the zonal currents and transports at 35 w in the tropical atlantic the total of 13 existing cross equatorial shipboard current profiling sections taken during the woce period between 1990 and 2002 along 35 w are used to determine the mean meridional structure of the zonal top to bottom circulation between the brazilian coast near 5 s and 5 n and to estimate mean transports of the individual identified shallow intermediate and deep current branches one of the results is that on the equator a mean westward equatorial intermediate current below the equatorial undercurrent exists

high resolution p cable 3d seismic imaging of gas chimney structures in gas hydrated sediments of an arctic sediment drift the newly developed p cable 3d seismic system allows for high resolution seismic imaging to characterize upper geosphere geological features focusing on geofluid expressions gas chimneys shallow gas and gas hydrate reservoirs seismic imaging of a geofluid system of an arctic sediment drift at the vestnesa ridge offshore western svalbard provides significantly improved details of internal chimney structures from the seafloor to not vert similar500 m bsf below seafloor the chimneys connect to pockmarks at the seafloor and indicate focused fluid flow through gas hydrated sediments the pockmarks are not buried and align at the ridge crest pointing to recent topography controlled fluid discharge chimneys are fuelled by sources beneath the base of gas hydrate stability zone ghsz that is evident at not vert similar160 170 m bsf as indicated by a bottom simulating reflector bsr conduit centres that are not vertically straight but shift laterally by up to 200 m as well as discontinuous internal chimney reflections indicate heterogeneous hydraulic fracturing of the sediments episodically active pressure driven focused fluid flow could explain the hydro fracturing processes that control the plumbing system and lead to extensive pockmark formation at crest of the vestnesa ridge high amplitude anomalies in the upper 50 m of the chimney structures suggest formations of near surface gas hydrates and or authigenic carbonate precipitation acoustic anomalies expressed as high amplitudes and amplitude blanking are irregularly distributed throughout the deeper parts of the chimneys and provide evidence for the variability of hydrate and or carbonate formation in space and time

gravitational symmetric and baroclinic instability of the ocean mixed layer abstract a hierarchy of hydrodynamical instabilities controlling the transfer of buoyancy through the oceanic mixed layer is reviewed if a resting ocean of horizontally uniform stratification is subject to spatially uniform buoyancy loss at the sea surface then gravitational instability ensues in which buoyancy is drawn from depth by upright convection but if spatial inhomogeneities in the ambient stratification or the forcing are present as always exist in nature then horizontal density gradients will be induced and within a rotation period horizontal currents in thermal wind balance with those gradients will be set up within the mixed layer there are two important consequences on the convective process upright convection will become modified by the presence of the thermal wind shear fluid parcels are exchanged not along vertical paths but rather along slanting paths in symmetric instability theoretical considerations suggest that this slantwise convection sets the potential vorticity of th

oxygen tongues and zonal currents in the equatorial atlantic 1 equatorial zonal currents and associated oxygen distributions are studied using shipboard hydrographic data trajectories from isopycnic floats drifting at about 300 m depth and velocity time series from the upper 1100 m obtained at two equatorial moorings located at 35 w and 23 w mean profiles of zonal velocity measured by moored acoustic doppler current profilers yielded a westward flowing equatorial intermediate current eic below the equatorial undercurrent euc at both locations the eic consists of two westward current cores at about 250 and 450 m the upper core of the eic deepens by about 30 m from 23 w where it has a mean velocity of 6 2 cm s 1 to 35 w where the mean is 5 3 cm s 1 the lower core of the eic is about twice as strong with 12 1 cm s 1 at 23 w and 9 2 cm s 1 at 35 w the flow below the euc is characterized by substantial interannual variability from may to december 2005 a strong zonally coherent eastward jet occurred at 300 to 350 m depth found to be an expression of shallow stacked jets superimposed on the mean eic shipboard hydrographic observations in june july 2006 revealed the existence of a high oxygen tongue that can be traced from 35 w to 10 w in the depth range of the eastward jet prevailing during the preceding year on the basis of an advection diffusion balance it is suggested that the oxygen decrease from 35 w to 10 w within the oxygen tongue is mainly balanced by lateral eddy diffusivity and oxygen consumption with diapycnal turbulent diffusivity playing only a minor role

surface microseismic in an extreme environment a surface microseismic survey was conducted in a noisy suburban active oil field environment unconventional patch acquisition survey design and careful processing allowed the extraction of more than 8000 events from the noisy data patch acquisition and multichannel noise attenuation were critical components of the success of the project the computation of microseismic source mechanisms from the surface depended on solving for accurate velocities and statics in the preprocessing stage

