Sedimentation rates in Baffin Island fiord cores from comparative radiocarbon dates

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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 .mu.m 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.