In order to understand the climate variability of the Holocene period, two sediment cores were extracted at the northeastern part of Lake Aoki, an intermontane freshwater body located near the northern Japanese Alps, central Japan. The sediments are mainly composed of silty clay with some intercalation of event sediments, including a tephra known as the Kikai-Aka-hoya (K-Ah) that dates 7, 250calBP. The sediment chronology yields the sedimentation rate of ca. 0.16 and 0.37 mm yr
-1 above and below the tephra, respectively. The sediments were investigated at 0.5 cm interval, providing a time resolution of 13-29 years, for total organic carbon (TOC) and total nitrogen (TN) contents. The record of the organic contents along with the diatom abundance at 50 horizons is used as limnological monitors and climate proxies. The diatom record suggests that the lake has been oligotrophic and alkaline. TOC content and diatom abundance yield close correspondence with both short- and long-term fluctuations, shifting between low- and high-values. Climate, which control surface-water temperature, appears to be the main factor to affect the variability in the proxy records in Lake Aoki. The climate is dynamic, abruptly switching from various degrees of cool to warm conditions in centennial to millennial scale. Warm conditions prevail from ca. 750-1300, 1750-3050, 4000-5250, 6150-7250, and 8800-10000 cal BP, and cooling occurs during 150-750, 1300-1750, 3050-4000, 5250-6150, and 8350-8800 cal BP. The period between 7250-8350 cal BP is rather fluctuating. Climatic events such as the Little Ice Age (LIA), the Medieval Warm Period (MWP), the Kofun cold stage, and the Holocene Optimum (HOP) are evident, and some other warm and cool events not well recorded before in Japan and abroad are also recognized. The lake also provides a valuable window into the recent climate change and the modern hydraulic changes in the lake system.
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