ALBERT

Description: The first meeting of the South West Indian Ocean EAF Regional Task Group (RTG) was held in Mombasa, Kenya, from 27 to 30 January 2009, together with an ecological risk assessment methodology workshop. It was attended by 20 partic ipants from the South West Indian Ocean (SWIO) countries, the South West Indian Ocean Fisheries Project (SWIOFP), the Agulhas and Somali Currents Large Marine Ecosystems (ASCLME) project, the Scientific Committee of the South West Indian Ocean Fisheries Commission, the United Nations Environment Programme (UNEP)/Nairobi Convention Implementation Unit, the African Union Commission and FAO. The RTG is an implementation structure under the EAF-Nansen project GCP/INT/003/NOR and serves as the forum for training in ecological risk assessment that is the methodology used for the identification and prioritization of issues requiring management attention. The main objectives of the meeting and workshop we re to discuss and facilitate key processes and activities for the implementation of the ecosystem approach to fisheries management in the South West Indian Ocean region including the modalities for the formation and functioning of the RTG and National Task Groups (NTGs). It was explained that, to be able to achieve the objectives of implementing an ecosystem approach to fisheries at the national level, certain key structures have to be in place including the NTG with representatives of key stakeholders in a given fishery and that would take the lead in the process. An overview of the key concepts and process of the ecological risk assessment methodology were clarified. Participants were also introduced to the preparation of EAF baseline reports to be used as initial input for the work on ecosystems approach to fisheries. It was explained that the preparation of the report is to be led by national and regional experts and overseen by the NTG. For the exercises the participants worked in three subgroups formed during the meeting with each group selecting a chairman who moderate d the discussions and a rapporteur. The participants expressed satisfaction with the development of a communication strategy for the project and especially with the participatory approach used.

Description: FAO, NORAD, Institute of Marine Research

Description: Published

Description: National task groups

Description: Regional task groups

Description: Ecosystem Approach to Fisheries

Description: Published

Description: Fisheries newsletter

Description: Published

Description: Fisheries newsletter

Description: Published

Description: Fisheries newsletter

Description: Published

Description: Fisheries newsletter

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2014

Description: This thesis explores the buoyancy-driven circulation in the Red Sea, using a combination of observations, as well as numerical modeling and analytical method. The first part of the thesis investigates the formation mechanism and spreading of Red Sea Overflow Water (RSOW) in the Red Sea. The preconditions required for open-ocean convection, which is suggested to be the formation mechanism of RSOW, are examined. The RSOW is identified and tracked as a layer with minimum potential vorticity and maximum chlorofluorocarbon-12. The pathway of the RSOW is also explored using numerical simulation. If diffusivity is not considered, the production rate of the RSOW is estimated to be 0.63 Sv using Walin’s method. By comparing this 0.63 Sv to the actual RSOW transport at the Strait of Bab el Mandeb, it is implied that the vertical diffusivity is about 3.4 x 10-5m2 s-1 . The second part of the thesis studies buoyancy-forced circulation in an idealized Red Sea. Buoyancy-loss driven circulation in marginal seas is usually dominated by cyclonic boundary currents on f-plane, as suggested by previous observations and numerical modeling. This thesis suggests that by including β-effect and buoyancy loss that increases linearly with latitude, the resultant mean Red Sea circulation consists of an anticyclonic gyre in the south and a cyclonic gyre in the north. In mid-basin, the northward surface flow crosses from the western boundary to the eastern boundary. The observational support is also reviewed. The mechanism that controls the crossover of boundary currents is further explored using an ad hoc analytical model based on PV dynamics. This ad hoc analytical model successfully predicts the crossover latitude of boundary currents. It suggests that the competition between advection of planetary vorticity and buoyancy-loss related term determines the crossover latitude. The third part of the thesis investigates three mechanisms that might account for eddy generation in the Red Sea, by conducting a series of numerical experiments. The three mechanisms are: i) baroclinic instability; ii) meridional structure of surface buoyancy losses; iii) cross-basin wind fields.

Description: This work is supported by Award Nos. USA 00002, KSA 00011 and KSA 00011/02 made by King Abdullah University of Science and Technology (KAUST) , National Science Foundation OCE0927017, and WHOI Academic Program Office.

Description: This data report is for midwater fishes taken on the time-series cruises in and around cold-core Gulf Stream rings in 1976 and 1977 - KNORR cruises 62, 65, and 71 and ENDEAVOR cruise 11. The MOCNESS-10 system was used for sampling on the three KNORR cruises. Most often, five nets were fished at each station; one (Net 0) generally sampled down to near 1000 m where the second net (Net 1) was opened and retrieval of the gear begun; successive closure-openings were done at 250-m intervals on the way up. On ENDEAVOR cruise 11, for want of a suitable winch, a single net was fished down to and up from 1000 m.

Description: This work was done under Contract N00014-79-C-0071 NR083-004 and its predecessors with the Office of Naval Research.

Description: It is well recognized in the oceanography of the Western North Atlantic that a distinct hydrographic regime exists between the continental shelf and the Gulf Stream, once the latter has effectively separated from the coast at Cape Hatteras. Denoted as the Slope Water, this hydrographic regime has been considered as one of confusing complexity, presumably arising from irregular mixing processes between it and the neighboring shelf and Gulf Stream regimes. Although previously noted in the literature, it has recently become very strongly evident as a result of the satellite image coverage of this region that a dominant role in this variability can be ascribed to well organized and persistent circulation features. These have been given the name warm core Gulf Stream rings, in order to emphasize their complementary dynamic origin relative to the more generally known cold core rings in the Sargasso Sea. A scientific workshop was held in Woods Hole under the auspices of the NSF/ IDOE to review in detail the status of our knowledge about the biology, chemistry and physics of the shelf-Slope Water regime and the associated rings, and the general biological, chemical and physical processes likely to be taking place in rings. Also considered were the prospect for advancing this knowledge through a multidisciplinary study of the warm core rings and the region impacted by them. Out of extensive background review in papers presented in plenary sessions, and program discussions in working groups, there arose a consensus that such a multidisciplinary effort would be both feasible and timely.

Description: Funded by the National Science Foundation, Office for International Decade of Oceanographic Exploration, Grant OCE77-00924

Description: Originally published in the Journal of marine research, v. 36, 1, 1978, pp. 119-142

Description: The hydrographic limit of the distribution of Nematoscelis megalops in the Northwestern Atlantic Ocean is usually marked by the abrupt changes in water properties across the Gulf Stream. There are, however, isolated but repeated occurrences of this species in the Sargasso Sea. In our study, individuals in the Sargasso Sea were expatriates from the Slope Water which had been transported to the collection site by Gulf Stream cold core rings with but two exceptions. The exceptional cases can be indirectly linked to the presence of rings. Expatriated populations do not persist. Extinction in a ring appears to take place in one or two generations, and for N. megalops it is related to changes in hydrographic properties, and in particular, the vertical temperature structure. Both in the Slope Water and in the ring 50% or more of the population is found in a restricted temperature regime centered about 10°C. As a ring ages, the preferred temperature regime and N. megalops along with it move deeper into the water column. The physiological and biochemical data given by Boyd, Wiebe and Cox (1978) combined with data given here indicate that withdrawal from the surface results in progressive deterioration of the nutritional condition of the population, a cessation of growth, a drastic reduction in the number of males relative to females, reproductive incapacitation, and ultimate extinction. It is conceivable that a process similar to that occurring in rings is responsible for the maintenance of the Gulf Stream as a hydrographic limit in the distribution of N. megalops.

Description: Prepared for the Office of Naval Research under Contracts N00014-66-C-0241; NR 083-004 and N00014-74-C-0262; NR 083-004 and for the National Science Foundation under Grant DES 74-02783 A01

Description: A workshop on the physics, chemistry and biology of warm core rings was held at the New Zealand Oceanographic Institute in Wellington during 18-22 January 1982, under the auspices of the U.S./Australia and U.S./New Zealand Cooperative Science Programs. The purpose of the workshop was to elicit joint discussions and exchange of ideas between groups of scientists actively working on warm core rings or eddies. The workshop consisted of 34 scientific papers summarizing accomplishments resulting from work in warm core rings; working group discussions on particular disciplinary and multi-disciplinary problems associated with ring structure and dynamics; and a final session summarizing the current state of knowledge about rings, and indicating directions for future research.

Description: U.S.-Australia Cooperative Science Program; U.S.-New Zealand Cooperative Science Program; DSIR (New Zealand); CSIRO (Australia)

Description: Ship drift velocity observations were used to calculate and plot monthly mean and yearly mean velocities in 2° latitude by 5° longitude boxes for the Atlantic, Pacific, and Indian Oceans. The vector maps shown here provide a visualization of the mean and seasonally varying currents.

Description: Funding was provided by the National Science Foundation through grant Number OCE 87-16509.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2014

Description: The nitrogen fixation and abundance of Trichodesmium colonies and their connections with physical processes were investigated through Video Plankton Recorder (VPR) and other observations collected in fall 2010 and spring 2011 in the western subtropical–tropical North Atlantic. A data processing procedure for estimating rare taxon abundance was devised to leverage the accuracy of manual classification and the effort savings of automatic classification. In fall 2010, local maxima in colony abundance were observed in a series of cyclones. We hypothesized Ekman transport convergence/divergence in cyclones/anticyclones as a driving mechanism and investigated the process using idealized three-dimensional models. Elevated abundances in anticyclones in spring 2011 were correlated with anomalously fresh water connected to river outflow. A bio-optical model based on carbon-normalized nitrogen fixation rates measured in fall 2010 and spring 2011 was used to estimate nitrogen fixation over the VPR transects. Mean VPR-based estimates of abundance and volume-specific nitrogen fixation rates at depth in the tropical North Atlantic were not inconsistent with estimates derived from conventional sampling methods compiled in a database by Luo et al. (2012). These findings did not reveal the systematic underestimation of deep colony populations and nitrogen fixation hypothesized by Davis and McGillicuddy (2006).

Description: This work was supported through a NASA Earth and Space Science Fellowship (NASA NNX11AL59H Understanding the role of the nitrogen- xing cyanobacterium Trichodesmium in the oceanic nitrogen and carbon cycles: in situ measurement, satellite observation, and biogeochemical modeling) as well as fellowship support from the Ocean Life Institute and Academic Programs O ce at WHOI. Additional grant support was provided by NSF OCE-0925284 Quanti cation of Trichodesmium spp. Vertical and Horizontal Abundance Patterns and Nitrogen Fixation in theWestern North Atlantic, NSF OCE-1048897 MOBY: Modeling Ocean Variability and Biogeochemical Cycles, NASA NNX13AE47G Physical and Biological Dynamics of Nonlinear Mesoscale Eddies: Satellite Observations, in situ Measurements, and Numerical Simulations on a Global Scale, and NASA NNX08AL71G Carbon cycling in the North Atlantic from regional to basin scales: satellite data, in situ observations, and numerical models.

Description: This report presents trajectories and time series of velocity, pressure, and temperature for twelve neutrally-buoyant floats launched during the Gulf Stream Recirculation EXperiment (GUSREX) and two from earlier experiments, that continued to operate after May 1982. These float data were obtained from Autonomous Listening Stations (ALSs) deployed from May 1982 to August 1985.

Description: Funding was provided by the national Science Foundation under Grant Numbers OCE 81-09145 and OCE 81-17467

Description: Originally published in the Journal of Marine Research, v. 36, 1, 1978, pp. 143-159

Description: Nematoscelis megalops, a cold water euphausiid commonly found in Northwestern Atlantic Slope Water, is frequently transported in the cores of Gulf Stream cyclonic rings into the Sargasso Sea. The inner core made of cold Slope Water gradually assumes physical and biological characteristics of the surrounding Sargasso Sea. These changes gradually lead to a localized extinction of this species in the core of the ring. Samples of N. megalops taken from the same ring at 6 and 9 months after its formation show a weakened physiological and biochemical condition. Deterioration of ring individuals is evidenced by an increase in body water content and a reduction in total body lipid, carbon, respiration rates, and nitrogen relative to Slope Water individuals. By 6 months it appears that ring N. megalops must supplement food intake by metabolizing some of their body protein and by 9 months they appear to use lipids as well. A shipboard starvation experiment involving 40 Slope Water individuals showed that physiological and biochemical states similar to those found in individuals from the 9 months old ring could be duplicated in 4 days of complete starvation.

Description: Prepared for the Office of Naval Research under Contracts N00014-66-C-0241; NR 083-004 and N00014-?4-C-0262; NR 083-004 and for the National Science Foundation under Grant DES ?4-02?83 A01 .

Description: This is the final data report of all mooring data collected by the Woods Hole Oceanographic Institution in 2010-2012 during the experiment A Crossroads of the Atlantic Meridional Overturning Circulation: The Charlie-Gibbs Fracture Zone. The objectives of this experiment were (1) to obtain an improved direct estimate of the mean and low-frequency variability of the deep westward transport of the Iceland-Scotland Overflow Water through the Charlie-Gibbs Fracture Zone (CGFZ), and (2) to gain a better understanding of the causes of the low-frequency variability in the transport of overflow waters through the CGFZ, especially of the role of the North Atlantic Current in generating this variability. The mooring deployment and recovery cruises were on German research vessels, courtesy of Drs. Monika Rhein and Dagmar Kieke: the R/V Meteor cruise M82/2 in August 2010 and R/V Maria S. Merian cruise MSM 21/2 in June 2012, respectively. The CGFZ moored array complemented other moored arrays being maintained by German scientists just west of the CGFZ (Pressure Inverted Echo Sounders, or PIES) and the Faraday Fracture Zone (current meter and microcat moorings). A set of eight moorings were set up across the CGFZ to measure the intermediate and deep water variability for a two-year period, from a depth of 500 m to the ocean floor. The moorings held a total of three McClane Moored Profilers (MMPs), 10 Nortek and 18 Aanderaa current meters, and 36 Seabird MicroCATs, deployed from 18-20 August 2010 through 28-30 June 2012. This yielded a nearly two-year record of velocity, temperature, salinity and pressure. The MMPs profiled every five days, and resulted in a high-resolution time series of temperature, salinity, pressure and velocity data across the interface between the generally eastward flowing Labrador Sea Water carried underneath the North Atlantic Current, and the westward flowing deep Iceland-Scotland Overflow Water.

Description: Funding was provided by the National Science Foundation Grant OCE-0826656

Description: The results of multiple deployments of surface drifters in warm core rings of the Gulf Stream are presented. Four satellite drifters (tracked by the Argos system) were deployed on nine separate occasions and two LORAN-C drifters (operated by the University of Miami) were deployed three times. Drifter studies were conducted during four cruises aboard the R/V Endeavor in 1982 in conjunction with the Warm Core Rings Experiment and one cruise of the USNS Bartlett in January 1983 which was sponsored by the Office of Naval Research. Translational velocities and periods of rotation are provided for two rings: 82B and 82H.

