Significant shifts of sedimentary environment and carbon burial during the middle Holocene on the Sunda Shelf

Changes in sedimentary environments and carbon burial exert significant impacts on regional and global environmental and climatic systems. However, the long-term evolution of sedimentary environment and carbon burial on the Sunda Shelf remains poorly understood. In this study, we analyzed the elemental geochemistry and organic carbon composition of core CJB01–64 from the central Sunda Shelf to elucidate the evolutionary history of sedimentary environments and carbon burial since the last deglaciation, as well as to reveal their controlling mechanisms and climatic-environmental implications. Our results indicate a significant shift in sediment provenance in the central Sunda Shelf around 7.5 ka. Prior to this time, sediments were primarily derived from Thai rivers and the Mekong River, whereas after 7.5 ka, sediment contributions expanded to the Mekong River, Thai rivers, and Malay Peninsula rivers. The intensity of chemical weathering on the Sunda Shelf markedly weakened after 7.5 ka, with the East Asian Summer Monsoon serving as the primary controlling factor. The sedimentary environment transitioned from a nearshore terrestrial-dominated setting to a marine-dominated regime around 7.5 ka. Furthermore, the organic carbon burial flux decreased significantly after 7.5 ka, dropping by nearly sixfold. Since the last deglaciation, organic carbon burial on the low-latitude Sunda Shelf has been predominantly regulated by sea-level fluctuations and East Asian Summer Monsoon variability, whereas high-latitude shelves exhibited carbon burial principally governed by global climatically driven processes. Notably, during low sea-level periods of the last deglaciation, the Sunda Shelf exhibited a sedimentary carbon burial flux of 8.816 Tg/a, indicating that the Sunda Shelf was a critical carbon sink during this period. Our findings highlight the Sunda Shelf's sedimentary environmental dynamics and carbon burial evolution as potential responders to and influencers of regional and global environmental and climatic changes.