Pine Island Glacier in Antarctica is sensitive to climatic variability

British Antarctic Survey: A new study published in Science this month suggests the thinning of Pine Island Glacier in West Antarctica is much more susceptible to climatic and ocean variability than at first thought. Observations by a team of scientists at British Antarctic Survey, and other institutions, show large fluctuations in the ocean heat in Pine Island Bay. The team discovered that oceanic melting of the ice shelf into which the glacier flows decreased by 50 per cent between 2010 and 2012, and this may have been due to a La Ninã weather event.

Pine Island Glacier has thinned continuously during past decades driven by an acceleration in its flow. The acceleration is thought to be caused by thinning of the floating ice shelf created as the glacier slides into the sea. Understanding the processes driving ice shelf thinning and the glacier’s response is key to assessing how much it will contribute to rising sea levels.

It’s now known that much of the thinning is due to a deep oceanic inflow of Circumpolar Deep Water (CDW) on the continental shelf neighbouring the glacier. This warmer water then makes its way into a cavity beneath the ice shelf melting it from below. The passage of this warmer water was made easier by the unpinning of the ice shelf from an underwater ridge. The ridge had, in effect, acted as a wall preventing warmer water from getting to the thickest part of the shelf. This ungrounding event was one of the major driving forces behind the glacier’s rapid change.

In 2009, a higher CDW volume and temperature in Pine Island Bay contributed to an increase in ice shelf melting compared to the last time measurements were taken in 1994. But observations made in January 2012, and reported now in Science, show that ocean melting of the glacier was the lowest ever recorded. The top of the thermocline (the layer separating cold surface water and warm deep waters) was found to be about 250 metres deeper compared with any other year for which measurements exist....

This MODIS image taken by NASA’s Aqua satellite on Nov. 10, 2013, shows an iceberg that was part of the Pine Island Glacier and is now separating from the Antarctica continent. What appears to be a connection point on the top left portion of the iceberg is actually ice debris floating in the water.