CHANGES IN VEGETATION TYPE ON THE CHINESE LOESS PLATEAU SINCE 75 KA RELATED TO EAST ASIAN SUMMER MONSOON VARIATION (Invited Presentation)

Floral communities in continental habitats such as steppes are highly sensitive to regional climate changes. In order to investigate changes in floral communities on the Chinese Loess Plateau (CLP) and their relationship to climate variation since 75 ka, we generated carbon and nitrogen isotope profiles for soil organic matter (SOM) in the Weinan loess-paleosol section. δ¹³C_SOM at Weinan ranges from ‒23.6 to ‒18.0 ‰ and δ¹⁵N_SOM ranges from +3.4 to +5.5 ‰. Modeling based on the δ¹³C_SOM record suggests that the proportion of C4 plants (%C4) has varied from lower during cold intervals (with minima of 24-32 % at 73.1 ka, 20.9 ka (LGM), and 0.6 ka) to higher during warm intervals (with maxima of 62-64 % at 53.0 ka and 8.2 ka). The δ¹³C_SOM and δ¹⁵N_SOM profiles are strongly correlated (r = +0.82; p(a) <0.001), suggesting that the N-isotope composition of SOM was also largely controlled by inputs of C4 versus C3 plants. The %C4 profile exhibits significant covariation with reconstructed mean annual temperatures (MAT) (r = +0.42; p(a) <0.001), mean annual precipitation (MAP) (r = +0.42; p(a) <0.001), and summer monsoon intensity (r = +0.50; p(a) <0.001), suggesting that paleovegetation was controlled by each of these climate variables to a degree. Comparing the Weinan record to SOM profiles across the CLP region, we identify three zones in which monsoonal influence varied, with the East Asian Summer Monsoon (EASM) exerting the strongest influence on the southeastern margin of the CLP, and the East Asian Winter Monsoon (EAWM) greater influence on its northwestern margin. This paper provides new insights into deciphering paleovegetation patterns and their links to paleoclimate change on the basis of paired C- and N-isotope records.