East Asian Monsoonal Climate Sensitivity Changed in the Late Pliocene in Response to Northern Hemisphere Glaciations. Issue 23 (12th December 2022) - Zhang, Ze
Abstract: Mio‐Pliocene sedimentary archives of the East Asian summer monsoon (EASM) in NE Tibet record a monotonic response to orbital forcing, dominated by eccentricity. By contrast, Pleistocene archives display a more stochastic response that varies regionally and temporally. When and why this response changed is poorly understood. Here, we present a new high‐resolution Rb/Sr ratio data set of EASM intensity from the Sanmenxia Basin, North China, that spans the Plio‐Pleistocene transition. Our results indicate decreased monsoonal rainfall in the late Pliocene, dated at 2.75–2.6 Ma, associated with an intensified response to obliquity and enhanced climate stochasticity. This transition is attributed to the increase of Northern Hemisphere ice volume. Quaternary monsoons display a sensitivity unique to the modern icehouse with large bipolar ice sheets, while pre‐Quaternary monsoons were solely impacted by Antarctic ice sheet dynamics on orbital time‐scales. Plain Language Summary: The late Pliocene‐early Pleistocene transition (LP/EP) is a period of global cooling and the intensification of Northern Hemisphere glaciation. Yet, the evolution of the East Asian summer monsoon (EASM) during this time remains a topic of ongoing discussion and debate. Here we present high‐resolution paleoclimate data from a record of lake sediments across the Pliocene‐Pleistocene transition period. We show that there was a reorganization of the East Asian monsoon system 2.75–2.6 million years ago, associated with an increase in climate forcing caused by cyclic changes in Earth's tilt and in climate stochasticity. This transition is attributed to the appearance of new high‐latitude forcing mechanisms on monsoon intensity caused by the growth of ice sheets in the Northern Hemisphere. Key Points: Cyclic patterns in East Asian summer monsoonal intensity during the Pliocene were mainly driven by Antarctic ice sheet variations A major reorganization of the East Asian climate system occurred at 2.75–2.6 Ma in response to Northern Hemisphere glaciation Quaternary East Asian summer monsoon on orbital scales displays a sensitivity that is unique to the modern icehouse with bipolar ice sheets