the source scanning algorithm mapping the distribution of seismic sources in time and space summary we introduce a new method which we call the source scanning algorithm ssa for imaging the distribution of seismic sources in both time and space using trial locations and origin times the method calculates the brightness function by summing the absolute amplitudes observed at all stations at their respective predicted arrival times the spatial and temporal distribution of sources is then identified by a systematic search throughout the model space and time for the maximum brightness the greatest advantages of this method are that 1 it exploits waveform information both arrival times and relative amplitudes without the need to calculate highfrequency synthetic seismograms and 2 it requires neither pre assembled phase picking data nor any a priori assumptions about the source geometry a series of tests using synthetic data have shown that this method is robust and can faithfully recover the input source configuration to within 1 grid interval finally we demonstrate the value of the algorithm by locating a typical tremor event with emergent waveforms that occurred during the recent episodic tremor and slip ets sequence in the northern cascadia subduction zone

evidence for the maintenance of slowly varying equatorial currents by intraseasonal variability recent evidence from mooring data in the equatorial atlantic reveals that semi annual and longer time scale ocean current variability is close to being resonant with equatorial basin modes here we show that intraseasonal variability with time scales of 10 s of days provides the energy to maintain these resonant basin modes against dissipation the mechanism is analogous to that by which storm systems in the atmosphere act to maintain the atmospheric jet stream we demonstrate the mechanism using an idealised model set up that exhibits equatorial deep jets the results are supported by direct analysis of available mooring data from the equatorial atlantic ocean covering a depth range of several thousand meters the analysis of the mooring data suggests that the same mechanism also helps maintain the seasonal variability

submarine glacigenic debris flows deep sea channels and past ice stream behaviour of the east greenland continental margin abstract former glacigenic debris flow gdf and deep sea channel build up is shown from side scan sonar seismic and sediment core data of the passive continental margin of the greenland sea the well developed deep sea channel systems cross gdf systems and point towards sediment laden meltwater production there is no indication for large scale submarine sliding such as observed on several locations on the norwegian margin where deep sea channels are far less frequent or do not exist whereas seabed erosion gdf stacking and trough mouth fans dominate the observed pattern on the east greenland margin reflects a contrast to the norwegian margin in paleo ice stream extent dynamics and type of sediment delivery a conceptual model for ice sheet behaviour on the continental margin of the greenland sea has been developed based on the characteristics distribution and morphology of gdfs and deep sea channels in four periods at ca 2 5 ma 1 5 ma 0 2 ma and 25 ka we argue that the erosional capabilities of ice streams on the ne greenland margin indicated by aggradation versus progradation were less then those of the fast flowing ice streams of the norwegian margin and that the ice streams in cross shelf troughs remained probably distal from the shelf break during the late weichselian

structure of the atlantic ocean equatorial deep jets the equatorial deep jets in the atlantic ocean are described using vertical strain jz estimated from all available deep ctd stations in the region wavelet analysis reveals a distinct energy peak around 661 sdbar vertical wavelength 1232 dbar pressure and 61 58 latitude from the equator this high vertical wavenumber and off equatorial maximum coupled with previously published velocity data that show nodes in zonal velocity near 61 58 is grossly consistent with the structure of first meridional mode equatorial rossby waves however the meridional scale obtained from the observations exceeds by about 1 5 the theoretical meridional scale for these waves the jets are strong with zonal velocities similar in magnitude to the kelvin wave phase speed for their vertical wavelength harmonics of jz at vertical wavelengths of 1 2 1 4 and perhaps 1 8 that of the primary peak provide evidence of a large amplitude structure although sparse available phase data at the 661 sdbar vertical wavelength suggest downward and westward phase propagation assuming sinusoidal character in time and longitude gives estimates of a 5 61 yr period and a 708 6608 zonal wavelength these vertical temporal and zonal scales are roughly consistent with first meridional mode equatorial rossby wave dynamics however although vertical and zonal phase propagation are discernible there is no obvious signature of upward energy propagation in the variance vertical maxima which is problematic for a simple linear rossby wave interpretation

deep velocity measurements in the western equatorial indian ocean abstract vertical profiles of horizontal current collected in april and june 1979 in the western indian ocean revealed the presence of short vertical scale 150 300 m deep zonal jets trapped to within 1 of the equator meridional velocity records displayed in general higher temporal and spatial variability and significantly less energy at the larger vertical scales as compared with zonal records vertical wavenumber spectra of velocity showed no statistically significant peaks the conspicuous alternating zonal jets were identified with the slightly more energetic as compared to background levels 500 429 stretched meter sm wavelengths for most vertical wavenumbers zonal currents were not significantly coherent at distances greater than 400 km downstream at shorter zonal separations phase lags were indistinguishable from zero on the equator there is an indication of upward shift of approximately 100 sm over the 500 429 sm band also on the equator zonal current u and vertical displacement

