Hidrologia dos bancos e ilhas oceânicas do nordeste brasileiro. Uma contribuição ao Programa Revize.
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This work has as objectives to supply data on the temperature, salinity, dissolved oxygen, pH and nutrients (nitrite, nitrate, phosphate and silicate), of the areas of the banks and oceanic islands of the Zone Economic Exclusive of North-East Brazil, to describe seasonal and the spatial variations of these parameters and to systematize the obtained data, through the elaboration of a database, with views to facilitate a posterior analysis, integrated with the other areas of the knowledge, of areas thankfully important of the economic and lacking point of view, of the scientific point of view, of this type of information, so that the relationship can be established between the nutrients salts and the responsible elements by the productivity of the aquatic way. The researched area is inserted in the sub-area II / section 1 and 2 of the Program REVIZEE at 1°N e 5°S and 29° e 40°W, including the North Chain of Brazil, Fernando of Noronha chain and Sain Peter and Saint Paul archipelago, embracing 67 stations and 443 samples the summer of 1997 and 66 stations and 418 samples in the fall of 1998, profaned a total of 133 stations and 861 samples and a researched area of 600.000 km². The studied area presented a marked permanent termocline, so much in the summer as in the fall, with the depth varying with the latitude and with them season, being more superficial and with larger gradient in the fall, in agreement with the typical pattern of the areas equatorial and tropical. The mixture layer was more homogeneous in the summer, of smaller thickness in the fall and decreasing in higher latitudes. The superficial distribution of the temperature of the sea presented larger homogeneity degree in the summer and larger width of thermal variation in the fall. The smallest temperatures were registered in the area of Saint Peter and Saint Paul archipelago and close Oceanic area to this archipelago, in the two seasons. The area of Saint Peter and Saint Paul archipelago went to that presented the samllest salinity values, in the two seasons. A maximum of sub-surface salinity was present in the approached depth of the I begin of the termoclina, being more accentuated in the lowest latitudes, so much in the summer as in the fall. The diagrams T-S indicates the presence of three characteristic masses of water of the area: The Equatorial Surface Water, with salinity of 35,5 to 36,5 UPS and temperature >26°C, that occupies a strip very it narrows in the area; the Subtropical Salinity Maximum, with temperature between 20° and 5°C and salinity between 36,0 and 37,0 UPS, occupying a strip between the 50 and 200 m; South Atlantic Central Water, with temperatures between 20° and 5°C and salinity 36,00 to 34,34 UPS, placed below the Subtropical Salinity Maximum. Upwelling was observed, in the stations located in the close Oceanic area to the Saint Peter and Saint Paul archipelago, based on the elevations of the isotherms, low oxygen and high superficial concentration of the nutrients, in the two perios of the year. The concentration of the dissolved oxygen was close of the saturation in the superficial and sub-superficial layers and conditions anaerobic they were not observed in the column of water. The pH was always in the alkaline strip and with values more elevated in the area of Saint Peter and Saint Paul archipelago. The most abundant form of the nitrogen was the nitrate, mainly in the summer where the obtained values, in the layer eufotic, they were larger than in the fall. the same vertical distribution was obtained for the nitrate, phosphate and silicate, along the column of water, so much in the summer as in the fall and the vertical distribution of the nitrite is associated with the nitracline, in both studied periods. The statistical analysis of the results showed that the temperature didn't present seasonal influence, while the salinity and the nutrients, mainly the silicate, varied its distribution with them researched season. The area that showed larger variability with the periods of the studied year, in the tests of contrasts, went the one of to North Chain of Brazil, suggesting a seasonal influence with the discharge of the Amazonas River. For the obtained results it was verified that three areas statistical different exist: (the) Area of the banks of the North Chain of Brazil, (b) Area of Fernando of Noronha chain and (c) Area now denominated East of Sain Peter and Saint Paul archipelago, that includes the area of oceanic domain and Saint Peter and Saint Paul archipelago.