IceStation: Identifying ice at sea

Identifying types of cloud is a task that weather observers are used to around the globe, but for those travelling the polar seas there's another challenge - putting a name to the ice they see.

Ice comes in a bewildering range of shapes and sizes. Some forms are dangerous to shipping, others less so, but you need a common language if you want to communicate the information to other mariners. So definitions have been agreed to make reports consistent, and the terminology is full of colourful phrases.

Ice ahead! The view from the Ernest Shackleton ship, on which Peter Gibbs is travelling to Antarctica

Ice to see you

Icebergs are massive chunks of ice that start life on land, but sail out to sea when they break off - or 'calve' - from glaciers or ice shelves. The most common type in Antarctica is the tabular berg which looks like a giant white aircraft carrier, although after many years of wearing away by the sea they can take on fantastic shapes, with caves, arches and pinnacles. As these disintegrate they break up into 'bergy bits' which are defined as being 'about the size of a small cottage' or if it's dense green ice they might end up as 'growlers' which roll around low in the waves ready to catch a captain unawares.

Ice floating on the water, as seen from the Ernest Shackleton ship

Sea ice on the other hand is simply frozen seawater. Except it's not simple. If seas are calm as the water freezes the crystals make it look as if there's an oily film, hence 'grease ice'. If the sea's rougher, as temperatures fall the crystals clump together as 'frazil ice'. As the ice thickens, it may form rounded plates with raised edges called 'pancake ice'. Over winter the ice continues to thicken and form large floes which can be a few metres thick and when winds force the floes together they will form 'hummocks'. To the delight of young children the opposite of a hummock, protruding under the ice, is called a 'bummock'!

Peter Gibbs is travelling to Antarctica, 36 years after he worked there as a young meteorologist. Peter will be travelling to the British Antarctic Survey research station Halley, to give us a unique glimpse into the life and discoveries being made at Britain's most remote scientific station. You can follow Peter's journey to Antarctica on Weather Watchers, @bbcweather, BBC News Channel and using the hashtag #IceStation.

Click here to find out more about Peter's trip.