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| Deepwater Ventilation and Stratification in the Neogene South China Sea | |
| 作者姓名： | 李前裕 赵泉鸿 钟广法 翦知湣 田军 成鑫荣 汪品先 陈木宏 |
| 作者单位： | State Key Laboratory of Marine Geology Tongji University School of Earth and Environmental Sciences The University of Adelaide Adelaide SA 5005 Australia，State Key Laboratory of Marine Geology Tongji University，State Key Laboratory of Marine Geology Tongji University，State Key Laboratory of Marine Geology Tongji University，State Key Laboratory of Marine Geology Tongji University，State Key Laboratory of Marine Geology Tongji University，State Key Laboratory of Marine Geology Tongji University，South China Sea Institute of Oceanology Chinese Academy of Sciences，Shanghai 200092 China，Shanghai 200092 China，Shanghai 200092 China，Shanghai 200092 China，Shanghai 200092 China，Shanghai 200092 China，Shanghai 200092 China，Guangzhou 510301 China |
| 摘 要： | Combined data of physical property, 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 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, 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 enlarged 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 a local deep water due to shallow waterways or rise of 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 close to the modern level. 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 up to 40% CaCO3 difference between Sites 1148 and 1146. Apart from a strengthening PDW as a result of global cooling and ice cap buildup on 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 relative stable 10% CaCO3 difference between the two sites and increase in infaunal benthic species which prefer a low oxygenated environment. Thesubsequent reduction of 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 SCS deep water started to form only during the "Mid-Pleistocene climatic transition" probably due to the rise of sill depths under the Bashi Strait. |
| 关 键 词： | 中国 南海 新第三纪 深海通风 碳酸盐沉积物 氧同位素 碳同位素 |
| 收稿时间： | 29 January 2007 |
| 修稿时间： | 2007-01-292007-03-20 |
Deepwater Ventilation and Stratification in the Neogene South China Sea |
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| Li Qianyu,Zhao Quanhong,Zhong Guangfa,Jian Zhimin,Tian Jun,Cheng Xinrong,Wang Pinxian,Chen Muhong.Deepwater Ventilation and Stratification in the Neogene South China Sea[J].Journal of China University of Geosciences,2007,18(2):95-108. | |
| Authors: | Li Qianyu Zhao Quanhong Zhong Guangfa Jian Zhimin Tian Jun Cheng Xinrong Wang Pinxian Chen Muhong |
| Institution: | 1. State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China;School of Earth and Environmental Sciences, The University of Adelaide, Adelaide SA 5005, Australia 2. State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China 3. South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China |
| Abstract: | Combined data of physical property, 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 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, 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 enlarged significantly, and benthic species which prefer oxygen-rich bottom conditions dramatically decreased. Coupled with a major negative excursion of benthic δ13 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 a local deep water due to shallow waterways or rise of 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 close to the modern level. 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 up to 40% CaCO3 difference between Sites 1148 and 1146. Apart from a strengthening PDW as a result of global cooling and ice cap buildup on 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 relative stable 10% CaCO3 difference between the two sites and increase in infaunal benthic species which prefer a low oxygenated environment. The subsequent reduction of PBW and PDW marker species at about 1.2 Ma and 0.9 Ma and another significant negative excursion of benthic d3C 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 SCS deep water started to form only during the “Mid-Pleistocene climatic transition” probably due to the rise of sill depths under the Bashi Strait. |
| Keywords: | South China Sea Miocene Pliocene Pleistocene deep water evolution ventilation carbonate accumulation oxygen and carbon isotopes |
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