shell mounds as environmental proxies on the southern coast of brazil despite the multiple constraints of using shell mounds for building relative sea level rsl curves one of the premises behind this use is still valid in modern archaeological research this refers to the sites being continuously built near bodies of water rich in fish species and mollusk beds studies that combine the evolution of settlement patterns with the geological evolution of coastal areas in brazil reach analogous results the distribution of shell mounds in time and space follows the landscape transformations induced by rsl variations through the holocene although shell mounds are not precise indicators of rsl they provide evidences of the paleo geographical changes during the holocene of which rsl is one of the many control variables by collecting and transporting mollusks to the shell mounds humans inevitably carry sediments from the substrate where mollusks live for example the beaches and lagoons near the sites in this work the geoarchaeological study of three shell mounds located in the southern coast of santa catarina state combined with mollusk taxa identification show the direct association of shell mound content with the changing landscape the predominance of ostrea sp versus anomalocardia brasiliana the presence of colluvial versus lagoonal sediments and the occurrence of echinoid spines versus muddy aggregates with diatoms gastropods and glauconitic clay characterize the distinction between sites built before and after the maximum holocene transgression respectively this attests the potential of geoarchaeological analyses in shell mounds as a complementary proxy for paleo environmental reconstructions

seismic tomography a window into deep earth abstract the goal of this paper is to provide an overview of the current state of the art in seismic tomography and trace its origins from pioneering work in the early 1970s to its present status as the pre eminent tool for imaging the earth s interior at a variety of scales due to length limitations we cannot hope to cover every aspect of this diverse topic or include mathematical derivations of the underlying principles rather we will provide a largely descriptive coverage of the methodology that is targeted at readers not intimately familiar with the topic the relative merits of local versus global parameterization ray tracing versus wavefront tracking backprojection versus gradient based inversion and synthetic testing versus model covariance are explored a variety of key application areas are also discussed including body wave traveltime tomography surface wave tomography attenuation tomography and ambient noise tomography established and emerging trends many of which are driven by the ongoing rapid increases in available computing power will also be examined including finite frequency tomography full waveform tomography and joint tomography using multiple datasets several practical applications of seismic tomography including body wave traveltime attenuation and surface waveform are presented in order to reinforce prior discussion of theory

an assessment of the importance of chaotic stirring and turbulent mixing on the west florida shelf application of dynamical systems tools has recently revealed in surface ocean currents produced by a hybrid coordinate ocean model hycom simulation the presence of a persistent large scale lagrangian coherent structure lcs on the southern portion of the west florida shelf wfs consistent with satellite tracked drifter trajectories this lcs constitutes a cross shelf barrier for the lateral transport of passive tracers because of the constraints that the above lcs as well as smaller scale lcss lying shoreside can impose on pollutant dispersal and its potentially very important biological consequences a study was carried out on the nature of the surface ocean lagrangian motion on the wfs the analysis is based on the same simulated surface ocean velocity field that has been able to sustain the aforementioned persistent cross shelf transport barrier examination of several diagnostics suggests that chaotic stirring dominates over turbulent mixing on time scales of up to two months or so more specifically it is found on those time scales that tracer evolution at a given length scale is governed to a nonnegligible extent by coarser scale velocity field features fluid particle dispersion is spatially inhomogeneous and the lagrangian evolution is more irregular than the driving eulerian flow

burning peat and reworking loess contribute to the formation and evolution of a large carolina bay basin abstract carolina bays are nearly ubiquitous along 1300 km of the north american atlantic coastal plain but relatively few bays have been examined in detail making their formation and evolution a topic of controversy the lake mattamuskeet basin eastern north carolina usa is a conglomeration of multiple carolina bays that form a 162 km2 lake the eastern shoreline of the lake is made up of a 2 9 km wide plain of parabolic ridges that recorded rapid shoreface progradation the lower shoreface deposit contains abundant charcoal beds and laminae dated 6465 6863 cal yr bp corresponding with initiation of a lacustrine environment in the eastern part of the lake a core from the western part of the lake sampled a 1541 1633 cal yr bp charcoal bed at the base of the lacustrine unit indicating formation of this part of the basin postdates the eastern basin lake mattamuskeet has no relationship to the younger dryas or a linked impact event because rim accretion significantly postdates 12 000 cal yr bp the shoreline progradation and association of charcoal beds with the oldest lake sediment in both main parts of the basin suggest that fire and subsequent hydrodynamic processes were associated with initial formation of these carolina bays

radarfacies and sedimentological analysis study of sedimentary substrate from an archaeological site shell mound southern brazil integrated results of gpr ground penetrating radar and sedimentological analysis are presented for the jabuticabeira ii archaeological site shell mound santa catarina brazil by means of rada

the correlation between surface drifters and coherent structures based on high frequency radar data in monterey bay this paper investigates the transport structure of surface currents around the monterey bay ca region currents measured by radar stations around monterey bay indicate the presence of strong spatial and temporal nonlinear patterns to understand the geometry of the flow in the bay lagrangian coherent structures lcs are computed these structures are mobile separatrices that divide the flow into regions of qualitatively different dynamics they provide direct information about the flow structure but are geometrically simpler than particle trajectories themselves the lcs patterns were used to reveal the mesoscale flow conditions observed during the 2003 autonomous ocean sampling network aosn ii experiment drifter paths from the aosn experiment were compared to the patterns induced by the lcs computed from high frequency radar data we verify that the fate of the drifters can be better characterized based on the lcs than direct interpretation of the current data this property can be exploited to optimize drifter deployment

