coherence of western boundary pressure at the rapid wave array boundary wave adjustments or deep western boundary current advection this study investigates the coherence between ocean bottom pressure signals at the rapid climate change programme rapid west atlantic variability experiment wave array on the western north atlantic continentalslope includingthewoodsholeoceanographicinstitutionlinew highlycoherentpressuresignals propagate southwestward along the slope at speeds in excess of 128 m s 21 consistent with expectations of barotropic kelvin like waves coherent signals are also evidenced in the smaller pressure differences relative to 1000 m depth which are expected to be associated with depth dependent basinwide meridional transport variations or an overturning circulation these signals are coherent and almost in phase for all time scales from 3 6 years down to 3 months coherence is still seen at shorter time scales for which group delay estimates are consistent with a propagationspeedofabout1 m s 21 over990 kmofcontinentalslopebutwithlargeerrorboundsonthespeed this is roughly consistent with expectations for propagation of coastally trapped waves though somewhat slower than expected a comparison with both eulerian currents and lagrangianfloat measurements shows that the coherence is inconsistent with a propagation of signals by advection except possibly on time scales longer than 6 months

propagation of signals in basin scale ocean bottom pressure from a barotropic model 1 the exchange of atmospheric plus oceanic mass between ocean basins is investigated using a global barotropic ocean model we find two particular cases of exchange between two basins at periods of 4 6 days the exchange is between the atlantic and pacific basins and represents a known oscillation forced by atmospheric pressure this mode represents a failure of the inverse barometer relationship due to the large scale and high frequency of atmospheric forcing and the presence of continents significant exchange between atlantic and pacific also occurs at longer periods the second case is most prominent at periods longer than 30 days strongest at periods longer than 100 days and represents a mass exchange between the southern ocean and the pacific the southern ocean part of this exchange is clearly related to the southern mode of fluctuations in antarctic circumpolar transport forced by southern ocean wind stress the reason for the exchange being with the pacific rather than other basins is explored and is found to be related to the balance of wind stress by form stress in drake passage exchange with the atlantic and indian oceans becomes dominant if drake passage topography is removed while recognizing the limitations of a barotropic model we contend that it is necessary to understand the barotropic adjustment process in order to make sense of longer timescale processes accordingly we end with speculation on the possible importance of the barotropic results for global sea level and tropical dynamics

spatial variation in solutional denudation and soil moisture over a hillslope hollow a spatial pattern of relative solutional denudation is described for a hillslope hollow and adjacent spurs at bicknoller combe somerset the pattern was obtained from a network of micro weight loss rock tablets emplaced in the soil the results show that the hollow is the main locus of solutional denudation the soil moisture distribution over the hollow indicates that it is a transmission zone for acid soil water percolating from the adjacent spurs to the saturated wedge at the base of the hollow the wetter acid soils in the hollow are responsible for the relatively higher solutional denudation taking place in the hollow

boundary wave communication of bottom pressure and overturning changes for the north atlantic 1 the relationship between changes in sea surface height bottom pressure and overturning is explored using isopycnal model experiments for the north atlantic changes in high latitude forcing are communicated rapidly over the basin through boundary wave propagation along the continental slope involving a hybrid mixture of kelvin and topographic rossby waves as well as spreading more slowly through advection along the western boundary this wave communication leads to coherent signals in sea surface height and bottom pressure variability extending for several thousand kilometers along the continental slope the model results are in broad agreement with altimetric diagnostics and the patterns only alter in detail with the realism of the topography the adjustment in bottom pressure is directly linked to a change in overturning since west east contrasts in bottom pressure are associated with a zonal integral in the meridional geostrophic flow correlation patterns reveal that temporal changes in overturning are primarily connected to the vertical contrast in bottom pressure across the shelf and continental slope along the western boundary

