16:45 〜 17:00
[MIS06-11] 東アジア夏季モンスーン降水の過去6千年間の千年スケール変動は、偏西風ジェットの挙動に規定されたモンスーン降水フロントの南北振動に起因する
キーワード：East Asian summer monsoon, precipitation front, westerly jet, Yangtze River, Lake Suigetsu, Holocene
Precipitation by East Asian summer monsoon (EASM) plays a dominant role in the hydrological cycle of the area and exerts significant impact on lives of people living there. Thus, it is important to understand time-scale and magnitude of the variability and their controlling factors. Centennial- to millennial-scale variability of EASM precipitation could have been especially significant judging from Chinese historical records, but its magnitude, spatial distribution, and controlling factor(s) are largely unknown.
In this study, we estimated movement of EASM (precipitation) front in Yangtze River drainage basin during the last ~6 kys based on reconstruction of provenance changes of fine silt fraction of the sediments, representing suspended particulate (SPM) from Yangtze River, using cores from Yangtze Delta and the Mud Belt along the South China coast. The results show centennial- to millennial-scale NW-SE oscillation of EASM front with NW ward penetration during 6-5.1, 3.5-1.8, and 0.2-0 ka, and SE ward retreat during 5.1-3.5 and 1.8-0.2 ka, respectively.
We compared the result with N-S oscillation of westerly jet over the Japan Sea during the Holocene by Nagashima et al. (2013). The result suggests the oscillation of EASM front is in parallel with oscillation of the westerly jet, supporting the idea that subtropical westerly jet bounds the northern limit of EASM precipitation.
We also reconstructed flood and heavy precipitation record in SW Japan during the last 6 kyrs using SG-12 cores from Lake Suigetsu, and compared the record with the provenance changes of SPM discharged from Yangtze River. The comparison revealed a striking similarity between temporal changes in flood and heavy rain frequencies in Lake Suigetsu, SW Japan and temporal changes in provenance of SPM discharged from Yangtze River.
The observed relationships suggest that N-S movement of westerly jet has been controlling millennial-scale changes in EASM intensity through modulating the position of EASM front, and southward shifts of westerly jet and EASM front have caused more rain and frequent floods in SE part of South China and SW Japan.
In this study, we estimated movement of EASM (precipitation) front in Yangtze River drainage basin during the last ~6 kys based on reconstruction of provenance changes of fine silt fraction of the sediments, representing suspended particulate (SPM) from Yangtze River, using cores from Yangtze Delta and the Mud Belt along the South China coast. The results show centennial- to millennial-scale NW-SE oscillation of EASM front with NW ward penetration during 6-5.1, 3.5-1.8, and 0.2-0 ka, and SE ward retreat during 5.1-3.5 and 1.8-0.2 ka, respectively.
We compared the result with N-S oscillation of westerly jet over the Japan Sea during the Holocene by Nagashima et al. (2013). The result suggests the oscillation of EASM front is in parallel with oscillation of the westerly jet, supporting the idea that subtropical westerly jet bounds the northern limit of EASM precipitation.
We also reconstructed flood and heavy precipitation record in SW Japan during the last 6 kyrs using SG-12 cores from Lake Suigetsu, and compared the record with the provenance changes of SPM discharged from Yangtze River. The comparison revealed a striking similarity between temporal changes in flood and heavy rain frequencies in Lake Suigetsu, SW Japan and temporal changes in provenance of SPM discharged from Yangtze River.
The observed relationships suggest that N-S movement of westerly jet has been controlling millennial-scale changes in EASM intensity through modulating the position of EASM front, and southward shifts of westerly jet and EASM front have caused more rain and frequent floods in SE part of South China and SW Japan.