structure of large amplitude internal solitary waves the horizontal and vertical structure of large amplitude internal solitary waves propagating in stratified waters on a continental shelf is investigated by analyzing the results of numerical simulations and in situ measurements numerical simulations aimed at obtaining stationary solitary wave solutions of different amplitudes were carried out using a nonstationary model based on the incompressible two dimensional euler equations in the frame of the boussinesq approximation the numerical solutions which refer to different density stratifications typical for midlatitude continental shelves were obtained by letting an initial disturbance evolve according to the numerical model several intriguing characteristics of the structure of the simulated large amplitude internal solitary waves like for example wavelength amplitude and phase speed amplitude relationship as well as form of the locus of zero horizontal velocity emerge consistent with those obtained previously using stationary euler models the authors approach which tends to exclude unstable oceanic internal solitary waves as they are filtered out during the evolution process was also employed to perform a detailed comparison between model results and characteristics of large amplitude internal solitary waves found in high resolution in situ data acquired north and south of the strait of messina in the mediterranean sea from this comparison the importance of using higher order theoretical models for a detailed description of large amplitude internal solitary waves observed in the real ocean emerge implications of the results showing the complexity related to a possible inversion of sea surface manifestations of oceanic internal solitary waves into characteristics of the interior ocean dynamics are finally discussed

faunal and stable isotopic analyses of benthic foraminifera from the southeast seep on kimki ridge offshore southern california usa abstract we investigated the benthic foraminiferal faunal and stable carbon and oxygen isotopic composition of a 15 cm push core na075 092b obtained on a telepresence enabled cruise to the southeast seep on kimki ridge offshore southern california the seep core was taken at a depth of 973 m in the vicinity of a beggiatoa bacterial mat and vesicomyid clams calyptogena and compared to previously published data of living assemblages from 714 m four reference cores obtained at 1030 m and another one at 739 m all of the reference sites are also from the inner continental borderland but with no evidence of methane seepage no endemic species were found at the seep site and most of the taxa recovered there have been reported previously from other seep or low oxygen environments q and r mode cluster analyses clearly illustrated differences in the faunal assemblages of the seep and non seep sites the living assemblage at southeast seep was characterized by abundant takayanagia delicata cassidulina translucens and spiroplectammina biformis whereas the non seep san pedro basin reference assemblage was comprised primarily of chilostomella oolina and globobulimina pacifica density and species richness were lower at the seep site compared to the non seep site reflecting the harsher living conditions there the dead assemblage at the seep site was dominated by gyroidina turgida compared to cassidulina translucens at the 1030 m non seep site and cassidulina translucens pseudoparrella pacifica and takayanagia delicata at the 739 m non seep site density was three times lower at southeast seep than at the non seep sites of comparable water depth but species richness was 30 higher stable carbon isotopic values were considerably depleted in the seep samples compared to the non seep samples with a progression from lightest to heaviest average 13c values evident at the seep site reflecting microhabitat preference and vital effect the deep infaunal species of globobulimina the shallow infaunal species uvigerina peregrina the epifaunal species cibicidoides wuellerstorfi and the shallow infaunal but aragonite shelled species hoeglundina elegans the 13c values downcore among each benthic species indicates ongoing fluid seepage through at least the last 3800 cal yr b p at southeast seep besides the continual local seepage evidence from 13c values of planktic foraminifera in the seep core suggest two pulses of methane at 3000 and 3700 cal yr b p were released that were large enough to influence much of the water column paired benthic and planktic foraminiferal stable oxygen isotope records provide evidence that there were no paleoenvironmental changes such as increased bottom water temperature or changes in oxygen isotopic composition of bottom and pore waters during this 3800 year record to induce the methane releases instead southeast seep appears to be the result of local faulting providing pathways for fluid to flow to the seafloor at a fault stepover or transpressional bend in the regional strike slip system

airborne synthetic aperture radar tracking of internal waves in the strait of gibraltar abstract as part of the international gibraltar experiment we realized on june 22 and 24 1986 two surveys of the strait of gibraltar on board an aircraft equipped with a synthetic aperture radar our objective was to observe at spring tides and during two twelve hour tidal cycles at 24 h interval the generation of internal wave trains linked to the hydraulic jump formed west of the sill during the westward phase of the tidal current and their eastward propagation in the strait the speed of propagation of these waves and the effect of the diurnal component of the tide on their generation and propagation could then be determined our results suggest that two solitary waves of equal amplitude propagated eastwards in the strait on june 22 the tidal coefficient being equal to 92 with a speed relative to the ground of 2 1 to 2 6 m s 1 24 h later during the second survey on june 24 tidal coefficient 90 we observed the propagation of a train of non linear waves the speed of the leading wave of which being about 1 9 ms 1 our data show that other waves pass over the camarinal sill after the release of the bore and secondary internal wave trains are shown to propagate eastwards from there although our sar data show the appearance of waves west of the northern sill at about 4 h after high water hw the mechanism leading to their generation is not clear these waves could propagate eastwards all along the strait and or northwestwards along the western spanish coast they could be responsible for the solitary type events observed at the eastern entrance of the strait at about 7 h after hw by ziegenbein 1969 1970 these events are noticeable in the hydrological parameters time series of armi and farmer 1988 and in the high rate current data 2 min apart from their april 1986 cruise besides these alongstrait waves our sar data show the existence of cross strait waves and give an idea of their wavelength and speed of propagation their presence leads to perturbations in the current revealed by simultaneous current data at the camarinal sill and north of cape cires

anaerobic diagenesis of silica and carbon in continental margin sediments discrete zones of tco2 production pore water profiles of dissolved si ca2 so42 ch4 and tco2 dissolved inorganic carbon dic were determined from multicores and gravity cores collected at nine sites off southern california the west coast of mexico and within the gulf of california these sites were located within the eastern north pacific oxygen minimum zone at depths of 400 to 900 m and in settings where bottom water oxygen concentrations were 3 m and sediments were laminated pore water profiles were defined at a resolution of millimeters whole core squeezing centimeters sectioning and squeezing and meters gravity core sectioning and squeezing and diffusive fluxes were calculated for different zones within the sediment column the flux of dissolved silica across the sediment water interface swi ranged from 0 3 to 3 4 mmol si m 2d 1 and tco2 fluxes ranged from 0 8 to 4 6 mmol c m 2d 1 a positive correlation r 0 74 existed between these fluxes yet these two constituents exhibited significantly different diagenetic behavior downcore dissolved si generally reached a constant concentration between 450 and 900 m in the upper few cm whereas tco2 concentrations increased monotonically with depth methane was detected at micromolar levels in sediment intervals between 0 and 60 cm and at five sites increased to millimolar levels at depths of 80 to 170 cm at the horizon marking the appearance of millimolar levels of methane there was a distinct change in slope of the sulfate and tco2 gradients a flux budget for this horizon was determined by using linear fits to pore water profiles these budgets indicate that the upward tco2 flux away from this horizon is 40 to 50 greater than the downward sulfate flux to this horizon given that the tco2 flux to this horizon from below was quite small this imbalance suggests that anaerobic oxidation of methane by sulfate is not the only process producing tco2 within this horizon a budget for tco2 at this horizon is balanced when 40 to 80 of the sulfate flux is attributed to organic carbon remineralization of the dic that diffuses across the swi 20 to 40 is generated by reactions occurring within or below this deep reaction horizon

surface deformation of westerly granite during creep holographic interferometry has been used to observe the surface deformation of westerly granite during creep experiments at 50 mpa 500 bars confining pressure interference fringes on the holograms produced by this technique constitute contour maps of the sample surface shape change between exposures several distinctive characteristics of the surface shape change have been observed in general surface deformation during primary and secondary creep while highly inhomogeneous is distributed fairly uniformly no large scale pattern is seen in the surface shape changes at approximately the onset of tertiary creep surface displacements become more locallized eventually approx 85 90 of time to failure a distinct ridge is formed which exactly coincides with the location of the final fracture

