Radionuclide ^239+240Pu for Dating and Sedimentation Rate in Chinese Lakes

Abstract

Radionuclide 239+240Pu dating and sedimentation rate is a crucial parameter for studying lake sedimentary processes. To comprehensively investigate 239+240Pu vertical distributions and relevant processes in Chinese lakes, this study collects and summarizes 54 sediment core samples from 40 lakes and reservoirs globally. First, the results suggest that two typical vertical distributions of 239+240Pu are summarized in Chinese lakes. The location of the 239+240Pu peak corresponds to the age of global atmospheric nuclear test deposition in 1963 ± 1. Second, 239+240Pu based on 1963 peak is far more suitable for lake dating compared to 137Cs, and a significant linear correlation (R 2 = 0.924) between the depth of 239+240Pu maximum value (cm) and sedimentation rate (cm a–1) in Chinese lakes was established. For the first time, this study has found that this significant linear relationship can be generalized globally (R 2 = 0.909), regardless of where the lake sediment cores were sampled. Third, we identify three typical vertical distributions for the 240Pu/239Pu atom ratio in Chinese lake sediment cores: invariant distribution, mutation distribution, and gradient distribution. This result implies that 239+240Pu in Chinese lakes mainly originate from the global fallout; yet this does not rule out the potential contribution from local sources of 239+240Pu, such as the Lop Nor nuclear tests, the atomic city nuclear activities, and the Chernobyl nuclear accident. However, the trend in the average 240Pu/239Pu ratio varies independent of latitude. Moreover, a significant positive linear correlation is detected between average 239+240Pu inventory in the soil and lake cores, with a coefficient of 0.538. In particular, the high 239+240Pu inventory background value in Northwest China closely correlates with the deposition of 239+240Pu in some lakes (e.g., Lake Sugan). This manuscript provides insights into 239+240Pu vertical patterns and processes in Chinese lakes and sheds light on future research using 239+240Pu for dating and sedimentation rate in lakes outside China.