the topology of evolving rift fault networks single phase vs multi phase rifts rift fault networks can be complex particularly those developed by multiple periods of non coaxial extension comprising non colinear faults with many interactions thus topology rather than simple geometry is required to characterise such networks as it provides a way to describe the arrangement of individual faults in the network topology is analysed here in terms of nodes isolated i nodes or connected y or x nodes and branches i i i c c c branches in map view the relative proportions of these parameters vary in natural single and multi phase rift fault networks and in scaled physical models at different stages of development and strain interactions in single phase rifting are limited to fault splays and along strike fault linkage i node and i i or i c branch dominated networks whereas in multi phase rifting the topology evolves towards y node and c c branch dominated networks with the degree of connectivity increasing with greater strain the changes in topology and network connectivity have significant implications for fluid flow and reservoir compartmentalisation studies furthermore topology helps to distinguish single and multiple phase extension i e tectonic histories and thus provide constraints on the geodynamic context of sedimentary basins

probabilistic modeling of faults below the limit of seismic resolution in pelican field north sea offshore united kingdom faults which can compartmentalize a reservoir and which are too small to be seen on seismic can be predicted using a self similar or fractal model of faulting at various scales a computerized method has been developed for statistical analysis of a fault pattern interpreted from three dimensional 3 d seismic in order to fractally derive the distributions of fault size frequency and spatial variations and to verify their invariance within the seismic resolution range this analysis can be used for quality control of seismic interpretation and as input for extrapolation toward smaller scales using probabilistic techniques the application of this program to pelican field united kingdom north sea validated the interpretation of the complex fault pattern of that field but suggested that only limited extrapolations could be confidently made probabilistic maps showing distribution of faults down to 3 m 10 ft of throw and not resolved by 3 d seismic were made these maps subsequently were used as a qualitative aid in full field reservoir simulations to model differently zones of potential dense faulting from zones of reduced faulting this was done because nearby field behavior had shown that faulting is a significant factor in reservoir behavior and ultimately field deliverability field development planning therefore could be optimized

the importance of structural model availability on seismic interpretation interpretation of faults in seismic images is central to the creation of geological models of the subsurface the use of prior knowledge acquired through learning allows interpreters to move from singular observations to reasoned interpretations based on the conceptual models available to them the amount and variety of fault examples available in textbooks articles and training exercises is therefore likely to be a determinant factor in the interpreters ability to interpret realistic fault geometries in seismic data we analysed the differences in fault type and geometry interpreted in seismic data by students before and after completing a masters module in structural geology and compared them to the characteristics of faults represented in the module and textbooks we propose that the observed over representation of normal planar faults in early teaching materials influences the interpretation of data making this fault type and geometry dominant in the pre module interpretations however when the students were exposed to a greater range in fault models in the module the range of fault type and geometry increased this work explores the role of model availability in interpretation and advocates for the use of realistic fault models in training materials

an ice ocean coupled model an ice model an ocean model and a method of coupling the models are described the ice model is a synthesis with variations and extensions of previous modeling ideas ice thickness concentration velocity and internal energy are prognostic variables the ice thermodynamics are represented by temperatures at the snow surface ice surface the interior and the bottom surface melting and freezing rates are calculated at the ice atmosphere ice ocean and atmosphere ocean interfaces a prescribed portion of summer meltwater can be stored on the surface and refrozen in the fall the ocean model includes a second moment turbulence closure submodel and enables one to solve for oceanic heat flux the interfacial stress and subsurface properties in this paper the model is applied to one dimensional simulations but the equations are cited in a form for implementation by two and three dimensional models in a companion paper kantha and mellor this issue the model is used for two dimensional vertical plane simulations in the bering sea several one dimensional sensitivity studies are performed in the case where the ice model is decoupled from the ocean here the oceanic heat flux and sea surface temperature are prescribed constants the studies reveal the role and sensitivity of surface trapped meltwater ice concentration and ice divergence with the coupled ice ocean model the seasonally varying oceanic heat flux and mixed layer properties are determined by the model some comparisons with observations in the central arctic ocean are possible the role of the molecular sublayer immediately adjacent to the ice is examined frazi ice production is related to the large disparity in the molecular diffusivities for temperature and salinity the mixed layer model contains empirical constants which are known from turbulence data the molecular sublayer parameterization requires one empirical parameter b which is uncertain but from this study is assuredly greater than zero the value implicit in previous models the ice model requires the empirical parameters ci f and ci u to quantitatively account for freezing or melting processes in open leads their values are also uncertain but we present reasoning and sensitivity studies to suggest specific values finally an empirical parameter g is introduced it is the ratio of the value of the ice thickness used to represent average ice volume in the dynamic and thermodynamic equations to the value of the thickness needed in the heat conduction equation estimates of g are made from observed thickness distribution functions sensitivity studies show it to be an important parameter

