the mid norwegian margin a discussion of crustal lineaments mafic intrusions and remnants of the caledonian root by 3d density modelling and structural interpretation the high density lower crustal body lcb on the mid norwegian margin is almost universally interpreted to represent magmatically underplated material added to the crust during early tertiary opening of the ne atlantic the thickness of the lcb is uneven and its distribution along the margin is sharply limited by margin perpendicular lineaments three dimensional density modelling constrained by petrophysical and seismic data was performed to investigate the expression of the various lineaments bivrost jan mayen gleipne etc in the crustal architecture with and without the lcb the bivrost lineament separating the voring and lofoten margin segments is clearly expressed and so is arguably a lineament in the sw voring margin notably most of the lineaments can be interpreted as offshore prolongations of major onshore detachments stemming from late caledonian orogenic collapse an alternative interpretation of the lcb is thus that it represents high grade metamorphic rocks remnant from the caledonian root determining the nature of the lcb has profound effects for the volume estimate of magmatic rocks in the north atlantic igneous province and consequently also for the degree of crustal thinning and heat flow

on estimating the surface wind stress over the sea abstractour study analyzes measurements primarily from two floating instrument platform flip field programs and from the air sea interaction tower asit site to examine the relationship between

wind wave nonlinearity observed at the sea floor part ii wavenumbers and third order statistics abstract this is part 2 of a study of nonlinear effects on natural wind generated surface gravity waves in 13 m depth 30 km offshore of virginia at the sea floor in this depth free surface gravity waves are only weakly attenuated at sea and swell frequencies 0 05 0 30 hz but are very strongly attenuated at frequencies higher than about 0 35 hz hence above 0 35 hz relatively long wavelength forced waves excited by nonlinear interactions between directionally opposing free wind waves are exposed at the sea floor an array of pressure transducers at middepth was used to estimate the frequency directional spectrum of free primary sea and swell waves and the associated forced secondary pressure fluctuations were measured with an array on the sea floor in part 1 it was shown that forced wave energy levels at the sea floor increase sharply in response to directionally opposing wind waves in agreement with weakly nonlinear theory in part 2 wavelengths propagation directions and non gaussian

measurements of the angle between the wind vector and wind stress vector in the surface layer over the north sea measurements of surface layer turbulence in addition to full meteorological and oceanography quantities over the north sea indicated that the stress vector on long time scales is often aligned with a direction slightly different from the mean wind flow when stratifications were near neutral the angle difference between the stress and wind exhibited a dependence on the heat and momentum fluxes in general the stress vector was observed to be to the left of the flow during stable stratifications while for unstable stratifications it was to the right this finding was consistent using two independent sets of wind stress data i e from marsen 1979 and the north sea platform winter exercise 1985

a moderate melting model for the voring margin norway based on structural observations and a thermo kinematical modelling implication for the meaning of the lower crustal bodies high p wave velocities 7 1 7 8 km s lower crustal bodies lcbs imaged along volcanic margins are commonly interpreted as plume and breakup related thick mafic underplating this interpretation is partly challenged in this paper based on new seismic observations and modelling of the outer voring basin norway an exceptional strong amplitude reflection the t reflection is particularly well defined below the north gjallar ridge ngr between 7and 8 s twt the t reflection is located near the volcanic lava flows emplaced during the ne atlantic breakup 55 54 ma ago and coincides with the top of the lcb forming a mid crustal dome based on structural and temporal relationships we show that the dome clearly influences the structural development of the ngr and predates the continental breakup at least by 10 15 ma using a thermo kinematical model we tried also to investigate and quantify the relationships between the extension lcb and the magmatic production modelling suggests that significant paleocene early eocene magmatism can be produced without any temperature anomaly in the mantle if differential stretching occurs during the breakup initiation the conclusion of 2d thermo kinematical parametric analysis is that the magmatic model predicts either little extension 5 with significant melting along the outer voring basin we suggest that the continental part of the lcb could not necessarily be breakup related and so magmatic as has often been stated previously it is concluded here that the continental part of the lcb observed beneath the outer voring basin may be partly or fully attributed to inherited high pressure granulite eclogite lower crustal rocks the real amount of mafic material emplaced along the outer voring basin could be 20 40 less than thought

brazilian and african passive margins of the central segment of the south atlantic ocean kinematic constraints the thinning of passive continental margins is usually explained by models using pure stretching or simple shear these models imply hypothetical extensional structures and large horizontal movements between the two conjugate margins more than 250 km for the brazilian and angolan margins refraction reflection data together with the most recent and tightest pre opening fit using continental and oceanic geological and geophysical constraints show that the substratum of the sag basin is divided into an autochthonous part upper continental crust and an allochthonous part exhumed material the thinning process which evolves in an elevated position of the system until at least the break up seems to be depth dependent and to mainly concern the lower middle crust which we postulate is exhumed this exhumation does not explain the entire thinning of the system horizontal motions cannot alone explain the formation of the huge angolan brazilian basin similar observations are made on the whole central segment of the south atlantic ocean part of the lower continental crust is still missing and it seems most improbable that the continental crust maintains its integrity throughout the thinning process

weathering of the oporto granite geotechnical and physical properties abstract this paper characterizes the weathering products of the two mica oporto granite in terms of its mineralogical chemical geotechnical and physical properties this information is used to identify a physical property that can be used as an index of the degree of weathering and to estimate other properties in outcrop the oporto granite is always weathered and weathering profiles frequently exceed 20 m within these profiles granitic saprolites are composed of quartz feldspars and some mica with kaolinite and gibbsite as final weathering products the average percentage of secondary minerals determined by bulk x ray diffraction xrd is low in both weathered rock 2 4 and saprolite 8 7 geotechnically the saprolites exhibit no or low plasticity plasticity index pi 12 the skeleton character of the saprolites is reflected in the significant proportion of fines 29 5

deep structure of the western south african passive margin results of a combined approach of seismic gravity and isostatic investigations abstract the passive margin of the south atlantic shows typical features of a rifted volcanic continental margin encompassing seaward dipping reflectors continental flood basalts and high velocity density lower crust at the continent ocean transition probably emplaced during initial seafloor spreading in the early cretaceous the springbok profile offshore western south africa is a combined transect of reflection and refraction seismic data this paper addresses the analysis of the seismic velocity structure in combination with gravity modelling and isostatic modelling to unravel the crustal structure of the passive continental margin from different perspectives the velocity modelling revealed a segmentation of the margin into three distinct parts of continental transitional and oceanic crust as observed at many volcanic margins the lower crust is characterised by a zone of high velocities with up to 7 4 km s the conjunction with gravity modelling affirms the existence of this body and at the same time substantiated its high densities found to be 3100 kg m 3 both approaches identified the body to have a thickness of about 10 km yet the gravity modelling predicted the transition between the high density body towards less dense material farther west than initially anticipated from velocity modelling and confirmed this density gradient to be a prerequisite to reproduce the observed gravity signal finally isostatic modelling was applied to predict average crustal densities if the margin was isostatically balanced the results imply isostatic equilibrium over large parts of the profile smaller deviations are supposed to be compensated regionally the calculated load distribution along the profile implies that all pressures are hydrostatic beneath a depth of 45 km

engineering and geological characteristics of granite weathering profiles in south china granite weathering profiles are widely distributed in south china their engineering and geological characteristics are major geotechnical subjects that are important in the design and construction of civil engineering projects this paper presents a summary of the weathering characteristics and zoning of granite weathering profiles in south china and discusses their engineering and geological properties a five grade scheme has been adopted in the zoning of a granite weathering profile studies have shown that the completely weathered granites cwg in south china have the following characteristics low moisture content low to medium plasticity w l 22 5 39 0 i p 6 5 11 8 medium void ratio 0 36 1 29 weak shrinkage and medium compressibility a 1 2 0 24 0 8 mpa 1 and high shear strength phi 20 30degrees c 20 40 kpa the cwgs are usually at a low or high plastic state and most of them are over consolidated soils a majority of the physical and mechanical properties have good statistical correlations with the degree of weathering the data presented in the paper are important in geotechnical engineering projects such as slope stability evaluation in china c 2002 elsevier science ltd all rights reserved

