Contributions to the understanding of physical oceanographic processes of the Marajó Bay - PA, North Brazil

Abstract

The island of Colares is located in the northeast of Pará and bathed by the Pará river estuary. This study intended to characterize the hydrodynamic and hydrological processes of the lower estuary of the Pará river during the dry period. The field research was conducted at December 17th and 18th , 2009, during the dry season, with spring tide of new moon, on board of a catamaran, a sounder Conductivity-Temperature-and-Depth (CTD), an Acoustic Doppler Current Profiler (ADCP) and a digital anemometer. Weather showed different conditions, which may be consequences of the El Niño event, the currents system of the estuary showed variations of intensity and direction related mainly to changes in tide and the channel morphology. The average speed in the water column obtained values maximum to 1.15 m/s and minimum of 0.04 m/s. The surface current speed was more intense than the bottom. The results of the wind showed many fluctuations, with hours of great gusts, reaching 13m/s, and other of calm, with speed very close to 0 m/s. The tide on the island Colares presented maximum amplitude of 3 m, 0.36 m higher amplitude compared to Mosqueiro island, and an advance of 47 minutes. The salinity in the estuary is strongly influenced by the tide, being some what peculiar, with higher values and stratification in the water column in the early hours of ebb. According to the stratification-circulation diagram of Hansen & Rattray (1966) the Pará River estuarine system assumes characteristics of type 1 (well-mixed) without vertical stratification.