The Influence of Particle Size, Composition, and Transport on the Distribution of 230Thxs, 231Paxs, and 10Be in Marine Sediments

The study focuses on the grain-size dependent distribution of particle-reactive, natural radionuclides (230Th, 231Pa, 10Be) in marine sediments from the Southern Ocean, the South East Atlantic, and the Equatorial Pacific. Particle-size specific isotope analyses show that a large amount (53-89 %) of the total 230Th is concentrated in clay-size material. It is discussed to what extent a lateral transport of fine particles could generate a biasing to particle flux calculations based on 230Th. In the Southern Ocean sediment the distribution of 231Pa and 10Be strongly depends on the concentration of biogenic silica of particles. 231Pa/230Th and 10Be/230Th in opal-rich particles largely exceed their production ratio in seawater. This supports the application of bulk 231Pa/230Th as a proxy for past opal fluxes to Southern Ocean sediments. The study of compound-specific 231Pa/230Th and 10Be/230Th, as conducted here, allows a more detailed picture of the origin of the isotopic signatures.