foraminiferal radiocarbon record of northeast pacific decadal subsurface variability 1 the decadal dynamics of the subsurface north pacific ocean are largely inaccessible beyond sparse instrumental observations spanning the last 20 years here we present a 200 year long record of benthic foraminiferal radiocarbon 14c extracted at biennial resolution from the annually laminated sediments at the santa barbara basin sbb depocenter 600 m the close match between core top benthic foraminiferal 14c values and the 14c of seawater dissolved inorganic carbon dic suggests that benthic foraminifera faithfully capture the bottom water radiocarbon concentrations as opposed to that of the deeper 0 5 cm sediment porewater zone the full time series of benthic foraminiferal 14c displays significant variability on decadal timescales with excursions on the order of 40 these excursions are overprinted by a unidirectional trend over the late 20th century that likely reflects the sedimentary incorporation of bomb radiocarbon via remineralized particulate organic carbon we isolate this trend by means of a one dimensional oxidation model which considers the possible contribution of remineralized particles to the total ambient carbon pool this oxidation model also considers the possible influence of carbon with a variety of sources ages though variable oxidation of preaged carbon could exert a strong influence on benthic foraminiferal radiocarbon variability the totality of evidence points to the vertical density structure along the southern california margin scm as the primary driver of the sbb benthic foraminiferal 14c record for example intervals characterized by significantly lower 14c values correspond to periods of enhanced upwelling and subsurface equatorward flow along the scm

path dependence of acoustic velocity and attenuation in experimentally deformed westerly granite brittle failure in rocks is generally preceded by a localization of deformation in the region of the final macrofracture this process is associated with a non uniform distribution of subcritical microcracks which should be reflected in the distribution of acoustic velocities and surface deformation the temporal and spatial development of such deformation zones has been studied by monitoring these quantities during the deformation of westerly granite samples

molybdenum and uranium geochemistry in continental margin sediments paleoproxy potential abstract we measured solid phase mo and u concentrations in marine sediments from the california mexico peru and chile margins to ascertain the behavior of mo and u during early diagenesis in continental margin settings at sites along the california mexico and peru margins where there are estimates of mass accumulation rates authigenic u accumulation rates range from 0 50 nmol m 2 day 1 at the california and mexico margin sites mo accumulation rates range from 0 to 134 nmol m 2 day 1 whereas at the peru margin site rates may be as high as 550 nmol m 2 day 1 we observe relationships between metal accumulation rates and the delivery and burial rates of organic carbon corg in the case of mo there appears to be at least two relationships between metal accumulation rate and organic carbon burial for most of the data presented in this manuscript continental margin sediments have a mo corg accumulation rate ratio of 20 mol mol 1 this value is significantly lower however than those reported for anoxic basins 100 mol mol 1 but is consistent with reported mo corg rain ratios from mexico margin sediment traps in contrast to mo there appears to be a single u corg burial ratio of 5 mol mol 1 which includes a range of environments from anoxic basins and open ocean sites we interpret the relationships between metal accumulation and organic carbon to indicate that the reactions that govern authigenic metal accumulation are primarily sensitive to the delivery and burial of organic carbon in these particular settings however we note that any relationship between metal accumulation and organic carbon could be indirect in the particular case of mo based on what is known about mo geochemistry from the literature it is possible that mo authigenesis is coupled to sulfur cycling in many of the environments covered by this study and that the observed association between mo and organic carbon burial is a consequence of the coupling between carbon and sulfur burial using the observed relationships between mo and corg burial as well as constraints from the mo isotope budget we estimate that continental margin sediments are an important sink for mo the magnitude of this sink 0 4 108 mol y 1 or larger may be as much as one quarter of the oceanic removal term and is likely to be larger than the modern anoxic basin sink

theory of radar imaging of internal waves radar images taken over ocean areas in particular those obtained by the synthetic aperture radar sar onboard the american seasat satellite in 19781 2 sometimes show features that seem to be surface manifestations of oceanic internal waves3 11 here i present a theory explaining the large radar signatures of internal waves in which the imaging is attributed to variations in the short scale surface roughness induced by current variations associated with internal waves

geochemical and sedimentologic variations in inter annually laminated sediments from santa monica basin abstract laminated sediments were recently discovered in the center of santa monica basin california continental borderland and extend from the present day to at least the little ice age ca 1600 a d unlike the annual varves observed in santa barbara basin the light dark lamination couplets observed in 210 pb dated cores from the center of santa monica basin occur at 3 to 6 year intervals very similar in length to the el nino southern oscillation enso phenomena the mechanisms that control the temporal patterns of laminations in this basin are unknown potential causal mechanisms of lamination formation in santa monica basin include 1 changes in the flux of terrigenous vs marine organic carbon and detritus 2 surface water processes which affect marine productivity and organic carbon flux to the sediments and 3 deep water processes which affect oxygen renewal and preservation of organic matter within the basin a box core from the central portion of santa monica basin was analyzed using a suite of geochemical sedimentary and micropaleontologic techniques in order to a investigate which if any of these mechanisms has contributed to the occurrence of laminations and b reconstruct proxy records of climate change samples were extracted from this core at 1 mm increments and provide a temporal resolution of 1 3 years per sample a resolution which is comparable in length to the thickness of individual laminae within the core geochemical and micropaleontologic analyses of core samples provide paleoclimatic and paleoceanographic records which are comparable to and extend beyond historical regional and global climate records in addition to direct comparisons between these records spectral analysis was used to investigate whether there were similar patterns of variability that would implicate dominant forcing functions in the historic and proxy records herein we present preliminary results of records from ca 1860 to the present our results suggest that organic carbon fluxes are the dominant factors that affect lamination variability input of organic carbon is primarily a function of primary productivity and to a lesser extent a function of percentage of terrestrial input thus 1 and 2 are both mechanisms of lamination formation stability of 3 only allows preservation of the record of these variations variations in southern california rainfall appear to be linked to decadal scale variations in downcore density profiles and thus cause variations in the thickness and character of the laminations in the deepest portions of this basin thus filtered density records can be used to reconstruct general paleo rainfall trends which compare well with historic rainfall records variations in the isotopic composition of total organic carbon toc are compared to historic enso and climate records and primarily reflect changes in the relative contribution of marine organic carbon to the basin variations in the carbon isotopic composition of n pachyderma mirror changes in the sedimentary 13 c toc record from santa monica basin and suggest that primary productivity is the primary control on the flux of organic carbon to the sediments and exerts a strong influence on the interannual variability in lamination composition variations in paleo sea surface temperatures generated from the oxygen isotopic composition of n pachyderma correlate well with historical sst records and suggest potential usage as a proxy for general paleosst patterns oxygen sensitive assemblages of benthic foraminifera bolivina argentea and b spissa have been used to identify potential large scale flushing events and construct a historical record of variations in deep water oxygen levels spectral analysis of regional historic records indicate dominance of short term enso length and long term decadal patterns of climate variability the short term enso signal is not dominant in the santa monica proxy records however strong decadal length signals are identified in all of the proxy records and suggest that the dominant forcing mechanisms in santa monica basin may be decadal in length

impacts of basin restriction on geochemistry and extinction patterns a case from the guadalupian delaware basin usa abstract geochemical data from carbonates often constrain the nature of environmental change during biotic turnover events many ancient carbonates however formed in geographically isolated basins subject to local environmental factors resulting in varying extinction rates between open ocean and restricted settings it follows that high resolution data from restricted basins may help unravel poorly understood biotic crises such as the mid capitanian extinction which had especially high extinction rates in restricted settings this study examines factors controlling salinity stratification and oxygenation in the capitanian middle permian delaware basin usa elemental and carbon isotope measurements from time equivalent strata reveal differences between shallow and deep water masses pointing to local controls such as stratification and de oxygenated bottom water basinal dolomites and evaporites mark periods of elevated salinity tied to sea level lowstands which correspond with turnovers in fusulinid and brachiopod communities faunal turnover in the delaware basin demonstrates a fundamental attribute of restricted basins water chemistry is often tightly coupled to physical process such as sea level change we suggest that the relationships among sea level fluctuations chemical changes and biotic turnover may explain why the capitanian mass extinction was more severe in isolated basins than the open ocean

internal waves in the strait of messina studied by a numerical model and synthetic aperture radar images from the ers 1 2 satellites a new numerical two layer model is presented which describes the generation of internal tidal bores and their disintegration into internal solitary waves in the strait of messina this model is used to explain observations made by the synthetic aperture radar sar from the european remote sensing satellites ers 1 and ers 2 the analysis of available ers 1 2 sar data of the strait of messina and adjacent sea areas show that 1 northward as well as southward propagating internal waves are generated in the strait of messina 2 southward propagating internal waves are observed more frequently than northward propagating internal waves 3 sea surface manifestations of southward as well as northward propagating internal waves are stronger during periods where a strong seasonal thermocline is known to be present 4 southward propagating internal bores are released from the sill between 1 and 5 hours after maximum northward tidal flow and northward propagating internal bores are released between 2 and 6 hours after maximum southward tidal flow and 5 the spatial separation between the first two internal solitary waves of southward propagating wave trains is smaller in the period from july to september than in the period from october to june the numerical two layer model is a composite of two models consisting of 1 a hydrostatic generation model which describes the dynamics of the water masses in the region close to the strait s sill where internal bores are generated and 2 a weakly nonhydrostatic propagation model which describes the dynamics of the water masses outside of the sill region where internal bores may disintegrate into internal solitary waves due to a technique for movable lateral boundaries the generation model is capable of simulating the dynamics of a lower layer that may intersect the bottom topography the proposed generation propagation model depends on one space variable only but it retains several features of a fully three dimensional model by including a realistic channel depth and a realistic channel width it is driven by semidiurnal tidal oscillations of the sea level at the two open boundaries of the model domain numerical simulations elucidate several observed characteristics of the internal wave field in the strait of messina such as north south asymmetry times of release of the internal bores from the strait s sill propagation speeds and spatial separations between the first two solitary waves of internal wave trains

