Production of N₂O by ammonia oxidizing bacteria at subfreezing temperatures as a model for assessing the N₂O anomalies in the vostok ice core

It was suggested that the abnormally high N2O values found in 130,000-160,000 year-old Vostok ice core samples, characterized by high δ¹⁵N and low δ¹⁸O values, resulted from in situ microbial N₂O production. To substantiate these observations we obtained new geochemical data from the last glacial period and showed the existence of additional small N₂O anomalies. To test the hypothesis that microbial metabolism could contribute to these anomalies, we developed protocols for examining the ability of Nitrosomonas cryotolerans cells to produce N₂O at subfreezing temperatures. Our results show that these model, frozen cultures produce N₂O at temperatures as low as -32°C.