Mid-Pliocene Asian Monsoon Development and the Onset of Northern Hemisphere Glaciation

Although ice sheet build up in Northern Hemisphere appeared up to 11 million years ago, the initiation and sustain of major Northern Hemisphere glaciation was not succeeded until ~2.7 Ma. This step finalized the Cenozoic global cooling trend, switching the Earth from a greenhouse world, to an icehouse world with periodically waning and waxing of ice sheets. To understand what drives this important climate change a number of hypothesis have been proposed, most of which focused on the climate effects high-latitudes played, because apparently, high-latitudes are the places where ice-sheet occurs. However, the dynamics of low-latitude climate system such as Asian monsoon, which have been documented by recently studies to be significant in regulating global climate, and its interplay with the Northern Hemisphere glaciation, is largely unexplored. Here we present high-resolution Asian monsoon precipitation variability records for the past five million years, reconstructed from South China Sea sediments. Our results, with supporting evidence from other regions, indicate that the Asian monsoon developed and culminated, preceding the onset of Northern Hemisphere glaciation at ~2.7 Ma. The 1.4-million-year long monsoon intensification probably elevated the monsoon-induced continental erosion. This may have left fingerprints in marine calcium isotopes. Furthermore, enhanced rock weathering and/or organic carbon burial probably lowered the contemporary atmospheric CO2, and finally triggered the initiation of the Northern Hemisphere glaciation. Different from previous studies, here we propose a low-latitude forcing mechanism in important global climate change.