New Iceland current could sway N. Atlantic climate

WASHINGTON Sun Aug 21, 2011 1:09pm EDT

Related Topics

WASHINGTON (Reuters) - A newly discovered deep, cold current flowing off Iceland's coast may reveal that the North Atlantic is less sensitive to climate change than previously thought, researchers reported Sunday.

The new current, the North Icelandic Jet, feeds the Atlantic Meridional Overturning Circulation, a giant pattern known as the "great ocean conveyor belt," or by the disconcerting acronym AMOC.

Because this pattern is critically important for regulating Earth's climate, including European and North American climates, any strong influences on it, and their response to a warming Earth, are of keen scientific and practical interest.

The "conveyor belt" current, introduced to movie-goers in the Al Gore environmental film "An Inconvenient Truth," 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, flowing as a deep stream at lower ocean depths.

Climate specialists reckoned that most of the cold water that made up that deep south-flowing stream came from off the Greenland coast and was made up of fresh glacier-melt water, produced by new warmth in glacier-covered Greenland.

Because fresh water freezes at a higher temperature than salt water, these specialists suggested that this fresh water from glaciers and other warming-related phenomena would get into the North Atlantic, where it could freeze and prevent the water from sinking to make up the bottom of the conveyor belt.

AMOC RUNNING AMOK?

If that happened, and the AMOC 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.

However, the newly confirmed North Icelandic Jet appears to contribute more to the deeper part of the AMOC than the Greenland current does, according to research published in the journal Nature Geoscience. (For a graphic, see: link.reuters.com/qev33s)

"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 Woods Hold Oceanographic Institution.

This might not be the case if the overturning occurs in the interior of the Iceland Sea, which feeds the North Icelandic Jet, Pickart said in an email interview from Reykjavik.

"It is not inconceivable that this open-ocean process is less sensitive to fresh water forcing than the presently accepted mechanism ... which might lead one to speculate that the deepest part of the overturning may be less sensitive to climate change," he said.

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. The NIJ current can't be seen by satellites or detected by its temperature or salinity, but it does move a bit faster than the surrounding water, Pickart said.

Pickart and researchers from Norway and Iceland don't know whether the North Icelandic Jet flows year round or how it varies with time. They are beginning a research voyage this week to deploy oceanographic instruments to directly measure the NIJ over the course of a full year to try to figure out where and how this current forms.

(Editing by Paul Simao)

FILED UNDER: