Science http://dx.doi.org/10.1126/science.1208239 (2011)

About a third of all atmospheric nitrous oxide originates in the oceans, where, it had been believed, bacteria produce the majority of this potent greenhouse gas. An analysis, however, shifts the blame to another group of single-celled microorganisms more closely related to eukaryotes — archaea.

Alyson Santoro, from the Woods Hole Oceanographic Institution, and colleagues cultured archaea from the Pacific Ocean in the laboratory to investigate their role in nitrous oxide cycling. They also undertook nitrogen- and oxygen-isotope analyses to investigate the dominant origin of marine nitrous oxide.

The results indicate that nitrous oxide produced by archaea through the oxidation of ammonia has an isotopic signature more similar to that found in ocean surface waters than the signature produced by bacteria. This finding suggests that archaea, rather than bacteria, are responsible for most of the nitrous oxide released from the oceans into the atmosphere.