the meandering gulf stream as seen by the geosat altimeter surface transport position and velocity variance from 73 to 46 w the surface geostrophic velocity field for the gulf stream region was analyzed for the position structure and surface transport of the gulf stream for 2 5 years of the geosat altimeter exact repeat mission synthetic data using a gaussian velocity profile were generated and fit to the sea surface residual heights to create a synthetic mean sea surface height field and profiles of absolute geostrophic currents most of cross track velocity variance was due to the meandering of the gulf stream rather than to rings or complicated velocity profiles which suggested that the simple model parameters are an efficient description of the gulf stream fluctuations an analysis of the model parameters and the actual geostrophic velocity profiles revealed two different flow regimes for the gulf stream connected by a narrow transition region coincident with the new england seamount chain the upstream region was characterized by relatively straight gulf stream paths long eulerian time scales and eastward propagating meanders the downstream region had more large meanders no consistent propagation direction and shorter eulerian time scales a 25 reduction in surface transport occurred in the transition region with a corresponding reduction in current speed and no change in gulf stream width a significant anomaly in surface transport near 69 w suggested the existence of small scale recirculation gyres there the highest variance empirical orthogonal functions of position and surface transport were significantly correlated with larger surface transports leading more northerly positions by a month

mean stream coordinates structure of the subantarctic front temperature salinity and absolute velocity 1 the mean synoptic structure of the northern strongest branch of the antarctic circumpolar current southwest of tasmania at the subantarctic front saf is estimated by a stream coordinates analysis of data from overlapping arrays of inverted echo sounders iess and horizontal electric field recorders deployed during the 1995 1997 sub antarctic flux and dynamics experiment the stream coordinates are derived from a daily objective mapping of the temperature field obtained from combining the ies travel time measurements with an empirical look up table constructed from the extensive hydrography acquired during woce full water column stream coordinates sections of temperature salinity and absolute velocity are presented and compared with prior observations the along stream current has a single peak with surface velocities reaching about 50 cm s 1 the vertical structure of the along stream velocity is roughly consistent with a combined external and first internal normal mode description that is adapted to the buoyancy frequency as it varies across the front although there are some significant differences the cross stream structure of along stream velocity is very nearly symmetric about the jet axis but the lateral shear magnitude is slightly larger on the cold side of the saf separating the baroclinic and barotropic currents reveals that the saf currents are diffluent primarily baroclinically in the cross stream direction baroclinic cross stream diffluence of approximately 0 23 sv per km sv 106 m3 s 1 or about 16 sv per degree of longitude at 51 s the 2 year mean total saf transport is 75 sv for a 220 km width the barotropic contribution is small 8 sv but not negligible

the structure and transport of the gulf stream at 73 w abstract between september 1980 and may 1983 16 sections of temperature and velocity were obtained with the pegasus instrument along a transect crossing the gulf stream at 73 w the mean temperature and velocity fields of the upper 2000 meters were calculated the transport above 2000 meters calculated from the sections had a mean of 87 8 17 3 106 m3 s 1 a comparison with mass flux measurements obtained by previous investigators at cape fear indicated that the addition to the transport of the stream in the region was uniform with depth above 800 meters the mean inflow measured at the pegasus line was found to be uniform above 800 meters and to decrese substantially below this depth the increase in transport at the line estimated from the mean cross stream velocity field was 15 4 5 8 106 m3 s 1 per 100 km downstream distance the temporal fluctuation of the pegasus transport measurements was consistent with an annual cycle with a maximum in april the mean eddy kinetic energy at the surface

bottom temperatures in drake passage abstractlong time series of bottom temperatures in the southern ocean are rare the cdrake array with over 40 current and pressure recording inverted echo sounders moored across drake passage to monitor the antarctic circumpolar current acc variability and transport measured temperature at 1 and 50 m above the seafloor at depths 3500 m and at the southern continental margin the 4 yr dataset provided an opportunity to examine the temporal and spatial scales of bottom temperature variability high variability was observed ranges were 0 5 0 9 c in the northern passage and 0 3 0 6 c in the southern passage standard deviations in the two regions were 0 1 0 15 c and 0 05 c respectively meandering of the acc with its deep reaching thermocline accounted for up to 50 of the observed bottom temperature variance northern passage temperatures spaced less than 40 km apart were correlated with each other while those in the southern portion separated by 60 70 km were not a gap in the west scotia

using motionally induced electric signals to indirectly measure ocean velocity instrumental and theoretical developments abstract the motion of conductive sea water through the earth s magnetic field generates electromagnetic em fields through a process called motional induction direct measurements of oceanic electric fields can be easily converted to water velocities by application of a first order theory this technique has been shown to obtain high quality velocities through instrumental advances and an accumulation of experience during the past decades em instruments have unique operational considerations and observe for instance vertically averaged horizontal velocity from stationary sensors or vertical profiles of horizontal velocity from expendable probes or autonomous profiling floats the first order theory describes the dominant electromagnetic response in which vertically averaged and vertically varying horizontal velocities are proportional to electric fields and electric currents respectively after discussions of the first order theory and deployment practices operational capabilities are shown through recently published projects that describe stream coordinate velocity structure of the antarctic circumpolar current quickly evolving overflow events in the denmark strait and time development of momentum input into the ocean from a hurricane a detailed analysis of the gulf stream at its separation point from the continental slope serves as a case study for interpreting em measurements including the incorporation of geophysical knowledge of the sediment in addition the first order approximation is tested by the many features at this location that contradict the approximation s underlying assumptions sharp horizontal velocity gradients steep topography and thick and inhomogeneous sediments numerical modeling of this location shows that the first order assumption is accurate to a few percent a few cm s 1 in almost all cases the errors in depth varying velocity are 1 are substantiated by the direct observations and can be corrected by iterative methods though errors in the depth uniform velocity are 1 1 or less in almost all regions of the ocean an error similar to the instrumental accuracy of em instruments

aspects of the antarctic circumpolar current dynamics investigated with drifter data interactions between eddies and mean flow are essential to close the momentum budget of the southern ocean as well as to determine the structure of the global meridional overturning circulation both the structure of the antarctic circumpolar current and the eddy dynamics arising at its heart are importantfor water mass circulation and global ocean ventilation and therefore for the global climate however the characterization of the eddy fields of heat and momentum are still poorly sampled by direct observations and are difficult to accurately resolve or parameterize in numerical models here we present observation based eddy statistics and eddy heat flux ehf from a consistent dataset and estimate southern ocean surface ehf from direct measurements without any parameterization assumption observations obtained from near surface drifters represent a very useful dataset to analyze the eddy field because of their ability to catch a large number of scales of motion while providing a quasi synoptic coverage of the investigated area differences between winter and summer distributions of mean velocities mean kinetic energy and eddy kinetic energy are shown to be strongly constrained by bottom topography and suggest a winter shift of the polar front in specific areas around the circumpolar belt overall the flow follows the contours of constant planetary vorticity set by the depth of the ocean and creates anisotropy in eddy dispersion with maximum dispersion along these contours furthermore eddy mean flow interactions are strongly influenced by topography with eddies having a tendency to accelerate jets upstream of ridges and decelerate them further downstream these strong regional variabilities introduced by topography affect the flux of heat induced by eddies and therefore affect formation and subduction of the main surface and intermediate southern ocean water masses integrated over the southern ocean subduction of water masses induced by ehf appears as an order on component for the southern ocean thermocline ventilation our results based on direct observations emphasizes once more the importance of continuing sustained effort to better represent the effect of mesoscale eddies in a coarse climate model if we are to represent and predict future climate

