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Circulation And Water Masses Of The Southwest Pacific: Woce Section P11, Papua New Guinea To Tasmania, Serguei Sokolov, Stephen Rintoul

Journal of Marine Research

The circulation near the western boundary of the South Pacific is described on the basis of water properties and geostrophic velocities measured on a meridional section along 155E through the East Australian and Coral Basins. The section was occupied in winter 1993 as part of the World Ocean Circulation Experiment (WOCE, Section P11S). The primary objective of P11 was to quantify the zonal flows entering and leaving the western boundary of the basin. The primary inflow to the Tasman and Coral seas is supplied by the South Equatorial Current (SEC), which crosses the P11 section as a wide band of …

Emergence Of Modons From Collapsing Vortex Structures On The Β-Plane, Z. Kizner, D. Berson

Journal of Marine Research

The evolution of unstable barotropic vortices is studied numerically. Exact solutions to the equation of potential vorticity conservation under the "rigid lid" condition, as well as nonsteady-state configurations, are set as initial states in the evolutionary experiments. The examined "shielded modon" structures usually collapse within one to several synoptic periods and radiate vortex pairs propagating westward and eastward. The latter are shown to be modons of Larichev and Reznik. The westward dipoles are identified as "nonlocal modons," that is, vortical cores of stationary nonlinear Rossby waves. In the case of standing Stern modons, some small initial perturbations induce slow westward …

A Baroclinic Western Boundary Current Over A Continental Slope, Rupert Ford

Journal of Marine Research

Baroclinic flow over a western continental slope is investigated using a simple model in which inertia is completely neglected and the temperature of the ocean depends only on horizontal position. Solutions of this model are also solutions of the three-dimensional equations without inertia. This model is arguably the simplest model in which the Joint Effect of Baroclinicity and Relief (JEBAR) can affect the mass transport on the slope. Offshore, we suppose that a classical double-gyre circulation exists, in which the subpolar gyre is colder than the subtropical gyre. Using asymptotic expansions based on small viscosity and small thermal diffusivity, we …

The Equatorial Thermostad And Subsurface Countercurrents In The Light Of The Dynamics Of Atmospheric Hadley Cells, Frédéric Marin, Bach Lien Hua, Sophie Wacongne

Journal of Marine Research

The simple Held and Hou (1980) nearly inviscid model of the axisymmetric atmospheric circulation, rationalizing the existence of Hadley cells, Jet Streams, and tropical homogenization of potential temperature and vorticity, is adapted to the oceanic subthermocline region. The meridional profile of radiative equilibrium temperature, which provides the driving in the atmospheric case, is replaced, in the oceanic case, by the large-scale equatorial doming of the thermocline. The meridional structure of the equatorial thermostad and the existence, at its poleward flanks, of eastward subsurface countercurrents coincident with sharp potential vorticity gradients are thus explained via angular momentum redistribution by secondary ageostrophic …

The Role Of Biologically-Enhanced Pore Water Transport In Early Diagenesis: An Example From Carbonate Sediments In The Vicinity Of North Key Harbor, Dry Tortugas National Park, Florida, Yoko Furukawa, Samuel J. Bentley, Alan M. Shiller, Dawn L. Lavoie, Philippe Van Cappellen

Journal of Marine Research

Biologically enhanced pore water irrigation affects the course of early diagenesis in shallow marine sediments, as illustrated here for the carbonate sediments from North Key Harbor, Dry Tortugas National Park, Florida. Whereas macrofaunal activity at the study site extends approximately 15 cm below the water-sediment interface, measured O₂ microprofiles only show O₂ penetration to depths of a few mm. This apparent discrepancy can be explained by considering the 3-D O₂ distribution in the burrowed sediments. Calculations based on an idealized tube model for burrow irrigation show that measureable O₂ concentrations are limited to the immediate vicinity …

Recipe For Banda Sea Water, Jorina M. Waworuntu, Rana A. Fine, Donald B. Olson, Arnold L. Gordon

Journal of Marine Research

Water from the western Pacific flows through the Indonesian Seas following different pathways and is modified by various processes to form the uniquely characterized isohaline Banda Sea Water. The processes contributing to the isohaline structure are studied using data from three ARLINDO cruises in 1993, 1994, and 1996. An inverse-model analysis using salinity and CFC-11 data is applied to a vertical section along the main path of flow, from the Makassar Strait to the Flores Sea and Banda Sea. The model reproduces the seasonal and interannual variability of the throughflow and shows reversals of flow in the vertical structure. The …

