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Eastward Surface Jets In The Central Equatorial Pacific, November 1991–March 1992, D. E. Harrison, G. A. Vecchi, R. H. Weisberg Jan 2000

Eastward Surface Jets In The Central Equatorial Pacific, November 1991–March 1992, D. E. Harrison, G. A. Vecchi, R. H. Weisberg

Journal of Marine Research

The central equatorial Pacific typically has westward surface and near-surface flow, interrupted by periods of eastward flow. The processes that may have been responsible for two periods of eastward flow during the 1991-92 El Niño between October 1991 and March 1992 are explored here, based on realistic hindcasts from a high-vertical resolution ocean general circulation model. The model balances indicate that the November-December 1991 surface trapped jet is fully nonlinear, and both wind stress and horizontal pressure gradient forcing are significant. The January-February 1992 jet is less strongly nonlinear. Both jets are strongly affected by local and remote westerly wind …

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Spatial Variations In Nutrient Utilization, Production And Diagenesis In The Sediments Of A Coastal Upwelling Regime (Nw Africa): Implications For The Paleoceanographic Record, Philippe Martinez, Philippe Bertrand, Stephen E. Calvert, Thomas F. Pedersen, Graham B. Shimmield, Elisabeth Lallier-Vergès, Michel R. Fontugne Jan 2000

Spatial Variations In Nutrient Utilization, Production And Diagenesis In The Sediments Of A Coastal Upwelling Regime (Nw Africa): Implications For The Paleoceanographic Record, Philippe Martinez, Philippe Bertrand, Stephen E. Calvert, Thomas F. Pedersen, Graham B. Shimmield, Elisabeth Lallier-Vergès, Michel R. Fontugne

Journal of Marine Research

A biogeochemical study of recent (multicores) sediments of the northwest African slope was undertaken to understand how the sediment composition varies with respect to the location of core sites relative to the centers of coastal upwelling, and how this has affected the palaeoceanographic record. Sedimentary organic carbon contents are inversely correlated with the nitrogen isotopic composition (δ15N), high Corganic concentrations and low δ15N occurring at proximal (shallow) sites and the opposite at distal (deep) ones. These spatial differences are interpreted to result from higher relative nutrient utilization and a decrease in production as waters are advected offshore from the …

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Relative Dispersion In The Subsurface North Atlantic, J. H. Lacasce, A. Bower Jan 2000

Relative Dispersion In The Subsurface North Atlantic, J. H. Lacasce, A. Bower

Journal of Marine Research

Pair statistics are calculated for subsurface floats in the North Atlantic. The relative diffusivity (the derivative of the mean square particle separation) is approximately constant at large scales in both eastern and western basins, though the implied scale of the energy-containing eddies is greater in the west. But the behavior at times soon after pair deployment is quite different in the two basins; in the west the diffusivity grows approximately as distance to the 4/3 power, consistent with an inverse turbulent cascade of energy (or possibly of mixing superimposed on a mean shear), but in the east the diffusivity grows …

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Buoyancy-Forced Circulations Around Islands And Ridges, Michael A. Spall Jan 2000

Buoyancy-Forced Circulations Around Islands And Ridges, Michael A. Spall

Journal of Marine Research

Observations, theory, and modeling studies indicate that dominant components of both the upwelling and downwelling limbs of the thermohaline circulation take place near boundaries and in regions of steep and/or rough topography. Analytic and numerical results are used here to show that the interaction of upwelling regions with lateral boundaries fundamentally alters the resulting large-scale circulation compared to cases of open ocean upwelling. For narrow upwelling regions, viscous fluxes emerge as a leading term in the potential vorticity budget. The strong horizontal recirculation gyres that are found for sub-basin-scale open ocean upwelling (β-plumes) are replaced by weak, unidirectional flow into …

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Islands As Eddy Splitters, Harper Lightfoot Simmons, Doron Nof Jan 2000

Islands As Eddy Splitters, Harper Lightfoot Simmons, Doron Nof

Journal of Marine Research

Previous theoretical work has shown that, in an unbounded domain, anticyclones are prohibited from splitting on their own due to limitations imposed by the conservation of angular momentum. By explicitly considering the role of angular momentum exchange between eddies and boundaries (neglected by previous theories), splitting criteria for an anticyclonic lens colliding with a long and thin island are established analytically. The inviscid analytical model consists of an isolated patch of fluid in a reduced gravity regime. Nonlinear analytical solutions are constructed by connecting the initial and final states using conserved quantities (integrated angular momentum, vorticity and mass) and the …

