Wednesday 10 July 2013

Huge iceberg calves from Pine Island Glacier.

The DLR satellite TerraSAR-X observed a 720 km² iceberg calve away from the Pine Island Glacier in Antarctica and float free into the Amundsen Sea on Monday 8 July 2013. The glacier, which flows along the south side of the Hudson Mountains into Pine Island Bay (named for the seaplane USS Pine Island which first explored the area, not for any local flora) drains about 10% of Antarctica's Western Ice Shelf and has both accelerated and thinned notably since observations began, increasing in speed by about 73% and losing an average of 46 gigatonnes of mass per year between 1973 and 2007.

The newly formed iceberg (upper left) calving away from Pine Island Glacier. DLR.

The loss of icebergs from Pine Island Glacier into the sea is a natural process; all glaciers flow, and eventually either calve into the sea (or sometimes a big lake) or reach an area warm enough to melt, feeding streams and rivers. However the increase in the rate at which Pine Island Glacier is flowing and thinning is reason for concern. 

Glaciers are fed by precipitation, like rivers, but increased precipitation will not necessarily lead to increased flow as it will with a river, as the flow of a glacier is determined by its mass-balance ratio. Effectively this means a glacier's flow is driven by a combination of input and temperature. It the amount of precipitation increases and the temperature drops the glacier will slow and thicken. I the case of Pine Island Glacier it is thought that the increased flow is driven primarily by the warming of the Amundsen Sea, which removes more material at the calving front (warm a glacier and it calves more rapidly) causing the glacier to flow more rapidly, which in the absence of a notable increase in precipitation, has led the glacier to thin.

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