The Influence Of Deposit-Feeding On Chlorophyll-A Degradation In Coastal Marine Sediments, Anitra E. Ingalls, Robert C. Aller, Cindy Lee, Ming-Yi Sun

Journal of Marine Research

To determine how macrofaunal activity affects rates and mechanisms of Chlorophyll-a (Chl-a) decomposition, we measured Chl-a concentrations during laboratory incubations of surface sediment with varying abundances of a subsurface deposit-feeder, Yoldia limatula. Decomposition patterns of Chl-a in sediment cores with and without a layer of algal-enriched sediment added to the surface were compared. Decomposition rate constants, k_d, were calculated from the loss of reactive Chl-a and further quantified using a nonsteady state, depth-dependent, reaction-diffusion model. Values of k_d decreased approximately exponentially with depth and were directly proportional to the number of …

The Cyclonic Turning And Propagation Of Buoyant Coastal Discharge Along The Shelf, Alexander E. Yankovsky

Journal of Marine Research

Buoyant coastal discharge typically forms a current flowing along the coast in the direction of Kelvin wave propagation (hereinafter referred to as the downstream direction). In this paper the opposite, upstream penetration of buoyancy-driven current is studied using numerical modeling. Previous models of coastal buoyancy-driven currents repeatedly predicted the upstream spreading while in the field this feature was not commonly observed. The mechanism responsible for the propagation of buoyant flow along the coast upstream from its source is identified as follows. In many cases, the boundary conditions applied for buoyant discharge oversimplify the actual dynamics at the mouth blocking landward …

Selecting A Global Optimization Method To Estimate The Oceanic Particle Cycling Rate Constants, Véronique Athias, Pierre Mazzega, Catherine Jeandel

Journal of Marine Research

The objective is to select an inverse method to estimate the parameters of a dynamical model of the oceanic particle cycling from in situ data. Estimating the parameters of a dynamical model is a nonlinear inverse problem, even in the case of linear dynamics. Generally, biogeochemical models are characterized by complex nonlinear dynamics and by a high sensitivity to their parameters. This makes the parameter estimation problem strongly nonlinear. We show that an approach based on a linearization around an a priori solution and on a gradient descent method is not appropriate given the complexity of the related cost functions …

Feeding Selectivity And Rapid Particle Processing By Deep-Sea Megafaunal Deposit Feeders: A 234th Tracer Approach, Robert J. Miller, Craig R. Smith, David J. Demaster, William L. Fornes

Journal of Marine Research

Deposit-feeding megafauna occur in virtually all deep-sea environments, yet their feeding selectivity and particle processing rates are poorly known. Excess 234Th activity is commonly used asa geochemical tracer for recently settled (, 100-d old) particles in the quiescent deep sea, but it has rarely been applied to the study of deposit feeders. To explore the selectivity and rates of megafaunal deposit feeding, we compared excess 234Th activities in the gut contents of deposit feeders from Santa Catalina Basin (SCB) (~ 1200 m depth) and the Hawaiian slope (~ 1680 m) to the activity of surface sediments and, in SCB, to …

Detection Of Bay Of Bengal Eddies From Topex And In Situ Observations, A. K. S. Gopalan, V. V. Gopala Krishna, M. M. Ali, Rashmi Sharma

Journal of Marine Research

Oceanic eddies have warm or cold temperatures and high or low sea surface height (SSH) at the center depending upon the direction of rotation. However, since the Bay of Bengal waters are highly stratified, sea surface temperature (SST) gradients may not be detectable even though the subsurface temperature sections and the SSH show prominent eddy signatures. In this investigation, SSH observations from TOPEX altimeter data and the expendable bathy thermograph (XBT) temperature sections along the Madras-Andamans track have been analyzed to study the Bay of Bengal eddies. Several cyclonic and anticyclonic eddies are identified from the TOPEX altimeter observations. These …

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 …

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 C_organic 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 …

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 …

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 …

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 …

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 …

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 …

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 …

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 …

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 …

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, …

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 …

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 …

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.

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 …

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 …

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 …

G00-1778 Field Windbreaks, James R. Brandle, Laurie Hodges

University of Nebraska-Lincoln Extension: Historical Materials

gricultural producers face many challenges as they try to balance efficient production systems with increasing environmental demands. For these systems to be successful, they must optimize the balance between inputs and final production. Field windbreaks are one way to increase yields while at the same time reducing inputs and improving both environmental quality and production efficiency. Windbreaks reduce wind speed and alter the microclimate in sheltered areas. Field windbreaks reduce wind erosion and the damage to crops caused by wind-blown soil. They improve water use efficiency, reduce risks associated with drought, and manage blowing snow.

Field windbreaks provide positive economic …

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 …