Lake Suigetsu

Lake Suigetsu
Name	Suigetsu
Location	Higashisakae, Sera District, Hiroshima Prefecture, Japan
Coords	34°37′N 133°05′E
Type	kellalake
Inflow	Nita River, Sera River
Outflow	none (endorheic)
Area	4.06 km²
Max-depth	38 m
Elevation	75 m

Lake Suigetsu is a tectonic lake in Sera District, Hiroshima Prefecture, Japan, noted for its annually laminated sediments that provide a continuous varve chronology used in global palaeoclimatology and radiocarbon calibration. The lake occupies a closed basin near Miyoshi, Hiroshima and lies within a landscape shaped by Seto Inland Sea–region tectonics and Quaternary volcanism. Researchers from institutions including the University of Tokyo, the Nihon University, and the Utrecht University have conducted multidisciplinary studies integrating sedimentology, geochemistry, and geochronology.

Geography and Hydrology

Lake Suigetsu sits in the eastern sector of Hiroshima Prefecture adjacent to the Chūgoku Mountains and within the Setouchi drainage mosaic. The lake basin receives inflow from tributaries including the Nita River and the Sera River but lacks surface outflow, rendering it hydrologically endorheic like Lake Biwa in seasonal behaviour though much smaller in scale. The climate influence is maritime from the Seto Inland Sea and continental via the Chūgoku ranges, producing precipitation patterns monitored by the Japan Meteorological Agency and regional hydrologic studies by the Ministry of Land, Infrastructure, Transport and Tourism. Seasonal stratification creates anoxic bottom waters analogous to those observed in Meromictic lakes such as Lake Baikal and Lake Tanganyika, promoting preservation of laminae.

Geology and Formation

The basin originated from late Pleistocene tectonics linked to the Itoigawa-Shizuoka Tectonic Line–affected crustal deformation and local faulting in the Chūgoku region. Sediment fill records inputs from Holocene fluvial systems and tephra layers correlated with eruptions of nearby volcanic centres like Mount Aso and Mount Fuji through tephrochronology studies conducted by teams from the Geological Survey of Japan and the Japan Agency for Marine-Earth Science and Technology. The underlying bedrock includes Mesozoic accretionary complexes comparable to terranes studied in San-in geologic syntheses, and Quaternary deposits record fluctuations tied to glacial–interglacial cycles examined alongside datasets from Greenland ice cores and Lake Suigetsu varve series.

Ecology and Biodiversity

Lake Suigetsu supports lacustrine and riparian habitats that harbour taxa documented by surveys from the Japanese Society of Limnology and regional conservation groups such as Hiroshima Prefectural Museum of Nature and History. Aquatic vegetation is analogous to assemblages recorded in Lake Kasumigaura and Lake Biwa, providing habitat for fish species reported in faunal lists by the Ministry of the Environment (Japan), including endemic or regionally significant taxa. Avifauna utilises marshy littoral zones in migration routes recorded by the Wild Bird Society of Japan, and macroinvertebrate and microbial communities contribute to organic-matter deposition studied by researchers at Tohoku University and the University of Tokyo. The lake’s anoxic profundal zone fosters unique microbial mats comparable to studies from Monterey Bay oxygen-minimum zones and supports preservation of organic biomarkers used in palaeoenvironmental reconstructions.

Varved Sediments and Radiocarbon Calibration

The laminated, annually deposited varves of Lake Suigetsu form one of the world’s most important chronological archives, integrated with international calibration efforts such as IntCal and cross-checked against dendrochronology records from European oak and Japanese cedar chronologies. Collaborative projects involving the Max Planck Institute for Chemistry, the University of Tokyo, the British Geological Survey, and Wuhan University produced a continuous varve-counted chronology extending through the Holocene that enabled refinement of the radiocarbon calibration curve. The sediments contain well-preserved plant macrofossils, tephra horizons correlated with named eruptions like the AD 946 eruption of Mount Baekdu analogue tephras, and isotopic signatures (δ13C, δ15N) employed in palaeoclimate reconstructions aligned with Greenland ice cores and Tree-ring records. The Lake Suigetsu varve series played a key role in resolving radiocarbon plateaus and improving age models used by archaeologists working on sites such as Jomon period settlements and by paleoclimatologists studying Holocene climate variability.

Human History and Cultural Significance

The lake and its environs lie within a cultural landscape shaped by prehistoric to modern occupations, with archaeological finds from the Jomon period, Yayoi period, and Kofun period recorded in regional surveys by the Agency for Cultural Affairs (Japan). Local communities in Sera, Hiroshima Prefecture historically utilised the lake for fishing and reed harvesting, activities documented in municipal archives and folk records curated by the Hiroshima Prefectural Library and regional museums. Scholars from Kyoto University and the National Museum of Nature and Science have examined human-environment interactions, linking sedimentary evidence to land-use change during periods contemporaneous with documented events such as the rise of Heian court influence in western Honshū.

Conservation and Environmental Issues

Conservation efforts involve prefectural policies coordinated with the Ministry of the Environment (Japan) and local municipalities to monitor water quality, invasive species, and watershed land-use changes tracked by the International Union for Conservation of Nature–aligned assessments. Nutrient loading from agricultural catchments, sediment disturbance from infrastructure projects assessed by the Ministry of Land, Infrastructure, Transport and Tourism, and the potential impacts of climate change scenarios modelled by groups at the University of Tokyo and the Meteorological Research Institute pose management challenges. Ongoing scientific monitoring and community engagement, involving NGOs such as the Wild Bird Society of Japan and academic partners like Tohoku University, aim to balance heritage protection with sustainable use while safeguarding the varve archive essential to global chronologies.

Category:Lakes of Hiroshima Prefecture