Enhanced silicate weathering during glacial lowstands: new evidence from shelf sediments in the northern South China Sea

Abstract

The enhanced silicate weathering on tropical continental shelves has been linked to the exposure of unconsolidated sediments during glacial lowstands, contributing to atmospheric CO₂ consumption. However, the lack of sedimentary record from the exposed continental shelf limited our understanding of glacial weathering regimes. To address this, Core DG from the shelf of the northern South China Sea (SCS) was analyzed to investigate sediment provenance and weathering intensity during the late Quaternary (39–287 ka). Geochemical determination revealed five units (I to V) corresponding to two transgressive-regressive cycles. Sediment of Unit I, III, IV, and V primarily originated from southwestern Taiwan rivers, while Unit II derived mainly from the small streams in Hong Kong. Chemical weathering indices indicated three episodes of enhanced silicate weathering and which contributed mainly by secondary weathering due to the long-term exposure, however, with different patterns. One was the exposure of the continental shelf under favorable temperature and precipitation conditions during the early Marine Isotope Stage 6 (MIS6). Another one was the re-transport of secondary weathered sediments from the SCS shelf near Taiwan by glacially reactivated shelf channels during the end of MIS 6 and early MIS 5. This study provides new sedimentary evidence for enhanced silicate weathering during glacial lowstands, emphasizing the role of secondary weathering and source-to-sink processes in carbon sink on shelf and theimpact on the global carbon cycle.