Single-celled marine organism first to be found releasing oxygen in the dark

A previously unknown biological pathway allows a widespread type of oceanic archaeon to release both oxygen and nitrogen in the dark – the first time such a phenomenon has been seen in nature in an anoxic environment. The process, whose details are not yet fully understood, could transform scientists’ understanding of the cycle of key nutrients through oceans.

Ammonia-oxidising archaea are among the most abundant microbes in the world’s oceans. They obtain energy by using oxygen to oxidise ammonia to nitrite. However, they have been found in ecosystems with no detectable oxygen. ‘Are they settling out from the overlying water column or is there some small or periodic introduction of oxygen that we just don’t see?’ says Donald Canfield of the University of Southern Denmark. ‘Those are the kinds of explanations that people would typically use.’