the santa monica basin tracer experiment a study of diapycnal and isopycnal mixing we have studied cross isopycnal diapycnal and lateral mixing and stirring below the sill of santa monica basin by releasing two tracers sulfur hexafluoride and perfluorodecalin as close as possible to an isopycnal surface and measuring their subsequent dispersion the target for the release was a potential temperature surface at about 790 m depth roughly 100 m above the bottom and 50 m below the sill three surveys performed immediately after about 7 weeks after and about 6 months after the release showed that the time scales for lateral stirring and mixing in the basin were between 2 and 5 months the diapycnal diffusivity for the whole period was found to be 0 29 0 06cm2 s near the injection surface where the buoyancy frequency was about 1 1 cph this estimate may include some mixing in the turbulent boundary layer near the walls of the basin our best estimate for the diapycnal diffusivity in the basin interior is 0 25 0 08 cm2 s

on the dynamics of internal waves in a nonlinear weakly nonhydrostatic three layer ocean aspects of the dynamics of internal solitary waves evolving in a three layer ocean are investigated using a new numerical multilayer model that solves the nonlinear weakly nonhydrostatic boussinesq equations and uses high resolution in situ data the model applications refer to two different phenomena frequently observed in the real ocean which can be described using a three layer model rather than a two layer model in the first application the influence of the strength of a shallow seasonal thermocline superimposed on a two layer permanent stratification on the structure of internal solitary waves is studied it is found that while for small to medium wave amplitudes a decrease in the strength of the thermocline yields an increase in the simulated wavelengths for large wave amplitudes this dependence is no longer monotonic in particular in the limiting case of a vanishing thermocline first mode internal solitary wave solutions of the three layer numerical model tend to the analytical internal solitary wave solutions of the miyata equations a two layer model in which the full nonlinearity of the shallow water theory up to first order phase dispersion is retained in the second application that refers particularly to high resolution observations made north and south of the strait of messina in the eurafrican mediterranean basin the generation of internal solitary waves by the evolution of surface and subsurface water jets is investigated the analysis of the in situ data shows in fact that from very energetic surface and subsurface jet like disturbances subject to strong turbulent mixing internal solitary waves emerge as robust quasi nondissipative oceanic features idealized flow conditions aimed at approximating possible initial stages of the observed water jets are imposed to force our numerical model in general good agreement is found between characteristics of observed and simulated wave fields our investigation identifies the observed water jets as peculiar features of the complex ocean dynamics and suggests that layered numerical models can represent helpful tools in understanding fundamental processes inherent in their intricate dynamics

a nonlinear model of the shoaling and refraction of interfacial solitary waves in the ocean part i development of the model and investigations of the shoaling effect abstract oceanic internal waves are frequently observed to be of large amplitude and to exhibit significant wave front curvature as seen in synthetic aperture radar images the aim of this paper is to present a refraction model in two horizontal dimensions including moderate amplitude effects to model these common properties of internal waves the model incorporates second order nonlinearity and uses a ray method to allow arbitrary refraction for these preliminary investigations with the model a two layer ocean is assumed with an upper layer thickness of 50 m and a density difference across the layers of 0 5 kg m 3 an important aspect affecting the refraction of nonlinear waves is shoaling as the phase speed of a nonlinear wave depends on its amplitude in part i of this paper the development of the model is described and the shoaling phenomenon is investigated in detail the shoaling of interfacial internal solitary waves over both slowly varying and rapidly varying bathymetry is studied a wedg

internal waves in the gulf of california observations from a spaceborne radar pronounced signatures of internal waves were detected repeatedly in the gulf of california by the seasat synthetic aperture radar sar a series of nine images with exactly repeating ground coverage was used to study the temporal variability of the internal wave field in the area it was found that the number of observed wave groups was highly correlated with the strength of the local tides the maximum number occurred during spring tides and the minimum number occurred during neap tides indicating that the internal waves were tidally forced most of the wave activity was found to the north of 28 n where the tides were the strongest in the gulf the application of a simple nonlinear internal wave model to the observations indicated that the peak to peak amplitude of the observed waves was about 50 m with an uncertainty of a factor of 2 the estimated upper bound for the rate of the loss of tidal energy to internal waves was about 5 1015 erg s representing only 10 of the rate of the dissipation of the dominant m2 tide in the gulf

solitary internal waves in the celtic sea abstract an examination is made of tidally generated high frequency internal wave trains propagating from the shelf break of the celtic sea and armorican shelf the waves propagate on shelf after maximum off shelf tidal streaming at speeds of about 70 cm s 1 giving a wavelength between successive tidal disturbances of 30 km as the waves travel on shelf they are advected by the barotropic tide and can take on a solitary wave form

a model for the alboran sea internal solitary waves abstract the propagation into the alboran sea of the interface depression generated at the strait of gibraltar by the interaction of the semidiurnal tidal current with the main camarinal sill is studied numerically by using a unidirectional model with two horizontal space dimensions an initial waveform within the strait is determined whose evolution corresponds with the train of internal solitary waves detected in the alboran sea by means of current measurements at different depths as described by kinder the agreement is good for two points located at about 45 km east of the strait the first aligned with the strait axis and the second 20 km to the north moreover the shape and amplitude of this initial condition are in agreement with a typical interface depression generated in the strait by the interaction of the tidal current with the sill a series of numerical experiments with different initial conditions is also performed to study the sensitivity of the model results to changes in the initial i

on the discrimination of radar signatures of atmospheric gravity waves and oceanic internal waves on synthetic aperture radar images of the sea surface synthetic aperture radar sar images acquired over the ocean frequently show sea wave like patterns that have wavelengths well above those of ocean surface waves and that are sea surface signatures of oceanic internal waves oiws or of atmospheric gravity waves agws however it is often difficult to decide whether they result from the first or the second kind of waves which has led many investigators to misinterpret sar images of the sea surface based on solitary wave and radar imaging theories of agws and oiws we present criteria that help distinguish between them however there are cases where these criteria which are based solely on the shape and structure of the features visible on the sar images yield ambiguous results in these cases one must resort to additional information on the generation of agws and oiws which are listed in this paper

scylla and charybdis observed from space scylla and charybdis are in greek mythology two immortal and irresistible monsters who beset the narrow waters separating the italian peninsula from sicily they give poetic expressions to exceptional oceanographic features encountered in the strait of messina recently the seasat satellite has added new information on the oceanography of this strait for the first time experimental evidence is presented that internal waves are generated in the strait of messina the generation mechanism is linked to tidal currents washing over the shallow sill within the strait the experimental data originate from a synthetic aperture radar sar image obtained from the seasat satellite on sept 15 1978 and from subsequent in situ measurements carried out from the italian research vessel bannock in nov 1980 the circular wave pattern visible on the seasat sar image is interpreted in terms of internal solitons furthermore the seasat sar image also reveals tagli special types of tidal bores encountered in the strait of messina

circulation in the point conception santa barbara channel region during spring and early summer 1983 fifteen current moorings were deployed around the periphery of santa barbara channel and over the continental shelf to the west off point conception data from these moorings have been used to describe the regional circulation and to address problems of wind forcing and the spatial coherency scales for current fluctuations the mean circulation in santa barbara channel was dominated by a westward jet which occupied the northwestern portion of the channel current and temperature fluctuations were generally well correlated among all locations around the channel and time lags suggested cyclonic propagation of events around the channel the time fluctuations were dominated by a relatively few low frequency events it was impossible to determine exactly either the driving mechanisms for these events or their relationships to regional flow the flow regime was considerably different off point conception than in the channel locally wind driven upwelling was observed in both the mean and fluctuating flows and the time scales of current variability i e spectral shapes mimicked those of the local winds a dramatic change in the regime off point conception occurred in late may before the transition currents and sea levels had been well correlated in time with both local and remote winds after late may the relation to fluctuating winds was less clear and the alongshore structure of sea level variability had changed radically

