locating and quantifying geological uncertainty in three dimensional models analysis of the gippsland basin southeastern australia abstract geological three dimensional 3d models are constructed to reliably represent a given geological target the reliability of a model is heavily dependent on the input data and is sensitive to uncertainty this study examines the uncertainty introduced by geological orientation data by producing a suite of implicit 3d models generated from orientation measurements subjected to uncertainty simulations the resulting uncertainty associated with different regions of the geological model can be located quantified and visualised providing a useful method to assess model reliability the method is tested on a natural geological setting in the gippsland basin southeastern australia where modelled geological surfaces are assessed for uncertainty the concept of stratigraphic variability is introduced and analysis of the input data is performed using two uncertainty visualisation methods uncertainty visualisation through stratigraphic variability is designed to convey the complex concept of 3d model uncertainty to the geoscientist in an effective manner uncertainty analysis determined that additional seismic information provides an effective means of constraining modelled geology and reducing uncertainty in regions proximal to the seismic sections improvements to the reliability of high uncertainty regions achieved using information gathered from uncertainty visualisations are quantified in a comparative case study uncertainty in specific model locations is identified and attributed to possible disagreements between seismic and isopach data further improvements to and additional sources of data for the model are proposed based on this information finally a method of introducing stratigraphic variability values as geological constraints for geophysical inversion is presented

uncertainty estimation for a geological model of the sandstone greenstone belt western australia insights from integrated geological and geophysical inversion in a bayesian inference framework

geological modelling from field data and geological knowledge part ii modelling validation using gravity and magnetic data inversion the analysis of multiple data sets is required to select a realistic 3d geological model among an infinite number of possibilities an inverse method that aims at describing the 3d geometry of geological objects is presented the method takes into account the geology and the physical properties of rocks while respecting the topological properties of an a priori model the a priori model is built from the geological data set and its geometry is largely dependent upon assumptions about inaccessible geology at depth this method referred to as total litho inversion is a generalized 3d inversion that results in quantifying the lithology and the distribution of rock property in a probabilistic way its application is demonstrated through i a simple synthetic case and ii the relative distribution characterization of granites and diorites in an orogenic domain

three dimensional model and late stage warping of the plattengneis shear zone in the eastern alps abstract the plattengneis shear zone is a 250 600 m thick flat lying cretaceous eclogite facies mylonitic shear zone with north over south transport direction that is exposed over almost 1000 km2 in the koralpe region along the eastern margin of the alps although the shear zone is one of the largest in the alps its role in the eoalpine metamorphic evolution and the subsequent exhumation of the region remain enigmatic and its large scale geometry is not well understood the outcrop pattern suggests that the shear zone is made up of a single sheet that is folded into a series of open syn and antiforms with wavelengths of about 10 km eclogite bodies occur above within and below the shear zone and there is no metamorphic grade change across the shear zone in the south the fold axes strike east west and plunge shallowly to the east in the north the fold axes are oriented in north south direction and form a dome shaped structure of the shear zone total shortening during this late stage warping event was of the order of 5 indirect evidence constrains this folding event to have occurred between 80 and 50 ma and the fold geometry implies that the final exhumation in the koralpe occurred somewhat later than further north interestingly the shear zone appears to strike out of the topography in the south and dip into the topography in the north so that north of the shear zone only hanging wall rocks are exposed and south of it only foot wall rocks possibilities for the geometric relationship of the plattengneis shear zone with the surrounding south dipping detachments are discussed

a conceptual model of the surface salinity distribution in the oceanic hadley cell a conceptual model of the salinity distribution in the oceanic hadley cell is presented the model pertains to the region of tropical easterly surface winds where the surface salinity increases po

structural overprinting criteria determined from regional aeromagnetic data an example from the hill end trough east gondwana abstract determining overprinting relationships in the geological record has underpinned our understanding of the evolution of the earth and has provided the context in which to interpret geoscientific datasets geological overprinting relationships are generally determined from outcrop relationships when outcrop is absent or limited overprinting relationships using geological observations is often ineffective or ambiguous we show how aeromagnetic data can be used to inform superposition of geological structures using a combination of folded stratigraphy faults both high angle and low angle and plutons from the well exposed hill end trough in the phanerozoic eastern lachlan orogen overprinting relationships reveal episodic inversion of the late silurian to early devonian back arc basin succession preserved within the hill end trough occurred during superimposed shortening events the first event resulted in the development of regional folds associated with the tabberabberan orogeny and the second event resulted in the development of overprinting north south and north northwest trending faults during the early carboniferous kanimblan orogeny inversion structures are overprinted by a carboniferous granite which is overprinted by previously unrecognised northeast and northwest conjugate faults which we interpret to be related to the permo triassic hunter bowen orogeny

method and analysis for the upscaling of structural data abstract 3d geological models are created to integrate a set of input measurements into a single geological model there are many problems with this approach as there is uncertainty in all stages of the modelling process from initial data collection to the approach used in the modelling scheme itself to calculate the geological model this study looks at the uncertainty inherent in geological models due to data density and introduces a novel method to upscale geological data that optimises the information in the initial dataset this method also provides the ability for the dominant trend of a geological dataset to be determined at different scales by using self organizing maps som s to examine the different metrics used to quantify a geological model we allow for a larger range of metrics to be used compared to traditional statistical methods due to the som s ability to deal with incomplete datasets the classification of the models into clusters based on the geological metrics using k means clustering provides a useful insight into the models that are most similar and models that are statistical outliers our approach is guided and can be calculated on any input dataset of this type to determine the effect that data density will have on a resultant model these models are all statistical derivations that represent simplifications and different scales of the initial dataset and can be used to interrogate the scale of observations

younger dryas style cooling events at glacial terminations i vi at odp site 658 associated benthic δ13c anomalies constrain meltwater hypothesis high resolution planktonic and epibenthic stable isotope records from ocean drilling program site 658 off northwest africa provide a basis for a detailed study of glacial terminations i vi during the last 650 000 years the duration of the terminations was about one half to one quarter of an orbital precession cycle 5800 10 700 years when its amplitude was high at low amplitudes the terminations lasted longer than half an obliquity cycle 29 000 years marked climatic rebounds similar to the younger dryas each with a duration of 1000 2500 years subdivided all six terminations into distinct steps a b and c important parts of the deglacial steps were as brief as 700 1000 years the speed of climatic change suggests that special associations existed between orbital forcing and inherent instability of the ice sheets in harmony with published models the more rapid pulses of glacial meltwater incursions to the northern north atlantic led to one or more brief short term shut downs of north atlantic deep water formation this process is reflected by pronounced benthic 13c minima that precisely coincide in most cases with the end of the 18o deglaciation steps and immediately terminate with succeeding younger dryas style cooling events thus we conclude that the rebounds resulted from a short term antecedent estuarine circulation regime in the north atlantic except for the younger dryas itself which succeeded the allerod with its well ventilated atlantic deepwater circulation and hence continues to be an enigma

