Sedimentation rates in Baffin Island fiord cores from comparative radiocarbon dates

Abstract

Five accelerator (TAMS system, University of Arizona) radiocarbon dates on small (30–50 mg) paired bivalves or shell fragments have been obtained on two piston cores. These dates are compared with conventional and accelerator 14C dates on the total organic fraction (< 2 μm size fraction) from similar levels in the two cores. The shell dates are always younger by several thousands of years. We argue that the shell dates are the more reliable; for example, we demonstrate that pre-Quaternary pollen is abundant in the lowermost 6 m in core HU77-159 from Frobisher Bay. Since the occurrence of shells is rare in piston cores, we have developed an empirical relation that enables us to change dates on organic matter to a more probable "true" age. If this correction is applied to dates on the total organic fraction that we obtained on an additional five cores from fiord and shelf sites, a consistent pattern of sedimentation rate variations is shown. This indicates that sedimentation rates were highest between ca. 9000 and 6500 years BP, a time when fiord glaciers in Baffin Island were undergoing substantial retreat.