Oceans and Seas and the Water Cycle Completed

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Water cycle components  »  Atmosphere  ·  Condensation  ·  Evaporation  ·  Evapotranspiration  ·  Freshwater lakes and rivers  ·  Groundwater flow  ·  Groundwater storage  ·  Ice and snow  ·  Infiltration  ·  Oceans  ·  Precipitation  ·  Snowmelt  ·  Springs  ·  Streamflow  ·  Sublimation  ·  Surface runoff
 

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The ocean is a huge storehouse of water

When we talk about the water cycle, we must consider both where water is stored in pools, and the fluctuation of water between those storehouses. Much more water is "in storage" for long periods of time than is actively moving through the cycle. It is estimated that of the 332,500,000 cubic miles (mi³) (1,386,000,000 cubic kilometers (km³)) of the world's water supply, about 321,000,000 mi³ (1,338,000,000 km³) is stored in oceans. That is about 96.5 percent of all Earth's water. It is also estimated that the oceans supply about 90 percent of the evaporated water that goes into the water cycle.

The water in the oceans is saline (saltwater). Saline water contains significant amounts (referred to as "concentrations") of dissolved salts. In this case, the concentration is the amount (by weight) of salt in water, as expressed in "parts per million" (ppm). Water is saline if it has a concentration of more than 1,000 ppm of dissolved salts; ocean water contains about 35,000 ppm of salt.

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The volume of the oceans does change ... slowly

Of course, nothing involving the water cycle is permanent, even the amount of water in the oceans. Over the "short term" of hundreds of years, the oceans' volumes don't change much. But the amount of water in the oceans does change over the long term. During the last Ice Age, sea levels were lower, which allowed humans to cross over to North America from Asia at the (now underwater) Bering Strait.

During colder climatic periods, more ice caps and glaciers form, and enough of the global water supply accumulates as ice which lessens the amount in other parts of the water cycle. The reverse is true during warm periods. During the last ice age glaciers covered almost one-third of Earth's land mass, with the result being that the oceans were about 400 feet (122 meters) lower than today. During the last global "warm spell," about 125,000 years ago, the seas were about 18 feet (5.5. meters) higher than they are now. About three million years ago the oceans could have been up to 165 feet (50 meters) higher.
 

Oceans in movement: Tides

The oceans are always in movement. The moon influences daily tides, which make the beach a more interesting place to go. Tides vary greatly around the world, and in some places can be quite dramatic. The highest tides occur in confined estuaries, such as the Bay of Fundy, Nova Scotia, Canada, Ungava Bay, Quebec, and Bristol Channel in Britain. The Bay of Fundy has maximum tides of up to 53 feet (16 meters) during certain times of the year (Bay of Fundy Com).
 

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Oceans in movement: "Rivers" in the oceans

Did you know that the oceans move because of more than just waves driven by winds? There are currents and "rivers" in the oceans that move massive amounts of water around the world. These movements have a great deal of influence on the water cycle. The Kuroshio Current, off the shores of Japan, is the largest current. It can travel between 25 and 75 miles (40 and 121 kilometers) a day, 1-3 miles (1.4-4.8 kilometers) per hour, and extends some 3,300 feet (1,000 meters) deep.

The Gulf Stream is a well-known stream of warm water in the Atlantic Ocean, moving water from the Gulf of Mexico across the Atlantic Ocean towards Great Britain. At a speed of 60 miles (97 kilometers) per day, the Gulf stream moves 100 times as much water as all the rivers on Earth. Coming from warm climates, the Gulf Stream moves warmer water to the North Atlantic. Cornwall, at the southwest corner of Great Britain, is sometimes referred to as the "Cornish Riviera" because of the milder climate attributable to the Gulf Stream—palm trees (albeit a hardy variety) can even grow there, all because of the Gulf Stream.

The Gulf Stream carries warm, salty water northward along the Northeast Shelf (Gulf of Maine to Cape Hatteras, NC), bringing heat from the tropics to higher latitudes. The northward and landward extent of warm Gulf Stream waters affects ecological processes in the ocean, including the distribution of commercially important fish species. It also affects weather in the region. The Gulf Stream returns a considerable amount of heat to the atmosphere. See NASA’s data visualizations of the Gulf Stream. 
 

How much water exists in the oceans?

Where is Earth's water?

For an estimated explanation of where Earth's water exists, look at this bar chart. You may know that the water cycle describes both the storage and the movement of Earth's water, so realize that the chart and table below represent the presence of Earth's water at a single point in time. If you check back in a thousand or million years, no doubt these numbers will be different as the distribution of water changes.

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Notice how of the world's total water supply of about 332.5 million cubic miles of water, over 96 percent is saline. And, of the total freshwater, over 68 percent is locked up in ice and glaciers. Another 30 percent of freshwater is in the ground. Fresh surface-water sources, such as rivers and lakes, only constitute about 22,300 cubic miles (93,100 cubic kilometers), which is about 1/150th of one percent of total water. Yet, rivers and lakes are the sources of most of the water people use everyday.

Source: Gleick, P. H., 1996: Water resources. In Encyclopedia of Climate and Weather, ed. by S. H. Schneider, Oxford University Press, New York, vol. 2, pp. 817-823.