Читать книгу Life in the Open Ocean - Joseph J. Torres - Страница 20

Since the year 2000, when the Southern Ocean gained official status from the International Hydrographic Organization, the Earth has had five officially recognized major oceans: The Arctic Ocean, The Atlantic Ocean, The Indian Ocean, The Pacific Ocean, and the Southern Ocean. Vital statistics for the five oceans are given in Table 1.1.

The largest and deepest ocean basin is the Pacific, whose sheer vastness really requires a globe to appreciate. The Atlantic and Indian Oceans, each somewhat less than half the size of the Pacific, follow in size. The two polar oceans, the Southern and Arctic, are the smallest. The Southern Ocean, extending from a latitude of 60° south to the Antarctic Continent, comprises the southernmost portions of the Pacific, Atlantic, and Indian Oceans, which is why it was only recently officially recognized as an Ocean in and of itself. It is worth mentioning here that the Arctic and Antarctic are fundamentally quite different. Both are quite cold, of course, and sea ice plays a large role in the ecology of each. However, the Antarctic is a land mass surrounded by ocean, whereas the Arctic is an ocean surrounded by land (Figure 1.4a and b).

The continents define the boundaries of the ocean basins. Within each of the basins, a characteristic circulation transports large quantities of water with all the elements that such bodies of water contain, including plants, animals, gases, salt, and heat. Energy for the water movement is provided by the radiation of the Sun and the rotation of the Earth. The Sun’s heat drives circulation within the atmosphere, producing the Earth’s prevailing wind patterns that in turn drive surface ocean circulation. Deep ocean circulation, which has a more profound vertical component, is driven by changes in seawater density. Cooler or more saline water will sink below a warmer or less saline body of water. Since the density of seawater is determined by its temperature and salinity, solar radiation ultimately is responsible for deep‐ocean circulation as well. Latitudinal gradients in temperature cause heat loss or gain across the ocean–atmosphere interface. Changes in salinity result from evaporation, precipitation, and in polar regions from the freezing and melting of sea ice. An understanding of the influence of the Earth’s rotation on ocean circulation is less intuitive; that influence is described in the next section.

Figure 1.4 The Polar Oceans. (a) Arctic Ocean basin. (b) Southern Ocean surrounding Antarctica.

Source: NASA.