eddy diffusivities estimated from observations in the labrador sea eddy diffusivities in the labrador sea ls are estimated from deep eddy resolving float trajectories moored current meter records and satellite altimetry a mean residence time of 248 days in the central ls is observed with several floats staying for more than 2 years by applying a simple random walk diffusion model the observed distribution of float residence times in the central ls could be explained by a mean eddy diffusivity of about 300 m2 s 1 estimates from float trajectories themselves and from moored current meter records yield significantly higher eddy diffusivities in the central ls of 950 1100 m2 s 1 this discrepancy can be explained by an inhomogeneity of the eddy diffusivity at middepth with high low values in the central ls region between central ls and deep labrador current which could be conjectured from the mean altimetric eddy kinetic energy eke distribution the different diffusivities explain both 1 a fast lateral homogenization of water masses in the central ls and 2 a weak exchange between central ls and boundary current the mean lagrangian length scale of 11 5 0 7 km as estimated from deep float trajectories is only slightly larger than the mean rossby radius of deformation 8 8 km largest eddy diffusivities within the central ls are associated with strong eddy drifts rather than with large swirl velocities and associated large eke between central ls and deep labrador current which could be conjectured from the mean altimetric eddy kinetic energy eke distribution the different diffusivities explain both 1 a fast lateral homogenization of water masses in the central ls and 2 a weak exchange between central ls and boundary current the mean lagrangian length scale of 11 5 0 7 km as estimated from deep float trajectories is only slightly larger than the mean rossby radius of deformation 8 8 km largest eddy diffusivities within the central ls are associated with strong eddy drifts rather than with large swirl velocities and associated large eke

convergence rates across a displacement transfer zone in the western transverse ranges ventura basin california three cross sections are balanced and retrodeformed to the top of the pleistocene saugus formation and to a horizon close to the base of the jaramillo subchron to yield crustal shortening and shortening rates for the western transverse ranges of california the cross sections compare the shortening that occurs along a transfer zone in which displacement is transferred eastward from a surface reverse fault red mountain fault to a blind thrust and from that to a combination of both a surface reverse fault san cayetano fault and the blind thrust using an age of 250 50 ka for the top of the saugus formation based on amino acid racemization of fossil mollusks crustal shortening rates appear to have abruptly accelerated through time from 3 4 3 to 5 4 mm yr between 250 and 975 ka to 20 6 to 28 1 mm yr since 250 50 ka using an age of 500 ka for the top of the saugus formation based on paleomagnetic stratigraphy there is little increase in deformation rates through time ranging from 5 5 to 8 6 mm yr between 975 500 ka and from 10 3 to 14 1 mm yr since 500 ka more crustal convergence rates determined by global positioning system surveys taken over 4 6 years indicate a shortening rate of 7 10 mm yr across the basin this is consistent with the slower rates of deformation calculated using an age of 500 ka for the top of the saugus formation less

corrections to heat flow and energetics of the san andreas fault zone and some additional comments on the relation between fault friction and observed heat flow

deformation rates across the placerita northridge mw 6 7 aftershock zone and hopper canyon segments of the western transverse ranges deformation belt abstract aftershocks of the 1994 northridge m w 6 7 earthquake provide insights into the geometry of the seismic source faults in the san fernando valley and the east ventura basin and allow the calculation of deformation rates for the region the northridge thrust and santa susana faults dip in opposite directions with the northridge thrust entirely beneath the santa susana fault these opposing reverse faults interact resulting in a folded active santa susana fault and uplift in the footwall block of that reverse fault two balanced cross sections suggest thick skinned deformation of the western transverse ranges the western section across the modelo lobe segment of the north dipping san cayetano fault and the easternmost surface trace of the south dipping oak ridge fault is west of any aftershocks of the northridge earthquake and has been termed the hopper canyon segment of the deformation belt structural modeling predicts a dip of 46 s on the oak ridge fault at seismogenic depths horizontal shortening rates are calculated by adding the products of the dip slip displacements and the cosines of the dips of both faults the eastern cross section shows the northridge mainshock with a 45 south dipping nodal plane at a depth of 18 km aftershocks reach a depth of 20 km in a thin skinned paradigm a hinge should occur at the surface near the santa monica mountains due to rocks moving from a decollement at the brittle plastic transition and changing dip as they move up the ramp no hinge of that magnitude occurs there calculation of horizontal short ening rates across this part of the western transverse ranges must take into account the displacement on both the northridge thrust eastern extension of the oak ridge fault and the santa susana fault placerita segment horizontal shortening rates are 8 2 2 4 mm yr across the modelo lobe segment of the san cayetano fault and the oak ridge fault and 5 7 2 5 mm yr across the northridge thrust and the santa susana fault these rates are consistent with those based on tectonic geodesy using gps dip slip displacement rates on the faults are 1 7 mm yr for the northridge thrust since 2 3 ma 4 1 0 4 mm yr for the oak ridge fault since 500 ka 5 9 3 9 3 8 mm yr for the santa susana fault since 600 to 2300 ka and 7 4 3 0 mm yr for the modelo lobe segment of the san cayetano fault since 500 ka this indicates that the slip rates on the north dipping the eastern san cayetano and the santa susana faults are comparable but the slip rate on the south dipping faults decreases eastward the slip rate on the oak ridge fault in the ventura basin is more than double that of the northridge thrust

