[H-QR04] Deep time perspective on the geological response to climate change

[HQR04-P04] Utilizing stable carbon isotope and diatom records to reconstruct the Holocene hydroclimate changes in the mountainous region of northeastern Taiwan

*Shi-Ting Zhan¹, Abdur Rahman¹, Liang-Chi Wang¹, Ludvig Löwemark² (1.Department of Earth and Environmental Sciences National Chung Cheng University, Taiwan, 2.Department of Geosciences, National Taiwan University, Taiwan)

Keywords:Sanxingmei Pond, Stable carbon isotope, Diatom, Paleoclimate, Holocene

Modern climate observations show that in northeastern Taiwan, precipitation mainly comes from the plum rain in spring and early summer, typhoons during the summer, and the northeast monsoon in winter. To reconstruct the change in environmental conditions of this region in the past, a study was designed focusing on the analysis of a 250 cm long sediment core extracted from Sanxingmei Pond (SXMP), situated at an altitude of 2100 meters above sea level in Yilan. The ²¹⁰Pb and ¹⁴C dating of the sediment core revealed that it covers the last 11000 cal BP, representing the Holocene period. In order to achieve the goal of the current study, the stable carbon (C) isotopic composition (δ¹³C) along with elemental concentration of total organic C (TOC) and total nitrogen (N), elemental ratios of TOC and N (C/N) and diatom data were analyzed. The SMXP sediment samples exhibited overall low δ¹³C values, falling within the range typical for C3 plants, which represent the dominance of woody and deciduous plants during the studied period. This observation in line with the proportion of high woody plants indicated in the pollen records. From 10400 to 8000 cal BP, the presence of high TOC and C/N ratios, coupled with low δ¹³C values, pointed to increased runoff conditions and a predominance of C3 plants, indicative of wetter climate conditions in the region. Further, a decrease in C/N and TOC were noticed along with an increase in δ¹³C, indicating lower runoff conditions and growth of C4 plants in the region during 8000-3410 cal BP. It indicated relatively drier climate conditions in the region. Additionally, during 3410-790 cal BP, high TOC and δ¹³C alongside low C/N ratios indicated drier climate conditions which attributed to Holocene cooling event. Since 790 cal BP, there has been a notable decrease in C/N ratios to their lowest levels, whereas TOC and δ¹³C have slightly increased. It indicated more drier conditions in the region. The sediment core's topmost 50 cm (corresponding to 480 cal BP) exclusively contains diatoms, predominantly of the Eunotia species, a benthic genus, pointing to an acidic sedimentary environment with reduced water levels.