observation of a turbid plume using modis imagery the case of douro estuary portugal abstract the douro is one of the longest rivers in the iberian peninsula and represents the most important freshwater input into the atlantic ocean in the northwestern portuguese coast in order to fill the gaps on the comprehension of the spatial variability of the douro estuarine plume an innovative methodology was applied to observe and characterize this plume and its spatial and temporal variability using images of normalized water leaving radiance at 555 nm from modis moderate resolution imaging spectroradiometer in combination with long term concurrent wind tidal and river discharge data 2003 2011 this work evaluates the effect of the main drivers river discharge wind and tide on the plume features expected strong relationships between river discharge and turbid levels were detected a circular pattern is well distinct off douro estuary when the flow exceeds 500 m 3 s 1 under upwelling favorable winds and high river discharge regime an offshore expansion is observed during southerly winds there is a plume confinement to the coast easterly winds produce a bulge formation with an offshore detachment from the coast while westerly winds tend to confine freshwater close to the shoreline and decrease the cross shore advection under high river discharges a remarkable tidal influence in the near field regions is observed close to the coast and near the river mouth

surface climate variations over the north atlantic ocean during winter 1900 1989 abstract the low frequency variability of the surface climate over the north atlantic during winter is described using 90 years of weather observations from the comprehensive ocean atmosphere data set results are based on empirical orthogonal function analysis of four components of the climate system sea surface temperature sst air temperature wind and sea level pressure an important mode of variability of the wintertime surface climate over the north atlantic during this century is characterized by a dipole pattern in ssts and surface air temperatures with anomalies of one sign cast of newfoundland and anomalies of the opposite polarity off the southeast coast of the united states wind fluctuations occur locally over the regions of large surface temperature anomalies with stronger than normal winds overlying cooler than normal ssts this mode exhibits variability on quasi decadal and biennial time scales the decadal fluctuations are irregular in length averaging 9 years before 1945 and 1

on the persistence of cold season sst anomalies associated with the annular modes abstractin this study a simple stochastic climate model is used to examine the impact of the ocean mixed layer depth surface turbulent energy fluxes and ekman currents on the persistence of cold season extratropical sea surface temperature sst anomalies associated with variability in the annular modes of atmospheric circulation in both hemispheres observational analysis reveals that during the cold season sst anomalies associated with the southern annular mode sstsam persist considerably longer than those associated with the northern annular mode sstnam using the simple model it is shown that the persistence of the cold season sstsam is consistent with the simple stochastic climate paradigm in which the atmospheric forcing is approximated as white noise and the persistence of sst anomalies can be largely determined by the thermal inertia of the ocean mixed layer in the north atlantic however the simple climate model overestimates the persistence of the cold season sstnam it is thought th

evolution of fault zones in carbonates with mechanical stratigraphy insights from scale models using layered cohesive powder abstract we present analogue models of the formation of dilatant normal faults and fractures in carbonate fault zones using cohesive hemihydrate powder caso 4 h 2 o the evolution of these dilatant fault zones involves a range of processes such as fragmentation gravity driven breccia transport and the formation of dilatant jogs to allow scaling to natural prototypes extensive material characterisation was done this showed that tensile strength and cohesion depend on the state of compaction whereas the friction angle remains approximately constant in our models tensile strength of the hemihydrate increases with depth from 9 to 50 pa while cohesion increases from 40 to 250 pa we studied homogeneous and layered material sequences using sand as a relatively weak layer and hemihydrate graphite mixtures as a slightly stronger layer deformation was analyzed by time lapse photography and particle image velocimetry piv to calculate the evolution of the displacement field with piv the initial predominantly elastic deformation and progressive localization of deformation are observed in detail we observed near vertical opening mode fractures near the surface with increasing depth dilational shear faults were dominant with releasing jogs forming at fault dip variations a transition to non dilatant shear faults was observed near the bottom of the model in models with mechanical stratigraphy fault zones are more complex the inferred stress states and strengths in different parts of the model agree with the observed transitions in the mode of deformation

ekman heat transport for slab oceans a series of schemes designed to include various representations of the ekman driven heat fluxes in slab ocean models is introduced they work by computing an ekman mass flux then deducing heat fluxes by the surface flow and an opposite deep return flow the schemes differ by the computation of the return flow temperature either diagnosed from the sst or given by an active second layer both schemes conserve energy and use as few parameters as possible simulations in an aquaplanet setting show that the schemes reproduce well the structure of the meridional heat transport by the ocean compared to a diffusive slab ocean the simulated sst is more flat in the tropics and presents a relative minimum at the equator shifting the itcz into the summer hemisphere in a realistic setting with continents the slab model simulates correctly the mean state in many regions especially in the tropics the lack of other dynamical features such as barotropic gyres means that an optimal mean state in regions such as the mid latitudes will require additional flux corrections 2011 springer verlag

enhancement of alongshore freshwater transport in surface advected river plumes by tides abstracta recent numerical study by isobe showed that imposing alongshore tidal forcing on buoyant coastal discharge enhances the net freshwater transport in the coastal currents the mechanisms for this transport enhancement are studied using a three dimensional primitive equation ocean model regional ocean modeling system roms lagrangian drifters are used to trace the freshwater transport paths it is found that the river plume bulge circulation largely follows the rigid body motion i e constant vorticity the buoyant fluid near the bulge s outer edge is thinner and faster behaving as a baroclinic jet the bulge currents then split after impinging on the coast the outer fluid feeds the downshelf flowing coastal currents while the inner fluid recirculates to form the bulge the coastal current transport estimated from the present and prior studies corresponds well to a baroclinic jet theory with the incident angle of bulge currents at the coast being a key parameter without tides the bulg

surface river plume in a large lake under wind forcing observations and laboratory experiments abstract observations of a small riverine plume grand river on in the nearshore zones of lake erie were analyzed to describe its spatial variability and its thickness under different wind forcing conditions during late spring of 2012 observational results reveal a well marked frontal region in the vicinity of the river mouth causing the plume to discharge into the lake in the surface layers positive buoyant wind driven alongshore currents at the mid depth had speeds of 2 9 cm s in comparison to those in the cross shore 3 6 cm s which transported the plume along the shore during the measurement period series of laboratory experiments were conducted to obtain the propagation speed u of the buoyant plume in terms of buoyancy anomaly ba richardson number ri dimensionless time t and aspect ratio a based on our experiments we developed two non dimensional relationships describing the speed of propagation u as u ba 1 2 8 ri 1 2 t 1 3 a and the plume thickness h as h h 0 8 ri 1 4 t 1 2 a in the water depth h which are in agreement with field observations

characteristics of a surface buoyant jet tidal outflow from leschenault estuary in winter forms an unsteady surface buoyant jet in koombana bay on each outgoing tide as the water moves away from the exit channel and spreads radially over the bay it assumes a plumelike nature the mean features of this buoyant outflow such as the plume shape frontal celerity internal circulation and the bulk entrainment were measured in an intensive field program these features are shown to compare favorably with results from previous laboratory investigations and predictions from a simple inertia buoyancy force balance which includes entrainment at the front the stability of the plume frontal region was examined and it is shown that subfronts were present but their behavior cannot be explained by reference to previous work

an airborne real aperture radar study of the chesapeake bay outflow plume an airborne real aperture radar rar has been used to study the fronts associated with the chesapeake bay outflow plume during spring outflow conditions the rar produced images of the ocean surface with a range resolution of 10 m an azimuthal resolution of approximately 30 m and an image size of 2 5 km 24 km two sampling strategies were utilized one to synoptically map the entire mouth of the chesapeake bay at roughly hourly intervals and a second to capture the rapid evolution of particular features in addition flight times were chosen such that over the course of the entire experiment data were collected over all phases of the semidiurnal tidal cycle three distinct frontal signatures were observed in the imagery a primary front extended from inside the estuary along the chesapeake channel to an anticyclonic turning region east of cape henry and then extended southward along the coast toward cape hatteras this is the classic expression of the plume front inertial turning region and coastal jet a second front with a north south orientation was observed approximately 20 km east of the bay mouth this secondary front appears to mark the residual offshore density gradient a third front was identified east and south of cape henry within 2 km of the coast this front appears to mark the inshore edge of the plume and has not been documented previously time sequences of the imagery indicate that when moving in a clockwise sense around the primary front the frontal translation speed varies systematically from 20 cm s in the northern section to 50 cm s in the south the position of the primary front and the locations and trajectories of small scale frontal cusps suggest that bathymetry may be both a significant determinant of the front location as well as a source of along front variability these observations are possible due to the airborne rar s ability to collect high frame rate image sequences a capability that is not shared by present space based radar systems

identification of rain freshened plumes in the coastal ocean using ra isotopes and si office of global programs noaa silver spring maryland abstract two transient plumes of freshened water in the south atlantic bight off the coast of south carolina were measured and mapped during a continental shelf cruise in july 1994 salinity in the plumes was depressed 1 2 parts per thousand compared to surrounding shelf waters one plume was at least 160 kin long 20 kin wide and 5 7 m deep the other was 75 km long 25 kin wide and 5 7 m deep both plumes disintegrated almost completely in 6 days due to mixing or advection away from the sampling area measurement and analysis of short lived ra isotopes and si indicated that the plumes were not caused by river discharge but were rather due to an intense rain event a few days prior to the sampling cruise with only salinity measurements we would have incorrectly concluded that the freshened water was a result of river plumes having entered the shelf the rain was associated with the system that spawned tropical storm alberto we estimate that 220 330 mm of rain fell on the coastal ocean immediately before the cruise accompanying the rain were pesticides and nutrients we estimate that the flux of nitrate from the rain was twice the riverine flux of nitrate to the study area in the month preceding the cruise plumes of freshened water in the coastal ocean may be derived from river runoff or heavy offshore rain events large rivers may cause ocean freshening at scales of over 1000 km atkinson and wallace 1975 ortner et ai 1995 moore et ai 1986 distinguishing the source of the fresh water after the fact is difficult here we employ si and ra tracers previously used to distinguish between amazon derived water and rainfall in the tropical atlantic to identify rainfall as the agent of a freshened plume off the coast of south carolina the estuary shelf ocean exchange experiment esoe was conducted to establish techniques to determine the rate of cross shelf exchange of estuarine and nearshore waters with waters of the middle and outer continental shelf the experiment was conducted in the south atlantic bight sab a misnamed region off the southeast u s coast between cape hatteras and cape canaveral july 6 17 1994 during a prolonged period of vertical shelf stratification esoe was designed to use the distributions of 223ra t 112 11 4d and 224ra t 112 3 66d as an index of the exchange time five shore perpendicular transects between the cape fear river cf and the savannah river sv were sampled from the coastline to the edge of the shelf two transects myrtle beach mb and charleston ch were resampled two more times and the winyah bay transect wb was sampled three more times to determine if the tracer distributions were stable on a 2 week timescale figure 1 illustrates these transects and gives the station locations for the first pass no single river dominates freshwater input to the south atlantic bight sab the savannah santee and pee dee are the largest rivers each discharged 100 500 m3 s i during the

