Using hydrographic data sampled during four successive late summer-early autumn cruises in 2004-2007, vertical stratification along transects in the lee of Taiwan Island was analyzed to investigate upper ocean respons...Using hydrographic data sampled during four successive late summer-early autumn cruises in 2004-2007, vertical stratification along transects in the lee of Taiwan Island was analyzed to investigate upper ocean responses to orographically induced dipole wind stress curl (WSC). Results indicate that mixed-layer depth (MLD) and its relationship with thermocline depth varied under different local wind forcings. Average MLD along the transects from the 2004 to 2007 cruises were 18.5,30.7,39.2 and 24.5m, respectively. The MLD along the transects deepened remarkably and resulted in thermocline ventilation in 2005 and 2006, whereas ventilation did not occur in 2004 and 2007. Estimates indicate that frictional wind speed was the major factor in MLD variations. To a large degree, the combined effects of frictional wind speed and Ekman pumping are responsible for the spatial pattern of MLD during the cruises.展开更多
The Dongsha submarine canyon is a large canyon belonging to a group of canyons on the northeastern South China Sea margin Investigation of the Dongsha canyon is important for understanding the origin of this canyon gr...The Dongsha submarine canyon is a large canyon belonging to a group of canyons on the northeastern South China Sea margin Investigation of the Dongsha canyon is important for understanding the origin of this canyon group as well as the transport mechanism of sediments on the margin, and the evolution of the Taixinan foreland basin and the associated Taiwan orogenic belt. In this study, the morphology, sedimentary characteristics, and origin of the Dongsha canyon were investigated by inte- grating high-resolution multi-channel seismic reflection profiles and high-precision multibeam bathymetric data. This is a slope-confined canyon that originates in the upper slope east of the Dongsha Islands, extends downslope in the SEE direction, and finally merges with the South Taiwan Shoal canyon at a water depth of 3000 m. The total length and average width of the canyon are around 190 and 10 km, respectively. Eleven seismic sequence boundaries within the canyon fills were identified and interpreted as incision surfaces of the canyon. In the canyon fills, four types of seismic facies were defined： parallel onlap fill, chaotic fill, mounded divergent facies, and migrated wavy facies. The parallel onlap fill facies is interpreted as altemating coarser turbidites or other gravity-flow deposits and fine hemipelagic sediments filling the canyon valley. The chaotic fill faci- es is presumed to be debrites and/or basal lag deposits filling the thalwegs. The mounded divergent and migrated wavy seismic facies can be explained as canyon levees consisting mainly of overspilled fine turbidites and sediment waves on the levees or on the canyon-mouth submarine fans. Age correlation between the sequence boundaries and the ODP Site 1144 data suggests that the Dongsha canyon was initiated at approximately 0.9 Ma in the middle Pleistocene. Mapping of the canyon indicates that the canyon originated at the upstream portion of the middle reach of the modem canyon, and has been continuously expanding both upstream and downstream by retrogressive erosion, incision, and deposition of turbidity currents and other gravity transport processes. The ages of the sequence boundaries representing major canyon incision events are in good agreement with those of global sea-level lowstands, indicating that sea-level changes may have played an important role in the canyon＇s development. The Dongsha canyon developed in a region with an active tectonic background characterized by the Taiwan up- lifting and the development of the Taixinan foreland basin. However, no evidence suggests that the canyon formation is directly associated with local or regional faulting and magmatic activities. Turbidity currents and other gravity transport processes （includ- ing submarine slides and slumps） may have had an important influence on the formation and evolution of the canyon.展开更多
基金Supported by the Knowledge Innovation Program of Chinese Academy of Sciences (No. KZCX2-YW-Q11-02)the National Basic Research Program of China (973 Program) (No. 2011CB403503)the National Natural Science Foundation of China (Nos. 40876009,41176028)
文摘Using hydrographic data sampled during four successive late summer-early autumn cruises in 2004-2007, vertical stratification along transects in the lee of Taiwan Island was analyzed to investigate upper ocean responses to orographically induced dipole wind stress curl (WSC). Results indicate that mixed-layer depth (MLD) and its relationship with thermocline depth varied under different local wind forcings. Average MLD along the transects from the 2004 to 2007 cruises were 18.5,30.7,39.2 and 24.5m, respectively. The MLD along the transects deepened remarkably and resulted in thermocline ventilation in 2005 and 2006, whereas ventilation did not occur in 2004 and 2007. Estimates indicate that frictional wind speed was the major factor in MLD variations. To a large degree, the combined effects of frictional wind speed and Ekman pumping are responsible for the spatial pattern of MLD during the cruises.
基金supported by the National Natural Science Foundation of China(Grant Nos.91028003,41076020)the Guangzhou Marine Geological Survey(GMGS)(Grant No.GZH2011003-05)
文摘The Dongsha submarine canyon is a large canyon belonging to a group of canyons on the northeastern South China Sea margin Investigation of the Dongsha canyon is important for understanding the origin of this canyon group as well as the transport mechanism of sediments on the margin, and the evolution of the Taixinan foreland basin and the associated Taiwan orogenic belt. In this study, the morphology, sedimentary characteristics, and origin of the Dongsha canyon were investigated by inte- grating high-resolution multi-channel seismic reflection profiles and high-precision multibeam bathymetric data. This is a slope-confined canyon that originates in the upper slope east of the Dongsha Islands, extends downslope in the SEE direction, and finally merges with the South Taiwan Shoal canyon at a water depth of 3000 m. The total length and average width of the canyon are around 190 and 10 km, respectively. Eleven seismic sequence boundaries within the canyon fills were identified and interpreted as incision surfaces of the canyon. In the canyon fills, four types of seismic facies were defined： parallel onlap fill, chaotic fill, mounded divergent facies, and migrated wavy facies. The parallel onlap fill facies is interpreted as altemating coarser turbidites or other gravity-flow deposits and fine hemipelagic sediments filling the canyon valley. The chaotic fill faci- es is presumed to be debrites and/or basal lag deposits filling the thalwegs. The mounded divergent and migrated wavy seismic facies can be explained as canyon levees consisting mainly of overspilled fine turbidites and sediment waves on the levees or on the canyon-mouth submarine fans. Age correlation between the sequence boundaries and the ODP Site 1144 data suggests that the Dongsha canyon was initiated at approximately 0.9 Ma in the middle Pleistocene. Mapping of the canyon indicates that the canyon originated at the upstream portion of the middle reach of the modem canyon, and has been continuously expanding both upstream and downstream by retrogressive erosion, incision, and deposition of turbidity currents and other gravity transport processes. The ages of the sequence boundaries representing major canyon incision events are in good agreement with those of global sea-level lowstands, indicating that sea-level changes may have played an important role in the canyon＇s development. The Dongsha canyon developed in a region with an active tectonic background characterized by the Taiwan up- lifting and the development of the Taixinan foreland basin. However, no evidence suggests that the canyon formation is directly associated with local or regional faulting and magmatic activities. Turbidity currents and other gravity transport processes （includ- ing submarine slides and slumps） may have had an important influence on the formation and evolution of the canyon.
