138 HISTORY OF THE OCEAXS 



together with the cooHng from the inland ice over North America, 

 northern Europe, and part of Siberia would lead to the sudden 

 freezing over of the Arctic Ocean. The source of nourishment for 

 the ice sheets and glaciers would thereby be sealed off, and they 

 would start to wane and return their water to the ocean; the sea 

 level would rise above the effective sill depth, the influx of warm 

 water from the Atlantic would be increased, the ice cover over the 

 Arctic Ocean would vanish, and the cycle could start over again. 



Some authorities have questioned the assumption that there is 

 really a lag effect in the system, causing it to overshoot, and leading 

 to self-sustained oscillations rather than to a steady state. Also, 

 it has been debated whether the heat effects involved would be 

 sufficient. The hypothesis, however, possesses another interesting 

 feature, namely, that it can be checked experimentally. To explain 

 the start of the series of oscillations mentioned, Ewing and Donn 

 (1956) assume that the North Pole in Tertiary time was in the 

 Pacific Ocean, that is at least thirty degrees away from its present 

 position, and that the first ice age occurred as a result of the motion 

 of the pole into the Arctic basin. It must be said that such a motion 

 is indicated neither by the numerous Tertiary sequences available 

 from the Pacific Ocean floor, nor by paleomagnetic measurements, 

 however, further evidence for or against the theory could probably 

 be obtained from cores about 20 m long in the Pacific equatorial 

 zone; this is within the reach of present coring methods. 



The density of solid particles in the atmosphere and in the space 

 between us and the sun has attracted great interest as possible 

 variables in the past, responsible for climatic change and other 

 phenomena, and again, the best record of worldwide or large- 

 regional changes in source, path, and amount of such particles 

 seems to be the ocean sediments. Singular events like volcanic 

 eruptions are of special interest, as they provide us with useful 

 stratigraphic marking horizons. The Late Glacial eruption in 

 Laacher See in Germany is a famous example in which the ash 

 spread over large parts of Northern Europe making it possible to 

 recognize the Allerod interstadial during which the eruption 

 happened. In Iceland the archeological development is tagged by 

 widespread ash layers, and in Patagonia the local records of the 