determining mineral weathering rates based on solid and solute weathering gradients and velocities application to biotite weathering in saprolites abstract chemical weathering gradients are defined by the changes in the measured elemental concentrations in solids and pore waters with depth in soils and regoliths an increase in the mineral weathering rate increases the change in these concentrations with depth while increases in the weathering velocity decrease the change the solid state weathering velocity is the rate at which the weathering front propagates through the regolith and the solute weathering velocity is equivalent to the rate of pore water infiltration these relationships provide a unifying approach to calculating both solid and solute weathering rates from the respective ratios of the weathering velocities and gradients contemporary weathering rates based on solute residence times can be directly compared to long term past weathering based on changes in regolith composition both rates incorporate identical parameters describing mineral abundance stoichiometry and surface area weathering gradients were used to calculate biotite weathering rates in saprolitic regoliths in the piedmont of northern georgia usa and in luquillo mountains of puerto rico solid state weathering gradients for mg and k at panola produced reaction rates of 3 to 6 10 17 mol m 2 s 1 for biotite faster weathering rates of 1 8 to 3 6 10 16 mol m 2 s 1 are calculated based on mg and k pore water gradients in the rio icacos regolith the relative rates are in agreement with a warmer and wetter tropical climate in puerto rico both natural rates are three to six orders of magnitude slower than reported experimental rates of biotite weathering

some measurements of turbulence over an antarctic ice shelf profiles of wind speed temperature and turbulent fluxes of heat and momentum in the lowest 32 m have been measured at a station on an antarctic ice shelf during the antarctic winter the surface layer often shows strong static stability with temperature gradients as large as 1 km 1 in the lowest few metres the surface inversion is destroyed during periods of high wind speed but the wind profile shows significant deviation from the expected logarithmic form under such conditions measurements of stress at 5 m indicate that the roughness length of the snow surface is about lo 4 m at 5 m height the variations of the dimensionless wind shear m and potential temperature gradient t agree with previously determined forms of the monin obukhov similarity functions above 5 m the behaviour of m and t is only qualitatively similar and surface layer similarity theory does not provide a good description of the profiles turbulence length scales have been deduced from vertical velocity power spectra under near neutral conditions the ratio of turbulence length scale to measurement height is observed to decrease with increasing height of measurement this observation is consistent with the variation of turbulence length scale with height implied by the measurements of m it is suggested that the stability of the overlying atmosphere restricts the depth of the turbulent boundary layer and hence the length scales of turbulence within this layer increasing stability causes a decrease of turbulence length scales at all levels the ratios of turbulence kinetic energy to stress and temperature variance to heat flux are examined measurements are somewhat scattered but the distribution of values varies little with height or stability the form of the distribution suggests that large scale motions possibly internal gravity waves may be playing an important role in boundary layer processes

convective boundary layer structure in the presence of wind following swell the marine boundary layer is known to be influenced by fast long ocean swell waves travelling away from their generation area where they were initiated by momentum transferred to the ocean wave field during storms the atmospheric boundary layer during wind following swell and various stability states has been investigated using large eddy simulation les data the dominant energy containing motions in the near neutral atmospheric boundary layer over flat terrain are known to be dominated by near ground shear induced regions of high and low speed flow wind fields and momentum fluxes from les for swell dominated situations have been used to interpret field measurements suggesting that these motions are disrupted by effects related to the underlying wave field in the presence of swell waves statistical analysis and visualization are used to further describe the effects of stratification during swell for convective boundary layer winds and fluxes a mechanism for transport of momentum to the upper levels of the boundary layer is suggested from interpretation of les data coherent detached eddies from the directly wave induced motions near the surface are found to maintain an upward momentum transfer this mechanism is found to strengthen during stronger swell conditions and also during slightly convective conditions in this way it is argued that processes related to both the wave field and surface convection can have a significant influence on the global structure of neutral and convective boundary layers during swell this has implication for the turbulence length scales during wind following swell copyright 2012 royal meteorological society

airborne scatterometer detection of winds and sea surface roughness changes across the gulf stream front abstract this article investigates the scatterometer radar cross section distributions and wind stress spatial variability across a sea surface temperature sst front under different wind directions and synoptic scale atmospheric forcings shipboard meteorological measurements in concert with airborne k u band 14 0 ghz rotating scatterometer data show evidence of mesoscale circulation near the front during low ambient winds 4 m s blowing from the cold side of the sst front to the warm side the mesoscale signature is characterized by a 25 35 counterclockwise shift in the wind direction and a maximum of 4 9 db increase in the backscattering cross section across the front the mesoscale circulation is reduced when the wind direction reverses and the ambient wind flow increases to 13 6 m s the maximum cross section change across the front is reduced to 3 6 db the azimuthal characteristics of the scatterometer data are compared with the predictions of two scatterometer model functions according to the models the anisotropy of the short waves is inversely related to the wind speed such that the short wave directional spreads tend to broaden as the wind speed increases the scatterometer data however show greater short wave anisotropy at the higher wind speeds this measured difference could be caused by current velocity changes or by longwave directional changes across the front

evolution of the northeast german basin inferences from a 3d structural model and subsidence analysis abstract a 3d structural model of the northeast german basin was evaluated with special emphasis on its evolution as an intracontinental depression the study includes investigations on subsidence history and structural setting of the basin thickness evolution and calculated tectonic subsidence volumes of permian to quaternary sediments in the northeast german basin indicate that the subsidence history was related to five stages of basin evolution which differ in their subsidence mechanisms for the initial rift phase in the late carboniferous to early permian a dominant thermal event and subordinate horizontal stresses were indicated by thickness variation evolution and by structural evidence the main part of basin subsidence occurred in a nw se oriented basin in the subsequent phase of thermal relaxation with maximum subsidence from early permian rotliegend to middle triassic muschelkalk from middle triassic the thermal subsidence pattern was superposed by further tectonic events in the middle triassic regional extension led to a reconfiguration of the southern part of the basin where new nne ssw trending troughs rheinsberg and gifhorn troughs developed in the jurassic the northwestern part of the basin was uplifted while in the south the keuper subsiding areas continued to sink and nw se trending depressions related to salt margins became important differentiation continued into cretaceous times when regional compression caused uplift of the southeastern part of the basin and basin margins a final subsidence phase occurred in the cenozoic this was accompanied by intensive salt movement recent basin configuration reflects the superposition of structural elements resulting from different evolution stages the main structural characteristics of the basin are 1 a vertical tectonic zonation in a pre zechstein succession which lacks significant internal structures and a strongly deformed post zechstein succession which was decoupled due to the thick zechstein salt and 2 a marked asymmetry of the basin with a shallow northern slope and a steep bounding fault at the southern margin elbe fault system the northwestern part of the basin shows the structural properties of an intracratonic sag basin with persisting subsidence and with minor salt mobilisation in contrast initial structures in the southeastern part are strongly overprinted by younger tectonic events including middle triassic to jurassic extension late cretaceous inversion and late to post cretaceous salt movements tectonic elements that deform the whole sedimentary succession are restricted to the basin s southern eastern and northeastern margins where salt thickness decreases combined volumetric and backstripping investigations show that 2 3 of the total subsidence was induced by the sediment load and 1 3 was caused by tectonics the tectonic subsidence history varies laterally across the basin while tectonic subsidence curves in the northwestern part of the basin show fast subsidence during the permian and early triassic decreasing exponentially with time subsidence curves in the southeastern part indicate repeated tectonic activity however the tectonic subsidence volume created during permian to late triassic is significantly higher than the tectonic subsidence during younger phases of basin history

basement control in the development of the early cretaceous west and central african rift system abstract the structural framework of the precambrian basement of the west and central african rift system wcars is described in order to examine the role of ancient structures in the development of this early cretaceous rift system basement structures are represented in the region by large pan african mobile belts built at ca 600 ma surrounding the 2 ga west african congo and sao francisco cratons except for the small gao trough eastern mali located near the contact nappe of the pan african iforas suture zone along the edge of the west african craton the entire wcars is located within the internal domains of the pan african mobile belts within these domains two main structural features occur as the main basement control of the wcars 1 an extensive network of near vertical shear zones which trend north south through the congo brazil nigeria niger and algeria and roughly east west through northeastern brazil and central africa the shear zones correspond to intra continental strike slip faults which accompanied the oblique collision between the west african congo and sao francisco cratons during the late proterozoic 2 a steep metamorphic nw se trending belt which corresponds to a pre pan african ca 730 ma ophiolitic suture zone along the eastern edge of the trans saharian mobile belt the post pan african magmatic and tectonic evolution of the basement is also described in order to examine the state of the lithosphere prior to the break up which occurred in the earliest cretaceous after the pan african thermo tectonic event the basement of the wcars experienced a long period of intra plate magmatic activity this widespread magmatism in part relates to the activity of intra plate hotspots which have controlled relative uplift subsidence and occasionally block faulting during the paleozoic and the early mesozoic this tectonic activity was restricted to west of the hoggar west of air and northern cameroon during the late jurassic early cretaceous the st helena mantle plume may have had an important effect in weakening the lithosphere across a broad zone from brazil to sudan however causes of extension and stretching are likely to be found in a plate tectonic framework at that time the opening of both the indian and atlantic oceans were the dominant forces which favoured the development of the wcars and its propagation by strike slip movements and extensional displacements along pre existing pan african lithospheric zones of weakness

