Astronomical Cyclicity in Loess Magnetic Proxy Records from Western Arid Central Asia During the Early Pleistocene

The Earth orbital precession cycle is expected to have a sustained impact on global climate; however, precession signals are absent from global benthic δ18O records—a discrepancy known as the “41-kyr problem”. Here, we present new evidence of dominant ~21-kyr precession cycles in terrestrial climate proxies from western arid Central Asia (ACA) during the Early Pleistocene, demonstrating the significant influence of precession on mid-latitude Asian climate. We found the ratio of anhysteretic remanent magnetization susceptibility (χARM) to low-frequency magnetic susceptibility (χlf) in loess sediments is a robust proxy for paleoprecipitation. A well-dated, ~600 ka χARM/χlf record from loess deposits in western ACA shows clear 21-kyr cycles between ~2.24 and 2.0 Ma, when the regional climate was relatively dry and the pedogenic intensity was weak. Our results elucidate the role of precession as a driver of terrestrial climate dynamics and they also address the origin of the “41-kyr problem” in Milankovitch theory.

地球轨道岁差周期预计将对全球气候产生持续影响，但全球底栖δ18O记录中却缺失岁差信号，这一差异被称为“41千年问题”。本文报道了中亚西部干旱区（ACA）早更新世陆地气候代用指标中显著的~21千年岁差周期新证据，证实了岁差对中纬度亚洲气候的重要影响。研究发现，黄土沉积物中非滞后剩余磁化强度磁化率（χARM）与低频磁化率（χlf）的比值可作为可靠的古降水代用指标。经高精度定年的中亚西部黄土沉积约60万年χARM/χlf记录显示，在约2.24 Ma至2.0 Ma期间，该区域气候相对干旱且成壤强度较弱，清晰呈现出21千年周期。本研究阐明了岁差作为陆地气候动力学驱动因子的作用，同时也解答了米兰科维奇理论中“41千年问题”的成因。