integrated seismic tomography and ground penetrating radar gpr for the high resolution study of burial mounds tumuli the study primarily aims at providing adequate imaging resolution of large and prominent targets of archaeological interest such as pyramids and tumuli at all depth levels we implemented an integrated seismic tomography and georadar stg technique to perform high resolution imaging and characterization of tumuli burial mounds we tested the proposed technique on a preserved late bronze age burial mound in northern italy for which stg succeeded in performing an accurate 3 d reconstruction of the structure and stratigraphy as proved by later archaeological excavations we completed two transmission seismic tomography measurements at present ground level and at 1 5 m elevation with a 24 channel seismograph and 15 angular separation between geophones the ground penetrating radar gpr dataset encompasses 12 250 mhz radial profiles and 12 common mid point gathers for velocity analysis shallow layers of the mound are successfully imaged by gpr whilst the structure of the deep central part of the tomb is reconstructed from seismic traveltime inversion in particular gpr images lenses and layers of sediments forming the external part of the tumulus evidences of a looting attempt peripheral structures associated with later exploitation of the mound furnaces and in the external sector of the tumulus the top of the deep layer of silty sediments covering the funeral chamber tomographic results reveal seismic velocity anomalies of potential archaeological interest at ground level which were successively validated by archaeological excavations the integration of gpr and tomographic datasets is an effective strategy to overcome the imaging and interpretation problems related to the structure of such peculiar funeral monuments stg can be applied to a virtually unlimited dimensional range and requires a limited data acquisition processing and inversion effort the results of the study allowed the identification of the funeral chamber and a detailed imaging of layering and structural details

near surface transport pathways in the north atlantic ocean looking for throughput from the subtropical to the subpolar gyre abstractmotivated by discrepancies between eulerian transport estimates and the behavior of lagrangian surface drifters near surface transport pathways and processes in the north atlantic are studied using a combination of data altimetric surface heights statistical analysis of trajectories and dynamical systems techniques particular attention is paid to the issue of the subtropical to subpolar intergyre fluid exchange the velocity field used in this study is composed of a steady drifter derived background flow upon which a time dependent altimeter based perturbation is superimposed this analysis suggests that most of the fluid entering the subpolar gyre from the subtropical gyre within two years comes from a narrow region lying inshore of the gulf stream core whereas fluid on the offshore side of the gulf stream is largely prevented from doing so by the gulf stream core which acts as a strong transport barrier in agreement with past studies the transport barrier near the gulf stream core is r

repeated century scale droughts over the past 13 000 yr near the hudson river watershed usa abstract long term sediment and ground penetrating radar data from davis pond a small lake near the hudson river valley reveal past droughts in a historically humid region that presently supplies water to millions of people in and around new york city a minimum of eleven sandy paleoshoreline deposits in the lake date from 13 4 to 0 6 cal ka bp the deposits span 1500 to 200 yr between bracketing radiocarbon ages and intrude into lacustrine silts up to 9 0 m below the modern lake surface in a transect of six sediment cores three low stands ca 13 4 10 9 9 2 and 8 2 cal ka bp indicate low regional moisture balance when low temperatures affected the north atlantic region consistent with insolation trends water levels rose from ca 8 0 cal ka bp to present but five low stands interrupted the rise and are likely associated with ocean atmosphere interactions similar to evidence from other studies the data from davis pond indicate repeated multi century periods of prolonged or frequent droughts super imposed on long term regional trends toward high water levels the patterns indicate that water supplies in this heavily populated region have continuously varied at multiple time scales and confirm that humid regions such as the northeastern united states are more prone to severe drought than historically expected

ground penetrating radar and its use in sedimentology principles problems and progress abstract ground penetrating radar gpr also referred to as ground probing radar surface penetrating radar subsurface radar georadar or impulse radar is a noninvasive geophysical technique that detects electrical discontinuities in the shallow subsurface

vertical seismic profiling separation of upgoing and downgoing acoustic waves in a stratified medium one of the essential steps in the processing of a vertical seismic profile is the separation of upgoing and downgoing signals with this perspective in mind seismic data recorded in a borehole are modeled in terms of these waves and a mathematically optimal least squares technique for extracting them is derived the method imposes practically no constraints on the spacing between recording levels and allows almost perfect rejection of a coherent downgoing signal the exact formulation of the one dimensional model requires that acoustic impedance information be included but a reasonable and realistic approximation can neglect impedance we derive frequency wavenumber response plots for the two limiting cases of even and randomly spaced levels and compare these to the response of a conventional velocity filtering technique by a careful study of available logs recording levels can be chosen to optimize geophone coupling rather than insisting on uniform spatial sampling data editing normalization a

persistent transport barrier on the west florida shelf 1 analysis of drifter trajectories in the gulf of mexico has revealed the existence of a region on the southern portion of the west florida shelf wfs that is not visited by drifters that are released outside of the region this socalled forbidden zone fz suggests the existence of a persistent cross shelf transport barrier on the southern portion of the wfs in this letter a year long record of surface currents produced by a hybrid coordinate ocean model simulation of the wfs is used to compute lagrangian coherent structures lcss which reveal the presence of a persistent cross shelf transport barrier in approximately the same location as the boundary of the fz the location of the cross shelf transport barrier undergoes a seasonal oscillation being closer to the coast in the summer than in the winter a month long record of surface currents inferred from high frequency hf radar measurements in a roughly 60 km 80 km region on the wfs off tampa bay is also used to compute lcss and these also reveal the presence of transient transport barriers while the hf radarderived transport barriers cannot be unambiguously linked to the boundary of the fz this analysis does demonstrate the feasibility of monitoring transport barriers on the wfs using a hf radar based measurement system the implications of a persistent cross shelf transport barrier on the wfs for the development of harmful algal blooms on the shoreward side of the barrier are considered citation olascoaga m j i i rypina m g brown f j

crosshole seismic tomography many tomographic interpretations of crosshole seismic traveltimes have approximated the raypaths with straight lines connecting the source and receiver this approximation is valid where the velocity does not vary greatly but in many regions of interest velocity variations of 10 20 percent or more are observed causing significant ray curvature other work has taken this nonlinear effect into account but there do not appear to be many cases of demonstrated success in its application to the crosshole seismic problem we present here an iterative inversion scheme based on two dimensional ray tracing and its successful application to field data the interpretation method iteratively ray traces and then updates the velocity model within each iteration the differences between the data and the current model traveltimes obtained by ray tracing are related to the unknown velocity perturbations through a system of linear equations a damped least squares method solves for the velocity perturbations which updat

