Rapid measurement of strontium in speleothems using core-scanning micro X-ray fluorescence
Rapid measurement of strontium in speleothems using core-scanning micro X-ray fluorescence
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DOI：
10.1016/j.chemgeo.2018.04.008
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发表时间：
2018-05
期刊：
影响因子：
3.9
通讯作者：
N. Scroxton;S. Burns;P. Dawson;J. M. Rhodes;K. Brent;D. McGee;H. Heijnis;P. Gadd;W. Hantoro;M. Gagan
中科院分区：
文献类型：
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作者：
N. Scroxton;S. Burns;P. Dawson;J. M. Rhodes;K. Brent;D. McGee;H. Heijnis;P. Gadd;W. Hantoro;M. Gagan
洞穴沉积物微量元素比值如Mg/Ca和Sr/Ca越来越多地用于洞穴沉积物古气候学，作为稳定的氧和碳同位素比值的补充，作为水文系统过去变化的代理。使用多个代理一起允许更好地了解本地和远端的水文变化记录在洞穴化学，因此在过去的降雨量的变化。尽管有潜在的好处，洞穴沉积物的微量元素分析还没有变得普遍，这可能是由于传统的微量元素分析技术需要大量的时间和成本。本文研究了一种快速、相对无损、价格低廉的测定洞穴沉积物中Sr/Ca的新技术：芯扫描微区X射线荧光（CS-μXRF），结果表明CS-μXRF能可靠、准确地记录洞穴沉积物中Sr的含量。与近化学计量的Ca成比例，Sr/Ca比说明了射束强度和机器设置的变化，从而为运行内和运行间比较产生更可靠的报告测量。CS-μXRF与四极杆ICP-MS和ICP-AES等传统微量元素分析方法相比，具有更高的准确性，因此CS-μXRF能够产生具有古气候意义的Sr/Ca结果。我们还确定了与洞穴沉积物结晶度有关的次要问题，Ca光谱峰的优势，以及相对较低能量的X射线，这些X射线可能会干扰精确的CS-μXRF分析。如果能克服这些问题，CS-μXRF可能为洞穴沉积物研究提供一种更有用的微量元素分析方法。
Speleothem trace element ratios such as Mg/Ca and Sr/Ca are increasingly used in speleothem paleoclimatology as a supplement to stable oxygen and carbon isotope ratios as proxies for past variability in the hydrologic system. Using multiple proxies together allows for a better understanding of both the local and distal hydrologic changes recorded in speleothem chemistry, and therefore of changes in past rainfall. Despite the potential benefits, trace element analysis of speleothems has yet to become widespread, which is likely due to the significant time and costs required by traditional trace element analytical techniques. In this study, we present an in-depth investigation into a rapid, relatively non-destructive and competitively priced technique for measuring Sr/Ca in speleothems: Core-Scanning micro X-ray Fluorescence (CS-μXRF).We show that CS-μXRF reliably and precisely records Sr concentration in speleothems. Ratioed to near-stoichiometric Ca, the Sr/Ca ratio accounts for variations in beam strength and machine settings, producing a more reliable reported measurement for both intra- and inter-run comparisons. CS-μXRF compares favorably with more conventional trace element procedures such as Quadrupole ICP-MS and ICP-AES, giving confidence in the ability of CS-μXRF to produce paleoclimatologically significant Sr/Ca results. We also identify secondary issues relating to speleothem crystallinity, the dominance of Ca spectral peaks, and comparatively lower energy X-rays that can interfere with precise CS-μXRF analyses. If these can be overcome then CS-μXRF may provide an even more useful method of trace element analysis in speleothem studies.