UNIS

 

Antarctica: December 2001

 By Dr Khalid Siddiqui
Ohio

Icebergs and Sea Ice

As the ship couldn’t anchor too close to the shore, the tourists were taken to the landing site on the zodiacs. To avoid damage, the zodiac needed to move very carefully around the floating sea-ice and small icebergs. From a distance both could look alike, just white ice floating, but up close they appeared different.

Sea-ice is the frozen ocean water. It forms when seawater freezes at the ocean surface. It looks flat and thin compared to icebergs. It is often broken into floes, plates, or slushy chunks (pancake ice, brash ice). The surface may look grainy, bubbly, or slightly gray from salt and trapped air. Edges tend to be rounded or crumbly.

Small icebergs (“bergy bits” and growlers), on the other hand, are the pieces of ice that have broken off from the glaciers (calving) or freshwater ice (ice shelves). Larger ones are called Bergy Bits, and the smaller ones Growlers. It is thicker, harder, denser, and often bluish. The surface is angular, sculpted or glossy. It sits higher above water. Its edges could be sharp and irregular.

The distinction matters a lot because small iceberg fragments are far harder and more dangerous than sea-ice of similar size. Accidents, however, are rare because the zodiacs have reinforced, multi-chamber tubes; the drivers are specially-trained guides; boats carry repair kits, radios, and survival gear; and operations stop instantly if ice conditions are unfavorable. Please watch the four video clips.

https://youtu.be/EteS_PREEWI

https://youtu.be/aBbEzyKnuL0

https://youtu.be/fwJl9O_Hwxw

https://youtu.be/_IBRJxeAZKE

Brash ice is a collection of small, irregular, chunks of floating ice packed loosely together. It is formed when a large piece of sea-ice or ice floe breaks apart by wind, waves, or ship movement. It is also produced by the breakdown of icebergs. So it is often a mix of the two floating together - freshwater brash from glacier pieces and brackish brash from sea-ice breakup. It floats at the surface like a slushy layer. It could be dense enough to slow or stop the zodiac. Please watch the video.