role of subsurface loads and regional compensation in the isostatic balance of the transverse ranges california evidence for intracontinental subduction bouguer gravity anomalies in the transverse ranges of southern california show a pronounced asymmetry in north south profiles across the mountains and a characteristic shape which is largely insensitive to variations in the topographic load along strike while individual gravity topography profile pairs could be consistent with a number of isostatic compensation mechanisms the unusual relationship between gravity and topography in the san bernardino mountains severely limits the class of acceptable models if the bouguer gravity field is caused by flexure of the crust mantle boundary the simplest solution consistent with the data in the western transverse ranges the san gabriel mountains and the san bernardino mountains models the great valley and mojave provinces to the north as a 50 km thick elastic plate supporting the mountains which are underthrust by a much weaker plate to the south the best fit to the gravity data in the san bernardino mountains requires a terminal bending moment on the southern plate beneath the mountains the magnitude of the terminal bending moment decreases to the west in the san gabriel and western transverse ranges we equate the load responsible for this terminal moment with the high velocity slablike feature mapped in the upper mantle beneath the transverse ranges using seismic tomography the coupling between the subsurface load and the overlying lithosphere suggests that the slab represents lithospheric subduction with an extremely small density contrast rather than a small scale convective feature

how does labrador sea water enter the deep western boundary current abstract labrador sea water lsw a dense water mass formed by convection in the subpolar north atlantic is an important constituent of the meridional overturning circulation understanding how the water mass enters the deep western boundary current dwbc one of the primary pathways by which it exits the subpolar gyre can shed light on the continuity between climate conditions in the formation region and their downstream signal using the trajectories of profiling autonomous lagrangian circulation explorer p alace floats operating between 1996 and 2002 three processes are evaluated for their role in the entry of labrador sea water in the dwbc 1 lsw is formed directly in the dwbc 2 eddies flux lsw laterally from the interior labrador sea to the dwbc and 3 a horizontally divergent mean flow advects lsw from the interior to the dwbc a comparison of the heat flux associated with each of these three mechanisms suggests that all three contribute to the transformation of the boundary current a

boundary current eddies and their role in the restratification of the labrador sea an idealized model is used to study the restratification of the labrador sea after deep convection with emphasis on the role of boundary current eddies shed near the west coast of greenland the boundary current eddies carry warm buoyant irminger current water into the labrador sea interior for a realistic end of winter state it is shown that these irminger current eddies are efficient in restratifying the convected water mass in the interior of the labrador sea in addition it is demonstrated that irminger current eddies can balance a significant portion of the atmospheric heat loss and thus play an important role for the watermass transformation in the labrador sea

chronology and rates of faulting of ventura river terraces california new evidence concerning the chronology of four late pleistocene terraces of the ventura river near oak view california that are vertically offset and tilted by reverse and reverse flexural slip faults provides a means of estimating rates of fault movement and downcutting by the ventura river radiocarbon ages of charcoal contained within terrace deposits date two of the terraces correlation of soils that have developed on terrace deposits and extrapolation of the rate of vertical displacement of the arroyo parida santa ana fault not a flexural slip fault date the others resulting age estimates for the four main late pleistocene terraces are qt5b 30 000 qt6a 38 000 qt6b 54 000 and qt6c 92 000 yr b p vertical slip rates on flexural slip faults range from 0 3 to 1 1 mm yr and apparently are related to the rate form and mechanics of folding of the north limb of the ayers creek canada larga syncline average rates of downcutting of the ventura river for several intervals during the late pleistocene estimated from the chronology and relative elevation of river terraces north of the arroyo panda santa ana fault upstream from the zone of faulting vary from 0 5 to 1 3 mm yr the range in rates probably reflects variations in local uplift as well as adjustments to changing eustatic sea level climatic conditions and or regional deformation of the western transverse ranges the average rate of downcutting of the ventura river north of the zone of flexural slip faulting is 0 8 mm yr compared with 1 2 to 2 2 mm yr in the deformation zone immediately to the south this apparently indicates that during tectonic deformation there is an approximate balance between the rate of uplift due to faulting and folding and the rate of downcutting by the fluvial system

observations inferences and mechanisms of the atlantic meridional overturning circulation a review this is a review about the atlantic meridional overturning circulation amoc its mean structure temporal variability controlling mechanisms and role in the coupled climate system the amoc plays a central role in climate through its heat and freshwater transports northward ocean heat transport achieved by the amoc is responsible for the relative warmth of the northern hemisphere compared to the southern hemisphere and is thought to play a role in setting the mean position of the intertropical convergence zone north of the equator the amoc is a key means by which heat anomalies are sequestered into the ocean s interior and thus modulates the trajectory of climate change fluctuations in the amoc have been linked to low frequency variability of atlantic sea surface temperatures with a host of implications for climate variability over surrounding landmasses on intra annual timescales variability in amoc is large and primarily reflects the response to local wind forcing meridional coherence of anomalies is limited to that of the wind field on interannual to decadal timescales amoc changes are primarily geostrophic and related to buoyancy anomalies on the western boundary a pacemaker region for decadal amoc changes is located in a western transition zone along the boundary between the subtropical and subpolar gyres decadal amoc anomalies are communicated meridionally from this region amoc observations as well as the expanded ocean observational network provided by the argo array and satellite altimetry are inspiring efforts to develop decadal predictability systems using coupled atmosphere ocean models initialized by ocean data

