Water Isotopic Signature of Surface Snow Metamorphism in Antarctica

Abstract

<p>Water isotope ratios of ice cores are a key source of information on past temperatures. Through fractionation within the hydrological cycle, temperature is imprinted in the water isotopic composition of snowfalls. However, this signal of climatic interest is modified after deposition when snow remains at the surface exposed to the atmosphere. Comparing time series of surface snow isotopic composition at Dome C with satellite observations of surface snow metamorphism, we found that long summer periods without precipitation favor surface snow metamorphism altering the surface snow isotopic  composition. Using excess parameters (combining dD, d<sup>17</sup>O, and d<sup>18</sup>O fractions) allow the identification of this alteration caused by sublimation and condensation of surface hoar. The combined measurement of all three isotopic compositions could help identifying ice core sections influenced by snow metamorphism in sites with very low snow accumulation.</p>

Post-depositional modication on seasonal and 1 interannual timescales resets the deuterium excess 2 signals in summer snow layers in Greenland

“…The δ 18 O content of snow is often used as a regional temperature proxy, whether local atmospheric temperature or cloud temperature, because of aforementioned strong spatial and temporal relationships between δ 18 O and temperature. However, our results in the context of broader literature base (e.g., Casado et al, 2021;Wahl et al, 2022) indicate that the δ 18 O is probably much better interpreted as a surface energy budget proxy, or a combined temperature and latent heat ux proxy.…”

“…We infer that under common conditions at EastGRIP redistributed snow can have a sublimation/deposition signal. Modeling by Casado et al (2021) indicates this process could decrease δ 18 O and increase d. We presume this mechanism results in a net mass deposition at the surface.…”

“…We suspect seasonally-and synopticallyinduced vapor-pressure gradients in the near-surface snow to be an important metamorphic process during Spring, Summer, and Autumn months. They ought to be less im- , 2002;Neumann et al, 2005;Steen-Larsen et al, 2014;Casado et al, 2021;Hughes et al, 2021;Wahl et al, 2021), and demonstrate that more general revisions to interpretations of water isotope proxies in polar snow are needed.…”

“…This would manifest as longer sampling periods, possibly annual in duration, over a period of years to document the scope of post-depositional change at a range of sites vulnerable to post-depositional change. Data sets such as these would help our second recommendation: further development of streamlined, site-agnostic process-based models that manuscript submitted to JGR: Atmospheres include the impact of the surface energy budget, near-surface snow vapor dynamics, and redistribution processes on the isotopic content of near-surface snow (e.g., Touzeau et al, 2018;Stevens et al, 2020;Kahle et al, 2021;Hughes et al, 2021;Casado et al, 2021;Wahl et al, 2022). This combination will allow for training of model parameters and investigation into compensating impacts of all potential processes impacting post-depositional isotopic change of near-surface snow.…”

“…We observe in our snow proles changes much larger than 2 o /oo over 47 days in 2017 (Figure7(a)). We are not observing a pure isotopic-gradient diusion situation because the real snow surface is open to the atmosphere, its isotopic content uctuating on many time scales Casado et al (2021). show that summer surface snow δ 18 O at Dome C, Antarctica responds to more than surface temperature, with sublimation and deposition being important aspects to simulating isotope observations.…”