High Frequency Current Fluctuations and Cross-shelf Flows around the Pycnocline near the Shelf Break in the East China Sea

Relation between internal waves with short time scale and density distribution near the shelf break in the East China Sea is studied utilizing moored current meters, thermometers and conductivity-temperature-depth (CTD) casts. A well developed pycnocline was frequently observed around 150–200 m depth near the shelf break accompanied with the development of internal waves with short time scale. During the cruise in May 1998, the intensified internal wave motion with short time scale and the distinct offshore flow were observed just below the lower pycnocline, which shoaled and extended above the shelf area. It is suggested that vertical mixing generated by amplified internal waves would produce cross-shelf ageostophic density current around the pycnocline. During the cruise in May 1999, on the other hand, the lower pycnocline was located offshore below the shelf break, and the internal wave motion was amplified just above the lower pycnocline. In this case, the offshore flow should be generated above the lower pycnocline, but vertical profiles of current velocity were not obtained because acoustic Doppler current profiler (ADCP) data were not available around the lower pycnocline.     

Exchange flow of oil and sea-water in a ruptured submarine pipeline

The rupture of a submarine oil pipeline starts various mechanisms leading to an oil spill. Among these mechanisms the leakage of oil driven by the difference in specific gravities of oil and sea-water is difficult to estimate. A simple mathematical model has been developed and laboratory experiments have been carried out to obtain an insight into the density-driven exchange flow and to determine the leak rate. The mathematical model is predictive and takes account of the effects of friction, inclination of the pipeline, and inertia of the fluid. The experiments were done in a horizontal model pipeline. Theoretical and experimental results are in satisfactory agreement.     

Consequences of winter upwelling events on biogeochemical and phytoplankton patterns in a western Galician ria (NW Iberian peninsula)

The consequences of two upwelling events in mid- (MW) and late (LW) winter on biogeochemical and phytoplankton patterns were studied in the Pontevedra Ria and compared with the patterns measured under typical winter conditions and under a summer upwelling event. Thermohaline patterns measured during the mid-winter upwelling event (MW-up) revealed the intrusion of saltier seawater (35.9) into the ria associated with the Iberian Poleward Current (IPC). During the late-winter upwelling event (LW-up), the seawater which had welled up into the ria showed characteristics of the Eastern North Atlantic Central Water mass (ENACW). In both cases the measured water residence time (4 days during MW-up and 10 days during LW-up) was related to both meteorological and fluvial forcing. This residence time contrasts with that of summer upwelling (7 days) and with that estimated under unfavorable upwelling atmospheric conditions (2–4 weeks). During MW-up, the ria became poor in nutrients due to continental freshwater dilution, associated with the shorter residence time of the water, and the intrusion of IPC, which is a water body poor in nutrient salts: 2.9 μM of nitrate, 0.1 μM of phosphate and 1.5 μM of silicate. During this event, the ria exported 3.4 mol_DIN s⁻¹, compared with 6.9 mol_DIN s⁻¹ in non-upwelling conditions. Phytoplankton showed a uniform distribution throughout the ria, as during unfavorable upwelling conditions, and was characterized by the dominance of diatoms, mainly Nitzschia longissima and Skeletonema costatum. During LW-up, a nutrient depletion in the photic layer also occurred, but as a result of a phytoplankton spring bloom developing at this time. The ria was a nutrient trap where 4.1 mol_DIN s⁻¹ were processed by photosynthesis. This budget is three times higher than the one under non-upwelling conditions. In contrast with the MW-up, which had no effect on primary production, during LW-up the ria became more productive, although not as productive as during a summer upwelling event (9.9 mol_DIN s⁻¹). The taxonomic composition of the phytoplankton community did not change noticeably during LW-up and the summer upwelling, with the same species present and changing only in relative proportions. Diatoms were always the dominant microphytoplankton community, with Pseudonitzschia pungens, Thalassionema nitzschioides and several species of Chaetoceros as characteristic taxons.     

九州西侧海域129°E断面的流速和温盐结构特征

根据中、日合作黑潮调查研究期间（1987－1993年）在九州西侧海域获得的水文资料，计算了129°E断面的地转流速和流量。着重提出129°E断面北侧存在一支较稳定的西向流；分析这支西向流的去向，指出它是向对马暖流输送黑潮水的重要途径；给出了这支西向流及黑潮通过该断面的流速、流轴、流幅及流量的变化特征。     

台风"杜鹃"影响期间福建大风天气的特点及成因

台风“杜鹃”影响期间，福建大风天气出现的比较早，而且范围比较大．本文通过对天气尺度的环境场、具有代表性的单站资料的对比分析，寻求大风出现的原因．还深入利用MM5模式对台风的气压场、风场、流场等进行数值模拟，分析结果表明台湾地形倒槽的形成对此次大风天气出现有着重要的作用，此外从流场分型的角度进一步分析台湾地形倒槽的形成原因．     

The permeability of faults within siliciclastic petroleum reservoirs of the North Sea and Norwegian Continental Shelf

Faulting in Middle Jurassic reservoirs occurred at shallow depth during regional extension. Clean sandstones (<15% clay) deformed without significant grain fracturing and permeability reduction. Faults in impure sandstones (15–40% clay) experienced significant syn-deformation compaction and permeability reduction. Enhanced compaction during deeper burial reduced their permeabilities further from an average of 0.05 mD at <2.5 km to 0.001 mD at >4 km. Clay-rich sediments (>40% clay) deformed to produce clay smears with very low permeabilities (<0.001 mD). Faulting in the Rotliegendes occurred at greater depth during both basin extension and inversion. Extensional faulting produced cataclasites with permeability reductions of <10–>10⁶; their permeabilities range from 0.2 to 0.0001 mD and are inversely related to their maximum burial depth. Faults formed or reactivated during inversion experienced permeability increase. These results can be extrapolated to other hydrocarbon reservoirs if differences in stress and temperature history are taken into account.The permeability of most (>80%) faults is not sufficiently low, compared to their wallrock, to retard single-phase fluid flow on a km-scale. Nevertheless, most faults could retard the flow of a non-wetting phase if present at low saturations. It may be necessary to incorporate the two-phase fluid flow properties of fault rocks into reservoir simulators using upscaling or pseudoisation techniques. Fault property data should be calibrated against production data before it can be used confidently.     

Estimation of Land Subsidence Based on Groundwater Flow Model

This article presents an approach for estimating land subsidence due to withdrawal of groundwater. The proposed method calculates the groundwater seepage in 3-D-condition and calculates the land subsidence one-dimensionally. The governing equation on groundwater seepage is based on the three-dimensional mass conservation law and the principle of effective stress. The land subsidence calculation method is derived based on the following assumptions: (1) displacements occur only in the vertical direction, and (2) in vertical direction the total stresses do not change. The governing equation is solved by numerical method, i.e., finite element method (FEM) in spatial discretization and finite difference method (FDM) in time series discretization. In FEM Galerkin method is adopted and in FDM, lumped matrix method is employed. The proposed method is calibrated via analyzing 1-D consolidation problem and the results are compared with those from Terzaghi's one-dimensional consolidation theory and oedometer test. The proposed method is employed to analyze the consolidation of a soft layer due to withdrawal of groundwater from an aquifer under it. Moreover, this method is also applied to a field case of land subsidence due to groundwater pumping in a gas production field in Japan. The analytical results are compared with the field observed data. The results show that this approach simulates the field case well.