The effects of monsoon precipitation and organic matter distribution, process and evolution in the Pearl River Estuary, China

• Main Author: Strong, David
• Published: University of Bristol 2011
• Subjects: 577.786
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.559491

The Asian Summer Monsoon (ASM) is an important climate system, affecting over half of the global population. Understanding past ASM changes is therefore crucial for assessing potential impacts of future climate change in Asia. However, previous reconstructions of ASM precipitation intensity generally rely on the local-scale catchments of lake, cave and vegetation-based records. There is significant disparity between these records, possibly attributable to local microclimate responses overprinting the regional signal. This thesis reconstructs precipitation-driven river flux to the Pearl River Estuary (PRE), a major river system in China, to record monsoon variability over a more regional scale. A suite of biornarker-based ratios indicative of terrestrial organic matter (TOM) flux (the concentration ratio of terrestrial to marine n-fatty acids, n-alcohols and sterols, and the BIT Index), are analysed in contemporary grab samples and a sediment core from 6.5 ka to present. Additionally, carbon isotope (813C) values of leaf wax n-fatty acids are analysed from 6.5 ka to present to assess potential vegetation change. TOM input to the modem PRE generally decreases from river to ocean. Superimposed on this decrease, the biomarker distributions record a rapid decrease across the delta toe, indicating that organic matter (OM) burial is largely dictated by the sedimentary regime. From 6.5 ka to present, BIT indices show strong covariance with a precipitation record within the drainage basin, indicating that soil OM input to the PRE covaried with paleoprecipitation 6.5 ka to present. The other three biomarker ratios also record a general decrease in TOM. However, these ratios record some disparity at 5.5 ka, suggesting a change in vegetation OM input to the core. Leaf wax 813C values record a significant enrichment at 2 ka, consistent with a previously published bulk 813C record, suggesting an anthropogenically-driven shift to a greater C4 plant component with the onset of agriculture. 111.