N2O changes from the Last Glacial Maximum to the preindustrial - Part I: Quantitative reconstruction of terrestrial and marine emissions using N2O stable isotopes in ice cores.

Using high precision and centennial resolution ice core information on atmospheric nitrous oxide concentrations and its stable nitrogen and oxygen isotopic composition, we quantitatively reconstruct changes in the terrestrial and marine N₂O emissions over the last 21,000 years. We show that N₂O emissions from land and ocean increased largely in parallel by 1.7±0.3TgNyr^-1 and 0.7±0.3TgNyr^-1 over the deglaciation, respectively. However, during the abrupt Northern Hemisphere warmings at the onset of the B⊘lling/Aller⊘d and the end of the Younger Dryas, terrestrial emissions respond more rapidly to the northward shift in the Intertropical Convergence Zone connected to the resumption of the Atlantic Meridional Overturning Circulation. 90% of these large step increases were realized within maximum two centuries. In contrast, marine emissions start to slowly increase already many centuries before the rapid warmings, possibly connected to a re-equilibration of subsurface oxygen in response to previous changes. Marine emissions decreased, concomitantly with changes in atmospheric CO₂ and δ¹³C(CO₂), at the onset of the termination and remained minimal during the early phase of Heinrich Stadial 1. During the early Holocene a slow decline in marine N₂O emission of 0.4TgNyr^-1 is reconstructed, suggesting an improvement of subsurface water ventilation in line with slowly increasing Atlantic overturning circulation. In the second half of the Holocene total emissions remain on a relatively constant level, however with significant millennial variability which is currently still difficult to attribute to marine or terrestrial sources. Our N₂O emission records provide important quantitative benchmarks for ocean and terrestrial nitrogen cycle models to study the influence of climate on nitrogen turnover on time scales from several decades to glacial/interglacial changes. [ABSTRACT FROM AUTHOR]