equilibration of baroclinic meanders and deep eddies in a gulf stream type jet over a sloping bottom abstract spatiotemporal evolution of a small localized meander on a gulf stream type baroclinically unstable jet over a topographic slope is investigated numerically using a three dimensional primitive equation model an unperturbed jet is prescribed by a potential vorticity front in the upper thermocline overlaying intermediate layers with weak isentropic potential vorticity gradients and a quiscent bottom layer over a positive same sense as isopycnal tilt cross stream continental slope a series of numerical experiments with the same initial conditions over a slope and flat bottom on the plane and on the f plane has been carried out an initially localized meander evolves into a wave packet and generates deep eddies that provide a positive feedback for the meander growth meanders found growing over a flat bottom are able to pinch off resembling warm and cold core rings while in the presence of a weak bottom slope such as 0 002 the maximum amplitudes of meanders and associated deep eddies saturat

gulf stream meander propagation past cape hatteras the propagation and growth characteristics of gulf stream meanders past the stream s separation point at cape hatteras are analyzed using yearlong time series from a mooring program sponsored by the minerals management service which included moorings imbedded in the gulf stream cyclonic flank both upstream south and downstream north of cape hatteras in the upstream region energetic meanders of 3 8 day period 180 380 km wavelength propagate downstream along the gulf stream at speeds of 40 55 km day 21 this variability decays almost completely across the gulf stream separation with growth in lower frequency variability 30 120 day in the downstream direction wavelength and phase speed in the 3 8 day band are strong functions of frequency with increasing phase speed for increasing wavenumber phase speeds upstream from cape hatteras and across the gulf stream separation point are faster for a given wavenumber than downstream from cape hatteras in keeping with prior published estimates at the upstream end of the study site both baroclinic and barotropic mechanisms contribute to the decay of 3 8 day meanders and growth of lower frequency 30 120day variability in the downstream direction at the downstream end of the study region the reverse holds with both baroclinic and barotropic mechanisms contributing to growth of 3 8 day meanders and decay of lowerfrequency 30 120 day variability

foraminiferal ecozones a high resolution proxy for the late quaternary biochronology in the central mediterranean sea the planktic foraminiferal distribution identified in 60 cores collected in different basins of the mediterranean sea allowed to establish an ecostratigraphical scheme which provides a very important tool for the biochronological subdivision of the uppermost quaternary we identified a succession of ten ecozones during the last 23 ka in the tyrrhenian basin and eight ecozones in the adriatic sea during the last 15 ka the ecozones boundaries have been calibrated by 14c ams radiometric data and by the stable oxygen isotope record the chronological framework defined by the successive bioevents shows a very high resolution millenary scale and evidences that the changes in the planktic microfauna occurred more or less synchronously throughout the central mediterranean sea differences due to different oceanographic settings of the basins do not affect the general distributional pattern of planktic foraminifera

kinetic characteristics of debris flows as exemplified by field investigations and discrete element simulation of the catastrophic jiweishan rockslide china abstract the jiweishan rockslide of june 5 2009 in china provides an important opportunity to elucidate the kinetic characteristics of high speed long runout debris flows a 2d discrete element model whose mechanical parameters were calibrated using basic field data was used to simulate the kinetic behavior of this catastrophic landslide the model output shows that the jiweishan debris flow lasted about 3 min released a gravitational potential energy of about 6 10 13 j with collisions and friction dissipating approximately equal amounts of energy and had a maximum fragment velocity of 60 70 m s almost twice the highest velocity of the overall slide mass 35 m s notable simulated characteristics include the high velocity and energy of the slide material the preservation of the original positional order of the slide blocks the inverse vertical grading of blocks and the downslope sorting of the slide deposits field observations that verify these features include uprooted trees in the frontal collision area of the air blast wave downslope reduction of average clast size and undamaged plants atop huge blocks that prove their lack of downslope tumbling the secondary acceleration effect and force chains derived from the numerical model help explain these deposit features and the long distance transport our back analyzed frictions of the motion path in the pfc model provide a reference for analyzing and predicting the motion of similar geological hazards

connections between surface fluxes and the deep circulation in the sea of japan 1 the extent to which seasonably variable surface fluxes and bottom friction can exert a control on the abyssal circulation above localized bottom topography is analyzed in the japan sea region through the use of a three dimensional eddy resolving ocean model our simulations show that the bottom friction exerts a first order control on the magnitude of the eddy driven deep circulation over f h geostrophic contours which is inversely dependent on the bottom drag in accordance with theory seasonal surface flux variability acts as a modifier to this theory depending on the timescale of active forcing relative to bottom friction spin down time possible physical mechanisms for a varying bottom drag coefficient are proposed winter ventilation of isopycnals during deep convection is followed by enhanced drain energy to small scale turbulence and strong energy dissipation in intermediate layers leading to a weakening of deep circulation that contradicts the classic ventilation theory

interaction of the gulf stream and deep western boundary current where they cross the long timescale variability of the deep western boundary current dwbc where it crosses under the gulf stream is analyzed using a 3 year array of bottom current meters and inverted echo sounders the relationship of this variability to fluctuations in the upper layer gulf stream is specifically addressed at periods shorter than a year the dwbc variability shows no relationship to the local gulf stream 100 day fluctuations show a pulsing of the dwbc transport whereas longer period fluctuations are indicative of a meandering type variability by contrast on timescales greater than a year variations in the orientation and transport of the dwbc are directly related to such fluctuations in the local gulf stream the coupling reveals that the dwbc is forced by changes in the gulf stream rather than causing such variations which is in contrast to earlier modeling results

temporal variability of the meridional overturning circulation at 34 5 s results from two pilot boundary arrays in the south atlantic data from two boundary arrays deployed along 34 5 s are combined to produce the first continuous in situ time series observations of the basin wide meridional overturning circulation moc in the south atlantic daily estimates of the moc between march 2009 and december 2010 range between 3 sv and 39 sv 1 sv 106 m3 s 1 after a 10 day low pass filter is applied much of the variability in this 20 month record occurs at periods shorter than 100 days approximately two thirds of the moc variability is due to changes in the geostrophic baroclinic plus barotropic volume transport with the remainder associated with the direct wind forced ekman transport when low pass filtered to match previously published analyses in the north atlantic the observed temporal standard deviation at 34 5 s matches or somewhat exceeds that observed by time series observations at 16 n 26 5 n and 41 n for periods shorter than 20 days the basin wide moc variations are most strongly influenced by ekman flows while at periods between 20 and 90 days the geostrophic flows tend to exert slightly more control over the total transport variability of the moc the geostrophic shear variations are roughly equally controlled by density variations on the western and eastern boundaries at all time scales captured in the record the observed time mean moc vertical structure and temporal variability agree well with the limited independent observations available for confirmation

