Oxygen dependency of aerobic and anaerobic N-transformations in Oxygen Minimum Zones

Oxygen dependency of aerobic and anaerobic N-transformations in Oxygen Minimum Zones Tim Kalvelage, Marlene Jensen, Gaute Lavik & Marcel Kuypers Recent studies have shown that anammox is tightly coupled to aerobic ammonium oxidation and nitrate reduction in oxygen minimum zones (OMZs). The co-occurrence of aerobic and anaerobic N-cycling processes indicates that anaerobic microorganism like anammox bacteria can tolerate oxygen. Here we performed O2 manipulation experiments (0-25µM O2) with 15N-labelled substrates to investigate the O2-sensitivity of anaerobic and aerobic N-transformations in the Namibian and Peruvian OMZs. Anammox activity decreased with increasing O2 concentration but was still measurable at levels up to ~15 µM of O2. This relatively high O2 tolerance implies that a significantly larger ocean volume might be affected by N-loss than previously assumed Aerobic ammonia oxidizers remained equally active over the entire range of adjusted O2 concentrations hinting at a high affinity for O2. Nitrate reduction to nitrite remained active at ~25 µM of O2. These results provide insight into the possible response of the oceanic N-cycle to the predicted future changes in dissolved O2 due to global warming.