Minerals/Ices/Sea ices

Welcome to the sea ices learning project.

"Sea ice is simply frozen ocean water."

Learning project summary

 * School: Marine Sciences

Content summary
Sea ice has special properties that differentiate it from fresh water ice.

Goals
Recognize the differences between sea ice and fresh water ice.

Understand how the special properties of sea ice allow microorganisms to colonize it.

Learn about how global warming threatens sea ice.

Readings and other resources

 * Sea_ice
 * National Snow and Ice Data Center
 * Wikiversity:global warming/Brainstorming

Geomorphology
Def. a "ridge or hill of ice in an ice field" or a "small hill; a hillock; a knoll" is called a hummock.

On the right is hummocky sea ice on the coast of Estonia in the Gulf of Finland.

Microstructures
A thin section of sea ice [is shown at the right] through cross-polarized light. All crystals (they have different interference colors) contain inclusions of brine (saline solution) and air - these lie within the (0001) crystallographic plane.

Oceanography
"The oceanic ... mixed layer is a layer in which active turbulence has homogenized [variables such as temperature and salinity to] some range of depths. The surface mixed layer is a layer where this turbulence is generated by winds, cooling, or processes such as evaporation or sea ice formation which result in an increase in salinity."

"The mixed layer is characterized by being nearly uniform in properties such as temperature and salinity throughout the layer. Velocities, however, may exhibit significant shears within the mixed layer. The bottom of the mixed layer is characterized by a gradient, where the water properties change."

"The depth of the mixed layer is often determined by hydrography—making measurements of water properties."

Hydrology
"This spectacular “blue marble” image is the most detailed true-color image of the entire Earth to date. Using a collection of satellite-based observations, scientists and visualizers stitched together months of observations of the land surface, oceans, sea ice, and clouds into a seamless, true-color mosaic of every square kilometer (.386 square mile) of our planet."

"Much of the information contained in this image came from a single remote-sensing device-NASA’s Moderate Resolution Imaging Spectroradiometer, or MODIS. Flying over 700 km above the Earth onboard the Terra satellite, MODIS provides an integrated tool for observing a variety of terrestrial, oceanic, and atmospheric features of the Earth. The land and coastal ocean portions of these images are based on surface observations collected from June through September 2001 and combined, or composited, every eight days to compensate for clouds that might block the sensor’s view of the surface on any single day. Two different types of ocean data were used in these images: shallow water true color data, and global ocean color (or chlorophyll) data. Topographic shading is based on the GTOPO 30 elevation dataset compiled by the U.S. Geological Survey’s EROS Data Center. MODIS observations of polar sea ice were combined with observations of Antarctica made by the National Oceanic and Atmospheric Administration’s AVHRR sensor—the Advanced Very High Resolution Radiometer. The cloud image is a composite of two days of imagery collected in visible light wavelengths and a third day of thermal infra-red imagery over the poles."

Glaciology
A "climate interpretation was supported by very low δ’s in the 1690’es, a period described as extremely cold in the Icelandic annals. In 1695 Iceland was completely surrounded by sea ice, and according to other sources the sea ice reached half way to the Faeroe Islands."

"The correlation is astonishing, because it implies that the dramatic climate changes during the first more than 50 kyrs of the glaciation elapsed nearly in parallel on both sides of the North Atlantic Ocean, presumably controlled by varying sea ice cover. Thus, the Gulf Stream was not just deflected toward North Africa in cold periods, it was rather turned off."

Def. a "thick, floating platform of ice that forms where a glacier or ice sheet flows down to a coastline and onto the ocean surface" is called an ice shelf.

"Ice shelves are permanent floating sheets of ice that connect to a landmass."

"Ice shelves fall into three categories: (1) ice shelves fed by glaciers, (2) ice shelves created by sea ice, and (3) composite ice shelves (Jeffries 2002). Most of the world's ice shelves, including the largest, are fed by glaciers and are located in Greenland and Antarctica."

"One example of an ice shelf composed of compacted, thickened sea ice is the Ward Hunt Ice Shelf off the coast of Ellesmere Island in northern Canada. Canadian RADARSAT image shows the shelf in August 2002, when a crack made its way down the length of the shelf."

Def. a "large consolidated mass of floating sea ice" is called pack ice.

Pack ice in the image on the third right is drifting southward in the East Greenland current during July 1996.

In the first image on the left, when "waves buffet the freezing ocean surface, characteristic "pancake" sea ice forms."

"Sheets of sea ice form when frazil crystals float to the surface, accummulate and bond together. Depending upon the climatic conditions, sheets can develop from grease and congelation ice, or from pancake ice."

"If the ocean is rough, the frazil crystals accummulate into slushy circular disks, called pancakes or pancake ice, because of their shape. A signature feature of pancake ice is raised edges or ridges on the perimeter, caused by the pancakes bumping into each other from the ocean waves. If the motion is strong enough, rafting occurs. If the ice is thick enough, ridging occurs, where the sea ice bends or fractures and piles on top of itself, forming lines of ridges on the surface. Each ridge has a corresponding structure, called a keel, that forms on the underside of the ice. Particularly in the Arctic, ridges up to 20 meters (60 feet) thick can form when thick ice deforms. Eventually, the pancakes cement together and consolidate into a coherent ice sheet. Unlike the congelation process, sheet ice formed from consolidated pancakes has a rough bottom surface."

Ice cores
At the right is a thin section of Antarctic sea ice. It was taken from an ice core.

Cryosphere
"The cryosphere ... is [a] term which collectively describes the portions of [an astronomical object's] surface where water is in solid form, including sea ice, lake ice, river ice, snow cover, glaciers, ice caps and ice sheets, and frozen ground (which includes permafrost). Thus there [may be] a wide overlap with [a] hydrosphere. The cryosphere is an integral part of the global climate system with important linkages and feedbacks generated through its influence on surface energy and moisture fluxes, clouds, precipitation, hydrology, atmospheric and oceanic circulation. Through these feedback processes, the cryosphere plays a significant role in global climate and in [any] climate model response to global change."

Shown in the northern hemisphere images is the rock distribution of sea ice and ice sheets [first image on the right].

At the south pole, Antactica, there is also an extensive ice sheet [second image on the right]. Apparently, when the North polar sea ice and ice sheet has been contracting, the South polar sea ice and ice sheet has been expanding.

Ridging
Def. "process that occurs when wind, ocean currents, and other forces push sea ice around into piles that rise and form small mountains above the level sea ice surface; ridges are initially thin and transparent with very sharp edges from blocks of ice piling up" is called ridging.

Electromagnetics
Def. "crystals of ice that form when water vapor becomes a solid (bypassing the liquid phase) and deposits itself on the sea ice surface" are called frost flowers.

"[F]rost flowers [in the image at the right] roughen the surface and dramatically affect its electromagnetic signal."

New Siberian Islands
The New Siberian Islands north of Yakutia have a nominal position of 75°16′N 145°15′E.

"The winter sea ice in the east Siberian Sea is looking a bit like a cracked windshield in these true-color Moderate Resolution Imaging Spectroradiometer (MODIS) images from June 16 and 23, 2002. North of the thawing tundra, the sea ice takes on its cracked, bright blue appearance as it thins, which allows the reflection of the water to show through. Numerous still-frozen lakes dot the tundra."

The Laptev Sea is on the left in the image on the right and part of the East Siberian Sea is on the right.

Scott Island
Scott Island has a nominal location of 67°22.7'S 179°54.7'W.

Theoretical sea ices
Def. "frozen seawater; pack ice" is called sea ice.