Kuroshio extension variability explored through assimilation of TOPEX/POSEIDON altimeter data into a quasi-geostrophic model

Mesoscale features in the eastward extension of the Kuroshio were investigated using assimilation of TOPEX/POSEIDON (T/P) data into a three-layer quasi-geostrophic model. The T/P data exhibited an elongated state of the southern recirculation gyre in 1993–95 and 1997, between whose two periods the gyre had a contracted state in 1995–96. A few stationary eddies were located in the southern gyre during the contracted state. The baroclinic instability, which was indicated by the phase shift from the uppermost-to the lowest-layer anomalies toward the downstream side, was evident near the Kuroshio Extension (KE) path. Since the instability never appeared in the artificial model without bottom topography, the topographic barrier for the eastward flow in the lowest layer was a necessary condition for the instability. The instability synchronized with the transition in the western region of the KE axis from the elongated to the contracted states. This evolution was interpreted as if the baroclinic instability played some part in the KE states and was a trigger for the transition from the elongated to the contracted states.     

Further evidence for non-reemergence of winter SST anomalies in the North Pacific eastern subtropical mode water area

Following our previous study (Sugimoto and Hanawa, 2005b), we further investigate the reason why reemergence of winter sea surface temperature anomalies does not occur in the North Pacific eastern subtropical mode water (NPESTMW) area, despite its occurrence in the North Pacific subtropical mode water and North Pacific central mode water areas. We use vertical temperature and salinity profiles of the World Ocean Circulation Experiment Hydrographic Program and Argo floats with high vertical and temporal resolution, together with heat flux data through the sea surface. We point out first that one of the causes for non-occurrence of reemergence is that the thickness of NPESTMW is very thin. In addition to this basic cause, two major reasons are found: a vigorous mixing in the lower portion of NPESTMW and less heat input from the atmosphere in the warming season. Since, in the lower portion of NPESTMW and deeper, the stratification is favorable for salt-finger type convection to occur compared with the other mode water areas, vigorous mixing takes place. This is confirmed by both a large Turner Angle there and the existence of staircase structures in vertical temperature and salinity profiles. From the viewpoint of heat input, the NPESTMW area gradually gains heat in the warming season compared with other mode water areas. As a result, NPESTMW cannot be capped so quickly by the shallow summer mixed layer, and water properties of NPESTMW are to be gradually modified, even in the upper portion.     

Geomorphological evidence for upslope canyon-forming processes on the northern KwaZulu-Natal shelf,SW Indian Ocean,South Africa

A geomorphological and statistical analysis of slope canyons from the northern KwaZulu-Natal continental margin is documented and compared with submarine canyons from the Atlantic margin of the USA. The northern KwaZulu-Natal margin is characterized by increasing upslope relief, concave slope-gradient profiles and features related to upslope growth of the canyon forms. Discounting slope-gradient profile, this morphology is strikingly similar to canyon systems of the New Jersey slope. Several phases of canyon incision indicate that downslope erosion is also an important factor in the evolution of the northern KwaZulu-Natal canyon systems. Despite the strong similarities between the northern KwaZulu-Natal and New Jersey slope-canyon systems, key differences are evident: (1) the concavity of the northern KwaZulu-Natal slope, contrasting with the ∼linear New Jersey slope; (2) the relative isolation of the northern KwaZulu-Natal canyons, rather than the dense clustering of the New Jersey canyons; and (3) the absence of strongly shelf-breaching canyons along the northern KwaZulu-Natal margin. In comparison with the New Jersey margin, we surmise a more youthful stage of canyon evolution, a result of either the canyons themselves being younger or the formative processes being less active. Less complicated patterns of erosion resulting from reduced sediment availability have developed in northern KwaZulu-Natal. The reduction in slope concavity on the New Jersey margin may be the result of grading of the upper slope by intensive headward erosion, a process more subdued—or less evident—on the KwaZulu-Natal margin.     

