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Impacts On The Global Ocean Circulation From Vertical Mixing And A Collapsing Ice Sheet, J. A. M. Green, G. R. Bigg Jan 2011

Impacts On The Global Ocean Circulation From Vertical Mixing And A Collapsing Ice Sheet, J. A. M. Green, G. R. Bigg

Journal of Marine Research

The current view of the global meridional overturning circulation (MOC) is one where the Atlantic is a dominant basin for deep water formation, but with the potential for bipolar seesaws between the Southern Ocean and the North Atlantic during catastrophic freshening events in either hemisphere. Here we investigate the stability of this paradigm through the response of an intermediate complexity coupled climate model, set in an oceanically more sensitive glacial configuration, to variation in the vertical mixing rates. It is found that the convective basin is set by the upper ocean diffusivity, with higher such diffusivities leading to a Pacific-dominated …

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The Decadal Mean Ocean Circulation And Sverdrup Balance, Carl Wunsch Jan 2011

The Decadal Mean Ocean Circulation And Sverdrup Balance, Carl Wunsch

Journal of Marine Research

Elementary Sverdrup balance is tested in the context of the time-average of a 16-year duration time-varying ocean circulation estimate employing the great majority of global-scale data available between 1992 and 2007. The time-average circulation exhibits all of the conventional major features as depicted both through its absolute surface topography and vertically integrated transport stream function. Important small-scale features of the time average only become apparent, however, in the time-average vertical velocity, whether near the surface or in the abyss. In testing Sverdrup balance, the requirement is made that there should be a mid-water column depth where the magnitude of the …

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Ocean Stratification Under Oscillatory Surface Buoyancy Forcing, Ross W. Griffiths, Nicola Maher, Graham O. Hughes Jan 2011

Ocean Stratification Under Oscillatory Surface Buoyancy Forcing, Ross W. Griffiths, Nicola Maher, Graham O. Hughes

Journal of Marine Research

Laboratory experiments with overturning circulation driven by oscillatory heat fluxes at one boundary are used to explore implications, for the ocean stratification, of a cyclic fluctuation in sea-surface buoyancy forcing. Fluctuations having a range of periods spanning the timescale for global recycling of the ocean volume through the thermocline are considered, with emphasis on inter-hemispheric 'see-saw' oscillations. Episodic sinking of dense water in the oceans is represented by convection in a channel with a base that is cooled over a central region and subjected to oscillatory heating near both ends, while providing a constant total heat input. For this simplified …

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Submesoscale Generation By Boundaries, W. K. Dewar, Pavel Berloff, Andrew Mcc. Hogg Jan 2011

Submesoscale Generation By Boundaries, W. K. Dewar, Pavel Berloff, Andrew Mcc. Hogg

Journal of Marine Research

An important dynamical question involves how oceanic balanced flows lose energy. Recent numerical and analytical studies suggest topography catalyzes energy exchanges between balanced flows and a variety of unbalanced phenomena, which presumably leads to dissipation. We here develop a general theory of inviscid balanced flow interactions with walls that predicts submesoscale and unbalanced flow generation. Comparison with primitive equation-based numerical experiments supports the basic tenets of the theory.

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A Pedagogical Example Of Eulerian And Lagrangian Flows Induced By Rossby Wave Rectification In An Ocean Basin, John Marshall Jan 2011

A Pedagogical Example Of Eulerian And Lagrangian Flows Induced By Rossby Wave Rectification In An Ocean Basin, John Marshall

Journal of Marine Research

The time-mean flow of eddying wind-driven gyres is used as a tutorial example of the relationship between Eulerian and Lagrangian mean flow. The Eulerian mean in the far field of the baroclinically unstable jet is shown to be well represented as the rectified flow of Rossby basin modes. The Stokes drift of particles released in the wave field all but cancel out the Eulerian mean, resulting in vanishingly small Lagrangian mean flow. By reformulating the interaction between eddies and mean flow in terms of, so-called, residual mean velocities and residual eddy fluxes, it becomes clear that only the component of …

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Defining The Spicity, Rui Xin Huang Jan 2011

Defining The Spicity, Rui Xin Huang

Journal of Marine Research

Spicity is defined as a thermodynamic variable whose isopleths are 'perpendicular” to those of density in the (T, S) diagram. A new set of Matlab codes are defined based on the following criteria: First, the isopleths of spicity should be orthogonal to those of density. Second, the ocean is vertically separated into many pressure levels, and the zero point of spicity is set for the water mass with the mean salinity and temperature at each pressure level. This new definition of spicity can provide more accurate information of the water mass properties for the study of thermohaline perturbations.

