Preprints
https://doi.org/10.5194/egusphere-2022-1219
https://doi.org/10.5194/egusphere-2022-1219
 
09 Dec 2022
09 Dec 2022
Status: this preprint is open for discussion and under review for Climate of the Past (CP).

Effective diffusivity of sulfuric acid in Antarctic ice cores

Tyler J. Fudge1, Raphael Sauvage1, Linh Vu1, Benjamin H. Hills1, Mirko Severi2, and Edwin D. Waddington1 Tyler J. Fudge et al.
  • 1Department of Earth and Space Sciences, University of Washington
  • 2Department of Chemistry “Ugo Schiff”, University of Florence, Florence, Italy

Abstract. Volcanic deposition of sulfuric acid in ice cores is important both for understanding past volcanic activity and for synchronizing ice core timescales. Sulfuric acid has a low eutectic point, so it can potentially exist in liquid at grain boundaries and veins, accelerating chemical diffusion. A high effective diffusivity would allow post-depositional diffusion to obscure the climate history and the peak matching among older portions of ice cores. Here, we use records of sulfate from the EPICA Dome C (EDC) ice core to estimate the effective diffusivity of sulfuric acid in ice. We focus on EDC because multiple glacial-interglacial cycles are preserved, allowing analysis for long timescales and deposition in similar climates. We calculate the mean concentration gradient and the width of prominent volcanic events, and analyze the evolution of each with depth/age. We find the effective diffusivities for interglacials and glacial maximums to be 5 ± 2 × 10-9 m2 a-1, an order of magnitude lower than a previous estimate derived from the Holocene portion of EDC (Barnes et al., 2003). The effective diffusivity may be even smaller if artificial diffusion from the sampling is accounted for. Effective diffusivity is not obviously affected by the ice temperature until about -10 °C, 3000 m depth, which is also where anomalous sulfate peaks begin to be observed (Traversi et al., 2009). Low effective diffusivity suggests that sulfuric acid is not readily diffusing in liquid-like veins in the upper portions of the Antarctic ice sheet and that records may be preserved in deep, old ice if the ice temperature remains well below the pressure melting point.

Tyler J. Fudge et al.

Status: open (until 22 Feb 2023)

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Tyler J. Fudge et al.

Tyler J. Fudge et al.

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Short summary
We use the oldest Antarctic ice core to estimate the rate of diffusion of sulfuric acid. Sulfuric acid is a marker of past volcanic activity and is critical in developing ice-core timescales. The rate of diffusion is uncertain and is important to know both for selecting future ice core locations and interpreting ice-core records. We find the effective diffusivity of sulfate is 10 times smaller than previously estimated, indicating the sulfuric acid signals will persist for longer.