Ice-Volume Forcing of East Asian Winter Monsoon Variations in the Past 800,000 Years

TLDR

The grain‑size ratio of <2 µm to <10 µm in loess‑soil samples from the Chinese Loess Plateau serves as a proxy for East Asian winter monsoon intensity. The study aimed to elucidate the dynamic linkage between global ice‑volume changes and winter monsoon circulation by comparing the Baoji grain‑size time series with the SPECMAP marine isotope record. The authors performed this comparison by aligning the loess grain‑size record with the marine isotope data to assess temporal and frequency correlations. The records show strong agreement, a dominant 100‑kyr cycle over the past 800 kyr, and suggest that glacial‑age boundary conditions, rather than local insolation, primarily paced the strength and timing of the East Asian winter monsoon.

Abstract

Abstract Particle-size measurements of some typical loess-soil samples taken in different localities of the Chinese Loess Plateau demonstrate that the grain size ratio of &lt;2 μm/&gt;10 μm (%) can be used as an indicator of variations in intensity of the East Asian winter monsoon winds. Grain-size curves of the Baoji and Weinan sections show that this proxy indicator is very sensitive to loess-soil alterations. Analytical results also suggest that during soil-forming periods, eolian dust accumulation was still substantial and, hence, loess deposition can be regarded as a nearly continuous process during the Quaternary period. In this study we compared the Baoji grain-size time series with the SPECMAP marine isotope record with the objective of elucidating the dynamic linkage between changes in global ice volume and the winter monsoon circulation. Both records show good agreement at both time and frequency domains. In particular, the winter monsoon variations are also dominated by a 100,000 yr period over the past 800,000 yr. It is thus inferred that direct local insolation forcing could be less important in driving the East Asian winter monsoon variability, and, alternatively, variations in glacial-age boundary conditions may have played a key role in modulating and pacing its strength and timing.