Description: National Science Foundation under grant OCE80-16983

Description: The ”Mach’s Principle” has beenconsidered for more than a century as the highest expression of the philosophical rationality of the western world, but it is possible to proof that it is built on a unstable ground and with uncomplete assumptions. With a great intellectual honesty, Ernst Mach showed in his works some awareness of the incompleteness of his reasoning about inertia. Moreover the Mach Principle is often misinterpreted by scientific community with an illegitimate extrapolation of the Mach words.

Description: Published

Description: 239-242

Description: 5.9. Formazione e informazione

Description: open

Description: Over the last decade eutrophication of freshwater artificial reservoirs in Cuba occurred in parallel to oligotrophication of estuarine and coastal waters. These two processes influenced both freshwater and marine fisheries. A dramatic shift in species composition in freshwater fisheries has occurred, from dominance by cichlids (tilapia) to dominance by cyprinids. The high fishery yield from some reservoirs, and shift in species composition, seems related to progressive eutrophication of reservoirs by nutrient subsidies from different anthropogenic activities; particular those related to the size of urban areas within their watersheds. On the other hand, marine landings of estuarine-dependent species declined more significantly than for other groups associated with seagrass beds–coral reefs and oceanic waters. The ratio between catches of estuarine-dependent species and those associated with seagrass beds and coral reefs, decreased significantly over the last 20 years. The decrease in landings was more evident in typical estuarine species, such as shrimps (Litopenaeus schmitti and Farfantopenaeus notialis), mangrove oyster (Crassostrea rhizophorae) and mullets (Mugil spp.). River damming increased during the same period and is significantly correlated with these decreases. It is hypothesized that two different processes acted synergistically, leading to dramatic decreases of several orders of magnitude, in the catches of estuarine species over the last decade: the trapping of nutrients and sediments by river damming, and a drastic reduction in nutrient inputs from land-based sources due to reduced fertilizer use. These are postulated to have affected not only estuarine resources, but also the whole coastal ecosystem.

Description: Durante la última década, la eutrofización de los embalses artificiales de agua dulce en Cuba se produjo en paralelo a oligotrophication de estuarios y costeras aguas. Estos dos procesos de influencia de agua dulce y la pesca marina. Un cambio dramático en la composición de las especies en la pesca de agua dulce se ha producido, de la dominación de los cíclidos (tilapia) a la dominación de ciprínidos. La alta producción de la pesca de algunos embalses, y el cambio en las especies composición, parece relacionada con la progresiva eutrofización de los embalses de las subvenciones de nutrientes de diferentes actividades antropogénicas, especialmente las relacionado con el tamaño de las zonas urbanas dentro de sus cuencas. Por otro lado, los desembarques de especies marinas de estuario-dependientes disminuyeron significativamente más que para otros grupos asociados con algas marinas Los arrecifes de coral-camas y las aguas oceánicas. La relación entre las capturas de las especies que dependen de los estuarios y las asociadas a las praderas marinas y Los arrecifes de coral, se redujo significativamente en los últimos 20 años. La disminución en los desembarques fue más evidente en especies típicas de estuarios, tales como camarones (Litopenaeus schmitti y Farfantopenaeus notialis), ostra de mangle (Crassostrea rhizophorae) y la lisa (Mugil spp.). El represamiento del Río aumentó durante el mismo período y se correlaciona significativamente con estas disminuciones. Se planteó la hipótesis de que dos procesos diferentes actúan de forma sinérgica, que conduce a una disminución drástica de varios órdenes de magnitud, en las capturas de las especies de estuario en la última década: la captura de nutrientes y sedimentos por represas río, y una reducción drástica de los aportes de nutrientes de fuentes terrestres, debido a la reducción del uso de fertilizantes. Se postula que han afectado no sólo a los recursos estuarinos, sino también todo el ecosistema costero.

Description: Published

Description: ríos

Description: impactos antropogénicos

Description: Se muestra la evolución de las capturas de las sierras y pintadas, se describen las 3 maneras en que las especies pueden quedar atrapadas en la redes de enmalles, así como también los tipos de redes (deriva, media agua y de fondo).

Description: Published

Description: Scomberomorus regalis

Description: Scomberomorus maculatus

Description: Scomberomorus cavalla

Description: spanish mackerel

Description: king mackerel

Description: painted mackerel

Description: enmalle

Description: arte de pesca

Description: Published

Description: Mugil curema

Description: Mugil liza

Description: Mugil cephalus

Description: Gerres cinereus

Description: patao

Description: coastal lagoons

Description: Ce travail représente une contribution à l'étude de l'activité de pêche hauturière dans le gouvernorat de Médenine, particulièrement, au niveau du port de Zarzis ; durant la période (juin 2005-juin 2006). Il consiste à réaliser, grâce à des enquêtes menées au port, deux types d'analyses : une analyse quantitative afin de déterminer les débarquements saisonniers moyens des espèces les plus débarquées par la pêche hauturière et une analyse qualitative pour établir les structures démographiques des espèces les plus exploitées dans la région. Les résultats obtenus ont montré que, durant la période d'étude, les principales espèces débarquées par la pêche hauturière sont la sardinelle, le maquereau, le saurel, le rouget blanc, le pageot, la thonine, la seiche et la crevette royale. En examinant les débarquements saisonniers moyens des espèces les plus débarquées par type de pêche, nous avons remarqué que deux ou trois espèces dominent pour chaque saison. De plus, l'analyse des structures démographique des apports a montré que la majorité des individus débarqués sont matures, à l’exception du maquereau dont les captures sont constituées d’individus immatures, surtout pendant les saisons d’été et d’automne.

Description: This work represents a contribution to the study of the offshore fishing activity in the governorate of Medenine, particularly at the port of Zarzis, during the period (june 2005-june 2006. It is to realize, through surveys conducted at the port, two types of analyzes: a quantitative analysis to determine the average seasonal landings of most landed species by fishing offshore units and qualitative analysis to determine the demographic structure of the most exploited species in the region. The obtained results showed that during the period of study, the main landed species by offshore fishing are sardinella, mackerel, horse mackerel, white mullet, sea bream, skipjack tuna, cuttlefish and the caramote prawn. By examining the average seasonal landings of the most landed species, we noticed that, for each season, two or three species dominate. Furthermore, analysis of demographic structures of the landings showed that the majority of landed individuals are mature, with the exception of mackerel catches which are composed of immature individuals, especially during the seasons of summer and autumn.

Description: Published

Description: analyse qualitative

Description: pêche hauturière

Description: Se muestran las capturas históricas de la biajaiba (1935-2000), la evolución de las capturas del pargo (una de las especies de mayor interés económico en Cuba). Se evalúa la utilización de éstas artes de pesca en especies comerciales y su implicación con daños al medio ambiente. Se tiene en cuenta que los pargos criollos, la biajaiba y el caballerote representan el 20 % de las capturas.

Description: Published

Description: pesquería artesanal

Description: cubera

Description: cherna criolla

Description: pesca del alto

Description: pargo

Description: rabirrubia

Description: caballerote

Description: biajaiba

Description: Un análisis de los datos arqueológicos e históricos sobre la pesca en Cuba muestra que el impacto de la población aborigen sobre los recursos pesqueros no fue significativo debido a su baja densidad poblacional y a las tecnologías de pesca. El interés por el oro, el tamaño de la población, las limitaciones tecnológicas para la pesca y preservación de las capturas así como las preferencias dietéticas de los españoles todas indican que la pesca tampoco fue una actividad económica importante durante los tres siglos que siguieron a la llegada de Colón. Las preferencias por la carne de res y el bacalao salado y la baja tasa de crecimiento poblacional durante el período colonial determinaron que la mayor parte de los recursos pesqueros, con la excepción del manatí y las tortugas marinas, permanecieran prácticamente inexplorados durante varios siglos después de la Conquista. Los datos estadísticos e históricos revelan que la pesca experimentó un rápido crecimiento desde 1950 y este patrón parece ser una característica común en el Caribe así como en otras partes del mundo. Las presiones sobre la vida marina fueron más evidentes en la segunda mitad del siglo xx cuando el crecimiento poblacional, las mejoras tecnológicas y las demandas del mercado aceleraron el sector pesquero así como la urbanización en la mayoría de los países del caribe.

Description: Published

Description: A yield per recruit model has been used to compare the effects of mesh size increment on the yields and revenues of the fisheries of Cameroon under two different cases. Case 1 assumes the commercial fishery to move from the exploitation of three age-groups to two age-groups with no interactions with the artisanal fishery, whereas Case 2 takes into account these interactions. The difference in the percentage increase of yield per recruit between case 1 and case 2 is 61% at current fishing (46% and 18% yield per recruit increment in cases 1 and 2 respectively). The usually accepted long-term yield per recruit increment with increase of age at first capture (with a single non-interacting fisheries) is, in this case, cancelled out. However, the revenues increase by 72% and 63% in cases 1 and 2 respectively. Therefore the economic approach, compared with purely biological analyses, is more convincing. In general, as fisheries always interact, a single-fishery management approach should not be the rule as it is at present; management strategies should consider interactions between different fisheries and be based on their economic performances and not, as said earlier, on purely biological considerations. This is because a biological approach to fisheries management will, at best, be modified by economic factors, or, at worst, be ignored totally in favour of economic policies.

Description: Published

Description: UNESCO, bourses MAB/Jeunes scientifiques

Description: Published

Description: pêche artisnale; courant marin; houle; pêcheur; érosion côtière; température; repos biologique; environnement; hydroclimat; aires marines protégées; gestion durable; sécurité en mer; maille des filets; surexploitation; récif artificiel; poulpe; cymbium; aquaculture

Description: La pêche au Sénégal joue un rôle économique et social très important par une contribution globale de près de 11% du PIB primaire et 2,3% du PIB total. Elle occupe de façon directe et indirecte environ 600 000 personnes, soit près de 17% de la population active selon la DP M. Cependant ces dernières décennies, les études ont montré que le secteur traverse une crise aiguë se traduisant par une raréfaction croissante des ressources, notamment les espèces nobles qui ont une forte valeur commerciale. Cette crise est due entre autres à une surexploitation de ces ressources qui est le résultat d’un manque de maîtrise de l’effort de pêche surtout pour les pêcheries artisanales (80% des débarquements et plus de 60% des approvisionnements des industries de la place) au regard du volume de ressources disponibles. Ce manque de maîtrise est dû essentiellement par un défaut du suivi contrôle et surveillance au niveau de la pêche artisanale par l’Etat, qui n’a pas les moyens humains et matériels pour appliquer des mesures de gestion, qui pour la plupart ne sont pas adaptées aux réalités des acteurs à la base. L’objet de cette étude est d’analyser une nouvelle approche axée sur la surveillance participative basée sur l’émergence d’initiatives locales de cogestion au niveau des quatre (04) sites du programme GIRMaC que sont ; Ouakam, Ngaparou, Foundiougne et Bétenty. Il ressort de cette étude que : • Le secteur de la pêche traverse une crise aiguë due principalement selon les acteurs à un défaut de suivi, contrôle et surveillance tel que appliqué actuellement ; • L’approche de cogestion avec des bases juridiques cohérentes, comme le propose le programme GIRMaC peut être un moyen viable pour solutionner à la crise que traverse la pêche ; • D’une part le système Suivi Contrôle et Surveillance coûte cher, d’autre part que ces coûts sont fortement amoindris lorsque les acteurs participent à l’effort de surveillance, par une démarche de surveillance participative en cogestion.

Description: Président : Omar Thiom THIAW, Professeur UCAD Membres : • Niokhor DIOUF, Chercheur IUPA. • Luis Tito Morais, Chercheur IRD Dakar. • Djiby THIAM, Chercheur GIRMac

Description: Published

Description: surveillance; contrôle; cogestion; effort de pêche; pêcherie; surexploitation; biodiversité; pêche artisanale

Description: Published

Description: espéces pélagiques

Description: sardine

Description: pêche industrielle

Description: Unpublished

Description: conservation

Description: chaine froide

Description: poisson

Description: Published

Description: Pêche

Description: Senneur

Description: ACDI;CRDI; République Française, Ministère des Affaires Etrangéres; CDE; Enda Graf Sahel;

Description: Conseil Info MPEA, Projer d'Accés à l'information et au Conseil pour les microet petites entreprises agroalimentaires; Projet d'Appui aux Opérateurs/trices de l'Agroalimentaires (PAOA); Cintech Agroalimentaire; Groupe de Recherche et d'Echanges Technologiques (GRET); Enda GRaf Sahel; SNC-LAVALIN International

Description: Published

Description: transformation; transformation artisanale; échantillonage; collecte de données; commercialisation

Description: Français - Les traits essentiels de la côte sénégalaise, repères historiques de la pêche, communautés de pêcheurs, caractéristiques des flottes et modes d’accès à la ressource et d’interaction sont analysés. Les caractéristiques, tendances décroissantes de l’abondance,niveaux d’exploitation, mesures d’aménagement, relations interspécifiques, changements potentiels et sources de variation des stocks démersaux côtiers sont précisés. Les notions de tactiques et stratégies de pêche sont passées en revue, conceptualisées puis étudiées.Le modèle «Dynamique Conjointe Exploitation Ressource» utilisé repose sur la définition de 4 typologies. L’utilisation de méthodes de classification et de connaissances d’experts conduit à considérer 32 stocks, 31 strates, 82 tactiques et 25 flottilles artisanales et chalutières. Les typologies sont articulées avec la prise en compte de paramètres relatifs à l’économie, aux stocks, flottilles et règles de décisions. L’ajustement est satisfaisant en partie. Toutefois, le modèle garde son importance en matière de prospective et d’objectifs à atteindre via la définition de variables de contrôle. Notre travail peut être considéré comme une esquisse invitant à un groupe de travail élargi aux experts des institutions halieutiques nationales voire, sous-régionales. Des propositions sont faites sur les bases de données, les licences de pêche et l’étude des tactiques et stratégies à mener suivant des pas de temps raisonnables pour tenir compte du grand dynamisme des pêcheries. Dès lors qu'il s’agit de caractériser l'impact de la pêche sur l'écosystème, ces travaux sont des éléments essentiels des recherches à faire sur la dynamique des écosystèmes exploités. English - The essential features of the Senegalese coast, fisheries history, fishermen's communities, artisanal and trawling fleet’s characteristics and their way of accessing to the resource and interactions are described. The characteristics, evolutionary tendencies of abundance, level of exploitation, measures of fisheries management, interspecific relationship, potential evolutionary changes and sources of variation of coastal demersal stocks are specified. Tactics and strategies are reviewed, conceptualized and studied. We used the model "Dynamique Conjointe Exploitation Ressource" which lies on 32 stocks, 31 strata, 82 tactics, 25 fleets and several other parameters dealing with stocks, fleets, economy and making decision rules. The adjustment is partially satisfactory but the model is of great interest for prospective studies and objectives to reach once defined variables of control. Our work is an outline calling for an enlarged working group implying national or sub regional fisheries institutional experts. Tactics and strategies studies, re-actualized in artisanal fisheries, are performed for the first time in industrial fisheries. The typological approach is simple, pertinent, efficacy and fast. Propositions are made relatively to databases, fishing licenses and tactics and strategies studies that should be implemented according to a reasonable time steps in order to take into account the big dynamism of the Senegalese fisheries. As it is intended to characterize fisheries impact on ecosystem, these works are one of essential research elements on the dynamic of exploited ecosystems.