prediction of the gulf stream path from upstream parameters a linear wiener least squares optimal filter is used to predict the path of the gulf stream in the region between cape hatteras and 70 w using upstream inlet conditions as filter inputs although position angle curvature geostrophic velocity and curvature vorticity measured at 73 w were tested as multiple inlet parameters it was found that inlet position alone was the best predictor with inlet position as the predictor this filter is equivalent to propagating meanders downstream with a typical phase speed and growth rate forecasts of the downstream path position are produced more accurate than persistence 12 days in advance at 140 km from the inlet 24 days in advance at 240 km from the inlet and 28 days in advance at 340 km from the inlet

comparison of alkenone estimates with other paleotemperature proxies 1 to a certain degree all sea surface temperature sst proxies suffer from uncertainty due to signal preservation problems and to perturbations by other environmental variables however a multiproxy reconstruction is justified because most biases should in principle cancel out as they are specific to the biological groups and or to the analyzed chemical species such a multiproxy strategy has proven crucial for calibrating these proxies and is also useful in assessing downcore profiles until now there have been only a dozen deep sea cores where it is possible to compare directly alkenone based ssts with other paleotemperature records from this still limited data set the broad picture is of general agreement for the amplitude of changes at low and middle latitudes the few observed discrepancies suggest that alkenone based temperatures are more comparable to those based on mg ca ratios than those obtained through statistical analysis of the foraminiferal distribution more systematic differences are noted at higher latitudes where alkenones indicate warmer temperatures during the glacial period than transfer functions based on foraminifera or diatoms several reasons have been invoked to resolve the mismatch but more ground truthing work is needed before deciding which temperature changes are the most accurate

the effect of the new england seamounts on gulf stream meandering as observed from satellite ir imagery abstract it is commonly held belief that meandering of the gulf stream increases dramatically downstream of the new england seamount chain in fact this appears not to be the case the envelope of gulf stream northern edges derived from 30 months of satellite data remains constant from 65 to 58 w only the mean of the integrated path length normalized by the mean path length appears to increase downstream of the seamounts but at very nearly the same rate as upstream of them

an observational streamfunction in the gulf stream abstract contours of the main thermocline 12 c isotherm depth z12 topography objectively generated from inverted echo sounder observations in the gulf stream may be treated as a baroclinic geostrophic streamfunction as preliminary steps the authors developed techniques to estimate geostrophic velocity v k g f z12 and geostrophic vorticity g f 2z12 in doing this the authors also determined a reduced gravity g 1 53 cm s 2 by least squares fitting the estimated v to observed vbc velocities i e fine tuned for the at 400 m relative to 3000 m accuracy of the objective maps of is investigated by comparing v against vbc directly measured from tall current meter moorings and against vorticity p separately estimated using a rigid stream velocity section and path curvature the v values with speeds up to 100 cm s 1 are correlated with vbc at the 99 confidence level and the two measurements differ by only 10 cm s 1 rms error vorticity estimates ranging between 0 44

profiling the gulf stream with a current meter mooring a current meter mooring was deployed for one year at the mean position of the gulf stream at 68 w with instruments from 400 m to 4000 m it provides the first unambiguous evidence that the gulf stream extends from top to bottom of the water column using the strong cross stream temperature structure to derive a horizontal coordinate related to temperature we estimate the width and transport of the gulf stream for four individual events and we determine an average profile of the vertical and cross stream structure of the gulf stream a conservative estimate of transport for this average profile indicates that the gulf stream has a transport of 103 106 m s 1 at 68 w

meanders of the gulf stream downstream from cape hatteras 1975 1978 abstract weekly gulf stream paths within 1000 km downstream of cape hatteras were obtained for 1975 78 from the navy s weekly eofa charts based on satellite ir imagery they displayed two dominant meander modes first a standing meander energetic over periods between 4 months and at least 4 years and second down stream propagating meanders that were most energetic at periods of several weeks the long period standing meander was confined between nodes located at the separation point near cape hatteras i e where the stream s mean path turns seaward and at a point about 600 km farther downstream the rms amplitude was 36 km at the antinode the amplitude of propagating meanders increased rapidly in the first 200 km downstream of the separation point where the capture of warm core eddies was common farther down stream the predominant meanders had a wavelength averaging 330 km a period averaging 1 5 month a phase speed averaging 8 cm s 1 a downstream group speed averaging 17 cm s 1 and downstrea

observed ocean bottom temperature variability at four sites in the northwestern argentine basin evidence of decadal deep abyssal warming amidst hourly to interannual variability during 2009 2019

strong bottom currents and cyclogenesis in drake passage 1 observations from 38 bottom moored current and pressure recording inverted echo sounders cpies deployed in drake passage during the 2007 2008 international polar year provide unprecedented coverage of near bottom currents and pressures spanning the entire antarctic circumpolar current year long mean currents exceed 10 cm s 1 north of the polar front and mean directions are not in general aligned with the surface fronts topographic steering is most evident at the continental margins deep eddy kinetic energy eke is maximum at about 200 cm2 s 2 between the subantarctic and polar fronts coinciding with the location but about one quarter of the value of a maximum in surface eke multiple high speed current events with peak speeds of 60 70 cm s 1 and lasting 30 to 70 days are coherent across sites separated by 45 km the observed spinup of eddies coinciding with meanders in the surface fronts is consistent with deep cyclogenesis

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

eddy mean flow interaction in the kuroshio extension region abstractthe authors use data collected by a line of tall current meter moorings deployed across the axis of the kuroshio extension ke jet at the location of maximum time mean eddy kinetic energy to characterize the mean jet structure the eddy variability and the nature of eddy mean flow interactions observed during the kuroshio extension system study kess a picture of the 2 yr record mean jet structure is presented in both geographical and stream coordinates revealing important contrasts in jet strength width vertical structure and flanking recirculation structure eddy variability observed is discussed in the context of some of its various sources jet meandering rings waves and jet instability finally various scenarios for eddy mean flow interaction consistent with the observations are explored it is shown that the observed cross jet distributions of reynolds stresses at the kess location are consistent with wave radiation away from the jet with the sense of the eddy feedback effect on