the role of debris flow on total denudation in small basins of the ashio mountains japan abstract total and continuing denudation rates were estimated using cosmogenic nuclides and intensive field observations of sediment transport in two small basins c3 and s3 from the ashio mountains japan the c3 basin underlain by triassic bedded chert while the s3 basin has evolved in altered jurassic sandstone shale continuing denudation rates were estimated from the records of coarse sediment transport and stream discharge for 6 years 2004 2009 soil grain size distribution and dissolved load in stream water a debris flow was observed and the volume was measured in c3 chert concentrations of cosmogenic 10be and 26al in fluvial sand were measured to determine spatially averaged total denudation rates for these basins on the basis of steady state assumption continuing denudation rate for c3 chert basin excluding the debris flow mass accounted for 75 of the total denudation rate as measured from the cosmogenic nuclides assuming a difference between the total and continuing denudation rates indicates the impact of repeat debris flows the debris flows with the observed magnitude the mass of 24 t occur with the recurrence intervals of 100 550 years mean 167 years for c3 chert basin for s3 sandstone basin the continuous denudation rates were significantly smaller than the total rates where debris flow had not occurred for at least 17 years the large gap in the denudation rates with different time scales shows contribution of higher magnitude debris flow events with longer recurrence intervals

on wind wave current interactions during the shoaling waves experiment 1 this paper presents a case study of wind wave current interaction during the shoaling waves experiment showex surface current fields off duck north carolina were measured by a high frequency ocean surface current radar oscr wind wind stress and directional wave data were obtained from several air sea interaction spar asis buoys moored in the oscr scanning domain at several times during the experiment significant coastal currents entered the experimental area high horizontal shears at the current edge resulted in the waves at the peak of wind sea spectra but not those in the higher frequency equilibrium range being shifted away from the mean wind direction this led to a significant turning of the wind stress vector away from the mean wind direction the interactions presented here have important applications in radar remote sensing and are discussed in the context of recent radar imaging models of the ocean surface

effect of large eddies on atmospheric surface layer turbulence and the underlying wave field to improve existing models for air sea interaction a better understanding of the energy transfer across the boundary layer and in particular of the coupling of large atmospheric eddies with the air sea interface is needed recent investigations have already shown a possible coupling of large structures in atmospheric turbulence and surface ripples this was done using synthetic aperture radar sar imagery of ocean surface and almost simultaneous advanced very high resolution radiometer avhrr imagery of cloud streets at a cold air outbreak the intent of our study is to further validate this hypothesis in a general case of coastal circulation for this purpose we analyze a suite of collocated simultaneous records of airflow radar return and surface elevations from a coastal platform we investigate the influence of large eddies 20 60 min on the turbulent properties of the airflow in the first 2 m above the ocean surface the analysis shows very prominent peaks in the magnitude of 12 to 16 min fluctuations which are further modulated in 20 to 40 min intervals these scales and modulations are characteristic for all variables of interest here the detected scales and their modulation suggest significant interaction of surface layer within the first 1 2 m with large eddies of scales of o 1 and o 10 km the intermittent structure of turbulence responds by alternating contributions from bursts and sweeps the frequency of occurrence of bursts and sweeps also reveals the influence of large structures the instantaneous cross correlation between the shorter scales of momentum flux and radar return corresponding to the individual burst events can be 4 times as strong as the overall cross correlation

directional attributes of the ocean surface wind stress vector in a recent paper by geernaert 1988 it was suggested that the stress and wind vectors are rarely aligned and that the deviation of the stress vector direction from the wind vector is related to the surface heat flux it was argued that since cold air advection over the open ocean generally corresponds to upward heat flux the consequent rotation of the winds to the right with height during cold air advection could be responsible for observations of the stress vector to be to the right of the wind flow for unstable stratifications conversely observations of the stress vector to the left of the flow for stable stratifications were suggested to be associated with the turning of the wind vector to the left of the flow for warm air advection or downward heat flux in that study only 30 of the statistical variance of the angle between the wind and wind stress vectors could be explained by air sea heat flux and it was suggested that the orbital velocity spectrum of surface waves i e data unavailable in that study could be important for explaining at least part of the remaining variance in this study we report on measurements of the wind stress vector and wave directional spectrum collected during the synthetic aperture radar x band ocean nonlinearities experiment conducted on the chesapeake light tower during 1988 the experiment yielded data reported herein that provide convincing evidence that the stress vector direction during light winds and near zero air sea heat flux is governed in large part by the direction of long waves on the ocean surface further the measurements suggest that the stress vector has a direction which is a blend between the wind direction and the swell direction

momentum transfer over the coastal zone spatial variations of surface stress over the coastal shoaling zone are studied offshore of duck north carolina by the longez research aircraft equipped to measure both atmospheric turbulence and oceanic waves we find that the spatial variation of the friction velocity with offshore distance is much larger with offshore flow than with onshore flow in general the mean square slope of the short waves wavelength shorter than 2 m decreases with offshore distance while the mean square slope of the long waves wavelength longer than 2 m increases with offshore distance with onshore flow the friction velocity is strongly correlated with surface waves in addition the variation of the neutral drag coefficient is well correlated with the atmospheric bulk richardson number with offshore flow the observed momentum flux significantly decreases with offshore distance within the first few kilometer offshore the relationship between the friction velocity and the mean square slope of the short waves and the relationship between the neutral drag coefficient and the atmospheric bulk richardson number are obscured by the direct influence of the upstream land surface on the measured turbulence these relationships for offshore flow agree well with those for onshore flow if the fetch is beyond the immediate influence of the land surface the results in this study suggests that the effects of the strong turbulence advected from over the nearby land surface in offshore flow may lead to ambiguous physical interpretation of the correlation between the momentum flux and the wave state

compactional behavior of fine grained sediments examples from deep sea drilling project cores laboratory experiments statistical analysis of field data and theoretical models are combined in the attempt to derive standard compaction curves for various deep sea sediments which are in compaction equilibrium with the overburden a revised and generalized version of athy s law together with laboratory experiments allows the classification of sediments in terms of the amount of porewater structurally bound to the particles surfaces especially suction pressure experiments are useful in quantifying the forces that bind water on the particle surfaces the sediments analyzed almost range from systems of suspended grains to nearly perfect colloidal systems the methods and equations required to derive the relevant parameters are given for both downhole porosity density measurements and laboratory experiments

3d lithosphere scale density model of the central european basin system and adjacent areas abstract to analyze the first order structural features characterizing the crust and the lithospheric mantle below the central european basin system and adjacent areas a new lithosphere scale 3d structural density model has been derived that integrates published knowledge with 3d gravity modeling with this study we aim to integrate previous results on sub domains of the study area and regional results of limited resolution in conjunction with 3d gravity analysis to derive the configuration of the lower crust and lithospheric mantle that is consistent with the known density distribution of the sediment fill and with observed deep seismic data as well as with observed gravity the derived 3d density model resolves the internal configuration of the crystalline crust below the central european basin system and adjacent areas at the regional scale and shows that the crystalline crust is characterized by a layered structure the upper to middle crystalline crust is characterized by relatively low seismic p wave velocities and densities it shows strong variations in thickness across the study area that partly correlate spatially with the inherited segmentation in response to crustal amalgamation this upper to middle crystalline crust is underlain by a continuous high density high velocity lower crustal layer locally more than 30 km thick beneath the east european craton and generally decreasing in thickness from the older to the younger tectonic domains though the thickness of this high density lower crust is generally small below the permo cenozoic central european basin system it can reach locally more than 18 km below the northeast german and the norwegian danish basins the derived depth to the lithosphere asthenosphere boundary confirms previously proposed geometries and is up to 230 km deep beneath the precambrian domain but less than 100 km deep beneath the phanerozoic domains implying that the average thermal gradient is higher in the phanerozoic lithosphere than in the precambrian part

