Potential of calcite crystallinity in paleoclimate reconstruction of loess in Northern Central Asia

In the Loess Plateau of China, carbonate minerals are important proxies for paleoclimate reconstruction. However, relationships between carbonate mineral characteristics and climatic factors remain poorly constrained in the arid region of the Central Asia, concerning particularly the discrimination between different genesis of calcites and their crystallinity as climatic proxies. This study focuses on the climatic significance of calcite crystallinity in topsoils and loess in the arid region of Central Asia, aiming to assess its potential for paleoclimatic reconstruction. A total of 48 topsoils of loess sediments and 6 samples from two loess profiles deposited since the last glacial periods were collected from northern Xinjiang, China, and southern Kazakhstan. X-ray diffraction (XRD) analysis was performed to analyze the mineralogical characteristics of calcite. The crystallinity was quantified using a peak shape parameter (height/area ratio, H/A value) of the calcite (104) diffraction peak. Generalized Additive Models were employed to systematically evaluate the relationship between various climatic factors and calcite crystallinity of topsoils. Results demonstrate that secondary calcite exhibited significantly lower H/A values (4.21±0.62) compared to mixed-origin calcite (6.25±0.82). The H/A values show a significant negative correlation with annual evapotranspiration, suggesting their potential as a proxy of paleo-evapotranspiration intensity. Except for winter, the separate introduction of precipitation and temperature factors in other seasons did not significantly improve the explanatory power of the model.. However, non-linear interactions between annual evapotranspiration and mean annual temperature accounted for 76% of the variance in H/A values. The H/A values were closely related to the evapotranspiration as a single factor in the cold (0～2°C) or warm (6～10.5°C) thermal regimes; however, there was a threshold effect of the H/A value change with the evapotranspiration in the transitional thermal regimes (2.5～5.5°C or 11～12°C). This research provids critical insights into applying calcite crystallinity for paleoclimate reconstruction in the Central Asia, which deepens understanding of the paleoclimate characteristics and offers a novel mineralogical tool for deciphering Quaternary environmental evolution in arid Central Asia.