Abstract
Concentrations of radionuclides such as 14C, 137Cs, 210Pb, and 214Pb, the contents of organic C and N, and 13C/12C ratios were measured for near surface sediments collected from Tilitso, a high altitude lake in Nepal, Himalayas. Living attached algae obtained from the streams feeding Lake Tilitso were also analyzed on their 14C abundances. The 14C concentration, Δ14C, was measured by direct detection of 14C atoms using a Tandetron accelerator mass spectrometer, on the acid-insoluble organic carbon that was extracted from each sediment or each algae sample. Activities of 137Cs, 210Pb, and 214Pb in the sediments were measured with a coaxial-well-type high-purity-germanium detector.
The sedimentation rate was estimated to be 0.56±0.27 cm y-1 by the 210Pb method. The content of carbon as acid-insoluble organic compounds was from 0.5 to 0.7%, and such carbon was depleted in 14C, yielding Δ14C values between -855±5 and -905±4‰ (apparent 14C ages between 15,520±250 and 18,910±360 y BP). Values of Δ14C for attached algae samples were also low, ranging from -463±31 to -701±29‰ (apparent ages from 4,980±460 to 9,700±780 y BP). The unexpectedly low 14C concentrations of these sediment and attached algae samples can be reasonably explained by considering geological and climatic environments around Lake Tilitso.
