Nitrous oxide measurements during EIFEX, the European Iron Fertilization Experiment in the subpolar South Atlantic Ocean

We measured the vertical water column distribution of nitrous oxide (N 2 O) during the European Iron Fertilization Experiment (EIFEX) in the subpolar South Atlantic Ocean during February/March 2004 (R/V Polarstern cruise ANT XXI/3). Despite a huge build‐up and sedimentation of a phytoplankton bloom, a comparison of the N 2 O concentrations within the fertilized patch with concentrations measured outside the fertilized patch revealed no N 2 O accumulation within 33 days. This is in contrast to a previous study in the Southern Ocean, where enhanced N 2 O accumulation occurred in the pycnocline. Thus, we conclude that Fe fertilization does not necessarily trigger additional N 2 O formation and we caution that a predicted radiative offset due to a Fe‐induced additional release of oceanic N 2 O might be overestimated. Rapid sedimentation events during EIFEX might have hindered the build‐up of N 2 O and suggest, that not only the production of phytoplankton biomass but also its pathway in the water column needs to be considered if N 2 O radiative offset is modeled.