(Text by ZHAO Debo, zhaodebo@qdio.ac.cn)
Debo and the X-ray diffractometer. This instrument has helped him analyze thousands of marine sediment samples. Credit: Institute of Oceanology, Chinese Academy of Sciences
History is fascinating. I am a historian, but one who studies the history of earth climate. The tool I use is marine sediment.
The ocean basins are the ultimate repositories of the world's sediments. Accumulating slowly and continuously, these sediments inform much of our knowledge of the magnitudes and rates of past ocean circulation and global climate changes, as well as regionally specific paleoclimatic histories of adjacent continental land areas.
Clay minerals are the important components in terrigenous marine sediments. They are mainly delivered by river drainage systems and wind transport to the ocean basins. This picture shows my partner, an X-ray diffractometer, which is mainly used to analyze the contents of clay minerals including illite, chlorite, smectite and kaolinite. Content of each clay mineral usually has specific response to different climate conditions. For instance, kaolinite is typically formed in soils developed in regions with warm humid climates and good drainage conditions, whereas illite is the product of physical erosion from bedrock or formed by weathering of feldspar and micas under moderate hydrolysis conditions. Thus their content ratios can be used to indicate the chemical alteration degree of land sediment, and further the history of paleoclimate (e.g., monsoon rainfall and temperature) shifts.
Over the past ten years, we have been studying the Quaternary East Asian monsoon evolution with mineralogical methods based on sediments from East Asian marginal seas. Our results found the latitudinal difference of trends and rhythms of monsoon evolution over East Asia. We have tried to explain these complex features with the interaction of external forcing of insolation and internal forcings including high-latitude ice sheet, subtropical westerlies, Intertropical Convergence Zone (ITCZ) and El Nino-Southern Oscillation (ENSO) processes. These findings of past monsoon climate may provide some references for predicting future long-term climate changes in this densely population region.
(Editor: ZHANG Yiyi)