Climate-induced length of day variations since Late Pliocene

The duration of a day is not constant and changes due to gravitational effect of the Moon, and various geophysical processes acting within the Earth’s interior, on its surface, and in the atmosphere. Among these processes, the role of climate is less studied, particularly in terms of barystatic processes, i.e., the continental-ocean mass redistribution due to melting of polar ice sheets and global glaciers, as well as changes in terrestrial hydrology. Although previous research has estimated the variations in length of day (ΔLOD) caused by barystatic processes, these estimates are limited to the Common Era, which prevents us from putting the contemporary ΔLOD induced by sea level change into the context of past climate change. Here we use the output of a climate model that is constrained with paleoclimate proxies to reconstruct ΔLOD caused by sea level change since Late Pliocene (∼3.6 Myr ago), based on a probabilistic deep learning algorithm called physics-informed diffusion model. We unravel large-amplitude fluctuations due to sea level change driven by waxing and waning of large continental ice sheets during the Quaternary ice ages, but also that 21st century climate change might be increasing ΔLOD by a rate that is among the highest in the past 3.6 Myr.