Ice Age - Ice Age

A period during a glacial age when ice sheets and glaciers advanced and expanded on a large scale up to mid-latitude regions. In contrast, periods when glaciers did not develop much are called interglacial periods. A glacial period is not always a continuation of cold weather, but there are two or three warm periods during which glaciers retreat and shrink, called interglacial periods. On the other hand, cold periods between interglacial periods when glaciers advance and expand again are called subglacial periods. A glacial period is a global climate change that lasts for 100,000 years. The periods of glacial advance and retreat differ between high and low latitude regions, and the higher the latitude, the longer the glacial period. Therefore, the age of a glacial period varies from region to region, and it is difficult to determine its absolute age precisely. The rise and fall of glaciers in the Quaternary glacial period has long been studied from glacial deposits (such as moraine and varved clay) around the Alps, the former Soviet Union, and North America. Five glacial periods have been recognized north of the Alps, and they are called the Danube Glacial Age, the Gunz Glacial Age, the Mindel Glacial Age, the Riss Glacial Age, and the Würm Glacial Age from the oldest to the oldest, and have long been used as the standard for dividing the Quaternary ice ages. However, recent research on deep-sea sediments has revealed that there have been ten cold periods (glacial ages) in the past million years.

[Yoshiaki Matsushima]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

氷河時代において中緯度地域まで氷床や氷河が大規模に進出拡大して存在した時期。反対に氷河があまり発達しなかった時期を間氷期という。氷期はつねに寒冷な気候の継続ではなく、そのなかにあっても氷河の後退縮小した温暖な時期が2～3回あり、これを亜間氷期といい、一方、亜間氷期と亜間氷期の間で氷河がふたたび前進拡大する寒冷な時期を亜氷期という。氷期は地球規模の気候変動で、その周期は10万年とされる。氷河の前進と後退の時期は高緯度と低緯度地域とではずれ、高緯度地域ほど氷期が長期間となる。したがって一つの氷期の年代は地域により異なり、その絶対年代を厳密に決めることは困難である。第四紀の氷期については、古くからアルプス周辺、旧ソ連地域、北アメリカなどで氷河性堆積(たいせき)物（氷堆石、氷縞(ひょうこう)粘土など）から氷河の消長が研究されてきた。アルプス北方では5回の氷期が認められ、古いほうからドナウ氷期、ギュンツ氷期、ミンデル氷期、リス氷期、ビュルム氷期とよばれて、長く第四紀氷河時代の区分の標準とされてきた。しかし、最近の深海底堆積物の研究によると、この100万年の間に10回の寒冷期（氷期）のあったことがわかってきた。

［松島義章］

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