Fractionation of 230 Th, 231 Pa, and 10 Be induced by particle size and composition within an opal-rich sediment of the Atlantic Southern Ocean

Details Fractionation of 230 Th, 231 Pa, and 10 Be induced by particle size and composition within an opal-rich sediment of the Atlantic Southern Ocean Fractionation of 230 Th, 231 Pa, and 10 Be induced by particle size and composition within an opal-rich sediment of the Atlantic Southern Ocean

Nov 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011gecoa..75.6971k&link_type=abstract

Geochimica et Cosmochimica Acta, Volume 75, Issue 22, p. 6971-6987.

Computer Science

Scientific paper

This study centers on the question: How sensitive are 231 Pa/ 230 Th and 10 Be/ 230 Th to sediment composition and redistribution? The natural radionuclides 231 Pa, 230 Th and 10 Be recorded in deep sea sediments are tracers for water mass advection and particle fluxes. We investigate the influence of oceanic particle composition on the element adsorption in order to improve our understanding of sedimentary isotope records. We present new data on particle size specific 231 Pa and 10 Be concentrations. An additional separation step, based on settling velocities, led to the isolation of a very opal-rich phase. We find that opal-rich particles contain the highest 231 Pa and 10 Be concentrations, and higher 231 Pa/ 230 Th and 10 Be/ 230 Th isotope ratios than opal-poor particles. The fractionation relative to 230 Th induced by the adsorption to opal-rich particles is more pronounced for 231 Pa than for 10 Be. We conclude that bulk 231 Pa/ 230 Th in Southern Ocean sediments is most suitable as a proxy for past opal fluxes. The comparison between two neighboring cores with rapid and slow accumulation rates reveals that these isotope ratios are not influenced significantly by the intensity of sediment focusing at these two study sites. However, a simulation shows that particle sorting by selective removal of sediment (winnowing) could change the isotope ratios. Consequently, 231 Pa/ 230 Th should not be used as paleocirculation proxy in cases where a strong loss of opal-rich material due to bottom currents occurred.

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