Abstract
We integrated multiple geochemical analysis of a 13.75 m-long core 973-4 recovered from the northeastern South China Sea (SCS) to detect the response of deep-sea sediment archives to sea-level change spanning the last 42 kyr. The age-depth model based on AMS 14C dating, together with the sediment grain size, shows an occurrence of turbidity current at around 14 kyr, which was associated with submarine landslides caused by gas hydrate dissociation. A dominantly terrigenous sediment input was supplied from southwestern Taiwan rivers. By synthesizing environment-sensitive indexes, four distinct stages of paleoenvironmental evolutions were recognized throughout the studied interval. Well-oxygenated condition occurred during the stage I (42.4-31.8 kyr) with low sea-level stand below -80 m, accompanied by flat terrigenous input. The largest amounts of terrigenous sediment input occurred during the late phase of stage II (31.8-20.4 kyr) with the lowest sea-level stand below -120 m because of a short distance from paleo-Taiwan river estuaries to the core location. An occurrence of Ca-enriched turbidity current disturbed the original sediments during the stage III (20.4-13.9 kyr). The stepwise elevated sea-level stand resulted in an enclosed (semi-enclosed) system and contributed to a relatively low-oxygen environment in deep ocean during the stage IV (13.9 kyr—present). Temporal variations of TOC and CaCO3 display contrary pattern synchronously, indicating a decoupled relationship between organic carbon burial and carbonate productivity. Our results highlight that these sedimentary records as reflected in the paleoenvironmental changes in the northeastern SCS were mainly driven by sea-level fluctuations and later, since the mid-Holocene, the strengthening East Asian summer monsoon (EASM) overwhelmed the stable sea level in dominating the environmental changes.
Highlights
As the largest marginal sea of the western Pacific, the South China Sea (SCS) receives large amounts of sediment annually, with possible terrigenous supplies from the Pearl, Red, and Yangtze Rivers, as well as the island of Taiwan and Luzon [1,2,3,4]
There is a rapid increase in grain size in unit 3 (450-610 cm) to an average of 7.95 μm due to the influence of turbidity current, and the sediments are foraminifera-enriched silt with plant fragments
Vertical variations of Al, K, Fe, Mg, Ti, V, and Cr show a similar temporal pattern, which exhibits more depleted in unit 3 while a dramatic increase in concentrations is observed in unit 2
Summary
As the largest marginal sea of the western Pacific, the South China Sea (SCS) receives large amounts of sediment annually, with possible terrigenous supplies from the Pearl, Red, and Yangtze Rivers, as well as the island of Taiwan and Luzon [1,2,3,4]. The area in the east of the Pearl River (EPR) has been considered as another potential source for sediment supply to the northern SCS [6]. These fluvial sediments are further transported by various coastal, surface, and deep currents after entering the SCS, such as the East Asian monsoon (EAM), which is the major control on the surface circulation.
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