Centennial variations of atmospheric nitrous oxide during the past two millennia

Abstract

Atmospheric nitrous oxide (N2O) is an important long-lived greenhouse gas and effective stratospheric ozone destroyer. Despite its essential roles in climate, the control mechanisms of atmospheric N2O remains poorly understood. In order to reconstruct atmospheric N2O during pre-industrial era, I precisely analyzed ice core samples from NEEM site in North Greenland and Styx Glacier in East Antarctica. The N2O records cover the last two millennia with a precision better than 1.9 ppb and averaged temporal resolution of ~10 years, sufficient to constrain centennial-scale variations. The N2O records from Styx and NEEM ice commonly show distinctive centennial-scale variations. The timings of rapid N2O changes are coincident each other. The rates of rapid N2O changes are comparable to current ones which is strongly affected by anthropogenic sources. These findings suggest that there was significant natural and/or anthropogenic variability of atmospheric N2O during pre-industrial era. In these centennial-scale N2O variation, the portion of oceanic source changes seemed to be more significant than terrestrial sources, although temperature and precipitation changes in the terrestrial regions also seemed relevant with short-term N2O change in part. The negative correlation with sea surface temperature near Peruvian margin and productivity and denitrification reconstruction data suggests enhanced oceanic N2O flux during the La Niña-like state, and possibly, the solar activity changes contributed to the centennial N2O variation as an ultimate cause.