the younger dryas termination and north atlantic deep water formation insights from climate model simulations and greenland ice cores results from the gisp2 and grip ice cores show that the termination of the younger dryas yd climate event in greenland was a large and extremely fast climate change a reinitiation of north atlantic deep water formation following a shutdown and its associated winter release of heat to the atmosphere has been suggested as the most likely cause of this climate transition to test this idea two general circulation model experiments using genesis have been completed for yd time 12 000 calendar years ago one with low heat flux in the nordic seas 10 w m deep water shutdown and one with high nordic sea heat flux 300 w m active deep water formation comparison of greenland climate differences between these experiments with the ice core records shows that when deep water is turned on much of the yd termination warming is achieved the increase in precipitation is underestimated because of a model tendency to overestimate summertime precipitation which obscures the dominantly wintertime response to the specified forcing the winter storm track shift toward greenland contributes much of the climate change at the yd termination

the thermohaline circulation and the control of ice ages abstract it is found that the global salinity variations associated with the thermohaline circulation may have a tendency to make the circulation increasingly asymmetric with respect to the equator as a consequence the salinity difference between the pacific and the atlantic ocean may be slowly increasing such a process could have a time scale long enough to be comparable with the time span between major glaciations a speculative glaciation cycle is proposed which involves the above mentioned property of the thermohaline circulation in this cycle the role of a northern hemisphere glaciation is to bring excess freshwater from the pacific to the atlantic

weak oceanic heat transport as a cause of the instability of glacial climates the stability of the thermohaline circulation of modern and glacial climates is compared with the help of a two dimensional ocean atmosphere sea ice coupled model it turns out to be more unstable as less freshwater forcing is required to induce a polar halocline catastrophy in glacial climates the large insulation of the ocean by the extensive sea ice cover changes the temperature boundary condition and the deepwater formation regions moves much further south the nature of the instability is of oceanic origin identical to that found in ocean models under mixed boundary conditions with similar strengths of the oceanic circulation and rates of deep water formation for warm and cold climates the loss of stability of the cold climate is due to the weak thermal stratification caused by the cooling of surface waters the deep water temperatures being regulated by the temperature of freezing weaker stratification with similar overturning leads to a weakening of the meridional oceanic heat transport which is the major negative feedback stabilizing the oceanic circulation within the unstable regime periodic millennial oscillations occur spontaneously the climate oscillates between a strong convective thermally driven oceanic state and a weak one driven by large salinity gradients both states are unstable the atmosphere of low thermal inertia is carried along by the oceanic overturning while the variation of sea ice is out of phase with the oceanic heat content during the abrupt warming events that punctuate the course of a millennial oscillation sea ice variations are shown respectively to damp amplify the amplitude of the oceanic atmospheric response this sensitivity of the oceanic circulation to a reduced concentration of greenhouse gases and to freshwater forcing adds support to the hypothesis that the millennial oscillations of the last glacial period the so called dansgaard oeschger events may be internal instabilities of the climate system

incorporating geological dip information into geophysical inversions geological bodies are often linear structures that have well defined strike direction and dip angle we develop a new model objective function that allows this important information to be incorporated into geophysical inversions a rotation matrix is applied to the horizontal and vertical derivatives of the model so that the derivative in an arbitrary direction is obtained a model objective function that measures the flatness with respect to the rotated derivatives favors models that have elongated features with the specified strike and dip angle formulations for both 2 d and 3 d cases are presented and they are illustrated using examples from dc resistivity and induced polarization ip problems synthetic and field examples show that an inversion carried out using known dip information produces a model that has higher resolution and provides a better representation of the true structure

integrated 3d geophysical and geological modelling of the hercynian suture zone in the champtoceaux area south brittany france this paper combines geological knowledge and geophysical imagery at the crustal scale to model the 3d geometry of a segment of the hercynian suture zone of western europe in the champtoceaux area brittany france the champtoceaux complex consists of a stack of metamorphic nappes of gneisses and micaschists with eclogite bearing units the exhumation of the complex during early carboniferous times was accompanied by deformation during regional dextral strike slip associated with a major hercynian shear zone the south armorican shear zone sasz dextral shearing produced a km scale antiformal structure with a steeply dipping axial plane and a steeply eastward plunging axis armor 2 deep seismic profile shows that the regional structure was cut by a set of faults with northward thrusting components based on the seismic constraint direct 2d crustal scale modelling was performed throughout the champtoceaux fold on seven radial gravity profiles also using geological data and density measurements from field and drill hole samples the 3d integration of the cross sections the digitised geological map and the structural information foliation dips insure the geometrical and topological consistency of all sources of data the 2d information is interpolated to the whole 3d space using a geostatistical analysis finally the 3d gravity contribution of the resulting model is computed taking into account densities for each modelled geological body and compared to the bouguer anomaly the final 3d model is thus compatible with the seismic and gravity data as well as with geological data main geological results derived from the modelling are i the overall 3d geometry of the south dipping thrust system interpreted on the seismic profile emphasises northward thrusting and folding of the champtoceaux complex which was coeval with strike slip along the south armorican shear zone ii the gravity modelling suggests the presence of a relatively dense body below the champtoceaux complex that could be interpreted as a result of relative uplift of midcrustal material during thrusting along the e w trending wrench thrust system iii the northern limb of the champtoceaux anticline is a relatively shallow feature and iv vigneux synkinematic granitic body is a laccolith sheared and rooted along the southern branch of the sasz and spreads away from the strike slip zone within weak country rocks d 2004 elsevier b v all rights reserved

