Floaters vs. sinkers: How do marine phytoplankton combat the biological pump?

Industrialisation has short-circuited the Earth's carbon cycle; converting ~0.4 trillion tons of organic carbon back to CO2 from the burning of fossil fuels. The most rapidly cycled pool of carbon is in the Oceans. In the surface oceans, single celled microbes convert CO2 to particulate organic carbon (POC) through photosynthesis. POC can sink into the ocean interior, through the activity of the biological carbon pump (BCP), effectively storing it for hundreds of years. Without the BCP, the predicted atmospheric CO2 concentration would be doubled.

We currently have a poor understanding of the processes that determine the strength of the BCP However, it is thought that buoyancy traits of surface marine phytoplankton plays a key role. These organisms face a consistent challenge to fight the BCP and maintain themselves in the upper surface ocean, where light can drive photosynthesis. Meanwhile, many biotic and abiotic stresses act upon phytoplankton to force them downward. We have evidence that the propensity to combat the activity of the BCP is genetically encoded. This project seeks to unravel the genetic mechanisms that phytoplankton employ to fight the BCP and understand how external stresses can overpower these mechanisms. The project combines cutting-edge high-throughput genetics with whole genome sequencing to identify genes required for buoyancy in model marine phytoplankton. These genes are then validated by standard genetic manipulation to test the effect of a range of abiotic and biotic stressors on these mutants. The data will have strong implications for our understanding of the Earth's carbon cycle.