View from the DC-8 research plane as it flies through marine boundary layer. This is the area of the atmosphere near the ocean's surface that affects processes such as cloud formation. Sam Hall
You'll notice the distinctive salty scent of the sea when you stand on the shore of the ocean. Is that a rotting, almost ripe smell? That's sulfur.
The marine plankton inhale more than 20,000,000 tons of sulfur each year into the atmosphere, mostly as dimethyl sulfide. This chemical can be transformed into sulfuric acid in the air. This helps to produce clouds and provides a place for water droplets. This process has a profound impact on the climate, regardless of how large the oceans are.
New research by the University of WisconsinMadison and the National Oceanic and Atmospheric Administration has revealed that more than a third of the DMS emitted in the ocean cannot help create new clouds because it is lost to them. These new findings will significantly change our understanding of how marine life affects clouds. They may also alter how scientists predict how changes in the oceans can impact cloud formation.
Clouds play a significant role in global climate by reflecting sunlight back into space and controlling rain. It is crucial to accurately predict them in order to understand the impacts of climate change.
Tim Bertram, UWMadison professor in chemistry and senior author on the new report, says that "it turns out that this story about cloud formation was really incomplete." "Over the past three to four years, we have been investigating parts of this story with laboratory experiments as well as large-scale field studies. We can now better link the dots between the ocean's emissions and the formation of particulates that promote cloud formation.
Gordon Novak, a UWMadison graduate student, created the analysis with 13 collaborators. It will be published in the Proceedings of the National Academy of Sciences on Oct. 11.
Gordon Novak, the first author of the study, is pictured with the National Oceanic and Atmospheric Administration chemical sensing equipment used in this study. Credit: Gordon Novak
This group of collaborators led by Patrick Veres from NOAA discovered that DMS, on its way to becoming sulfic acid, first becomes a molecule called HPMTF. This was a new discovery. The team used a NASA-owned instrument-laden aircraft to take detailed measurements of the chemicals in the open ocean, both within clouds and under sunlit skies.
"This is a huge DC-8 aircraft. It's a flying laboratory. Bertram says that virtually all the seats have been removed and that very precise chemical instrumentation was installed to allow the team to measure at very low concentrations both the emitted molecules and the chemical intermediates."
The flight data revealed that HPMTF easily dissolves in the water droplets of clouds. This permanently removes the sulfur from cloud nucleation. More HPMTF can survive in cloudy areas to form sulfuric acid, which helps create new clouds.
The team was led by Florida State University collaborators. They accounted for the new measurements in a large-scale global model of ocean atmospheric chemical. This led to the discovery that 36% sulfur from DMS is lost through clouds. The result is that 15% of the sulfur from DMS is also lost to other processes.
"This sulfur loss to the clouds decreases the formation of small particles, so it lowers the formation of cloud nuclei." Bertram says that further research will be needed to determine the impact of cloud brightness on other properties.
Researchers have ignored the impact clouds have on chemical processes in the ocean. This is partly because it is hard to get good data from the cloud layer. The new study demonstrates both the power and importance of the right tools to obtain that data, as well as the important role clouds can play in influencing the processes that create them.
Bertram says, "This work has really opened this area of marine chemical,"
Further investigation: Mechanism deciphered: Organic acids formed in the atmosphere
More information: Rapid cloud removal of dimethyl sulfide oxidation products limits SO and cloud condensation nuclei production in the marine atmosphere, Proceedings of the National Academy of Sciences, doi.org/10.1073/pnas.2110472118 Journal information: Proceedings of the National Academy of Sciences Rapid cloud removal of dimethyl sulfide oxidation products limits SO and cloud condensation nuclei production in the marine atmosphere,