long internal waves and columnar disturbances in the strait of messina during a pilot cruise in the strait of messina we observed the interface time evolution between atlantic and levantine water layers due to semidiurnal tides our data are in fairly good agreement with the models computed by del ricco 1982 and by hopkins et al 1984 as regards long lasting 1 hour or more water movements quick transient perturbations of columnar shape probably eddies which we have called bignami columns were also observed and analyzed using both a koden fish finder and moored temperature sensors

evidence for enhanced boundary mixing in the santa monica basin transients in the heat content in santa monica and san pedro basins imply a basin wide diapycnal eddy diffusivity greater than 1 cm sup 2 s this is significantly larger than the value for sf sub 6 of 0 25 0 08 cm sup 2 s determined for the interior of santa monica basin for september 1985 to february 1986 by ledwell and watson however the exodus of sf sub 6 from santa monica basin after february 1986 by which time the tracer had mixed to the boundaries of the basin was fast enough to be consistent with a greatly enhanced vertical flux since the kinetic energy in the basin had not changed significantly it is unlikely that a temporal increase in forcing resulted in enhanced fluxes in the interior of the basin the most likely interpretation is that diapycnal fluxes in the basin are dominated by processes in the boundary regions temperature and sf sub 6 profiles from near the edges of the basin do not give conclusive evidence either for or against such enhanced mixing 20 refs 19 figs 5 tabs

the flushing of two deep sea basins southern california borderland a time series of water temperature salinity and nutrient measurements has been made in san pedro and san nicolas basins of the southern california borderland between i977 and 1988 these basins exhibit temporally coincident changes in temperature and nutrient content defining a period of basin flushing 1982 1984 and a period of stagnation 1984 1987 during the flushing period cooler oxygenand no rich water replaces warmer oxygenand no depleted bottom water flushing produces a decrease of 0 2 c in the average temperature of san pedro basin bottom water 790 900 m and an increase in the average oxygen content by 12 pm these values are 0 i and 3 for san nicolas basin 1 400 l 800 m the residence time of water in san pedro basin during the flushing period is 12 6 months and j t2 months in san nicolas basin a box model approach constrained by the time series data for the stagnation period was used to determine values of the effective vertical eddy diffusivities for the 790 m horizon in san pedro basin and 1 400 m horizon in san nicolas basin 1 3 0 4 and 9 9k3 4 cm sk respectively

analysis of nonlinear internal waves observed by landsat thematic mapper in this work we test the compatibility between the theoretical parameters of a nonlinear wave model and the quantitative information that one can deduce from satellite derive0 data the theoretical parameters are obtained by applying an inverse problem to the solution of the cauchy problem for the korteweg de vries equation our results are applied to the case of internal wave patterns elaborated from two different satellite sensors at the south of messina the thematic mapper and at the north of messina the synthetic aperture radar

modeling the oceanic circulation in the area of the strait of sicily the remotely forced dynamics in order to describe aspects of the baroclinic dynamics in the region of the strait of sicily a high resolution multilayer numerical model has been implemented in a central mediterranean region including the tyrrhenian and the ionian seas three layers have been considered representing water of atlantic origin maw the levantine intermediate water liw and deep water of the mediterranean quasi stationary circulations representing the local manifestation of the large scale mediterranean conveyor belt are obtained after an adjustment time of o 2 months by imposing steady fluxes along the remote open boundaries in the absence of meteorological forcings these circulations can be interpreted as possible dynamic scenarios of the seasonal variability in the strait of sicily in the numerical simulations an inflow of maw and an outflow of liw through the strait of sardinia an outflow of maw and an inflow of liw through the ionian boundary and an outflow of maw through the corsica channel are imposed resulting in a vanishing total net transport in each layer for realistic values of these transports the model captures the main features of the observed circulation such as i the separation of the algerian current into two branches one directed toward the tyrrhenian sea and the other entering the strait ii a secondary bifurcation of maw within the strait giving rise to a southward moving current that follows the tunisian continental slope and to a current that flows southeastward along the southern sicilian coast and then northward along the southern italian coasts the so called atlantic ionian stream iii a bifurcation of liw at the strait level leading to a main current directed toward the strait of sardinia and to a weaker current that after having crossed the strait bends eastward and enters the tyrrhenian sea sensitivity experiments carried out by imposing different boundary fluxes have shed light on the functioning of the maw and liw bifurcations first of all for a given net transport of maw and liw through the strait imposed indirectly by the boundary fluxes the ratio rmaw between the transport of maw entering the tyrrhenian sea and that entering the strait is found to be virtually independent of the boundary imposed algerian current transport it is on the contrary determined by a local dynamic control which selects the value rmaw 0 43 for a net maw liw strait transport of 61 sv in excellent agreement with observations second for decreasing baroclinic transports the ratio rmaw is found to decrease up to the limiting value rmaw 0 2 corresponding to the linear regime for transports o 0 1 sv finally rmaw is found to be very sensitive to the barotropic transport t through the strait whereas the corresponding ratio for the liw rliw is virtually independent of t for t 5 20 5 sv rmaw 1 1 while for t 51 0 5 sv rmaw decreases by one order of magnitude rmaw 0 1 in other words a weakening of the liw or a strengthening of the maw net transport through the strait reduces the relative intensity of the tyrrhenian branch of maw and vice versa on the other hand for values of t within the same range one always findsrliw 20 3 it thus appears that the local control exerted by the topography through the liw potential vorticity budget forces the transport of the tyrrhenian branch of liw to be always 1 3 of that directed toward the strait of sardinia

environmental analysis of paleoceanographic systems based on molybdenum uranium covariation abstract modern low oxygen marine systems exhibit patterns of molybdenum uranium covariation that can be linked to specific attributes and processes of the depositional system including 1 variation in benthic redox conditions 2 the operation of particulate shuttles within the water column and 3 the evolution of watermass chemistry the importance of these factors in each depositional system can be assessed both from the degree of enrichment of authigenic molybdenum mo auth and uranium u auth and from the mo u auth ratio of the sediment relative to the seawater mo u molar ratio of 7 5 7 9 in open ocean systems with suboxic bottomwaters u auth enrichment tends to exceed that of mo auth owing to onset of u auth accumulation at the fe ii fe iii redox boundary resulting in sediment mo u auth ratios less than that of seawater as bottomwaters become increasingly reducing and at least occasionally sulfidic the rate of accumulation of mo auth increases relative to that of u auth and sediment mo u auth ratios equal or exceed that of seawater in restricted marine systems with permanently sulfidic deepwaters the relative enrichment of mo auth and u auth depends on additional factors in the cariaco basin which has an aqueous mo u ratio similar to that of seawater the operation of a particulate mn fe oxyhydroxide shuttle serves to accelerate the transfer of mo to the seafloor leading to strong enrichments in mo auth relative to u auth in the black sea the chemistry of the deep watermass has evolved to the point where its aqueous mo u ratio is only 0 04 that of seawater as a consequence of which sediments deposited under deepwater influence are depleted in mo auth relative to u auth these mo u covariation patterns can be used to gain a better understanding of the watermass attributes and processes of ancient low oxygen marine systems analysis of anoxic facies from two north american paleomarine systems the late pennsylvanian midcontinent sea lpms and the late devonian seaway lds reveals authigenic mo u relationships similar to those of the modern marine environments above implying similar redox and hydrographic controls the observed patterns are consistent with laterally unconfined circulation and strong watermass exchange within the lpms and with markedly restricted deepwater circulation in silled basins of the lds patterns of authigenic mo u covariation may prove useful in analysis of other paleoceanographic systems to reveal aspects of watermass composition and environmental dynamics

analysis of nonlinear internal waves in the new york bight this paper presents the results on internal wave analysis of the current meter mooring data in the new york bight from the sar internal wave signature experiment sarsex selective sets of current and temperature measurements are analyzed for a parametric study of internal wave characteristics and shear effects on wave parameters are studied based on the limited data from moorings the solitary wave theory has been extended for the wave evolution on a continental shelf by including dissipation and shoaling effects a series of numerical simulations are performed to demonstrate the relative importance of dissipation and shoaling effects from an observed initial wave packet at the upstream mooring the numerical evolution simulation compares reasonably well with the measurements at the distant mooring for the leading two large solitons

