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Internal Wave Band Eddy Fluxes Above A Continental Slope, Johannes R. Gemmrich, Hans Van Haren

Journal of Marine Research

Three weeks of velocity and temperature measurements from the bottom 45 m above the continental slope in the Bay of Biscay are used to evaluate the role of the internal wave band in boundary mixing near a sloping bottom. Utilizing acoustic Doppler current profilers and thermistor strings, internal wave band eddy fluxes of momentum and heat are estimated. The instrumentation is specifically designed to resolve internal wave band processes. Due to unresolved Doppler shifting, this wave band may include turbulence as well as internal waves. A very energetic and highly variable near-bottom environment is found. Periods of mixing and restratification …

A Note On Evanescent Behavior Of Arctic Thermohaline Intrusions, David Walsh, Eddy Carmack

Journal of Marine Research

Temperature/salinity interleaving is a signature of thermohaline transition in the Arctic Ocean. These interleaving features, or "intrusions," are observed to decrease in amplitude as they spread laterally from warmer toward cooler water. Here this phenomenon is investigated by considering the effect of a nonlinear equation of state on intrusion structure and behavior. The analysis shows that large-scale gradients of the thermal expansion coefficient (α) can induce a spatial decay of intrusion temperature, salinity, and velocity amplitudes toward cooler water. Spatial decay implies a recirculating flow between adjacent layers, which induces a slow vertical propagation of the intrusions. The temperature-dependence of …

Hourly Variations In Planktonic Larval Concentrations On The Inner Shelf: Emerging Patterns And Processes, Elizabeth D. Garland, Cheryl Ann Zimmer

Journal of Marine Research

Planktonic larvae are unlikely to be randomly distributed over time or in space. Fluctuations in larval density may result from a variety of physical and biological processes. To identify relatively high-frequency patterns of larval variation for an inner-shelf environment, zooplankton were sampled hourly for 3 d using an automated plankton pump. Moored ~80 cm above bottom, the pump was located in 8 m of water on the Outer Banks of North Carolina. Densities of all larval groups were highly variable: 5-746 m^-3 for barnacle cyprids, 0-668 m^-3 for polychaetes, 0-516 m^-3 for bivalves, 6-414 m^-3 for …

Downward Particle  Fluxes And Sediment Accumulation Rates In The Western Bransfield Strait: Implications Of Lateral Transport For Carbon Cycle Studies In Antarctic Marginal Seas, Albert Palanques, Enrique Isla, Pere Masqué, Pere Puig, Joan-Albert Sánchez-Cabeza, Josep M. Gili, Jorge Guillén

Journal of Marine Research

Downward particle and carbon fluxes were studied along with sediment and carbon accumulation fluxes in the western Bransfield Strait. Particle fluxes at 1000 m depth indicate that most of the carbon accumulated in the seabed at the study site is transported laterally. Biogenic components of the near-bottom particle fluxes included well-preserved organic matter with benthic diatoms, amphipoda and polychaetes that were resuspended and/or winnowed in shallow environments and transported basinward. High near-bottom particle and carbon fluxes were in agreement with high sediment and carbon accumulation fluxes. About 12% of the near-bottom OC downward flux is buried below the SML in …

Linear Planetary Wave Dynamics In A 2.5-Layer Ventilated Thermocline Model, Atsushi Kubokawa, Maki Nagakura

Journal of Marine Research

Linear planetary wave dynamics in a 2.5-layer ventilated thermocline model is investigated by a local eigenvalue analysis and simple numerical computations. It is known that there are two types of waves in this system; we refer to one of them as the N-mode (Non-Doppler shift mode), which propagates almost westward, and the other as the A-mode (Advection mode), which propagates almost along the second layer basic current. First, we study the local longwave dynamics, assuming that the wavelength is much longer than the deformation radius and shorter than the gyre scale. It is shown that the N-mode …

On The Relative Importance Of The Remote And Local Wind Effects On The Subtidal Exchange At The Entrance To The Chesapeake Bay, Kuo-Chuin Wong, Arnoldo Valle-Levinson

Journal of Marine Research

Water velocity data from acoustic Doppler current profilers and electromagnetic current meters deployed at six separate locations across the entrance of the Chesapeake Bay from mid-April to early July of 1999 and from early September to mid-November of 1999 were used in conjunction with wind velocity and sea level records to describe the characteristics of the wind-induced subtidal volume exchange between the bay and the adjacent continental shelf. The current measurements were used to estimate volume fluxes associated with the local and remote wind-induced bay-shelf exchange over time scales of 2–3 days. The results show that at these relatively short …