ice growth and oceanic heat flux models and measurements heat fluxes at the ice ocean interface and ice thickness are investigated by comparing field data from the coordinated eastern arctic experiment cearex drift phase with model calculations the calculations are based on two types of models the first one is a one dimensional ice ocean model with high vertical resolution this model is based on the conservation equations for heat salt and momentum and uses turbulence models to achieve closure a discrete element approach is also introduced to explicitly parameterize the ice roughness the second model is a simple one dimensional bulk heat transfer model in this version the interfacial salinity is modelled on the basis of salt conservation at the ice ocean interface the bulk heat transfer model is then calibrated using the former model the two models predict ocean heat fluxes that are quite variable in time owing to short term variations in the ice drift both models calculate realistic ice thicknesses it is demonstrated that the observed time variation in ice thickness from eight different experimental sites with varying initial thicknesses and bottom topographies can be reproduced by applying bulk heat transfer coefficients in the range 2 8 1 10 4 horizontal variation of the thermal state within a single pack ice floe results in simultaneous freezing and melting over relatively small spatial scales when modeling or averaging ice data in space these aspects need to be considered

statistical properties of the atmospheric pressure field over the arctic ocean abstract many useful statistical properties can be derived for isotropic stationary homogeneous gaussian random fields the field of surface pressure in the region north of 70 n is shown to approximately satisfy these conditions under these conditions all properties of the field are related to the autocovariance which is a function of time and space lag in particular the following quantities are derived the time and space covariance functions for the geostrophic wind the covariance functions for the vorticity of the geostrophic wind the average number of highs lows and saddles per unit area the average number of highs lows and saddles at which the vorticity exceeds a specified threshold and the probability density function for the gaussian curvature of the pressure surface the horizontal shear in the geostrophic wind is also investigated as is the number of umbilic points per unit area estimates for all these quantities are constructed using observations of surface pressure from the arct

regional variations in provenance and abundance of ice rafted clasts in arctic ocean sediments implications for the configuration of late quaternary oceanic and atmospheric circulation in the arctic abstract the composition and distribution of ice rafted glacial erratics in late quaternary sediments define the major current systems of the arctic ocean and identify two distinct continental sources for the erratics in the southern amerasia basin up to 70 of the erratics are dolostones and limestones the amerasia suite that originated in the carbonate rich paleozoic terranes of the canadian arctic islands these clasts reached the arctic ocean in glaciers and were ice rafted to the core sites in the clockwise beaufort gyre the concentration of erratics decreases northward by 98 along the trend of the gyre from southeastern canada basin to makarov basin the concentration of erratics then triples across the makarov basin flank of lomonosov ridge and siltstone sandstone and siliceous clasts become dominant in cores from the ridge and the eurasia basin the eurasia suite the bedrock source for the siltstone and sandstone clasts is uncertain but bedrock distribution and the distribution of glaciation in northern eurasia suggest the taymyr peninsula kara sea regions the pattern of clast distribution in the arctic ocean sediments and the sharp northward decrease in concentration of clasts of canadian arctic island provenance in the amerasia basin support the conclusion that the modern circulation pattern of the arctic ocean with the beaufort gyre dominant in the amerasia basin and the transpolar drift dominant in the eurasia basin has controlled both sea ice and glacial iceberg drift in the arctic ocean during interglacial intervals since at least the late pleistocene the abruptness of the change in both clast composition and concentration on the makarov basin flank of lomonosov ridge also suggests that the boundary between the beaufort gyre and the transpolar drift has been relatively stable during interglacials since that time because the beaufort gyre is wind driven our data in conjunction with the westerly directed orientation of sand dunes that formed during the last glacial maximum on the north slope of alaska suggests that atmospheric circulation in the western arctic during late quaternary was similar to that of the present

the relationship between the geometry of normal faults and that of the sedimentary layers in their hanging walls abstract we derive an analytical expression that relates the shape of a fault in cross section to the shape of the bedding horizons in its hanging wall block the expression assumes that the hanging wall deforms by simple shear and that the footwall remains undeformed throughout although this paper concentrates on normal faults the expression is equally valid and applicable to thrust faults the direction of simple shear in the hanging wall block is arbitrary and has a dramatic effect on the predicted fault or bedding geometry there is no reason to believe that the simple shear occurs on vertical planes as is commonly assumed in graphical approaches to this problem and ignoring the presence of inclined simple shear is likely to lead to considerable underestimates of the amount of extension across normal faults and in the amount of shortening across thrusts similar though more complicated expressions can be obtained when compaction within the hanging wall block is taken into account for a planar normal fault such compaction may result in the development of a hanging wall syncline

seasonal variations of sea ice motion in the canada basin and their implications ice velocities and sea level pressure data from arctic drifting buoys for 1979 85 are used to examine the seasonal variation of sea ice drift in the canada basin a recurring reversal of the mean anticyclonic gyre is demonstrated in late summer in response to changes in atmospheric forcing the identification of this reversal of ice motion is significant for numerical modeling of arctic atmosphere ocean ice interactions

a model to interpret driftwood transport in the arctic abstract driftwood is frequently used to estimate past changes of sea ice extent and circulation in the arctic nevertheless driftwood observations are difficult to interpret because of the potentially complex relation with climate change in order to determine the origin of the observed changes we built a driftwood transport model dtm simulating the driftwood trajectories from the boreal forest to arctic coasts the model is driven by three main variables which are the sea ice velocity concentration and the sea surface current velocity that can be derived from observations or climate model outputs e g from a general climate model gcm overall the dtm model agrees with the observations although this comparison needs to be taken with caution because of the sparse data and the uncertainties of driftwood provenance through simulations performed with the dtm model we confirm the strong influence of the variability of the atmospheric circulation on the spatial driftwood distribution model simulations of the mid holocene period driven by six gcms show that small local changes in sea ice circulation a westward shift in the transpolar drift and a reduced beaufort gyre during the mid holocene compared to the present period suffice to explain the driftwood landing change during the mid holocene with a non negligible contribution from reduced sea ice concentration consequently a change in driftwood deposit should not be directly interpreted as large modifications in atmospheric circulation and the complexity of the response of driftwood trajectories to past climate changes clearly highlights the interest of using a model to interpret driftwood records