on the connection between dense water formation overturning and poleward heat transport in a convective basin an isopycnal two layer idealized model for a convective basin is proposed consisting of a convecting interior region and a surrounding boundary current buoyancy and wind driven parameterized eddy fluxes govern the exchange between the two to balance the interior buoyancy loss the boundary current becomes denser as it flows around the basin geostrophy imposes that this densification be accompanied by sinking in the boundary current and hence by an overturning circulation the poleward heat transport associated with convection in the basin can thus be viewed as a result of both an overturning and a horizontal circulation when adapted to the labrador sea the model is able to reproduce the bulk features of the mean state the seasonal cycle and even the shutdown of convection from 1969 to 1972 according to the model only 40 of the poleward heat buoyancy transport of the labrador sea is associated with the overturning circulation an exact solution is presented for the linearized equations when changes in the boundary current are small numerical solutions are calculated for variations in the amount of convection and for changes in the remotely forced circulation around the basin these results highlight how the overturning circulation is not simply related to the amount of dense water formed a speeding up of the circulation around the basin due to wind forcing for example will decrease the intensity of the overturning circulation while the dense water formation remains unvaried in general it is shown that the fraction of poleward buoyancy or heat transport carried by the overturning circulation is not an intrinsic property of the basin but can vary as a result of a number of factors

impact of labrador sea convection on the north atlantic meridional overturning circulation abstract the overturning and horizontal circulations of the labrador sea are deduced from a composite vertical section across the basin the data come from the late spring early summer occupations of the world ocean circulation experiment woce ar7w line during the years 1990 97 this time period was chosen because it corresponded to intense wintertime convection the deepest and densest in the historical record suggesting that the north atlantic meridional overturning circulation moc would be maximally impacted the composite geostrophic velocity section was referenced using a mean lateral velocity profile from float data and then subsequently adjusted to balance mass the analysis was done in depth space to determine the net sinking that results from convection and in density space to determine the diapycnal mass flux i e the transformation of light water to labrador sea water the mean overturning cell is calculated to be 1 sv 1 sv 106 m3 s 1 as compared with a horizontal gyre of 18 sv the

gps observations of fault afterslip and upper crustal deformation following the northridge earthquake global positioning system gps observations indicate that significant aseismic deformation occurred in the year following the january 17 1994 northridge earthquake the postseismic observations show the same sense of motion as the coseismic compared with the coseismic displacements the far field postseismic motions 1 2 fault dimensions away are proportionally larger than those seen in the near field the postseismic data are best modeled with two faults one on the rupture plane and one located in the shallow crust the upper crustal fault may represent an actual fault or may be indicative of viscous relaxation occurring in the upper crust the inferred afterslip and or relaxation moment is approximately 2 9 1018 n m or 22 of the mainshock moment release we expect that the moment release due to the afterslip and relaxation effectively reduce the earthquake hazard locally it is not clear from this study how the postseismic deformation loads the surrounding faults or alters the state of stress on those faults

distribution and circulation of labrador sea water abstract labrador sea water is the final product of the cyclonic circulation of subpolar mode water in the open northern north atlantic mccartney and talley 1982 the temperature and salinity of the convectively formed subpolar mode water decrease from 14 7 c 36 08 to 3 4 c 34 88 on account of the cumulative effects of excess precipitation and cooling the coldest mode water is labrador sea water which spreads at mid depths and is found throughout the north atlantic ocean north of 40 n and along its western boundary to 18 n a vertical minimum in potential vorticity is used as the primary tracer for labrador sea water labrador sea water is advected in three main directions out of the labrador sea 1 northeastward into the irminger sea 2 southeastward across the atlantic beneath the north atlantic current and 3 southward past newfoundland with the labrador current and thence westward into the slope water region crossing under the gulf stream off cape hatteras the labrador sea water core is

deep convection in the irminger sea forced by the greenland tip jet open ocean deep convection one of the processes by which deep waters of the world s oceans are formed is restricted to a small number of locations for example the mediterranean and labrador seas recently the southwest irminger sea has been suggested as an additional location for open ocean deep convection the deep water formed in the irminger sea has the characteristic temperature and salinity of the water mass that fills the mid depth north atlantic ocean which had been believed to be formed entirely in the labrador basin here we show that the most likely cause of the convection in the irminger sea is a low level atmospheric jet known as the greenland tip jet which forms periodically in the lee of cape farewell greenland and is associated with elevated heat flux and strong wind stress curl using a history of tip jet events derived from meteorological land station data and a regional oceanic numerical model we demonstrate that deep convection can occur in this region when the north atlantic oscillation index is high which is consistent with observations this mechanism of convection in the irminger sea differs significantly from those known to operate in the labrador and mediterranean seas

a tomographic image of mantle structure beneath southern california we determined the variations in seismic structure beneath southern california by using a tomographic method of inversion on teleseismic p delays recorded with the southern california array the algorithm employed was a modified form of an algebraic reconstruction technique art used in medical x ray imaging deconvolution with an empirically estimated point spread function was also used to help in focusing the image the inversion reveals two prominent features beneath the region the first is a thin vertical wedge directly beneath the transverse ranges that is 2 3 faster than the surrounding region this feature deepens to the east attaining a maximum depth of about 250 km beneath the san bernardino mountains the second feature is a major zone of low velocity material that is 2 4 slow under the salton trough rift valley extending to a depth of about 125 km two possible explanations for the spatial association of the transverse ranges with the velocity anomaly below are lithospheric subduction or small scale sublithospheric convection in the region of the big bend of the san andreas fault the low velocity anomaly beneath the salton trough is consistent with convective upwelling there

