Upward decrease of organic C/N ratios in the Okinawa Trough cores: proxy for tracing the post-glacial retreat of the continental shore line

Six piston cores were collected along the NW-SE line in the Okinawa Trough close to the Chinese continental shelf edge and dated by 23 AMS C-14 measur ements, along with planktonic delta O-18 stratigraphy and an ash layer date d as similar to6.3 ka. On a time scale to similar to 19 ka, the ratio of to tal organic carbon to total nitrogen concentration (C/N ratio) displays gra dual decreases toward the present and suggests the decrease of vascular pla nt fragment input to the trough from continental rivers. This suggestion is confirmed by similar decreases of lignin phenol content and ratio of C-28 fatty acid to C-16 fatty acid content in core RN93-PC3. The gradual decreas e of land plant fragment input is interpreted to be a consequence of the re treat of the continental coastline during the deglacial period. (C) 2001 El sevier Science B.V. All rights reserved.