Northeastern South China Sea Research Articles

Palaeoceanographic change in the northeastern South China Sea during the last 15000 years

The sedimentary succession of piston core RC26-16, dated by 14 C accelerator mass spectrometry, provides a nearly continuous palaeoceanographic record of the northeastern South China Sea for the last 15 000 yr. Planktic foraminiferal assemblages indicate that winter sea-surface temperatures (SSTs) rose from 18°C to about 24°C from the last glacial to the Holocene. A short-lived cooling of 1°C in winter temperature centred at about 11 000 14 Cy r ago may reflect the Younger Dryas cooling event in this area. Summer SSTs have remained between 27°C and 29°C throughout the record. The temperature difference between summer and winter was about ca. 9°C during the last glacial, much higher than the Holocene value of ca. 5°C. During the late Holocene a short-lived cooling event occurred at about 4000 14 Cy r ago. Oxygen and carbon isotopic gradients between surface (0-50 m) and subsurface (50-100 m) waters were smaller during the last glacial than those in the Holocene. The fluctuation in the isotopic gradients are caused most likely by changes in upwelling intensity. Smaller gradients indicate stronger upwelling during the glacial winter monsoon. The fauna-derived estimates of nutrient content of the surface waters indicate that the upwelling induced higher fertility and biological productivity during the glacial. The winter monsoon became weaker during the Holocene. The carbonate compensation depth and foraminiferal lysocline were shallower during the Holocene, except for a short-lived deepening at about 5000 14 C yr ago. A preservation peak of planktic foraminifera and calcium carbonate occurred between 13400 and 12 000 14 C

Late quaternary pteropods in the South China Sea: carbonate preservation and paleoenvironmental variation

Pteropod fossil assemblages were studied in four sediment cores selected from the South China Sea (SCS) in order to investigate carbonate preservation 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. S050-37KL (2695 m w.d.), S049-8KL (1040 m w.d.), and, SCS-12 (543 m w.d.) and RC14-79 (706 m w.d.), respectively. The abundance of the aragonitic shells down core reveals an increase in pteropod preservation during glacial times in the cores which are below the present ACD (∼1000 m w.d.). Carbonate dissolution increasesin interglacials as in the Pacific open ocean, even at the water depths above the present lysocline where higher carbonate contents was found in interglacials. A carbonate preservation maximum, however, exists at the last deglaciation. At sites shallower than the present pteropod lysocline (∼800 m w.d.) carbonate dissolution shows little influence on the glacial-interglacial change in carbonate preservation. The glacial presence of pteropods on the northern continental slope reveals drastic ACD fluctuations through glacial-interglacial cycles, and sinking of the ACD to below or near 2700 m present water depths in the northern SCS during glacial periods. Pteropod faunal composition indicates a western Pacific open 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 water influence from the western Pacific open ocean increased during glacial periods through the remaining water passageway of the Bashi Strait in the northeastern SCS. Hence, decreases in both the tropical warm-water group and bathypelagic species, as well as increases of subtropical-temperate water species, provide further evidence that glacial-interglacial contrast in faunal composition is related to the lowered sea level which altered the configuration of the glacial SCS.

Winter upwelling off Luzon in the northeastern South China Sea

A major upwelling region centered about 100 km offshore between 16° and 19°N off northwest Luzon in the South China Sea is revealed in the distributions of temperature, salinity, and dissolved oxygen concentration during a cruise in December 1990. Upward movement of water low in dissolved oxygen can be identified to a depth of 300 m. Climatological distributions of temperature and upper ocean heat content and tracer distribution obtained from a recent numerical experiment lend support to the existence of this upwelling region. Results from a general circulation model of the South China Sea further show that upwelling off Luzon occurs between October and January, in agreement with the climatological data. Current structures obtained from a simple two‐layer model and the general circulation model both suggest that this upwelling is not driven by local winds but contains a large, remotely forced component arising from the basin circulation. The upwelling is sustained by offshore Ekman drift from above and a converging northward undercurrent from below. The would‐be downwind coastal jet in the surface layer is largely offset by currents associated with the winter circulation gyre. Upwelled water with high nutrient content spreads southwestward in January and could be an important nutrient source for the surface water in the interior South China Sea in spring.

A preliminary study of glauconites in the northeastern South China Sea: Su, Guangqing and Tiaxing Wang, 1985. Tropic Oceanol., 4(3):36–44. (In Chinese, English abstract.) South China Sea Inst. of Oceanol., Acad. Sin., People's Republic of China

A preliminary study of glauconites in the northeastern South China Sea: Su, Guangqing and Tiaxing Wang, 1985. Tropic Oceanol., 4(3):36–44. (In Chinese, English abstract.) South China Sea Inst. of Oceanol., Acad. Sin., People's Republic of China

Distribution of iron in the seawater of the northeastern South China Sea: Li, Pengcheng, Wuying Han and Xineng Huang, 1985. Tropic Oceanol., 4(4):77–82. (In Chinese, English abstract.) South China Sea Inst. of Oceanol., Acad. Sin., People's Republic of China

Distribution of iron in the seawater of the northeastern South China Sea: Li, Pengcheng, Wuying Han and Xineng Huang, 1985. Tropic Oceanol., 4(4):77–82. (In Chinese, English abstract.) South China Sea Inst. of Oceanol., Acad. Sin., People's Republic of China