On the basis of accelerator mass spectrometer radiocarbon （AMS ^14C） dating, sedimentation rates of 11 cores collected from the northern to southern Okinawa Trough are discussed. The sedimentation rates in the Okina...On the basis of accelerator mass spectrometer radiocarbon （AMS ^14C） dating, sedimentation rates of 11 cores collected from the northern to southern Okinawa Trough are discussed. The sedimentation rates in the Okinawa Trough roughly range from 11 to 39cm/ka, and the average is 23.0cm/ka. China＇s continental matter is the main sediment source of the middle Okinawa Trough and has important contribution to the northern and southern Okinawa Trough. The sedimentation rates during the marine oxygen isotope （MIS） 2 are uniformly higher than those during MIS 1 in the northern and middle Okinawa Trough while they are on the contrary in the southern Okinawa Trough. Sedimentation rates in the Okinawa Trough can be one of the proxies of sediment source and an indicator of cooling events.展开更多
As a high-sedimentation rate depocenter along the path of the Kuroshio Current, the southwesternmost part of the Okinawa Trough is a key area to understand the Kuroshio history and sediments transpor-tation. A 34.17-m...As a high-sedimentation rate depocenter along the path of the Kuroshio Current, the southwesternmost part of the Okinawa Trough is a key area to understand the Kuroshio history and sediments transpor-tation. A 34.17-m-long sediment core was obtained by the advanced piston corer of Marco Polo/IMAGES XII MARION DUFRESNE during the May 2005 from the Southern Okinawa Trough at site MD05-2908. The recovered sediments were analyzed by AMS 14C dating, coarse size fraction (>63 μm) extraction and moisture content determination in order to study its sedimentation flux and provenance. The depth-age relationship of core MD05-2908 was well constrained by 17 14C dating points. The sediments span across the mid-Holocene (6.8 ka B.P.) and have remarkablely high sedimentation rates between 1.8 and 21.2 m ka?1, which is well consistent with the modern observations from sediment traps. We identified five 70―200 a periods of abnormally rapid sedimentation events at 6790―6600 a B.P., 5690―5600 a B.P., 4820―4720 a B.P., 1090―880 a B.P., and 260―190 a B.P., during which the highest sedimentation rate is up to 21.2 m/ka. In general, the lithology of the sediments were dominated by silt and clay, associated with less than 5% coarse size fraction (>63 μm). As the most significant sediment source, the Lanyang River in northeastern Taiwan annually deliver about 10Mt materials to the coastal and offshore region of northeast Taiwan, a portion of which could be carried northward by currents toward the study area. Therefore, we concluded that the 5 abnormally rapid sedimentation events may be related to intensified rainfall in Taiwan and thus increased materials to our study area at that time. However, a few extreme-rapid sedimentation events cannot be explained by normal river runoff alone. The large earth-quakes or typhoons induced hyperpycnal discharge of fluvial sediment to the ocean may also act as a potential source supply to the Okinawa Trough.展开更多
基金This study was supported by the National Natural Science Foundation of China under contract Nos 40176018,40421150011 and 49776292the Ministry of Science and Technology,State Oceanic Administration,China,and IFR EMER,France.
文摘On the basis of accelerator mass spectrometer radiocarbon （AMS ^14C） dating, sedimentation rates of 11 cores collected from the northern to southern Okinawa Trough are discussed. The sedimentation rates in the Okinawa Trough roughly range from 11 to 39cm/ka, and the average is 23.0cm/ka. China＇s continental matter is the main sediment source of the middle Okinawa Trough and has important contribution to the northern and southern Okinawa Trough. The sedimentation rates during the marine oxygen isotope （MIS） 2 are uniformly higher than those during MIS 1 in the northern and middle Okinawa Trough while they are on the contrary in the southern Okinawa Trough. Sedimentation rates in the Okinawa Trough can be one of the proxies of sediment source and an indicator of cooling events.
基金Supported by National Basic Research Program of China (Grant No. 2007CB815903)Key Project of National Natural Science Foundation of China (Grant No. 90411014)National Natural Science Foundation of China (Grant Nos. 40776030 and 40506016)
文摘As a high-sedimentation rate depocenter along the path of the Kuroshio Current, the southwesternmost part of the Okinawa Trough is a key area to understand the Kuroshio history and sediments transpor-tation. A 34.17-m-long sediment core was obtained by the advanced piston corer of Marco Polo/IMAGES XII MARION DUFRESNE during the May 2005 from the Southern Okinawa Trough at site MD05-2908. The recovered sediments were analyzed by AMS 14C dating, coarse size fraction (>63 μm) extraction and moisture content determination in order to study its sedimentation flux and provenance. The depth-age relationship of core MD05-2908 was well constrained by 17 14C dating points. The sediments span across the mid-Holocene (6.8 ka B.P.) and have remarkablely high sedimentation rates between 1.8 and 21.2 m ka?1, which is well consistent with the modern observations from sediment traps. We identified five 70―200 a periods of abnormally rapid sedimentation events at 6790―6600 a B.P., 5690―5600 a B.P., 4820―4720 a B.P., 1090―880 a B.P., and 260―190 a B.P., during which the highest sedimentation rate is up to 21.2 m/ka. In general, the lithology of the sediments were dominated by silt and clay, associated with less than 5% coarse size fraction (>63 μm). As the most significant sediment source, the Lanyang River in northeastern Taiwan annually deliver about 10Mt materials to the coastal and offshore region of northeast Taiwan, a portion of which could be carried northward by currents toward the study area. Therefore, we concluded that the 5 abnormally rapid sedimentation events may be related to intensified rainfall in Taiwan and thus increased materials to our study area at that time. However, a few extreme-rapid sedimentation events cannot be explained by normal river runoff alone. The large earth-quakes or typhoons induced hyperpycnal discharge of fluvial sediment to the ocean may also act as a potential source supply to the Okinawa Trough.