pin stripe lamination a distinctive feature of modern and ancient eolian sediments abstract pin stripe laminations are a distinctive feature of modern and ancient eolian sediments in sets of eolian ripple or translatent strata they represent deposition of silt and very fine sand in the troughs of the advancing wind ripples in sets of avalanche strata they probably result from the downward settling of fine sand and silt within the moving avalanche to the interface of moving and unmoving sands wind tunnel experiments suggest that pin stripe laminations can also form in grainfall deposits the textural segregation associated with deposition of the fine layers in most cases leads to early cementation along and near the finest sand and silt comprising the pin stripe lamination the pin stripe effect seen in outcrops is usually due to resistance to weathering along such cemented zones the cementation of the pin stripe laminations can occur early in the history of diagenesis and thus may provide clues to the post depositional history of the rock pin stripe laminations in many instances represent the sequestering of the small population of ultrafine sediment present in most eolian depositional systems they may prove useful in the recognition of ancient eolian sediments

eolian depositional episodes controlled by late quaternary relative sea level changes on the imbituba laguna coast southern brazil the late quaternary coastal eolian deposits of the imbituba laguna region santa catarina state southern brazil comprise two eolian depositional sequences separated by an unconformity the older eolian sequence a is correlated to the relative sea level rise of the last interglacial period the eolian sequence b was initiated during the relative sea level rise in the post glacial period and extends up to active dunefields the correspondence between the two eolian depositional episodes represented by these sequences and the relative sea level highstand phases is confirmed by thermoluminescence and optically stimulated luminescence dating this correspondence is explained by a conceptual model that links the availability of coastal sediments for eolian transport with relative sea level changes the link between relative sea level changes and coastal eolian sedimentation can be used to integrate coastal eolian systems to the sequence stratigraphy model

a critical review of mid to late holocene sea level fluctuations on the eastern brazilian coastline abstract the eastern coast of brazil is 7000 km long and has been the subject of systematic paleo sea level investigations for more than 35 years more than 1000 samples have been radiocarbon dated and paleo sea level trends have been determined for 14 coastal sectors these trends have in common a mid holocene sea level maximum pmt above present sea level and a subsequent fall to the present time the time and elevation of the pmt the time when relative sea level rose above present mean sea level and the nature of late holocene sea level fall can however differ significantly discrepancies are observed not only between neighboring coastal sectors but also between different studies in a same coastal sector this paper discusses all the key radiocarbon dated samples used to establish regional trends in relative sea level on the eastern coast of brazil it is concluded that although many of the key sea level indicators are imprecise in time and space there is widespread evidence 30 of the data set for a progressive decline possibly with uneven rates of relative sea level since the end of the pmt

geological characteristics and spatial distribution of paleo inlet channels beneath the outer banks barrier islands north carolina usa abstract nearly 200 km of high resolution ground penetrating radar gpr data were acquired along the outer banks barrier island system of north carolina usa gpr data combined with lithofacies and biofacies data reveal multiple depositional facies including inlet channel flood tide delta overwash peat and inner shelf previously undocumented paleo inlet channels constitute a significant portion of the shallow geologic framework between oregon inlet and cape hatteras gpr data reveal the complex stratigraphy associated with multiple sequences of cut and fill within inlet channels two types of paleochannels non migrating and migrating were classified based on geometry and fill patterns sediments and foraminifera collected from vibracores were correlated to gpr data to define the regional shallow stratigraphic framework channel fill facies are characterized by clinoform packages sometimes bounded by erosional surfaces indicating variable sediment transport directions from the ocean and sound sides channels are incised into older flood tide delta deposits corresponding to older inlet activity when barriers existed further seaward flood tide delta deposits are capped with marsh peat and overwash units migrating inlet facies occur under the widest portions of the island whereas narrow portions of the island are underlain by the non migrating inlet facies or flood tide delta overwash facies this geologic geomorphic relationship is attributed to the successional stage of island evolution during transgression and sediment transport processes associated with the different inlet types the radar facies lithofacies and biofacies provide a comprehensive dataset that will permit more precise identification of barrier island facies in the geologic record

lagoa da apulia a residual lagoon from the late holocene nw coastal zone of portugal the lagoa da apulia is a unique feature in the nw coastal zone of portugal a remaining form from a lagoon complex system that during the late holocene was dominant in the region this system was mainly neotectonically controlled occupying a depressed area bounded by faults on a palaeozoic rocky lower platform today observable on beaches at low tide with the intention of knowing the main architecture of the palaeo lagoon geophysical prospecting with gpr and resistivity was carried out accordingly six cores were taken and the sedimentary and mineralogical facies and diatom and foraminifer contents were analysed and five rich organic layers were dated by radiocarbon analysis with the data an evolutionary environment reconstruction model was created for this palaeo lagoon and the main structural features of the neighbouring area

barrier island response to late holocene climate events north carolina usa the outer banks barrier islands of north carolina usa contain a geologic record of inlet activity that extends from ca 2200 cal yr bp to the present and can be used as a proxy for storm activity optically stimulated luminescence osl dating 26 samples of inlet fill and flood tide delta deposits recognized in cores and geophysical data provides the basis for understanding the chronology of storm impacts and comparison to other paleoclimate proxy data osl ages of historical inlet fill compare favorably to historical documentation of inlet activity providing confidence in the technique comparison suggests that the medieval warm period mwp and little ice age lia were both characterized by elevated storm conditions as indicated by much greater inlet activity relative to today given present understanding of atmospheric circulation patterns and sea surface temperatures during the mwp and lia we suggest that increased inlet activity during the mwp responded to intensified hurricane impacts while elevated inlet activity during the lia was in response to increased nor easter activity a general decrease in storminess at mid latitudes in the north atlantic over the last 300 yr has allowed the system to evolve into a more continuous barrier with few inlets