density contrasts in the upper mantle and lower crust across the continent ocean transition constraints from 3 d gravity modelling at the norwegian margin summary 3 d gravity models that consider the highly complex density structure of the norwegian passive volcanic continental margin require a significantly lower density in the mantle below the ocean than below the continent this is especially pronounced on the crust free residual gravity anomalies obtained by 3 d gravity stripping this density contrast in the mantle indicates different physical properties either related to thermal or compositional conditions beneath the two domains we assess the gravity response of thermal differences and find that a hotter oceanic mantle compared to a colder continental mantle could cause the density contrast accordingly 3 d lithospheric scale gravity models considering temperature dependent mantle densities indicate that the transition between continental and oceanic lithosphere is rather sharp with a steep gradient in thickness beneath the continent ocean transition zone furthermore a mantle wedge of reduced density extends from the oceanic jan mayen fracture zone to the continental jan mayen lineament and points to increased mantle temperatures and or compositional changes beneath the lineament the models further indicate the presence of high density bodies within the lower crust at the continent ocean transition that are continuous with the lowermost oceanic layer 3b in terms of geometry and density this supports the concept of underplated lower crust beneath the western norwegian margin finally ne sw trending linear zones of increased density are required in the lower crust beneath the eastern voring and more basins to fit the short wavelength gravity signal

role of subaerial volcanic rocks and mantle plumes in creation of south atlantic margins implications for salt tectonics and source rocks abstract seaward dipping reflectors sdrs represent flood basalts rapidly extruded during either rifting or initially subaerial sea floor spreading evaporites can form on this basaltic proto oceanic crust as in the afar triangle today evidence for sdrs in south atlantic deep water regions comes from proximity to the uniquely large parana etendeka volcanic province onshore the tristan and gough hot spots drilled volcanic rocks and seismic profiles showing sdr provinces more than 100 km wide as much as 7 km thick and thousands of kilometers long sdrs are clearest adjoining the aptian salt basins however we speculate that sdrs are also present but seismically obscured below the salt basins we argue that the conjugate aptian salt basins are post breakup not pre breakup they were separated from the start by a mid oceanic ridge distal salt accumulated on proto oceanic crust not rift basins this hypothesis is supported by seismic stratigraphy and structure magnetic anomalies plate reconstructions and hydrothermal potash evaporites an important implication for exploration is that thick basalts rather than rift age source rocks may underlie distal parts of the salt basins

character and origin of deep arenaceous weathering mantles on the bega batholith southeastern australia summary arenaceous weathering mantles on the bega batholith southeastern australia are similar to those described from europe by millot as in europe they have been formed by hydrothermal alteration of the parent rock and later by chemical weathering of biotites and feldspars but comparisons with nearby torfields shows that their distribution is determined largely by mineralogical variations in the parent rock unlike the examples cited by millot in the bega mantles kaolinite is the dominant clay mineral nonetheless these mantles seem to be contemporary not relict features and apparently formed under a temperate climate

the influence of swell on the atmospheric boundary layer under nonneutral conditions the anomalous phenomena induced by the prevailing swell at low wind speeds prevent a complete understanding of air sea interaction processes many studies have considered this complex problem but most have focused on near neutral conditions in this study the influence of the swell on the atmospheric boundary under nonneutral conditions was addressed by extending the turbulent closure models of makin and kudryavtsev and the monin obukhov similarity theory most monin and yaglom to the existence of swell and nonneutral conditions it was shown that wind profiles derived from these models were consistent with each other and both departed from the traditional most at low wind speeds a supergeostrophic jet appeared on the upper edge of the wave boundary layer which was also reported in earlier studies under nonneutral conditions the influence of buoyancy was significant the slope of the wind profile increased under stable conditions and became smoother under unstable conditions considering the effects of buoyancy and swell the wind stress derived from the model agreed quantitatively with the observations

the deep structure of the south atlantic kwanza basin insights from 3d structural and gravimetric modelling abstract we present results from 3d gravimetric modelling of the kwanza basin offshore angola accomplished to investigate the deep crustal structure beneath the basin and discuss our findings with respect to their implications for the opening of the central south atlantic the kwanza basin is located in the southern part of the central south atlantic although the post rift evolution of the kwanza basin is well studied little is known about the basin s early history this is mainly due to the missing knowledge of its crustal structure owing to the masking effect of an up to 4 km thick salt layer which seismically obscures the underlying basement to get an insight into the deeper structure of this part of the angolan margin we combined 3d structural isostatic and gravimetric modelling 2d seismic reflection data was used to determine the structural setting and the configuration of the stratigraphic units in the sedimentary part of the basin whereas its crustal structure was constrained by isostatic and gravity modelling our modelling results indicate that high density lower crustal bodies similar to ones found in the northern part of the central segment are present in the southern part and thus seem to be a general feature of the crust of the central south atlantic thinning of the crust occurs gradually rather than in an abrupt manner and block faulting seems to have played a significant role during rifting as is indicated by a strongly structured upper crust in contrast we find little evidence for ductile thinning or exhumation of the deeper lithosphere as previously suggested for the northern segment of the central south atlantic in its southern segment it appears more likely that magmatic intrusions prevented mantle exhumation by sealing crustal detachment faults and giving the margin a distinct magmatic signature

the near neutral marine atmospheric boundary layer with no surface shearing stress a case study abstract data from a marine coastal experiment over the baltic sea comprising airborne measurements and mast measurements have been used to highlight the turbulence dynamics of a case with most unusual flow characteristics the boundary layer had a depth of about 1200 m the thermal stratification was near neutral with small positive heat flux below 300 m and equally small negative heat flux above the entire situation lasted about 6 hours turbulence levels were unexpectedly high in view of the fact that momentum flux was negligible in fact positive in the layers near the surface and buoyancy flux was also small the turbulence was found to scale with the height of the boundary layer giving rise to velocity spectra having the shape of those characteristic of convectively mixed boundary layers analysis of the turbulence budget for the entire planetary boundary layer pbl revealed that energy was produced from shear instability in the uppermost parts of the pbl and was distributed to the lower par

a case study of air sea interaction during swell conditions air sea interaction data from a situation with pronounced unidirectional swell have been analyzed measurements of turbulence at three levels 10 18 and 26 m above mean sea level together with directional wave buoy data from the site ostergarnsholm in the baltic sea were used the situation which lasted for 48 hours appeared in the aftermath of a gale the wind direction during the swell situation turned slowly within a 90 sector both during the gale phase and the swell phase the over water fetch was 150 km the wind speed during the swell phase was typically 4 m s 1 during the swell phase a wind maximum near or below the lowest wind speed measuring level 10 m was observed the net momentum flux was very small resulting in cd values 0 7 10 3 throughout the lowest 26 m covered by the tower measurements turbulence intensities in all three components remained high despite the low value of the kinematic momentum flux u w resulting in a reduction of the correlation coefficient for the longitudinal and vertical velocity from its typical value around 0 35 to between 0 2 and 0 and with some positive values at the higher measuring levels appearing abruptly at wave age c0 u10 equal to 1 2 turbulence spectra of the horizontal components were shown not to scale with height above the water surface in contrast to vertical velocity spectra for which such a variation was observed in the low frequency range in addition spectral peaks in the horizontal wind spectra were found at a frequency as low as 10 3 hz from a comparison with results from a previous study it was concluded that this turbulence is of the inactive kind being brought down from the upper parts of the boundary layer by pressure transport

