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Dive into the research topics where Osmar O. Möller is active.

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Featured researches published by Osmar O. Möller.


Journal of Geophysical Research | 2000

Subtropical Shelf Front off eastern South America

Alberto R. Piola; Edmo J. D. Campos; Osmar O. Möller; Marcela Charo; Carlos Martinez

Historical hydrographic data from the continental shelf off eastern South America are used to examine the thermohaline properties of the water masses in the region between 20°S and 40°S. The continental shelf water masses are originated by dilution of open ocean waters of the western boundary currents of the South Atlantic Ocean. On the basis of temperature-salinity relation, two distinct water masses are identified, namely, the Subantarctic Shelf Water and the Subtropical Shelf Water. Subantarctic Shelf Water originates by dilution of Subantarctic Water, primarily in the southeast Pacific, due to excess precipitation and continental runoff and enters the continental shelf near 55°S. The Subtropical Shelf Water is modified South Atlantic Central Water diluted by continental runoff from the coast of Brazil. In addition, substantial dilution of the upper shelf waters takes place at the mouth of Rio de la Plata (approximately located at 36°S) and, in a lesser extent, at the Patos-Mirim Lagoon (at 32°S). The Rio de la Plata and the Patos outflows form a low-salinity tongue that caps the shelf water leading to a salinity decrease to values <30. The low-salinity tongue extends northward over the shelf penetrating farther north in winter than in summer. The extent of the low-salinity water has a strong impact on the vertical stratification and acts to limit winter convection to the layer above the halocline. There is little or no indication of mixing between Subantarctic Shelf Water and Subtropical Shelf Water. An intense temperature, salinity, and nutrient front separates these water masses. The front is oriented along the north-south direction, located on average near the 50 m isobath at 32°S and extends southward toward the shelf break near 36°S. Between 32° and 34°S the Subtropical Shelf Front follows the 100 to 200 m isobaths and separates Subantarctic Shelf Water from the oceanic South Atlantic Central Water. On the basis of the temperature and salinity distributions, beneath the low-salinity surface layer, the Subtropical Shelf Front appears as an extension of the Brazil-Malvinas Confluence over the continental shelf of South America. Thus the location of the Subtropical Shelf Front may be linked to the migrations of the separation point of the Brazil-Malvinas Confluence from the continental slope.


Continental Shelf Research | 1995

Freshwater outflow and Subtropical Convergence influence on phytoplankton biomass on the southern Brazilian continental shelf

Áurea Maria Ciotti; Clarisse Odebrecht; Gilberto Fillmann; Osmar O. Möller

Abstract The present study discusses the role of different continental shelf water masses on inorganic nutrient levels and on phytoplankton biomass along the southern Brazilian coast during October 1987 and September 1988. In this productive area, variability of phytoplankton biomass has been related to the seasonal latitudinal displacement of the Subtropical Convergence and to the freshwater outflow of La Plata River and Patos Lagoon. Very distinct precipitation rates, as a consequence of the ENSO (El Nin˜o-Southern Oscillation) cycle, preceding the two sampled periods of this study, allowed a first evaluation of the impact of this event on freshwater outflow and shelf phytoplankton biomass. The amount of chlorophyll in shelf waters was directly related to nutrients supplied by the Coastal Water (i.e. freshwater outflow), Subtropical and Subantarctic Waters. Comparing the results of this study with previous cruises performed in the area, it was found that high chl a concentrations are common features during periods of elevated precipitation rates. Apart from nutrient input by freshwater and the consequent changes in the vertical profiles of density, the extreme precipitation rates are also associated with different wind patterns, which, in turn, control the presence of particular water masses in the euphotic zone. Our results suggest that ENSO events have an important impact on the variability of phytoplankton production, and thus should affect biogeochemical cycles in the southern Brazilian coastal areas.


Estuaries | 2001

The influence of local and non-local forcing effects on the subtidal circulation of Patos Lagoon

Osmar O. Möller; Patrice Castaing; Jean-Claude Salomon; Pascal Lazure

Some basic features concerning the subtidal circulation of Patos Lagoon were studied through time series analysis of wind, freshwater discharge, and water level records, as well as by means of experiments carried out with a 3D numerical model. The results indicate that during low to moderate river discharge the wind is the main forcing mechanism in time scales associated with meteorological fronts. The two types of wind action, local and non-local effects, are distinguished and their relative importance is evaluated. Salt water enters the system due to a combination of both remote and local wind effects that favors the development of a pressure gradient towards the lagoon during southwesterly winds. This situation is reversed when northeasterly winds dominate. In the inner parts of the lagoon, local wind plays the major role by inducing set up/set down oscillations. An upwind return flow is then developed under these conditions. During high flood periods, normally observed in late winter, the circulation is driven by freshwater discharge.


