The minute, calcitic, skeletal elements (coccoliths) of the Coccolithophoridae constitute 5-20 per cent or

End_Page 624------------------------------

more of oceanic sediments in tropical and temperate zones. These planktonic algal remains have a long geologic record, as well as a high degree of evolutionary plasticity, and have been used, with some success, as stratigraphic tools. To date, however, no attempt has been made to determine their ecologic usefulness.

During investigation of the Coccolithophoridae in the Atlantic and Antarctic Oceans, the writers found several temperature-dependent species. To test the usefulness of these forms, their contemporary, post-glacial and Wisconsin-glacial distribution in the North Atlantic was examined. Twelve cores, representing a range of conditions from present subarctic to tropical, were chosen from those described by Ericson, Ewing, and Wollin as representing an unbroken sequence of sediments ranging from Recent through Wisconsin in age.

The colder-water fauna is defined by the presence of Coccolithus pelagicus and large numbers of Coccolithus huxleyi, Gephyrocapsa oceanica, and Coccolithus leptoporus. The warmer-water fauna is typified by Umbellosphaera tenuis, Umbellosphaera irregularis (erroneously called Discoaster murrayi by some workers), and in lower concentrations, Coccolithus annulus and Discolithus antillarum. In addition, the faunal diversity increases in such a way that non-placolith coccoliths constitute an increasingly significant percentage of the fauna as the temperature increases. It is from these forms that more sophisticated ecologic inferences will be drawn.

Comparison of Recent with glacial sediments indicates a faunal shift of about 10° latitude. During the Wisconsin, the C. pelagicus fauna occurred as far south as 25° North latitude, whereas today it is restricted to areas north of 35° North latitude.

End_of_Article - Last_Page 625------------