Seas of superoxide

In the past decade, sensitive analytical techniques have enabled a new look at the distributions, sources and chemical reactivity of superoxide (O₂⁻) in the ocean. Until recently superoxide was thought to form solely through photochemical reactions in the surface ocean, but now biological processes are considered to be equally important in generating superoxide. On page 1223 of this issue, Diaz et al. (1) show that heterogeneous bacteria produce superoxide and potentially represent a substantial source of superoxide in the sea.