equatorial deep jets and abyssal mixing in the indian ocean abstract vertical profiles of horizontal currents and hydrographic measurements from three cruises along 80 5 e from the coast of sri lanka to 6 s between december 1990 and september 1994 are used to investigate the scales of the indian ocean deep jets as well as internal wave parameters and dissipation at the equator the deep jets at 80 5 e have a vertical wavelength of 660 sm stretched meters and amplitudes exceeding 10 cm s 1 in zonal velocity they are observed throughout the water column and their flow direction reverses at 2 off the equator the vertical positions of the jets differ among the cruises and are consistent with a flow reversal between the data collected in winter and summer during september 1994 the jets were less pronounced due to the meridional distribution of their zonal velocity and the phase relationship between zonal velocity and vertical displacement the jets are best described as nondispersive first mode equatorial rossby waves the hydrographic data revealed thick layer

the sklinnadjupet slide and its relation to the elsterian glaciation on the mid norwegian margin abstract the sklinnadjupet slide scar is a large buried feature on the continental slope southeast of the voring plateau the mass flow occurred ca 250 000 years ago on a slope angle of ca 0 5 and removed glacial debris from the up to 350 m thick naust s sequence on the upper slope this part of the mid norwegian margin appears to have been fairly stable throughout the last 2 8 million years naust s represents the third last glacial unit in the skjoldryggen region and was deposited during the elsterian ca 400 200 ka bp during this glaciation a wide depression was formed on the continental shelf between haltenbanken and traenabanken with the strongest glacial erosion in the west trending sklinnadjupet palaeo trough this trough leads directly towards the deep 90 km wide slide scar indicating that a local depocentre was formed here before the mass flow occurred the shallowest crest of the helland hansen arch is located below the southern part of the slide scar and two large craters were formed on the surface of this anticlinal structure our model suggests that the deposition of glacial sediments above the helland hansen arch caused high excess pore pressures along the shallowest crest of this structure and formed a high pore pressure gradient towards the sea floor on its western flank an earthquake possibly triggered the initial slide where the slope was steepest west of the crest most of the slide scar was already formed when the slide finally eroded into the anticline high excess fluid pressure subsequently mobilised the diatomaceous oozes in the helland hansen arch and formed the craters much of this material flowed down slope without being totally disintegrated and was deposited as levee ridges and mounds above slide deposits from the first phase of the mass flow they have previously been wrongly interpreted as diapirs

late quaternary contourites and glaciomarine sedimentation in the fram strait two sites in the eastern fram strait the vestnesa ridge and the yermak plateau have been surveyed and sampled providing a depositional record over the last glacial interglacial cycle the fram strait is the only deep water connection from the arctic ocean to the north atlantic and contains a marine sediment record of both high latitude thermohaline flow and ice sheet interaction on the vestnesa ridge the western svalbard margin a sediment drift was identified in 1226 m of water gravity and multicores from the crest of the drift recovered turbidites and contourites 14c dating indicates an age range of 8287 to 26 900 years bp early holocene to late weichselian the yermak plateau is characterized by slope sediments in 961 m of water gravity and multicores recovered contourites and hemipelagites 14c ages were between 8615 and 46 437 years bp early holocene to mid weichselian downcore dinoflagellate cyst analyses from both sites provide a record of changing surface water conditions since the mid weichselian suggesting variable sea ice extent productivity and polynyas present even during the last glacial maximum four layers of ice rafted debris were also identified and correlated within the cores these events occurred ca at 9 24 to 25 26 to 27 and 43 ka asynchronous with heinrich layers in the wider north east atlantic and here interpreted as reflecting instability in the svalbard barents ice sheet and the northward advection of warm atlantic water during the late weichselian the activity of the ancestral west spitsbergen current is interpreted using mean sortable silt records from the cores on the vestnesa ridge drift the modern mass accumulation rate calculated using excess 210pb is 0 076 g cm 2 year 1 on the yermak plateau slope the modern mass accumulation rate is 0 053 g cm 2 year 1

