Y. Herman 1970 Sediment cores from the Arctic Ocean yield significant faunal and lithologic evidence of alternating cold and milder periods for the last 6 million years. Although high-latitude continental glaciation commenced prior to 6 million years ago, the Arctic Ocean remained free of permanent pack ice up to approximately 0.7 million years ago, after which successive ice-covered and ice-free conditions existed. application/pdf 10.1126/science.169.3944.474 en American Association for the Advancement of Science Arctic paleo-oceanography in late Cenozoic time article