Sediment samples were collected via a 4-barrel multi-corer (R/V Endeavor, segmented into 1-2 cm sections, dried in a drying oven (35°C) and homogenized via mortar and pestle. Sediments were decalcified using 10% hydrochloric acid. Black carbon was isolated using the chemothermal oxidation at 375°C method.
Radiocarbon data were analyzed at the National Ocean Sciences Accelerator Mass Spectrometry Facility (NOSAMS) at the Woods Hole Oceanic Institute using the “reconnaissance” method as described by Burke et al., 2010 and McIntyre et al., 2011. The blank-corrected fraction modern is also reported as described by Burke et al., 2010. The AMS is a commissioned continuous-flow AMS system.
Instruments:
Both the total organic carbon (~0.10 to 0.35 mgC) and black carbon (~0.15 to 0.80 mgC) samples were combusted into carbon dioxide using a modified elemental analyzer and then converted to graphite using a zinc reduction method before analysis on an Accelerator Mass Spectrometer.
LOCATION:
Amazon Delta (approximately: 4 N, 47 W; 2400-3500m); Sierra Leone Rise (approximately: 7 N, 20 W; 2800-3800m).