Magnetic parameters of surface soils and AB profile in NE Iran

The Earth orbital precession cycle (~21-kyr) 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 (~2.24-2.0 Ma), demonstrating the significant influence of precession on mid-latitude Asian climate. We found that the ratio of anhysteretic remanent magnetization susceptibility (χ_ARM) to low-frequency magnetic susceptibility (χ_lf) in loess sediments is a robust proxy for paleoprecipitation. A well-dated, ~600 ka χ_ARM/χ_lf 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.