Three moorings equipped with 10 current meters and 7 CTDs were deployed in the Bashi Channel, the main deep connection between the northwestern Pacific Ocean and the South China Sea, from August 2010 to April 2011 to ...
详细信息
Three moorings equipped with 10 current meters and 7 CTDs were deployed in the Bashi Channel, the main deep connection between the northwestern Pacific Ocean and the South China Sea, from August 2010 to April 2011 to investigate the deepwater overflow of the North Pacific Deep Water through it. Results from these observations provide, for the first time, valuable information on the spatial structure of the deep current and allow us to estimate the overflow transport with greater accuracy. The observed current is coherent both vertically and horizontally but exhibits a much stronger velocity in the central area compared to near the edges of the channel. The core of the overflow is found near 2600 m, with mean velocity, potential temperature, and salinity of 22.5 cm s(-1), 1.79 degrees C, and 34.64 psu, respectively. The current is approximately geostrophic, with isopycnals sloping upward to the right-hand side of the flow. The local Froude number is found much less than 1, implying that the deep flow in the Bashi Channel could not be hydraulically controlled. The observations yield an 8-month mean transport of 0.78 Sv with an rms error of 0.18 Sv. The transport time series exhibits significant intraseasonal variabilities, including variability on time scale close to the resonance period of the deep channel in the Luzon Strait (similar to 30 days). Higher transports are connected with a higher velocity and a thicker overflow layer, allowing colder and saltier (thus denser) North Pacific Deep Water to flow into the South China Sea. (C) 2016 Elsevier Ltd. All rights reserved.
On the basis of the latest version of a U.S. Navy generalized digital environment model （GDEM-V3.0） and World Ocean Atlas （WOA13）, the hydraulic theory is revisited and applied to the Luzon Strait, providing a fre...
详细信息
On the basis of the latest version of a U.S. Navy generalized digital environment model （GDEM-V3.0） and World Ocean Atlas （WOA13）, the hydraulic theory is revisited and applied to the Luzon Strait, providing a fresh look at the deepwater overflow there. The result reveals that： （1） the persistent density difference between two sides of the Luzon Strait sustains an all year round deepwater overflow from the western Pacific to the South China Sea （SCS）; （2） the seasonal variability of the deepwater overflow is influenced not only by changes in the density difference between two sides of the Luzon Strait, but also by changes in its upstream layer thickness; （3） the deepwater overflow in the Luzon Strait shows a weak semiannual variability; （4） the seasonal mean circulation pattern in the SCS deep basin does not synchronously respond to the seasonality of the deepwater overflow in the Luzon Strait. Moreover, the deepwater overflow reaches its seasonal maximum in December （based on GDEM-V3.0） or in fall （October-December, based on the WOA13）, accompanied by the lowest temperature of the year on the Pacific side of the Luzon Strait. The seasonal variability of the deepwater overflow is consistent with the existing longest （3.5 a） continuous observation along the major deepwater passage of the Luzon Strait.
[1] This study examines water property distributions in the deep South China Sea and [adjoining Pacific Ocean using all available hydrographic data. Our analysis reveals that below about 1500 m there is a persistent b...
详细信息
[1] This study examines water property distributions in the deep South China Sea and [adjoining Pacific Ocean using all available hydrographic data. Our analysis reveals that below about 1500 m there is a persistent baroclinic pressure gradient driving flow from the Pacific into the South China Sea through Luzon Strait. Applying hydraulic theory with assumptions of zero potential vorticity and flat bottom to the Luzon Strait yields a transport estimate of 2.5 Sv ( 1 Sv = 10(6) m(3) s(-1)). Some implications of this result include: ( 1) a residence time of less than 30 years in the deep South China Sea, ( 2) a mean diapycnal diffusivity as large as 10(-3) m(2) s(-1), and (3) an abyssal upwelling rate of about 3 x 10(-6) m s(-1). These quantities are consistent with residence times based on oxygen consumption rates. The fact that all of the inflowing water must warm up before leaving the basin implies that this marginal sea contributes to the water mass transformations that drive the meridional overturning circulation in the North Pacific. Density distributions within the South China Sea basin suggest a cyclonic deep boundary current system, as might be expected for an overflow-driven abyssal circulation.
The previous studies show that the SCS deep circulation is featured by a basin-scale cyclonic gyre. On the basis of the Hybrid Coordinate Ocean Model (HYCOM) and the Simple Ocean Data Assimilation (SODA), this study a...
详细信息
The previous studies show that the SCS deep circulation is featured by a basin-scale cyclonic gyre. On the basis of the Hybrid Coordinate Ocean Model (HYCOM) and the Simple Ocean Data Assimilation (SODA), this study attempts to examine its seasonal variability and to investigate the driving mechanism. During summer season, the basin-scale cyclonic gyre is dominant and strong, corresponding to higher value of the deepwater overflow transport. During winter season, the basin-scale cyclonic gyre can hardly be identified, corresponding to lower value of the deepwater overflow transport. The control run and the SODA show the similar results. Two sensitivity experiments are designed to investigate what could be possible responsible for the seasonal variation in the SCS deep circulation. The results reveal that the deepwater overflow through the Luzon Strait contributes to the seasonal variability of the SCS deep circulation, and the seasonal variation of the surface forcings have less influence on that. The mechanism is related to the potential vorticity flux by the deepwater overflow.
暂无评论