Description: Published

Description: pêcherie; démersale côtière; modélisation; stocks; écosystème; communauté de pêcheurs; eaux continentales; eaux marines; saison hydrologique; pêcheur; flottille; crevettier; capture; aménagement des pêcheries; pêche chalutière; pêche artisanale; licence de pêche; permis de pêche

Description: Published

Description: conservation

Description: produits

Description: pêche

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1996

Description: This thesis addresses the question of how a highly energetic eddy field could be generated in the interior of the ocean away from the swift boundary currents. The energy radiation due to the temporal growth of non-trapped (radiating) disturbances in such a boundary current is thought to be one of the main sources for the described variability. The problem of stability of an energetic current, such as the Gulf Stream, is formulated. The study then focuses on the ability of the current to support radiating instabilities capable of significant penetration into the far-field and their development with time. The conventional model of the Gulf Stream as a zonal current is extended to allow the jet axis to make an angle to a latitude circle. The linear stability of such a nonzonal flow, uniform in the along-jet direction on a beta-plane, is first studied. The stability computations are performed for piece-wise constant and continuous velocity profiles. New stability properties of nonzonal jets are discussed. In particular, the destabilizing effect of the meridional tilt of the jet axis is demonstrated. The radiating properties of nonzonal currents are found to be very different from those of zonal currents. In particular, purely zonal flows do not support radiating instabilities, whereas flows with a meridional component are capable of radiating long and slowly growing waves. The nonlinear terms are then included in the consideration and the effects of the nonlinear interactions on the radiating properties of the solution are studied in detail. For these purposes, the efficient numerical code for solving equation for the QG potential vorticity with open boundary conditions of Orlanski's type is constructed. The results show that even fast growing linear solutions, which are trapped during the linear stage of developement, can radiate energy in the nonlinear regime if the basic current is nonzonal. The radiation starts as soon as the initial fast exponential growth significantly slows. The initial trapping of those solutions is caused by their fast temporal growth. The new mechanism for radiation is related to the nonzonality of a current.

Description: This work was supported by NSF Grant OCE 9301845.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2013

Description: Two high-resolution mooring arrays extending from the outer shelf to the mid continental slope are used to elucidate shelf-basin exchange at the inflow to and the outflow from the Arctic Ocean. Pacific Water entering the Arctic Ocean forms the Western Arctic shelfbreak current along the Beaufort Sea slope. Data from the mooring array at 152°W—approximately 150 km east of Pt. Barrow, AK—reveals that this current has two distinct states in summer depending on the water mass it transports. When advecting Alaskan Coastal Water it is surface-intensified and both baroclinically and barotropically unstable. This configuration lasts about a month with an average transport of 0.7 Sv. When advecting Chukchi Summer Water the current is bottom-intensified and is only baroclinically unstable. This state also exists for approximately a month with an average transport of 0.6 Sv. The strong mean-to-eddy energy conversion causes both configurations of the current to spin down over a distance of a few hundred kilometers, suggesting that warm Pacific Water does not enter the Canadian Arctic Archipelago via this route. Dense water formed in the Nordic Seas overflows the Denmark Strait and undergoes vortex stretching, forming intense cyclones that propagate along the East Greenland slope. Data from the mooring array at 65°N—roughly 300 km downstream of Denmark Strait—was used to determine the full water column structure of the cyclones. On average a cyclone passes the array every other day in the vicinity of the 900 m isobath, although the depth range of individual cyclones ranges between the 500 m and 1600 m isobaths. The cyclones self-propagate at 0.45 m/s and are also advected by the mean flow of 0.27 m/s, resulting in a total propagation speed of 0.72 m/s. They have a peak azimuthal speed of 0.22 m/s at a radius of 7.8 km and contain overflow water in their core. In the absence of the cyclones, the background flow is dominated by the East Greenland Spill Jet. This is shown to be a year-round feature transporting 2–4 Sv of dense water equatorward along the upper continental slope.

Description: Financial support for this work was provided by National Science Foundation grants OCE-0726640 and OCE-0612143, by the Arctic Research Initiative at WHOI, by the Y-S Anonymous Fellowship from the Office of the Dean of Graduate Education at MIT, and by WHOI Academic Programs Office funds.

Description: Author Posting. © Ecological Society of America, 2013. This article is posted here by permission of Ecological Society of America for personal use, not for redistribution. The definitive version was published in Ecological Applications 23 (2013): 959–971, doi:10.1890/12-0447.1.

Description: The biological benefits of marine reserves have garnered favor in the conservation community, but “no-take” reserve implementation is complicated by the economic interests of fishery stakeholders. There are now a number of studies examining the conditions under which marine reserves can provide both economic and ecological benefits. A potentially important reality of fishing that these studies overlook is that fishing can damage the habitat of the target stock. Here, we construct an equilibrium bioeconomic model that incorporates this habitat damage and show that the designation of marine reserves, coupled with the implementation of a tax on fishing effort, becomes both biologically and economically favorable as habitat sensitivity increases. We also study the effects of varied degrees of spatial control on fisheries management. Together, our results provide further evidence for the potential monetary and biological value of spatial management, and the possibility of a mutually beneficial resolution to the fisherman–conservationist marine reserve designation dilemma.

Description: M. G. Neubert acknowledges the support of the National Science Foundation (DMS-0532378, OCE-1031256) and a Thomas B. Wheeler Award for Ocean Science and Society. H. V. Moeller acknowledges support from a National Science Foundation Graduate Research Fellowship. This research is based in part on work supported by Award No. USA 00002 made by King Abdullah University of Science and Technology (KAUST).

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution December 1996

Description: The transformation of potential vorticity within and stability of nonlinear deep western boundary currents in an idealized tropical ocean are studied using a shallowwater model. Observational evidence indicates that the potential vorticity of fluid parcels in deep western boundary currents must change sign as they cross the equator, but this evidence is otherwise unable to clarify the process. A series of numerical experiments investigate this transformation in a rectangular basin straddling the equator. A mass source located in the northwestern corner feeds fluid into the domain where it is constrained to cross the equator to reach a distributed mass sink. Dissipation is included as momentum diffusion. The Reynolds number, defined as the ratio of the mass source per unit depth to the viscosity, determines the nature of the flow, and a critical value, Rec, divides its possible behavior into two regimes. For Re 〈 Rec, the flow is laminar and well described by linear theory. For Re just above the critical value, the flow is time-dependent, with cyclonic eddies forming in the western boundary current near the equator. For still larger Reynolds number, eddies of both signs emerge and form a complicated, interacting network that extends into the basin several deformation radii from the western boundary, as well as north and south of the equator. The eddy field is established as the mechanism for potential vorticity transformation in nonlinear cross-equatorial flow. The analysis of vorticity fluxes follows from the flux-conservative form of the absolute vorticity equation. It is shown that the zonally integrated meridional flux of vorticity across the equator using no slip boundary conditions is virtually zero even in the strongly nonlinear limit suggesting that the eddies are extremely efficient vorticity transfer agents. A decomposition of the vorticity fluxes into components due to mean advection, eddy transport, and friction, reveals the growth with Reynolds number of a turbulent boundary layer that exchanges vorticity between the inertial portion of the boundary current and a frictional sub-layer where modification is straightforward. A linear stability analysis of the shallow-water system in the tropical ocean examines the initial formation of the eddy field. The formulation assumes that the basic state is purely meridional and on a local f-plane. Realistic western boundary current profiles undergo a horizontal shear instability that is partially stabilized by viscosity. Calculations at several latitudes indicate that the instability is enhanced in the tropics where the internal deformation radius is a maximum. The linear stability analysis predicts a length scale of the disturbance, a location for its origin, and a critical Reynolds number that agree well with numerical results.

Description: Financial support for this research was provided by NSF grant number OCE- 9115915 and ONR ASSERT grant number N00014-94-1-0844.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 1996

Description: This thesis addresses the issue, "Which approach to instabilities-temporal, spatial or pulse theory- is the most appropriate model for the Gulf Stream?" I also address the question of how the observations might be compared to theory. This thesis consists of two closely related parts: analytical studies that compare the three types of instability using the same realistic velocity and topography profiles; and numerical modeling that uses a continuous forcing function to examine the three types of theory in the direct context of the Gulf Stream.

Description: My first three years in the Joint Program were supported by the National Science Foundation under grant OCE-9011066 and last two and half years under NSF grant OCE-9314140.

Description: The 2012 GFD Program theme was Coherent structures with Professors Jeffrey Weiss of the University of Colorado at Boulder and Edgar Knobloch of the University of California at Berkeley serving as principal lecturers. Together they introduced the audience in the cottage and on the porch to a fascinating mixture of models, mathematics and applications. Deep insights snaked through the whole summer, as the principal lecturers stayed on to participate in the traditional debates and contributed stoutly to the supervision of the fellows. The first ten chapters of this volume document these lectures, each prepared by pairs of the summer's GFD fellows. Following the principal lecture notes are the written reports of the fellows' own research projects. In 2012, the Sears Public Lecture was delivered by Professor Howard Bluestein, of the University of Oklahoma on the topic of "Probing tornadoes with mobile doppler radars". The topic was particularly suitable for the summer's theme: a tornado is a special examples of a vortex, perhaps the mother of all coherent structures in fluid dynamics. Howie "Cb" showed how modern and innovative measurement techniques can yield valuable information about the formation and evolution of tornadoes, as well as truly amazing images.

Description: Funding was provided by the Office of Naval Research under Grant No. N00014-09-10844 and the National Science Foundation under Contract No. OCE-0824636.

Description: Description du secteur de la pêche Avec la Mauritanie, le Sénégal est de loin le plus grand producteur de produits de pêche de la sous région. Avec 718 km de cote et un territoire maritime de 198km2, 15 745 km2 de superficie fluviale, 2 estuaires, des mangroves et un lac de 350km2, le Sénégal possède tous les atouts des plus grands producteurs de pêche. Le potentiel annuel de captures s’élève à 500 000 tonnes. Le secteur a subi une croissance spectaculaire ces trente dernières années : les débarquements sont passés 50 000 tonnes en 1965 à plus de 450 000 en 1997. Le secteur se compose principalement de deux sous-secteurs : la pêche industrielle et la pêche traditionnelle ou artisanale. Cette dernière, vielle de plusieurs siècles a su s’adapter et se moderniser au cours des dernières décennies. La flotte de pêche artisanale est dynamique et diversifiée ; selon les estimations, en 2005 il y avait plus de 13 000 pirogues. La pêche artisanale se concentre dans sept régions maritimes et fluviales du pays: Dakar, Thiès, Saint Louis, Fatick, Zinguinchor, Louga et Kaolack. Le port de Kayar dans la région de Thiès correspond à la principale zone de débarquement de la pêche artisanale avec environ 70% des débarquements. Dans le secteur industriel, les pêcheurs travaillent à bord d’une flottille de petits sardiniers, de 143 chalutiers destinés à la pêche d’espèces demersales, de 3 sardiniers et de 42 thoniers. Alors que le Sénégal domine largement le sous-secteur demersale avec 70% des chalutiers opérants, le pays ne possède que 6 thoniers contre 38 étrangers, dont une partie seulement des captures est débarquée au Sénégal. La pêche industrielle est concentrée autour de la capitale dans le Port autonome de Dakar et des ports secondaires de Saint Louis, Kaolack et Ziguinchor. Aujourd’hui, le secteur de la pêche sénégalaise est largement dominé par la pêche artisanale, qui constituait 90% des cargaisons totales des produits de la mer en 2006 avec 350 000 tonnes. Plus de 60% des produits de la pêche artisanale sont destinés à l’exportation et la transformation. En 2006, le secteur dans son ensemble représentait 9% du PIB du secteur primaire, 1.5% du PIB total, et 1/3 des devises étrangères (250 millions de dollars par an). Plus importante que le poids économique du secteur, est son poids social : la pêche génère indirectement 600 000 emplois, dont 67% au sein du secteur artisanal. En outre, les produits de la pêche comblent les besoins en protéines animales de la population sénégalaise à hauteur de 75%1. La pêche a connu une expansion spectaculaire au cours des dernières décennies grâce à l’impulsion de politiques publiques de développement basées sur une logique sectorielle productiviste. Une flotte nationale artisanale et industrielle a été progressivement mise en place ainsi que de fortes capacités de transformation industrielle. Cet engagement de l’Etat a ensuite connu un net ralentissement du fait, entre autre, des politiques d’ajustement structurel. Le renchérissement des coûts de production subséquents à la dévaluation du franc CFA en 1994 a lourdement affecté les pêcheurs. Parallèlement, avec la forte demande en produits halieutiques et en l’absence de politiques adéquates et cohérentes de gestion durable des ressources exploitables, une situation de surexploitation des ressources halieutiques s’est installée. En conséquence de la raréfaction des ressources halieutiques, la pêche sénégalaise traverse une crise sans précédent, dont les effets commencent à se faire sentir à tous les niveaux : appauvrissement des communautés de pêcheurs, menace de l’approvisionnement en poisson des populations, baisse des captures à haute valeur ajoutée, baisse des exportations, baisse de la rentabilité et des revenus des unités de pêche. Par ailleurs, de plus en plus d’établissements de transformation industrielle ferment (23 entreprises entre 1999 et 2006).

Description: Ministerio de Medio Ambiente Y Medio Rural y Marino

Description: Pablo Manuel Xandri Royo CTP Proyecto (INT/07/16M/SPA) Este trabajo se ha realizado en el marco del Convenio de Colaboración entre el actual Ministerio de Medio Ambiente y Medio Rural y Marino de España y la Organización Internacional del Trabajo de 28 de diciembre de 2007

Description: Published

Description: environnement; socio-économie; pêche; capture; débarquement; engin de pêche; femme; pêcheur; convention internationale; réglementation

Description: Programme KURUKAN FUGAN (Union Européenne/Gouvernement du Sénégal/EndaGraf/GRET)

Description: Published

Description: politique de pêche; environnement marin; socio-économie; co-gestion; aquaculture; pêche artisanale; pêche industrielle; pêcherie; ONG; AMP; ressource halieutique; organisations professionnelles

Description: En la época colonial algunas especies de peces cubanos retienen sus nombres por los cuales eran conocidos por los aborígenes: biajaca, biajaiba, cojinúa, jiguagua, cibí. Aún hoy se designan de igual forma. En esta época aparece la primera obra científica impresa en Cuba, los primeros pueblos pescadores y los primeros científicos.

