A Multi-Proxy Approach to Unravel Late Pleistocene Sediment Flux and Bottom Water Conditions in the Western South Atlantic Ocean

Autor(es)

Mathias, G. L. ; Roud, S. C. ; Chiessi, C. M. ; Campos, M. C. ; Dias, B. B. ; Santos, T. P. ; Albuquerque, A. L. S. ; Toledo, F. A. L. ; Costa, K. B. ; Maher, B. A.

• Tipo de documento: Artigo Científico
• Fonte: PALEOCEANOGRAPHY AND PALEOCLIMATOLOGY; v. 36, n. 4, p. 22-pg., 2021-04-01.

Resumo

Magnetic signals in deep-sea sediments have the potential to unravel past continental environmental changes, via changes in primary terrigenous magnetic supply, but also record past marine environmental conditions, via in situ formation of secondary magnetic minerals, particularly when complemented by independent proxies. By combining environmagnetic, geochemical, and siliciclastic grain size data, we investigated marine sediment core GL-1090 (24.92 degrees S, 42.51 degrees W, 2,225 m water depth) aiming to unravel changes in terrigenous sediment input and bottom water conditions during the last similar to 184 ka at the western South Atlantic middepth. The Al/Si, Fe/kappa and siliciclastic grain size data show that terrigenous sediments at this core location derived from the Plata River (southeastern South America). This material was transported northwards by the Brazilian Coastal Current and their delivery to our core site was modulated by sea-level oscillations. Periods of low sea-level were characterized by the input of coarser and more abundant terrigenous sediments. Environmagnetic parameters indicate significant downcore variations in the magnetic domain state, which we interpret as changes in the content of biogenic magnetite following glacial-interglacial cycles. Coeval negative excursions in magnetic grain size and benthic delta C-13 suggests that concentrations of single domain magnetite (possibly magnetotactic bacterial magnetite) vary in response to middepth water ventilation. We suggest that reduced ventilation in the middepth western South Atlantic bottom waters during peak glaciations triggered a decrease in the production of biogenic magnetite. Peak glaciations were, in turn, linked with increases in the residence time of North Atlantic Deep Water (or its glacial counterpart). (AU)

• Processo FAPESP: 16/10242-0 - Ocorrência e impacto da mega-Zona de Convergência do Atlântico Sul na porção leste da América do Sul durante o último período glacial: uma abordagem paleoceanográfica
• Beneficiário: Marília de Carvalho Campos Garcia
• Modalidade de apoio: Bolsas no Brasil - Doutorado