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Circulation At The Western Boundary Of The South And Equatorial Atlantic: Exchanges With The Ocean Interior, Nicolas Wienders, Michel Arhan, Herlé Mercier Jan 2000

Circulation At The Western Boundary Of The South And Equatorial Atlantic: Exchanges With The Ocean Interior, Nicolas Wienders, Michel Arhan, Herlé Mercier

Journal of Marine Research

Data from a hydrographic section carried out in January-March 1994 offshore from the eastern coast of South America from 50S to 10N, are used to quantify the full-depth exchanges of water between the western boundary currents and the ocean interior. In the upper and intermediate layers, the westward transport associated with the southern branch of the South Equatorial Current was 49 Sv at the time of the cruise. The transports of the central and northern branches in the upper 200 m were 17 Sv and 12 Sv, respectively. After subtraction of the parts that recirculate in the subtropical, subequatorial, and …

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Improving Marine Ecosystem Models: Use Of Data Assimilation And Mesocosm Experiments, J. J. Vallino Jan 2000

Improving Marine Ecosystem Models: Use Of Data Assimilation And Mesocosm Experiments, J. J. Vallino

Journal of Marine Research

Our inability to accurately model marine food webs severely limits the prognostic capabilities of current generation marine biogeochemistry models. To address this problem we examine the use of data assimilation and mesocosm experiments to facilitate the development of food web models. The components of the data assimilation demonstrated include the construction of measurement models, the adjoint technique to obtain gradient information on the objective function, the use of parameter constraints, incorporation of discrete measurements and assessing parameter observability. We also examine the effectiveness of classic and contemporary optimization routines used in data assimilation. A standard compartment-type food web model is …

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Distributions Of Top, Ton And Toc In The North Pacific Subtropical Gyre: Implications For Nutrient Supply In The Surface Ocean And Remineralization In The Upper Thermocline, Jeffrey Abell, Steve Emerson, Paul Renaud Jan 2000

Distributions Of Top, Ton And Toc In The North Pacific Subtropical Gyre: Implications For Nutrient Supply In The Surface Ocean And Remineralization In The Upper Thermocline, Jeffrey Abell, Steve Emerson, Paul Renaud

Journal of Marine Research

We report measurements of total organic phosphorus, nitrogen, and carbon (TOP, TON, and TOC) along a meridional transect in the eastern subtropical North Pacific. In the surface waters, TOP and TON comprise 83% and 98% of the total dissolved phosphorus and nitrogen pools, respectively. Between the equatorial region and the subtropical gyre, there is a distinct gradient in surface TOP of about 0.25 µM, but very little gradient in TON. TOC increases by nearly 30 µM across the same region. Meridional advection of TOP along its gradient via Ekman transport can provide 40-80% of the phosphorus necessary to supply present …

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Mechanism Of Eddy Separation From Coastal Currents, Melvin E. Stern, Eric P. Chassignet Jan 2000

Mechanism Of Eddy Separation From Coastal Currents, Melvin E. Stern, Eric P. Chassignet

Journal of Marine Research

A series of multi-layer numerical experiments show that classical finite amplitude instabilities in boundary currents are not sufficient to account for the pinched-off eddies observed in the ocean and in laboratory experiments. These instabilities (barotropic or baroclinic) are shown to lead to an entrainment of offshore fluid into the boundary currents. Eddy separation, on the other hand, requires an additional process, such as a larger scale of motion containing a downstream velocity convergence of finite amplitude; this might be produced by long period fluctuations in the discharge from an upstream source region which controls the boundary current, or by topographic …

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Modeling Δ15n Evolution: First Palaeoceanographic Applications In A Coastal Upwelling System, Xavier Giraud, Philippe Bertrand, Véronique Garçon, Isabelle Dadou Jan 2000

Modeling Δ15n Evolution: First Palaeoceanographic Applications In A Coastal Upwelling System, Xavier Giraud, Philippe Bertrand, Véronique Garçon, Isabelle Dadou