volcanic rock alterations of the kwanza basin offshore angola insights from an integrated petrological geochemical and numerical approach the lower cretaceous presalt section of the kwanza basin angola is in the spotlight following the discoveries of petroleum systems in this basin and more generally in the south atlantic these systems are mostly composed of continental carbonates in close association with volcanic rocks this work is focused on the study of an offshore kwanza presalt volcanic sequence characterized as valanginian trachytic subaerial lava flows a detailed petrological analysis of the altered trachyte in association with fluid inclusion microthermometry was conducted in order to depict the initial mineralogy albite sanidine titanomagnetite and obtain a paragenetic sequence quartz siderite kaolinite calcite thermodynamic equilibrium modelling of the trachytes alteration by meteoric fluids over a range of temperatures 25 c 200 c and co2 partial pressure pco2 0 01 mbar to 100 bar were performed with phreeqc and compared to the observed paragenetic sequence some numerical simulations reflect the observed paragenesis as a result the pco2 is constrained by the occurrence of siderite from 0 1 bar at 50 c to 30 bar at 125 c and kaolinite from 0 2 bar at 50 c to 1 2 bar at 125 c the simulations emphasize the need for a high pco2 in the hydrothermal system to achieve the observed trachyte transformation after reaching equilibrium with the trachytes the simulated fluids highlight a mid alkaline to near neutral ph with high fe hco3 co3 and alkali concentrations the palaeofluids could have evolved from ca and mg rich to ca and mg poor with increasing temperature inversely si concentrations are positively correlated with increasing temperatures this methodology integrating a petrological approach and numerical simulations proves to be a powerful tool leading to better understanding of the proxies pco2 temperature redox conditions controlling paragenesis to push further these simulations are also a step toward improved understanding of palaeofluid evolutions in presalt systems and better prediction of reservoir quality

stable boundary layer vertical scales in the arctic observations and analyses at ny alesund svalbard an extensive set of measurements may august 2012 and june november 2013 taken at the amundsen nobile climate change tower located at ny alesund svalbard allowed investigation of some features of the vertical structure of the atmospheric stable boundary layer sbl at high latitudes the main sensors are three sonic anemometers and four low frequency thermo hygrometers and anemometers the momentum flux the sensible heat flux q and the turbulent kinetic energy k data at different levels demonstrated the occurrence of both the traditional and upside down sbl cases according to the classification proposed in the literature based on a linear approximation of the profiles the vertical scales were found to be different for the different second order moments in the traditional case the scales h hq and hk defined as levels for which fluxes became zero can be considered to approximate the boundary layer depth while the distributions of h and hq were found to be similar having the ratio hq h equally distributed around unity although with a positive skewness those of h and hk look quite different having the ratio hk h 1 in about 90 of the cases and with a median value 2 in the upside down case the scales s sq and sk defined as the height at which the value of the considered quantity doubles that at the surface give a measure of the vertical variations of the moments comparing the distributions of these three scales similar results to those for the traditional case were found although with slightly different statistics the values of the ratio between scales affect the vertical profile of the local obukhov length in both the traditional and upside down sbl cases

margin segmentation and volcano tectonic architecture along the volcanic margin off argentina uruguay south atlantic abstract some 25 000 kilometers of regional multichannel seismic data acquired by bgr along the continental margins off argentina and uruguay document that the early cretaceous south atlantic continental breakup and initial sea floor spreading were accompanied by large scale transient volcanism emplacing voluminous extrusives manifested in the seismic data by huge wedges of seaward dipping reflectors sdrs the emplacement of the deeply buried 60 120 km wide sdrs was probably episodic as documented by at least three superimposed sdrs units distinct along margin variations in architecture volume and width of the sdrs wedges are probably related to margin segmentation it is suggested that the margin can be divided at least in four compartments bounded by the falkland fracture zone falkland transfer the colorado transfer the ventana transfer and the salado transfer the individual margin segments reflect in the distribution and thickness of the post rift sediments the individual transfer zones may have acted as rift propagation barriers selectively directing rift segments in left stepping patterns along the western south atlantic margin although we found extensive variations in the architecture style and extent of the seaward dipping reflector sequences a general trend is that the largest volumes are emplaced close to the proposed transfer zones and the width of the sdrs wedges decreases northward within the individual margin segments we suggest that mainly adiabatic decompression and melt generation from shallow sources can explain distinct along margin variations in the volcano tectonic architecture and volumes of extruded magmas

deep structures and breakup along volcanic rifted margins insights from integrated studies along the outer voring basin norway three dimensional multichannel seismic survey and well data allows a deeper insight into rifting mechanisms and crustal structure of the norwegian volcanic rifted margin a surprising high velocity lower crustal dome marked by a strong amplitude reflection t reflection is described below the north gjallar ridge ngr near the volcanic plateau formed during the late paleocene early eocene breakup faulting along the ngr occurs during early campanian paleocene and is controlled by the crustal dome the t reflection was previously related to either the top of mafic underplated crust or soft lower crust updomed during the continental breakup the influence and timing of the crustal dome on the basin structure shows clearly that the dome predates the continental breakup based on the structural relationship and the results of the modelling it is therefore concluded that the t reflection does not necessarily originate from an anomalous tertiary magmatic event related to the breakup underplated material but could be also partly attributed to pre breakup mafic material or and inherited high pressure granulite eclogite rocks in the continental domain q 2004 elsevier ltd all rights reserved

a case study of two dimensional stratified turbulence data from a period with intensive measurements in the lowest 1000 m of a marine atmosphere over the baltic sea with strongly stable stratification and a turbulent boundary layer less than 50 m deep

observational study of marine atmospheric boundary layer characteristics during swell abstract by combining simultaneous data from an instrumented air sea interaction spar asis buoy and a 30 m tower profiles of wind and turbulence characteristics have been obtained at several heights from about 1 to 30 m above the water surface during swell conditions five cases formed as averages over time periods ranging from 2 5 to 9 5 h representing quasi steady conditions have been selected they represent a range of typical wave age and include wind following swell cases and cross swell cases for relatively large wave age the wind profile exhibits a well defined maximum in the height range 5 10 m for more modest wave age this maximum turns into a sharp knee in the wind profile below the maximum or knee the wind increases rapidly with height above that point the wind is very nearly constant up to the highest measuring level on the tower 30 m analysis of balloon data from one day with swell indicates that the layer with constant wind in fact extends to the top of the boundary layer

wave induced wind in the marine boundary layer recent field observations and large eddy simulations have shown that the impact of fast swell on the marine atmospheric boundary layer mabl might be stronger than previously assumed for low to moderate winds blowing in the same direction as the waves swell propagates faster than the mean wind the momentum flux above the sea surface will then have two major components the turbulent shear stress directed downward and the swell induced stress directed upward for sufficiently high wave age values the wave induced component becomes increasingly dominant and the total momentum flux will be directed into the atmosphere recent field measurements have shown that this upward momentum transfer from the ocean into the atmosphere has a considerable impact on the surface layer flow dynamics and on the turbulence structure of the overall mabl the vertical wind profile will no longer exhibit a logarithmic shape because an acceleration of the airflow near the surface will take place generating a low level wave driven wind maximum a wind jet as waves propagate away from their generation area as swell some of the wave momentum will be returned to the atmosphere in the form of wave driven winds a model that qualitatively reproduces the wave following atmospheric flow and the wave generated wind maximum as seen from measurements is proposed the model assumes a stationary momentum and turbulent kinetic energy balance and uses the dampening of the waves at the surface to describe the momentum flux from the waves to the atmosphere in this study simultaneous observations of wind profiles turbulent fluxes and wave spectra during swell events are presented and compared with the model in the absence of an established model for the linear damping ratio during swell conditions the model is combined with observations to estimate the wave damping for the cases in which the observations showed a pronounced swell signal and almost no wind waves the agreement between observed and modeled wind profiles is remarkably good the resulting attenuation length is found to be relatively short which suggests that the estimated damping ratios are too large the authors attribute this at least partly to processes not accounted for by the model such as the existence of an atmospheric background wind in the model this extra momentum must be supplied by the waves in terms of a larger damping ratio

evaluation of a roughness length model and sea surface properties with data from the baltic sea abstract the exchange of momentum between the oceans and atmosphere is important for many atmospheric and oceanic processes and is mainly governed by the roughness of sea surface the roughness can be expressed by a roughness length z0 a roughness length model based on the concept that z0 is determined by stochastic wave breaking is presented the model performance is evaluated using measurements from the ostergarnsholm site in the baltic sea and pertinent information from other recent investigations the wave field and the roughness length variations are investigated during various sea state conditions dominated by wind driven waves it is found that several parameters describing the characteristics of the wave field are dependent on the amount of energy that long waves have relative to the energy of short wind driven waves of the sea spectrum called the swell ratio the impact of swell ratio on z0 can explain the discrepancies found in various results among relevant investigations the roughne

