Abstract
The 405-kyrcycles in proxy records for the East Asian summer monsoon and global ice volume intensified and became phase-locked to eccentricity forcing at ~4.5Ma. We revised previous forcing mechanism hypothesis for Pliocene intensification of the 405-kyrcycles in paleoclimatic records and proposed that the establishment of salinity difference between the Pacific Ocean and the Caribbean Sea at ~4.5Ma triggered an ocean-air positive feedback mechanism. This feedback mechanism caused simultaneous climate cooling and East Asian summer monsoon intensification and made the two different climate components have a clipped response to insolation forcing and, thus, intensified sensitivity to eccentricity variations. Weakening of the 405-kyrcycles in monsoon and ice volume records between 2 and 1Ma (mid-Pleistocene transition) was likely to be attributed to frequency modulation that transfer power of the 405-kyr band to the 100-kyr band, which was triggered by changes in the oceanic carbon storage of the Southern Ocean.
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