structural data constraints for implicit modeling of folds a recent method for modeling folds uses a fold frame with coordinates based on the structural geology of folds fold axis direction fold axial surface and extension direction the fold geometry can be characterised by rotating the fold frame by the pitch of the fold axis in the axial surface and the angle between the folded foliation and the axial surface these rotation angles can be expressed as 1d functions of the fold frame coordinates in this contribution we present methods for extracting and automatically modeling the fold geometries from structural data the fold rotation angles used for characterising the fold geometry can be calculated locally from structural observations the fold rotation angles incorporate the structural geology of the fold and allow for individual structural measurements to be viewed in the context of the folded structure to filter out the effects of later folding the fold rotation angles are plotted against the coordinates of the fold frame using these plots the geometry of the folds can be interpolated directly from structural data where we use a combination of radial basis function and harmonic analysis to interpolate and extrapolate the fold geometry this contribution addresses a major limitation in existing methods where the fold geometry was not constrained from structural data we present two case studies a proof of concept synthetic model of a non cylindrical fold and an outcrop of an asymmetrical fold within the lachlan fold belt at cape conran victoria australia

ore shoots in folded and fractured rocks insights from 3d modelling of the fosterville gold deposit victoria australia abstract at the fosterville gold deposit high concentrations of visible and refractory gold are hosted in arrays of quartz and quartz carbonate veins they are distributed in elongate zones to form south plunging ore shoots within a folded and fractured turbidite sequence here we distinguish the influence of faults versus folds at fosterville by assessing the deposit scale structural framework and hydrothermal fluid flow using a combination of 3d implicit modelling structural analysis and 3d fault slip dilation tendency analyses gold assay and bedding trend data from a large drillhole dataset were spatially interpolated and used to analyse and measure the orientation of ore bodies and folded host rocks field measurements of fold axis orientations were compared to bedding measurements in oriented drillcore bingham axial analysis of bedding trends and orientation data from a 3d implicit model both field and drill core structural data show that ore shoots at fosterville do not parallel the first order gently 10 south plunging folds instead the orientation of the ore shoots is coincident with an intersection lineation between steeply west dipping bedding parallel faults and moderately dipping linkage faults that obliquely cut across the main structural grain resulting in ore shoot plunges larger than 20 slip and dilation tendencies suggest that linkage faults had a higher likelihood of activity in the inferred far field stress regimes at the time of mineralisation relative to other structures at fosterville these linkage faults are therefore interpreted to have been preferential fluid flux conduits in the system despite appearing to be subordinate structures at the scale of the deposit this new structural model for fosterville highlights that fluid flow and ore shoot formation are strongly controlled by obliquely oriented structures that are unlike the main structural grain of first order folds and faults

uncertainty reduction through geologically conditioned petrophysical constraints in joint inversion abstractwe have developed a joint geophysical inversion workflow that aims to improve subsurface imaging and decrease uncertainty by integrating petrophysical constraints and geologic data in this framework probabilistic geologic modeling is used as a source of information to condition the petrophysical constraints spatially and to derive starting models the workflow then uses petrophysical measurements to constrain the values retrieved by geophysical joint inversion the different sources of constraints are integrated into a least squares framework to capture and integrate information related to geophysical petrophysical and geologic data this allows us to quantify the posterior state of knowledge and to calculate posterior statistical indicators to test this workflow using geologic field data we have generated a set of geologic models which we used to derive a probabilistic geologic model in this synthetic case study we found that the integration of geologic information and petrophysical con

a 3d geological model for the ruiz tolima volcanic massif colombia assessment of geological uncertainty using a stochastic approach based on bezier curve design abstract the ruiz tolima volcanic massif rtvm is an active volcanic complex in the northern andes and understanding its geological structure is critical for hazard mitigation and guiding future geothermal exploration however the sparsity of data available to constrain the interpretation of this volcanic system hinders the application of standard 3d modelling techniques furthermore some features related to the volcanic system are not entirely understood such as the connectivity between the plutons present in its basement i e manizales stock el bosque batholith we have developed a methodology where two independent working hypotheses were formulated and modelled independently i e a case where both plutons constitute distinct bodies and an alternative case where they form one single batholith a monte carlo approach was used to characterise the geological uncertainty in each case bezier curve design was used to represent geological contacts on input cross sections systematic variations in the control points of these curves allows us to generate multiple realisations of geological interfaces resulting in stochastic models that were grouped into suites used to apply quantitative estimators of uncertainty this process results in a geological representation based on fuzzy logic and in maps of model uncertainty distribution the results are consistent with expected regions of high uncertainty near under constrained geological contacts while the non unique nature of the conceptual model indicates that the dominant source of uncertainty in the area is the nature of the batholith structure

ice dammed lakes and rerouting of the drainage of northern eurasia during the last glaciation during the quaternary period ice sheets centred over the barents and kara seas expanded several times onto mainland russia and blocked northflowing rivers such as the yenissei ob pechora and mezen large ice dammed lakes with reversed outlets e g toward the caspian sea formed south of these ice sheets some lakes are reconstructed from shorelines and lacustrine sediments others mainly from ice sheet configuration ice dammed lakes considerably larger than any lake on earth today are reconstructed for the periods 90 80 and 60 50 ka the ages are based on numerous optically stimulated luminescence osl dates during the global last glacial maximum lgm about 20 ka the barents kara ice sheet was too small to block these eastern rivers although in contrast to the 90 80 and 60 50 ka maxima the scandinavian ice sheet grew large enough to divert rivers and meltwater across the drainage divide from the baltic basin to the river volga and that way to the caspian sea climate modelling shows that the lakes caused lower summer temperatures on the continent and on the lower parts of the ice sheet the final drainage of the best mapped lake is modelled and it is concluded that it probably emptied within few months we predict that this catastrophic outburst had considerable impact on sea ice formation in the arctic ocean and on the climate of a much larger area c 2003 elsevier ltd all rights reserved less

geodiversity exploration of 3d geological model space abstract the process of building a 3d model necessitates the reconciliation of field observations geophysical interpretation geological data uncertainty and the prevailing tectonic evolution hypotheses and interpretations uncertainty is compounded when clustered data points collected at local scales are statistically upscaled to one or two points for use in regional models interpretation is required to interpolate between sparse field data points using ambiguous geophysical data in covered terranes it becomes clear that multiple interpretations are possible during model construction the various interpretations are considered as potential natural representatives but pragmatism typically dictates that just a single interpretation is offered by the modelling process uncertainties are introduced into the 3d model during construction from a variety of sources and through data set optimisation that produces a single model practices such as these are likely to result in a model that does not adequately represent the target geology a set of geometrical geodiversity metrics are used to analyse a 3d model of the gippsland basin southeastern australia after perturbing geological input data via uncertainty simulation the resulting sets of perturbed geological observations are used to calculate a suite of geological 3d models that display a range of geological architectures the concept of biodiversity has been adapted for the geosciences to quantify geometric variability or geodiversity between models in order to understand the effect uncertainty has models geometry various geometrical relationships depth volume contact surface area curvature and geological complexity are used to describe the range of possibilities exhibited throughout the model suite end member models geodiversity metrics are classified in a similar manner to taxonomic descriptions further analysis of the model suite is performed using principal component analysis pca to determine important geometrical characteristics the configuration of the model space is determined through identifying outlier model examples which potentially represent undiscovered model species

