Fin des Voies Rapides: Reason Why There's a Huge Cold Spot in the Atlantic between Greenland and Ireland and the UK

There are three extremely deep canyons in the southeast side of Greenland. The melt waters on top of Greenland's ice cap are forming des moulins bleues, running down to the bottom, pressing up on, cracking and melting the ice further, and flowing out to sea via these canyons.

There are three very deep canyons in southeastern Greenland, two close to the tip and one opposite Iceland.
Image Credit: LiveScience.com, via Colorado Bob on Robertscribbler.

UPDATE: a couple of days ago, the Daily Kos came out with an important article on this very subject: Sudden drainage, via massive chasm, of Subglacial lakes in Greenland described as catastrophic.

Streams and rivers that form on top of the Greenland ice sheet during spring and summer are the main agent transporting melt runoff from the ice sheet to the ocean. Image Credits: NASA’s Goddard Space Flight Center/Maria-José Viñas via the Daily Kos.

The Greenland ice sheet is the largest body of permanent ice in the Northern Hemisphere. Climate Change is happening swiftly in the Arctic, and consequently it is causing rapid and relentless melting of the sheet from both above (Albedo or dark ice) and below the ice due to warming ocean temperatures as well as large volumes of warm melt water at the bedrock). Most of us know that this run away melting is raising sea level rise across the Globe. The hydrologic system of the Greenland ice sheet is extremely complex and there has been little data about how it works for some time, but slowly we are beginning to solve some of it's mysteries. Each summer, the hydrological system becomes activated as massive amounts of melt water is produced on its surface, evaporates into the atmosphere, percolates into partially formed layers of ice, and feeds runoff into supraglacial lakes (a lake formed on top of the ice sheet), streams and rivers to the ice sheet margins. Recently 2 sub-glacial lakes were discovered in Greenland. These lakes form below the ice and can stay unfrozen for decades. Particularly unusual is the fact that these lakes are associated with Antarctica and not the Arctic. They were unknown there until recently. The sub-glacial lake can be stable for decades, but can drain in one season and refill quickly with melt water from the surface. We are familiar with the dramatic calving at marine terminating glaciers but what is less evident is the oddity of surface melting and what happens to the water for land terminating glaciers with it's sub and supra glacial lakes.

Scientists have discovered a crater, shown here, which had once been the site of a sub-glacial lake. Image credit: Ian Howat / DigitalGlobe Inc / Sci-News.com via the Daily Kos.

A 'whirlpool' and crack on the Petermann glacier. Geophysicist Dr Richard Bates, of the Scottish Oceans Institute at the University of St. Andrews, takes 'casts' of temperature, pressure, current and salinity. He makes casts - dropping a CTD probe (Conductivity Temp Depth) into the pool and pulling it back up at a slow speed...
Picture: NICK COBBING / GREENPEACE via the Daily Kos.

The central mystery related to Greenland hydrology is how much melt water is lost to the ocean and thereby contributing to the rate of global sea level rise. Prior to late 2013, many thought that the bedrock under the ice sheet was relatively flat and that melt from inland glaciers would pond there and perhaps not contribute to SLR. "We now know that there are many channels in the bedrock. These channels potentially connects the interior ice-sheet, its plumbing, and melt water to Petermann Fjord".

Hidden under a mile of ice is a canyon that stretches for at least 465 miles from Greenland’s interior to its northwest coast at Petermann Fjord. NASA's Operation Ice Bridge found that parts of the canyon are a half mile deep and over 6 miles wide. The Grand Canyon in Arizona, for comparison purposes, is 277 miles long and over a mile at its deepest and 18 miles at it's widest. The researchers who discovered it have named it "paleofluvial megacanyon". Not a sexy name to be sure, but the name means that the "canyon was carved by an ancient river well before Greenland’s ice sheet covered it up some 3.5 million years ago".

Climate Central notes the potential feedback loops. They are disturbing and grim.

Increased ice melt from this, as well as other surface melting due to increasing air temperatures could make Greenland a major contributor to sea level rise by the end of the 21st century. The melting of Greenland’s glaciers has also added a large boost of freshwater to the North Atlantic which could alter ocean currents and the ocean’s ability to take up carbon dioxide.