Millennial-Scale Changes in Atmospheric Nitrous Oxide During the Holocene

Abstract

Nitrous oxide (N2O) is an important greenhouse gas which destroys the ozone in the stratosphere. Primary sources of atmospheric N2O are nitrification and denitrification in terrestrial soils and the ocean, and the main sink is photolysis in the stratosphere. Studies have mostly focused on the climate-related response of N2O during glacial-interglacial periods. However, its mechanism of variation during the Holocene remains unclear. We present a high-resolution N2O record from the South Pole Ice (SPICE) core covering the Holocene epoch. The millennial-scale N2O trend agrees with existing records. We constructed a Holocene composite consisting of the new N2O measurements in SPICE and existing records from other ice core sites. The N2O composite reveals four distinct periods of N2O variation during 11.5-10.0 ka, 10.0-6.2 ka, 6.2-2.2 ka, and 2.2-1.4 ka, including two maxima in 11.0-10.0 ka and 3.0-2.2 ka and minima in 8.8-6.2 ka and approximately 1.4 ka. Apart from these, our new high-resolution record from SPICE shows a short-term N2O decrease around 2.8 ka which is not observed in other records possibly due to lower sample resolution and/or higher age smoothing. Comparison of our new Holocene N2O composite with the paleo-proxy records suggests the plausible linkage of major monsoon (Asian, North African, South and North American, and Australian-Indonesian monsoon) and upwelling (Arabian Sea and Eastern Tropical South Pacific) regions in regulating the atmospheric N2O during the Holocene. Nitrous oxide (N2O) is an important greenhouse and ozone-depleting gas. The growing level of N2O in the atmosphere is of global concern, and records of past N2O variations can provide an essential context for understanding the links between N2O and climate change. In this study, we report a new, high-quality N2O record covering the Holocene epoch using an ice core obtained from the South Pole. Our record shows four important periods of N2O variation during 11.5-10.0 ka, 10.0-6.2 ka, 6.2-2.2 ka, and 2.2-1.4 ka. These include two local N2O maxima in 11.0-10.0 ka and 3.0-2.2 ka and minima in 8.8-6.2 ka and approximately 1.4 ka. Comparison with climate records suggests that the variation in monsoon precipitation and ocean productivity contributed to centennial- to millennial-scale N2O variations during the Holocene. High-resolution N2O record from the South Pole Ice core covering the Holocene epoch is investigated for N2O variationInsight into the key drivers of atmospheric N2O on millennial time scales during the Holocene is providedN2O exhibits two local maxima during 11.0-10.0 ka and 3.0-2.2 ka, and two local minima during 8.8-6.2 ka and at around 1.4 ka