Description: Published

Description: Published

Description: especies nativas

Description: pesca

Description: Published

Description: Recuento en forma breve de las pesquerías de estas especies durante varios siglos, en los cuales los sabios Parra y Felipe Poey ofrecen descripciones. Precios, lugares de captura y pescadores son los protagonistas.

Description: Published

Description: Emperador-Xiphias gladius

Description: pez espada

Description: castero-Makaira nigricans

Description: aguja blanca-Tetrapturus albidus

Description: Causas del descenso en las pesquerías de estas especies a partir de 1975. Se describen las técnicas y artes de pesca empleadas y se abunda en la complejidad de las capturas y las características de los palangres empleados para cada especie. Una comparación es establecida además con países del área. De forma muy didáctica e instructiva.

Description: Published

Description: castero-Makaira nigricans

Description: Emperador-Xiphias gladius

Description: aguja blanca-Tetrapturus albidus

Description: The theme for the Program in Geophysical Fluid Dynamics for the summer of 2011 was Shear Turbulence: onset and structure. Ten days of principal lectures by FabianWale e and Rich Kerswell began the summer, and a large number of seminars on this and a variety of other topics then continued through the eighth week. These lectures are presented in these Proceedings and form (we believe) the most complete, connected account of this subject) Eleven fellows from around the globe helped to record the principal lectures, and each carried out a project of his/her own, presented in seminar during the tenth and nal week. All these lectures and projects are also presented in this Proceedings volume. The further seminars presented throughout the summer by visitors and (in some cases) by GFD faculty are also listed here. The popular Sears Lecture was given by L. Mahadevan. The title was On growth and form: geometry, physics and biology. It was indeed popular, drawing a large and enthusiastic audience.

Description: Funding was provided by the National Science Foundation under Grant No. OCE-0824636 and the Office of Naval Research under Contract No. N00014-09-10844

Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Walker, Cameron -- England -- Nature. 2013 Jul 4;499(7456):115-7.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23841144" target="_blank"〉PubMed〈/a〉

Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Normile, Dennis -- New York, N.Y. -- Science. 2013 May 3;340(6132):546-7. doi: 10.1126/science.340.6132.546.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23641089" target="_blank"〉PubMed〈/a〉

Description: Se presentan los resultados de monitoreo de las poblaciones comerciales de cobo en el área comprendida entre los cayos El Cabezo y Boca de Sagua (220 49`N--230 04`N y los 790 35W—800 07´ `W), plataforma Norte de la Provincia de Villa Clara. A partir de los resultados de las densidades de individuos como índice de la abundancia y la estructura poblacional encontrada, se propone un potencial de captura de 104 TM (peso entero). Además, se definen las medidas de manejo para el uso sostenible del recurso Eustrombus gigas en esta zona. El aprovechamiento en carne desembarcada (Eviscerada y sin manto) para individuos adultos con talla comercial se obtiene por un factor de 0,074 (7,4%) del peso entero, que representa 7,7 TM. Se excluye el área protegida desde Las Picúas hasta Cayo Cristo.

Description: cobo (Eustrombus gigas), Caibarién, Villa Clara

Description: Variación en las corrientes superficiales en el Panama Bight durante eventos El Niño y La Niña ocurridos entre 1993 y 2007. Las anomalías climáticas modifican el patrón de circulación oceánica y con ello la conectividad demográfica. Sin embargo, en muchas regiones geográficas no hay suficiente evidencia de este cambio. Por ello, en el Panama Bight se realizó la comparación entre años neutrales, años El Niño y La Niña de moderada intensidad, para la Contracorriente Norecuatorial (CCNE), la Corriente Surecuatorial (CSE), la Corriente Costera (CCos) y para el remolino anticiclónico principal. Datos diarios de la topografía dinámica proporcionados por AVISO usando el producto MADT y del estrés del viento proporcionados por el Centro Europeo de Meteorología a Medio Plazo (ECMWF) se usaron para calcular la velocidad de las corrientes superficiales (promedio trimestral multianual) para los meses con mayor cantidad de huevos y larvas liberados por las especies con fase pelágica (sepnov). Se encontró que la magnitud de la velocidad para las tres corrientes oceánicas fue estadísticamente diferente entre los distintos eventos comparados, excepto para el anticiclón. Obteniendo que los valores de velocidad fueron mayores en años neutrales en relación a años Niño y Niña para la CCNE; mayores en años Niña, seguido por neutrales y Niño para la CSE; mayor en años neutrales y Niña pero menor para años Niño en la CCos; y tendencia de mayores valores en años La Niña para el remolino anticiclónico. Adicionalmente, se observó un aumento en el número de remolinos en años Niño moderado. Los resultados sugieren que la disminución en la velocidad de circulación de la CCNE y las posibles barreras creadas por remolinos ciclónicos y el remolino anticiclónico presentes cerca a la costa Suramericana podrían disminuir la dispersión pasiva de larvas y la conectividad funcional potencial entre el Pacífico Occidental, Central y Tropical Oriental, lo cual tiene implicaciones a nivel evolutivo, biogeográfico y ecológico (tasa de dispersión y efecto de rescate poblacional). Contrariamente, durante La Niña la CSE podría favorecer el transporte de larvas teleplantónicas hacia el Pacífico Central, material exportado desde la costa Suramericana mediante la CCos, ayudado por el remolino anticiclónico. Se concluye que los eventos climáticos anómalos alteran la velocidad de las corrientes oceánicas en el Panama Bight, lo cual podría afectar la conectividad funcional potencial entre septiembre y noviembre.

Description: Climatic anomalies have changed the ocean circulation pattern and thus the demographic connectivity. However, in many geographical regions there is insufficient evidence of this change. Therefore, comparisons were made between neutral years and years of El Niño and La Niña with moderate intensity, for the North Equatorial Counter Current (NECC), the South Equatorial Current (SEC), the Coastal Current (CoaC) and the main anticyclonic eddy in the Panama Bight. Daily dynamics topography data of the Maps of Absolute Dynamic Topography (MADT) provided by AVISO and daily wind stress data provide by the European Centre for Medium Range Weather (ECMWF) were used to calculate the speed of surface currents (multi-year, quarterly average), during months with the highest number of eggs and larvae released by the species with a pelagic phase (Sept-Nov). It was found that the speed magnitude for the three oceanic currents was statistically different among the compared events, except for the anticyclonic eddy; obtaining higher values of speed for neutral years in relation to years with El Niño or La Niña for the NECC, for the SEC higher values for La Niña years, followed by neutral years and a moderate El Niño years; for the CoaC higher velocity for neutral and La Niña years but the lowest for El Niño years; and a tendency of higher values in La Niña years for the anticyclonic eddy. Additionally, the number of eddies increased in moderate El Niño years. The results suggest that the decreased velocity of the NECC and the potential barriers created by the cyclonic eddies and the anticyclonic eddy near the South American coast could diminish the passive dispersal of larvae and the potential functional connectivity between the Western, Central and Eastern Tropical Pacific. Therefore, there are implications at the evolutionary, biogeographic, and ecologic levels (dispersion rates and population rescue effect). In contrast, during La Niña the SEC could favor teleplanktonic larval transport to the Central Pacific, material which is exported from the South American coast by CoaC, aided by the anticyclonic eddy. In conclusion, anomalous climatic events alter the velocity of oceanic currents in the Panama Bight; consequently these could change the functional potential connectivity from September to November.

Description: INVEMAR

Description: Published

Description: ENSO; Climatic Anomalies

Description: Author Posting. © The Author(s), 2012. This is the author's version of the work. It is posted here by permission of Taylor & Francis for personal use, not for redistribution. The definitive version was published in Aquaculture Economics & Management 16 (2012): 167-181, doi:10.1080/13657305.2012.678551.

Description: This study presents a framework for analyzing the interactions between aquaculture and capture fisheries in the context of ecosystem-based management. We extend a model of the economic and ecological systems in coastal New England by incorporating an aquaculture sector in a computable general equilibrium (CGE) model and by examining the forage fish and aquaculture link in a marine food web. We show that aquaculture and commercial fisheries interact in a complex way throughout the economic and ecological systems.

Description: This work was supported by the NOAA Saltonstall-Kennedy Grant Program (Award No. NA09NMF4270097), the MIT Sea Grant College Program (NOAA Award No. NA10OAR4170086, Subaward No. 5710002974), and the Johnson Endowment of the WHOI Marine Policy Center.

Description: 2013-06-08

Description: Submitted in partial fulfillment of the requirements for the degree of Ocean Engineer at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution August 1989

Description: When ocean waves in deep water interact with a current, the direction of propagation and characteristics of the waves such as height and length are affected. Swell in the open ocean can undergo significant refraction as it passes through major current systems like the Gulf Stream or Antarctic Circumpolar Current. Remote sensing techniques such as synthetic aperture radars (SAR) have the potential to detect wave systems over a wide geographical area. Combining a model for wave refraction in the presence of currents with SAR measurements, the inverse problem of using the measured wave data can be solved to determine the direction and magnitude of the intervening currents. In this study the behavior of swell measured by SAR on a satellite pass over the Gulf Stream is examined. The refraction predicted by a numerical model under conditions of varying current profiles and velocities is compared to SAR generated wave spectra. By matching the current profile which results in the best correlation of wave refraction to the SAR data, the tomographic problem of measuring the Gulf Stream current is solved. The best correlation between the model and SAR data is obtained when a current is modeled by a top hat velocity profile with a direction of 75° and a current speed of 2 m/s. The direction agrees with that visually observed from the SAR images, and the direction and speeds are close to the Coast Guard estimates for the Gulf Stream at the time of the SEASAT,pass. The current profiles used did not take into account a possible widening of the Gulf Stream at the position of the satellite overpass. There is a great deal of scatter in the SAR data, both before and in the Gulf Stream, so it is difficult to correlate every point with specific current behavior, but the increase in wave length and change in wave angle in the center of the Gulf Stream seem to indicate that there may be a non-uniform feature such as the formation of an eddy or other lateral variability near the current's edge.

Description: I was supported by the U. S. Navy.

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2012

Description: Interactions between the ocean circulation in sub-ice shelf cavities and the overlying ice shelf have received considerable attention in the context of observed changes in flow speeds of marine ice sheets around Antarctica. Modeling these interactions requires parameterizing the turbulent boundary layer processes to infer melt rates from the oceanic state at the ice-ocean interface. Here we explore two such parameterizations in the context of the MIT ocean general circulation model coupled to the z-coordinates ice shelf cavity model of Losch (2008). We investigate both idealized ice shelf cavity geometries as well as a realistic cavity under Pine Island Ice Shelf (PIIS), West Antarctica. Our starting point is a three-equation melt rate parameterization implemented by Losch (2008), which is based on the work of Hellmer and Olbers (1989). In this form, the transfer coefficients for calculating heat and freshwater fluxes are independent of frictional turbulence induced by the proximity of the moving ocean to the fixed ice interface. More recently, Holland and Jenkins (1999) have proposed a parameterization in which the transfer coefficients do depend on the ocean-induced turbulence and are directly coupled to the speed of currents in the ocean mixed layer underneath the ice shelf through a quadratic drag formulation and a bulk drag coefficient. The melt rate parameterization in the MITgcm is augmented to account for this velocity dependence. First, the effect of the augmented formulation is investigated in terms of its impact on melt rates as well as on its feedback on the wider sub-ice shelf circulation. We find that, over a wide range of drag coefficients, velocity-dependent melt rates are more strongly constrained by the distribution of mixed layer currents than by the temperature gradient between the shelf base and underlying ocean, as opposed to velocity-independent melt rates. This leads to large differences in melt rate patterns under PIIS when including versus not including the velocity dependence. In a second time, the modulating effects of tidal currents on melting at the base of PIIS are examined. We find that the temporal variability of velocity-dependent melt rates under tidal forcing is greater than that of velocity-independent melt rates. Our experiments suggest that because tidal currents under PIIS are weak and buoyancy fluxes are strong, tidal mixing is negligible and tidal rectification is restricted to very steep bathymetric features, such as the ice shelf front. Nonetheless, strong tidally-rectified currents at the ice shelf front significantly increase ablation rates there when the formulation of the transfer coefficients includes the velocity dependence. The enhanced melting then feedbacks positively on the rectified currents, which are susceptible to insulate the cavity interior from changes in open ocean conditions.

Description: National Science and Engineering Research Council of Canada

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1989

Description: A triangular CTD/ADCP survey was made across the Kuroshio west of Kyushu aboard the R/V Thompson during January, 1986 in order to investigate the water properties and flow field in the Kuroshio. A similar CTD survey was made in July, 1986 aboard the R/V Washington to study the seasonal variability in the Kuroshio. The Kuroshio in this region exhibited a marked seasonal change in its near-surface stratification and water properties. In January, the Kuroshio water was separated from the vertically well-mixed coastal water over the shelf by a strong front located near the shelf break. Horizontal mixing between the Kuroshio and coastal water was observed but was limited near the shelf break. In July, surface coastal water extended far past the shelf break over the Kuroshio region near the surface, and in turn, Kuroshio water intruded onto the shelf near the bottom. Mixing between the Kuroshio and coastal water was found over much of the mid and outer shelf and upper slope, spanning a cross-stream distance of 75 km. In addition, evidence of deep vertical mixing within the Kuroshio itself was found near 32.0°N and 128.2°E, most likely due to internal tidal mixing over the slope. Since Loran C navigation coverage in the study region was poor during the R/V Thompson cruise, a simple averaging technique has been used to convert the ADCP data into an absolute velocity. An error analysis shows that the total error in the absolute ADCP velocity was about ±5 cm/s. The absolute geostrophic velocity using the absolute Doppler velocity at 60 m as the reference velocity was then calculated for the sides of the triangle. The results show that the ADCP velocity shear was in good agreement with the geostrophic shear in the Kuroshio. The Kuroshio flowed through the western section as a coherent current, then split into two streams around a tall seamount as it left through the eastern section. Some recirculation also occurred between the core of the Kuroshio and the slope as well as near the seamount. The geostrophic velocity field calculated relative to the bottom missed some of the important features of the true flow field such as splitting of the Kuroshio and the recirculation in the slope region. The volume, salt and heat transports of the Kuroshio during the January 1986 survey have been cakulated using the absolute geostrophic velocity and CTD data. The volume transport of the Kuroshio west of Kyushu in January 1986 was 31.7± 2.0 Sv, which is comparable to that of the Gulf Stream in the Florida Strait. The volume transport through the triangle was conserved within measurement uncertainty, so that a streamfuction field can be defined by the transport. The resulting streamlines clearly show the structure of the flow field in the Kuroshio and its adjacent currents during the survey. The advective heat transport of the Kuroshio west of Kyushu in January 1986 was 28.2 ± 1.8 x 1014 W. The salt transport in January 1986 was about 108.0 ± 7.3 x 1010 kg/s, and the net salt flux was zero within measurement error. Analysis of the potential vorticity based on the January 1986 absolute geostrophic velocity field shows that the total potential vorticity in the Kuroshio may be approximately given by the product of the vertical gradient of the potential density and the sum of the planetary and relative vorticities. The distribution of relative vorticity plays a significant role in determining the structure of the potential vorticity in the Kuroshio. The path of the Kuroshio can be traced in the field of potential vorticity. Facing in the direction of the current, the axis of the maximum velocity is located to the right of the core of maximum potential vorticity. Finally, the Kuroshio was potentially unstable since the gradient of potential vorticity changed its sign on potential density surfaces across the Kuroshio.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 1992

Description: This thesis consists of two parts: (I) variability of currents and water properties in late spring in the northern Great South Channel and (II) numerical study of stratified tidal rectification over Georges Bank. In part I, the combined analysis of CTD, ADCP, satellite-track drifters, and zooplankton distributions in the northern Great South Channel clearly shows (1) the seasonal evolution of the surface low salinity plume, (2) the threedimensional structure of residual flow, and (3) a coherent relationship between the surface low salinity plume and high concentration of zooplankton. In part II, the numerical model of Georges Bank shows that as the fluid becomes stratified , tidal mixing and rectification intensify both along- and cross-bank residual currents and modify the vertical structure of the flow. Along- and cross-bank residual currents increase as either stratification increases or the depth of the bank decreases. Model results over Georges Bank are in good agreement with observation, particularly in the position of the tidal mixing front and residual currents on the northern flank of the Bank.

