Please select your home edition
Edition
Auckland On Water Boat Show

Study finds surprising new pathway for North Atlantic circulation

by Woods Hole Oceanographic Institution on 27 May 2009
For this study, Dr. Amy Bower, shown here aside a RAFOS float on the deck of the research vessel Oceanus, and her colleagues deployed 76 RAFOS floats over three years. The floats are programmed to drift at a specific depth for two years, recording location information and temperature and pressure measurements once a day. After two years, the floats returned to the surface and transmitted all their data through the ARGOS satellite-based data retrieval system and downloaded to scientists in the lab. (Woods Hole Oceanographic Institution) Woods Hole Oceanographic Institution (WHOI) © http://www.whoi.edu/

Oceanographers have long known that the 20-year-old paradigm for describing the global ocean circulation – called the Great Ocean Conveyor – was an oversimplification. It’s a useful depiction, but it’s like describing Beethoven’s Fifth Symphony as a catchy tune.

The ocean conveyor paradigm says the Gulf Stream-warmed ocean releases heat to the atmosphere in the northern North Atlantic, leaving ocean water colder and denser as it moves north. The cold waters sink and flow southward along the 'deep western boundary current' that hugs the continental slope from Canada to the equator. To replace the down-flowing water, warm surface waters from the tropics are pulled northward along the conveyor’s upper limb.

But while the conveyor belt paradigm establishes the melody, the subtleties and intricacies of the symphony of global ocean circulation largely remain a puzzle.

Now, research led by oceanographers at Woods Hole Oceanographic Institution (WHOI) and Duke University have teased out a new piece of that puzzle, expanding our understanding of this circulation model. Using field observations and computer models, the study shows that much of the southward flow of cold water from the Labrador Sea moves not along the deep western boundary current, but along a previously unknown path in the interior of the North Atlantic.

The study by co-principal authors Amy Bower, a senior scientist in the WHOI Department of Physical Oceanography, and Susan Lozier, a professor of physical oceanography at Duke University’s Nicholas School of the Environment, will be published in the May 14 issue of the research journal Nature.

'This new path is not constrained by the continental shelf. It’s more diffuse,' said Bower. 'It’s a swath in the wide-open, turbulent interior of the North Atlantic and much more difficult to access and study.'

And since this cold southward-flowing water is thought to influence and perhaps moderate human-caused climate change, this finding may impact the work of global warming forecasters.

'This finding means it is going to be more difficult to measure climate signals in the deep ocean,' Lozier said. 'We thought we could just measure them in the Deep Western Boundary Current, but we really can’t.'

Lozier and Bower first conceived of this program eight years ago. Studies led by Lozier and other researchers had previously suggested cold northern waters might follow such 'interior pathways' rather than the conveyor belt in route to subtropical regions of the North Atlantic.
[Sorry, this content could not be displayed]
But testing the idea meant developing an elaborate WHOI-led field program involving the launching of 76 special Range and Fixing of Sound (RAFOS) floats into the current south of the Labrador Sea between 2003 to 2006. The ambitious program would have been prohibitively expensive had it not been for a collaboration with Eugene Colbourne of the Northwest Atlantic Fisheries Center in St. Johns, Newfoundland. Colbourne regularly conducts hydrographic surveys around the Grand Banks, and agreed to deploy the team’s RAFOS floats in groups of six every three months for three years.

Bower worked with a team at WHOI to build the floats and develop the plan for their deployment.

The RAFOS floats were configured to submerge at 700 or 1,500 meters depth – within the layer of the ocean where one constituent of the cold southward-flowing water, called Labrador Sea Water, travels. They drifted with the currents for two years, recording location information as well as temperature and pressure measurements once a day. After two years, the floats returned to the surface and transmitted all their data through the ARGOS satellite-based data retrieval system and were downloaded by scientists in the lab.

To communicate with the floats and to track their position, the team deployed anchored low-amplitude sound beacons in the general area of the experiment, which were set to 'ping' automatically every day. The RAFOS floats’s onboard hydrophones detect the sound from the beacons, enabling scientists to determine the distance from the float to the beacon, based on the time delay between when the ping went off and when it was detected.

But only 8 percent of the RAFOS floats followed the conveyor belt of the Deep Western Boundary Current (DWBC), according to the Nature report. About 75 percent of them 'escaped' that coast-hugging deep underwater pathway and instead drifted into the open ocean before rounding the Grand Banks. Eight percent 'is a remarkably low number in light of the expectation that the DWBC is the dominant pathway for Labrador Sea Water,' the researchers wrote.

Since the RAFOS float paths could only be tracked for two years, Lozier, her graduate student Stefan Gary, and German oceanographer Claus Boning also used a modeling program to simulate the launch and dispersal of more than 7,000 virtual 'e-floats' from the same starting point.

