Massas de água e circulação residual no estuário dos Bons Sinais

Abstract

The water masses and residual circulation in the estuaries are part of the set of processes that determine heat exchange, salt distribution and biological organisms adrift in this ecosystem. This fact makes the study of water masses and residual circulation relevant for both the scientific community and ecological processes. The main objective of the present work was to understand the behavior of the water masses and the residual circulation pattern of the Bons Sinais estuary and to classify it based on the Hansen and Rattray equation. For the materialization of the study, seasonal data of water temperature, salinity and currents measured at a fixed station during a tide cycle and data measured across the Estuary were used. The result obtained concerning the longitudinal gradients in salinity and density indicated that the estuary was dominated by the river during the rainy season and by the tide during the dry season, but the water column remained partially mixed in both seasons. Tidally averaged vertical profiles of temperature and salinity of the fixed station of the estuary revealed uniform temperature throughout the depth, warmer during the rainy season; lower salinity and stratified in depth during the rainy season, vertical homogeneous during the dry and transition seasons; and uniform density in depths but with high values during dry seasons. The vertical velocity profile presented a classic two-layer circulation model, with downstream flow intensifying on the surface and upstream flow at the bottom, during the rainy and transition seasons, when fresh water is discharged into the estuary. The flow velocities obtained from the calibrated Hansen and Rattray model adjusted to the observed data, confirming that the model proposed by Hansen and Rattray is adequate to describe the residual flow of the Bons Sinais Estuary.