17:15 〜 18:45
[HQR04-P03] The environmental changes in northeast mountain area of Taiwan during the Little Ice Age
Yuanyang Lake is situated in the Cilan Mountain area of northern Taiwan and is surrounded by Cryptomeria japonica at an altitude of 1620 meters above sea level. The lake remained undisturbed by humans until deforestation activities in 1963. To understand the affect of climate change on local forest and aquatic ecosystem, diatom fossils, elemental concentrations of total organic carbon (TOC) and total nitrogen (TN), TOC/TN ratios, carbon isotopic composition (δ13Corg), and charcoal were analyzed in a 40 cm sediment core collected from YK. The 210Pb and 14C dating showed the sediment core covered the time frame from 1300 to 2020 AD. Based on the current records, the last 600 years BP were categorized into three phases: Early Little Ice Age (1300-1510 AD), Late Little Ice Age (1510-1900 AD), and modern human development phase (1900-2020 AD).
During Early Little Ice Age, low TOC and high TOC/TN ratio, along with high δ13Corg and high charcoal indicated, indicated drier climate and frequent forest fires. It also suggested the fire likely to be the caused of lowering in TOC, due to loss of C through burning. Furthermore, during Late Little Ice Age conditions appeared to be less dry. This was indicated by a gradual decreasing trend in δ13Corg and TOC along with low TOC/TN ratios. Charcoal data showed low forest fire during this phase. Additionally, a steep increase in TOC observed during 1560 AD, indicating an increase in preservation of organic matter in the sediment. This could be attributed to frequent typhoon events, with strong rain flushing TOC into the lake. Moving to the third phase, spanning from 1900 to 2020 AD, there was a noticeable double increase in TOC, coinciding with two deforestation activities occurring in the nearby forest.
During Early Little Ice Age, low TOC and high TOC/TN ratio, along with high δ13Corg and high charcoal indicated, indicated drier climate and frequent forest fires. It also suggested the fire likely to be the caused of lowering in TOC, due to loss of C through burning. Furthermore, during Late Little Ice Age conditions appeared to be less dry. This was indicated by a gradual decreasing trend in δ13Corg and TOC along with low TOC/TN ratios. Charcoal data showed low forest fire during this phase. Additionally, a steep increase in TOC observed during 1560 AD, indicating an increase in preservation of organic matter in the sediment. This could be attributed to frequent typhoon events, with strong rain flushing TOC into the lake. Moving to the third phase, spanning from 1900 to 2020 AD, there was a noticeable double increase in TOC, coinciding with two deforestation activities occurring in the nearby forest.