where and how long ago was water in the western north atlantic ventilated maximum entropy inversions of bottle data from woce line a20 1 a maximum entropy me method is used to deconvolve tracer data for the joint distribution of locations and times since last ventilation the deconvolutions utilize world ocean circulation experiment line a20 repeat hydrography for cfc 11 potential temperature salinity oxygen and phosphate as well as global ocean data analysis project glodap radiocarbon data combined with surface boundary conditions derived from the atmospheric history of cfc 11 and the world ocean atlas 2005 and glodap databases because of the limited number of available tracers the deconvolutions are highly underdetermined leading to large entropic uncertainties which are quantified using the information entropy of relative to a prior distribution additional uncertainties resulting from data sparsity are estimated using a monte carlo approach and found to be of secondary importance the me deconvolutions objectively identify key water mass formation regions and quantify the local fraction of water of age or older last ventilated in each region ideal mean age and radiocarbon age are also estimated but found to have large entropic uncertainties that can be attributed to uncertainties in the partitioning of a given water parcel according to where it was last ventilated labrador irminger seawater l water is determined to be mostly less than 40 a old in the vicinity of the deep western boundary current dwbc at the northern end of a20 but several decades older where the dwbc recrosses the section further south pointing to the importance of mixing via a multitude of eddy diffusive paths overflow water lies primarily below l water with young waters 40 a at middepth in the northern part of a20 and waters as old as 600 a below 3500 m

determining north atlantic meridional transport variability from pressure on the western boundary a model investigation 1 in this paper we investigate the possibility of determining north atlantic meridional transport variability using pressure on the western boundary focusing on the 42 n latitude of the halifax wave array we start by reviewing the theoretical foundations of this approach next we present results from a model analysis both statistical and dynamic that demonstrate the feasibility of the approach we consider how well we can quantify the meridional transport variability at 42 n given complete knowledge of bottom pressure across the basin and to what degree this quantification is degraded by first ignoring the effect of intervening topography and then by using only bottom pressure on the western boundary we find that for periods of greater than 1 year we can recover more than 90 of the variability of the main overturning cell at 42 n using only the western boundary pressure provided that we remove the depth averaged boundary pressure signal this signal arises from a basin mode of bottom pressure variability which has power at all time scales but that does not in truth have a meridional transport signal associated with it and from the geostrophic depth independent compensation of the ekman transport an additional benefit of the removal of the depth averaged pressure is that this high frequency ekman signal which is essentially noise as far as monitoring the meridional overturning circulation for climatically important changes is concerned is clearly separated from other modes

geographical variability of the first baroclinic rossby radius of deformation global 1 83 18 climatologies of the first baroclinic gravity wave phase speed c1 and the rossby radius of deformation l1 are computed from climatological average temperature and salinity profiles these new atlases are compared with previously published 5 83 58 coarse resolution maps of l1 for the northern hemisphere and the south atlantic and with a 1 83 18 fine resolution map of c1 for the tropical pacific it is concluded that the methods used in these earlier estimates yield values that are biased systematically low by 5 15 owing to seemingly minor computational errors geographical variations in the new high resolution maps of c1 and l1 are discussed in terms of a wkb approximation that elucidates the effects of earth rotation stratification and water depth on these quantities it is shown that the effects of temporal variations of the stratification can be neglected in the estimation of c1 and l1 at any particular location in the world ocean this is rationalized from consideration of the wkb approximation

latitudinal dependence of atlantic meridional overturning circulation amoc variations 1 amoc variations are often thought to propagate with the kelvin wave speed resulting in a short time lead between high and low latitudes amoc variations however as shown in this paper using a coupled climate model gfdl cm2 1 with the existence of interior pathways of north atlantic deep water nadw from flemish cap to cape hatteras as that observed recently amoc variations estimated in density space propagate with the advection speed in this region resulting in a much longer time lead several years between subpolar and subtropical amoc variations and providing a more useful predictability the results suggest that amoc variations have significant meridional coherence in density space and monitoring amoc variations in density space at higher latitudes might reveal a stronger signal with a several year time lead

