Research Highlights

The Role of Ice in the Acceleration of Underwater Photosynthesis (2010.6.1)

2010-09-02 953

A Newly Discovered Mechanism May Lead to Climate RegulationAteam of environmental

photochemists led by Professor Wonyong Choi of POSTECH has succeeded in explaining how natural ice in Polar Regions can provide the ocean with bioavailable iron content, which ultimately contributes to the prevention of global warming. This achievement in research has gained substantial attention from the international community as it was introduced in several well-known publications in the field of science and technology such as the May 6th issue of Environmental Science & Technology, and the May 17th issue of Chemical & Engineering News, a recent newsletter for the American Chemical Society (ACS). Moreover, the May 28th issue of Science particularly selected the study as its Editors’ Choice, and provided a brief summary.

According to previous studies, the aqueous Fe(II) normally becomes available to phytoplankton when dust blows in by the wind, or the outflows of rivers let the Fe(III) oxide particles flow into the ocean. But the phytoplankton needs the iron oxides to be in a more soluble Fe(II) state, because they are unable to access the oxides when in a Fe(III) insoluble state. Iron oxides are the main content of mineral dust particles among the atmosphere, and the main provider of iron to the phytoplankton in the open ocean, but in order to intake the iron content, they must undergo a photochemical, biological transformation reaction. The major contributor in this particular process is sunlight. The electrons coming from sunlight transform the Fe(III) into Fe(II). Also, when bioavailable iron or aqueous Fe(II) is scarce in ocean waters, the primary productivity in the marine environment becomes limited.

But Professor Choi has stated that the ecology in polar settings is quite different from other regions because of the extremely low temperature. His study shows that before the iron particles enter the water, they are most likely to freeze into the ice or snow that exists in thick layers. Professor Choi has hypothesized that ice may be a crucial element in the process. “In Polar Regions, the sun constantly irradiates the surface for six months and most of the ground is covered in ice and snow,” said Professor Choi. “So I wondered what kind of unique chemistry might happen in that environment.”

Professor Choi and his research group proposed that photoreduction may occur more quickly when ice is involved because of a concentration effect. When the water freezes, the iron oxide particles get pushed out of the orderly ice lattice and become condensed in an area around the boundaries of the ice crystals that have liquid-like characteristics. These narrow channels are called grain boundary regions. Professor Choi has concluded that ice makes charge transfer more efficient by bringing iron oxide particles closer to electron donors, such as organic acids or other iron oxide particles.

An article in the journal Environmental Science & Technology reported that Professor Choi and his colleagues have been comparing the photoreduction of iron oxides caught in ice to those contained in liquid water. Both samples were irradiated with ultraviolet light for 48 hours in the presence of formic acid, which is an organic acid frequently seen in droplets of cloud water. The researchers were then able to observe greater than 10 times more Fe(II) ions in the ice than in liquid water. A similar experiment was conducted under natural sunlight outside the Korean Polar Research Institute’s Dasan station in Ny-Alesund, and the researchers discovered that ice accelerated photoreduction about five times more over liquid water.

This research achievement is significant in the sense that it discovered the role of ‘ice’ in the process of iron oxides transforming into a suitable form to nourish phytoplankton. Since the phytoplankton absorbs carbon dioxide content in the atmosphere and then stores it in seawater, the researchers pointed out that the process contributes to the prevention of global warming. “This unexpected discovery of the role of ice seems to have drawn domestic and worldwide attention on me,” said Professor Choi. “I believe this discovery will become of great help in enhancing the capability of microorganisms in performing photosynthesis.”

Professor Choi’s research team was under support of the Ministry of Education, Science and Technology of Korea, the Korean Polar Research Institute, and certain research support projects including the SRC project under the National Research Foundation of Korea.