Understanding the Mid-Pleistocene transition with a simple physical model

Abstract. The climate of the Quaternary period is dominated by glacial-interglacial variability due to changes in the Earth’s orbital parameters that control the incoming solar radiation. However, certain features of this variability remain puzzling. A notable example is the so-called Mid-Pleistocene Transition (MPT, circa 1 million years ago), characterized by the shift of the predominant periodicity in climate variability from 40 kyr during the Early Pleistocene to 100 kyr at the Late Pleistocene. Previous studies have tried to explain its origin by invoking two main hypotheses. The first one is based on the observed decreasing trends in temperature and CO₂ throughout various climatic proxies. The second one, the regolith hypothesis, is based on the change in the basal friction regime of the Northern Hemisphere ice sheets via a progressive elimination of sediment layers of sediments above the continents. Here, we use the Physical Adimensional Climate Cryosphere mOdel (PACCO) to reproduce orbital-scale climate variability throughout the entire Pleistocene through a physical albeit simplified approach. We find that the decreasing trends in CO₂ and temperature during the Pleistocene can be explained with PACCO as a consequence of an MPT triggered by regolith removal that changes the size of the Northern Hemisphere ice sheets. The pre- and post MPT world respectively yield dominant periodicities around 40 and 100 kyr, the timing of the MPT corresponds to what is observed in proxies and the amplitude of sea-level changes is well matched.