estimating lagrangian transport blending drifters with hf radar data and models results from the tosca experiment in the ligurian current north western mediterranean sea abstract lagrangian transport estimates are investigated using results from hf radar model and drifter data during a dedicated experiment in the ligurian current in the toulon area north western mediterranean sea uncertainty estimates on particle position d t are computed and compared to absolute dispersion d 0 t that provides an indication of the uncertainty in case of zero prior knowledge in agreement with previous studies radar results show that d t 1 2 d 0 t i e 6 km after 24 h model results are less reliable as it can be expected in highly nonlinear coastal flows without local data assimilation the central result of this paper is that when drifters are promptly deployed in an area of interest their data can be used to significantly improve transport estimates using the lagrangian blending algorithm lava with velocity fields from models or radar uncertainty can be reduced to 1 6 d 0 t i e 2 km after 24 h for both radar and model implying a much reduced search range in case of operational applications the method is also found to have some forecasting skills with uncertainty 1 2 d 0 t during the first 6 h sensitivity tests provide indications on relevant time and space scales of predictability and provide suggestions for appropriate drifter sampling strategies

gpr and inductive electromagnetic surveys applied in three coastal sambaqui shell mounds archaeological sites in santa catarina state south brazil abstract in this article gpr ground penetrating radar and inductive electromagnetic em38 equipment results are presented for three archaeological sites of shell mounds located between laguna and jaguaruna cities mid southern coast of santa catarina state brazil the jabuticabeira ii santa marta iv and encantada iii sites were studied these sites consist of carbonate shell mounds built by societies that inhabited this region during the pre colonial period 7 5 1 3 ky bp geophysical responses obtained in these archaeological sites had allowed the identification of anomalous regions related to archaeological point targets as well as continuous targets correlated to the shell mound s structure and buried geologic features gpr numerical modelling studies were done in order to evaluate the performance of the gpr method in relation to materials found in that environment besides helping interpretations of real results the synthetic gpr model was a good match with real data obtained in the field so the real and synthetic results serve as a reference guide to direct excavation activities in these archaeological and geological structures in the jabuticabeira ii shell mound lithic materials and burials were found amidst archaeological layers characterized by sediment rich in organic material ferruginous concretions and loose shells in the santa marta iv archaeological site a concentration of ceramic materials burials and fireplaces were found in the encantada iii site a strong anomaly characterized by a hyperbolic reflection was related to the presence of a silicified tree root a great example of ambiguity in shallow geophysics interpretation in archaeological applications results functioned as a guide to archaeological excavations allowing cost and time reduction as well as contributing to improve the knowledge of these archaeological sites situated in southern brazil

the holocene sedimentary history of the kangerlussuaq fjord valley fill west greenland abstract west greenland has been intensively studied to reconstruct and better understand past relative sea level changes and deglacial history this study extends these efforts by linking sea level and deglacial history to the sedimentary infill successions of kangerlussuaq fjord and associated landward valleys based on published and new land and sea based geophysical data radiocarbon dates and geological observations we have characterized the infill and reconstructed the sedimentation history during the holocene based on a revised sea level curve and data presented in this paper we defined three depositional phases phase i 7000 yr bp is represented by dominant glaciomarine deposition associated with a tide water glacier system as the greenland ice sheet gis continued to retreat it became land based during phase ii 7000 1500 yr bp two separate depocenters formed keglen delta depocenter arose from a temporary stabilization phase of the gis and prograded rapidly over the glaciomarine deposits of phase i further inland proglacial lake formation and subsequent sedimentary infill associated with the ongoing gis retreat is represents the second depocenter the watson river connected both depocenters by a flood plain which transferred sediment from the gis to the keglen delta ongoing sea level fall due to glacio isostastic uplift combined with a gradually cooler and dryer climate resulted in terrace formation along the watson river flood plain around 4000 yr bp the gis margin reached its most landward location and began to advance to its present location the final phase phase iii

sedimentary architecture of a spit end salisbury beach massachusetts the imprints of sea level rise and inlet dynamics abstract in the vicinity of tidal inlets the facies architecture of barrier islands is largely controlled by inlet channel shifting and the transfer of sand between the ebb tidal delta and the adjacent shore including processes of inlet sediment bypas sing merrimack river inlet is situated in a mixed energy setting and is characterized by episodic shifting of the ebb channel prior to being stabilized in 1881 here we delineate the internal structure and evolution of the updrift barrier spit terminus by integrating data obtained from ground penetrating radar transects and sediment cores to document the effects of inlet associated sedimentation processes our results document complex radar and sedimentological facies which define two distinctive associations of facies the inlet distal and proximal within the core of the present barrier these facies are associated with three phases of barrier terminus evolution i barrier retrogradation characterized by the preservation of washover and backbarrier marsh facies deposited during sea level rise ii downdrift barrier progradation characterized by channel fill and swash platform deposits overlain by foreshore deposits generated by long shore currents and swash bars migrating to the foreshore from the swash platform and iii foreshore seaward progradation characterized by cross beds this study illustrates the highly complex nature of inlet associated spit ends of barriers likewise our results shed light on the mechanisms of spit elongation and recurving in a setting where the estuary opening is narrowing

reverse time migration of offset vertical seismic profiling data using the excitation time imaging condition to apply reverse time migration to prestack finite offset data from variable velocity media the standard time zero imaging condition must be generalized because each point in the image space has a different image time or times this generalization is the excitation time imaging condition in which each point is imaged at the one way traveltime from the source to that point reverse time migration with the excitation time imaging condition consists of three elements 1 computation of the imaging condition 2 extrapolation of the recorder wave field and 3 application of the imaging condition computation of the imaging condition for each point in the image is done by ray tracing from the source point this is equivalent to extrapolation of the source wave field through the medium extrapolation of the recorded wave field is done by an acoustic finite difference algorithm imaging is performed at each step of the finite difference extrapolation by extracting from the propagating wave field the

