Ice shelves

The 'Agulhas' at her offloading site at the shelf ice edge Photo: Imares

Ice shelves are areas of large continentally based ice sheets (e.g. the Antarctic Ice Sheet or the Greenland Ice Sheet) which have flowed (by internal ice deformation and/or by sliding on the rock base) to the coast where they then float in the ocean.

Ice shelves terminate at the continental edge, where the ice calves off to form ice bergs. Ice shelves therefore are areas of floating, fresh-water ice (formed from snow accumulation), attached to the major ice sheets that make up the ice cover of Antarctica, Greenland and some smaller ice sheets.

Ice shelves are in contact with the atmosphere above, and the ocean below, making them the most vulnerable component of the Antarctic cryosphere. As they consist of ice that is already afloat, any change in their volume does not directly affect sea level. However they have a buttressing effect on the ice sheet, slowing the discharge of inland ice off the continent, so that changes in ice shelf morphology (shape and size) can affect the flow of grounded ice from the interior of the continent.

At the Amery Ice Shelf, where the Lambert Glacier (near the Prince Charles Mountains, in East Antarctica) flows out to sea, research aims to understand the thermal and salinity interactions between the ice and the underlying ocean. Scientists have found that ice near the base of the ice shelf is porous and infiltrated with sea water, making it highly vulnerable to rapid melting. 

The Amery Ice Shelf drains about one eighth of the ice from the East Antarctic ice sheet (about 33 gigatonnes of ice per year) and the ice movement rate at the front of the ice shelf is about 1200 m per year.

Schematic showing the relationship between ice sheets, attached to the continent, ice shelves, attached to the ice sheet but floating in the ocean, and sea ice, formed when the ocean surface freezes. Photo: IPCC AR4

It is impossible to know how many ice shelves there are in Antarctica as there are many coastal areas where narrow ice shelves stretch along the coast. The Ross Ice Shelf and the Ronne/Filchner Ice Self in Antarctica are the largest. The Ross Ice Shelf covers an area of half a million square kilometres, and is about 800 km across. 

Some of the larger ice shelves in Antarctica include:

• the Ross Ice Shelf,
• the Ronne/Filchner Ice Shelf,
• the Amery Ice Shelf,
• the Shackelton Ice Shelf,
• the George VI Ice Shelf,
• the Wilkins Ice Shelf,
• the Larsen Ice Shelf, and
• the Riiser-Larsen Ice Shelf.

Related links: