China
Africa
Explore chapters and articles related to this topic
A brief introduction to the marine environment
Published in Mark Zacharias, Jeff Ardron, Marine Policy, 2019
In the tropical areas of the oceans, both a north equatorial current and a south equatorial current can be recognized flowing from east to west. In the Atlantic and Pacific Oceans, an equatorial countercurrent is found between these two, running from west to east. The Pacific equatorial countercurrent is 8,000nmi in length and about 250nmi in width. The Atlantic equatorial countercurrent is more variable; it becomes stronger in summer, extending its influence westward towards South America.
Oceanographic Factors
Published in Ronald C. Chaney, Marine Geology and Geotechnology of the South China Sea and Taiwan Strait, 2020
Between the North and South Equatorial Currents flows a narrow, eastward-flowing current called the Equatorial Counter-current. Other eastward flowing currents move along the equator in the Pacific, Atlantic, and Indian (seasonally) Oceans in addition to the equatorial countercurrents. These are subsurface currents, generically referred to as equatorial undercurrents. An example is the Pacific equatorial undercurrent, also known as the Cromwell Current.
Eutrophication Status in the Regional Seas
Published in Michael Karydis, Dimitra Kitsiou, Marine Eutrophication A Global Perspective, 2019
Michael Karydis, Dimitra Kitsiou
The region of West and Central African Seas known as WACAF is made of 22 states, most of them coastal (Figure 4.15). Guinea, Sierra Leone, Liberia, Cote d’Ivoire, Ghana, Togo, Benin, Nigeria, Cameroon and Gabon are the most significant regarding population, economic activities and impact on the marine environment (UNEP/GPA, 2005). There are four narrow basins of sedimentary origin with a strong influence on the pattern of river drainage. The main river systems in the area are four, spaced out from Senegal to Congo (UNEP, 1999). The most important river is the Niger River that drains an area of about 1,000,000 km2. The Volta River is draining an area of about 390,000 km2. The Congo River is the second river regarding the catchment area in the world; the Comoe River in the Cote d’Ivoire is also considered as a large river in the area. Dams have been along these rivers for irrigation, energy production and flood control purposes. Various fresh water management policies in the region imply downstream impacts including the acceleration of coastal erosion processes and coastal hydrology. On the contrary, in the offshore areas of the Gulf of Guinea, there are five distinct currents that are relatively persistent. These are important from the point of view of transportation of substances, temperature stability and the biological regime. Briefly, these five currents are: (a) the Benguela current flowing along the coastal areas of Namibia and Angola (South West African coastal zone) (b) the Guinea current that carries warm waters along the coast of Guinea near the Equator, as it moves eastwards and southwards (c) the Equatorial Countercurrent which is the continuation of the Guinea current (d) the South Equatorial current that flows between 10°S and the Equator, some distance from the coast and (e) the Canary Current in the Northern Part that feeds the Guinea Currents as well as the North Equatorial Current. The Canary Current also drives an almost permanent upwelling mainly along the coasts of Gambia, Mauritania and Namibia. These cool, nutrient rich upwellings have profound effects on the productivity of the nearshore marine environment. The combination of high precipitation and significant riverine, freshwater outflow keeps the relatively warm coastal waters above 24°C and salinity values below 35 psu.
On the radius of spatial analyticity for Ostrovsky equation with positive dispersion
Published in Applicable Analysis, 2022
We consider the radius of spatial analyticity for the Ostrovsky equation with positive dispersion where u represents the free surface of a liquid and the positive parameter γ measures the effect of rotation. This Equation (1) was proposed by Ostrovsky [1] as a model for weakly nonlinear long waves in a rotating liquid, by taking into account of the Coriolis force. The Ostrovsky equation describes the propagation of surface and internal waves in the ocean in a rotating frame of reference. These unidirectional propagating waves in the ocean under the presentation of rotation, for example equatorial ocean current, have impacts on fisheries and climate. Controlled by the trade wind, the ocean current near the equator forms two westward-flowing currents, North Equatorial Current (NEC) and South Equatorial Current (SEC); within the doldrums, the eastward Equatorial Countercurrent passes between the NEC and SEC; the Equatorial Undercurrent in the thermocline keeps constant eastward flowing against the NEC and SEC. Research on such waves has important physical significance [2,3]. In Equation (1), β determines the type of dispersion, more precisely, (negative dispersion) for surface and internal waves in the ocean or surface waves in a shallow channel with an uneven bottom, and (positive dispersion) for capillary waves on the surface of a liquid or for oblique magneto-acoustic waves in plasma [4–9]. The Cauchy problem of the Ostrovsky Equation (1) has also been examined [10–17]. The results in [13,15,18] showed that is the critical regularity index for Equation (1) in Sobolev spaces. Recently, Yan et al. [19] proved that the Cauchy problem for the Ostrovsky equation with positive dispersion is locally well posed in .