SCAVENGING AND PARTICLE-FLUX - SEASONAL AND REGIONAL VARIATIONS IN THE SOUTHERN-OCEAN (ATLANTIC SECTOR)

Even with large variations in flux rates, the scavenging of Pb and Th remains closely coupled to particle flux. In the Bransfield Strait, more than 95% of the scavenging of Th-230 and Pb-210 occurs in two productive months, followed by negligible fluxes in winter. In winter, total Th-234 reaches equilibrium with its parent U-238. During the bloom period, it is rapidly adsorbed onto particles and removed from the surface water. Notwithstanding the short production period, the annual fluxes of Th-230(xs) and Pb-210(xs) (the subscript xs designates unsupported value) exceed their respective production rates in the water column by 60%. Pb-210(xs) inventories in the sediment reflect the distribution of average present-day particle flux: high inventories occur in a zone just south of the Polar Front, including the Bransfield Strait and Drake Passage; low inventories are found north of the Polar Front and in the Weddell Sea, with minimum values (4-5 dpm cm-2) in the central Weddell Gyre. This distribution is in agreement with data for primary production and oxygen penetration in the sediment. However, inventories are determined not only by particle fluxes but also by sediment focusing and hydrography. A general relationship between radionuclide fluxes and particle rain rates as a tool for hindcasting palaeoproductivities cannot be given.