Enviromagnetic response of marine sediments off NE Brazil to paleoclimatic and paleoceanographic changes in the last 85kyr BP

• Autor(a) principal: Mathias, Grasiane Luz
• Data de Publicação: 2016
• Tipo de documento: Tese
• Idioma: eng
• Título da fonte: Biblioteca Digital de Teses e Dissertações da USP
• Texto Completo: http://www.teses.usp.br/teses/disponiveis/14/14132/tde-02062017-051027/
• topic: environmental magnetism; Eventos Heinrich; Heinrich Events; magnetismo ambiental; NE Brasil; NE Brazil

NE Brazil is a semi-arid region influenced by the southward displacement of the Intertropical Convergence Zone (ITCZ), which is the main atmospheric system that modulates the seasonal increasing in precipitation over this region. It is well established that these wet periods correlate temporally with the Heinrich Events. However, the local oceanographic response to the fresh water pulses in North Atlantic and how it influences sediment transport along the margin off NE Brazil, is still a matter of discussion. This thesis presents a rock magnetic and element data along four marine cores collected in the south equatorial Atlantic Ocean, covering the last 85 ka BP. Moreover, it was performed an end-member analysis based on the IRM acquisition curves bringing better understanding about sediment sources. Magnetic characterization permitted us to investigate a possible relationship between river supply/longitudinal transport and precipitation enhancement caused by cold events over the North Atlantic. The results suggest a differential deposit of magnetic minerals along the coast, with highly coercive phases (hematite and goethite) further west, and gradually softer phases, like (titano)magnetite to the east. This difference is due mainly to differential oxidation over land, but secondarily we suggest a transport from W-E of coercive material, caused by weakness of NBC.