Deepwater ventilation and stratification in the Neogene South China Sea

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doi: 10.1016/S1002-0705(07)60024-7
Author(s): Li Qianyu; Zhao Quanhong; Zhong Guangfa; Jian Zhimin; Tian Jun; Cheng Xinrong; Wang Pinxian; Chen Muhong
Author Affiliation(s): Primary:
Tongji University, Key Laboratory of Marine Geology, Shanghai, China
Chinese Academy of Sciences, South China Sea Institute of Oceanology, China
Volume Title: Journal of China University of Geosciences
Source: Journal of China University of Geosciences, 18(2), p.95-108. Publisher: China University of Geosciences, Hubei, China. ISSN: 1002-0705
Note: In English. 43 refs.; illus., incl. charts, 1 table, sketch map
Summary: Combined data on physical properties, benthic foraminifera, and stable isotopes from ODP Sites 1148, 1146, and 1143 are used to discuss deep water evolution in the South China Sea (SCS) since the Early Miocene. The results indicate that 3 lithostratigraphic units, respectively 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 deep water ventilation. The first 2 periods show a closer link to contemporary production of the Antarctic Bottom Water (AABW) 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 from a lower deepwater setting and Site 1146 from an upper deepwater setting increased significantly, 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 a weakening in the control of the SCS deep water by the open ocean. Probably they mark the birth of local deep water due to shallow waterways or a rise in sill depths during the course of sea basin closing from south to east by the west-moving Philippine Arc after the end of SCS seafloor spreading at 16-15 Ma. However, it took another 5 Ma before the dissolved oxygen approached modern levels. Although the oxygen level continued to stabilize, several Pacific Bottom Water (PBW) and Pacific Deep Water (PDW) marker species rapidly increased since 6 Ma, followed by a dramatic escalation in planktonic fragmentation, which indicates high dissolution, especially after 5 Ma. The period of 5-3 Ma saw the strongest stratified deepwater in the then SCS, as indicated by an up to 40% CaCO3 difference between Sites 1148 and 1146. Apart from strengthening of the PDW as a result of 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 deep water entered a 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 of benthic δ13C to a Neogene minimum at 0.9 Ma together convey a clear message that the PBW largely disappeared and the PDW considerably weakened in the Mid-Pleistocene 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 of sill depths under the Bashi Strait.
Year of Publication: 2007
Research Program: ODP Ocean Drilling Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Benthic environment; Bottom water; Cenozoic; Deep-sea environment; Foraminifera; Invertebrata; Leg 184; Lithostratigraphy; Lower Miocene; Marine environment; Marine sediments; Microfossils; Miocene; Neogene; North Pacific; Northwest Pacific; ODP Site 1143; ODP Site 1146; ODP Site 1148; Ocean Drilling Program; Pacific Ocean; Paleo-oceanography; Pleistocene; Pliocene; Protista; Quaternary; Sediments; South China Sea; Stratification; Tertiary; Ventilation; West Pacific
Coordinates: N092143 N092143 E1131707 E1131707
N192724 N192724 E1161622 E1161622
N185010 N185010 E1163356 E1163356
Record ID: 2015009912
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