This digital document is a journal article from Palaeogeography, Palaeoclimatology, Palaeoecology, published by Elsevier in 2005. The article is delivered in HTML format and is available in your Amazon.com Media Library immediately after purchase. You can view it with any web browser.Description: The natural abundance of C"3 and C"4 plants is affected by multiple environmental factors including temperature, moisture balance and atmospheric pCO"2. The relative importance of these factors is a subject of considerable debate, and may vary in different natural ecosystems. Previous studies generally focus on single loess sequences in the Chinese Loess Plateau, and conflicting conclusions on C"4/C"3 have been reached when studying carbon isotope ratios in carbonate and organic matter. In this paper we report a comprehensive carbon isotopic characterization of total organic carbon (TOC) and individual higher plant leaf waxes from five loess sequences spanning the last 35 ka from the Chinese Loess Plateau (CLP). The five coring sites encompass large gradients of annual mean temperature (9.2-13.9 ^oC) and precipitation (402-673 mm), allowing us to assess the controlling mechanisms on C"4/C"3 plant ratios. Glacial-interglacial sequences provide carbon isotope data for comparison with other climatic and environmental proxies such as lithology and magnetic susceptibility. Our results demonstrate that increased C"4/C"3 ratios are positively correlated with higher temperature and increased summer rainfall which characterize stronger summer monsoon in all five sites. We conclude C"4 abundance increases from the last glacial to the Holocene in response to greater monsoon activity and that the C"4 expression is suppressed in the cold and drier intervals.