Journal of Marine Research

The δ15N signal in marine sediments appears to be a good palaeoceanographic tracer. It records biological processes in the water column and is transferred to and preserved in the sediments. Changes in forcing factors in upwelling systems may be recorded by δ15N. These forcing conditions can be of a biogeochemical nature, such as the initial isotopic signal of the nutrients or the trophic structure, or of a physical nature, such as wind stress, insolation, temperature or dynamic recycling. A simple nitrogen-based trophic chain model was used to follow the development of the nitrogen isotopic signal in …

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Abyssal Upwelling In The Indian Ocean: Radiocarbon Diagnostics, Ashwanth Srinivasan, Claes G. H. Rooth, Zafer Top, D. B. Olson Jan 2000

Abyssal Upwelling In The Indian Ocean: Radiocarbon Diagnostics, Ashwanth Srinivasan, Claes G. H. Rooth, Zafer Top, D. B. Olson

Journal of Marine Research

The GEOSECS Indian Ocean radiocarbon and carbonate chemistry data set are used to estimate the mean upwelling transport of bottom water in the Indian Ocean north of 30S. The study uses an "adjusted radiocarbon concentration" which is corrected for the effects of addition of particulate radiocarbon to the deep ocean. The cross-basin uniformity in the vertical gradients of "adjusted radiocarbon" allows quantification of vertical transfer processes using horizontally averaged concentration and fluxes. The estimated total upwelling flux, north of 30S, is 8.2 ± 1.5 × 106 m3 s-1. The mean upwelling velocity and the vertical diffusivity, …

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On The Use Of The Method Of Images To Investigate Nearshore Dynamical Processes, S. A. Thorpe, L. R. Centurioni Jan 2000

On The Use Of The Method Of Images To Investigate Nearshore Dynamical Processes, S. A. Thorpe, L. R. Centurioni

Journal of Marine Research

This note describes how the method of images may be used to determine the motion and evolution of two related kinds of phenomena within a wedge of inviscid fluid. The image field of a curved vortex within a wedge with vortex lines lying along sectors of circles around the apex of the wedge is that segment of a complete vortex ring which remains outside the wedge and of which the curved vortex forms a part. The image system can be used to describe the motion, interaction and stability of single or multiple vortices within the wedge. Axisymmetric jets form the …

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Water-Mass Formation And Potential Vorticity Balance In An Abyssal Ocean Circulation, Jiayan Yang, James F. Price Jan 2000

Water-Mass Formation And Potential Vorticity Balance In An Abyssal Ocean Circulation, Jiayan Yang, James F. Price

Journal of Marine Research

Our goal is to develop some understanding and intuition regarding abyssal ocean circulations. To do this we investigate highly idealized, source/sink-driven flows computed by a single layer, numerical ocean model forced by a prescribed source or sink. The interior circulation is always found to be very slow and Stommel-Arons like. On the other hand, the intense boundary currents may vary considerably from case to case, depending largely upon the potential vorticity (PV) associated with the source or sink. If the source is imposed by downwelling along a northern boundary, then the associated PV flux is zero, and the resulting steady …

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The Parameterization Of Baroclinic Instability In A Simple Model, A. Wirth Jan 2000

The Parameterization Of Baroclinic Instability In A Simple Model, A. Wirth

Journal of Marine Research

Baroclinic instability of zonally forced flow in a two mode quasi-geostrophic numerical model with periodic boundary conditions is considered. Only the largest scale of the baroclinic mode is forced and the scale dependence of a diffusive parameterization of baroclinic layer thickness is determined. It is shown that the effect of baroclinic instability is a decreasing function of scale with an exponent of about half of that corresponding to the commonly used Laplace operator. We furthermore show that there is no linear relation between the time averaged amplitude of the large scale streamfunction (or quasi-geostrophic potential vorticity) and the bolus velocity.