3d reconstruction of geological surfaces by the equivalent dip domain method an example from field data of the cerro bayo anticline cordillera oriental nw argentine andes abstract this paper presents a new method for the 3d reconstruction of geological structures the equivalent dip domain method it improves existing and currently used methods of structural reconstruction by taking advantage of the absolute position of dip data and by imposing geological constraints derived from the structural analysis of data it deals with the definition of the simplest 3d geometry that honours most of the data in the case presented here this geometry has been simplified to multiple cylindrical domains the geometric framework derived from these cylindrical domains fold axis and different planes enables the interpolation and extrapolation of dip data along the structure to fill gaps of information thus this method is useful to reconstruct the 3d geometry of structures in which available data are scarce and or sparse this method has been developed to reconstruct the 3d geometry of structures in remote areas where data acquisition is not always possible it has been applied to the reconstruction of the cerro bayo anticline a thrust related fold of the cordillera oriental in the north western argentine andes there the analysis of aerial and satellite images and its combination with field data add further constraints in the definition of the geometrical framework

modeling the effect of freshwater pulses on the early holocene climate the influence of high frequency climate variability freshwater 4 67 10 14 m 3 into the labrador sea at three different constant rates 1 5 sv 1 sv 1 10 6 m 3 s 1 i n 10 years 0 75 sv in 20 years and 0 3 sv in 50 years for each rate five ensemble experiments have been performed varying in initial conditions the freshwater pulses produce a weakening of the thermohaline circulation the perturbed state is in agreement with proxy evidence for the 8 2 ka event two types of recovery of the thermohaline circulation occurred differing in time scale 1 200 years and 2 200 years in the experiments with 10 year and 20 year pulses both types of recovery were observed this suggests that the model response is unpredictable in the range of parameters studied here it is hypothesized that the unpredictability is associated with annual to decadal climate variability our results demonstrate that several types of recovery may exist with the same kind of perturbation the interpretation of events observed in proxy data may be thus more complex than realized until now since the magnitude and duration of climatic events caused by freshwater pulses is likely to depend strongly on nonlinear dynamics inside the coupled atmosphere sea ice ocean system index terms 3344 meteorology and atmospheric dynamics paleoclimatology 4255 oceanography general numerical modeling 4532 oceanography physical general circulation 4215 oceanography general climate and interannual variability 3309 9325 information related to geographic region atlantic ocean keywords holocene thermohaline circulation predictability meltwater coupled climate model

inversion of geological knowledge for fold geometry abstract the process of building three dimensional 3d geological models can be framed as an inverse problem where a model describing the 3d distribution of rock units is non uniquely derived from geological observations the inverse problem theory provides a powerful framework for inferring these parameters from all geological observations in a similar way to how a geologist can iteratively update their structural interpretation while mapping existing geological knowledge is usually indirectly incorporated into 3d models using the geologist s non unique interpretation as form lines cross sections and level maps these approaches treat constraints derived from geological knowledge in the same way as direct observations diluting and confusing both information provided by geological knowledge and hard data resulting in significant subjectivity we present a geological inversion using bayesian inference where geological knowledge can be incorporated directly into the interpolation scheme with likelihood functions and informative prior distributions we demonstrate these approaches on a series of synthetic fold shapes as a proof of concept and a case study from the proterozoic davenport province in the northern territory australia the combined inversion of geological data and knowledge significantly reduces the uncertainty in possible fold geometries where data is sparse or highly ambiguous this could be used by geologists while mapping to propagate information about uncertainties throughout the mapping model building process and would allow for different structural interpretations to be rapidly tested for targeted data collection

gis based 3d prospectivity mapping a case study of jiama copper polymetallic deposit in tibet china abstract this paper reports a deposit scale gis based 3d mineral potential assessment of the jiama copper polymetallic deposit in tibet china the assessment was achieved through a sequential implementation of metallogenic modelling and 3d modelling of geology geochemistry and prospectivity a metallogenic model for the jiama deposit and 3d modelling workflow were used to construct multiple 3d layers of volumetric and triangular mesh models to represent geology geochemistry and ore controlling features in the study area a gis based 3d weights of evidence analysis was then used to estimate the subsurface prospectivity for cu mo orebodies in the area which led to the identification of three prospective deep seated exploration targets additionally the geochemical modelling indicates three potential fluid flow pathways based on the 3d zonation of major geochemical elements and their ratios particularly the zn pb ratios which support the results of the weights of evidence model

potential vorticity and vertical velocity at the iceland faerœs front abstract using data from high resolution surveys of the iceland faer s front the authors have calculated synoptic maps of the geostrophic velocity vorticity and potential vorticity on isopycnal surfaces the data have also been used to diagnose the vertical velocity field using the omega equation these results are used to elucidate the dynamical processes occurring at the front across the front there was a large change in potential vorticity on the density surfaces t 27 4 27 6 instability generates meanders that propagate eastward along the front a cyclonic vortex was observed to break off from a meander within the vortex the magnitude of the relative vorticity was large 0 8 f and the potential vorticity had high values similar to that of the water to the north of the front from which the vortex was derived the eddy propagated northeastward relative to the underlying water resulting in large upward downward vertical velocities of the order of 100 m d 1 ahead of behind the vortex

