Award: OCE-1029900

Motivation and background Phytoplankton are microscopic plants of the ocean: they combine energy from sunlight with dissolved carbon dioxide and nutrients to reproduce, creating new organic molecules. Some of this organic material is consumed by other plankton, which are in turn consumed by fish, fuelling an important resource for humans. A fraction of the organic matter sinks to the deep ocean where it leads to a store ofdissolved inorganic carbon that keeps atmospheric CO2 relatively low and the climate cooler than it otherwise would be. There is a very high diversity of phytoplankton, with very different lifestyles and implications for fisheries and ocean carbon storage. As a community, we are currently seeking to map out where these different types live (their biogeography) and to understand why they live in those particular environments. The "traits" of the plankton are characteristics of individuals which affect their interaction with the environment. Intellectual Merit We have examined the relationships between specific traits (for example cell size) and the biogeography of particular plankton species. We have developed mathematical models which encapsulate key traits and which can simulate their distribution in a virtual ocean. The success of such a model indicates a degree of qualitative and quantitative understanding of the real system. In this way, we have developed models which can predict the observed seasonal and regional distributions of two groups of phytoplankton, diatoms and dinoflagellates in the Atlantic Ocean, as well as the distribution of cell-sizes within those populations. By combining these simulations with analysis of observed populations, we have shown how a combination of nutrient supply and predation set the size structure of marine plankton populations. We have, for the first time, indicated that mixotrophy (combining photosynthesis and predation) leads to larger plankton and enhanced storage of carbon on the global scale. Broader Impacts A key outreach effort associated with this project has been to illustrate to the general public how plankton populations in the ocean (like trees on land) are arranged geographically into "biomes" (i.e. regions dominated by similar types). To this end we have worked with Dr. Jen Frazier and colleagues at the San Francisco Exploratorium to produce a hands-on exhibit for their Living Liquids display. The table-top exhibit shows animations of plankton populations in our global simulations. Visitors use a special maginifying glass throug which the exhibit reveals something of the diversity and cell size of the phytoplankton populations at the location where the user places it. See a video about the exhibit at http://www.exploratorium.edu/explore/videos/plankton-populations-exhibit Last Modified: 01/19/2015 Submitted by: Michael J Follows