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Low-Frequency Variability On The Western Flanks Of The Grand Banks, Nelson G. Hogg Jan 2000

Low-Frequency Variability On The Western Flanks Of The Grand Banks, Nelson G. Hogg

Journal of Marine Research

An array consisting of 21 current meters on nine moorings was set on the western flanks of the Grand Banks in August 1995 and recovered about two years later. The purpose was to explore the possibility that this might be a region of anomalously high topographic wave activity because the local topography so altered the dispersion relation for these waves that they could couple more readily to eastward-moving Gulf Stream meanders. Eddy kinetic energy is, indeed, found to be higher here than elsewhere in the region but only at periods shorter than about 10 days. At longer periods energy in …

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Modeling Of The Bottom Water Flow Through The Romanche Fracture Zone With A Primitive Equation Model—Part I: Dynamics, Bruno Ferron, Herlé Mercier, Anne-Marie Treguier Jan 2000

Modeling Of The Bottom Water Flow Through The Romanche Fracture Zone With A Primitive Equation Model—Part I: Dynamics, Bruno Ferron, Herlé Mercier, Anne-Marie Treguier

Journal of Marine Research

This paper investigates the dynamics of the Antarctic Bottom Water (AABW) flow through the Romanche Fracture Zone (RFZ) in a primitive equation model with a high horizontal and vertical resolution. Two examples of flows over simple bathymetries show that a reduced gravity model captures the essential dynamics of the primitive equation model. The reduced gravity model is then used as a tool to identify what are the bathymetric structures (sills, narrows) that mostly constrain theAABW flow through the RFZ. When only these structures are represented in the primitive equation model, the AABW flow is shown to be coherent with observations …

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Properties Of Vertical Current Shear Across Stratification In The North Sea, Hans Van Haren Jan 2000

Properties Of Vertical Current Shear Across Stratification In The North Sea, Hans Van Haren

Journal of Marine Research

Observations from the central North Sea show that, as soon as thermal stratification becomes established by solar insolation in the spring, the vertical smoothly varying horizontal current structure observed in winter becomes distorted, with strongest vertical shear coincident with the strongest buoyancy gradients (thermoclines). This shear is predominant at the local inertial frequency following strong wind-forcing or when the thermocline thickness is relatively large, and the semidiurnal tidal frequency otherwise. Although the currents at these frequencies have a completely different character, being circularly polarized and mode-1 at the inertial frequency and almost rectilinear and barotropic at the tidal frequency, their …

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Racing The Rising Tide: Legal Options For The Marshall Islands, J. Chris Larson Jan 2000

Racing The Rising Tide: Legal Options For The Marshall Islands, J. Chris Larson

Michigan Journal of International Law

This Note first describes the threat posed by accelerated sea-level rise. A review of scientific data shows that global warming causes ocean levels to rise and that RMI may need to be evacuated. The current diplomatic efforts to decrease global warming offer few assurances to RMI. In fact, the countries that have obligated themselves to reduce global warming are actually increasing emissions of gases that cause global warming.

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Fortnightly Modulation Of The Estuarine Circulation In Juan De Fuca Strait, Diane Masson, Patrick F. Cummins Jan 2000

Fortnightly Modulation Of The Estuarine Circulation In Juan De Fuca Strait, Diane Masson, Patrick F. Cummins

Journal of Marine Research

Riverine discharge into the Strait of Georgia sets up a well-defined estuarine circulation within Juan de Fuca Strait, the main path for the freshwater outflow to the continental shelf. At the landward end of Juan de Fuca Strait, the water flows through narrow channels in which strong tidal currents are known to induce significant mixing of the water column, and a spring-neap modulation of the estuarine exchange. A three-dimensional prognostic numerical model has been developed to study the circulation around Vancouver Island, British Columbia. In a series of simulations, the estuarine circulation within Juan de Fuca Strait is established by …

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Theoretical Calculations Based On Real Topography Of The Maximum Deep-Water Flow Through The Jungfern Passage, Karin Borenäs, Anna Nikolopoulos Jan 2000

Theoretical Calculations Based On Real Topography Of The Maximum Deep-Water Flow Through The Jungfern Passage, Karin Borenäs, Anna Nikolopoulos

Journal of Marine Research

A method for theoretically calculating the maximum transport through a strait, using the actual topography, is presented. The study is conducted within the framework of rotating hydraulics. The results are used for estimating the amount of North Atlantic Deep Water flowing through the Jungfern Passage into the Caribbean Sea. These appraisals are compared with previous theoretical estimates, for which a rectangular bottom profile has been used, and with transport calculations based on observations.