seismic imaging of the naga thrust using multiscale waveform inversion this case study images the structural features related to the naga thrust fault northeast india using a combination of multiscale waveform inversion and prestack depth migration psdm the waveform model and the psdm image complement each other the former provides a physical property map p wave velocity model and the latter provides a structural image the velocity model encompassing the starting model for waveform inversion is constructed using joint inversion of first and reflected traveltimes the 4 8 hz data are inverted consecutively in 1 hz bandwidths to yield the final waveform model which in turn is used for psdm the psdm image and the waveform model are consistent with the lithological interpretation of an inline exploratory well when interpreted jointly the psdm image and the waveform model reveal the presence of a conjugate fault system in the naga thrust and fold belt

crosshole seismology and seismic imaging in crystalline rocks a borehole to borehole audiofrequency seismic system using piezoelectric transducers as active elements has been developed and used to investigate crystalline rocks in canada high quality seismograms have been recorded for transmitter receiver distances of up to 230 meters it has been found that both travel times and signal amplitudes provide diagnostic information about rock quality two dimensional images of seismic velocity and transparency distributions between two boreholes derived from observed arrival times and amplitudes by simple back projection tomography reflect lithology and geological structure the results indicate the potential usefulness of crosshole seismic imaging as a tool for rock mass characterization

the occurrence drivers and implications of submesoscale eddies on the martha s vineyard inner shelf abstractthe occurrence drivers and implications of small scale o 2 5 km diameter coherent vortices referred to as submesoscale eddies over the inner shelf south of martha s vineyard massachusetts are examined using high frequency hf radar based high resolution 400 m observations of surface currents within the 300 km2 study area eddies occurred at rates of 1 and 4 day 1 in winter and summer respectively most were less than 5 h in duration smaller than 4 km in diameter and rotated less than once over their lifespan 60 of the eddies formed along the eastern edge of study area adjacent to wasque shoal and moved westward into the interior often with relative vorticity greater than f eddy generation was linked to vortex stretching on the ebb and flood tide as well as the interaction of the spatially variable tide and the wind driven currents however these features had complex patterns of surface divergence and stretching eddies located away from wasque shoal were related to the movem

the last glacial termination a major puzzle of paleoclimatology is why after a long interval of cooling climate each late quaternary ice age ended with a relatively short warming leg called a termination we here offer a comprehensive hypothesis of how earth emerged from the last global ice age a prerequisite was the growth of very large northern hemisphere ice sheets whose subsequent collapse created stadial conditions that disrupted global patterns of ocean and atmospheric circulation the southern hemisphere westerlies shifted poleward during each northern stadial producing pulses of ocean upwelling and warming that together accounted for much of the termination in the southern ocean and antarctica rising atmospheric co2 during southern upwelling pulses augmented warming during the last termination in both polar hemispheres

late holocene intensification of colds fronts in southern brazil as indicated by dune development and provenance changes in the sao francisco do sul coastal barrier abstract holocene coastal barriers from southern brazil present great geomorphological changes during their late stages of development in this study we investigate the holocene evolution of the sao francisco do sul sfs barrier through geomorphological heavy minerals and grain size analyses constrained by optically stimulated luminescence osl dating the sfs barrier stands out among the southern brazilian barriers due to its well preserved morphology with a parabolic dune belt in the seaward portion the progradation of the sfs barrier started at least 4914 478 years ago and had a pronounced morphodynamic shift around 1891 155 years ago this shift is characterized by episodic development of parabolic dunes migrating to nnw associated with sand coarsening and a marked variation in sediment provenance represented by the input of sands derived from local coastal watersheds southward from the sfs barrier this morphodynamic provenance shift resulted from the strengthening of sse winds and associated wave systems responsible for the northward alongshore drift implying intensification of cold fronts coupled with higher precipitation since 1891 155 years ago osl dating combined with grain size heavy minerals and geomorphological analyses allowed assessing the response of coastal barriers to the impacts of centennial to millenial climate events occurred during the late holocene reconstruction of the late holocene climate variability and associated impacts on coastal sedimentation is a key issue to evaluate the sensitivity of coastal barriers to future climate changes

gulf stream transport and mixing processes via coherent structure dynamics the gulf stream has been characterized as either a barrier or blender to fluid transfer a duality relevant to gyre scale climate adjustment however previous characterization depended on relatively sparse lagrangian in situ observations the finite time lyapunov exponent ftle is calculated from satellite altimetry to identify lagrangian coherent structures lcs in the gulf stream region these lcs provide dense sampling of flow and capture distinct regions associated with mixing independent observations of ocean color contain similar flow dependent structures providing verification of the method and highlighting transport and mixing processes that influence sea surface temperature and chlorophyll among other water properties diagnosed lcs support the existing bower kinematic model of the gulf stream but also highlight novel behavior of comparable importance these include vortex pinch off and formation of spiral eddies clearly identified by lcs and which may be explained by considering changes to flow topology and the dynamics of shear flow instability at both small and large rossby number such processes seen though lcs may further enable validation of climate models the spatial distribution of these intermittent processes is characterized in terms of the criticality of jet dynamics with respect to rossby wave propagation and whether the jet is in an unstable or wave maker regime the generation and connectivity of hyperbolic trajectories in the flow appears to play an important role in governing large scale transport and mixing across the gulf stream

surface ocean mixing inferred from different multisatellite altimetry measurements abstract two sea surface height ssh anomaly fields distributed by archiving validation and interpretation of satellite oceanographic aviso altimetry are evaluated in terms of the effects that they produce on mixing one ssh anomaly field tagged ref is constructed using measurements made by two satellite altimeters the other ssh anomaly field tagged upd is constructed using measurements made by up to four satellite altimeters advection is supplied by surface geostrophic currents derived from the total ssh fields resulting from the addition of these ssh anomaly fields to a mean ssh field emphasis is placed on the extraction from the currents of lagrangian coherent structures lcss which acting as skeletons for patterns formed by passively advected tracers entirely control mixing the diagnostic tool employed to detect lcss is provided by the computation of finite time lyapunov exponents it is found that currents inferred using upd ssh anomalies support mixing with characteristics similar t

