25,000-year late Quaternary records of carbonate preservation in the South China Sea
Pelagic sediments recovered from the South China Sea (SCS) exhibit characteristic carbonate preservation fluctuations that are closely linked to major cycles of climatic change. Two deep sea cores (SCS 90-36: 17°59.70′N, 111°29.64′E, water depth 2050 m; and 31-KL: 18°45.4′N, 115°52.4′E, 3360 m) that are located respectively above and below the regional lysocline (∼ 3000 m) were selected for studying the late Quaternary pattern of carbonate preservation in the SCS. Preservation indices measuring changes in the abundances of dissolution-resistant planktonic foraminifers and coccoliths, and in ratios of foraminiferal fragments, benthonic foraminifers, and radiolarians, have revealed increased carbonate preservation during the last glacial period and/or during the last deglaciation (Termination I; ∼ 12,000 k.y.), but stronger carbonate dissolution during the interglacial period of the Holocene. Detailed comparisons of preservation and oxygen isotope records further indicate that the level of carbonate preservation increased steadily from 25 k.y. through Termination I and that preservation reached a maximum during Termination I. From Termination I into the Holocene, however, the level of preservation decreased gradually to a minimum. Both records exhibit noticeable glacial/interglacial variations (1f on the order of 104 years), while the higher resolution record of 31-KL records a series of higher frequency oscillations (1f on the order of 103 years). These data confirm the observation that maximal carbonate preservation tends to occur during the later half of glacial stages as shown previously in many Indian and Pacific deep sea core studies.