impact of the equatorial deep jets on estimates of zonal transports in the atlantic the structure and variability of the zonal equatorial flow in the atlantic is studied on the basis of velocity profiles obtained with lowered acoustic doppler current profilers during multiple surveys the vertical extent of the zonal currents is found to vary considerably it can be as small as 100 m or as large as 1000 m in the atlantic vertical scales of 400 600 m have been associated with the equatorial deep jets they are also frequently called deep jets or stacked jets typical amplitudes of the zonal velocity are about 20 cm s 1 an analysis of quasi synoptic surveys indicates that the zonal extent of most jets is likely to be at least 27d they can rise or deepen from west to east although the deepening was observed more often and is often more pronounced the west to east deepening can be as large as 320 m 10d basin wide mean depth changes of the jets are mostly on the order of 50 m 10d and the largest depth changes are typically observed between 35d and 23d w the existence of these changes indicates that vertically propagating equatorially trapped waves might be one cause for the jet structure however the dependence of the slope on the longitude indicates that other processes must be involved as well the typical vertical extent of the jets is small enough to result in several direction changes of the zonal flow in the antarctic intermediate water aaiw and the north atlantic deep water nadw layer from transport estimates for 14 meridional sections it is found that the transport for the westward component of the flow within the aaiw layer 500 1000 m can be as large as 24 sv 1 sv 10 6 m s 1 within 1d of the equator for the eastward component of the flow in the aaiw layer the transport can be as large as 8 sv adding the transport components for each section results in a range of total aaiw transports from 24 to 7 sv this suggest that the annual mean transport of aaiw is westward the only months with eastward total transports are june and july this is consistent with earlier lagrangian and some other observations that indicated that the aaiw flow along the equator is governed by an annual cycle in the nadw layer 1200 3900 m the transport for the westward eastward flow can be as large as 25 sv 23 sv within 1d of the equator this results in a range of total nadw transports from 10 to 18 sv the variations of the total transports of aaiw and nadw are anti correlated with a correlation coefficient of 0 86 since only eight sections reached deep enough to allow transport estimates in the nadw layer it is more difficult to come to a conclusion about the mean transport in this layer than for the transport in the aaiw layer for the latter layer 14 sections were available nevertheless the obtained estimates suggest that the total nadw transport may be eastward

middepth equatorial tracer tongues in a model of the atlantic ocean 1 observational estimates of middepth tracer tongues in the equatorial atlantic are reviewed and are compared with results from several eddy resolving model simulations local maxima of chlorofluorocarbon cfc concentrations along the equator at around 1500 m depth are related to mean eastward jet structures in the models at similar depth ranges and can also be identified in several simulated tracer distributions similar to the observations strong eastward jets are located in the simulations 1 2 north and south of the equator the model simulations show in addition consistent with the cfc observations weaker jets at around 4 6 n s and 8 10 n s suggestive of a large scale alternating eastward westward current system in the western tropical atlantic in this depth range lagrangian transport estimates in the model using float diagnostics show a transport of 1 3 sv in each of the eastward jets 1 2 n s off the equator compared to 3 12 sv throughflow into the south atlantic with no seasonal cycle apparent in the transport fractioning comparing different model solutions reveals the choice of the subgrid scale mixing parameterization as important for the amplitudes of the jets enhanced reduced diapycnal mixing is related to stronger weaker jets

internal wave interactions with equatorial deep jets part ii acceleration of the jets abstract what drives the equatorial deep jets is a puzzle because of their isolation from surface forcing by the intervening main pycnocline and the equatorial undercurrent and from lateral boundaries by distances of tens of thousands of kilometers it would take decades for energy to propagate to the jets midbasin location from boundary sources their persistence points to some mechanism maintaining them in situ the authors hypothesize that the ambient internal wave field deposits momentum fluxes at critical layers within the deep jets and using calculated momentum and energy flux divergences as forcing estimate acceleration of the mean zonal flow in the deep jets internal wave momentum flux divergences are more than sufficient to sustain the jets acting to sharpen the shear between the jets on timescales of months to years predicted energy flux divergences produce turbulent dissipation rates compatible with those observed

interannual atmospheric variability forced by the deep equatorial atlantic ocean climate variability in the tropical atlantic ocean is determined by large scale ocean atmosphere interactions which particularly affect deep atmospheric convection over the ocean and surrounding continents1 apart from influences from the pacific el nino southern oscillation2 and the north atlantic oscillation3 the tropical atlantic variability is thought to be dominated by two distinct ocean atmosphere coupled modes of variability that are characterized by meridional4 5 and zonal6 7 sea surface temperature gradients and are mainly active on decadal and interannual timescales respectively8 9 here we report evidence that the intrinsic ocean dynamics of the deep equatorial atlantic can also affect sea surface temperature wind and rainfall in the tropical atlantic region and constitutes a 4 5 yr climate cycle specifically vertically alternating deep zonal jets of short vertical wavelength with a period of about 4 5 yr and amplitudes of more than 10 cm s 1 are observed in the deep atlantic to propagate their energy upwards towards the surface10 11 they are linked at the sea surface to equatorial zonal current anomalies and eastern atlantic temperature anomalies that have amplitudes of about 6 cm s 1 and 0 4 c respectively and are associated with distinct wind and rainfall patterns although deep jets are also observed in the pacific12 and indian13 oceans only the atlantic deep jets seem to oscillate on interannual timescales our knowledge of the persistence and regularity of these jets is limited by the availability of high quality data despite this caveat the oscillatory behaviour can still be used to improve predictions of sea surface temperature in the tropical atlantic deep jet generation and upward energy transmission through the equatorial undercurrent warrant further theoretical study

