横断山区树轮揭示的过去500年火山喷发信号及其气候效应

Volcanic eruptions are an important natural cause of climate change on many timescales. Studying the responses of climate to volcanic eruptions helps us to better understand important radiative and dynamical processes that respond in the climate system to both natural and anthropogenic forcings. The proposed project will detect volcanic eruption signals and investigate the volcanic effect on climate using tree-ring data in the Hengduan Mountain area for the past 500 years. Firstly, we need to sample tree-rings that are moisture- and temperature-sensitive respectively. And moreover, the tree-ring sites keep a relatively even distribution. Frost-ring, light-ring, narrow-ring (missing-ring) chronologies are developed as well as tree-ring width and latewood maximum density chronologies. Then, the temperature and precipitation series are reconstructed using the tree-ring data and instrumental data, and the extreme temperature and precipitation events are also investigated. Furthermore, we calculate the percentage of the frost-rings, light-rings, and narrow-rings (missing-rings) in the year when they occur. Combining the extreme temperature and precipitation events and the existing volcanic eruption chronology, we detect the volcanic eruption signals which can provide evidences for adjusting dating of volcanic eruptions in the past 500 years. Based on the reconstructing series and volcanic eruptions chronology, the characteristics of temperature and precipitation following five years of volcanic eruptions are also investigated using superposed epoch and time series analysis methods. The responses of climate to different types of volcanic eruptions are found out, which provide data for us to better understand mechanism of regional climate changes.

火山活动是影响全球气候变化的重要自然驱动因素之一，研究过去火山活动的区域气候效应，对深入了解气候系统变化的自然和人为因素等驱动机制有着重要作用。本项目拟利用横断山区的树轮资料，检测过去500年的火山喷发信号，并分析火山喷发的气候效应。首先分别选取对温度和降水敏感的样点进行野外采样，并尽可能保持样点在空间上均匀分布。利用获取的树轮资料建立霜轮、浅轮、窄轮（丢轮），以及树轮宽度和密度年表，并进行降水和温度重建，统计极端温度和降水事件。在霜轮、浅轮、窄轮（丢轮）等异常轮发生年，统计其所占比例，分析其协同发生特征。结合极端温度和降水事件，以及已有的火山喷发年表，检测火山信号，为定年有误差的早期火山喷发事件提供佐证。利用时序叠加和序列分析等统计方法分析火山喷发后研究区温度和降水变化规律，辨明不同位置、时间、强度等的火山喷发对研究区温度和降水影响的异同，为深入了解区域气候变化影响机制提供基础数据。

本项目利用横断山区树轮宽度和密度，以及全球强火山喷发序列，开展了相关研究。取得了如下进展：1）建立了11条树轮宽度序列和4条树轮晚材最大密度序列，并根据建立的宽度和密度序列重建了研究区过去五百年的温度变化过程。2）探讨了强火山喷发后，横断山区发生窄轮的概率，结果发现：强火山喷发后的1-2年发生窄轮的概率较大。该结果表明树轮序列可以检测火山喷发的信号。3）根据重建的温度序列、窄轮、火山喷发序列，探讨了不同位置强火山喷发对研究区气候变化的影响。结果表明：中低纬度的强火山喷发对研究区温度影响较大，并在强火山喷发后的1-2年内降温显著。4）基于器测资料和树轮资料，讨论了1991年皮纳图博火山喷发对青藏高原东部树木生长的影响，结果表明：1991年菲律宾强火山喷发后，研究区在1992年降温显著，树轮生长减缓显著，而降水变化不明显。该结果揭示了1991年火山喷发导致研究区温度降低显著，从而影响了该区树木生长。通过上述工作的开展，基本完成了本项目的预期目标。