Spatial and altitudinal variations in the magnetic properties of eolian deposits in the northern Tibetan Plateau and its adjacent regions: Implications for delineating the climatic boundary

Abstract

Delineating the climatic boundary (i.e., of precipitation and temperature) in the northern Tibetan Plateau and along its margins is important for understanding the dynamics of global atmospheric circulation and the processes of dust production in central Asia. To date, however, meteorological data are scarce for this vast region, which limits our understanding of regional climatic patterns and past climatic changes in Eurasia. In the present study, we use a synthesis of both new and published rock magnetic data from the late Pliocene, the last glacial-interglacial cycle, and modern eolian sediments to identify the climatic boundary in the northern Tibetan Plateau and its adjacent areas. The results demonstrate that eolian deposits under different environmental scenarios exhibit a clear contrast in the type and grain-size distribution of magnetic minerals. With the transition from humid to arid climatic regimes, a gradual shift from magnetic minerals of predominantly pedogenic origin to predominantly detrital origin can be observed in the surface soils. The spatial and altitudinal variations in the magnetic properties of surface soils reveal a distinct boundary of pedogenic intensity in the eastern Qilian Mountains, the western Pamir Plateau and the northern Tianshan Mountains. The inferred variations in pedogenic intensity, combined with analysis of the available meteorological data, demonstrate that the pedogenic boundary represents a critical climatic boundary between sub-humid to semi-arid and arid regions in the northern Tibetan Plateau and the adjacent regions. Stronger pedogenesis occurs in surface soils at higher altitudes on the windward side of the major mountains of the northern Tibetan Plateau, supporting the conclusion that precipitation rather than temperature exerts the dominant effect on the magnetic enhancement of surface soils. In addition, a comparison of several late Pliocene-Pleistocene and last glacial-interglacial loess-red clay sequences suggests that the modern spatial pattern of the climatic gradients in the northeastern Tibetan Plateau and the adjacent regions has been maintained since at least the late Pliocene or early Pleistocene. Moreover, the results demonstrate that during the warm and humid interglacial periods, a steepened rainfall gradient occurred in the northern Tibetan Plateau and its adjacent regions. In the future, detailed rock magnetic investigations of eolian deposits or surface soils could provide new insights into the dynamics of atmospheric circulation and the natural boundary conditions for paleoclimate modeling in the northern Tibetan Plateau.