The mystery of a growing “dark zone” Greenland‘s melting ice sheet is dissolved.
Researchers have found it phosphorus-rich dust blown over the ice can be the key to the phenomenon.
Greenland’s ice sheet is the second largest in the world. It covers approximately 1.71 million square kilometers (656,000 square miles), an area three times the size of Texas, according to the National Snow and Ice Data Center (NSIDC). However, the ice sheet is now in permanent decline and loses 500 gigatons (500 billion tons) of ice annually, Live Science reported earlier.
This is why the dark zone is so worrying. During the summer months, a portion of the western portion of the ice sheet changes from brilliant white to ink gray while algae bloom across the surface. Since 2000, these flowers have grown, causing the dark zone to expand, according to a statement by the researchers.
The darker color of the ice reduces the albedo – the amount of sunlight it reflects into space – and allows the ice sheet to absorb more heat. So far, however, it has remained a mystery causing these algae to bloom.
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“We see a lot of volatility in the blossoms that form on the ice sheet surface,” said Jenine McCutcheon, a microbiologist at the University of Waterloo in Ontario, and lead author of the new study describing the findings. “We wanted to better understand what was causing their growth,” she told WordsSideKick.
The algae blooms
In the Arctic sunless winter months, the ice algae consists mainly of Ancylonema nordenskioeldii and species in the Mesotaenium genus – stays deep in the ice in a dormant state. As the ice melts, these algae slowly migrate to the surface. When they reach the surface, the North Pole summer provides 24-hour sunlight for photosynthesis and growth. The algae are normally green, but when exposed to constant sunlight, they create dark-colored sunscreens to protect themselves from harmful ultraviolet rays. This is what darkens the ice and ironically causes it to absorb more sunlight.
But sunlight alone does not seem to be enough to cause the extensive blossoms that the researchers see.
After the researchers analyzed samples they collected from the surface, “it became clear that phosphorus is the most important nutrient for algae,” said co-author Jim McQuaid, a climate scientist at the University of Leeds in England. . “We then found it to be locally sourced.”
In Greenland comes the phosphorus of hydroxylapatite – a phosphate mineral that also contains calcium, oxygen and hydrogen – which is blown over the ice as dust from exposed rocky corners.
“As the atmosphere warms due to climate change, the exposed rock becomes drier and the wind gets stronger,” McQuaid said. “That means more dust is being transported across the ice.”
Melting ice in the area also exposes more hydroxyaplate-rich rocks, increasing the available phosphorus. The algae blossoms are therefore part of a positive feedback loop: the increased ice melt leads to a higher phosphorus input, which stimulates the algae growth which in turn increases the ice melt.
‘This kind of thing will continue to happen in the future; there is no doubt in my mind, ‘McQuaid said, referring to the accelerating meltdown.
However, now that scientists fully understand the phenomenon of the dark zone, they can more accurately predict how fast the Greenland ice will melt.
“If we can measure the amount of phosphorus in the environment, it is possible to translate it into an estimate of algae growth and enable us to better monitor the rate of ice melting,” McCutcheon said.
The study was published online in the journal on January 25. Nature communication.
Originally published on Live Science.