Millennial-Scale Organic Carbon Storage in Coastal Sediments Regulated by the Changes of Relative Sea Level in the Pearl River Estuary, South China

Estuaries and coastal seas play an important role in mitigating global warming due to their substantial storage of organic matters (OM) in sediments; and it is crucial to clarify the impact of relative sea level (RSL) changes on the efficiency and capacity of OM burial in coastal sediments in the context of the ongoing sea level rise. However, the capacity and controlling factors of OM storage in coastal sediments are not fully evaluated due to the complicated natural and anthropogenic processes. In this work, a three-segment merged sediment core from the Macao Sea in the Pearl River Estuary was selected to perform AMS 14 C dating and measure the contents and carbon isotope compositions of diverse organic matters as well as grain-size compositions for estimating the contributions of diverse-sourced OM and clarify the impact of RSL changes on OM storage at the millennial scale. The new data, together with the result of the Bayesian mixing modeling suggest that sedimentary OM mainly consists of total organic carbon (TOC) derived from marine organisms (TOC mar ) and C 3 plants (TOC C3 ) and incomplete combustion-produced black carbon (TOC BC ). Furthermore, the diverse-sourced OM synchronously responded to different RSL changes in the Macao Sea, i.e., RSL rise enhanced the production and degradation of TOC mar before burial, as shown by a weak increase in buried TOC mar ; RSL rise significantly enhanced the sediment loss and concomitant TOC C3 ; and RSL rise promoted to bury BC via intensifying the deposition of finer particles. Our work may provide a novel clue for accessing the contributions of diverse-sourced OM to the TOC storage in coastal sediments via the systematic analyses of a complicated superimposed core