黑潮水入侵南海的水文分析──Ⅱ.1994年8—9月期间的观测结果

利用1994年8－9月期间，由台湾海峡两岸的4艘海洋调查船在南海东北部海域所获之CTD和ADCP资料，并结合1992年3月间在同一海域获取的CTD资料及部分历史水文资料，对该区域的海水特性以及黑潮水入侵南海等问题进行了分析探讨。结果表明：调查期间，本海区水团分布与冬末、春初（1992年3月）航次基本相似，即南海和西北太平洋海域的海水结构有着各自相对独立的温、盐度特性。虽发现有黑潮水穿越巴上海峡进入南海，但其势力甚弱。因此，在夏末秋初，黑潮亦无直接的分支深入南海，即使在巴士海峡北端进入台湾海峡的黑潮水，其影响也是十分微弱的。由等密度面、地转流分析和实测ADCP资料显示，在调查海区的东南海域存在一支较强的N向流动。它沿菲律宾西海岸北上，绕过吕宋岛西北角流向东北，在巴上海峡呈现与黑潮水混合的迹象，其水体在冬季明显呈高温、低盐的特性；夏季则为相对低温、低盐。故在冬季的几幅卫星图像上也有较好的体现，很有可能长年存在。     

Mineralogical and geomicrobial examination of soil contamination by radioactive Cs due to 2011 Fukushima Daiichi Nuclear Power Plant accident

Soil contamination by radioactive Cs from Fukushima Daiichi Nuclear Power Plant accident was investigated. Absorption and desorption experiments of Cs were conducted for several phyllosillicates (kaolinite, sericite, montmorillonite, vermiculite, chrysotile and biotite), zeolite and solid organic matter (dead and green leaves). The results confirmed the characteristic sorption and desorption of Cs by these materials. The 2:1 type phyllosilicate, especially, vermiculite and montmorillonite absorbed Cs well. Heated vermiculite for agricultural use and weathered montmorillonite also adsorbed Cs. Leaves also absorbed Cs considerably but easily desorbed it. In summary, the relative capacity and strength of different materials for sorption of Cs followed the order: zeolite (clinoptilolite) > 2:1 type clay mineral > 1:1 type clay mineral > dead and green leaves. Culture experiments using bacteria of both naturally living on dead leaves in Iitate village, Fukushima Pref. and bacterial strains of Bacillus subtillis, Rhodococus erythropolis, Streptomyces aomiensis and Actinomycetospora chlora were carried out. Non-radioactive 1% Cs solution (CsCl) was added to the culture media. Two types of strong or considerable bacterial uptakes of Cs were found in bacterial cells. One is that Cs was contained mainly as globules inside bacteria and the other is that Cs was absorbed in the whole bacterial cells. The globules consisted mainly of Cs and P. Based on all these results, future diffusion and re-circulation behavior of Cs in the surface environment was discussed.     

Effects of steep topography on the flow and stratification near Palmyra Atoll

Two interdisciplinary cruises aimed at relating the ecology of marine fish populations to oceanographic conditions were fielded during the late summer and late winter seasons near Palmyra Atoll (5.9°N, 162.1°W) in the Line Islands. Ocean current and hydrographic measurements revealed interaction of the flow with the steep topography. During the first cruise (August/September 1990) satellite-tracked surface drifters and acoustic Doppler current profiler (ADCP) measurements showed a strong eastward setting North Equatorial Counter Current (NECC) with maximum speeds exceeding 1 m s^–1 at 80 m depth approximately. This current turned southeastward on closer approach to Palmyra. The drifter paths exhibited excursions with zonal wavelength of approximately 250 km, meridional amplitude of 25 km and period of approximately 5 days. During the second cruise (February/March 1992), the ADCP-derived speeds of the NECC were weaker (maxima approximately 33 cm s^–1) while the relative geostrophic flow component was of magnitude similar to 1990 and the signal of zonal geostrophic currents reached much deeper to approximately 650 m depth (150 m in 1990). Doming isopycnals beneath the surface mixed layer as well as thick (10–25 m) internal mixed layers were found near Palmyra during both cruises, with slightly different positions relative to the island. The discontinuous vertical temperature profiles may have been a result of strong boundary mixing due to breaking internal waves on Palmyras steep slopes. In the immediate vicinity of the island variations in flow speed, stratification and mixing in both the alongshore and cross-isobath directions were observed. Overall, the current speeds were reduced during February/March 1992, the peak time of the 1991–1993 warm event in the tropical Pacific. While parameters of turbulent two-dimensional wake theory are suggestive of formation and shedding of eddies in the lee of the island, no direct observations of circular motions were made in either expedition.Responsible Editor: Hans Burchard     

