Eldrett James S, Harding Ian C, Wilson Paul A, Butler Emily, Roberts Andrew P
School of Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton, European Way, Southampton SO14 3ZH, UK.
Nature. 2007 Mar 8;446(7132):176-9. doi: 10.1038/nature05591. Epub 2007 Feb 7.
The Eocene and Oligocene epochs (approximately 55 to 23 million years ago) comprise a critical phase in Earth history. An array of geological records supported by climate modelling indicates a profound shift in global climate during this interval, from a state that was largely free of polar ice caps to one in which ice sheets on Antarctica approached their modern size. However, the early glaciation history of the Northern Hemisphere is a subject of controversy. Here we report stratigraphically extensive ice-rafted debris, including macroscopic dropstones, in late Eocene to early Oligocene sediments from the Norwegian-Greenland Sea that were deposited between about 38 and 30 million years ago. Our data indicate sediment rafting by glacial ice, rather than sea ice, and point to East Greenland as the likely source. Records of this type from one site alone cannot be used to determine the extent of ice involved. However, our data suggest the existence of (at least) isolated glaciers on Greenland about 20 million years earlier than previously documented, at a time when temperatures and atmospheric carbon dioxide concentrations were substantially higher.
始新世和渐新世时期（约5500万至2300万年前）构成了地球历史上的一个关键阶段。一系列由气候模型支持的地质记录表明，在此期间全球气候发生了深刻变化，从基本上没有极地冰盖的状态转变为南极冰盖接近现代规模的状态。然而，北半球早期的冰川作用历史存在争议。在此，我们报告了在挪威-格陵兰海约3800万至3000万年前沉积的始新世晚期至渐新世早期沉积物中，存在地层广泛的冰筏碎屑，包括宏观漂砾。我们的数据表明是冰川冰而非海冰搬运了沉积物，并指出东格陵兰可能是其来源。仅从一个地点获得的这类记录无法用于确定涉及的冰的范围。然而，我们的数据表明，在比之前记录早约2000万年的时候，格陵兰岛上就存在（至少）孤立的冰川，而当时的温度和大气二氧化碳浓度要高得多。
