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Particle cycling and scavenging of protactinium and thorium isotopes based on dissolved and size-fractionated particulate distributions (ANTXXIV-3, Southern Ocean)

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Venchiarutti, C. , Rutgers v. d. Loeff, M. , Voege, I. and Cai, P. (2009): Particle cycling and scavenging of protactinium and thorium isotopes based on dissolved and size-fractionated particulate distributions (ANTXXIV-3, Southern Ocean) , ASLO Aquatic Sciences Meeting 2009, Center de Congres Acropolis Nice, France, 25-30 January 2009. .
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During the expedition ANTXXIV-3 (Feb-April 2008, GEOTRACES/IPY), Pa and Th isotopes (230Th, 232Th and 234Th) were determined in seawater and size-fractionated particles along 3 transects: Zero-Meridian, Weddell Sea and Drake Passage. These radionuclides, sampled in different environments (shelf, open-ocean, ice formation areas ), and for the first time in 3 different sizes of particles, give more insights into the particle dynamics in the water column. Pa and Th distributions are controlled by particle flux and boundary scavenging. Therefore, based on reversible scavenging models and distributions of these radionuclides, particle settling velocities, adsorption/desorption rates and aggregation/disaggregation rates were further investigated. At open ocean stations, most of the excess 230Th distributions display a linear increase with increasing depth down to 1000 m. These distributions are sometimes modified from the linear trend, in surface or deeper water masses, reflecting ice melting, downwelling of surface waters and ventilation of bottom waters. Terrigenous inputs are observed near the shelf. Our results will be compared with the distributions of other trace elements, analysed in the same samples (Nd, 227Ac) or in parallel sampling (CFC).

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