16:30 〜 16:45
[AOS09-11] A paleoclimatological approach to the multidecadal climate variability
キーワード：数十年周期気候変動、古気候記録、東アジア夏季モンスーン、同位体年輪年代学
[Introduction]
In general observational studies, high-frequency climate variability like subseasonal variations is investigated using short-term high-resolution meteorological records, while low-frequency climate variability like glacial-interglacial cycle is studied based on long-term low-resolution geological records. In multidecadal variability (MDV), however, the instrumental observed data are too short to collect many examples, so that it is difficult to compare various MDV cases for elucidating its underlying mechanism. Recently, a novel method in isotope dendrochronology has been developed to reconstruct summer monsoon in East Asia seamlessly from annual to millennial time scales (1). Here, we show the annually resolved 2600-year time series including MDV and investigate its temporal variability using a wavelet method to provide a new observational resource for research in the multidecadal climate variability and predictability.
[Data and Method]
In order to obtain long-term annually resolved summer monsoon records, 67 wood samples with hundreds of year rings, including living trees, architectural woods, archaeological woods, and buried logs covering last 2600 years, have been collected in central Japan and analyzed for their tree-ring cellulose oxygen and hydrogen isotope ratios. After fixing the date of all rings in all woods by a cross-dating method using the oxygen isotope ratio, hydrogen isotope ratios were integrated to remove long-term biological trends and extract climatological components purely from the time-series of oxygen isotope ratios (Fig.1A; 1). By comparison with meteorological observed data (Fig.1B-D; 2), numerous historical documents on past weather, and long-term low-frequency paleoclimate records, the time-series in Fig.1A has been demonstrated to reflect precisely the variation in summer monsoon activity seamlessly from annual to millennial time scales. In order to investigate temporal changes in MDV during last 2600 years, we applied a wavelet method for the time series (3-5).
[Result and Discussion]
By transforming Fig.1A into periodic domains (Fig. 2A-C), we find that MDV is enhanced at about every 400 years since 2600 years ago. The enhancements of MDV correspond to those of the Pacific Decadal Oscillation (PDO) (6) (Fig. 2B-C), reflecting the close relationship between the East Asian summer monsoon and the PDO (7). Interestingly, episodes of enhanced MDV were followed by political regime shifts in China and Japan in almost all cases (Fig. 2D-E). The synchronous MDV is found in Taiwan, too (Fig. 2B-C) (8), indicating that the periodic enhancements of MDV were universal through East Asia, reflecting the East Asian summer monsoon activity. The tight correlation between the MDV modulations and East Asian history during last 2600 years suggests that the enhancement of MDV underlies the periodic and simultaneous political regime shifts throughout East Asia. While the relationship between MDV of summer monsoon activity and East Asian human history are now being studied in historical and archaeological contexts (9), mechanisms of the periodical MDV enhancement at about every 400 years are still unclear and worth studying not only for understanding MDV itself but also for elucidating human history.
[Reference]
1. T. Nakatsuka et al., Clim. Past 16, 2153–2172 (2020) https://doi.org/10.5194/cp-16-2153-2020.
2. G. J. van Oldenborgh and G. Burgers, Geophys. Res. Lett. 32, L15701 (2005)
3. S. G. Mallat, A wavelet tour of signal processing (The Sparse Way (3rd Ed.), Academic Press, 14-21, 2009).
4. N. Delprat et al., IEEE Transact. Inform. Theory 38, 644 (1992).
5. S. G. Mallat, IEEE Transact. Patt. Anal. Mach. Intel. 11, 674 (1989).
6. R. Wilson et al., Clim. Dyn. 28, 425 (2007).
7. Z. Hao et al., PLOS ONE 10, e0131159 (2015).
8. Y. Liu et al., Nature Com. 8, 15386 (2017).
9. T. Nakatsuka (ed), Reconsidering Japanese history from climate variability (vol.1-6) (Rinsen-Shoten 2020-21) (in Japanese).
In general observational studies, high-frequency climate variability like subseasonal variations is investigated using short-term high-resolution meteorological records, while low-frequency climate variability like glacial-interglacial cycle is studied based on long-term low-resolution geological records. In multidecadal variability (MDV), however, the instrumental observed data are too short to collect many examples, so that it is difficult to compare various MDV cases for elucidating its underlying mechanism. Recently, a novel method in isotope dendrochronology has been developed to reconstruct summer monsoon in East Asia seamlessly from annual to millennial time scales (1). Here, we show the annually resolved 2600-year time series including MDV and investigate its temporal variability using a wavelet method to provide a new observational resource for research in the multidecadal climate variability and predictability.
[Data and Method]
In order to obtain long-term annually resolved summer monsoon records, 67 wood samples with hundreds of year rings, including living trees, architectural woods, archaeological woods, and buried logs covering last 2600 years, have been collected in central Japan and analyzed for their tree-ring cellulose oxygen and hydrogen isotope ratios. After fixing the date of all rings in all woods by a cross-dating method using the oxygen isotope ratio, hydrogen isotope ratios were integrated to remove long-term biological trends and extract climatological components purely from the time-series of oxygen isotope ratios (Fig.1A; 1). By comparison with meteorological observed data (Fig.1B-D; 2), numerous historical documents on past weather, and long-term low-frequency paleoclimate records, the time-series in Fig.1A has been demonstrated to reflect precisely the variation in summer monsoon activity seamlessly from annual to millennial time scales. In order to investigate temporal changes in MDV during last 2600 years, we applied a wavelet method for the time series (3-5).
[Result and Discussion]
By transforming Fig.1A into periodic domains (Fig. 2A-C), we find that MDV is enhanced at about every 400 years since 2600 years ago. The enhancements of MDV correspond to those of the Pacific Decadal Oscillation (PDO) (6) (Fig. 2B-C), reflecting the close relationship between the East Asian summer monsoon and the PDO (7). Interestingly, episodes of enhanced MDV were followed by political regime shifts in China and Japan in almost all cases (Fig. 2D-E). The synchronous MDV is found in Taiwan, too (Fig. 2B-C) (8), indicating that the periodic enhancements of MDV were universal through East Asia, reflecting the East Asian summer monsoon activity. The tight correlation between the MDV modulations and East Asian history during last 2600 years suggests that the enhancement of MDV underlies the periodic and simultaneous political regime shifts throughout East Asia. While the relationship between MDV of summer monsoon activity and East Asian human history are now being studied in historical and archaeological contexts (9), mechanisms of the periodical MDV enhancement at about every 400 years are still unclear and worth studying not only for understanding MDV itself but also for elucidating human history.
[Reference]
1. T. Nakatsuka et al., Clim. Past 16, 2153–2172 (2020) https://doi.org/10.5194/cp-16-2153-2020.
2. G. J. van Oldenborgh and G. Burgers, Geophys. Res. Lett. 32, L15701 (2005)
3. S. G. Mallat, A wavelet tour of signal processing (The Sparse Way (3rd Ed.), Academic Press, 14-21, 2009).
4. N. Delprat et al., IEEE Transact. Inform. Theory 38, 644 (1992).
5. S. G. Mallat, IEEE Transact. Patt. Anal. Mach. Intel. 11, 674 (1989).
6. R. Wilson et al., Clim. Dyn. 28, 425 (2007).
7. Z. Hao et al., PLOS ONE 10, e0131159 (2015).
8. Y. Liu et al., Nature Com. 8, 15386 (2017).
9. T. Nakatsuka (ed), Reconsidering Japanese history from climate variability (vol.1-6) (Rinsen-Shoten 2020-21) (in Japanese).