Deepwater ventilation and stratification during the Neogene in the South China Sea

Author(s): Li Qianyu; Zhao Quanhong; Zhong Guangfa; Jian Zhimin; Tian Jun; Cheng Xinrong; Chen Muhong
Author Affiliation(s): Primary:
Tongji University, Laboratory of Marine Geology, Shanghai, China
Chinese Academy of Sciences, South China Sea Institute of Oceanology, China
Volume Title: Earth Science. Journal of China University of Geoscience
Source: Earth Science. Journal of China University of Geoscience, 33(1), p.1-11. Publisher: China University of Geoscience, Wuhan, China. ISSN: 1000-2383
Note: In Chinese with English summary. 45 refs.; illus., incl. charts, sketch map
Summary: The physical properties, benthic Foraminifera, and stable isotopes from ODP Sites 1148, 1146 and 1143 are used to discuss the evolution of deepwater areas of the South China Sea (SCS) since the early Miocene. 3 lithostratigraphic units corresponding to 21-17 Ma, 15-10 Ma, and 10-5 Ma, with a positive red parameter (a) marking the red-brown sediment color represent 3 periods of deepwater ventilation. The first 2 periods show a closer link to contemporary production of the Antarctic Bottom Water (ABW) and Northern Component Water (NCW), indicating a free connection of deep waters between the SCS and the open ocean before 10 Ma. After 10 Ma, the red parameter dropped but stayed higher than the modern value (a=0), the CaCO3 percentage difference between Site 1148 (at a lower deepwater setting) and Site 1146 (at an upper deepwater setting) significantly increased, and benthic species which prefer oxygen-rich bottom conditions dramatically decreased. Coupled with a major negative excursion of benthic δ13C at 10 Ma, these parameters may denote weakened control of the SCS deepwater by the open ocean. They probably mark the birth of local deep water due to shallow waterways or a rise in sill depths during the course of sea basin closure after the end of SCS seafloor spreading at 16-15 Ma. Several Pacific Bottom Water (PBW) and Pacific Deep Water (PDW) marker species rapidly increased since 6 Ma, and from 5 Ma to 3 Ma the local deepwater became strongly stratified, as indicated by a difference of up to 40% CaCO3 between Sites 1148 and 1146. Apart from a strengthening PDW due to global cooling and ice cap buildup at northern high latitudes, a deepening sea basin due to stronger subduction eastward may also have triggered the influx of more corrosive waters from the deep western Pacific. Since 3 Ma, the evolution of the SCS deepwater entered the modern phase, as characterized by a relatively stable 10% CaCO3 difference between the two sites and an increase in infaunal benthic species which prefer a low oxygenation environment. The subsequent reduction in PBW and PDW marker species at about 1.2 Ma and 0.9 Ma and another significant negative excursion in benthic δ13C to a Neogene minimum at 0.9 Ma together convey a clear message that the PBW largely disappeared and the PDW weakened considerably during the mid-Pleistocene in the SCS. Therefore, the true modern mode of SCS deep water started to form only during the "mid-Pleistocene climate transition", probably due to the rise in sill depths under the Bashi Strait.
Year of Publication: 2008
Research Program: ODP Ocean Drilling Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Benthic taxa; C-13/C-12; Calcium carbonate; Carbon; Cenozoic; Deep-sea environment; Foraminifera; Isotope ratios; Isotopes; Leg 184; Marine environment; Microfossils; Neogene; North Pacific; Northwest Pacific; ODP Site 1143; ODP Site 1146; ODP Site 1148; Ocean Drilling Program; Pacific Ocean; Paleo-oceanography; Paleoclimatology; South China Sea; Stable isotopes; Tertiary; Ventilation; West Pacific
Coordinates: N185010 N185010 E1163356 E1163356
N192724 N192724 E1161622 E1161622
N092143 N092143 E1131707 E1131707
Record ID: 2019044712
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