Chinese loess record of monsoon climate during the last glacial–interglacial cycle

Abstract

The thick loess–paleosol succession of central China contains a detailed record of changes in East Asian monsoon climate since the late Miocene Epoch. The alternating loess–paleosol stratigraphy closely resembles the marine oxygen-isotope record, implying that episodic dust deposition and pedogenesis are in phase with global ice-volume fluctuations and controlled by variations in solar radiation reaching the land surface. Deposits equivalent to marine isotope stages (MIS) 5 through 1 have been dated by 14C, 10Be, luminescence, and magnetic susceptibility and grain-size models. Malan Loess (MIS 4–2) decreases in thickness southeastward from >30 m in the western Loess Plateau to <5 m east of Xi'an. Downwind, Asian dust is found in Japan, the North Pacific Ocean, and the Greenland Ice Sheet, where it has a chemical signature that points to a primary source in western China. During glacial times, the mean dust flux in the central Loess Plateau reached 0.35 mm/year, whereas in interglacial times it fell to <0.1 mm/year. Times of high dust influx and reduced soil development coincided with strengthened winter monsoon conditions, which are inferred from variations in loess grain size. Times of decreased dust accumulation and strong pedogenesis, marked by high values of magnetic susceptibility, represent times of strengthened summer monsoon conditions. High-frequency fluctuations in dust influx during deposition of the Malan Loess include peaks that likely correlate with North Atlantic Heinrich events. The Younger Dryas oscillation is recorded in Chinese eolian and organic deposits by a shift from cool, humid late-glacial conditions to cold and dry conditions, followed by a return to milder, humid climate at the beginning of the Holocene. Warm, moist climate, associated with a strong summer monsoon, characterized the first half of the Holocene Epoch when a widespread paleosol complex developed on the Loess Plateau. Increased dust deposition during the middle to late Holocene marked a shift to cooler, drier conditions.