The Climate Change in the Northeastern Iran Recorded by Loess-paleosol since the Last Two Glacial Cycles

The Arid Central Asia (ACA) is climatically controlled by the westerlies, which is an important part of the ancient "Silk Road" linking eastern and western culture exchange and trade. This area has perennial drought, low rainfall, strong evaporation, fragile ecosystems, making the humidity changes are extremely important to the regional ecological diversity and civilization evolution. Studies have shown that in the "summer rain type" of ACA, the moisture change in the eastern ACA and the monsoonal region have an anti-phase relationship in the Holocene, and have out of phase relationship in the Last Interglacial. However, the Holocene humidity changes in the "winter rain type" western ACA are still controversial, and reliable moisture change records during the Last Interglacial are scarce, which restricts the understanding of the overall moisture change characteristics of the whole ACA. In this study, we applied pIR50IR290 dating protocol to 38-63 μm K-feldspar fractions of loess samples from the Toshan section (TS19), Northern Iran. The Bacon age-depth model based on the pIRIR290 age estimates indicated that Toshan loess section could yield a reliable climate record since the last two glacial cycles (MIS 6). The climatic proxies such as grain size, chromaticity, magnetic susceptibility, TOC and organic carbon isotopic ratios (δ13C) have also been measured with high resolution. The main findings are as follows: (1) The TS19 loess-paleosol profile in northeastern Iran has been deposited intactly and with high resolution since the last two glacial cycles, and 3 obvious interglacial-stage peaks can be found in the MIS5, which are not clear in the loess profile of the Chinese Loess Plateau; (2) The TOC andδ13C based moisture records show that the most humid period occurred in MIS5c, instead of MIS5e. (3) Obvious 20,000-year precession cycle and 10,000-year half precession cycle of climate change during the Last Interglacial can be found in northeastern Iran. In the future, more K-feldspar pIRIR dating data will be obtained to increase absolute dating points, and the biomarkers such as GDGTs will be used to carry out high-resolution quantitative temperature reconstruction, to fully understand the characteristics of climate change in the "winter rain type" western ACA and its driving mechanism.