extended deep equatorial layering as a possible imprint of inertial instability the deep equatorial track of the world ocean is subject to intense zonal flow fields that still remain to be better understood inertial instability has been invoked to explain some of its features here we present possible in situ imprints of such a mechanism in the equatorial atlantic ocean below the thermocline we analyse the observed pattern of homogeneous density layers of 50 100 m vertical scale which are characterized by a large meridional coherency up to 2degrees of latitude a concentration in the vicinity of the equator and foremost a vertical localization within regions of well mixed angular momentum westward jets these distinctive properties suggest inertial instability to be a plausible mechanism for this extended layering numerical simulations forced by a time oscillating shear reproduce the observed density layering characteristics the prescription of deep jets in the background flow controls the vertical localization of the layering inside westward jets

atlantic equatorial deep jets space time structure and cross equatorial fluxes the so called equatorial stacked jets are analyzed with ship board observations and moored time series from the atlantic ocean the features are identified and isolated by comparing vertical wavenumber spectra at the equator with those a few degrees from the equator mode filtering gives clear views of the jets in meridional sections the typical extent being 618 in latitude the vertical structure can be well described explaining 82 of the variance by n21 stretched cosines with a gaussian amplitude tapering in the vertical the stretched wavelengths are somewhat variable fitting jets of a fixed stretched wavelength to four moored sensors in the depth range 1300 1900 m allows one to track the vertical phase of the jets with an rms error of 308 458 the resulting fit from a 20 month moored time series shows long periods of unchanging jet conditions and intermittent times of high variability there is no significant vertical propagation on these timescales nor a seasonal reversal using a composite from many different experiments interannual variability is visible however a possible mechanism for the stacked jets is inertial instability resulting from background meridional shears at the equator a condition is that the ertel potential vorticity becomes zero somewhere due to meridional asymmetries in the zonal flows the ship board observations show that this may be approximately fulfilled by the instantaneous zonal low mode flows at various depths resulting from an excess of zonal momentum south of the equator most of the time inertial instability should act to redistribute this zonal momentum and our mooring data show indeed persistent northward momentum flux but not at the depth levels expected the momentum transport might suggest that the jets can also flux or mix other properties across the equator

results from a velocity transect along the equator from 125 to 159 w abstract during march april 1980 a velocity and ctd transect was made in the pacific along the equator from 110 to 180 w the horizontal baroclinic pressure gradient was observed to be primary confined between 160 and 130 w direct velocity profiles between 125 and 159 w showed the equatorial undercurrent to be a continuous feature maximum eastward transport per unit width in the undercurrent was 2 5 108 cm2 s 1 at 150 w and decreased both westward and eastward to about 1 5 108 cm2 s 1 at 159 w and at 125 w despite these variations the maximum speeds along the transect remained 150 cm s 1 beneath the undercurrent the velocities decreased and were of the order of 25 cm s 1 they exhibited small scale variation in the vertical as has recently been observed at other equatorial locations above 1600 m the vertical wavelength of these variations in the zonal component was 300 m small scale features in these zonal velocities were identifiable over 10 of longitude 1000 km the small vertical an

the deep currents in the eastern equatorial atlantic ocean 1 in the atlantic ocean equatorial deep jets have been observed in the central and western equatorial basin here we present three meridional velocity sections carried out in boreal summer 2000 in the eastern equatorial atlantic at that time the deep equatorial jets were observed to weaken or to vanish in the gulf of guinea toward the african coast at 10 w the comparison with currents measured one year before in boreal summer 1999 along with tracer distributions confirm the existence of an eastward route along the equator of part of the north atlantic deep water

deciphering late cenozoic development of the western svalbard margin from odp site 986 results abstract the present work is based on sedimentological data from odp site 986 drilled off western svalbard the data include grain size distribution bulk mineralogy clay mineralogy total carbon total organic carbon and carbonate determinations from over 500 samples the results show interesting trends across the seismic sequence boundaries defined earlier and can be related to changes in climate and depositional styles the interpretation of these results together with the seismic observations and interpretations made earlier have shed new light on the timing of the onset of major glaciations and sedimentary processes on the svalbard margin during plio pleistocene the estimate for the timing of the first major glacial advance is revised to 1 6 ma from the earlier estimate of 2 3 ma barents sea was the likely source for the sediments in the 2 3 1 6 ma interval followed by svalbard as the main sediment source in the post 1 6 ma interval it is also suggested that in view of their morphology and proposed sedimentary processes the sedimentary wedges off svalbard barents sea margin are better described as slope aprons than in terms of glacial fans or trough mouth fans used earlier in the literature

