Variability of sulfate signal in ice core records based on five replicate cores

E Gautier,J Savarino,P Possenti,J Erbland,A Lanciki

doi:10.5194/cp-12-103-2016

Abstract

Abstract. Current volcanic reconstructions based on ice core analysis have significantly improved over the past few decades by incorporating multiple-core analyses with a high temporal resolution from different parts of the polar regions into a composite common volcanic eruption record. Regional patterns of volcanic deposition are based on composite records, built from cores taken at both poles. However, in many cases only a single record at a given site is used for these reconstructions. This assumes that transport and regional meteorological patterns are the only source of the dispersion of the volcanic products. Here we evaluate the local-scale variability of a sulfate profile in a low-accumulation site (Dome C, Antarctica), in order to assess the representativeness of one core for such a reconstruction. We evaluate the variability with depth, statistical occurrence, and sulfate flux deposition variability of volcanic eruptions detected in five ice cores, drilled 1 m apart from each other. Local-scale variability, essentially attributed to snow drift and surface roughness at Dome C, can lead to a non-exhaustive record of volcanic events when a single core is used as the site reference, with a bulk probability of 30 % of missing volcanic events and close to 65 % uncertainty on one volcanic flux measurement (based on the standard deviation obtained from a five-core comparison). Averaging n records reduces the uncertainty of the deposited flux mean significantly (by a factor 1∕ √ n); in the case of five cores, the uncertainty of the mean flux can therefore be reduced to 29 %.

Highlights

When a large and powerful volcanic eruption occurs, the energy of the blast is sufficient to inject megatons of material directly into the upper atmosphere (Robock, 2000)
Surface roughness, attributed to wind speed, temperatures and accumulation rate, is highly variable in time and space. These small features hardly contribute to the depth offset on a larger spatial scale, in which case glacial flow can control the offset between synchronized peaks, as seems to be the case at the South Pole site (Bay et al 2010)
While the first 40 m appear to be stochastic in nature, a feature consistent with the random local accumulation variations associated with snow drift at the Dome C site, it is surprising that at greater depth, www.clim-past.net/12/103/2016/

Summary

Introduction

When a large and powerful volcanic eruption occurs, the energy of the blast is sufficient to inject megatons of material directly into the upper atmosphere (Robock, 2000). SO2 is of particular interest due to its conversion to tiny sulfuric acid aerosols, which can potentially impact the radiative budget of the atmosphere (Rampino and Self, 1982; Timmreck, 2012). In the troposphere a combination of turbulence, cloud formation, rainout and downward transport are efficient processes that clean the atmosphere of sulfuric acid, and volcanic sulfuric acid layers rarely survive for more than a few weeks, limiting their impact on climate. There, the dry, cold and stratified atmosphere allows sulfuric acid layers to remain for years, slowly spreading an aerosol blanket around the globe. With a lifetime of 2 to 4 years, these aerosols of sulfuric acid fall into the troposphere where they are removed within weeks

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