Greenland's mysterious 'dark patch' could speed up climate change
Greenland has a 'dark zone' that could speed up the effects of - and scientists have warned the blemish is getting even bigger. The dark region stretches 250 miles (400km) across and absorbs more sunlight than 'clean' snow patches, threatening to speed up the melting of Greenland's ice sheet. From 2000 to 2012, the area of the dark zone increased by 12 per cent, but scientists remained baffled as to what caused the changing hue. In a new study, researchers studying drone imagery have found the region is shaded by trapped dust and soot from wildfires, as well as ice algae. Scroll down for video 'What we show is that the dark zone is covered in a finely distributed layer of dust and black carbon, which provide nutrition for dark-coloured algae,' said study co-author Professor Alun Hubbard, a researcher at Norway's Centre for Arctic Gas Hydrate, Environment and Climate. 'These are the main cause of the darkening.' Greenland's ice sheet covers more than 80 per cent of the country's landmass -about 656,000 square miles (1.7 million square km), an area three times the size of Texas, according to the National Snow and Ice Data Centre. The ice is more than a mile (1.6km) thick on average and holds 8 per cent of the world's fresh water. If it melts global sea levels would rise by around 23 feet (7m), according to Nasa. In a new study, researchers carried out a number of on Greenland's dark zone - a stripe of fast-melting ice towards the south-west of the ice sheet. The region, also known as the 'ablation zone', is around 250 miles (400 km) long and 62 miles (100km) at its widest point, meaning it is clearly visible in satellite imagery. Satellites show that, between 2000 and 2012, the dark zone's spatial extent increased by 12 per cent, and showed plenty of size changes within each year. This suggests the region is not simply the result of melting ice revealing dark soil sediments underneath. Researchers are concerned by the area as dark patches absorb more sunlight than bright snow, and so could speed up melting of the country's ice sheet. 'The fact that a large portion of the western flank of the Greenland ice sheet has become dark means that the melt is up to five times as much as if it was a brilliant snow surface,' Professor Hubbard said. By studying high-resolution images of the patch, the Norwegian team found that much of the dark zone had a uniform coating of 'impurities'. These include dust and soot from faraway fires and factories that have accumulated in the ice, as well as dark-coloured algal blooms. The blooms are caused by microbes that have recently been shown to thrive in Greenland's harsh, icy environment. The nature and origins of the dark zone's impurities are unclear, but the researchers write that they could be part of a complex feedback effect in the ice. The algal blooms may be fuelled by the soot and other impurities that get trapped in the sheet, creating a rapid positive feedback loop that may explain why the dark zone is getting worse. 'The algae need nutrients and food, essentially dust, organic carbon and water,' Professor Hubbard said. 'In summer, these are plentiful, and the algal bloom takes off. Because algae are dark in color, they reinforce the dark zone. 'Thereby you get a positive feedback effect where the ice sheet absorbs even more solar radiation, producing yet more melt.' Previously researchers had only imaged the patch using satellite data, but the scientists said using UAVs allowed them to take far more detailed photos. 'The UAV survey, with its amazing detail, allows us to identify and characterise all the different surface types and impurities across the entire dark zone, not just a small local little part of it,' Professor Hubbard said.