Ultraviolet radiation drives emission of climate‐relevant gases from marine phytoplankton

Marine phytoplankton contribute about one half of global primary production and play a key role in global biogeochemical cycles. High cell densities in extensive phytoplankton blooms are expected to be modified by global changes in ocean circulation and stratification, acidification and carbonation, solar radiation, temperature and eutrophication. Although, photochemical gas production from chromophoric dissolved organic matter (CDOM) has been widely studied, ultraviolet (UV) effects on emissions from phytoplankton cells themselves have not been fully explored. We therefore investigated UV-driven emissions of carbon monoxide (CO), carbon dioxide (CO2), methane (CH4), ethene (C2H4), ethane (C2H6), and nitrous oxide (N2O) from cell suspensions of 16 phytoplankton species and their filtrates under controlled experimental conditions. These gases make direct or indirect contributions to radiative forcing of the atmosphere or contribute to atmospheric chemistry including stratospheric ozone (O3) depletion. We observed production of CH4, CO, CO2, C2H4 and N2O from cell suspensions and CO, CO2 and N2O after 0.45 μm-filtration to remove phytoplankton cells. CH4 production was only observed with cells present, whereas N2O was still produced after filtration. Production of CO from filtrates was 30-90% of that from cell suspensions in all but two species with a CO2:CO mole ratio from filtrates always below one. Our results clearly demonstrate a need to quantify the production potentials of these climate-relevant gases in situ under natural sunlight using key phytoplankton species, especially those forming blooms which are predicted to change in prevalence and distribution with future global change scenarios.