Coupled 100‐kyr cycles between 3 and 1 Ma in terrestrial and marine paleoclimatic records

Earth's climate over the last one million years experienced several ∼100‐kyr glacial cycles, but no simple forcing mechanism has been identified. Numerous studies have tried to explain strong 100‐kyr glacial cycles without recognizable forcing, which has come to be known as the 100‐kyr problem. Few studies have examined 100‐kyr band paleoclimatic signals before 1 Ma. A recent study has demonstrated that benthic oxygen and carbon isotope records are phase‐locked and amplitude‐coupled at the 100‐kyr band, but that neither is phase‐locked to and amplitude‐coupled with the 100‐kyr eccentricity signal between 3 and 1 Ma. This phasing and amplitude mismatch of the 100‐kyr band between 3 and 1 Ma between marine records and the eccentricity forcing signal has been called the “late Pliocene‐early Pleistocene 100‐kyr problem.” However, it remains unknown whether terrestrial paleoclimate records are consistent with marine records at the 100‐kyr band. Here I show that loess monsoon records from China are amplitude‐coupled with benthic oxygen and carbon isotope records at the 100‐kyr band, but not with the 100‐kyr eccentricity forcing between 3 and 1 Ma. This observation provides further evidence in support of a free 100‐kyr oscillation as the cause of the 100‐kyr band amplitude variability in paleoclimatic records between 3 and 1 Ma. In contrast, benthic oxygen isotope records and loess monsoon records at the 100‐kyr band are not amplitude‐coupled with 100‐kyr benthic carbon isotope records over the last 0.4 million years, indicating that the late Pleistocene 100‐kyr climatic cycles may not result exclusively from a free oscillation.