[MIS08-P28] Correlation between stable isotope ratio of pollen and climate, as well as its possible application for paleoclimatology
Keywords:pollen, stable isotope, paleoclimate
Obtaining detailed paleoclimate information on terrestrial realms is essential for understanding the interaction between the atmosphere and the ocean. In particular, climate in mid- latitudinal land is closely related to the human’s life.
Fossil pollen analysis in lacustrine sediments is a widely used method for examining the paleoclimate on land (e.g. Tarasov et al., 2011; Kigoshi et al., 2014).
Quantitative reconstruction of paleoclimate using pollen data has also been attempted (Guiot, 1991; Nakagawa et al. 2002). However, direct correlation between pollen records and other high-quality data sets, such as ice core and ocean records, is not straightforward because of the response time of vegetation (Williams et al., 2002).
To solve this problem, the possibility of reconstructing paleoclimate using pollen isotope data has been pointed out (Loader and Hemming, 2004). Recently developed method of efficient high purity pollen extraction (Yamada et al.,2019, INQUA) made it realistic.
We aim at quantitative reconstruction of paleoclimate based on pollen isotope data. In this study, we evaluated the response of pollen isotope to climate using live arboreal pollen.
Studies on the relationship between pollen stable isotope ratios and climate in Europe suggests a correlation between hydrogen isotope ratio and precipitation. However, the data size is too small to use the results for application. In this study, we measured oxygen isotope ratio of cedar pollen that were collected from 125 sites across Japan. The measurement was made using TC/EA (thermo Scientific Co., Ltd.) of the University Museum, the University of Tokyo.
As the meteorological observation data, we used mesh agricultural meteorological data from National Agriculture and Food Research Organization (NARO). he mesh dataset has 1km resolution and was generated from AMeDAS weather observation records, taking into account temperature lapse rate, topography and other relevant factors (Kiyono, 1993; Ono et al., 2016).
Results and discussion
The 125 sites that we could include in this study covered an area with an average annual temperature of 12-17 ° C, precipitation of 1600-4000mm, altitude of 0-1000m, and latitude of 32-39 °.A strong correlation between pollen oxygen isotope ratio the mean annual temperature was found (r = 0.66).On the other hand, there was a systematic drift in isotope ratio according to the altitude of the pollen sampling point.
This study confirms that the oxygen isotope ratio of pollen responds to temperature.
In the future, although we still have to understand the isotope fractionation process of pollen and apply correction against altitude, it is possible to use the pollen oxygen isotope data for quantitatively reconstructing temperature.