gulf stream flow field and events near 68 w the synoptic ocean prediction synop experiment was designed to provide an accurate understanding of the energetic mesoscale processes in the gulf stream the central array measured velocity and temperature throughout the water column with horizontal extent large enough nearly to span the meander envelope and eulerian mean structure of the jet at 68 w the 55 to 70 km mooring spacing resolved mesoscale eddy interactions with the gulf stream and the 26 month duration allowed stable estimation of long term mean fields six steep meander troughs propagated into or developed within the array each lasting around 30 60 days thus impressing a small mean trough near 68 w in the predominantly eastward currents at jet level 1000 m and above at the deep level 3500m the mean flow was southwest at the shoreward sites shallower than 4300 m but it flowed cyclonically around a mean low pressure anomaly affecting all the deeper offshore sites the eddy kinetic energy per unit mass e k decreased by a factor of about 2 5 with each depth increment from 400 to 700 to 1000 m but was only a factor of 2 smaller at 3500 m than at 1000 m values of e k in the upper central jet 400 m were 100 to 230 mj kg 1 and were 4 13 mj kg 1 at 3500 m overall e k in the upper 1000m at 68 w was higher than previously published values at 55 w two extended case studies of meander propagation through the array demonstrate the development and intensification of deep cyclonic and anticyclonic flows beneath the gulf stream the cyclonic flow at 3500m associated with amplifying meander troughs often exceeded 0 35 ms 1 which was much larger than the typical 0 05 ms 1 deep mean velocities

lagrangian observations of the deep western boundary current in the north atlantic ocean part i large scale pathways and spreading rates twenty six rafos floats were deployed in the deep western boundary current dwbc of the north atlantic ocean between the grand banks and cape hatteras in 1994 95 and tracked acoustically for up to two years half of the floats were launched in the upper chlorofluorocarbon cfc maximum associated with upper labrador sea water 800 m and the other half near the deep cfc maximum that identifies the overflow water from the nordic seas 3000 m the float observations reveal the large scale pathways of these recently ventilated water masses in the subtropics the shallow float tracks show directly that upper labrador sea water is diverted away from the western boundary and into the interior at the location where the dwbc encounters the gulf stream near 368n the crossover region consistent with previous hydrographic studies east of the crossover region only one upper labrador sea water float out of seven 15 permanently crossed to the south side of the stream in two years caught in a cold core ring formation event the other shallow floats recirculated north of the gulf stream apparently confined by the mean potential vorticity gradient aligned with the stream the deep floats closely followed the topography to the crossover region then revealed a bifurcation in fluid parcel pathways one branch continues equatorward along the western boundary and the other turns first eastward along the gulf stream path then southward the deep float pathways including the bifurcation in the crossover region can be explained in terms of the deep potential vorticity distribution comparison of the float results with results from recent modeling studies suggests that the deep flow is strongly influenced by both the depth of the main pycnocline and bottom depth the effective spreading rates of upper labrador sea water and overflow water estimated directly from the float data southward at 0 6 6 0 2 cm s21 and 1 4 6 0 4 cm s21 respectively agree well with tracer derived spreading rates mean velocities in the dwbc equatorward at 2 4 cm s21 upper labrador sea water and 4 5 cm s21 overflow water are consistent with other in situ measurements one deep float drifted almost 4000 km along the western boundary in two years revealing a fast track for the spreading of overflow water in the dwbc these observations emphasize the importance of the crossover region in the spreading and mixing of recently ventilated water masses addressed in part ii of this study