wintertime heat flux to the underside of east antarctic pack ice in the sea ice zone there is a delicate balance between the heat loss from the surface of the snow covered sea ice and the heat supplied to the underside of the ice by the deep ocean the difference between these two heat fluxes determines the amount of ice growth or melt in global atmospheric models the ocean heat flux is often prescribed and has been shown to be an important parameter in determining how thick sea ice will grow thermodynamically although this ocean heat flux is a critical component in climate models there are relatively few direct measurements in the antarctic sea ice region in this study we use measurements of the temperature gradient through the sea ice and of ice growth during a field experiment to estimate the ocean heat flux in the east antarctic region around 140 e 65 s during august 1995 we find an average ocean heat flux of 13 0 14 5 w m 2 this is more than twice the winter values reported in the western weddell sea under multiyear sea ice but similar to the 19 w m 2 that has been estimated for the entire weddell gyre during august 1995 the air temperature showed large variations ranging from near freezing to 30 c this resulted in the thicker ice floes 50 60 cm alternating between a no growth or melting condition and an active ice growth at the base however it is likely that the thicker 60 cm ridged portions of the floes were continually melting

the connectivity of two dimensional networks of spatially correlated fractures 1 continuum percolation thresholds for fracture systems are based on models with random fracture locations resulting in uniformly clustered systems in which all connections are fracture intersections fractures in natural systems can be either clustered or anticlustered and a significant portion of the connectivity is achieved through fracture abutments or splays analytical and numerical methods are combined to define critical properties of isotropic networks of constant length lines as a function of fracture clustering and of the ratio of abutments to intersections a second suite of numerical results indicates that the influence of these parameters varies as a function of the fracture length distribution a preliminary predictor of critical density of anisotropic nonrandom systems with lognormal length distributions is derived and applied to a suite of natural fracture systems predicted connectivities are closer to the observed connectivities when the predictor is used than when connectivity is estimated from the random threshold

north pole ice thickness and association with ice motion history 1977 1992 ice drafts measured by u s navy submarine sonar near the north pole from 1977 to 1992 were used together with arctic ocean drifting buoy data from 1979 to 1992 to investigate north pole ice thickness changes during this 15 year period a primary objective was to determine dynamical forcing mechanisms and associated time scales relevant to ice thickness variation north pole ice thickness showed much interannual variability and no systematic decrease of ice thickness was observed changes in ice thickness were closely associated with long term directional deviation of ice motion from geostrophic wind forcing and with ice convergence and divergence at the north pole during the 1 2 weeks prior to submarine measurement the geographic origin of ice within the arctic ocean was not associated with its eventual thickness at the north pole

ocean heat flux under antarctic sea ice in the bellingshausen and amundsen seas two case studies we examine the role of ocean heat flux ohf in antarctic sea ice growth and melt using data from autonomous ice mass balance buoys deployed on pack ice in the bellingshausen sea and on fast ice in the amundsen sea during the spring summer october december 2007 and summer autumn february march 2009 transitions respectively ohfs are derived using two methods that examine changes in 1 sub ice ocean water properties ohf1 and 2 ice thickness ohf2 the latter only applying to thick snow covered ice i e a near zero temperature gradient near the ice bottom good agreement is found between the time averaged estimates of ohf1 and ohf2 average ohf measured was 8 2wm 2 under the pack ice and 17 2wm 2 under the landfast ice some short term ohf values ohf1 in both seas exceeded 55wm 2 the spring ohf variations in the bellingshausen sea were periodic and controlled by semi diurnal ice velocity fluctuations larger temperature fluctuations in the summer amundsen sea originating from incursions of warm deep water masses contributed to the ohf being twice as high as in the bellingshausen sea and also accounted for the irregular ohf variability there

sediment hosted micro disseminated gold mineralization constrained by basin paleo topographic highs in the youjiang basin south china abstract the youjiang basin is a devonian triassic rift basin on the southern margin of the yangtze craton in south china strong syndepositional faulting defined the basin and range style paleo topography that further developed into isolated carbonate platforms surrounded by siliciclastic filled depressions finally thick triassic siliciclastic deposits covered the platforms completely in the youjiang basin numerous sediment hosted micro disseminated gold smg deposits occur mainly in permian triassic chert and siliciclastic rocks smg ores are often auriferous sedimentary rocks with relatively low sulfide contents and moderate to weak alteration similar to carlin type gold ores in north america smg ores in the youjiang basin are characterized by low temperature mineral assemblages of pyrite arsenopyrite realgar stibnite cinnabar marcasite chalcedony and carbonate most of the smg deposits are remarkably distributed around the carbonate platforms accordingly there are platform proximal and platform distal smg deposits platform proximal smg deposits often occur in the facies transition zone between the underlying platform carbonate rocks and the overlying siliciclastic rocks with an unconformity often a paleo karst surface in between in the ores and hostrocks there are abundant synsedimentary syndiagenetic fabrics such as lamination convolute bedding slump texture soft sediment deformation etc indicating submarine hydrothermal deposition and syndepositional faulting numerous fluid escape and liquefaction fabrics imply strong fluid migration during sediment basin evolution such large scale geological and fabric evidence implies that smg ores were formed during basin evolution probably in connection with basinal fluids it is well known that basinal fluids especially sediment sourced fluids will migrate generally 1 upwards 2 towards basin margins or basin topographic highs 3 and from thicker towards thinner deposits during basin evolution the isolated carbonate platform as a basin paleo high and related syndepositional fault system together with the unconformity related facies succession may have controlled the migration pathway of ore forming basinal fluids and subsequently determined the location of smg deposits in the youjiang basin unlike carlin type gold deposits smg mineralization in the youjiang basin may represent an integral aspect of the dynamic evolution of extensional basins along divergent continental margins

