1:45 PM - 3:15 PM
[HQR03-P14] Lake-bed configuration and the last 800-year sedimentary environmental variations in Lake Satsuma, Kagoshima Prefecture, Japan
Keywords:Lake Satsuma, Lake-bed configuration, Lake sediments, Climate changes, Total organic carbon
This research has clarified lake-bed configuration and sedimentary environmental history in Lake Satsuma, Kagoshima Prefecture for getting new paleoclimate records in the south Kyushu Island.
Lake Satsuma is located about 1.5km apart from the coastal area of the East China Sea, separating by the Fukiage-hama sand dune. First, we made the lake bottom topography map by using an echo sounding chart plotter. The map shows that water depth (maximum water depth: 12.8 m) tend to increase from the east side (inland) to the west side (East China Sea) in this lake, and that underwater landslides with buried trees in south part of the lake.
Two sediment cores were collected both on a flat surface with a depth of 9.8m and a depth of 11.0m near the deepest part. The length of the cores were 140 cm (1c core) and 98 cm (2c core), respectively. The lithology of the 1c core is composed of massive dark gray silt throughout the horizon except for a fine-grained volcanic ash layer with a thickness of about 5 cm at depth 130 cm. Radiocarbon dating of plant remains included in the sediment also revealed that the lowest part of the core was about 800 years old. Assuming that the sedimentation rate other than the intercalated volcanic ash layer is constant, it can be estimated to be 1.5 to 2.5mm/year. In addition, CNS elemental analysis was performed on 1 cm interval samples to obtain total organic carbon (TOC), total nitrogen (TN) concentrations, and their ratio (C/N ratio) in the sediment, The sedimentary environment was estimated.
The result of the vertical profile of C/N ratio indicates that the organic matter in the sediments seems to be originated from aquatic plankton. This suggests that previous research such as Kumon (2008), which states that changes in TOC concentrations in lake sediments reflect climate change, can be used. It was clarified that the environmental changes over the past 800 years reconstructed from the TOC concentration of the Lake Satsuma sediments generally agree with the climate change curves reconstructed from the Yakusugi tree rings (Kitagawa et al., 1998).
Lake Satsuma is located about 1.5km apart from the coastal area of the East China Sea, separating by the Fukiage-hama sand dune. First, we made the lake bottom topography map by using an echo sounding chart plotter. The map shows that water depth (maximum water depth: 12.8 m) tend to increase from the east side (inland) to the west side (East China Sea) in this lake, and that underwater landslides with buried trees in south part of the lake.
Two sediment cores were collected both on a flat surface with a depth of 9.8m and a depth of 11.0m near the deepest part. The length of the cores were 140 cm (1c core) and 98 cm (2c core), respectively. The lithology of the 1c core is composed of massive dark gray silt throughout the horizon except for a fine-grained volcanic ash layer with a thickness of about 5 cm at depth 130 cm. Radiocarbon dating of plant remains included in the sediment also revealed that the lowest part of the core was about 800 years old. Assuming that the sedimentation rate other than the intercalated volcanic ash layer is constant, it can be estimated to be 1.5 to 2.5mm/year. In addition, CNS elemental analysis was performed on 1 cm interval samples to obtain total organic carbon (TOC), total nitrogen (TN) concentrations, and their ratio (C/N ratio) in the sediment, The sedimentary environment was estimated.
The result of the vertical profile of C/N ratio indicates that the organic matter in the sediments seems to be originated from aquatic plankton. This suggests that previous research such as Kumon (2008), which states that changes in TOC concentrations in lake sediments reflect climate change, can be used. It was clarified that the environmental changes over the past 800 years reconstructed from the TOC concentration of the Lake Satsuma sediments generally agree with the climate change curves reconstructed from the Yakusugi tree rings (Kitagawa et al., 1998).