late weichselian depositional processes fluxes and sediment volumes on the margins of the norwegian sea 62 75 n abstract quaternary continental margin sedimentation in the norwegian greenland sea has been a response to a combination of tectonic oceanographic and glacial activity using geophysical survey data 6 5 khz side scan sonar and 3 5 khz penetration echo sounding in association with bathymetric datasets the magnitude and frequency of the main forms of margin sedimentation into the lofoten and norwegian basins of the norwegian sea during the late weichselian and holocene are estimated by comparing these geophysically determined estimates of sediment fluxes with numerically modelled ice sheet sediment delivery the role of ice sheets in shaping the processes acting on this margin is assessed sediment flux at the shelf edge during the late quaternary is dominated by ice sheet delivery of sediments focused at the mouths of fast flowing ice streams formed in bathymetric troughs interglacials are by contrast characterised by comparatively little sediment accumulation submarine fans at the margins of cross shelf troughs are major depocentres on this glacier influenced margin however occasional large scale failures of the continental slope account for approximately 75 of the basin sediment accumulation during the past 30 000 yr by eroding substantial quantities of pre quaternary deposits trough mouth fan and a combination of hemipelagic and glacimarine processes are responsible for the accumulation of the remaining 15 and 7 of basin sediments respectively

on the width of the equatorial deep jets the equatorial deep jets edj are a striking feature of the equatorial ocean circulation in the atlantic ocean the edj are associated with a vertical scale of between 300 and 700 m a time scale of roughly 4 5 years and upward energy propagation to the surface it has been found that the meridional width of the edj is roughly 1 5 times larger than expected based on their vertical scale here we use a shallow water model for a high order baroclinic vertical normal mode to argue that mixing of momentum along isopycnals can explain the enhanced width a lateral eddy viscosity of 300 m2 s 1 10 is found to be sufficient to account for the width implied by observations

deep jets in the equatorial atlantic ocean deep velocity profiles taken in the equatorial atlantic ocean show equatorially trapped deep jets with similar features to those of the indian and pacific oceans a zonal velocity of the order of 10 to 20 cm s 1 and a meridional scale of 1 in the pacific and indian oceans the zonal extent of the jets is at least 15 of longitude owing to the lack of synoptic measurements we have no information on the zonal scale in the atlantic ocean but we present here zonal velocity profiles made at a 16 month interval that have identical baroclinic structure in the western 35 w and central basin 13 w the atlantic jets have a vertical scale larger 400 600 m than those observed in the pacific ocean 250 400 m our measurements confirm the opposite directions of the jets for different seasons in the atlantic ocean furthermore for a given season the vertical profiles of zonal velocity at 35 w 0 are astonishingly similar at a 5 year interval as in the pacific and indian oceans the jets are embedded in a large vertical scale current that changes direction with time the few profiles available in the equatorial atlantic ocean suggest a seasonal reversal of the jets but neither this nor the temporal variability of the large scale current has been adequately resolved

ventilation of the equatorial atlantic by the equatorial deep jets equatorial deep jets edjs are a prominent flow feature of the equatorial atlantic below the equatorial undercurrent down to about 3000 m here we analyze long term moored velocity and oxygen observations as well as shipboard hydrographic and current sections acquired along 23 degree sign w and covering the depth range of the oxygen minimum zones of the eastern tropical north and south atlantic the moored zonal velocity data show high baroclinic mode edj oscillations at a period of about 4 5 years equatorial oxygen observations which do not resolve or cover a full 4 5 yr edj cycle nevertheless reveal large variability with oxygen concentrations locally spanning a range of more than 60 mol kg 1 we study the effect of edjs on the equatorial oxygen concentration by forcing an advection diffusion model with the velocity field of the gravest equatorial basin mode corresponding to the observed edj cycle the advection diffusion model includes an oxygen source at the western boundary and oxygen consumption elsewhere the model produces a 4 5 yr cycle of the oxygen concentration and a temporal phase difference between oxygen concentration and eastward velocity that is less than quadrature implying a net eastward oxygen flux the comparison of available observations and basin mode simulations indicates that a substantial part of the observed oxygen variability at the equator can be explained by edj oscillations the respective role of mean advection edjs and other possible processes in shaping the mean oxygen distribution of the equatorial atlantic at intermediate depth is discussed key points equatorial deep jets strongly affect oxygen distribution variability mean oxygen ditribution in the equatorial atlantic at intermediate depth gravest equatorial basin mode forces an advection diffusion model

