Refractory Black Carbon Results and a Method Comparison between Solid-state Cutting and Continuous Melting Sampling of a West Antarctic Snow and Firn Core

Abstract

This work presents the refractory black carbon (rBC) results of a snow and firn core drilled in West Antarctica (79°55′34.6″S, 94°21′13.3″W) during the 2014–15 austral summer, collected by Brazilian researchers as part of the First Brazilian West Antarctic Ice Sheet Traverse. The core was drilled to a depth of 20 m, and we present the results of the first 8 m by comparing two subsampling methods—solid-state cutting and continuous melting—both with discrete sampling. The core was analyzed at the Department of Geological Sciences, Central Washington University (CWU), WA, USA, using a single particle soot photometer (SP2) coupled to a CETAC Marin-5 nebulizer. The continuous melting system was recently assembled at CWU and these are its first results. We also present experimental results regarding SP2 reproducibility, indicating that sample concentration has a greater influence than the analysis time on the reproducibility for low rBC concentrations, like those found in the Antarctic core. Dating was carried out using mainly the rBC variation and sulfur, sodium and strontium as secondary parameters, giving the core 17 years (1998−2014). The data show a well-defined seasonality of rBC concentrations for these first meters, with geometric mean summer/fall concentrations of 0.016 μg L−1 and geometric mean winter/spring concentrations of 0.063 μg L−1. The annual rBC concentration geometric mean was 0.029 μg L−1 (the lowest of all rBC cores in Antarctica referenced in this work), while the annual rBC flux was 6.1 μg m−2 yr−1 (the lowest flux in West Antarctica records so far).