On The Dispersion Of Pairs Of Internal Inertial Gravity Waves, S. A. Thorpe

Journal of Marine Research

The inclination of the group velocity vector to the horizontal, β, of internal inertial gravity waves propagating in a deep uniformly stratified fluid varies with wave frequency. Group velocity also depends on wavenumber. As a consequence, packets of waves with finite frequency and wavenumber bandwidths generated by intermittent processes at the sea surface or ocean floor will usually disperse. Waves may, however, interact with one-another to suppress or entirely remove such dispersion, resulting in packets or groups of waves which retain structure during propagation. Here conditions are sought in which dispersion is entirely suppressed by the interactions between waves composing …

On Turbulence And Normal Modes In A Basin, J. H. Lacasce

Journal of Marine Research

The problem of forced, geostrophic turbulence in a basin is revisited. The primary focus is the time dependent field, which is shown to be approximately isotropic (in contrast to the strongly zonally anisotropic fields seen in periodic domains). It is also approximately homogeneous, away from the boundaries. Phenomenological arguments suggest the isotropy occurs because the inverse cascade of energy is arrested by basin normal modes rather than by free Rossby waves. Peaks in the velocity spectra at modal frequencies are consistent with basin modes, as has been noted previously. We discuss which modes would be excited and whether dissipation or …

Potential Vorticity “Crises”, Adverse Pressure Gradients, And Western Boundary Current Separation, Andrew E. Kiss

Journal of Marine Research

The vorticity dynamics involved in western boundary current separation are investigated in a depth-averaged barotropic single-gyre circulation forced by a spatially uniform wind stress curl in a circular basin on a beta-plane. The mechanism of separation is of interest in this simple model because it lacks most of the features (such as a change in sign of the wind stress curl, collision with another western boundary current, outcropping of isopycnals or an abrupt change in bottom topography or boundary shape) often associated with boundary current separation. It has been suggested that a "crisis" due to insufficient recovery of potential vorticity …

Tidal Motion Enhancement Around Islands, Zygmunt Kowalik, Aleksey V. Marchenko

Journal of Marine Research

Tidally-generated, trapped motions can significantly enhance and modify sea level and currents in the island proximity. The analytical solution for incident waves interacting with a cylindrical island with a circular sill has been constructed to investigate this phenomenon. To derive solutions for the scattering problems simple Sverdrup and Kelvin waves are used as incident waves. The amplification of the signal along the island perimeter has shown to be a function of frequency, relative dimensions of the island and the circular sill surrounding the island, relative sill depth, and the bottom friction. Although the incident diurnal tide may be amplified through …

Intermingling Of Two Pseudocalanus Species On Georges Bank, D. J. Mcgillicuddy Jr., A. Bucklin

Journal of Marine Research

Physical and biological controls on the springtime distributions of Pseudocalanus moultoni and P. newmani on Georges Bank are examined by assimilating observations into a coupled physical-biological model. Monthly snapshots of abundance are derived from U.S. GLOBEC Georges Bank broad-scale surveys during 1997. The forward problem is posed as an advection-diffusion-reaction equation for the copepod concentration. The adjoint method of data assimilation is used to invert for the biological sources and sinks implied by the observed changes in abundance between surveys and the flow during the intervening period. Based on this analysis, the two species appear to have distinct population centers …

Distribution Of The Euryhaline Squid Lolliguncula Brevis In Chesapeake Bay: Effects Of Selected Abiotic Factors, I. K. Bartol, R. Mann, M. Vecchione

Biological Sciences Faculty Publications

The majority of cephalopods are thought to have limitations arising from physiology and locomotion that exclude them from shallow, highly variable, euryhaline environments. The brief squid Lolliguncula brevis may be a notable exception because it tolerates low salinities, withstands a wide range of environmental conditions, and swims readily in shallow water. Little is known about the distribution of L. brevis in Chesapeake Bay, a diverse and highly variable estuary. Therefore, a survey of L. brevis was conducted in the Virginia portion of Chesapeake Bay from 1993 to 1997 using a 9.1 m otter trawl, and the effects of selected factors …

