An unaccounted for N2O sink in the surface water of the eastern subtropical South Pacific: Physical versus biological mechanisms

摘要

Nitrous oxide (N2O) is a trace gas affecting atmospheric radiative forcing through its greenhouse effect in the troposphere and destroying the ozone in the stratosphere. The oceans account for one-third of the global atmospheric N2O emissions, in which they are primarily cycled by nitrification and denitrification, with high N2O production in the subsurface waters. The surface waters are generally reported to be in equilibrium or slightly supersaturated with respect to the atmosphere. However, surface N2O sub-saturations have been observed in several regions of the world's oceans, such as off south-central Chile, which is bathed by the Sub-Antarctic Water Mass (SAAW), where N2O subsaturations as low as 35% have been registered during the austral spring and summer. An analysis of the mechanisms driving such surface N2O subsaturations (physical or biological) showed that physical mechanisms were not responsible for the high surface N2O deficit. In contrast, in situ potential experiments in surface waters with 151120 addition showed an active biological N2O fixation (between 0.43 and 87.34 nmol/L/d), with the highest N2O fixation rates associated with the SAAW (25.25-25.75 kg/m(3)).