Voyage to Southern Ocean Aims to Understand Air-sea Fluxes of Greenhouse Gases

February 25, 2008

Study area, and Western hemisphere wind speeds, during March. Hotter colors denote higher winds. Courtesy NASA/Scatterometer Climatology of Ocean Winds. (Click for a larger image)

 

High winds and big waves are part of the data—and the challenge

Punta Arenas, Chile, Feb. 28, 2008 ---Scientists from over a dozen institutions will embark today from this port on the tip of South America to spend 42 days amid the high winds and big waves of the Southern Ocean, where they will make groundbreaking measurements to explain how large amounts of climate-affecting gases move between atmosphere and sea, and vice-versa. Researchers from Columbia University’s Lamont-Doherty Earth Observatory are taking a leading role in the expedition.

The cruise should provide important information on factors controlling the flux of the greenhouse gas carbon dioxide between the ocean and atmosphere, said Lamont geochemist David Ho, the cruise’s chief scientist and head of its science-planning committee. Comprising 30 percent of the surface area of global seas, “the Southern Ocean is a source of great uncertainty,” he said. “So it’s potentially important to our understanding of the global system.”

Humans currently put about 8 billion metric tons of CO2 into the atmosphere each year, mainly by fossil-fuel burning and deforestation. About a quarter is thought to be absorbed by the world's oceans, and a quarter by plants or other components of land. The rest stays in the air—much of the reason why atmospheric CO2 is now increasing and climate is warming. However, there are huge uncertainties in the calculations—made so far mostly through indirect means--and fluxes seem highly variable from year to year, with some parts of the oceans habitually giving up CO2 while others absorb it. (The Southern Ocean usually absorbs it.) "Understanding how atmospheric carbon dioxide reacts with these cold surface waters is important for determining how the ocean uptake of carbon dioxide will respond to future climate change,” said Christopher Sabine, an oceanographer at the U.S. National Oceanic and Atmospheric Administration (NOAA) who is co-chief scientist for the cruise. NOAA, NASA and the National Science Foundation are cosponsoring the voyage.

size="2">Mean annual carbon-dioxide flux between oceans and air, 1995. Cool-colored areas absorb CO2; hot-colored areas emit it. Courtesy Lamont-Doherty Earth Observatory.

 

About 30 scientists will focus their study on an area in the western Atlantic sector of the Southern Ocean, more than 1,000 miles east of Punta Arenas, aboard the 274-foot NOAA ship Ronald Brown. Here high, freezing winds unimpeded by landmasses roar much of the time, and waves can routinely top 30 feet. “The conditions are a little grim, but it’s ideal for study,” said Ho. He said that higher wind speeds correlate with faster exchange of gases, but there have been few studies aimed at directly measuring these exchanges under real-world conditions. The scientists say that wind itself does not drive gas exchange; the drivers are hard-to-observe phenomena driven by the wind, including turbulence and bubbles created by breaking waves. To examine these mechanisms, the scientists will dangle arrays of sophisticated instruments just above the water surface, and in the water column. “That will be a challenge, since the bow will be plunging off those big waves,” noted Sabine.

Another part of the team will measure the amount of phytoplankton in the water, by looking at optical properties such as ocean color, which is an indication of chlorophyll content. Phytoplankton takes up carbon during photosynthesis, and thus can influence surface ocean CO2 concentrations. “NASA’s ongoing effort to understand the global carbon cycle will benefit from the data this cruise will produce,” said Paula Bontempi, manager of NASA’s ocean biology and biogeochemistry research program. "NASA's global satellite observations of ocean color will be improved, as we validate what our space-based sensors see with direct measurements taken at sea."

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Other Lamont staff aboard the ship will be physical oceanographer Chris Zappa, who will study waves and turbulence; Paul Schmieder and Matthew Reid, who work in Ho's research group, and who will use tracers to measure gas exchange; and Bob Vaillancourt and Veronica Lance of the Biology & Paleo Environment division, who will investigate phytoplankton. Geochemists Wade McGillis and Peter Schlosser, who study air-sea gas exchanges, are principal investigators for the experiment, but will not participate in the cruise itself. The experiment builds on previous work on air-sea gas exchange by Lamont scientists Wallace Broecker and Bill Smethie, and global carbon-flux maps created by Doherty senior scholar Taro Takahashi.

“We know the world’s oceans play a key role in controlling how much carbon dioxide stays in the atmosphere, and yet we do not understand how,” said Lamont director G. Michael Purdy. “Lamont scientists are playing leadership roles in tackling these most fundamental of questions.”

The expedition is officially known as the Southern Ocean Gas Exchange Experiment, or GasEx III. It follows two similar experiments: GasEx I, which was conducted in the north Atlantic in 1998; and GasEx II, in the equatorial Pacific in 2001.

In order to keep the public informed of this important mission, the scientists will be available for remote interviews, and will feed a daily blog to the expedition’s website: http://so-gasex.org.

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