forced by the florida state university database winds and the chen et al 1994 hybrid scheme parameterization is assumed for the mixed layer the domain of application is the tropical pacific ocean basin between 120 e and 80 w longitude and 30 s and 30 n latitude the resolution is finest at the equator and steadily increases away from the equator in a first application validation twin experiments are conducted in which observations are assumed to be synthetic altimeter data sampled according to the topex poseidon mission features the method is shown to be efficient under various conditions and in particular to be capable of transferring information in the vertical from the surface only altimeter data to the deepest ocean layers and therefore of adequately constraining the thermal and the velocity profiles within the 300 or 400 m upper ocean in a second application real topex poseidon data are used and the results evaluated against independent in situ data namely tropical ocean global atmosphere toga tao mooring observations improvements in the model behavior are clear in terms of the time variability of the tropical ocean it therefore seems that the reduced state kalman filter with empirical orthogonal function eof initialization can be applied with success to such a primitive equation model of the pacific for the assimilation of altimeter data however at this stage the evolutivity of the filter seems to have a limited impact on the performances which was not the case for tests in the strongly nonlinear midlatitudes pham et al 1998a

assessment of diffusive isotopic fractionation in polar firn and application to ice core trace gas records abstract during rapid variations of the atmospheric mixing ratio of a trace gas diffusive transport in the porous firn layer atop ice sheets and glaciers alters the isotopic composition of that gas relative to the overlying atmosphere records of past atmospheric trace gas isotopic composition from ice cores and firn need to be corrected for this diffusive fractionation artifact we present a novel semi empirical method to accurately estimate the magnitude of the diffusive fractionation in the ice core record our method 1 consists of a relatively simple analytical calculation 2 requires only commonly available ice core data 3 is not subject to the uncertainties inherent to estimating the accumulation rate temperature close off depth and depth diffusivity relationship back in time 4 does not require knowledge of the true atmospheric variations but uses the smoothed records obtained from ice cores 5 arguably gives more accurate results than a combined firn densification firn air transport modeling study would we apply the method to records of ch4 co2 and n2o mixing ratios and we find that the correction is particularly important for 13 c ch 4 we apply the correction to 13 c ch 4 records over the last glacial termination and the 8 2 ka event in both cases the diffusive signal exceeds the analytical precision of the data and has a significant impact on the observed isotopic trends for the 8 2 ka event the corrected data show an isotopic enrichment in 13 c ch 4 for the duration of the event consistent with reduced wetland emissions

disappearing ink how pseudotachylytes are lost from the rock record abstract melt origin pseudotachylytes are the most widely accepted feature recording earthquake slip in the fault rock record however reports of pseudotachylytes are rare compared to the frequency and distribution of earthquakes in active faults suggesting melting occurs only under exceptional circumstances and therefore that pseudotachylytes are rarely formed in this paper we document the processes whereby pseudotachylytes are overprinted destroyed and otherwise removed from the rock record we present examples of recrystallized altered and cataclastically and crystal plastically deformed pseudotachylytes from a variety of ancient faults based on these observations we identify characteristics of pseudotachylytes that are resistant to change over geologic time and develop criteria to allow recognition of relict pseudotachylytes our results imply that pseudotachylytes are vastly under reported due to their vulnerability to destruction and the resulting difficulty in identification as a consequence the significance of frictional melting is underestimated the criteria we propose to distinguish relict pseudotachylytes can help to reconcile the observed frequency of earthquakes with the difficulty of demonstrating ancient seismic slip in the rock record