enhanced arctic sea ice drift estimation merging radiometer and scatterometer data satellites enable daily and global coverage of the polar oceans and provide a unique monitoring capability of sea ice dynamics sea ice drift maps can be estimated in arctic from several satellite sensors particularly from scatterometers and radiometers this study presents the benefits of combining single drift fields at the same resolution into a merged field built at three and six day lags during winters with a 62 5 km resolution it is shown that combining these drift fields not only increases the reliability of the displacement estimation and the number of estimated vectors to almost a full ice covered area but also expands the time period over which these estimations are reliable from freeze until the melt onset the autumn winter spring sea ice drift fields presented here are systematically produced at institut francais de recherche pour l exploitation de la mer centre d exploitation et de recherche satellitaire the sea ice drift 1992 2011 time series is available and the processing is ongoing these data are available for operational use and for the scientific community

beaufort chukchi seas summer and fall ice margin data from seasat conditions with similarities to the labrador sea the margin of the sea ice pack of the beaufort and chukchi seas is examined using the microwave data from seasat taken during the summer to early fall july 4 through october 8 1978 and the observations are compared to the analogous observations taken in limex 87 the sensors used are synthetic aperture radar sar the seasat a scatterometer system and the scanning multichannel microwave radiometer

an estimate of the mean field of arctic sea ice motion the observational basis for our understanding of sea ice motion comes from the trajectories of particular ice floes these ice floes may have been marked by a manned research station or more recently by an automatic data buoy since 1893 almost 100 station years of drift data have been recorded using the principles of optimal linear estimation these data are used to obtain a quantitative estimate of the field of mean motion

laboratory simulation of exchange through fram strait laboratory experiments and theory were conducted to observe the flow patterns and transport in both buoyancy driven and wind driven rotating fluids in lock exchange experiments water with one density flows into a second basin after a sliding gate is removed water of a second density flows back into the first basin the size and location of the currents for various values of density difference rotation rate and assorted sidewall geometries was recorded volume flux of the fluid was also measured and compared with a theory for lock exchange flow of a rotating fluid in a separate group of experiments with a passive upper layer easterly winds like those in the arctic ocean drive the upper level water into the arctic ocean and therefore oppose the buoyant exchange westerly winds would drive the water out of the arctic ocean this indicates that the exchange between the arctic ocean and the greenland norwegian sea is likely to be driven by buoyancy rather than by driven by wind crude estimates of the volumetric and fresh water exchange rate from the lock exchange formulas are compared with observed ocean fluxes and approximate agreement is found

arctic sea ice velocity field general circulation and turbulent like fluctuations 1 using buoy trajectories of the iabp data set we analyze the arctic sea ice velocity field as the superposition of a mean field and fluctuations we study how the mean field can be objectively defined using appropriate spatial and temporal averaging scales depending on the season considered 400 km and 5 months for winter i e approximately all the polar winter duration and 200 km and 2 months for summer i e approximately all the polar summer duration the mean velocity field shows a strong intra annual between winter and the following summer as well as interannual variability the fluctuations i e the remaining part of the velocity field after subtracting the mean field are analyzed in terms of diffusion properties although the arctic sea ice cover is a solid we show that the fluctuations follow the same diffusion regimes as the ones predicted for turbulent flows as observed in geophysical fluids like the ocean or the atmosphere we found that the integral time and the diffusivity of sea ice are in the same ranges as those estimated for the ocean i e 1 5 days in winter and 1 3 days in summer and 0 44 103 m2 s for winter and 0 45 103 m2 s in summer respectively however the statistics of the sea ice fluctuating velocity deviate from classical turbulence theory as they show exponential instead of gaussian distributions sea ice velocity and acceleration are intermittent and both are characterized by a multifractal scaling the oceanic and atmospheric dynamic forcing cannot explain solely the statistical properties of sea ice kinematics and dynamics we argue that sea ice dynamic is significantly influenced by the interplay of multiple fractures that are activated intermittently within the ice pack

arctic perennial ice cover over the last 14 million years knowledge of the long term history of the perennial ice is an important issue that has eluded study because the cenozoic core material needed has been unavailable until the recent arctic coring expedition acex detrital fe oxide mineral grains analyzed by microprobe from the last 14 ma 164 m of the acex composite core on the lomonosov ridge were matched to circum arctic sources with the same mineral and 12 element composition these precise source determinations and estimates of drift rates were used to determine that these sand grains could not be rafted to the acex core site in less than a year thus the perennial ice cover has existed since 14 ma except for the unlikely rapid return to seasonal ice between the average sampling interval of about 0 17 ma both north america and russia contributed significant fe grains to the acex core during the last 14 ma

