| 25 Aug 2026
Stratigraphic noise and post depositional effects in isotopic record of Antarctic firn: insights from a snow trench at Dome C
Abstract. Water isotopes are a key tool to reconstruct past climate variations from ice core records. At sites with low precipitation amounts, such as in Central Antarctica, redistribution by wind and post-depositional processes can alter the snow isotopic signal. This causes a shift in mean isotopic composition and adds stratigraphic noise, with a large spatial variability at the meter scale. In turn, this can modify the isotope-temperature relationship at inter-annual timescales. Here, we present a new dataset of water stable isotope measurements performed on 39 simultaneous 1.5 m deep snow pits dug along a 50 m trench in December 2019 at Dome C. It is combined to timeseries of observed isotopic composition in precipitation and surface-snow conducted over the last decade in order to study the isotope transfer function during snow archival processes. The trench isotopic records covering about 20 years depict no annual cycle and no correlation with local temperature, contrary to precipitation and surface snow time-series. Trench profiles show a very large spatial variability of the inter-annual signal archived in snow. The trench mean δ 18 O values show a a +7 ‰ offset (-6 ‰ for d-excess) compared to mean precipitation values, and +2 ‰ offset for δ 18 O (-1 ‰ for d-excess) compared to surface snow, indicating vapour exchanges acting beyond the surface snow layer. The power spectra of trench profiles imply a stronger smoothing at high frequencies than predicted by classical diffusion models. Individual trench profiles are dominated by stratigraphic noise, with a signal-to-noise ratio less than 0.35 across frequencies. This signal-to-noise ratio can be enhanced by up to 50 % by inter-profile alignment based on chemical tracers. The aligned core stack signal shows a multi-annual signal with some features not reproduced by a simple precipitation stacking model, hinting to a contribution of post-depositional effects in this common signal.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Climate of the Past.
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