Dependence of near-surface magnetic susceptibility on dust accumulation rate and precipitation on the Chinese Loess Plateau

Magnetic susceptibility (MS) of surface sediment varies systematically acro ss the Loess Plateau in central China, decreasing exponentially from >200 x 10(-8) m(3)/kg at the northern margin of the Qinling Shan to less than or equal to 30 x 10(-8) m(3)/kg near the southern margin of the Mu Us Desert. MS correlates highly with loess median grain size (r(2) = 0.79), which decr eases south-southeastward across the plateau. It also correlates with mean annual temperature (MAT) and mean annual precipitation (MAP) (r(2) = 0.58 a nd 0.60, respectively), and with their product MAT x MAP (r(2) = 0.83), whi ch is considered a measure of potential pedogenic activity. Because regiona l isopleths depicting grain size and the primary meteorological parameters are nearly parallel, it is difficult to determine their relative influence on MS. A simple MS model, based on the observed spatial variation in loess thickness, permits quantitative assessment of the effect of the dust accumu lation rate on the MS signal of surface sediment and isolates the likely ro le of climate in the production of magnetic minerals. The model suggests th at 84% of the loess MS variance is dictated by the diluting effect of dust and 10-11% is associated with meteorological factors, primarily precipitati on. The observed and modeled relationships support hypotheses that attribut e variations in MS in the loess-paleosol succession to varying rates of dus t deposition and in situ production of magnetic minerals in the accretionar y soils, both of which are controlled by monsoon climate. (C) 2001 Universi ty of Washington.