UTS MARINE BIOLOGY FACT SHEET Topic: Phytoplankton and Cloud Formation 1.The CLAW Hypothesis Background: In 1987 four people (Charlson, Lovelock, Andrea, & Warren) introduced a theory that a natural gas called Dimethylsulfide (DMS), produced by microscopic plants in the ocean (phytoplankton), was a major contributor to the formation of clouds in the atmosphere. This theory was named the CLAW Hypothesis (from the first letter of each of their surnames). Fast facts: . Phytoplankton produce DMSP (dimethylsulphoniopropionate), an organic sulphur compound, which is converted to DMS in the ocean. The majority of this DMS is consumed by bacteria but around 10% escapes into the atmosphere. When DMS is released into the air, a chemical reaction takes place (called an oxidation reaction) and sulphate aerosols are formed – a gas which acts as cloud condensation nuclei (CCN). This means it combines with water droplets in the atmosphere to form clouds. As a result, more clouds increase the reflectivity of the sun’s rays (earth albedo) which decreases the amount of light reaching the earth’s surface, and contributes to cooling the overall climate. A decrease in light causes a decrease in phytoplankton productivity of DMS. (Phytoplankton are primary producers which rely on light to function). This sequence of events is called a Negative Feedback Loop, because phytoplankton increase DMS production but DMS forms clouds which lowers the amount of light reaching the earth, resulting in less phytoplankton and less DMS. DMS emissions are a key step in the global sulphur cycle, which circulates sulphur throughout the earth, oceans, and atmosphere. It is an essential component in the growth of all living things. Did you know… DMS has a very strong smell which helps some marine animals and microbes find their food Diagram of the CLAW Hypothesis (adapted from Absolute Astronomy <http://www.absoluteastronomy.com/topics/CLAW_ hypothesis>) Learn more: Links/References 1. Charlson RJ, Lovelock JE, Andrea MO, Warren SG (1987) Oceanic phytoplankton, atmospheric sulphur, cloud albedo and climate. Nature 326: 655-661 2. Hill RW, Dacey JWH, Krupp DA (1995) Dimethylsulfoniopropionate in reef corals. Bulletin of Marine Science 57: 489-494 3. Raina J-B, Dinsdale EA, Willis BL and Bourne DG (2009) Do the organic sulfur compounds DMSP and DMS drive coral microbial associations? Trends in Microbiology 18: 101-108 4. Schwartz SE (1988) Are global cloud albedo and climate controlled by marine phytoplankton? Nature 336: 441-445 5. Chemoattraction to Dimethylsulfoniopropionate Throughout the Marine Microbial Food Web,” by Justin R. Seymour, Rafel Simó, Tanvir Ahmed and Roman Stocker. Science, July 16, 2010. .