What kind of iron is in the Southern Ocean?

Dec 11, 2012 by Paul Preuss
At bottom left, the kinds of iron species found in two transects of the Southern Ocean are shown in descending order from most soluble (yellow and red) to least soluble (purple and blue). The pie charts at right show the proportions of each species sampled at points between the SANAE base and Cape Town, and the pie charts at left show the samples between SANAE and South Georgia Island. (ACC stands for Antarctic Circumpolar Current.) The map shows chlorophyll concentrations in milligrams per square meter, per the scale at bottom right. There is a rough tendency for soluble iron regions to show greater chlorophyll concentrations.

(Phys.org)—The Southern Ocean, circling the Earth between Antarctica and the southernmost regions of Africa, South America, and Australia, is notorious for its High Nutrient, Low Chlorophyl zones, areas otherwise rich in nutrients but poor in essential iron. Sea life is less abundant in these regions because the growth of phytoplankton, the marine plants that form the base of the food chain, is suppressed. A study by scientists from South Africa's Steelenbosch University, Princeton University, and Berkeley Lab's Advanced Light Source (ALS) suggests the problem is not just a lack of iron but a lack of iron in easy-to-use form.

The researchers sampled two north-south corridors across the , traveling an easterly transect between the base of the South African National Antarctic Expeditions (SANAE IV) in Queen Maud Land and Cape Town, and a westerly transect between SANAE IV and South Georgia Island. Along the way they collected particles countaining solid iron from a series of ocean systems with different characteristics.

The samples were analyzed at the ALS Molecular Environmental Sciences beamline 11.0.2 by team member Tolek Tyliszczak, using scanning transmission X-ray microscopy (STXM). STXM combines microscopy with spectroscopy, allowing the researchers to distinguish a number of different iron species and compounds in particles of different shapes and sizes. In this way the research team could determine the solubility of the and how easily they could be taken up by plankton or other life.

The most common forms of iron are Fe(II) and Fe(III). There's plenty of highly oxidizing Fe(III) in sea water but it's insoluble, and life has developed special mechanisms to absorb it. Fe (II) is readily soluble and easily taken up by plants and bacteria but sparse in , except when freshly dumped there by continental run-off or wind-blown dust. Most dust is in the form of , however, a compound of both Fe(II) and Fe(III).

The researchers tested their particles for pure Fe(II), pure Fe(III), mixtures of these two with other materials (including aluminum), and magnetite. They found that the iron solubulity of their samples ranged over three orders of magnitude. Then they compared the predominant kinds of iron in a region with the pattern of summertime chlorophyll, that is, phytoplankton growth.

In the eastern transect, iron in the soluble Fe(II) form, either pure or dominant in a mixture, occurred relatively near the coasts of Africa and Antarctica. The regions of open ocean in between were dominated by Fe(III) or magnetite. The soluble Fe(II) regions clearly showed more growth of phytoplankton.

The westward transect was less cooperative: although the entire area was within the circumpolar current, close to the continental shelf of Antarctica, most of the iron on that leg was less soluble. Nevertheless, the team concluded that the abundance and distribution of more soluble forms of "reveals trends that allude to the effect of Fe speciation on biology, and vice versa."

Explore further: Researchers propose a novel mechanism to explain High Plains elevation

More information: www.sciencemag.org/content/338/6111/1199.abstract

Related Stories

Iron isotopes as a tool in oceanography

Jul 31, 2009

New research involving scientists from the National Oceanography Centre, Southampton (NOCS) highlights the potential utility of iron isotopes for addressing important questions in ocean science. The findings are published ...

Recommended for you

Stuck-in-the-mud plankton reveal ancient temperatures

6 hours ago

New research in Nature Communications showing how tiny creatures drifted across the ocean before falling to the seafloor and being fossilised has the potential to improve our understanding of past climat ...

NASA sees Mozambique Channel's new tropical storm

7 hours ago

Tropical Cyclone 15S formed in the Mozambique Channel of the Southern Indian Ocean, and the Global Precipitation Measurement or GPM core satellite gathered data on its rainfall rates.

How rain is dependent on soil moisture

7 hours ago

It rains in summer most frequently when the ground holds a lot of moisture. However, precipitation is most likely to fall in regions where the soil is comparatively dry. This is the conclusion reached by ...

ESA image: Hungarian mosaic

8 hours ago

This image of Hungary, with the political border in white, is a mosaic of 11 scans by Sentinel-1A's radar from October to December 2014.

User comments : 2

Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Dec 11, 2012
It is interesting to speculate the evolution of a species capable of easily handling the Fe(III) form of iron. Given the enormous advantage from being able to colonize areas of the ocean with low competition, I am surprised it hasn't already happened.

not rated yet Dec 11, 2012
What is the role of iron in these ecosystems? There is no iron in chlorophyll.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.