A CLIMATE RECORD FOR THE LAST 140 KA BASED ON DIATOM VALVE FLUX FROM LAKE BIWA, JAPAN

To reconstruct the pattern of past climate change in central Japan during the last 140 ka, diatom valve concentration (DVC; valves g-1) and flux (DVF; valves cm-2 yr-1) were examined using a 140 m core taken from Lake Biwa, Shiga Prefecture, central Japan. Sample resolution in most of the records was between 150 and 300 years. Based on the characteristics of past and modern diatom responses to possible climate variables, we interpret changes in DVC and DVF to reflect summer precipitation level and wind conditions, which are closely associated with changes in major summer meteorological phenomena, including the Baiu front, which mainly occurs from June to July (East Asian summer monsoon), other fronts during the other periods, typhoons, and mid-latitude cyclones. Thus the DVC and DVF observed in the Lake Biwa core can be used to infer the activities of these phenomena in central Japan. The DVF record shows millennial-scale fluctuations during the last 140 ka. During the Holocene (0 – 10 ka) and the last interglacial (70 – 135 ka), the DVF record shows levels near to or above those observed at present. By contrast, the DVF levels during the last glacial (10 – 70 ka) were relatively lower than at present, with frequent significant depletions below the present level. These results indicate that compared to the present, the activities of meteorological phenomena relating to summer rainfall were similar to, or enhanced, during the Holocene and the last interglacial, and weaker during the last glacial period.