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Earth from Space – Frozen fields of Antarctica

EO-1 image of ice in Antarctica

Satellite image of fields of ice on the Antarctic coast.

THOUGH IT IS ALL COMPOSED of frozen water, ice is hardly uniform. On October 7, 2011, the Advanced Land Imager (ALI) on NASA’s Earth Observing-1 (EO-1) satellite captured this image of a variety of ice types off the coast of East Antarctica.

Brilliant white ice fills the right half of this image. It is fast ice, and derives its name from the fact that it holds fast to the shore. This ice is thick enough to completely hide the underlying seawater, hence its brilliant white colour.

Trapped within the fast ice, and stuck along the edge of it, are icebergs. Icebergs form by calving off ice shelves—thick slabs of ice attached to the coast. Ice shelves can range in thickness from tens to hundreds of metres, and the icebergs that calve off of them can tower over nearby sea ice. One iceberg, drenched with meltwater, has toppled and shattered (image upper right). The water-saturated ice leaves a blue tinge.

The icebergs along the edge of the fast ice are likely grounded on the shallow sea floor, and their presence may help hold the fast ice in place.

Farther out to sea is pack ice that drifts with winds and currents. Much thinner than the fast ice, the translucent pack ice appears in shades of blue-grey.

The pack ice includes some newly formed sea ice. As seawater starts to freeze, it forms tiny crystals known as frazil (image centre). Although the individual crystals are only millimetres across, enough of them assembled together are visible from space.

Constantly moved by ocean currents, frazil often appears in delicate swirls. Frazil crystals can coalesce into thin sheets of ice known as nilas (image top). Sheets of nilas often slide over each other, eventually merging into thicker layers of ice.

NASA Earth Observatory image created by Jesse Allen and Robert Simmon, using EO-1 ALI data provided courtesy of the NASA EO-1 team. Text adapted from information issued by Michon Scott based on image interpretation by Ted Scambos, National Snow and Ice Data Centre.

Download the full-size (4MB) image here.

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Greenland’s swirling ice

Swirls of ice along Greenland's coast.

Like foam on a latte, seasonal swirls of ice congregate on Greenland's coast.

Various types of sea ice congregated along the east coast of Greenland in late March 2010. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite captured this relatively cloud-free natural-colour image on March 27, 2010. In the upper left quadrant of the image is the Greenland coast. Open ocean predominates in the lower right quadrant.

Closest to land, land-fast sea ice clings to the shore, impervious to ocean currents. This ice is often held in place by shallow ocean bottoms or continental shelves. Farther away from land, however, the situation changes as ocean currents play a greater role in moving and shaping ice.

The East Greenland Current flows southward from the Arctic along the island’s eastern coast, carrying sea ice with it. Ice carried by this current occurs in large, thick pieces, and the ice in this swath along the Greenland coast almost certainly originated elsewhere.

The large white circular shapes in this image are pieces of multiyear ice carried to this location by the East Greenland Current. Just as the relentless movement of water in rivers and streams can smooth the jagged edges of rocks over time, ocean currents can smooth ice fragments into round shapes.

Even farther out to sea than the large fragments of multiyear ice are much smaller pieces of ice—so small that they are at the mercy of even small surface currents. Collectively these tiny ice fragments form delicate swirls of ice that resemble foam on latte.

NASA image by Jeff Schmaltz, MODIS Rapid Response Team at NASA GSFC. Text adapted from information issued by Michon Scott based on image interpretation by Florence Fetterer, National Snow and Ice Data Centre.