The Irminger Sea is a marginal sea of the North Atlantic Ocean. It is bordered to the west by southern Greenland, to the north by Iceland and the Denmark Strait, to the east by the Reykjanes Ridge (a northern part of the Mid-Atlantic Ridge), and to the south by open waters of the North Atlantic.
It was named after Danish vice-admiral Carl Ludvig Christian Irminger (1802–1888), after whom the Irminger Current was also named.
2,000 meters deep
They create a seafloor barrier separating the seas to the north and the Irminger Sea to the south, all of which are more than 2,000 meters deep.
The Irminger Sea Array consists of a triangular set of moorings (white circles), with the sides of the triangle having a length roughly 10 times the water depth to capture mesoscale variability in each region.
Where is Irminger Current?
The Irminger Current is a north Atlantic ocean current setting westward off the southwest coast of Iceland. It is composed of relatively warm and saline waters from the eastern North Atlantic that are fed by the North Atlantic Drift. The Irminger Current is part of the North Atlantic subpolar gyre.
What is Irminger Current and East Greenland current?
The East Greenland Current flows south along Greenland's east coast, transporting large fields of ice, and then turns north into the Labrador Sea. The current mixes with the warmer Irminger and Norwegian currents, creating excellent fishing grounds near the coast of Iceland and in portions of the Norwegian Sea.
Beneath the water in the Denmark Strait, shallow continental shelves, only several hundred meters deep, extend east from Greenland and west from Iceland and nearly join. They create a seafloor barrier separating the seas to the north and the Irminger Sea to the south, all of which are more than 2,000 meters deep.
Cold, dense water fills the depths of the seas north of the Denmark Strait and then plunges down an increasingly steep bottom slope into the depths of the Irminger Sea. Though not as abrupt as Niagara, this submarine waterfall is thousands of times greater in volume than all terrestrial waterfalls combined. If visible, it would be a World Heritage site.
As the cold, dense water sinks into the depths of the Irminger Sea, the ocean performs another trick: It pulls in surrounding water and marshals it into a vast current that flows southward at depth. The current eventually crosses under the Gulf Stream near Cape Hatteras, then flows seaward of the Bahamas, into the Southern Hemisphere. This is the Deep Western Boundary Current (postulated in 1960 by the eminent WHOI oceanographer Henry Stommel before it had ever been observed in nature).
Thus the Denmark Strait/Irminger Sea is at once the southbound superhighway of the Ocean Conveyor and the headwaters of the Deep Western Boundary Current. And that's why we need to know how water navigates the strait.
A newly discovered ocean current?
In 2004, Icelandic oceanographers Steingrimur Jonsson and Hedinn Valdimarsson overturned previous thinking about how water enters the strait when they observed an entirely new current. They found that the old model was partly correct—the East Greenland Current flows into the strait from the north. However, they argued that most of the water that flowed over the Denmark Strait arrived via a deep, dense current flowing eastward along the northern border of Iceland. They called this deep current the Northwest Icelandic Jet.
Naturally, the new paradigm introduced more questions than it answered. Just what kind of water was contained in the Northwest Icelandic Jet? Where did it come from? How did it negotiate the submarine mountain ranges in its path?
To understand the net flow in the Northwest Icelandic Jet, Pickart needed to stop the ship every two miles to lower and retrieve a package of instruments called a “CTD,” which measures seawater conductivity (a proxy for salinity) and temperature at various depths. Then the ship moved to the next “station” to do it again. And again.
“The CTD operators probably want to throw me over the side,” Pickart would say later in the trip. “But there's no other way.”
The second question—how water exits the strait—also brought a new twist to conventional thinking. Recent evidence suggested that some of the dense water passing out of the strait actually remains up on the outer portion of the shallow Greenland shelf, thus bypassing the big waterfall in the deeper regions of the strait.
Addressing this question required Pickart to raise his gaze from the deep ocean to the surface and above, to the atmosphere. The notion was that the wind might be driving water off the shelf into the deeper Irminger Sea basin. And in this case, terrestrial geography, in the form of Greenland, was enhancing the wind. This expedition provided us firsthand experience of the exquisite interconnectedness of nature's great systems.