Description: This research was supported by the National Science Foundation under grants OCE 87-13988 and OCE 91-01034 and by the National Center for Atmospheric Research (NCAR) under computer time grants Nos. 35781029 and 35781035.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1994

Description: The thesis addresses the applicability of traditional hydraulic theory to an unstable, mid-latitude jet where the only wave present is the Rossby wave modified by shear. While others (Armi 1989, Pratt 1989, Haynes et al.1993 and Woods 1993) have examined specific examples of shear flow "hydraulics", my goal was to find general criteria for the types of flows that may exhibit hydraulic behavior. In addition, a goal was to determine whether a hydraulic mechanism could be important if smaller scale shear instabilities were present. A flow may exhibit hydraulic behavior if there is an alternate steady state with the same functional relationship between potential vorticity and streamfunction. Using theorems for uniqueness and existence of two point boundary value problems, a necessary condition for the existence of multiple states was established. Only certain flows with non-constant, negative dQ(ψ)/dψ have alternate states. Using a shooting method for a given transport and a given smooth relationship between potential vorticity and streamfunction, alternate states are found over a range of beta. Multiple solutions arise at a pitchfork bifurcation as a stability parameter is raised above the stability threshold determined by the necessary condition for instability. The center branch of the pitchfork is unstable to the gravest mode, while the two outer branches do not even have discrete modes. Other pitchfork bifurcations occur as higher meridional modes become unstable. Again, the inner branch is unstable to the next gravest mode, while the outer branches do not support this discrete mode. These results place the barotropic instability problem into a large set of nonlinear systems described by bifurcation theory. However, if the eastward transport across the channel is large enough, the normal modes may stabilize and these waves have a phase speed less than the minimum velocity of the flow. In this case, the flow is analogous to sub-critical hydraulic flow. The establishment of these states and the nature of transitions between them is studied in the context of an initial value problem, solved numerically, in which the zonally uniform jet is forced to adjust to the sudden appearance of an obstacle. The time-dependent adjustment of an initially stable flow exhibits traditional hydraulic behavior such as control and influence in the far-field. However, if the flow is unstable, the instability dominates the evolution. If the topographic slope renders the flow more unstable than the ambient flow, then the resulting adjustment can be understood as a local instability. The thesis has established a connection between hydraulic adjustment and the barotropic instability of the flow. Both types of dynamics arise from adjustments among multiple equilibria in an unforced, inviscid fluid.

Description: This research was supported by National Science foundation grants OCE 91-15359 and OCE 89-16446, and also by a Department of Defense AASERT grant administered under ONR N00014-89-J-1182.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 1993

Description: The dynamical aspects involved in the assimilation of altimeter data in a numerical ocean model have been investigated. The model used for this study is a quasi-geostrophic model of the Gulf Stream region. The data that have been assimilated are maps of sea surface height which have been obtained as the superposition of sea surface height variability deduced from the Geosat altimeter measurements and a mean field constructed from historical hydrographic data. The method used for assimilating the data is the nudging technique. Nudging has been implemented in such a way as to achieve a high degree of convergence of the surface model fields toward the observations. We have analyzed the mechanisms of the model adjustment, and the final statistical equilibrium characteristics of the model simulation when the surface data are assimilated. Since the surface data are the superposition of a mean component and an eddy component, in order to understand the relative role of these two components in determining the characteristics of the final st atistical steady state, we have considered two different experiments: in the first experiment only the climatological mean field is assimilated, while in the second experiment the total surface streamfunction field (mean + eddies) has been used. We have found that the mean component of the surface data determines, to a large extent, the structure of the flow field in the subsurface layers, while the eddy field, as well as the inflow/outflow conditions at the open boundaries, affect its intensity. In particular, if surface eddies are not assimilated only a weak flow develops in the two deeper model layers where no inflow/ outflow is prescribed at the boundaries. Comparisons of the assimilation results with available in situ observations show a considerable improvement in the degree of realism of the climatological model behavior, with respect to the model in which no data are assimilated. In particular, the possibility of building into the model more realistic eddy characteristics, through the assimilation of the surface eddy field, proves very successful in driving components of the mean model circulation that are in good agreement with the available observations.

Description: This research was carried out with the support of the National Aeronaut ics Space Administration, through a contract to MIT from the Jet Propulsion Laboratory, # 958208, as a part of the TOPEX-Poseidon investigation.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and Woods Hole Oceanographic Institution February 1994

Description: In this work we study motion of a baroclinic upper-ocean eddy over a large-scale topography which simulates a continental slope. We use a quasigeostrophic f-plane approximation with continuous stratification. To study this problem we develop a new numerical technique which we call "semi-lagrangian contour dynamics". This technique resembles the traditional 2-D contour dynamics method but differs significantly from it in the numerical algorithm. In addition to "Lagrangian" moving contours it includes an underlying "Eulerian" regular grid to which vorticity or density fields are interpolated. To study topographic interactions in a continuously stratified model we use density contours at the bottom in a similar manner as vorticity contours are used in the standard contour dynamics. For the case of a localized upper-ocean vortex moving over a sloping bottom the problem becomes computationally 2-dimensional (we need to follow only bottom density contours and the position of the vortex itself) although the physical domain is still 3-dimensional. Results of the numerical model lndicate importance of baroclinic effects in the vortex-topography interaction. After the initial surge of topographic Rossby waves a vortex moves almost steadily due to the interaction with a bottom density anomaly which is created and supported by a vortex itself. This anomaly is equivalent to a region of opposite-signed vorticity with a total circulation exactly compensating that of a vortex. This results in a vertically aligned dipolar structure with the total barotropic component equal to zero. Analytical considerations explaining this effect are presented and formulated in a more general statement which resembles but does not coincide with the "zero angular momentum theorem" of Flierl, Stern and Whitehead, 1983. In such steady translation the centroid of a bottom density anomaly is displaced horizon tally from the center of an upper-ocean vortex so the whole system moves due to this misalignment, which is known as a "he tonic mechanism". Cyclonic vortices go generally upslope, and anticyclones - in a downslope direction. The along-slope component of their motion depends upon the strength of a vortex, curvature of the bottom slope and background flows. When surrounded by a bowl-shaped topography anticyclonic vortices tend to stay near the deepest center of a basin, even resisting ambient flows which advect them outward. Application of this results to various oceanic examples (particularly to the "Shikmona eddy" in the Eastern Meditenanian) is discussed. Our results show that the behavior of a vortex over a sloping bottom differs significantly from its motion on the planetary beta-plane (but with a flat bottom). To explain this difference we introduce the concept of a "wave-breaking regime" relevant for the case of a planetary beta-effect, and a "wave-gliding regime" which characterizes the interaction of an eddy with a topographic slope.

Description: This work was supported by the NSF grant #OCE 90-12821.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and Woods Hole Oceanographic Institution October 1993

Description: Hydrographic and expendable current profiler (XCP) data taken during the Gulf of Cadiz Expedition in September 1988 are analyzed to diagnose the mixing and dynamics of the Mediterranean outflow. The overall structure of the outflow is consistent with that described in the historical literature (Heezen and Johnson, 1969). This data shows that the overflow transport doubles from .85 Sv to 1.9 Sv, and that the velocity weighted salinity decreases from 37.8 pss to 36.7 pss in the first 60 km of the path. The core salinity of the neutrally buoyant outflow near Cape St. Vincent is 36.6 pss, which indicates that most of the mixing has taken place close to the Strait in the initial descent of the outflow. Cross stream variations in the overflow T/S properties increase as the flow spreads from 10 km to 90 km wide. The outflow begins with less than a 0.5°C across-stream variation in temperature in the Strait with the saltiest, coldest water to the south and slightly fresher and warmer outflow to the north. As the outflow spreads, the northern near-shelf flow follows a path higher in the water column and mixes with warmer North Atlantic water than does the deeper offshore flow. Within the first 100 km, the cross stream variation in temperature on an isopycnal becomes more than a 2°C. The flow eventually settles along two preferred isopycnals: 27.5 and 27.8 (Zenk 1975b). The spreading of the flow contains both a barotropic and baroclinic character. The average change in angle above and below the maximum velocity of the outflow is 8°while at the edges of the flow the average direction of the outflow diverges by as much as 50°. Gradient Richardson numbers less than 1/4 are found in the interface (up to 50 m thick) between westward flowing Mediterranean water and eastward flowing North Atlantic water, even though there is a strong stabilizing stratification present. Bulk Froude numbers greater than 1 are found near the Strait coincident with the vigorous mixing noted above. Lower bulk Froude numbers were observed in regions where less entrainment was taking place. The momentum balances are diagnosed using hydrographic and XCP data. Evaluation of the cross stream momentum balance shows the importance of advection as the flow makes a 90 degree inertial turn upon entering the Gulf of Cadiz. A form of the Bernoulli function can be evaluated to infer the total stress (entrainment and bottom drag) acting on the outflow. This stress is as large as 5 Pa within 20 km of the Strait, while further downstream the stress decreases to about 1/2 Pa. The entrainment stress estimated from the property fluxes reaches a maximum of about 0.8 Pa near section C, indicating that bottom stress is dominant. Near the Strait, advection, bottom drag and the Coriolis force are all critical to the dynamics of the outflow. Further downstream, the outflow becomes a damped geostrophic current. A simple geostrophic adjustment model is used to show that in the absence of frictional stresses, the outflow would very quickly become geostrophically balanced and descend only about 10 m down the continental slope. Thus, friction is critical for the outflow to cross isobaths. A simple numerical model that uses a Froude number dependent entrainment and a quadratic bottom friction law is used to simulate the outflow (Price and Baringer, 1993). Some of the properties of the outflow including localized entrainment, large stresses and high Rossby number of the flow (initially as high as 0.6), are simulated rather well, though the model overestimates the magnitude of the outflow current. We suspect that this is a consequence of assuming a passive ocean. Two different methods for specifying the broadening of the flow are compared: one using the highly parameterized concept of Ekman spreading, the other using the conservation of potential vorticity. The potential vorticity broadening more accurately reproduces the observed width of the flow near Cape St. Vincent where the width varies inversely with the bottom slope. However, both methods produce essentially the same equilibrium temperature, salinity and transport of the outflow which is a testament to the robustness of the model solution. with the formation process of NADW.

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 1996

Description: During January-March, Scotian Shelf water has been observed to flow episodically from the southwestern Scotian Shelf directly across the Northeast Channel to Georges Bank. The possible factors that allow Scotian Shelf water to break the topographic constraint presented by the Northeast Channel and flow directly to Georges Bank are considered. As a simple analog to the flow over the southwestern Scotian Shelf near the Northeast Channel, the adjustment of a barotropic current near a shelf-break to a sharp bend in the shelf topography is studied numerically. For parameters within the oceanographic range, the adjustment to the bend is smooth and steady with no eddies shed at the corner. The vorticity dynamics allow a balance between the vortex stretching in the flow and the curvature in the flow. This is possible since the bend is a right-hand one facing downstream, a similar balance not being possible for a left-hand bend, in which case eddy formation is likely. A simple model of this balance clarifies the vorticity dynamics and provides the scaling rc = √eL/0.765 for any streamline in the flow, where rc is the radius of curvature at the corner, E = u0/fL and L = h0/b, where uo is the initial speed, f the coriolis parameter, h0 the initial depth and b the bottom slope. These results show that other factors such as stratification, wind stress, and time-dependent inflow must play a role in any flow across the Northeast Channel.

Description: I am very grateful to the US-GLOBEC program for providing the funding for this study (N.S.F. grant OCE-9313671).

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution August 1995

Description: The problem of estimating boundary and initial conditions for a regional open-ocean model is addressed here. With the objective of mimicking the SYNOP experiment in the Gulf Stream system, a meandering jet is modeled by the fully nonlinear barotropic vorticity equation. Simulated observations of current velocity are taken using current meters and acoustic tomography. Twin experiments are performed in which the adjoint method is used to reconstruct the flow field. The estimated flow is forced to resemble the true flow by minimizing a cost function with respect to some control variables. At the minimum, the error covariance matrix of the estimated control variables can be evaluated from the inverse Hessian of the cost function. The first major scientific objective of this work is the estimation of initial and boundary conditions for the model from sparse interior data. First the vorticity initial conditions are used as control variables and the boundary conditions are kept fixed. The jet-like flow is found to induce strong dependence of the model/data misfit upon the specified boundary conditions. Successively, the boundary values of streamfunction and vorticity are included among the control variables and estimated together with the initial conditions. Experiments are performed with various choices of scaling and first guess for the control variables, and various observational strategies. The first major new result obtained is the successful estimation of the complete set of initial and boundary conditions, necessary to integrate the vorticity equation forward in time. From a time-invariant first guess for the boundary conditions, the assimilation is able to create temporal variations at the boundaries that make the interior flow match well the velocity observations, even when noise is added. It is found that information from the observations is communicated to the boundaries by advection of vorticity and by the instantaneous domain-wide connections in the streamfunction field due to the elliptic character of the Poisson equation. The second major scientific objective is the estimation of error covariances in the presence of strongly nonlinear dynamics. The evaluation of the full error covariance matrix for the estimated control variables from the inverse Hessian matrix is investigated along with its dependence upon the degree of nonlinearity in the dynam1cs. Further major new results here obtained are the availability of off-diagonal covariances, the successful calculation of error covariances for all boundary and initial conditions, and the estimation of errors for the interior fields of streamfunction and vorticity. The role of the Hessian matrix is assessed in gauging the sensitivity of the estimated boundary and initial conditions to the data. Also, the importance is stressed of retaining off-diagonal structure of the Hessian to obtain more accurate error estimates.

