Morfodinâmica de formas de fundo em águas rasas na Plataforma Tropical Setentrional do Rio Grande do Norte

Abstract

Bedforms are important morphological elements of shallow marine environments, working as major contributors to the sediment flow on the shelf. This research proposes to analyze the shallow-water bedforms morphodynamic on the continental shelf adjacent to Galinhos – Guamaré (RN). We integrated singlebeam bathymetry, Landsat 8 OLI image, swath bathymetry and sonography, scuba diving video and sediment samples. Two data acquisition campaigns were realized with a difference of two years. The sand ridges field (SRF) is visible by satellite image. SRF is limited between 5 to 10 m depth, stretched to E-W. This field is composed by sand ridges parallel to the coastline in the west and oblique when near the coastline. The SRF is shaped by the dunes amalgamation with crest to SW-NE direction. The dunes have 1 to 4 meters, with 400 to 1200 meters wavelength. The sand ridge coastline flank is straighter, on the other hand the offshore side has reentrances. On the coast, from east to west, there is the spit of Galinhos, the ebb tidal delta of Guamaré, the Canto do Amaro barrier island system and the Minhoto beach. From the mosaic generated by the sonar data, ripples were described, with SE-NW crests, superimposing the dunes. Scuba diving videos show symmetrical ripples, sometimes with red algae (rhodolites) in the trough. Four backscatter patterns were identified. This pattern is related to the four sedimentary facies founded. The integration of remote sensing, current and sedimentological data of distinct periods allowed to identify the morphodynamic of the bedforms and sedimentary cover in the shallow water. The coastal drift and the ebb-tidal delta of Guamaré influenced the actual SRF shape. SR dunes asymmetry shows that NW current formed these dunes. But actually they are inactive. Ripples have SW drift. This movement of sediments between the dunes occurs in the troughs. These ripples probably have the dynamics difficult by the presence of red algae in seabed. SRF origins might be related to Holocene sea-level rise and ebb-tidal deltas.