non annual laminations and expansion of anoxic basin floor conditions in santa monica basin california borderland over the past four centuries sediments from box cores in the deep portion of santa monica basin have been examined by x radiography and the upper 10 20 cm are characterized by laminations 1 5 mm in thickness age dating of 9 cores by 210pb analysis has shown that accumulation rates on the central basin floor have been remarkably constant during the past century averaging 16 0 0 4 mg cm2 yr densitometer analysis of the x radiography films from 7 cores and spectral analysis of the resulting time series indicates that most lamination couplets have a periodicity in the 3 7 year range a range matching that of the el nino southern oscillation periodicity the median periodicity appears to have decreased slightly during the past 3 centuries from 7 0 years during 200 300 yrs b p to 5 2 yrs during 0 100 yrs b p this trend could be due to a decreasing sedimentation rate an increasing forcing frequency or an increasingly faithful response of the basin in more recent years multiple processes have contributed to creation of the laminations in santa monica basin the principal factors appear to be 1 variations in porosity due to the relative abundance of organic filaments probably formed by beggiatoa mats and 2 compositional variations that reflect variations in carbonate lithogenous ratios and in grain size both of these are expected to respond to enso events the presence of near anoxic bottom waters has prevented bioturbation permitting laminations to be preserved basin bottom waters became nearly anoxic about 350 years ago at the onset of warming as the little ice age waned expansion of the near anoxic area during the past century may have been augmented by 20th century anthropogenic effects the style of these non annual laminations in santa monica basin matches that of the annual laminations in the adjacent santa barbara basin and demonstrates the need for caution in interpreting all laminations as representing annual varves

a study of internal wave propagation in the strait of gibraltar using shore based marine radar images abstract an x band marine radar on windmill hill gibraltar was used to monitor the propagation of internal waves in the strait of gibraltar during march april and june 1986 surface roughness features of the waves were observed out to a range of 15 km from photographic images of the radar screen the positions of image features were measured manually using a digitizing table and these data were then computer processed to give wave arrival times and phase speeds during most tidal cycles an internal undular bore generated at camarinal sill was observed to pass eastward a waves these occurred throughout the experiments although less frequently near neap tides the time of travel to gibraltar varied significantly so that the bore arrived between four and nine hours after high water arrival times were found to be closely related to the amplitude of the upper layer tidal current this current had a strong diurnal component which was manifested as an inequality between the arrival times of success

remote imaging of internal solitons in the coastal ocean abstract during a combined in situ and airborne remote sensing exercise off oceanside ca a compact airborne spectrographic imager casi observed alongshore lineations which were associated with an internal soliton packet accompanying a tidally generated internal solitary wave solibore the soliton packets were most evident in the images at green wavelengths which penetrate the deepest into the water column and only weakly evident at optical wavelengths with shallower penetration we believe that this is the first observation of internal soliton packets determined from remotely sensed upwelled radiance we hypothesize that the lineations were produced by changes in the upwelling radiance from the interior of the water column not by changes in surface reflectance using a simulation it is demonstrated that such lineations can be produced by vertical modulation of the inherent optical properties iops during the passage of the internal soliton packet since surface manifestations are not always present this opens the potential for broadly based inventories of internal solitons in coastal waters

acoustic emission study of microfracturing during the cyclic loading of westerly granite a rectangular prism of westerly granite was deformed in a uniaxial cycling experiment acoustic emission ae activity was recorded using eight transducers in real time hypocenters of 116 events were determined using a standard least squares approach event clustering was definitely evident and could easily be assessed using a stereographic projection of hypocenters this clustering was observed at volumetric strains well below 0 03 the distribution of hypocenters changed from cycle to cycle suggestive of a spatial migration the cumulative distribution of hypocenters documents the strongly anisotropic development of dilatancy in westerly granite once the sample underwent the initial deformation and a zone of weakness was established subsequent events clustered in and about the initial zone volumetric strain differential stress acoustic emission event rate and cumulative numbers were continously measured during the experiment the cumulative number of events per cycle generally decreased with the number of cycles the majority of events occurred upon loading those that occured during unloading were few in number and not as systematically related to stress as were those for loading in general waveform quality deteriorated with increased cycling and in later cycles waveforms typically displayed low frequency components in initial onsets followed by a more typical higher frequency arrival

reconstructing benthic carbon oxidation rates using δ13c of benthic foraminifers abstract in non bioturbated organic rich marine sediments the concentration and carbon isotope gradient of total dissolved carbon dioxide co2 primarily reflects the rate of carbon oxidation and co2 diffusion within the sediment pore waters here we investigate whether the calcium carbonate secreted by benthic foraminifers that inhabit discrete depths within the sediments record the pore water 13c co2 gradient and hence can be used as proxies to reconstruct a history of carbon oxidation change the distribution and live abundance of bolivina argentea s l bolivina subadvena s l and buliminella tenuata inhabiting the dysoxic marine sediments along the california margin is similar among sites that differ in co2 gradient by up to a factor of three bolivina argentea inhabits the sediments at the sediment water interface whereas b subadvena s l is most abundant at depths of between 2 and 4 mm buliminella tenuata is most abundant at deeper depths of between 4 and 6 mm the 13c of calcite precipitated by these species matches the 13c of the pore water co2 at the depth of their maximum live abundance indicating that each species has a preferred depth for calcification the 13c difference between the species increases as the rate of carbon oxidation increases these results indicate the carbon isotopic difference between these species in fossil assemblages can be used to estimate changes in the rate of carbon oxidation

a new analytical model for internal solitons in the ocean abstract a new model for tidally generated internal solitons in the ocean is advanced based on a little known asymptotic analytical solution to the weakly nonlinear korteweg de vries equation the solution has many of the properties observed in oceanic internal solitary waves solitons it has been adapted to simulate the dynamics of stratified fluid flow driven by tidal forcing at continental shelves and sills and the adaptation describes the canonical behavior of such solitary wave trains it is shown that the solitons are positioned at the leading edge of an internal tidal bore on the shelf and that the distance between successive packets of solitons constitutes the internal tidal wavelength a future paper will apply the model to field observations from four geographical regions

oceanographic processes and morphosedimentary products along the iberian margins a new multidisciplinary approach abstract our understanding of bottom currents and associated oceanographic processes e g overflows barotropic tidal currents including intermittent processes e g vertical eddies deep sea storms horizontal vortices internal waves and tsunamis is rapidly evolving many deep water processes remain poorly understood due to limited direct observations but can generate significant depositional and erosional features on both short and long term time scales this paper represents a review work which describes for the first time these oceanographic processes and examines their potential role in the sedimentary features along the iberian continental margins this review explores the implications of the studied processes given their secondary role relative to other factors such as mass transport and turbiditic processes and highlights three major results a contourite depositional and erosional features are ubiquitous along the margins indicating that bottom currents and associated oceanographic processes control the physiography and sedimentation b the position of interfaces between major water masses and their vertical and spatial variation in time specifically appears to exert primary control in determining major morphologic changes along the slope gradient including the contourite terraces development and c contourites deposits exhibit greater variation than the established facies model suggests therefore a consistent facies model however faces substantial challenges in terms of the wide range of oceanographic processes that can influence in their development an integrated interpretation of these oceanographic processes requires an understanding of contourites seafloor features their spatial and temporal evolution and the near bottom flows that form them this approach will synthesize oceanographic data seafloor morphology sediments and seismic images to improve our knowledge of permanent and intermittent processes around iberia and evaluate their conceptual and regional role in the margin s sedimentary evolution given their complexes three dimensional and temporally variable nature integration of these processes into sedimentary oceanographic and climatological frameworks will require a multidisciplinary approach that includes geology physical oceanography paleoceanography and benthic biology

generation mechanism of internal waves by tidal flow over a sill the generation mechanism of internal waves by relatively strong tidal flow over a sill is clarified analytically special attention is directed to the role of the tidal advection effect which is examined by use of characteristics an internal wave which propagates upstream is gradually formed over the sill through the interference among infinitesimal amplitude internal waves elementary waves emanated from the sill at each instant of time in the accelerating decelerating stage of tidal flow the effective amplification of an internal wave takes place as the froude number exceeds falls below unity because during this period the internal wave slowly travels downstream upstream crossing over the sill where elementary waves are efficiently superimposed when the strength of the tidal advection effect is appropriate the internal wave formed in the accelerating stage ac wave and that formed in the decelerating stage dc wave overlap so that the resultant wave height becomes very large since the relative position of ac and dc waves varies depending on the strength of the tidal advection effect the resultant internal wave form is strongly affected by it when the tidal advection effect is strong the ac wave is carried too far downstream to interfere with the dc wave and hence the resultant wave form consists of two crests and two troughs when the tidal advection effect is moderate the optimum interference between ac and dc waves occurs and the resultant wave form consists of one crest and one trough with its horizontal scale approaching that of the sill when the tidal advection effect is weak the internal wave height becomes very small since elementary waves propagate almost freely in the tidal flow without coming close together and the resultant wave form approaches a sinusoidal wave of tidal frequency