crustal scale architecture and segmentation of the argentine margin and its conjugate off south africa summary integration of regional seismic reflection and refraction profiles and potential field data across the argentine margin and its conjugate off south africa complemented by crustal scale gravity modelling is used to reveal and illustrate the whole crust architecture onshore offshore crustal structure correlations the character of the continent ocean boundary transition and the relationship of crustal structure to regional variation of potential field anomalies the study reveals within these two provinces distinct along margin structural and magmatic changes that are spatially related to a number of conjugate transfer systems governing the margin segmentation and evolution clearly implying structural inheritance in particular the colorado transfer system on the argentina margin marks a distinct along margin boundary in the distribution and volume of breakup related magmatism similarly the hope transfer system on the conjugate south africa margin also marks a distinct along margin transition from a zone of relative magnetic quiescence to a zone of prominent magnetic anomalies furthermore the study indicates that the g magnetic anomaly along the south africa margin probably defines the eastern limit of the continent ocean transition cot rather than a discrete continent ocean boundary cob potential field plate reconstructions of the south atlantic suggest conjugate margin asymmetry characterized by a rather broad argentine margin conjugate to a narrow south africa margin in detail the argentine margin is characterized by a sharp and relatively constant cot whereas the cot along the conjugate south africa margin is considerably wider an along strike tectonomagmatic asymmetry variation is also observed and is expressed by the northward increase in width of the cot on the south african margin the study clearly shows that integration of regional seismic reflection and refraction profiles potential field data and gravity modelling provide a powerful resource for testing and validating alternative seismic profile structural interpretations and plate tectonic reconstructions as well as geodynamic models for lithospheric breakup and early drift

diversity and origin of quartz cements in continental carbonates example from the lower cretaceous rift deposits of the south atlantic margin abstract silica precipitation in continental carbonates is a common process occurring during sedimentation and diagenesis the lower cretaceous rift deposits of the south atlantic equatorial margin which are intensively explored by petroleum companies provide good examples of such silicifications in carbonates exhibiting a wide diversity of petrographic habit of early to late quartz cements in order to understand the palaeoenvironmental and diagenetic conditions leading to this diversity we integrated detailed petrography of diagenetic sequences and quartz habit with 18oquartz measurements by sims of individual cements observed in samples from the offshore and onshore basins of the west african margin the petrographic description highlights the omnipresence of early fibrous microquartz cements exhibiting either length fast or length slow habit in addition to laminated microquartz and micro or mega quartz forms amongst the isotopic analysis the 18oquartz data show that length slow cements are generally strongly enriched in 18o 18oquartz ranging from 31 to 37 smow whereas length fast forms show less elevated values 25 c and

observations of summer turbulent surface fluxes in a high arctic fjord the summer atmospheric boundary layer over a fjord in the high arctic has been investigated during three consecutive years 2008 2010 measurements of turbulent surface layer fluxes of momentum and sensible heat using a sonic anemometer and slow response instruments were taken from a tower on the coast of isfjorden svalbard and analysed for seasonal variability and differing fetch conditions the results resembled the atmospheric boundary layer characteristics previously found for ice free winter conditions the momentum flux was usually directed downwards but for low wind speeds there was a possible contribution of swell giving an upward directed momentum flux the cross wind component of the momentum flux sometimes contributed significantly to the total flux the sensible heat flux was very dependent on the origin of air whether it had a long over water fetch or originated from land areas with or without glaciers in addition to non stationarity of the flow due to the influence of the fjord s shape and its surrounding topography low wind speeds questioned the validity of the monin obukhov similarity theory whereas the over water fetch and off wind angle were of minor importance moreover some results especially the off wind angle were very sensitive to how the raw data were treated in particular which coordinate rotation method was employed the double rotation or the planar fit method

a mechanism to thin the continental lithosphere at magma poor margins crustal thinning where continental plates break apart can be accomplished by a system of conjugate concave downward faults instead of multiple normal faults through exhumation of mid crustal and mantle material where continental plates break apart slip along multiple normal faults provides the required space for the earth s crust to thin and subside1 after initial rifting however the displacement on normal faults observed at the sea floor seems not to match the inferred extension2 here we show that crustal thinning can be accomplished in such extensional environments by a system of conjugate concave downward faults instead of multiple normal faults our model predicts that these concave faults accumulate large amounts of extension and form a very thin crust 10 km by exhumation of mid crustal and mantle material this transitional crust is capped by sub horizontal detachment surfaces over distances exceeding 100 km with little visible deformation our rift model is based on numerical experiments constrained by geological and geophysical observations from the alpine tethys and iberia newfoundland margins3 4 5 6 7 8 9 furthermore we suggest that the observed transition from broadly distributed and symmetric extension to localized and asymmetric rifting is directly controlled by the existence of a strong gabbroic lower crust the presence of such lower crustal gabbros is well constrained for the alpine tethys system4 9 initial decoupling of upper crustal deformation from lower crustal and mantle deformation by progressive weakening of the middle crust is an essential requirement to reproduce the observed rift evolution this is achieved in our models by the formation of weak ductile shear zones

lithological effects in soil formation and soil slips on weathering limited slopes underlain by granitic bedrocks in japan abstract soil slips occur every few years due to heavy rains on biotite granite gb and hornblende biotite granite ghb slopes in the taga mountains ibaraki prefecture japan the occurrence density of soil slips per unit area is 2 7 times greater in the gb slopes than that in ghb slopes we examined the chemical mineral physical and mechanical properties of two soil profiles on soil slip scars in these slopes to study the effect of bedrock mineral composition on the density of soil slips for a given size of mineral grain the amount of biotite which is susceptible to chemical weathering in granitic bedrocks strongly influenced the density of soil slips in the gb slope the soil layer becomes thinner because of the smaller proportion of biotite in the bedrock this restricts the downward movement of soil water into the material below the slip plane during heavy rainfall the water surface then rises toward the slope surface above the slip plane this promotes soil slips increasing the density of soil slip scars in contrast in the ghb slope with more biotite in the bedrock the soil layer becomes thicker so that soil water moves easily into the material beneath the slip plane this limits the rise of water surface toward the slope surface above the slip plane even during heavy rainfalls there are consequently fewer soil slips and density of soil slip scars

deep structure of the west african continental margin congo zaire angola between 5 s and 8 s from reflection refraction seismics and gravity data summary the deep structure of the west african continental margin between 5 s and 8 s was investigated using vertical reflection and wide angle reflection refraction techniques during the zaiango project a joint programme conducted in 2000 april by ifremer and totalfinaelf to penetrate below the salt layer a non conventional low frequency seismic source was used in the single bubble mode together with ocean bottom instruments hydrophones and seismometers and a 4 5 km long streamer that recorded multichannel seismic reflection mcs the data show that the continental crust thins abruptly over a lateral distance of less than 50 km from 30 km thick below the continental platform based on gravity data to less than 4 km thick below the lower congo basin that formed prior to the aptian salt deposition this subsalt sedimentary basin 180 km wide 4 km thick with velocities varying from 4 7 km s 1 to 5 8 km s 1 at the bottom is located between the foot of the continental slope and the oceanic domain it is underlain by crust of an intermediary or transitional type between continental crust and what can be recognized as oceanic crust in the transitional zone a crustal upper layer is present below the pre salt sedimentary basin 3 to 7 km thick with velocities increasing from 5 8 km s 1 at the top to 6 8 km s 1 at the bottom of the layer this layer appears to thin regularly from 6 7 km thick below the depocentre of the pre salt sedimentary basin to 3 4 km thick below the western termination of the basin below this upper crustal layer an anomalous velocity layer 7 2 to 7 8 km s 1 is documented below the eastern side of the basin where the crustal thinning is at a maximum the origin of this layer is unknown several arguments like rifting duration between 15 ma and 30 ma or the absence of seaward dipping reflectors precludes the hypothesis of underplated mantle material but other hypotheses such as serpentinized material or high grade metamorphic crustal rocks or a mixture of mafic and ultramafic crustal rocks are plausible near the ocean termination of the basin the transitional zone is bounded to the west by a basement ridge that is clearly documented on two profiles 7 11 and 14 having a dense ocean bottom seismometer hydrophone obs obh spacing on these profiles an anomalous velocity layer is present in the westernmost part of the transitional zone below the basement ridge and in the oceanic domain this layer absent on profile 3 may be related either to oceanization and slow seafloor spreading processes or to a consequence of the rifting process

