Study On Paleoclimate And Paleoenvironment In The Southern South China Sea Since The Late Quaternary

This paper presents the records of planktonic foraminifera (PF) census, stable carbon and oxygen isotopes of PF G.ruber (white), element geochemical analysis, mineralogical analysis, grain size and AMS¹⁴C dating from the deep-sea sediments of core 86GC in the southern South China Sea (SCS). The 1.68m long profile covers the last ca. 31,400 years including the late part of Marine Oxygen Isotope Stage 3 (MIS 3, before 29 ka B.P.), the Last Glacial Maximum (LGM, ca. 18.5-29 ka B.P.), the Termination I (ca.11.5-18.5 ka B.P.) and the Holocene (since 11.5 ka B.P).The paleoenvironment changes, the close or open of the straits and the occurrence of upwelling induced by the glacial-interglacial climate changes, together led to changes in the sedimentary environment. During the last glaciation, the ecologic environment of the southern SCS was bad. At the same, owing to the closed water condition, the depositional environment at the sea bottom was dominated by reduction condition. When it came to the postglacial period, ecologic environment of the southern SCS got better and the water mass changes were enhanced. As a result, the oxygen content in the deep water also increased.Since the late MIS3, the paleoclimate in the southern SCS and its detrital sediments source areas had suffered obvious changes. During the MIS3, the paleoclimate was generally favorable. The worst climatic condition occurred during the LGM, especially during its early part (ca.26 - 28 ka B.P.) which we defined as the maximum of the LGM in our studied area. While between 18 and 24 ka B.P, that is, the period of LGM defined by the early studies, the climate in our studied area was not as bad as that during the early LGM. Nevertheless, the tropical climate had probably still prevailed in the adjacent land and islands of the southern SCS even during the LGM, although there had been temperature fall more or less.The climate during the last glacial and the Holocene was changeable in all probability, which, we suppose, was potentially associated with frequent occurrence of ENSO. Furthermore, five distinct climate events are identified in our studied area, which may correlate with the well-known climate events in high latitude including the Heinrich events (H3-H1), the Younger Dryas (YD) and the 8 200 event.Based on the tradeoff analysis, we deduce that the climate changes during the late quaternary in the tropic zones of the southern SCS were mainly controlled by the low -latitude processes, but born the imprints of the high-latitude processes at the same time.