Climatic and environmental changes in the westerlies Asia and monsoonal Asia since the Quaternary as recorded by loess chromaticity

The climatic conditions of westerlies Asia and monsoonal Asia differ substantially. Due to the scarcity of research on climatic proxies in the westerlies Asia, comparative studies of Quaternary climatic and environmental changes between these two regions remain scarce to date. In this study we analyzed the color parameters of surface loessic soils collected along a north-south climatic gradient in northern Iran, in the western part of arid central Asia (ACA), which is part of westerlies Asia. Our aims were to explore the relationship between loess color parameters and climatic factors in northern Iran; to make a comparison with monsoonal Asia; and then to evaluate its application based on well-dated loess-paleosol sequences on orbital timescales. The results show that: (1) L^* and b^* values of surface soils in northern Iran negatively correlate with mean annual precipitation (MAP), while a^*/b^* correlates positively with MAP, and a^* shows a non-linear relationship. (2) No significant correlation exists between color parameters and temperature. (3) While surface soil color parameters do not show consistent relationships with climatic factors across westerlies Asia and monsoonal Asia, loess-paleosol sequences on orbital timescales since the Quaternary demonstrate a consistent relationship. These findings highlight that chromaticity parameters of modern soils cannot be directly applied to loess sediment sequences, emphasizing the importance of considering soil development time when interpreting loess color data, particularly a^* in westerlies Asia. This study provides novel insights into the use of chromaticity for paleoclimate reconstruction and underscores the need for caution in applying modern soil color-climate relationships to ancient loess records.