the climatology of the north atlantic abstract data from approximately 144 000 hydrographic stations in the north atlantic have been retrieved from the national oceanic data centre and analysed to produce maps of mean pressure temperature salinity and oxygen on selected potential density surfaces for the domain bounded by 0 85 w and 0 65 n the data span the period from 1904 to 1990 with the majority of the data from the last four decades the data set for this region is 60 larger than that used in the production of levitus climatological world atlas this increase in stations coupled with smoothing scales specific to the north atlantic rather than the global ocean considerably improves the resolution of the basin s features the mean property fields and their associated standard deviations are resolved on a one degree grid with little smoothing contrasting with the levitus atlas where properties although presented on a one degree grid have been smoothed on the order of 1000km another important feature of this database is the process by which irregularly spaced data are averaged onto a regular grid in a significant departure from the levitus analysis which averaged on depth surfaces these data were averaged on potential density surfaces thus eliminating an artificial mixing of water mass properties the database is used to describe the baroclinicity of well known features such as the gulf stream the north atlantic current and the deep western boundary current and to elucidate the recirculations associated with these currents it additionally resolves several new features in the intermediate and deep north atlantic these features include the signature of a large scale deep recirculation that extends southwestward from the eastward extension of the north atlantic current to the separation point of the gulf stream near cape hatteras this recirculation which spans approximately 2000m of the water column encompasses more local recirculations and potentially mixes subpolar and subtropical waters furthermore in the upper thermocline this database reveals a coherent azores current that stretches from the gulf stream system south of the tail of the grand banks to madeira this flow is marked by divergences to the south and convergences from the north such that its downstream transport is not much changed

coherent sea level fluctuations along the global continental slope signals in sea level or more properly sub surface pressure ssp sea level corrected for the inverse barometer effect are expected to propagate rapidly along the continental slope due to the effect of sloping topography on wave modes resulting in strongly correlated ssp over long distances observations of such correlations around the arctic and antarctic are briefly reviewed and then extended using satellite altimetry to the rest of the global continental slope it is shown that such long distance correlations are common especially in extra tropical regions simple correlations from altimetry cannot however establish the wave speed or whether waves are responsible for the correlations as opposed to large scale coherence in the forcing a case study around south america is used to highlight some of the complications and is found to strengthen the case for the importance of wave modes in such long distance ssp coherence although more detailed in situ data are required to resolve the cause of the correlations

propagation pathways of classical labrador sea water from its source region to 26 n 1 more than two decades of hydrography on the abaco line east of the bahamas at 26 n reveals decadal variability in the salinity of classical labrador sea water clsw despite the long distance from its source region in the north atlantic ocean hydrographic time series from the labrador sea and from the abaco line show a pronounced step like decrease in salinity between 1985 and 1995 in the labrador sea and between 1995 and 2010 at the abaco line suggesting a time lag between the two locations of approximately 9 years the amplitude of the anomaly at the abaco line is 50 of the amplitude in the labrador sea a similar time lag and reduction of amplitude is found in the high resolution ofes model in which salinity anomalies can be observed propagating through the deep western boundary current as well as through a broad interior pathway on its way south to the abaco line the clsw becomes 8 standard deviations saltier due to isopycnal mixing with mediterranean outflow water mow climatological data in the north atlantic suggests that the mixing ratio of mow to clsw at the abaco line is 1 4 and that no variability in mow is required to explain the observed variability at the abaco line the data studied here suggest that decadal clsw anomalies stay relatively coherent while getting advected despite the important role of interior pathways

topographic waves over the continental slope abstract current meter data taken during a one year period over the continental slope and upper rise in three cross isobath sections have been examined for energy distribution coherence and phase propagation of topographic waves a peak at 15 days is present in the energy preserving spectrum of the near bottom currents on the rise and slope phase propagation is offshore and little energy is found in reflected waves these results are consistent with earlier findings on the lower rise at site d onshore energy flux associated with topographic waves is deflected by the continental slope and wave energy propagates along isobaths on the lower slope and upper rise the along isobath coherence scale is about 200 km the waves are probably generated by meanders in the gulf stream

