Currents and Tides

The surface currents move at speeds of roughly two to four miles per hour (3 to 6 km/h). Their motions are affected by such factors as the prevailing surface winds, the density of the water, gravity, the rotation of the earth on its axis, and the shape of the ocean basin.

General circulation of the currents is clockwise in the North Pacific, counterclockwise in the South Pacific. It is somewhat like the rotations of two giant disks turning in opposite directions. As a result, warm equatorial water is constantly being carried poleward along the Asian and Australian coasts, while cold water is flowing toward the equator along the coasts of North and South America. Thus, the currents have distinct climatic effects on nearby lands. In some areas, such as the coast of Chile and Peru, they are cooling effects; in others, such as southern Japan, they are tempering and warming. In regions where warm and cold currents meet, notably northern Japan to southern Alaska, dense fogs frequently occur.

The chief currents of the North Pacific, beginning at the equator, are the North Equatorial Current, Kuroshio (Japan Current), North Pacific Current, or Drift, and California Current. Entering this circulation from the Arctic is the cold Oyashio (Okhotsk, or Kamchatka, Current). The Alaska Current starts off the coast of Oregon and flows northward along the coast of North America as far as Kodiak Island, bringing warmth to the coastal areas in winter. In the South Pacific are the South Equatorial Current, East Australian Current, West Wind Drift, and Peru (Humboldt) Current. Separating the two systems in the vicinity of the equator is the Equatorial Countercurrent, which flows eastward from Indonesia and the Philippines to the South American coast. map titled Major Surface Currents.)

There are also deep, underwater currents, but little is known of them. They tend to form separate layers flowing in different directions, each layer being denser than the layer above. For example, Antarctic water is known to subside suddenly beneath warmer water at a line called the Antarctic Convergence. From here it flows northward far below the surface of the ocean.

In general, the Pacific has low tides. In certain inlets, however, the water rises to significant heights. The tidal bore of Cook Inlet in Alaska ranks second only to that of the Atlantic's Bay of Fundy. Significant bores also occur in other Alaskan inlets and in southern Chile, Siberia, and Korea's west coast.