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Penetration Of A Salinity Front Into A Rotating Basin: Laboratory Experiments And A Simple Theory, O. Marchal, J. A. Whitehead, A. Jensen Jan 2011

Penetration Of A Salinity Front Into A Rotating Basin: Laboratory Experiments And A Simple Theory, O. Marchal, J. A. Whitehead, A. Jensen

Journal of Marine Research

Freshwater is released along a wall of a basin containing salt water and rotating anticlockwise. The freshwater source is located near the surface between the center of the cylindrical basin and a corner along the wall. Experiments are performed with different discharge rates and the same rotation rate. The freshwater initially forms a bulge near the source, and then a buoyant gravity current bends to the right and flows along the wall toward the periphery of the basin. Separation of the current at the corner is never observed. The salinity front along the wall moves persistently away from the wall …

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Salt Flux In A Laboratory Model Estuary, R. Krishnamurti, T. N. Krishnamurti Jan 2011

Salt Flux In A Laboratory Model Estuary, R. Krishnamurti, T. N. Krishnamurti

Journal of Marine Research

Motivated by recent field observations, a laboratory model estuary experiment was conducted for the study of its flow and stratification. We find that a small inflow of cold freshwater, on top of warm saline water can lead to a large counter flow in the lower layer. This counter flow is part of a large aspect ratio convective cell driven by the horizontally varying diffusive cooling from above. Particle Image Velocimetry (PIV) measurement of the Reynolds stresses associated with transient tilted plumes embedded in this convective cell show that the viscous dissipation of the large-scale cellular flow is largely balanced by …

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Thermohaline Convection At Density Ratios Below One: A New Regime For Salt Fingers, Raymond W. Schmitt Jan 2011

Thermohaline Convection At Density Ratios Below One: A New Regime For Salt Fingers, Raymond W. Schmitt

Journal of Marine Research

New experimental results on haline convection show a surprising preference for narrow fingers over large-scale convection when even a small stabilizing temperature gradient is present (Hage and Tilgner, 2010). This regime has heat/salt density ratios below one, a parameter range that has not been explored in traditional salt finger theory. Here the properties of the exact (long finger) solutions of Schmitt (1979, 1983) are explored at low density ratios. It is found that narrow finger solutions are indeed obtained and remain the fastest growing in some circumstances, though the selective advantage of the “Stern scale” can disappear as the density …

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Mean-Flow And Topographic Control On Surface Eddy-Mixing In The Southern Ocean, J. B. Sallée, K. Speer, S. R. Rintoul Jan 2011

Mean-Flow And Topographic Control On Surface Eddy-Mixing In The Southern Ocean, J. B. Sallée, K. Speer, S. R. Rintoul

Journal of Marine Research

Surface cross-stream eddy diffusion in the Southern Ocean is estimated by monitoring dispersion of particles numerically advected with observed satellite altimetry velocity fields. To gain statistical significance and accuracy in the resolution of the jets, more than 1,5 million particles are released every 6 months over 16 years and advected for one year. Results are analyzed in a dynamic height coordinate system. Cross-stream eddy diffusion is highly inhomogenous. Diffusivity is larger on the equatorward flank of the Antarctic Circumpolar Current (ACC) along eddy stagnation bands, where eddy displacement speed approaches zero. Along such bands, diffusivities reach typical values of 3500 …

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Foam Patches Behind Spilling Breakers, J. Stewart Turner, Ian L. Turner Jan 2011