a tracer study of mixing in the santa cruz basin a tracer release experiment to study diapycnal and isopycnal mixing was performed in santa cruz basin in 1988 1989 approximately 1450 g of sulfur hexafluoride were injected close to an isopycnal surface at 1500 m depth in may 1988 this depth is midway between the bottom of the basin at 1920 m and the sill at 1084 m the diapycnal dispersion measured during the first few months while the tracer was still mixing to the walls of the basin yielded a diapycnal eddy diffusivity of 1 0 cm2 s 1 within a factor of 1 5 this is approximately 4 times larger than the diffusivity found by ledwell and watson 1991 in the interior of santa monica basin where the buoyancy frequency was 5 times greater the tracer was well mixed to the walls 6 months after the injection and at that time the diapycnal spread of the tracer was greater near the walls than in the interior the rate of diapycnal dispersion of the tracer increased dramatically after the tracer had mixed to the walls of the basin indicating enhanced boundary mixing an effective basin wide diapycnal diffusivity of 10 cm2 s 1 would be required to support the fluxes of tracer observed a one dimensional model for tracer and heat diffusion does not simulate the results very well however probably because of the finite mixing time between the boundary region and interior and because of the complexity of the processes in the boundary region

application of a transient reduced gravity plume model to the denmark strait overflow a hydrostatic reduced gravity two dimensional primitive equation numerical model for the simulation of transient bottom arrested gravity plumes was developed by adopting an algorithm from a wadden sea model a model that simulates the wetting and drying of mud flats sand banks etc with a movable lateral boundary the vertically integrated nonlinear rotational model accounts for the dissipation of momentum due to bottom friction and for the entrainment of water mass properties from a spatially structured but stagnant ambient water body it predicts the temporal and spatial evolution of the flow field and the water mass modification within a gravity plume that descends on an arbitrary topography previous model investigations considered a laterally integrated streamtube whereas our model resolves the plume horizontally in the streamtube approach it was assumed that the plume descends in a stationary almost geostrophic balance modified only by bottom drag and entrainment the results of this model demonstrate that this balance may be disturbed whenever the plume encounters topographic disturbances which for the initial intruding phase in particular accounts for its highly transient character the model results are in good agreement with theoretical and laboratory investigations and with observations as is demonstrated by some basic test experiments an application to the overflow of dense water through the denmark strait is presented

tidal forcing of the water mass interface in the strait of messina the tidal currents of the strait of messina and their effect on the displacement of the water mass interface are discussed utilizing the historical velocity data of francesco vercelli taken from 100 anchor stations during 1922 and 1923 the data show a complex strongly tidal behavior in which speeds of 200 300 cm s are attained over the sill messina is an amphidromic point for the tides of the two main basins of the mediterranean sea and two distinct water masses flow through the strait at different stages of the tide the subsurface levantine intermediate water flowing north alternating with surface tyrrhenian water flowing south the time evolution of the interface between the two marine water layers at the semidiurnal periodicity is computed from the observed distribution of acceleration term for the baroclinic component this interface shows large vertical oscillations with amplitudes of 100 m intersecting both the surface and bottom the results are in reasonable agreement with recent satellite data and other recent field observations and numerical experiments an estimate of the mean position of the interface is made by assuming that the potential energy required to uplift the interface from the equilibrium depth of 150 m to the observed 30 m depth over the sill is derived from the time independent contribution of the nonlinear field acceleration term the results are in reasonable agreement with observations

episodes of nonlinear internal waves in the northern east china sea 1 episodes of high frequency internal waves which lasted approximately 3 hours were detected in the northern east china sea during a specific phase of the barotropic tide i e low tide at 32 n 125 e the observed internal waves influenced the whole water column the wave packets were presumably generated near the ocean shelf break approximately 200 km to the southeast of the test site during several internal wave episodes which coincided with the neap tide large amplitude solitary wave like features emerged preceding higher frequency internal waves shear instability of tidal currents is explored as a possible mechanism for sustaining or regenerating internal waves in the packets during the course of their propagation it is suggested that rotating velocity field of tidal current supports sufficient vertical shear within wave packets to cause outbreaks of k h instability these instabilities may gradually transition to more symmetric holmboe waves following the increase of the bulk richardson number

yellow sea ocean acoustic solitary wave modeling studies 1 this study is in an area south of the shandong peninsula near the region where zhou et al 1991 observed anomalous drops in acoustical intensity solitary wave generation and propagation simulations are performed using the lamb 1994 nonhydrostatic model the model simulations show that for summer conditions the existing semi diurnal tidal flow over the topographic variations formed internal bores and solitary waves for the shandong area we analyzed summer observations from synthetic aperture radar sar that tracked solitary wave trains from their surface roughness signatures the images contained seven events consisting of internal bores and solitary waves that traveled in a well defined direction for 2 5 days the origin of the trains appeared at a well defined point along a steep topographic drop the sar observations guided and tuned the model simulations by comparing spectra of observed and modeled wavelengths the tuned model yields wavelengths within factors of 2 or less of those derived from sar data wavelength and amplitude dispersion analysis showed two dispersion regimes modeled phase speeds were at the lower limit of phase speeds deduced from sar data from about 0 8 to 1 0 m s acoustical intensity calculations in the presence of solitary wave trains will be undertaken in a subsequent paper using a parabolic equation acoustical model along the path of solitary wave train propagation

anomalous chlorofluorocarbons in the southern california borderland basins 1 during the past two decades unexpectedly high concentrations of chlorofluorocarbons cfcs have been observed in the bottom waters of the southern california borderland basins scbb with relatively constant spatial distribution patterns in contrast to offshore waters in this region cfc concentrations below the oxygen minimum layer oml in the deep scbb increase with depth the uniformity of the bottom enhanced cfc signals and the near zero levels of tritium suggest that this feature is likely maintained by release of cfcs from sediments and vertical mixing and not by dumped cfc bearing materials or an intrusion of recently ventilated waters we hypothesize that cfc scavenging processes either on particulate organic matter or hydrocarbon residues from the adjacent natural seeps occur in these high productivity near surface coastal waters the subsequent release of cfcs at the bottom boundary layer during the degradation of particulate material may cause the anomalous cfc distributions in the scbb

copper isotope signatures in modern marine sediments abstract the development of metal stable isotopes as tools in paleoceanography requires a thorough understanding of their modern marine cycling to date no cu isotope data has been published for modern sediments deposited under low oxygen conditions we present data encompassing a broad spectrum of hydrographic and redox regimes including continental margin and euxinic sulphide containing settings taken together with previously published data from oxic settings these data indicate that the modern oceanic sink for cu has a surprisingly homogeneous isotopic composition of about 0 3 65cu relative to nist srm976 we suggest that this signature reflects one of two specific water column processes 1 an equilibrium isotope fractionation between soluble isotopically heavy cu complexed to strong organic ligands and an isotopically light pool sorbed to particles that deliver cu to the sediment or 2 an equilibrium isotope fractionation between the same isotopically heavy ligand bound pool and the particle reactive free cu2 species with the latter being scavenged by particulates and thereby delivered to the sediment an output flux of about 0 3 into sediments is isotopically light relative to the known inputs to the ocean at around 0 6 and the seawater value of 0 6 to 0 9 suggesting the presence of an as yet unidentified isotopically light source of cu to the oceans we hypothesize that this source may be hydrothermal or may result from the partial dissolution of continentally derived particles

a deliberate tracer experiment in santa monica basin the mixing of heat and chemical constituents across density strata in the ocean plays a major role in ocean circulation and in the response of the climate to thermal and chemical perturbations we are developing a tracer technique which in conjunction with fluid dynamical measurements promises to improve our understanding and our estimates of such diapycnal mixing in a prototype tracer experiment in santa monica basin 50km west of los angeles two tracers sulphur hexafluoride sf6 and per fluorodecalin pfd have been injected on an isopycnal surface near the centre of the basin after 50 days the tracers had mixed along the isopycnal surface to nearly every part of the basin although relatively little had penetrated to the basin walls the diapycnal spreading of the tracer distributions during this first stage of the experiment yielded an apparent eddy diffusivity of 0 33 0 08 cm2s 1 at the ambient density gradient of 4 0 0 5 10 9g cm 4

composition and origins of laminae in late quaternary and holocene sediments from the santa barbara basin late quaternary and holocene sediments from the santa barbara basin have been analyzed using back scattered electron imaging bsei techniques to identify the origins of laminae and document intra and interannual ocean climate variability over the last glacial cycle laminae observed in x ray radiography and bsei are entirely defined by variations in the relative abundance and grain size of biogenic and terrigenous components there is no evidence to suggest that bacterial mat mediation may have played a role in lamina formation the simplest lamination type comprises silt rich silt poor couplets that originate from seasonal variation in the supply of silt to the basin the second lamination type contains an additional lamina of diatom ooze to form terrigenous sediment diatomaceous triplets the thicker diatom ooze laminae commonly exhibit a vertical succession of diatom floras which represents intra annual variation in productivity the variation in thickness and assemblage of diatom ooze laminae is probably a function of the amount of diatom flux which is controlled by upwelling dri ven primary productivity in the basin laminated sediments deposited during cooler periods generally contain thicker diatom ooze laminae consistent with more vigorous regional circulation and increased upwelling

