Icebergs Reveal New Role in Climate Cycles

A team of investigators from the United States has discovered that icebergs floating around in the Southern Ocean, near Antarctica, are not only contributing to sea level rise, but that they also play a previously-unknown role in the global carbon cycle and in climate control.

What the team discovered was that the huge ice blocks tend to dilute the waters through which they pass, while at the same time cooling them considerably. As this happens, the levels of chlorophyll in the seas increase beyond regular levels.

According to experts, this means that the waters around the Southern Ocean become more fertile, and also more capable of storing atmospheric carbon dioxide (CO2). This phenomenon will soon be included in computer models seeking to explain the Earth's carbon cycle.

High chlorophyll levels are indicators that organisms called phytoplankton – the basis of the marine food web – are booming. These microorganisms are the ones responsible for endowing the world's oceans with the ability to absorb CO2.

They use the chemical for photosynthesis, and store it themselves. When they die, they sink to the bottom of the ocean, depositing the carbon at those locations. The more phytoplankton there is, the more CO2 is absorbed, trapped and stored under the waters.

The new study found that “iceberg transport and melting have a role in the distribution of phytoplankton in the Weddell Sea,” which is something researchers had no clue about until now, explains team member John J. Helly.

He is based at the University of California in San Diego (UCSD) and the Scripps Institution of Oceanography (SIO). The expert is also the director of the Laboratory for Environmental and Earth Sciences (LEES), at the UCSD Supercomputer Center.

Details of the new research appear in the latest issue of the top scientific journal Nature Geosciences. The work was funded in part by the US National Science Foundation (NSF). The paper is entitled “Cooling, Dilution and Mixing of Ocean Water by Free-drifting Icebergs in the Weddell Sea.”

“These new findings amplify the team's previous discoveries about icebergs and confirm that icebergs contribute yet another, previously unsuspected, dimension of physical and biological complexity to polar ecosystems,” adds Roberta L. Marinelli.

She holds an appointment as the director of the NSF Antarctic Organisms and Ecosystems Program.

The work also revealed “that icebergs influence oceanic surface waters and mixing to greater extents than previously realized,” adds paper author Ronald S. Kaufmann, who is an associate professor of marine science and environmental studies at the UCSD.