Radiocarbon Age Offset Between Shell and Plant Pairs in the Holocene Sediments Under Hakata Bay, Western Japan

To measure chronological changes in the marine reservoir effect in western Japan, 47 marine shells and 35 terrestrial plants from the same horizons in two cores of Holocene sediments were radiocarbon dated by the KIGAM AMS facility. These cores were obtained from the central and northern parts of Hakata Bay using a Geoslicer device. This drilling tool provided us continuous coverage and many samples. In order to determine the species effects on the marine reservoir effect, both filter feeders and a deposit feeder were selected for study. Based on the analysis of lithology, mollusk assemblage, and C-14 dating, two sedimentary units were determined: the upper bay floor sediment and lower estuarine sediment. Reservoir ages of 280 +/- 150 yr (n = 17) and 340 +/- 140 yr (n = 18) were obtained from the central and northern parts of Hakata Bay during 2000 to 10,000cal BP, respectively. Based on these results, it is clear that a paleoenvironmental change occurred here as a result of sea-level rise during the deglacial period.