wind driven motion near inner shelf fronts the response of inner shelf fronts to wind forcing is numerically studied here by using a three dimensional primitive equation model the front and its associated circulation are maintained by discharging light water near the surface and withdrawing heavier water from below along one vertical wall of a cyclic channel subsequently a spatially uniform alongshore wind is applied responses to an upwelling favorable wind and to a downwelling favorable wind are highly asymmetric upwelling favorable wind forces the light water pool to surface and expand offshore the pool is quickly detached from the source by the newly upwelled water even for a moderate plume and strong wind it is unlikely that a downwind coastal jet can develop and force the plume to turn against its natural direction of propagation recent observations of chesapeake plume support this finding downwelling favorable wind slowly narrows the plume inside which a strong coastal jet is developed for a density anomaly of finite alongshore extent the jet intensifies downstream reaches a maximum near the lead isopycnal and decays thereafter to compensate for the downstream acceleration strong onshore flow develops near the upstream edge of the plume if the wind persists the enhanced onshore flow further narrows the plume and triggers a second intrusion unstable waves develop behind the second intrusion they are however limited to small amplitudes by the prevailing onshore ekman drift

the interaction of two closely spaced cracks a rock model study the influence of preexisting fractures on fracture development and the geometric patterns of crack growth have been investigated experimentally rectangular specimens of berea sandstone with two parallel thin cuts were compressed along their longest dimension at a confining pressure of 60 mpa a pore pressure of 20 mpa an average displacement rate of 2 10 4 cm s and room temperature the precuts are inclined 35 to the loading direction they are en echelon with each other each extending only part way from the specimen boundary when the sense of shear left or right lateral overlap left or right stepping and the amount of separation are changed significant difference of fracture interaction occurs an extensional fracture zone forms between left stepping precuts subjected to left lateral shear or right stepping precuts under right lateral shear secondary fractures tend to develop from one precut and toward the other precut the sequence of the fracture development is as follows a fractures which are about 60 to the precuts fractures which are about 30 to the precuts and fractures for large overlap pattern which are about 70 to the precuts but opposite in direction the fracture zone is confined by precuts and fractures therefore the larger the overlap the larger the fracture zone that develops for large overlap patterns a set of fractures forms nearly parallel and equally spaced within the fracture zone in cross sections fractures are normal faults with surface depression microscopic study shows that microfractures are highly concentrated in the area immediately adjacent to the macrofractures and at angles less than 30 to the macrofracture grains away from macrofractures remain unfractured for right stepping precuts subject to left lateral shear or left stepping precuts under right lateral shear a compression zone forms between the precuts the fractures propagate at precut tips and diverge away the fractures develop within the compression zone and are bounded by precuts and fractures the fractures develop within the compression zone and are bounded by precuts and fractures the fractures have reverse offsets in cross section

maximum link distance between strike slip faults observations and constraints the maximum fault link distance lateral separation between two interacting strike slip faults is studied in relation to fault length combined length of the two interacting faults data collected for laboratory generated strike slip faults indicate that fault linkage takes place when the lateral separation between two strike slip faults is less than one tenth of the combined length of the two faults strike slip faults developed in clay models require a smaller link distance than those developed in gouge materials about 98 of the data collected for natural strike slip faults and 93 of earthquake rupture data derived from knuepfer 1989 follow the rule these observations support a simple scaling relationship for strike slip faults i e w 0 1 l where wis lateral link distance and l the combined fault length an and sammis 1996a two possible explanations are discussed assuming a fault continues to be dominantly strike slip after various fault coalescences the fault link distance for both compressional coalescence leading to restraining bend and extensional coalescence leading to releasing bend can be constrained within 0 134 l assuming fault coalescence is caused by interaction between breakdown zones at fault tips then the scaling relationship b 0 1 l between the size of a breakdown zone b and the individual fault length l scholz et al 1993 leads to the scaling relationship w max 0 1 l where w max is the maximum link distance the above observed relationship between w max and l may not hold if faults coalesce through preexisting faults if a fault has a mixed mode other than strike slip or if a fault bend is caused by cross faulting rather than fault coalescence limited exposure of natural fault traces may also lead to errors in link distance measurements

coastal atmospheric forcing in the northern gulf of alaska a comparison of winds over the northern gulf of alaska found measured winds to be significantly weaker than calculated geostrophic winds the latter required more than the standard 30 reduction to correct for frictional effects in the maritime boundary layer an additional 11 is calculated based on principal axis analysis a counterclockwise rotation of the instantaneous geostrophic wind vectors of 44 59 total beyond the standard 15 was required to align them with those measured at a coastal weather station however events in these two wind sets were well correlated throughout the year and the rotary coherence was significant for frequencies lower than 0 895 cpd on the basis of empirical orthogonal function analysis most of the seasonal variability in this coastal current is associated with wind changes freshwater discharge is also important in driving the alongshore baroclinic flow and a secondary cross shelf flow

the nearshore current along a high rainfall trade wind coast nicaragua abstract runoff from abundant rainfall on the watersheds along the east coast of nicaragua results in a well defined nearshore current extending 20 40 km out from the coast important terms in the controlling dynamical balance are the coriolis forces and eddy frictional forces calculations of the diabathic surface slope 0 10 5 show a smooth setup of 4 5 cm from the outer edge of the current to the shoreline a longshore surface slope of 0 10 8 appears to be set up by the longshore wind stress and further computations allow an estimate of 6 gr cm 1 s 1 for the dynamic eddy viscosity an analytical expression including diabathic surface slope and density gradient parabathic surface slope wind stress and quadratic bottom friction reproduces the salient observed features of the nearshore current these include the pronounced maximum in the parabathic along shelf current about 10 km off the coast a complex diabathic velocity structure and a shelf countercurrent just seaward of the outer edge further calculations suggest that the dominant driving arises from the freshwater induced density gradients accounting for upward of 80 of the flow velocity as suggested by royer 1982 the prevailing trade wind exerts an onshore wind stress that serves the important role of maintaining the integrity of the density gradients via the convergence of a surface ekman layer toward the coast

observations of gulf stream induced and wind driven upwelling in the georgia bight using ocean color and infrared imagery ocean color and infrared imagery from aircraft and satellite sensors are combined with in situ measurements of currents chlorophyll temperature salinity coastal winds and sea level to study upwelling events in the georgia bight where the gulf stream and continental shelf waters strongly interact these interactions were observed over an 8 day period in april 1980 during which five independent upwellings occurred the upwellings included a nearshore wind driven upwelling enhanced by topographic effects three gulf stream filament induced upwellings and what appears to have been a gulf stream meander induced event the chlorophyll distributions as inferred from the imagery are found to be reliable tracers which indicate filamentary circulation and propagation and advective routes by which nearshore water moves offshore the propagation of two of the filaments and the meander are studied in detail using the imagery and mooring array temperature time series both techniques yield nearly identical results for the phase speeds of each event there is evidence that one of the filaments accelerated as it entered into the charleston bump area where the gulf stream deflects offshore the other filament exhibited a steady deceleration as it moved past cape canaveral and eventually lost any semblance of wave motion also includedmore are data from april 1979 which offer corroborating evidence of filamentary structure and circulation intercomparisons of field measurements and the nimbus 7 coastal zone color scanner estimates of surface pigment concentrations show excellent agreement over the range of 0 1 7 0 mg m sup 3 54 references 22 figures 6 tables less

analogue modelling of intraplate strike slip tectonics a review and new experimental results abstract intraplate strike slip zones commonly display intricate 3 d geometries with rapid changes in structural style along strike and with depth strike slip deformation typically results in complex vertical and horizontal sections that can be difficult to interpret coherently physical modelling of strike slip fault systems is a powerful and graphic tool to help in providing a unified picture of the evolution of strike slip zones with considerable spatial and temporal detail a large number of experimental studies have investigated different aspects of strike slip tectonics using materials such as dry sand wet clay or silicone the choice of analogue material and experimental design exerts a strong control on the structures that form in the model here we present a review of different experimental setups used to investigate intraplate strike slip tectonics from the classical riedel experiment to more sophisticated setups using brittle and viscous analogue materials we review our current understanding from models of distributed shear transtension transpression pull apart basins formed in releasing stepovers and popups formed in restraining stepovers in addition we present the results of two new experimental series that investigated 1 the effect of crustal weak zones on strike slip fault zone segmentation and 2 strike slip and transpressional reactivation of extensional basins

variation of upper layer dynamics during breakup of the seasonal ice cover in hudson bay the present study describes circulation and stratification changes associated with the melt and breakup of the seasonal ice cover in the coastal waters of southeast hudson day field work was carried out at a station located 25 km north of the great whale river buoyancy fluxes and dissipation rates were calculated as well as changes in potential energy surface velocity data were partitioned into frequency bands and complex demodulated throughout the sampling period most of the current energy was found to be in the semi diurnal tidal band after ice breakup however low frequency and inertial motions became relatively more important in response to direct wind forcing at the sea surface changes in amplitudes and phases of the major tidal constituents occurred and are related to the presence of the sea ice cover between early april and mid june semi diurnal current amplitude doubled while its phase shifted by 45 to 60 degrees in early june the ice cover was sufficiently dispersed to allow the surface turbulence to overcome the buoyancy flux and mix the upper water column

development of pull apart basins a comparative study of well mapped active and ancient pull apart basins suggests a qualitative model for their continuous development pull aparts evolve from incipient to extremely developed basins through a sequence of closely related states new and compiled map data from several areas including the northern caribbean and turkey suggests the following stages in pull apart development 1 in rigid intracontinental strike slip plate boundary zones larger pull aparts nucleate at releasing fault bends along segments of the principal displacement strike slip fault zone which are oblique to the theoretical interplate slip lines 2 initial opening across releasing fault bends produces spindle shaped basins defined and often bisected by oblique slip faults connecting the discontinuous ends of the strike slip faults 3 increased strike slip offset produces basin shapes which we colloquially call lazy s shape for basins between sinistral faults and lazy z shape for basins between dextral faults 4