珠江口水域微表层中的痕量金属

采用自制滚筒式自动采样器采样，研究了珠江口水域微表层中Ｆｅ，Ｍｎ，Ｃｕ，Ｐｂ，Ｚｎ，Ｃｄ的含量、分布变化及富集状况。并通过颗粒痕量金属／颗粒Ｆｅ比值计算，探讨了痕量金属的来源。结果表明：Ｃｕ，Ｐｂ，Ｚｎ，Ｃｄ在微表层的平均富集系数分别为２．３，１．４，３．０和１．９。颗粒态Ｆｅ，Ｍｎ的平均富集系数为１．１和０．９。各种金属有明显的季节和空间变化，有各种不同的来源。     

东海浮游动物量的分布特征

浮游动物生物量属于海洋次级生产力的范畴,在海洋食物链中是极其重要的环节。对其生产力大小的探讨,可以评价海洋渔业资源的潜力和开发远景,由此可以看出浮游动物生物量,是渔场调查中必要的基础资料。东海是我国海洋渔业十分重要的开发区域。这里有鲐鲹等中上层鱼类;有带鱼、大黄鱼、小黄鱼等底层鱼类。这些鱼类都有比较广泛的食性[2,3],在它们发育早期或者直到成年阶段,必须有依赖浮游动物为食的时期。因此浮游动物的数量分布与经济鱼类的幼鱼或成鱼的数量分布都有密切的关系。本文根据为1971年7月至1974年6月,共历时4年,在北纬27°—32°、东经127°以西海区所进行的35个航次,1577个测站的调查资料。采集系用大型浮游动物网(口径80厘米,网目每厘米15个)由底到表垂直拖网。     

美国红鱼试养的初步研究

笔者自行培育的美国红鱼苗体长25～30mm．1996年6月上、中旬到当年12月中旬．其个体的平均重量分别达到了750g和800g，生长速度优于我国其他养殖鱼种。     

A finite element model of interaction between viscous free surface waves and submerged cylinders

This paper describes the simulation of the flow of a viscous incompressible Newtonian liquid with a free surface. The Navier–Stokes equations are formulated using a streamline upwind Petrov–Galerkin scheme, and solved on a Q-tree-based finite element mesh that adapts to the moving free surface of the liquid. Special attention is given to fitting the mesh correctly to the free surface and solid wall boundaries. Fully non-linear free surface boundary conditions are implemented. Test cases include sloshing free surface motions in a rectangular tank and progressive waves over submerged cylinders.     

Effects of scattering and resonance on energy dissipation of an internal tide in a narrow shelf

The effects of scattering and resonance on the energy dissipation of an internal tide were investigated using a two-dimensional model which is a reassembled version of the theoretical generation model devised by Rattray et al. (1969) for internal tide. The basic character of the scattering process at the step bottom was first investigated with a wide shelf model. When the internal wave incited from a deep region (Region II) into the shallow shelf region (Region I), a passing wave into the shallow region, a reflected wave into the deep region, and a beam-like wave, i.e. a scattered wave (SW), emanated at the step bottom. The SW, which consists of the superposition of numerous internal modes, propagated upward/downward into both regions. The general properties of the SW were well expressed around the shelf edge, even in the present model with viscosity effect. The amplitude of the SW decreased dramatically when the depth of the velocity maximum of the incident internal wave in Region II corresponded with the depth of the shelf edge. In the narrow shelf model, where the decay distance of the internal wave in Region I is longer than the shelf width, the incident internal wave reflected at the coast to form a standing wave. When the internal wave in Region I is enhanced by the resonance, the energy of the SW in Region II is also intensified. Furthermore, the energy of the modes in Region II predominated when the velocity maximum is identical to that of the dominant mode in Region I. These results suggest that the spatial scale of shelf region is a very important factor governing the energy dissipation of the internal tide through reflection and scattering in a narrow shelf.     

茶皂素对几种鱼类和对虾的毒性研究

本研究以茶皂素类作为“清池剂”,试图解决对虾养殖的基础和应用技术问题。试验结果表明:对虾对茶皂素和油茶皂素有较高的耐受力;茶皂素与油茶皂素均具鱼毒活性,油茶皂素则较强。鱼种不同,中毒反应也略有差异;两种茶皂素的鱼毒速度快,在致死浓度时16h内出现中毒死亡,毒性降解也快,浓度为5×10~(-6)时40h后不再引起鱼类中毒。     

海洋细菌抑菌活性菌株的筛选

从不同海区的海洋底质，生物样，水样中分离到480株海洋细菌，其中包括150株芽孢细菌和108株粪大肠杆菌，利用纸片法对其抑菌活性进行检测，结果表明：117株海洋细菌具有抑菌活性，占总分离菌株的24.4%；一般细菌，芽孢细菌，粪大肠杆菌的抑菌活性菌株分别占各供测菌株的17.1%,27.3%,35.2%；抑菌活性菌株的比例与样品来源密切相关，且各类海洋细菌的抗菌谱有很大的不同。