Mineral and elemental indicators of post-glacial changes in sediment delivery and deposition under a western boundary upwelling system (Cabo Frio, southeastern Brazil)

Minerals and elements are important proxies that can provide information about variations in the delivery and deposition of coastal ocean sediments associated with past climate changes. In this study, postglacial changes in the accumulation of sediments on the upper shelf of southeastern Brazil are linked to the evolution of regional paleoceanographic and continental paleoclimatic conditions during the last 14.4kyr CAL BP. Mineralogical and major and trace element analyses of a ¹⁴C-dated sediment core identify three main lithostratigraphic units of this core that reveal a succession of changes in sediment delivery and accumulation as postglacial sea level rose and Holocene climate on land evolved. The depositional setting has transitioned in response to the large sea level rise prior to 9.9kyr CAL BP from being a shallow water high energy environment to a deeper water one. This location has since then been a lower energy environment that has persisted into modern times. Due to the high marine productivity associated with the Cabo Frio upwelling system in an oxygenated water column, the sediments have shown a complex and dynamic redox condition, making variations in redox-sensitive trace elements indicative of changes in primary production and organic matter diagenesis at this location. After sea level stabilized ~9kyr CAL BP, variations in fluxes of Al, Fe, Ca, and minerals were small, indicating that climate driven changes had only secondary controls on delivery of detrital sediment components to the Cabo Frio shelf. Modern coastal upwelling conditions and the onset of mid-shelf organic-rich sediment deposition were established after 9.9CAL kyr BP.