Development of large scale mapping method of precipitation isotopic ratios using tree-ring cellulose oxygen and hydrogen isotopic ratios

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Oxygen and hydrogen isotopic ratios of tree-ring cellulose were monitored at several sites in Japan, Russia and China together with those isotopic ratios of environmental waters in order to develop methods to reconstruct past-climate changes especially changes of water cycles in very high time and space resolutions during last several centuries and millenniums. In 2005, relationships between isotopic ratios of tree-ring clullose and environmental waters were analyzed in Hokkaido and western China, which represents cold, humid and hot, dry environments, respectively, and 230 years of summer relative humidity in northern Hokkaido were reconstructed using oak tree-ring cellulose. In 2006, tree rings of larch in Kamchatka, Russia and cypress in Nagano, Japan were investigated for their oxygen and hydrogen isotopic ratios in order to reconstruct past winter temperature and summer relative humidity, respectively.Tree rings can usually record the climate in summer during which photosynthetic activity of plant is most active. However, as winter precipitation can remain even in summer as soil water in the high latitudinal area with heavy snow cover, tree-ring O and H isotopic ratios may hold signals of winter climate. 180 years of larch tree rings in Kamchatka were analyzed and the d-exess values of tree-ring cellulose and temperature of Feb. and Mar. were found to have very strong negative correlation, which demonstrated the stepwise increase of winter temperature there during last 150 years.Contrary to Kamchatka, it is very warm and humid in Honshu Japan, where tree growths are not usually limited by precipitation or temperature and tree ring width does not hold signal of past climate there. However, the O isotopic ratios in cypress tree rings were found to vary corresponding to summer relative humidity there, and changes in summer relative humidity were illustrated during last 260 years.