【作者】 杨涛；

【导师】 勾晓华；

【作者基本信息】 兰州大学 ， 自然地理学， 2012， 博士

【摘要】 树木年轮以其较高的气候分辨率、准确而较为成熟的定年技术,越来越多地被应用于气候变化的研究中,成为一种重要的气候代用指标。由于样本分布广‘泛并且便于采集,基于树轮数据的气候变化研究在过去的全球气候变化研究中发挥了重要的作用。采集青藏高原东南部的树轮样本进行研究,讨论树轮径向生长对月均温、月降水量的响应关系,进而反演过去的区域气候变化,了解青藏高原东南部气候变化特征和规律,对全球气候变化及其区域响应研究有重要的现实意义。对研究区多个树种的树轮样本建立的标准年表与邻近气象站点的气温、降水月变化数据进行相关分析,结果显示,较高海拔的树轮样本多响应温度,而较低海拔的树轮样本多响应降水。生长季前期的湿度,特别是春末夏初的降水量对树木的生长影响较大,对研究区的树木生长限制作用较为明显。对比不同树种对于其邻近气象站点气温和降水的响应,结果显示不同地区相同树种对气候的响应方式类似,邻近地区不同树种对气温、降水的响应几乎相同。研究区北部的鳞皮冷杉树轮记录与区域6-7月的温度表现出较高的正相关关系,利用该树轮记录,重建了过去五百多年的夏初气温变化,重建方程方差解释量达到51.2%。在重建结果中,存在7个明显的寒冷时期和4个明显的温暖时期。这一变化与周围地区的气温重建序列吻合较好。同时,空间相关分析结果显示重建的气温变化数据对于青藏高原东南部有一定的代表性。周期分析结果显示,其主要的变化周期有2-6a的准周期、11a,51a的年代际周期和102a、205a左右的世纪周期,这一结果表明研究区气候变化可能受ENSO和太阳活动影响。利用横断山地区采集到的冷杉年轮样本建立了一个近500年的树轮宽度年表,与气候要素的相关分析结果表明该地区树木生长主要受干旱限制,树轮年表与多个月份的PDSI和降水相关显著,其中与前一年9月至当年6月降水的相关性最好(相关系数达0.738)。在此相关关系基础上,利用该年表重建了横断山地区1509-2006年的降水变化历史,重建方程的方差解释量高达54.4%。重建可靠时段(1549-2006年)结果显示,重建的降水序列中包含了较多的低频变化信息,并显示近20多年该区域有显著变湿趋势。在过去的457年中该地区降水存在6个明显的干旱时期和5个湿润时期,其中17世纪的干旱持续时间最长。与邻近地区其他基于树轮数据的湿度重建结果对比发现,该地区树轮记录的干湿变化时段比较一致。空间相关分析结果进一步表明,重建的降水变化序列对整个青藏高原东南部横断山地区都具有较好的空间代表性。周期分析结果显示该地区降水变化存在显著的3-5年准周期,以及60a、79-85a左右的变化周期,这表明该地区的降水可能与ENSO、PDO、NAO以及太阳活动变化等有一定联系。对比青藏高原南北部反映5、6月降水胁迫的两个树轮记录,发现这两个地区的树木生长变化序列存在明显的区域差异,在低频变化中存在较多变化趋势相反的时段,特别是在近几十年来,表现最为明显。‘其变化驱动机制有待于进一步深入研究。更多还原

【Abstract】 High-resolution, accurate and mature dating technology makes tree-ring become one important climate proxy and have been applied for the past climate change researches. Tree-ring samples are widly distributed and easy to be collected, therefore the climate researches based on tree-ring data played a significant role for the global change studies in the past.Collected tree-ring samples from southeastern Qinghai-Tibetan Plateau and analysised the tree radii growth’s response to the monthly mean temperature and precipitation change, we reconstructed the climate change history in this area. Understanding the district’s climate change characters and roles has significant realistic meanings to the global change and local reaction studies.Core samples were collected from different species, and their standard chronologies were developed. Correlation between the tree-ring data and the monthly temperature and precipitation from the local meterological stations revealed that those tree-ring chronologies from high elevation are highly correlated with temperature and those from low elevation are highly correlated with rainfall change. Moisture in the early period of the grow season, especially the precipitation in late spring and early summer, is the main limit factor of the tree growth in this area. Comparing with the response pattern of different tree species, results showed that tree-ring sampes of same species had a similar growth-climate response pattern in different regions, and different species showed a nearly same growth-climate response in the.neighboring regions.Abies squamata tree-ring records from the north part of the study area was highly positive correlated with June-July average temperature, therefore we developed a chronology based on these samples and reconstructed more than500years’ early summer temperature change history. The reconstruction explained51.2%of the instrumental variances.Seven cold periods and five warm periods could be foung in the reconstruction results. That agrees well with nearby’s tree ring based temperature reconstructions. Spatial correlation analyses suggested that our reconstruction could represent the early summer temperature change of southeastern Qinghai-Tibetan Plateau well. The spectral results, which showed significant peaks at about2-6,1151,102and205years, revealed the temperature variability in this area may be affected by ENSO and solar activity.A nearly500-year reconstruction of precipitation in the southeast of the Qinghai-Tibet Plateau was developed based on fir samples collected from the Hengduan Mountains. Correlation analysis between the tree-ring chronology and the climate change data showed that moisture is the main limiting factor for the trees’ growth in this region. Ring-widths were significantly correlated with the Palmer Drought Severity Index and precipitation in many months. And the highest correlation coefficient is found between the annual growth of trees and rainfall from previous September to current June (0.738). Based on this relationship, we reconstructed the precipitation history from1509to2006. The reconstruction explains54.4%of the actual precipitation variation. In the reliable period (1549-2006) of the reconstruction, some low-frequency climate signal was included and indicating this region has been getting wetter in the last20years. There are6apparent dry and5pluvial periods in this reconstruction, and the drought period lasted longer in the17th century than other time. Compared with other works done recently, the reconstructed chronology shows a similar drought/hum idn ess variation trend. Further spatial correlation analysis confirms that the reconstructed precipitation could represent the rainfall history of the total Hengduan Mountains. Spectral analysis reveals that the precipitation in this area had significant spectral peaks in the years of3-5,60and79-85years.Compared tree-ring chronologies of the northern and the southern part of the Qinghai-Tibet Plateau which were affected by the May and June’s water stress, we found their tree-ring chronologies had obvious district difference. Opposite change periods could be found in the the low-frequency variations, and it was highlighted in the last a few decades. Drive mechanism of this phenomenon needs further study.更多还原