A role for DMS in regulating climate was proposed by Robert Charlson, James Lovelock, Meinrat Andreae and Stephen Warren in the 1980s. According to the CLAW hypothesis, warming oceans lead to more growth of green phytoplankton, which in turn release a precursor to DMS when they die. Rising levels of DMS in the atmosphere cause cloud formation, and clouds reflect sunlight, helping to cool the planet. It's a negative feedback loop to control the planet's temperature.
Savoca and Nevitt looked at 50 years of records on seabirds' stomach contents, combined with Nevitt's experimental results of which species use DMS to forage. They found that species that respond to DMS overwhelmingly fed on krill, which graze on phytoplankton.
On land, there are several known examples of plants that respond to attack by insects by producing chemicals that attract predators that eat those insects. Nevitt and Savoca propose the same thing happens in the open ocean: when phytoplankton come under attack by krill, the DMS released as they die attracts predators that eat the krill.
The birds have something else to contribute. The Southern Ocean lacks large land masses, and is relatively poor in iron, which has to be washed out from land by rivers. Krill are rich in iron, but birds can absorb relatively little of it so the rest is excreted back into the ocean, promoting plankton growth.
The work suggests that by linking predatory seabirds and phytoplankton the top and bottom levels of the food chain DMS plays an important role in the ocean ecosystem, which affects climate by taking up carbon, as well as a physical role in generating clouds, Nevitt said.
"Studying how seabirds use scent cues to forage has shown us a mechanism by which the seabirds themselves contribute to climate regulation. That's not what we expected, but I really think our results will have global significance," she said.<
|Contact: Andy Fell|
University of California - Davis