the coupled ocean atmosphere hydrothermohaline circulation abstractthe thermohaline circulation of the ocean is compared to the hydrothermal circulation of the atmosphere the oceanic thermohaline circulation is expressed in potential temperature absolute salinity space and comprises a tropical cell a conveyor belt cell and a polar cell whereas the atmospheric hydrothermal circulation is expressed in potential temperature specific humidity space and unifies the tropical hadley and walker cells as well as the midlatitude eddies into a single global circulation the oceanic thermohaline streamfunction makes it possible to analyze and quantify the entire world ocean conversion rate between cold warm and fresh saline waters in one single representation its atmospheric analog the hydrothermal streamfunction instead captures the conversion rate between cold warm and dry humid air in one single representation it is shown that the ocean thermohaline and the atmospheric hydrothermal cells are connected by the exchange of heat and freshwater through the sea surface

north pacific climate response to freshwater forcing in the subarctic north atlantic oceanic and atmospheric pathways abstract sudden changes of the atlantic meridional overturning circulation amoc are believed to have caused large abrupt climate changes over many parts of the globe during the last glacial and deglacial period this study investigates the mechanisms by which a large freshwater input to the subarctic north atlantic and an attendant rapid weakening of the amoc influence north pacific climate by analyzing four different ocean atmosphere coupled general circulation models gcms under present day or preindustrial boundary conditions when the coupled gcms are forced with a 1 sv sv 106 m3 s 1 freshwater flux anomaly in the subarctic north atlantic the amoc nearly shuts down and the north atlantic cools significantly the south atlantic warms slightly shifting the atlantic intertropical convergence zone southward in addition to this atlantic ocean atmosphere response all of the models exhibit cooling of the north pacific especially along the oceanic frontal zone consistent with paleoclimate recons

modelling tempo spatial signatures of heinrich events influence of the climatic background state abstract different sea surface temperature sst reconstructions for the last glacial maximum are applied to a hybrid coupled climate model the resulting oceanic states are perturbed by north atlantic meltwater inputs in order to simulate the effect of heinrich events on the atlantic thermohaline circulation thc and sst the experiments show that both the atlantic sst signature of the meltwater event and the time span of thc recovery strongly depend on the climatic background state data model comparison reveals that the overall spatial signature of sst anomalies is captured much better in the glacial meltwater experiments than in an analogous experiment under present day conditions in particular a breakdown of the modern thc would induce a much stronger temperature drop in high northern latitudes than did heinrich events during the ice age moreover our results suggest that the present day circulation can settle into a stable off mode whereas the glacial thc was mono stable mono stability may serve as an explanation for the recovery of the thc after heinrich event shutdowns during the last glaciation

a simple model of the mass exchange between the subtropical and tropical ocean abstract a simple ventilated thermocline model is used to study the subtropical tropical mass exchange it is found that the water subducted in the western subtropical gyre recirculating window tends to recirculate within the subtropical gyre while the water subducted in the eastern part exchange window tends to penetrate equatorward the exchange window expands with an increased easterly wind or basin width on the southern boundary of the subtropical gyre but shrinks with an increased wind curl within the subtropical gyre furthermore the total exchange transport increases with the easterly wind or the width of the basin on the southern boundary of the subtropical gyre but it is independent of subtropical wind the ventilation mechanism is important in supporting the exchange transport for wind with realistic strength at the southern boundary the reduction of the exchange transport is about 15 30 of the ekman transport finally relative to the exchange transport in the interior of the ocean

the pliocene paradox mechanisms for a permanent el nino during the early pliocene 5 to 3 million years ago globally averaged temperatures were substantially higher than they are today even though the external factors that determine climate were essentially the same in the tropics el nino was continual or permanent rather than intermittent the appearance of northern continental glaciers and of cold surface waters in oceanic upwelling zones in low latitudes both coastal and equatorial signaled the termination of those warm climate conditions and the end of permanent el nino this led to the amplification of obliquity but not precession cycles in equatorial sea surface temperatures and in global ice volume with the former leading the latter by several thousand years a possible explanation is that the gradual shoaling of the oceanic thermocline reached a threshold around 3 million years ago when the winds started bringing cold waters to the surface in low latitudes this introduced feedbacks involving ocean atmosphere interactions that along with ice albedo feedbacks amplified obliquity cycles a future melting of glaciers changes in the hydrological cycle and a deepening of the thermocline could restore the warm conditions of the early pliocene

small synoptic mesoscale eddies and energetic variability of the eastern levantine basin mesoscale eddies are energetically dominant over most of the world s ocean1 the local dynamics of eddies is now a central problem of physical oceanography2 and their statistics control aspects of the general circulation3 the horizontal scale of eddies is generally related to but somewhat larger than the rossby internal deformation radius the depth scale multiplied by the buoyancy frequency divided by the coriolis frequency in the eastern mediterranean which is not well explored or understood the internal radius is known to be 12 km or 4 times smaller than in the north atlantic the study of such eddies requires very fine sampling which hinders their accidental discovery by using a dedicated data set and objective analysis methods we have estab ished the existence of small synoptic mesoscale eddies and jets which constitute a variable and turbulent current regime and dominate the general circulation flow of the levantine basin their existence in the mediterranean has an impact on all aspects of basic and applied marine science there both conceptually and with respect to experimental and monitoring programme designs

least squares palinspastic restoration of regions of normal faulting application to the campos basin brazil we have developed an iterative least squares method for palinspastic restoration of regions of normal faulting the method closes the gaps cut off lenses across normal faults on a structure contour map of a given stratigraphie horizon such data are often available for sedimentary basins covered by seismic surveys before restoration we first produce a fault block map where each block is completely surrounded by faults whether real or artificial we then apply an algorithm to minimize d the sum of the squares of the distances across cut off lenses with respect to unknown rigid block translations and rotations minimization results in non linear equations which we solve by an iterative method we deem the solution to have converged when d falls below a given critical level in general restoration not only closes the original gaps but also results in strike slip displacements between blocks thus the deformation need not be a plane strain and displacement vectors need not be parallel we have applied the method to an area of the campos basin on the atlantic margin of brazil where the stratigraphy and structure are well known from seismic surveys and from wells cretaceous and tertiary sediments have glided downslope on a lubricating layer of aptian evaporites producing an uppermost domain of normal faulting the normal faults occupy a strip lying between undisturbed continental crust to the west and relatively unstructured sediments to the east assuming the western boundary to be stationary we have restored an upper oligocene stratigraphie level the marco azul convergence was achieved rapidly and the degree of fit is good according to our restoration the eastern boundary of the area has bowed out seawards since the oligocene block displacement vectors form a fan like pattern with an element of mirror symmetry about a line trending nw se maximum displacements occur in an apical domain bounded by a horseshoe pattern of faults there is a general pattern of block rotations counterclockwise in the northeast clockwise in the southwest some notable exceptions to this general pattern are due to local domino motions we attribute the overall displacement field to divergent gravitational gliding off a local salient in the sea bottom topography because of the three dimensional nature of the displacement field restoration of vertical cross sections alone would yield gross errors this demonstrates the value of palinspastic methods such as ours

