There is a dark zone on Greenland's Ice Sheet, and new drone research shows it's getting darker. It also seems to melt faster than it should – and the scientists finally have a better idea of it.
The dark zone is a strip of fast-melting ice southwest of the ice cap. It is about 400 kilometers (248 miles) in length and 100 kilometers (62 miles) at its widest point.
It is also clearly visible in satellite imagery.
As well as being strangely dark, it is also known as the ablation zone, as this area melts faster than other parts of the ice sheet.
In 2014, field researchers attributed this melting to mineral and microbial deposits on the surface of ice.
Now new drone research from the Norwegian Center for Arctic Gas Hydrate, Environment and Climate (CAGE) confirms this data ̵
"What we're showing is that the dark zone is covered with a finely dispersed layer of dust and black carbon. They are the main cause of darkening," said co-author Alun Hubbard, glaciologist at CAGE.
This rapid melting is by no means only a problem for Greenland, but bad news for the entire planet, especially the areas that will be affected by sea-level rise.
Currently, global sea level is about 3 millimeters per year, but this value is not constant – it jumps another 0.08 millimeter every 12 months, and researchers know that Greenland's decline is particularly strong this terrible trend.
The mechanism behind the accelerated melting of the dark zone is simple. As darker hues absorb more radiation and more reflect lighter shades, the darker ice absorbs more heat from the sun and melts faster.
How much light is reflected from a given surface is called albedo – a high albedo means high reflectivity. The relatively low albedo of the dark zone means the ice melts up to five times faster than pure white snow.
When the ice melts, it also loses its reflexivity, and liquid water promotes the growth of algae. Even a slight increase in temperature can cause the ice to melt and the algae bloom. This is usual for spring and summer.
"The algae need nutrients and food, essentially dust, organic carbon and water," Hubbard said.
"These are plentiful in summer and algae blooms begin, as algae are dark in color, reinforcing the dark zone, giving you a positive feedback effect where the ice layer absorbs and melts more sunlight."
The use of drones has several advantages over satellite data. You can control a drone on the spot and maneuver to the areas you want to investigate – and they are much closer to the ground. This means they can capture fine details that satellites in orbit are too far away to pick them up.
Combining the two technologies has allowed the team to get a better picture of the Dark Zone than ever before.  They found that meltwater sloshing across the surface of the sheet, along with Cryconit – the darkest type of dust in some bags – played a relatively minor role, though earlier they were considered major factors in lowering the albedo of the ice sheet  Meanwhile, dust, soot (soot from forest fires and burning) and algae account for 73 percent of the variability of albedo, they have found.
"We propose that the progressive emergence and spread of distributed contaminants is compounded by increased ablation and biological activity that will fuel the future expansion of the Greenland's dark zone," the researchers wrote in their publication.
However, they note that further studies are needed to determine the extent of the effect of melting and carbon nutrients on algae growth and concentration.
The work of the team was published in the journal Nature Communications