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The Role Of Eddies In The Isopycnic Transfer Of Nutrients And Their Impact On Biological Production, Mei-Man Lee, Richard G. Williams Jan 2000

The Role Of Eddies In The Isopycnic Transfer Of Nutrients And Their Impact On Biological Production, Mei-Man Lee, Richard G. Williams

Journal of Marine Research

Eddies provide a systematic, large-scale transfer of tracers and nutrients along isopycnals through a combination of eddy-induced diffusion and advection. The nutrient distribution is controlled by advection, rather than diffusion, when the nutrient lifetime exceeds a timescale given by κ/V2 where κ is the lateral diffusivity and V is the characteristic transport velocity. Idealized, eddy-resolving experiments are conducted using an isopycnic model configured for a zonal channel. Whether the eddies act to enhance or inhibit biological production depends on the location of the nutrient source and the nutrient lifetime. For a subtropical gyre and the Southern Ocean, the …

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Trajectories Of Sinking Particles And The Catchment Areas Above Sediment Traps In The Northeast Atlantic, Joanna Waniek, Wolfgang Koeve, Ralf D. Prien Jan 2000

Trajectories Of Sinking Particles And The Catchment Areas Above Sediment Traps In The Northeast Atlantic, Joanna Waniek, Wolfgang Koeve, Ralf D. Prien

Journal of Marine Research

A Lagrangian analysis of particles sinking through a velocity field observed by Eulerian frame measurements was used to evaluate the effects of horizontal advection and particle sinking speed on particle fluxes as measured by moored sediment traps. Characteristics of the statistical funnel above moored deep-ocean sediment traps at the German JGOFS quasi-time series station at 47N, 20W (Biotrans site) were determined. The analysis suggests that the distance and direction between a given sediment trap and the region at the surface where the particles were produced depends on the mean sinking velocity of the particles, the horizontal velocity field above the …

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Floats And Ƒ/H, J. H. Lacasce Jan 2000

Floats And Ƒ/H, J. H. Lacasce

Journal of Marine Research

The sensitivity of oceanic float dispersion to f/H, where H is a spatially filtered representation of the water depth, is examined with floats from the Atlantic and Pacific oceans. The first and second moments of the displacements relative to f/H were found and compared to those for zonal and meridional displacements. In all cases, the moments relative to f/H display equal or greater anisotropy than those relative to geographical coordinates, suggesting a preferred tendency for spreading along f/H. In regions where the topography is flat (at the equator, in the …

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Measurements Of Salinity In The Coastal Ocean: A Review Of Requirements And Technologies, Catherine Woody, Eddie Shih, Jerry Miller, Thomas Royer, Larry P. Atkinson, Richard S. Moody Jan 2000

Measurements Of Salinity In The Coastal Ocean: A Review Of Requirements And Technologies, Catherine Woody, Eddie Shih, Jerry Miller, Thomas Royer, Larry P. Atkinson, Richard S. Moody

CCPO Publications

Salinity, a measure of the dissolved salts in seawater, is a fundamental property of seawater and basic to understanding biological and physical processes in coastal waters. In the open ocean long term salinity measurements are identified as necessary to understand global climate studies, hydrological cycle, and circulation. In the coastal oceans, information on salinity is critical to understanding biological effects on ecosystem function such as disease, nursery grounds, or harmful algal blooms and on physical processes such as freshwater runoff estuarine mixing, and coastal currents. While the importance of salinity is recognized, little attention has been given to making routine …

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Imperfections Of The North Atlantic Wind-Driven Ocean Circulation: Continental Geometry And Windstress Shape, Henk A. Dijkstra, M. Jeroen Molemaker Jan 1999

Imperfections Of The North Atlantic Wind-Driven Ocean Circulation: Continental Geometry And Windstress Shape, Henk A. Dijkstra, M. Jeroen Molemaker

Journal of Marine Research

Multiple equilibria of the wind-driven gyres have been found in idealized quasi-geostrophic and shallow water models. In this paper we demonstrate that multiple equilibria persist within a reduced gravity shallow water model under quite realistic continental geometry and windstress forcing for the North Atlantic. Multiple mean flow patterns of the Gulf Stream exist and differ with respect to their separation behavior along the North American coast. The origin of these equilibria is investigated by determining the structure of steady solutions within a hierarchy of equivalent barotropic ocean models using continuation techniques. Within each model, the magnitude of lateral friction is …

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Evaluating Eddy Mixing Coefficients From Eddy-Resolving Ocean Models: A Case Study, A. M. Treguier Jan 1999

Evaluating Eddy Mixing Coefficients From Eddy-Resolving Ocean Models: A Case Study, A. M. Treguier

