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Temporal changes in the magnitude and geographic distribution of different sources of nitrous oxide (N₂O) are not well constrained. To better understand the dynamics of N₂O in the atmosphere over the last century, we have reconstructed the mole fraction, δ¹⁵N^bulk, δ¹⁸O, and δ¹⁵N^SPvalues of N₂O from ice cores, firn air archives, and modern atmospheric samples. We have provided new firn air records from the Styx Glacier, Antarctica, and the North Greenland Eemian Ice drilling Project, and updated the firn air transport modeling of the published records. The composite reconstruction shows that the N₂O growth rates were 0.26 ± 0.05, 0.15 ± 0.05 and 0.75 ± 0.01 ppb yr⁻¹during 1850–1930 (P1), 1931–1965 (P2) and 1966–2021 CE (P3), respectively. The temporal slope found in a linear least squares fit in δ¹⁵N^bulkand δ¹⁸O were −0.010 ± 0.025 and −0.004 ± 0.031‰ yr⁻¹, −0.014 ± 0.013 and −0.009 ± 0.017‰ yr⁻¹, and −0.040 ± 0.013 and −0.022 ± 0.005‰ yr⁻¹during P1, P2 and P3 phases, respectively. Overall, a significant long‐term trend was not observed in δ¹⁵N^SPdata. Two‐box model calculations using N₂O mole fraction suggest that the total N₂O flux (F_T) at 2015 CE was 17.5 ± 1.1 TgN yr⁻¹, where flux from the natural (F_N) and anthropogenic (F_A) sources were ∼60% and 40% ofF_T, respectively, and the contribution ofF_Awas ∼30% ofF_Tat 1900 CE. EstimatedF_Aand δ¹⁵N^bulkof atmospheric N₂O suggest that the anthropogenic emissions from continental regions were 12%, 25% and 76% ofF_Aduring P1, P2 and P3 phases, respectively.

 

Marine sediments, speleothems, paleo-lake elevations, and ice core methane and δ¹⁸O of O₂ (δ¹⁸O_atm) records provide ample evidence for repeated abrupt meridional shifts in tropical rainfall belts throughout the last glacial cycle. To improve understanding of the impact of abrupt events on the global terrestrial biosphere, we present composite records of δ¹⁸O_atm and inferred changes in fractionation by the global terrestrial biosphere (Δε_LAND) from discrete gas measurements in the WAIS Divide (WD) and Siple Dome (SD) Antarctic ice cores. On the common WD timescale, it is evident that maxima in Δε_LAND are synchronous with or shortly follow small-amplitude WD CH₄ peaks that occur within Heinrich stadials 1, 2, 4, and 5 – periods of low atmospheric CH₄ concentrations. These local CH₄ maxima have been suggested as markers of abrupt climate responses to Heinrich events. Based on our analysis of the modern seasonal cycle of gross primary productivity (GPP)-weighted δ¹⁸O of terrestrial precipitation (the source water for atmospheric O₂ production), we propose a simple mechanism by which Δε_LAND tracks the centroid latitude of terrestrial oxygen production. As intense rainfall and oxygen production migrate northward, Δε_LAND should decrease due to the underlying meridional gradient in rainfall δ¹⁸O. A southward shift should increase Δε_LAND. Monsoon intensity also influences δ¹⁸O of precipitation, and although we cannot determine the relative contributions of the two mechanisms, both act in the same direction. Therefore, we suggest that abrupt increases in Δε_LAND unambiguously imply a southward shift of tropical rainfall. The exact magnitude of this shift, however, remains under-constrained by Δε_LAND. 

Water-stable isotopes in polar ice cores are a widely used temperature proxy in paleoclimate reconstruction, yet calibration remains challenging in East Antarctica. Here, we reconstruct the magnitude and spatial pattern of Last Glacial Maximum surface cooling in Antarctica using borehole thermometry and firn properties in seven ice cores. West Antarctic sites cooled ~10°C relative to the preindustrial period. East Antarctic sites show a range from ~4° to ~7°C cooling, which is consistent with the results of global climate models when the effects of topographic changes indicated with ice core air-content data are included, but less than those indicated with the use of water-stable isotopes calibrated against modern spatial gradients. An altered Antarctic temperature inversion during the glacial reconciles our estimates with water-isotope observations.