Chapter 4 The north and northeast Brazilian tropical shelves

Abstract

Abstract The Brazilian tropical north shelf (BT N shelf) and the Brazilian tropical northeast shelf (BT NE shelf) along the Atlantic Ocean display unique conditions for tropical passive margins. Together they encompass approximately 3000 km in length, extending from Cape Orange in the north to Abrolhos Bank in the south. Both the north and NE shelves are very shallow and highly energetic systems. The first one is subject to energetic forcing from a number of different sources, including near-resonant semi-diurnal tides, large buoyancy flux from the Amazon River discharge, wind stress from the northeasterly trade winds and strong along-shelf flow associated with the North Brazil Current. The second one is subject to the full strength of the westerly-flowing South Equatorial Current, combined with high winds, moderate–high tidal range and/or waves. The BT N shelf is the largest shelf in Brazil, and is mostly covered with siliciclastic mud and sands because of the enormous water and sediment discharge from the Amazon River. In contrast, the BT NE shelf is narrow and open, and almost entirely covered by carbonate sediments due to the small amount of freshwater and sediment input.