inverse theory applied to multi source cross hole tomography part 1 acoustic wave equation method1 frequency domain methods are well suited to the imaging of wide aperture cross hole data however although the combination of the frequency domain with the wavenumber domain has facilitated the development of rapid algorithms such as diffraction tomography this has also required linearization with respect to homogeneous reference media this restriction and association restrictions on source receiver geometries are overcome by applying inverse techniques that operate in the frequency space domain in order to incorporate the rigorous modelling technique of finite differences into the inverse procedure a nonlinear approach is used to reduce computational costs the method of finite differences is applied directly to the frequency domain wave equation the use of high speed high capacity vector computers allow the resultant finite difference equations to be factored in place in this way wavefields can be computed for additional source positions at minimal extra cost allowing inversions to be generated using data from a very large number of source positions synthetic studies show that where weak scatter approximations are valid diffraction tomography performs slightly better than a single iteration of non linear inversion however if the background velocities increase systematically with depth diffraction tomography is ineffective whereas non linear inversion yields useful images from one frequency component of the data after a single iteration further synthetic studies indicate the efficacy of the method in the time lapse monitoring of injection fluids in tertiary hydrocarbon recovery projects

upper pleistocene to holocene peatland evolution in southern brazilian highlands as depicted by radar stratigraphy sedimentology and palynology paleoenvironmental interpretation of proxy data derived from peatlands is largely based upon an evolutionary model for ombrotrophic bogs in which peat accumulates in still environments reports on proxies obtained from minerotrophic fens where hydrologic inputs are variable are less common in this study a highland peatland in southern brazil is presented through ground penetrating radar gpr and sedimentological palynological and geochronologic data the radar stratigraphic interpretation suggests a relatively complex history of erosion and deposition at the site since the beginning of marine isotope stage 3 mis 3 interstadial period in spite of this radar stratigraphic and palynologic interpretations converge electromagnetic reflections tend to group in clusters that show lateral coherence and correlate with different sediment types while pollen grains abound and are well preserved as a result the study of minerotrophic fens provides a source of proxies suggesting that ombrotrophic bogs are not the only reliable source of data in wetlands for palynological analysis

multidomain analysis and wavefield separation of cross well seismic data while cross well traveltime tomography can be used to image the subsurface between well pairs the use of cross well reflections is necessary to image at or below the base of wells where the reservoir unit is often located one approach to imaging cross well reflections is to treat each cross well gather as an offset vsp and perform wavefield separation of direct and reflected arrivals prior to stacking or migration wavefield separation of direct and reflected arrivals in vsp is accomplished by separating the total wavefield into up and downgoing components since reflectors can exist both above and below the borehole wavefield separation of cross well data into up and downgoing components does not achieve separation of direct and reflected arrivals in our technique we use moveout filters applied in the domain of common vertical source receiver offset to extract reflected arrivals from the complex total wavefield of a cross well seismic data set the multiple domains available for filtering and analysis make cross well data more akin to multifold surface seismic data which can also be filtered in multiple domains rather than typical vsp data where there is only one domain common source in which to filter wavefield separation of cross well data is shown to be particularly effective against multiples when moveout filters are applied in common offset space

seismic waveform inversion in the frequency domain part 2 fault delineation in sediments using crosshole data a crosshole experiment was carried out in a layered sedimentary environment in which a normal fault is known to cut through the section initial traveltime inversions produced stable but low resolution images from which the fault could be only vaguely inferred to image the fault wavefield inversion was used to produce a velocity model consistent with the detailed phase and amplitude of the data at a number of frequencies our wavefield inversion scheme uses a classical descent type algorithm for decreasing the data misfit by iteratively computing the gradient of this misfit by repeated forward and backward propagations our propagator is a full wave equation frequency domain acoustic finite difference method the use of the frequency space domain yields computational advantages for multisource data and allows an easy incorporation of viscous effects by running wavefield inversion on the field data a quantitative velocity image was produced that yielded a significantly improved image of the fault when compared with the original traveltime inversions because the original field data were noisy and contained a high degree of multiple scattering from the layering of the sediments the transmitted arrivals were selectively windowed to enhance the image the sediments at the site were strongly attenuating we therefore used a viscoacoustic model during the modeling and the inversion that correctly simulated the observed decrease in amplitude with increasing frequency and source receiver offset furthermore since the traveltime inversion indicated a high degree of anisotropy at the site a fixed homogeneous level of anisotropy was used during the inversion tests at varying levels of anisotropy confirmed the improvement in image quality and in data fit when anisotropy was incorporated the final image was verified by examining the distribution of the residuals in the frequency domain by comparing time domain modeled wavefields with the observed data and by direct comparison with borehole logs

applications of seismic travel time tomography summary this paper describes the application of tomography to seismic travel time inversion there are various implementations of travel time tomography in reflection tomography sources and receivers are on the surface of the earth and the principal seismic events are reflections from subsurface velocity discontinuities in transmission tomography sources and or receivers may be buried beneath the surface and the events correspond to direct or unreflected arrivals this is the analogue of medical tomography there are also cases in which both direct as well as reflected arrivals are important such as in vertical seismic profiling the latter is a direct application of the first two but is not discussed in any detail here it is also shown how the iterative use of travel time tomography and depth migration can produce much enhanced subsurface images examples of both transmission tomography and reflection tomography combined with depth migration illustrate the methods

combining wave equation imaging with traveltime tomography to form high resolution images from crosshole data traveltime tomography is an appropriate method for estimating seismic velocity structure from arrival times however tomography fails to resolve discontinuities in the velocities wave equation techniques provide images using the full wave field that complement the results of traveltime tomography we use the velocity estimates from tomography as a reference model for a numerical propagation of the time reversed data these backpropagated wave fields are used to provide images of the discontinuities in the velocity field the combined use of traveltime tomography and wave equation imaging is particularly suitable for forming high resolution geologic images from multiple source multiple receiver data acquired in borehole to borehole seismic surveying in the context of crosshole imaging an effective implementation of wave equation imaging is obtained by transforming the data and the algorithms into the frequency domain this transformation allows the use of efficient frequency domain numerical propagat

