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).

摘要

本文研究了由巴西西南极冰盖考察队科研人员在2014-2015年南极夏季在西南极(79°55′34.6″S, 94°21′13.3″W)钻取的雪冰芯中的耐热黑炭(rBC)特征。冰芯钻探深度为20 m,我们通过比较两种具有离散采样的二级采样方法(固态切割和连续融解)来分析冰芯上层8 m的结果。我们在美国中央华盛顿大学(CWU)地质科学系使用与CETAC Marin-5雾化器耦合的单颗粒黑炭光度计(SP2)对冰芯进行了分析。中央华盛顿大学近期组装了连续融解系统,此处展示了其初步成果。本文还介绍了有关单颗粒黑炭光度计重现性的实验性结果。实验表明,相较分析时间而言,样品浓度能够对南极冰芯低浓度rBC的重现性产生更大的影响。使用rBC变率以及硫、钠和锶等次要参数,估算出该冰芯的形成历时17年(1998-2014年)。数据显示,冰芯上层数米的rBC浓度具有显著的季节性,夏季/秋季几何平均浓度为0.016 µg L-1,冬季/春季几何平均浓度为0.063 µg L-1。rBC浓度的年度几何平均值为0.029 µg L-1(是本文引用的所有南极冰芯中rBC的最低值),年度rBC平均通量为6.1 µg m-2 yr-1(迄今为止西南极最低的通量记录)。