The Sargasso Sea, located entirely within the Atlantic Ocean, is the only sea without a land boundary

The Sargasso Sea is a vast patch of ocean is named for a genus of free-floating seaweed called Sargassum. While there are many different
types of algae found floating in the ocean all around world, the Sargasso Sea is unique in that it harbors species of sargassum that are 'holopelagic' — this means that the algae not only freely floats
around the ocean, but it reproduces vegetatively on the high seas. Other seaweeds reproduce and begin life on the floor of the ocean.

Sargassum provides a home to an amazing variety of marine species. Turtles use sargassum mats as nurseries where hatchlings have food and shelter. Sargassum also provides essential habitat for marine species,such as shrimp, crab, and fish, that have adapted specifically to this floating algae. The Sargasso Sea is a spawning site for threatened and endangered eels, as well as white marlin, porbeagle shark, and dolphinfish. Humpback whales annually migrate through the Sargasso Sea. Commercial fish, such as tuna, and birds also migrate through the Sargasso Sea and depend on it for food.

While all other seas in the world are defined at least in part by land boundaries, the Sargasso Sea is defined only by ocean currents. It lies within the Northern Atlantic Subtropical Gyre. The Gulf Stream establishes the Sargasso Sea's western boundary, while the Sea is further defined to the north by the North Atlantic Current, to the east by the Canary Current, and to the south by the North Atlantic Equatorial Current. Since this area is defined by boundary currents, it's borders are dynamic, correlating roughly with the Azores High Pressure Center for any particular season.

For more information:
What's the difference between an ocean and a sea? (Ocean Fact)

Sargassum: A Complex 'Island' Community at Sea (NOAA's Ocean Explorer)

Sampling the Sargassum Community: Dip Nets and Green-Light Lures (NOAA's Ocean Explorer)

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The cryosphere is the frozen water part of the Earth system

There are places on Earth that are so cold that water is frozen solid. These areas of snow or ice, which are subject to temperatures below 0°C for at least part of the year, compose the cryosphere. The term “cryosphere” comes from the Greek word, “krios,” which means cold.

Ice and snow on land are one part of the cryosphere. This includes the largest parts of the cryosphere, the continental ice sheets found in Greenland and Antarctica, as well as ice caps, glaciers, and areas of snow and permafrost. When continental ice flows out from land and to the sea surface, we get shelf ice.

The other part of the cryosphere is ice that is found in water. This includes frozen parts of the ocean, such as waters surrounding Antarctica and the Arctic. It also includes frozen rivers and lakes, which mainly occur in polar areas.

The components of the cryosphere play an important role in the Earth’s climate. Snow and ice reflect heat from the sun, helping to regulate our planet’s temperature. Because polar regions are some of the most sensitive to climate shifts, the cryosphere may be one of the first places where scientists are able to identify global changes in climate.

For more information:
Why is the ocean salty?
U.S. National Ice Center
What is an iceberg?
NOAA's Arctic Theme Page

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Tide and current data is available from NOAA's Center for Operational Products and Services website

Tides Tide Predictions. Generate a graphical display or a tabular listing of daily high and low tide predictions for more than 3,000 locations around the nation. Predictions may be generated up to two years in advance.

Real-Time Tide Data. Access current water levels from over 3,000 tidal stations. For the Great Lakes region, see Great Lakes Real-Time Water Level Data.

Historic Tide Data. For a given NOAA tide station, retrieve historic tide data from the earliest to the most recent dates for which data is available. For the Great Lakes region, see Great Lakes Historic Water Level Data.

Sea Levels. View a global map depicting regional trends in sea level, with arrows representing the direction and magnitude of change.

Tides Online. Choose a tide station by state and location to view current tidal information, wind speeds, air pressure, and air temperature. For the Great Lakes region, visit Great Lakes Online.

Tsunami-Capable Tide Stations. Access high resolution, one-minute water level sample data used to support national tsunami warning and mitigation efforts.

Tide Station Index. Generate a per-state list of all NOAA tide stations, including station number, name, location, installation date, and more.