uncertainties in the mean ocean dynamic topography before the launch of the gravity field and steady state ocean circulation explorer goce 1 in anticipation of the future observations of the gravity mission gravity field and steady state ocean circulation explorer goce the present day accuracy of mean dynamic topography mdt is estimated from both observations and models a comparison of five observational estimates illustrates that rms differences in mdt vary from 4 2 to 10 5 cm after low pass filtering the fields with a hamming window with wavenumber n 120 corresponding to an effective resolution of 167 km rms differences in observational mdt reduce to 2 4 8 3 cm for n 15 1334 km differences in data sources geoid model in situ data are mostly visible in the small scale oceanic features while differences in processing filtering inverse modeling techniques are reflected at larger scales a comparison of seven different numerical ocean models demonstrates that model estimates differ mostly in western boundary currents and in the antarctic circumpolar current rms differences between modeled and observed mdt are at best 8 8 cm for n 120 and reduce to 6 4 cm for n 15 for models with data assimilation a minimal rms difference of 6 6 cm n 120 to 3 4 cm n 15 is obtained with respect to the observational mdts the reduction of differences between mdts with increasing filtering scales is smaller than expected while it is expected that goce will improve mdt estimates at small spatial scales improvement of mean sea surface estimates from satellite altimetry may be needed to improve mdt estimates at larger scales

cyclogenesis in the deep ocean beneath the gulf stream 1 description one of the primary scientific results of the synoptic ocean prediction synop observational program was the discovery of strong cyclones in the deep ocean beneath the large amplitude gulf stream meander troughs that routinely form at about 68 w these strong well organized cyclones extend to at least 3500 m below the sea surface and are an important component of the overall dynamical variability of the gulf stream and adjacent deep waters typically a small amplitude gulf stream meander stalls near 68 w and begins to amplify as the amplitude of troughs in the gulf stream jet increases the currents at 3500 m strengthen and turn forming a cyclonic circulation pattern during synop six well defined instances of meander trough amplification and deep cyclogenesis occurred the cyclones were characterized by strong swirl speeds up to 0 5 m s 1 and were long lived typically lasting 6 9 weeks frequent occurrences present 35 of the time during the 25 month deployment period the structure of the cyclones at 3500 m is characterized by increasing velocity from the cyclone center out to some radius of maximum velocity and decreasing velocity beyond that radius this structure was robust over the lifetime of an event and from event to event cyclone radius and the radius to maximum velocity were consistently 130 km and 55 km respectively evidence of cyclones at upper measurement levels and the low vertical shear values apparent in the deep water below the thermocline indicate that the cyclones extended throughout the entire water column from the benthic boundary layer through the thermocline and to the ocean s surface

vertical motion in the gulf stream and its relation to meanders vertical motion at 700 m in the gulf stream main thermocline is computed using the adiabatic heat equation and a combination of data from inverted echo sounders and moored current meter measurements of t and u v at 400 700 1000 and 3500 m daily maps of all data on a regular grid were created using optimal estimation from these maps the tendency and advection terms in the heat equation were calculated the mapped vertical motions w agree well with w observed contemporaneously along isopycnal rafos float tracks strong events occur frequently within the gulf stream diagnosed vertical motions greater than 2 mm s 1 that persist for days are common occurring roughly every week within the 250 km mapped region upwelling and downwelling regions have horizontal scales of about 100 km both along and across stream case studies and animation elucidate the relationship between meander properties and the structure phasing and amplitude of the w fields typically the largest w is positioned near the steepest thermocline slope downwelling upwelling occurs entering exiting troughs strongest vertical motions occur in slowly propagating features and vertical motions are usually weaker for rapidly propagating features this observed dependence upon phase speed is opposite to predictions of recent kinematic and conceptual models the main contribution to observed w and the factor missing in those models is the existence of strong abyssal flow serving as a barotropic reference for the entire water column with a component which may flow orthogonal to the baroclinic front along sloping isopycnals the strongest vertical and cross frontal components are usually associated with slowly moving or stalled steep meanders associated with which abyssal cyclones or anticyclones have developed the vertical motion which is forced in these cases can significantly alter the vertical vorticity and or frontal strength through tilting of the strong vertical shear and of the strong vertical stratification vertical and cross frontal transports of 5 sv occur in steep meanders

a dynamically consistent analysis of the mesoscale eddy field at the western north pacific subarctic front 1 in this study we analyze the energetics of the quasigeostrophic qg currents observed in the course of an extensive soviet field experiment in 1987 the analyzed data span over the period of 1 month and cover the region 37 5 42 5 n 151 5 158 e at an average horizontal resolution of 35 km the processed data set includes the results of measurements at 668 hydrographic stations 118 moorings geosat sea surface height anomalies ecmwf winds and etop05 bottom topography a variational data assimilation method is employed to interpolate observations onto a regular space time grid an ensemble average over optimized ocean states is utilized to estimate posterior error bars assimilation has shown that the observed mesoscale structures are well described by qg dynamics which can explain 80 85 of the variability in the velocity and density fields the model data misfits lie within the observational error bars for all the data types used in assimilation the standard laplacian type parameterization of the small scale processes was found to be inconsistent with observations as the least model data misfits were obtained with zero diffusivity coefficients analysis of the interpolated patterns revealed a pronounced mesoscale mixing event characterized by the development of a warm streamer swirling around the upper cold core of an old anticyclonic kuroshio extension eddy the process was accompanied by a fast northwestward displacement of the eddy and induced detachment of a warm elongated vortex from its eastern rim within a week the vortex penetrated northward into the subarctic zone and eventually split into several smaller scale eddies energy analysis of the optimal solution indicates that baroclinic instability is the likely source of their energy computation of energy exchanges between depth averaged and shear components of the observed currents reveals the vertical energy cascade barotropization of the shear flow at a rate of 29 4 10 7 cm2 s 3 and the weaker kinetic energy transfer of opposite sign due to topographic interaction mean currents in the region are baroclinically unstable with an estimate of the available potential energy flux from the mean current to the eddies 53 8 10 7 cm2 s 3 potential enstrophy is transferred to mesoscale at a rate of 33 7 10 19 s 3 these figures can be considered as experimental evidence of the properties of free geostrophic turbulence which were predicted by theory and observed in numerical experiments

asymmetry of an equilibrated gulf stream type jet over topographic slope abstract the symmetry properties of the gulf stream type jet equilibrated over topographic slope are investigated in a series of idealized numerical experiments a baroclinically unstable zonal jet equilibrates over a sloping bottom through the process of potential vorticity pv homogenization underneath the main thermocline by the bottom intensified eddy activity associated with the stream meandering potential vorticity homogenization underneath the main thermocline leads to formation of recirculation gyres on both sides of the jet the magnitude of the northern recirculation gyre as measured by its westward transport is larger than the magnitude of the southern recirculation gyre this asymmetry in recirculations is shown to be the result of an asymmetric pv mixing underneath the thermocline produced by an asymmetric jet in particular the lateral shift of the velocity maximum near the surface relative to the velocity maximum at depth is shown to be responsible for the asymmetry the results are re