probabilistic analysis and comparison of stress dependent rock physics models a rock physics model attempts to account for the nonlinear stress dependence of seismic velocity by relating changes in stress and strain to changes in seismic velocity and anisotropy understanding and being able to model this relationship is crucial for any time lapse geophysical or geohazard modelling scenario in this study we take a number of commonly used rock physics models and assess their behaviour and stability when applied to stress versus velocity measurements of a large dry core data set of different lithologies we invert and calibrate each model and present a database of models for over 400 core samples the results of which provide a useful tool for setting a priori parameter constraints for future model inversions we observe that some models assume an increase in vp vs ratio hence poisson s ratio with stress a trait not seen for every sample in our data set we demonstrate that most model parameters are well constrained however third order elasticity models become ill posed when their equations are simplified for an isotropic rock we also find that third order elasticity models are limited by their approximation of an exponential relationship via functions that lack an exponential term we also argue that all models are difficult to parametrize without the availability of core data therefore we derive simple relationships between model parameters core porosity and clay content we observe that these relationship are suitable for estimating seismic velocities of rock but poor when comes to predicting changes related to effective stress the findings of this study emphasize the need for improvement to models if quantitatively accurate predictions of time lapse velocity and anisotropy are to be made certain models appear to better fit velocity depth log data than velocity stress core data thus there is evidence to suggest a limitation in core data as a representation of the stress dependence of the subsurface the differences in the stress dependence of the subsurface compared to that measured under laboratory conditions could potentially be significant although potentially difficult to investigate its importance is of great significance if we wish to accurately interpret the stress dependence of subsurface seismic velocities

forcing of the atlantic equatorial deep jets derived from observations the equatorial deep jets edjs are an ubiquitous feature of the equatorial oceans in the atlantic ocean they are the dominant mode of interannual variability of the zonal flow at intermediate depth on the basis of more than 10 years of moored observations of zonal velocity at 23 w the vertically propagating edjs are best described as superimposed oscillations of the 13th to the 23th baroclinic modes with a dominant oscillation period for all modes of 1650 days this period is close to the resonance period of the respective gravest equatorial basin mode for the dominant vertical modes 16 and 17 it is argued that since the equatorial basin mode is composed of linear equatorial waves a linear reduced gravity model can be employed for each baroclinic mode driven by spatially homogeneous zonal forcing oscillating with the edj period the fit of the model solutions to observations at 23 w yields a basin wide reconstruction of the edjs and the associated vertical structure of their forcing from the resulting vertical profile of mean power input and vertical energy flux on the equator it follows that the edjs are locally maintained over a considerable depth range from 500 2500 m with the maximum power input and vertical energy flux at 1300 m the strong dissipation closely ties the apparent vertical propagation of energy to the vertical distribution of power input and together with the edjs prevailing downward phase propagation require the phase of the forcing of the edjs to propagate downward

deep currents and their interpretation as equatorial waves in the western pacific ocean abstract vertical profiles of current and density made within 5 latitude of the equator along longitudes 168 and 179 e the vicinity of the gilbert islands reveal multiple deep current reversals which are confined to the equator these current jets have amplitudes of roughly 5 20 cm s 1 vertical scales of order hundreds of meters and time scales longer than the one month of measurements during the cruise spectral analysis of profiles indicates that 1 meridional trapping varies roughly as the square root of the vertical scale 2 both east and north currents are coherent over meridional separations of 0 45 within roughly 1 30 of the equator and 3 zonal current lags vertical displacement by 4 in depth within 0 45 of the equator zonal coherence scales are smaller than the smallest separation of 3 30 along the equator kinetic energy decreases near the island chain current meter records taken over nearly two years near the islands suggest strong quasi annual variability in deep currents near t

the glacier fed fan at the mouth of storfjorden trough western barents sea a comparative study the middle and late pleistocene succession on the glacier fed fan at the mouth of storfjorden trough was studied using high resolution seismic data seven glacial advances to the shelf break during middle and late pleistocene resulted in episodic high sediment input to the fan with real sedimentation rates of up to 172 cm 1000 years separated by sediment starved interstadials and interglacials on the upper fan the high sediment input resulted in frequent slides and slumps generating debris flows which dominate the mid fan strata compared with the larger neighbouring bear island trough mouth fan the storfjorden trough mouth fan has a steeper fan gradient narrower thinner and shorter debris flow deposits and lower frequency of large scale sliding glacier fed submarine fans receive their main sediment input from a glacier margin at the shelf break as opposed to river fed fans where sediment input occurs through a channel levee complex as a result the depocentre of a river fed fan is found on the mid fan and the upper slope is mainly an area of sediment bypass whereas the glacier fed fan has an elongated depocentre across the uppermost fan the river fed fans are dominated by deposition from turbidity currents whereas glacier fed fans are dominated by debris flow deposits

stacked jets in the deep equatorial atlantic ocean 1 middepth current measurements in the equatorial atlantic are characterized by elevated levels of energy contained in zonal flows of high baroclinic mode number these alternating zonal flows often called equatorial stacked jets have amplitudes up to 20 cm s 1 and vertical wavelengths of 600 m the jets are most pronounced in the depth range between 500 and 2500 m repeated direct velocity observations at 35 w indicate that the jets are coherent within 1 of the equator individual jets can persist for 1 2 years but they appear and decay rather irregularly the equatorial stacked jets are also found in realistic general circulation model simulations the features grow in amplitude with increasing horizontal and vertical model resolution however even at very high model resolutions their amplitudes are still underestimated in all model simulations high levels of energy related to the stacked jets are found in the vicinity of the western boundary currents wbcs depth range and strength of the wbcs in different experiments are related to depth range and strength of the jets in the interior stacked jets are characterized by eastward wave propagation suggesting that high baroclinic mode kelvin waves radiate energy generated in the wbc into the interior and form the stacked jets

