Residual β activity of particulate (234)Th as a novel proxy for tracking sediment resuspension in the ocean

Sediment resuspension occurs in the global ocean, which greatly affects material exchange between the sediment and the overlying seawater. The behaviours of carbon, nutrients, heavy metals, and other pollutants at the sediment-seawater boundary will further link to climate change, eutrophication, and marine pollution. Residual β activity of particulate (234)Th (RA(P234)) is used as a novel proxy to track sediment resuspension in different marine environments, including the western Arctic Ocean, the South China Sea, and the Southern Ocean. Sediment resuspension identified by high activity of RA(P234) is supported by different lines of evidence including seawater turbidity, residence time of total (234)Th, Goldschmidt’s classification, and ratio of RA(P234) to particulate organic carbon. A conceptual model is proposed to elucidate the mechanism for RA(P234) with dominant contributions from (234)Th-(238)U and (212)Bi-(228)Th. The ‘slope assumption’ for RA(P234) indicated increasing intensity of sediment resuspension from spring to autumn under the influence of the East Asian monsoon system. RA(P234) can shed new light on (234)Th-based particle dynamics and should benefit the interpretation of historical (234)Th-(238)U database. RA(P234) resembles lithophile elements and has broad implications for investigating particle dynamics in the estuary-shelf-slope-ocean continuum and linkage of the atmosphere-ocean-sediment system.