Simulations Reveal Causes of Inter-Regional Differences in Pliocene Climatic Periodicity

The Pliocene Epoch (5.33−2.58 Ma) is a generally warmer interval with atmospheric CO2concentrations at or slightly above modern levels. Many geological records show dominant periodicities of about 41 ka and/or 21 ka during the Pliocene and have been ascribed to variations in Earth’s orbital parameters. However, the mechanism for inter-regional differences in climatic cycle remains unclear. Here we perform four idealized experiments of orbit parameter’s extremes, using a sophisticated coupled ocean–atmosphere global climate model, HadCM3. Our results show that changes in temperature induced by obliquity are large (>5 ℃) over high latitudes and relatively small (~0−2 ℃) over low latitudes, whereas those induced by precession or eccentricity are comparatively small (~0−3 ℃) worldwide. In contrast, precipitation changes driven by obliquity, precession, and eccentricity are all very small (~0.5 mm day−1) over high latitudes, while over low latitudes, precession-induced changes in precipitation are dramatic (>2 mm day−1) and those induced by obliquity or eccentricity are significant (~0−1 mm day−1). These results indicate that the most notable effect of obliquity on climate occurs over high latitudes, whereas precession affects the climate mainly at low latitudes. Our findings reasonably explain not only the predominant 41 ka climatic periodicity at high latitudes and in marine oxygen isotope records regulated by high-latitude ice volume, but also the dominant 21 ka climatic cycle over low latitudes and the Mediterranean region.