Description: Funding for this research was provided by Office of Naval Research (ONR) Grant N00014-90-J-1481 and, since 1/1/95, ONR Grant N00014-95-1-0226.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 1995

Description: Geosat altimeter data and numerical model output are used to examine the circulation and dynamics of the Antarctic Circumpolar Current (ACC). The mean sea surface height across the ACC has been reconstructed from height variability measured by the Geosat altimeter, without assuming prior knowledge of the geoid. For this study, an automated technique has been developed to estimate mean sea surface height for each satellite ground track using a meandering Gaussian jet model, and errors have been estimated using Monte Carlo simulation. The results are objectively mapped to produce a picture of the mean Subantarctic and Polar Fronts, which together comprise the major components of the ACC. The locations of the fronts are consistent with in situ observations and indicate that the fronts are substantially steered by bathymetry. The jets have an average Gaussian width of about 44 km in the meridional direction and meander about 75 km to either side of their mean locations. The width of the fronts is proportional to 1/f, indicating that with constant stratification, the width is proportional to the baroclinic. Rossby radius. The average height difference across the Subantarctic Front (SAF) is 0.7 m and across the Polar Front (PF) 0.6 m. The mean widths of the fronts are correlated with the size of the baroclinic Rossby radius. The meandering jet model explains between 40% and 70% of the height variance along the jet axes. Bathymetric constrictions are associated with increased eddy variability, a smaller percentage of which may be explained by the meandering of the ACC fronts, indicating that propagating eddies and rings may be spawned at topographic features. Detailed examination of spatial and temporal variability in the altimeter data indicates a spatial decorrelation scale of 85 km and a temporal e-folding scale of 34 days. The sea surface height variability is objectively mapped using these scales to define autocovariance functions. The resulting maps indicate substantial evidence of mesoscale eddy activity. Over 17-day time intervals, meanders of the PF and SAF appear to elongate, break off as rings, and propagate. Statistical analysis of ACC variability from altimeter data is conducted using empirical orthogonal functions (EOFs ). The first mode EOF describes 16% of the variance in total sea surface height across the ACC; reducing the domain into basin scales does not significantly increase the variance represented by the first EOF, suggesting that the scales of motion are relatively short, and may be determined by local instability mechanisms rather than larger basin scale processes. Likewise, frequency domain EOFs indicate no statistically significant traveling wave modes. The momentum balance of the ACC has been investigated using both output from a high resolution primitive equation model and sea surface height measurements from the Geosat altimeter. In the Semtner-Chervin general circulation model, run with approximately quarter-degree resolution and time varying ECMWF winds, topographic form stress is the dominant process balancing the surface wind forcing. Detailed examination of form stress in the model indicates that it is due to three large topographic obstructions located at Kerguelen Island, Campbell Plateau, and Drake Passage. In order to reduce the effects of standing eddies, the model momentum balance is considered in stream coordinates; vertically integrated through the entire water column, topographic form drag is the dominant balance for wind stress. However, at mid-depth the cross-stream momentum transfer is dominated by horizontal biharmonic friction. In the upper ocean, horizontal friction, mean momentum flux divergence, transient momentum flux divergence, and mean vertical flux divergence all contribute significantly to the momentum balance. Although the relative importance of individual terms in the momentum balance does not vary substantially along streamlines, elevated levels of eddy kinetic energy are associated with the three major topographic features. In contrast, altimeter data show elevated energy levels at many more topographic features of intermediate scales, suggesting that smaller topographic effects are better able to communicate with the surface in the real ocean than in the model. Transient Reynolds stress terms play a small role in the the overall momentum balance; nonetheless, altimeter and model measurements closely agree, and suggest that transient eddies tend to accelerate the mean flow, except in the region between the major fronts which comprise the ACC. Potential vorticity is considered in the model output along Montgomery streamfunction. Even at about 1000 m depth, it varies in response to wind forcing, largely as a result of changes in vertical stratification, indicating that forcing and dissipation do not locally balance in the Southern Ocean. In order to compare model and altimeter potential vorticity estimates, two different proxies for potential vorticity on surface streamlines are considered. Both proxies show very similar results for model and altimeter, suggesting that differences in surface streamlines estimated by the altimeter and the model are not significant in explaining the Southern Ocean flow. The proxies are both roughly conserved along surface height contours but undergo substantial jumps near topographic features. However, they cannot capture stratification changes which may be critically important to the overall potential vorticity balance.

Description: Funding for this research was provided by an Office of Naval Research graduate student fellowship and National Aeronautics and Space Administration contract NAGW-1666.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 1991

Description: A set of four hydrographic sections through the Brazil Current are analyzed to identify downstream changes in the Brazil Current. The data, from the Thomas Washington Marathon Cruise, Leg 9, are at 27, 31, 34 and 36°S. The region they span details the change of the current from a relatively small near surface feature to a large, deep current. While the Brazil Current does not appear to develop transports as large as those found in the Gulf Stream, the calculated transports greatly exceed previous estimates. At 27°S the current extends down to approximately 700 m and transports 12 Sv southward; this value is consistent with previous estimates farther north. Downstream, surface layer transport increases, the current deepens, and the transport reaches a maximum of 80 Sv at 36°S. Part of the growth comes from the tight recirculation found just offshore of the Brazil Current. The recirculation strengthens and deepens to the south, with a minimum transport of 4 Sv north at 27°S and a maximum of 33 Sv at 36°S. The change in the current is also reflected in its shear profiles. At 27°S Brazil Current shear is found only in the upper portion of the water column, over the continental slope. Downstream, the current moves off the slope into deeper water and develops top-to-bottom, monotonic shear. To obtain velocity from the shear profiles, zero velocity surfaces are chosen based on conservative use of tracer information. A simple basin-wide model is used at 31°S to tie limits on the size of the Brazil Current and recirculation to various limits on layer-to-layer exchanges south of the section. The multi-layer model - based on changes in depth of several isotherms is used to extend the interpretation of the current beyond that of an isolated ocean feature. The model is required to conserve mass in each layer, either by applying barotropic transports or by allowing layer-to-layer exchanges south of the section. Solutions are deemed acceptable if the sense, or direction, of the various layer-to-layer conversions are consistent with accepted ideas of water mass formation. Initially, a two layer model is employed. Governed by the conservation of mass in each layer, the two layer model has only one constraint on the resulting solutions: a conversion of cold-to-warm water in the south (or the surface layer flowing north and the deep layer flowing south). Such a meridional flow pattern is consistent with the equatorward heat flux in the South Atlantic. The single constraint, however, is not strong enough to limit the solution region in any significant way. The final model presented has four layers, and acceptable solutions have the net transports of the surface layer and the bottom water northward and form intermediate water from North Atlantic Deep Water in the south. The resulting solution set has a fairly small range of transports for the Brazil Current, with surface layer transports between 20 and 35 Sv; this range is consistent with the value calculated from hydrographic data at 31°S. Given the complex interleavings of the South Atlantic water masses, the four layer model performs remarkably well. Finally, total potential vorticity is calculated from the hydrographic sections. Contrary to what one might expect, the reference level choice is not a significant problem: where currents are large, most of the signal in relative potential vorticity comes from the measured shear, and where currents are small, the relative potential vorticity is not significant compared to the planetary vorticity. Unfortunately, the process of taking two horizontal derivatives of the density field results in a jittery relative potential vorticity signal. As a result, a clear potential vorticity profile could not be constructed for the current. This variablitiy may be real -the ocean is frequently much noisier than one imagines. It may also be possible, though, to smooth the data sufficiently so that a cleaner picture emerges. Despite the problems involved in obtaining a quantitative profile of the potential vorticity, qualitative changes are useful in detecting different flow regimes. By comparing the downstream changes in total and planetary potential vorticity, one can deduce frictional and inertial regimes in the different layers. The presence of a frictional regime at the inshore edge suggests that care should be taken in assuming that potential vorticity is conserved in western boundary currents. In addition the potential vorticity sections trace a pattern of the recirculation feeding into the Brazil Current in the upper layers; other tracers did not provide a clear image. The final picture which emerges is not of a small, surface-trapped Brazil Current; rather, it is that of a classic western boundary current, increasing in strength and depth before turning east into the interior ocean.

Description: Financial support for the data collection and initial analysis was provided through the Office of Naval Research South Atlantic Accelerated Research proposal under contract N00014-82-C-0019. Continued analysis was supported by the National Science Foundation under grant OCE86-14486.

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution August 1991

Description: Using a semi-geostrophic, reduced gravity thin jet model, we analytically study the evolution of initial meanders into pinched-off rings. The model used is similar to the path equation developed by Flierl and Robinson {1984) for vertically coherent meanders. However, in the present model, the meanders are baroclinic, and a stretching term arises due to the motion of the interface. It can be shown that the equation governing the time-dependent meander of this jet (Pratt, 1988) can be transformed into the Modified Korteweg- deVries (MKdV) equation in intrinsic coordinates. The MKdV equation admits two types of solitary wave solutions, loop solitons and breathers. The breathers are permanent meanders which propagate on the path , and some are able to form rings. Using the inverse scattering transform , we can predict breather and ring formation for simple initial meanders. The inverse scattering t ransform is applied to S and Ω shaped meanders with piecewise constant and continuous curvature. S shaped meanders, or steps, must be multi-valued to form breathers, and must have very steep angles in order to form rings. Due to integral constraints, Ω shaped meanders, or lobes, are unable to pinch together to form rings unless they are wide enough so that the two side flanks of the lobe act as two independent steps. The numerical solutions indicate that the breathers predicted by the inverse scattering is a very good approximation to the full solution.

Description: This work has been supported by NSF contract number OCE 89-16446 and ONR contract number N00014-S9-J-1182.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution March 1992

Description: Rotating baroclinic and barotropic boundary currents flowing around a corner in the laboratory were studied in order to discover the circumstances under which eddies were produced at the corner. Such flows are reminiscent of oceanic coastal flows around capes. When the baroclinic currents, which consisted of surface flows bounded by a density front, encountered a sharp corner, immediately downstream of the corner an anticyclone grew in the surface layer for an angle of greater than 40 degrees. Varying the initial condition of the flow or the depth of the lower layer did not noticeably affect the gyre's properties except for its growth speed, which was greater when the lower layer was shallower. The barotropic currents were pumped along a sloping bottom, and also formed anticyclonic gyres which quickly attained an approximately steady state. For a given topography, the size of the gyre was proportional to the inertial radius u/f. Volume flux calculations based on the surface velocity revealed vertical shear which increased with gyre size. Hydraulic models were also applied to flow around gently curving topography to determine the critical separation curvature as a function of upstream parameters.

Description: This work was supported by the National Science Foundation grant OCE 89-15408.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1991

Description: This thesis examines the effect of mean large-scale currents on the vertical structure of the upper ocean during two recent observational programs: the Long Term Upper Ocean Study (LOTUS) and the TROPIC HEAT experiments. The LOTUS experiment took place in the northwest Atlantic Ocean, a mid-latitude region away from strong mean currents, and extended over one entire seasonal cycle. The TROPIC HEAT experiments took place in the central equatorial Pacific Ocean during two 12-day periods in 1984 and 1987, at opposite extremes of the seasonal cycle. We use observations from these field experiments as well as one-dimensional numerical models of the upper ocean to analyze the dynamics of the vertical structure of the upper ocean at the equator and in mid-latitudes. Due to the different nature of the observations, we focus on the long term mean structure of the upper ocean in the LOTUS observations (Chapters 2 and 3), and on the diurnal cycle in the equatorial upper ocean in our analysis of the TROPIC HEAT observations (Chapters 4 and 5). In the LOTUS observations, we find that the observed current is coherent with the wind over low frequencies (greater than an inertial period). Using a wind-relative averaging method we find good agreement with Ekman transport throughout the first summer and winter of the LOTUS experiment, with the exception of a downwind component in the wintertime. The mean current spiral is flat compared to the classic Ekman spiral, in that it rotates less with depth than does the Ekman spiral. The mean current has an e-folding depth scale of 12m in the summer and 25 min the winter. Diurnal cycling is the dominant variability in the summer and determines the vertical structure of the spiral. In the winter, diurnal cycling is almost non-existent due to greatly reduced solar insolation. There is a persistent downwind shear in the upper 15 m during the winter which may be partially due to a bias induced by surface wave motion but which is also consistent with a logarithmic boundary layer. The Price et al. (1986) model is reasonably successful in simulating the current structure during the summer, capturing both the mean and the diurnal variation. The model is less successful in the winter, though it does capture the overall depth scale of the current spiral. In our analysis of the TROPIC HEAT observations, we extend the Price et al. (1986) model to the equatorial upper ocean. The model is initialized with the stratification and shear of the Equatorial Undercurrent (EUC), and is driven with heating and wind stress. A surface mixed layer is determined by bulk stability requirements, and a transition layer below the mixed layer is simulated by requiring that the gradient Richardson number be no less than 1/4. A principal result is that the nighttime phase of the diurnal cycle is strongly affected by the EUC, resulting in deep mixing and large dissipation at night consistent with observations of the equatorial upper ocean during TROPIC HEAT. Other features of the equatorial circulation (upwelling and the zonal pressure gradient) are of little direct importance to the diurnal cycle. The daytime (heating) phase of the simulated diurnal cycle is unaffected by equatorial circulation and is very similar to its mid-latitude counterpart. Solar heating produces a stably stratified surface layer roughly 10 m thick within which there is little, 0(3 x 10-8 W kg-1), turbulent dissipation. The diurnal stratification, though small compared to the EUC, is sufficient to insulate the EUC from wind stress during the day. For the typical range of conditions at the equator, diurnal warming of the sea surface is 0.2-0.5°C, and the diurnal variation of surface current (diurnal jet) is 0.1-0.2 m s-1, consistent with observations. The nighttime (cooling) phase of the simulated diurnal cycle is quite different from that seen at mid-latitudes. As cooling removes the warm, stable surface layer, the wind stress can work directly against the shear of the EUC. This produces a transition layer that can reach to 80 m depth, or nearly to the core of the EUC. Within this layer the turbulent dissipation is quite large, 0(2 x 10-7 W kg-1). Thus, the simulated dissipation has a diurnal range of more than a factor of five, as observed in the 1984 TROPIC HEAT experiment, though the diurnal cycle of stratification and current are fairly modest. Dissipation estimated from the model is due to wind working directly against EUC, and is similar to observed values of dissipation in both magnitude and depth range. Overall dissipation values in the model are set by the strength of the wind stress rather than the structure of the EUC, and rise approximately like u*3 for a given Undercurrent. This suggests that the lower values of dissipation observed in the 1987 TROPIC HEAT experiment were due to the lower wind stress values rather than the relatively weak Undercurrent. The main findings of this thesis are: 1) When the diurnal cycle in solar heating is strong, it determines the local vertical structure of the upper ocean (in both the LOTUS and TROPIC HEAT observations). The Price et al. (1986) model and its extension to the equator simulate the upper ocean fairly well when the diurnal cycle is strong. Under these conditions it is necessary to make measurements very near the surface ( 〈 10 m depth) to fully resolve the wind-driven flow. 2) When surface waves are strong, surface-moored measurements of current may have a significant wave bias. To accurately estimate this bias, simultaneous measurements of current, current meter motion, and surface waves are needed. 3) Mean currents strongly amplify the nighttime phase of the diurnal cycle in the equatorial upper ocean, and therefore alter the mean structure of the equatorial upper ocean.