onset and growth of trough mouth fans on the north western barents sea margin implications for the evolution of the barents sea svalbard ice sheet abstract the aim of this study is to discuss the onset and growth of the bellsund hornsund and storfjorden trough mouth fans tmfs on the north western barents sea margin this is done on the basis of a seismo stratigraphic analysis of new 2d seismic reflection profiles and a new correlation between odp site 986 west of spitsbergen and the seismo stratigraphic network in the central part of the western barents sea margin we infer that reflector r4a marks the onset of both the development of the tmfs and the contourite deposition which dominate this part of the margin from this time onward we conclude that these deposits were frequently affected by episodes of small scale mass wasting focused at the mouth of the glacially eroded cross shelf troughs with a new interpolation between the few available constraints we propose an age of about 1 3 ma for the onset of both the development of the tmfs and the contourite deposition thus we hypothesize from our results and from previous studies that the barents sea svalbard ice sheet expanded first beyond the coast north of svalbard later reaching the shelf edge at the mouth of bjornoyrenna and then to storfjorden southern spitsbergen

deep circulation in the equatorial atlantic ocean in the atlantic ocean the northward export of warm surface water is compensated by a southward flow of cold north atlantic deep water nadw the nadvv is transported southward along the american continental margin within the deep western boundary current dwbc some tracer and float observations have shown that part of the dwbc water flows eastward along the equator here we present three meridional velocity sections which give an instantaneous image of the lop to bottom zonal circulation along the equatorial atlantic they reveal the presence of equatorial deep jets edjs between 1 30 n and 1 30 s alternating eastward westward currents with short vertical scale surrounded by columns of eastward currents the extra equatorial jets or eejs at 2 n and 2 s in addition to direct velocity measurements tracer distributions give indications of water mass feeding of the edjs and eejs by the dwbc

quaternary seismic stratigraphy of the north sea fan glacially fed gravity flow aprons hemipelagic sediments and large submarine slides abstract approximately 1000 km of high resolution sleeve gun array transects on the north sea fan located at the mouth of the norwegian channel reveal three dominant styles of sedimentation within a thick 900 m quaternary sediment wedge comprising numerous sequences these are interpreted as terrigenous hemipelagic sedimentation large scale translational slides and aprons of glaciogenic debris flow deposits contributing to considerable fan construction four large buried translational slides involved sediment volumes upwards of 3000 km 3 each and preceded the similarly dimensioned first storegga slide on the ne fan flank several thick 100 m terrigenous hemipelagic deposits apparently represent long lived 150 200 kyr periods of sedimentation whose distribution indicates fan input via the norwegian channel the upper sequences are each made upper sequences are each made up of one or several thick 100 m aprons comprising stacked lensoid and or lobate forms which range from 2 to 40 km in width and 15 to 60 m in thickness they characterize debris flows attributed to periodic input from several phases of a norwegian channel ice stream reaching the shelf edge subsidence in the outer norwegian channel allowed preservation of several glaciation cycles represented by sheet erosion bounded tills and progradational units much of the shelf slope transition has been preserved allowing a preliminary chronology of the fan sequences through correlation with borehole sediments in the norwegian channel debris flows which signal the initial shelf edge glaciation are not recognized from the initial glaciation in the channel 1 1 myr but are associated with a middle pleistocene and all following glacial erosion surfaces ges in the outer norwegian channel this was followed by six further sequences probably totalling over 13 000 km 3 of sediment at least four of these were shelf edge ice maximum events the last of which was late weichselian age 14 c ams considering earlier glaciation related hemipelagic sedimentation material since removed by the large slides and extensive unmapped areas total quaternary fan sedimentation was in the vicinity of 20 000 km 3

a simple model for deep equatorial zonal currents forced at lateral boundaries abstract deep lateral boundary processes e g western boundary currents are hypothesized as an alternative energy source exciting the equatorial wave guide at long time scales a linear continuously stratified model is used to study the equatorial zonal currents generated by a time dependent short vertical scale deep zonal jet located at the meridional walls and centered at the equator examples of solutions with periodic transient and spectral forcing are presented for low frequency forcing at the western or eastern boundaries energy travels from the source along ray paths associated with kelvin and long rossby waves respectively linearly damped solutions look similar in both cases solutions show in general a rich baroclinic structure and a complex time dependence e g periodic solutions can exhibit both upward and downward phase propagation and standing mode oscillations at different depths in the water column with the vertical structure depending among other factors on the vertical sca