LATE QUATERNARY PTEROPODS IN THE SOUTH CHINA SEA - CARBONATE PRESERVATION AND PALEOENVIRONMENTAL VARIATION

Pteropod fossil assemblages were studied in four sediment cores select ed from the South China Sea (SCS) in order to investigate carbonate pr eservation change through late Quaternary glacial-interglacial cycles. These cores were selected at water depths (w.d.) below, near, and/or above the present Aragonite Compensation Depth (ACD), i.e. SO50-37KL ( 2695 m w.d.), SO49-8KL (1040 m w.d.), and, SCS-12 (543 m w.d.) and RC1 4-79 (706 m w.d.), respectively. The abundance of the aragonitic shell s down core reveals an increase in pteropod preservation during glacia l times in the cores which are below the present ACD (similar to 1000 m w.d.). Carbonate dissolution increases in interglacials as in the Pa cific open ocean, even at the water depths above the present lysocline where higher carbonate contents was found in interglacials. A carbona te preservation maximum, however, exists at the last deglaciation. At sites shallower than the present pteropod lysocline (similar to 800 m w.d.) carbonate dissolution shows little influence on the glacial-inte rglacial change in carbonate preservation. The glacial presence of pte ropods on the northern continental slope reveals drastic ACD fluctuati ons through glacial-interglacial cycles, and sinking of the ACD to bel ow or near 2700 m present water depths in the northern SCS during glac ial periods. Pteropod faunal composition indicates a western Pacific o pen ocean origin, and variations in fossil assemblages correlate well with sea surface temperature change. As most of the straits around the SCS emerged due to lower glacial sea-level, subtropical-temperate wat er influence from the western Pacific open ocean increased during glac ial periods through the remaining water passageway of the Bashi Strait in the northeastern SCS. Hence, decreases in both the tropical warm-w ater group and bathypelagic species, as well as increases of subtropic al-temperate water species, provide further evidence that glacial-inte rglacial contrast in faunal composition is related to the lowered sea level which altered the configuration of the glacial SCS.