Provenance discrimination of the last glacial sediments from the northeastern South China Sea and its paleoenvironmental indications

Abstract

A total of 849 core samples collected from two drilling core STD235 and ZSQD289 in the northeastern South China Sea were analyzed for elemental composition including total organic carbon (TOC), total nitrogen (TN), stable carbon and nitrogen isotopic composition (δ¹³C, δ¹⁵N), and clay mineral composition. Based on clay mineral assemblages and organic geochemistry characteristics, it is supposed that the terrestrial source for sediments at STD235 and ZSQD289 is mainly from southwestern Taiwan. Moreover, the sedimentary organic matter of site ZSQD289 was probably directly inputted from southwestern Taiwan submarine canyon, while the sedimentary organic matter of core STD235 was probably transported by deep water current. The chronology suggested that it covered the record since ~19.7 and 34.6 ka BP in site STD235 and ZSQD289 respectively. Before the Last Glacial Maximum (LGM), high TOC/TN ratios with low δ¹³C and δ¹⁵N values might indicate that terrestrial organic input and nitrogen fixation was enhanced. During the LGM, gradually increased TOC, TN, δ¹³C, and δ¹⁵N values might result from the enhanced burial of organic carbon and higher marine primary production constrained by the strong winter monsoon. TOC/TN ratios and δ¹³C values generally present a decreased trend from LGM to Holocene (18 - 11 cal ka BP), strongly correlated to the terrestrial organic input and marine primary production reduced during this period. Since Holocene, the terrestrial organic input to both sites further reduced and maintained a low level, in according with a high sea level and a gradual intensified summer monsoon.

Key points

• Mineral/organic geochemical compositions of the northern SCS sediments were reported

• Detrital sediments from Taiwan and South China contributed to the study area

• The vertical geochemical proxy variations showed the environmental evolution