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The Last Continent: Massive iceberg afloat off Antarctica for 17 years

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SCOTIA SEA — Overnight, the Akademik Ioffe changed course. Instead of heading toward Elephant Island as was initially planned, we detoured to take a look at a massive iceberg.

It’s called B15Z. It’s a tabular ’berg, flat-topped with steep, dirty grey walls, which makes it seem more island than iceberg. But in front of and behind it are smaller tabular icebergs that glisten white and blue.

It is 24 kilometres long and 11 kilometres wide.

It took nearly an hour to pass by it — more than long enough to start a debate on the bridge about B15Z’s height. To settle the argument, the watch officer took out a sextant, a navigational device used for nearly four centuries. Now, navigation is done by radar and GPS. But the Russian officers who operate this ship are all able to use sextants so that if there’s a power failure, they will still be able to find their way.

What the officer concluded is that B15Z is 78 metres high. That means there’s likely another 400 metres of ice below, since only a fifth or a sixth of icebergs is visible above the surface.

This ’berg was birthed nearly 18 years ago when a huge chunk broke off the Ross Ice Sheet. It was — and remains — one of the 10 largest icebergs recorded. The largest broke off in 1957 and was three times the size of B15 at 177 miles long and 27 miles wide.

For the past 17 years, B15 has done a stately circuit around Antarctica travelling at between one and two nautical miles an hour. Over the years, it has birthed 28 smaller icebergs and an uncountable number of bits too small to merit being named.

It was named B15 for the quadrant of Antarctica that it broke off from and 15 because it was the 15th to separate from that particular ice sheet.

It’s a testament to B15’s initial size that even some of the smaller icebergs that have split off from it are named and tracked by satellites so that ships in the area don’t inadvertently bump into them.

Ice sheets are collapsing at faster rate than before as the air and sea temperatures are rising. In July, a 5,000-square-kilometre piece broke off the Larsen Ice Sheet, which is double the size of Luxembourg, half the size of Haida Gwaii and half the size of B15.

According to the 2016 Canadian Antarctic Research Workshop Report report, the Southern Ocean is responsible for 50 per cent of the ocean uptake of anthropogenic carbon and has absorbed over 65 per cent of the heat associated with global warming.

It goes on to say that the Southern Ocean is warming at twice the rate of the global ocean and this has been attributed to changes in the concentrations of atmospheric greenhouse gases.

When an ice sheet breaks off from the land, it doesn’t contribute to sea level rise because it is already floating. The easiest way to explain it is to think about an ice cube in a drink. It melts, but it won’t change the level of the liquid in a glass.

Because of rising sea and air temperatures, the ice sheets are collapsing are faster rates than in the past as they melt from both the top and the bottom.

“There is not an immediate impact. But we know that ice shelves provide a buttressing affect against glaciers. If the ice shelves are reduced, glacier potential to flow in faster,” says Thomas James, a research scientist with the Geological Survey of Canada, who forecasts sea level rise for Canadian coastal areas.

There is research that suggests that glaciers behind ice shelves may accelerate by as much as five times following an ice shelf collapse.

For now, James, says the consensus scientific forecast is that the Antarctic melt will probably deliver about 30 centimetres to sea rise by 2100. But the most recent studies suggest that the Antarctic melt could raise sea level by as much as a metre.

Did you know?

• In July 2017, a 5,000 square kilometre iceberg (that’s twice the size of Luxembourg or half the size of Haida Gwaii) broke off from the Larsen Ice Shelf on the Antarctic Peninsula and was set adrift in the Weddell Sea. Although it is one of the 10 largest icebergs ever recorded, it was half the size of one that split off from the Ross Ice Shelf in 2000. The iceberg accounted for about 12 per cent of the ice shelf’s total area, leaving it at the lowest extent ever recorded.

• The Larsen Ice Shelf remains Antarctica’s fourth largest with an area of about 50,000 square kilometres.

• Ice shelves are permanent floating ice sheets connected to a land mass that can be thousands of years’ old. Enormous ice sheets slowly ooze into the sea through glaciers and ice streams and, if the ocean is cold enough, the ice doesn’t melt. Instead, it floats and grows larger as it’s fed by the glacier.

• Most ice shelves are found on Antarctica’s coast, although there are several on the northern coast of Canada’s Ellesmere Island.

• Because they’re already floating, ice shelves don’t contribute directly to sea level rise when they break up — just as melting ice in a glass doesn’t cause an overflow. However, collapse can indirectly contribute to it because the glaciers that fed the ice shelf now flows more quickly to the sea.

• Research suggests that glaciers behind ice shelves may accelerate by as much as five times following a rapid ice shelf retreat.

• Scientists believe that the collapsing ice shelves in both the Antarctic and Arctic are linked to climate change, which is warming both the ocean water and the air temperatures and resulting in decreased sea ice. As the air temperatures warm, meltwater forms ponds on the ice shelves. The water trickles through small cracks in the ice shelf, deepening, eroding and expanding the cracks. Warmer water melts the ice shelf from below.

Source: National Sea & Ice Data Center, The Guardian

dbramham@postmedia.com

Twitter.com/daphnebramham


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