along or across front survey strategy an operational example at an unstable front we present results of the optimization of near real time on board sampling strategy in the iceland faroes oceanic frontal area based on the outputs of a mesoscale 3d operational data assimilation forecasting experiment by minimizing a root mean square error cost function we show that in this example an along front sampling strategy i e with transects parallel to the front produces smaller errors in temperature salinity nitrate phytoplankton and zooplankton fields as a result of a combination of the direction of the sampling of the front and errors associated with the asynopticy of observations doppler effect this is contrary to the classic across front sampling strategies that are used in most field experiments reported in the literature i e where transects are perpendicular to the front a control model shows that at these spatio temporal scales the along front sampling strategy is optimal when the frontal instability has sufficiently developed

a probability box model of a convective ocean abstract a new modeling approach is proposed for representing a subpolar ocean whose upper layer is partly convected with the lower layer a simple box model built as a reference has one active box to be the upper layer of a colder ocean which interacts with the warmer box and the lower box the active box receives atmospheric forcing cooling and precipitation and a parameterized freshwater or sea ice flux as well while the other boxes have their properties fixed the active box interacting with the warmer box possesses a thermal driven state at which the warmer water enters the active box is cooled by the atmosphere and becomes denser the lower box adds another solution a convected state appears in the vicinity of the nonconvected state the nonconvected state either separates from or is absorbed into the convected state that is the entire upper box is convected with the lower box once the lower box density is close to the upper box density the new component to the simple model is a p

ocean gyres and abrupt change in the thermohaline circulation a conceptual analysis the implications are investigated of representing ocean gyre circulations by a diffusion term in the stommel and rooth box models of the thermohaline circulation thc in one and two hemispheres respectively the approach includes mostly analytical solution and study of the bifurcation structure but also numerical integration and feedback analysis sufficient diffusion gyre strength eliminates multiple equilibria from either model highlighting the need for accurate gyre circulation strength in general circulation models gcms when considering the potential for abrupt climate change associated with thc shutdown with diffusion steady state flow strength in the rooth model depends on freshwater forcing i e implied atmospheric water vapor transport in both hemispheres not only on that in the upwelling hemisphere as in the nondiffusive case with asymmetric freshwater forcing two solutions strong stable and weak unstable are found with sinking in the hemisphere with stronger forcing and one solution with sinking in the other hemisphere under increased freshwater forcing the two solutions in the hemisphere with stronger forcing meet in a saddle node bifurcation if diffusion is sufficiently strong to prevent a subcritical hopf bifurcation first followed by flow reversal thus the bifurcation structure with respect to freshwater forcing of the diffusive rooth model of two hemisphere thc is similar to that of the stommel model of single hemisphere thc albeit with a very different dynamical interpretation gyre circulations stabilize high latitude sinking in the stommel model in the rooth model gyre circulations only stabilize highlatitude sinking if the freshwater forcing is weaker in the sinking hemisphere than in the upwelling hemisphere by an amount that increases with diffusion the values of diffusion and freshwater forcing at which qualitative change in behavior occurs correspond to the range of the values used in and obtained with gcms suggesting that this analysis can provide a conceptual foundation for analyzing the stability of the interhemispheric thc and also for the potential of the atlantic thc to undergo abrupt change

along or across front ocean survey strategy the estimation of quasi geostrophic vertical velocities and temperature fluxes in a companion paper we have shown that at the mesoscale the unusual across front sampling strategy al is more accurate than the usual across front sampling strategy ac on hydrographic and bio chemical properties when the front is sufficiently developed the cruise design based on the optimal reconstruction of the density fields does however not imply that derived variables like quasi geostrophic qg vertical velocities and temperature fluxes also exhibit minimal associated errors here we present results of optimized sampling strategies for diagnostic qg vertical velocities wqg and temperature fluxes qg derived from the omega equation results are illustrated in the same framework for the iceland faroes oceanic frontal area and for a control model and reveal that at these spatio temporal scales the unusual al may also provide better estimations of vertical velocities and temperature fluxes compared to the classic ac especially when the front is sufficiently developed

climate impact of late quaternary equatorial pacific sea surface temperature variations magnesium calcium data from planktonic foraminifera in equatorial pacific sediment cores demonstrate that tropical pacific sea surface temperatures ssts were 2 8 0 7 c colder than the present at the last glacial maximum glacial interglacial temperature differences as great as 5 c are observed over the last 450 thousand years changes in sst coincide with changes in antarctic air temperature and precede changes in continental ice volume by about 3 thousand years suggesting that tropical cooling played a major role in driving ice age climate comparison of sst estimates from eastern and western sites indicates that the equatorial pacific zonal sst gradient was similar or somewhat larger during glacial episodes extraction of a salinity proxy from the magnesium calcium and oxygen isotope data indicates that transport of water vapor into the western pacific was enhanced during glacial episodes