Foam Patches Behind Spilling Breakers, J. Stewart Turner, Ian L. Turner

Journal of Marine Research

Previous theoretical and laboratory studies of spilling breakers on a beach are described and discussed, paying particular attention to models that emphasize the importance of air bubbles in the spill. At first such a spill forms at a sharp crest, and accelerates down the front of the wave as it propagates towards the shore. Then the crest becomes more rounded and this allows part of the aerated water to flow backwards over or under the crest, leaving a foam patch behind. Laboratory experiments in channels of constant width have documented many features of these flows. But recent new observations on …

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South Atlantic Overturning Circulation At 24°S, Harry L. Bryden, Brian A. King, Gerard D. Mccarthy Jan 2011

South Atlantic Overturning Circulation At 24°S, Harry L. Bryden, Brian A. King, Gerard D. Mccarthy

Journal of Marine Research

To estimate the size of the meridional overturning circulation and the meridional heat and freshwater transports in the South Atlantic, we made a new transatlantic hydrographic section along 24°S in 2009 and we compare the resulting transports with those estimated for a historical section made in 1983. For the two sections, the overturning is estimated to be 21.5 Sv (2009) or 16.5 Sv (1983), the heat transport is northward at 0.7 PW (2009) or 0.4 PW (1983), and the freshwater transport is small but northward at 0.04 Sv (2009) or 0.17 Sv (1983). The differences in transports are primarily due …

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Role Of The Southern Ocean In Setting The Atlantic Stratification And Meridional Overturning Circulation, Igor Kamenkovich, Timour Radko Jan 2011

Role Of The Southern Ocean In Setting The Atlantic Stratification And Meridional Overturning Circulation, Igor Kamenkovich, Timour Radko

Journal of Marine Research

This study examines the importance of the Southern Ocean (SO) stratification in determining the upper cell of the Atlantic meridional overturning circulation (MOC) and stratification. Main results are based on a suite of idealized numerical simulations of the Atlantic with the prescribed density structure at the Atlantic southern boundary, intended to explore the importance of various factors. The results demonstrate that the density distribution at the SO-Atlantic boundary is the key factor controlling the Atlantic stratification and MOC, whereas the main importance of the Ekman and eddy (parameterized) exchanges is in setting the SO stratification. Among all aspects of the …

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Ellipsoidal Vortex In A Nonuniform Flow: Dynamics And Chaotic Advections, V. V. Zhmur, E. A. Ryzhov, K. V. Koshel Jan 2011

Ellipsoidal Vortex In A Nonuniform Flow: Dynamics And Chaotic Advections, V. V. Zhmur, E. A. Ryzhov, K. V. Koshel

Journal of Marine Research

Quasi-geostrophic dynamics of an ellipsoidal vortex embedded in a nonuniform flow is studied in the approximation of the infinitely deep rotating ocean with a constant buoyancy frequency. The vortex core is an ellipsoid with a constant vorticity different from the background vorticity value. The core is shown to move along with the flow and to deform under the effect of it. Regimes of the core's behavior depend on the flow characteristics and the initial values of the vortex parameters (the shape and the orientation relative to the flow). These regimes are (i) rotation (along with the eccentricity oscillation), (ii) oscillation …

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Secondary Toroidal Vortices Above Seamounts, Valery N. Zyryanov 0 Jan 2011

Secondary Toroidal Vortices Above Seamounts, Valery N. Zyryanov 0

Journal of Marine Research

The classical Taylor-Couette flow appears in a homogeneous fluid between two coaxial cylinders rotating with different angular velocities. The stability loss by a Taylor-Couette flow leads to a bifurcation and generation of Taylor toroidal vortices. In this study we consider an analog to this effect in the case of seamounts in a homogeneous ocean on a f-plane. A seamount is approximated by two coaxial cylinders with heights h1, h2 standing one upon the other, the lower cylinder having a larger diameter. Taylor-Couette flow forms in a circular area above the ledge as follows from the differential …

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Topographic Rectification In A Stratified Ocean, K. H. Brink Jan 2011

Topographic Rectification In A Stratified Ocean, K. H. Brink

Journal of Marine Research

Mean flow generation by oscillating currents is considered in an idealized stratified ocean with a corrugated shelf-slope topography. Numerical model results for near-bottom mean along-isobath flow show a general parameter dependence similar to that found with no stratification (Brink, 2010). Stratification, however, makes the interior rectified flow depth-dependent, and usually bottom-intensified. Scalings for both the mean flow and its vertical dependence are developed and evaluated. Two crude comparisons against observed mean oceanic flows suggest that the present results may parameterize the mean flow magnitude correctly.

