Thursday, 25 August 2016

Delaware-Sized Chunk of Ice Could Dislodge from Antarctic Shelf

An 80-mile long crack in the Larsen C ice shelf threatens to dislodge a chunk of ice measuring about 2,300 square miles, nearly the size of Delaware and twice the size of the massive Larsen B ice shelf collapse in 2002.

As the long Southern Hemisphere polar night is ending, satellites have been able to see that the rift has grown nearly 14 miles, or about three miles per month, since it was last observed in March 2016. The fracture in the ice has also widened from 200 meters (656 feet) to about 350 meters, or 1,148 feet. According to Project MIDAS , a UK-based Antarctic research project, “As this rift continues to extend, it will eventually cause a large section of the ice shelf to break away as an iceberg.”

Researchers who have reviewed satellite imagery dating back to 1963 have determined that destabilization of the Larsen B ice shelf was already underway at that time, and began accelerating in more recent decades. Prior to that, it had been stable for 12,000 years. Between January and April of 2002, the ice shelf began to break apart, eventually losing a 1,235 square mile area into the sea. At that time, it was the largest collapse ever seen.

Antarctic ice shelves, which ride atop ocean waters, ring the continent and hold back land-based glaciers. The most vulnerable regions are in West Antarctica and the Antarctic Peninsula. Ice shelves in this region protect a very large portion of glacial ice. The Earth’s crust jumped upward following the collapse of Larsen B. Sensitive GPS instrumentation around the ice shelf show that tectonic uplift is now 1.8 centimeters per year as the disappearance of glaciers allows the Earth below to rebound.

However, some of the ice in the shelves is considered “passive” by scientists, in that it doesn’t play any role in buttressing glaciers. Some scientists think this may be the case with the Larsen C ice shelf.

The most recent event was the disintegration of the Wilkins Ice Shelf in 2009, the tenth major ice shelf collapse in modern times. Scientists cannot predict the timing of the Larsen C collapse, but say it could happen in the next two to three years. A study published in 2015 showed that Larsen C is rapidly thinning , having lost four meters, or 13 feet, between 1998 and 2012. As the ice thins, it is susceptible to melting from underneath.

Of itself, the loss of this portion of the ice shelf will not raise sea levels as it is already floating on the water. However, as these ice shelves disintegrate, the land-locked glaciers they hold back may begin sliding into the sea. If all of the ice the Larsen C ice shelf holds back slides into the ocean, it will raise sea levels globally by four inches.

Warmer air temperatures were blamed for the collapse of Larsen B. By melting the top layer, pools of meltwater form and seep through crevasses causing fracturing of the ice. This process is now being seen on the Langhovde Glacier in East Antarctica, on the opposite side of the continent from the Larsen ice shelf.

Temperatures at the Antarctic Peninsula , where the Larsen ice shelf is found, have risen by 2.5 degrees Celsius in the past 50 years. On March 24, 2015, a record high of 63.5 degrees Fahrenheit was recorded on the peninsula at Esperanza Base.

Antarctica is losing ice at a rate of 25 cubic kilometers, or 6 miles, per year. Current Intergovernmental Panel on Climate Change estimates of sea level rise do not account for this rate of loss.

No comments:

Post a Comment