Tide-induced reworking of planktonic foraminifers on the outer shelf and slope off the Miyako Island, southern Ryukyus, Japan: Preliminary results

Significance of sediment reworking to a shallower environment is preliminarily discussed by occurrences and oxygen isotopes of planktonic foraminifer (Globolotalia inflata) tests collected from the sea bottom sediments on the insular shelf to slope, off the Miyako Islands, southern Ryukyus, Japan. The isotopic data and comparison with the present water temperature-depth profile indicate that vertical distribution of G. inflata with size of 300-355µm ranges from 135 to 250m (average 160m). Strong tidal currents between the East China Sea and the Pacific Ocean developed in the study area may induce the transpotation of sediment particles to a shallower environment. This is demonstrated by the occurrences of this species in sediment deposited in depth shallower than inhabiting depth. The analyzed tests were not altered by long-time contact with bottom water because they preserve surface structures and a narrow range of oxygen isotopic composition. Shortly after G. inflata died and settled on sea bottom, the tests were commonly transported to the shallower environment by the upwelling, which may result from strong tidal currents and the topographic feature of the Ryukyu Island Arc.