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Rossby Wormholes, David P. Marshall Jan 2011

Rossby Wormholes, David P. Marshall

Journal of Marine Research

The influence of bottom topography on the westward propagation of long, baroclinic Rossby waves is studied analytically in a two-layer ocean model. In the limit of a thin upper layer, scaling analysis suggests that the waves should be relatively insensitive to variable bottom topography however, this insensitivity can break down in regions of closed f/H contours, where f is the Coriolis parameter and H the ocean depth. An integral constraint is derived in the planetary-geostrophic limit, showing that the net radiative flux of upper layer thickness anomalies into a closed f/H contour, at its eastern margin, is balanced by an …

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Fluid Mixing By Swimming Organisms In The Low-Reynolds-Number Limit, Eric Kunze Jan 2011

Fluid Mixing By Swimming Organisms In The Low-Reynolds-Number Limit, Eric Kunze

Journal of Marine Research

Recent publications in the fluid physics literature have suggested that low-Reynolds-number swimming organisms might contribute significantly to ocean mixing. These papers have focussed on the mass transport due to fluid capture and disturbance by settling or swimming particles based on classical fluid mechanics flows but have neglected the role of molecular property diffusion. Scale-analysis of the property conservation equation finds that, while properties with low molecular diffusivities can have enhanced mixing for typical volume fractions in aggregations of migrating zooplankton, this mixing is still well below that due to internal-wave breaking so unlikely to be important in the ocean.

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The Nonlinear Downstream Development Of Baroclinic Instability, Joseph Pedlosky Jan 2011

The Nonlinear Downstream Development Of Baroclinic Instability, Joseph Pedlosky

Journal of Marine Research

The downstream development in both space and time of baroclinic instability is studied in a nonlinear channel model on the f-plane. The model allows the development of the instability to be expressed on space and time scales that are long compared to the growth rates and wavelengths of the most unstable wave. The unstable system is forced by time-varying boundary conditions at the origin of the channel and so serves as a conceptual model for the development of fluctuations in currents like the Gulf Stream and Kuroshio downstream of their separation points from their respective western boundaries. The theory …

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Meddy, Spiral Arms, And Mixing Mechanisms Viewed By Seismic Imaging In The Tagus Abyssal Plain (Sw Iberia), Haibin Song, Luis Menezes Pinheiro, Barry Ruddick, Francisco Curado Teixeira Jan 2011

Meddy, Spiral Arms, And Mixing Mechanisms Viewed By Seismic Imaging In The Tagus Abyssal Plain (Sw Iberia), Haibin Song, Luis Menezes Pinheiro, Barry Ruddick, Francisco Curado Teixeira

Journal of Marine Research

Seismic imaging of the water column is used to investigate the relative roles of thermohaline intrusive mixing and stirring (straining and shearing) by mesoscale eddies in the NE Atlantic, in and around a Meddy, and in waters between the Meddy and the coast of Portugal. The images show that mixing is virtually absent within the core but anomalously high in the top, bottom, and surrounding frontal region, as previously found by conventional means. In the immediate periphery of the Meddy, bands of water with numerous reflectors consistent with thermohaline intrusions, and with anomalously high mixing rate can be seen. We …

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Anomalous Diffraction Approach To The Visible Spectra Of Absorption By Marine Particles With Power-Law Size Distributions, Maciej Matciak, Bożena Wojtasiewicz Jan 2011

Anomalous Diffraction Approach To The Visible Spectra Of Absorption By Marine Particles With Power-Law Size Distributions, Maciej Matciak, Bożena Wojtasiewicz

Journal of Marine Research

The spectral shape of the light absorption by marine particles with power-law size distribution was analyzed. The anomalous diffraction approximation (ADA) in its conventional form for optically “soft” homogenous particles was used to model the absorption cross section. Based on this theory, particular formulas describing the spectral shape of absorption of an assemblage of particles were derived. Exemplary calculations were performed for particles of selected shapes (spheres, thin cylinders and disks). The results suggest that relative absorption spectra of marine particles in many cases can be approximated by a simple formula, i.e. a power function of the ratio of their …