origin of rollover rollover is the folding of hanging wall fault blocks by bending or collapse in response to slip on nonplanar commonly listric normal faults the shapes of rollover folds are controlled by a number of variables including 1 the shape of the fault 2 the total fault slip after a bed is deposited 3 the direction of relative particle motion in hanging wall collapse 4 the history of sedimentation rate relative to fault slip rate and 5 compaction the importance and role of each of these variables is illustrated by a two dimensional balanced structural modeling technique that treats continuously curved faults as though composed of a large number of straight fault segments in this modeling an active axial surface oriented parallel to the direction of relative p rticle motion in hanging wall collapse emanates from each fault bend and is the instantaneous locus of folding the quantitative correctness of this theory of rollover is tested by modeling natural structures from the gulf of mexico for which both fault shape and fold shape are known from high quality seismic and well sections the direction of hanging wall collapse commonly is in the antithetic or synthetic normal fault or coulomb shear orientations although sliding along weak bedding planes also is an important collapse mechanism in some regions collapse is in the antithetic shear direction for concave fault bends and in the synthetic shear direction for convex bends these collapse directions can be observed directly in some high quality seismic images as axial surfaces emanating from fault bends the shapes of rollovers within growth strata depend strongly on the sedimentation rate relative to fault slip rate as well as the total slip after a bed is deposited the crests of classic gulf coast rollovers are growth axial surfaces along which are abrupt changes in sedimentation rate within the growth st atigraphic interval these changes are produced by deformation of the sediment water interface along active axial surfaces compaction can substantially modify the relationship between fault shape and rollover shape however under certain common conditions the history of compaction can be neglected if the folding is modeled in the compacted state

early spring oceanic heat fluxes and mixing observed from drift stations north of svalbard abstract from several drifting ice stations north of svalbard norway observations were made in early spring of the ocean turbulent characteristics in the upper 150 m using a microstructure profiler and close to the under ice surface using eddy correlation instrumentation the dataset is used to obtain average heat fluxes at the ice water interface in the mixed layer across the main pycnocline as well over different water masses in the region the results are contrasted with proximity to the branches of the warm and saline atlantic water current the west spitsbergen current wsc which is the main oceanic heat and salinity source both to the region and to the arctic ocean hydrographic properties show that the surface water mass modification is typically due to atmospheric cooling with relatively less influence of ice melting surface heat fluxes of o 100 w m 2 are found within the branches of the wsc and over shelf areas with elevated levels of mixing due to strong tides away from the shelves and

mechanisms for the variation of sea ice extent in the northern hemisphere using daily sea ice data derived from satellite borne sensors and atmospheric data we examined processes controlling the variation of sea ice extent in the northern hemisphere the daily ice motion field was computed from imagery of the defense meteorological satellite program dmsp special sensor microwave imager ssm i for seven winters december to april from 1991 1992 to 1997 1998 by employing the maximum cross correlation method in order to examine mechanisms of the temporal variation of the ice extent we analyzed 50 specified lines across the daily ice edge although a high correlation between the ice motion and the geostrophic wind speed was observed in all the ice edge areas the degree for correlation between the speed of the ice edge displacement and the wind speed varied with region the degree for response of the ice edge speed to the wind speed largely depended upon that of the ice edge speed to the ice motion the following mechanisms controlling the variation of ice extent for regions in the northern hemisphere were anticipated in the barents sea bering sea and the sea of okhotsk the ice extent advances by wind driven ice advection and the daily scale variation of the ice extent were also controlled by the variation in wind speed in contrast the ice extent in the labrador sea and the greenland sea seemed to be considerably affected by oceanographic factors such as the location of the thermal front and was not related to the variation in wind speed the regional difference of the variation mechanism was also reflected in the interannual variation in maximum ice extent

interannual variability of summer sea ice thickness in the siberian and central arctic under different atmospheric circulation regimes extensive drill hole and electromagnetic induction measurements of sea ice thickness in the siberian and central arctic seas in the summers of 1993 1995 and 1996 reveal significant interannual variability in the laptev sea minimum and maximum modal first year ice thicknesses amounted to 1 25 and 1 85 m in 1995 and 1996 respectively ice thickness correlates with ice extent which reached a record minimum in august 1995 and was well above average in 1996 these differences are explained by the strength and location of a summer cyclonic atmospheric circulation pattern affecting both ice advection and surface melt from drifting buoys deployed in 1995 and satellite radar backscatter data first and second year ice regimes are delineated differences in first year ice backscatter coefficients between 1993 1995 and 1996 are explained by differences in level ice surface roughness the lagrangian evolution of ice thickness between 1995 and 1996 is studied while the shape of the thickness distribution does not change significantly the mean modal ice thickness of the ice field increases from 1 80 m 1 25 m in 1995 to 2 86 m 2 25 m in 1996 the thickness distribution of second year ice in 1996 closely agrees with that of level multiyear ice downstream in the transpolar drift obtained in 1991 in 1996 mean level ice thickness increases at 0 23 and 0 16 m deg 1 with latitude in the kara and laptev sea sectors of the arctic ocean respectively

