2:00 PM - 2:15 PM
[MTT38-02] High-resolution dating of surface peat based on natural and anthropogenic radionuclides
Keywords:Wetland, Peat, Radiocarbon dating, Pb-210 dating, Cs-137, Bomb peak
Establishing high-resolution chronologies of peat sequences is crucial for estimating peat carbon storage and elucidating the evolutionary processes of wetland sediments. Some natural (lead-210, 210Pb) and anthropogenic radionuclides (carbon-14, 14C; cesium-137, 137Cs; americium-241, 241Am) are known to provide high-resolution sedimentation ages from their concentration profiles in surface sediment sequences (e.g., Appleby & Oldfield, 1978; Davies et al., 2018; Li et al., 2019). However, their age estimates often show offset due to differences in their environmental dynamics (e.g., Goodsite et al., 2001; van der Plicht et al., 2013). Here we hypothesized that high-resolution profiles of these radionuclides record their behaviors in the environment. In this study, we measured 14C, 137Cs, 210Pb, and 241Am concentrations of a surface peat from a wetland in eastern Hokkaido in high resolution to understand their environmental dynamics and to establish an accurate age-depth model.
Our study site (43°08’23.3”N, 145°01’23.5”E, 49.2 m above sea level) is located at one member of Hamanaka-Chanai wetland group, on a marine terrace on the western edge of the Konsen Plateau, eastern Hokkaido, Japan. The wetland sediment core (CG-1-1) used in this study was manually extracted at the site in the fall of 2020. A total of 9 samples from the upper 13 cm of the peat sequence were processed for 14C analyses. 137Cs, 210Pb, and 241Am radioactivity measurements of the sediment samples were carried out at 13 points along the upper 14 cm of the core.
The result of the 14C measurements suggests that the sediment in the surface 13 cm spans the last 65 years. The 14C peaked at the depth between 11 and 12 cmbs (centimeters below the surface), while the 137Cs activity of the core sequence showed a significant peak at 10-11 cmbs. Although both 14C and 137Cs detected in the measured layers are introduced by the nuclear bomb tests from the mid-1950s to mid-1960s (Evrard et al., 2020; Hua et al., 2022), the bomb peaks in the sample showed a small gap in their depths. This discrepancy in peak depths may be due to their difference of dynamics in the environment. Further results (i.e., 210Pb, 241Am, etc.) will be discussed in the presentation.
Acknowledgement
The authors would like to thank the members of JSPS KAKENHI research group (18H00762) who took part in the core sampling.
Our study site (43°08’23.3”N, 145°01’23.5”E, 49.2 m above sea level) is located at one member of Hamanaka-Chanai wetland group, on a marine terrace on the western edge of the Konsen Plateau, eastern Hokkaido, Japan. The wetland sediment core (CG-1-1) used in this study was manually extracted at the site in the fall of 2020. A total of 9 samples from the upper 13 cm of the peat sequence were processed for 14C analyses. 137Cs, 210Pb, and 241Am radioactivity measurements of the sediment samples were carried out at 13 points along the upper 14 cm of the core.
The result of the 14C measurements suggests that the sediment in the surface 13 cm spans the last 65 years. The 14C peaked at the depth between 11 and 12 cmbs (centimeters below the surface), while the 137Cs activity of the core sequence showed a significant peak at 10-11 cmbs. Although both 14C and 137Cs detected in the measured layers are introduced by the nuclear bomb tests from the mid-1950s to mid-1960s (Evrard et al., 2020; Hua et al., 2022), the bomb peaks in the sample showed a small gap in their depths. This discrepancy in peak depths may be due to their difference of dynamics in the environment. Further results (i.e., 210Pb, 241Am, etc.) will be discussed in the presentation.
Acknowledgement
The authors would like to thank the members of JSPS KAKENHI research group (18H00762) who took part in the core sampling.