Two deep channels that cut through the Luzon Strait facilitate deep (>2000 m) water exchange between the western Pacific Ocean
and the South China Sea. Our observations rule out the northern channel as a major exchange conduit. Rather, the southern
channel funnels deep water from the western Pacific to the South China Sea at the rate of 1.06 ± 0.44 Sv (1 Sv = 106 m3s−1). The residence time estimated from the observed inflow from the southern channel, about 30 to 71 years, is comparable to
previous estimates. The observation-based estimate of upwelling velocity at 2000 m depth is (1.10 ± 0.33) × 10−6 ms−1, which is of the same order as Ekman pumping plus upwelling induced by the geostrophic current. Historical hydrographic observations
suggest that the deep inflow is primarily a mixture of the Circumpolar Deep Water and Pacific Subarctic Intermediate Water.
The cold inflow through the southern channel offsets about 40% of the net surface heat gain over the South China Sea. Balancing
vertical advection with vertical diffusion, the estimated mean vertical eddy diffusivity of heat is about 1.21 × 10−3 m2s−1. The cold water inflow from the southern channel maintains the shallow thermocline, which in turn could breed internal wave
activities in the South China Sea. 相似文献
Dissolved and particulate 234Th activities in surface seawater were determined at 27 stations along the coastline of western Taiwan during 19–23 November
2004. Contrasting scavenging settings were observed between the northern and southern regimes of the nearshore water off western
Taiwan, separated by the Cho-Shui River. The northern regime is characterized by a large quantity of suspended load contributed
by northward transport of a suspension plume from the Cho-Shui River, while the southern regime, low in suspended load and
high in chlorophyll concentration, is a system controlled by biological activity. A scavenging model that takes account of
the physical transport was used to estimate the 234Th budget in order to estimate the scavenging and removal rates from the nearshore water. The scavenging and removal rates
ranged from 21 to 127 dpm m−3d−1 and from 36 to 525 dpm m−3d−1, for dissolved and particulate 234Th, respectively. The removal fluxes of particulate organic carbon (POC) and particulate organic nitrogen (PON) were estimated
by multiplying the particulate 234Th removal flux to the organic carbon/234Th and nitrogen/234Th ratios in suspended particles, which ranged from 4.5 to 275.2 mmol-C m−2d−1 and from 1.3 to 50.1 mmol-N m−2d−1, respectively. These fluxes resulted in residence times of 1∼20 days for the POC in the surface water of nearshore water
off western Taiwan. 相似文献
The mafic dykes (dolerites) during the Early Paleozoic are widely spread in Langao-Ziyang, southern Qiling Block, and the investigation on these dykes are very important. Previous studies have mainly focused on the Silurian mafic dykes; however, research on the Earlier Paleozoic mafic dykes is relatively weak at present. Therefore, the overall understanding of the mantle source and genetic dynamic setting during the Early Paleozoic in this area is lacking. To study the accurate age and origin of the Early Paleozoic mafic dykes in Ziyang, southern Shaanxi Province, the mafic dykes from dabacunand Qinmingzhai were selected and the petrology, zircon U–Pb chronology, geochemistry, and Sr–Nd–Hf isotopes were studied. Analysis indicates that the mafic dykes studied are mainly composed of dolerite, and they are the products of the Early Ordovician (475.8–480.7 Ma). Furthermore, the dolerites belong to alkaline rock series, and they are characterized by enrichment in LREE, Rb, Ba, Sr, Nb, (87Sr/86Sr)i = 0.7020–0.7050, εNd(t) = 3.0–4.0), εHf (t) = 4.5–12.1,176Hf/177Hf = 0.282681–0.282844. This suggests that the mafic dyke were derived from the partial melting of a depleted lithospheric mantle, and the genetic process is mainly controlled by the mantle plume based on the discussion of the genetic model. Furthermore, the genetic process experienced the separation and crystallization of olivine and clinopyroxene at the same time, with little crustal contamination.
Based on the spherical earth dislocation theory and a fault slip model of the Tohoku-Oki MW9.0 earthquake, the co-seismic Coulomb failure stress changes (ΔCFS) on the northern Tanlu fault zone at depths of 0–40 km are calculated. By comparing two sets of results from the spherical earth dislocation theory and the semi-infinite space one, the effect of earth curvature on the calculation results is analyzed quantitatively. First, we systematically summarize previous researches related to the northern Tanlu fault zone, divide the fault zone as detailed as possible, give the geometric parameters of each segment, and establish a segmented structural model of the northern Tanlu fault zone. Second, we calculate the Coulomb stress changes on the northern Tanlu fault zone by using the spherical earth dislocation theory. The result shows the Coulomb stress changes are no more than 0.003 MPa, which proves the great earthquake did not significantly change the stress state of the fault zone. Finally, we quantitatively analyze the disparities between the results of semi-infinite space dislocation theory and the spherical earth one. The average disparity between them is about 7.7% on the northern Tanlu fault zone and is 16.8% on the Fangzheng graben, the maximum disparity on this graben reaches up to 25.5%. It indicates that the effect of earth curvature can not be ignored. So it’s necessary to use the spherical earth dislocation theory instead of the semi-infinite space one to study the Coulomb stress change in the far field. 相似文献
A near-inertial oscillation (NIO) burst event in the west South China Sea (SCS) was observed by an upward-looking mooring
Acoustic Doppler Current Profiler (ADCP) in summer 2004. The mooring station was located at 13.99°N, 110.52°E. The spectral
analysis reveals that typhoon Chanchu is a major mechanism in triggering the NIO burst event. Before typhoon Chanchu passed
over, the NIO signals were quite weak. The NIO band becomes the most energetic constituent of the circulation during the typhoon-wake
period. The average peak power density (PD) reaches (5.3 ± 2.6) × 102 cm2 s−2 (cycles per hour, cph)−1 with a maximum value of 9.0 × 102 cm2 s−2 cph−1, i.e., 3.1 times higher than that of diurnal tide (DT), (1.7 ± 0.5) × 102 cm2 s−2 cph−1. At the upper (80 m) and sub-upper (208 m) layers, the central frequency of the NIO band is 0.022 cph with a blueshift of
about 9% above the inertial frequency f (0.02015 cph). At the lower layer (400 m), the central frequency of the NIO band is 0.021 cph with a blueshift of about 4%
above the inertial frequency. The blueshifts are explained partially by the Doppler shift induced by the vorticity of mesoscale
eddies. During the after-typhoon period, a resonance-like process between NIO and DT is observed in the upper layer. As the
NIO frequency approaches the DT subharmonic frequency (0.5K1), the PD of the NIO band rises sharply accompanied by a sharp drop of the PD of the DT band. The PD ratio of the two bands
increases from 4.5 during the typhoon-wake period to 8 during the after-typhoon period, indicating the effect of the parametric
subharmonic instability (PSI) mechanism. 相似文献
Mast is defined as Grade A equipment which is essential for the safety and continued combat capability of the ship. Therefore, in order to evaluate shock resistance under shock environments, this research adopts response spectrum analysis method in conjunction with a shock design spectrum inducted by US Navy after performing full-scale trials in establishing a shock response spectrum analysis, to be coordinated by using finite element’s discrete and calculating procedure. The cantilever beam was used to take the explosion shock as an example to verify the effectiveness of the proposed numerical procedure. Analysis results demonstrate a sufficient correlation. Also described herein in detail is the shock response of a quadrupod-mast. Analysis results provide a valuable reference for mast design. 相似文献