Continental Shelf Research | 1996

The Patos Lagoon summertime circulation and dynamics

Osmar O. Möller; Joa˜o A. Lorenzzentti; JoséL. Stech; Mauricio M. Mata

Abstract The main aspects of the summertime circulation and dynamics of the Patos Lagoon, a system located in southern Brazil and considered as one of the worlds largest choked coastal lagoons, are studied through the analysis of time series of wind stress, water level and freshwater discharge, combined with the results of a barotropic circulation model. The longitudinal wind component has been verified as the main driving force, generating a set-up/set-down mechanism of oscillation with the nodal line in the midlagoon area. The period of this oscillation coincides with the passages of frontal systems for this region. The sea breeze acts as a secondary effect, being clearly observed in the northern part of the lagoon. Freshwater discharge is expected to cause variations in water level on the seasonal band and to a lesser degree in the 8–15 day time-scale. The tidal signal is of importance only near the exit to the ocean, being strongly reduced in the interior of the lagoon. Model results suggest a wind set-up momentum balance in the longitudinal direction in the deeper parts of the lagoon; near the margins, the longitudinal momentum balance is mostly of frictional form, with the wind stress being balanced by the bottom friction. In the lateral direction, a geostrophic balance is verified in both regions. The wind forced circulation is characterized by the presence of several cells with downwind velocity near the margins and upwind return flow occurring in the central areas.


Continental Shelf Research | 1996

Ocean surface processes on the southern Brazilian shelf: characterization and seasonal variability

Ivan D. Lima; Carlos Alberto Eiras Garcia; Osmar O. Möller

Abstract The oceanographic environment in the southern Brazilian shelf was investigated using maritime weather reports from the U.S. National Climatic Center and data from three hydrographic cruises. The circulation in the area shows a clear seasonal pattern in which the interaction between wind forcing, geostrophic circulation and meso-scale variability of the Brazil Current produce southward and offshore flow over the shelf during summer, and northward and onshore flow during winter. The interaction between eddy-induced upwelling and wind-generated transport in summer and winter results in enhanced upwelling and a strong bottom intrusion of SACW on the shelf in summer, whereas in winter the upwelling is restricted to the shelf break. Thus, the combination of the aforementioned processes produces a complex and highly dynamic hydrographic system with a high degree of seasonal variation in both direction of flow and water mass composition.


Estuaries | 2005

Drought Effects on Pelagic Properties in the Shallow and Turbid Patos Lagoon, Brazil

C. Odebrecht; Paulo Cesar Abreu; Osmar O. Möller; L. F. Niencheski; L. A. Proença; L. C. Torgan

The effect of a 7-mo drought (La Niña 1988) was evaluated on pelagic properties in the large Patos Lagoon (30°12′–32°12′S, 50°40′–52°15′W). From December 1987 to December 1988, surface water was sampled along the longitudinal axis of the lagoon for temperature (10–29°C), salinity (0–31.4), dissolved inorganic phosphate (0.02–4.73 μM), nitrate (0.05–66.25 μM), nitrite (0.01–3.54 μM), ammonium (0.09–33.19 μM), silicate (1.11–359.20 μM), phytoplankton chlorophylla (chl; 0.4–41.2 mg m−3), primary production (gross PP 1.72–161.82 mg C m3 h−1; net PP 0.04–126.19 mg C m3 h−1), and species composition and abundance (42–4,961 ind ml−1). In the wet season the whole system acted as a river and light availability limited phytoplankton growth. During the drought from February to August monthly freshwater runoff was low and the inflow of marine water to the southern sector generated spatial variability of the analyzed properties and five functional areas were recognized. The northernmost Guaíba River (1) presented low light availability and phytoplankton chl concentration compared to the northern limnetic area (2) (chl mean 13.3 μg I−1; max 41.2 μg I−1; gross PP mean 52.6 mg C m3 h−1), which acted as a biological filter removing dissolved inorganic nutrients. Silicate concentration was strongly diminished in this area due to diatom uptake (Aulacoseira granulata, 9,330 cells ml−1). In the northern limnetic and central oligohaline (3) areas, phytoplankton biomass was controlled by light but nitrogen also played a limiting role. In the southern area (4) that is under marine influence, low chl concentration (mean 4.5 μg I−1) and gross PP (mean 28.1 mg C m3 h−1) coincided with co-limitation of nitrogen and light while the channel to the ocean (5) was strongly light limited. This study demonstrated that low light and high silicate input had a buffer effect at Patos Lagoon, hampering negative expression of cultural eutrophication. The main effect during the drought period occurred in the northern limnetic region, where low silicate values due to diatom uptake led to higher cyanobacteria abundance, and enhanced mineralization occurred in the central oligohaline lagoon. Increased rainfall resulted in light limitation and decreasing primary production in the entire freshwater lagoon, and the adjacent coastal region benefited from nutrient enrichment.