Casco Bay Watershed Wetlands Characterization, State Planning Office

Maine Collection

Casco Bay Watershed Wetlands Characterization

State of Maine Executive Department - State Planning Office

Augusta, Maine, May 2001

Contents: Abstract / Background / Getting Started / Designing the System / The Characterization / The Prioritization / Results / Cautions / Significance of the Approach / Literature Cited / Figure 1 - Biophysical Regions of Maine / Appendix A: Steering Committee Members / Appendix B: Field Verification Form / Appendix C: Contacts

On The Insensitivity Of The Wind-Driven Circulation To Bottom Topography, David P. Marshall, James C. Stephens

Journal of Marine Research

An analytical model is developed for the wind-driven circulation in a continuously stratified ocean overlying variable bottom topography. In the ocean interior we adopt a linear relation between potential vorticity, density and Montgomery potential, resulting in Welander's solution for an adiabatic internal thermocline. The horizontal structure of the circulation is described by a characteristic equation, obtained by imposing a boundary condition of no-normal flow at the sea floor and a prescribed vertical velocity through the base of the surface Ekman layer. The characteristics, which determine the extent to which bottom topography "steers" the circulation within the upper ocean, are dominated …

Absorbed Mn2+ And Mn Redox Cycling In Iberian Continental Margin Sediments (Northeast Atlantic Ocean), Claar Van Der Zee, Wim Van Raaphorst, Eric Epping

Journal of Marine Research

Although Mn²⁺ sorption has been investigated extensively in the laboratory, the role of Mn²⁺ sorption in natural marine sediments remains speculative. Our objectives were to study (1) the role of Mn²⁺ sorption in the redox cycling of Mn, (2) to quantify Mn cycling and (3) to identify its rate-determining factors at the Iberian margin. Profiles of pore water Mn²⁺, adsorbed Mn²⁺ and solid phase Mn were measured together with benthic oxygen fluxes along three transects across the margin from the shelf to the deep sea as well as in the Nazeré Canyon. In the …

Annual To Interannual Variations Of Ƒco2 In The Northwestern Mediterranean Sea: Results From Hourly Measurements Made By Carioca Buoys, 1995–1997, E. M. Hood, L. Merlivat

Journal of Marine Research

A time series of fCO₂, SST, and fluorescence data was collected between 1995 and 1997 by a CARIOCA buoy moored at the DyFAMed station (Dynamique des Flux Atmospheriques en Mediterranée) located in the northwestern Mediterranean Sea. On seasonal timescales, the spring phytoplankton bloom decreases the surface water fCO₂ to approximately 290 µatm, followed by summer heating and a strong increase in fCO₂ to a maximum of approximately 510 µatm. While the ΔfCO₂ shows strong variations on seasonal timescales, the annual average air-sea disequilibrium is only 2 µatm. Temperature-normalized fCO …

North Pacific Internal Tides From The Aleutian Ridge: Altimeter Observations And Modeling, Patrick F. Cummins, Josef Y. Cherniawsky, Michael G. G. Foreman

Journal of Marine Research

Internal tides radiating into the North Pacific from the Aleutian Ridge near Amukta Pass are examined using 7 years of Topex/Poseidon altimeter data. The observations show coherent southward phase propagation at the M₂ frequency over a distance of at least 1100 km into the central Pacific. Barotropic and baroclinic models are applied to study this internal tidal signal. Results from the barotropic model show that the strongest cross-slope volume and energy fluxes occur in the vicinity of Amukta Pass, helping to establish this region as an important site for baroclinic energy conversion along the eastern half of the ridge. …

Internal And Interfacial Tides: Beam Scattering And Local Generation Of Solitary Waves, Theo Gerkema

Journal of Marine Research

Analytical solutions of a linear internal-tide generation problem are presented for a stratification that involves both an interface (thermocline) and a lower layer of constant stratification. It is shown that an internal tidal beam scatters strongly at a moderately developed thermocline but much less at a thermocline that is either very weak or very strong. This scattering goes along with a local wave activity at the thermocline as well as with a downward leaking from the thermocline. It is argued that these processes offer a clue to explaining observations in the Bay of Biscay of 'local generation' of internal soliton …

The Impact Of Model Configuration In Studies Of Buoyant Coastal Discharge, Richard W. Garvine