Tidal Datums. Access NOAA's tidal datums. Scientists use datums to define "normal" water levels as a starting point from which all measurements are made. The numbers that appear on a nautical chart represent water depths measured relative to such a datum.

Currents Real-Time Current Data. View real-time current data collected by NOAA current meters around the nation.

Historic Current Data. View historic current data collected by active and retired NOAA current meters around the nation.

Tidal Current Predictions. Obtain tidal current predictions for more than 2700 tidal current stations nationwide.

Other CO-OPS Products and Services PORTS®. NOAA's Physical Oceanographic Real-Time System (PORTS®) improves the safety and efficiency of maritime commerce and coastal resource management through the integration of real-time environmental observations, forecasts and other geospatial information. PORTS® measures and disseminates observations and predictions of water levels, currents, salinity, and meteorological parameters (e.g., winds, atmospheric pressure, air and water temperatures) that mariners need to navigate safely in and around key maritime ports around the nation.

NowCOAST. NowCOAST is a web mapping portal that provides spatially referenced links to thousands of real-time coastal observations and NOAA forecasts of interest to the marine community.

Storm QuickLook. Access near real-time oceanographic and meteorological observations at locations affected by a tropical cyclone.

Operational Forecast System. This service offers nowcasts and short-term forecasts for select regions (critical ports, harbors, estuaries, Great Lakes, and coastal waters). These real-time observations and forecasts deliver present and future states of water levels, along with currents and other relevant oceanographic variables, such as salinity and temperature.

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NOAA's Storm QuickLook Provides Near Real-Time Ocean and Meteorological Conditions During a Tropical Storm. When NOAA's National Weather Service issues a tropical storm warning for the U.S. or its territories, the Storm QuickLook is activated. This free online tool is a snapshot of near real-time coastal and weather observations for areas affected by a storm.

As the name suggests, the Storm QuickLook provides a ‘quick look’ at how a storm is affecting the coast. Here are some of the details provided by this report:

Real-time water level and meteorological observations along the coast
GIS map integrating storm track and intensity, satellite imagery, and NOS water level station locations
Summary of present conditions across the affected region
Predicted high tides at specific locations along the coast
Latest NOAA Weather Service Public Advisory Text
QuickLook is served up by the Center for Operational Oceanographic Products and Services, NOAA’s tides and currents experts. While updates are generally published online four times a day, QuickLook data is updated once every six minutes during storm events. The online product may be released more frequently as circumstances (such as storm landfall) dictate.


For more information:
In-Depth Description of NOAA's Storm QuickLook
Center for Operational Oceanographic Products and Services
QuickLook Archive


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Ferdinand Magellan named the Pacific Ocean. In 1519, Portuguese explorer Ferdinand Magellan, in the employ of Spain, began a journey across the Atlantic Ocean to seek a western route to the Spice Islands via South America.

After braving perilous seas and navigating through what are now known as the Straits of Magellan, his small fleet entered an unfamiliar ocean in Nov. 1520. ...

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At sea level, the air that surrounds us presses down on our bodies at 14.7 pounds per square inch (1 bar). You don't feel it because the fluids in your body are pushing outward with the same force.

Dive down into the ocean even a few feet, though, and a noticeable change occurs. You can feel an increase of pressure on your eardrums. This is due to an increase in hydrostatic pressure, the force per unit area exerted by a liquid on an object.

The deeper you go under the sea, the greater the pressure of the water pushing down on you. For every 33 feet (10 meters) you go down, the pressure increases by 14.7 psi (1 bar). In the deepest ocean, the pressure is equivalent to the weight of an elephant balanced on a postage stamp, or the equivalent of one person trying to support 50 jumbo jets!

Many animals that live in the sea have no trouble at all with high pressure. Whales, for instance, can withstand dramatic pressure changes because their bodies are more flexible. Their ribs are bound by loose, bendable cartilage, which allows the rib cage to collapse at pressures that would easily snap our bones.

A whale's lungs can also collapse safely under pressure, which keeps them from rupturing. This allows sperm whales to hunt for giant squid at depths of 7,000 feet (2,100 meters) or more.

