Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Iron in Northwest rivers fuels phytoplankton, fish populations

02.03.2007
A new study suggests that the iron-rich winter runoff from Pacific Northwest streams and rivers, combined with the wide continental shelf, form a potent mechanism for fertilizing the nearshore Pacific Ocean, leading to robust phytoplankton production and fisheries.

The study, by three Oregon State University oceanographers, was just published by the American Geophysical Union in its journal, Geophysical Research Letters.

West coast scientists have observed that ocean chlorophyll levels, phytoplankton production and fish populations generally increase in the Pacific Ocean the farther north you go (from southern California to northern Washington). No one has a definitive explanation for the increase, the OSU scientists say, though some researchers have suspected river runoff may play a role. That theory has generally been discounted, they added, because river flows are low in the summer when phytoplankton blooms occur.

In their study, however, the OSU scientists found that Northwest rivers churn out huge amounts of iron in the winter and deposit it on the continental shelf, where it sits until the spring and summer winds begin the ocean upwelling process. The authors studied the relationships between phytoplankton, river runoff and shelf width all along the West Coast.

"If we consider just river flows or shelf width by themselves, they explain part of the northward increase in productivity," said Zanna Chase, an assistant professor in OSU’s College of Oceanic and Atmospheric Sciences and lead author of the study. "But if we analyze both together, they provide a more complete picture. The shelf increases in width as you move north. If the shelf wasn’t there, the iron from rivers would be lost to the open ocean.

"Our shelf acts as a ‘capacitor,’" she added, "storing the iron for the high-productivity upwelling season."

In their studies, the OSU scientists sampled water from Oregon rivers in the winter and found iron concentrations that were roughly 1,000 times higher than that found in samples of sea water taken from the Pacific Ocean off Oregon. And though previous studies, based on East Coast rivers, have suggested that almost all of the iron in rivers gets trapped in estuaries, this latest study found very different results for Oregon rivers in winter.

The researchers measured iron, ammonium, silicate and salinity levels at the mouth Alsea River during the winter, and tracked how much of it went into the ocean, said Burke Hales, an OSU associate professor of oceanic and atmospheric sciences.

The answer: more than half.

"Iron just doesn’t like to be dissolved," Hales said, "especially in sea water. When fresh water meets salt, almost all of the iron sticks to particles that sink to the floor of the continental shelf, waiting for the winds to trigger upwelling. In contrast, Monterey, Calif., has a very narrow shelf and if you step off the beach it almost immediately goes to 6,000 feet deep."

Chase said there doesn’t seem to be a direct relationship between the amount of winter runoff in Northwest streams and the level of phytoplankton production the following summer, indicating the broad Northwest shelf is storing more iron than the phytoplankton need in any given year. As a result, she added, phytoplankton production off the Oregon coast doesn’t seem to be limited by a lack of iron, whereas their cousins off central California – where river flow and shelf width are much less than off Oregon – are "iron-starved" in comparison.

The iron from the Northwest’s winter runoff is trapped on the continental shelf in the winter by downwelling winds that create an oceanographic circulation barrier that prevents the iron from being transported into the open ocean. The Columbia River also plays a role, spilling out into the Pacific and turning north in the winter, further pinning the iron deposits in Washington’s nearshore waters.

Further research is needed to test how much iron is stored in the sediments on Oregon’s continental shelf, the scientists say, and how much gets used during a typical season of upwelling.

"We probably have several years of iron stored out there," Hales pointed out, "but we don’t know whether ‘several’ means five, 10 or 50 years."

The importance of iron as a catalyst for ocean productivity invariably raises the question of whether humans can ‘fertilize’ the oceans to boost phytoplankton growth. All three of the authors have been involved in research in the Southern Ocean off Antarctica that tested that concept.

"It’s more complex than simply adding iron to seawater," said Pete Strutton, an OSU assistant professor of oceanic and atmospheric sciences. "Experiments so far have generally shown an increase in productivity that was less than expected – and it didn’t last long. Adding iron also changes the type of phytoplankton that grew, which might have important ecological consequences we don’t yet understand."

The Northwest’s system of iron-rich winter river water, a wide continental shelf, and summer upwelling has the overall effect of making this part of the Pacific Ocean a net "carbon sink" – or sequestering more carbon dioxide than the region produces. The ocean off central California, by contrast, "seems to be poised between a carbon source and a sink, depending on the year," Strutton said.

Zanna Chase | EurekAlert!
Further information:
http://www.oregonstate.edu

More articles from Earth Sciences:

nachricht World’s oldest known oxygen oasis discovered
18.01.2018 | Eberhard Karls Universität Tübingen

nachricht A close-up look at an uncommon underwater eruption
11.01.2018 | Woods Hole Oceanographic Institution

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Artificial agent designs quantum experiments

On the way to an intelligent laboratory, physicists from Innsbruck and Vienna present an artificial agent that autonomously designs quantum experiments. In initial experiments, the system has independently (re)discovered experimental techniques that are nowadays standard in modern quantum optical laboratories. This shows how machines could play a more creative role in research in the future.

We carry smartphones in our pockets, the streets are dotted with semi-autonomous cars, but in the research laboratory experiments are still being designed by...

Im Focus: Scientists decipher key principle behind reaction of metalloenzymes

So-called pre-distorted states accelerate photochemical reactions too

What enables electrons to be transferred swiftly, for example during photosynthesis? An interdisciplinary team of researchers has worked out the details of how...

Im Focus: The first precise measurement of a single molecule's effective charge

For the first time, scientists have precisely measured the effective electrical charge of a single molecule in solution. This fundamental insight of an SNSF Professor could also pave the way for future medical diagnostics.

Electrical charge is one of the key properties that allows molecules to interact. Life itself depends on this phenomenon: many biological processes involve...

Im Focus: Paradigm shift in Paris: Encouraging an holistic view of laser machining

At the JEC World Composite Show in Paris in March 2018, the Fraunhofer Institute for Laser Technology ILT will be focusing on the latest trends and innovations in laser machining of composites. Among other things, researchers at the booth shared with the Aachen Center for Integrative Lightweight Production (AZL) will demonstrate how lasers can be used for joining, structuring, cutting and drilling composite materials.

No other industry has attracted as much public attention to composite materials as the automotive industry, which along with the aerospace industry is a driver...

Im Focus: Room-temperature multiferroic thin films and their properties

Scientists at Tokyo Institute of Technology (Tokyo Tech) and Tohoku University have developed high-quality GFO epitaxial films and systematically investigated their ferroelectric and ferromagnetic properties. They also demonstrated the room-temperature magnetocapacitance effects of these GFO thin films.

Multiferroic materials show magnetically driven ferroelectricity. They are attracting increasing attention because of their fascinating properties such as...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

10th International Symposium: “Advanced Battery Power – Kraftwerk Batterie” Münster, 10-11 April 2018

08.01.2018 | Event News

See, understand and experience the work of the future

11.12.2017 | Event News

Innovative strategies to tackle parasitic worms

08.12.2017 | Event News

 
Latest News

Let the good tubes roll

19.01.2018 | Materials Sciences

How cancer metastasis happens: Researchers reveal a key mechanism

19.01.2018 | Health and Medicine

Meteoritic stardust unlocks timing of supernova dust formation

19.01.2018 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>