Orbitally paced climate oscillations across the Oligocene/Miocene boundary

The late Oligocene and early Miocene periods, some 21 to 27 million years ago, have generally been viewed as times of moderate global warmth and ice-free conditions. Yet several lines of evidence suggest that this interval was punctuated by at least one, and possibly several, episodes of high-latitude cooling and continental glaciation1,2,3. Here, we present stable-isotope and per cent coarse-fraction data from an equatorial, western Atlantic deep-sea-sediment core that provide high-resolution records of the climate variability across the Oligocene/Miocene transition (22.5–25.7 million years ago). A strong 40-kyr periodicity in the oxygen isotope record is consistent with a high-latitude orbital (obliquity) control on ice-volume and temperature. Orbital influences are also apparent at precession and eccentricity frequencies, including a series of ∼400-kyr oscillations that culminate in distinct maxima at the Oligocene/Miocene boundary, about 23.7 million years ago. Covariance between the carbon and oxygen isotope records suggests that the oceanic carbon cycle may have contributed to global cooling during the ∼400-kyr cycles, particularly at the Oligocene/Miocene boundary.