The great ocean conveyor moves water around the globe.

The ocean is not a still body of water. There is constant motion in the ocean in the form of a global ocean conveyor belt. This motion is due to thermohaline currents (thermo = temperature; haline = salinity). Cold, salty water is dense and sinks to the bottom of the ocean while warm water is less dense and rises to the surface.

The ocean conveyor gets it “start” in the Norwegian Sea, where warm water from the Gulf Stream heats the atmosphere in the cold northern latitudes. This loss of heat to the atmosphere makes the water cooler and denser, causing it to sink to the bottom of the ocean. As more warm water is transported north, the cooler water sinks and moves south to make room for the incoming warm water. This cold bottom water flows south of the equator all the way down to Antarctica. Eventually, the cold bottom waters are able to warm and rise to the surface, continuing the conveyor belt that encircles the globe.

It takes almost 1,000 years for the conveyor belt to complete one “cycle.”

For more information:
The Global Conveyor Belt, NOS Education
Ocean Conveyor Belt, NOAA Science on A Sphere

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Winds blowing across the ocean surface push water away. Water then rises up from beneath the surface to replace the water that was pushed away. This process is known as “upwelling.”

Upwelling occurs in the open ocean and along coastlines. The reverse process, called “downwelling,” also occurs when wind causes surface water to build up along a coastline and the surface water eventually sinks toward the bottom.

Water that rises to the surface as a result of upwelling is typically colder and is rich in nutrients. These nutrients “fertilize” surface waters, meaning that these surface waters often have high biological productivity.  Therefore, good fishing grounds typically are found where upwelling is common.

For more information:
What Is Upwelling, Pacific Fisheries Environmental Laboratory
Upwelling, NOAA Ocean Explorer
Coastal Currents - Upwelling, NOS Education

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Tsunamis are giant waves caused by earthquakes or volcanic eruptions under the sea. Out in the depths of the ocean, tsunami waves do not dramatically increase in height. But as the waves travel inland, they build up to higher and higher heights as the depth of the ocean decreases. The speed of tsunami waves depends on ocean depth rather than the distance from the source of the wave. Tsunami waves may travel as fast as jet planes over deep waters, only slowing down when reaching shallow waters. While tsunamis are often referred to as tidal waves, this name is discouraged by oceanographers because tides have little to do with these giant waves.

The largest tsunami on record rushed past Ishigaki Island, Japan, in 1971. It was an incredible 84.7 meters (278 feet) high. While it caused little damage, the giant wall of water relocated a 750-ton block of coral 2.4 kilometers (1.5 miles) inland.

For more information:
NOAA Deep-ocean Assesment and Reporting of Tsunamis (DART)
Map and Real-time DART Data
NOAA Tsunami Program
National Geophysical Data Center
NOAA Enhances Its Ability to Provide Tsunami Warnings (NOAA 200th Anniversary Web site) ...

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There is strong evidence that global sea level is now rising at an increased rate and will continue to rise during this century.

While studies show that sea levels changed little from AD 0 until 1900, sea levels began to climb in the 20th century.

The two major causes of global sea-level rise are thermal expansion caused by the warming of the oceans (since water expands as it warms) and the loss of land-based ice (such as glaciers and polar ice caps) due to increased melting.

Records and research show that sea level has been steadily rising at a rate of 1 to 2.5 millimeters (0.04 to 0.1 inches) per year since 1900.

This rate may be increasing. Since 1992, new methods of satellite altimetry (the measurement of elevation or altitude) indicate a rate of rise of 3 millimeters (0.12 inches) per year.

This is a significantly larger rate than the sea-level rise averaged over the last several thousand years.

For more information:
Sea Levels Online, Center for Operational Oceanographic Products and Services
Global Warming: Frequently Asked Questions, NOAA National Climatic Data Center
Warming of the World Ocean, NOAA 200th Anniversary Web Site
Sea level rise, NOAA Science on a Sphere®

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