Late summer temperature reconstruction based on tree-ring density for Sygera Mountain, southeastern Tibetan Plateau

Although several tree-ring density-based summer/late summer temperature reconstructions have been developed on the Tibetan Plateau (TP), the understanding of the local/regional characteristics of summer temperature fluctuations on a long-term scale in some regions is still limited. To improve our understanding in these aspects, more local or regional summer temperature reconstructions extending back over several centuries are required. In this study, a new mean latewood density (LWD) chronology from Abies georgei var. smithii from the upper tree line of Sygera Mountain on the southeastern TP was developed to reconstruct the late summer temperature variability since 1820 CE. The bootstrapped correlation analysis showed that the LWD chronology index was significantly and positively correlated with the late summer (August-September) mean temperatures (r1950-2008 = 0.63, p < 0.001) recorded at the nearest meteorological station and that this reconstruction has considerable potential to represent the late summer temperature variability at the regional scale. Our late summer temperature reconstruction revealed three obvious cold periods (i.e., 1872-1908, 1913-1937 and 1941-1966) and two relatively warm phases (i.e., 1821-1871 and 1970-2008) over the past two centuries. Comparisons of our reconstruction with other independent tree-ring-based temperature reconstructions, glacier fluctuations and historical documental records from neighboring regions showed good agreement in these relatively cold and warm intervals. Our reconstruction exhibits an overall increasing temperature trend since the 1960s, providing new evidence supporting the recent warming of the TP. Moreover, our results also indicate that the late summer temperature variability of Sygera Mountain on the southeastern TP has potential links with the Pacific Decadal Oscillation (PDO).