Chapter 6. Oceans, Rivers, Lakes and Ice

Oceans. There are five named oceans: Pacific (largest and deepest), Atlantic, Indian, Southern and Arctic. Together they form one connected world ocean [4].

Ocean currents redistribute heat. Warm currents such as the Gulf Stream warm adjacent coasts; cold currents such as the Humboldt (Peru) Current cool them and often support productive fisheries.

Rivers. A river basin (watershed) collects water from all land that drains to it. The Nile and the Amazon are the two longest rivers (their exact order depends on how source and mouth are measured), and the Amazon carries by far the greatest volume of water. Other major rivers include the Yangtze, Mississippi–Missouri, Congo, Ganges–Brahmaputra and Mekong [9].

Lakes. The Caspian Sea is the largest inland body of water by area; Lake Baikal in Russia is the deepest lake and holds about a fifth of the world’s unfrozen surface fresh water. The North American Great Lakes together form the largest group of fresh-water lakes [9].

Ice. Glaciers and ice sheets hold most of Earth’s fresh water. The Antarctic and Greenland ice sheets together contain enough ice to raise global sea level by many metres if melted [4][16].

Fresh water is scarce. About 97% of Earth’s water is salt water, and only a small fraction of the fresh water is easily accessible to people [4].

Review: What is a watershed, and why do countries sharing a river basin need to cooperate?