effects of magnetite on high frequency ground penetrating radar large concentrations of magnetite in sedimentary deposits and soils with igneous parent material have been reported to affect geophysical sensor performance we have undertaken the first systematic experimental effort to understand the effects of magnetite for ground penetrating radar gpr characterization of the shallow subsurface laboratory experiments were conducted to study how homogeneous magnetite sand mixtures and magnetite concentrated in layers affect the propagation behavior velocity attenuation of high frequency gpr waves and the reflection characteristics of a buried target important observations were that magnetite had a strong effect on signal velocity and reflection at magnitudes comparable to what has been observed in small scale laboratory experiments that measured electromagnetic properties of magnetite silica mixtures magnetite also altered signal attenuation and affected the reflection characteristics of buried targets our results indicated important implications for several fields including land mine detection martian exploration engineering and moisture mapping using satellite remote sensing and radiometers

transport in an idealized three gyre system with application to the adriatic sea abstract motivated by observations of surface drifters in the adriatic sea transport in a three gyre system is studied with the aid of dynamical systems techniques particular attention is paid to the issue of intergyre transport the velocity field is assumed to be two dimensional and incompressible and composed of a steady three gyre background flow on which a time dependent perturbation is superimposed two systems of this type are considered 1 an observationally motivated analytically prescribed model consisting of a steady background on which a multiperiodic time dependent perturbation is superimposed and 2 an observationally based model of the adriatic sea consisting of the mean surface circulation derived from surface drifter trajectories on which a time dependent altimetry based perturbation velocity field is superimposed it is shown that for a small perturbation to the steady three gyre background two of the gyres exchange no fluid with the third gyre when the perturbation strength excee

a study of methods for tomographic velocity estimation in the presence of low velocity zones this paper deals with the problem of seismic velocity estimation from first arrival traveltimes in a two dimensional 2 d cross hole geometry where explosions are detonated in one borehole while recordings are made in another borehole and on the surface standard tomographic procedures are based on decomposition of the cross hole area into a number of cells and a simplifying assumption of straight raypaths in the presence of significant low velocity zones the resulting images may be contaminated different ways of performing tomographic inversion are tested on a number of synthetic examples images obtained by direct unrestricted least squares inversion are often seriously distorted however methods using more cells and some kind of damping often give more satisfactory results because the risk of distorted images is always present in inversion procedures comparison with synthetic data forward modeling is a valuable tool in the interpretation process with a reasonably good initial solution impro

facies associations and controls on the evolution from a coastal bay to a lagoon system santa catarina coast brazil abstract the diverse holocene morphological features along the south coast of the state of santa catarina include lagoons and residual lakes a barrier a delta constructed by the tubarao river and pre existing incised valleys that have flooded and filled this scenario contains the sedimentary record of the transition from a bay to a lagoon system which occurred during the rise and subsequent semi stabilisation of the relative sea level during the holocene the geomorphological evolution of this area was investigated using a combination of morphology stratigraphic analysis of rotary push cores vibracores and trenches with radiocarbon dating taxonomic determination and taphonomic characterisation of holocene fossil molluscs palaeogeographic maps were constructed to illustrate how the bay evolved over the last 8000 years the relative sea level rise and local sedimentary processes were the prime forcing factors determining the depositional history and palaeogeographic changes the holocene sedimentary succession began between 8000 and 5700 cal bp with the deposits of transgressive sandsheets these deposits correspond to the initial marine flooding surface that was formed while the relative sea level rose at a higher rate than the input of sediments prior to the formation of the coastal barrier the change from a bay to a lagoon system occurred around 5700 and 2500 cal bp during the mid holocene highstand with the formation of the barrier and with the achievement of a balance between sea level rise and sedimentary supply until 2500 cal bp the presence of this barrier the following gentle decline in sea level and the initial emergence of back barrier features restricted the hydro dynamic circulation inside the bay and favoured an increase in the tubarao river delta progradation rate the final stage during the last 2500 years was marked by the increasing back barrier width with the establishment of salt marshes the arrival of the delta in the back barrier and the advance of aeolian dunes along the outer lagoon margins this study shed light on the mechanisms of coastal bay evolution in a setting existed prior to the beginning of barrier lagoon sedimentation

chlorophyll dispersal by eddy eddy interactions in the gulf of mexico 1 a lagrangian analysis of the transport and dispersal of plumes observed in satellite derived ocean color images was conducted using a data assimilating model of the gulf of mexico the interaction between pervasive cyclonic and anticyclonic eddies in the gulf generated advective paths that connect remote shelf regions these paths aligned remarkably well with the plume events recorded with the chlorophyll a ocean color product from seawifs two such events were studied in one event material was transported in a thin strip between the northern wall of the loop current and an adjacent cyclone connecting the eastern campheche shelf off the yucatan peninsula and south florida shelves the other event began off the louisiana shelf break as a small plume traced by chlorophyll and then developed into a long and thin feature which meandered to the shelf break off the northern yucatan peninsula moving between a large anticyclone and several adjacent cyclones these results indicate that inter eddy advection plays a crucial role in developing the ocean color patterns observed in the satellite ocean color data

paleoenvironmental reconstruction of a late quaternary lagoon system in southern brazil jaguaruna region santa catarina state based on multi proxy analysis this paper provides a paleoenvironmental reconstruction of a late quaternary lagoon system in the jaguaruna region of santa catarina state southern brazil integrated results of bulk sedimentary organic matter characterization d 13 c d 15 n and c n microfossil pollen and diatom and grain size analysis from three shallow cores 2 5 m depth allowed us to propose an evolving paleogeographic scenario in this coastal region for the last ca 5500 cal a bp the lagoonal system in this area was more extensive during the mid holocene than today with a gradual and continuous lagoon sea disconnection until the present we add to the debate regarding relative sea level rsl variations for the brazilian coast during the holocene and discuss the importance of sedimentary dynamics for interpreting changes in coastal ecosystems the multi proxy analysis suggests that changes in coastal ecosystems could be directly related to local sedimentary processes which are not necessarily linked to rsl fluctuations and or to climatic variations copyright 2011 john wiley sons ltd