discrepancy between geological and geodetic deformation rates in the ventura basin space geodesy provides a new tool for measuring neotectonic deformation which when combined with geological and geophysical observations and models can be used to infer rates and styles of deformation in the ventnra basin region of southern california the geodetically measured convergence rates of 7 10 mm yr 1 ref 1 are significantly lower than the 20 25 mm yr 1 estimated from geological data2 3 here we investigate the possible implications of this discrepancy it might be for example that temporal variations cause the short and long term convergence rates to differ but if this were the case we would expect to observe the long term rate by extending the geodetic measurements over a broader region yet only 11 3 mm yr 1 of regional convergence is observed4 our preferred explanation of the discrepancy is that the geological models require revision and to this end we present two deformation models that satisfy both the geological and geodetic constraints our modelling suggests that the faults bounding the basin are locked at the surface but are slipping at depths below 2 5 km

kinematics of present crust and mantle flow in southern california in the southern california region published geologic studies of prehistoric fault offsets yield at least 81 rates of slip covering various periods of time chiefly since the opening of the gulf of california these rates together with the known geometries of active faults are used to constrain a hand fit block model for present horizontal velocity of the crust the assumptions employed are that these rates apply to the present that the blocks are internally rigid down to the greatest depth of earthquakes and that the over all pacific north american plate motion is correctly given by global models the resulting model fits 67 data within their uncertainties 10 more with a small discrepancy 1 mm yr and fails to accommodate only 4 data 2 of which are inconsistent with other data nominal precision is good 3 mm yr but accuracy and uniqueness are both suspect because many block boundaries are questionable despite its many local defects this model suggests four reliable regional conclusions first the rate of shortening on the south side of the transverse ranges varies from 6 to 14 mm yr increasing eastward which implies an unrecognized seismic hazard unless the motion is taken up by folding or fault creep second the pattern of block rotation rates is quite different from the pattern of rotations shown by tertiary paleomagnetic declinations which implies some major pliocene reorganization of blocks third the great bend left step of the plate boundary fault system in the transverse ranges appears to be straightening gradually by a 3 m y clockwise rotation relative to both plates finally if it is assumed that plate shortening has been occurring at this bend since the early pliocene and that crust and upper mantle velocities are similar then this model predicts mantle lithosphere downwelling to at least 250 km depth beneath the transverse ranges this prediction is consistent with upper mantle seismic velocity structure

seasonal and interannual variations of irminger ring formation and boundary interior heat exchange in flame abstractthe contribution of warm core anticyclones shed by the irminger current off west greenland known as irminger rings to the restratification of the upper layers of the labrador sea is investigated in the 1 12 family of linked atlantic models experiment flame model the model output covering the 1990 2004 period shows strong similarities to observations of the irminger current as well as ring observations at a mooring located offshore of the eddy formation region in 2007 09 an analysis of fluxes in the model shows that while the majority of heat exchange with the interior indeed occurs at the site of the irminger current instability the contribution of the coherent irminger rings is modest 18 heat is provided to the convective region mainly through noncoherent anomalies and enhanced local mixing by the rings facilitating further exchange between the boundary and interior the time variability of the eddy kinetic energy and the boundary to interior heat flux in the model are strongly corr

earthquake locations in southern california obtained using source specific station terms we relocate 297 400 events recorded by the southern california seismic network scsn between 1975 and 1998 using spatially varying station terms to improve relative location accuracy our method uses existing scsn p and s picks a smooth one dimensional velocity model and an iterative grid search approach based on the l1 norm we apply empirical corrections for three dimensional structure by computing station timing corrections that continuously vary as a function of source position station terms for each event are obtained by smoothing the residuals from nearby events using a natural neighbor delaunay tessellation of the seismicity and then iterating until a stable set of locations and station terms is achieved our approach achieves relative location accuracy comparable locally to master event methods but can be applied uniformly over large regions median estimated standard errors for our final locations are 328 m in horizontal position and 741 m in depth our locations exhibit much less scatter particularly in depth than those of the scsn catalog and a greater tendency to align into linear and planar features suggestive of fault structures our results appear comparable to and in some cases better than previous scsn relocation studies using joint hypocenter velocity inversion techniques plots of daytime versus nighttime events permit discrimination between clusters of natural and artificial seismicity we observe no simple relationship between the maximum depth of seismicity and surface geology

hydrography of the labrador sea during active convection the hydrographic structure of the labrador sea during wintertime convection is described the cruise part of the deep convection experiment took place in february march 1997 amidst an extended period of strong forcing in an otherwise moderate winter because the water column was preconditioned by previous strong winters the limited forcing was enough to cause convection to approximately 1500 m the change in heat storage along a transbasin section relative to an occupation done the previous october gives an average heat loss that is consistent with calibrated national centers for environmental prediction surface heat fluxes over that time period 200 wm 22 deep overturning was observed both seaward of the western continental slope which was expected as well as within the western boundary current itself something that had not been directly observed previously these two geographical regions separated by roughly the 3000 m isobath produce separate water mass products the offshore water mass is the familiar cold fresh dense classical labrador sea water lsw the boundary current water mass is a somewhat warmer saltier lighter vintage of classical lsw though in the far field it would be difficult to distinguish these products the offshore product was formed within the cyclonic recirculating gyre measured by lavender et al in a region that is limited to the north most likely by an eddy flux of buoyant water from the eastern boundary current the velocity measurements taken during the cruise provide a transport estimate of the boundary current throughput and offshore recirculation finally the overall trends in stratification of the observed mixed layers are described