identification of savannah river water on the south atlantic bight shelf using tritium tritium and salinity data were used in an investigation of the transport and fate of freshwater on the south atlantic bight sab shelf simultaneous tritium and salinity samples were collected at selected locations as part of the april 1985 spring removal experiment sprex a three source mixing model was used with tritium and salinity as tracers to determine if fresh water from the savannah river could be distinguished from other freshwater sources on the sab inner shelf variations in tritium concentration integrated freshwater fraction and model results were related to hydrographic and meteorological conditions results suggest that salinity and tritium concentration can be used to identify savannah river water on the shelf and that savannah river water maintains a distinct tritium salinity relationship at least as far north as charleston south carolina thus tritium may be a convenient and useful tool for studying nearshore mixing and transport processes in the sab

interaction and linkage of extension fractures and normal faults examples from the rift zone of iceland abstract field and photogeological studies were made of 90 zones of interacting fracture segments along the rift zone of iceland each zone consists of a pair of extension fractures or a pair of normal faults with lengths from metres to kilometres these zones evolve from an underlapping stage through an overlapping stage the most common configuration and finally to a linkage stage of all the zones only 7 are underlapping whereas 93 are overlapping with hook shaped fracture pairs the length width ratios of the overlapping zones have a mean value of 3 5 the preferred geometry of the overlapping zones depends upon the initial configuration of the interacting fractures length overstep and the development of the interaction in the overlapping zones most fracture pairs show moderate shear strike slip components related to local variations in the extension opening directions vertical displacements on normal faults decrease as the overstep and length of overlapping zones increase both in turn are proportional to the total lengths of the faults forming the pair the geometrical and kinematic features of overlapping spreading centres at mid ocean ridges show close similarities to those reported here these similarities indicate that the architecture and evolution of overlapping zones are scale independent

effects of ekman transport on the nao response to a tropical atlantic sst anomaly abstract a recent study showed that a tropical atlantic sea surface temperature sst anomaly induces a significant coupled response in late winter february april fma in a coupled model in which an atmospheric general circulation model is coupled to a slab mixed layer ocean model agcm ml the coupled response comprises a dipole in the geopotential height like the north atlantic oscillation nao and a north atlantic tripole in the sst the simulated nao response developed 1 or 2 months later in the model than in observations to determine the possible effects of ekman heat transport on the development of the coupled response to the tropical forcing an extended coupled model agcm eml including ekman transport in the slab mixed layer ocean is now used large ensembles of agcm eml experiments are performed parallel to the previous agcm ml experiments with the model forced by the same tropical atlantic sst anomaly over the boreal winter months september april the inclusion of ekman heat tra

structural imprints at the front of the choco panama indenter field data from the north cauca valley basin central colombia abstract the northern andes are a complex area where tectonics is dominated by the interaction between three major plates and accessory blocks in particular the choco panama and northern andes blocks the studied cauca valley basin is located at the front of the choco panama indenter where the major romeral fault system active since the cretaceous changes its kinematics from right lateral in the south to left lateral in the north structural studies were performed at various scales dem observations in the central cordillera between 4 and 5 7 n aerial photograph analyses and field work in the folded oligo miocene rocks of the serrania de santa barbara and in the flat lying pleistocene quindio risaralda volcaniclastic sediments interfingering with the lacustrine to fluviatile sediments of the zarzal formation the data acquired allowed the detection of structures with a similar orientation at every scale and in all lithologies these families of structures are arranged similarly to riedel shears in a right lateral shear zone and are superimposed on the cretaceous romeral suture they appear in the central cordillera north of 4 5 n and define a broad zone where 060 oriented right lateral distributed shear strain affects the continental crust the romeral fault system stays active and strain partitioning occurs among both systems the southern limit of the distributed shear strain affecting the central cordillera corresponds to the e w trending garrapatas ibague shear zone constituted by several right stepping en echelon right lateral active faults and some lineaments north of this shear zone the romeral fault system strike changes from nne to n paleostress calculations gave a wnw ese trending maximum horizontal stress and 69 of compressive tensors the orientation of 1 is consistent with the orientation of the right lateral distributed shear strain and the compressive state characterizing the romeral fault system in the area it bisects the synthetic and antithetic riedels and is sub perpendicular to the active romeral fault system it is proposed that the continued movement of the choco panama indenter may be responsible for the 060 oriented right lateral distributed shear strain and may have closed the northern part of the cauca valley thereby forming the cauca valley basin conjugate extensional faults observed at surface in the flat lying sediments of the zarzal formation and quindio risaralda volcaniclastic fan are associatedwith soft sediment deformations these faults are attributed to lateral spreading of the superficial layers during earthquakes and testify to the continuous tectonic activity from pleistocene to present finally results presented here bring newinformation about the understanding of the seismic hazard in this area whereas the romeral fault systemwas so far thought to be themost likely source of earthquakes themore recent cross cutting fault systems described herein are another potential hazard to be considered

spatial variability in sedimentary processes on the eel continental slope the northern california continental margin receives episodically large quantities of sediment from the eel river which seasonally discharges to the shelf regional circulation broadcasts this sediment widely not only affecting sedimentation on the shelf but on the slope as well a suite of 60 cores has been collected to examine the processes of sediment accumulation and sediment delivery to the eel continental slope in waters 800 m deep spatial surveys of accumulation rate 0 2 1 3 g cm 2 year 1 and surficial sediment grain size 4 8 5 demonstrate that sediment is accumulating throughout the eel margin reflecting a rapid and widespread redistribution of the fluvial discharge downcore grain size profiles of heterogeneous sediments suggest that hemipelagic and other episodic sediment delivery processes may be important for the slope in areas proximal to the river in more distal areas downcore profiles reveal relatively homogeneous sediments delivered dominantly by hemipelagic processes a budget for fine grained sediment shows that this upper portion of the slope contains at a maximum 20 of the river s annual discharge a combined budget for the shelf and upper slope suggests that at least 60 of the annual sediment load is not accounted for in these areas the eel continental slope because of the large terrigenous sediment input the narrow width of the adjacent shelf and its energetic environment is a good analogue for slopes during transitional stands of sea level and for modern tectonically active settings processes typically associated with these geological settings i e supply of sediment to the slope and downslope mass movement are actively occurring 1999 elsevier science b v all rights reserved

atmosphere ocean thermal coupling in the north atlantic a positive feedback in this article it is examined whether a positive atmosphere ocean feedback is found over the north atlantic through a series of general circulation model gcm experiments a 60 year integration of an atmospheric gcm agcm coupled with a 50 m deep motionless ocean was conducted the coupled run was compared with two uncoupled runs one with prescribed mid latitude climato logical sea surface temperatures ssts and the other with daily ssts derived from the coupled experiment the uncoupled atmosphere forces the slab ocean to obtain sst responses in these runs consistent with previous studies the coupled atmosphere ocean fields show interannual variances larger than those in the uncoupled runs due to reduction in the local thermal damping patterns of maximum atmosphere ocean covariability show the north atlantic oscillation nao and tripole sst anomalies both in the coupled and uncoupled fields indicating a dominant role of the atmosphere in generating the sst anomalies on the other hand analyses of the temporal variability in the three runs suggest an active role of sst anomalies in determining the polarity of the air sea coupled variability longer than the interannual time scale a combined analysis of forcing sst upper air height and the response sst anomalies in the uncoupled run identified that a patch of positive sst anomalies in the mid latitude band around 40 n effectively excite the positive phase of the nao which in turn reinforces the tripole sst anomalies this relationship was further confirmed by a nine member ensemble agcm experiment forced by the relevant sst anomalies since the forcing and response sst anomaly patterns bear some resemblance these results manifest positive feedback at work in the coupled atmosphere ocean patterns the processes responsible for this positive feedback were elaborated by a series of linear model experiments the local thermal adjustment of the atmosphere to the sst anomalies results in increased precipitation over the gulf stream region associated diabatic heating applied to a linear baroclinic model yields a positive height response to the east which highly influences the southern part of the nao this stationary response in turn induces a northward deflection in the storm track activity leading to an eddy vorticity feedback that tends to force the positive phase of the nao

tropical atlantic sst forcing of coupled north atlantic seasonal responses recent observational studies reveal that a fall pan atlantic sea surface temperature sst anomaly composed of a horseshoe like dipole in the north atlantic and a southern center in the equatorial atlantic tends to precede the winter north atlantic oscillation nao and its related sst tripole by several months this study seeks to understand this relationship using large ensembles of atmospheric general circulation model agcm experiments and experiments with the agcm coupled to a mixed layer ocean agcm ml the models are forced either by the north atlantic horseshoe nah or by the tropical sst anomalies over the boreal winter months the agcm results show that the nah anomaly induces a baroclinic response in geopotential heights throughout the winter with little projection on the nao since the nah anomaly is ineffective in forcing the wintertime nao it cannot account for observations that the nah sst leads the nao in contrast in the agcm ml the coupled north atlantic response forced by the tropical anomaly exhibits a strong seasonal dependence in early winter the positive anomaly induces a trough east of newfoundland with a wave train to the northeast and in late winter the response projects strongly on a negative nao correspondingly the extratropical sst response features an nah like pattern in early winter and a tripole in late winter these results suggest that tropical atlantic sst anomalies can significantly influence the coupled extratropical variability the observed relationship between the fall nah sst and the winter nao or the sst tripole may be a consequence of persistent forcing of the seasonally varying atmosphere by tropical sst anomalies comparisons with the parallel agcm results indicate that the largely sign symmetric nao responses developed in the agcm ml are in part due to active extratropical sst feedbacks diagnostic experiments using a linear model further illustrate that in the absence of transient eddy feedbacks an idealized tropical heating induces anomalous flows that are qualitatively similar in early and late winter with a trough southeast of newfoundland and a ridge to the northeast the enhanced seasonality in the sst induced coupled response likely arises from the seasonal modulation of transient eddy feedbacks on the heatingforced anomalous flow

role of the gulf stream and kuroshio oyashio systems in large scale atmosphere ocean interaction a review abstract ocean atmosphere interaction over the northern hemisphere western boundary current wbc regions i e the gulf stream kuroshio oyashio and their extensions is reviewed with an emphasis on their role in basin scale climate variability sst anomalies exhibit considerable variance on interannual to decadal time scales in these regions low frequency sst variability is primarily driven by basin scale wind stress curl variability via the oceanic rossby wave adjustment of the gyre scale circulation that modulates the latitude and strength of the wbc related oceanic fronts rectification of the variability by mesoscale eddies reemergence of the anomalies from the preceding winter and tropical remote forcing also play important roles in driving and maintaining the low frequency variability in these regions in the gulf stream region interaction with the deep western boundary current also likely influences the low frequency variability surface heat fluxes damp the low frequency sst anomalies ove