a hydrologic and geomorphic model of estuary breaching and closure abstract to better understand how the hydrology of bar built estuaries affects breaching and closing patterns a model is developed that incorporates an estuary hydrologic budget with a geomorphic model of the inlet system erosion of the inlet is caused by inlet flow whereas the only morphologic effect of waves is the deposition of sand into the inlet when calibrated the model is able to reproduce the initial seasonal breaching seasonal closure intermittent closures and breaches and the low streamflow closed state estuary hydrology of the carmel lagoon located in central california model performance was tested against three separate years of water level observations when open during these years the inlet was visually observed to drain directly across the beach berm in accordance with model assumptions the calibrated model predicts the observed 48 h estuary stage amplitude with root mean square errors of 0 45 m 0 39 m and 0 42 m for the three separate years for the calibrated model the probability that the estuary inlet is closed decreases exponentially with increasing inflow streamflow plus wave overtopping decreasing 10 fold in probability as mean daily inflow increases from 0 2 to 1 0 m 3 s seasonal patterns of inlet state reflect the seasonal pattern of streamflow though wave overtopping may become the main hydrologic flux during low streamflow conditions infrequently causing short lived breaches in a series of sensitivity analyses it is seen that the status of the inlet and storage of water are sensitive to factors that control the storage transmission and inflow of water by varying individual components of the berm system and estuary storage the amount of the time the estuary is open may increase by 57 or decrease by 44 compared to the amount of time the estuary is open during calibrated model conditions for the 18 2 year model period the individual components tested are berm height width length and hydraulic conductivity estuary hypsometry storage to stage relationship two factors that control wave swash sedimentation of the inlet and sea level rise the elevation of the berm determines the volume of water that must enter the estuary in order to breach and it modulates the wave overtopping flux and frequency by increasing estuary storage capacity the estuary will breach less frequently 27 change in time open for modeled excavation scenario and store water up to 3 months later into the summer altering beach aquifer hydraulic conductivity affects inlet state and patterns of breaching and water storage as a result of sea level rise of 1 67 m by 2100 and a beach berm that remains in its current location and accretes vertically the amount of time the estuary remains open may decrease by 44 such a change is an end member of likely scenarios given that the berm will translate landwards model results indicate that the amount of time the estuary is open is more sensitive to changes in wave run up than the amount of sand deposited in the inlet per each overtopping wave

mechanisms of eddy driven variability of the florida current abstractin this study mechanisms causing year to year changes in the florida current seasonality are investigated using controlled realistic numerical experiments designed to isolate the western b

transport of the north atlantic deep western boundary current about 39 n 70 w 2004 2008 abstract begun in spring 2004 a sustained measurement program line w is returning high resolution observations of the north atlantic s deep western boundary current dwbc southeast of new england the study focuses on the cold limb of the atlantic meridional overturning circulation near the boundary between the subpolar and subtropical gyres the field study consists of a 6 element continental slope spanning moored array on a line underlying an altimeter satellite ground track and periodic reoccupations of a full depth hydrographic section along the line extending from the continental shelf towards bermuda here data from the first 4 years of the array may 10 2004 april 9 2008 are analyzed along with 9 realizations of the section the array a mix of moored profiler and discrete fixed depth instrument moorings returned temperature salinity and horizontal velocity data with various temporal and depth resolutions after averaging to filter inertial tidal and other high frequency motions the combined moored data set was binned to the lowest common temporal resolution of 5 days the nominal burst sample interval of the moored profilers and interpolated to 2 dbar vertical resolution temperature salinity dissolved oxygen tracer chemical concentrations and direct velocity data were acquired on the hydrographic cruises the present work focuses on the 4 year mean and time varying meridional transport in 4 layers bounded by neutral density surfaces upper and classical labrador sea waters iceland scotland overflow waters and denmark strait overflow waters the 5 d 4 layer summed meridional transport estimates range between 3 5 and 79 9 sv with a record mean average transport of 25 1 sv and standard deviation of 12 5 sv bias adjustment to account for the finite width of the moored array increases the 4 layer mean transport estimate to 28 7 sv at time scales longer than about 1 month the variations in equatorward dwbc transport appear correlated with meridional position of the gulf stream north wall with stronger transport observed when the stream is displaced south

