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Evaluating Zr/Rb Ratio From XRF Scanning as an Indicator of Grain‐Size Variations of Glaciomarine Sediments in the Southern Ocean
Geochemistry, Geophysics, Geosystems ( IF 4.480 ) Pub Date : 2020-10-25 , DOI: 10.1029/2020gc009350
Li Wu 1 , David J. Wilson 2 , Rujian Wang 1 , Xuebo Yin 3, 4 , Zhihua Chen 5 , Wenshen Xiao 1 , Mengxue Huang 1
Affiliation  

The ln(Zr/Rb) count ratio derived from X‐ray fluorescence (XRF) core scanning holds potential as a high‐resolution tracer for grain‐size variations of glaciomarine sediments, and hence current strength. To evaluate this approach, we conducted high‐resolution grain‐size measurements, together with Rb and Zr measurements by XRF core scanning and inductively coupled plasma‐mass spectrometry (ICP‐MS), on a series of sediment cores from different regions of the Southern Ocean. Downcore changes of the ln(Zr/Rb) count ratio from XRF core scanning are consistent with Zr/Rb concentration ratios derived from ICP‐MS analyses, even though Rb and Zr counts deviate significantly from concentrations due to specimen and matrix effects. The ln(Zr/Rb) count ratio displays discrepancies with the bulk mean grain‐size, but correlates well with the mean grain‐size of the sediment fractions that do not include unsorted sand delivered by ice‐rafting. These observations are supported by evidence from a grain‐size separation experiment, which indicates that Zr and Rb are concentrated in different grain‐size fractions. Consistent with its lack of sensitivity to coarse grain‐size fractions derived from ice‐rafting, the ln(Zr/Rb) ratio records similar trends to the sortable silt percent (SS%) and sortable silt mean (urn:x-wiley:15252027:media:ggge22348:ggge22355-math-0001) grain‐size. Universal gradients exist in plots of SS% versus ln(Zr/Rb), and urn:x-wiley:15252027:media:ggge22348:ggge22355-math-0002 versus ln(Zr/Rb), such that the ln(Zr/Rb) ratio provides a convenient way to estimate the magnitude of changes in SS% and urn:x-wiley:15252027:media:ggge22348:ggge22355-math-0003. Overall, our results support the use of the ln(Zr/Rb) ratio as an indicator of bottom current strength in cases where the sediment is current‐sorted.

中文翻译:

通过XRF扫描评估Zr / Rb比,作为南大洋海洋沉积物粒度变化的指标

从X射线荧光(XRF)核心扫描得出的ln(Zr / Rb)计数比具有作为高分辨率示踪剂的潜力,可用于冰川海洋沉积物的粒度变化以及电流强度。为了评估这种方法,我们对南部南部不同地区的一系列沉积岩心进行了高分辨率的晶粒度测量,以及通过XRF核扫描和电感耦合等离子体质谱法(ICP-MS)进行的Rb和Zr测量海洋。XRF核心扫描得到的ln(Zr / Rb)计数比的下限变化与ICP-MS分析得出的Zr / Rb浓度比一致,即使Rb和Zr计数由于样品和基质效应而明显偏离浓度。ln(Zr / Rb)计数比显示出与平均晶粒度的差异,但与沉积物部分的平均粒度有很好的相关性,其中不包括通过浮冰运送的未分类沙子。这些观察结果得到了粒度分离实验的支持,表明Zr和Rb集中在不同的粒度级分中。ln(Zr / Rb)比率由于对浮冰过程中产生的粗粒级分数缺乏敏感性,因此记录的趋势与可分类粉尘百分比(SS%)和可分类粉尘平均值(骨灰盒:x-wiley:15252027:media:ggge22348:ggge22355-math-0001) 晶粒尺寸。SS%与ln(Zr / Rb)和ln(Zr / Rb)的关系图中存在通用梯度骨灰盒:x-wiley:15252027:media:ggge22348:ggge22355-math-0002,因此ln(Zr / Rb)比提供了一种方便的方法来估算SS%和的变化幅度骨灰盒:x-wiley:15252027:media:ggge22348:ggge22355-math-0003。总体而言,我们的结果支持使用ln(Zr / Rb)比作为沉积物分流情况下底部电流强度的指标。
更新日期:2020-11-16
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