seasonal variability of alongshore geostrophic velocity off central california seasonal variability of alongshore geostrophic velocity relative to 500 dbar is examined from 23 years of hydrographic data along two sections off central california one off point sur and the other off point conception the seasonal cycles are determined by least square fits of the gappy data records to harmonics with annual and semiannual periods attention is focused on variability over the outer continental slope geostrophic flow in the upper 100 m along both sections is coherent and predominantly annual with equatorward flow from february to september and poleward flow from october to january the flow deeper than 100 m is distinctly different along the two sections the nearshore deep flow is predominantly semiannual off point conception notably different from surface flow and poleward all year with maxima in december and june this semiannual variability at depth is a prevalent feature of the california current system the nearshore deep flow off point sur is unusual in that it is predominantly annual with maximum poleward flow in december and weak equatorward flow from march to may the seasonal variations over the continental slope compare favorably with existing models of eastern boundary current systems in two respects 1 the surface flow leads the predominantly annual wind forcing in this region by about one month and 2 the deep poleward counterflow is coherent with the local poleward barotropic pressure gradient at both locations with a phase lag of approximately 2 months however contrary to the results of existing dynamical models the semiannual poleward pressure gradient and undercurrent off point conception appear to be unrelated to the wind forcing which is predominantly annual in this region these semiannual variations are highly coupled to the semiannual flow throughout the water column inside the southern california bight suggesting that they may be topographically generated

variability in two deep coastal basins santa monica and san pedro off southern california time series of midbasin hydrographic samples and of an array of moored temperature velocity sensors are used to examine subtidal to interannual scale variability in two 900 m deep basins off the southern california coast the deepest sill that allows entry into the basins is at 740 m and the two basins santa monica and san pedro are separated by a sill about 40 m high the mean flow 40 m above and 60 m below the 740 m sill depth is in the counterclockwise direction and the magnitude is 0 5 1 0 cm s 1 the data indicate that the waters at deeper levels of the basins are neither quiescent at one extreme nor are they filled with random noise at the other extreme rather at all scales examined the variability is significant and much of it is spatially coherent the amplitude of the subtidal velocity fluctuations is 4 cm s 1 almost an order of magnitude greater than that of the mean flow the amplitude of the subtidal temperature fluctuations is 0 1 c at 700 m and 0 05 c at 800 m the temperature variance is roughly a factor of 2 smaller at midbasin than on the basin perimeter this is not the case with the velocity variance which is generally greatest at midbasin and on the coastal edges of both basins much of the subtidal variability in both temperature and velocity appears to be associated with topographic waves that travel counterclockwise around the pair of basins the observed period of the waves 10 20 days is roughly consistent with that predicted by a barotropic model of free waves in an elliptical basin mysak 1985 comparison of time series of currents in the upper 200 m water column with those in the lower water column suggests that the waves are forced by the circulation in the upper water column which is directed over rather than around the basins seasonal variability was observed in both temperature and velocity fields as deep as 800 m i e below the depth of the deepest sill along the perimeters of both basins and at midbasin in santa monica but not in san pedro temperature increases and salinity and density decrease from spring to fall consistent with the seasonal development of the poleward flowing california countercurrent in the upper water column the seasonal cycle of water properties has significant spatial variability over the basins the amplitude is a factor of 2 greater on the seaward side of santa monica basin than at midbasin and on its coastal edges and on the edges of san pedro basin the variance of the subtidal velocity and temperature fields also exhibit a seasonal signal maximum variance occurs during fall minimum variance occurs during spring interannual variability dominates the 4 year time series of water properties of the near bottom water in each basin and differs somewhat between the two basins the interannual variability is dominated by events associated with renewal of basin bottom water two such events were identified a minor one in 1987 and a major one in 1988 each beginning in may of that year in both cases the actual renewal occurs in less than a month and the most rapid return to near normal conditions occurs over a period of about 3 5 months

study of the generation and propagation of internal waves in the strait of gibraltar using a numerical model and synthetic aperture radar images of the european ers 1 satellite a weakly nonhydrostatic two layer numerical model based on the boussinesq equations is presented which is capable of describing among others the generation and propagation of nonlinear weakly dispersive internal waves in the strait of gibraltar the model depends on one space coordinate only but it retains several features of a fully three dimensional model by including a realistic bottom profile a variable channel width and a trapezoidal channel cross section the nonlinear primitive boussinesq equations include horizontal diffusion bottom friction and friction between the two water layers the model is driven by a height difference of the mean interface depth between the atlantic and the mediterranean boundaries and by semidiurnal tidal oscillations of the barotropic transport the model presented in this paper describes 1 the mean and tidal flow in the strait of gibraltar 2 the variation of the depth of the interface during a tidal cycle 3 the generation of strong depressions of the interface at the western sides of the spartel sill and the camarinal sill 4 the generation of strong eastward propagating internal bores and 5 their disintegration into trains of internal solitary waves the surface convergence patterns associated with depressions of the interface at the camarinal sill internal bores and internal solitary waves are calculated and compared with roughness patterns visible on synthetic aperture radar sar images of the first european remote sensing satellite ers 1 in total 155 ers 1 sar scenes from 94 satellite overflights over the strait of gibraltar which were acquired in the period from january 1992 to march 1995 have been analyzed it is shown that the proposed model is capable of explaining the observed temporal and spatial evolution of surface roughness patterns associated with eastward propagating internal waves inside the strait of gibraltar as well as the observed east west asymmetry of the internal wave field

resolving varve and radiocarbon chronology differences during the last 2000 years in the santa barbara basin sedimentary record california abstract santa barbara basin sbb is well known for producing high quality paleoclimate reconstructions but the validity of correlations between the basin and other regions rests upon age model accuracy yet the two independent and well established chronologies based on varve counting and radiocarbon dating do not consistently agree during the last two millennia here the validity of age model assumptions is tested including whether 1 the regional reservoir age of surface waters was invariably 641 119 years through time and or 2 sbb laminae couplets are consistently annual varves and counted with sufficient precision this high resolution 14 c study of sbb sediments compares 49 mixed planktonic foraminiferal carbonate and 20 terrestrial organic carbon 14 c dates to the varve chronology to extend the high resolution paleoclimate chronology of the basin back 2000 years evidence indicates that regional reservoir ages do not remain constant through time with r i e regional reservoir age minus variations in the global mixed layer ocean reservoir age fluctuating between 80 and 350 years second there is a consistent r 2 0 96 undercounting of the varves between 150 and 1700 ad based on a new varying r 14 c chronology indicating that some laminae couplets may not be annual loss of varves may occur when low riverine input and infrequent winter storm activity during drought intervals fail to supply a siliciclastic layer

modeling of hydraulically controlled exchange flow in the bosphorus strait abstract recent hydrographic observations obtained in the bosphorus strait illustrate several features of the flow that may be related with the internal hydraulics a two layer numerical model indicates that the two way exchange flow may indeed be subject to a series of internal hydraulic adjustments along the strait due to morphological features such as sills a contraction and abrupt expansion of the width of the strait the model identifies three distinct regions of the supercritical flow the lower layer flow of the marmara sea origin is directed to the north towards the black sea in a progressively thinning layer and is controlled by the sill located near the black sea entrance of the strait the upper layer water of the black sea origin flows in the opposite direction and is controlled upon reaching the constricted region located about 10 12 km away from the marmara end of the strait the upper layer flow is then matched to the subsequent subcritical conditions by undergoing an internal hydraulic ju