frequency domain multimodel analysis of the response of atlantic meridional overturning circulation to surface forcing the dynamics of the atlantic meridional overturning circulation amoc vary considerably among different climate models for example some models show clear peaks in their power spectra while others do not to elucidate these model differences transfer functions are used to estimate the frequency domain relationship between surface forcing fields including sea surface temperature salinity and wind stress and the resulting amoc response these are estimated from the outputs of the coupled model intercomparison project phase 5 cmip5 and phase 3 cmip3 control runs for eightdifferent models with a specificfocus on geophysical fluid dynamics laboratory climate model version 2 1 gfdl cm2 1 and the community climate system model version 4 ccsm4 which exhibit rather different spectral behavior the transfer functionsshowvery littleagreement amongmodelsforany ofthe pairsofvariablesconsidered suggestingthe existence of systematic model errors and that considerable uncertainty in the simulation of amoc in current climate models remains however a robust feature of the frequency domain analysis is that models with spectral peaks in their amoc correspond to those in which amoc variability is more strongly excited by high latitude surface perturbations that have periods corresponding to the frequency of the spectral peaks this explains why different models exhibit such different amoc variability these differences would not be evident without using a method that explicitly computes the frequency dependence rather than a priori assuming a particular functional form finally transfer functions are used to evaluate two proposed physical mechanisms for model differences in amoc variability differences in labrador sea stratification and excitation by westward propagating subsurface rossby waves

buoyancy driven circulation in an ocean basin with isopycnals intersecting the sloping boundary abstract the dynamics that govern the spreading of a convectively formed water mass in an ocean with sloping boundaries are examined using an isopycnal model that permits the interface between the layers to intersect the sloping boundaries the simulations presented here use a two layer configuration to demonstrate some of the pronounced differences in a baroclinically forced flow between the response in a basin with a flat bottom and vertical walls and a more realistic basin bounded by a sloping bottom each layer has a directly forced signal that propagates away from the forcing along the potential vorticity pv contours of that layer paired opposed boundary currents are generated by refracted topographic rossby waves rather than kelvin waves it is impossible to decompose the flow into globally independent baroclinic and barotropic modes topography causes the barotropic i e depth averaged response to buoyancy forcing to be just as strong as the baroclinic response because layer pv contours di

a theory for the surface atlantic response to thermohaline variability abstract the response of the upper warm limb of the thermohaline circulation in the north atlantic to a rapid change in deep water formation at high latitudes is investigated using a reduced gravity ocean model changes in deep water formation rate initiate kelvin waves that propagate along the western boundary to the equator on a timescale of months the response in the north atlantic is therefore rapid the southern hemisphere response is much slower limited by a mechanism here termed the ldquo uatorial buffer since to leading order the flow is in geostrophic balance the pressure anomaly decreases in magnitude as the kelvin wave moves equatorward where the coriolis parameter is lower together with the lack of sustained pressure gradients along the eastern boundary this limits the size of the pressure field response in the southern hemisphere interior adjustment is by the westward propagation of rossby waves but only a small fraction of the change in thermohaline circulation strength is commun

temporal variability of the atlantic meridional overturning circulation at 26 5 n the vigor of atlantic meridional overturning circulation moc is thought to be vulnerable to global warming but its short term temporal variability is unknown so changes inferred from sparse observations on the decadal time scale of recent climate change are uncertain we combine continuous measurements of the moc beginning in 2004 using the purposefully designed transatlantic rapid climate change array of moored instruments deployed along 26 5 n with time series of gulf stream transport and surface layer ekman transport to quantify its intra annual variability the year long average overturning is 18 7 5 6 sverdrups sv range 4 0 to 34 9 sv where 1 sv a flow of ocean water of 106 cubic meters per second interannual changes in the overturning can be monitored with a resolution of 1 5 sv

gulf stream generated topographic rossby waves abstract an inverse ray tracing model is applied to observations of 40 day topographic rossby waves on the continental slope off of cape hatteras north carolina to determine their origin the rays are traced seaward and extend into the deep gulf stream where the bottom slope remains strong enough that topographic dominates planetary this enable coupling to occur between eastward propagating gulf stream meanders and topographic waves with eastward phase speed and matching zonal wavelength previous satellite observations indicate that the most frequently occurring gulf stream meanders have a period of 40 days and the model reveals that as these meanders pass a topographic bend near 71 72 w they are able to couple to the observed topographic waves traced back from cape hatteras the 40 day gulf stream meanders occur in bursts which leads to associated bursts of the topographic waves