SOIL EROSION CAUSED THE INCREASING HOLOCENE RADIOCARBON RESERVOIR EFFECT OF LAKE KANAS IN THE ALTAI MOUNTAINS

Radiocarbon (C-14) dating of the total organic carbon (TOC) content of lacustrine sediments is always affected by a C-14 reservoir effect and the C-14 dates are often systematically older than the true ages. However, there are few studies of the temporal changes of the C-14 reservoir effect, with reference to the specific influencing factors. We collected TOC samples from the Holocene sediments of Lake Kanas, in the southern Altai Mountains, for AMS C-14 dating and compared the results with AMS C-14 ages based on terrestrial plant macrofossils from the same depths. The results show that the reservoir ages progressively increased from similar to 0 to similar to 2800 yr between similar to 9700 cal BP and similar to 530 cal BP. As the lake catchment was glaciated prior to the Holocene, and Holocene soils and peats are the main sources of the TOC in the lake sediments, we argue that soil erosion is the major factor contributing to the progressive increase in the reservoir age. Based on previously reported evidence for increasing moisture in central Asia and glacier advances in the mid-to-late Holocene, we suggest that the intensified soil erosion on the hillslopes was caused by increased precipitation during the mid-to-late Holocene and by anthropogenic forest clearance after 1500 cal BP.

Automated summary

Radiocarbon (C-14) dating of lacustrine sediments is influenced by C-14 reservoir effect, resulting in systematically older ages. This study investigated the temporal changes of the C-14 reservoir effect in Lake Kanas sediments and found that the reservoir ages progressively increased from approximately 0 to 2800 years between 9700 and 530 cal BP. Soil erosion, caused by increased precipitation during the mid-to-late Holocene and anthropogenic forest clearance, was identified as the major factor contributing to the increase in reservoir age.