vertical structure variability and equatorial waves during central pacific and eastern pacific el ninos in a coupled general circulation model recent studies report that two types of el nino events have been observed one is the cold tongue el nino or eastern pacific el nino ep el nino which is characterized by relatively large sea surface temperature sst anomalies in the eastern pacific and the other is the warm pool el nino a k a central pacific el nino cp el nino or el nino modoki in which sst anomalies are confined to the central pacific here the vertical structure variability of the periods during ep and cp is investigated based on the gfdl cm2 1 model in order to explain the difference in equatorial wave dynamics and associated negative feedback mechanisms it is shown that the mean stratification in the vicinity of the thermocline of the central pacific is reduced during cp el nino which favours the contribution of the gravest baroclinic mode relatively to the higher order slower baroclinic mode energetic kelvin and first meridional rossby wave are evidenced during the cp el nino with distinctive amplitude and propagating characteristics according to their vertical structure mostly first and second baroclinic modes in particular the first baroclinic mode during cp el nino is associated to the ocean basin mode and participates to the recharge process during the whole el nino cycle whereas the second baroclinic mode is mostly driving the discharge process through the delayed oscillator mechanism this may explain that the phase transition from warm to neutral cold conditions during the cp el nino is delayed and or disrupted compared to the ep el nino our results have implications for the interpretation of the variability during periods of high cp el nino occurrence like the last decade

equatorially forced intraseasonal propagations along the peru chile coast and their relation with the nearshore eddy activity in 1992 2000 a modeling study 1 a regional eddy resolving oceanic model spanning the 1992 2000 period is used to study the influence of 50 to 80 day intraseasonal equatorial kelvin waves iekw on mesoscale eddy activity off the west coast of peru and northern and central chile the model is shown to realistically simulate nearshore intraseasonal sea level variability poleward propagation of equatorially forced coastal trapped waves along the coastal waveguide and offshore variability related to mesoscale eddies and rossby waves rw in agreement with linear theory rw are confined equatorward of 12 s in the 50 80 days period range south of that critical latitude westward propagation is dominated by energetic mesoscale signals resulting mainly from coastal flow instability sensitivity experiments to the open boundary conditions are then used to estimate to what extent eddy activity is impacted by the remote equatorial forcing a coastal increase in eddy kinetic energy related to the energetic 60 day iekw activity present in the open boundary forcing is evidenced and is largest off northern peru whereas no major changes are observed offshore additional regional simulations with different open boundary conditions corroborate our findings and suggest that this limited effect of iekw on the offshore eddy kinetic energy may be a robust feature citation belmadani a v echevin b dewitte and f colas 2012 equatorially forced intraseasonal propagations along the peru chile coast and their relation with the nearshore eddy activity in 1992 2000 a modeling study j geophys res 117 c04025 doi 10 1029 2011jc007848

deposition and flux of sediment from the po river italy an idealized and wintertime numerical modeling study abstract recent studies of sediment dynamics and clinoform development in the northern adriatic sea focused on winter 2002 2003 and provided the data and motivation for development of a detailed sediment transport model for the area near the po river delta we used both idealized test cases and more realistic simulations to improve our understanding of seasonal sediment dynamics there we also investigated the relationship between physical processes and the observed depositional products e g the accumulation of sediment very near the po river distributary mouths sediment transport near the po river was evaluated using a three dimensional ocean model coupled to sediment transport calculations that included wave and current induced resuspension suspended sediment transport multiple grain classes and fluvial input from the po river high resolution estimates from available meteorological and wave models were used to specify wind wave and meteorological forcing model results indicated that more than half of the discharged sediment remained within 15 km of the po river distributary mouths even after two months of intensive reworking by winter storms during floods of the po river transport in the middle to upper water column dominated sediment fluxes otherwise sediment fluxes from the subaqueous portion of the delta were confined to the bottom few meters of the water column and correlated with increases in current speed and wave energy spatial and temporal variation in wind velocities determined depositional patterns and the directions of sediment transport northeasterly bora winds produced relatively more eastward transport while southwesterly sirocco winds generated fluxes towards both the north and the south eastward transport accounted for the majority of the sediment exported from the subaqueous delta most likely due to the frequent occurrence of bora conditions progradation of the po river delta into the adriatic sea may restrict the formation of the western adriatic coastal current increasing sediment retention at the po delta and reducing the supply of sediment to the apennine margin a positive morphodynamic feedback may therefore be present whereby the extension of the delta into the adriatic increases sediment accumulation at the delta and facilitates further progradation