north atlantic decadal variability air sea coupling oceanic memory and potential northern hemisphere resonance in this paper the causes and mechanisms of north atlantic decadal variability are explored in a series of coupled ocean atmosphere simulations the model captures the major features of the observed north atlantic decadal variability the north atlantic sst anomalies in the model control simulation exhibit a prominent decadal cycle of 12 16 yr and a coherent propagation from the western subtropical atlantic to the subpolar region a series of additional modeling experiments are conducted in which the air sea coupling is systematically modified in order to evaluate the importance of air sea coupling for the north atlantic decadal variability being studied this shall be referred to as modeling surgery the results suggest the critical role of ocean atmosphere coupling in sustaining the north atlantic decadal oscillation at selected time scales the coupling in the north atlantic is characterized by a robust north atlantic oscillation nao like atmospheric response to the sst tripole anomaly which tends to intensify the sst anomaly and meanwhile also provide a delayed negative feedback this delayed negative feedback is predominantly associated with the adjustment of the subtropical gyre in response to the anomalous wind stress curl in the subtropical atlantic atmospheric stochastic forcing can drive sst patterns similar to those in the fully coupled ocean atmosphere system but fails to generate any preferred decadal time scales the simulated north atlantic decadal variability therefore can be viewed as a coupled ocean atmosphere mode under the influence of stochastic forcing this modeling study also suggests some potential resonance between the pacific and the north atlantic decadal fluctuations mediated by the atmosphere the modeling surgery indicates that the pacific climate although not a necessary precondition can impact the north atlantic climate variability substantially

the fate of river discharge on the continental shelf 2 transport of coastal low salinity waters under realistic wind and tidal forcing a three dimensional numerical simulation of shelf circulation is presented we employ realistic forcing for the southeast u s continental shelf during the spring season we show that the strongest offshore transport of river induced coastal low salinity waters and associated materials occurs near the surface the preferred mean pathway is in the northeastward direction and it takes about 2 months to cross the entire shelf owing to the mean direction of surface transport and the topography of the south atlantic bight shelf the preferred location for springtime removal is off charleston south carolina and presumably in the vicinity of the charleston bump the transport and fate of the river induced coastal low salinity waters during the spring season are determined by 1 the stratification of nearshore waters which is due to the high river runoff and causes the decoupling between near surface and near bottom layers 2 the prevailing northeastward winds which cause significant offshore transport within the shallow near surface ekman layer and 3 the tidally induced bottom stirring m2 tides comparison of model and data time series of currents shows very good agreement standard deviations of the model and data computed empirical orthogonal functions are almost identical while the respective variance conserving spectra agree both in amplitude and phase

ocean currents along a nearshore frontal zone on the continental shelf of the southeastern united states abstract river and estuarine discharges mix to form a frontal zone along a 400 km length of the coast of the south eastern united states the frontal width extends from the coast outward 10 20 km two ships anchored across the frontal zone during autumn obtained simultaneous hourly profiles of currents and density for five consecutive tidal cycles the frontal zone contained a baroclinic coastal current flowing southward the flow was strongly convergent more water entered on the coastal side than exited on the seaward side much of the inflow was apparently turned southward thus the frontal zone acted as a dynamic barrier that inhibited the advection of mixed river discharge farther offshore a thermal wind relationship suitably predicted vertical shear through the frontal zone bottom friction seemed to play only a secondary role data suggest that the baroclinic coastal current was modified by the presence of a barotropic current seaward of the frontal zone the force responsible for the barotrop

wind driven shifts in the latitude of the kuroshio oyashio extension and generation of sst anomalies on decadal timescales abstract the causes of decadal variations of north pacific sea surface temperatures ssts are examined using a hindcast performed with an ocean general circulation model thermodynamically coupled to an atmospheric mixed layer model ogcm aml model and forced by the time history of observed surface winds the shift in north pacific ocean climate that occurred around 1976 77 is focused on since this is the best observed example available after the 1976 77 shift the aleutian low deepened and moved to the southeast of its previous position this placed anomalous cyclonic flow over the north pacific the sst response as simulated by the ocean model consisted of two components a fast and local part and a delayed and remote part in the central pacific stronger westerlies cool the ocean by increased equatorward ekman drift here the dynamical cooling is sufficiently large that the surface fluxes damp the sst anomaly this ekman response is fast and local and cools the ssts beginning in 1977 and persistin

local and remote impacts of a tropical atlantic salinity anomaly the climatic impacts of an enhanced evaporation prescribed during 50 years in the tropical atlantic are investigated in a coupled ocean atmosphere general circulation model locally the salinity increase leads to a rapid deepening and cooling of the surface mixed layer this induces a deepening of the equatorial undercurrent and an intensification of the south equatorial current a remote atmospheric response to the tropical atlantic perturbation is detected in the north atlantic sector after ten years it has the form of a robust wave like tropospheric perturbation seemingly excited by the weakening of atmospheric deep convection over the amazonian basin meanwhile the salt anomaly is carried northward by the mean oceanic circulation it is traced up to the convection sites and then on its return path at depth towards lower latitudes consistent with the density increase deep convection is enhanced after the arrival of the salt anomaly and the atlantic meridional overturning circulation amoc intensifies about 20 years after the beginning of the perturbation the adjustment of the tropical atlantic to the amoc intensification then modifies its initial response to the freshwater forcing leading to a weaker cooling in the northern tropical atlantic than in the southern tropical atlantic a slight northward shift of the tropical atlantic precipitation pattern and an intensification of the north brazil current on the other hand no significant anomalous precipitations are found in the pacific the initial remote atmospheric response is also modulated by an nao like response to the amoc intensification

interdecadal variations in north atlantic sea surface temperature and associated atmospheric conditions abstract evidence is presented for a distinct pattern of ocean atmosphere relationship associated with interdecadal variability in the north atlantic region using a century of surface marine observations it is shown that middle and high latitude sea surface temperature sst display a long term fluctuation with negative anomalies before 1920 and during the 1970s and 1980s positive sst conditions prevailed from about 1930 to 1960 the pattern of interdecadal sst variability is constructed by subtracting the average field during 15 cold years from that during a similar interval of warm years the early century warming and the more recent cooling display a similar spatial pattern in both cases the pattern is basin scale and largely of one polarity with maxima in the vicinity of iceland in the labrador sea and northeast of bermuda the corresponding differences in surface atmospheric conditions are determined by averaging and subtracting in the same manner fields of sea level pressure slp and surf

the reemergence of sst anomalies in the north pacific ocean abstract sea surface temperature sst data and two different upper ocean temperature analyses are used to study the winter to winter recurrence of sst anomalies in the north pacific ocean the ssts recur when temperature anomalies that form in the deep ocean mixed layer in late winter early spring are isolated from the atmosphere in the summer seasonal thermocline and then reemerge at the surface when the mixed layer deepens during the following fall winter this reemergence mechanism is evaluated over the basin by correlating the time series of the leading pattern of ocean temperature anomalies in the summer seasonal thermocline 60 85 m in august september with sst anomalies over the course of the year the results indicate that the dominant large scale sst anomaly pattern that forms in the north pacific during late winter with anomalies of one sign in the central pacific and the opposite sign along the coast of north america is sequestered in the seasonal thermocline in summer and returns to the

on the transport of buoyant coastal plumes abstract the role of discharge conditions and shelf geometry on the transport of coastal plumes is studied with a fully nonlinear primitive equation hydrodynamic model the physical setting is an estuarine channel with a small discharge rossby number by simulating different discharge magnitudes buoyant plumes are shown to be succinctly described by a simple coastal front model three results emerge from the model analysis first the plume transport is given by t 0 g ph2 2f where 0 is a parameter dependent on the ratio of the front and the plume widths g p is the plume reduced gravity h is the plume maximum depth and f is the coriolis parameter second this model links the plume transport directly to upstream river conditions with t qr where qr is the river outflow and is a parameter that relates to entrainment the geometry of the plume front and shelf slope and the fraction of freshwater carried downshelf third these equations reduce to analytic results previously established for

convergence and downwelling at a river plume front abstract the small scale structure of the circulation and hydrography at the frontal boundary of the connecticut river plume in long island sound has been resolved using a novel combination of instruments a towed acoustic doppler current profiler adcp and a rigid array of current meters and conductivity temperature sensors observations were made during the latter half of the eastward ebb tide when the river plume was well established and the front was moving to the west at approximately 0 3 m s 1 two across front transects revealed a horizontal convergence rate in the across front velocity components at 0 6 m of 0 05 0 1 s 1 this was associated with a salt induced horizontal density gradient of 10 2 kg m4 observations obtained during a period in which the towed adcp was caught in the zone of maximum surface convergence showed significant downwelling with a near surface maximum of 0 2 m s 1 vertical velocities of this magnitude are consistent with observed magnitudes of the convergence rate at 0 6

transport and fate of river discharge on the continental shelf of the southeastern united states the authors analyzed 8 years of wind and salinity data from a frontal zone in a region of the inner continental shelf off the southeastern united states the changes in low salinity water stored in the frontal zone have been parameterized by analyzing the monthly rate of change in freshwater content when the rate of change in freshwater content was negative this was interpreted as a loss of low salinity water from the frontal zone when this parameter was compared with seasonally averaged alongshore wind stress the rate of loss was independent of the alongshore wind stress magnitude until threshold of about 0 1 dyne cm sup 2 was reached above the threshold there was a clear relationship between northward alongshore wind stress and rate of loss of freshwater from the inner shelf experimental evidence suggests that horizontal currents in the inner shelf frontal zone have cyclonic shear with increasing depth when wind stress is northward and offshore near surface low salinity water is transported offshore by ekman transport while near bottom high salinity water is transported shoreward 9 figures 2 tables

a modeling study of tidally driven estuarine exchange through a narrow inlet onto a sloping shelf the circulation and particle transport through a narrow inlet kelvin number 0 5 and onto a sloping shelf are numerically examined using a three dimensional hydrodynamic model the model domain consists of an estuarine basin with vertical density stratification separated from a well mixed sloping shelf by a narrow inlet forcing is supplied by semidiurnal tides and buoyancy differential strong ebb flows resulting from this combined forcing transport estuarine water seaward through the inlet to form a radially spreading buoyant surface plume over the shelf a series of radial density fronts corresponding with the ebbing tidal outflow are found on the seaward side of the inlet mouth and are convergence zones for floating particles strong anticyclonic frontal flow advects particles around the boundary of the outflow plume particles released nearest the seaward side of the inlet mouth are able to enter the inlet at depth and remain while those particles released farther offshore rarely enter the inlet this result has clear implications for the shelf to estuary transport of pollutants or the larval phase of marine species asymmetric tidally induced eddies which appear on both sides of the inlet also contribute to the near field circulation calculations of gradient richardson number in the inlet show that regions susceptible to enhanced mixing occur during periods of maximum tidal velocities due to increased shear

