树木年轮稳定同位素与放射性碳揭示火山过程对意大利西西里岛埃特纳火山树木的喷发前与喷发后效应
Tree-ring stable isotopes and radiocarbon reveal pre- and post-eruption effects of volcanic processes on trees on Mt. Etna (Sicily, Italy)
AI总结：
本研究通过分析埃特纳火山树木年轮的碳氧稳定同位素与放射性碳，揭示了火山岩浆脱气导致的水分吸收促进了光合作用，从而解释了2002/2003喷发前NDVI的局部升高，表明年轮氧同位素可作为过去火山喷发的指标。
摘要：
火山喷发的早期探测对于保护人类生命至关重要。地面形变以及地震活动、地球化学、岩石学和重力学的变化被用于评估喷发前的火山活动。针对埃特纳火山（意大利）的研究表明，植被在喷发开始前可能会受到喷发前活动的影响。在埃特纳火山2002/2003侧翼喷发之前的连续两年中，沿着一条后来发展为喷发裂缝的明显线路检测到了增强型植被指数（NDVI）值的升高。然而，火山活动导致喷发前树木生长过程发生变化的机制目前仍不十分清楚。为了评估水蒸气或化石火山CO2的吸收是否可能促进了NDVI的增强，我们分析了在观察到喷发前NDVI增加的线路附近生长的幸存树木年轮中的$δ^{13}$C、$δ^{18}$O和$^{14}$C。我们发现，在靠近喷发裂缝的树木中，于2002/2003之前形成的树木年轮中$δ^{18}$O出现剧烈下降，这表明树木在喷发前岩浆脱气期间吸收了火山水。上升岩浆除气引起的湿润条件也可能导致了喷发后观察到的树木年轮$δ^{13}$C的降低。此外，仅发现了树木吸收脱气CO2的模糊证据。我们的结果表明，从脱气水蒸气中凝结的额外土壤水分可能促进了光合作用，解释了2002/2003埃特纳火山侧翼喷发前NDVI的局部增加。树木年轮氧稳定同位素可能被用作过去火山喷发的指标。
英文摘要：
Early detection of volcanic eruptions is of major importance for protecting human life. Ground deformation and changes in seismicity, geochemistry, petrology, and gravimetry are used to assess volcanic activity before eruptions. Studies on Mt. Etna (Italy) have demonstrated that vegetation can be affected by pre-eruptive activity before the onset of eruptions. During two consecutive years before Mt. Etna's 2002/2003 flank eruption, enhanced vegetation index (NDVI) values were detected along a distinct line which later developed into an eruptive fissure. However, the mechanisms by which volcanic activity can lead to changes in pre-eruption tree growth processes are still not well understood. We analysed $δ^{13}$C, $δ^{18}$O and $^{14}$C in the rings of the survived trees growing near to the line where the pre-eruptive increase in NDVI was observed in order to evaluate whether the uptake of water vapour or fossil volcanic CO2 could have contributed to the enhanced NDVI. We found a dramatic decrease in $δ^{18}$O in tree rings formed before 2002/2003 in trees close to the eruption fissure, suggesting uptake of volcanic water by trees during pre-eruptive magma degassing. Moist conditions caused by outgassing of ascending magma may also have led to an observed reduction in tree-ring $δ^{13}$C following the eruption. Furthermore, only ambiguous evidence for tree uptake of degassed CO2 was found. Our results suggest that additional soil water condensed from degassed water vapour may have promoted photosynthesis, explaining local increases in NDVI before the 2002/2003 Mt. Etna flank eruption. Tree-ring oxygen stable isotopes might be used as indicators of past volcanic eruptions.
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