Sediment loads in the Amazon River

Abstract

ESTIMATES published in the past 20 years of the sediment load delivered to the sea by the Amazon River range from 4 to 10 × 10⁸ tonnes yr⁻¹ Estimates published around 1960, when few data were available on either the sediment concentration or the river discharge, were in the range 9–10 × 10⁸ tonnes yr⁻¹ (refs 1, 2). Estimates published in 1967 and 1968, after significant new data had been collected, were in the lower range of 4–5 × 10⁸ tonnes yr⁻¹ (refs 3, 4). Our more comprehensive data collected mostly since 1970 (and especially in 1977) suggest that the earlier higher estimates may have been more nearly correct. We show here that the mean annual load of suspended sediment at Óbidos, Brazil is between 8 and 9 × 10⁸ tonnes yr⁻¹. Most of this sediment is discharged onto the continental shelf.