Top ten weather stories for 2011: story eight
8. Arctic Sea Ice near Record Low
According to Environment Canada and the National Snow and Ice Data Centre in Colorado, sea ice covering the Arctic Ocean declined to its second-lowest extent on record in September 2011. The near-record ice melt was surprising owing to the absence of the unusual warm weather and oceanic conditions that contributed to the super melt in 2007. Thin, year-old ice less than a metre thick that now dominates the Arctic ice pack is much more prone to melting than durable, multi-year ice. Since 1979, September Arctic sea ice extent has declined by 12 per cent per decade. Additionally, the five greatest ice retreats of the satellite era have occurred in the past five years.
Arctic sea ice cover fell below 4.33 million square km on September 9, 2011, with only 310,000 square km more than the previous record of minimal ice extent in 2007 – the lowest seasonal ice minimum extent since record-keeping began more than 50 years ago. This year’s minimum level was 35 per cent below the 1979 to 2000 average minimum of 7 million square km.
Although it’s much more difficult to measure, it’s estimated that sea ice volume shrunk to a new record low of 4,200 cubic km – some 8 per cent less than the record set in 2010.
The melt season started with more first-year ice and less of the thicker multi-year ice. The oldest and hardest multi-year ice, which ranges in thickness from 2 to 5 metres, now accounts for only 20 per cent of all sea ice compared to 90 per cent 30 years ago. Arctic sea ice is now estimated to be 40 to 50 per cent thinner than it used to be. Continued loss of the oldest, thickest ice has reduced the summer minimum extent.
Ice cleared again from both the Northwest Passage and the Russian Northern Sea Route, along with much of the Beaufort Sea north of the Yukon-Alaska border. According to the Canadian Ice Service, sea ice extent in the wider and deeper northern route through Parry Channel was the lowest in September 2011 since record-keeping began in 1968. The Northern Sea Route opened in mid-August and was still open at the end of September. The southern route of the Northwest Passage, through the straits of the Canadian Arctic Archipelago, opened for the sixth year in a row. The area around the magnetic North Pole would have 75 per cent ice coverage in a typical year. However, in August 2011, ice covered just 40 per cent of the area.
By late January, waters in the Miramichi Bay and much of the Gulf of St. Lawrence and Northumberland Strait are usually frozen solid, with ice as thick as 30 cm. In 2011, the ice was half that thick as a result of unseasonably mild temperatures, strong winds and a high storm surge. And it marked the second year in a row that these water bodies encountered abnormally low ice concentrations. Last year, ice cover was the lowest since the 1969 season. For some veteran fishers, the last two winters were the worst in more than four decades – just too thin and “slushy” to hold an ice-fishing shack.
At the start of the East Coast seal hunt in late March, only a couple of boats could get into the Gulf of St. Lawrence to hunt on small patches of ice. The ice also broke up faster than normal, causing hundreds of seal pups to drown. In the end, only a fraction of the seal hunt quota was taken. In August 2010, a huge tabular sheet of ice fractured off the Petermann Glacier near Greenland. It was initially thought to be 251 square km – the biggest ice island bobbing around the North Atlantic in nearly 50 years. Once the size of Manhattan, it came down the Labrador coast through May and June 2011 and became visible off Newfoundland’s Northern Peninsula in mid-July, much to the thrill of locals and iceberg tourists. The ice behemoth was one-fifth its original size, weighing between 3.5 and 4 billion tonnes, and featured its own geography of hills, waterfalls and ponds, but was weathering quickly from wave action and warmer sea water.
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