365 Days of climate Awareness 56 - Ice Shelves

An ice shelf is the extension of an ice sheet or ice cap onto the ocean, where the water becomes deep enough that the ice floats (being roughly 90% as dense as liquid water). Shelves are much thicker than sea ice--by more than two orders of magnitude (10², or 100)--being anywhere from 300 to 1000 m thick, versus 3 m (typically) for sea ice. Ice shelves occur near the poles, around Antarctica, Greenland, and arctic Canada and Russia.

Ice shelf processes.

Where the glacial ice becomes a shelf, and begins to float, is called the grounding line. For any given sea level this is fairly constant, though tides to cause the shelf's flotation to change. Tidal ranges around Antarctica can reach 7 m, around Greenland over 2 m. Tides are a regular, cyclical aspect of the ocean but in combination with melting factors can accelerate mass loss episodes, since partially-melted shelves are structurally weaker and likelier to break up.

Schematic of an ice shelf.

In recent years ice shelves have melted back, largely in response to the warming planet. A number of factors influence their behavior, however. An instance of rapid glacial flow down to the shelf, brought about by greater basal warming or overall loss of stability in the upland glacier, will cause the shelf to extend farther out into the sea. The greater extent of ice farther into deeper, usually warmer waters will lead to a large calving event. Warming sea water will have a similar effect, even without the initial surge from the shelf.

Median extent of the Antarctic ice shelf.

Glaciers as a system act to remain in balance with their surrounding environment. Structural instability and higher temperatures lead to meltback, calving and mass loss. Lower temperatures lead either to stability or mass gain, depending on snow patterns (some theories hold that warming over Antarctica will gain glacial ice mass in some regions because the slightly warmed air will allow more snow to fall).

Global tidal ranges.

Tomorrow: tundra and permafrost.

Be well!