analog modeling of normal faulting above middle east domes during regional extension we study the effects of planform dome shape on fault patterns developing with and without concurrent regional extension oriented oblique to the long axis of the dome the motivation was the need to understand fault and fracture patterns in two adjacent mature hydrocarbon fields in the middle east one an elliptical dome and one an irregularly shaped dome the largest faults have throws of approximately 30 m 98 ft which is close to the resolution limit of older two dimensional seismic reflection data the known fault trends are not parallel to the highest transmissivity direction but could form compartment boundaries fault and fracture patterns developed over the modeled domes provide insight into the populations of faults and fractures that are likely to exist in the reservoirs but have been undetected because they are at or below the resolution limit of reflection seismic data major domal structural elements crestal fault systems end splay systems and radial faults are observed in modeled domes rising both with and without concurrent regional extension experimental results indicate that fault and fracture patterns are influenced by the effects of dome shape regional extension and relative timing of uplift with respect to regional extension the expression of particular sets of faults and fractures associated with concurrent doming and regional extension depends on the interaction among regional extension outer arc extension over the dome and tangential extension around the dome margins our results also indicate that the two adjacent natural domes possibly experienced different kinematic histories from those previously interpreted

interannual long equatorial waves in the tropical atlantic from a high resolution ocean general circulation model experiment in 1981 2000 we investigate the tropical atlantic vertical structure variability 1981 2000 based on the clipper ocean general circulation model ogcm we aim at determining to what extent the observed interannual variability can be explained by the low frequency wave dynamics the linear vertical modes of the ogcm climatological stratification are estimated along the equator the baroclinic mode contributions to surface zonal current and sea level anomalies are calculated and analyzed at interannual timescales the second baroclinic mode is the most energetic the first third mode exhibits a variability peak in the west east the summed up contribution of the high order baroclinic modes 4 6 is as energetic as the gravest modes and is largest in the east wave components are then derived by projection onto the associated meridional structures the effect of longitudinal boundaries near the equator is taken into consideration equatorial kelvin and rossby waves propagations with phases speed close to the theory are identified for the first three baroclinic modes the comparison with a multimode linear simulation corroborates the propagating properties of the ogcm waves coefficients an estimation of the meridional boundary reflection efficiency indicates that wave reflections take place at both boundaries a 65 reflection efficiency is found at the eastern boundary our study suggests that low frequency wave dynamics is to a large extent at work in the tropical atlantic on the basis of what is known on the pacific el nino southern oscillation mode this may provide a guidance for investigating ocean atmosphere mechanisms that can lead to the atlantic zonal equatorial mode

sensitivity of an intermediate ocean atmosphere coupled model of the tropical pacific to its oceanic vertical structure an intermediate ocean atmosphere coupled model icm of the tropical pacific is used to investigate the sensitivity of the coupled system to the oceanic vertical structure the model consists of a three baroclinicmode tropical pacific ocean and a gill tropical atmosphere the mixed layer is similar to the zebiak and cane zc coupled atmosphere ocean model but uses a different parameterization for subsurface temperature derived from xbt data a 100 yr simulation is made and the long term variability of the icm is briefly discussed and compared with the the observations and the zc model the icm reproduces regular enso events with a spectrum peak centered at the period 3 5 yr the presence of higher order vertical modes in the oceanic component of the model allows for reduced off equatorial variability of zonal current and thermocline anomalies and for finer meridional scale for sst anomaly variability in comparison with a simulation with one baroclinic mode only the nature of the processes sustaining the oscillations in the icm is then investigated based on the coupled instabilities and delayed oscillator theories it

low latitude dusty events vs high latitude icy heinrich events it has been proposed that tropical events could have participated in the triggering of the classic high latitude iceberg discharge heinrich events he we explore low latitude heinrich events equivalents at high resolution in a piston core recovered from the tropical north western african margin they are characterized by an increase of total dust lacustrine diatoms and fibrous lacustrine clay minerals thus low latitude events clearly reflect severe aridity events that occurred over africa at the saharan latitudes probably induced by southward shifts of the inter tropical convergence zone at a first approximation it seems that there is more likely synchronicity between the high latitude heinrich events hes and low latitude events lle rather than asynchronous behaviours

