Origins and variations of nitrate in south polar precipitation

Abstract

South polar firn cores spanning the last millennium have been analyzed to determine the nitrate background level of high‐latitude precipitation and its temporal variations. The resulting data reveal no evidence of a positive correlation between solar activity (11‐year solar cycle, low solar activity time periods, and solar proton events) and the NO3 content of south polar snow. These data therefore suggest that NOx production in the upper stratosphere, mesosphere, and thermosphere does not contribute significantly to the antarctic NO3 budget. This study of the NO3 content of high latitude precipitation suggests a major contribution by lightning (from a third to a half of the total) and by NOx produced in the lower stratosphere (approximately a third from N2O oxidation and to a lesser extent galactic cosmic rays) to the NO3 budget of this background atmosphere, the remaining portion being related to the present NOx surface sources of the southern hemisphere. For the first time, our data point to a decrease of NO3 content when very large amounts of sulfuric acid are present in South Pole snow layers. This observation suggests a possible interaction (via the hydroxyl radical) between S‐ and N‐derived species when large quantities of SO2 are injected by volcanic eruptions. Although the deposition mechanism of HNO3 in South Pole snow layers is far from well understood, our data suggest that only a minor amount of this compound is deposited directly on surface snow layers. Finally, the role played by particles (volcanic ash, terrestrial impurities, or ice particles) to enhance the uptake of odd nitrogen from the atmosphere by heteregeneous processes is discussed. In particular, it is suggested that in late winter, under certain meteorological conditions leading to ice particle formation, a significant uptake of HNO3 from the lower stratosphere can occur.

Loss of volatile acid species from upper firn layers at Vostok, Antarctica

“…We even suspect that some additional HCI is formed from marine NaCI and expelled to the border of the acid peak. This general effect caused by volcanic acidity has also been detected also in Greenland ice [Laj et al, 1993;De Angelis and Legrand, 1994;Yang et al, 1996] and Antarctic ice cores [Legrand and Kirchner, 1990]. It has sometimes been attributed to stratospheric, tropospheric, or postdeposition processes.…”

Spatial variability of climate and past atmospheric circulation patterns from central West Antarctic glaciochemistry

“…Surface values at the CWA sites show either a distinct recent peak or a well-developed upward trend confirming the summer season peak. Nitrate peaks during spring/summer in Antarctica [Mayewski and Legrand, 1990; Mulvaney and Wolff, 1993;Whitlow et al, 1992] though the linkages between atmospheric NO3 concentrations and snow concentrations are not well understood [Legrand and Kirchner, 1990;Wolff, 1995]. The spring/summer NO3 peak is likely related to the sedimentation of polar stratospheric clouds (PSCs) which releases NO 3 into the polar troposphere where it can be removed by precipitation to the snow surface [Mayewski and .…”

Supernovae and solar cycles embedded in a Dome F ice core

“…Rood et al (1979) were the first to suggest that nitrate ion (NO − 3 ) concentration spikes observed in the depth profile of a South Pole ice core might correlate with the known historical supernovae: Tycho (AD 1572), Kepler (AD 1604) and SN 1181 (AD 1181). Their findings, however, were not supported by subsequent examinations by different groups using different ice cores (e.g., Risbo et al 1981;Herron 1982;Legrand & Kirchner 1990), and the results have remained controversial and confusing (Green & Stephenson 2004;Dreschhoff & Laird 2006). Motizuki et al (2009) presented a precision analysis of an ice core drilled in 2001 at Dome F station in Antarctica.…”