geodetic measurement of deformation in the ventura basin region southern california we have measured the deformation in the ventura basin region southern california with global positioning system gps measurements carried out over 4 6 years between 1987 and 1992 the deformation within our network is spatically variable on scales of tens of kilometers with strain rates reaching 0 6 1 micro rad yr in the east central basin blocklike rotations are observed south and northwest of the basin where the maximum shear strain rates are an order of magnitude lower 0 06 1 micro rad yr to the south we also observed clockwise rotations of 1 deg 7 deg m y shear strain rates determined by comparing angle changes from historical triangulation spanning several decades and gps measurements give consistent though less precise results the geodetic rates of shortening across the basin and western transverse ranges are lower than those estimated from geological observations but the patterns of deformation from the two methods agree qualitatively

north atlantic surface circulation during the 1990 s observed with satellite tracked drifters a new compilation of lagrangian velocity observations describes the state of the north atlantic surface circulation during the 1990s gridded fields of velocity and eddy kinetic energy eke are constructed from trajectories of more than 1500 15 m drogued satellite tracked surface drifters in service between january 1990 and december 1999 this time period overlaps a coordinated field study of circulation and variability in the north atlantic completed between 1996 2000 as part of the world ocean circulation experiment we describe the construction of a self consistent drifter climatology present decadal mean quasi eulerian velocity and eke fields computed on a 1 grid and compare these results with contemporary satellite measurements detailed discussion of the inferred surface circulation is focused on three regions 1 the gulf stream and north atlantic current 2 the labrador sea and subpolar gyre and 3 the caribbean sea the swiftest drifter motions were found in the equatorial region and along the tropical subtropical and subpolar western boundaries the maximum instantaneous speed determined from a single quality controlled and filtered drifter observation was 273 cm s 1 in the gulf stream southeast of cape cod the highest eke value in the north atlantic 2790 cm2 s 2 was found in the gulf stream just downstream of the new england seamounts over most of the atlantic basin drifter derived eke values were found to be o 100 cm2 s 2 higher than corresponding values derived from satellite altimetry in the labrador sea a region of sharply elevated eke appears to be geographically related to the localized ejection of drifters and by extension mass and kinetic energy from the energetic west greenland current between 60 and 62 n when compared to drifter measurements made in the late 1970s our results suggest but do not statistically confirm an enhancement and slight northward shift of the zonal gulf stream extension such a shift is consistent in sign with expectations based on observed interdecadal variations in wind stress and subtropical gyre potential energy associated with the north atlantic oscillation

ekman and eddy exchange of freshwater and oxygen across the labrador shelf break abstracttransport of freshwater from the labrador shelf into the interior labrador sea has the potential to impact deep convection via its influence on the salinity of surface waters to examine this transport the authors deployed two underwater gliders on a mission to traverse the continental shelf break multiple times between 5 july and 22 august 2014 the period when arctic meltwater has historically peaked in transport down the labrador shelf the field campaign yielded a unique dataset of temperature salinity and oxygen across the shelf break to a depth of 1000 m at unprecedented spatial resolution two mechanisms of cross shelf transport were examined ekman transport and transport due to mesoscale eddies ekman transport is quantified using satellite wind stress and near surface hydrographic properties and eddy induced transport is scaled using a parameterized eddy diffusivity and thickness gradients of layers of uniform potential density as well as the tracer gradients along those isopycnals

is there a north south phase shift in the surface labrador current transport on the interannual to decadal scale 1 the transport of the labrador current has substantial interannual to decadal variability that may significantly impact the ocean climate and marine ecosystem off atlantic canada and northeast united states nevertheless the alongshore coherence of the labrador current on the interannual to decadal scales has been a long standing question here we have used satellite altimetry data to study interannual to decadal variability of the unit depth surface labrador current in the past two decades in the context of the subpolar gyre of the north atlantic the study for the first time reveals that the transport over the labrador and northeastern newfoundland slope is out of phase with that over the scotian slope the surface labrador current transport is positively and negatively correlated with the winter north atlantic oscillation nao index with the transport lagging by about 1 year in the north the labrador and northeastern newfoundland slope and in the south the scotian slope respectively in addition the surface labrador current transport declines over the labrador slope and northeastern newfoundland slope and increases over the scotian slope the north south phase shift suggests two distinct regimes which warrants further studies of underlying dynamic mechanisms and may have important implications for regional ecosystems and climate

boundary circulation at the exit of the labrador sea the deep circulation and related transports of the southern labrador sea are determined from direct current observations from ship surveys and a moored current meter array the measurements covered a time span from summer 1997 to 1999 and show a well defined deep boundary current extending approximately out to the 3300 m depth contour and weak reverse currents farther offshore the flow has a strong barotropic component and significant baroclinic flow is only found in the shallow labrador current at the shelf break and associated with a deep core of denmark strait overflow water the total deep water transport below 27 74 kg m 3 was 26 5 sv sv 106 m3 s 1 comprising labrador sea water lsw gibbs fracture zone water gfzw and denmark strait overflow water dsow intraseasonal variability of the flow and transport was high ranging from 15 to 35 sv and the annual means differed by 17 a seasonal cycle is confined to the shallow labrador current in its deeper part where the mean flow is still strong no obvious seasonality could be detected the transport of the interior anticyclonic recirculation was estimated from lowered acoustic doppler current profiler stations and geostrophy yielding about 9 sv thus the net deep water outflow from the labrador sea was about 17 sv the baroclinic transport of gfzw and dsow referenced to the depth of the isopycnal 27 80 kg m 3 is only about one third of the total transport in these layers longer term variations of the total transports are not represented well by the baroclinic contribution