estimation of wind friction velocity and direction at the ocean surface from physical models and space borne radar scatterometer measurements this paper presents a new technique for estimating the wind friction velocity at the ocean surface from c band radar scatterometer measurements this technique uses physical models of ocean surface waves and electromagnetic backscattering from a rough surface at intermediate angles of incidence to generate predictions of the normalized radar cross section nrcs or 0 of the ocean surface for a given wind friction velocity and observational geometry the ocean spectral model used in this technique has been developed specifically for this application it combines in situ wave measurements at low wave numbers with the phillips 1985 equilibrium spectral model this choice of ocean wave model is supported by a set of open ocean wave measurements summarized in this paper a suite of models derived from both in situ and remote measurements of the sea surface is used to characterize the directional spreading of ocean waves relative to the wind direction the resulting two dimensional ocean wave spectra are used with a composite surface model to predict radar backscattering from the ocean surface at c band these radar cross section predictions are combined with ers 1 scatterometer measurements in a cost function minimization scheme to yield estimates of the friction velocity vector at the ocean surface we present examples of this technique and compare friction velocity retrievals obtained via this scheme with buoy based measurements under a variety of wind and wave conditions on the basis of the analysis of a limited number of cases this technique yielded friction velocity estimates for which the magnitude was within 22 and the direction was within 25 given that scientific applications require magnitude estimates within 10 15 and directional estimates within 20 of in situ measurements these preliminary results suggest that this is a promising approach to wind retrieval

observed directional characteristics of the wind wind stress and surface waves on the open ocean sonic anemometer data were taken during the surface waves processes program swapp in march 1990 in the north pacific measurements of the wind stress vector span several strong wind events significant angles between the wind stress vector and the mean wind vector are seen simultaneous measurements of the directional wave field were made with a surface scanning doppler sonar the data suggest that the wind stress direction is influenced by the direction of the surface waves especially for stronger winds overall the stress vector lies between the mean wind and the mean wave directions at the higher wind speeds over 8 6 m s there is a nonzero correlation between the variations in wave directions and stress directions as well finally the stress and wave component directions have similar frequency dependence over the frequency band where wave energy is nonnegligible suggesting a dynamic link

weathering of granites in a temperate climate nw portugal granitic saprolites and arenization abstract saprolites or in situ weathering products from granitoid rocks of northwest portugal were studied by means of x ray diffraction xrd of their clay fraction and observations of polished thin sections combined with transmission electron microscopy tem scanning electron microscopy with energy dispersive spectrometer sem eds microanalyses their principal features are 1 depths of more than 10 m 2 mean material loss of 40 as calculated by an isovolumetric method 3 low clay content mean value of 7 and a high degree of mineralogical evolution the clay fraction is characterized by a predominance of kaolinite and gibbsite with subordinate 2 1 minerals illite chlorite vermiculitic mixed layers vermiculite the significance of the secondary minerals in granitic saprolites from northwest portugal is compared to published data from atlantic europe this allows the definition of a climatic zonality for weathering products and identifies arenization as an important weathering process

the influence of oblique waves on the azimuthal response of a ku band scatterometer a laboratory study the authors conducted experiments in the large wind wave tank at irphe to examine the influence of longer waves propagating at oblique angles to the wind direction on microwave backscattering measurements were made of wind wave directional spectra and cross sections from a 13 5 ghz scatterometer at 30 spl deg from nadir incidence angle the authors characterize the scatterometric azimuthal scans with respect to the magnitude and the direction of the maximum backscattered power scans of solely wind waves are used to assess the effects of oblique waves for which the scans yield trends that are related to the oblique wave direction relative to the wind and the oblique wave steepness in particular cross section maxima are enhanced by oblique waves and the direction of maxima rotates from the wind axis toward the oblique wave direction these scatterometer data in addition to other oblique wave studies led the authors to conclude that wind vectors produced from standard retrieval algorithms for scatterometers should be used with prudence in regions with significant veering winds such as near meteorological fronts

the great west african tertiary coastal uplift fact or fiction a perspective from the angolan divergent margin 1 we explore exhumation in the coastal kwanza basin by combining analyses of tertiary hiatuses and apatite fission tracks planktonic biozones show five major hiatuses in the oligo miocene and plio pleistocene between gaps oligo miocene strata accumulated under marine conditions a marine setting refutes the idea of a massively raised coastal plateau in the mid tertiary marine conditions continued until 5 ma fission track data suggest three thermal events 150 ma during rifting and volcanism 100 70 ma during shortening and volcanism and 20 10 ma during exhumation tertiary uplift was spatially highly variable for the kwanza basin we infer that tertiary uplift on the west african margin is indeed a fact but that estimates of uplift timing and size are unreliable when extrapolated to adjoining areas massive uplift 2000 4000 m of the precambrian craton had little structural effect in the outer basin instead minor uplifts on the shelf drove late tertiary deformation on the slope

modelling the vertical structure of the atmospheric boundary layer over arctic fjords in svalbard the vertical structure of the atmospheric boundary layer abl simulated with the mesoscale model weather research and forecasting wrf as well as with its polar optimized version polar wrf was compared to tethered balloon soundings and mast observations taken in march and april 2009 from two arctic fjords in svalbard from twelve short 48 h simulations the quasi normal scale elimination scheme for the abl and the noah land surface scheme for the surface were found to perform best and were selected for one long 16 day simulation the differences in performance of the standard wrf and polar wrf were marginal a warm bias especially near the surface was found in the modelled temperature profiles related to underestimated temperature inversion strength and depth the modelled humidity inversions were generally deeper but weaker than the observed and often occurred independently of temperature inversions the largest errors in temperature and humidity occurred under high pressure conditions multiple temperature and humidity inversions were usually not captured by wrf compared to the compact sea ice east of svalbard the modelled temperature and humidity inversions were weaker and less frequent over the fjords the biases in modelled wind speed profiles were closely related to low level jets lljs the modelled lljs were stronger and deeper and typically located at higher altitudes than the observed lljs errors in the near surface variables were notably reduced by applying post processing equations based on other modelled variables copyright 2012 royal meteorological society

use of conventional stability parameters during swell the situation with swell is of climatological importance over the baltic sea since swell is present during as much as 40 of the time in this study two periods with unstable and two periods with stable stratification and wind following swell are investigated data are taken at a small flat island in the baltic sea during unstable stratification the turbulent structure shows great resemblance to the free convective boundary layer and scales with the boundary layer height since surface heat flux is too small to support the high levels of turbulence present inactive turbulence is probably the dominating source for the stably stratified layer there are smaller differences between data with and without swell the turbulence is mainly transported upward into the atmosphere with the aid of pressure fluctuations induced by the waves for most of the data with swell the gradients are smaller than for growing sea during unstable conditions the wind gradients are negative indicating the presence of a wave driven wind the gradients increase with increasing height above the surface the drag coefficient is smaller than is usually found for both stable and unstable stratification and varies very little with wind and stratification there are only small variations in the heat transfer coefficients with changing stratification but they are significantly different for stable and unstable stratification

structural segmentation inversion and salt tectonics on a passive margin evolution of the inner kwanza basin angola the kwanza basin angola is divided into the inner and outer kwanza salt basins separated by a chain of synrift basement highs on which aptian 112 122 ma salt is thin or absent north to northwest trending basement structures in the inner kwanza basin have repeatedly been reactivated since neocomian 144 127 ma rifting reactivation formed three northwest striking fold and thrust belts near basement uplifts the thrust belts are bounded by northeast striking rift related transfer fault zones that were apparently reactivated during subsequent shortening three episodes of postrift basement involved shortening are documented in the inner kwanza basin 1 albian early cenomanian 112 96 ma 2 senonian 89 65 ma and 3 oligocene holocene 34 0 ma we relate the albian early cenomanian event to ridge push the senonian event to global plate reorganization and oligocene holocene shortening to uplift of the african superswell structural segmentation of the inner kwanza basin controlled the evolution of salt structures adjacent to basement uplifts diapirs were initiated as buckle folds some anticlines were unroofed by erosion and evolved into passive salt walls elsewhere broad salt walls were triggered by either detached extension or basement block uplift these walls grew until they exhausted their supply of salt thereafter dissolution rates exceeded rates of salt inflow so the walls began to subside withdrawal of salt from the walls produced the elongate sedimentary troughs for which the basin is famous trough fill ranges in age from cenomanian to pliocene and this age varies greatly from trough to trough and along strike within troughs

grus weathering mantles problems of interpretation abstract grus is an ill defined product of deep weathering of coarse grained rocks whose relationships to other weathering changes remain unclear this paper attempts to address this issue by reviewing a number of examples of coarse saprolites from a variety of climatic and topographic settings grus is the category of weathering mantle that possesses the following characteristics sand gravel 75 100 silt clay

