Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Duke scientists explain gaps in nutrient availability within North Atlantic

29.09.2005


Seasonal wedges of undersea water block upwelling of plant sustaining nitrates



Duke University oceanographers have developed an explanation for why a vast North Atlantic circulation zone can have a large variability in nutrient supplies needed to sustain ocean plants and, by extension, support the food web of marine life.

The circulating zone in the North Atlantic Ocean, known as a "subtropical gyre," swirls in a clockwise direction between the Gulf Stream -- the warm current that bisects the Atlantic between the southern U.S. and northern Europe -- and the Tropic of Cancer. This gyre is also the location of the Sargasso Sea.


In a paper in the Sept. 29, 2005, issue of the journal Nature, graduate student Jaime Palter and professors Susan Lozier and Richard Barber show that pockets of water that seasonally wedge themselves into the gyre from the Gulf Stream prohibit deep-ocean nutrients from directly upwelling to the "euphotic" zone, the region near the surface where there is enough light to support plant life.

The scientists are in Duke’s Nicholas School of the Environment and Earth Sciences. Their work was sponsored by the National Science Foundation.

Using satellites to detect the presence of chlorophyll in ocean-borne plant life, the investigators noted a striking correlation between where these nutrients were kept wedged off far below the euphotic zone and where the chlorophyll was low.

As seen from space, this satellite-detected chlorophyll was spread out in ring-shaped patterns on the ocean’s surface, with minimum readings corresponding with the low nutrient concentrations, according to the Duke team. Depressed nutrient levels ultimately limit the "primary productivity" that supports the food chain.

"Researchers have tried for years to look at what processes brings nutrients to the surface," said Lozier, a professor of physical oceanography, in an interview. "Do winds cause upwelling? Do surface waters cool and then overturn and sink to drive nutrients up? Do we get a mixing of waters by winds and waves?

"The answer to all those questions is ’yes.’ But none of those processes, even combined, could really explain the patterns of productivity we saw."

Lozier, Palter and Barber -- a professor of biological oceanography -- made their deductions by consulting satellite information and years of data on water density, temperature and nutrients from previous ocean studies.

Their study focused on "North Atlantic Subtropical Mode Water." Lozier described that as "a large volume of water with the same properties" that gets isolated from the Gulf Stream’s edge when cooled by the air above it during winter.

Because cooler water is denser and heavier, this mode water overturns and sinks to form a large wedge-shaped mass. Sinking below the surface, it has lower nutrient concentrations than that of the surrounding waters. Only with time are the nutrients in this mode water mass restored by the sinking and decay of organic matter from the sunlit surface layers. Since the subtropical gyre has a circulation, the mode water also begins moving around it, potentially blocking nutrients from upwelling in larger areas, Lozier said.

"In parts of the ocean where there is no such wedge of low nutrient water beneath the euphotic zone, vertical processes are much more effective at moving nutrients to the surface, and can therefore have a greater biological effect," added Palter, who is first author of the Nature paper.

How far the mode water moves, and how extensively it blocks the underlying trapped nutrients, depends on the gyre’s power. The power of the gyre is determined by a large scale, cyclical climate pattern called the North Atlantic Oscillation (NAO) -- which irregularly swings between "high" and "low" phases over periods of decades, said the researchers.

During the last "low" NAO, occurring in the 1950s and 60s, "really thick" subtropical mode water spread throughout the subtropical gyre, Lozier said. By contrast, the authors determined that mode water layers should be shallower and less extensive during "high" NAOs, potentially making nutrients more accessible to the euphotic zone.

Indeed, the Duke investigators found that that nitrate concentrations were 25 percent greater in the mode water during the high NAO that began in the 1980s than in the low-NAO 1950s. And primary productivity rates observed in the 50s and 60s were only half those recorded in the last two decades, according to their Nature paper.

These conclusions about NAO effects on nutrient availability are the opposite of what would be expected without accounting for the varying effects of mode water, Lozier said. "We’ve been able to explain that with our ideas."

When a robust gyre spreads around the blanket of mode water, the nutrient recycling system is disrupted. Lozier said. Floating surface plants "can go to the bank, but there’s no money there."

The researchers are now preparing to put out instruments that will give scientists their first time series of nutrient level readings in these subtropical waters, Lozier said.

"The ideas that we lay out here don’t just apply to the subtropical North Atlantic," she said. "We happened to have a lot of available data there to test our ideas. That’s why we have focused there.

"But what we want to do next is start looking at other ocean basins to get a broader view. We may not get the same patterns in other gyres, because the mode waters are different in other basins. But we believe the same mechanics are going to apply."

Monte Basgall | EurekAlert!
Further information:
http://www.duke.edu

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

7th International Conference on Crystalline Silicon Photovoltaics in Freiburg on April 3-5, 2017

03.04.2017 | Event News

 
Latest News

DGIST develops 20 times faster biosensor

24.04.2017 | Physics and Astronomy

Nanoimprinted hyperlens array: Paving the way for practical super-resolution imaging

24.04.2017 | Materials Sciences

Atomic-level motion may drive bacteria's ability to evade immune system defenses

24.04.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>