long term coordinated changes in the convective activity of the north atlantic the north atlantic is a peculiarly convective ocean the convective renewal of intermediate and deep waters in the labrador sea and greenland iceland sea both contribute significantly to the production and export of north atlantic deep water thus helping to drive the global thermohaline circulation while the formation and spreading of 18 degree water at shallow to intermediate depths off the us eastern seaboard is a major element in the circulation and hydrographic character of the west atlantic for as long as time series of adequate precision have been available to us it has been apparent that the intensity of convection at each of these sites and the hydrographic character of their products have been subject to major interannual change as shown by aagaard 1968 clarke et al 1990 and meincke et al 1992 for the greenland sea in the ows bravo record from the labrador sea eg lazier 1980 et seq and at the panulirus hydrostation s site in the northern sargasso off bermuda eg jenkins 1982 talley and raymer 1982 this paper reviews the recent history of these changes showing that the major convective centres of the greenland and labrador seas are currently at opposite convective extrema in our postwar record with vertical exchange at the former site limited to 1000 m or so but with labrador sea convection reaching deeper than previously observed to over 2300 m as a result greenland sea deep water has become progressively warmer and more saline since the early 70 s due to increased horizontal exchange with the arctic ocean through fram strait while the labrador sea water has become progressively colder and fresher over the same period through increased vertical exchange most recently convection has become deep enough there to reach into the more saline nadw which underlies it so that cooler but now saltier and denser lsw has resulted

heat flow and thermotectonic problems of the central ventura basin southern california the ventura basin southern california is located near the big bend area of the san andreas fault system within the transverse ranges physiographic province continuous equilibrium temperature logs were measured in 12 idle oil wells located within the onshore ventura avenue san miguelito filmore oxnard and west montalvo fields to an average depth of about 3100 m 10 200 feet thermal conductivities were measured on all available samples heat flows were calculated with the aid of a thermostratigraphic scheme based on correlative gradient intervals and average thermal conductivity for the appropriate units negative curvature of the ventura avenue temperature profiles may be explained by an increase in thermal conductivity associated with tectonic compaction of the underlying pliocene clastic sequence temperature profiles at fillmore are enigmatic but suggest highly unusual geotectonic conditions basinwide heat flow averages about 48 mw m2 a value which is low relative to most of southern california as heat flow does not vary systematically to the maximum measured depth of about 4 km this anomaly is not easily explained in terms of hydrologic effects or recent uplift and erosion however a diminution of heat flow is an expectable consequence of the accumulation of cold sediments up to 12 km since eocene time if 70 mw m2 is accepted as the background heat flow then the sedimentation effect is probably sufficient to explain the anomaly

eddies of newly formed upper labrador sea water a new type of submesoscale eddy has been observed south of the labrador sea during late winter embedded in equatorward flow along the western boundary the eddy radius is 20 km with a weak dynamic signature swirl speed of 0 5 cm s the center of the eddy is characterized by weak stratification elevated concentrations of oxygen and anthropogenic tracers and low tracer ages all indicative of newly ventilated water strong lateral intrusions distort the shape of the feature the water mass contained in the eddy is not classical labrador sea water from the central labrador sea but is significantly fresher and hence lighter it is of the correct density to be the source of the high chlorofluorocarbon layer of the shallow deep western boundary current observed further south and hence is termed upper labrador sea water using a combination of hydrographic data sets along the western boundary to implement a simple lateral diffusion model it is shown that such eddies decay of the order of several months and are difficult to observe equatorward of the grand banks of newfoundland this is in contrast to deeper lenses of classical labrador sea water which persist further equatorward tracer derived ages of the upper labrador sea water eddy range from 3 to 5 years much older than the lifetime deduced from their lateral diffusion a simple convection model of tracer age shows that this age discrepancy is caused by gas exchange being unable to maintain equilibrium between the deep convecting mixed layer and the atmosphere during formation

evidence from a cluster of small earthquakes for a fault at 18 km depth beneath oak ridge southern california abstract a swarm of about 50 small earthquakes m 1 5 occurred for a month during 1989 beneath oak ridge southern california location accuracy using conventional analysis of arrival time picks is limited for these events by the weak emergent nature of arrivals on the available seismograms however waveform cross correlation techniques are found to provide precise relative event locations due to the similarity of the waveforms recorded at individual stations the relocated events form a small cluster about 1 km across at a depth of 18 km and are aligned along a plane that dips 35 to the northwest estimated standard errors for the locations are generally less than 50 m the time evolution of the sequence shows a gradual migration of activity away from its initiation point three additional events occurred several months later these align along the same plane but are displaced about 500 m to the southeast from the main swarm reliable fault plane solutions are difficult to obtain for these events due to the small number of station records available the limited range of takeoff angles and the weak initial arrivals on many of the seismograms stacking the records at each station over the different events greatly reduces prearrival noise levels and assists in resolving the average p first motions analysis of these first motion data indicates that the slip planes of probable focal mechanisms are not in agreement with the plane defined by the seismicity the seismicity alignment may represent the extension of the simi fault in which case some shallowing of the fault dip would be required to match the observed 35 dip at 18 km

