Using Tree Ring Stable Oxygen Isotope to Reconstruct Historical Climates in Taijiang Inland Sea in Taiwan

Abstract

The existence of the Taijiang Inland Sea provided important shipping functions for the early society in Taiwan and thus became the main scope of activities during the Dutch Zheng and Qing periods It was not only where the political military and economic centers were established but also where historical events happened The heavy rainfall in July 1823 changed the mainstream of Tsengwen River and the flooding brought a large amount of sediment into the Taijiang Inland Sea exacerbating the process of degradation Due to the limited time span of meteorological observations we aimed to reconstruct the past hydrological climate in southwestern Taiwan with tree-ring stable oxygen isotopes and compared the reconstructed climate chronology with the climate records of historical documents trying to supplement the qualitative historical records Here a 1553-2015 stable oxygen isotope chronology based on six Chamaecyparis formosensis from the Alishan was presented and was adopted to reconstruct the annual precipitation and the average precipitation from May to October Precipitation reconstruction and disaster severity index showed that there were no rainfall peaks or severe flooding in 1823 but 1800-1835 was a period with abundant rainfall and continuous flooding Our results supported that the degradation of the Taijiang Inland Sea was not only because of the heavy rainfall event in 1823 but the abundant rainfall from 1800 to 1835 coupled with the fragile geology of the upstream of the Tsengwen River the gentle slope of the downstream and a large amount of sediment in the mainstream flew to downstream Thus sedimentation in the downstream caused river channel of the Tsengwen River diverted into the Taijiang Inland Sea in 1823 and made the Taijiang Inland Sea degradation in nearly two hundred years

Date of Award	2020
Original language	English
Supervisor	I-Ching Chen (Supervisor)