regional dome evolution and its control on ore grade distribution insights from 3d implicit modelling of the navachab gold deposit namibia abstract we introduce a novel approach to analyse and assess the structural framework of ore deposits that fully integrates 3d implicit modelling in data rich environments with field observations we apply this approach to the early palaeozoic navachab gold deposit which is located in the damara orogenic belt namibia compared to traditional modelling methods 3d implicit modelling reduces user based modelling bias by generating open or closed surfaces from geochemical lithological or structural data without manual digitisation and linkage of sections or level plans instead a mathematically defined spatial interpolation is used to generate 3d models that show trends and patterns that are embedded in large drillhole datasets in our 3d implicit model of the navachab gold deposit distinctive high grade mineralisation trends were identified and directly related to structures observed in the field the 3d implicit model and field data suggest that auriferous semi massive sulphide ore shoots formed near the inflection line of the steep limb of a regional scale dome where shear strain reached peak values during fold amplification this setting generated efficient conduits and traps for hydrothermal fluids and associated mineralisation that led to the formation of the main ore shoots in the deposit both bedding parallel and highly discordant sets of auriferous quartz sulphide veins are interpreted to have formed during the later lock up stage of the regional scale dome additionally pegmatite dykes crosscut and remobilise gold mineralisation at the deposit scale and appear to be related to a younger joint set we propose that kilometre scale active folding is an important deformation mechanism that influences the spatial distribution and orientation of mineralisation in ore deposits by forming structures traps and pathways for fluids at different preferred sites and orientations we also propose that areas that experience high shear strain located along the inflection lines of folds can act as preferred sites for syn deformational hydrothermal mineralisation and should be targeted for regional scale exploration in fold and thrust belts our research also suggests that examination of existing drillhole datasets using 3d implicit modelling is a powerful tool for spatial analysis of mineralisation patterns when combined with fieldwork this approach has the potential to improve structural understanding of a variety of ore deposits

towards an integrated inversion of geoscientific data what price of geology abstract the inversion of multiple geoscientific datasets to define structures in hard rock terrains has for the most part been limited to geophysical methods supported by rock property constraints in this paper we expand the range of constraints available to geological modellers by defining a series of misfit functions that are used to define the quality of a given geological model with respect to the available geological data these misfit functions encompass both spatial and temporal observations and include primary data such as the location of an outcrop or bore hole location of a given rock type the orientation of its different generations of foliations as well as secondary geologic observations such as age relationships when we combine geologic conditions with geophysical misfit functions which already exist for many geophysical measures we have the potential to better constrain two and 3d models of the earth as a first test a subset of these misfit functions are applied to a set of synthetic three dimensional volumetric models built with an implicit surface modelling scheme by perturbing the input structural data within a narrow range we can simulate a range of significantly different three dimensional models for which we can then apply both geological and geophysical misfit functions several joint geological geophysical inversion schemes may be developed based on this methodology with the ultimate goal being an inversion scheme that simultaneously minimizes both geological and geophysical misfit

large fluctuations of dissolved oxygen in the indian and pacific oceans during dansgaard oeschger oscillations caused by variations of north atlantic deep water subduction a s and s h were supported by the paleoclimate program of the national science foundation as part of the paleovar project atm 0602395

southern ocean sea ice control of the glacial north atlantic thermohaline circulation 1 a coupled model simulates a shallower and weaker north atlantic deep water circulation at the last glacial maximum compared to the modern with an enhanced intrusion of antarctic bottom water into the north atlantic these circulation changes are caused by the enhanced antarctic bottom water formation which is triggered by the enhanced equatorward sea ice transport ultimately by increased westerlies in the southern ocean at the last glacial maximum

implicit modeling of folds and overprinting deformation abstract three dimensional structural modeling is gaining importance for a broad range of quantitative geoscientific applications however existing approaches are still limited by the type of structural data they are able to use and by their lack of structural meaning most techniques heavily rely on spatial data for modeling folded layers but are unable to completely use cleavage and lineation information for constraining the shape of modeled folds this lack of structural control is generally compensated by expert knowledge introduced in the form of additional interpretive data such as cross sections and maps with this approach folds are explicitly designed by the user instead of being derived from data this makes the resulting structures subjective and deterministic this paper introduces a numerical framework for modeling folds and associated foliations from typical field data in this framework a parametric description of fold geometry is incorporated into the interpolation algorithm this way the folded geometry is implicitly derived from observed data while being controlled through structural parameters such as fold wavelength amplitude and tightness a fold coordinate system is used to support the numerical description of fold geometry and to modify the behavior of classical structural interpolators this fold frame is constructed from fold related structural elements such as axial foliations intersection lineations and vergence poly deformed terranes are progressively modeled by successively modeling each folding event going backward through time the proposed framework introduces a new modeling paradigm which enables the building of three dimensional geological models of complex poly deformed terranes it follows a process based on the structural geologist approach and is able to produce geomodels that honor both structural data and geological knowledge

vorticity and vertical circulation at an ocean front abstract density and velocity data with 4 km horizontal resolution from a survey of a front during fasinex frontal air sea interaction experiment are combined to describe the structure of the top 300 m of the ocean the geostrophic velocity field is derived and is used to examine the relative importance of stratification relative vorticity and twisting terms in ertel s potential vorticity q tenfold isopycnic changes in q are found across a horizontal scale of only 10 km these changes are confined to isopycnals that outcrop from the seasonal thermocline into the mixed layer the ageostrophic velocity field is quantified by solution of the omega equation and vertical velocities of up to 40 m day 1 are found small 40 km surface trapped top 200 m eddies are found to play a crucial role in the transport and effective diffusion of properties across the thermocline out of the mixed layer

a numerical model of the ventilated thermocline abstract a steady state numerical solution is found for an idealized rectangular ocean basin driven by wind and surface buoyancy flux a three dimensional primitive equation model is used in agreement with recent analytical modeling the thermocline in the numerical solution consists of three regions quite distinct in their ventilation characteristics forming the greater part of the subtropical thermocline is an unventilated pool zone located in the core of the subtropical gyre and a ventilated zone to the east the unventilated shadow zone lies farther east and toward the equator analysis of potential vorticity on constant density surfaces is used to study the structure of the thermocline a small but intense zone of convection located in the western boundary outflow caused by rapid heat loss to the atmosphere produces source water for the ventilated zone this water of extremely low potential vorticity mode water is distributed widely into the subtropical thermocline the pool forms equ

on the freshwater forcing of the thermohaline circulation in the limit of low diapycnal mixing 1 a conjecture is offered on the stability characteristics of the thermohaline circulation in the limit of very low diapycnal mixing in this limit the action of the winds on the antarctic circumpolar current acc can sustain a deep overturning pattern known as the reconfigured conveyor consisting of upwelling around antarctica and sinking in the north atlantic as shown by the work of toggweiler and others it is conjectured that in this limit northern sinking should be stabilized in an on state because of the penetration of freshwater into the ocean interior via isopycnal layers that outcrop to the surface within and south of the acc this conjecture is supported by qualitative arguments and by a hydraulic model for the reconfigured conveyor the hydraulic model takes into account the freshwater budgets of the atlantic basin antarctic surface waters and the remaining oceans it also takes into account in simple terms wind driven antarctic upwelling eddy transports and mixing within the acc changes in pycnocline depth the role of temperature forcing and advective feedbacks on salinity the hydraulic model suggests that multiple on off states of the reconfigured conveyor are possible but only if the deep waters that form in the northern hemisphere are fresher than the intermediate waters that form in the vicinity of the acc in the southern hemisphere a condition that is not satisfied in the modern ocean