Subjecting those e-floats to the same underwater dynamics as the real ones, the researchers then traced where they moved. 'The spread of the model and the RAFOS float trajectories after two years is very similar,' they reported.

'The new float observations and simulated float trajectories provide evidence that the southward interior pathway is more important for the transport of Labrador Sea Water through the subtropics than the DWBC, contrary to previous thinking,' their report concluded.

Next, Bower and Lozier hope to extend their research to study the southward flow of cold water originating even farther north in the Greenland Sea.

This research was supported by the National Science Foundation.

The Woods Hole Oceanographic Institution is a private, independent organization in Falmouth, Mass., dedicated to marine research, engineering, and higher education. Established in 1930 on a recommendation from the National Academy of Sciences, its primary mission is to understand the oceans and their interaction with the Earth as a whole, and to communicate a basic understanding of the oceans’ role in the changing global environment - http://www.whoi.edu

Naiad/Oracle SupplierBakewell-White Yacht DesignBarz Optics - Kids range

Related Articles

America’s Cup World Series – More final day images by Ingrid Abery
Ingrid Abery has provided this gallery of images from final day Ingrid Abery has provided this gallery of images from final day
Posted today at 11:37 am
America’s Cup World Series – Final race day images by Ingrid Abery
Ingrid Abery provided this gallery of images from final day Ingrid Abery provided this gallery of images from final day
Posted today at 11:21 am
LV America’s Cup World Series - Up and down for Groupama Team France
The new leader is none other than the local team lead by Sir Ben Ainslie, who was rallied along throughout the six races 2016 America’s Cup World Series - This weekend the overall ranking for the Louis Vuitton America’s Cup World Series has been turned on its head and with the Portsmouth act complete, the new leader is none other than the local team lead by Sir Ben Ainslie, who was rallied along throughout the six races by strong support from a home crowd.
Posted today at 6:45 am
LV America's Cup World Series - Land Rover BAR take two from two
While Oracle Team USA did all but everything they could to take the win with a two, one, one scorecard today 2016 Louis Vuitton America's Cup World Series - While Oracle Team USA did all but everything they could to take the win with a two, one, one scorecard today, it wasn't enough to topple the fast and furious tenacity of a Ben Ainslie led Land Rover BAR on the final day of racing at the Louis Vuitton America's Cup World Series in Portsmouth.
Posted today at 5:39 am
2016 LV America’s Cup World Series - More images by Carlo Borlenghi
Carlo Borlenghi provided this gallery of images from America’s Cup World Series - Race Day 2 and Prize-giving ceremony. 2016 America’s Cup World Series - Carlo Borlenghi provided this gallery of images from 2016 Louis Vuitton America’s Cup World Series - Race Day 2 and Prize-giving ceremony.
Posted today at 4:46 am
2016 LV America’s Cup World Series - Day 2 images by Carlo Borlenghi
Carlo Borlenghi provided this gallery of images from America’s Cup World Series - Race Day 2 and Prize-giving ceremony 2016 America’s Cup World Series - Carlo Borlenghi provided this gallery of images from 2016 Louis Vuitton America’s Cup World Series - Race Day 2 and Prize-giving ceremony.
Posted today at 4:22 am
America's Cup - Southern Spars to build AC50 for Emirates Team NZ
Southern Spars has been appointed to build Emirates Team New Zealand’s AC50 wingsailed foiling catamaran One of the world's leading composite engineering companies, Southern Spars has been appointed to build Emirates Team New Zealand’s AC50 wingsailed foiling catamaran for the 35th America’s Cup campaign. The move marks a shift away from Cookson Boats who have been Team New Zealand's boatbuilder since 2000. No reasons have been given for the decision to change the builder.
Posted on 24 Jul
America's Cup - Emirates Team New Zealand foiled in Portsmouth
Super Sunday saw more breeze in Portsmouth today, giving all the teams the opportunity for fast racing up on their foils Super Sunday saw more breeze in Portsmouth today, giving all the teams the opportunity for fast racing up on their foils. For Emirates Team New Zealand the regatta finished as realistically expected when lining up to race against an exceptionally strong fleet with with a almost entirely rejigged crew due to Blair Tuke and Peter Burling’s absence in their build up to the Rio Olympics in the 49e
Posted on 24 Jul
LV America’s Cup World Series – Big Ben takes a big win in Portsmouth
The Duke and Duchess of Cambridge were on hand to present the awards and it was a fitting end to an amazing weekend. It really was Super Sunday for Ben Ainslie and Land Rover BAR whose second place in the last of Sunday’s three races gave them the overall regatta win at the Portsmouth event.
Posted on 24 Jul
America's Cup World Series – Two win day closes the gap on leaderboard
Oracle Team USA opened Super Sunday with a second place finish and followed it up with two race victories Oracle Team USA opened Super Sunday with a second place finish and followed it up with two race victories to close within just one point of the winning home team.
Posted on 24 Jul