the impact of resolution on the adjustment and decadal variability of the atlantic meridional overturning circulation in a coupled climate model variations in the atlantic meridional overturning circulation moc exert an important influence on climate particularly on decadal time scales simulation of the moc in coupled climate models is compromised to a degree that is unknown by their lack of fidelity in resolving some of the key processes involved there is an overarching need to increase the resolution and fidelity of climate models but also to assess how increases in resolution influence the simulation of key phenomena such as the moc in this study we investigate the impact of significantly increasing the ocean and atmosphere resolution of a coupled climate model on the simulation of moc variability by comparing high and low resolution versions of the same model in both versions decadal variability of the moc is closely linked to density anomalies that propagate from the labrador sea southward along the deep western boundary we demonstrate that the moc adjustment proceeds more rapidly in the higher resolution model due the increased speed of western boundary waves however the response of the atlantic sea surface temperatures to moc variations is relatively robust in pattern if not in magnitude across the two resolutions the moc also excites a coupled ocean atmosphere response in the tropical atlantic in both model versions in the higher resolution model but not the lower resolution model there is evidence of a significant response in the extratropical atmosphere over the north atlantic 6 years after a maximum in the moc in both models there is evidence of a weak negative feedback on deep density anomalies in the labrador sea and hence on the moc with a time scale of approximately ten years our results highlight the need for further work to understand the decadal variability of the moc and its simulation in climate models

a kinematic model of southern california we propose a kinematic model for southern california based on late quaternary slip rates and orientations of major faults in the region internally consistent motions are determined assuming that these faults bound rigid blocks relative to north america most of california west of the san andreas fault is moving parallel to the san andreas fault through the transverse ranges and not parallel to the motion of the pacific plate this is accomplished by counterclockwise rotation of california south of the san andreas fault and by the westward movement of central california north of the gar lock fault the velocities of the blocks are calculated along several paths in southern california that begin in the mojave desert and end off the california coast a path that crosses the western transverse ranges accumulates the accepted relative north america pacific plate velocity whereas paths to the north and south result in a significant missing component of motion this implies the existence of a zone of active deformation in southern california that is interpreted to include the western transverse ranges and northwest trending predominately strike slip faults close to the coast both north and south of the transverse ranges strain on this system accounts for about a third of the total north america pacific plate motion

lagrangian observations of the deep western boundary current in the north atlantic ocean abstract in this study the authors analyze the trajectories of 18 rafos floats launched in the deep western boundary current dwbc between the grand banks and cape hatteras to investigate the kinematics and dynamics in the region where the dwbc crosses under the gulf stream near 36 n the crossover region floats deployed in the chlorofluorocarbon cfc maximum associated with upper labrador sea water depth 800 m illustrate the entrainment process of this water mass into the gulf stream the behavior of the floats and fluid parcels in the crossover region is strongly dependent on the meandering of the gulf stream when the stream is close to its mean position fluid parcels entrained from the upper dwbc travel along the northern edge of the stream when a meander trough is present downstream of the entrainment location dwbc fluid parcels cross the gulf stream and sometimes are expelled on the south side this represents a previously unrecognized mechanism for transporting upper labrador sea w

labrador sea water tracked by profiling floats from the boundary current into the open north atlantic fifteen profiling floats were injected into the deep boundary current off labrador they were ballasted to drift in the core depth of labrador sea water lsw at 1500 m depth and were deployed in two groups during march and july august 1997 initially for about three months the floats were drifting within the boundary current and the flow vectors were used to determine the mean horizontal structure of the deep labrador current which was found to be about 100 km wide with an average core speed of 18 cm s 1 north of flemish cap the boundary current encounters complicated topography around orphan knoll and there the lsw outflow splits up into different routes one obvious lsw path is eastward through the charlie gibbs fracture zone and another route is a narrow recirculation toward the central labrador sea a surprising result was that none of the floats were able to follow the boundary current southward to the grand banks area and exit into the subtropics trajectories and temperature profiles of the eastward drifting floats indicate the importance of the north atlantic current for dispersing the floats even at the level of lsw

on the linkage between labrador sea water volume and overturning circulation in the labrador sea a case study on proxies abstractalthough proxies have generally been used to study deep ocean convection and overturning circulation in the labrador sea their efficacy has not been explicitly evaluated because observations that directly measure those variables are scarce in this study the volume of newly formed labrador sea water lsw and the overturning circulation in the labrador sea are estimated using observational data and output from a high resolution ocean model and then compared to proxies used to represent those variables the comparisons reveal the limitations of proxies highlighting the desirability of robust estimates derived from direct monitoring in the region i e from argo and overturning in the subpolar north atlantic program osnap a linkage among lsw formation overturning circulation in the labrador sea and the export of lsw from the basin on interannual time scales is found in the model

large scale quaternary detachments in ventura basin southern california the ventura basin is an east north east trending trough in the california transverse ranges which records major quaternary detachment faulting at three levels the earliest thrusting occurred along weak siltstone interbeds in a sequence dominated by competent basin plain turbidite sandstone because sedimentation continued during thrusting the age rate and direction of thrusting can be worked out faulting began 1 3 m y ago and ceased 0 65 m y ago with a maximum slip rate of 2 8 mm yr to the southeast the fault set moved up a 45 ramp and ended as a blind thrust the ramp had topographic expression on the seafloor diverting turbidites around the ramp and preserving ash beds along with other hemipelagic sediments on its crest following the end of deposition 0 2 m y ago the competent basin plain turbidites underwent flexural slip folding over an incompetent miocene sequence dominated by shale underlying competent paleogene strata were not folded the south flank of the ventura avenue anticline tilted at 3 4 rad yr the anticlinal crest rose at a rate of 15 16 mm yr decelerating to 4 3 5 2 mm yr and the anticline and an adjacent syncline shortened at a rate of 20 mm yr the high rate of folding in the ventura avenue oil field resulted in overpressured sandstone reservoirs and oil water interfaces which have not had time to reach gravity equilibrium the red mountain san cayetano and santa susana faults mark the surface expression of a seismically active midcrustal detachment which produced convergence across the ventura basin at rates as high as 23 mm yr total convergence across the eastern san cayetano fault near fillmore is 11 600 2000 m in the last million years