the flux of iron and iron isotopes from san pedro basin sediments iron is an important nutrient in the ocean but the different sources and sinks of iron are not well constrained here we use measurements of fe concentration and fe stable isotope ratios to evaluate the importance of reducing continental margins as a source of fe to the open ocean dissolved iron concentration fe and iron stable isotope ratios 56 fe were measured in the san pedro and santa barbara basins dissolved 56 fe ranges from 1 82 to 0 00 in the san pedro basin and from 3 45 to 0 29 in the santa barbara basin and in both basins the lowest 56 fe values and highest fe concentrations are found at the bottom of the basin reflecting the input of isotopically light fe from reducing sediment porewaters in the san pedro basin we are also able to fingerprint an advective source of fe from shallow continental shelves next to the basin and the atmospheric deposition of fe into surface waters a one dimensional model of the fe isotope cycle has been constructed for the deep silled san pedro basin by fitting model output to data values of several important iron cycle parameters are predicted including a flux of fe from sediment porewaters into the water column of 0 32 1 14 mol m 2 d 1 a first order dissolved fe precipitation rate constant of 0 0018 0 0053 d 1 a flux 56fe of 2 4 and an isotope effect for fe precipitation of 56 fe particulate dissolved 0 8 applying our model predicted fe cycle parameters to the global ocean suggests that continental margins contribute 4 12 of world ocean dissolved fe and make the ocean s fe lighter by 0 08 to 0 26 the dramatically negative 56 fe signature seen in the water column of the san pedro and santa barbara basins demonstrate the utility of fe isotopes as a tracer for continental margin fe input from reducing sediments to the oceans while the isotopic fractionation observed during loss of fe from the dissolved phase suggests that this signature will be modified by subsequent reactions our modeling provides an initial framework for testing how these signals are transmitted into the open ocean

the role of internal waves in the late quaternary evolution of the israeli continental slope abstract internal waves are widely present in world s oceans propagating in stratified ocean layers such as the seasonal pycnocline at continental shelves and slopes breaking of internal waves may create turbulence of sufficient energy to erode and transport sediments in this study we investigate the late pleistocene to recent impact of internal waves on the morphology of the israeli mediterranean continental slope based on mooring data we show that the internal wave spectrum on the upper slope contains significant energy at near inertial and semidiurnal tidal frequencies sediment subbottom profiler data show two fields of nearly contour parallel sediment waves located in water depths of 80 m 130 m and 190 m 350 m respectively a zone of flat seafloor morphology and remarkably constant slope inclination of 1 0 1 2 separates both sediment wave fields the entire stretch of seafloor between 80 m and 350 m corresponds to depths of major ocean density stratification supporting the propagation of internal waves in addition this area is critically inclined with respect to semidiurnal internal tides and supercritically inclined with respect to near inertial waves two scenarios previously related to internal wave breaking we propose that breaking internal waves control the inclination of the israeli continental slope and contribute to sediment starvation within the zone of flat seafloor morphology the formation of sediment waves is attributed to high frequency trailing internal waves of similar wavelengths as sediment waves observed within a seismic image of the water column we correlate subbottom profiler data to a radiocarbon dated sediment core no sediment waves formed from 16 cal ka 8 cal ka indicating that the seafloor impact of internal waves ceased during a time of rapid sea level rise and fresh water input in the eastern mediterranean realm the end of this period coincides with the formation of sapropel s1

summertime hydrographic features in the southeastern hwanghae abstract ctd casts in the southeastern hwanghae yellow sea were made in august 1983 and 1984 to describe the spatial structure of the summertime hydrographic features cold coastal water appeared around the southwestern coast of korea which was formed by strong tidal stirring tidal mixing in the study area seems to have been enhanced by the presence of many small islands in the deeper region beyond the tidal front stratification became much stronger and the bottom layer below seasonal thermocline was occupied mostly by the hwanghae cold water characterized by a temperature lower than 10 c and salinity of 32 5 33 0 the northeastward extension of the changjiang diluted water was shown by a tongue like plume of relatively warm fresh water confined to the thin surface layer 10 m thick there was no evidence for the hwanghae warm current carrying high salinity water into the eastern hwanghae along the korean coast the warm current was found to flow in a narrow band close to the west and north coast of chejudo cheju island and then to pass eastward through the cheju strait thus the eastern part of the cyclonic circulation in the surface layer cannot be considered to be a northward continuation of the hwanghae warm current the local salinity maximum in the lower layer off kunsan and the higher salinity on the west side of the central trough than on the east side would imply a northward flow on the west flank of the trough to compensate for the southward intrusion of the hwanghae cold water from which an anticyclonic circulation could be expected in the lower layer

productivity and organic carbon rain to the california margin seafloor modern and paleoceanographic perspectives 1 we have developed a proxy measurement for the determination of organic carbon corg oxidation rates cox on the seafloor utilizing the 13c values of two benthic foraminifera bolivina argentea a near surface dwelling species and buliminella tenuata an infaunal species the 13c isotopic composition of these tests preserve a record of the 13co2 pore water gradient which is directly related to cox on the seafloor of santa monica basin cox has fluctuated between 0 6 and 2 5 mmolc m 2 d 1 and generally increased from 1600 to 1980 ad between 1920 and 1970 cox increased from 1 to 2 mmolc m 2 d 1 and then decreased into the 1980s by adding cox to a high resolution record of corg burial rate we have derived the pattern of corg rain to the seafloor which fluctuated between 2 9 and 3 8 mmolc m 2 d 1 over the last 80 years the ratio of corg rain at 900 m to primary productivity is constant at 10 1 over a 40 change in mean annual primary productivity sediments in santa monica basin accumulate 50 of the corg raining to the seafloor however there is a trend toward lower burial efficiency with higher productivity and rain rate

sensitivity of the phosphate cadmium carbon isotope relation in the ocean to cadmium removal by suboxic sediments reconstructions of past deep ocean nutrient concentrations rely largely on the carbon isotopic composition and cadmium content of shells of benthic foraminifera when comparing records of these two paleonutrient tracers a relation similar to the phosphate cadmium carbon isotope relation in the water column today is generally assumed we present new water column sediment and pore water data from the california continental margin which demonstrate that cd accumulation is enhanced in suboxic sediments these results suggest that the oceanic cd inventory is sensitive to changes in the areal extent and redox intensity of suboxic sediments and thus that the phosphate cadmium relation in the ocean could have been different in the past the magnitude of this effect and its evolution through time is presently hard to quantify because the oceanic cd budget is poorly constrained

evolution of nonlinear internal waves in the east and south china seas synthetic aperture radar sar images from ers i have been used to study the characteristics of internal waves northeast and south of taiwan in the east china sea and east of hainan island in the south china sea rank ordered packets of internal solitons propagating shoreward from the edge of the continental shelf were observed in the sar images on the basis of the assumption of a semidiurnal tidal origin the wave speed can be estimated and is consistent with the internal wave theory by using the sar images and hydrographic data internal waves of elevation have been identified in shallow water by a thicker mixed layer as compared with the bottom layer on the continental shelf the generation mechanism includes the influences of the tide and the kuroshio intrusion across the continental shelf for the formations of elevation internal waves the effects of water depth on the evolution of solitons and wave packets are modeled by the nonlinear kortweg devries kdv type equation and linked to satellite image observations the numerical calculations of internal wave evolution on the continental shelf have been performed and compared with the sar observations for a case of depression waves in deep water the solitons first disintegrate into dispersive wave trains and then evolve to a packet of elevation waves in the shallow water area after they pass through a turning point of approximately equal layer depths that has been observed in the sar image and simulated by the numerical model the importance of the dissipation effect in the coastal area is also discussed and demonstrated

the sulu sea internal soliton experiment abstract we present the results of a comprehensive study of large amplitude internal solitons generated in the sulu sea in the philippines by intense tidal flow over a sharp bathymetric feature surface signatures of these waves have been observed in images from the dmsp landsat and nimbus 7 satellites and the space shuttle sir a synthetic aperture radar a two week experiment was conducted in the sulu sea in may 1980 from r v oceanograher during which a three mooring phased array of current meters and thermistors was implanted near the wave source and at 82 km and 200 km from the source seventeen soliton packets were observed whose properties underwent significant change as they propagated across the sea vertical profiles of density temperature and acoustic backscatter as well as radar and photographic surface signatures were obtained from the ship data from satellites moorings and the ship give unprecedented information on the spatial and temporal characteristics of solitary waves which ha

evidence for the influence of atlantic ionian stream fluctuations on the tidally induced internal dynamics in the strait of messina abstract on 24 and 25 october 1995 high resolution oceanographic measurements were carried out in the strait of messina by using a towed conductivity temperature depth chain and a vessel mounted acoustic doppler current profiler during the period of investigation the surface water of the tyrrhenian sea north of the strait sill was heavier than the surface water of the ionian sea south of the strait sill as a consequence during northward tidal flow surface water of the ionian sea spread as a surface jet into the tyrrhenian sea whereas during southward tidal flow heavier surface water of the tyrrhenian sea spread after having sunk to a depth of about 100 m as a subsurface jet into the ionian sea both jets had the form of an internal bore which finally developed into trains of internal solitary waves whose amplitudes were larger north than south of the strait sill these measurements represent a detailed picture of the tidally induced internal dynamics in the strait of messina during the period of i