an unexpected seasonal variability of salinity in the beaufort sea upper layer in 1996 1998 1 the salinity in the upper beaufort sea from the mixed layer to the thermocline layer was observed by drifting buoys from 1996 to 1998 the salinity in this depth range was lower in winter and higher in the summer the exact opposite from what one would expect from the seasonal cycle of the freshwater flux associated with the ice melting freezing and river runoff in this study we calculated the daily ekman transport and upwelling velocity in the beaufort sea using both satellite and buoy data in fall and winter months the offshore transport of low salinity water from the coastal area toward the interior where the buoys were located was observed to be strong this horizontal ekman transport led to the freshening of the surface ekman layer in the buoy location the convergence of the ekman transport resulted in a strong downwelling in the offshore regions and so the halocline and thermocline were pushed downward the downwelling then results in the freshening of the subsurface salinity as observed by buoys other processes such as lateral advection may have also played a role in the subsurface freshening the lack of in situ observations needed to estimate the salinity gradient makes it difficult to assess more accurately the contribution from lateral advection a scaling analysis using the salinity climatology suggests that the lateral salinity advection though considerably smaller than the vertical one may not be negligible

calcite twinning strain constraints on the emplacement rate and kinematic pattern of the upper plate of the heart mountain detachment two models that address the emplacement rate of the upper plate of the heart mountain detachment hmd have been advanced these are the catastrophic tectonic denudation model and the slow incremental continuous allochthon model we compared the two models by analyzing upper and lower plate rocks for a detachment related overprint of the older layer parallel laramide sevier calcite twinning strain fabric lower plate pilgrim limestone samples even those collected a few meters below the detachment show no evidence of a detachment related twinning strain overprint negative expected values nevs avg 8 3 of the laramide sevier layer parallel fabric the allochthonous upper plate carbonate rocks preserve the layer parallel laramide sevier shortening strain but the shortening axis e1 for each block occurs in different non ew and both subhorizontal and non subhorizontal orientations for the six upper plate blocks that preserve chaotic shortening axis orientations no evidence of any detachment related twinning strain overprint nevs avg 7 5 was found in the absence of any hmd related twinning overprint the upper plate allochthon motion must have been rapid enough to be accommodated by fracturing of upper plate rocks without additionally twinning any calcite we conclude that the emplacement of the upper plate of the hmd was not accompanied by an overprint of the laramide sevier twinning fabric and that models that require catastrophic rather than slow incremental emplacement rates are best supported by these data

simultaneous parameter optimization of an arctic sea ice ocean model by a genetic algorithm abstractimprovement and optimization of numerical sea ice models are of great relevance for understanding the role of sea ice in the climate system they are also a prerequisite for meaningful pred

on the ice and heat balance in fram strait the sea ice margin northwest of spitsbergen is schematically represented by a stationary wedge maintained by opposing ice and warm atlantic water advection ice melt and cooling of the surface water generate a mixed layer with properties approximating those found elsewhere in the arctic basin the heat energy required to melt the advancing ice is roughly comparable to the rate of heat loss of the west spitsbergen current and suggests that direct heat exchange with the atmosphere is less important only a small fraction of the nearly fresh water from ice melt exits through eastern fram strait and most of it appears to return to the arctic basin whether or not it contributes to the formation and maintenance of the arctic mixed layer depends on the largely unknown circulation pattern north of fram strait an example of the large interannual variation of the mean wind stress field is shown to illustrate the likelihood of an equally large variance of the ice and surface water circulation

modeling of antarctic sea ice in a general circulation model a dynamic thermodynamic sea ice model is developed and coupled with the melbourne university general circulation model to simulate the seasonal cycle of the antarctic sea ice distribution the model is efficient rapid to compute and useful for a range of climate studies the thermodynamic part of the sea ice model is similar to that developed by parkinson and washington the dynamics contain a simplified ice rheology that resists compression the thermodynamics is based on energy conservation at the top surface of the ice snow the ice water interface and the open water area to determine the ice formation accretion and ablation a lead parameterization is introduced with an effective partitioning scheme for freezing between and under the ice floes the dynamic calculation determines the motion of ice which is forced with the atmospheric wind taking account of ice resistance and rafting the simulated sea ice distribution compares reasonably well with observations the seasonal cycle of ice extent is well simulated in phase as well as in magnitude simulated sea ice thickness and concentration are also in good agreement with observations over most regions and serve to indicate the importance of advection and ocean drift in the determination of the sea ice distribution

large scale drift of arctic sea ice retrieved from passive microwave satellite data a method of determining the large scale sea ice drift using 85 5 ghz special sensor microwave imager data are presented a cross correlation method is applied to sequential images of gridded data covering the entire arctic individual correlation results are validated with ice velocities derived from buoy data the satellite derived mean drift values and the variabilities of the ice drift correspond closely with the buoy data similarly time series of buoy data and associated satellite data are in good agreement even over large time periods an example of a satellite retrieved 3 day mean drift field demonstrates the potential of the method for providing large scale ice circulation patterns mean drift fields of the winter periods 1987 1988 and 1992 1993 indicate a considerable interannual variability of the sea ice drift pattern in the arctic ocean the arctic region is divided into seven larger areas and the area flux between these regions has been derived the kara sea and the laptev sea show the largest area ice export with 0 02 and 0 015 km 2 s 1 respectively the central arctic export through fram strait amounts to 0 12 sv during the winter of 1992 1993 with a maximum of 0 15 sv in january