Journal of Marine Research

Observations and model studies of large-scale buoyant plumes show three major types for the horizontal distribution of density. Type 1 represents the typical coastal freshwater plume of observations. The buoyant discharge turns right in the northern hemisphere (toward downshelf) under earth rotation at its source. Type 2 is common in many numerical model studies. Most of the buoyant water at the inlet turns left (upshelf) along the coast to form a continuously growing intrusion. Type 3 turns right but exhibits a massive anticyclonic bulge which grows with time; its coastal current is weak and carries a small fraction of the …

The Evolution And Energetics Of Large Amplitude Nonlinear Internal Waves On The Portuguese Shelf, D. R. G. Jeans, T. J. Sherwin

Journal of Marine Research

Intensive in-situ observations of nonlinear internal waves on the Portuguese shelf were made in August 1994, including measurements of the same wavepacket at three locations as it propagated on-shelf. The waves were characterized by sudden isotherm depressions of up to 45 m lasting 10-35 minutes, accompanied by current surges of up to 0.45 m s^-1 and shears of up to 0.7 m s^-1 over 60 m. The waves propagated away from the shelf break with an estimated phase speed of 0.57 m s^-1. The amplitude of the waves was comparable to the theoretical maximum. The kinetic …

Barotropic Instabilities Of The Agulhas Current System And Their Relation To Ring Formation, Henk A. Dijkstra, Wilhelmus P. M. De Ruijter

Journal of Marine Research

Recent work has shown that different steady retroflection regimes, a viscous and an inertial regime, exist for the Agulhas Current system in an idealized geometry. In this paper, instabilities of the barotropic steady flows are considered by solving the linear stability problem numerically. Barotropic instabilities occur as so-called Hopf bifurcations in the viscous regime, with corresponding patterns related to Rossby basin modes. Depending on the value of the reduced gravity parameter, these instabilities may introduce intermonthly to interannual variability into the retroflection region. Finite amplitude development of these instabilities display 'ring-like' localized anomaly patterns which travel around the tip of …

On The Summer Mesoscale Variability Of The Black Sea, Şükrü T. Beşiktepe, Carlos J. Lozano, Allan R. Robinson

Journal of Marine Research

The evolution of the Black Sea temperature, salinity and circulation, from large scale to mesoscale, is studied using a data-driven primitive equation simulation. The data are drawn from (i) a basin-wide hydrographic survey, CoMSBlack'92, obtained in the Summer of 1992; (ii) wind stress derived from wind analyses of the Sevastopol MSIA/URHI Office; (iii) climatological heat fluxes; and (iv) climatological river outflows. The primitive equation model is from the Harvard Ocean Prediction System. The simulation is used to examine the evolution of the circulation at mesoscale resolution, its dominant variabilities and dependencies in the summer period. The large-scale upper layer circulation …

The Origin Of Low-Frequency Variability Of Double-Gyre Wind-Driven Flows, Janine J. Nauw, Henk A. Dijkstra

Journal of Marine Research

Bifurcation analysis on flows in a two-layer shallow-water model is used to clarify the dynamical origin of low-frequency variability of the double-gyre wind-driven ocean circulation. In many previous model studies, generic low-frequency variations appear to be associated with distinct regimes, characterized by the level of kinetic energy of the mean flow. From these transient flow computations, the current view is that these regimes, and transitions between them, arise through a complex nonlinear interaction between the mean flow and its high-frequency instabilities (the eddies). On the contrary, we demonstrate here, for a particular (but relevant) case, that the origin of these …

Impact Of Sub-Mesoscale Physics On Production And Subduction Of Phytoplankton In An Oligotrophic Regime, Marina Lévy, Patrice Klein, Anne-Marie Treguier

Journal of Marine Research

Using a protocol of numerical experiments where horizontal resolution is progressively increased, we show that small-scale (or sub-mesoscale) physics has a strong impact on both mesoscale physics and phytoplankton production/subduction. Mesoscale and sub-mesoscale physics result from the nonlinear equilibration of an unstable baroclinic jet. The biogeochemical context is oligotrophy. The explicitly resolved sub-mesoscales, at least smaller than one fifth of the internal Rossby radius of deformation, reinforce the mesoscale eddy field and contribute to double the primary production and phytoplankton subduction budgets. This enhancement is due to the reinforced mesoscale physics and is also achieved by the small-scale frontal dynamics. …

A Bifurcation Study Of The Three-Dimensional Thermohaline Ocean Circulation: The Double Hemispheric Case, Wilbert Weijer, Henk A. Dijkstra