global comparison of benthic nepheloid layers based on 52 years of nephelometer and transmissometer measurements abstract global maps of maximum bottom particle concentration benthic nepheloid layer thickness and integrated particle mass in benthic nepheloid layers bnl based on 2412 global profiles collected using the lamont thorndike nephelometer from 1964 to 1984 are compared with maps of those same properties compiled from 6392 global profiles measured by transmissometers from 1979 to 2016 outputs from both instruments were converted to particulate matter concentration pm the purposes of this paper are to compare global differences and similarities in the location and intensity of bnls measured with these two independent instruments over slightly overlapping decadal time periods to combine the data sets in order to expand the time scale of global in situ measurements of bnls and to gain insight about the factors creating sustaining bnls the similarity between general locations of high and low particle concentration bnls during the two time periods indicates that the driving forces of erosion and resuspension of bottom sediments are spatially persistent during recent decadal time spans though in areas of strong bnls intensity is highly episodic topography and well developed current systems play a role these maps will help to understand deep ocean sediment dynamics linkage with upper ocean dynamics the potential for scavenging of adsorption prone elements near the seafloor and provide a comprehensive comparison of these data sets on a global scale during both time periods bnls are weak or absent in most of the pacific indian and atlantic basins away from continental margins high surface eddy kinetic energy is associated with the kuroshio current east of japan both data sets show weak bnls south of the kuroshio but no transmissometer data have been collected beneath the kuroshio itself sparse nephelometer data show moderate bnls just north of the kuroshio extension but with much lower concentrations than beneath the gulf stream strong bnls are found in areas where eddy kinetic energy in overlying waters mean kinetic energy near bottom and energy dissipation within the bottom boundary layer are high areas of strongest bnls include the western north atlantic argentine basin south atlantic areas around south africa tied to the agulhas current region and somewhat random locations in the antarctic circumpolar current of the southern ocean

atlantic core top calibration of the u37k index as a sea surface palaeotemperature indicator abstract a field calibration of the uk index with sea surface temperature is discussed through analysis of an extensive suite of surface sediments n 109 from the northeastern atlantic 2 s 75 n values of u 37 k are compared with sea surface temperatures for overlying waters measured at different depths and seasons to obtain a correlation suitable for palaeotemperature reconstructions the best fit is obtained using surface 0 m temperatures corresponding to caloric winter and autumn months however the annual average spring and summer surface temperature equations also have high correlation coefficients and are also appropriate for climatic studies the results further validate the general applicability of the u 37 k as a climatic proxy because the calibration equations are valid over a wide range of surface water temperatures 0 28 c for different algal populations and are representative of the average contribution of alkenones to sediments as found in sediment cores

global assessment of benthic nepheloid layers and linkage with upper ocean dynamics abstract global maps of the maximum bottom concentration thickness and integrated particle mass in benthic nepheloid layers are published here to support collaborations to understand deep ocean sediment dynamics linkage with upper ocean dynamics and assessing the potential for scavenging of adsorption prone elements near the deep ocean seafloor mapping the intensity of benthic particle concentrations from natural oceanic processes also provides a baseline that will aid in quantifying the industrial impact of current and future deep sea mining benthic nepheloid layers have been mapped using 6 392 full depth profiles made during 64 cruises using our transmissometers mounted on ctds in multiple national international programs including woce save jgofs clivar repeat hydrography and go ship during the last four decades intense benthic nepheloid layers are found in areas where eddy kinetic energy in overlying waters mean kinetic energy 50 m above bottom mab and energy dissipation in the bottom boundary layer are near the highest values in the ocean areas of intense benthic nepheloid layers include the western north atlantic argentine basin in the south atlantic parts of the southern ocean and areas around south africa benthic nepheloid layers are weak or absent in most of the pacific indian and atlantic basins away from continental margins high surface eddy kinetic energy is associated with the kuroshio current east of japan data south of the kuroshio show weak nepheloid layers but no transmissometer data exist beneath the kuroshio a deficiency that should be remedied to increase understanding of eddy dynamics in un sampled and under sampled oceanic areas

diagnoses of an eddy resolving atlantic ocean model simulation in the vicinity of the gulf stream part ii eddy potential enstrophy and eddy potential vorticity fluxes abstract output of an eddy resolving model of the north atlantic is diagnosed in the vicinity of the gulf stream gs using quasigeostrophic potential vorticity qgpv quasigeostrophic potential enstrophy qgpe and modified divergent eddy potential vorticity flux v hq d a tongue or an elongated island of large mean qgpv along the model gs in the top 1000 m is associated with predominantly downgradient v hq d suggesting that the horizontal eddy fluxes are balancing a sink of eddy qgpe in most of the tongue or island by converting the mean qgpe into eddy qgpe some large upgradient v hq d is observed to the north of the center of the tongue or island however suggesting that some of the eddy fluxes in the northern half of the tongue or island of high qgpv are balancing a source of eddy qgpe there by converting eddy qgpe into the mean qgpe at the intermediate levels of the model under the gs eddy qgpe is small and the role of eddies appears to be mixed they are forcing the mean to some

determining geostrophic velocity shear profiles with inverted echo sounders it is known that vertical acoustic travel time round trip from the seafloor to the sea surface as measured by inverted echo sounders iess can be interpreted in terms of dynamic height this relationship is generalized and quantified in this paper for dynamic height di j integrated between a variety of pressure limits pi pj which span different portions of the main thermocline the generalized form of the di j relationships is nonlinear the conventional linear relationship is valid when the limits of integration span the entire main thermocline velocity and temperature records are shown to be highly correlated vertically indicating that the variability of the gulf stream and adjacent eddy field is dominated by the lowest baroclinic mode which is called a gravest empirical mode gem a parallel isotherms model is used to approximate the gem and to develop analytic expressions for the observed di j relationships in the gulf stream the analytic expressions represent the observations well with noise to signal variance ratios that are typically 1 using these new di j relationships the baroclinic velocity structure can be determined geostrophically by measuring the horizontal gradients with laterally separated measurements from iess baroclinic velocities determined from a two dimensional array of iess in the gulf stream during 1988 1990 agree with velocity shears directly measured by current meters the rms velocity difference between these two measurements of velocity shear at 400 dbar relative to 1000 dbar was 12 cm s 1 in the presence of typical currents of 50 cm s 1 ageostrophic motions at both mesoscale and submesoscale measured by the current meters but not by the iess contribute most of the velocity differences

molecular stratigraphy of cores off northwest africa sea surface temperature history over the last 80 ka the molecular stratigraphy of biogeochemical oceanic flux study core 31k 19 n 20 10 w and ocean drilling program hole 658c 20 45 n 18 35 w has been studied for c37 alkenone abundances over the past 80 ka at high resolution circa 200 500 years the derived uk37 sea surface temperature record for both cores shows a range of temperatures from about 18 c during the last glacial to 21 5 c during the early holocene both records also reveal changes in sea surface temperature as much as 2 4 c over a few hundred years which correlate well with similar abrupt climatic changes observed in cores from elsewhere in the ne atlantic associated with heinrich events our results indicate that meltwater produced by these ice rafting events was transmitted southward by the canary current where it had considerable impact on sea surface temperatures in the subtropical eastern atlantic

