Atmospheric Carbon Dioxide Concentration Across the Mid-Pleistocene Transition

Abstract

A Change in the Air? Between around 1.2 million and 500,000 years ago, Earth's glacial cycle changed from one with a period of roughly 40,000 years to one with a period of about 100,000 years. Although there has been much speculation about why this transition may have occurred, no potential explanation seemed more likely than that it was caused by decreasing concentrations of atmospheric CO 2 . Hönisch et al. (p. 1551 ) present a record of atmospheric p CO 2 for the past 2.1 million years, derived from the boron isotopic composition of planktonic foraminifera, and show that the amount of CO 2 in the atmosphere has remained relatively constant over that period. While p CO 2 was approximately 30 ppm higher before the start of the mid-Pleistocene transition than after the transition, atmospheric CO 2 did not decrease gradually as would be expected were it to be the driver of the transition.