4.2 kiloyear event

2019年3月5日 火曜日 晴れ

4.2 kiloyear event について調べてみた。

ウィキペディア 4.2 kiloyear event

The 4.2-kiloyear BP aridification event was one of the most severe climatic events of the Holocene epoch.[1] It defines the beginning of the current Meghalayan age in the Holocene epoch. Starting in about 2200 BC, it probably lasted the entire 22nd century BC. It has been hypothesised to have caused the collapse of the Old Kingdom in Egypt as well as the Akkadian Empire in Mesopotamia, and the Liangzhu culture in the lower Yangtze River area.[2][3] The drought may also have initiated the collapse of the Indus Valley Civilisation, with some of its population moving southeastward to follow the movement of their desired habitat,[4] as well as the migration of Indo-European speaking people into India.[5]

 https://en.wikipedia.org/wiki/4.2_kiloyear_event

effect: メソポタミアではアッカド帝国の崩壊、インドではインダス文明の崩壊、インドヨーロッパ語族(いわゆるアーリア人)のインドへの移住、パミール語・ドラヴィダ語族の南下など。東アジア(いわゆる中国)は禹の治水の時代か? 以下にエジプト古王朝に関するものを引用:

In c. 2150 BC, the Old Kingdom was hit by a series of exceptionally low Nile floods. This may have influenced the collapse of centralised government in ancient Egypt after a famine.[23]Contemporary texts claim that famines, social disorder and fragmentation subsequently occurred.  ナイル川の氾濫が少なく、飢饉を来たし、古王朝崩壊へとつながった、という説。  Stanley, Jean-Daniel; et al. (2003). “Nile flow failure at the end of the Old Kingdom, Egypt: Strontium isotopic and petrologic evidence”. Geoarchaeology18 (3): 395–402. doi:10.1002/gea.10065. この論文を調べてみると以下の通り(ただし、私が読むことのできた無料部分のみ、以下に引用)

Nile flow failure at the end of the Old Kingdom, Egypt: Strontium isotopic and petrologic evidence

Jean‐Daniel StanleyMichael D. KromRobert A. CliffJamie C. WoodwardFirst published: 21 February 2003 https://doi.org/10.1002/gea.10065

Abstract: Strontium isotopic and petrologic information, obtained from sediment cores collected in the Nile delta of Egypt, indicate that paleoclimatic and Nile baseflow conditions changed considerably from about 4200 to 4000 cal yr B.P. in the Nile basin. Our study records a higher proportion of White Nile sediment transported during the annual floods at ca. 6100 cal yr B.P. than towards 4200 cal yr B.P., at which time suspended sediment from the Blue Nile formed a significantly larger fraction of the total load. This resulted from a decrease in vegetative cover and an increase in erosion rate accompanying the marked decline in rainfall. These new geoscience data indicate major changes in annual flooding and baseflow of the river Nile, marked short‐term paleoclimatic‐related events that may in part have led to the collapse of the Old Kingdom. © 2003 Wiley Periodicals, Inc.

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グリーンランドの氷には4.2kyの証拠は見つからない:

ウィキペディアによると・・・https://upload.wikimedia.org/wikipedia/commons/5/57/Greenland_Gisp2_Temperature.svg Central Greenland reconstructed temperature. Data source:http://www.ncdc.noaa.gov/paleo/pubs/alley2000/alley2000.html

Central Greenland reconstructed temperature. Unlike the 8.2-kiloyear event, the 4.2-kiloyear event has no prominent signal in the Gisp2 ice core that has an onset at 4.2 ka BP. 補註 ウィキペディアで引かれている上記のグラフからは 8.2 kiloyear event は読み取れるのだが、4.2ky event を読み取れない。4.8ky event と名づけたいような寒冷化の少ピークは見えるのだが・・。即ち、グリーンランドの氷の中には4.2kyの証拠は見つからないのである。

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補註 日本の縄文時代の「4.3kaイベント」に関する記載は、ウィキペディアの英語版の 4.2ky event の項目には見当たらなかった。対応する気候変動か否かは慎重を期して「保留」としておきたい。

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