Archive | 1999

Hydrographical Characteristics of the Estuarine Area of Patos Lagoon (30°S, Brazil)

Osmar O. Möller; Patrice Castaing

The Patos Lagoon (Fig. 5.1a) situated in Southern Brazil, between 30 and 32°S is a very important water resource system for the Rio Grande do Sul State. It serves as nursery ground for important commercial fish and shrimp species sustaining a fishery production of 182 kg ha-1 yr-1 in average (Castello 1985). Major man activities are navigation and recreation. It also receives untreated domestic, agricultural and industrial sewage disposals produced by population living along the margins of the lagoon. The construction of two 4 km long jetties fixed the entrance and allowed navigation along the entrance channel. About 14 million m3 of sediments where trans-ported to the coastal zone in the first two years after the construction of these structures (Motta 1969). In recent years the channel has been constantly dredged to keep depth around 14 m.


Brazilian Journal of Oceanography | 2006

A modeling study of Patos lagoon (Brazil) flow response to idealized wind and river discharge: dynamical analysis

Renato M. Castelao; Osmar O. Möller

B S T R A C T A three-dimensional numerical model is used to investigate the Patos Lagoon flow response to idealized northeasterly winds and river inflow. North of Ponta da Feitoria, in the central lagoon, the main balance in the alongshore direction at steady state is between the surface stress and the pressure gradient, with a small contribution from the bottom stress. The alongshore variability in the pressure gradient is balanced by the Coriolis acceleration. In the cross-shore direction, the balance is nearly geostrophic, with deviations from that balance in the shallow regions, where the bottom stress term makes a significant contribution. Close to headlands, nonlinear terms are also important, leading to an additional increase in the cross-shore pressure gradient. Relaxation events were found to be important for seiche generation in the central lagoon. Close to the lagoons mouth, nonlinear terms were found to be the major terms balancing the pressure gradient generated in response to the wind forcing. After the wind relaxation, the pressure gradient in the estuarine region is reversed, driving a landward flow. River inflow acts to dampen out the generation of seiches following wind relaxations. A river inflow Q = 2000 m


Estuaries and Coasts | 2007

Tidal frequency dynamics of a Southern Brazil coastal lagoon: Choking and short period forced oscillations

Osmar O. Möller; Patrice Castaing; Elisa Helena Leão Fernandes; Pascal Lazure

The Patos Lagoon is a choked, microtidal coastal laggon situated in southern Brazil between 30°S and 32°S. The response of the lagoon to tidal oscillations is studied through data analysis and numerical modeling experiments. Two types of high frequency oscillations are observed in the tidal frequency band: mixed tides, predominantly diurnal; and forced oscillations having a period of 24 h occurring in the inner lagoon. In the southern portion of the lagoon, tides are selectively filtered by the entrance channel. The main diurnal constituent O1 is linearly attenuated as it progresses landwards. In the inner parts of the lagoon, 24-h oscillations are mainly forced by the combined effect of diurnal tides and sea breeze action. They are tied with a natural period of oscillation of 24 h. Results also indicate that these are not inertial frequency oscillations, despite the lagoon being placed in a critical 30°S area. The interaction between astronomical tides and meteorological effects produces a complicated picture for tidal forecasting derived from data collected inside the lagoon.


Anais Da Academia Brasileira De Ciencias | 2014

Use of a mathematical model to estimate the impact of shrimp pen culture at Patos Lagoon estuary, Brazil

Luís Henrique da Silva Poersch; Ângela Machado Milach; Ronaldo O. Cavalli; Wilson Wasielesky; Osmar O. Möller; Jorge Pablo Castello

Ecological modeling has been used as a tool to estimate potential impacts caused by aquaculture to the surrounding environment. In this work, a mathematical model was applied to estimate the maximum amount of pink shrimp (Farfantepenaeus paulensis) culture units (3,100m2 pen enclosures) that could be installed at two shallow estuarine bays of Patos Lagoon (known as Coreia and Porto do Rei) with no significant effects on either water quality or viability of the culture system. To calibrate the model, information about the culture of Litopenaeus vannamei and F. paulensis as well as field data (influence of netting material, water current speed and nitrogen concentrations) were used. Under a bad scenario (water current velocity of 0.01m s-1 and a mesh clogging effect of 40%), it would be possible to install up to 29 pens at the Coreia bay, and 39 pens at the Porto do Rei bay. Results indicate that the model was useful in determining the maximum number of culture units that could be installed at these bays, and thus have the potential to become an important tool in the definition of environmental management strategies in relation to aquaculture development.

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Alberto R. Piola

University of Buenos Aires

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Carlos Martinez

University of the Republic

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Elisa Helena Leão Fernandes

Centre national de la recherche scientifique

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Jorge Pablo Castello

Universidade Federal do Rio Grande do Sul

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Wilian Correa Marques

Universidade Federal do Rio Grande do Sul

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Elbio D. Palma

Universidad Nacional del Sur

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Derek Burrage

United States Naval Research Laboratory

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