Abstract
Foraminifera abundance patterns and accompanying sediment analysis from Arctic Ocean sediment cores are useful tools in paleoecologic interpretations. In the Brunhes interval, there are at least two abundance peaks of Foraminifera; one, representing present conditions, in the top part of all cores, and the other near the Brunhes-Matuyama boundary (700,000 yrs B.P.). In addition, many cores show a continual fluctuating abundance pattern throughout the Brunhes interval. Cores with older age sediment have two additional Foraminifera abundance peaks, both in the Maruyama. The younger is in the middle part of the Maruyama and the older is near the time of the Olduvai Event in the early part of the Matuyama.
Study of the oldest age sediment available (middle Pliocene) confirms that Foraminifera never have been more abundant in the Arctic Ocean than they are today. Therefore, the ice-covered conditions of the present are taken to represent the warmest conditions necessary to explain other older abundance peaks in the cores. If carbonate solution is eliminated as an explanation, the intervals of few or no Foraminifera must represent conditions quite different from those represented by the abundance peaks and the present. The equilibrium ice conditions of the modern Arctic Ocean could be altered by minor atmospheric variations. Thicker ice could form rather quickly and rather simply and this could upset plankton productivity. Thicker ice could also prevent a free accumulation of coarse detritus and erratics such as accumulate in the Arctic Basin today. These sediment types generally are most abundant during times of abundant Foraminifera deposition and are rare in the intervals during which few or no Foraminifera were deposited.
These factors considered together lead to the theory that the Arctic Ocean has been frozen since at least the middle Pliocene and that the most significant change in the Arctic ice has been in its thickness. Thicker ice restricted photosynthesis and Foraminifera productivity. Times of thinner ice with conditions more like those of the present are represented by abundance peaks of Foraminifera and concentrations of glacially rafted material.
None of the patterns of Foraminifera abundance or glacially rafted material show good correlation with the classical continental glacial stages. Continental glaciers advanced and retreated in the northern hemisphere while the Arctic ice-cover remained relatively stable.
There would be important ecologic, economic, and political problems if the Arctic Ocean were to become ice-free. The historical evidence does not support the idea that a renewed pattern of Pleistocene glaciation would be one of the problems, however.