Description: The Office of Naval Research supported this work under contract N00014-89-J-1053.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution April 1992

Description: A pair of simple models representing the interaction of a continuously stratified f-plane quasigeostrophic lens with a uniform external shear flow is examined. The study is motivated by the desire to understand the processes that affect Mediterranean Salt Lenses and other mesoscale lenses in the ocean. The first model represents the eddy as a pair of quasigeostrophic 'point potential vortices' in uniform external shear, where the two point vortices are imagined to represent the top and bottom of a baroclinic eddy. While highly idealized, the model succeeds in qualitatively reproducing many aspects of the behavior of more complex models. In the second model the eddy is represented by an isolated three dimensional patch characterized by quasigeostrophic potential vorticity linear in z, in a background flow with constant potential vorticity. The boundary of the lens may be deformed by interactions with a uniform background shear. A family of linearized analytical solutions representing such a vortex is discussed in Chapter 3. These solutions represent lens-like eddies with trapped fluid cores, which may propagate through the surrounding water when there is external vertical shear. The analysis predicts the possible forms of the boundary deformation in a specified external flow, and the precession rate of normal mode boundary perturbations in the absence of external flow. The translation speed of the lens with respect to the surrounding fluid is found to be a simple function of the external vertical shear and the core baroclinicity. A numerical algorithm which is a generalization of the contour dynamics technique to stratified quasigeostrophic flow is used to extend the linear results into the nonlinear regime. This numerical analysis allows a determination of the range of environmental conditions (e.g., the maximum shear and/ or core baroclinicity) in which coherent vortex solutions can be found, and allows the stability of the steadily translating solutions to be examined directly. It is found that the solutions are stable if neither the external shear nor the core baroclinicity is too large, and that the breakdown of the unstable solutions is characterized by the loss of an extrusion of core fluid to the surrounding waters. The translation speeds of the large amplitude numerical solutions are found to have the same functional dependence on the external vertical shear and the core baroclinicity that was found in the linear analysis, and it is demonstrated that the solutions translate at a rate which is equal to the background flow speed at the center of potential vorticity of the lens. As a test of the model results, new data from a recent SOFAR float experiment are presented and compared with the model predictions. The data show that the cores of two different Mediterranean Salt Lenses are tilted, presumably as a result of interactions with external flows. Both the sense of the tilt and its relation to the translation of the lens are in qualitative agreement with the model solutions.

Description: I am happy to acknowledge the support of the Office of Naval Research (grant N00014-89-J-1182) and the National Science Foundation (grants OCE 8916446 and OCE 87-00601).

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1992

Description: This study concerns the barotropic interactions between a mesoscale eddy and a straight monotonic bottom topography. Through simple to relatively complicated modeling effort, some of the fundamental properties of the interaction are investigated. In chapter two, the fundamental aspects of the interaction are examined using a simple contour dynamics model. With the simplest model configuration of an ideal vortex and a step topography, the basic dynamical features of the observed oceanic eddy-topography interaction are qualitatively reproduced. The results consist of eddy-induced cross-topography exchange, formation of topographic eddies, eddy propagation and generation of topographic waves. In chapter three, a more complicated primitive equation model is used to investigate a mesoscale eddy interacting with an exponential continental shelf/slope topography on both f and β-planes. The f-plane model recasts the important features of chapter two. The roles of the eddy size and strength and the geometry of topography are studied. It is seen that the multiple anticyclonic eddy-slope interactions strongly affect the total cross-slope volume transport and the evolution of both the original anticyclone and the topographic eddy. Since a cyclone is trapped at the slope and eventually moves on to the slope, it is most effective in causing perturbation on the shelf and slope. The responses on the shelf and slope are mainly wavelike with dispersion relation obeying that of the free shelf-trapped wave modes. On the β-plane, the problem of an eddy colliding onto a continental shelf/slope from a distance with straight or oblique incident angles is investigated. It is found that the straight eddy incident is more effective in achieving large onslope eddy penetration distance than the oblique eddy incident. The formation of a dipole-like eddy pair consisting of the original anticyclone and the topographic cyclone acts to suppress the eddy decay due to long Rossby wave radiation. A weak along-slope current near the edge of the slope is found, which is part of a outer slope circulation cell originated from the Rossby wave wake trailing the propagating eddy. Model-observation comparisons in_chapter four show favorable qualitative agreement of the model results with some of the observed events in the eastern U.S. continental margins and in the Gulf of Mexico. The model results give dynamical interpretations to some observed features of the oceanic eddy-topography interactions and provide enlightening insight into the problem.

Description: A computational fluid dynamics (CFD) study was performed of the wind flow around two ocean buoys used to collect meteorological data from sensors mounted on the buoy tower. The CFD approach allowed wind velocity perturbations to be evaluated as a step towards quantifying the impacts of flow distortion on buoy wind measurements. The two buoys evaluated were the Wood Hole Oceanographic Institution WHOI Modular Ocean Buoy System and the University of New Hampshire (UNH) 2.1 m discus buoy. Engineering drawings were used to create a computational mesh for each buoy. Suitable solution methods were then developed and tested, CFD simulations were performed, and the results evaluated. Eleven CFD runs were performed, six for the WHOI buoy and five for the UNH buoy. Highlights of analysis for the WHOI buoy were that horizontal flow distortion was relatively small (〈1%) for head-on flow, but that the tendency of the buoy to establish an angle of about 30 degrees relative to the flow resulted in acceleration at one anemometer location and deceleration at the other. Highlights of the analysis for the UNH buoy were that flow distortion of about 5% at the wind sensor location could be cut by about a factor of two by either raising the sensor by 2 ft or removing solar panels.

Description: Funding was provided by the National Oceanic and Atmospheric Administration under Grant No. NA17RJ1223 for the Cooperative Institute for Climate and Ocean Research (CICOR).

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1990

Description: The contribution of tropical instability waves to the momentum and energy balances of the Pacific Equatorial Undercurrent is investigated using velocity and temperature time series from the three-dimensional Equatorial Pacific Ocean Climate Study mooring array at 110°W. Tropical instability waves are an energetic band of variability typically with periods between 14 and 36 days which are thought to be generated by instability of the equatorial currents. They are frequently observed as meanders of the equatorial front in satellite sea surface temperature maps. Here, they are observed as large oscillations in the meridional velocity records at l10°W with an energy peak at 21 days. Westward phase propagation is observed in this band with a phase speed of -0.9 (±0.3) m s-1 and a wavelength of 1660 km. Upward phase propagation is observed which is consistent with downward energy propagation. The observed propagation characteristics are compared with those of the mixed Rossby-gravity wave. The variability in this band produces large northward fluxes of eastward momentum and southward fluxes of temperature which affect the dynamics of the mean Undercurrent through the Reynolds stress divergence, and the Eliassen-Palm flux divergence. The waves produce a northward flux of eastward momentum, uv, which is largest at the northern mooring in the upper part of the array. The meridional divergence of eastward momentum, -δ(uv)/δy, decelerates the Undercurrent core down to 150 m. This implies a coupling between the Undercurrent and the South Equatorial Current with the eastward momentum of the Undercurrent transferred to the westward flowing South Equatorial Current. To estimate the vertical momentum flux divergence, the vertical eddy flux of eastward momentum, uw, is inferred using the eddy temperature equation. The vertical eddy momentum flux is positive and largest at the core of the Undercurrent, implying an acceleration of the eastward flow above the core and a deceleration below. The Eliassen-Palm flux divergence is small above the core of the Undercurrent at 75 m, but below the core, is sufficient to balance the deeply penetrating eastward pressure gradient force. The instability waves are important to the energetics of the mean Undercurrent. An exchange of kinetic energy from the mean Undercurrent to the waves through shear production is estimated. A local exchange is suggested since the rate at which the mean Undercurrent loses kinetic energy through instability is comparable to the rate at which the waves gain energy through shear production. The conversion from mean to eddy potential energy is an order of magnitude smaller with the waves gaining potential energy through conversion of mean available potential energy. The observations of upward phase propagation and downward Eliassen-Palm flux suggest that the waves propagate energy downward into the deep ocean. The energetics and momentum balance of the mean Undercurrent is investigated further by analyzing the downstream change in the Bernoulli function on the equator along isentropes or potential density surfaces using mean hydrographic sections at 150°W and 110°W. A downstream decrease in the Bernoulli function is observed which is due to a decrease in the Acceleration Potential since the mean kinetic energy of the Undercurrent changes little from 150°W to 110°W. The lateral divergence of eddy momentum fluxes calculated on isotherms is sufficient to balance the observed decrease in the Acceleration Potential. The downstream decrease in the Acceleration potential has further implications for the mean energetics since this "downhill" flow releases mean available potential energy stored in the east-west sloping thermocline. The rate at which the Undercurrent releases available potential energy, is shown to be comparable to the rate at which the mean flow loses kinetic energy by interaction with the waves, with the waves gaining kinetic energy in the process. Thus, it is hypothesized that in the eastern Pacific this downstream release of available potential energy is ultimately converted into a downstream increase in the kinetic energy of the waves rather than the kinetic energy of the mean flow as occurs in the western Pacific. To maintain an equilibrium, the waves radiate energy into the deep ocean as is suggested by the upward phase propagation and the downward Eliassen-Palm flux.

Description: Financial support of the National Science Foundation under contracts OCE 82-14955 and OCE 85-19551, for participation in Tropic Heat, and OCE 85-04125.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1992

Description: Variations in the abundances of elements and radiogenic isotopes in mantle derived peridotites and volcanic rocks are chemical integrals over time, space, and process, which ultimately contain information about the role of convection in the earth's mantle in creating, maintaining, and destroying geochemical heterogeneities. Successful inversion of these integrals requires extensive knowledge of the geochemical behavior of elements, the length scales of chemical variability, the evolution with time of geologic systems, the physical properties of mantle rocks, and the driving forces of phenomena which govern heat and mass transport in a dynamic earth. This dissertation attempts to add to this knowledge by examining the trace element and isotope geochemistry of mantle peridotites and oceanic island basalts, and by studying aspects of the flow of viscous fluids driven by thermal buoyancy. The trace element and isotopic systematics of peridotites and associated mafic layers from the Ronda Ultramafic Complex, southern Spain (Chapter 2), provides information bearing on the geochemical behavior of the highly incompatible elements U, Th, and Pb in the mantle, and on the length scales of geochemical variability in a well exposed peridotite massif. Garnet is demonstrated to be a significant host for U in the mantle, and together with clinopyroxene, these two minerals control the abundances and partitioning relationships of U and Th during the melting of anhydrous peridotite. Clinopyroxene, plagioclase, and to a lesser extent garnet are hosts for Pb in mantle peridotite; however, the role of trace sulfide may exert some control over the abundance and partitioning of Pb in some samples. Due to the possibility that Pb is partitioned into sulfide, the U/Pb, Th/Pb, and Ce/Pb ratios measured in clinopyroxene are likely to be higher than the bulk rock. U-Pb age systematics of garnet-clinopyroxene pairs from Ronda peridotites and mafic layers indicate Pb isotopic equilibrium in these samples up to 20-50 Ma ago. The Pb-Pb systematics of garnet- and spinel-facies peridotites and mafic layers indicate a heterogeneity on the order of 3 Ga old. This Pb isotope signature may have been created within the massif 3 Ga ago, or may have been metasomatically imprinted on the massif 1.3 Ga ago by basaltic melts with island arc affinities. The isotopic evolution of Ronda is consistent with at 1.3 Ga ago, and was subsequently incorporated into the subcontinental lithosphere. The very low U, Th, and Pb concentrations in depleted peridotite indicate that recycled crustal materials, with U-Th-Pb concentrations 102-104 times higher than peridotite, will have a larger influence on the isotopic composition of Pb in the mantle than on the Sr and Nd isotopic composition. An investigation of the trace element and isotopic compositions of clinopyroxenes in peridotite xenoliths from Savaii, Western Samoa and Tubuai, Austral Islands (Chapter 3) reveals geochemical signatures which are not present in basalts from these islands, due to the inherent averaging of melting processes. The data indicate similarities in the melting and melt segregation processes beneath these isotopically extreme islands. Samples with LREE depleted clinopyroxenes, with positive Zr and negative Ti anomalies, are the result of poly baric fractional melting of peridotite in the garnet- and spinel lherzolite stability fields, with the Savaii samples having experienced a larger mean degree of melting than the Tubuai samples. The extreme fractionation of HREE in the Savaii samples requires that they have melted to the clinopyroxene-out point (about 20%) while retaining residual garnet; the low concentrations ofHREE in these same samples requires a further 10-20% melting in the spinel lherzolite stability field. The extremely high total degrees of melting experienced by the Savaii samples (33-42%), as well as the high degree of melting in the garnet lherzolite stability field, suggests a mantle plume origin for these xenoliths. A large majority of the xenolith clinopyroxenes from both Savaii and Tubuai are LREE enriched to varying degrees, and many samples display significant intergrain trace element heterogeneity. This highly variable yet systematic heterogeneity was the result of metasomatism by percolating melts undergoing chromatographic trace element fractionation. The trace element compositions of some LREE enriched clinopyroxenes are consistent with the percolating melt being typical oceanic island basalt. The clinopyroxenes with the highest LREE concentrations from both islands, which also have very low Ti and Zr concentrations and large amounts of grain-boundary hosted Ba, require that the percolating melt in these cases had the trace element signature of carbonatite melt. The isotopic composition of one of these "carbonatitic" samples from Tubuai is similar to basalts from this island. The isotopic composition of clinopyroxene in a "carbonatitic" sample from Savaii records 87Sr/86Sr and l43Nd/l44Nd values of .71284 and .512516 respectively, far in excess of the most extreme Samoa basalt values (87Sr/86Sr=.70742, 143Nd/l44Nd=.51264). These "carbonatitic" signatures indicate the presence of volatilerich, isotopically extreme components in the mantle beneath Tubuai and Savaii, which likely have their origins in recycled crustal materials. The Re-Os isotope systematics of oceanic island basalts from Rarotonga, Savaii, Tahaa, Rurutu, Tubuai, and Mangaia are examined (Chapter 4). Os concentration variations suggest that olivine, or a low Re/Os phase associated with olivine, controls the Os concentration in basaltic magmas. The Savaii and Tahaa samples, with high 87Sr/86Sr and 207Pb/204Pb ratios (EMII), as well as basalts from Rarotonga, have 1870s/1860s ratios of 1.026-1.086, within the range of estimates of bulk silicate earth and depleted upper mantle. The basalts from Rurutu, Tubuai, and Mangaia (Macdonald hotspot), characterized by high Pb isotope ratios (HIMU), have 1870sfl860s ratios of 1.117-1.248, higher than any estimates for bulk silicate earth, and higher than Os isotope ratios of metasomatized peridotites. The high 1870s/1860s ratios indicate the presence of recycled oceanic crust in the mantle sources of Rurutu, Tubuai, and Mangaia. Inversion of the isotopic data for Mangaia (endmember HIMU) indicate that the recycled crustal component has Rb/Sr, Sm/Nd, Lu/Hf, and Th/U ratios which are very similar to fresh MORB glasses, and U/Pb and Th/Pb ratios which are within the range of MORB values, but slightly higher than average N-MORB. These results indicate that the low-temperature alteration signature of altered oceanic crust may be largely removed during subduction, and that oceanic crust was recycled into to the lower mantle source of the Macdonald hotspot plume. Furthennore, the high 187Os/l86Os ratios of the Tubuai and Mangaia basalts indicates that percolation through depleted mantle peridotite (187Os/186Qs=1.00-1.08), observed to occur in the Tubuai xenoliths, had little influence on the composition of the erupted basalts. A fluid dynamic model for mantle plumes is developed (Chapter 5) by examining a vertical, axisymmetric boundary layer originating from a point source of heat, and incorporating experimentally constrained rheological and physical properties of the mantle. Comparison of linear (n=l) and non-Newtonian (olivine, n=3) rheologies reveals that non-Newtonian plumes have narrower radii and higher vertical velocities than corresponding Newtonian plumes. The non-Newtonian plumes also exhibit "plug flow" at the conduit axis, providing a mechanism for the transport of deep mantle material, through the full depth of the mantle, in an unmixed state. Plumes are demonstrated to entrain ambient mantle via the horizontal conduction of heat, which increases the buoyancy and lowers the viscosity of mantle at the plume boundary. Streamlines calculated from the fluid dynamic model demonstrate that most of the entrained mantle originates from below 1500 km depth. Parameterization of the entrainment mechanism indicates that the factional amount of entrained mantle is lower in stronger, hotter plumes due to their higher vertical velocities. Examination of the global isotopic database for oceanic island basalts reveals the presence of a mantle component (FOZO), common to many hotspots worldwide, characterized by depleted 87Sr/86Sr and 143Nd/l44Nd, radiogenic 206,207,208Pb/204Pb, and high 3He/4He. This component is isotopically distinct from the source of MORB; thus, with the exception of ridge centered hotspots such as Iceland and the Galapagos, upper mantle does not appear to be a component in most hotspots, in agreement with entrainment theory. The combined fluid dynamic and isotopic results indicate that both FOZO and the enriched mantle components (EMI, EMil, and HIMU) are located in the lower mantle. Furthermore, high 3He/4He in FOZO precludes an origin for FOZO-bearing plumes in a thermal boundary layer at 670 km depth in the mantle. Since a 670 km thermal boundary layer would be replenished by the downward motion of the upper mantle, an origin for FOZO at 670 km would require either 1) a high 3He/4He signature in the MORB source, or 2) entrainment of MORB mantle into intraplate plumes, neither of which is observed in the OIB isotope data. This indicates that the 670 km discontinuity is not a barrier to mantle convection. The preservation of isotopically different upper and lower mantles does not require layered convection, but is probably the result of an increasing residence time with depth in the mantle, possibly caused by an increase in the mean viscosity of the mantle with depth.