silica gel in a fault slip surface field evidence for palaeo earthquakes high velocity friction experiments have shown an almost complete loss of strength associated with silica gel formation on slip surfaces the identi cation of frictional silica gel products in palaeo seismic faults is however problematic because there are multiple natural sources of silica gel and recrystallization of gel to quartz complicates preservation the importance of gel formation on natural faults is therefore unknown here we report a structurally distinct and semi continuous 0 5 10 mm thick layer of microcrystalline quartz along a major carbonate hosted fault the olive fault in the naukluft nappe complex namibia the quartz layer is distinguished by ow banding like textures and unusual cathodoluminescence characteristics the layer consists of 2 20 m hexagonal quartz crystals which include distinct crystalline pore bearing micro to nano spheres separated by pore geometries indicative of volumetric contraction and with grain boundaries enriched in aluminium we interpret these features to indicate that the quartz crystals formed from recrystallization and dehydration of a silica gel because it is found in a carbonate hosted fault and crosscuts lithological layering the silica source is not from comminution of local wall rocks rather the gel likely formed from reshear of a quartz coated fault surface or incremental shear slip associated with precipitation of silica driven by co seismic pressure drops this example of fault related silica gel may have formed by a different mechanism than the gels produced in high velocity friction experiments but once formed may have comparable rheological effects

formation erosion and exposure of early amazonian dikes dike swarms and possible subglacial eruptions in the elysium rise utopia basin region mars hundreds of narrow linear ridge segments are found in the transition zone between the elysium rise and the utopia basin occurring as both single and multiple ridges the ridges are distinctive because of their very linear steep sided nature their often sharp ridge crest which sometimes is fractured their association with stubby flows their continuity over long distances and their cross cutting of different terrain the linear ridges are interpreted to be single dikes and dike swarms either emplaced as normal dikes or as dikes emplaced subglacially feeding an explosive or effusive eruption five dike swarms are identified having lengths ranging from 10 45 km and being between 1 7 km wide while single ridges are up to 20 km long and 100 500 m wide in the areas of dike swarms crustal dilatation is estimated to vary from 15 60 dikes emplaced en echelon suggest that variations in the local stress field caused rotation during dike emplacement and dikes crosscutting flow units imply that dike emplacement can account for some of the observed linear fractures in the area the ridges both modify and constrain early amazonian flows and flood plain deposits suggesting intense dike emplacement in the early amazonian the association with different stages of inverted craters as well as some features of ice related origin possible ice cauldron and tindar like features indicate that the dikes may have been exposed due to eolian erosion and loss of volatile rich units subsequent to their emplacement

vertically propagating annual and interannual variability in an ogcm simulation of the tropical pacific ocean in 1985 94 abstract the annual and interannual variability in the subthermocline equatorial pacific is studied in a simulation of the tropical pacific for the 1985 94 decade using a primitive equation high resolution model the study focuses on temperature variability and vertical energy fluxes similar to the observations made by w s kessler and j p mccreary the annual harmonic of vertical isotherm displacements presents phase lines sloping downward from east to west with off equatorial maxima estimates of zonal and vertical phase speeds the location of the maxima of isotherm displacements and an analysis of ernergy fluxes suggest the presence of l 1 rossby waves the simulated field is somewhat more trapped toward the equator than the observations a linear simulation is carried out for the vertical standing modes with characteristics derived from the ogcm simulation in the linear simulation high order meridional mode rossby waves are more prominent than in the ogcm simulation however the l 1 ros