relative sea level changes in the last 5500 years in southern brazil laguna imbituba region santa catarina state based on vermetid ages abstract twenty six new radiocarbon dates from vermetid shells collected in the southernmost sector of the brazilian rocky coast presented dates ranging from 5410 80 to 190 65 years b p with associated paleosea levels varying from 2 10 m to 0 20 m above present sea level the overall suggested trend of the relative sea level rsl declining until at least 190 years b p is somewhat contradictory to a proposed rsl rise in the last 1000 years in southern brazil the data also seem to undermine a more widely accepted rsl trend that suggests that at least two negative rsl oscillations occurred between 4100 and 3800 years b p and between 3000 and 2700 years b p the maximum elevation of the rsl in the holocene in southern brazil was possibly lower than that observed in most of the brazilian eastern coast discrepancies between ancient sea levels of similar ages are attributed to coincidental methodological problems to imprecisions in determining past relative sea levels and to possible changes in the geomorphology and wave climate close to shore during the last 5000 years a general trend of increasing 18 o with a reduction in age in the studied samples may suggest a gradual reduction of water temperature in the region during the same period

parabolic dune reactivation and migration at napeague ny usa insights from aerial and gpr imagery abstract observations from mapping since the 19th century and aerial imagery since 1930 have been used to study changes in the aeolian geomorphology of coastal parabolic dunes over the last 170 years in the walking dune field napeague ny the five large parabolic dunes of the walking dune field have all migrated across or are presently interacting with a variably forested area that has affected their migration stabilization and morphology this study has concentrated on a dune with a particularly complex history of stabilization reactivation and migration we have correlated that dune s surface evolution as revealed by aerial imagery with its internal structures imaged using 200 mhz and 500 mhz ground penetrating radar gpr surveys both 2d transect and high resolution 3d gpr imagery image downwind dipping bedding planes which can be grouped by apparent dip angle into several discrete packages of beds that reflect distinct decadal scale episodes of dune reactivation and growth from aerial and high resolution gpr imagery we document a unique mode of reactivation and migration linked to upwind dune formation and parabolic dune interactions with forest trees this study documents how dune dune and dune vegetation interactions have influenced a unique mode of blowout deposition that has alternated on a decadal scale between opposite sides of a parabolic dune during reactivation and migration the pattern of recent parabolic dune reactivation and migration in the walking dune field appears to be somewhat more complex and perhaps more sensitive to subtle environmental pressures than an idealized growth model with uniform deposition and purely on axis migration this pattern believed to be prevalent among other parabolic dunes in the walking dune field may occur also in many other places where similar observational constraints are unavailable

internal architecture of a raised beach ridge system anholt denmark resolved by ground penetrating radar investigations abstract the internal architecture of raised beach ridge and associated swale deposits on anholt records an ancient sea level the holocene beach ridges form part of a progradational beach ridge plain which has been interpreted to have formed during an isostatic uplift and a relative fall in the sea level over the past 7700 years the ridges are covered by pebbles and cobbles and commonly show evidence of deflation material presumably removed from the beach ridges and adjacent swales form the present dune forms on anholt ground penetrating radar gpr reflection lines have been collected with 250 mhz shielded antennae across the fossil ridge and swale structures the signals penetrate the subsurface to a maximum depth of 10 m below the fossil features the gpr data resolve the internal architecture of the beach ridges and swales with a vertical resolution of about 0 1 m gpr mapping indicates that the holocene beach ridges are composed of seaward dipping beachface deposits as well as minor amounts of inland dipping deposits of wash over origin the beachface deposits downlap on underlying shoreface deposits and we use these surfaces as markers of a relative palaeo sea level the new data indicate that the highest relative sea level at about 8 5 m was reached 6500 years ago 700 years later the relative sea level had dropped 0 7 m indicating a change in the relative sea level around 1 mm year this fall in the relative sea level most likely records the influence of an isostatic rebound causing younger beach ridge deposits to indicate lower sea levels

diffraction tomography and multisource holography applied to seismic imaging seismic tomography is emerging as an imaging method for determining subsurface structure when the view angle coverage is limited and the scale of the medium inhomogeneities is comparable with the wavelength as is often true in geophysical applications the performance of ordinary ray tomography becomes poor other tomographic methods are needed to improve the imaging process here we study diffraction tomography and multisource holography and evaluate their performances for surface reflection profiling srp vertical seismic profiling vsp and cross hole measurements theoretical formulations are derived for two dimensional geometry in terms of line sources along a source line and line receivers along a receiver line the theory for diffraction tomography is based on the born or rytov approximation the performances of diffraction tomography and multisource holography are evaluated by examining the information coverage in the spatial frequency domain and by numerical examples multisource holography

distinctions and uses of stratification types in the interpretation of eolian sand abstract eolian and subaqueous cross strata cannot be distinguished reliably by many commonly cited criteria they can however generally be distinguished by the characteristics of their component types of stratification which represent processes of sorting and transport of the grain population on dunes eolian dune stratification types consist of grainflow cross strata grainfall laminae and wind ripple generated climbing translatent strata some of these types especially translatent strata have characteristics unique to the eolian realm these same stratification types are found to compose some ancient cross strata and their occurrence confirms the eolian interpretations of pans of the entrada jurassic navajo triassic jurassic and galesville cambrian formations a well as revealing emergent islands in the curtis formation jurassic previously considered to be totally marine in origin stratification types show a characteristic distribution on modern eolian dunes and differ in their relative abundances and structure on dunes of differing size and kind these same relations allow some estimates of the type shape and original height of ancient dune deposits as well as influencing the occurrences of surface features such as tracks and tipple forms the geological record of stratification types and other dune features is greatly affected however by the extent of the post depositional truncation of dunes