There are now evidences that during the past 700,000 years, the Brunhes Normal Magnetic Epoch, temperatures were significantly cooler in both polar areas, in temperate regions, and even in tropical areas. In the Arctic there was a significant ice cover during the Brunhes; in the Antarctic, temperatures ranged between about 0 and 5°C in contrast to temperatures mostly above this during the Matuyama Reversed Magnetic Epoch.

Evidences of cooler temperatures in temperate areas during the Brunhes consist of invasions in both hemispheres of sinistrally coiled populations of Globorotalia pachyderma (Ehrenberg), a cold-water planktonic foraminifer. Some climatic cooling took place in tropical areas during the Brunhes as shown by the invasions of tropical areas by temperate species of planktonic foraminifers, the Globorotalia inflata and G. puncticulata padana groups, and the marked decline in the abundance of the tropical index Sphaeroidinella dehiscens. Bipolar synchroneity of paleoclimatic events is supported by independent isotope analyses of ice samples for the Wisconsin cold interval.

Earlier major bipolar cooling cycles occur in the Pliocene, Neogene Zone 21, and the late Miocene, with the maximum cooling in the Neogene Zone 17. Evidences consist of the major expansions of polar sinistrally coiled populations of Globorotalia pachyderma (Ehrenberg) into temperate areas during these cooling cycles, paleobotanical indications of cooling, and the association of marine glacial deposits with late Neogene polar faunas beginning in the late Miocene.

End_of_Article - Last_Page 2468------------