Radiocarbon ages were determined on samples of benthic and planktic foraminifera separated from two cores (NGC102 and NGC108) collected from the Shatsky Rise, northwestern Pacific. In paleoceanographic studies, benthic–planktic foraminiferal age differences from same horizon have been used as a proxy for the ventilation age of deep water. Paleoceanographic data from the middle-latitude northwestern Pacific are lacking, due to poor carbonate preservation on the abyssal plain. The Shatsky Rise, which is located in a central part of the northwestern Pacific and has thick deposits of carbonate sediments, is an especially important area for understanding the Quaternary climate record. However, the paleoclimatic information recorded in the sediments would necessarily be degraded by sediment mixing resulting from bioturbation. We evaluate benthic–planktic foraminiferal age differences from low sedimentation core samples collected from the Shatsky Rise, in order to identify the effects of bioturbation on understanding of the paleoclimatic record in deep-sea sediments. Two cores consisted mostly of homogeneous, yellowish-brown, calcareous ooze. Radiocarbon analysis was made at AMS facility at National Institute for Environmental Studies (NIES-TERRA). Planktic foraminiferal ages in core NGC102 range from 2,600 to 14,730 yr BP, corresponding to the Holocene–last glacial episode. On the other hand, benthic foraminiferal radiocarbon ages range from 8,690 to 15,015 yr BP. As a result, benthic–planktic age differences showed large variance from 7,000 to 200 yr BP. The age differences (about 7,000 yr) in the mixing layer are approximately 5,000 yr older than present ventilation age (2,000 yr), reflecting the upward mixing of old benthic foraminiferal specimens.
See more of Poster Session I
See more of The 10th International Conference on Accelerator Mass Spectrometry (September 5-10, 2005)