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Linear Instability Of Uniform Shear Zonal Currents On The Β-Plane, Nathan Paldor, Yona Dvorkin, Doron Nof Jan 2011

Linear Instability Of Uniform Shear Zonal Currents On The Β-Plane, Nathan Paldor, Yona Dvorkin, Doron Nof

Journal of Marine Research

A unified formulation of the instability of a mean zonal flow with uniform shear is proposed, which includes both the coupled density front and the coastal current. The unified formulation shows that the previously found instability of the coupled density front on the f-plane has natural extension to coastal currents, where the instability exists provided that the net transport of the current is sufficiently small. This extension of the coupled front instability to coastal currents implies that the instability originates from the interaction between Inertia-Gravity waves and a vorticity edge wave and not from the interaction of the two …

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Primary And Secondary Intrusions In Double-Diffusively Stable Vertical Gradients, Julian A. Simeonov Jan 2011

Primary And Secondary Intrusions In Double-Diffusively Stable Vertical Gradients, Julian A. Simeonov

Journal of Marine Research

The purpose of this paper is to show that molecularly-driven double-diffusive intrusions can produce significant lateral and vertical double-diffusive mixing even when the initial temperature and salinity are both stably stratified in the vertical. Assuming uniform density-compensated horizontal gradients and periodic disturbances, three-dimensional direct numerical simulations (DNS) for the fastest growing intrusion show that the latter equilibrates due to the generation of salt fingers which reduce the driving buoyancy pressure gradient. The DNS also provided statistical data for a new parameterization of the salt finger fluxes which includes the effects of shear and variable vertical gradients. This parameterization makes it …

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Effects Of Surface Quasi-Geostrophic Turbulence On Phytoplankton Competition And Coexistence, Coralie Perruche, Pascal Rivière, Guillaume Lapeyre, Xavier Carton, Philippe Pondaven Jan 2011

Effects Of Surface Quasi-Geostrophic Turbulence On Phytoplankton Competition And Coexistence, Coralie Perruche, Pascal Rivière, Guillaume Lapeyre, Xavier Carton, Philippe Pondaven

Journal of Marine Research

This paper aims at studying numerically the competition between two mutually exclusive phytoplankton species in a fully-turbulent field consisting of interacting mesoscale and submesoscale structures. A simple NPPZD ecosystem model is embedded in a Surface Quasi-Geostrophic model which is able to reproduce frontogenesis and the associated nutrient vertical pump. The two simulated phytoplankton species differ by their size and their affinity for nutrients. In this study, we rationalize the role played by eddies and filaments in the distribution of the two phytoplankton species. We show that the SQG dynamics are responsible for the coexistence of the two phytoplankton species on …

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Modeling The Evolution Of Intrathermocline Lenses In The Atlantic Ocean, B. N. Filyushkin, M. A. Sokolovskiy Jan 2011

Modeling The Evolution Of Intrathermocline Lenses In The Atlantic Ocean, B. N. Filyushkin, M. A. Sokolovskiy

Journal of Marine Research

The existence of a tongue of Mediterranean Water (MW) at the depths of 500–1500 m is a characteristic feature of the hydrological regime in the northeastern part of the Atlantic Ocean. Anticyclonic eddies filled with MW (meddies or lenses) are observed in this region. They are identified via their high temperature and salinity anomalies, which compensate in density, yielding nearly homogeneous meddy cores. The analysis of historical observations has showed that approximately 100 lenses can exist simultaneously in this part of the ocean. High concentration of large water volumes (>4000 km3 each) can be found both in the …

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Modeling Of The M2 Surface And Internal Tides And Their Seasonal Variability In The Arctic Ocean: Dynamics, Energetics And Tidally Induced Diapycnal Diffusion, B. A. Kagan, E. V. Sofina, A. A. Timofeev Jan 2011

