Accelerator radiocarbon ages on foraminifera separated form deep-sea sediments

A first set of accelerator radiocarbon dates for foraminifera shells separated from a deep-sea core from the western equatorial Pacific is reported. While the ultimate objective of this work is to obtain evidence for changes in the rate of deep-sea ventilation over the last 20,000 years, this preliminary study concentrates on illuminating some of the possible biases which will surely complicate such studies. The results reveal that while whole shells and shell fragments of a single species give ages which agree within experimental error, there are significant differences among the ages for coexisting whole shells of different planktonic species. It is not possible as yet to pin down the source of these differences. Because of this, the finding that the benthic-planktonic age difference was greater 6000 to 12,000 years ago than over the last 5000 years does not necessarily mean that the ventilation rate for the deep sea was significantly slower during late glacial and early Holocene times than it is today. Other equally plausible explanations are possible. Much has yet to be learned about the origin and seafloor history of the material in deep-sea cores before any firm answers regarding paleocirculation rates can be obtained by this approach. Such studies should initially be concentrated on cores from areas of the seafloor characterized by a higher ratio of sedimentation rate to bioturbation depth than is found for typical open sea sediments.