inner shelf circulation patterns and nearshore flow reversal under downwelling and stratified conditions off a curved coastline 1 the role of a curved coastline and associated bathymetry in the development of downwelling circulation in a stratified inner shelf is examined through a number of numerical experiments different scenarios include constant versus variable wind forcing and variations in bottom friction the three dimensional response of the shelf within the domain embayment enclosed by capes is associated with the generation of a velocity pycnocline disturbance at the upstream cape and its subsequent downstream advection this disturbance is more pronounced under variable wind conditions its downstream advection through the bay exhibits different patterns depending on the competition between inertia and bottom friction near the cape when inertia dominates the disturbance separates from the cape and travels downwind with an enhanced downstream flow offshore and a countercurrent inshore the separation occurs at a low rossby number ro 0 15 which is attributed to the positive curvature of the coastline forming the cape when friction dominates the advection path is constrained along the coastline resulting in an alongshore temperature gradient and a transient thermal front running almost perpendicular to the coast isobaths simulations with spatially variable bottom friction with higher friction toward the coast result in the generation of eddy like features the numerical results are in agreement with both observations and surface temperature imagery from long bay south carolina an embayment enclosed by two capes and emphasize the role that coastline and associated shelf morphology can play in enhancing cross shelf transport and exchange

dynamics of fault interaction parallel strike slip faults we use a two dimensional finite difference computer program to study the effect of fault steps on dynamic ruptures our results indicate that a strike slip earthquake is unlikely to jump a fault step wider than 5 km in correlation with field observations of moderate to great sized earthquakes we also find that dynamically propagating ruptures can jump both compressional and dilational fault steps although wider dilational fault steps can be jumped dilational steps tend to delay the rupture for a longer time than compressional steps do this delay leads to a slower apparent rupture velocity in the vicinity of dilational steps these dry cases assumed hydrostatic or greater pore pressures but did not include the effects of changing pore pressures in an additional study we simulated the dynamic effects of a fault rupture on undrained pore fluids to test sibson s 1985 1986 suggestion that wet dilational steps are a barrier to rupture propagation our numerical results validate sibson s hypothesis by demonstrating that the effect of the rupture on the undrained pore fluids is to inhibit the rupture from jumping dilational stepovers the basis of our result differs from sibson s hypothesis in that our model is purely elastic and does not necessitate the opening of extension fractures between the fault segments

observed impact of atlantic sst anomalies on the north atlantic oscillation the large scale patterns of covariability between monthly sea surface temperature sst and 500 mb height anomalies z500 in the atlantic sector are investigated as a function of time lag in the ncep ncar reanalysis 1958 97 in agreement with previous studies the dominant signal is the atmospheric forcing of sst anomalies but statistically significant covariances are also found when sst leads z500 by several months in winter a panatlantic sst pattern precedes the north atlantic oscillation nao by up to 6 months such long lead time covariance is interpreted in the framework of the stochastic climate model reflecting the forcing of the nao by persistent atlantic sst anomalies a separate analysis of midlatitudes 208 708n and tropical 208s 208n sst anomalies reveals that the bulk of the nao signal comes from the midlatitudes a dipolar anomaly with warm sst southeast of newfoundland and cold sst to the northeast and southeast precedes a positive phase of the nao and it should provide a prediction of up to 15 of its monthly variance several months in advance since the forcing sst pattern projects significantly onto the tripole pattern generated by the nao these results indicate a positive feedback between the sst tripole and the nao with a strength of up to 25 mk 21 at 500 mb or 2 3 mb k21 at sea level additionally a warming of the tropical atlantic 208s 208n roughly symmetric about the equator induces a negative nao phase in early winter this tropical forcing of the nao is nearly uncorrelated with and weaker than that resulting from the midlatitudes and is associated with shorter lead times and reduced predictive skill

fault development and interaction in distributed strike slip shear zones an experimental approach analogue model experiments using both brittle and viscous materials were performed to investigate the development and interaction of strike slip faults in zones of distributed shear deformation at low strain bulk dextral shear deformation of an initial rectangular model is dominantly accommodated by left stepping en echelon strike slip faults riedel shears r that form in response to the regional bulk stress field push up zones form in the area of interaction between adjacent left stepping riedel shears in cross sections faults bounding push up zones have an arcuate shape or merge at depth adjacent left stepping r shears merge by sideways propagation or link by short synthetic shears that strike subparallel to the bulk shear direction coalescence of en echelon r shears results in major through going faults zones master faults several parallel master faults develop due to the distributed nature of deformation spacing between master faults is related to the thickness of the brittle layers overlying the basal viscous layer master faults control to a large extent the subsequent fault pattern with increasing strain relatively short antithetic and synthetic faults develop mostly between old but still active master faults the orientation and evolution of the new faults indicate local modifications of the stress field in experiments lacking lateral borders closely spaced parallel antithetic faults cross faults define blocks that undergo clockwise rotation about a vertical axis with continuing deformation fault development and fault interaction at different stages of shear strain in our models show similarities with natural examples that have undergone distributed shear

seasonal fluctuations in sea level on the south carolina shelf and their relationship to the gulf stream near bottom pressure measurements obtained over a 9 month period in 1978 on the outer continental shelf off south carolina document that sea level rose 35 to 50 cm between july and october records of coastal sea level showed a similar rise when the pressure and coastal sea level records were corrected for the effects of wind stress and temperature the largest portion of the rise in the two variables remained the amplitude of the change in residual sea level was largest at the shelf break 28 cm and decayed to 22 cm at the coast the relatively small magnitude of the decay suggests that alongshelf pressure gradients imposed at the shelf break have minimum alongshelf wavelengths of 2000 km the changes in residual sea level were seasonal and associated with seasonal changes in the transport of the gulf stream the 3 years of residual sea level records examined here indicate that the amplitude of a typical decrease in transport of the gulf stream off south carolina between july and october has a strong interannual variability the change in transport can be 50 lower to over 100 higher than the historical average the residual sea level records also suggest that a change in transport of the gulf stream is not strongly related to the onshore offshore position of the gulf stream

a 400 km scale strike slip zone near the boundary of thetis regio venus we present a structural analysis of an area of venus surface centred on 3 s 116 e the area is dominated by a wide zone of deformation striking 050 n distinguished from the terrain on either side of it by markedly different structural and morphological characteristics the deformation zone contains two principal fault sets defined by form position and orientation members of the first set are present along the length of the deformation zone they are discontinuous consistently right stepping and are interpreted as riedel shears in a sinistral strike slip regime members of the second fault set are interpreted as normal faults and are often seen in pairs forming extensional grabens these faults are most prominent in the central region of the deformation zone and coincide with a deflection in strike of both the first fault set and the boundaries of the deformation zone a detailed kinematic analysis of all fault orientations and the boundaries of the deformation zone fit the predictions of transtensional theory supporting the hypothesis that this sinistral strike slip zone contains an extensional jog this interpretation is further supported by analysis of the interaction between faults belonging to the two sets variation in intercept geometry kinematic linking of the two fault sets and rotation of fault strike between the two fault sets all strongly suggest simultaneous development of these structures and therefore a common tectonic origin a driving mechanism for such large scale horizontal deformation on venus has yet to be established

hornblende content of georgia south carolina u s a nearshore sands support for shoreward sediment transport in the nearshore zone core top samples from 51 box cores taken about 1 km apart in several transects off hilton head island south carolina and tybee wassaw and ossabaw islands georgia have been analyzed for heavy mineral composition of acid insoluble 3 2 fractions to determine hornblende content and for acid soluble principally calcium carbonate plus carbonate fluorapatite content and grain size data for acid insoluble sand and gravel fractions 4 and for unacidified samples heavy mineral contents of acid insoluble 3 2 fractions range from 0 2 to 2 3 with hornblende and epidote the most abundant heavy minerals individual hornblende and epidote abundances range from 16 2 to 52 0 hornblende and epidote contents vary antithetically with maxima in hornblende content and minima in epidote content at nearshore and offshore ends of transects and with minima in hornblende content and maxima in epidote content over middle portions of transects ilmenite is the most abundant opaque mineral identified with abundances from 1 3 to 24 5 ilmenite maxima are associated with hornblende minima at several stations off hilton head and tybee islands apparently due to winnowing acid insoluble residues are very fine to fine 4 2 sands with very fine sand recent dominant within 5 km of shore and fine sand relict or palimpsest most abundant farther offshore acid soluble contents in our study area are 25 of total sample weight for nearly all samples analyzed and are often 15 high hornblende contents at seaward ends of transects indicate shoreward transport of hornblende rich sediments from the adjacent inner continental shelf low hornblende contents in middle portions of transects indicate dilution of hornblende rich sands by hornblende poor coastal plain sediments derived from coastal plain rivers and exposed by shoreface erosion 4 8 m deep and by tidal inlet erosion high hornblende contents at nearshore ends of transects reflect contribution of hornblende rich sediment from piedmont rivers to the nearshore zone

structure of the hanmer strike slip basin hope fault new zealand hanmer basin 10 x 20 km located in northern south island new zealand is evolving where two major segments of the dextral strike slip hope fault are projected to converge across a 6 to 7 km wide releasing step over the structural geometry and development of hanmer basin does not conform to traditional pull apart basin models the respective fault segments do not overlap but are indirectly linked along the southwest margin of the basin by an oblique normal fault the hope river segment terminates in an array of oblique normal faults along the northwestern basin range front and east west striking normal faults on the west hanmer plain faulted holocene alluvial fan surfaces indicate west hanmer basin is actively subsiding evolving under north south extension the conway segment along the southeastern margin of the basin terminates in a complex series of active fault traces small pop up ridges and graben depressions early basin fill sediments of pleistocene age are being folded elevated and dissected as the eastern part of hanmer basin is progressively inverted and destroyed by north south contraction the north margin of the basin is defined by a series of topographic steps caused by normal faulting outside of the area of the releasing step over these normal faults we interpret to reflect large scale upper crustal collapse of the hanging wall side of the hope fault new seismic reflection data and geologic mapping reveal a persistent longitudinal and lateral asymmetry to basin development four seismic stratigraphic sequences identified in the eastern sector of the basin thicken and are tilted southward with insequence lateral onlaps occurring to the north and east and also onto basement near the fault controlled basin margins the basin depocenter currently contains 1000 m of sediment adjacent to the south margin and is disrupted by faulting only at depth in the western part of the basin the sediment fill is thinner today the rate of basin deepening under transtension at the western end is matched by its progressive inversion and destruction under transpression in the eastern sector with the oldest basin fill now being recycled we propose a hybrid model for hanmer strike slip basin one in which geometric elements of a fault wedge basin downward and upward tipped spindle shaped ends are combined with those of a pull apart basin step over region between the major fault segments we also conclude that changes in fault geometry releasing and restraining bends and step overs at a variety of scales and over short distances control the development of the extensile and contractile parts of the basin and three dimensional basin asymmetry strain partitioning is complex and cannot be related simply to local reorientation of the regional stress field

