Deep-Sea Temperature and Ice Volume Changes Across the Pliocene-Pleistocene Climate Transitions

Abstract

Stepping Down Earth's environment changed markedly over the past 5.2 million years, when a permanent ice sheet has developed in the Northern Hemisphere and the glacial cycle has changed its period from roughly every 40,000 years to the dominantly 100,000-year duration of the past half-million years. One of the biggest questions about these changes is whether they were “threshold” responses to a gradual, uniform cooling trend or whether they represent reactions to discrete episodes of cooling. Sosdian and Rosenthal (p. 306 ) present deep-ocean temperature records from the North Atlantic that show that the cooling happened in distinct steps, at 3 to 2.5 million years ago and at 1.2 to 0.85 million years ago. Combining their record with that of deep ocean water oxygen isotopes allowed the distinction between effects due to global cooling and ice-sheet dynamics.