RADIOCARBON DATING OF SMALL-SIZED FORAMINIFER SAMPLES: INSIGHTS INTO MARINE SEDIMENT MIXING

Radiocarbon (C-14) can be used to build absolute chronologies and reconstruct ocean ventilation over the last 40 ka. Sample size requirements have restricted C-14 measurements in marine cores with low foraminifer content, impeding C-14-based studies focused on abrupt climate events. Recent developments have demonstrated that small-sized foraminifer samples can now be dated using a gas introduction system at the cost of a small decrease in precision. We explore the potential of gas measurements on benthic and planktonic foraminifers from core SU90-08 (43 degrees 03'1 '' N, 30 degrees 02'5 '' W, 3080 m). Gas measurements are accurate, reproducible within 2 sigma uncertainty and comparable to graphite measurements. Both techniques yield negative C-14 benthic-planktonic (B-P) age-offsets after Heinrich event 1. We argue that negative B-P ages result from bioturbation and changes in foraminifer abundances, with the chance of negative B-P especially increased when the C-14 age gradient between the deep and surface waters is decreased. Small-sized C-14 measurements seem to capture the variance of the foraminifera age distribution, revealing the active mixing in those archives. Sediment deposition and mixing effects possibly pose a greater obstacle for past C-14-based dating and ocean ventilation reconstructions than the measurement precision itself, particularly in relatively low sedimentation rate settings.