Helama Samuli, Heikkilä Pasi, Rinne Katja, Nielsen Jan Kresten, Nielsen Jesper Kresten
Arctic Centre, University of Lapland, P.O. Box 122, 96101, Rovaniemi, Finland,
Environ Monit Assess. 2015 May;187(5):260. doi: 10.1007/s10661-015-4495-5. Epub 2015 Apr 17.
Understanding of the uranium uptake processes (both in vivo and post-mortem) into the skeletal structures of marine calcifiers is a subject of multi-disciplinary interest. U-concentration changes within the molluscan shell may serve as a paleoceanographic proxy of the pH history. A proxy of this type is needed to track the effects of fossil fuel emissions to ocean acidification. Moreover, attaining reliable U-series dates using shell materials would be a geochronological breakthrough. Picturing the high-resolution changes of U-concentrations in shell profiles is now possible by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Here, we analyzed in situ U-concentration variations in sub-fossilized shells of ocean quahog (Arctica islandica), a commonly studied bivalve species in Quaternary geoscience, using LA-ICP-MS. Microstructural details of the shell profiles were achieved by the scanning electron microscopy (SEM). Comparison of the shell aragonite microstructure with the changes in U-concentration revealed that uranium of possibly secondary origin is concentrated into the porous granular layers of the shell. Our results reinforce the hypothesis that U-concentration variations can be linked with microstructural differences within the shell. A combination of LA-ICP-MS and SEM analyses is recommended as an interesting approach for understanding the U-concentration variations in similar materials.
了解铀在海洋钙化生物骨骼结构中的吸收过程（包括体内和死后）是一个具有多学科研究兴趣的课题。软体动物贝壳内的铀浓度变化可作为古海洋学中pH历史的一个代用指标。需要这样一个代用指标来追踪化石燃料排放对海洋酸化的影响。此外，利用贝壳材料获得可靠的铀系年代将是一项地质年代学上的突破。现在通过激光烧蚀-电感耦合等离子体质谱法（LA-ICP-MS）可以描绘贝壳剖面中铀浓度的高分辨率变化。在这里，我们使用LA-ICP-MS分析了北极蛤（Arctica islandica）亚化石贝壳中的原位铀浓度变化，北极蛤是第四纪地球科学中常用的双壳类研究物种。通过扫描电子显微镜（SEM）获得了贝壳剖面的微观结构细节。将贝壳文石的微观结构与铀浓度变化进行比较后发现，可能是次生来源的铀集中在贝壳的多孔颗粒层中。我们的结果强化了这样一个假设，即铀浓度变化可能与贝壳内部的微观结构差异有关。建议将LA-ICP-MS和SEM分析结合起来，作为理解类似材料中铀浓度变化的一种有趣方法。