Annual and decadal variability in the western subtropical North Atlantic: signal characteristics and sampling methodologies

Upper ocean (above 750 m) temperature structure of the northwestern subtropical Atlantic, including the Gulf Stream and a recirculation gyre south of the Stream, is characterized using primarily bathythermograph (BT) data collected between 1950 and 2003. Geostrophic calculations, using mean temperature-salinity relationships to compute dynamic height, are used to estimate velocities and transports. The mean annual Gulf Stream transport at 72° W relative to 750 m, 36.1 Sv, is approximately equal to the sum of the transport of the Florida Current, 32.0 Sv, and a shallow recirculation gyre described by Wang and Koblinsky [Journal of Physical Oceanography 26 (1996) 2462-2479], 5.5 Sv. The annual cycle of geostrophic transport relative to 750 m at 72° W is in phase with both an earlier published annual cycle of transport relative to 2000 m derived from hydrographic observations and the annual cycle of Florida Current transport measured indirectly by a submarine cable (i.e., maximum transports are observed in the summer and minimum in the fall, early winter). However, simple Sverdrup dynamics are inadequate to explain these cycles as maximum Sverdrup transports extend from winter to summer, while observed transports are minimum (maximum) in fall/winter (summer). The annual cycles derived from the BT data of the size of the shallow southern recirculation gyre, Gulf Stream position and upper layer transport (relative to 300 m) are in phase (maximum size, northern position and transport in fall) and consistent with the WK results derived from altimetry. However, the shallower annual cycles are out of phase with the deeper signals (i.e., maximum for the former (latter) are observed in fall (summer)). Decadal signals after 1965 in Gulf Stream position, geostrophic transport relative to 450 m, and the size of a recirculation gyre south of the Stream are approximately in phase as observed for the annual signal. This gyre and the shallow WK gyre exhibit the same horizontal structure, however, the decadal signal propagates deeper into the water column (at least to 700 m). The eastern expansion and contraction of the gyre on decadal time-scales is correlated with propagating SST signals. The sampling implications of these findings are addressed.     

两种有机毒物在对虾养殖中的毒性效应研究

采用重复循环生物检测法,比较氯苯对氯硝基苯在中国对虾养殖中的毒性效应。获得毒物的剂量——反应率回归方程。氯苯96h—LC_(50)为1.72×10~(-6),对氯硝基苯为2.14×10~(-6)根据最小致死剂量、应用系数,建设养殖用水标准分别为氯苯0.01×10~(-6),对氯硝基苯0.004×10~(-6)。     

Alternative measures of dispersion applied to flow in a convoluted channel

Steady flow in a convoluted channel is studied via Particle Tracking Velocimetry. The channel is constructed from a sequence of closed parallel cylindrical tubes welded together in plane which are then sliced down the lateral mid-plane and the lower complex is laterally shifted relative to the upper complex. Flow is induced in the lateral direction normal to the axis of the tubes. The a-time, T_a, finite-size Lyapunov exponent, λ_a, and the real-space self- and distinct-part of the intermediate scattering functions, G_s and G_d, and the pair density function, G_p, are computed from the data. Particle trajectories, velocity maps and streamlines show the channel has two prominent recirculation zones and a main flow region. The first passage time probability density function of tagged particles past a plane transverse to the mean flow illustrates how particles are delayed by recirculation zones. The delay caused by fluid element folding is manifested in single particle statistics such as the first passage time and the slowing increase in horizontal evolution of G_s. G_p describes initial particle distribution and allows areas in the flow domain trapping particles to be identified and visualized. G_d shows the evolution of the average separation of pairs of particles and when examined in a recirculation zone, it evolves little because of fluid element rotation. λ_a gives information on what transpires at a fixed scale and provides an estimate of the rate at which particles initially separated by a distance x separate to a distance ax as opposed to G_d which allows one to view changes over time. At small separations, λ_1.3 approaches a constant and for intermediate separations it scales as x^−0.8.     