active tectonic studies in the united states 1987 1990 the techniques and instrumentation used in active tectonic studies are discussed and recent results are reviewed it is suggested that a critical mass of data on several particular regions has been accumulated making possible critical debates and attempts to assess earthquake hazards particular attention is given to studies of the pacific northwest region basin and range deformation studies and distributed deformation and hidden earthquake sources also included is a comprehensive bibliography for the period

role of resolved and parameterized eddies in the labrador sea balance of heat and buoyancy abstractdeep convection in the labrador sea is an important component of the global ocean ventilation the associated loss of heat to the atmosphere from the interior of the sea is thought to be mostly supplied by mesoscale eddies generated either remotely or as a result of convection itself processes that are not resolved by low resolution ocean climate models the authors first employ a high resolution ocean model forced with high resolution 33 km 3 h atmospheric fields to further elaborate on the role of mesoscale eddies in maintaining the balance of heat and buoyancy in the labrador sea in general agreement with previous studies it is found that eddies remove heat along the coast and supply it to the interior some of the eddies that are generated because of the barotropic instability off the west coast of greenland are recaptured by the boundary current in the region of deep convection the convergence of heat and buoyancy by eddies significantly increases with the deepening of the winter

variability of the deep western boundary current east of the grand banks the deep western boundary current east of the grand banks has been observed during 1999 2005 by moored current meter stations and shipboard current profiling sections these recent observations can be compared with those of a woce moored array deployed during 1993 95 at the same location overall the observations of deep water currents east of the grand banks reported here do not support suggestions of a basin wide slowdown of the atlantic meridional overturning circulation

observations of open ocean deep convection in the labrador sea from subsurface floats abstract the occurrence and extent of deep convection in the labrador sea in winters 1996 97 and 1997 98 is investigated from measurements of over 200 neutrally buoyant subsurface profiling autonomous lagrangian circulation explorer palace and sounding oceanographic lagrangian observer solo floats in addition to providing drift velocity data and vertical profiles of temperature and salinity 55 floats are equipped with vertical current meters vcms time series of vertical velocity derived from measured pressure and vertical flow past the float and temperature are obtained from the vcm floats mixed layer depths estimated from profile measurements indicate that convection reached depths greater than 1300 m in 1997 but no deeper than 1000 m in 1998 deep mixed layers were concentrated in the western basin although a number of deep mixed layers were observed southwest of cape farewell and also north of 60 n the highest variance in vertical velocity and the lowest mean temperatures were found in t

reconciling rapid strain accumulation with deep seismogenic fault planes in the ventura basin california global positioning system measurements across the east central ventura basin transverse ranges southern california before the nearby 1994 northridge earthquake show high strain rates interpreting this rapid strain accumulation using the usual model of deep slip on a dislocation in a uniform elastic half space requires slip to extend to within 5 km of the surface such shallow slip is difficult to reconcile with the substantial coseismic displacement at depths from 7 to 19 km during the northridge earthquake here we model the displacement and velocity fields throughout the earthquake cycle using a two dimensional finite element model with a viscoelastic rheology displacements are driven by far field and basal velocity boundary conditions and by imposed periodic earthquakes on the thrust faults bounding the basin the thrust faults rupture through an elastic upper crust to a depth of 15 km after a transient stage during which stresses and strains build up to quasi equilibrium values the behavior of the model becomes periodic the sum of the coseismic displacement divided by the repeat interval plus the average interseismic velocity is equal to the geologic velocity the temporal variation in surface velocity depends mainly on the elsasser relaxation time proportional to the product of the maxwell time of the lower crust and the ratio of the thicknesses of the entire crust and viscoelastic lower crust we are able to match the observed high strain rate only if we include the observed variations in elastic modulus associated with the deep basin sediments the model reconciles geologic geodetic and seismological observations of deformation there are trade offs among the far field convergence rate the elsasser time the earthquake repeat time and the time into the earthquake cycle acceptable convergence rates range from 8 mm yr for a relaxation time of the lower crust of 300 years to 12 mm yr for a 30 year relaxation time

variability of the directly observed middepth subpolar north atlantic circulation satellite views of the ocean have suggested a decline of the subpolar north atlantic surface circulation during the 1990s and 2000s this was a period of unprecedented observational capacity in the basin thanks to the presence of many hundreds of profiling floats we use more than 40 000 subsurface displacements of these floats to characterize the circulation at 1000 m depth and its evolution from 1997 2013 we show a statistically significant slowdown in the labrador sea boundary currents of 0 8 cm s 1 per decade 95 confidence interval of 1 4 to 0 15 cm s 1 per decade a conservative estimate of the uncertainty otherwise the middepth circulation field was largely stable our analysis of the location where the north atlantic current crosses the mid atlantic ridge shows that profiling floats can reveal steering by bathymetric features but do not reveal of decadal variability in the position where the current crosses the ridge