Magnetic susceptibility of soils as an ambiguous climate proxy for paleoclimate reconstructions

In soils of the temperate zone, there is an increase in the magnetic susceptibility. of an upper layer compared to chi(C) of parent rocks. The difference between chi and chi(C) characterizes the magnetic "enhancement"Delta chi, which is usually considered as associated with mean annual precipitation (MAP), allowing the reconstruction of MAP of the past from Delta chi values of paleosols. which is widely enough used. However, in regions with a wide MAP range, non-monotonic dependence of Delta chi on MAP is observed, making this reconstruction ambiguous. To construct climatic functions for reconstructing the past climate, we subdivided the south of European Russia into three regions, where climatic functions such as MAP(Delta chi) of modern soils are monotonic and close to linear. These regions are relatively dry, humid, and semi-humid cold. We considered an extended set of climatic features including potential evapotranspiration (PET), actual evapotranspiration (AET), water deficit (WD = PET-AET), moisture index (MI = MAP/PET), an index of De Martonne (IDM = MAP/(MAT+10), where MAT is the mean annual temperature). The links of Delta chi with MAP were positive in dry and negative in humid and semi-humid cold where they are weaker, but there were closer links with temperature-dependent WD and PET. Reliable (with R-2 > 0.7) climatic functions were constructed for dry and semi-humid cold, but such reliable functions were absent in humid part. Since the differences in soil - forming material, it is necessary to identify some parameter to characterize lithological factors. For this reason, we include in consideration median grain sizes (lgSz) in soil profiles and total iron (Fet) to obtain some explanations for the results. Although the use of Delta chi, lgSz and Fe-t together made the climatic functions more reliable (R-2 similar to 0.8), but.. played the main role, while lgSz and Fe-t were not always significant. Based on the obtained data, it appears possible to provide a more detailed subdivision of paleoecological periods in the Late Holocene for the steppe and forest-steppe zones of the Eastern Europe. Taking into account the diversity of soil conditions in different regions, equations using soil profile MS enhancement to reconstruct rainfall should be used locally and regionally, taking into account the identified limitations and eliminating the possible ambiguity of reconstructions.