Journal of Marine Research

Within a low-resolution primitive-equation model of the three-dimensional ocean circulation, a bifurcation analysis is performed of double-hemispheric basin flows. Main focus is on the connection between results for steady two-dimensional flows in a nonrotating basin and those for three-dimensional flows in a rotating basin. With the use of continuation methods, branches of steady states are followed in parameter space and their linear stability is monitored. There is a close qualitative similarity between the bifurcation structure of steady-state solutions of the two- and three dimensional flows. In both cases, symmetry-breaking pitchfork bifurcations are central in generating a multiple equilibria structure. The …

Particle Flux In The Rainbow Hydrothermal Vent Field (Mid-Atlantic Ridge): Dynamics, Mineral And Biological Composition, Alexis Khripounoff, Annick Vangriesheim, Philippe Crassous, Michel Segonzac, Ana Colaço, Daniel Desbruyères, Roxane Barthelemey

Journal of Marine Research

In order to provide information about the export and the distribution of hydrothermal particulate material to the surrounding deep ocean, four moorings were deployed in the vicinity of the hydrothermal Rainbow vent field (Mid-Atlantic Ridge, 36°14′N, 2250 m depth). The first mooring was a sediment trap with a current meter deployed at 2 m from a chimney of the Rainbow vent field and 1.5 m above the bottom (a.b.) for 16 days. It represented the reference for the initial composition of particles produced by the vent. The total mean mass particle flux (6.9 g m^-2 d^-1) was …

Mechanism Of Offshore Nutrient Supply In The Western Arabian Sea, Michio Kawamiya

Journal of Marine Research

The mechanism to maintain the high surface chlorophyll in the western Arabian Sea during the southwest monsoon (SWM) season is studied with an eddy-permitting, biological-physical coupled model. Using a set of artificial tracers, it is revealed that horizontal transport of nutrient subsequent to the coastal upwelling is by far more important than the open ocean upwelling due to the Ekman pumping. The horizontal transport can be classified into three processes, the Ekman transport, transport by the large-scale circulation and that by the mesoscale currents. In the model, the first has only a minor effect within the area of high chlorophyll …

The Role Of Colonization In Establishing Patterns Of Community Composition And Diversity In Shallow-Water Sedimentary Communities, Paul V. R. Snelgrove, J. Frederick Grassle, Judith P. Grassle, Rosemarie F. Petrecca, Karen I. Stocks

Journal of Marine Research

To determine whether pattern and diversity in benthic sedimentary communities are set primarily at colonization or by post-settlement biological interactions, we collected faunal cores and conducted reciprocal sediment transplant experiments at a sandy and a muddy site at 12 m depth, ~3 km apart off New Jersey. Multivariate analyses of cores collected at these sites in September 1994 indicated differences in the taxa determining local pattern, with the bivalve Spisula solidissima and the polychaete Polygordius sp. being dominant at the sandy site, and oligochaetes, several polychaete species and the bivalve Nucula annulata dominant at the muddy site. Individual cores from …

Phytoplankton Seasonal Distribution From Seawifs Data In The Agulhas Current System, E. Machu, V. Garçon

Journal of Marine Research

The interocean conduit for warm Indian Ocean water into the Atlantic Ocean is the Agulhas system which plays an important role in maintaining the global thermohaline circulation. The frontal system formed by the Agulhas Return Current (ARC) and the Subtropical Convergence (STC) is also a region of intense mesoscale activity presenting enhanced levels of biological production and chlorophyll a. We jointly analyzed three different satellite data sets to relate the remotely sensed distribution of phytoplankton (SeaWiFS ocean color data) to the dynamical environment (Topex/Poséidon-ERS sea level anomalies-SLA- and sea-surface temperature-SST-) to gain insight into the seasonal behavior of the …

A Data Assimilative Marine Ecosystem Model Of The Central Equatorial Pacific: Numerical Twin Experiments, Marjorie A. M. Friedrichs

Journal of Marine Research

A five-component, data assimilative marine ecosystem model is developed for the high-nutrient low-chlorophyll region of the central equatorial Pacific (0N, 140W). Identical twin experiments, in which model-generated synthetic 'data' are assimilated into the model, are employed to determine the feasibility of improving simulation skill by assimilating in situ cruise data (plankton, nutrients and primary production) and remotely-sensed ocean color data. Simple data assimilative schemes such as data insertion or nudging may be insufficient for lower trophic level marine ecosystem models, since they require long time-series of daily to weekly plankton and nutrient data as well as adequate knowledge of the …