Journal of Marine Research

A numerical model of a baroclinically unstable jet in a zonally periodic channel is used to analyze mesoscale eddy fluxes and their relationship with the gradients of the mean flow. The quasi-geostrophic approximation proves the best way to calculate potential vorticity fluxes in the primitive equation model. Away from the surface layers, eddy fluxes of potential density are consistent with advection by eddy-induced velocities v* and w* as suggested by Gent et al. (1995). Eddies mix potential vorticity along isopycnals, so that v* is related to the gradients of potential vorticity rather than potential density as …

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Biogeochemistry Of Dimethylsulfide In The South China Sea, Gui-Peng Yang, Xin-Tong Liu, Li Li, Zheng-Bin Zhang Jan 1999

Biogeochemistry Of Dimethylsulfide In The South China Sea, Gui-Peng Yang, Xin-Tong Liu, Li Li, Zheng-Bin Zhang

Journal of Marine Research

The distribution of dimethylsulfide (DMS) was studied in surface seawater and vertical profiles at nineteen stations in the Nansha Islands sea area of the South China Sea. The concentrations of DMS in surface-layer (0-1 m) seawater vary from 64 to 140 ng S/L with high values found in the productive regions, in agreement with the horizontal distribution of chlorophyll a. The vertical profiles of DMS show a single peak shape with maximum concentrations occurring at depths between 30-75 m. The DMS concentrations are correlated with chlorophyll a levels both in the upper 20 m of seawater as well as …

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Mode Waters And Subduction Rates In A High-Resolution South Atlantic Simulation, Anne P. De Miranda, Bernard Barnier, William K. Dewar Jan 1999

Mode Waters And Subduction Rates In A High-Resolution South Atlantic Simulation, Anne P. De Miranda, Bernard Barnier, William K. Dewar

Journal of Marine Research

Water mass production and destruction in the subtropical South Atlantic gyre is studied. A high resolution numerical model is used to examine regional mode water formation and estimate the associated instantaneous and mean subduction rates. Primitive equation dynamics expressed in depth following (sigma) coordinates are employed. The main hydrographic and kinematic features of the South Atlantic are faithfully reproduced by the model. In particular, the principle current systems appear and the model exhibits a sequence of ventilated potential vorticity minima on density surfaces coinciding with those of observed South Atlantic mode waters. The formation sequence within the model of these …

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The Importance Of Open-Boundary Estimation For An Indian Ocean Gcm-Data Synthesis, Kate Q. Zhang, Jochem Marotzke Jan 1999

The Importance Of Open-Boundary Estimation For An Indian Ocean Gcm-Data Synthesis, Kate Q. Zhang, Jochem Marotzke

Journal of Marine Research

The Indian Ocean general circulation is estimated by fitting the MIT Ocean General Circulation Model to the annual mean climatological hydrography and surface forcing, using the model and its computer-generated adjoint. Open boundary conditions are implemented to the west of the Indonesian Archipelago and near 30S. The approach simultaneously optimizes the initial conditions of the hydrographic fields, surface fluxes, and the open boundary conditions (temperature, salinity, and horizontal velocities). Compared to previous results obtained in a closed domain, the estimated velocity field shows a marked improvement near the southern boundary, with a reasonably strong Agulhas Current leaving the model domain. …

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Bioturbation And Particle Transport In Carolina Slope Sediments: A Radiochemical Approach, W. L. Fornes, D. J. Demaster, L. A. Levin, N. E. Blair Jan 1999

Bioturbation And Particle Transport In Carolina Slope Sediments: A Radiochemical Approach, W. L. Fornes, D. J. Demaster, L. A. Levin, N. E. Blair

Journal of Marine Research

In situ tracer experiments investigated short-term sediment mixing processes at two Carolina continental margin sites (water depth = 850 m) characterized by different organic C fluxes, 234Th mixing coefficients (Db) and benthic assemblages. Phytoplankton, slope sediment, and sand-sized glass beads tagged with 210Pb, 113Sn, and 228Th, respectively, were placed via submersible at the sediment-water interface at both field sites (Site I off Cape Fear, and Site III off Cape Hatteras). Experimental plots were sampled at 0, 1.5 days, and 90 days after tracer emplacement to examine short-term, vertical transport. Both sites are initially …

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