water mass structure and boundaries in the mackenzie shelf estuary the mackenzie shelf is a broad estuarine region bordering the southeastern beaufort sea in the arctic ocean its fields of temperature and salinity result from the modification of offshore water masses by river inflow ice melting and freezing solar insolation and air sea exchange we here relate water masses resident on the mackenzie shelf to the large scale oceanography of the arctic mediterranean the summertime exchange between the shelf and open ocean is largely confined to waters lying above the main halocline s 34 2 psu cross shelf property distributions show that individual water masses maintain their structural identity i e core properties and buoyancy frequency as they move across the shelf and participate in the estuarine circulation shelf waters are strongly influenced by river inflow however the concept of a single plume issuing from the incoming river and forming a strictly two layered structure over uniform shelf water is misleading since a variety of temperature salinity and turbidity fronts co exist on the shelf at any given time

the transient atmospheric response to midlatitude sst anomalies abstract to study the transient atmospheric response to midlatitude sst anomalies a three layer quasigeostrophic qg model coupled to a slab oceanic mixed layer in the north atlantic is used as diagnosed from a coupled run in perpetual winter conditions the first two modes of sst variability are linked to the model north atlantic oscillation nao and eastern atlantic pattern eap respectively the dominant atmospheric modes in the atlantic sector the two sst anomaly patterns are then prescribed as fixed anomalous boundary conditions for the model atmosphere and its transient responses are established from a large ensemble of simulations in both cases the tendency of the air sea heat fluxes to damp the sst anomalies results in an anomalous diabatic heating of the atmosphere that in turn forces a baroclinic response as predicted by linear theory this initial response rapidly modifies the transient eddy activity and thus the convergence of eddy momentum and heat fluxes the latter transforms t

observed atlantic sst anomaly impact on the nao an update abstract the pan atlantic sea surface temperature sst anomaly pattern that was found in a previous study to have a significant impact on the north atlantic oscillation nao in early winter seemed to reflect the nearly uncorrelated influence of a horseshoe sst anomaly in the north atlantic and an sst anomaly in the eastern equatorial atlantic a lagged rotated maximum covariance analysis of a slightly longer dataset shows that the horseshoe sst anomaly influence is robust but it deemphasizes the center of action southeast of newfoundland canada on the other hand it suggests that the link between equatorial sst and the nao was artificial and due both to enso teleconnections and the orthogonality constraint in the maximum covariance analysis

fault trace complexity cumulative slip and the shape of the magnitude frequency distribution for strike slip faults a global survey summary we examine whether the shape of the magnitude frequency distribution for strike slip faults is described by the gutenburg richter relationship log n a bm or by the characteristic earthquake model by analysing a data set of faults from california mexico japan new zealand china and turkey for faults within regional seismic networks curves of the form log n yrpl a bm where n yr is the number of events per year equal to magnitude m are fit to the instrumental record of seismicity and geological data are used to estimate independently the size and recurrence rate of the largest expected earthquakes that would rupture the total length of the fault extrapolation of instrumentally derived curves to larger magnitudes agrees with geological estimates of the recurrence rate of the largest earthquakes for only four of the 22 faults if uncertainties in curve slope are considered and significantly underestimates the geological recurrence rates in the remaining cases also if we predict the seismicity of the faults as a function of fault length and slip rate and the predicted seismicity is distributed in accord with the gutenburg richter relationship we find the predicted recurrence rate to be greater than the observed recurrence rates of smaller earthquakes along most faults if individual fault zones satisfy the gutenburg richter relationship over the long term our observations imply that during the recurrence interval of the largest expected earthquakes the recurrence of lesser sized events is not steady but rather strongly clustered in time however if the instrumental records provide an estimate of the long term rate of small to moderate earthquakes along the faults our observations imply that the faults generally exhibit a magnitude frequency distribution consistent with the characteristic earthquake model also we observe that the geometrical complexity of strike slip faults is a decreasing function of cumulative strike slip offset the four faults we observe to be consistent with the gutenburgrichter relationship are among those characterized by the least amount of cumulative slip and greatest fault trace complexity we therefore suggest that the ratio of the recurrence rate of small to large earthquakes along a fault zone may decrease as slip accumulates and the fault becomes smoother

the inner shelf response to wind driven upwelling and downwelling abstract a two dimensional numerical model is used to study the response to upwelling and downwelling favorable winds on a shelf with a strong pycnocline during upwelling or downwelling the pycnocline intersects the surface or bottom forming a front that moves offshore the characteristics of the front and of the inner shelf inshore of the front are quite different for upwelling and downwelling for a constant wind stress the upwelling front moves offshore at roughly a constant rate while the offshore displacement of the downwelling front scales as t because the thickness of the bottom layer increases as the front moves offshore the geostrophic alongshelf transport in the front is larger during downwelling than upwelling for the same wind stress magnitude because the geostrophic shear is near the bottom in downwelling as opposed to near the surface in upwelling during upwelling weak stratification is maintained over the inner shelf by the onshore flux of denser near bottom water this weak stratif

analysis of current observations on the georgia shelf abstract an analysis is made of hf radar measurements of surface currents in shallow water near the georgia coast and also of vertical profile measurements of current and density the dominant structure is found to be a clockwise ellipse of semidiurnal periodicity the ellipses becoming smaller narrower and turning clockwise with depth there is a definite phase lead of the bottom currents with respect to the upper currents and some evidence of veering of the currents in the non ekman sense in order to explain the observed vertical variations a simple analytical expression is developed for periodic rotary currents in a barotropic ocean of constant eddy viscosity and depth h when the free surface elliptic motion is known the solution depends on the ratios f and h hekman and also on the sense of turning of the free surface ellipse the model is able to explain several features of the observed vertical variations as frictional effects

the influence of wind forcing on the chesapeake bay buoyant coastal current observations of the buoyant coastal current that flows southward from chesapeake bay are used to describe how the thickness width and propagation speed vary in response to changes in the along shelf wind stress three basic regimes were observed depending on the strength of the wind for weak wind stresses from 0 02 to 0 02 pa the buoyant coastal current was relatively thin the front slope was not steep and the width was variable 1 20 km for moderate downwelling southward wind stresses 0 02 0 07 pa wind driven cross shelf advection steepened the front causing the plume to narrow and thicken for stronger downwelling wind stresses greater than 0 07 pa vertical mixing dominated bulk richardson numbers were approximately 0 25 isopycnals were nearly vertical and the plume front widened but the plume width did not change plume thickness and width were normalized by the theoretical plume scales in the absence of wind forcing normalized plume thickness increased linearly from 1 to 2 as downwelling wind stresses increased from 0 to 0 2 pa normalized plume widths were approximately 1 for downwelling wind stresses from 0 02 to 0 2 pa the observed along shelf propagation speed of the plume was roughly equal to the sum of the theoretical propagation speed and the wind driven along shelf flow

development of fault discontinuities in shear experiments abstract shear experiments using clay and fault gouge cakes were performed to study the origin of discontinuities along strike slip faults simple continuous strike slip faults initially nucleated in the samples and they were separated from each other discontinuities began to develop when these faults interacted each other two processes were especially important for the development of fault discontinuities cross faulting which caused segmentation and offsetting of originally continuous faults and fault interaction which changed fault propagation paths created various types of bends abandoned some old fault segments and caused coplanar faults to avoid each other cross faulting created type i fault discontinuities in which all fault segments in a fault stepped in one direction either all left or all right and fault interaction created type ii discontinuities in which fault segments in a fault stepped in both directions the experimental results are compared with some natural fault patterns to demonstrate that this type of experiments can be used to investigate the origin of discontinuities along natural strike slip faults

dominant modes of variability in the south atlantic a study with a hierarchy of ocean atmosphere models using an atmosphere model of intermediate complexity and a hierarchy of ocean models the dominant modes of interannual and decadal variability in the south atlantic ocean are studied the atmosphere simplified parameterizations primitive equation dynamics speedy model has t30l7 resolution the physical package consists of a set of simplified physical parameterization schemes based on the same principles adopted in the schemes of state of the art agcms it is at least an order of magnitude faster whereas the quality of the simulated climate compares well with those models the hierarchy of ocean models consists of simple mixed layer models with an increasing number of physical processes involved such as ekman transport wind induced mixing and wind driven barotropic transport finally the atmosphere model is coupled to a regional version of the miami isopycnal coordinate ocean model micom covering the south atlantic with a horizontal resolution of 1 and 16 vertical layers the coupled modes of mean sea level pressure and sea surface temperature simulated by speedy micom strongly resemble the modes as analyzed from the ncep ncar reanalysis indicating that this model configuration possesses the required physical mechanisms for generating these modes of variability using the ocean model hierarchy the authors were able to show that turbulent heat fluxes ekman transport and wind induced mixing contribute to the generation of the dominant modes of coupled sst variability the different roles of these terms in generating these modes are analyzed variations in the wind driven barotropic transport mainly seem to affect the sst variability in the brazil malvinas confluence zone the spectra of the mixed layer models appeared to be too red in comparison with the fully coupled speedy micom model due to the too strong coupling between sst and surface air temperatures sats resulting from the inability to advect and subduct sst anomalies by the mixed layer models in speedy micom anomalies in the southeastern corner of the south atlantic are subducted and advected toward the north brazilian coast on a time scale of about 6 yr

observations of the response of a buoyant estuarine plume to upwelling favorable winds 1 the response of the buoyant plume from the chesapeake bay to upwelling favorable winds and during conditions of low freshwater discharge is examined using an offshore array of bottom deployed acoustic doppler current profilers adcps as well as ancillary data during periods of northward upwelling favorable winds the observed response is strong offshore flow u 0 2 m s in a shallow layer of plume water and a rapid reversal of the near surface flow from the usual southward flow associated with inertial turning of the plume the offshore migration of the plume front is deduced from sequential arrivals at the various mooring locations the orientation of the plume front is approximately alongshore north south suggesting that the upwelling response is two dimensional a plume thickness calculated from the adcp data is relatively constant at about 4 m as the plume moves across the moorings the offshore propagation speed of the plume front of about 0 20 m s matched the advection speed predicted by ekman theory using the calculated plume layer thickness the mooring velocity profiles provide a view of the across plume structure in a reference frame fixed to the front this reveals a pattern of circulatory motion with sinking of plume and ambient water at the front and an ascending motion occurring inshore suggesting a recirculation between the seaward and inshore portions of the plume these results are consistent with recent model simulations of the response of a river plume during upwelling favorable winds

