Periodical sedimentation in Scandinavian eskers

Abstract

Glacial-meltwater sediments in Scandinavia occur often as eskers subdivided into separate hills or short ridges. A periodical distribution of these segments is visible in many cases. The alternation between hills and breaks reflects variations in sedimentation rate caused by changes in the transport of debris with the glacial meltwater and may reflect climatic changes. The periodicity of the esker segments is different in different areas. This is an indication that different factors controlled the melting of the ice sheet during different times. A few examples are described in this paper. The Stockholm region was deglaciated around clay-varve year 10,300 BP, which probably means 11,000 to 11,100 calendar years BP. The Stockholm esker shows esker centers alternating with low or entirely missing parts. These centres correspond to an 11-year cycle. In southern Värmland, some 300 km west of Stockholm and deglaciated at about the same time, there is a similar separation of eskers into segments. In most cases the periodicity is the same as in the Stockholm area. A mean value from seven eskers gives a periodicity of 10.2 years. One esker along the eastern side of Lake Vänern shows a similar, very well developed subdivision, but is interpreted as corresponding to annual retreat of the ice margin. Some 200 km north of Stockholm eskers are more uniform suggesting that the amount of transported sediments was more continuous after 11,000–10,500 calendar years BP. In the province of Ångermanland, some 300 km farther north and deglaciated 10,500–10,100 BP, a distinct 3-yr periodicity can be distinguished. Towards the supra-aquatic region, esker centers appear to be annual features. The observed periodicities are interpreted as corresponding to the 11-year sunspot cycle, the 3–6-year cyclicity related to the ENSO events, and the annual melting cycle, respectively.