An international team of researchers has confirmed the presence of a newly discovered deep-ocean circulation system off Iceland that could significantly influence the ocean's response to climate change.
The North Icelandic Jet contributes to a key component of the Atlantic Meridional Overturning Circulation, also known as the “great ocean conveyor belt,” which is critically important for regulating Earth’s climate, the scientists say.
As part of the planet's reciprocal relationship between ocean circulation and climate, this conveyor belt carries warm surface water from the tropical Atlantic toward the Arctic. In the process, the water warms the air in high latitudes, then cools, sinks and returns toward the equator as a deep flow.
Crucial to this warm-to-cold oceanographic choreography is the Denmark Strait Overflow Water, the largest of the deep, overflow plumes that feed the lower limb of the AMOC and return the dense water south through gaps in the Greenland-Scotland Ridge, the National Science Foundation says.
For years it has been thought that the primary source of the Denmark Overflow is a current adjacent to Greenland known as the East Greenland Current.
But this view was recently called into question by two oceanographers from Iceland who discovered a deep current flowing southward along the continental slope of Iceland. Their findings were published in the Aug. 21 online issue of the journal Nature Geoscience.
The researchers who discovered the current have confirmed that the Icelandic Jet is not only a major contributor to the DSOW but is the primary source of the densest overflow water.
Climate specialists are concerned that the giant conveyor belt is slowing down due to global warming. As Arctic sea ice vanishes, more fresh water is predicted to flow into the northern North Atlantic, where it could freeze and decrease the need for the conveyor belt to deliver as much warm water as it does now.
If the conveyor belt was disrupted or slowed at the place in the far north where the warm water at the surface cools and sinks -- called the overturning -- it could eventually lead to a colder Northern Hemisphere.
Present thinking contends that increased fresh water delivered to the North Atlantic, due to melting ice and increased precipitation under a warming climate, will slow down or halt the overturning of the AMOC, said study co-author Robert Pickart of the Woods Hold Oceanographic Institution, Reuters reported.
But that might not happen if the North Icelandic Jet is as big a contributor to the overall ocean flow as the study suggests.
If a large fraction of the overflow water comes from the NIJ, then we need to rethink how quickly the warm-to-cold conversion of the AMOC occurs, as well as how this process might be altered under a warming climate, said Pickart.
The existence of the NIJ was suspected for decades but was only confirmed recently by Icelandic researchers using underwater velocity measurements taken from a ship.