model simulations of the bay of fundy gyre 1 climatological results 1 the characteristics of a persistent gyre in the mouth of the bay of fundy are studied using model simulations a set of climatological runs are conducted to evaluate the relative importance of the different forcing mechanisms affecting the gyre the main mechanisms are tidal rectification and density driven circulation stronger circulation of the gyre occurs during the later part of the stratified season july august and september october the density driven flow around the gyre is set up by weak tidal mixing in the deep basin in the central bay of fundy and strong tidal mixing on the shallow flanks around grand manan island and western nova scotia spring river discharge has an important influence on near surface circulation but only a small effect when averaged over the entire water column retention of particles in the gyre is controlled by the residual tidal circulation increased frontal retention during stratified periods wind stress and interactions with the adjacent circulation of the gulf of maine residence times longer than 30 days are predicted for particles released in the proximity of the gyre

late cenozoic right lateral strike slip faulting in southern tibet field observations collected during the sino french himalaya tibet cooperation project 1980 1982 show that right lateral faulting between southern and northern tibet roughly along the chord joining the eastern and western syntaxes of the himalayan arc is a major component of the active tectonics north of the himalayas just north of the well developed rifts of southern tibet we studied three right lateral 100 200 km long strike slip faults forming an en echelon array along that chord evidence for earthquake surface breaks was found on each of these faults for the m 8 beng co or damxung strike slip earthquake of november 18 1951 rupture parameters could be constrained to be 8 2 m and l 90 km offset glacial and postglacial morphological markers 105 years and 104 years b p imply displacement rates of the order of 1 2 cm yr on the three faults the en echelon fault zone appears to extend westward 2000 km across the plateau to the karakorum fault and is thus referred to as the karakorum jiali fault zone kjfz fast rates of slip on it and on faults along the northern rim of tibet appear to contrast with the slower rates of deformations in the interior of the plateau our estimates of slip rates on the strike slip and normal faults of southeastern tibet suggest that eastward extrusion of north tibet between the right lateral kjfz and the left lateral altyn tagh and kun lun faults absorbs at least 30 of the present convergence between india and asia we propose an instantaneous velocity model of the active tectonics of asia compatible with such faulting rates and geometries evidence for tertiary right lateral strike slip movements in southern tibet and around the eastern syntaxis of the himalayas is also found in the structural record offsets of various large scale geological features imply that these movements have been large

radium 228 in the south atlantic bight radium 228 in surface ocean waters is derived from sedimentary fluxes generated in estuaries salt marshes and fine grained sediments of the inner shelf thus the sup 228 ra activity of shelf waters is a measure of their interaction with these sediments mixing of the sup 228 ra signal offshore follows known circulation patterns and examination of the sup 228 ra field as determined by the sup 228 ra sup 226 ra activity ratio ar reveals details of these patterns during february sinking of chilled shelf waters carries high ar water to depths of 80 130 m just below the shelf break in april upwelling from 500 700 m depth brings low ar water to the shelf break where it replaces the high ar waters present 2 months earlier during august low ar waters at the shelf break could be traced to the surface where they separated higher ar waters both inshore and offshore of the shelf break because of such short term variability one dimensional steady state models which balance sup 228 ra decay with mixing do not provide a true measure of horizontal mixing rates fluxes necessary to support the sup 228 ra standing crop in the south atlantic bight are of the order of 2 5 x 10 sup 14 dpm yr thesemore are similar to estimates from the new york bight but 25 times lower than the apparent flux from the amazon system copyrightamerican geophysical union 1987 less

scaling analysis for the interaction between a buoyant coastal current and the continental shelf experiments and observations abstract this paper addresses how the geometrical parameters ambient ocean depth h bottom slope of coastal bathymetry affect the evolution of buoyant coastal currents flowing over a sloping continental shelf scaling arguments are presented that show the coastal current dynamics can be classified by a two variable nondimensional parameter space the ambient depth parameter h h and the bottom slope parameter r yb the ratio h h is the fraction of the available depth occupied by the buoyant layer the bottom slope parameter is the ratio of two horizontal length scales the internal rossby radius r to the bottom trapped width yb the scale depth h is derived from geostrophic dynamics and is representative of the depth of the buoyant layer of the coastal current the resulting parameter space is delineated by surface advected currents that do not depend upon the bottom slope parameter and bottom trapped currents that do for bottom trapped coastal currents the across shore width and downstream velo

structural features of an active strike slip fault on the sliding flank of mt etna italy abstract the strike slip pernicana fault system pfs was activated along the eastern flank of mt etna during an earthquake in september 2002 and one month later during the eruption of the ne rift structural and volcanological data suggest that the pfs was activated as a result of the slide of the ne flank of etna this activation produced surface fracturing on walls and on paved and unpaved roads the segments of the pfs arranged in a right stepping en echelon configuration show a an inverse proportion between length and frequency b fractal behavior over scales of 10 2 10 1 m between their length overstep and overlap c consistent strike with regard to their fault array and d a progressive eastward decrease in the displacement along the smallest faults the consistent geometric and kinematic features of the pfs related to the sector collapse of etna are similar to those of faults in strike slip settings

cross shore variation of wind driven flows on the inner shelf in long bay south carolina united states and exceeded 0 1 n m 2 vertical mixing occurred the two layered flow pattern disappeared and currents were directed alongshore with the wind at all sites and throughout the water column in the fall near bed flows close to the shore water depth 7 m were often reduced compared to or opposed those measured farther offshore under southwestward winds a simplified analysis of the depth averaged alongshore momentum balance illustrates that the alongshore pressure gradient approached or exceeded the magnitude of the alongshore wind stress at the same time that the nearshore alongshore current opposed the wind stress and alongshore currents farther offshore in addition the analysis suggests that the wind stress is reduced closer to shore so that the alongshore pressure gradient is large enough to drive the flow against the wind

an intimate coupling of ocean atmospheric interaction over the extratropical north atlantic and pacific the inter basin teleconnection between the north atlantic and the north pacific ocean atmosphere interaction is studied using a coupled ocean atmosphere general circulation model in the model an idealized oceanic temperature anomaly is initiated over the kuroshio and the gulf stream extension region to track the coupled evolution of ocean and atmosphere interaction respectively the experiments explicitly demonstrate that both the north pacific and the north atlantic ocean atmosphere interactions are intimately coupled through an inter basin atmospheric teleconnection this fast inter basin communication can transmit oceanic variability between the north atlantic and the north pacific through local ocean to atmosphere feedbacks the leading mode of the extratropical atmospheric internal variability plays a dominant role in shaping the hemispheric scale response forced by oceanic variability over the north atlantic and pacific modeling results also suggest that a century two centuries long observations are necessary for the detection of pacific response to atlantic forcings atlantic response to pacific forcing

coupled ocean atmosphere response to indian ocean warmth 1 the coupled ocean atmosphere response to indian ocean warmth is studied it is shown with atmospheric models that indian ocean warmth forces a positive polarity phase of the north atlantic oscillation nao confirming results of previous studies coupled model experiments show that this nao response forces a local air sea feedback over the north atlantic ocean which intensifies the nao response this enhancement is realized through a positive feedback between the nao atmospheric circulation anomaly and a tripolar north atlantic sst pattern consistent with other studies on north atlantic air sea interactions it is concluded that the north atlantic and european climate response to indian ocean warming may be considerably greater than hitherto judged from the analyses of atmospheric model experiments alone

structure and deformational character of strike slip fault zones strike slip fault zones observed either in the field or in model experiments generally consist of several subparallel faults which make these zones complicated in geometry and kinematics the geometry of a strike slip fault or shear zone is dependent on arrangement pinnate or en echelon on step left step or right step and on the rank smaller faults within larger faults of the subparallel fault the relations and interactions of these three factors create a variety of dynamic circumstances and tectonic settings within the strike slip fault zones these include pull aparts in the release area between subparallel faults push ups in the jogs where the subparallel faults overlap and pivotal movements or rotation of single faults along the whole fault zone each kind of tectonic setting is in itself characteristic each setting consists of many subtypes which are controlled chiefly by the geometric parameters of the subparallel faults one of the most important phenomena revealed in the field work is two different kinds of evolution of strike slip fault zones one is the evolution of a zone with a tensile component which is related to the growth of rock bridges and the other of one with a compressional component which develops by the destruction of rock bridges in this paper we discuss on the basis of recent research on four strike slip fault zones in china the essential characteristics of strike slip faults and the possible causes of the observed structural phenomena attention is focussed on the deformation development and distribution of horizontal displacements within strike slip fault zones

gravity current structure of the chesapeake bay outflow plume measurements made across the edge of the chesapeake bay outflow plume in september 1996 are examined for evidence of the frontal head structure expected for a buoyant gravity current shipboard acoustic doppler current profiler and hydrographic data from two distinct 2 hour long sets of frontal transects are analyzed one set of observations was acquired just south of the bay mouth near cape henry virginia during late flood tide in water depth of 8 m these measurements show a nearly steady frontal structure and a frontal head that is approximately 5 m deep and 20 m wide the second data set was acquired about 20 km southeast of the bay mouth where the plume bulges horizontally outward over the continental shelf these measurements show a 9 m deep frontal head in water depth of 18 m that ultimately dissipates during early flood tide in both sets of observations relative inflow of plume water into the frontal head is confined to a shallow surface layer estimated to be no more than about 2 m deep referenced to this layer frontal propagation is supercritical froude number greater than 1 also measured was an expected sinking motion of the order of 3 cm s along the front overall the results are consistent with previous measurements made across smaller buoyant plumes and in the laboratory and they are compatible with the use of fixed values of froude number and entrainment parameter in two layer plume models additional study of the plume front during ebb tide is recommended

enhanced turbulence due to the superposition of internal gravity waves and a coastal upwelling jet to vertical aspect ratios of 10 2 to 10 3 median value 300 these patches are clearly defined by regions of low richardson number and occur where and when the linear superposition of the three dominant shear constituents near inertial m2 and thermal wind interferes constructively this is most pronounced at the base of the coastal jet where the thermal wind shear is largest while the effect of the turbulence stress divergence on the jet is small compared to geostrophy 1 it is significant in the second order force balance governing secondary circulation the timescale associated with the decay of the thermal wind shear via turbulence stress is o 10 days we confirm that the vertical salt flux due to mixing is comparable to the net ekman transport of salt onto the shelf within the bottom boundary layer because numerical models of coastal circulation lack turbulence in midwater column any vertical transport of scalars including salt and heat must be achieved inshore of the 40 m isobath this is inconsistent with the observations presented in this study in which significant vertical turbulent salt transport is found to exist across the entire shelf

