A network of ever-growing lakes on ice shelves in Greenland are speeding up the melting of ice sheets and causing them to increase their flow. This could lead to these ice shelves to lose stability, which are considered among the largest in the northern hemisphere.
So far, this phenomenon of melt lake networks and their effects on the ice sheet itself was unknown, say, researchers. Now, based on 3D modeling and real-world observations, a team of researchers from the UK, Norway, Sweden and the US has simulated what they are calling profound, dynamic consequences that these lakes have, reports Phys.org.
As the weather warms, melt lakes often form on the surface of the ice sheets every summer. While they last for weeks and months on the surface, when they drain, they go out fast. Within a few hours, massive amounts of fresh water from the surface of the ice sheets will seep through over a kilometer of ice and into the sea.
"This growing network of melt lakes, which currently extends more than 100 kilometers inland and reaches elevations as high a 2,000 meters above sea level, poses a threat for the long-term stability of the Greenland ice sheet," said lead author Dr. Poul Christoffersen, from Cambridge's Scott Polar Research Institute.
"This ice sheet, which covers 1.7 million square kilometers, was relatively stable 25 years ago, but now loses one billion tonnes of ice every day. This causes one millimeter of global sea level rise per year, a rate which is much faster than what was predicted only a few years ago," he added.
The lakes, along with dumping a huge quantity of water into the sea, also carries heat with it to the base of the ice sheet, causing calving at the bottom. These are parts of ice sheets that are particularly sensitive and the impact of ice and water flows are felt strongly and the effect is potentially large, note researchers.
Till now, scientists believed that these drainage events, as they call it, were isolated and by themselves. The new research reports that these lakes form intricate networks that are spread out over large swathes of ice shelves and they are getting bigger as the weather warms.
Considering the fact that this February, the temperatures were about 50 degrees over the normal winter levels and there is no sunlight reaching the Arctic, these melt lakes are a cause of concern.
When a lake drains, notes the report, water quickly flows under the ice sheet and it reposnds by flowing faster. This flow of fast water, opens up weakened fractures in the shelf and they act as conduits for this fast flowing water and connects to other lakes that might be on the surface.
This chain reaction can drain lakes far away, the researchers found, some as far as 80 km away, within hours.
In one such event, researchers recorded 124 lakes draining out in just 5 days. Such events, says the team, can temporarily accelerate the flow of ice sheets by about 400 percent, greatly affecting the stability of said ice shelf.