Modeling Of The M2 Surface And Internal Tides And Their Seasonal Variability In The Arctic Ocean: Dynamics, Energetics And Tidally Induced Diapycnal Diffusion, B. A. Kagan, E. V. Sofina, A. A. Timofeev

Journal of Marine Research

Modeling results for the M2 surface and internal tides in the Arctic Ocean (AO) are presented. These incorporate the data on tidal dynamics and energetics and tidally induced diapycnal diffusion. A modified version of the 3D finite-element hydrostatic model QUODDY-4 is used as a basis for modeling. It is shown that the predicted surface tide differs slightly from that obtained from other tidal models, whereas the internal tidal waves (ITW) are less than those in oceans of moderate and low latitudes. It also appears that ITW themselves belong to the family of trapped waves. This finding, together with the …

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On Trend Analysis In Climatic Time Series, With Application To Surface Temperature, Victor Privalsky, Marina Fortus, Vladimir Komchatov, Eugene Borisov Jan 2011

On Trend Analysis In Climatic Time Series, With Application To Surface Temperature, Victor Privalsky, Marina Fortus, Vladimir Komchatov, Eugene Borisov

Journal of Marine Research

The deletion of a trend as an initial step in the analysis of climatic time series may result in the elimination of low-frequency components which constitute an integral part of climatic variability. An example is given here showing that linear trend deletion from the time series of the World Ocean annual sea-surface temperature (1850–2009) reduces the low-frequency (from 0.02 year–1 to 0.001 year–1) part of the time series spectrum by ∼40% to 80% thus severely distorting the spectrum of climate. As an additional result, it is shown that the current warming can be explained in full within …

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The Arrested Agulhas Retroflection, Doron Nof, Volodymyr Zharkov, Joseph Ortiz, Nathan Paldor, Wilton Arruda, Eric Chassignet Jan 2011

The Arrested Agulhas Retroflection, Doron Nof, Volodymyr Zharkov, Joseph Ortiz, Nathan Paldor, Wilton Arruda, Eric Chassignet

Journal of Marine Research

Paleoceanographic proxy data indicate that the Agulhas leakage into the South Atlantic was dramatically reduced during glacial times. In our former papers, we suggested that this was due to a northward shift of the zero wind stress curl that, in turn, forced the retroflection to occur farther north, where the slant of the coastline relative to the north is steep. In the present paper, we propose that strong westerlies (0.4 Pa, implying a wind speed of ∼12 m s–1 at zero degrees centigrade), which were supposedly common during glaciations, can also arrest the leakage. This arrest occurred because the …

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Variational Assimilation Of Glider Data In Monterey Bay, Chudong Pan, Max Yaremchuk, Dmitri Nechaev, Hans Ngodock Jan 2011

Variational Assimilation Of Glider Data In Monterey Bay, Chudong Pan, Max Yaremchuk, Dmitri Nechaev, Hans Ngodock

Journal of Marine Research

Temperature and salinity profiles observed by gliders in the Monterey Bay in August 2003 are assimilated into NCOM model in the framework of a 3dVar scheme with a hybrid background error covariance (BEC) representation. The model performance is validated against independent mooring observations for the assimilation runs with 1-hour analysis cycle. In the first experiment the background error statistics was estimated using the ensemble of model states spanning the entire observation period, whereas in the second experiment the BEC information was acquired by averaging over the 3day floating temporal window (FTW) centered at the analysis time. It is found that …

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A Tribute To Melvin E. Stern (1929–2010), George Veronis Jan 2011

A Tribute To Melvin E. Stern (1929–2010), George Veronis

Journal of Marine Research

Melvin Stern was a brilliant theoretician who introduced a number of innovative ideas in oceanography. These include his (a) penetrating introduction of double diffusive processes, (b) introduction of MODONS, the important, small scale, coherent features in the ocean, (c) incisive studies of rotating hydraulics, (d) investigation into bores, jumps and boundary flows, (e) analyses of the role of vortices in ocean dynamics, and (f) frequent contributions to instabilities in the ocean. He tended to think very intuitively, not unlike Henry Stommel. When he introduced a new idea, he accompanied it with a very thorough analysis. Generally speaking, he communicated most …

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