The seasonal and spacial distributions of dissolved oxygen, temperature and salinity of surface and bottom waters over the continental shelf south of Torres, southern Brazil, were investigated from April 1968 to March 1969. The maxima and minima values of oxygen concentration in the upper layers were observed during the winter and summer along the coast (10-35 nm), respectively. Near the bottom this characteristics changes reflecting the northward advection of low oxygen water along the coast. For the sections along the continental shelf covering distances up to 100 nautical miles, the association of high oxygen concentration with low temperatures and low oxygen concentration with higher temperatures was also observed for distances no longer than 60 ran. Further east and below the surface layer, this tendency is modified by the advection of oceanic water from tropical and subantarctic origin. Near the coast, the oxygen maxima (5.0 ml/l) is associated with salinity values ranging from 30 to 33‰ (temperature values between 12 and 15ºC), indicating that (its occurrence) is probably due to the fresh water run-off from La Plata River. Some results of the changes in the nutrient concentrations during 1972 are also described.

As observações oceanográficas realizadas em fevereiro de 1971, na plataforma continental entre Cabo Frio e a Ponta de Guaratiba, mostraram a presença e a atenuação de efeitos do fenomeno de ressurgência observados na superfície. A análise detalhada da distribuição térmica na camada superficial evidencia que o processo físico responsável pela atenuação desse fenomeno foi a advecção de uma corrente costeira de aguas quentes, fluindo para leste. A componente zonal dessa corrente costeira atingiu nas proximidades da costa o valor máximo de 5 mn. dia 1 e a sua intensidade decresceu com o aumento da distancia á costa, anulando-se aproximadamente sobre a isobata de 100 m. Os efeitos do fenomeno de ressurgência na superficíe, observados ao largo da Ponta de Saquarema, eram claramente indicados pelos mínimos de temperatura (17ºC) e da concentração de oxigênio dissolvido (4,2 ml/l) bem como pelo máximo na concentração de fosfato (0,6 µg-at/l), que sao característicos de aguas mais profundas. No intervalo de tempo (4-7 dias) decorrido entre as observações, verificou-se não somente aumentos de temperatura e do oxigênio dissolvido, como também um decréscimo na concentração de fosfatos de aproximadamente 50% de seu valor inicial.

An upwelling event was observed during February 1971 in the coastal region between Cabo Frio and Saquarema Point. Isolated upwelled water observed on a first survey, with a temperature of 17ºC, oxygen concentration of 4.2 ml/liter and inorganic phosphate concentration of 0.6 µg-at/liter, cleanly indicating its subsurface origin, was replaced, after a period of four to seven days, by coastal water with a temperature of 22ºC, oxygen concentration of 5.0 ml/liter and inorganic phosphate concentration of less than 0.3 µg-at,/liter. The evidence indicates that this replacement took place due to an eastward coastal current with a maximum velocity of nearly 5.0 nautical miles per day. The subsurface distribution of the chemical and physical properties indicates that the upwelling occurred mostly in the narrowest portion of the continental shelf.

In the South Atlantic nearly the Brazilian coast, at low latitudes, the layer of minimum oxygen concentration shows distinct values between the Equatorial region (7ºS) and the region limited by latitudes of 18-22ºS. In the vicinity of the Equator the minimum concentration is remarkably clear (2,0 ml/l at 7ºS) and at 22ºS the minima values raise up to 4.0-4.5 ml/l. The minimum oxygen layer follows the isopynics surfaces (σt = 26.8-27.2) in depths of 300-400 m (7ºS) and 600-800 m (22ºS) . The oxygen concentration in this area results from a biochemical and physical processes, due to the presence of poor water Brazil Current southward and the rich one Intermediate Antartic water flowing northward.

1 - A penetração da água doce dos rios Amazonas e Pará, extende-se na direção NE atingindo a borda da plataforma continental, onde são retidas pela corrente da - Guiana tomando a direção dessa corrente, isto é, NW. 2 - A temperatura das águas menos salinas (<35‰) esta entre 27ºC - 27,5ºC, inferior à temperatura da massa d'água originária da costa nordeste do Brasil (>27,5ºC). 3 - Os altos valores de oxigênio dissolvido (5,23 ml/l) são encontrados próximos à costa em águas com 15‰ de salinidade e 27,4ºC de temperatura, nos primeiros 5 m. Os valôres de oxigênio dissolvido decrescem na medida em que as águas dos rios se misturam com as águas oceânicas. 4 - A água dos rios Amazonas e Pará transportam grandes quantidades de matéria em suspensão pronta a fornecer fósforo ao atingir o estuário. Pela sedimentação e consequente redução de turbidês, o fosfato liberado é prontamente consumido. 5 - Além da plataforma continental e fora da influência dos rios as condições prevalecentes são as mesmas para o Atlântico Equatorial.

This paper describes the salinity, temperature, dissolved oxygen and inorganic phosphate distributions for the Brazil northern coast, with special reference to the marine environment off the Amazon and Pará rivers. The change in direction of the coast with the consequent change in the axis of the Guiana Current together with the large amount of suspended matter contributed by river waters, create peculiar conditions on the continental shelf. These conditions are also influenced by the wind and rain system. Out from the continental shelf Tropical Atlantic oceanic conditions are prevalent. In contrast to the very low fertility of the Guiana Current the coastal waters, directly influenced by the rivers, show a supersatu ration of dissolved oxygen. The nutrients absorbed by suspended matter are partly liberated when the rivers mix with the oceanic water. However, the low light penetration restricts the oxygen production to only few meters.