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

[HQR04-P12] Analysis of Diatoms and Organic matter in the Sediments of Tianchi in DaXue Mountain Revealing Paleoenvironment Changes over the last 1000 years

*Yi-Chen Ho¹, Abdur Rahman¹, Liang-Chi Wang¹ (1.National Chung Cheng University, Taiwan)

The current study focused on Tian pond, located in the DaXue Mountain at an altitude of 2600 meters above sea level. It is dominated by coniferous forests and was free of human activities until 1911 A.D. To investigate the paleoenvironment of the region, a 46 cm long core, named DSS-TL-3 was collected. The ²¹⁰Pb and ¹⁴C dating techniques has established chorology, which revealed that core was covering the past 1000 years BP. The diatom fossils and carbon isotopic composition of organic materials (δ¹³C_org), and elemental concentrations of carbon (TOC) and total nitrogen (TN), along with their ratio (TOC/TN), were analyzed to the reconstruction of paleoenvironment and assess the impact of human activities on the local forest and aquatic ecosystems during the studied period. The current records showed an increase in TOC, significant fluctuations in the TOC/TN ratio, and a high δ¹³C_org during the period of 900-770 cal BP, which indicated dominance of C4 plants in the region due to drier climate conditions. Furthermore, TOC remained stable with slight increases till 40 cal BP. The TOC/TN ratio showed significant fluctuation from 770-550 cal BP and later stabilized towards 40 cal BP along an increasing trend of δ¹³C_org, which showed lowering in the contribution of C3 plants. It indicated climate were improving and became wetter during 770-550 cal BP and later transitioned into a drier climate towards 40 cal BP.
Since 40 cal BP (1910 AD), TOC showed an increased, while the TOC/TN ratio has begun to decline, and δ¹³C_org has become high. Historical records showed high human activities in during this period, likely to enhance agriculture and settlement in the region. The lower TOC/TN ratios can be caused by an increase N-nutrients into the region, however, TOC and δ¹³C_org was caused by irrigation of C4 crops in the region. However, diatom data are still undergoing analysis and will provide further clarity regarding changes in paleoenvironment conditions and the impact of human activities in the region.