spatial and temporal evolution of a gulf stream crest warm core ring interaction an intensive near synoptic hydrographic study of the reabsorption of a warm core ring into the gulf stream at a meander crest was conducted near 70 w in fall 1988 using a mixture of measurement techniques and statistical optimal interpolation to map the velocity and density fields the study documents how the normally robust cross stream structure of the gulf stream breaks down and the process by which a high pressure ridge between the stream and the ring develops examination of the layer potential vorticity lpv structure on two specific volume anomaly surfaces approximately 18 c and 10 c showed different characteristics of cross stream lpv structure on the shallower surface the cross stream lpv structure was dominated by the cross stream gradient of layer thickness on the deeper surface the much weaker cross stream lpv structure reflected the structure of the relative vorticity field during the 10 day period of ringstream contact considerable water was exchanged rupturing the ring and eventually resulting in the ring s reentrainment by the gulf stream time varying transports as large as 30 sv were exchanged to the north and south between the surface and 5 c the gulf stream bifurcates in such a way that the anticyclonic southern side continues through the meander crest uninterrupted while the cyclonic side is diverted to the north to replace the low potential vorticity waters of the ring with waters of high potential vorticity contact between the ring and the stream is established first at the surface and progresses downward with increasing time the decreased time needed to remove the ring s vorticity in the lower layers is consistent with the geometrical picture of the gulf stream colliding with a bowl shaped ring the flushing time for the lens of 18 c water in the ring is on the order of 5 days slightly longer than the 2 3 days for the relative vorticity of the 10 c surface

complexity of holocene climate as reconstructed from a greenland ice core glaciochemical time series developed from summit greenland indicate that the chemical composition of the atmosphere was dynamic during the holocene epoch concentrations of sea salt and terrestrial dusts increased in summit snow during the periods 0 to 600 2400 to 3100 5000 to 6100 7800 to 8800 and more than 11 300 years ago the most recent increase and also the most abrupt coincides with the little ice age these changes imply that either the north polar vortex expanded or the meridional air flow intensified during these periods and that temperatures in the mid to high northern latitudes were potentially the coldest since the younger dryas event

eddy mean flow interactions in the along stream development of a western boundary current jet an idealized model study a theoretical study on the role of eddy mean flow interactions in the time mean dynamics of a zonally evolving unstable strongly inertial jet in a configuration and parameter regime that is relevant to oceanic western boundary current wbc jets is described progress is made by diagnosing the eddy effect on the time mean circulation examining the mechanism that permits the eddies to drive the time mean recirculation gyres and exploring the dependence of the eddy effect on system parameters it is found that the nature of the eddy mean flow interactions in this idealized configuration is critically dependent on along stream position in particular relative to the along stream evolving stability properties of the time mean jet just after separation from the western boundary eddies act to stabilize the jet through downgradient fluxes of potential vorticity pv downstream of where the time mean jet has through the effect of the eddies been stabilized eddies act to drive the time mean recirculations through the mechanism of an upgradient pv flux this upgradient flux is permitted by an eddy enstrophy convergence downstream of jet stabilization which results from the generation of eddies in the upstream region where the jet is unstable the advection of that eddy activity along stream by the jet and the dissipation of the eddies in the region downstream of jet stabilization it is in this region of eddy decay that eddies drive the time mean recirculations through the mechanism of nonlinear eddy rectification resulting from the radiation of waves from a localized region it is found that similar mechanisms operate in both barotropic and baroclinic configurations although differences in the background pv gradient on which the eddies act implies that the recirculation driving mechanism is more effective in the baroclinic case this study highlights the important roles that eddies play in the idealized wbc jet dynamics considered here of stabilizing the jet and driving the flanking recirculations in the absence of eddy terms the magnitude of the upper ocean jet transport would be significantly less and the abyssal ocean recirculations and their significant enhancement to the jet transport would be missing altogether

temperature and velocity structure of the gulf stream northeast of cape hatteras modes of variability thirty five expendable bathythermograph sections and 10 pegasus velocity sections taken approximately normal to the gulf stream northeast of cape hatteras were used to examine the variability of the current s structure the regridded profiles were superimposed in a stream coordinate system such that the temperature variance associated with the superposition was minimized the resulting variance field was examined using empirical orthogonal functions the temperature variability is heavily weighted by seasonal warming hence the following results exclude temperatures from the upper 200 m the first mode 48 of the variance is due to a deepening of the thermocline relative to the mean on the offshore side of the gulf stream and a shoaling on the inshore edge associated with a change of geostrophic velocity and baroclinic transport the amplitudes of this transport mode indicate a slight downstream increase in baroclinic transport 2 per 100 km and a seasonal modulation 5 sverdrups rms that peaks in may june the second temperature mode below 200 m 13 21 of the variance is associated with a change in horizontal shear a vorticity mode and is positively correlated with measured path curvature and layer thickness the directly observed pegasus velocity sections were combined with corresponding temperature sections to compute their joint empirical modes the dominant combined mode has a thermocline structure change as in the transport mode that is coupled with an increase in alongstream velocity and for levels above the main thermocline an inflow from both sides toward the center both temperature and velocity data indicate that high transport in the gulf stream is associated with lateral displacement offshore of its mean position

tropical pacific climate at the mid holocene and the last glacial maximum simulated by a coupled ocean atmosphere general circulation model 1 simulations for the mid holocene 6000 years before present 6 ka and the last glacial maximum lgm 21 ka have been performed by a global ocean atmosphere coupled general circulation model gcm after the initial spin up periods both runs were integrated for about 200 years for 6 ka the model shows an enhanced seasonal variation in surface temperature and a northward shift of the african and the indian summer monsoon rain area overall circulation features in the tropics correspond to a strong walker circulation state with negative sea surface temperature sst and precipitation anomalies in the central pacific and positive precipitation anomalies over the indian and australian monsoon regions it is noted that there is about a 0 35 c cooling of the global mean sst in contrast to the 6 ka result the simulated tropical climate anomaly at 21 ka corresponds to a weak walker circulation state the simulated lgm sst decrease is about 2 c over the tropical western pacific it is larger about 5 c over the caribbean sea this sst anomaly is in broad agreement with the observed proxy data interestingly the model simulates a warmer than present sst over the subtropical pacific this may be related to a weaker subtropical anticyclone due to weakened monsoon circulation at the lgm

observations on the variability of the gulf stream path between 74 w and 70 w abstract the gulf stream path varies in a wavelike fashion in the deep water downstream of cape hatteras energetic within a range of wavelengths from 150 km to over 1000 km and periods from 4 d to over 500 d the authors determined the path from the 12 c isotherm at 400 m depth which was obtained daily for 740 days april 1983 may 1985 from objective analysis maps of the thermocline topography measured by inverted echo sounders iess the iess were deployed in a region 400 km long from 74 to 70 w to find propagating and standing mode characteristics of this large array of data frequency domain empirical orthogonal functions and wavenumber frequency spectra were calculated using fft in time combined with autoregressive ar modeling in space this study reveals smooth transitions from i downstream propagating and growing short period meander modes to ii standing modes at intermediate period to iii upstream propagating long period modes for periods shorter than semiannual meanders pro