fault rock injections record paleo earthquakes fault rocks such as pseudotachylyte melt or granular gouge are sometimes injected into cracks off a fault surface the width to height ratio of the injection veins is a direct measure of the shear strain in the wall rock required to accommodate the injection so the aspect ratios preserve a record of the overpressure opening the cracks and injecting melt or fluidized granular material from the fault zone we measured the aspect ratios for 201 pseudotachylyte injections and 29 granular injections they have aspect ratios of 0 2 0 177 0 025 and 0 227 0 077 respectively within 99 confidence these are significantly proportionally wider than the aspect ratios of ordinary dikes from 10 4 to 10 3 the injection aspect ratios exceed the usual limit of elastic strain in the wallrock 1 so we infer that the injection veins were accommodated by permanent deformation by microcracking and slip on foliation surfaces in the host rock which is difficult to detect observationally the fully elastic model therefore offers an upper bound on the stress required to open these injection veins 10 8 210 10 pa with higher pressures in stiffer host rock lithologies these overpressures cannot be achieved by expansion of the fault rock fluids during melting or gouge fluidization mechanisms as the pressure along the fault is limited to 10 7

thin viscous middle crust and evolving fault distribution during continental rifting insights from analog modeling experiments abstract analog modeling of continental rifting assuming a crustal scale jelly sandwich like rheology was carried out to test the mechanical effect of varying the absolute thickness of a weak viscous middle crust silicone layer interbedded between a brittle upper crust sand layer and a strong lower crust results consistently show a delocalization of the brittle deformation i e a uniform scattering of the faults throughout the upper brittle layer this effect is interpreted to be associated with pressure driven flow in the viscous layer caused by the tectonic collapse of upper brittle fault blocks into the viscous substratum a reduction of the overall viscous layer thickness increases its resistance to accommodate internal thickness variations which promotes delocalization of the fault pattern in the upper brittle layer our results contribute to the understanding of the mechanics of the so called upper plate paradox a large scale structure often recognized at non volcanic rifted margins a thin viscous middle crust provides means of decoupling the deformation affecting upper and lower crust during rifting on one hand this promotes a uniform scattering of faults throughout the upper brittle crust on the other hand it allows for a strong localization of the deformation in lower crust and upper mantle expressed by the lithospheric necking in the rift center

assimilation of topex poseidon altimetric data in a primitive equation model of the tropical pacific ocean during the 1992 1996 el nino southern oscillation period four years of topex poseidon data october 1992 to october 1996 are assimilated into a high resolution primitive equation model gent and cane 1989 of the tropical pacific ocean the assimilation method used is a degraded version of the singular evolutive extended kaiman filter approach pham et al 1998 in which the reduced order basis is fixed the along track topex poseidon sea surface height residuals are introduced in the model every 3 days initialization of the model runs appears to be crucial this is particularly true for the 1992 1996 period which is characterized by several el nino and la nina events and exhibits quite anomalous climatological behavior an in situ database dedicated to this period was built and used to initialize the model properly the simulation results with and without assimilation were compared with expendable bathythermograph and tropical atmosphere ocean in situ observations the impact of sea surface height assimilation is observed both on the surface and subsurface temperature and velocity fields the deficiencies of the free model in terms of means and variability structures are significantly reduced more importantly the evolution of the model fields over time is considerably improved by the assimilation these supposedly more realistic assimilated four dimensional fields are used to investigate the mechanism responsible for the 1992 1996 warm pool replenishment and depletion this approach provides insights into the combined role of zonal and meridional transports in balancing volume changes in the warm pool

crust and mantle thickening beneath the southern portion of the southern alps new zealand summary an 8 54 0 20 km s 1pn speed is estimated on a line oriented ca n5 e from the alpine fault beneath the southern alps of south island based on a refraction experiment that uses the fiordland earthquake of august 2003 as a source this high pn speed results from both strong anisotropy in the mantle lid of 7 13 per cent and a high pn speed average of 8 3 0 3 km s 1 a maximum crustal thickness of 48 4 km is calculated for the southern south island near the town of wanaka this represents a crustal root of about 18 km compared to measured crustal thicknesses at the east and west coasts of the south island the average topography in the southern southern alps is of the order of 1000 m which is less than half that predicted by airy isostasy for an 18 km crustal root as recently proposed for the central south island 120 km to the north we propose that thickened cold and therefore more dense mantle lithosphere exists beneath southern south island and that this excess of mass is an effective load that pulls down the overlying crust the load is similar to that beneath the central southern alps despite the predicted convergence across the alpine fault there being nearly twice that at wanaka gravity modelling of crustal structure along a profile through wanaka suggests that this mass excess has a minimum density contrast of 35 5 kg m 3 between thickened mantle and asthenosphere assuming an across moho density contrast of 300 kg m 3 we speculate that the reason for the enhanced thickening beneath wanaka is that the subducted australian plate at the southwestern corner of the south island acts like a backstop onto which pacific mantle collides at 26 mm yr 1 ca 3 4 the full plate speed

