HOLOCENE TERRIGENOUS INPUT CHANGES IN THE NORTHERN OKINAWA TROUGH AND THEIR PALEOCLIMATIC IMPLICATIONS

In the present study multi-approach has been employed to investigate the Holocene sedimentations of the river discharge and volcanic particles in the northern Okinawa Trough. During 11.0~6.0 kaBP,amounts of terrigenous particles and organic matter input to the northern Okinawa Trough as well as the particle grain sizes were found to have obviously decreased, which was a result from 50~60 m global sea level rise and a rapid retreat of coastline in the East China Sea. Thereby, the terrigenous input to the Okinawa Trough should be first orderly controlled by sea level changes in the early to middle Holocene. The volcanic glass shard concentration prominently increased during 8.1~7.8 kaBP, which was recognized as the K-Ah tephra derived from Kikai volcano in southern Japan. However, the K-Ah tephra age in the deep sea sediment sequence is much older than that of 7.3 kaBP in a variety of terrigenous records. This inconsistence was probably induced by the uncertainty of marine ¹⁴C age calibration.Reservoir age of the northern Okinawa Trough in the early Holocene was considered to be 300~500 years older than that of the present. A set of proxy records based on the distribution of terrigenous alkane show an increasing expansion of the C₄ plant in the East Asia continent during the Holocene, hinting the aridity was gradually enhanced in the inner part of China, which is consistent with the Holocene decrease in summer monsoon precipitation in this region.