Chapter 4 The north and northeast Brazilian tropical shelves

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.

The xeric side of the Brazilian Atlantic Forest: The forces shaping phylogeographic structure of cacti

“…However, sea level fluctuations probably promoted massive changes in the extension of oceanic island areas, which might have affected conditions for immigration, speciation, and extinction in such islands (Weigelt, Steinbauer, Cabral, & Kreft, ). In glacial periods of the Pleistocene, the average sea level was much lower than at present, exposing the northeast Brazilian continental shelf, which has around 40 km of extension in this region (Vital, ), and probably reducing the linear distance between Fernando de Noronha and the continent. More meaningfully, the lowering of sea level exposed some of the present‐day submerged seamounts, which might have allowed a stepping stone colonization that reached Fernando de Noronha islands during the Pleistocene.…”

“…This is justified by the occurrence of intense volcanic activity until late Pleistocene (Cordani, ) that must have promoted recurrent extinctions and precluded the maintenance of terrestrial biota in these islands. The Fernando de Noronha archipelago is nowadays located at about 350 km from the continent (Figure ) as the easternmost of a chain of seamounts aligned in an east–west direction to the Brazilian continental shelf (Vital, ). In this chain, only the Fernando de Noronha and Atol das Rocas archipelagos are emergent nowadays.…”

Inner Shelf Currents Off Ponta Negra Beach, Natal, Rn, Brazil

“…The area studied is the inner continental shelf (ICS) off the eastern coast of the state of Rio Grande do Norte, adjacent to Ponta Negra Beach in Natal (5 • 51'S and 35 • 8'W). The region is located in the eastern sector of the Northeast Brazilian Tropical Shelf (NEBTS), which extends from the Parnaíba Delta at 2 • S to the Abrolhos Bank at 20 • S (Vital, 2014). This portion of the shelf presents mixed sedimentation (carbonaceous-siliciclastic sediments) and is characterized by narrow width and shallow waters, when compared to other parts of the Brazilian shelf (Vital et al, 2010;Vital, 2014).…”

“…Geyer & Kineke (1995), Beardsley et al (1995) and Lentz (1995) all conducted circulation studies for the Amazon continental shelf. There is, however, a strong need for systematic studies of the NEBTS, especially the eastern part of Rio Grande do Norte (RN) state, where the capital of Natal is located (Vital et al, 2010;Vital, 2014).…”

Vulnerabilidade costeira e dinâmica sedimentar - Campo de dunas de Mangue Seco, Guamaré/RN, NE do Brasil.

“…Essas atividades normalmente situam-se em compartimentos geomorfológicos de estrutura frágil diante das intervenções antrópicas, devido a sua complexidade ambiental, onde atuam conjuntamente vários elementos naturais, tais como: ventos, ondas, correntes, precipitações, marés, insolação, evaporação, erosão e deposição. O estudo da região costeira em escala mundial tem convergido para um grande problema que é a erosão costeira (Hesp et al, 2005;Vital, 2014). Atualmente, estima-se que 70% das linhas de costa do mundo estão sendo afetadas pela erosão, com grande prejuízo para a economia local (Dominguez, Bittencourt, & Martin, 1992).…”