Palaeoreconstruction of the Amazon River freshwater and sediment dischargeusing sediments recovered at Site 942 on the Amazon Fan

A continuous reconstruction of palaeoclimate has been generated for the las t 12 000 C-14 yr BP, from ODP site 942 (5 degrees 45'N, 49 degrees 6'W at a water depth of 3346 m), drilled to the west of the Amazon Fan. Records fro m the site suggest that during the Younger Dryas, the Amazon Basin was extr emely dry, and Amazon River discharge was low. This increased aridity is hy pothesised to be due predominantly to reduced precipitation. In addition, t here is evidence for a discharge event at the end of the Younger Dryas, coe val with Termination 1B, that produced an estimated Amazon River outflow eq uivalent to present-day values, and an increase in sediments derived from t he Andes. The timing of this event, coincident with the warming of the Ande an Ice Sheet, suggests that it was at least partly driven by meltwater prod uced by the retreat of Andean glaciers, but also required an increase in re gional rainfall resulting from changes in climate. Site 942 also demonstrat es that the sediment input to the western part of the Amazon Fan from the r iver ceased between 9900 and 9500 C-14 yr BP, at a time when sea level was 40-50 m below the present level. If this value is truly indicative of the s ea levels at which the sediment supply to the fan switched 'off', then it i s far greater than the 30 m below current sea-level suggested previously. C opyright (C) 2000 John Wiley & Sons, Ltd.