Oceanic microbes are remnants of Earth’s history – this is how life began and spread. They are invisible to the naked eye, although overall they are so abundant they change the colour of the ocean and can be spotted from satellites.

This invisible life metabolises elements, breathes and generates wastes, and by doing so has shaped much of the functioning of the planet over billions of years. Indeed it still does, e.g., by exchanging chemicals with the atmosphere: removing or releasing greenhouse gases; releasing gaseous essential elements for life, such as sulphur and iodine, and shipping them back to continents that otherwise would have run out of them through erosion; regulating ozone concentration; or making airborne particles (aerosols) that seed cloud formation and brightness, thereby regulating how much sunlight reaches the ocean. It is on this natural setting that humans have perturbed the Earth so profoundly that some advocate we entered a new geological era, the Anthropocene.

We do not yet fully understand the ecophysiological mechanisms that make marine microbes produce reactive trace gases and aerosol precursors, and how important these mechanisms are for the pelagic ecosystem. We have seen that microbes communicate among themselves using chemical signals, similarly to how marine animals use olfactory sensing to forage. We have also seen that oxidative stress drives the production of reactive trace gases and gel-like substances by micro and macroalgae. We have observed that underwater solar radiation plays a critical role through photobiological processes and photochemical reactions, and that trace gases are by-products of tight biogeochemical cycling within planktonic food webs. We are discovering the genes involved, and deciphering their activation switches. And we are finding old and new marine aerosol precursors and tracking their paths in the atmosphere all the way to clouds and climate.