Concentrations of the rare earth elements (REE) and Thorium-232 (232Th) in glacial dust from the northern Gulf of Alaska region

Concentrations of the rare earth elements (REE) and Thorium-232 (232Th) are presented for filtered air (dust) samples collected from the northern Gulf of Alaska region, including from Middleton Island (AK)(59.4214 N, 146.3493 W) and the Copper River delta (60.4324 N, 145.0954 W). Size-fractionated samples were collected in November 2019, using a Tisch Volumetric Flow Controlled (VFC) high volume sampler (Tisch Environmental, TE-5170V- BL) outfitted with a Cascade impactor. The six size fractions collected ranged from <0.49 micrometers (um) to >7.2 um in diameter. This sampler technology is discussed in greater detail in Morton et al, 2013. Samples were filtered with acid-washed Whatman 41 (W41) cellulose fiber filters. Additional bulk dust samples were collected in October 2012, using a Thermo Partisol Plus 2025 using Teflon filters. Samples were fully digested using concentrated nitric and hydrofluoric acids, following the approach of Morton et al, 2013. Samples were analyzed using a Thermofisher iCAP inductively coupled plasma mass spectrometer (ICP-MS) in KED mode, with He as a collision cell gas, adapted from the approach of Trommetter et al (2020). Concentrations were determined from standard curves using a REE ICP-MS standard from High-Purity Standards (that also contained 232Th). Three internal standards (Ge, In, and Bi) were added to both samples and standards, to correct for short-term variability in the instrument response and to evaluate stability of mass response during the ICP-MS run. Concentration estimates for the REE and 232Th were blank-corrected using full-process blanks that included filters deployed during times when there was no known dust deposition. Most of the full-process blank concentrations were 100 times or more smaller than the concentrations of our lowest standard (with the exception of Ce, the concentration of which was ~seven times smaller than our lowest standard. This means that our blank concentrations were very low but also not quantified extremely accurately. Our best estimates are that the full-process blanks, including filters, ranged from 0.02 picograms per square centimeter (pg cm-2) for Eu, Tb, and Ho, to 2 pg cm-2 for Ce. These blank concentrations were in all cases 40 times or more smaller than our lowest REE sample concentration for the <0.49 um size fraction with the smallest amount of dust, and ~3 orders of magnitude smaller than the signal of the largest samples. The REE data are also presented in a double-normalized format that first normalizes to concentrations of Post Archean Australian Shale and then normalizes to the mean REE concentration. The normalization approach is slightly modified from that of Serno et al, 2014.

本数据集收录了阿拉斯加湾北部区域（包括米德尔顿岛（美国阿拉斯加州，坐标59.4214°N，146.3493°W）与铜河三角洲（60.4324°N，145.0954°W））采集的过滤空气（粉尘）样品中的稀土元素（rare earth elements, REE）与钍-232（²³²Th）浓度数据。2019年11月，研究团队采用配备级联撞击器的Tisch体积流量控制（Volumetric Flow Controlled, VFC）大容量采样器（Tisch Environmental，型号TE-5170V-BL）采集分粒径分级样品，所获6个粒径分级的直径范围为<0.49微米（μm）至>7.2 μm，该采样器的技术细节可参见Morton等人2013年的研究。样品采用经酸洗处理的Whatman 41（W41）纤维素纤维滤膜进行过滤；2012年10月，研究团队还采用搭载特氟龙滤膜的Thermo Partisol Plus 2025采集了额外的全量粉尘样品。所有样品均采用浓硝酸与氢氟酸进行全消解，消解方案参照Morton等人2013年的研究方法。样品分析采用Thermo Fisher iCAP电感耦合等离子体质谱仪（inductively coupled plasma mass spectrometer, ICP-MS）的动能歧视模式（KED mode），以氦气作为碰撞池气体，分析方法改编自Trommetter等人2020年的研究。浓度测定通过标准曲线法完成，所用稀土元素ICP-MS标准溶液购自High-Purity Standards（该标准溶液同时包含²³²Th）。向样品与标准溶液中均加入锗（Ge）、铟（In）、铋（Bi）3种内标元素，以校正仪器响应的短期波动，并评估ICP-MS运行过程中质量响应的稳定性。稀土元素与²³²Th的浓度估算值通过全流程空白进行空白校正，全流程空白包含无已知粉尘沉降期间部署的滤膜。绝大多数全流程空白浓度较本研究最低浓度标准低100倍以上（铈Ce除外，其空白浓度约为最低标准的1/7），这表明本研究的空白浓度极低，但无法实现极高精度的定量。经最优估算，包括滤膜在内的全流程空白浓度范围为：铕（Eu）、铽（Tb）与钬（Ho）为0.02皮克每平方厘米（pg·cm⁻²），铈（Ce）为2 pg·cm⁻²。该空白浓度在所有情况下均较<0.49 μm粒径分级中粉尘含量最低的样品的最低稀土元素浓度低40倍以上，且较最大粉尘样品的信号低约3个数量级。本数据集还提供了双标准化格式的稀土元素数据：首先以太古代后澳大利亚页岩（Post Archean Australian Shale）浓度进行标准化，随后以稀土元素平均浓度进行二次标准化，该标准化方法对Serno等人2014年的方案进行了小幅修改。