thermal regime in the central alpine fault zone new zealand constraints from microstructures biotite chemistry and fluid inclusion data abstract the thermal state within plate boundary fault zones is likely to influence the dimensions of large co seismic fault ruptures and strain localisation in underlying mylonitic shear zones vein microstructures biotite chemistry and fluid inclusion data offer new insights into the thermal structure of the mylonitic shear zone down dip of the alpine fault the main pacific australian plate boundary structure through southern new zealand quartz veins within the fault rocks were formed and deformed at temperatures ranging from 500 c to immediately above that of the brittle viscous transition 325 c illustrating that fluids are present throughout the fault zone microthermometric data from primary mixed co 2 h 2 o fluid inclusions in boudin neck quartz carbonate veins indicate that these inclusions were trapped at temperatures of 325 15 c and pressures of c 40 mpa vein microstructures indicate that fluid temperatures were equal to rock temperatures assuming hydrostatic fluid pressure the veins were trapped at depths of 2 o co 2 fluids in the shallower crust of 500 kg m 3 biotite grains in the mylonites are a mixture of porphyroclastic grains with high r ti mg inherited from the parent alpine schist and smaller low r grains that recrystallised during mylonitisation particularly those that are found within syn mylonitic shear bands assuming a simple step function model approximating diffusive equilibration the changes in biotite chemistry indicate t during mylonitic deformation of 340 c according to the ti in biotite thermometer of henry et al 2005 a best fit uplift p t path to existing data and these new results indicate that the uplift path p t gradient of fault zone rocks above the brittle viscous transition is of the order of 40 c km 1 below the brittle viscous transition the uplift path p t gradient is 10 c km 1 the p t profile within the fault rocks is comparable to that in the immediate hanging wall alpine schist indicating there is no peak in the crustal isotherms in the fault hanging wall as was indicated by previous numerical models and analyses that did not consider data from the fault rocks themselves

evidence of boundary reflection of kelvin and first mode rossby waves from topex poseidon sea level data the topex poseidon sea level data lead to new opportunities to investigate some theoretical mechanisms suggested to be involved in the el nino southern oscillation phenomenon in the tropical pacific ocean in particular we are interested in studying the western boundary reflection a process crucial for the delayed action oscillator theory by using the topex poseidon data from november 1992 to may 1995 we first projected the sea level data onto kelvin and first mode rossby waves then we estimated the contribution of wind forcing to these waves by using a single baroclinic mode simple wave model forced by the ers 1 wind data wave propagation was clearly observed with amplitudes well explained by the wind forcing in the ocean interior evidence of wave reflection was detected at both the western and eastern boundaries of the tropical pacific ocean at the eastern boundary kelvin waves were seen to reflect as first mode rossby waves during the entire period the reflection efficiency in terms of wave amplitude of the south american coasts was estimated to be 80 of that of an infinite meridional wall at the western boundary reflection was observed in april august 1993 in january june 1994 and later in december 1994 to february 1995 although the general roles of these reflection events in the variability observed in the equatorial pacific ocean are not clear the data suggest that the reflections in january june 1994 have played a role in the onset of the warm conditions observed in late 1994 to early 1995 indeed during the january june 1994 period as strong downwelling first mode rossby waves reflected into downwelling kelvin waves easterly wind and cold sea surface temperature anomalies located near the date line weakened and eventually reversed in june july 1994 the presence of the warm anomalies near the date line then favored convection and westerly wind anomalies that triggered strong downwelling kelvin waves propagating throughout the basin simultaneously with the beginning of the 1994 1995 warm conditions