The Kuroshio Current System as a jet and twin “relative” recirculation gyres embedded in the Sverdrup circulation

By analyzing the results of a realistic ocean general circulation model (OGCM) and conducting a series of idealized OGCM experiments, the dynamics of the Kuroshio Current System is examined. In the realistic configuration, the Kuroshio Current System is successfully simulated when the horizontal resolution of OGCMs is increased from 1/2° to 1/10°. The difference between the two experiments shows a jet, the model’s Kuroshio Extension, and a pair of cyclonic and anticyclonic, “relative,” recirculation gyres (RRGs) on the northern and southern flanks of the jet. We call them recirculation gyres because they share some features with ordinary recirculation gyres in previous studies, and we add the adjective “relative” to emphasize that they may not be apparent in the total field. Similar zonal jet and RRGs are obtained also in the idealized model with a rectangular basin and a flat bottom with a horizontal resolution of 1/6°. The northern RRG is generated by the injection of high potential vorticity (PV) created in the viscous sublayer of the western boundary current, indicating the importance of a no-slip boundary condition. Since there is no streamline with such high PV in the Sverdrup interior, the eastward current in the northern RRG region has to lose its PV anomaly by viscosity before connecting to the interior. In the setup stage this injection of high PV is carried out by many eddies generated from the instability of the western boundary current. This high PV generates the northern RRG, which induces the separation of the western boundary current and the formation of the zonal jet. In the equilibrium state, the anomalous high PV values created in the viscous sublayer are carried eastward in the northern flank of the zonal jet. The southern RRG is due to the classical Rhines–Young mechanism, where low PV values are advected northward within the western boundary inertial sublayer, and closed, PV-conserving streamlines form to the south of the Kuroshio Extension, allowing slow homogenization of the low PV anomalies. The westward-flowing southern branch of this southern RRG stabilizes the inertial western boundary current and prevents its separation in the northern half of the Sverdrup subtropical gyre, where the western boundary current is unstable without the stabilizing effect of the southern RRG. Therefore, in the equilibrium state, the southern RRG should be located just to the north of the center of the Sverdrup subtropical gyre, which is defined as the latitude of the Sverdrup streamfunction maximum. The zonal jet (the Kuroshio Extension) and the northern RRG gyre are formed to the north of the southern RRG. This is our central result. This hypothesis is confirmed by a series of sensitivity experiments where the location of the center of the Sverdrup subtropical gyre is changed without changing the boundaries of the subtropical gyre. The locations of the zonal jets in the observed Kuroshio Current System and Gulf Stream are consistent as well. Sensitivities of the model Kuroshio Current System are also discussed with regard to the horizontal viscosity, strength of the wind stress, and coastline.     

The Effects of Canopy Leaf Area Index on Airflow Across Forest Edges: Large-eddy Simulation and Analytical Results

The structure of turbulent flows along a transition between tall-forested canopies and forest clearings continues to be an active research topic in canopy turbulence. The difficulties in describing the turbulent flow along these transitions stem from the fact that the vertical structure of the canopy and its leaf area distribution cannot be ignored or represented by an effective roughness length. Large-eddy simulation (LES) runs were performed to explore the effect of a homogeneous variation in the forest leaf area index (LAI) on the turbulent flow across forest edges. A nested grid numerical method was used to ensure the development of a deep boundary layer above the forest while maintaining a sufficiently high resolution in the region close to the ground. It was demonstrated that the LES here predicted first-order and second-order mean velocity statistics within the canopy that agree with reported Reynolds-Averaged Navier–Stokes (RANS) model results, field and laboratory experiments. In the simulations reported here, the LAI was varied between 2 and 8 spanning a broad range of observed LAI in terrestrial ecosystems. By increasing the forest LAI, the mean flow properties both within the forest and in the clearing near the forest edge were altered in two fundamental ways: near the forest edge and into the clearing, the flow statistical properties resembled the so-called back-facing step (BFS) flow with a mean recirculation zone near the edge. Another recirculation zone sets up downstream of the clearing as the flow enters the tall forest canopy. The genesis of this within-forest recirculation zone can be primarily described using the interplay between the mean pressure gradients (forcing the flow) and the drag force (opposing the flow). Using the LES results, a simplified analytical model was also proposed to explain the location of the recirculation zone inside the canopy and its dependence on the forest LAI. Furthermore, a simplified scaling argument that decomposes the mean velocity at the outflow edge into a superposition of ‘exit flow’ and BFS-like flow with their relative importance determined by LAI was explored.