Very old firn air linked to strong density layering at Styx Glacier, coastal Victoria Land, East Antarctica

Abstract

Abstract. Firn air provides plenty of old air from the near past, and can therefore be useful for understanding human impact on the recent history of the atmospheric composition. Most of the existing firn air records cover only the last several decades (typically 40 to 55 years) and are insufficient to understand the early part of anthropogenic impacts on the atmosphere. In contrast, a few firn air records from inland sites, where temperatures and snow accumulation rates are very low, go back in time about a century. In this study, we report an unusually old firn air effective CO2 age of 93 years from Styx Glacier, near the Ross Sea coast in Antarctica. This is the first report of such an old firn air age (>55 years) from a warm coastal site. The lock-in zone thickness of 12.4 m is larger than at other sites where snow accumulation rates and air temperature are similar. High-resolution X-ray density measurements demonstrate a high variability of the vertical snow density at Styx Glacier. The CH4 mole fraction and total air content of the closed pores also indicate large variations in centimeter-scale depth intervals, indicative of layering. We hypothesize that the large density variations in the firn increase the thickness of the lock-in zone and, consequently, increase the firn air ages because the age of firn air increases more rapidly with depth in the lock-in zone than in the diffusive zone. Our study demonstrates that all else being equal, sites where weather conditions are favorable for the formation of large density variations at the lock-in zone preserve older air within their open porosity, making them ideal places for firn air sampling.

Atmospheric Nitrous Oxide Variations on Centennial Time Scales During the Past Two Millennia

“…Both ice cores have fairly high accumulation rates (NEEM: 0.22 and Styx Glacier: 0.13 m ice equivalent/yr; supporting information Table S1), resulting in a small smoothing effect on gas records due to gas diffusion and gradual bubble close‐off processes in the firn layer (transition zone from snow to ice on top of the ice sheet). The estimated widths of the gas age distribution at half height from firn densification models for both ice cores are smaller than 40 yr (Buizert et al, 2012; Jang et al, 2019). Thus, both ice cores can resolve centennial‐scale changes in atmospheric composition.…”

Multi-tracer study of gas trapping in an East Antarctic ice core

“…Secondly, due to the progressive closure of bubbles, an ice layer does not contain air corresponding to a single date, but rather from a wide distribution of ages (e.g., Buizert et al, 2012;Witrant et al, 2012). These distributions act as a moving average on the recorded gas signal, and they attenuate the variability in the record compared to the true variability in the atmosphere (Spahni et al, 2003;Joos and Spahni, 2008;Köhler et al, 2011;Fourteau et al, 2017). Finally, due to the heterogeneous stratification of the firn at the centimeter scale, some layers might close in advance or late compared to their surroundings (Etheridge et al, 1992;Mitchell et al, 2015).…”

Chronological characteristics for snow accumulation on Styx Glacier in northern Victoria Land, Antarctica

“…frequency, path, timing and strength) (Kreutz and others, 2000; Goodwin and others, 2003; Kaspari and others, 2004). Jang and others (2019) have mentioned that the strong wind effect (as blizzards) could have induced the large variation in density of snow in the Styx Glacier.

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“…During the Korean ice core drilling program (2014-15), the firn core (Styx-B) was drilled from the adjacent position (at a distance of ∼100 m) of the longer ice core (Styx-M) by Korea Polar Research Institute (KOPRI). The annual mean temperature was −32.5°C, based on the 15 m depth borehole temperature measurement (Yang and others, 2018) and a horizontal ice flow was estimated to be ∼0.9 m a -1 , and an ice thickness was determined to be 550 m by using a ground-penetrating radar (Hur, 2013).…”