Life in the dead zones: Oceanic oxygen minimum zones as hotspots of marine biogeochemistry
By Professor Bo Thamdrup, Nordcee, Faculty of Science, University of Southern Denmark
Almost 100 years ago, the Dana expeditions provided the first report that parts of the open ocean contain ”virtually no oxygen at all”. We now know that waters with severe oxygen depletion are found in the eastern tropical Pacific and the northern Indian Ocean, and that these waters, although often referred to as ”dead zones”, house a diverse assembly of microbes which contribute substantially to the biogeochemical cycling of, e.g., nitrogen and methane in the oceans. However, we are only beginning to understand which microbes carry out specific processes, and how this activity is regulated by environmental factors and microbial interactions. The importance of these questions is emphasized by observations of an expansion of the oxygen minimum zones over recent decades and predictions of further growth in the future. I present examples of our recent investigations of microbial nitrogen and methane cycling in oxygen minimum zones, which have revealed that novel and highly specialised types of microbes play key roles, and that oxygen even at extremely low concentrations exerts strong control on the microbial processes. I will discuss the implications of these discoveries for the role of the oxygen minimum zones in marine environments the future.