Climate and vegetation variations since the LGM recorded by biomarkers from a sediment core in the northern South China Sea

Variations in stable carbon isotopic compositions of n-alkanes (delta C-13(alk)) and n-alkane proxies (CPI, C-31/C-27 and ACL) from core MD05-2905 (20 degrees 08.17' N, 117 degrees 21.6' E) in the northern South China Sea (SCS), provided evidence of biological responses on adjacent land areas in the form of changes in terrestrial vegetation and provenance of the remains of land plants during and since the Last Glacial Maximum (LGM). Decreased values of n-alkane proxies and delta C-13(alk) over the last 28ka marked the transition from glacial to interglacial conditions and indicated a greater extent of herbaceous vegetation at the LGM than present and an increased abundance in woody vegetation during the Holocene. Relatively larger delta C-13(alk) values at the LGM indicated that n-alkanes of terrestrial herbs in the sediment core were not only from the leaf waxes of C-3 plants, such as herbs of Artemisia, growing on proximate parts of the exposed continental shelf, but also from C-4 grasses likely from subtropical parts of southeastern China and Taiwan Island. Reconstructed sea-surface temperatures (SSTs), based on U-37(K') data from the same core, revealed that temperatures were 3 degrees C lower than present during the LGM, with abrupt variations during both glacial and interglacial periods. During the LGM, lower temperature and sea level and greater aridity relative to present resulted in an expansion of herbaceous vegetation over an enlarged extent of exposed continental shelf. Following deglaciation, warming and enhanced summer monsoonal activity led to increased humidity and to an expansion of woody vegetation (mostly C-3 plants) during the Holocene. Results also revealed rapid oscillations in C-31/C-27 ratios over millennial scales, with lower values associated with cold stages. These low C-31/C-27 ratios indicated increased input of woody plant material possibly from more extensive gallery forest and greater transport of their plant debris to the coring site, perhaps facilitated by enhanced runoff under a strengthened Northern Hemisphere winter monsoon during short-duration cold events. Copyright (c) 2012 John Wiley & Sons, Ltd.