physical and logistical considerations of using ultrasonic anemometers in aeolian sediment transport research abstract recently ultrasonic anemometers uas have become available for precise high frequency measurement of three dimensional velocity and turbulence properties except for a few wind tunnel and computational fluid dynamics cfd simulations advances in aeolian sediment transport and bedform research have been limited to field studies using instrumentation that is either incapable of measuring turbulence e g cup anemometers or unable to withstand sediment laden airflow e g hotfilms in contrast extensive progress has occurred in fluvial research where turbulence instrumentation has been available for some time this paper provides a pragmatic discussion on using uas in aeolian research recent advances using this technology are reviewed and key physical and logistical considerations for measuring airflow properties and near surface shear stress using uas over complex terrain are discussed physical considerations include limitations of applying boundary layer theory to flow over natural surfaces such as non logarithmic velocity profiles resulting from roughness and topographically induced effects and the inability of instrumentation to measure within the thin constant stress region these constraints hinder accurate shear velocity u shear stress and sand transport estimation uas allow measurement of turbulent reynolds stress rs that in theory should equal profile derived shear stress discrepancies often exist between these quantities however due to three dimensional spanwise flow components and rapid distortion effects i e unbalanced production and dissipation of turbulence common in flow over complex terrain while the rs approach yields information on turbulent contributions to near surface stress generation little evidence exists showing that rs is a better measure of forces responsible for sediment transport consequently predictive equations for sediment transport using rs do not exist there is also a need to identify the role of micro turbulent events e g burst sweep cycles and macro turbulent structures e g separation cells shear layers in aeolian dynamics in field settings to validate recent wind tunnel and cfd simulations a conundrum exists regarding whether velocity data should be rotated to correct for potential sensor misalignment effects in unsteady non uniform flow over complex terrain streamline angles vary spatially and temporally with height and location thus determination of and correction to true streamline coordinates is difficult caution should be exercised with correction methods that remove implicit vertical velocity trends as this may preclude detection of geomorphically important flow behaviour e g lift at a dune crest and may complicate interpretations of rs instruments should be aligned with the underlying surface and flow visualization should be used to adjust sensor measurement planes as close as possible to local streamlines logistical considerations include sensor design advantages and operational limitations data communication formats and field deployment strategies each can affect measurement accuracy and are easily overlooked sampling range frequency and period are also important as they limit the range of velocities and scales of turbulence that can be characterized ultrasonic anemometers offer a new sampling resolution to measure turbulent airflow properties in field settings with proper considerations of their limitations uas may allow researchers to close the gap between fluvial research and develop more robust models of aeolian processes and morphodynamics

swell impact on wind stress and atmospheric mixing in a regional coupled atmosphere wave model over the ocean the atmospheric turbulence can be significantly affected by swell waves change in the atmospheric turbulence affects the wind stress and atmospheric mixing over swell waves in thi

complex rifted continental margins explained by dynamical models of depth dependent lithospheric extension observations from a number of rifted margins e g south atlantic salt basin mid norwegian margin exmouth plateau reveal wide regions of extremely attenuated crust and depositional environments that indicate depth dependent lithospheric extension although the one dimensional thermal kinematic consequences of depth dependent extension are understood no comprehensive process based explanation for the complex style of these margins exists here we present self consistent numerical models of passive margin formation that explain the depth dependent extension the width of the margin its characteristic tripartite nature and why such margins are prone to deposition of evaporites under appropriate climatic conditions some features that are important to reproducing the observed characteristics include decoupling between upper and lower parts of the lithosphere during stretching contrasting wide and narrow extensional styles above and below the decoupling level and progressive focusing of crustal extension toward the rift axis

soil slips on weathering limited slopes underlain by coarse grained granite or fine grained gneiss near seoul republic of korea abstract the chemical mineral physical and mechanical properties of two soil layers on soil slip scars in slopes underlain by coarse grained granite and fine grained granitic gneiss near seoul republic of korea were examined our aim is to study the effect of the mineral grain size of the bedrock on the soil layer structure and the return period of shallow soil slips because of the coarser slope materials in granite resulting from weathering the permeability is larger and the weathering front has a copious water supply also because of the smaller specific surface area of the minerals restricted leaching produces grus from the bedrock so that the rate of formation of soil and in particular the slip plane due to chemical weathering is faster since on granite slopes the leaching proceeds toward the surface the sliding plane is deeper with coarser soft grus resulting in the existence of a minimum c value in the soil layer on gneiss slopes by contrast leaching cannot proceed with decreasing soil depth and the sliding plane is deeper with finer soft grus just above hard grus and has similar c and values as the upper soft grus because the grain size of both soils is the same in the granite soil layers the sliding plane corresponds to the minimum shearing resistance whereas in the gneiss soil layers the shearing resistance increases gradually with soil depth and the sliding plane is formed when the weathering front is located deeper because of the faster soil formation rate and the shallower slip depth in granite slopes the return period of occurrence of soil slips should be shorter in granite slopes than in gneiss slopes

large eddy simulations and observations of atmospheric marine boundary layers above nonequilibrium surface waves abstract winds and waves in marine boundary layers are often in an unsettled state when fast running swell generated by distant storms propagates into local regions and modifies the overlying turbulent fields a large eddy simulation les model with the capability to resolve a moving sinusoidal wave at its lower boundary is developed to investigate this low wind fast wave regime it is used to simulate idealized situations with wind following and opposing fast propagating waves swell and stationary bumps les predicts momentum transfer from the ocean to the atmosphere for wind following swell and this can greatly modify the turbulence production mechanism in the marine surface layer in certain circumstances the generation of a low level jet reduces the mean shear between the surface layer and the pbl top resulting in a near collapse of turbulence in the pbl when light winds oppose the propagating swell turbulence levels increase over the depth of the boundary layer and the surface drag increases

ers 1 scatterometer measurements i the relationship between radar cross section and buoy wind in two oceanic regions extensive european remote sensing satellite ers 1 spacecraft scatterometer measurements were collocated within spl plusmn 25 km of buoy measurements at midlatitudes and in the equatorial pacific during 1992 1994 two different directional functional forms for the geophysical model were fit to these measurements described by cross section maxima aligned and offset with respect to the mean wind direction the two models exhibit fits with similar residuals for each of three years in the equatorial region thus neither of these two model functions can convincingly be identified as more accurate than the other unless additional factors are considered nevertheless the offset model results in an average directional offset near 10 spl deg for each season during the three year period whereas no such offset was inferred at midlatitudes the cross section dependence on wind direction also exhibits another unexpected average property a larger downwind compared to upwind cross section a sub 10 spl ap 0 25 db in the equatorial pacific this characteristic could be caused by a concentration of the short bragg waves on the backside of the long wave crests both of these unexpected characteristics are likely related to a dominant systematic swell traveling nearly perpendicular to the prevailing easterly winds across the equatorial pacific ocean the possible cross section dependence on wind stress and wind speed is due to long waves when adjusting the buoy measurements to a common height are discussed

variation of the drag coefficient and its dependence on sea state using a gill propeller vane anemometer and resistance wave wires over a water column depth of 15 m simultaneous measurements of the momentum flux and sea surface wave spectra were acquired from the pisa mast 28 km offshore in the german bight during autumn and winter 1979 these data were analyzed to identify the relationship between wind stress and surface waves it was found that wind stresses for wind speeds above 15 m s were regularly higher than open ocean wind stresses as reported by smith 1980 and by large and pond 1981 for the same mean wind speed these results when described in terms of the drag coefficient compared closely with the results of sheppard et al 1972 who collected surface layer statistics over lough neagh northern ireland after modeling the surface waves of the north sea as a function of wave saturation or wave age it became evident that variations in the magnitude of the drag coefficient could be explained by coincident variations in the surface wave energy spectrum by applying the wave dependent roughness length model described by kitaigorodskii 1973 the north sea drag coefficient was predicted to be larger than drag coefficients reported from the open sea

some evidence of colinear wind stress and wave breaking abstract data collected during the surface waves and processes program are employed to investigate a possible interrelation between wind stress and surface wave breaking from comparison of data from 15 half hour long time segments the directions of the wind stress and the whitecap motion are observed to be generally colinear with both lying between the mean wind and the swell as well a nondimensionalized whitecap speed is found to correlate with the drag coefficient these results suggest that the magnitude and direction of the wind stress might be estimated from wave breaking information