near 5 day nonisostatic response of the atlantic ocean to atmospheric surface pressure deduced from sub surface and bottom pressure measurements 1 nonisostatic ocean responses to atmospheric pressure have been observed in tropical regions of the pacific and atlantic oceans at periods near 5 days barotropic ocean model simulations coupled to atmospheric forcing predicted that this nonisostatic ocean response is driven not regionally but globally by the rossby haurwitz wave to date little observational evidence has been provided to support the model simulations especially at extratropical latitudes here we present the basin scale nature of the nonisostatic response in the atlantic ocean near 5 day periods using four historical long term 1 5 year sub surface and bottom pressure measurements spanning from 16 s to 37 n joint analysis of them together with global gridded atmospheric pressure reveals a basin scale nonisostatic sea level fluctuation in the north and tropical atlantic oceans near 5 day periods with almost uniform phase it also confirms that the driving force for this near 5 day fluctuation is the westward propagating rossby haurwitz wave

gulf stream path and thermocline structure near 74 w and 68 w the synoptic ocean prediction synop experiment had the goal of providing a physical understanding of energetic mesoscale eddy processes in the gulf stream in the synop inlet array off cape hatteras and in the central array near 68 w modred observations were collected from october 1987 through august 1990 the inlet array measured the surface path and bottom currents where the gulf stream leaves the continental margin to enter the deep water regime small amplitude propagating and growing meanders characterized the variability there the central array measured velocity and temperature as a proxy for density at four levels in the water column as well as the upper and deep level streamfunctions all with mesoscale resolution near 70 w the path envelope exhibited a relative node confined within a 40 km band 55 of the time near 68 w the path envelope was over 3 times as wide due to several elongated steep meander troughs and relatively steep meander crests the crests typically propagated downstream without much growth the troughs often stalled near 68 w steepened and persisted for one to several months two cases evolved into s shaped paths and subsequently formed rings even the time averaged fields showed a small trough in the mean path and thermocline structure whereas meanders of 20 to 60 day periods had similar spectral levels throughout 70 67 w meanders with long periods 85 day accounted for the local minimum in variance at 70 w bottom pressure and velocity observations revealed repeated periods of intense swirl speeds 0 30 m s 1 abyssal eddies the time averaged deep currents exhibited a mean cyclone centered 30 km offshore and downstream of the upper layer mean trough the cross stream slope of the thermocline steepened linearly with path curvature consistent with gradient wind balance structures are illustrated in the mapped fields consistent with baroclinic instability wherein troughs steepen and rings form

bottom pressure torque and the vorticity balance from observations in drake passage the vorticity balance of the antarctic circumpolar current in drake passage is examined using 4 years of observations from current and pressure recording inverted echo sounders the time varying vorticity planetary and relative vorticity advection and bottom pressure torque are calculated in a two dimensional array in the eddy rich polar frontal zone pfz bottom pressure torque is also estimated at sites across drake passage mean and eddy nonlinear relative vorticity advection terms dominate over linear advection in the local 50 km scale vorticity budget in the pfz and are balanced to first order by the divergence of horizontal velocity most of this divergence comes from the ageostrophic gradient flow which also provides a second order adjustment to the geostrophic relative vorticity advection bottom pressure torque is approximately one third the size of the local depth integrated divergence although the cdrake velocity fields exhibit significant turning with depth throughout drake passage even in the mean surface vorticity advection provides a reasonable representation of the depth integrated vorticity balance observed near bottom currents are strongly topographically steered and bottom pressure torques grow large where strong near bottom flows cross steep topography at small angles upslope flow over the northern continental slope dominates the bottom pressure torque in cdrake and the mean across this drake passage transect 3 to 4 10 9 m s 2 exceeds the mean wind stress curl by a factor of 15 20

divergent eddy heat fluxes in the kuroshio extension at 144 148 e part ii spatiotemporal variability the kuroshio extension system study kess provided 16 months of observations to quantify divergent eddy heat flux dehf from a mesoscale resolving array of current and pressure equipped inverted echo sounders kess observations captured a regime shift from a stable to unstable state there is a distinct difference in the spatial structure of dehfs between the two regimes the stable regime had weak downgradient dehfs the unstable regime exhibited asymmetry along the mean path with strong downgradient dehfs upstream of a mean trough at 1478e the spatial structure of dehfs resulted from episodic mesoscale processes the first 6 months were during the stable regime in which fluxes were associated with eastward propagating 10 15 day upper meanders after 6 months the kuroshio extension underwent a regime shift from a stable to unstable state this regime shift corresponded with a red shift in mesoscale phenomena with the prevalence of 40 day deep externally generated eddies dehf amplitudes more than quadrupled during the unstable regime cold core ring ccr formation ccr jet interaction and coupling between 40 day deep eddies were responsible for asymmetry in downgradient fluxes in the mean maps not observed during the stable regime the kuroshio extension has prominent deep energy associated with externally generated eddies that interact with the jet to drive some of the biggest dehf events these eddies play an important role in the variability of the jet through eddy mean flow interactions the dehfs that result from vertical coupling act in accordance with baroclinic instability the interaction is not growth from an infinitesimal perturbation but from the start is a finite amplitude interaction

millennial scale storminess variability in the northeastern united states during the holocene epoch for the purpose of detecting the effects of human activities on climate change it is important to document natural change in past climate1 in this context it has proved particularly difficult to study the variability in the occurrence of extreme climate events such as storms with exceptional rainfall1 previous investigations have established storm chronologies using sediment cores from single lakes2 3 4 5 6 7 8 but such studies can be susceptible to local environmental bias here we date terrigenous inwash layers in cores from 13 lakes which show that the frequency of storm related floods in the northeastern united states has varied in regular cycles during the past 13 000 years 13 kyr with a characteristic period of about 3 kyr our data show four peaks in storminess during the past 14 kyr approximately 2 6 5 8 9 1 and 11 9 kyr ago this pattern is consistent with long term changes in the average sign of the arctic oscillation9 suggesting that modulation of this dominant atmospheric mode may account for a significant fraction of holocene climate variability in north america and europe

hydrological impact of heinrich events in the subtropical northeast atlantic reconstructing the impact of heinrich events outside the main belt of ice rafting is crucial to understanding the underlying causes of these abrupt climatic events a high resolution study of a marine sediment core from the iberian margin demonstrates that this midlatitude area was strongly affected both by cooling and advection of low salinity arctic water masses during the last three heinrich events these paleoclimatic time series reveal the internal complexity of each of the last three heinrich events and illustrate the value of parallel studies of the organic and inorganic fractions of the sediments

monitoring gulf stream transport by radar altimeter and inverted echo sounders abstract profiles of the gulf stream sea surface height ssh from the geosat altimeter were compared with thermocline depth measurements from inverted echo sounders ies for a period of about 19 months the correlation between ssh anomalies and thermocline depth anomalies at about 68 w was 0 92 to distinguish between agreement in the location of the gulf stream jet and agreement in the strength of the jet separate comparisons were made for jet location and the ssh difference across the gulf stream based on an error function fit to each geosat and ies profile the correlation between the jet centers from the two types of measurements was 0 97 and the correlation between the amplitudes of the error functions was 0 76 although the altimeter measures surface geostrophic velocity the high degree of vertical correlation in the gulf stream velocity profiles allows the altimeter to monitor transport fluctuations as well as changes in jet position based on this assessment of the accuracy of the altimeter