the sensitivity of the atlantic meridional overturning circulation to enhanced freshwater discharge along the entire eastern and western coast of greenland the possible responses of the atlantic meridional overturning circulation amoc to increased freshwater discharge along the greenland coast has become an issue of growing concern given the increasing rate of the greenland ice sheet gris melting a recent model study suggested a weakened amoc of about 13 30 when a freshwater anomaly of 0 1 sv 1 sv 106 m3 s 1 was released along the entire greenland coast during the late twentieth century 1965 2000 in this study we use a fully coupled climate model to examine the sensitivity of amoc to a similar amount of freshwater forcing but released separately along the eastern the western and the entire greenland coast our results show that in all three cases there is a general weakening of the amoc mainly due to a reduced formation of labrador sea water moreover when additional freshwater is released along the eastern coast of greenland the amoc weakens more compared to the other two cases the different degree of convective mixing reduction in the irminger sea is the main reason for the spread in amoc responses in the three freshwater hosing experiments compared to the other two experiments the eastern coast experiment shows a relative warming in the labrador sea and the generation of a negative greenland tip jet like wind pattern anomaly these anomalies lead to a weaker convective mixing in the southern irminger sea and result subsequently in less formation of the simulated upper labrador sea water ulsw in the eastern coast experiment this study therefore highlights a potential important role for ulsw formation in determining the sensitivity of the amoc in response to large gris melting

deep circulation of the north atlantic over the last 200 000 years geochemical evidence variations in the cadmium calcium ratio of north atlantic deep water are recorded in the fossil shells of benthic foraminifera the oceanic distribution of cadmium is similar to that of the nutrients hence the cadmium calcium ratio in shells records temporal variations in nutrient distributions data from a north atlantic sediment core show that over the past 200 000 years there has been a continuous supply of nutrient depleted waters into the deep north atlantic the intensity of this source relative to nutrient enriched southern waters diminished by about a factor of 2 during severe glaciations this evidence combined with carbon isotope data indicates that the continental carbon inventory may have been less variable than previously suggested

high latitude salinity effects and interhemispheric thermohaline circulations a general circulation model for the ocean is used to investigate the interaction between the global scale thermohaline circulation and the salinity distribution it is shown that an equatorially asymmetric circulation can be maintained even under equatorially symmetric basin geometry and surface forcing multiple equilibrium solutions are obtained for the same forcing by perturbing the high latitude salinity field in an otherwise equatorially symmetric initial condition the timescale of the transition from the symmetric circulation to an asymmetric circulation depends critically on the sign of the initial salinity perturbation

could changing ocean circulation have destabilized methane hydrate at the paleocene eocene boundary 1 during the paleocene eocene thermal maximum petm 55 ma marine and terrestrial carbon isotope values exhibit a negative shift of at least 2 5 indicative of massive destabilization of marine methane hydrates releasing 2000 gigatons of methane carbon the cause of the hydrate destabilization is unknown but has been speculated to be warming due to a change from high latitude to low latitude deepwater formation here we present results from a numerical ocean model indicating that a sudden switch of deepwater formation from southern to northern high latitudes caused middepth and deep ocean warming of 3 5 c the switch is caused by a slow increase in the intensity of the atmospheric hydrologic cycle as expected under increasing temperatures and consistent with petm sedimentary evidence deepened subtropical subduction prior to the thermohaline circulation switch causes warming of 1 4 c in limited areas at thermocline through upper intermediate depths which could destabilize methane hydrates gradually and at progressively greater depths warming accompanying a south to north switch in deepwater formation would produce sufficient warming to destabilize seafloor gas hydrates over most of the world ocean to a water depth of at least 1900 m

geologically driven 3d modelling of physical rock properties in support of interpreting the seismic response of the lalor volcanogenic massive sulphide deposit snow lake manitoba canada 3d lithofacies and physical rock property models were generated to interpret 3d seismic data acquired over the lalor volcanogenic massive sulphide deposit manitoba canada the lithofacies model revealed that strong seismic reflectivity is associated with ore host rock and mafic felsic lithofacies contacts including their hydrothermally altered equivalents different physical rock property models were subjected to 3d seismic forward modelling using the sofi3d finite difference code seismic synthetics from discrete and interpolated models in which kriging of p wave velocity and density was conditioned by curvilinear grids conformable to the 3d modelled geological structure showed a much better match to the seismic data in comparison to those generated by kriging in cartesian space synthetics from these curvilinear grid models corroborate the origin of seismic reflectors as qualitatively inferred from the lithofacies model seismic synthetics generated from physical rock property models in which physical rock properties were augmented by densely sampled secondary variables such as feo percentage enhanced lateral continuity of seismic reflectivity although these co kriged petrophysical models were not more accurate than their kriged equivalents the physical rock property modelling methodology was also useful for testing the utility of passive interferometric seismic surveys as this highlighted the limitations of the discrete physical rock property model

the historical development of the magnetic method in exploration the magnetic method perhaps the oldest of geophysical exploration techniques blossomed after the advent of airborne surveys in world war ii with improvements in instrumentation navigation and platform compensation it is now possible to map the entire crustal section at a variety of scales from strongly magnetic basement at regional scale to weakly magnetic sedimentary contacts at local scale methods of data filtering display and interpretation have also advanced especially with the availability of low cost high performance personal computers and color raster graphics the magnetic method is the primary exploration tool in the search for minerals in other arenas the magnetic method has evolved from its sole use for mapping basement structure to include a wide range of new applications such as locating intrasedimentary faults defining subtle lithologic contacts mapping salt domes in weakly magnetic sediments and better defining targets through 3d inversion these new applications have increased the method s utility in all realms of exploration in the search for minerals oil and gas geothermal resources and groundwater and for a variety of other purposes such as natural hazards assessment mapping impact structures and engineering and environmental studies

high heat geodynamic setting during the palaeozoic evolution of the mount painter province sa australia evidence from combined field structural geology and potential field inversions