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Millennial‐Scale Changes in Terrestrial and Marine Nitrous Oxide Emissions at the Onset and Termination of Marine Isotope Stage 4

Ice core measurements of the concentration and stable isotopic composition of atmospheric nitrous oxide (N2O) 74,000–59,000 years ago constrain marine and terrestrial emissions. The data include two major Dansgaard‐Oeschger (D‐O) events and the N2O decrease during global cooling at the Marine Isotope Stage (MIS) 5a‐4 transition. The N2O increase associated with D‐O 19 (~73–71.5 ka) was driven by equal contributions from marine and terrestrial emissions. The N2O decrease during the transition into MIS 4 (~71.5–67.5 ka) was caused by gradual reductions of similar magnitude in both marine and terrestrial sources. A 50 ppb increase in N2O concentration at the end of MIS 4 was caused by gradual increases in marine and terrestrial emissions between ~64 and 61 ka, followed by an abrupt increase in marine emissions at the onset of D‐O 16/17 (59.5 ka). This suggests that the importance of marine versus terrestrial emissions in controlling millennial‐scale N2O fluctuations varied in time.