synchronous tropical south china sea sst change and greenland warming during deglaciation the tropical ocean plays a major role in global climate it is therefore crucial to establish the precise phase between tropical and high latitude climate variability during past abrupt climate events in order to gain insight into the mechanisms of global climate change here we present alkenone sea surface temperature sst records from the tropical south china sea that show an abrupt temperature increase of at least 1 c at the end of the last glacial period within the recognized dating uncertainties this sst increase is synchronous with the bolling warming observed at 14 6 thousand years ago in the greenland ice sheet project 2 ice core

modulation of gulf stream surface subsurface frontal separation by path curvature abstract observations of surface subsurface frontal separation have inconsistently demonstrated a relationship between surface subsurface frontal separation and subsurface front path curvature an analytical model of surface subsurface frontal shows that this separation is modulated by curvature of the path of the subsurface front and that the strength of this modulation is approximately proportional to the surface subsurface frontal separation a comparison of the theory with observations shows agreement

synoptic maps of temperature and velocity within the subantarctic front south of australia 1 from april 1995 to march 1997 a 450 km array of inverted echo sounders horizontal electric field recorders and current meters measured the horizontal and vertical structure of the current temperature and salinity fields associated with the subantarctic front saf south of australia synoptic maps of the temperature and velocity fields often show the saf divided into two zonally separated jets which are also found in the mean these jets were in close proximity yet directed toward different azimuths the daily maps also show that the saf often flowed as a single strong jet during which times it underwent vigorous meandering with crest to trough meridional distances 250 km these meanders stalled within the array and contorted to form s shaped paths in one case a cold core ring was formed propagating meanders have periods of 20 70 days wavelengths of 240 420 km and phase speeds of 12 6 km d 1 deep currents reveal strong cyclones and anticyclones propagating primarily eastward through the array beneath the meandering jet thus at times the deep flow is aligned with the upper flow whereas at other times significant barotropic flows cross the upper front occasionally the northern polar front was also found within the array the observed variability illustrates how the interaction of a meandering current with transient features such as meanders and eddies makes the identification of a front difficult when a single isotherm or isopycnal is utilized as the definition

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

holocene climate variability as derived from alkenone sea surface temperature and coupled ocean atmosphere model experiments holocene climate modes are identified by the statistical analysis of reconstructed sea surface temperatures ssts from the tropical and north atlantic regions the leading mode of holocene sst variability in the tropical region indicates a rapid warming from the early to mid holocene followed by a relatively weak warming during the late holocene the dominant mode of the north atlantic region sst captures the transition from relatively warm cold conditions in the eastern north atlantic and the western mediterranean sea the northern red sea to relatively cold warm conditions in these regions from the early to late holocene this pattern of holocene sst variability resembles the signature of the arctic oscillation north atlantic oscillation ao nao the second mode of both tropical and north atlantic regions captures a warming towards the mid holocene and a subsequent cooling the dominant modes of holocene sst variability emphasize enhanced variability around 2300 and 1000 years the leading mode of the coupled tropical north atlantic holocene sst variability shows that an increase of tropical sst is accompanied by a decrease of sst in the eastern north atlantic an analogy with the instrumental period as well as the analysis of a long term integration of a coupled ocean atmosphere general circulation model suggest that the ao nao is one dominant mode of climate variability at millennial time scales

cyclogenesis in the deep ocean beneath western boundary currents a process oriented numerical study 1 a two layer shallow water equation model is applied to a flat bottom ocean on the f plane to explore instability mechanisms in western boundary current wbc that lead to the formation of strong cyclones in the deep ocean underneath findings reveal a tight coupling of surface meandering and deep cyclogenesis in agreement with observational evidence barotropic cyclones develop in timescales of 5 10 days and attain swirl speeds of 50 cm s depends on initial strength of wbc on a diameter of 100 km cyclogenesis is driven by advection of relative vorticity in the surface ocean and failure of the thermocline to respond rapidly enough to the associated sea level variations findings suggest that cyclogenesis and the associated strong abyssal flows benthic storms are ubiquitous features of wbcs and other frontal flows

jet streaks in the gulf stream mesoscale alongstream speed changes of the gulf stream are diagnosed from an array of current meters at depths 400 700 and 1000 m near 688w during the development of steep ratio of amplitude to wavelength o 1 meanders speed maxima jet streaks are generally found between trough and crest axes in steep meanders with local speed minima near the trough and crest axes speed changes along streamlines can be quite dramatic speed changes along the jet axis between jet streaks and local minima in excess of 0 60 0 40 and 0 35 m s 21 are observed at depth 400 700 and 1000 m respectively this is in comparison with peak speeds in a frontal coordinates system mean of 1 22 0 67 and 0 28 m s21 at depth 400 700 and 1000 m respectively from a previous study the presence of the jet streaks can be explained kinematically as a superposition of the gulf stream and barotropic vortices the development of these jet streaks in relation to the developing steep meanders differs from the canonical picture of jet streak baroclinic wave development in the atmospheric jet stream in that the jet streaks in the gulf stream are predominantly fixed in place with respect to meanders as they steepen

gulf stream structure transport and recirculation near 68 w an analysis of the structure and transport of the gulf stream is undertaken using direct current meter observations from a 13 mooring array deployed near 68 w from june 1988 to august 1990 the analysis is based on a stream coordinate approach in which velocities are rotated into a local downstream coordinate frame and averaged according to their relative cross stream location within the current the picture so obtained represents the average synoptic structure of the gulf stream rather than the eulerian averaged structure in which the current is weakened and broadened by lateral meandering of the current and adjacent recirculations many familiar features of the gulf stream are reproduced in the analysis including an asymmetric velocity profile with larger shear on the cyclonic shoreward side of the current an offshore displacement of the velocity core with depth and a subsurface velocity maximum on the offshore side of the current westward recirculations are also seen on both sides of the gulf stream maximum downstream speeds at the axis of the gulf stream reach approximately 2 0 m s at the surface and 0 7 m s at 1000 m roughly twice the corresponding eulerian averaged values the analysis also reveals a deep extension of the gulf stream at 3500 m depth with a width of 130 km and average speeds of 3 4 cm s the transport of the gulf stream in the stream coordinate frame is 113 8 sv approximately 30 larger than the eulerian averaged transport of 88 sv on the basis of these results and other recent studies the downstream transport increase of the gulf stream and the inflow structure to the gulf stream are reconsidered it is concluded that approximately 30 sv or over half of the transport increase between cape hatteras and 68 w is fed by inflow from the northern side of the gulf stream and that this inflow is concentrated near cape hatteras and 68 w where the gulf stream flows steeply across isobaths converging from the north