on the scaling laws derived from ice beacon trajectories in the southern beaufort sea during the international polar year circumpolar flaw lead study 2007 2008 1 sea ice motion is an important element in mass balance calculations ice thermodynamic modeling ice management plans for industry and ecosystems studies in the historical literature sea ice motion in the beaufort sea was characterized by a predominantly anticyclonic motion during winter months with episodic reversals to cyclonic activity during summer however recent studies have shown an increase in cyclonic activity throughout the annual cycle in this paper we examine circulation in the beaufort sea based on the trajectories of 22 ice beacons launched in the franklin bay area during the international polar year circumpolar flaw lead ipy cfl study during an over wintering experiment in 2007 2008 dispersion characteristics of ice motion show that absolute zonal dispersion follows a t2 scaling law characteristic of advection associated with beaufort gyre circulation whereas absolute meridional dispersion follows a scaling law of t5 4 characteristic of floaters and dispersion in 2 d turbulence temporal autocorrelations of ice velocity fluctuations highlight definitive timescales with values of 1 2 0 7 days in the zonal meridional direction near gaussian behavior is reflected in higher order moments for ice velocity fluctuation probability density functions pdfs non gaussian behavior for absolute displacement pdfs indicates spatial heterogeneity in the ice motion fields atmospheric forcing of sea ice is explored through analysis of daily north american regional reanalysis and in situ wind data where it is shown that ice in the cfl study region travels with an average speed of approximately 0 2 and an average angle of 51 5 to the right of the surface winds during the 2007 2008 winter the results from this analysis further demonstrate seasonality in ice drift to wind ratios and angles that corresponds to stress buoy data indicative of increases in internal ice stress and connectivity due to consolidation of the seasonal ice zone to the coast and perennial ice pack during winter in the beaufort sea region

a comparison of sea ice dynamics models at high resolution abstract an elastic viscous plastic evp model for sea ice dynamics has recently been proposed as a computationally efficient alternative to the viscous plastic vp model widely in use the evp model features a fully explicit discretization that improves the model s efficiency particularly on high resolution grids and adapts easily to parallel computation comparison of two high resolution arctic sea ice simulations identical except for the ice dynamics indicates that the evp model reproduces the vp model behavior on timescales relevant to climate studies the ice concentration and thickness distributions over a 1 yr integration period are remarkably similar in the two models although the evp model responds more rapidly and accurately to strong synoptic weather systems than does the vp model compared to drifting arctic buoys a close look at rates of strain shows that elastic waves in the evp model do not significantly alter the ice behavior in highly compact areas where the waves most benefit nu

kinematic analysis of a growth fault system in the niger delta from restoration in map view by restoring six stratigraphic markers in map view we have studied the kinematics of a growth fault system involving a major fault its antithetic and a faulted roll over located within the niger delta offshore nigeria restoration yields for each marker the horizontal displacements due to normal faulting and the associated fields of block rotation about vertical axes as expected for a continuous history of growth faulting the amount of extension computed for each stratigraphic marker increases with depth from the fields of finite displacement and block rotation we find that horizontal extension perpendicular to fault traces is associated with a minor amount of bulk left lateral wrenching accommodated by counterclockwise rotation of blocks because the overall deformation differs from a plane strain balancing of cross sections alone would lead to some errors we also computed incremental displacement fields for time intervals between successive stratigraphic markers according to our results during the first stages of growth faulting displacement occurred only on the major faults whereas during later stages larger horizontal displacements were accommodated by numerous small faults probably responsible for the collapse of the roll over

heat flux at the ice ocean interface the role of the oceanic heat flux fw in the sea ice energy and mass balance is discussed and a method is described for determining fw from measurements of the temperature and thickness of sea ice results obtained using this method and data collected in the fall of 1988 during a drift in the eastern arctic northeast of fram strait are presented estimates of fw ranged from 0 to 37 w m 2 and varied in both time and space the gradual variation over the course of the drift reflects transformation of the west spitsbergen current into arctic water masses a significant intersite variability on horizontal scales of 10 to 100 m is ascribed to the interaction between under ice topographic features and turbulent energy and mass transfer in the boundary layer in addition there is a variability in the ice growth rate on horizontal scales of 0 1 to 1 m which is ascribed to the instability of the ice ocean phase boundary in the presence of turbulent flow these observations have implications for modeling and future experiments

the anatomy of a freezing lead winter leads are regions of intense ice growth with resultant large fluxes of heat to the atmosphere and salt to the ocean they constitute a major source of new ice in the arctic basin during the 1988 drift phase of the coordinated eastern arctic experiment we were afforded a unique opportunity to conduct a detailed long term study of a freezing lead measurements were made from september 17 to november 18 during which time the ice grew from open water to a thickness of 0 56 m cores were removed from the lead ice on a routine basis and analyzed for ice temperature salinity density and structure from these measurements the derived quantities of brine volume porosity heat flux to the atmosphere and salt flux to the ocean were computed in addition to this 2 month time series study of ice cores the spatial variation in lead ice properties was investigated on september 30 thin section studies of ice structure indicated that the upper 0 05 0 15 m of the ice sheet was granular and that the lower portion was columnar typically a portion of the granular layer was snow ice once the transition from granular to columnar ice had occurred granular ice did not reappear as the ice grew thicker the c axes of the ice crystals became aligned within the horizontal plane this alignment direction corresponded closely with the inferred direction of the current at the ice water interface vertical temperature profiles in the ice were approximately linear salinity profiles were usually c shaped with bulk salinities ranging from 9 to 6 before stabilizing at 6 for ice thicker than 0 35 m core data were used to compute the flux of heat to the atmosphere and the flux of salt to the ocean for seven time intervals during the experiment heat fluxes ranged from 89 to 29 w m2 with an average of 50 w m 2 roughly 3 times the corresponding value from multiyear ice the flux of salt from the lead ice to the ocean varied from 0 51 to 0 06 kg m 2 d 1 averaging 0 21 kg m 2 d 1

