In all cases, radiocarbon ages were obtained from the organic carbon fraction extracted from bulk sediment samples cut from 1-cm-thick sample slices taken from the sample half of the nominated core. Samples were pretreated with addition of dilute 2-M HCl for 3 hr at 60°C in order to remove any carbonate materials, including microfossils and detrital matter. The residue was then washed three times with water, dried, and combusted to convert all organic carbon to CO2. The CO2 was reduced to graphite by conventional means (Hua et al., 2001). All sample processing steps were carried out at ANSTO. AMS measurements were carried out at the ANSTO ANTARES AMS facility. All Holocene 14C dates were completed with radiocarbon age precision between 0.3% and 0.7% error (Fink et al., 2004).
The initial sample batch collected during Leg 201 (sample numbers OZG and OZF in Table T1) were shipped under frozen carbon dioxide from Valparaiso, Chile, to Sydney and then refrigerated until analysis. A second batch of samples (sample numbers OZH in Table T1) was dispatched from the Gulf Coast Core Repository at Texas A&M University (TAMU; USA) under ice and similarly refrigerated until analysis. Initially, a single sample from a depth between ~10 and 20 cm at each site was 14C dated. For those yielding sedimentation rates of <5 cm/k.y., no further age dating was carried out, as the sedimentation rate was too low to allow subcentury resolution for geochemical, magnetic susceptibility, or reflected light study for paleoceanographic purposes. This resulted in solitary 14C dates for uppermost sections (approximately <20 cm) at Sites 1225, 1226, 1230, and 1231. The stratigraphic position of these dated samples within each core and geographic core location are shown in Figure F1. Comprehensive dating of a core from each of the remaining three sites (1227, 1228, and 1229), all from the Peru continental margin, was then carried out. Sedimentation patterns and the stratigraphy defined by the dates are discussed in the following section.