Nitrous oxide dynamics in low oxygen regions of the Pacific: insights from the MEMENTO database

[摘要] The eastern tropical Pacific (ETP) is believed to be one of the largestmarine sources of the greenhouse gas nitrous oxide (N₂O). FutureN₂O emissions from the ETP are highly uncertain because oxygen minimumzones are expected to expand, affecting both regional production andconsumption of N₂O. Here we assess three primary uncertainties in howN₂O may respond to changing O₂ levels: (1) the relationship betweenN₂O production and O₂ (is it linear or exponential at low O₂concentrations?), (2) the cutoff point at which net N₂O productionswitches to net N₂O consumption (uncertainties in this parameterisationcan lead to differences in model ETP N₂O concentrations of more than20%), and (3) the rate of net N₂O consumption at low O₂. Basedon the MEMENTO database, which is the largest N₂O dataset currentlyavailable, we find that N₂O production in the ETP increases linearlyrather than exponentially with decreasing O₂. Additionally, netN₂O consumption switches to net N₂O production at ~ 10 μM O₂,a value in line with recent studies that suggestconsumption occurs on a larger scale than previously thought. N₂Oconsumption is on the order of 0.01–1 mmol N₂O m⁻³ yr⁻¹ inthe Peru-Chile Undercurrent. Based on these findings, it appears that recentstudies substantially overestimated N₂O production in the ETP. In lightof expected deoxygenation and the higher than previously expected point atwhich net N₂O production switches to consumption, there is enoughuncertainty in future N₂O production that even the sign of futurechanges is still unclear.

[学科分类] 地球化学与岩石