upper ocean velocities in the beaufort gyre a 23 month time series of upper ocean velocities in the beaufort gyre was obtained from an autonomous drifting buoy equipped with an acoustic doppler current profiler the buoy was deployed in the beaufort sea and drifted over the canada basin chukchi shelf and chukchi plateau time evolving spectral analysis was used to examine velocity variability in three frequency bands an eddy band 2 5 day periods a diurnal band and a semidiurnal band the eddy band and the semidiurnal band dominated the horizontal kinetic energy although eddy energy was clearly confined to the beaufort sea and canada basin eddies were found further to the south and west than in previous observations the semidiurnal band was dominated by near inertial motions with amplitude that varied seasonally largest in late summer and smallest in late winter diurnal tides were weak 1 cm s 1 except over a shallow portion of the chukchi shelf

drivers of declining sea ice in the arctic winter a tale of two seas 1 while the summer perennial arctic sea ice has declined markedly in recent decades the maximum extent of the winter ice cover had decreased only slightly until the past few years when it also receded dramatically this investigation reveals that the timing of maximum extent varies greatly and the drivers of ice edge location differ strikingly between two of the areas where it varies most the bering and barents seas between 1979 and 2005 in the bering sea the ice edge is influenced mainly by anomalies in easterly winds associated with the aleutian low which was particularly strong during the 1980s the barents sea ice edge in contrast is driven primarily by two factors anomalies in sea surface temperature particularly close in time to the maximum extent and by southerly wind from the south anomalies integrated back to mid and early winter the hemispheric mean decline in winter ice extent is due in large part to increasing sea surface temperatures in the barents sea and adjoining waters which are consistent with increased concentrations of greenhouse gases

interpretational variability of structural traps implications for exploration risk and volume uncertainty we would like to acknowledge and thank frank peel and seb turner for taking time to review this paper also thanks to marguerite fleming for perpetual encouragement from richards f l richardson n j rippington s j wilson r w bond c e eds 2015 industrial structural geology principles techniques and integration geological society london

dynamics and thermodynamics of the ice upper ocean system in the marginal ice zone of the greenland sea measurements were made of the ice upper ocean system in the marginal ice zone of the greenland sea during a 4 day storm in which wind blew the ice south across a frontal region coinciding with the ice edge that had existed when the storm began in response to wind stress of about 0 2 pa a turbulent boundary layer developed under the ice that exhibited marked ekman rotation in both mean velocity average surface speed about 0 17 m s 1 deflection angle about 33 and turbulent stress profiles typical reynolds stress about 0 1 pa ablation of the ice undersurface increased rapidly after crossing the surface temperature front and the observed melt rate corresponded with direct heat flux measurements in the oceanic boundary layer with maximum upward heat flux of about 200 w m 2 we discuss overall momentum and energy balances interpret observed boundary layer measurements with a numerical model and show that molecular effects are important for heat and mass transport at the hydraulically rough ice ocean interface we also develop a simple model for predicting ice melt from interfacial stress and temperature and salinity of the mixed layer

industrial structural geology principles techniques and integration an introduction the authors wish to acknowledge the generous financial support provided in association with this volume to the geological society and the petroleum group by badley geoscience ltd bp cgg robertson dana petroleum ltd getech group plc maersk oil north sea uk ltd midland valley exploration ltd rock deformation research schlumberger and borehole image core specialists wildcat geoscience walker geoscience and prolog geoscience we would like to thank the fine team at the geological society s publishing house for the excellent support and encouragement that they have provided to the editors and authors of this special publication

satellite derived maps of arctic and antarctic sea ice motion 1988 to 1994 standard image processing methods applied to 85 5 ghz special sensor microwave imager ssm i data provide previously unseen details about sea ice motion in the arctic and southern oceans means calculated from daily ice motions for 1988 1994 confirm the basic circulation patterns established from drifting stations and buoys but extend these observations to illustrate less well known transport patterns in the arctic coastal zones and sub arctic seas in the antarctic the gridded motion fields show a nearly continuous westward transport along the antarctic coast with well defined regions of exchange between this east wind drift and the antarctic circumpolar current this detailed view of mean ice motion in the southern ocean is unique and presents a comprehensive overview not previously available for antarctic ice motions

wind induced ice floe rotation and icequakes north of the alaskan beaufort sea coast linear sea ice canopy fractures leads and ice floe rotation appear to be interrelated this study focused on a highly persistent storm wind event as the wind stress increased over the ice pack a separate rotation threshold for four floe attached buoys was observed the northwestern most buoy recorded the start of clockwise ice floe rotation just as hydrophones recorded increased oceanic ambient noise several days later when the surface wind speeds and computed stress at all four buoys dropped to 60 and e 1 of their respective peak storm values a counterclockwise rotation began at each buoy with a concomitant impulsive ambient noise peak the rotationally induced noise bursts are called icequakes in an analogy with earthquakes