Catchment environmental change over the 20th Century recorded by sedimentary leaf wax n-alkane δ13C off the Pearl River estuary

The compound-specific stable carbon isotope compositions(δC) of leaf wax n-alkanes from two short sediment cores recovered off the Pearl River estuary(PRE) were analyzed to check for their capability of indicating decadal scale catchment environmental change. Sedimentary long-chain n-alkanes exhibited an odd-over-even predominance, with a maximum at n-Cor n-C, indicating their leaf wax origin was from vascular plants. The δC values of Cand Cn-alkane in all the sediment samples were in the range of -28.8‰ to -31.2‰, consistent with the Cplant-dominated vegetation in the Pearl River catchments. The time series of δC records from the two cores were comparable and displayed a decreasing trend from the early 20 th century to the end of the 1970s, followed by a reversal in that change leading to continued increase for ca. 15 years. After being corrected for the effect of atmospheric COrise and δCdecline, the δCrecords largely retained their raw changing pattern; the post-1980 increase being more conspicuous. The slightly decreasing trend in corrected δC records before around 1980 may have been caused by an increase in precipitation, whereas the subsequent increase of δC is likely associated with the observed dry climate and/or intensive anthropogenic deforestation. Our results thus demonstrate that leaf wax n-alkanes buried in the sediments off the PRE may well reflect change in the regional climate and/or human activity in the river catchments over the past century.