Cooperative Institute for Research in Environmental Sciences

Ocean Interactions
Ocean and Atmosphere connecting Scientists, Teachers & Students

Phytoplankton and the ocean carbon cycle

Today, we will explain how ocean algae are crucial to clouds.

Over the open ocean, the primary source for sulfur compounds in the atmosphere comes from a algae. Dimethylsulfide (DMS) is a gas and is a by-product of the waste process of algae, and algae are produced in the upper ocean very close to the surface. Some of the DMS which is produced in the water escapes into the atmosphere (there is a 'flux' of DMS from the ocean to the air). Photochemical reactions take place which use the DMS to form particles, which then can become 'cloud condensation nuclei (CCN)'. CCN are sites where cloud droplets form.

Clouds provide essential feedbacks to the Earth climate system, which includes shielding the surface from sunlight, keeping the surface from cooling at night, providing rain, etc. The process of DMS-to-CCN (and therefore the formation of clouds) is quite complex, and there are plenty of unknowns about each step in the process. University of Hawaii scientists Barry Huebert, Baozhong Duan, and Byron Blomquist, along with myself (Jeff Hare) and NOAA PMEL scientist Jim Johson, hope that research conducted on this cruise leads to a better understanding of how much DMS is transfered between the air and sea and to a better understanding of the mechanisms which force the variability in the air-sea DMS flux.

An improved understanding of these processes will lead to better computer models of our Earth System climate. Given the uncertainty of potential Climate Change ('Global Warming'), it is important that scientists be able to accurately represent the Earth System in computer models. For example, warmer oceans might mean more production of algae, which means more DMS flux into the air, which means more CCN and more clouds. The increase in clouds may provide a shielding of sunlight from the surface which may help to offset the warming. However, the processes are too complex to accurately model at this point. Our DMS team hopes to resolve one small piece of the puzzle.

The scientists from the University of Hawaii have brought a unique instrument which is so large it requires its own 20 foot trailer. The instrument is used to measure DMS twenty times per second. Every second, a few liters of air gets sucked into the instrument by using pumps and tubes. The air is then 'ionized' (a proton is added), and the ionized air passes through a 'mass spectrometer'. All molecules have a distinct mass, and we can make use of this fact. The mass spectrometer sorts the molecules by mass, and so Byron, Barry, and Baozhong can see how many molecules of DMS are in the air. They actually count the molecules, and they recently told me that there were about 2000 molecules of DMS passing through their system every second. This is remarkable sensitivity, since there are many billions of total molecules in that sample.