Frontal upwelling is an important phenomenon in summer in the Yellow Sea (YS) and plays an essential role in the distribution of nutrients and biological species. In this paper, a three-dimensional hydrodynamic model is applied to investigate the characteristics and influencing factors of frontal upwelling in the YS. The results show that the strength and distribution of frontal upwelling are largely dependent on the topography and bottom temperature fronts. The frontal upwelling in the YS is stronger and narrower near the eastern coast than near the western coast due to the steeper shelf slope. Moreover, external forcings, such as the meridional wind speed and air temperature in summer and the air temperature in the preceding winter and spring, have certain influences on the strength of frontal upwelling. An increase in air temperature in the previous winter and spring weakens the frontal upwelling in summer; in contrast, an increase in air temperature in summer strengthens the frontal upwelling. When the southerly wind in summer increases, the upwelling intensifies in the western YS and weakens in the eastern YS. The air temperature influences the strength of upwelling by changing the baroclinicity in the frontal region. Furthermore, the meridional wind speed in summer affects frontal upwelling via Ekman pumping. 相似文献
The mesopelagic communities are important for food web and carbon pump in ocean, but the large-scale studies of them are still limited until now because of the difficulties on sampling and analyzing of mesopelagic organisms. Mesopelagic organisms, especially micronekton, can form acoustic deep scattering layers (DSLs) and DSLs are widely observed. To explore the spatial patterns of DSLs and their possible influencing factors, the DSLs during daytime (10:00–14:00) were investigated in the subtropical northwestern Pacific Ocean (13°–23.5°N, 153°–163°E) using a shipboard acoustic Doppler current profiler at 38 kHz. The study area was divided into three parts using k-means cluster analysis: the northern part (NP, 22°–24°N), the central part (CP, 17°–22°N), and the southern part (SP, 12°–17°N). The characteristics of DSLs varied widely with latitudinal gradient. Deepest core DSLs (523.5 m±17.4 m), largest nautical area scattering coefficient (NASC) (130.8 m2/n mile2±41.0 m2/n mile2), and most concentrated DSLs (mesopelagic organisms gathering level, 6.7%±0.7%) were observed in NP. The proportion of migration was also stronger in NP (39.7%) than those in other parts (18.6% in CP and 21.5% in SP) for mesopelagic organisms. The latitudinal variation of DSLs was probably caused by changes in oxygen concentration and light intensity of mesopelagic zones. A positive relationship between NASC and primary productivity was identified. A four-months lag was seemed to exist. This study provides the first basin-scale baselines information of mesopelagic communities in the northwest Pacific with acoustic approach. Further researches are suggested to gain understandings of seasonal and annual variations of DSLs in the region. 相似文献
This research investigated eight stations in Clarion-Clipperton Fracture Zone(CCFZ) in the eastern tropical Pacific in 2017 to study the spatial distribution characteristics of nutrients and chlorophyll a(Chl a) concentration,and compared nutrient concentrations and molar ratios with those of other investigations 20 years ago in the same area. The study found that dissolved inorganic nutrient(N, P and Si) concentrations were lowest in the upper layer, and increased from surface to some depths, t... 相似文献
During the self-weight penetration process of the suction foundation on the dense sand seabed, due to the shallow penetration depth, the excess seepage seawater from the outside to the inside of the foundation may cause the negative pressure penetration process failure. Increasing the self-weight penetration depth has become an important problem for the safe construction of the suction foundation. The new suction anchor foundation has been proposed, and the self-weight penetration characteristics of the traditional suction foundation and the new suction anchor foundation are studied and compared through laboratory experiments and analysis. For the above two foundation types, by considering five foundation diameters and two bottom shapes, 20 models are tested with the same penetration energy. The effects of different foundation diameters on the penetration depth, the soil plug characteristics, and the surrounding sand layer are studied. The results show that the penetration depth of the new suction foundation is smaller than that of the traditional suction foundation. With the same penetration energy, the penetration depth of the suction foundation becomes shallower as the diameter increases. The smaller the diameter of the suction foundation, the more likely it is to be fully plugged, and the smaller the height of the soil plug will be. In the stage of self-weight penetration, the impact cavity appears around the foundation, which may affect the stability of the suction foundation.
Storm surges are cataclysmic natural disasters that occur along the coasts and are usually accompanied by large waves. The effects of coupled storm surges and waves can pose a significant threat to coastal security. Previous laboratory studies on the effects of storm surges and waves on coastal structures have typically utilized steady water levels and constant wave elements. An indoor simulation of the coupled processes of tides and waves is developed by adding a tide generation system to an existing laboratory wave basin to model continuous dynamic tide levels so that tide generation and wave-making occur synchronously in the pool. Specific experimental methods are given, which are applied to further study waves overtopping on artificial sea dikes and coastal flooding evolution under the coupled actions of tides and waves. The results of the overtopping discharge obtained by the test with a dynamic water level are compared with those obtained from steady water level tests and the existing empirical formula. In addition, the impacts of ecological coastal shelterbelts and structures on coastal flood processes and distributions are also investigated. The proposed simulation methods provide a new approach for studying the effects of storm surges and waves on coastal areas. The study also aims to provide a reference for coastal protective engineering.
Urban land-use change is the result of coupling interaction between planning and environment systems. The aim of our study was to construct an effective model to show how the urban land-use changes under the planning–environment interaction system with multi-hierarchy and major function oriented zoning. Combining the Cellular automata (CA) model with logistic regression model, the proposed multi-hierarchal vector CA model (MH-VCA3) was constructed by mining multi-hierarchal land-use transition rules under the planning–environment interaction system. Taking Jiangyin City (China) as an example, we compared the simulated result of the proposed model to those of the well-accepted Logistic CA and traditional multi-level CA models to demonstrate the effectiveness of the consideration of top-down decomposition constraint and bottom-up updating. Furthermore, by simulating the land-use changes under different population regionalization scenarios, we found that in order to form the spatial pattern of “agglomeration in the north and ecology in the south,” the planned population growth at the global hierarchal level should be allocated to the district units according to the law of Central district > Chengxi district > Chengdong district > Chengnan district > Chengdongnan district. The proposed model is expected to provide scientific support for the formulation of urban planning schemes in the future. 相似文献