Description: Author(s): Roeland C. A. van der Veen, Tuan Tran, Detlef Lohse, and Chao Sun A drop impacting on a solid surface deforms before the liquid makes contact with the surface. We directly measure the time evolution of the air layer profile under the droplet using high-speed color interferometry, obtaining the air layer thickness before and during the wetting process. Based on the... [Phys. Rev. E 85, 026315] Published Thu Feb 23, 2012

Description: Author(s): L. Šebestíková and M. J. B. Hauser Traveling waves in an extended reactor, whose width cannot be neglected, represent a three-dimensional (3D) reaction-diffusion-convection system. We investigate the effects of buoyancy-driven convection in such a setting. The 3D waves traveled through horizontal layers of the iodate–arsenous acid (I... [Phys. Rev. E 85, 036303] Published Wed Mar 14, 2012

Description: Author(s): Grégoire Lemoult, Jean-Luc Aider, and José Eduardo Wesfreid We present an experimental study of the transition to turbulence in a plane Poiseuille flow. Using a well-controlled perturbation, we analyze the flow by using extensive particle image velocimetry and flow visualization (using laser-induced fluorescence) measurements, and use the deformation of the ... [Phys. Rev. E 85, 025303] Published Tue Feb 21, 2012

Description: Author(s): B. Ghanbarian-Alavijeh, T. E. Skinner, and A. G. Hunt In this study, we develop a saturation-dependent treatment of dispersion in porous media using concepts from critical path analysis, cluster statistics of percolation, and fractal scaling of percolation clusters. We calculate spatial solute distributions as a function of time and calculate arrival t... [Phys. Rev. E 86, 066316] Published Wed Dec 19, 2012

Description: Author(s): L. L. F. Agostinho, G. Tamminga, C. U. Yurteri, S. P. Brouwer, E. C. Fuchs, and J. C. M. Marijnissen Experiments were conducted in order to study and characterize electrohydrodynamic atomization in the simple-jet mode for inviscid liquids. The operational window of this mode regarding the electric potential and liquid flow rate is presented. From the data it could be concluded that this mode can be... [Phys. Rev. E 86, 066317] Published Thu Dec 20, 2012

Description: Author(s): F. Wang, A. Choudhury, M. Selzer, R. Mukherjee, and B. Nestler In this paper, we study the effect of solutal Marangoni convection (SMC) on the microstructure evolution in a monotectic system, using the convective Cahn-Hilliard and Navier-Stokes equations with a capillary tensor contributed by the chemical concentration gradient. At first, we simulate the sponta... [Phys. Rev. E 86, 066318] Published Thu Dec 20, 2012

Description: Author(s): Robert A. Van Gorder We review two formulations of the fully nonlinear local induction equation approximating the self-induced motion of the vortex filament (in the local induction approximation), corresponding to the Cartesian and arc-length coordinate systems. The arc-length representation put forth by Umeki [ Theor.... [Phys. Rev. E 86, 057301] Published Fri Nov 02, 2012

Description: Author(s): Lingling Shi, Tsorng-Whay Pan, and Roland Glowinski Lateral migration and equilibrium shape and position of a single red blood cell (RBC) in bounded two-dimensional Poiseuille flows are investigated by using an immersed boundary method. An elastic spring model is applied to simulate the skeleton structure of a RBC membrane. We focus on studying the p... [Phys. Rev. E 86, 056308] Published Tue Nov 13, 2012

Description: Author(s): J. J. H. Brouwers We derive a comprehensive statistical model for dispersion of passive or almost passive admixture particles such as fine particulate matter, aerosols, smoke, and fumes in turbulent flow. The model rests on the Markov limit for particle velocity. It is in accordance with the asymptotic structure of t... [Phys. Rev. E 86, 066309] Published Thu Dec 13, 2012

Description: Author(s): Wenxian Lin and S. W. Armfield Recent studies have used scaling analysis to obtain simple power-law relations that accurately predict the Prandtl (Pr) number dependency of natural-convection boundary layers subjected to both isothermal and ramped heating conditions, when Pr〉1. The analysis used in those studies cannot be exten... [Phys. Rev. E 86, 066312] Published Fri Dec 14, 2012

Description: Author(s): Siddhartha Das, Prashant R. Waghmare, and Sushanta K. Mitra In this paper we analyze the inviscid regime (for which viscosity is unimportant and the flow occurs due to the balance between the capillary and the inertial effects) that invariably precedes the classical century-old Washburn regime during capillary filling. We demonstrate that a new nondimensiona... [Phys. Rev. E 86, 067301] Published Fri Dec 14, 2012

Description: Author(s): A. Bronfort and H. Caps A nearly two-dimensional foam is generated inside a Hele-shaw cell and left at rest on its liquid bath. The system is then vertically shaken and, above a well-defined acceleration threshold, surface waves appear at the foam-liquid interface. Those waves are shown to be subharmonic. The acceleration ... [Phys. Rev. E 86, 066313] Published Fri Dec 14, 2012

Description: Author(s): Randy Back and J. Regan Beckham A vertically draining thin ferrofilm under the influence of gravity and a nonuniform magnetic field is considered. It is observed experimentally that the presence of the magnetic field greatly alters the drainage of the film. A mathematical model is developed to describe the behavior. Experiments ar... [Phys. Rev. E 86, 046301] Published Mon Oct 01, 2012

Description: Author(s): S. Laizet and J. C. Vassilicos Using top-end high fidelity computer simulations we demonstrate the existence of a mechanism present in turbulent flows generated by multiscale or fractal objects and which has its origin in the multiscale or fractal space-scale structure of such turbulent flow generators. As a result of this space-... [Phys. Rev. E 86, 046302] Published Mon Oct 01, 2012

Description: Author(s): Nat J. Lund, Xingyou Philip Zhang, Keoni Mahelona, and Shaun C. Hendy We present an expression for the effective slip length of a nanoscale rough chemically heterogeneous surface. A heterogeneous surface may be regarded as having an effective slip length generated by extrapolating the uniform velocity profile found in the far field. We consider two-dimensional steady-... [Phys. Rev. E 86, 046303] Published Tue Oct 02, 2012

Description: Author(s): P. Caillol and R. Grimshaw Recent studies of the evolution of weakly nonlinear long waves in shear flows have revealed that when the wave field contains a critical layer, a new nonlinear wave equation is needed to describe the wave evolution. This equation is of the same type as the well-known Korteweg-de Vries equation but h... [Phys. Rev. E 86, 046311] Published Fri Oct 12, 2012

Description: Author(s): S. Kokou Dadzie and Howard Brenner Different nonkinetic approaches are adopted in this paper towards theoretically predicting the experimentally observed phenomenon of enhanced mass flow rates accompanying pressure-driven rarefied gas flows through microchannels. Our analysis utilizes a full set of mechanically consistent volume-diff... [Phys. Rev. E 86, 036318] Published Fri Sep 21, 2012

Description: Author(s): Louis Salkin, Laurent Courbin, and Pascal Panizza Combining experiments and theory, we investigate the break-up dynamics of deformable objects, such as drops and bubbles, against a linear micro-obstacle. Our experiments bring the role of the viscosity contrast Δ η between dispersed and continuous phases to light: the evolution of the critical capill... [Phys. Rev. E 86, 036317] Published Fri Sep 21, 2012

Description: Author(s): L. Fiabane, R. Zimmermann, R. Volk, J.-F. Pinton, and M. Bourgoin We investigate experimentally the spatial distributions of heavy and neutrally buoyant particles of finite size in a fully turbulent flow. Because their Stokes number (i.e., the ratio of the particle viscous relaxation time to a typical flow time scale) is close to unity, one may expect both classes... [Phys. Rev. E 86, 035301] Published Fri Sep 21, 2012

Description: Author(s): S. A. Galindo-Torres, A. Scheuermann, and L. Li Pore-scale flow simulations were conducted to investigate the permeability tensor of anisotropic porous media constructed using the Voronoi tessellation method. This construction method enabled the introduction of anisotropy to the media at the particle level in a random and yet controllable way. Si... [Phys. Rev. E 86, 046306] Published Wed Oct 10, 2012

Description: Author(s): Bin Liu, J. Goree, and Yan Feng Motion in a one-dimensional (1-D) microfluidic array is simulated. Water droplets, dragged by flowing oil, are arranged in a single row. Due to their hydrodynamic interactions, the spacing between these droplets oscillates with a wave-like motion that is longitudinal or transverse. The simulation yi... [Phys. Rev. E 86, 046309] Published Thu Oct 11, 2012

Description: Author(s): Amrik Sen, Pablo D. Mininni, Duane Rosenberg, and Annick Pouquet Rapidly rotating turbulent flow is characterized by the emergence of columnar structures that are representative of quasi-two-dimensional behavior of the flow. It is known that when energy is injected into the fluid at an intermediate scale L f , it cascades towards smaller as well as larger scales. I... [Phys. Rev. E 86, 036319] Published Fri Sep 21, 2012

Description: Author(s): Rajesh Patel A significant effect of aggregation dynamics for aqueous ferrofluid (AF) and kerosene based ferrofluid (KF) using magnetic field dependent capillary viscosity and magneto-optical relaxation measurements is studied. For better comparison parameters of AF and KF are kept similar. Ferrohydrodynamic equ... [Phys. Rev. E 86, 016324] Published Mon Jul 30, 2012

Description: Author(s): Ping Wei (韦萍), Rui Ni (倪睿), and Ke-Qing Xia (夏克青) We present an experimental study of turbulent Rayleigh-Bénard convection with polymer additives made in two convection cells, one with a smooth top and bottom plates and the other with a rough top and bottom plates. For the cell with smooth plates, a reduction of the measured Nusselt number (Nu) was... [Phys. Rev. E 86, 016325] Published Mon Jul 30, 2012

Description: Author(s): Tomas Teitelbaum and Pablo D. Mininni We derive statistical equilibrium solutions of the truncated inviscid surface quasigeostrophic (SQG) equations, and verify the validity of these solutions at late times in numerical simulations. The results indicate the pseudoenstrophy thermalizes while the pseudoenergy can condense at the gravest m... [Phys. Rev. E 86, 016323] Published Mon Jul 30, 2012

Description: Author(s): Jongho Lee, Faizur Rahman, Tahar Laoui, and Rohit Karnik Bubble damping in displacement-driven microfluidic flows was theoretically and experimentally investigated for a Y-channel microfluidic network. The system was found to exhibit linear behavior for typical microfluidic flow conditions. The bubbles induced a low-pass filter behavior with a characteris... [Phys. Rev. E 86, 026301] Published Wed Aug 01, 2012

Description: Author(s): A. G. Yiotis, D. Salin, E. S. Tajer, and Y. C. Yortsos In a recent paper [Yiotis et al. , Phys. Rev. E 85 046308 (2012) ] we developed a model for the drying of porous media in the presence of gravity. It incorporated effects of corner film flow, internal and external mass transfer, and the effect of gravity. Analytical results were derived when gravity... [Phys. Rev. E 86, 026310] Published Thu Aug 16, 2012

Description: Author(s): Carl Fredrik Berg In this article we investigate the electrical conductance of an insulating porous medium (e.g., a sedimentary rock) filled with an electrolyte (e.g., brine), usually described using the Archie cementation exponent. We show how the electrical conductance depends on changes in the drift velocity and t... [Phys. Rev. E 86, 046314] Published Wed Oct 17, 2012