High time-resolution alkenone paleotemperature variations in Tokyo Bay during the Meghalayan: Implications for cold climates and social unrest in Japan
High time-resolution alkenone paleotemperature variations in Tokyo Bay during the Meghalayan: Implications for cold climates and social unrest in Japan
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DOI：
10.1016/j.quascirev.2019.106160
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发表时间：
2020-02
影响因子：
4
通讯作者：
Hiroto Kajita;N. Harada;Y. Yokoyama;Miyako Sato;N. Ogawa;Y. Miyairi;Chikako Sawada;A. Suzuki;H. Kawahata
中科院分区：
文献类型：
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作者：
Hiroto Kajita;N. Harada;Y. Yokoyama;Miyako Sato;N. Ogawa;Y. Miyairi;Chikako Sawada;A. Suzuki;H. Kawahata
为了丰富我们对东亚气候变化及其对日本文明的影响的理解，日本中部东京的区域古环境记录是必要的。之前的研究基于对东京湾沿岸贝壳丘和陆地钻孔岩心的花粉的分析，产生了古温度记录。然而，不存在连续的、高时间分辨率的、定量的古温度记录。在东京湾发现了一个活塞芯，从中提取了22个软体贝壳。由加速器质谱仪(AMS)14C测年确定的岩心年龄模型表明，该岩芯包含公元前2400年左右的连续记录。我们分析了烯烃不饱和度比(UK‘37)，以重建古温度的变化。Meghalayan期间的气温总体上比现在高，呈下降趋势，这与夏季轨道强迫日照的变化和东北太平洋次北极锋千年尺度的纬向移动大致相符。最大的冷期发生在公元前2300年左右，最低气温为19.5摄氏度，中断了温暖的条件。这一冷期可能对应于全球变冷/变干的“4.2ka BP事件”，该事件标志着北冰洋和梅加拉雅之间的分界线。我们的结果还显示，出现了几个冷期，这可能是由于太阳活动减少或大规模火山喷发造成的。特别是，在弥生时代(约公元前900年-公元前300年)，观察到了大约公元前440年和公元前100年的十年至百年规模的大冷期。中央政府制度建立后最冷的时期(约公元300年至今)记录到约公元1050年，这可能是由于强烈的厄尔尼诺模式和太阳活动减少造成的。这些气候变化事件都可以联系在一起，因此，可能是日本历史上重大饥荒和内战时期的潜在原因，最终导致日本社会制度的重大转变。
The regional paleoenvironmental record of Tokyo, central Japan, is required to enrich our understanding of climate change in East Asia and its impact on Japanese civilizations. Previous studies have generated paleotemperature records based on the analysis of shell mounds along the coast of Tokyo Bay and pollen from terrestrial borehole cores. However, a continuous, high time-resolution, quantitative paleotemperature record does not exist. A piston core was recovered from Tokyo Bay from which 22 mollusk shells were extracted. An age model for the core, determined via accelerator mass spectroscopy (AMS)14C dating of the shells and a scoria layer from the Hoei eruption (1707 CE), showed that the core contains continuous record from ca. 2400 BCE. We analyzed the alkenone unsaturation ratios (UK’37) to reconstruct the variations in the paleotemperature. The temperature during the Meghalayan was generally warmer than that at present exhibiting a declining trend, which roughly matches the changes in the orbital-forcing summer insolation and the millennial-scale latitudinal shift of the subarctic front in the northeastern Pacific Ocean. The largest cold period, which occurred ca. 2300 BCE and had a minimum temperature of 19.5 °C, interrupted the warm conditions. This cold period may correspond to the global cooling/drying “4.2 ka BP event,” which marks the boundary between the Northgrippian and Meghalayan. Our results also revealed that several cold periods occurred, which may have been caused by decreases in solar activity or large volcanic eruptions. Particularly, large decadal to centennial-scale cold periods were observed ca. 440 BCE and 100 CE during the Yayoi era (ca. 900 BCE–300 CE). The coldest period after the establishment of a centralized system of government (ca. 300 CE–present) was recorded ca. 1050 CE, which may have been caused by the combination of a strong El-Niño mode and reduced solar activity. These climate change events can all be linked and, therefore, may be the potential causes of significant periods of famine and civil war in Japanese history, which eventually led to major shifts in Japanese social systems.