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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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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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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Of the three percent of the water that is not in the ocean, about 69 percent is locked up in glaciers and icecaps. Ninety percent of that frozen water is in Antarctica and about nine percent covers Greenland.

Of the remaining freshwater, 30 percent of it is groundwater, captured below our feet. About 0.3 percent is found in rivers and lakes. This means that the water source we are most familiar with in our everyday lives, rivers and lakes, accounts for less than one percent of all freshwater that exists on Earth.

A very small percentage of water (0.1 percent of all water) is also found in the atmosphere.

For more information:
The Ocean’s Role in Weather and Climate, NOS Education
The Hydrologic Cycle, National Weather Service Northwest River Forecast Center

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El Niño and La Niña are opposite phases of what is known as the El Niño-Southern Oscillation (ENSO) cycle. The ENSO cycle is a scientific term that describes the fluctuations in temperature between the ocean and atmosphere in the (approximately between the International Date Line and 120 degrees West).

La Niña is sometimes referred to as the cold phase of ENSO and El Niño as the warm phase of ENSO. These deviations from normal surface temperatures can have large-scale impacts not only on ocean processes, but also on global weather and climate.

El Niño and La Niña episodes typically last nine to 12 months, but some prolonged events may last for years. They often begin to form between June and August, reach peak strength between December and April, and then decay between May and July of the following year. While their periodicity can be quite irregular, El Niño and La Niña events occur about every three to five years. Typically, El Niño occurs more frequently than La Niña.

El Niño El Niño means The Little Boy, or Christ Child in Spanish. El Niño was originally recognized by fishermen off the coast of South America in the 1600s, with the appearance of unusually warm water in the Pacific Ocean. The name was chosen based on the time of year (around December) during which these warm waters events tended to occur.

The term El Niño refers to the large-scale ocean-atmosphere climate interaction linked to a periodic warming in sea surface temperatures across the central and east-central Equatorial Pacific.

Typical El Niño effects are likely to develop over North America during the upcoming winter season. Those include warmer-than-average temperatures over western and central Canada, and over the western and northern United States. Wetter-than-average conditions are likely over portions of the U.S. Gulf Coast and Florida, while drier-than-average conditions can be expected in the Ohio Valley and the Pacific Northwest.

La Niña La Niña means The Little Girl in Spanish. La Niña is also sometimes called El Viejo, anti-El Niño, or simply "a cold event."

La Niña episodes represent periods of below-average sea surface temperatures across the east-central Equatorial Pacific. Global climate La Niña impacts tend to be opposite those of El Niño impacts. In the tropics, ocean temperature variations in La Niña also tend to be opposite those of El Niño.

During a La Niña year, winter temperatures are warmer than normal in the Southeast and cooler than normal in the Northwest.

For more information:
NOAA El Niño Page
NOAA La Niña Page
NOAA National Weather Service Climate Prediction Center, El Niño/La Niña
NOAA Pacific Marine Environmental Laboratory: El Niño theme page

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Ocean water freezes just like freshwater, but at lower temperatures. Fresh water freezes at 0 degrees Celsius (32 degrees Fahrenheit), but seawater freezes at about -1.9 degrees Celsius (28.4 degrees Fahrenheit) because of the salt in it. When seawater freezes, however, the ice contains very little salt because only the water part freezes. It can be melted down to use as drinking water.

At least 15 percent of the ocean is covered by sea ice some part of the year. On average, sea ice covers almost about 25 million square kilometers (10 million square miles) of the Earth.

Sea water becomes more and more dense as it becomes colder, right down to its freezing point. Fresh water, on the hand, is most dense while still at 4 degrees Celsius (39.2 degrees Fahrenheit), well above the freezing point. The average temperature of all ocean water is about 3.5 degrees Celsius (38.3 degrees Fahrenheit).

For more information:
National Ice Center
NOAA's Arctic Theme Page
National Weather Service National Centers for Environmental Prediction: Sea Ice (sea ice data)
Salinity Data, National Oceanographic Data Center ...

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Many people use the terms "ocean" and "sea" interchangeably when speaking about the ocean, but there is a difference between the two terms when speaking of geography (the study of the Earth's surface).

Seas are smaller than oceans and are usually located where the land and ocean meet. Typically, seas are partially enclosed by land.

For more information:
Office of Coast Survey
A History of Charting America's Waters, NOAA 200th
Anniversary Web Site

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To be classified as an iceberg, the height of the ice must be greater than 16 feet (five meters) above sea level and the thickness must be 98-164 feet (30-50 meters) and the ice must cover an area of at least 5,382 square feet (500 square meters).

There are smaller pieces of ice known as “bergy bits” and “growlers.” Bergy bits and growlers can originate from glaciers or shelf ice, and may also be the result of a large iceberg that has broken up. A bergy bit is a medium to large fragment of ice. Its height is generally greater than three feet (one meter) but less than 16 feet (five meters) above sea level and its area is normally about 1,076-3,229 square feet (100-300 square meters). Growlers are smaller fragments of ice and are roughly the size of a truck or grand piano. They extend less than three feet (one meter) above the sea surface and occupy an area of about 215 square feet (20 square meters).

Icebergs are also classified by shape, most commonly being either tabular or non-tabular. Tabular icebergs have steep sides and a flat top. Non-tabular icebergs have different shapes, with domes and spires.

Icebergs are monitored worldwide by the U.S. National Ice Center (NIC). NIC produces analyses and forecasts of Arctic, Antarctic, Great Lakes, and Chesapeake Bay ice conditions. NIC is the only organization that names and tracks all Antarctic Icebergs.

For more information:
U.S. National Ice Center

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Rogue, freak, or killer waves have been part of marine folklore for centuries, but have only been accepted as a real phenomenon by scientists over the past few decades.

Rogues, called 'extreme storm waves' by scientists, are those waves which are greater than twice the size of surrounding waves, are very unpredictable, and often come unexpectedly from directions other than prevailing wind and waves.

Most reports of extreme storm waves say they look like "walls of water." They are often steep-sided with unusually deep troughs.

Since these waves are uncommon, measurements and analysis of this phenomenom is extremely rare. Exactly how and when rogue waves form is still under investigation, but there are several known causes:

Constructive interference. Extreme waves often form because swells, while traveling across the ocean, do so at different speeds and directions. As these swells pass through one another, their crests, troughs, and lengths sometimes coincide and reinforce each other. This process can form unusually large, towering waves that quickly disappear. If the swells are travelling in the same direction, these mountainous waves may last for several minutes before subsiding.

Focusing of wave energy. When waves formed by a storm develop in a water current against the normal wave direction, an interaction can take place which results in a shortening of the wave frequency. This can cause the waves to dynamically join together, forming very big 'rogue' waves. The currents where these are sometimes seen are the Gulf Stream and Agulhas current. Extreme waves developed in this fashion tend to be longer lived.

For more information:
Wind, Swell and Rouge Waves, JetStream Online School for Weather, National Weather Service
Rogue Waves, Ocean Prediction Center, National Weather Service

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