For more information:
NOAA's Ocean Explorer

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Part of each station is a recorder which sends an audio signal down a half-inch-wide sounding tube and measures the time it takes for the reflected signal to travel back from the water's surface.

In addition to measuring tidal heights, these stations also record 11 different oceanographic and meteorological parameters including wind speed and direction, water current speed and direction, air and water temperature, and barometric pressure.

The stations collect data every six minutes with timing controlled by a Geostationary Operational Environmental Satellite (GOES). The stations also use these satellites to transmit their data hourly to NOAA headquarters. In the event of a storm, the stations can be programmed to transmit their data every six minutes. Field teams can quickly check and maintain the systems using laptop computers. In addition, all of the raw and processed data are available over the Internet. For more information:
Center for Operational Oceanographic Products and Services
Measuring Tides (Diving Deeper podcast, 6.16.10)

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In the beginning, the primeval seas were probably only slightly salty. But over time, as rain fell to the Earth and ran over the land, breaking up rocks and transporting their minerals to the ocean, the ocean has become saltier.

Rain replenishes freshwater in rivers and streams, so they don’t taste salty. However, the water in the ocean collects all of the salt and minerals from all of the rivers that flow into it.

It is estimated that the rivers and streams flowing from the United States alone discharge 225 million tons of dissolved solids and 513 million tons of suspended sediment annually to the ocean. Throughout the world, rivers carry an estimated four billion tons of dissolved salts to the ocean annually.

About the same tonnage of salt from ocean water probably is deposited as sediment on the ocean bottom and thus, yearly gains may offset yearly losses. In other words, the ocean today probably has a balanced salt input and output (and so the ocean is no longer getting saltier).

For more information:
Why is the ocean salty?
Salinity Data, National Oceanographic Data Center (NODC)



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Cold water has a higher density than warm water. Deep water gets colder at depth because cold, salty ocean water sinks to the bottom of the ocean basins. Less dense, warmer water rises to the surface. This process of rising and sinking water creates a complex pattern of ocean circulation called the 'global conveyor belt.'

In contrast, the Earth gets hotter and hotter at depth primarily because the energy of radioactive decay is leaking outwards from the core of the planet. While this geothermal energy is transferred to ocean water along the sea floor, the effect is so small that it's immeasurable by direct means.

Why? The actual amount of heat generated per square meter of Earth is quite small, especially compared to the amount of heat necessary to warm the ocean. Geothermal energy emanating from the Earth averages only about one tenth of a watt per square meter. At that rate of heat flow (without taking ocean currents into account), it would take well over a year just to heat the bottom meter of the ocean by one degree Centigrade.

However, the ocean is not standing still. Complex deep ocean currents driven by density variations in temperature and salinity are constantly replacing the bottom layer of ocean water with colder water.

For more information:
What is a current?
What is the global ocean conveyor belt?
Ocean Conveyor Belt, NOAA Science on A Sphere

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The ocean is a huge body of water that is constantly in motion. General patterns of ocean flow are called currents. Sometimes theses currents can pinch off sections and create circular currents of water called an eddy.

You may have seen an eddy if you've ever gone canoeing and you see a small whirlpool of water while you paddle through the water. The swirling motion of eddies in the ocean cause nutrients that are normally found in colder, deeper waters to come to the surface.

Significant eddies are assigned names similar to hurricanes. In the U.S., an oceanographic company called Horizon Marine assigns names to each eddy as they occur. The names follow chronologically along with the alphabet and are decided upon by staff at Horizon Marine. The staff try to think of creative ways to assign names.

For example, an eddy that formed in the Gulf of Mexico in June 2010 is named Eddy Franklin after Ben Franklin, as he was known to have done research on the Gulf Stream.

For more information:
Ocean Mesoscale Eddies, NOAA's Geophysical Fluid Dynamics Laboratory
Center for Operational Oceanographic Products and Services
National Current Observation Program
Currents Tutorial, NOS Education
Diving Deeper Podcast, Episode 15 (August 12, 2009) - What are currents?
Horizon Marine

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