philippine fault a key for philippine kinematics on the basis of new geologic data and a kinematic analysis we establish a simple kinematic model in which the motion between the philippine sea plate and eurasia is distributed on two boundaries the philippine trench and the philippine fault this model predicts a velocity of 2 to 2 5 cm yr along the fault geologic data from the visayas provide an age of 2 to 4 ma for the fault an age in good agreement with the date of the beginning of subduction in the philippine trench the origin of the philippine fault would thus be the flip of subduction from west to east after the locking of convergence to the west by the collision of the philippine mobile belt with the eurasian margin

mixing of a dye tracer in the delaware plume comparison of observations and simulations 1 in april 2003 we injected rhodamine wt fluorescent dye into the halocline at the base of the delaware river plume during an upwelling event the dye immediately bifurcated one third of the dye moved offshore with a portion of the plume while the other 2 3 remained within the halocline near the coastline this behavior has not been previously observed and it presents a strong challenge to contemporary coastal ocean models here we employ a numerical model of delaware bay and the adjacent coastal region that incorporates the mellor yamada level 2 5 turbulence closure scheme to simulate the observed dye injection event comparison between the simulation and observations reveals that the model is able to successfully reproduce the flow field simulating the separation and subsequent advection of the dye consequently the simulation is used to examine the relative effects of wind and buoyancy driven transport on mixing and advection of the dye comparison of simulated and observed plumes reveals that the model accurately reproduces the observed mixing and accompanying vertical salt flux within the offshore plume examination of the simulation reveals a unique combination of wind and buoyancy driven flow that results in the dye remaining in the halocline of the onshore plume despite significant vertical mixing due to winds the strong stratification within the inshore plume causes the closure scheme to shut off the vertical diffusivities leaving the circulation model with arbitrarily chosen constant background values varying these values reveals only a weak dependence of the salt flux within the highly stratified regions due to the highly localized nature of the salt flux

development of strike slip faults shear experiments in granular materials and clay using a new technique abstract a new experimental technique has been developed to study fault development in layers of moist granular materials clay and fault gouge in shear faults nucleated on pre existing pores and on low displacement protofaults in flaw free areas only a small number of the protofaults developed significant displacement forming conjugate simple fault sets after nucleation simple faults propagated in plane as these simple faults grew in length and new simple fault sets nucleated they began to interact and coalesce simple faults linked up to form compound faults and compound faults linked up to form even larger through going strike slip faults the fault patterns produced in the shear experiments were integrated fault networks consisting of several sets of conjugate shears and tensile structures compound faults exhibited both releasing and restraining steps formed during fault coalescence displacement along such a compound strike slip fault caused a mismatch of the two walls a few points became resistant barriers while the remaining segments became pull apart basins both releasing and restraining steps led to the development of pull apart basins fault displacement and propagation rate were linear functions of fault length the difference between the experiment described here and traditional riedel experiments is that the new experiments do not have a pre existing fault in the experimental setup therefore they are more suitable to study fault nucleation and evolution in a broad shear zone

subtidal flow structure at the turning region of a wide outflow plume 1 a series of underway current velocity profiles and near surface temperature and salinity measurements were combined with temperature and salinity profiles to characterize the subtidal flow structure at the turning region of a wide plume the chesapeake bay outflow plume in this context wide refers to the ratio of lateral plume expansion to internal radius of deformation being greater than one observations were obtained in september and november of 1996 and in february and may of 1997 with the idea of capturing the variability in forcing conditions typically associated with these seasons however regional precipitation patterns yielded similar buoyancy forcing conditions for the four surveys and among the wettest years on record this buoyancy forcing produced a well delineated outflow plume that separated from the coast on its way out the estuary the plume separation acted in conjunction with frictional effects to delineate an inshore front in addition to the customarily described offshore front the outflow plume was markedly constrained by the chesapeake channel which was also the main conduit of shelf waters toward the estuary the bathymetric influence was also evident in the surface salinity field the mean flows and the volume fluxes the offshore extent of the plume was found between the scale predicted by geostrophic dynamics internal rossby radius and that predicted by cyclostrophic dynamics such offshore extent was most likely linked to the plume interactions with the bathymetrically steered up estuary flow this was corroborated by an analytical solution that explored the dynamical balance among pressure gradient coriolis accelerations and friction in addition to being influenced by bathymetry the chesapeake bay outflow plume was modified by local and remote effects related to atmospheric forcing

a description of tides near the chesapeake bay entrance using in situ data with an adjoint model 1 time series of surface elevation and current velocity in the vicinity of the chesapeake bay entrance are assimilated into a linear barotropic model using an iterative adjoint method tide surface elevations noaa nos tidal data moored acoustic doppler current profiler adcp and ocean surface current radar oscr data are included in the assimilation data are analyzed for three tidal constituents m2 s2 o1 tidal series are constructed from these constituents and then used in the model assimilations statistics of predicted currents compare favorably with those calculated from data not used in the assimilation an error analysis of the data distribution is performed for the m2 tidal component showing lower errors near assimilation data series but large errors particularly for velocity at some locations addition of a hypothetical current mooring dramatically reduces errors over most of the domain we believe these results give the most demonstrably accurate description now available of tidal currents for this region of strong currents and heavy shipping

strike slip fault geometry in turkey and its influence on earthquake activity the geometry of turkish strike slip faults has been reviewed and described from this data set it appears that fault geometry the distribution of discontinuities such as bends and stepovers along the main fault trace plays an important role in controlling the location of large earthquake rupture segments along the fault zones large earthquake ruptures generally do not propagate past individual stepovers that are wider than 5 km or bends that have angles greater than about 30 more important than the size of each discontinuity however is the total geometric pattern i e the distribution of adjacent bends and stepovers based not only on distance from one another but also on relative discontinuity size certain geometric patterns restraining single or double bends are particularly common and can be viewed as responsible for strain accumulation along portions of the fault zone fault geometry not only plays a role in the extent of earthquake rupture but also in characteristics of earthquake behavior for example large earthquake epicenters often occur near restraining bends or double bends furthermore aftershocks and swarm activity can often be associated with releasing areas areas along the strike slip fault that are undergoing a relatively large amount of extension

circulation and larval distribution in internal tidal bore warm fronts internal tidal bore warm fronts were observed during the summer of 1996 off the coast of southern california warm bore fronts had concentrating currents resulting from high frequency internal motions and from a larger two way flow the two way flow featured surface currents onshore and bottom currents offshore a sharp thermocline depression and high frequency large amplitude internal motions followed the leading edge of the bore with downwelling currents on the trailing side of the crest of the nonlinear internal waves and upwelling currents in front of the crest warm bores propagated onshore with a propagation speed c that ranged from 10 6 to 19 6 cm s 1 while time averaged frontal currents varied from 11 2 to 17 6 cm s 1 in the shallowest bin in one out of three cases c which implied that there were faster currents than the rate of advance of the front and which implied that the origin of surface frontal material is behind the front not in front of it three invertebrate larval taxa were found at all sites across fronts but only two intertidal barnacles pollicipes polymerus and chthamalus spp were concentrated at the front s surface while the subtidal bryozoan membranipora spp was not frontal pollicipes were more concentrated than were chthamalus the frontal downwelling currents observed suggested that concentrated larvae would have to swim upward in order to maintain depth pollicipes were abundant on the offshore warm side of the fronts but were absent or rare on the onshore colder side suggesting that the origin of frontal pollicipes was behind the front although an alternative cannot be ruled out conclusively chthamalus were more abundant at depth than at the surface at all sites except at the front where this pattern was reversed the origin of frontal chthamalus is uncertain membranipora were more abundant on the onshore colder side of the fronts and abundances were usually higher at depth than at surface lack of accumulation in this species may be due to its limited swimming capability

sea surface temperature anomalies planetary waves and air sea feedback in the middle latitudes the mechanisms that contribute to the generation and damping of large scale mid latitude sea surface temperature sst anomalies are discussed the sst anomalies reflect primarily the response of the upper ocean to the changes in air sea fluxes that are associated with daily weather fluctuations heat flux forcing is dominant in the lower middle latitudes while wind driven entrainment may be most effective in the high latitudes advection by anomalous ekman current is generally less important and ekman pumping is negligible the sst anomalies decay in part because of entrainment effects associated with mixed layer deepening and oceanic mixing and in part because of heat exchanges with the atmosphere the three approaches commonly used to model the evolution of sst anomalies are reviewed case studies based on monthly or seasonal anomaly maps of the large scale sst and atmospheric anomalies numerical simulations with one dimensional mixed layer models and stochastic forcing models we stress the similarities in the different approaches and discuss their main advantages and limitations the response of the atmosphere to mid latitude sst anomalies is considered first we discuss the poorly known relationship between sst anomalies and diabatic heating using a crude assumption for the air sea coupling we consider a two layer quasi geostrophic channel model and discuss the stationary wave response to sst anomaly forcing and the resulting air sea feedback it is found that the back interaction of the sst anomalies onto the atmosphere causes a weak sst anomaly damping at large scales and a strong one at small scales the air sea coupling should also act as an eastward propagator for the sst anomalies the response of more realistic linear wave models to prescribed diabatic heating is then reviewed and it is suggested that realistic mid latitude sst anomalies have a weak influence on the atmospheric circulation corresponding to changes in the geopotential height of 10 30 m at most this order of magnitude is consistent with the results of general circulation model experiments and with the limited climate predictability associated with mid latitude sst anomalies

circulation mixing and exchange processes in the vicinity of tidal inlets a numerical study the circulation in the vicinity of an idealized tidal inlet connecting a continental shelf and a coastal sound is examined the circulation is forced by an m2 tide and a weakly buoyant discharge the buoyant discharge forms a plume in the coastal ocean and induces a distinct anticyclonic circulation at the plume edge that is maintained throughout the tidal cycle we focus on the plume s onset and its evolution over 5 10 tidal cycles over the timescales considered the plume was roughly circular slightly skewed in the along coast direction the model solution yielded high vertical ekman numbers e o 5 in the vicinity of the inlet mouth decreasing seaward from the inlet to an order of magnitude smaller e 0 25 at the seaward edge of the plume passive particles released in the region seaward of the inlet mouth were used to describe the exchange between the coastal region and the inlet a marked asymmetry between ebb and flood flows is observed in the vicinity of the inlet with jet like ebbing currents and weaker potential flow like flooding currents over a tidal cycle net exchanges between the coastal ocean and the inlet are found to be spatially and temporally dependent that is particle trajectories depend on the release point and the time of the release in the tidal cycle the near inlet residual circulation shows significant differences in the absence of stratification