Featured Research

from universities, journals, and other organizations

Impact of ocean deoxygenation on iron release from continental margin sediments

Date:
May 18, 2014
Source:
Oregon State University
Summary:
A new study examining the impact of iron released from continental margin sediments has documented a natural limiting switch that may keep these ocean systems from developing a runaway feedback loop that could lead to unchecked hypoxic areas, or persistent 'dead zones.' The findings are particularly important, scientists say, because as the climate warms oxygen minimum zones are expected to expand in coming decades and could affect coastal fisheries as well as the global carbon cycle. But the study suggests that there may be a limit to the expansion of these OMZs.

A new study examining the impact of iron released from continental margin sediments has documented a natural limiting switch that may keep these ocean systems from developing a runaway feedback loop that could lead to unchecked hypoxic areas, or persistent "dead zones."

The findings are particularly important, scientists say, because as the climate warms oxygen minimum zones are expected to expand in coming decades and could affect coastal fisheries as well as the global carbon cycle. But the study, which was led by researchers at Oregon State University, suggests that there may be a limit to the expansion of these OMZs.

The results are being published this week in the journal Nature Geoscience.

It is well-documented that iron is a crucial catalyst for fueling biological productivity in the oceans. When there is an insufficient amount of iron in the water column, microscopic plants called phytoplankton cannot fully consume nitrates and phosphates, limiting their growth. There are several potential sources of iron -- including river sediments, windblown dust and continental margin sediments -- but to be useful to plankton, the iron must be dissolved rather than locked up in sediments.

Oxygen may be a key that unlocks the storehouse of iron.

In high-oxygen environments, most of the iron that is dissolved in the water precipitates -- turning into iron oxide coatings (similar to rust) on particles, which sink to the seafloor. Organic remains of plants and animals also sink to the seafloor and their rotting remains consume the oxygen dissolved in seawater. As oxygen lowers, a hypoxic dead zone may form. When it does the iron oxides dissolve and may diffuse back into the water column where the iron again becomes available to fertilize plankton growth, as long as other major nutrients such as nitrate and phosphate are available.

"When this moderate hypoxic state occurs, the iron release fuels more biological productivity and the organic particles fall to the sea floor where they decay and consume more oxygen, making hypoxia worse," said Florian Scholz, a postdoctoral researcher in OSU's College of Earth, Ocean, and Atmospheric Sciences and lead author on the Nature Geoscience study. "That leads to this feedback loop of more iron release triggering more productivity, triggering more iron release.

"But we found that when the oxygen approaches zero a new group of minerals, iron sulfides, are formed," Scholz added. "This is the key to the limit switch because when the iron gets locked up in sulfides, it is no longer dissolved and thus not available to the plankton. The runaway hypoxia stops and the hypoxic region is limited."

An important part of the study was the development of indicators for sedimentary iron release during past periods of ocean deoxygenation, the researchers said. Scholz and his colleagues investigated a sediment core from the upwelling area of Peru, where the subsurface water column has one of the lowest ongoing oxygen levels on Earth.

In their study, the researchers looked at concentrations of iron, uranium and molybdenum in ocean sediments dating back 140,000 years.

The key to the discovery, they say, was determining whether sediments buried during a past period of ocean deoxygenation had an iron deficit. Sediment with an iron deficit suggests that the iron was removed and potentially transported offshore into iron-limited ocean regions. Conversely, when the sediments held a lot of iron, it likely was retained and thus not available for fertilization.

"Florian found that there are two states in which iron is locked up and unavailable to fuel plant growth," said Alan Mix, an Oregon State geochemist and co-author on the study. "When there is a lot of iron in the sediment, but no molybdenum, the iron is stored in oxide minerals.

"This happens when oxygen is abundant," Mix added. "But if there is iron and molybdenum, then the iron is stored in sulfide minerals like pyrite, meaning the system has little or no oxygen available.

What the researchers discovered in the Peru system "is a window for iron release, which could be a key to the biological productivity in this iron-limited ocean region," Scholz said.

The near-anoxic Peru system differs from the Pacific Northwest coast of the United States, which has experienced several hypoxic events over the past decade. The Northwest waters are not yet as low in oxygen or iron as Peru.

"These basic reactions have been known for a while," Mix said, "but documenting them in the real world on a large scale -- and associating them with climate change -- is quite significant and especially important given projections of growing hypoxia in a warming climate."


Story Source:

The above story is based on materials provided by Oregon State University. Note: Materials may be edited for content and length.


Journal Reference:

  1. Florian Scholz, James McManus, Alan C. Mix, Christian Hensen, Ralph R. Schneider. The impact of ocean deoxygenation on iron release from continental margin sediments. Nature Geoscience, 2014; DOI: 10.1038/ngeo2162

Cite This Page:

Oregon State University. "Impact of ocean deoxygenation on iron release from continental margin sediments." ScienceDaily. ScienceDaily, 18 May 2014. <www.sciencedaily.com/releases/2014/05/140518164427.htm>.
Oregon State University. (2014, May 18). Impact of ocean deoxygenation on iron release from continental margin sediments. ScienceDaily. Retrieved July 29, 2014 from www.sciencedaily.com/releases/2014/05/140518164427.htm
Oregon State University. "Impact of ocean deoxygenation on iron release from continental margin sediments." ScienceDaily. www.sciencedaily.com/releases/2014/05/140518164427.htm (accessed July 29, 2014).

Share This




More Earth & Climate News

Tuesday, July 29, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Climate Change Could Cost Billions, According To White House

Climate Change Could Cost Billions, According To White House

Newsy (July 29, 2014) A report from the White House warns not curbing greenhouse gas emissions could cost the U.S. billions. Video provided by Newsy
Powered by NewsLook.com
Climate Change Could Cost Billions According To White House

Climate Change Could Cost Billions According To White House

Newsy (July 29, 2014) A report from the White House warns not curbing greenhouse gas emissions could cost the U.S. billions. Video provided by Newsy
Powered by NewsLook.com
Jane Goodall Warns Great Apes Face Extinction

Jane Goodall Warns Great Apes Face Extinction

AFP (July 29, 2014) The world's great apes face extinction within decades, renowned chimpanzee expert Jane Goodall warned Tuesday in a call to arms to ensure man's closest relatives are not wiped out. Duration: 00:58 Video provided by AFP
Powered by NewsLook.com
Rat Infestation at Paris' Tuileries Garden

Rat Infestation at Paris' Tuileries Garden

AFP (July 29, 2014) An infestation of rats is causing concern among tourists at Paris' most famous park -- the Tuileries garden next to the Louvre Museum. Duration: 00:54 Video provided by AFP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins