A preliminary palynological and magnetic susceptibility record from the southern Sanjiang Plain, NE China: implications for orbital-scale monsoon variability since the Middle Pleistocene

Abstract

The Sanjiang Plain, characterized by thick Quaternary sedimentary sequences and limited anthropogenic disturbance, represents an ideal archive for regional paleoenvironmental reconstruction. While extensive studies have focused on Holocene variability, the Pleistocene climatic evolution of this region remains inadequately constrained. Here, we present a tentative paleoclimate record spanning approximately the past 868 ka, retrieved from borehole BWZK03 in the southern Sanjiang Plain. A chronological framework was established using a combination of AMS 14 C, optically stimulated luminescence, and ESR dating. Pollen analysis and magnetic susceptibility were analyzed to reconstruct vegetation and climate changes. Our results reveal a persistent alternation between forest-steppe and steppe-dominated landscapes, reflecting repeated shifts between cold-dry and warm-humid climatic phases. These alternating patterns broadly correspond to glacial-interglacial cycles, Marine Isotope Stages, Northern Hemisphere summer insolation, and global sea-level fluctuations, indicating that orbital-scale forcing of the East Asian summer monsoon was the primary driver of regional climate change. Notably, after the Mid-Pleistocene Transition glacial (cold-dry) phases became markedly longer and more stable, suggesting an enhanced positive feedback of high-latitude ice-sheet expansion and Tibetan Plateau uplift on the East Asian winter monsoon. This record provides new regional evidence for understanding orbital-scale monsoon dynamics and its sensitivity to high-latitude forcing since the middle Pleistocene.