Synchronizing climate-carbon cycle heartbeats in the Phanerozoic vegetated icehouses

Earth experienced state-specific climate-carbon cycle feedbacks during the Late Cenozoic Ice Age (LCIA). Whether similar feedbacks existed in the penultimate icehouse, the Late Paleozoic Ice Age (LPIA), remains uncertain. Here, we present phase relationships between eccentricity-paced climate cycles and carbonate carbon isotope across ~337-300 Ma. Up to 307 Ma, low-latitude continental carbon reservoirs expanded during eccentricity-forced coolings, resembling the Oligocene and Miocene climate-carbon cycle dynamics. After 307 Ma, this relationship reversed, analogous to the Plio-Pleistocene dynamics. We attribute this reversal to the increasing importance of high-latitude biome dynamics, comparable to what occurred at 6 Ma in the LCIA. Paralleling LPIA (335-301 Ma) and LCIA (past 34 Myr) records using this event reveals quasi-synchronization in the interaction of astronomical forcing, carbon cycling and glacial events from onset to apex of two icehouses. We propose that, despite different boundary conditions, extraterrestrial forcing shaped the evolutionary trajectory of Phanerozoic vegetated icehouses.