Late Pliocene monsoon linkage in the tropical South China Sea

Abstract

The onset of Northern Hemisphere Glaciation (NHG) ∼2.7 Ma ago coincided with prominent climate changes in the tropical regions such as the African and the Asian monsoons. However, the relationship between tropical and sub-tropical monsoonal variations and high northern latitude ice sheet expansion as well as processes such as late Pliocene tropical sea surface temperature (SST) change is not clear. Our late Pliocene (2.5–3.3 Ma) monsoon proxy records and Mg/Ca derived SST records at Ocean Drilling Program (ODP) Site 1143 from the southern South China Sea (SCS) reveal that while tropical SST shows a stepwise decrease of 2–3 °C during this period, the East Asian monsoon gradually strengthens in response to the onset of the NHG. At the 41-kyr and 23-kyr bands, ice volume change lags tropical SST by ∼4 kyr, but leads the East Asian monsoon by ∼12–17 kyr. Our finding highlights the significant role of the tropical Pacific region in driving global climate change in the late Pliocene, which has invariable leading phase relative to the ice volume change as in the late Pleistocene. However, the East Asian monsoon shows a linear response to the onset of the NHG in the late Pliocene, with much bigger phase lagged at the 41-kyr and 23-kyr bands than in the Pleistocene, which suggests that at the obliquity and precession bands the phases of the Plio-Pleistocene East Asian monsoon variations relative to the global ice volume changes are not constant, but variable. Therefore, the East Asian monsoons are not only simply driven by northern summer insolation at the precession period but also modulated by global ice volume change in high latitudes.